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RFC 806 - Proposed Federal Information Processing Standard: Spec


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Network Working Group
Request for Comments: 806

      Proposed Federal Information Processing Standard

      SPECIFICATION FOR MESSAGE FORMAT FOR 
      COMPUTER BASED MESSAGE SYSTEMS

      National Bureau of Standards
      Institute for Computer Sciences and Technology

      September 1981

                              TABLE OF CONTENTS

                                                                   Page

      EXECUTIVE SUMMARY                                               1

      1.  INTRODUCTION                                                3

          1.1  Guide to Reading This Document                         3
          1.2  Vendor-Defined Extensions to the Specification         4
          1.3  The Scope of the Message Format Specification          4
          1.4  Issues Not Within the Scope of the Message Format      4
               Specification
          1.5  Relationship to Other Efforts                          5

      2.  A SIMPLE MODEL OF A CBMS ENVIRONMENT                        6

          2.1  Logical Model of a CBMS                                8
          2.2  Relationship to the ISO Reference Model for Open      10
               Systems Interconnection
          2.3  Messages and Fields                                   10
          2.4  Message Originators and Recipients                    11

      3.  SEMANTICS                                                  12

          3.1  Semantics of Message Fields                           12
               3.1.1  Types of fields                                12
               3.1.2  Semantic Compliance Categories                 13
               3.1.3  Originator fields                              13
               3.1.4  Recipient fields                               14
               3.1.5  Date fields                                    15
               3.1.6  Cross-reference fields                         16
               3.1.7  Message-handling fields                        16
               3.1.8  Message-content fields                         17
               3.1.9  Extensions                                     18

                                      i                                 

          3.2  Message Processing Functions                          18
               3.2.1  Message creation and posting                   19
               3.2.2  Message reissuing and forwarding               20
                    3.2.2.1  Redistribution                          22
                    3.2.2.2  Assignment                              22
               3.2.3  Reply generation                               23
               3.2.4  Cross referencing                              24
                    3.2.4.1  Unique identifiers                      24
                    3.2.4.2  Serial numbering                        24
               3.2.5  Life span functions                            25
               3.2.6  Requests for recipient processing              25
                    3.2.6.1  Message circulation                     26
          3.3  Multiple Occurrences and Ordering of Fields           26

      4.  SYNTAX                                                     28

          4.1  Introduction                                          28
               4.1.1  Message structure                              28
               4.1.2  Data elements                                  29
                    4.1.2.1  Primitive data elements                 30
                    4.1.2.2  Constructor data elements               30
               4.1.3  Properties                                     30
                    4.1.3.1  Printing-names                          30
                    4.1.3.2  Comments                                31
               4.1.4  Data compression and encryption                31
               4.1.5  Data sharing                                   31
          4.2  Overview of Syntax Encoding                           32
               4.2.1  Identifier Octets                              32
               4.2.2  Length code and Qualifier components           33
                    4.2.2.1  Length Codes                            35
                    4.2.2.2  Qualifier                               36
               4.2.3  Property-List                                  38
               4.2.4  Data Element Contents                          38
          4.3  Data Element Syntax                                   39
               4.3.1  Data elements                                  39
                    4.3.1.1  Primitives                              42
                    4.3.1.2  Constructors                            44
               4.3.2  Using data elements within message fields      48
               4.3.3  Properties and associated elements             49
               4.3.4  Encryption identifiers                         49
               4.3.5  Compression identifiers                        49
               4.3.6  Message types                                  50

      SUMMARY OF APPENDIXES                                          51

                                     ii                                

      APPENDIX A.  FIELDS -- IMPLEMENTORS' MASTER REFERENCE          52

      APPENDIX B.  DATA ELEMENTS -- IMPLEMENTORS' MASTER REFERENCE   57

      APPENDIX C.  DATA ELEMENT IDENTIFIER OCTETS                    65

      APPENDIX D.  SUMMARY OF MESSAGE FIELDS BY COMPLIANCE           66
                   CATEGORY

          D.1  REQUIRED Fields                                       66
          D.2  BASIC Fields                                          66
          D.3  OPTIONAL Fields                                       66

      APPENDIX E.  SUMMARY OF MESSAGE SEMANTICS BY FUNCTION          68

          E.1  Circulation                                           68
          E.2  Cross Referencing                                     68
          E.3  Life spans                                            68
          E.4  Delivery System                                       68
          E.5  Miscellaneous Fields Used Generally                   69
          E.6  Reply Generation                                      69
          E.7  Reissuing                                             69
          E.8  Sending (Normal Transmission)                         69

      APPENDIX F.  SUMMARY OF DATA ELEMENT SYNTAX                    70

      APPENDIX G.  SUMMARY OF DATA ELEMENTS BY COMPLIANCE CATEGORY   72

          G.1  BASIC Data Elements                                   72
          G.2  OPTIONAL Data Elements                                72

      APPENDIX H.  EXAMPLES                                          74

                                     iii                               

          H.1  Primitive Data Elements                               74
          H.2  Constructor Data Elements                             76
          H.3  Fields                                                81
          H.4  Messages                                              84
          H.5  Unknown Lengths                                       88

      REFERENCES                                                     92

      INDEX                                                          94

                                     iv                                

                               LIST OF FIGURES

      FIG. 1.    LOGICAL MODEL OF A COMPUTER BASED MESSAGE SYSTEM     8
      FIG. 2.    MESSAGE FORWARDING AND REDISTRIBUTION               21
      FIG. 3.    EXAMPLE OF MESSAGE CIRCULATION                      27
      FIG. 4.    STRUCTURE OF IDENTIFIER OCTETS                      34
      FIG. 5.    ENCODING MECHANISM FOR QUALIFIERS AND LENGTH        35
                 CODES
      FIG. 6.    REPRESENTATION OF LENGTH CODES                      36
      FIG. 7.    EXAMPLES OF LENGTH CODES                            37
      FIG. 8.    EXAMPLES OF QUALIFIER VALUES                        38

                                      v

                               LIST OF TABLES

      TABLE 1.    FIELDS USED IN MESSAGE PROCESSING FUNCTIONS        19
      TABLE 2.    TYPE BITS IN THE IDENTIFIER OCTET                  33

                                     vi                                

                                                      Executive Summary

                              EXECUTIVE SUMMARY

           The  message  format  specification addresses the problem of
      exchanging  messages  between  different  computer-based  message
      systems  (CBMSs).    This interchange problem can be addressed on
      several   levels.      One   level   specifies    the    physical
      interconnections,   another  specifies  how  information  travels
      between CBMSs, another specifies form  and  meaning  of  messages
      being  interchanged.  The highest level specifies operations on a
      message.  Each of these levels would be covered  by  a  different
      standard.

           This  message format specification addresses only the issues
      of form and meaning of messages at the points in time  when  they
      are  sent  from  one  CBMS and received by another.  Messages are
      composed of fields, containing different classes of  information.
      These  fields  contain  information about the message originator,
      message recipient, subject matter, precedence and  security,  and
      references  to  previous  messages,  as  well  as the text of the
      message.  Standard formats (syntax) for messages ensure that  the
      contents  of  messages  generated by one CBMS can be processed by
      another CBMS.  Standard meanings (sematics) for the components of
      a message ensure standard interpretation of a  message,  so  that
      everyone  receiving  a  message  gets the meaning intended by its
      sender.

           Each CBMS that implements this message format  specification
      will  be  compatible  with  any  other  CBMS  that implements the
      specification.  Compatibility ensures  that  the  contents  of  a
      message  posted  by one CBMS can be received and interpreted by a
      different CBMS.

           This message format specification has been  developed  as  a
      result  of  examining  CBMSs  currently  in use in commercial and
      research environments.  Three major  design  perspectives  helped
      shape the message format specification.

        o  Viability.     The  message  format  specification  uses
           concepts that already work.  It has been  designed  with
           implementation concerns in mind.

        o  Compatibility.      The   message  format  specification
           contains concepts from existing CBMSs.  For this reason,
           many CBMS would already contain functions and components
           similar to  those  required  to  implement  the  message
           format specification.

                                      1                          

                                                      Executive Summary

        o  Extensibility.      This  message  format  specification
           defines a broad range of message content components  and
           requires  only an elementary subset of them.  This means
           that even a very simple CBMS can implement  the  message
           format  specification.  The message format specification
           contains a rich  set  of  optional  components  and,  in
           addition,  mechanisms  for  user  extensions  and future
           extensions to the message format specification.

           The  message  format  specification  defines  the  form  and
      meaning  of  message  contents  and their components as they pass
      from one CBMS to another through a message transfer system.   The
      message   format  specification  does  not  address  any  of  the
      following major issues.

        o  Functions or services provided to a user by a CBMS.
                For  example,  the  message  format   specification
                assumes  that  every CBMS allows a user to send and
                receive messages.  It does not specify any  of  the
                details of how a send function or a message-reading
                function  might  work or how it might appear to the
                user.  That is, the  message  format  specification
                neither limits nor mandates functions.

        o  Storage or format of message contents in a CBMS.
                The  message  format specification defines the form
                and contents of messages when they are  transferred
                between  systems.   A CBMS may or may not choose to
                use the same format for internal storage.

        o  Message transfer system protocols.
                The message format specification does  not  specify
                how  a  message  travels  between  CBMSs.   It does
                specify the form of its contents as it  leaves  and
                arrives,  assuming  only  that the message is moved
                transparently by the transfer system.

        o  Message envelopes.
                While a message is traveling between CBMSs,  it  is
                enclosed  in a message envelope.  Message envelopes
                contain all the information about a message that  a
                message transfer system needs to know.  The message
                format  specification does not define the format or
                content of a message envelope.

        o  How message originators and recipients are identified.
                The message format specification does not provide a
                representation scheme for the names or addresses of
                message originators  and  recipients  as  they  are
                known to a CBMS.

                                      2                          

                                                              Section 1

      1.  INTRODUCTION

           A  computer-based message system (CBMS) allows communication
      between "entities" (usually people) using computers.    Computers
      serve  both  to mediate the actual communications between systems
      and to provide users with facilities for creating and reading the
      messages.

           CBMSs have  been  developing  for  over  ten  years.    More
      recently,  CBMSs  have  been one of the bases in industry for the
      introduction  of  office  automation.    A  growing   number   of
      organizations  use  either  their own or a commercially available
      CBMS.  The design and complexity of these  systems  vary  widely.
      This   message   format   specification   provides  a  basis  for
      interaction between different CBMSs by  defining  the  format  of
      messages passed between them.

      1.1  Guide to Reading This Document

           The  method of presenting the material in this specification
      is  to  combine  the  technical   specification   with   tutorial
      information.     This  approach  has  been  taken  to  place  the
      specification in context and improve its readability.

           The core of the technical information in the document is  in
      Section  2  "A  Simple  Model of a CBMS Environment", Section 3.1
      "Semantics of Message Fields", Section 4.2  "Overview  of  Syntax
      Encoding",  and  Section 4.3 "Data Element Syntax".  Appendixes A
      and B consolidate the technical informations.   These  appendices
      are  designed  for  ease  of  reference  and  should  be  read in
      conjunction  with  the  body  of  the  report  for   a   complete
      understanding   of   the   message   format   presented   in  the
      specification.

           Section 2 presents a simple model of operation  of  a  CBMS.
      Section  3 discusses the components of messages and their meaning
      (semantics).    This  includes  discussions  of  the  recommended
      relationship  between message components and CBMS user functions.
      (See Section 3.2.)   Section  4  presents  details  of  the  form
      (syntax) required for components of a message.

           Appendix  D  summarizes the components of messages according
      to whether they are required or optional for  CBMSs  implementing
      the  message  format  specification.    Appendix  E organizes the
      message components according  to  the  functional  class  of  the
      components.    Appendix  F  provides an overview of the syntactic
      elements defined by this message format specification; Appendix G

                                      3                          

                                                            Section 1.1

      summarizes  those elements according to whether they are required
      or  optional  for  a  CBMS  implementing   the   message   format
      specification.    Examples  of  each  syntactic element appear in
      Appendix H,  displaying  syntax  and  describing  the  associated
      semantics.

      1.2  Vendor-Defined Extensions to the Specification

           This  specification provides the capability of extending the
      range of functionality by the use  of  vendor-defined  qualifiers
      and  vendor-defined  data  elements.    Any  vendor who uses this
      capability to provide services which are  essentially  equivalent
      to  those already designated as required, basic, or optional does
      not comply with the specification.

      1.3  The Scope of the Message Format Specification

           The purpose of  this  message  format  specification  is  to
      present  the  semantics  and syntax to be used for messages being
      exchanged between CBMSs.  Specifically, it defines the following.

        o  The meaning and form of standard fields to  be  used  in
           messages.

        o  Which fields must be present in all messages.

        o  Which fields complying CBMSs must be able to process.

        o  How  messages,  fields, and the data contained in fields
           are represented.

      1.4  Issues Not Within the Scope of the Message Format
           Specification

           The  message  format  specification  does  not  address  the
      following  issues,  some  of which are being covered by other NBS
      standards developments.  (See [BlaR-80] for a description of  the
      NBS protocols program.)

        o  The nature of a message transfer system, except to state
           the assumption that it transfers messages transparently.

                                      4                          

                                                            Section 1.4

        o  The  form  or  nature  of the protocols used to transfer
           messages (posting, relay, and delivery protocols).

        o  The content and representation of message envelopes.

        o  Representations for unique identifiers  (in  particular,
           message identifiers).

        o  Network and internetwork addressing.

        o  Representations  for  identities  of message originators
           and recipients.

        o  Functions that CBMSs provide for users.

        o  Presentation of messages to users.

        o  Representations for multi-media objects.

        o  Data representation for messages within CBMSs.

        o  Data sharing or any storage management within CBMSs.

        o  Representations for fixed  or  floating  point  numbers.

      1.5  Relationship to Other Efforts

           The   message  format  specification  is  based  on  several
      documents and the current state of many CBMSs available  both  in
      industry and the research community.  These documents include the
      standardization efforts in the ARPANet [CroD-77, PosJ-79] and the
      CCITT,  proposed  ISO  and  ANSI  header  format standards [TasG-
      80, ISOD-79], the work of IFIPS Working Group  6.5,  and  various
      papers  about the general nature of mail systems, addressing, and
      mail delivery.  (See [FeiE-79] for references.

                                      5                          

                                                              Section 2

      2.  A SIMPLE MODEL OF A CBMS ENVIRONMENT

           In  order  to provide a framework for presenting the message
      format specification, this section describes a simple  functional
      model for a CBMS.  The model provides a high-level description of
      both  user  facilities  and  system architecture.  Discussions of
      messages, message originators and  message  recipients  serve  to
      further clarify the nature of a CBMS.

           A  CBMS permits the transfer of a message from an originator
      to a recipient.  "Originator" and "recipient" are used  in  their
      normal  English  senses.    (See Section 2.4.)  A message (in its
      most abstract definition) is simply a unit of communication  from
      an  originator  to a recipient.  A CBMS offers several classes of
      functions to its users:

        o  Message Creation:  The  facilities  used  by  a  message
           originator  to  create messages and specify to whom they
           are to be sent.

        o  Message  Transfer:  The  facilities  used  to  convey  a
           message to its recipient(s).

        o  Recipient  Processing:  The facilities used by a message
           recipient to process messages that have arrived.

           These classes of functions are presented in more  detail  in
      Section 3.2.

           CBMSs  differ  from  other  office automation/communications
      systems in a number of ways.

        o  Unlike other types of  electronic  communications,  CBMS
           messages  are  sent  to  particular  individuals, not to
           stations or telephone sets.  If a recipient moves  to  a
           different  location, messages sent to that recipient are
           delivered to the recipient at the new location.

        o  Transmission of CBMS  messages  is  asynchronous.    The
           recipient's  system  need  not  be  available  when  the
           message leaves the originator's system.  That  is,  CBMS
           message transfer facilities are store-and-forward.

        o  CBMS  messages can contain a wide variety of data.  They
           are not constrained to any single kind of communication.
           CBMS messages are often simple  memoranda  but  are  not
           restricted to text.  A CBMS message may contain any kind

                                      6                          

                                                              Section 2

           of   data  that  an  originator  wishes  to  send  to  a
           recipient.      By   contrast,   Teletex   systems   and
           communicating  word  processors  handle  the transfer of
           final  form  documents;  compatible  communicating  word
           processors  can  exchange  documents  in  editable form;
           Telex and TWX deal in unformatted text.

        o  CBMSs offer message creation facilities as an  important
           part   of  the  system.    CBMSs  assist  users  in  the
           preparation  of  messages   by   having   text   editing
           facilities  available and allowing users to include data
           stored on-line in messages.  Some CBMSs  also  interface
           to   other   office   automation   facilities,  such  as
           formatters and spelling correctors.  This is not true of
           Telex, TWX, or similar services.

        o  CBMSs  offer  recipient  processing  facilities  as   an
           important  part of the system.  This is not true of most
           other forms of electronic communications.  For  example,
           Telex  and  TWX  systems  simply print messages on paper
           when they are received, without retaining a copy in  the
           system.   (Teletex systems are similar to Telex systems,
           but some can retain a copy  of  the  document  in  local
           storage.)    Communicating  word processors might notify
           their operators that a document has been received and is
           stored on-line, but offer little in  the  way  of  other
           recipient  processing  facilities.   Most CBMSs offer at
           least the following recipient processing facilities.

             .  The ability to retain a copy of a  message  on-line
                after it has been read.

             .  The  ability  to  examine or delete stored messages
                individually.

             .  The ability to organize messages using some form of
                electronic "file folder".

             .  The ability to determine if  a  message  is  recent
                (has arrived since the last time the recipient used
                the CBMS) or unseen (has never been examined by the
                recipient).

             .  The  ability  to  summarize  stored  messages.    A
                summary  usually  includes  information   such   as
                whether  the  message  is recent or unseen, when it
                was received, its length, who it is from,  and  its
                subject.

             .  The ability to retrieve a stored message based upon

                                      7                          

                                                              Section 2

                one  or  more  of its attributes (for example, when
                the message was received, whether  or  not  it  has
                been  seen  or deleted, and the values contained in
                its fields).

             .  A forward facility that allows users to include all
                or part of a message in a new outgoing message.

             .  A  reply  facility  that  allows  users  to  answer
                messages  without  having  to  enter  a new list of
                recipients.

      2.1  Logical Model of a CBMS

           CBMS  facilities  for  message   creation,   transfer,   and
      recipient  processing  are reflected in a logical model of a CBMS
      developed by IFIP Working Group 6.5 [SchP-79].   (An  essentially
      identical  model is being used by CCITT Study Group VII, Question
      5, regarding Message Handling Facilities.)  The model consists of
      a Message Transfer System and a number  of  User  Agents.    (See
      Figure 1.)

                    |                       |
                    |     *************     |
      *********  ------>  *  Message  *  ------->  *********
      * User  *  Posting  * Transfer  *  Delivery  * User  *
      * Agent *  Protocol *  System   *  Protocol  * Agent *
      *********  <------- *************  <-------  *********
                    |                       |
                    |                       |
                 Posting                Delivery
                  Slot                    Slot

                          Message Flow
      Originator --------------------------------> Recipient

      FIG. 1.  LOGICAL MODEL OF A COMPUTER BASED MESSAGE SYSTEM

           A User Agent is a functional entity that acts on behalf of a
      user,   assisting  with  creating  and  processing  messages  and
      communicating with the Message Transfer System.

           The Message Transfer System] is an  entity  that  accepts  a

                                      8                          

                                                            Section 2.1

      message from its originator's User Agent and ultimately passes it
      to  each  of  its  recipients' User Agents.  The Message Transfer
      System may perform routing and storage functions  (among  others)
      in order to accomplish its task.

           Transferring  a  message  from an originator's User Agent to
      the Message Transfer System is called Posting;  the  originator's
      User  Agent  and  Message  Transfer  System  engage  in a Posting
      Protocol in order to accomplish Posting.  Transferring a  message
      from  the  Message Transfer System to a recipient's User Agent is
      called Delivery; the recipient's User Agent and Message  Transfer
      System  engage  in  a  Delivery  Protocol  in order to accomplish
      Delivery.

           The  point  at  which  responsibility  for  a   message   is
      transferred  is  called a Slot.  The Posting Slot is the point at
      which responsibility for a message passes  from  an  originator's
      User  Agent  to the Message Transfer System; the Delivery Slot is
      the point at which responsibility for a message passes  from  the
      Message Transfer System to a recipient's User Agent.

           The  model  divides  messages  into  two  parts, the message
      content and the message envelope.  The  message  content  is  the
      information  that the originator wishes to send to the recipient;
      this message format specification deals solely with  the  message
      content.    The  message envelope consists of all the information
      necessary for the Message Transfer System to  do  its  job;  this
      message   format  specification  does  not  specify  the  message
      envelope.  Some of the data appearing  on  the  message  envelope
      could  be  redundant with some data found in the message content.
      The Message Transfer  System  is  not  expected  to  examine  the
      message content unless it is told to do so by the originator's or
      recipient's User Agent.

           This  message format specification places no restrictions on
      the Message Transfer System itself, except that it be transparent
      to the contents of messages.  In addition,  this  message  format
      specification does not dictate the form or nature of any protocol
      used  by  the  Message  Transfer  System.   Finally, this message
      format specification does not specify the content or form of  the
      message  envelope.    That  is,  the message format specification
      defines the format for the contents of messages, not  the  manner
      in which they are transmitted.

           Many of today's commercially available CBMSs incorporate all
      of  the  facilities  represented  in  the  logical  model.  Their
      architectures may reflect the economies that can  be  taken  when
      implementing  systems  that  are  self-contained.    For example,
      stand-alone systems that  store  messages  in  a  single  central
      database  require  no  Message Transfer System; an implementation
      may integrate software for User Agent and Message Transfer System
      functions, doing away with Posting or Delivery Protocols.

                                      9                          

                                                            Section 2.1

      2.2  Relationship to the ISO Reference Model for Open Systems
           Interconnection

           Subcommittee   TC97/SC16   of  the  International  Standards
      Organization (ISO) has developed a reference model for describing
      communications between "open" systems [ISOD-81].  This  model  is
      known as the ISO Reference Model for Open Systems Interconnection
      (OSI).    It  divides communications protocols into seven layers,
      ranging from physical interconnection at the lowest layer to data
      exchange by application programs at the top.

           This message format specification deals with data used by an
      application within a system.   Thus,  the  message  format  being
      specified here is not a protocol.  Since it is not a protocol, it
      lies outside of the model for open systems interconnection.  User
      Agents are application layer entities (layer 7), however, and the
      protocols used by a message transfer system are above the session
      layer (layer 5).

      2.3  Messages and Fields

           A message is a unit of communication from an originator to a
      recipient.    A message consists of a series of components called
      fields.  Fields can be described according to their meaning in  a
      message (semantics) and according to the format required for them
      in a message (syntax).

           Semantically,  a field is just a component of a message; the
      meanings of particular fields are defined by this message  format
      specification.    Syntactically,  a field is a unit of data whose
      form is defined by this message format specification.  Additional
      fields can be defined by users or vendors as long as they conform
      to the syntactic and semantic  rules  that  this  message  format
      specification defines for additional fields.

           (A  note  on  terminology:  A message consists of components
      called fields.  The words "message" and "field" are used both  in
      the  informal  sense  of  the  previous  sentence  and  in a more
      restricted sense as names of particular syntactic elements.    As
      syntactic   element   names,   Message   and   Field  are  always
      capitalized.)

           Some CBMS functions are based on the contents of  particular
      fields;  other  functions (such as the ability to read a message)
      may have little to do with the fields themselves.    Section  3.2
      discusses  some  of  the  specific  functions  that  a CBMS might
      provide to users and the fields that  must  be  used  to  support
      those functions.

                                     10                          

                                                            Section 2.3

      2.4  Message Originators and Recipients

           This   message   format   specification  refers  to  message
      originators  and  recipients.      These   terms   were   defined
      functionally  in Figure 1.  When the message format specification
      refers to the identity of a message originator or  recipient,  it
      means  "that  information  which  uniquely identifies the message
      originator or recipient within the domain of  the  given  message
      system."   The syntax and semantics of message addressing are not
      within the scope of the message format specification.

           Originators  and  Recipients  can  be  people,   roles,   or
      processes.

           People.    People as originators and recipients are specific
      individuals.

           Roles.  Roles identify  functions  within  organizations  as
      opposed  to  the  specific  individuals  who  perform  them.  For
      example, consider a newspaper  that  produces  both  morning  and
      evening editions and therefore operates with more than one shift.
      Someone  wishing to contact the city desk would send a message to
      the city desk role rather than trying to  determine  exactly  who
      was  assigned  to  the city desk at a specific time.  (Of course,
      messages can usually be sent to the individuals directly  whether
      or not they are actually performing a role at the time.)

           Processes.  A process in a computer could serve as either an
      originator  or a recipient for messages.  A computer system might
      originate a message to notify a recipient  about  the  status  of
      some  task.    For example, an archive utility could notify users
      about files that have been archived; a  distributed  file  system
      could  notify  a  user that a remote file has been deposited on a
      local file system.  Messages could be used by computer systems to
      warn about some  impending  condition  or  even  to  monitor  the
      performance  of the computer itself.  Some computer processes may
      also be message recipients,  taking  action  based  upon  message
      contents.

           In addition, some CBMSs allow messages to be sent to groups.
      A  group  is  a  predefined  list of message recipients.  Using a
      group  name  as  a  recipient  permits  message  originators   to
      designate a potentially large number of recipients using a single
      recipient  identifier.  This makes using the CBMS more convenient
      and accurate.

                                     11                          

                                                              Section 3

      3.  SEMANTICS

           This  section discusses two major topics, message processing
      functions and message field meanings.  Section 3.1 describes  the
      six  functional  groups of message fields.  The functional groups
      are Origination, Dates, Recipients,  Cross-referencing,  Message-
      handling, and Message-contents.  They are explained more fully in
      Section 3.1.1, along with detailed discussion of the semantics of
      all  the  fields in each functional group.  Section 3.2 describes
      message processing functions whose  operation  is  based  on  the
      meanings of particular message fields.

      3.1  Semantics of Message Fields

           The  definition  of  a  message  is  discussed  generally in
      Sections 1 and 2.  Semantically valid messages must  contain  one
      From  field,  one  To field, and one Posted-Date field.  They may
      contain, in addition, any number of other  fields,  depending  on
      the  processing  and  functions  supplied  by  the originating or
      receiving CBMS.  (Section  3.2  describes  classes  of  functions
      supplied by CBMSs.)

      3.1.1  Types of fields

           Message  receiving programs are required to interpret fields
      according to the semantics described in  the  remainder  of  this
      se.  The message fields defined in this document are grouped
      into the following functional categories.

        o  Originator  fields  indicate who or what participated in
           the creation of the message and where replies should  be
           directed.  (See Section 3.1.3.)

        o  Date fields record when events take place, for a variety
         events, such as message creation or expiration.  (See
           Section 3.1.5.)

        o  Recipient  fields  indicate  who  or what is intended to
           receive a message.  (See Section 3.1.4.)

        o  Cross-reference fields label a message or refer to other
           messages.  (See Section 3.1.6.)

        o  Message-handling fields record the  type  of  service  a

                                     12                          

                                                          Section 3.1.1

           message's  sender requested of a message transfer system
           or indicate how the message should  be  treated  by  its
           recipients.  (See Section 3.1.7.)

        o  Message-content   fields   either  contain  the  primary
           content of a message or index or  summarize  it.    (See
           Section 3.1.8.)

        o  Extension  fields  provide  mechanisms for extending the
           message format specification.  (See Section 3.1.9.)

      3.1.2  Semantic Compliance Categories

           For purposes of determining whether a CBMS complies with the
      semantic  requirements  of  this  message  format  specification,
      message fields have been divided into three categories:

      REQUIRED  These  fields  must be present in all messages and must
                be processed by message receiving programs  as  defined
                by the message format specification.

      BASIC     These  fields  need  not be present in all messages but
                when they do appear they must be processed  by  message
                receiving  programs  as  defined  by the message format
                specification.

      OPTIONAL  These fields need not be present in  all  messages  and
                may  be  ignored  by  message  receiving programs.  The
                exact meaning of "ignored"  is  not  specified  by  the
                message  format specification.  In general, a CBMS must
                recognize the existence of an optional field (that  is,
                optional  fields  should not cause errors) and must not
                process the field in a manner contrary to the semantics
                defined  for  that  field   by   the   message   format
                specification.

           (Syntactic compliance is defined in Section 4.1.2.)

      3.1.3  Originator fields

           A  message  originator  may  be  a person, role, or process.
      Originator fields identify a message's author, who is responsible
      for  the  message,  who  or  what  sent   it,   and   where   any
      replies should be directed.  (See Section 2.4.)

                                     13                          

                                                          Section 3.1.3

      From                     (REQUIRED)

                This  field  contains the identity of the originator(s)
                taking formal responsibility for  this  message.    The
                contents  of  the  From field is to be used for replies
                when no Reply-to field appears in a message.
      Reply-To                 (BASIC)

                This field identifies any recipients of replies to  the
                message.
      Author                   (OPTIONAL)

                This  field  identifies the individual(s) who wrote the
                primary contents of the message.   Use  of  the  Author
                  is  discouraged  when the contents of the Author
                field and the From field would be completely redundant.
      Sender                   (OPTIONAL)

                This field identifies the agent who sent  the  message.
                It is used either when the sender is not the originator
                responsible  for the message or to indicate who among a
                group  of  originators  responsible  for  the   message
                actually   sent  it.    Use  of  the  Sender  field  is
                discouraged when the contents of the Sender  field  and
                From  field  would  be  completely redundant.  Only one
                Sender field is permitted in a message.

      3.1.4  Recipient fields

           Message recipients may be people, roles, or processes.  (See
      Section 2.4).  Recipient  fields  identify  who  or  what  is  to
      receive the message.
      To                       (REQUIRED)

                This  field  identifies  the  primary  recipients  of a
                message.
      Bcc                      (OPTIONAL)

                This  field  identifies  additional  recipients  of   a
                message  (a  "blind carbon copies" list).  The contents
                of this field are not to be included in copies  of  the
                message  sent  to the primary and secondary recipients.
                See section 3.2.1 for further discussion of the use  of
                blind carbon copies lists.
      Cc                       (BASIC)

                This field identifies secondary recipients of a message
                (a "carbon copies" list).

                                     14                          

                                                          Section 3.1.4

      Circulate-Next           (OPTIONAL)

                This field is used in conjunction with the Circulate-To
                field.    (See  Section  3.2.6.1.)    It identifies all
                recipients in a circulation list who have not  received
                the message.
      Circulate-To             (OPTIONAL)

                This   field  identifies  recipients  of  a  circulated
                message.   (See  Section  3.2.6.1.)    It  is  used  in
                conjunction with the Circulate-Next field.

      3.1.5  Date fields

           Date  fields  for two kinds of uses are provided.  Dates can
      be associated with some event in the history  of  a  message  and
      dates  can  delimit  the span of time during which the message is
      meaningful (its life span).
      Posted-Date              (REQUIRED)

                This field contains the  posting  date,  which  is  the
                point  in  time  when  the  message  passes through the
                posting slot into a message transfer system.  Only  one
                Posted-Date field is permitted in a message.
      Date                     (OPTIONAL)

                This   field   contains   a  date  that  the  message's
                originator wishes to associate with  a  message.    The
                Date field is to the Posted-Date field as the date on a
                letter is to the postmark added by the post office.
      End-Date                 (OPTIONAL)

                This  field  contains the date on which a message loses
                effect.  (See also Section 3.2.5.)
      Received-Date            (OPTIONAL)

                Delivery date.  This field may be added to a message by
                the  recipient's  message  receiving   program.      It
                indicates when the message left the delivery system and
                entered the recipient's message processing domain.
      Start-Date               (OPTIONAL)

                This  field  contains the date on which a message takes
                effect.  (See also Section 3.2.5.)
      Warning-Date             (OPTIONAL)

                This field is used either alone or in conjunction  with
                an  End-Date  field.    It  contains one or more dates.
                These dates could  be  used  by  a  message  processing

                                     15                          

                                                          Section 3.1.5

                program  as  warnings of an impending end-date or other
                event.  (See also Section 3.2.5.)

      3.1.6  Cross-reference fields

           Cross reference fields can be used to identify a message and
      to provide cross references to  other  messages.    (See  Section
      3.2.4.)
      In-Reply-To              (OPTIONAL)

                This  field designates previous correspondence to which
                this message is a reply.  The usual  contents  of  this
                field  would be the contents of the Message-ID field of
                the message(s) being replied to.
      Message-ID               (OPTIONAL)

                This field contains a unique identifier for a  message.
                This  identifier is intended for machine generation and
                processing.   Further  definition  appears  in  Section
                3.2.4.1.    Only one Message-ID field is permitted in a
                message.
      Obsoletes                (OPTIONAL)

                This field identifies one or more  messages  that  this
                one supplants.
      Originator-Serial-Number (OPTIONAL)

                This field contains one or more serial numbers assigned
                by  the  message's  originator.  Messages with multiple
                recipients  should  have  the   same   value   in   the
                Originator-Serial-Number field.
      References               (OPTIONAL)

                This  field  identifies  other correspondence that this
                message  references.    If  the  other   correspondence
                contains  a  Message-ID  field,  the  contents  of  the
                References field must be the message identifier.

      3.1.7  Message-handling fields

           Message-handling fields describe aspects of how a message is
      to be handled or categorized.
      Precedence               (OPTIONAL)

                This  field  indicates  the  precedence  at  which  the
                message  was posted.  Ordinarily, message precedence or
                priority is a service request  to  a  message  transfer

                                     16                          

                                                          Section 3.1.7

                system.    A  message  originator, however, can include
                precedence information in a message.   One  example  of
                precedence  categories  are  those  used  by  the  U.S.
                Military: "ROUTINE",  "PRIORITY",  "IMMEDIATE",  "FLASH
                OVERRIDE", and "EMERGENCY COMMAND PRECEDENCE".
      Message-Class            (OPTIONAL)

                This  field  indicates  the  purpose of a message.  For
                example, it might contain values  indicating  that  the
                                                             1
                message is a memorandum or a data-base entry. 
      Reissue-Type             (OPTIONAL)

                This   field   is  used  in  conjunction  with  message
                encapsulating  (see  Section  2.4.1)  to  differentiate
                between messages being assigned or redistributed.
      Received-From            (OPTIONAL)

                This  field  contains  a  record  of  a  message's path
                through   a   message    transfer    system.        The
                recipient's  message receiving program could store here
                any information about the  transfer  that  it  obtained
                from a message transfer system.

      3.1.8  Message-content fields

           The   intent   of  most  messages  is  to  communicate  some
      particular information from originator  to  recipient.    Several
      fields in a message are designed to contain that information.
      Subject                  (BASIC)

                This  field  contains  any  information  the originator
                provided to summarize or indicate  the  nature  of  the
                message.
      Text                     (BASIC)

                This field contains the primary content of the message.
      Attachments              (OPTIONAL)

                This  field  contains  additional  data  accompanying a
                message.  It is similar in intent to  enclosures  in  a
                conventional mail system.

      _______________

        1
         The message format specification is not intended to be used as
      a  specification  for  exchanging  data-base  records.  Messages,
      however, sometimes contain data from or for a database.

                                     17                          

                                                          Section 3.1.8

      Comments                 (OPTIONAL)

                This  field  permits  adding  comments  to  the message
                without  disturbing  the  original  contents   of   the
                message.
      Keywords                 (OPTIONAL)

                This  field  contains  keywords  or  phrases for use in
                retrieving a message.

      3.1.9  Extensions

           This message  format  specification  allows  two  additional
      types  of  fields,  vendor-defined  fields  and  as-yet-undefined
      (extension) fields that will be introduced by extensions to  this
      message format specification.

      vendor-defined-field
                Any   field   not   defined   in  this  message  format
                specification or any extension or successor to it is  a
                vendor-defined  field.  Names for vendor-defined fields
                could be preempted by extensions to this message format
                specification.

      extension-field
                Any field that is defined in a document published as  a
                formal  extension or replacement to this message format
                specification.

      3.2  Message Processing Functions

           A CBMS provides three basic classes of  functions,  creating
      messages,  transmitting  messages  to  their recipient, and post-
      receipt processing.  Although the  message  format  specification
      does  not define the number or nature of user functions in CBMSs,
      the meanings for the  fields  clearly  assume  certain  kinds  of
      functions.   For example, fields specifying recipients of replies
      to messages assume some kind of reply function; fields specifying
      message life span assume some kind of date processing functions.

           This section provides more detail  on  the  processing  that
      might be done by these kinds of functions, discussing the message
      fields  that  would  be  used  and  how they would be used.  (See
      summary in Table 1.)

                                     18                          

                                                          Section 3.2.1

      Processing Function    Fields Involved

      Message creation       Author, From, Sender, To,
        and posting          Cc, Bcc
      Message reissuing      Reissue-Type
      Reply generation       Reply-To
      Cross-referencing      Message-ID, In-Reply-To, References,
                             Obsoletes, Originator-Serial-Number
      Life span functions    Start-Date, End-Date,
                             Warning-Date
      Recipient processing   Circulate-To, Circulate-Next

      TABLE 1.  FIELDS USED IN MESSAGE PROCESSING FUNCTIONS

      3.2.1  Message creation and posting

           Messages  can  be  created  either  by reissuing an existing
      message to a new recipient (see Section 2.4.1) or by  creating  a
      new  message.    The  process of message creation might mean that
      some fields of a new message are filled in from the  contents  of
      some  other  message.  Reply functions (Section 3.2.3) provide an
      example of this.

           Different individuals could be involved in different  phases
      of  originating a message: creating it, taking responsibility for
      it, and explicitly interacting with a CBMS  to  send  it  to  its
      recipient.    One or more individuals may create (that is, write,
      but not necessarily enter into the CBMS) a message; they are said
      to be the message's authors, identified by the Author field.  One
      or more individuals may take responsibility for its contents  and
      the  decision  to post it; they are identified by the From field.
      One individual explicitly posts a given message; this  person  is
      called the message's sender (identified by the Sender field).

           The   sender  and  author(s)  are  often,  but  not  always,
      responsible for the message.  A common case in which  the  sender
      is not responsible for the message is when a secretary enters and
      posts  messages  for  someone else.  An example of a situation in
      which a message's author  is  not  responsible  for  the  message
      itself is when an administrative assistant prepares a report that
      is sent under a manager's signature.

           Messages  containing  Bcc  fields  are  treated specially by
      CBMSs.  The contents of this field are not included in copies  of
      the  message  sent  to the recipients designated in the To and Cc
      fields.  Some systems include the contents of the Bcc field  only

                                     19                          

                                                          Section 3.2.1

      in  the  originator's copy, others include include all or part of
      the Bcc field in the copies sent to the recipients  indicated  in
      the  Bcc  field.  This specification does not mandate how the Bcc
      field is to be treated.

           Audit trail entries (such as the  posting  time  and  sender
      identity)  are  automatically  appended  to a message by the CBMS
      each time the message passes through a posting slot to a  message
      transfer  system;  a  message  transfer system could also provide
      timestamps at each transfer between user agent and  the  transfer
      system.   A message identifier (Sections 3.2.4 and 3.1.6), placed
      in the message by the original sender's User Agent, is  preserved
      throughout  this  message  flow.    This means that when the same
      message is sent twice to the same recipients by the same  Sender,
      the audit trail information for the two messages is different.

      3.2.2  Message reissuing and forwarding

           Reissuing and forwarding both serve the general user goal of
      passing  a  message on to a new set of recipients.  Forwarding is
      the term used for an informal mechanism, which CBMSs implement by
      copying some or all of the original message into the contents  of
      a  field  in  the  new message.  Reissuing is the term used for a
      formal mechanism to ensure that the message being passed on never
      loses its integrity as a previously  sent  message.    CBMSs  use
      reissuing  to implement several different functions, depending on
      the purposes being served.

        o  Redistribution.  Make others aware of the  complete  and
           unaltered contents of the message.

        o  Assignment.    Delegate the responsibility for a message
           to somebody else.

      These purposes are exemplified in Figure 2.

           When a CBMS examines a forwarded message, it  cannot  always
      distinguish  the  old  message  from  what  was  added  when  the
      forwarding took place.  In addition,  the  forwarded  information
      might  no  longer  have  the  form of a message.  This is usually
      because the format of the message has been changed (for  example,
      to pure unformatted text).  (See Figure 2 for an example of how a
      CBMS  might  forward a message.)  In contrast, a reissued message
      can always be separated from  its  enclosing  message  and  never
      loses its identity as a correctly formed message.

           This  specification  provides  the  Reissue-Type  field  for

                                     20                          

                                                          Section 3.2.2

                            The Original Message
      John Doe wishes Jane Jones to get a copy of the following
      message:
                      Message:
                        Field: From "Jean Smith"
                        Field: Posted-Date "15 June 1980"
                        Field: To "John Doe"
                        Field: Subject "Next sales meeting"
                        Field: Text "The agenda for ..."

                               Redistribution
      Message:
        Field: From "John Doe"                  John Doe is responsible
        Field: Posted-Date "16 June 1980"       for the redistribution.
        Field: To "Jane Jones"
        Field: Reissue-Type "Redistribution"    This message directly
        Message:                                incorporates a
          Field: From "Jean Smith"              redistributed message.
          Field: Posted-Date "15 June 1980"
          Field: To "John Doe"
          Field: Subject "Next Sales Meeting"
          Field: Text "The agenda for ..."

                                 Forwarding
      Message:
        Field: From "John Doe"
        Field: Posted-Date "16 June 1980"
        Field: To "Jane Jones"
        Field: Text                             A realization of the
          "From Jean Smith                      original message is
           To John Doe                          copied into the Text field.
           Sent on 15 June 1980                 Note that John's CBMS
           Subject Next Sales Meeting           has chosen to represent
                                                it as a text string.
           The agenda for ..."

      FIG. 2.  MESSAGE FORWARDING AND REDISTRIBUTION

                                     21                          

                                                          Section 3.2.2

      supporting re-issuing.  Forwarding, since it is an informal means
      of  serving  the  purpose  of  passing  on  information,  has  no
      supporting fields in the specification.

           This specification provides for  reissuing  of  messages  by
      encapsulating.    This  method embeds the entire original message
      inside a new message.  Encapsulating adds  structure  around  the

             2
      message .  This allows any part of it to be easily extracted.

           Authentication is an organizational policy issue  associated
      passing  on  previously  sent  messages.   Each organization must
      decide if the CBMS it acquires should support reissuing or simply
      supply forwarding.

      3.2.2.1  Redistribution

           Redistribution is a CBMS function for sending  the  original
      contents  of a message intact and unchanged to new recipients.  A
      redistributed message is identical to the original  message  with
      the  exception  of  added  information  about the reissuing.  For
      reissuing with this purpose, the Reissue-Type field contains  the
      ASCII  string  "Redistribution".    The original message has been
      included directly in a new message.  (See Figure 2.)

      3.2.2.2  Assignment

           Assignment is the process of designating responsibility.  In
      some organizations, formal message traffic  is  funneled  through
      one  or  more parts of the organization (called offices) where it
      is directed to the appropriate individuals or other  offices  for
      final  disposition.    Assignment  is done by reissuing a message
      with  the  Reissue-Type  field  containing   the   ASCII   string
      "Assigned."    A  message  which  contains  this  field  is to be
      interpreted as meaning that the addressees in the "To" field have
      had the reissued message assigned to them for some action.    Any
      addressee  in  the  "Cc"  field  has had the message assigned for
      information.  The "From" field records who assigned  the  message
      and   the  "Posted-Date"  field  records  when  the  message  was
      assigned.

      _______________

        2
         A message can contain another message, and  that  message  can
      contain another message, and so on to any depth of encapsulating.
      This can occur by reissuing a message repeatedly.

                                     22                          

                                                          Section 3.2.3

      3.2.3  Reply generation

           Reply  generation  involves creating a new message in direct
      reply to some other message by drawing on the contents of  fields
      in  the  other  message  to fill fields in the new message.  Many
      CBMSs  provide  reply  facilities  that  determine  the  intended
      recipients of a reply to a message.

        o  A  Reply-To  field  is  defined  by  this message format
           specification.   When  a  message  contains  a  Reply-To
           field,  the  CBMS  should send replies to the recipients
           designated in the  Reply-To  field  instead  of  to  the
           recipients designated in the From field.  This statement
           applies  to  original  messages  only,  not  to reissued
           messages.  The message  format  specification  makes  no
           recommendations concerning replies to reissued messages.

           Reply-To has several possible applications.

             1.  The  individual(s)  responsible  for  the  message
                 might not have regular access to a CBMS and  would
                 indicate  an  alternate  recipient, for example, a
                 secretary.

             2.  The people  responsible  for  receiving  responses
                 might  not  be the people who were responsible for
                 creating the message.

             3.  Discussion and conference groups  could  use  this
                 feature  to  ensure  correct  distribution  of any
                 submission by having the conference  group  itself
                 designated in the Reply-To field.

        o  When  the message does not contain a Reply-To field, the
           recipient should reply to the originators enumerated  in
           the  From  field.   The sender and authors should not be
           added automatically to the list of those  receiving  the
           reply.

           Replies  could  also  be sent to the other recipients of the
      original  message.    Vendors  might   offer   additional   reply
      facilities,  depending  on  their  view  of users' organizational
      requirements.

                                     23                          

                                                          Section 3.2.4

      3.2.4  Cross referencing

           A  CBMS  message  may  include  designator(s) which identify
      other message(s).  The designators are used to refer  to  related
      messages so that all information in a chain of correspondence can
      be  determined  by  a CBMS user.  The designator used to identify
      and cross-reference messages can take either of two forms, unique
      identifiers or serial numbers.

      3.2.4.1  Unique identifiers

           Unique identifiers are machine-generated quantities that are
      intended primarily for processing by computers.  While they could
      be  examined  by  a  human  user,  unique  identifiers  are   not
      necessarily useful or convenient for people.

           Unique  identifiers  occur  in  several  contexts.  They are
      often used  to  identify  the  contents  of  individual  messages
      unambiguously.    When unique identifiers are used this way, they
      are called message identifiers.  Different versions of a  message
      (for  example,  the  message  when  it is reissued with comments)
      receive new message identifiers.

           When a CBMS generates a message identifier, it must be  able
      to  guarantee  that  it  is unique, both within the domain of the
      individual CBMS and globally, across all connected CBMSs.   CBMSs
      could  generate  globally unique identifiers in several ways, all
      of which require prior  agreement  on  behalf  of  the  connected
      CBMSs.    One  method  is  to assign each connected CBMS a unique
      code.  A CBMS then generates unique identifiers by using its code
      as a prefix to some other quantity that it can  guarantee  to  be
      unique  within  its  domain.    (This  second quantity could be a
      counter or a timestamp/user-id combination.)

           A  CBMS  can  provide  functions  for  tracing   chains   of
      correspondence  by  using  unique identifers.  The message format
      specification defines fields for which  a  CBMS  provides  unique
      identifiers   as   values.    They  are  Message-ID,  References,
      Obsoletes, and In-Reply-To.  (See Section 3.1.6.)

      3.2.4.2  Serial numbering

           Serial  numbers  are  for  users  to  maintain  a   personal
      numbering  system for messages.  The numbers are composed of both
      letters and digits so that users could maintain several  sets  of
      sequences  concurrently  (for  example, A1, A2, A3... and B1, B2,
      B3...).

                                     24                          

                                                        Section 3.2.4.2

           Serial  numbers  are  assigned  at  a  defined  point in the
      history of a message.  Serial numbers are not unique identifiers;
      they differ from unique identifiers  (Section  3.2.4.1)  in  that
      they are not necessarily either generated or processed by a CBMS.
      They  are  designed to be typed and read by CBMS users.  They can
      be as simple or complex as the user requires.  Serial numbers are
      intended to be used to designate messages about a specific topic,
      or messages a given user has sent.  Serial numbers  are  intended
      to be a permanent part of the message, just as unique identifiers
      are.

           A  CBMS  can  provide  functions allowing originators to add
      serial numbers to messages.  A field has been provided to  permit
      this.    Originator-Serial-Number  is  for an originator to add a
      serial number to a message before sending it.

      3.2.5  Life span functions

           Messages have life spans, usually delimited by the  creation
      date and the time when the last copy of the message is destroyed.
      Messages could be meaningless before a certain time or irrelevant
      after  a  certain  time.    For  example,  a reminder to attend a
      meeting on 5 June loses  most  of  its  value  on  the  sixth;  a
      reminder  to  attend  that same meeting is likely to be of little
      use on 5 May (although not for the same reason).

           A CBMS can define a message's life span explicitly using the
      Start-Date and End-Date fields.   A  third  field,  Warning-Date,
      when used in conjunction with the End-Date, may be used to signal
      the  approach  of  the  End-Date.  It may also stand alone and be
      used by a periodic warning (alarm clock) mechanism.

           A CBMS could use these fields to  help  users  manage  their
      message  stores.  For example, a message whose start date has not
      yet passed could be bypassed by a retrieval  command  unless  the
      user  requested  such  messages explicitly.  A CBMS could use the
      end date to  help  with  message  store  housekeeping  either  by
      archiving  or  deleting  the expired messages automatically or by
      asking the user for some action to be taken on them.  The warning
      date could be  used  to  automatically  remind  the  user  of  an
      impending end date, such as a meeting reminder.

      3.2.6  Requests for recipient processing

           Recipients  have  a  wide variety of needs for examining and
      processing a message,  ranging  from  automatic  output  on  some
      specified  device  to  the execution of a program embedded in the

                                     25                          

                                                          Section 3.2.6

      message   itself.    Because  many  of  these  needs  are  highly
      specialized, and support for them not  widely  implemented,  this
      message  format specification does not constrain the requests for
      processing that may be included in a message.

           The message format specification  does  provide  two  fields
      that  permit an originator to request circulation list processing
      from the recipient.  These fields are Circulate-To and Circulate-
      Next.

      3.2.6.1  Message circulation

           Message  circulation  involves  serial  distribution  of   a
      message  to  its recipients, based on a distribution list that is
      part of the message.  The message is delivered first to the first
      recipient on the distribution list.  This recipient,  or  someone
      the  recipient  delegates,  sends  the  message  on to the second
      recipient on the list, perhaps after commenting on or  adding  to
      the  message.    This  continues  until  all  recipients  on  the
      distribution list have received the message.

           This message format specification  provides  two  fields  to
      support message circulation.  The Circulate-To field contains the
      complete   distribution   list,   indicating   the  full  set  of
      recipients,  and  the  Circulate-Next   field   indicates   which
      recipients  have  not  seen  the  message.    See Figure 3 for an
      example of message circulation using these two fields.

      3.3  Multiple Occurrences and Ordering of Fields

           Most message fields may occur more than once in  a  message;
      the  exceptions  are  the  Posted-Date,  Sender,  and  Message-ID
      fields, which may occur at most once.  What this means is that  a
      received  message  may  contain  any  number  of  instances  of a
      particular field (such as the "To" field).  If a message contains
      more than one instance of a particular field, that field  "occurs
      multiply"  and  that  message  has "multiple occurrences" of that
      field.

           A particular instance of a message field is  not  superseded
      by later instances of the same field.  The To field is an example
      of this.

           Multiple   occurrences   of  a  field  are  not  necessarily
      equivalent to a single field containing the concatenated contents
      of the several instances of the given field.  For  example,  with
      the  Text  field, concatenating the contents of several instances

                                     26                          

                                                            Section 3.3

      -----------------------------------------------------------------
           A  message  originator wishes to circulate a message to
           recipients A, B  and  C. The  originator  includes  the
           following fields in the message:

                     To:              A
                     Circulate-To:    A, B, C
                     Circulate-Next:  B, C

           When  recipient  A  or  somebody A delegates causes the
           message to be further circulated, the message  is  sent
           to  the  first address in the Circulate-Next field, and
           that name is removed from that field:

                     To:              B
                     Circulate-To:    A, B, C
                     Circulate-Next:  C

           B now sends the message on to its final recipient:

                     To:              C
                     Circulate-To:    A, B, C

      FIG. 3.  EXAMPLE OF MESSAGE CIRCULATION

      -----------------------------------------------------------------

      might lose important distinctions between the contents.  A single
      message could be used to send three different documents, each one
      in a different Text field.  However, putting the three  documents
      into  a  single  Text  field would make it much more difficult to
      extract any individual document.

           The fields found in a single message may occur in any order.
      The order in which they occur does not  necessarily  reflect  the
      order  in  which  they  were  created.  Nor does it constrain the
      order in which the  message  recipient  examines,  processes,  or
      displays them.

                                     27                          

                                                              Section 4

      4.  SYNTAX

           This section begins with an introduction to the concepts and
      elements  that  constitute  the  syntax for messages.  The second
      section presents an overview of the encoding scheme.   The  third
      section describes in detail the elements of the message syntax.

      4.1  Introduction

           This   specification   defines  syntactic  requirements  for
      messages when they are passed from one  CBMS  to  another.    The
      specification is designed to meet the following goals.

        o  Provide a concise flexible representation scheme.

        o  Simplify message parsing.

        o  Support non-textual components in messages (for example,
                                         3
           facsimile, graphics, or speech ).

      4.1.1  Message structure

           Messages   have   two  classes  of  components,  fields  and
      messages.  A field corresponds to one of the semantic  components
      defined  in  this  message  format  specification.   A message is
      simply another message.

           The type of a field in a message determines both its meaning
      and the form for its contents.  (See Section 4.3.2.)

           Fields in a  message  are  composed  of  syntactic  elements
      called  data  elements.    A  Message  data  element  is  used to
      represent messages; a Field data element  is  used  to  represent
      fields.    (The  term  "field"  is  simply  a semantic construct,
      distinct  from  "Field  Data  Element",  which  is  a   syntactic

      _______________

        3
         While  this message format specification is not intended to be
      used as a basis for the intnge of all facsimile information,
      it does  recognize  that  CBMS  messages  may  contain  facsimile
      components.

                                     28                          

                                                          Section 4.1.1

      construct.)    Many  of the fields defined in this message format
      specification estricted to containing only one kind of  data
      element.  (See Section 4.3.2.)

           Each  field defined in this message format specification has
      been assigned  a  unique  numeric  identifier  that  is  used  in
      conjunction  with  the  Field data element.  Separate identifiers
      are provided for vendor-defined  fields  and  for  extending  the
      identifier  encoding  space.    A  list of fields and identifiers
      appears in Section 4.3.2 and in Appendix C.

           Throughout the  message  format  specification,  fields  are
      referred   to   by  label  name  rather  than  by  their  numeric
      identifiers.  Field labels are  names  like  "Sender",  "Warning-
      Date",  or  "Circulate-To".    The  field  labels  chosen for the
      specification are names that are in common use in current  CBMSs.
      The  specification  does  not  require  a CBMS to use these field
      labels in displaying fields to the user, although such  usage  is
      encouraged to provide a common user interface.  

      4.1.2  Data elements

           For  the  purpose  of determining compliance with the syntax
      defined in this specification, data elements are divided into two
      groups, basic and optional.

      BASIC     All  message  receiving  systems  must  process   these
                syntactic elements, interpreting their values according
                to the message format specification.

      OPTIONAL  Message   receiving  systems  need  not  process  these
                syntactic elements in order to be in compliance.

           In  addition,  complying  CBMSs   must   meet   requirements
      regarding  their  ability  to process the components found inside
      data elements.   These  requirements  are  discussed  in  Section
      4.2.2.  (Semantic compliance is defined in Section 3.1.2.)

           This  message  format  specification classifies data element
      types as  either  primitives  or  constructors.    (See  Sections
      4.1.2.1  and  4.1.2.2.)   Primitive data elements, such as ASCII-
      String, are basic building blocks.   Constructor  data  elements,
      such  as  Message  or  Sequence, contain one or more primitive or
      constructor data elements.  Some constructors, such as  Sequence,
      may  be  composed  of  any  other  data  element.   Some, such as
      Message, may contain only certain data elements.    (See  Section
      4.3.1.)

                                     29                          

                                                        Section 4.1.2.1

      4.1.2.1  Primitive data elements

           A   primitive   data   element  contains  a  basic  item  of
      information; it is not composed  of  other  data  elements.    In
      current  CBMSs,  the most commonly used primitive data element is
      ASCII-String, a series of ASCII characters.  Other primitive data
      elements are Integer,  2's  complement  integers;  Bit-String,  a
      series of bits; and Boolean, either True or False.

           One primitive data element, End-Of-Constructor, is used only
      as  a structural element within constructor data elements and has
      no meaning by itself.  End-of-Constructor is used to  provide  an
      end  marker  for  constructor  data  elements that do not have an
      explicit length.  (See Section 4.2.2.1.)  Any other  use  is  not
      valid syntactically.

      4.1.2.2  Constructor data elements
         The  Data  Element  Contents  of  constructor  data elements
      contain one or more data elements.  The most general  form  of  a
      constructor is a Sequence or a Set, since both Sequences and Sets
      may contain any data element.  Other constructors are specialized
      forms of sequences.

           A  Message  data  element  is a constructor.  It may contain
      only  Field  data  elements,  other  Message  data  elements,  or
      encrypted  or  data  compressed forms of these elements.  A Field
      data element can contain any data element.    It  also  indicates
      which  specific field is being represented.  The contents of some
      fields are restricted to a single type of data element,  such  as
      ASCII-String or Date.

      4.1.3  Properties

           Any  data  element  may  have associated with it a Property-
      List, which contains properties such as a Printing-Name  (Section
      4.1.3.1)  or one or more Comments (Section 4.1.3.2).  A mechanism
      to support vendor-defined properties has been  supplied  by  this
      specification,  as  well  as  a  mechanism  to extend the list of
      property identifiers.

      4.1.3.1  Printing-names

           Printing-Names are  used  to  provide  labels  that  can  be
      displayed  along  with  their  respective  data  elements.    For
      example, a message originator may use a Printing-Name property to
      request that the To field of a message be labeled "Distribution:"
      when it is printed by its recipients.

                                     30                          

                                                        Section 4.1.3.1

      4.1.3.2  Comments

           The  Comment  property  is  used  to  allow  comments  to be
      associated with any data element  without  affecting  its  actual
      contents.    For example, someone reviewing the text of a message
      could add the comment "This looks good" to the Text field without
      either altering the body itself  or  adding  a  separate  comment
      field.

      4.1.4  Data compression and encryption

           Two  constructor  data  elements,  Compressed and Encrypted,
      have  been  provided  for  use  by  a  CBMS  that  supports  data
      compression  or  encryption.    They  may  be  used  to  hold the
      compressed or encrypted contents of any data  element,  including
      Messages  and  Fields, and may occur wherever their compressed or
      encrypted contents may appear.  A mechanism is included to  allow
      the user to identify the encryption or compression algorithm used
      (Sections 4.3.4 and 4.3.5).

      4.1.5  Data sharing

           Data  sharing  is  the  multiple  use  of a data element via
      references to a single copy.  It is used in two situations.

        o  For economy when a large object appears more  than  once
           in  a  message.    Data  sharing  may  be  used  in this
           situation  to  economize  on  storage  and  transmission
           costs.

        o  For  consistency  when the same object appears more than
           once in a message.  If one instance of  that  object  is
           altered, all instances must reflect this alteration.  In
           this  case  several  copies  of the same object will not
           serve the purpose as well as data sharing.

           While there is a demonstrable need for facilities to support
      data  sharing,  this  specification  does  not  define   such   a
      mechanism.    At  this time there is insufficient experience with
      data  sharing  in  messages  to  allow  standardization.      The
      specification   is   sufficiently   flexible   however  to  allow
      extensions to the syntax for supporting data sharing at  a  later
      time.

                                     31                          

                                                            Section 4.2

      4.2  Overview of Syntax Encoding

           This  section  provides  an  overview  of  the  notation and
      terminology  used  to  represent  the  syntactic  elements  (data
      elements) defined in this message format specification.

           All  data  elements consist of a series of components.  Each
      of the components is composed of a series of 8-bit groups  called
      octets.    In  this document, the bits are numbered starting from
      the low-order bit.  That is, the low-order (or least significant)
      bit is called "bit 0" and the high-order  (or  most  significant)
      bit is called "bit 7".  

           Five different components may appear in a data element.

        o  Identifier  octet  (identifying  particular type of data
           element)

        o  Length Code (specifying number  of  octets  that  appear
           following it in a data element)

        o  Qualifier (supplying additional identifying information)

        o  Property-List  component  (a  Property-List data element
           containing Property data elements)

        o  Data Element Contents (containing  actual  data  of  the
           data element)

      These components always appear in this order.  Not all components
      are  present  in  all  data  elements but the components that are
      present maintain this relative order.

      4.2.1  Identifier Octets

           The  identifier  octet  is   a   numeric   code   containing
      information  that  identifies  a  data element.  It is always the
      first component in a data element.  The Identifier octet contains
      a one-bit flag,  indicating  whether  or  not  the  data  element
      contains  a  Property-List, and a seven-bit unique identifier for
      the data element.  The value of the data element identifier  also
      indicates  whether  the data element has a Qualifier.  (See Table
      2.)

                                     32                          

                                                          Section 4.2.1

          Bit Value     Meaning

           7    0   The data element does not have properties
                      associated.
                1   The data element has properties associated.

           6    0   The data element does not have a Qualifier.
                1   The data element has a Qualifier.

          TABLE 2.  TYPE BITS IN THE IDENTIFIER OCTET

           The  most significant bit (Bit 7) of the identifier octet is
      set to 1  if  there  are  properties  associated  with  the  data
      element;  it  is  set  to  0  if  there  are  none.   This bit is
      independent of the remaining seven bits in the identifier  octet,
      which   are   called   the   identifier,   and   provide   unique
      identification for data elements.  The associated properties  are
      specified in a Property-List component.

           The  second  most  significant bit (Bit 6) of the identifier
      octet  (the  most  significant  bit  of  the  identifier  itself)
      signifies  whether  or  not the data element has a Qualifier.  If
      the bit is set to 1, then the data element has a Qualifier; if it
      is a 0, the data element does not have a Qualifier.    The  seven
      bits  of the identifier uniquely identify the data element.  (See
      Figure 4.)

           Data elements all have a Length Code  component  immediately
      following the identifier octet.  (See 4.2.2.1.)

      4.2.2  Length code and Qualifier components

           The Length Code and the Qualifier are both usually one octet
      in  length.    They use an encoding scheme that permits extending
      the component to the size necessary to represent  the  length  of
      the data element or the value of the Qualifier component.

           The  most  significant  bit  of the Length Code or Qualifier
      components determines whether it is  one  or  several  octets  in
      length.  When the most significant bit is 0, the component is one

                                     33                          

                                                          Section 4.2.2

      -----------------------------------------------------------------

           bit 7 6 5 4 3 2 1 0
              +---------------+
              |P 0 x x x x x x|     P0xxxxxx uniquely identifies a
              +---------------+     data element without a Qualifier.

              +---------------+
              |P 1 x x x x x x|     P1xxxxxx uniquely identifies a
              +---------------+     data element with a Qualifier.

      FIG. 4.  STRUCTURE OF IDENTIFIER OCTETS

      -----------------------------------------------------------------

      octet  in  length.  When the most significant bit is 1, the other
      seven bits of the first octet encode the number of octets in  the
      rest of the component.  The actual value begins in the next octet
      and is interpreted as an unsigned integer.

           A  single  octet  is  sufficient  for  most  Length Code and
      Qualifier components.  For those cases where  the  value  of  the
      Length  Code  or  the  Qualifier  must be greater than 127, extra
      octets can be added, up to a maximum of 127  octets.    Figure  5
      shows  the encoding scheme, as well as an example of a value less
      than 127 and one greater than 127.

           In order to comply with this message  format  specification,
      CBMSs  must  be able to determine the value of any length code or
      qualifier that is expressed  in  three  octets  or  less.    (The

       16
      2  -1).  This message format specification places  no  limitation
      on  the  value  of a length code or qualifier generated by a CBMS
      (except   for   the   absolute   limitation   inherent   in   the
      representation  scheme).    However,  the use of length codes and

       32
      2  -1)  should  be  avoided unless it is known that the receiving
      system can handle them.  

           Both Length Codes and Qualifiers have a  special  convention
      for  dealing  with  special situations.  Length Codes can specify
      that a data element had indeterminate  length;  a  Qualifier  can
      specify  that  a  data  element is implementation defined.  These
      cases are explained further in Sections 4.2.2.1 and 4.2.2.2.

                                     34                          

                                                        Section 4.2.2.1

      -----------------------------------------------------------------

           bit 7 6 5 4 3 2 1 0
              +---------------+
              |0 x x x x x x x|                   xxxxxxx is the value.
              +---------------+

              +---------------+------//-------+
              |1 n n n n n n n|y y y y y y y y|          nnnnnnn is the
              +---------------+------//-------+        number of octets
                                                       that contain the
                                                        value yyyyyyyy.

              +---------------+
              |0 0 0 0 1 0 0 1|               This is an example with a
              +---------------+                   value of 9 (decimal).

              +---------------+---------------+
              |1 0 0 0 0 0 0 1|1 0 0 0 0 0 1 0|      This example has a
              +---------------+---------------+   value of 130 decimal.

      FIG. 5.  ENCODING MECHANISM FOR QUALIFIERS AND LENGTH CODES

      -----------------------------------------------------------------

      4.2.2.1  Length Codes

           The  Length Code indicates the number of octets following it
      in a data element (that is, excluding the  identifier  octet  and
      the  length  code  itself).   Length Codes appear in one of three
      formats, short, long, and indefinite.

           A short Length Code is one octet long.  Its most significant
      bit (Bit 7) is set to 0 and its value is in the range  0  through
      127.

           A  long  Length Code is at least two octets long.  The first
      octet always has its most significant bit (Bit 7) set to 1.   The
      other  seven  bits  of  this  octet  contain the number of octets
      making up the rest of the Length Code and  these  octets  contain

        1016
      (2     - 1) (that is, 127 octets to represent the value).

           An indefinite Length Code is  one  octet  long.    Its  most
      significant bit (Bit 7) is set to 1 and its other bits are all 0.
      (See  Figure  6.)    An indefinite Length Code may appear only as

                                     35                          

                                                        Section 4.2.2.1

      -----------------------------------------------------------------

           bit 7 6 5 4 3 2 1 0
              +---------------+
              |0 x x x x x x x|             xxxxxxx is the value of the
              +---------------+                            length code.

              +---------------+------//-------+
              |1 n n n n n n n|y y y y y y y y|   nnnnnnn is the number
              +---------------+------//-------+  of octets that contain
                                                the value of the length
                                            code; these are represented
                                                            as yyyyyyy.
              +---------------+
              |1 0 0 0 0 0 0 0|            The "indefinite" length code
              +---------------+

      FIG. 6.  REPRESENTATION OF LENGTH CODES

      -----------------------------------------------------------------

      part  of  a  constructor  data  element;  it  may  not occur in a
                            4
      primitive data element .  A  constructor  data  element  with  an
      indefinite  length code has an End-Of-Constructor data element as
      the last data element in its Data Element Contents.  (The  length
      of  such  a  constructor data element is unrestricted although it
      must contain at least one data element -- the  End-of-Constructor
      that terminates it -- in its Data Element Contents.)

           Figure  7  shows  the Length Codes for three elements; their
      values are 38, 201, and 300.

      4.2.2.2  Qualifier

           The Qualifier component of a data element is used to provide
      information essential to the interpretation of the  data  element
      contents  that  is beyond that encoded in the identifier octet or
      length code.  For example, the identifier octet could contain the

      _______________

        4
         This is the result of most primitive elements  being  able  to
      contain  any  bit  pattern  (including the identifier for End-Of-
      Constructor).

                                     36                          

                                                        Section 4.2.2.2

      -----------------------------------------------------------------

            +--------+
            |00100110|                          Length code for 38
            +--------+

            +--------+--------+
            |10000001|11001001|                 Length code for 201
            +--------+--------+

            +--------+--------+--------+
            |10000010|00000001 00101100|        Length code for 300
            +--------+--------+--------+

      FIG. 7.  EXAMPLES OF LENGTH CODES

      -----------------------------------------------------------------

      code  for  a field and the Qualifier component would specify what
      kind of field.

           The Qualifier component appears in only a few data elements.
      In the Bit-String data element, it indicates the number of unused
      bits in the final octet of the Data Element  Contents.    In  the
      Field  and  Property  data  elements, it indicates which field or
      property the data element represents.    In  the  Compressed  and
      Encrypted  data  elements,  it  indicates  which  compression  or
      encryption algorithm has been used.  In the Message data element,
      it indicates the type of message.

           In the sequence of data element  components,  the  Qualifier
      occurs  between the Length Code and the Property-List components.
      The length of the Qualifier component depends on the encoding  of
      the  Qualifier.   (See Figure 8.)  A short Qualifier is one octet
      long.  Its most significant bit is 0 and  its  value  is  in  the
      range  0 through 127.  A long Qualifier is at least two octets in
      length.  The most significant bit is always 1  and  the  other  7
      bits indicate the number of octets in the value of the Qualifier.

           This  message format specification allows implementations to
      define  their  own  values  for  Qualifiers.    A  vendor-defined
      Qualifier  is  any long Qualifier in which the first octet in the
      value is 0.  The value used to identify  this  Qualifier  is  not
      guaranteed  to  be  unique  and  the  same  value  may be used by
      different implementations to define different Qualifiers.

                                     37                          

                                                          Section 4.2.3

      -----------------------------------------------------------------

               +--------+
               |00011011|            Qualifier with value 28 (decimal).
               +--------+

               +--------+--------+--------+
               |10000010|00000001 00001010|        Qualifier with value
               +--------+--------+--------+              266 (decimal).

               +--------+--------+--------+--------+
               |10000011|00000000|00000001 00001010|     Vendor-Defined
               +--------+--------+--------+--------+     Qualifier with
                                                             value 266.

               +--------+
               |10000000|              Undefined value for a Qualifier.
               +--------+

      FIG. 8.  EXAMPLES OF QUALIFIER VALUES

      -----------------------------------------------------------------

      4.2.3  Property-List

           A  Property  is  an  attribute  being associated with a data
      element.  The properties currently defined by this message format
      specification are Printing-Name and  Comment.    A  Property-List
      component  of  a  data  element is represented by a Property-List
      data element that in turn contains Property data elements.

           A data element contains at most one Property-List.  The most
      significant bit in the  identifier  octet  of  the  data  element
      indicates  whether  a  Property-List  is  present.   (See Section
      4.2.1.)

      4.2.4  Data Element Contents

           The Data Element Contents component of a data element is the
      actual data or information represented by a data element.    (The
      other  components  provide  the information necessary to identify
      and interpret the Data Element Contents.)

                                     38                          

                                                          Section 4.2.4

           In  a primitive data element, the Data Element Contents is a
      series of octets interpreted according to  the  identifier  octet
      and any qualifier.

           In  a constructor data element, the Data Element Contents is
      a series of data elements.  When the Length Code component  of  a
      constructor  data  element is "indefinite", the last data element
      in the constructor's Data Element Contents is End-of-Constructor.

           The length of the Data Element Contents (in octets)  is  the
      difference  between  the  value of the Length Code and the sum of
      the following:

        o  the length of the Qualifier component  (depends  on  the
           data element)

        o  the length of the Property-List component

      4.3  Data Element Syntax

           This  message  format  specification  defines  nineteen (19)
      different data elements.  Section 4.3.1 defines the encoding form
      for data elements  in  general  and  the  syntax  for  each  data
      element.    Section  4.3.2  describes  the  use  of specific data
      elements as part of the Data Element Contents  of  a  Field  data
      element.   A summary of the syntactic form appears in Appendix F;
      summaries of the data element syntax appear in Appendix G.

      4.3.1  Data elements

           This section presents the general  syntactic  form  for  all
      data  elements  defined  by this message format specification and
      the detailed syntax for each data element.  The data elements are
      presented by syntactic class: primitive  data  elements  (Section
      4.3.1.1), and constructors (Section 4.3.1.2).

           For  convenience,  the following terminology is used in this
      section.

                                     39                          

                                                          Section 4.3.1

                  Term            Meaning

              Primitive       a Primitive Data Element

              Constructor     a Constructor Data Element

              Element         any Data Element

           The  syntax  of  each  Element is presented in graphic form.
      The following conventions apply in the diagrams.  A single  octet
      is represented as follows.

          +--------+
          |        |
          +--------+

           Components that vary in length are represented as follows.

          +---//---+
          |        |
          +---//---+

           Each  Element  has  up to five components:  an Identifier, a
      Length Code, a Qualifier, a Property-List and  the  Data  Element
      Contents.  (See Section 4.2.)

           In  the  diagrams,  the  contents of the identifier octet is
      shown as a "P" followed by an identifier represented  in  binary.
      (See  Figure  4.)  The identifier itself is a seven bit quantity,
      right justified  in  the  identifier  octet.    Full  details  on
      identifier octets appear in Section 4.2.1.

           A length code is always represented in the following manner:

          +---//---+
          |Lxxxxxxx|
          +---//---+

           A qualifier is always represented in the following manner:

          +---//---+
          |Qxxxxxxx|
          +---//---+

                                     40                          

                                                          Section 4.3.1

           A Property-List (if present) always immediately precedes any
      occurrence of Data Element Contents.

           The  Data Element Contents appears in diagrams as one of the
      following.

        o  "element(s)", which may be any data element(s)

        o  "anything",  which  is  undefined   and   may   be   any
           combination of bits

        o  a specific data element

        o  the  interpretation to be applied to the bits within the
           octets that constitute the element  (such  as  ASCII  or
           Integer)

           Two  data  elements have been reserved for special purposes.
      The Extension data  element  is  provided  to  allow  for  future
      expansion of the possible data elements.  The Vendor-Defined data
      element  allows  CBMS  vendors to define their own data elements.
      Vendor-Defined data elements are not  guaranteed  to  be  unique,
      since  two  implementations  could define different data elements
      using the same identifier.  Vendor-Defined data  elements  should
      be used and interpreted by prior agreement.

           In  the  following  sections, each element is presented with
      its name, compliance  classification  (BASIC  or  OPTIONAL),  its
      identifier   (both   in   hexadecimal  and  in  octal),  a  brief
      description of its use, and a graphic representation.  Each  data
      element description has the following form.

                                     41                          

                                                          Section 4.3.1

      -----------------------------------------------------------------
      Data Element             (Compliance)   identifier   identifier
          Name                 ( Category )    octet         octet 
                                                    16            8

                     Description of the syntax of the data element.

                 +---//---+
                 |        |     Diagram representing data element
                 +---//---+

      -----------------------------------------------------------------

      4.3.1.1  Primitives

           The   data   elements   in  this  section  are  arranged  in
      alphabetical order by name.  (Appendix C presents the identifiers
      in numeric order.)
      ASCII-String             (BASIC)        02        002 
                                                16         8
                    This  data  element  contains  a  series  of  ASCII
                characters,   each  character  right-justified  in  one
                octet.    For  seven-bit  ASCII  characters,  the  most
                significant bit of each octet must be 0.

                 +--------+---//---+----//-----+
                 |P0000010|Lxxxxxxx|ASCII chars|
                 +--------+---//---+----//-----+

                                     42                          

                                                        Section 4.3.1.1

      Bit-String               (OPTIONAL)     43        103 
                                                16         8
                This  data  element contains a series of bits.  It uses
                the Qualifier data  element  component  to  record  the
                number  of  bits  of  padding (as an eight bit unsigned
                integer) needed to fill the final  octet  of  the  Data
                Element  Contents  to  an  even  octet boundary.  These
                padding bits have no meaning and occur in the low order
                bits of the final octet.   The  valid  values  for  the
                Qualifier  component  are  0  through 7.  The number of
                bits in the Data Element Contents  is  calculated  from
                the following formula.

                8   *   number of octets   -   value of
                        in the Data            Qualifier component
                        Element Contents

                 +--------+---//---+---//---+---//---+
                 |P1000011|Lxxxxxxx|Qxxxxxxx|  bits  |
                 +--------+---//---+---//---+---//---+

      Boolean                  (OPTIONAL)     08        010 
                                                16         8
                This  data  element  contains  one octet whose value is
                either true or false.  False is represented by all bits
                being 0; true  is  represented  by  all  bits  being  1
                (although  any  non-zero value should be interpreted as
                true).

                 +--------+---//---+--------+
                 |P0001000|Lxxxxxxx| T or F |
                 +--------+---//---+--------+

      End-of-Constructor       (BASIC)        01        001 
                                                16         8
                This data element terminates the Data Element  Contents
                in  a  constructor  data  element  that  has indefinite
                length.  This data element has no  Contents  component.
                (Use of this element is described in Section 4.2.2.1.)

                 +--------+---//---+
                 |P0000001|Lxxxxxxx|
                 +--------+---//---+

                                     43                          

                                                        Section 4.3.1.1

      Integer                  (OPTIONAL)     20        040 
                                                16         8
                This  data element contains a 2's complement integer of
                variable  length,  high  order  octet  first.    It  is
                recommended  that the data element contents be either 2
                or 4 octets long whenever possible.

                 +--------+---//---+---//---+
                 |P0100000|Lxxxxxxx| Integer|
                 +--------+---//---+---//---+

      No-Op                    (OPTIONAL)     00        000 
                                                16         8
                This data element does nothing.  No-Op is used whenever
                it is necessary to include a data  element  that  means
                "no operation".  It is a short placeholder.

                 +--------+---//---+
                 |P0000000|Lxxxxxxx|
                 +--------+---//---+

      Padding                  (OPTIONAL)     21        041 
                                                16         8
                This data element is used to fill any number of octets.
                The  contents  of  a  Padding element are undefined and
                convey no information.

                 +--------+---//---+---//---+
                 |P0100001|Lxxxxxxx|anything|
                 +--------+---//---+---//---+

      4.3.1.2  Constructors

           The  data  elements  in  this  section   are   arranged   in
      alphabetical order.

                                     44                          

                                                        Section 4.3.1.2

      Compressed               (OPTIONAL)     46        106 
                                                16         8
                This  data  element  must  contain  a  Bit-String  data
                element.  It is used to represent  any  data  that  has
                been   compressed;   it   may   be  used  wherever  its
                uncompressed contents may appear.    A  Qualifier  data
                component  appears  in each Compressed data element; it
                contains a  compression identifier  (CID)  to  identify
                the  compression  algorithm used.  (See Section 4.3.5.)
                The Data Element Contents contains the product  of  the
                compression process.

                 +--------+---//---+---//---+--------//--------+
                 |P1000110|Lxxxxxxx|Qxxxxxxx|Bit-String Element|
                 +--------+---//---+---//---+--------//--------+

      Date                     (BASIC)        28        050 
                                                16         8
                This   data   element  contains  an  ASCII-String  data
                element, which is a representation of a date  and  time
                formatted   in   accordance   with   PUBS  4 [NatB-68],
                58 [NatB-79a] and 59 [NatB-79b].

                 +--------+---//---+------//------+
                 |P0101000|Lxxxxxxx| ASCII-String |
                 +--------+---//---+------//------+

      Encrypted                (OPTIONAL)     47        107 
                                                16         8
                This data element must contain a  Bit-String.    It  is
                used  to represent any data that has been encrypted; it
                may be  used  wherever  its  unencrypted  contents  may
                appear.    A  Qualifier  data component appears in each
                Encrypted  data  element;  it  contains  an  encryption
                identifier  (EID)  identifying the encryption algorithm
                used.  (See Section 4.3.4.)  The Data Element  Contents
                is the product of the encryption process.

                 +--------+---//---+---//---+--------//--------+
                 |P1000111|Lxxxxxxx|Qxxxxxxx|Bit-String Element|
                 +--------+---//---+---//---+--------//--------+

                                     45                          

                                                        Section 4.3.1.2

      Extension                (OPTIONAL)     7E        176 
                                                16         8
                This  data  element  is  used  to  extend the number of
                available  data  elements  beyond  the  128  that   are
                possible   using  a  7-bit  identifier.    A  Qualifier
                component extends the encoding space  for  identifiers.
                (Extension and Vendor-Defined have the same syntax.)

                 +--------+---//---+---//---+---//---+
                 |P1111110|Lxxxxxxx|Qxxxxxxx|Anything|
                 +--------+---//---+---//---+---//---+

      Field                    (BASIC)        4C        114 
                                                16         8
                This   data  element  uses  a  Qualifier  data  element
                component.  The Qualifier component  contains  a  Field
                Identifier  (FID)  indicating  which  specific field is
                being represented.  (See Section 4.3.2.)

                 +--------+---//---+---//---+---//---+
                 |P1001100|Lxxxxxxx|Qxxxxxxx|elements|
                 +--------+---//---+---//---+---//---+

      Message                  (BASIC)        4D        115 
                                                16         8
                This data element may contain  Field  or  Message  data
                elements.    Its Qualifier component contains a Message
                type (MID) indicating the type of the  message.    (See
                Section  4.3.6.)  (The MID is completely different from
                the message identifier  in  the  Message-ID  field  and
                should not be confused with it.)

                 +--------+---//---+---//---+
                 |P1001101|Lxxxxxxx|Qxxxxxxx|
                 +--------+---//---+---//---+

                 +--------//---------//---------//---------//--------+
                 | Field, Message, Encrypted, or Compressed Elements |
                 +--------//---------//---------//---------//--------+

                                     46                          

                                                        Section 4.3.1.2

      Property-List            (OPTIONAL)     24        044 
                                                16         8
                This  data  element  contains a series of Property data
                elements to be associated another data element.

                 +--------+---//---+-------//--------+
                 |P0100100|Lxxxxxxx|Property Elements|
                 +--------+---//---+-------//--------+

      Property                 (OPTIONAL)     45        105 
                                                16         8
                This  data  element  uses  a  Quali data   element
                component.       The   Qualifier   component   contains
                a  Property-Identifier (PID) to indicate which specific
                property is being represented.  (See Section 4.3.3.)

                 +--------+---//---+---//---+---//---+
                 |P1000101|Lxxxxxxx|Qxxxxxxx|elements|
                 +--------+---//---+---//---+---//---+

      Sequence                 (OPTIONAL)     0A        012 
                                                16         8
                This data element contains any series of data elements.
                Sequence differs from Set in  that  the  data  elements
                making  up the Data Element Contents must be considered
                as an ordered sequence (according  to  their  order  of
                appearance in the sequence.)

                 +--------+---//---+---//---+
                 |P0001010|Lxxxxxxx|elements|
                 +--------+---//---+---//---+

      Set                      (OPTIONAL)     0B        013 
                                                16         8
                This  data element contains any series of data elements
                with no ordering of the elements  implied.    (Sequence
                provides   an  ordered  series.)    Although  the  data
                elements  contained   in   a   Set   must   be   stored
                sequentially, the order in which they are stored is not
                defined and not processed.

                 +--------+---//---+---//---+
                 |P0001011|Lxxxxxxx|elements|
                 +--------+---//---+---//---+

                                     47                          

                                                        Section 4.3.1.2

      Unique-ID                (OPTIONAL)     09        011 
                                                16         8
                This  data element is a unique identifier.  It need not
                be human-readable.  The Data Element Contents may be an
                ASCII-String, a Bit-String, or an Integer.

                 +--------+---//---+---//---+
                 |P0001001|Lxxxxxxx| element|
                 +--------+---//---+---//---+

      Vendor-Defined           (OPTIONAL)     7F        177 
                                                16         8
                This data element is  used  to  represent  vendor-  and
                user-defined  data  elements.    A  Qualifier component
                extends  the  encoding  space  for  identifiers.    The
                Qualifier  component  is  not  guaranteed  to be unique
                among all interconnected systems.  This data element is
                interpreted  according  to  prior   agreement   between
                systems.    (Extension and Vendor-Defined data elements
                have the same syntax.)

                 +--------+---//---+---//---+---//---+
                 |P1111111|Lxxxxxxx|Qxxxxxxx|Anything|
                 +--------+---//---+---//---+---//---+

      4.3.2  Using data elements within message fields

           The Data Element Contents of a particular field in a message
      must contain at least one  data  element.    The  types  of  data
      elements  that can appear in the Data Element Contents of a field
      are restricted according to what kind of field it is.  Appendix A
      (the master reference appendix for  fields) nes  which  data
      elements are valid as the Contents for each of the fields.

           Some  fields  have  a  Data  Element  Contents that contains
      "originators" or "recipients."  No data  element  represents  the
      identities of originators or recipients (because that encoding is
      not  within  the  scope  of  this  message format specification.)
      These descriptions simply  list  "originators"  or  "recipients",
      implying  no  restrictions on how the identifiers for originators
      or recipients are represented.

                                     48                          

                                                          Section 4.3.3

      4.3.3  Properties and associated elements

           This message format specification defines two properties.
      Comment                                 01        001 
                                                16         8
                This  property may contain any series of data elements;
                it most commonly contains one or more ASCII-Strings.
      Printing-Name                           02        002 
                                                16         8
                This property contains one ASCII-String.  In this case,
                the ASCII-String may contain only  the  printing  ASCII
                characters plus the "space" character.

      4.3.4  Encryption identifiers

           This  message  format  specification  defines two encryption
      identification codes.
      Unspecified                             00        000 
                                                16         8
                Use of  this  encryption  identifier  as  part  of  the
                Encrypted  data  element  indicates that the encryption
                method being used was not specified  for  inclusion  as
                part of the data element.
      NBS-Standard                            01        001 
                                                16         8
                Use  of  this  encryption  identifier  as  part  of the
                Encrypted data element indicates that the NBS  standard
                method for data encryption [NatB-77] was used.

      4.3.5  Compression identifiers

           This  message  format  specification defines two compression
      identification codes for use with the Compressed data element.
      Unspecified                             00        000 
                                                16         8
                Use of this  compression  identifier  as  part  of  the
                Compressed  data element indicates that the compression
                method being used was not specified  for  inclusion  as
                part of the data element.
      NBS-Standard                            01        001 
                                                16         8
                Use  of  this  compression  identifier  as  part of the
                Compressed data element  is  reserved  at  the  present
                time.    It will be used in the future to indicate that
                the NBS standard method for data compression  was  used
                once the data compression standard is defined.

                                     49                          

                                                          Section 4.3.6

      4.3.6  Message types

           This message format specification defines message type (MID)
      codes  for use in classifying the type of a message.  The message
      type could  be  confused  with  the  message  identifier  in  the
      Message-Id field; they are completely distinct concepts.
      NBS-Standard                            01        01 
                                                16        8
                This  message  type  marks  messages  defined  by  this
                message format specification.

                                     50                          

                            SUMMARY OF APPENDIXES

      Appendix A  Defines    the   fields   in   the   message   format
                  specification.  This  alphabetical  appendix  is  for
                  reference  use by implementors.  It contains semantic
                  definitions of fields from  Section  3.1.    It  also
                  defines  Field  Identifier values and specifies which
                  data elements are valid as the Contents for  each  of
                  the fields.

      Appendix B  Defines  the  data  elements  in  the  message format
                  specification.  This alphabetically ordered  appendix
                  is   for   reference   use   by   implementors.    It
                  consolidates information from Section 4.3.

      Appendix C  Provides a reference table listing the data  elements
                  in numerical order by their identifier octets.

      Appendix D  Provides a reference table summarizing the components
                  of messages according to whether they are required or
                  otional for CBMSs implementing the specification.

      Appendix E  Provides  a  reference  table  organizing the message
                  components according to the functional class  of  the
                  components.

      Appendix F  Provides   an  overview  of  the  syntactic  elements
                  defined by this message format specification.

      Appendix G  Summarizes syntactic elements  according  to  whether
                  they are required or optional for a CBMS implementing
                  the message format specification.

      Appendix H  Examples  of  each syntactic element displaying their
                  syntax and describing their associated semantics.

                                     51                          

                                                             Appendix A

                                 APPENDIX A
                  FIELDS -- IMPLEMENTORS' MASTER REFERENCE

           This  appendix  defines  all  of  the  fields in the message
      format specification for  reference  use  by  implementors.    It
      contains  semantics  definitions  of fields from Section 3.1.  It
      also defines Field Identifier values and which data elements  are
      valid  as  the  Contents  for  each  of  the  fields.   The field
      definitions appear alphabetically.

           Each field in the list has the following form:

      -----------------------------------------------------------------
      Field Name               Compliance   identifier  identifier
                                              value       value 
                                                   16          8

                   Description of the field semantics.   Names  of
              data  elements  that  are  valid in the Data Element
              Contents of this kind of field.

      -----------------------------------------------------------------

      Attachments              OPTIONAL       08        010 
                                                16         8
                This field  contains  additional  data  accompanying  a
                message.    It  is similar in intent to enclosures in a
                conventional mail system.  Contents of this  field  are
                unrestricted.
      Author                   OPTIONAL       0C        014 
                                                16         8
                This  field  identifies the individual(s) who wrote the
                primary contents of the message.   Use  of  the  Author
                field  is  discouraged  when the contents of the Author
                field and the From field would be completely redundant.
                This field contains one or more originator identities.
      Bcc                      OPTIONAL       0D        015 
                                                16         8
                This  field  identifies  additional  recipients  for  a
                message  (a  "blind carbon copies list").  The contents
                of this field are not to be included in copies  of  the
                message  sent  to the primary and secondary recipients.
                See section 3.2.1 for further discussion of the use  of
                blind  carbon  copies lists. This field contains one or
                more recipient identities.

                                     52                          

                                                             Appendix A

      Cc                       BASIC          06        006 
                                                16         8
                This   field  identifies  secondary  recipients  for  a
                message (a "carbon copies" list).  This field  contains
                one or more recipient identities.
      Circulate-Next           OPTIONAL       0E        016 
                                                16         8
                This field is used in conjunction with the Circulate-To
                field.    (See  Section  3.2.6.1.)    It identifies all
                recipients in a  circulation  list  who  have  not  yet
                received  the message.  This field contains one or more
                recipient identities.
      Circulate-To             OPTIONAL       0F        017 
                                                16         8
                This  field  identifies  recipients  for  a  circulated
                message.    (See  Section  3.2.6.1.)    It  is  used in
                conjunction with the Circulate-Next field.  This  field
                contains one or more recipient identities.
      Comments                 OPTIONAL       10        020 
                                                16         8
                This  field  permits  adding  comments onto the message
                without  disturbing  the  original  contents   of   the
                message.  While the Comments field will usually contain
                one or more ASCII-Strings, there are no restrictions on
                its contents.
      Date                     OPTIONAL       11        021 
                                                16         8
                This   field   contains   a  date  that  the  message's
                originator wishes to associate with  a  message.    The
                Date field is to the Posted-Date field as the date on a
                letter  is  to  the  postmark added by the post office.
                This field contains one Date.
      End-Date                 OPTIONAL       12        022 
                                                16         8
                This field contains the date on which a  message  loses
                effect.  (See also Section 3.2.5.)  This field contains
                one Date.
      From                     REQUIRED       01        001 
                                                16         8
                This  field  contains  the  identity of the originators
                taking formal responsibility for  this  message.    The
                contents  of  the  From field is to be used for replies
                when no Reply-to field appears  in  a  message.    This
                field contains one or more originator identities.
      In-Reply-To              OPTIONAL       13        023 
                                                16         8
                This  field designates previous correspondence to which
                this message is a reply.  The usual  contents  of  this
                field  would be the contents of the Message-ID field of
                the message(s) being replied to.  This  field  contains
                one or more Unique-IDs or ASCII-Strings.

                                     53                          

                                                             Appendix A

      Keywords                 OPTIONAL       14        024 
                                                16         8
                This  field  contains  keywords  or  phrases for use in
                retrieving a message.  This field contains one or  more
                ASCII-Strings.   (Each keyword or phrase is represented
                by a separate ASCII-String.)
      Message-Class            OPTIONAL       15        025 
                                                16         8
                This field indicates the purpose of  a  message.    For
                example,  it  might  contain values indicating that the
                message is a memorandum or a  data-base  entry.    This
                field contains one data element, an ASCII-String.
      Message-ID               OPTIONAL       16        026 
                                                16         8
                This  field contains a unique identifier for a message.
                This identifier is intended for machine generation  and
                processing.    Further  definition  appears  in Section
                3.2.4.1.  Only one Message-ID field is permitted  in  a
                message.    This  field  contains  one  data element, a
                Unique-ID.
      Obsoletes                OPTIONAL       26        046 
                                                16         8
                This field identifies one or more  messages  that  this
                one  supplants.    This  field  contains  at  least one
                Unique-ID and may contain more than one.
      Originator-Serial-Number OPTIONAL       17        027 
                                                16         8
                This field contains one or more serial numbers assigned
                by the message's originator.  (Messages  with  multiple
                recipients  should  all  have  the  same  value  in the
                Originator-Serial-Number field.   This  field  contains
                one  or  more ASCII-Strings.  (One ASCII-String is used
                for each serial number.)
      Posted-Date              REQUIRED       02        002 
                                                16         8
                This field contains the  posting  date,  which  is  the
                point  in  time  when  the  message  passes through the
                posting slot into a message transfer system.  Only  one
                Posted-Date  field  is  permitted  in  a message.  This
                field contains one Date.
      Precedence               OPTIONAL       18        030 
                                                16         8
                Ordinarily, message precedence or priority is a service
                request to  a  message  transfer  system.    A  message
                originator, however, can include precedence information
                in  a  message.  This field indicates the precedence at
                which the  message  was  posted.    One  example  of  a
                precedence   scheme   is  the  US  Military  categories
                "ROUTINE", "PRIORITY", "IMMEDIATE",  "FLASH  OVERRIDE",
                and   "EMERGENCY   COMMAND  PRECEDENCE".    This  field
                contains one ASCII-String.

                                     54                          

                                                             Appendix A

      Received-Date            OPTIONAL       19        031 
                                                16         8
                Delivery date.  This field may be added to a message by
                the   recipient's   message   receiving  program.    It
                indicates when the message left the delivery system and
                entered  the  recipient's  message  processing  domain.
                This field contains one Date.
      Received-From            OPTIONAL       1A        032 
                                                16         8
                This  field  contains  a  record  of  a  message's path
                through   a   message    transfer    system.        The
                recipient's  message  receiving  program  may store any
                such  information  that  it  obtains  from  a   message
                transfer  system  in  this field.  The contents of this
                field are unrestricted.
      References               OPTIONAL       20        040 
                                                16         8
                This field identifies other  correspondence  that  this
                message   references.    If  the  other  correspondence
                contains  a  Message-ID  field,  the  contents  of  the
                References  field must be the message identifier.  This
                field contains one or more Unique-IDs or ASCII-Strings.
      Reissue-Type             OPTIONAL       25        045 
                                                16         8
                This  field  is  used  in  conjunction   with   message
                encapsulating  (see  Section  3.2.2)  to  differentiate
                between messages being assigned or redistributed.  This
                field contains one  data  element,  usually  an  ASCII-
                String.
      Reply-To                 BASIC          03        003 
                                                16         8
                This field identifies any recipients for replies to the
                message.    This  field  contains one or more recipient
                identities.
      Sender                   OPTIONAL       22        042 
                                                16         8
                This field identifies the agent who sent  the  message.
                It  is  intended  either for when the sender is not the
                originator responsible for the message or  to  indicate
                who  among  a  group of originators responsible for the
                message actually sent it.  Use of the Sender  field  is
                discouraged  when  the contents of the Sender field and
                From field would be completely  redundant.    Only  one
                Sender  field  is  permitted  in a message.  This field
                contains one originator identity.
      Start-Date               OPTIONAL       23        043 
                                                16         8
                This field contains the date on which a  message  takes
                effect.  (See also Section 3.2.5.)  This field contains
                one Date.

                                     55                          

                                                             Appendix A

      Subject                  BASIC          07        007 
                                                16         8
                This field contains whatever information the originator
                provided  to  summarize  or  indicate the nature of the
                message.   This  field  contains  one  or  more  ASCII-
                Strings.
      Text                     BASIC          04        004 
                                                16         8
                This field contains the primary content of the message.
                Contents of this field are unrestricted.
      To                       REQUIRED       05        005 
                                                16         8
                This field identifies primary recipients for a message.
                This field contains one or more recipient identities.
      Warning-Date             OPTIONAL       24        044 
                                                16         8
                This  field is used either alone or in conjunction with
                an End-Date field.  It  contains  one  or  more  dates.
                These  dates  could  be  used  by  a message processing
                program as warnings of an impending end-date  or  other
                event.   (See also Section 3.2.5.)  This field contains
                one or more Dates.

                                     56                          

                                                             Appendix B

                                 APPENDIX B
               DATA ELEMENTS -- IMPLEMENTORS' MASTER REFERENCE

           The appendix defines all of the data elements in the message
      format  specification,  for  reference  use  by implementors.  It
      contains no new information but rather consolidates the syntactic
      information from Section 4.3.

           Each data element description has the following form.

      -----------------------------------------------------------------

      Data Element        (Compliance)   identifier   identifier
          Name            ( Category )    octet         octet 
                                               16            8

                Constructive class (primitive or constructor)

                Description of the syntax of the data element.

                +---//---+
                |        |     Diagram representing data element
                +---//---+

      -----------------------------------------------------------------

      ASCII-String             (BASIC)        02        002 
                                                16         8
                primitive

                This  data  element  contains   a   series   of   ASCII
                characters,   each  character  right-justified  in  one
                octet.    For  seven-bit  ASCII  characters,  the  most
                significant bit of each octet must be 0.

                 +--------+---//---+----//-----+
                 |P0000010|Lxxxxxxx|ASCII chars|
                 +--------+---//---+----//-----+

                                     57                          

                                                             Appendix B

      Bit-String               (OPTIONAL)     43        103 
                                                16         8
                primitive

                This  data  element contains a series of bits.  It uses
                the Qualifier data  element  component  to  record  the
                number  of  bits  of  padding (as an eight bit unsigned
                integer) needed to fill the final  octet  of  the  Data
                Element  Contents  to  an  even  octet boundary.  These
                padding bits have no meaning and occur in the low order
                bits of the final octet.   The  valid  values  for  the
                Qualifier  component  are  0  through 7.  The number of
                bits in the Data Element Contents  is  calculated  from
                the following formula.

                8   *   number of octets   -   value of
                        in the Data            Qualifier component
                        Element Contents

                 +--------+---//---+---//---+---//---+
                 |P1000011|Lxxxxxxx|Qxxxxxxx|  bits  |
                 +--------+---//---+---//---+---//---+

      Boolean                  (OPTIONAL)     08        010 
                                                16         8
                primitive

                This  data  element  contains  one octet whose value is
                either true or false.  False is represented by all bits
                being 0; true  is  represented  by  all  bits  being  1
                (although  any  non-zero value should be interpreted as
                true).

                 +--------+---//---+--------+
                 |P0001000|Lxxxxxxx| T or F |
                 +--------+---//---+--------+

                                     58                          

                                                             Appendix B

      Compressed               (OPTIONAL)     46        106 
                                                16         8
                constructor

                This  data  element  must  contain  a  Bit-String  data
                element.  It is used to represent  any  data  that  has
                been   compressed;   it   may   be  used  wherever  its
                uncompressed contents may appear.    A  Qualifier  data
                component  appears  in each Compressed data element; it
                contains a compression identifier (CID) to identify the
                compression algorithm used.  (See Section 4.3.5.)   The
                Data  Element  Contents  contains  the  product  of the
                compression process.

                 +--------+---//---+---//---+--------//--------+
                 |P1000110|Lxxxxxxx|Qxxxxxxx|Bit-String Element|
                 +--------+---//---+---//---+--------//--------+

      Date                     (BASIC)        28        050 
                                                16         8
                constructor

                This  data  element  contains  an   ASCII-String   data
                element,  which  is a representation of a date and time
                formatted in accordance with FIPS Publications 4 [NatB-
                68], 59 [NatB-79b], and 58 [NatB-79a].

                 +--------+---//---+------//------+
                 |P0101000|Lxxxxxxx| ASCII-String |
                 +--------+---//---+------//------+

                                     59                          

                                                             Appendix B

      Encrypted                (OPTIONAL)     47        107 
                                                16         8
                constructor

                This  data  element  must  contain a Bit-String.  It is
                used to represent any data that has been encrypted;  it
                may  be  used  wherever  its  unencrypted  contents may
                appear.  A Qualifier data  component  appears  in  each
                Encrypted  data  element;  it  contains  an  encryption
                identifier (EID) identifying the  encryption  algorithm
                used.   (See Section 4.3.4.)  The Data Element Contents
                is the product of the encryption process.

                 +--------+---//---+---//---+--------//--------+
                 |P1000111|Lxxxxxxx|Qxxxxxxx|Bit-String Element|
                 +--------+---//---+---//---+--------//--------+

      End-of-Constructor       (BASIC)        01        001 
                                                16         8
                primitive

                This data element terminates the Data Element  Contents
                in  a  constructor  data  element  that  has indefinite
                length.  This data element has no  Contents  component.
                (Use of this element is described in Section 4.2.2.1.)

                 +--------+---//---+
                 |P0000001|Lxxxxxxx|
                 +--------+---//---+

      Extension                (OPTIONAL)     7E        176 
                                                16         8
                constructor

                This  data  element  is  used  to  extend the number of
                available  data  elements  beyond  the  128  that   are
                possible   using  a  7-bit  identifier.    A  Qualifier
                component extends the encoding space  for  identifiers.
                (Extension and Vendor-Defined have the same syntax.)

                 +--------+---//---+---//---+---//---+
                 |P1111110|Lxxxxxxx|Qxxxxxxx|Anything|
                 +--------+---//---+---//---+---//---+

                                     60                          

                                                             Appendix B

      Field                    (BASIC)        4C        114 
                                                16         8
                constructor

                This   data  element  uses  a  Qualifier  data  element
                component.  The Qualifier component  contains  a  Field
                Identifier  (FID)  indicating  which  specific field is
                being represented.  (See Section 4.3.2.)

                 +--------+---//---+---//---+---//---+
                 |P1001100|Lxxxxxxx|Qxxxxxxx|elements|
                 +--------+---//---+---//---+---//---+

      Integer                  (OPTIONAL)     20        040 
                                                16         8
                primitive

                This data element contains a 2's complement integer  of
                variable  length,  high  order  octet  first.    It  is
                recommended that the data element contents be either  2
                or 4 octets long whenever possible.

                 +--------+---//---+---//---+
                 |P0100000|Lxxxxxxx| Integer|
                 +--------+---//---+---//---+

      Message                  (BASIC)        4D        115 
                                                16         8
                constructor

                This  data  element  may  contain Field or Message data
                elements.  Its Qualifier component contains  a  Message
                type  (MID)  indicating  the type of the message.  (See
                Section 4.3.6.)  (The MID is completely different  from
                the  message  identifier  in  the  Message-ID field and
                should not be confused with it.)

                 +--------+---//---+---//---+
                 |P1001101|Lxxxxxxx|Qxxxxxxx|
                 +--------+---//---+---//---+

                 +--------//---------//---------//---------//--------+
                 | Field, Message, Encrypted, or Compressed Elements |
                 +--------//---------//---------//---------//--------+

                                     61                          

                                                             Appendix B

      No-Op                    (OPTIONAL)     00        000 
                                                16         8
                primitive

                This data element does nothing.  No-Op is used whenever
                it  is  necessary  to include a data element that means
                "no operation".  It is a short placeholder.

                 +--------+---//---+
                 |P0000000|Lxxxxxxx|
                 +--------+---//---+

      Padding                  (OPTIONAL)     21        041 
                                                16         8
                primitive

                This data element is used to fill any number of octets.
                The contents of a Padding  element  are  undefined  and
                convey no information.

                 +--------+---//---+---//---+
                 |P0100001|Lxxxxxxx|anything|
                 +--------+---//---+---//---+

      Property-List            (OPTIONAL)     24        044 
                                                16         8
                constructor

                This  data  element  contains a series of Property data
                elements to be associated with another data element.

                 +--------+---//---+-------//--------+
                 |P0100100|Lxxxxxxx|Property Elements|
                 +--------+---//---+-------//--------+

                                     62                          

                                                             Appendix B

      Property                 (OPTIONAL)     45        105 
                                                16         8
                constructor

                This   data  element  uses  a  Qualifier  data  element
                component.      The   Qualifier   component    contains
                a  Property-Identifier (PID) to indicate which specific
                property is being represented.  (See Section 4.3.3.)

                 +--------+---//---+---//---+---//---+
                 |P1000101|Lxxxxxxx|Qxxxxxxx|elements|
                 +--------+---//---+---//---+---//---+

      Sequence                 (OPTIONAL)     0A        012 
                                                16         8
                constructor

                This data element contains any series of data elements.
                Sequence  differs  from  Set  in that the data elements
                making up the Data Element Contents must be  considered
                as  an  ordered  sequence  (according to their order of
                appearance in the sequence.)

                 +--------+---//---+---//---+
                 |P0001010|Lxxxxxxx|elements|
                 +--------+---//---+---//---+

      Set                      (OPTIONAL)     0B        013 
                                                16         8
                constructor

                This data element contains any series of data  elements
                with  no  ordering  of the elements implied.  (Sequence
                provides  an  ordered  series.)    Although  the   data
                elements   contained   in   a   Set   must   be  stored
                sequentially, the order in which they are stored is not
                defined and not processed.

                 +--------+---//---+---//---+
                 |P0001011|Lxxxxxxx|elements|
                 +--------+---//---+---//---+

                                     63                          

                                                             Appendix B

      Unique-ID                (OPTIONAL)     09        011 
                                                16         8
                constructor

                This  data element is a unique identifier.  It need not
                be human-readable.  The Data Element Contents may be an
                ASCII-String, a Bit-String, or an Integer.

                 +--------+---//---+---//---+
                 |P0001001|Lxxxxxxx| element|
                 +--------+---//---+---//---+

      Vendor-Defined           (OPTIONAL)     7F        177 
                                                16         8
                constructor

                This data element is used to  represent  vendor-defined
                data  elements.    A  Qualifier  component  extends the
                encoding  space  for  identifiers.      The   Qualifier
                component  is  not  guaranteed  to  be unique among all
                interconnected ems.     This   data   element   is
                interpreted   according   to  prior  agreement  between
                systems.  (Extension and Vendor-Defined  data  elements
                have the same syntax.)

                 +--------+---//---+---//---+---//---+
                 |P1111111|Lxxxxxxx|Qxxxxxxx|Anything|
                 +--------+---//---+---+---//---+

                                     64                          

                                                             Appendix C

                                 APPENDIX C
                       DATA ELEMENT IDENTIFIER OCTETS

       Identifier  Identifier Data Element Name

      00          000         No-Op
      01          001         End-of-Constructor
      02          002         ASCII-String
      08          010         Boolean
      09          011         Unique-ID
      0A          012         Sequence
      0B          013         Set
      20          040         Integer
      21          041         Padding
      24          044         Property-List
      28          050         Date
      43          103         Bit-String
      45          105         Property
      46          106         Compressed
      47          107         Encrypted
      4C          114         Field
      4D          115         Message
      7E          176         Extension
      7F          177         Vendor-Defined

                                     65                          

                                                             Appendix D

                                 APPENDIX D
              SUMMARY OF MESSAGE FIELDS BY COMPLIANCE CATEGORY

           This  appendix  is  for  reference  use.  It contains no new
      information, but rather abstracts from that presented in  Section
      3.1.

           This  appendix  contains  the  message  field names arranged
      alphabetically within compliance category.   (Appendix  E  orders
      the  field  names  within  functional  category.)  Complete field
      definitions appear in Appendix A.

           Required fields must appear in a message.  Basic fields must
      be recognized and processed by all CBM systems.  Optional  fields
      need  not  be  supported  by  a  CBMS  but, if supported, must be
      processed according to the meanings defined by the message format
      specification.

      D.1  REQUIRED Fields

      From
      Posted-Date
      To

      D.2  BASIC Fields

      Cc
      Reply-To
      Subject
      Text

      D.3  OPTIONAL Fields

      Attachments
      Author
      Bcc
      Circulate-Next
      Circulate-To
      Comments

                                     66                          

                                                             Appendix D

      Date
      End-Date
      In-Reply-To
      Keywords
      Message-Class
      Message-ID
      Obsoletes
      Originator-Serial-Number
      Precedence
      Received-Date
      Received-From
      References
      Reissue-Type
      Sender
      Start-Date
      Warning-Date

                                     67                          

                                                             Appendix E

                                 APPENDIX E
                  SUMMARY OF MESSAGE SEMANTICS BY FUNCTION

           This  appendix  is  for  reference  use.  It contains no new
      information, but rather abstracts from that presented in  Section
      3.1.

           This  appendix  contains  the  message  field names arranged
      alphabetically within functional class.  (Appen  orders  the
      field names within compliance class.)  Complete field definitions
      appear in Appendix A.

      E.1  Circulation

      Circulate-Next
      Circulate-To

      E.2  Cross Referencing

      In-Reply-To
      Message-ID
      Obsoletes
      Originator-Serial-Number
      References

      E.3  Life spans

      End-Date
      Start-Date
      Warning-Date

      E.4  Delivery System

      Received-Date
      Received-From

                                     68                          

                                                             Appendix E

      E.5  Miscellaneous Fields Used Generally

      Attachments
      Comments
      Keywords
      Message-Class
      Precedence
      Subject
      Text

      E.6  Reply Generation

      Reply-To

      E.7  Reissuing

      Reissue-Type

      E.8  Sending (Normal Transmission)

      Author
      Bcc
      Cc
      Date
      From
      Posted-Date
      Sender
      To

                                     69                          

                                                             Appendix F

                                 APPENDIX F
                       SUMMARY OF DATA ELEMENT SYNTAX

           This  appendix summarizes data element syntax by diagramming
      the components of data elements.  Detailed presentation  of  data
      element syntax appears in Section 4.3.1.

           In  these  diagrams,  required  components of a data element
      appear as follows.  (The double border signifies "required".)

                +========+        +===//===+
                |        |        |        |
                +========+        +===//===+
                always one        one or more
                octet long        octets long

           Optional components of  data  elements  are  represented  as
      follows.  (The single border signifies "not required".)

                +--------+        +---//---+
                |        |        |        |
                +--------+        +---//---+
                always one        one or more
                octet long        octets long

           The  first  octet in a data element is the identifier octet.
      In diagrams of data elements, all eight bits  of  the  identifier
      octet  are  always  shown.  Bits with fixed values show the fixed
      values as 1s and 0s.  Bits with variable values are shown as  x's
      and y's.

           The  first  bit  in  an  identifier octet is the P-bit.  Its
      value indicates whether a data element contains a property  list.
      (A  P-bit  value of 1 indicates the presence of a property list.)
      The remaining seven bits contain the rest of the identifier.

           Other octets in  a  data  element  belong  to  one  of  four
      classes, Length Code, Qualifier, Property-List, and Contents.  In
      diagrams  of  syntax  the  data  element  components  are labeled
      according to their class.

                                     70                          

                                                             Appendix F

           Component Class             Label

          Length code                  Length
          Qualifier                    Qual
          Property-List                P-List
          Contents                     Contents

           Data elements must follow this form.

                +========+===//===+---//---+---//---+---//---+
                |Pxxxxxxx| Length |  Qual  | P-List |contents|
                +========+===//===+---//---+---//---+---//---+

      The  value  of the Length component is the total number of octets
      following the length code octet in the data element.

                                     71                          

                                                             Appendix G

                                 APPENDIX G
               SUMMARY OF DATA ELEMENTS BY COMPLIANCE CATEGORY

           Compliance  categories  for syntactic elements are basic and
      optional.  Every CBMS is required to recognize and process  basic
      elements.    A  CBMS is not required to process optional elements
      although many are strongly recommended by the semantics.

           This appendix  summarizes  data  elements  by  listing  them
      according to their compliance category.

      G.1  BASIC Data Elements

      ASCII-String             (primitive)    02        002 
                                                16         8
      Date                     (constructor)  28        050 
                                                16         8
      End-Of-Constructor       (primitive)    01        001 
                                                16         8
      Field                    (constructor)  4C        114 
                                                16         8
      Message                  (constructor)  4D        115 
                                                16         8

      G.2  OPTIONAL Data Elements

      Bit-String               (primitive)    43        103 
                                                16         8
      Boolean                  (primitive)    08        010 
                                                16         8
      Compressed               (constructor)  46        106 
                                                16         8
      Encrypted                (constructor)  47        107 
                                                16         8
      Extension                (constructor)  7E        176 
                                                16         8
      Integer                  (primitive)    20        040 
                                                16         8
      No-Op                    (primitive)    00        000 
                                                16         8
      Padding                  (primitive)    21        041 
                                                16         8

                                     72                          

                                                             Appendix G

      Property                 (constructor)  45        105 
                                                16         8
      Property-List            (constructor)  24        044 
                                                16         8
      Sequence                 (constructor)  0A        012 
                                                16         8
      Set                      (constructor)  0B        013 
                                                16         8
      Unique-ID                (constructor)  09        011 
                                                16         8
      Vendor-Defined           (constructor)  7F        377 
                                                16         8

                                     73                          

                                                             Appendix H

                                 APPENDIX H
                                  EXAMPLES

           This  appendix presents at least one example for each of the
      data elements defined in this message format specification.    In
      these examples, identifier octets are represented in binary form.
      All  other  numbers  are presented in hexadecimal.  ASCII strings
      are   shown   as   characters   rather   than   their   numerical
      representation.   Although this message format specification does
      not define the syntax of names and addresses, message originators
      and recipients are identified by their  names.    This  does  not
      imply  anything  about how naming and addressing can or should be
      done;  it  is  simply  a  convenient  way  to  identify   message
      originators and recipients in these examples.

      H.1  Primitive Data Elements

           This  section  contains  an example of each of the primitive
      data elements.  Each example contains a short explanation  and  a
      series of octets.
           No-Op data element:

           +--------+--------+
           |00000000|00000000|
           +--------+--------+

           End-of-Constructor data element:

           +--------+--------+
           |00000001|00000000|
           +--------+--------+

                                     74                          

                                                             Appendix H

           Boolean data element whose value is true:

           +--------+--------+--------+
           |00001000|00000001|11111111|
           +--------+--------+--------+

           Integer  data  element  containing five octets of data.  Its
      value is 4,294,967,296 (decimal):

           +--------+--------+--------+--------+--------+
           |00100000|  0   5 |  0   1    0   0    0   0
           +--------+--------+--------+--------+--------+

                    +--------+--------+
                       0   0    0   0 |
                    +--------+--------+

           Padding data element containing  three  octets  of  padding.
      The values of those three octets are meaningless:

           +--------+--------+--------+--------+--------+
           |00100001|  0   3 |  F   F    F   F    F   F |
           +--------+--------+--------+--------+--------+

           ASCII-String  data  element containing nine characters.  Its
      value is "Hi There.":

           +--------+--------+---- ----+
           |00000010|  0   9 |Hi There.|
           +--------+--------+---- ----+

                                     75                          

                                                             Appendix H

           Bit-String data element containing 44 bits of data (((7-1) x
      8)  - 4).  Six octets are used to hold those 44 bits.  The last 4
      bits in the final octet are padding and are therefore ignored.

           Bit-String  Length   Spare
           +--------+--------+--------+--------+--------+
           |01000011|  0   7 |  0   4 |  0   A    3   B
           +--------+--------+--------+--------+--------+

                    +--------+--------+--------+--------+
                       5   F    2   9    1   C    D   0 |
                    +--------+--------+--------+--------+

      H.2  Constructor Data Elements

           This section contains an example of each of the  constructor
      data  elements.    Each  example contains a short explanation and
      then an annotated series of  the  data  elements  making  up  the
      constructor.
           Property-List  data  element  containing  one  Property data
      element.    The  property  is  Printing-Name  and  its  value  is
      "Distribution":

           Prop-List  Length  Property  Length    PID
           +--------+--------+--------+--------+--------+
           |00100100|  1   1 |01000101|  0   F |  0   2 |
           +--------+--------+--------+--------+--------+

                      ASCII    Length
                    +--------+--------+----    ----+
                    |00000010|  0   C |Distribution|
                    +--------+--------+----    ----+

                                     76                          

                                                             Appendix H

           Printing-Name  Property.   The value of the Printing-Name is
      "Distribution":

            Property  Length    PID     ASCII    Length
           +--------+--------+--------+--------+--------+
           |01000101|  0   F |  0   2 |00000010|  0   C |
           +--------+--------+--------+--------+--------+

                    +----    ----+
                    |Distribution|
                    +----    ----+

           Compressed data element.  Its contents were compressed using
      an as-yet-undefined NBS standard data compression algorithm.  The
      compressed data is in a bit-string that is 56  bits  long,  fully
      filling 7 octets:

           Compressed  Length   CID   Bit-String  Length
           +--------+--------+--------+--------+--------+
           |01000110|  0   B |  0   1 |01000011|  0   8 |
           +--------+--------+--------+--------+--------+

                       Spare
                    +--------+--------+--------+--------+
                    |  0   0 |  1   C    5   F    2   D
                    +--------+--------+--------+--------+

                    +--------+--------+--------+--------+
                       7   7    B   A    F   6    2   9 |
                    +--------+--------+--------+--------+

                                     77                          

                                                             Appendix H

           Encrypted  data  element.    The  encryption  method used to
      encrypt its contents has been intentionally not specified.   This
      element contains a Bit-String which contains 22 bits (((4-1) x 8)
      - 2) of data.  These 22 bits are represented in octets; the final
      2 bits in the final octet are padding and are therefore ignored:

           Encrypted   Length   EID   Bit-String  Length
           +--------+--------+--------+--------+--------+
           |01000111|  0   7 |  0   0 |01000011|  0   4 |
           +--------+--------+--------+--------+--------+

                       Spare
                    +--------+--------+--------+--------+
                    |  0   2 |  A   3    7   8    1   C |
                    +--------+--------+--------+--------+

           Date  data  element.    This  example includes a date but no
      time.  The date shown in this example is August 15, 1980:

             Date     Length   ASCII    Length
           +--------+--------+--------+--------+---  ---+
           |00101000|  0   A |00000010|  0   8 |19800815|
           +--------+--------+--------+--------+---  ---+

           Unique-ID data element, which is represented as  an  Integer
      data element whose value is 129 (decimal).

           Unique-ID  Length   Integer  Length
           +--------+--------+--------+--------+--------+--------+
           |00001001|  0   4 |00100000|  0   2 |  0   0    8   1 |
           +--------+--------+--------+--------+--------+--------+

                                     78                          

                                                             Appendix H

           Sequence  data  element  containing  two  ASCII-String  data
      elements.  The first ASCII-String is "This is" while  the  second
      string is " a list":

            Sequence  Length   ASCII    Length
           +--------+--------+--------+--------+--- ---+
           |00001010|  1   2 |00000010|  0   7 |This is|
           +--------+--------+--------+--------+--- ---+

                      ASCII    Length
                    +--------+--------+--- ---+
                    |00000010|  0   7 | a list|
                    +--------+--------+--- ---+

           Set  data element containing two Integer data elements.  The
      first integer has a value of 519 (decimal) while the value of the
      second is 71 (decimal).    (These  two  value  have  no  ordering
      because they belong to a set.)

              Set     Length   Integer  Length
           +--------+--------+--------+--------+--------+--------+
           |00001011|  0   8 |00100000|  0   2 |  0   2    0   7 |
           +--------+--------+--------+--------+--------+--------+

                      Integer  Length
                    +--------+--------+--------+--------+
                    |00100000|  0   2 |  0   0    4   7 |
                    +--------+--------+--------+--------+

           Field  data  element.   The specific field shown is the Text
      field with the contents "I will see you at lunch.":

             Field    Length    FID      ASCII   Length
           +--------+--------+--------+--------+--------+
           |01001100|  1   B |  0   4 |00000010|  1   8 |
           +--------+--------+--------+--------+--------+

                    +----                ----+
                    |I will see you at lunch.|
                    +----                ----+

                                     79                          

                                                             Appendix H

           Message containing four fields, Posted-Date, From, Text, and
      To.  It was sent on July 4, 1980 at 6 p.m. eastern daylight time.
      It  is  from  a person named Smith.  The text of the message is a
      question asking  the  recipient  "Are  you  going  to  watch  the
      fireworks?".  The message is sent to Jones:

            Message   Length    Type    Field    Length
           +--------+--------+--------+--------+--------+
           |01001101|  5   8 |  0   1 |01001100|  1   7 |
           +--------+--------+--------+--------+--------+

                       FID      Date    Length   ASCII
                    +--------+--------+--------+--------+
                    |  0   2 |00101000|  1   4 |00000010|
                    +--------+--------+--------+--------+

                      Length
                    +--------+----          ----+
                    |  1   2 |19800704-180000EDT|
                    +--------+----          ----+

                      Field    Length    FID     ASCII
                    +--------+--------+--------+--------+
                    |01001100|  0   8 |  0   1 |00000010|
                    +--------+--------+--------+--------+

                      Length
                    +--------+-- --+
                    |  0   5 |Smith|
                    +--------+-- --+

                       Field   Length    FID     ASCII
                    +--------+--------+--------+--------+
                    |01001100|  2   8 |  0   4 |00000010|
                    +--------+--------+--------+--------+

                      Length
                    +--------+
                    |  2   5 |
                    +--------+

                    +----                             ----+
                    |Are you going to watch the fireworks?|
                    +----                             ----+

                      Field    Length    FID     ASCII
                    +--------+--------+--------+--------+
                    |01001100|  0   8 |  0   5 |00000010|
                    +--------+--------+--------+--------+

                                     80                          

                                                             Appendix H

                      Length
                    +--------+-- --+
                    |  0   5 |Jones|
                    +--------+-- --+

           Extension  data  element  containing  a  length  code  and 3
      octets.    The  octet  immediately  following  the  length   code
      identifies  it  as  Extension  Data  Element 7.  The Data Element
      Contents is the final two octets.  The interpretation of the Data
      Element Contents would be defined in an extension or successor to
      this message format specification.  [Note: this  is  an  example.
      Any  actual extension data element 7 (if it were ever used) would
      be completely different from anything done here.]:

           Extension  Length
           +--------+--------+--------+--------+--------+
           |01111110|  0   3 |  0   7 |  4   A    E   9 |
           +--------+--------+--------+--------+--------+

           Vendor-Defined data element containing a length code  and  3
      octets.    The first octet identifies this as vendor-defined data
      element number 114 (decimal), which this  particular  vendor  has
      defined  to  contain  three  printable  ASCII  characters  in two
      octets.  (Data element 114 (decimal) for another  user  would  be
      completely  different.   For example, it might contain a floating
      point number.):

              User    Length
           +--------+--------+--------+--------+--------+
           |01111111|  0   3 |  7   2 |   P    O    E   |
           +--------+--------+--------+--------+--------+

      H.3  Fields

           This  section  contains  examples  of  Field  data   element
      constructors  for  each several different fields (Keywords, Text,
      Subject, Vendor-Defined).

                                     81                          

                                                             Appendix H

           Field  data  element  for keywords .  The field contains two
      keywords, Message and Computer, each represented  in  a  separate
      ASCII-string data element.

              Field   Length  Keywords   ASCII   Length
           +--------+--------+--------+--------+--------+
           |01001100|  1   4 |  1   4 |00000010|  0   7 |
           +--------+--------+--------+--------+--------+

                    +--- ---+
                    |Message|
                    +--- ---+

                      ASCII    Length
                    +--------+--------+---  ---+
                    |00000010|  0   8 |Computer|
                    +--------+--------+---  ---+

           Field  data  element  for  Text  with  a  Property-List data
      element containing a comment attached.  The text  field  contains
      the ASCII-String data element "Do you want lunch?"; the Property-
      List  data element contains a comment property, which consists of
      an ASCII-string data element containing "Now?":

             Field    Length   Text    Prop-List  Length
           +--------+--------+--------+--------+--------+
           |11001100|  2   0 |  0   4 |00100100|  0   9 |
           +--------+--------+--------+--------+--------+

                     Property  Length    PID     ASCII
                    +--------+--------+--------+--------+
                    |01000101|  0   7 |  0   1 |00000010|
                    +--------+--------+--------+--------+

                      Length
                    +--------+-  -+
                    |  0   4 |Now?|
                    +--------+-  -+

                      ASCII    Length
                    +--------+--------+----          ----+
                    |00000010|  1   2 |Do you want lunch?|
                    +--------+--------+----          ----+

                                     82                          

                                                             Appendix H

           Field  data  element  for Subject containing an ASCII-String
      data  element  ("Good  restaurants  in  Detroit"  followed  by  a
      carriage  return and a line feed).  (A recipient would expect the
      message to contain some  information  about  restaurants  in  the
      Detroit area.):

             Field    Length   Subject   ASCII   Length
           +--------+--------+--------+--------+--------+
           |01001100|  2   1 |  0   7 |00000010|  1   E |
           +--------+--------+--------+--------+--------+

                    +----                            ----+
                    |Good restaurants in Detroit.<cr><lf>|
                    +----                            ----+

                                     83                          

                                                             Appendix H

           Field  data  element whose form and meaning was defined by a
      vendor.    This  vendor  has  defined  vendor-defined  field   12
      (decimal)  to  be  a field with a printing name of "Reply-by" and
      contents consisting of a date; January  7,  1981  in  this  case.
      (The  meaning of vendor-defined field 12 is unique to the vendor;
      the same field number would  have  different  meaning  for  other
      vendors.):

             Field    Length  Qualifier   User   number
           +--------+--------+--------+--------+--------+
           |11001100|  1   F |  8   2 |  0   0    0   C |
           +--------+--------+--------+--------+--------+

                     Prop-List Length  Property  Length
                    +--------+--------+--------+--------+
                    |00100100|  0   E |01000101|  0   C |
                    +--------+--------+--------+--------+

                        PID    ASCII    Length
                    +--------+--------+--------+---- ----+
                    |  0   2 |00000010|  0   9 |Reply-By:|
                    +--------+--------+--------+---- ----+

                       Date    Length   ASCII    Length
                    +--------+--------+--------+--------+
                    |00101000|  0   A |00000010|  0   8 |
                    +--------+--------+--------+--------+

                    +---  ---+
                    |19810107|
                    +---  ---+

      H.4  Messages

           This  section contains several examples of complete messages
      and shows the results of  reissuing  a  message.    (See  Section
      3.2.2.)

                                     84                          

                                                             Appendix H

           The  following  sample message had Stevens as its originator
      and Johnson as its recipient.  The message was sent on August 14,
      1980 at 10 am EDT.   The  subject  of  the  message  is  "Project
      Deadline"  and the message is a reminder that the deadline is the
      next day and that the section of the report for the project being
      done by Johnson should be turned in to Stevens by 3 pm that day.

            Message       Length         Type
           +--------+--------+--------+--------+
           |01001101|  8   1 |  B   4 |  0   1 |
           +--------+--------+--------+--------+

              Field   Length    FID     ASCII
           +--------+--------+--------+--------+
           |01001100|  0   A |  0   5 |00000010|
           +--------+--------+--------+--------+

                      Length
                    +--------+--- ---+
                    |  0   7 |Johnson|
                    +--------+--- ---+

             Field    Length    FID      ASCII
           +--------+--------+--------+--------+
           |01001100|  0   A |  0   1 |00000010|
           +--------+--------+--------+--------+

                      Length
                    +--------+--- ---+
                    |  0   7 |Stevens|
                    +--------+--- ---+

             Field    Length    FID     ASCII    Length
           +--------+--------+--------+--------+--------+
           |01001100|  1   3 |  0   7 |00000010|  1   0 |
           +--------+--------+--------+--------+--------+

                    +----        ----+
                    |Project Deadline|
                    +----        ----+

             Field    Length    FID      Date    Length
           +--------+--------+--------+--------+--------+
           |01001100|  1   5 |  0   2 |00101000|  1   2 |
           +--------+--------+--------+--------+--------+

                      ASCII    Length
                    +--------+--------+----        ----+
                    |00000010|  1   0 |19800814-1000EDT|
                    +--------+--------+----        ----+

                                     85                          

                                                             Appendix H

             Field    Length    FID      ASCII   Length
           +--------+--------+--------+--------+--------+
           |01001100|  6   D |  0   4 |00000010|  6   A |
           +--------+--------+--------+--------+--------+

                    +----
                    |Don't forget the project report is
                    +----

                     due tomorrow.  Please have<CrLf>

                     your section to me by three this

                           ----+
                     afternoon.|
                           ----+

           The  following  example illustrates the results of reissuing
      the first message in this section.   This  message  contains  the
      original  message  (as  a  Message  data  element), To, From, and
      Posted-Date fields, and a Reissue-Type field  with  Redistributed
      as its value:

            Message       Length         Type
           +--------+--------+--------+--------+
           |01001101|  8   1 |  F   8 |  0   1 |
           +--------+--------+--------+--------+

              Field   Length    FID      ASCII
           +--------+--------+--------+--------+
           |01001100|  0   9 |  0   5 |00000010|
           +--------+--------+--------+--------+

                      Length
                    +--------+--  --+
                    |  0   6 |Cooper|
                    +--------+--  --+

             Field    Length    FID      ASCII
           +--------+--------+--------+--------+
           |01001100|  0   A |  0   1 |00000010|
           +--------+--------+--------+--------+

                                     86                          

                                                             Appendix H

                      Length
                    +--------+--- ---+
                    |  0   7 |Johnson|
                    +--------+--- ---+

             Field    Length    FID      Date    Length
           +--------+--------+--------+--------+--------+
           |01001100|  1   5 |  0   2 |00101000|  1   2 |
           +--------+--------+--------+--------+--------+

                       ASCII   Length
                    +--------+--------+----        ----+
                    |00000010|  1   0 |19800814-1030EDT|
                    +--------+--------+----        ----+

             Field    Length    FID      ASCII   Length
           +--------+--------+--------+--------+--------+
           |01001100|  1   0 |  2   5 |00000010|  0   D |
           +--------+--------+--------+--------+--------+

                    +----     ----+
                    |Redistributed|
                    +----     ----+

            Message       Length         Type
           +--------+--------+--------+--------+
           |01001101|  8   1 |  B   4 |  0   1 |
           +--------+--------+--------+--------+

              Field   Length    FID      ASCII
           +--------+--------+--------+--------+
           |01001100|  0   A |  0   5 |00000010|
           +--------+--------+--------+--------+

                      Length
                    +--------+--- ---+
                    |  0   7 |Johnson|
                    +--------+--- ---+

             Field    Length    FID      ASCII
           +--------+--------+--------+--------+
           |01001100|  0   A |  0   1 |00000010|
           +--------+--------+--------+--------+

                      Length
                    +--------+--- ---+
                    |  0   7 |Stevens|
                    +--------+--- ---+

                                     87                          

                                                             Appendix H

             Field    Length    FID     ASCII    Length
           +--------+--------+--------+--------+--------+
           |01001100|  1   3 |  0   7 |00000010|  1   0 |
           +--------+--------+--------+--------+--------+

                    +----        ----+
                    |Project Deadline|
                    +----        ----+

             Field    Length    FID      Date    Length
           +--------+--------+--------+--------+--------+
           |01001100|  1   5 |  0   2 |00101000|  1   2 |
           +--------+--------+--------+--------+--------+

                      ASCII    Length
                    +--------+--------+----        ----+
                    |00000010|  1   0 |19800814-1000EDT|
                    +--------+--------+----        ----+

             Field    Length    FID      ASCII   Length
           +--------+--------+--------+--------+--------+
           |01001100|  6   D |  0   4 |00000010|  6   A |
           +--------+--------+--------+--------+--------+

                    +----
                    |Don't forget the project report is
                    +----

                     due tomorrow.  Please have<CrLf>

                     your section to me by three this

                           ----+
                     afternoon.|
                           ----+

      H.5  Unknown Lengths

           This  section contains two examples of data elements with an
      unknown length.  The two examples have been presented in sections
      H.2 and H.4, but with a known rather than an unknown length.

                                     88                          

                                                             Appendix H

           Set  data  element  with  an  unknown  length containing two
      Integer data elements.  The first integer  has  a  value  of  519
      (decimal)  while the value of the second is 71 (decimal).  (These
      two value have no ordering because they belong to a set.)

              Set     Length   Integer  Length
           +--------+--------+--------+--------+--------+--------+
           |00001011|  8   0 |00100000|  0   2 |  0   2    0   7 |
           +--------+--------+--------+--------+--------+--------+

                      Integer  Length
                    +--------+--------+--------+--------+
                    |00100000|  0   2 |  0   0    4   7 |
                    +--------+--------+--------+--------+

                    End-of-Con Length
                    +--------+--------+
                    |00000000|00000000|
                    +--------+--------+

           The following sample message  with  an  unknown  length  had
      Stevens  as  its  originator  and  Johnson as its recipient.  The
      message was sent on August 14, 1980 at 10 am EDT.  The subject of
      the message is "Project Deadline" and the message is  a  reminder
      that  the  deadline  is  the next day and that the section of the
      report for the project being done by Johnson should be turned  in
      to Stevens by 3 pm that day.

            Message   Length    Type
           +--------+--------+--------+
           |01001101|  8   0 |  0   1 |        +--------+--------+--------+

              Field   Length    FID     ASCII
           +--------+--------+--------+--------+
           |01001100|  0   A |  0   5 |00000010|
           +--------+--------+--------+--------+

                      Length
                    +--------+--- ---+
                    |  0   7 |Johnson|
                    +------- ---+

                                     89                          

                                                             Appendix H

             Field    Length    FID      ASCII
           +--------+--------+--------+--------+
           |01001100|  0   A |  0   1 |00000010|
           +--------+--------+--------+--------+

                      Length
                    +--------+--- ---+
                    |  0   7 |Stevens|
                    +--------+--- ---+

             Field    Length    FID     ASCII    Length
           +--------+--------+--------+--------+--------+
           |01001100|  1   3 |  0   7 |00000010|  1   0 |
           +--------+--------+--------+--------+--------+

                    +----        ----+
                    |Project Deadline|
                    +----        ----+

             Field    Length    FID      Date    Length
           +--------+--------+--------+--------+--------+
           |01001100|  1   5 |  0   2 |00101000|  1   2 |
           +--------+--------+--------+--------+--------+

                      ASCII    Length
                    +--------+--------+----        ----+
                    |00000010|  1   0 |19800814-1000EDT|
                    +--------+--------+----        ----+

             Field    Length    FID      ASCII   Length
           +--------+--------+--------+--------+--------+
           |01001100|  6   D |  0   4 |00000010|  6   A |
           +--------+--------+--------+--------+--------+

                    +----
                    |Don't forget the project report is
                    +----

                     due tomorrow.  Please have<CrLf>

                     your section to me by three this

                           ----+
                     afternoon.|
                           ----+

                    End-of-Con Length
                    +--------+--------+
                    |00000000|00000000|
                    +--------+--------+

                                     90                          

                                     91                          

                                 REFERENCES

      [BlaR-80]
           R. P. Blanc and J. F. Heafner. The NBS Program in Computer
           Network Protocol Standards. In Proceedings, ICCC 80.  1980.

      [CroD-77]
           David H. Crocker, John J. Vittal, Kenneth T. Pogran,
           D. Austin Henderson, Jr. Standard for the Format of ARPA
           Network Text Messages. RFC 733, The Rand Corporation, Bolt
           Beranek and Newman Inc, Massachussets Institute of
           Technology, Bolt Beranek and Newman Inc., November, 1977.

      [FeiE-79]
           E. Feinler, J. Pickens, and A. Sjoberg. Computer Message
           Services Bibliography. Technical Report NIC-BIBLIO-791201,
           SRI International, December, 1979.

      [ISOD-79]
           ISO/TC97/SC6 Data Communications. Second Draft Proposed
           Communication Heading Format Standard. ISO/TC97/SC6 N 1948,
           ISO International Organization for Standardization
           Organization Internationale de Normalisation, September,
           1979. Secretariat: USA (ANSI).

      [ISOD-81]
           ISO/TC97/SC16. Open Systems Interconnection Basic Reference
           Model. ISO/TC97/SC16 N, ISO International Ozation for
           Standardization Organization Internationale de
           Normalisation, 1981.

      [NatB-68]
           National Bureau of Standards. Calendar Date. Federal
           Information Processing Standards Publication 4, U.S.
           Department of Commerce / National Bureau of Standards,
           November, 1968.

      [NatB-77]
           National Bureau of Standards. Data Encryption Standard.
           Federal Information Processing Standards Publication 46,
           U.S. Department of Commerce / National Bureau of Standards,
           January, 1977.

      [NatB-79a]
           National Bureau of Standards. Representations of Local Time
           of the Day for Information Interchange. Federal Information
           Processing Standards Publication 58, U.S. Department of
           Commerce / National Bureau of Standards, February, 1979.

                                     92                          

      [NatB-79b]
           National Bureau of Standards. Representations of Universal
           Time, Local Time Differentials, and United States Time Zone
           References for Information Interchange. Federal Information
           Processing Standards Publication 59, U.S. Department of
           Commerce / National Bureau of Standards, February, 1979.

      [PosJ-79]
           Jonathan B. Postel. INTERNET MESSAGE PROTOCOL. RFC 753,
           Information Sciences Institute, March, 1979.

      [SchP-79]
           Peter Schicker. The Computer Based Mail Environment: An
           Overview. Technical Report, Bell-Northern Research Ltd.,
           Ottawa, Ontario, Canada, December, 1979.

      [TasG-80]
           Task Group X3S33 on Data Communications Formats, ANSI
           Subcommittee X3S3 on Data Communications. Third Draft
           Proposed American National Standard for Heading Format
           Structure for Code Independent Communication Headings. ANSI
           document X3S37/80-01, Computer and Business Equipment
           Manufacturers Association, 1980.

                                     93                          

                                    INDEX

                ASCII-String   29, 30, 42, 45, 47, 49, 53, 54, 55, 57,
                        59, 63
                Assignment   17, 22, 55
                Attachments   17, 52
                Audit trail   20
                Author   14, 52

                BASIC   13
                BASIC Data Elements
                   ASCII-String   42, 57
                   Date   45, 59
                   End-of-Constructor   43, 60
                   Field   46, 60
                   Message   46, 61
                BASIC fields
                   Cc   14
                   Reply-To   14
                   Subject   17
                   Text   17
                BASIC syntactic elements   29
                Bcc   14, 19, 20, 52
                Bit numbering in octets   32
                Bit-String   30, 37, 42, 44, 45, 47, 57, 58, 59, 63
                Boolean   30, 43, 58

                Cc   14, 19, 52
                Chains of correspondence   24
                Circulate-Next   15, 26, 53
                Circulate-To   15, 26, 53
                Circulation   26
                Comment   30, 31, 38, 49
                Comments   18, 53
                Compliance requirements   34
                Compressed   31, 37, 44, 49, 58
                Compression identifier   44, 58
                Compression Identifiers
                   NBS-Standard   49
                   Unspecified   49
                Constructor data element   29, 30
                Contents   32, 70
                Cross Referencing   24

                Data Element Contents   37, 38, 39, 81, 36, 39, 47, 63,
                        36, 38, 39, 41, 42, 47, 57, 63, 81
                Data Elements

                                     94                          

                   ASCII-String (BASIC)   42, 57
                   Bit-String (OPTIONAL)   42, 57
                   Boolean (OPTIONAL)   43, 58
                   Compressed (OPTIONAL)   44, 58
                   Date (BASIC)   45, 59
                   Encrypted (OPTIONAL)   45, 59
                   End-of-Constructor (BASIC)   43, 60
                   Extension (OPTIONAL)   45, 60
                   Field (BASIC)   46, 60
                   Integer (OPTIONAL)   43, 61
                   Message (BASIC)   46, 61
                   No-Op (OPTIONAL)   44, 61
                   Padding (OPTIONAL)   44, 62
                   Property (OPTIONAL)   47, 62
                   Property-List (OPTIONAL)   46, 62
                   Sequence (OPTIONAL)   47, 63
                   Set (OPTIONAL)   47, 63
                   Unique-ID (OPTIONAL)   47, 63
                   Vendor-Defined (OPTIONAL)   48, 64
                Date   15, 45, 53, 54, 55, 56, 59
                Dating   25
                Delivery   9, 15, 54
                Delivery Protocol   9
                Delivery Slot   9

                Encapsulating   22
                Encrypted   31, 37, 45, 49, 59
                Encryption identifier   45, 59
                Encryption Identifiers
                   NBS-Standard   49
                   Unspecified   49
                End-Date   15, 25, 53, 56
                End-Of-Constructor   30, 36, 39, 43, 60
                Extension   41, 45, 60

                Field   10, 26, 29, 30, 31, 37, 46, 60, 61, 66
                Field Identifier   46, 60
                Field label presentation   29
                Fields
                   Attachments (OPTIONAL)   52, 17
                   Author (OPTIONAL)   52, 14
                   Bcc (OPTIONAL)   52, 14
                   Cc (BASIC)   52, 14
                   Circulate-Next (OPTIONAL)   53, 15
                   Circulate-To (OPTIONAL)   53, 15
                   Comments (OPTIONAL)   53, 18
                   Date (OPTIONAL)   53, 15
                   End-Date (OPTIONAL)   53, 15
                   From (REQUIRED)   53, 14
                   In-Reply-To (OPTIONAL)   53, 16
                   Keywords (OPTIONAL)   53, 18

                                     95                          

                   Message-Class (OPTIONAL)   54, 17
                   Message-ID (OPTIONAL)   54, 16
                   Obsoletes (OPTIONAL)   54, 16
                   Originator-Serial-Number (OPTIONAL)   54, 16
                   Posted-Date (REQUIRED)   54, 15
                   Precedence (OPTIONAL)   54, 16
                   Received-Date (OPTIONAL)   54, 15
                   Received-From (OPTIONAL)   55, 17
                   References (OPTIONAL)   55, 16
                   Reissue-Type (OPTIONAL)   55, 17
                   Reply-To (BASIC)   55, 14
                   Sender (OPTIONAL)   55, 14
                   Start-Date (OPTIONAL)   55, 15
                   Subject (BASIC)   55, 17
                   Text (BASIC)   56, 17
                   To (REQUIRED)   56, 14
                   Warning-Date (OPTIONAL)   56, 15
                From   12, 14, 23, 52, 53, 55

                Globally unique identifiers   24

                Identifier octet   33, 35, 32, 33, 36, 39, 40, 70
                Identifiers
                   globally unique   24
                In-Reply-To   16, 24, 53
                Indefinite length code   35
                Integer   30, 43, 47, 61, 63

                Keywords   18, 53, 81

                Length Code   34, 36, 32, 33, 34, 35, 36, 37, 39, 40,
                        70, 71, 81
                Long length code   35

                Message Transfer System   8, 9, 17, 54
                Message   10, 12, 29, 30, 31, 37, 46, 61
                Message content   9
                Message envelope   9
                Message stores   25
                Message Transfer System   9, 17, 20, 55, 8, 9, 10, 12,
                        15, 16, 20, 54, 55
                Message Types
                   NBS-Standard   50
                Message-Class   17, 54
                Message-ID   16, 24, 26, 53, 54, 55

                NBS-Standard   49, 50
                No-Op   44, 61
                Numbering bits in octets   32

                Obsoletes   16, 24, 54

                                     96                          

                Octets
                   bit numbering in   32
                OPTIONAL   13
                OPTIONAL Data Elements
                   Bit-String   42, 57
                   Boolean   43, 58
                   Compressed   44, 58
                   Encrypted   45, 59
                   Extension   45, 60
                   Integer   43, 61
                   No-Op   44, 61
                   Padding   44, 62
                   Property   47, 62
                   Property-List   46, 62
                   Sequence   47, 63
                   Set   47, 63
                   Unique-ID   47, 63
                   Vendor-Defined   48, 64
                OPTIONAL fields
                   Attachments   17
                   Author   14
                   Bcc   14
                   Circulate-Next   15
                   Circulate-To   15
                   Comments   18
                   Date   15
                   End-Date   15
                   In-Reply-To   16
                   Keywords   18
                   Message-Class   17
                   Message-ID   16
                   Obsoletes   16
                   Originator-Serial-Number   16
                   Precedence   16
                   Received-Date   15
                   Received-From   17
                   References   16
                   Reissue-Type   17
                   Sender   14
                   Start-Date   15
                   Warning-Date   15
                OPTIONAL syntactic elements   29
                Originator   11, 13, 15, 25, 52, 53, 55
                Originator-Serial-Number   16, 25, 54

                Padding   44, 62
                Person   13
                Posted-Date   12, 15, 26, 53, 54
                Posting   9
                Posting Protocol   9
                Posting Slot   9

                                     97                          

                Precedence   16, 54
                Precedence categories   17
                Precedence scheme   54
                Presentation
                   field label   29
                Primitive data element   30, 29, 30
                Printing-Name   30, 38, 49, 76
                Process   13
                Properties
                   Comment   49
                   Printing-Name   49
                Property   32, 37, 46, 47, 62
                Property-Identifier   47, 62
                Property-List   30, 32, 33, 38, 39, 40, 46, 62, 70

                Qualifier   32, 33, 34, 36, 37, 39, 40, 42, 44, 45, 46,
                        47, 48, 57, 58, 59, 60, 62, 64, 70
                Qualifiers   37

                Received-Date   15, 54
                Received-From   17, 55
                Recipient   11, 14, 17, 52, 53, 55, 56
                Redistribution   17, 22, 55
                References   16, 24, 55
                Reissue-Type   17, 55
                Reply   13, 23
                Reply-to   14, 23, 53, 55
                REQUIRED   13
                REQUIRED fields
                   From   14
                   Posted-Date   15
                   To   14
                Requirements
                   compliance   34
                Role   13

                Sender   14, 26, 55
                Sequence   29, 30, 47, 63
                Sequences   30
                Serial Numbers   16, 24, 54
                Set   30, 47, 63
                Short length code   35
                Slot   9
                Start-Date   15, 25, 55
                Subject   17, 55
                Syntactic reissuing   22

                Text   17, 26, 56
                To   12, 14, 19, 26, 30, 56

                Unique identifiers   24

                                     98                          

                Unique-ID   47, 53, 54, 55, 63
                Unspecified   49
                User Agent   8, 9, 20
                User interface   29

                Vendor-Defined   41, 48, 64

                Warning-Date   15, 25, 56

                                     99                                

 

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