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RFC 2524 - Neda's Efficient Mail Submission and Delivery (EMSD)


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Network Working Group                                         M. Banan
Request for Comments: 2524                   Neda Communications, Inc.
Category: Informational                                  February 1999

                                 Neda's
             Efficient Mail Submission and Delivery (EMSD)
                   Protocol Specification Version 1.3

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1999).  All Rights Reserved.

IESG Note

   The protocol specified in this document may be satisfactory for
   limited use in private wireless IP networks.  However, it is
   unsuitable for general-purpose message transfer or for transfer of
   messages over the public Internet, because of limitations that
   include the following:

   - Lack of congestion control

      EMSD is layered on ESRO [RFC 2188], which does not provide
      congestion control.  This makes EMSD completely unsuitable for
      end-to-end use across the public Internet.  EMSD should be
      considered for use in a wireless network only if all EMSD email
      exchanged between the wireless network and the public Internet
      will transit an EMSD<->SMTP gateway between the two regions.

   - Inadequate security

      The document specifies only clear-text passwords for
      authentication.  EMSD should be used across a wireless network
      only if sufficiently strong encryption is in use to protect the
      clear-text password.

   - Lack of character set internationalization

      EMSD has no provision for representation of characters outside of
      the ASCII repertoire or for language tags.

   - Poorly defined gatewaying to and from Internet Mail

      Because Internet Mail and EMSD have somewhat different and
      conflicting service models and different data models, mapping
      between them may provide good service only in limited cases, and
      this may cause operational problems.

   The IESG therefore recommends that EMSD deployment be limited to
   narrow circumstances, i.e., only to communicate with devices that
   have inherent limitations on the length and format of a message (no
   more than a few hundred bytes of ASCII text), using either:

   a. wireless links with adequate link-layer encryption and gatewayed
      to the public Internet, or

   b. a private IP network that is either very over-provisioned or has
      some means of congestion control.

   In the near future, the IESG may charter a working group to define an
   Internet standards-track protocol for efficient transmission of
   electronic mail messages, which will be highly compatible with
   existing Internet mail protocols, and which wil be suitable for
   operation over the global Internet, including both wireless and wired
   links.

ABSTRACT

   This document specifies the protocol and format encodings for
   Efficient Mail Submission and Delivery (EMSD). EMSD is a messaging
   protocol that is highly optimized for submission and delivery of
   short Internet mail messages.  EMSD is designed to be a companion to
   existing Internet mail protocols.

   This specification narrowly focuses on submission and delivery of
   short mail messages with a clear emphasis on efficiency.  EMSD is
   designed specifically with wireless network (e.g., CDPD, Wireless-IP,
   Mobile-IP) usage in mind.  EMSD is designed to be a natural
   enhancement to the mainstream of Internet mail protocols when
   efficiency in mail submission and mail delivery are important.  As
   such, EMSD is anticipated to become an initial basis for convergence
   of Internet Mail and IP-based Two-Way Paging.

   The reliability requirement for message submission and message
   delivery in EMSD are the same as existing email protocols.  EMSD
   protocol accomplishes reliable connectionless mail submission and
   delivery services on top of Efficient Short Remote Operations (ESRO)
   protocols as specified in RFC-2188 [1].

   Most existing Internet mail protocols are not efficient.  Most
   existing Internet mail protocols are designed with simplicity and
   continuity with SMTP traditions as two primary requirements.  EMSD is
   designed with efficiency as a primary requirement.

   The early use of EMSD in the wireless environment is manifested as
   IP-based Two-Way Paging services.  The efficiency of this protocol
   also presents significant benefits for large centrally operated
   Internet mail service providers.

Table of Contents

   1  PRELIMINARIES                                                 4
      1.1 Internet Mail Submission and Delivery     .   .   .   .   4
      1.2 Relationship Of EMSD To Other Mail Protocols  .   .   .   5
      1.3 EMSD Requirements and Goals   .   .   .   .   .   .   .   7
      1.4 Anticipated Uses Of EMSD  .   .   .   .   .   .   .   .   8
      1.5 Definitions of Terms Used in this Specification   .   .   9
      1.6 Conventions Used In This Specification    .   .   .   .   9
      1.7 About This Specification  .   .   .   .   .   .   .   .  10
   2  EFFICIENT MAIL SUBMISSION AND DELIVERY OVERVIEW              10
   3  EFFICIENT MAIL SUBMISSION AND DELIVERY PROTOCOL              11
      3.1 Use Of Lower Layers   .   .   .   .   .   .   .   .   .  13
          3.1.1 Use of ESROS    .   .   .   .   .   .   .   .   .  13
          3.1.2 Use Of UDP  .   .   .   .   .   .   .   .   .   .  13
          3.1.3 Encoding Rules  .   .   .   .   .   .   .   .   .  13
          3.1.4 Presentation Context    .   .   .   .   .   .   .  14
      3.2 EMSD-UA Invoked Operations    .   .   .   .   .   .   .  14
          3.2.1 submit  .   .   .   .   .   .   .   .   .   .   .  14
          3.2.2 deliveryControl     .   .   .   .   .   .   .   .  17
          3.2.3 deliveryVerify  .   .   .   .   .   .   .   .   .  21
      3.3 EMSD-SA Invoked Operations    .   .   .   .   .   .   .  23
          3.3.1 deliver     .   .   .   .   .   .   .   .   .   .  23
          3.3.2 submissionControl   .   .   .   .   .   .   .   .  25
          3.3.3 submissionVerify    .   .   .   .   .   .   .   .  28
      3.4 EMSD Common Information Objects   .   .   .   .   .   .  30
          3.4.1 SecurityElements    .   .   .   .   .   .   .   .  30
          3.4.2 Message Segmentation and Reassembly     .   .   .  30
          3.4.3 Common Errors   .   .   .   .   .   .   .   .   .  33
          3.4.4 ContentType     .   .   .   .   .   .   .   .   .  35
          3.4.5 EMSDMessageId   .   .   .   .   .   .   .   .   .  35
          3.4.6 EMSDORAddress   .   .   .   .   .   .   .   .   .  36
          3.4.7 EMSDAddress     .   .   .   .   .   .   .   .   .  36
          3.4.8 DateTime    .   .   .   .   .   .   .   .   .   .  36
          3.4.9 AsciiPrintableString    .   .   .   .   .   .   .  37
          3.4.10 ProtocolVersionNumber  .   .   .   .   .   .   .  37
      3.5 Submission and Delivery Procedures    .   .   .   .   .  38
   4  DUPLICATE OPERATION DETECTION SUPPORT                        40

      4.1 Duplicate Operation Detection Support Overview    .   .  40
          4.1.1 Operation Value     .   .   .   .   .   .   .   .  40
          4.1.2 Operation Instance Identifier   .   .   .   .   .  41
   5  EMSD PROCEDURE FOR OPERATIONS                                42
      5.1 MTS Behavior  .   .   .   .   .   .   .   .   .   .   .  43
          5.1.1 MTS Performer   .   .   .   .   .   .   .   .   .  43
          5.1.2 Message-submission  .   .   .   .   .   .   .   .  44
          5.1.3 Delivery-control    .   .   .   .   .   .   .   .  46
          5.1.4 Delivery-verify     .   .   .   .   .   .   .   .  46
          5.1.5 MTS Invoker     .   .   .   .   .   .   .   .   .  46
      5.2 UA Behavior   .   .   .   .   .   .   .   .   .   .   .  49
          5.2.1 UA Performer    .   .   .   .   .   .   .   .   .  49
          5.2.2 UA Invoker  .   .   .   .   .   .   .   .   .   .  52
   6  EMSD FORMAT STANDARDS                                        54
      6.1 Format Standard Overview  .   .   .   .   .   .   .   .  54
      6.2 Interpersonal Messages    .   .   .   .   .   .   .   .  54
          6.2.1 Heading fields  .   .   .   .   .   .   .   .   .  55
          6.2.2 Body part types     .   .   .   .   .   .   .   .  61
   7  ACKNOWLEDGMENTS                                              62
   8  SECURITY CONSIDERATIONS                                      62
   9  AUTHOR'S ADDRESS                                             62
   A  EMSD-P ASN.1 MODULE                                          63
   B  EMSD-IPM ASN.1 MODULE                                        74
   C  RATIONALE FOR KEY DESIGN DECISIONS                           78
      C.1 Deviation From The SMTP Model     .   .   .   .   .   .  78
          C.1.1 Comparison of SMTP and EMSD Efficiency  .   .   .  78
      C.2 Use of ESRO Instead of TCP    .   .   .   .   .   .   .  79
      C.3 Use Of Remote Procedure Call (RPC) Model  .   .   .   .  79
      C.4 Use Of ASN.1  .   .   .   .   .   .   .   .   .   .   .  80
   D  FURTHER DEVELOPMENT                                          81
   E  REFERENCES                                                   82
   F  FULL COPYRIGHT STATEMENT                                     83

1  PRELIMINARIES

   Mail in the Internet was not a well-planned enterprise, but instead
   arose in more of an "organic" way.

   This introductory section is not intended to be a reference model and
   concept vocabulary for mail in the Internet.  Instead, it only
   provides the necessary preliminaries for the concepts and terms that
   are essential to this specification.

1.1  Internet Mail Submission and Delivery

   For the purposes of this specification, mail submission is the
   process of putting mail into the mail transfer system (MTS).

   For the purposes of this specification, mail delivery is the process
   of the MTS putting mail into a user's final mail-box.

   Throughout the Internet, presently most of mail submission and
   delivery is done through SMTP.

   SMTP was defined as a message *transfer* protocol, that is, a means
   to route (if needed) and deliver mail by putting finished (complete)
   messages in a mail-box.  Originally, users connected to servers from
   terminals, and all processing occurred on the server.  Now, a split-
   MUA (Mail User Agent) model is common, with MUA functionality
   occurring on both the user's own system and the server.

   In the split-MUA model, getting the messages to the user is
   accomplished through access to a mail-box on the server through such
   protocols as POP and IMAP. In the split-MUA model, user's access to
   its message is a "Message Pull" paradigm where the user is required
   to poll his mailbox.  Proper message delivery based on a "Message
   Push" paradigm is presently not supported.  The EMSD protocol
   addresses this shortcoming with an emphasis on efficiency.

   In the split-MUA model, message submission is often accomplished
   through SMTP. SMTP is widely used as a message *submission* protocol.
   Widespread use of SMTP for submission is a reality, regardless of
   whether this is good or bad.  EMSD protocol provides an alternative
   mechanism for message submission which emphasizes efficiency.

1.2  Relationship Of EMSD To Other Mail Protocols

   Various Internet mail protocols facilitate accomplishment of various
   functions in mail processing.

   Figure 1, categorizes the capabilities of SMTP, IMAP, POP and EMSD
   based on the following functions:

   +------------------+------+-------+-----+------+
   |         Protocols| SMTP |  IMAP | POP | EMSD |
   |Functions         |      |       |     |      |
   |------------------|------|-------|-----|------|
   |Submission        | XX   |       |     | XXX  |
   |------------------|------|-------|-----|------|
   |Delivery          | XXX  |       |     | XXX  |
   |------------------|------|-------|-----|------|
   |Relay (Routing)   | XXX  |       |     |      |
   |------------------|------|-------|-----|------|
   |Retrieval         |      |  XXX  | XXX |  XX  |
   |------------------|------|-------|-----|------|
   |Mailbox Access    |      |  XXX  |  X  |      |
   |------------------|------|-------|-----|------|
   |Mailbox Synch.    |      |  XXX  |     |      |
   +------------------+------+-------+-----+------+

   Figure 1:  Messaging Protocols vs.  Supported Functions

     o Mail Submission

     o Mail Delivery

     o Mail Routing (Relay)

     o Mail Retrieval

     o Mail-box Access

     o Mail-box Synchronization

   In Figure 1, the number of "X"es in each box denotes the extent to
   which a particular function is supported by a particular protocol.

   Figure 1 clearly shows that combinations of these protocols can be
   used to complement each other in providing rich functionality to the
   user.  For example, a user interested in highly mobile messaging
   functionalities can use EMSD for "submission and delivery of time
   critical and important messages" and use IMAP for comprehensive
   access to his/her mail-box.

   For mail submission and delivery of short messages EMSD is up to 5
   times more efficient than SMTP both in terms of the number of packets
   transmitted and in terms of number of bytes transmitted.  Even with

   PIPELINING and other possible optimizations of SMTP, EMSD is up to 3
   times more efficient than SMTP both in terms of the number of packets
   transmitted and in terms of number of bytes transmitted.  Various
   efficiency studies comparing EMSD with SMTP, POP and IMAP are
   available.  See Section C.1.1 for more information about comparison
   of SMTP and EMSD's efficiency.

1.3  EMSD Requirements and Goals

   The requirements and goals driving design of EMSD protocol are
   enumerated below.

    1. Provide for submission of short mail messages with the same level
       of functionality (or higher) that the existing Internet mail
       protocols provide.

    2. Provide for delivery of short mail messages with the same level
       of functionality (or higher) that the existing Internet mail
       protocols provide.

    3. Function as an extension of the existing mainstream Internet
       mail.

    4. Minimize the number of transmissions.

    5. Minimize the number of bytes transmitted.

    6. Be quick:  minimize latency of message submission and delivery.

    7. Provide the same level of reliability (or higher) that the
       existing email protocols provide.

    8. Accommodate varying sizes of messages:  the size of a message may
       determine how the system deals with the message, but the system
       must accommodate it.

    9. Be power efficient and respect mobile platform resources:
       including memory and CPU levels, as well as battery power
       longevity (i.e.  client-light and server-heavy).

    10. Highly extendible:  different users will demand different
        options, so the solution cannot require every feature to be a
        part of every message.  Likewise, usage will emerge that is not
        currently recognized as a requirement.  The solution must be
        extendible enough to handle new, emerging requirements.

    11. Secure:  provide the same level of security (or higher) that the
        existing email protocols provide.  Content confidentiality,
        originator/recipient authentication and message integrity must
        be available options to users.

    12. Easy to implement:  Re-use existing technology as much as
        possible.

1.4  Anticipated Uses Of EMSD

   Any network and network operator which has significant bandwidth and
   capacity limitations can benefit from the use of EMSD. Any network
   user who must bear high costs for measured network usage can benefit
   from the use of EMSD.

   Initial uses of EMSD is anticipated to be primarily over IP-based
   wireless networks to provide two-way paging services.

   EMSD can also function as an adjunct to Mail Access Protocols for
   "Mail Notification Services".

   Considering:

      o that most wireless networks shall converge toward being IP-
        based;

      o that two-way paging is the main proven application in most
        wide-area wireless networks;

      o that two-way paging industry and the Internet Email industry can
        and should converge based on a set of open protocols that
        address the efficiency requirements adequately;

      o that existing Internet email protocols are not bandwidth
        efficient;

      o that existing Internet email protocols do not properly support
        the "push" model of delivery of urgent messages,

   the EMSD protocol is designed to facilitate the convergence of IP-
   based two-way paging and Internet email.

   Mail submission and delivery take place at the edges of the network.
   More than one mail submission and delivery protocols which address
   requirements specific to a particular user's environment are likely
   to be developed.  Such diversity on the edges of the network is

   desirable and with the right protocols, this diversity does not
   adversely impact the integrity of the mail transfer system.  EMSD is
   the initial basis for the mail submission and delivery protocol to be
   used when the user's environment demands efficiency.

1.5  Definitions of Terms Used in this Specification

   The following informal definitions and acronyms are intended to help
   describe EMSD model described in this specification.

   Efficient Mail Submission and Delivery Protocol (EMSD-P): The
       protocol used to transfer messages between the EMSD - Server
       Agent (e.g., a Message Center) and the EMSD - User Agent (e.g., a
       Two-Way Pager), see Figure 2.
   Message Transfer Agent (MTA)

   Message Transfer Service (MTS)

   Message Routing Service (MRS): Collection of MTAs responsible for
       mail routing.
   Message User Agent (MUA)

   Efficient Mail Submission Server Agent (EMS-SA): An Application
       Process which conforms to this protocol specification and accepts
       mail from an EMS-UA and transfers it towards its recipients.

   Efficient Mail Delivery Server Agent (EMD-SA): An Application Process
       which conforms to this protocol specification and delivers mail
       to an EMD-UA.
   Efficient Mail Submission and Delivery Server Agent (EMSD-SA): An
       Application Process which incorporates both EMS-SA and EMD-SA
       capabilities.

   Efficient Mail Submission User Agent (EMS-UA): An Application Process
       which conforms to this protocol specification and submits mail to
       EMS-SA.

   Efficient Mail Delivery User Agent (EMD-UA): An Application Process
       which conforms to this protocol specification and accepts
       delivery of mail from EMD-SA.
   Efficient Mail Submission and Delivery User Agent (EMSD-UA): An
       Application Process which incorporates both EMS-UA and EMD-UA
       capabilities.

1.6  Conventions Used In This Specification

   The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY"
   in this specification are to be interpreted as defined in [2].

   This specification uses the ES-OPERATION notation defined in
   Efficient Short Remote Operations (ESRO) protocols as specified in
   RFC-2188 [1].

   Operations and information objects are typically described using the
   ES-OPERATION and ASN.1 notations in the relevant sections of the
   specification.

   The complete machine verifiable ASN.1 modules are also compiled in
   one place in Appendix A and Appendix B.

1.7  About This Specification

   This protocol specification constitutes a point-of-record.  It
   documents information exchanges and behaviors of existing
   implementations.  It is a basis for implementation of efficient mail
   submission and delivery user agents and servers.

   This specification has been developed entirely outside of IETF. It
   has had the benefit of review by many outside of IETF. Much has been
   learned from existing implementations of this protocol.  A number of
   deficiencies and areas of improvement have been identified and are
   documented in this specification.

   This protocol specification is being submitted on October 23, 1998
   for timely publication as an Informational RFC.

   Future development and enhancements to this protocol may take place
   inside of IETF.

2  EFFICIENT MAIL SUBMISSION AND DELIVERY OVERVIEW

   This section offers a high level view of the Efficient Mail
   Submission and Delivery Protocol and Format Standards (EMSD-P&FS).

   The EMSD-P&FS are used to transfer messages between the EMSD - Server
   Agent (e.g., a Message Center) and the EMSD - User Agent (e.g., a
   Two-Way Pager), see Figure 2.

   This specification defines the protocols between an EMSD - User Agent
   (EMSD-UA) and an EMSD - Server Agent (EMSD-SA). The EMSD - P&FS
   consist of two independent components:

    1. EMSD Format Standard (EMSD-FS).

       EMSD-FS is a non-textual form of compact encoding of Internet
       mail (RFC-822) messages which facilitates efficient transfer of
       messages.  EMSD-FS is used in conjunction with the EMSD-P but is

       not a general replacement for RFC-822.  EMSD-FS defines a method
       of representation of short interpersonal messages.  It defines
       the "Content" encoding (Header + Body).  Although EMSD-FS
       contains end-to-end information its scope is purely point-to-
       point.  EMSD-FS relies on EMSD-P (see 2 below) for the transfer
       of the content to its recipients.

       This is described in the section entitled EMSD Format Standards.

    2. Efficient Mail Submission and Delivery Protocol (EMSD-P).

       EMSD-P is responsible for wrapping an EMSD-FS message (see 1
       above) in a point-to-point envelope and submitting or delivering
       it.  EMSD-P relies on the services of Efficient Short Remote
       Operation Services (ESROS) as specified in RFC-2188 [1] for
       transporting the point-to-point envelope.  Some of the services
       of EMSD-P include:  message originator authentication and
       optional message segmentation and reassembly.  The EMSD-P is
       expressed in terms of abstract services using the ESROS notation.
       This is described in the section entitled Efficient Mail
       Submission and Delivery Protocol.

   It is important to recognize that EMSD-P and EMSD-FS are not end-to-
   end, but focus on the point-to-point transfer of messages.  The two
   points being EMSD-SA and EMSD-UA. EMSD-P function as elements of the
   Internet mail environment, which provide end-to-end (EMSD-User to any
   other Messaging Originator or Recipient) services.

   Figure 2 illustrates how the EMSD-P&FS defines the communication
   between a specific EMSD-UA and a specific EMSD-SA. The Message
   Transfer System may include a number of EMSD-SAs.  Each EMSD-SA may
   have any number of EMSD-UAs with which it communicates.

   The Efficient Mail Submission and Delivery Services use the Efficient
   Short Remote Operation Services (ESROS). They also use the Duplicate
   Operation Detection Support Functions as described in the section
   entitled Duplicate Operation Detection Support Functions.  These
   functions guarantee that an operation is performed no more than once.

3  EFFICIENT MAIL SUBMISSION AND DELIVERY PROTOCOL

   EM Submission is the process of transferring a message from EMSD-UA
   to EMSD-SA. EM Delivery is the process of transferring a message from
   EMSD-SA to EMSD-UA.

   The Message-submission service enables an EMSD-UA to submit a message
   to the EMSD-SA for transfer and delivery to one or more recipients.
   The Message-submission Service comprises of the submit operation --
   invoked by the EMSD-UA -- and possibly the submitVerify operation --
   invoked by the EMSD-SA.

   The Message-delivery service enables the EMSD-SA to deliver a message
   to an EMSD-UA. The Message-delivery Service comprises of the deliver
   operation -- invoked by the EMSD-SA -- and possibly the deliverVerify
   operation -- invoked by the EMSD-UA.

   EMSD-UA uses the following services:

        o Message-submission

   +---------------------------------------------+
   | MTS                                         |
   |                                             |
   |  +-------------------------+                |
   |  | MRS                     |                |
   |  |  +---+          +---+   |                |
   |  |  |   |          | M |   |         +---+  |
   |  |  |   |<-------->| T |<----------->|   |  |
   |  |  |   |          | A |   |         |   |  |               +---+
   |  |  |   |          +---+   |         | E |  |               | E |
   |  |  |   |                  |         | M |  |               | M |
   |  |  | M |                  |         | S |  |   EMSD-P&FS   | S |
   |  |  | T |<-------------------------->| D |<---------------->| D |
   |  |  | A |                  |         | - |  |               | - |
   |  |  |   |          +---+   |         | S |  |               | U |
   |  |  |   |          | M |   |         | A |  |               | A |
   |  |  |   |<-------->| T |<----------->|   |  |               +---+
   |  |  |   |          | A |   |         |   |  |
   |  |  +---+          +---+   |         +---+  |
   |  |                         |                |
   |  +-------------------------+                |
   |                                             |
   |                                             |
   +---------------------------------------------+

         Figure 2:  Efficient Mail Submission and Delivery Protocol

      o Delivery-control (the deliveryControl operation).

   EMSD-SA uses the following services:

      o Message-delivery

      o Submission-control (the submissionControl operation).

   This specification expresses information objects using ASN.1 [X.208].

   This specification expresses Remote Operations based on the model of
   ESROS as specified in Efficient Short Remote Operations (RFC-2188)
   [1].  The ES-OPERATION notation of (RFC-2188) is used throughout this
   specification to define specific operations.

   This specification uses the Duplicate Operation Detection Support
   functions as specified in Section 4.

3.1  Use Of Lower Layers

3.1.1  Use of ESROS

   ESRO protocol, as specified in (RFC-2188 [1]), provides reliable
   connectionless remote operation services on top of UDP [6] with
   minimum overhead.  ESRO protocol supports segmentation and
   reassembly, concatenation and separation.

   ESRO Services (2-Way and 3-Way handshake) shall be used by the EMSD-
   P.

   ESRO Service Access Point (SAP) selectors used by EMSD-P are
   enumerated in the protocol.

3.1.2  Use Of UDP

   EMSD-P through ESRO MUST use UDP [6] port number 642 (esro-emsdp).

   Note that specification of Service Access Points (SAP) for EMSD-P
   include the UDP Port Number specification in addition to ESRO SAP
   selector specifications.  In other words, EMSD-P's use of ESRO SAPs
   does not preclude use of the same SAP selectors by other protocols
   which use a UDP port other than port 642.  Such usage of ESRO is a
   design characteristic of ESRO which results into bandwidth efficiency
   and is not a scalability limitation.

3.1.3  Encoding Rules

   Use of Basic Encoding Rules (BER) [5] is mandatory for both EMSD
   Format Standards and EMSD Protocol.

   In order to minimize data transfer, the following restrictions shall
   be maintained in the formatting of EMSD PDUs:

      o Specifically, when ASN.1 Basic Encoding Rules are being used:

         A. Only the "Definite" form of Length encoding MUST be used,

         B. The "Short" form of Length encoding MUST be used whenever
            possible (i.e.  when the Length is less than 128), and

         C. OCTET STRING and BIT STRING values, and any other native
            ASN.1 types which may be encoded as either "Primitive" or
            "Constructed", MUST always be encoded as "Primitive" and
            MUST never be "Constructed".

3.1.4  Presentation Context

   Parameter Encoding Type of "0" MUST be used in ESRO Protocol to
   identify Basic Encoding Rules for operation arguments.

3.2  EMSD-UA Invoked Operations

   The following operations are invoked by EMSD-UA:

    a. submit

    b. deliveryControl

    c. deliveryVerify

   The submit operation uses the duplication detection functional unit
   while deliveryControl and deliveryVerify don't use the duplication
   detection.

   The complete definition of these operations follows.

3.2.1  submit

   The submit ES-OPERATION enables an EMSD-UA to submit a message to the
   EMSD-SA for transfer and delivery to one or more recipients.

   submit ES-OPERATION

       ARGUMENT SubmitArgument
       RESULT SubmitResult
       ERRORS
       {
           submissionControlViolated,
           securityError,
           resourceError,
           protocolViolation,
           messageError
       } ::= 33;

   Duplicate operation detection is necessary for this operation.

   The successful completion of the ES-OPERATION signifies that the
   EMSD-SA has accepted responsibility for the message (but not that it
   has delivered it to its intended recipients).

   The disruption of the ES-OPERATION by an error signifies that the
   EMSD-SA cannot assume responsibility for the message.

   Arguments

   This operation's arguments are:

   SubmitArgument ::= SEQUENCE
   {
     -- Security features
     security                [0]    IMPLICIT SecurityElement OPTIONAL,

     -- Segmentation features for efficient transport
     segment-info                            SegmentInfo OPTIONAL,

     -- Content type of the message
     content-type                            ContentType,

     --
     -- THE CONTENT --
     --

     -- The submission content
     content                                 ANY DEFINED BY content-type
   };

   The fields are:

   Security

   See Section 3.4.1, "SecurityElements".

   Segment-info

   See Section 3.4.2, "Message Segmentation and Reassembly".

   Content-type

   This argument identifies the type of the content of the message.  It
   identifies the abstract syntax and the encoding rules used.

   Content

   This argument contains the information the message is intended to
   convey to the recipient(s).  It shall be generated by the originator
   of the message.

   Results

   This operation's results are:

   SubmitResult ::= SEQUENCE

       {
           -- Permanent identifier for this message.
           -- Also contains the message submission time.
           -- See comment regarding assignment of message identifiers,
           -- at the definition of EMSDLocalMessageId.

           message-id                              EMSDLocalMessageId

       };

   The fields are:

   Message-id

   This result contains an EMSD-SA-identifier that uniquely and
   unambiguously identifies the message-submission.  It shall be
   generated by the EMSD-SA.

   Errors

   See Section 3.4.3.

3.2.2  deliveryControl

   The deliveryControl ES-OPERATION enables the EMSD-UA to temporarily
   limit the operations that the EMSD-SA may invoke, and the messages
   that the EMSD-SA may deliver to the EMSD-UA via the Message delivery
   ES-OPERATION.

   deliveryControl ES-OPERATION
       ARGUMENT DeliveryControlArgument
       RESULT DeliveryControlResult
       ERRORS
       {
           securityError,
           resourceError,
           protocolViolation
       } ::= 2;

   The duplicate operation detection is not required for this operation.

   The EMSD-SA shall hold until a later time, rather than abandon, ES-
   OPERATIONS and messages that are presently suspended.

   The successful completion of the ES-OPERATION signifies that the
   specified controls are now in force.

   The ES-OPERATION returns an indication of any ES-OPERATIONS that the
   EMSD-SA would invoke, or any message types that the EMSD-SA would
   deliver, were it not for the prevailing controls.

   Arguments

   This operation's arguments are:

   DeliveryControlArgument ::= SEQUENCE
   {
     -- Request an addition of or removal of a set of restrictions

     restrict                [0]     IMPLICIT Restrict DEFAULT update,

     -- Which operations are to be placed in the restriction set
     permissible-operations  [1]     IMPLICIT Operations OPTIONAL,

     -- What maximum content length should be allowed
     permissible-max-content-length

                                     [2]     IMPLICIT INTEGER
                                      (0..ub-content-length) OPTIONAL,

     -- What is the lowest priority message which may be delivered
     permissible-lowest-priority

                                     [3]     IMPLICIT ENUMERATED
                                              {
                                                non-urgent     (0),
                                                normal         (1),
                                                urgent         (2)
                                              } OPTIONAL,

     -- Security features
     security                        [4]     IMPLICIT SecurityElement
                                             OPTIONAL,

     -- User Feature selection
     user-features                   [5]     IMPLICIT OCTET STRING
                                             OPTIONAL
   };

   Restrict

   This argument indicates whether the controls on ES-OPERATIONS are to
   be updated or removed.  It may be generated by the EMSD-UA.

   This argument may have one of the following values:

      o update:  The other arguments update the prevailing controls;

      o remove:  All temporary controls are to be removed

   In the absence of this argument, the default update shall be assumed.

   Permissible-operations

   This argument indicates the ES-OPERATIONS that the EMSD-SA may invoke
   on the EMSD-UA. It may be generated by the EMSD-UA.

   This argument may have the value allowed or prohibited for each of
   the following:

      o message-delivery:  The EMSD-SA may/may not invoke the deliver
        ES-OPERATIONS; and

      o Other ES-OPERATIONS are not subject to controls, and may be
        invoked at any time.

   In the absence of this argument, the ES-OPERATIONS that the EMSD-SA
   may invoke on the EMSD-UA are unchanged.

   Permissible-max-content-length

   This argument contains the content-length, in octets, of the
   longest-content message that the EMSD-SA shall deliver to the EMSD-UA
   via the deliver ES-OPERATIONS. It may be generated by the EMSD-UA.

   In the absence of this argument, the permissible-maximum-content-
   length of a message that the EMSD-SA may deliver to the EMSD-UA is
   unchanged.

   Permissible-lowest-priority

   This argument contains the priority of the lowest priority message
   that the EMSD-SA shall deliver to the EMSD-UA via the deliver ES-
   OPERATIONS. It may be generated by the EMSD-UA.

   This argument may have one of the following values of the priority
   argument of the submit ES-OPERATIONS: normal, non-urgent or urgent.

   In the absence of this argument, the priority of the lowest priority
   message that the EMSD-SA shall deliver to the EMSD-UA is unchanged.

   Security

   See Section 3.4.1, "SecurityElements".

   User-features

   This argument contains information that allows the EMSD-UA to convey
   to MTS the feature set that the user is capable of supporting.  This
   argument will be defined when the setConfiguration and
   getConfiguration operations are defined.

   Results

   DeliveryControlResult ::= SEQUENCE
   {
     -- Operation types queued at the EMSD-SA due to existing
     -- restrictions.
     waiting-operations      [0]     IMPLICIT Operations DEFAULT { },

     -- Types of messages queued at the EMSD-SA due to
     -- existing restrictions
     waiting-messages        [1]     IMPLICIT WaitingMessages
                                     DEFAULT { },

     -- Content Types of messages queued at the EMSD-SA
     waiting-content-types   SEQUENCE SIZE (0..ub-content-types) OF
                                            ContentType DEFAULT { }

   };

   Restrict ::= ENUMERATED
   {
       update                                      (1),
       remove                                      (2)
   };

   Operations ::= BIT STRING
   {
       submission                                  (0),
       delivery                                    (1)
   };

   WaitingMessages ::= BIT STRING
   {
       long-content                                (0),
       low-priority                                (1)

   };

   Waiting-operations

   This result indicates the ES-OPERATIONS being held by the EMSD-SA,
   and that the EMSD-SA would invoke on the EMSD-UA if it were not for
   the prevailing controls.  It may be generated by the EMSD-SA.

   This result may have the value holding or not-holding for each of the
   following:

      o message-delivery:  The EMSD-SA is/is not holding messages, and
        would invoke the deliver ES-OPERATIONS on the EMSD-UA if it were
        not for the prevailing controls.

   In the absence of this result, it may be assumed that the EMSD-SA is
   not holding any messages for delivery due to the prevailing controls.

   Waiting-messages

   This result indicates the kind of messages the EMSD-SA is holding for
   delivery to the EMSD-UA, and would deliver via the deliver ES-
   OPERATIONS, if it were not for the prevailing controls.  It may be
   generated by the EMSD-SA.

   This result may have one or more of the following values:

      o long-content:  The EMSD-SA has messages held for delivery to the
        EMSD-UA which exceed the permissible maximum-content-length
        control currently in force;

      o low-priority:  The EMSD-SA has messages held for delivery to the
        EMSD-UA of a lower priority than the permissible-lowest-priority
        control currently in force;

   In the absence of this result, it may be assumed that the EMSD-SA is
   not holding any messages for delivery to the EMSD-UA due to the
   permissible-maximum-content-length, permissible-lowest-priority or
   permissible-security context controls currently in force.

   Errors

   See Section 3.4.3.

3.2.3  deliveryVerify

   The deliveryVerify ES-OPERATIONS enables the EMSD-UA to verify
   delivery of a message when it receives FAILURE.indication for deliver
   ES-OPERATIONS.

   deliveryVerify ES-OPERATION

       ARGUMENT DeliveryVerifyArgument
       RESULT DeliveryVerifyResult
       ERRORS
       {
           verifyError,
           resourceError,
           protocolViolation
       } ::= 5;

   The duplicate operation detection is not required for this operation.

   Arguments

   This operation's arguments are:

   DeliveryVerifyArgument ::= SEQUENCE

   {
     -- Identifier of this message. This is the same identifier that
     -- was provided to the originator in the Submission Result.
     -- See comment regarding assignment of message identifiers,
     -- at the definition of EMSDMessageId.
     message-id                                      EMSDMessageId
   };

   Message-id

   This argument contains an EMSD-SA-identifier that distinguishes the
   message from all other messages.  It shall be generated by the EMSD-
   SA, and shall have the same value as the message-submission-
   identifier supplied to the originator of the message when the message
   was submitted.

   Results

   DeliveryVerifyResult ::= SEQUENCE
   {
            status  DeliveryStatus
   };

    DeliveryStatus  ::= ENUMERATED
   {
           no-report-is-sent-out                   (1),
           delivery-report-is-sent-out             (2),
           non-delivery-report-is-sent-out         (3)
    };

   No-report-is-sent-out

   This result indicates that EMSD-SA has received the delivery verify
   and no report is sent out (either because it has not been requested
   or EMSD-SA has problems and can not send it out).

   Delivery-report-is-sent-out

   This result indicates that EMSD-SA has received the delivery verify

   and has sent the delivery report out.

   Non-Delivery-report-is-sent-out

   This result indicates that EMSD-SA has received the delivery verify
   but it has already sent out a non-Delivery report.  This should not
   happen in normal cases but a wrong user profile on EMSD-SA side can
   result in this outcome.

   Errors

   See Section 3.4.3.

3.3  EMSD-SA Invoked Operations

   This section defines the operations invoked by the EMSD-SA:

      a. deliver;

      b. submissionControl;

      c. submissionVerify.

   The deliver operation uses 3-Way handshake service of ESROS. This
   operation always uses the duplication detection functional unit.

   The submissionControl and submissionVerify operations use 2-Way
   handshake service of ESROS without duplication detection.

3.3.1  deliver

   The deliver ES-OPERATIONS enables the EMSD-SA to deliver a message to
   an EMSD-UA.

   deliver ES-OPERATION

       ARGUMENT DeliverArgument
       RESULT NULL
       ERRORS
       {
           deliveryControlViolated,
           securityError,
           resourceError,
           protocolViolation,
           messageError
       } ::= 35;

   The EMSD-UA MUST not refuse performing the deliver ES-OPERATION
   unless the delivery would violate the deliveryControl restrictions
   then in force.

   Arguments

   This operation's arguments are:

   DeliverArgument ::= SEQUENCE
   {
     -- Identifier of this message. This is the same identifier that
     -- was provided to the originator in the Submission Result.
     -- See comment regarding assignment of message identifiers,
     -- at the definition of EMSDMessageId.
     message-id                                      EMSDMessageId,

     -- Time the message was delivered to the recipient by EMSD-SA
     message-delivery-time                           DateTime,

     -- Time EMSD-SA originally took responsibility for processing
     -- of this message. This field shall be omitted if the message-id
     -- contains an EMSDLocalMessageId, because that field contains
     -- the submission time within it.
     message-submission-time [0]  IMPLICIT DateTime OPTIONAL,

     -- Security features
     security                [1]  IMPLICIT SecurityElement OPTIONAL,

     -- SegContentTypementation features for efficient transport
     segment-info                              SegmentInfo OPTIONAL,

     -- The type of the content
     content-type                                ContentType,

     --
     -- THE CONTENT --
     --

     -- The submitted (and now being delivered) content
     content                           ANY DEFINED BY content-type
   };

   message-id

   This argument contains an EMSD-SA-identifier that distinguishes the
   message from all other messages.  When within the EMSD, it MUST be
   generated by the EMSD-SA, and MUST have the same value as the
   message-submission-identifier supplied to the originator of the
   message when the message was submitted.

   Message-delivery-time

   This argument contains the Time at which delivery occurs and at which
   the EMSD-SA is relinquishing responsibility for the message.  It
   shall be generated by the EMSD-SA.

   Results

   This operation returns an empty result as indication of success.

   Errors

   See Section 3.4.3.

3.3.2  submissionControl

   submissionControl ES-OPERATION
       ARGUMENT SubmissionControlArgument
       RESULT SubmissionControlResult
       ERRORS
       {
           securityError,
           resourceError,
           protocolViolation
       } ::= 4;

   The submissionControl ES-OPERATIONS enables the EMSD-SA to
   temporarily limit the operations that the EMSD-UA may invoke, and the
   messages that the EMSD-UA may submit to the EMSD-SA via the submit
   ES-OPERATIONS.

   The duplicate operation detection is not required for this operation.

   The EMSD-UA should hold until a later time, rather than abandon, ES-
   OPERATIONS and messages that are presently suspended.

   The successful completion of the ES-OPERATIONS signifies that the
   specified controls are now in force.  These controls supersede any
   previously in force, and remain in effect until the association is
   released or the EMSD-SA re-invokes the submissionControl ES-
   OPERATIONS.

   The ES-OPERATIONS returns an indication of any ES-OPERATIONS that the
   EMSD-UA would invoke were it not for the prevailing controls.

   Arguments

   This operation's arguments are:

   SubmissionControlArgument ::= SEQUENCE
   {
     -- Request an addition of or removal of a set of restrictions
     restrict               [0]     IMPLICIT Restrict DEFAULT update,

     -- Which operations are to be placed in the restriction set
     permissible-operations  [1]     IMPLICIT Operations OPTIONAL,

     -- What maximum content length should be allowed
     permissible-max-content-length
                             [2]     IMPLICIT INTEGER
                                     (0..ub-content-length) OPTIONAL,

     -- Security features
     security                [3]     IMPLICIT SecurityElement
                                                     OPTIONAL
   };

   Restrict

   This argument indicates whether the controls on ES-OPERATIONS are to
   be updated or removed.  It may be generated by the EMSD-SA.

   This argument may have one of the following values:

      o update:  The other arguments update the prevailing controls;

      o remove:  All temporary controls are to be removed

   In the absence of this argument, the default update shall be assumed.

   Permissible-operations

   This argument indicates the ES-OPERATIONS that the EMSD-UA may invoke
   on the EMSD-SA. It may be generated by the EMSD-SA.

   This argument may have the value allowed or prohibited for each of
   the following:

      o submit:  The EMSD-UA may/may not invoke the submit ES-
        OPERATIONS; and

      o Other ES-OPERATIONS are not subject to controls, and may be
        invoked at any time.

   In the absence of this argument, the ES-OPERATIONS that the EMSD-UA
   may invoke on the EMSD-SA are unchanged.

   Permissible-max-content-length

   This argument contains the content-length, in octets, of the
   longest-content message that the EMSD-UA shall submit to the EMSD-SA
   via the submit ES-OPERATIONS. It may be generated by the EMSD-SA.

   In the absence of this argument, the permissible-maximum-content-
   length of a message that the EMSD-UA may submit to the EMSD-SA is
   unchanged.

   Security

   See Section 3.4.1, "SecurityElements".

   Results

   SubmissionControlResult ::= SEQUENCE
   {
     -- Operation types queued at the EMSD-SA due to existing
     -- restrictions.
     waiting-operations    [0]   IMPLICIT Operations DEFAULT { }

   };

   Waiting-operations

   This result indicates the ES-OPERATIONS being held by the EMSD-UA,
   and that the EMSD-UA would invoke if it were not for the prevailing
   controls.  It may be generated by the EMSD-UA.

   This result may have the value holding or not-holding for each of the
   following:

      o submit:  The EMSD-UA is/is not holding messages, and would
        invoke the submit ES-OPERATIONS if it were not for the
        prevailing controls.

   In the absence of this result, it may be assumed that the EMSD-UA is
   not holding any messages for submission due to the prevailing
   controls.

   Errors

   See Section 3.4.3.

3.3.3  submissionVerify

   The submissionVerify ES-OPERATIONS enables the EMSD-SA to verify if
   the EMSD-UA has received the result of its submission.

   submissionVerify  ES-OPERATION

       ARGUMENT SubmissionVerifyArgument
       RESULT SubmissionVerifyResult
       ERRORS
       {
           submissionVerifyError,
           resourceError,
           protocolViolation
       } ::= 6;

   The duplicate operation detection is not required for this operation.

   Arguments

   This operation's arguments are:

   SubmissionVerifyArgument ::= SEQUENCE

     -- Identifier of this message. This is the same identifier that
     -- was provided to the originator in the Submission Result.
     -- See comment regarding assignment of message identifiers,
     -- at the definition of EMSDMessageId.
     {
        message-id                                  EMSDMessageId
     };

   Message-id

   This argument contains an EMSD-SA-identifier that distinguishes the
   message from all other messages.  It shall be generated by the EMSD-
   SA, and shall have the same value as the message-submission-
   identifier supplied to the originator of the message when the message
   was submitted.

   Results

   SubmissionVerifyResult ::= SEQUENCE
   {
           status  SubmissionStatus
   };

   SubmissionStatus::= ENUMERATED
   {
           send-message            (1),
           drop-message            (2)
   };

   Send-message

   This result indicates that EMSD-SA is supposed to send the message
   out.

   Drop-message

   This result indicates that EMSD-SA is supposed to drop the message.

   Errors

   See Section 3.4.3.

3.4  EMSD Common Information Objects

3.4.1  SecurityElements

   SecurityElement ::= SEQUENCE

   {
     credentials                          Credentials,
     contentIntegrityCheck                ContentIntegrityCheck OPTIONAL
   };

   Credentials ::= CHOICE
   {
     simple                          [0]     IMPLICIT SimpleCredentials

     -- Strong Credentials are for future study
     -- strong                       [1]     IMPLICIT StrongCredentials
     -- externalProcedure            [2]     EXTERNAL
   };

   SimpleCredentials ::= SEQUENCE
   {
     eMSDAddress                     EMSDAddress OPTIONAL,
     password                [0]     IMPLICIT OCTET STRING
                             SIZE (0..ub-password-length)) OPTIONAL
   };

   -- StrongCredentials ::= NULL
   -- for now.
   -- ContentIntegrityCheck is a 16-bit checksum of content
   ContentIntegrityCheck ::= INTEGER (0..65535);

3.4.2  Message Segmentation and Reassembly

   Small messages can benefit from the efficiencies of connectionless
   feature of ESROS (See Efficient Short Remote Operations, RFC-2188
   [1]).

   Very large messages are transferred using protocols (e.g., SMTP) that
   rely on Connection Oriented Transport Service (e.g., TCP).

   When a message is too large to fit in a single connectionless PDU but
   is not large enough to justify the overhead of connection
   establishment, it may be more efficient for the message to be
   segmented and reassembled while the connectionless service of ESROS
   is used.  If the underlying Remote Operation Service is capable of
   efficient segmentation/reassembly over connectionless (CL) services,

   then use of the segmenting/reassembly mechanism introduced in this
   section is not necessary.  This feature is accommodated in this layer
   by:

   SegmentInfo ::= CHOICE

   {
     first           [APPLICATION 2]         IMPLICIT FirstSegment,
     other           [APPLICATION 3]         IMPLICIT OtherSegment
   };

   FirstSegment ::= SEQUENCE
   {
     sequence-id                             INTEGER,
     number-of-segments                      INTEGER
     -- number-of-segments must not exceed ub-total-number-of-segments
   };

   OtherSegment ::= SEQUENCE
   {
     sequence-id                             INTEGER,
     segment-number                          INTEGER
   };

   Segmentation and reassembly only applies to Message-submission and
   Message-delivery.

   The sender of the message is responsible for segmenting the message
   content into segments that fit in CL PDUs.  The segmented content is
   sent in a sequence of message-segments each carrying a segment of the
   content.  sequence-Id is a unique identifier that is present in all
   message-segments.  In addition to sequence identifier, the first
   message-segment specifies the total number of segments (number-of-
   segments).  Other message-segments have a segment sequence number
   (segment-number).  The receiver is responsible for sequencing (based
   on segment-number) and reassembling the entire message.

   Segmenting over the Connectionless ESRO Service

   The sender of the message maps the original message into an ordered
   sequence of message-segments.  This sequence shall not be interrupted
   by other messages over the same ESROS association.

   All message-segments in the sequence shall be assigned a sequence
   identifier by sender.  The sequence identifier shall be incremented
   by one by the sender after transmission of a complete message
   sequence.

   The first message-segment specifies the total number of segments.
   All message-segments in the sequence except the first one shall be
   sequentially numbered, starting at 1 (first message-segment has
   implicit segment number of 0).

   Each message-segment is transmitted by issuing a Message-submission
   or Message-delivery ES-OPERATIONS. All segments of a segmented
   message are identified by the same sequence-id.  For a given message,
   the receiver should not impose any restriction on the order of
   arrival of message-segments.

   There is no requirement that any message-segment content be of
   maximum length allowed by ESROS for connectionless transmission;
   however, no more than ub-total-number-of-segments segments can be
   derived from a single message.

   The receiver reassembles a sequence of message-segments into a single
   message.  A message shall not be further processed unless all
   segments of the message are received.  Failure to receive the message
   shall be determined by the following events:

      o Expiration of Reassembly Timer (see Section 3.4.3).

      o Receipt of a message-segment with different sequence identifier.

   In the event of the above mentioned failures, the receiver shall
   discard a partially assembled sequence.

   In Reassembly process, all arguments other than content are ignored
   in all segments except the first one.  The content parts of all
   segments are concatenated to compose the original message content.

   When sender receives FAILURE.indication (as opposed to a
   resourceError) for a message-segment, the whole message shall be
   retransmitted.

   In the case of submission and delivery operations, the verify
   function is used as described below:

   Receiver ignores FAILURE.indications received for message-segments,
   and just collects the message-segments to complete the message.
   However, it keeps a failure status for a segmented message which says
   if any segment of the message has received FAILURE.indication.  When
   receiver succeeds to assemble the whole segmented message, then if
   the status of the message shows there has been a FAILURE.indication
   for any of the message-segments, it verifies the message through
   verify operation.  It's not enough to invoke verify operation just
   based on the last message-segment because the sender might send a

   segment without waiting for the result of the previous segment.  In
   such cases, there might be any combination of success and failure for
   message-segments on the sender side.

   Receiver uses the error code ResourceError (see Section 3.4.3) to ask
   for retransmission of a single segment and uses the error code
   MessageError (see Section 3.4.3) to ask for retransmission of all
   segments (the whole message).

   Reassembly Timer

   The Reassembly Timer is a local timer maintained by the receiver of
   message-segments that assists in performing the reassembly function.
   This timer determines how long a receiver waits for all segments of a
   message-segment sequence to be received.  The timer protects the
   receiver from the loss of a series of segments and possible sequence
   identifier wrap-around.

   The Reassembly Timer shall be started on receipt of a message-segment
   with different sequence identifier than that previously received.
   The timer shall be stopped on receipt of all segments composing the
   sequence.

   The value of Reassembly Timer is defined based on the network
   characteristics and the number of segments.  This requires that the
   transmission of all segments of a single message must be completed
   within this time limit.

3.4.3  Common Errors

   protocolVersionNotRecognized  ERROR PARAMETER NULL ::= 1;

   submissionControlViolated  ERROR PARAMETER NULL ::= 2;

   messageIdentifierInvalid  ERROR PARAMETER NULL ::= 3;

   securityError ERROR PARAMETER security-problem SecurityProblem ::= 4;

   deliveryControlViolated   ERROR PARAMETER NULL ::= 5;

   resourceError  ERROR PARAMETER NULL ::= 6;

   protocolViolation  ERROR PARAMETER NULL ::= 7;

   messageError  ERROR PARAMETER NULL ::= 8;

   SecurityProblem ::= INTEGER (0..127);

   protocolVersionNotRecognized

   The major and minor protocol versions presented do not match those
   recognized as being valid.

   submissionControlViolated

   The Submission control violated error reports the violation by the
   MTS-user of a control on submission services imposed by the MTS via
   the Submission control service.  The Submission control violated
   abstract-error has no parameters.

   messageIdentifierInvalid

   The Message Identifier Invalid error reports that the Message
   Identifier presented to the MTS is not considered valid.

   securityError

   The Security error reports that the requested operation could not be
   provided by the MTS or MTS-user because it would violate the security
   policy in force.

   deliveryControlViolated

   The Delivery control violated error reports the violation by the MTS
   of a control on delivery operations imposed by the MTS-user via the
   Delivery-control operation.

   resourceError

   The messaging agent cannot currently support this operation.  In the
   case of segmentation and reassembly, resourceError is by the receiver
   used to request that the sender retransmit of a single segment.

   protocolViolation

   Indicates that one or more mandatory argument(s) were missing.

   messageError

   For a multi-segment message, this error indicates that the messaging
   agent has not received the message completely and that the message
   must be retransmitted.

   SecurityProblem

   To ensure the security-policy is not violated during delivery, the
   message-security-label is checked against the security-context.  If
   delivery is barred by the security-policy then, subject to the
   security policy, a report instruction for this is generated.

3.4.4  ContentType

   ContentType ::=  INTEGER
   {
     -- Content type 0 is reserved and shall never be transmitted.
     reserved                                 (0),
     -- Content types between 1 and 31 (inclusive) are for
     -- internal-use only
     probe                                    (1), -- reserved
     delivery-report                          (2), -- reserved

     -- Content types between 32 and 63 (inclusive) are for
     -- message types  defined within this specifications.
     emsd-interpersonal-messaging-1995        (32),
     voice-messaging                          (33) -- reserved

     -- Content types beyond and including 64 are for
     -- bilaterally-agreed use between peers.
   } (0..127);

3.4.5  EMSDMessageId

   If this message was originated as an RFC-822 message, then this
   EMSDMessageId shall be the "Message-Id:" field from that message.  If
   this message was originated within the EMSD domain, then this
   identifier shall be unique for the EMSD-SA generating this id.

   EMSDMessageId ::= CHOICE
   {
     EMSDLocalMessageId  [APPLICATION 4]
                         IMPLICIT EMSDLocalMessageId,

     rfc822MessageId     [APPLICATION 5]
                         IMPLICIT AsciiPrintableString

                         (SIZE (0..ub-message-id-length))
   };

   EMSDLocalMessageId ::= SEQUENCE
   {
     submissionTime            DateTime,
     messageNumber             INTEGER (0..ub-local-message-nu)
   };

3.4.6 EMSDORAddress

   EMSDORAddress ::= CHOICE
   {
     -- This is the local-format address
     emsd-local-address-format            EMSDAddress,

     -- This is a globally-unique RFC-822 Address
     rfc822DomainAddress                 AsciiPrintableString
   };

   In the global sense Originators and Recipients are represented by
   EMSDORAddress.  The rfc822Domain may be used to address any
   recipient.

3.4.7  EMSDAddress

   EMSDAddress ::= SEQUENCE
   {
     emsd-address        OCTET STRING (SIZE
                         (1..ub-emsd-address-length)),
     -- emsd-address is a decimal integer in BCD
        (Binary Encoded Decimal) format.
     -- If it had an odd number of digits, it is
     -- padded with 0 on the left.

     emsd-name          [0]  IMPLICIT OCTET STRING
                             (SIZE (0..ub-emsd-name-length))
                             OPTIONAL
   };

   Originator and Recipients in the scope of EMSD network are identified
   by a digit based addressing scheme.  EMSDAddress can only be used
   where the scope of addressing has clearly been limited to the EMSD
   network.

3.4.8  DateTime

   DateTime ::= INTEGER;

   DateTime is a Julian date, expressed as the number of seconds since
   00:00:00 UTC, January 1, 1970.

3.4.9  AsciiPrintableString

   Iso8859String ::=  GeneralString;

   AsciiPrintableString ::= [APPLICATION 0]
                            IMPLICIT Iso8859String (FROM

       (" "|"!"|"#"|"$"|"%"|"&"|"'"|"("|")"|"*"|"+"|","|"-"|"."|"/"|
        "0"|"1"|"2"|"3"|"4"|"5"|"6"|"7"|"8"|"9"|":"|";"|"<"|"="|">"|
        "?"|"@"|"A"|"B"|"C"|"D"|"E"|"F"|"G"|"H"|"I"|"J"|"K"|"L"|"M"|
        "N"|"O"|"P"|"Q"|"R"|"S"|"T"|"U"|"V"|"W"|"X"|"Y"|"Z"|"["|"]"|
        "^"|"_"|"`"|"a"|"b"|"c"|"d"|"e"|"f"|"g"|"h"|"i"|"j"|"k"|"l"|
        "m"|"n"|"o"|"p"|"q"|"r"|"s"|"t"|"u"|"v"|"w"|"x"|"y"|"z"|"{"|
        "|"|"}"|"~"|"\"|""""));

3.4.10  ProtocolVersionNumber

   ProtocolVersionNumber ::= [APPLICATION 1]    SEQUENCE
   {
     version-major                   INTEGER,

  +------------------+-------+----+---------+----+---------+-----+-----+
  |Operation         |Invoker|Sap |Performer|Sap |Duplicate|OpId |ESROS|
  |                  |       |Sel |         |Sel |Detect   |     |Use  |
  |__________________|_______|____|_________|____|_________|_____|_____|
  |submit            |UA     |4   |MTS      |5   |Yes      |33   |3-Way|
  |__________________|_______|____|_________|____|_________|_____|_____|
  |deliver           |MTS    |2   |UA       |3   |Yes      |35   |3-Way|
  |__________________|_______|____|_________|____|_________|_____|_____|
  |deliveryControl   |UA     |8   |MTS      |9   |No       |2    |2-Way|
  |__________________|_______|____|_________|____|_________|_____|_____|
  |submissionControl |MTS    |6   |UA       |7   |No       |4    |2-Way|
  |__________________|_______|____|_________|____|_________|_____|_____|
  |submissionVerify  |MTS    |6   |UA       |7   |No       |6    |2-Way|
  |__________________|_______|____|_________|____|_________|_____|_____|
  |deliveryVerify    |UA     |8   |MTS      |9   |No       |5    |2-Way|
  |__________________|_______|____|_________|____|_________|_____|_____|
  |getConfiguration  |UA     |8   |MTS      |9   |No       |7    |2-Way|
  |__________________|_______|____|_________|____|_________|_____|_____|
  |setConfiguration  |MTS    |6   |UA       |7   |No       |8    |2-Way|
  +------------------+-------+----+---------+----+---------+-----+-----+

                   Table 1:  EMSD-P Operations Summary

     version-minor           [0]     IMPLICIT INTEGER DEFAULT 0
   }

3.5  Submission and Delivery Procedures

   Table 1 provides a comprehensive summary of EMSD-P operations, the
   SAP selectors used and the operation IDs used.

   Submission

   The semantics of a submission operation is Exactly Once.  Exactly
   Once means that every operation is carried out exactly one time, no
   more and no less.  This semantic can not be fully implemented
   because, if after invoking the operation, an invoker has a Success
   (e.g.  result) indication and the performer has a FAILURE.indication,
   and the network goes down, the result of the operation will be Zero
   (and not Exactly Once).

   No more than one is controlled and guaranteed by the performer by
   using the Duplicate Operation Detection Support Functions (see the
   chapter entitled Duplicate Operation Detection Support).

   Not zero but one is realized by performer by using the
   SubmissionVerify operation.  When the performer receives
   FAILURE.indication, it's responsibility is to resolve the case by
   using SubmissionVerify resulting in Not zero but one.

   Submission procedure is as follows:

      o Submit operation with 3-Way handshake and Duplicate Operation
        Detection Support Function is invoked.

      o If performer at EMSD-SA receives FAILURE.indication, it invokes
        SubmissionVerify.

      o Message is sent out by EMSD-SA only if result operation is
        confirmed or the operation is verified (in the case of
        FAILURE.indication).

   The semantic of SubmissionVerify operation is At Least Once.  This
   type of semantics corresponds to the case that invoker keeps trying
   over and over until it gets a proper reply.  This operation can be
   performed more than once without any harm.

   Implications:

      o MTS sends out the message if and only if it's sure that UA knows
        about it.

   Delivery

   The semantics of Deliver operation is Exactly Once.  Exactly Once
   means that every operation is carried out exactly one time, no more
   and no less.  This semantic can not be fully implemented and if after
   invoking the operation, invoker has Success indication and performer
   has FAILURE.indication, and the network goes down, the result of the
   operation will be Zero (and not Exactly Once).

   No more than one is controlled and guaranteed by performer and by
   using the Duplicate Operation Detection Support Functions.

   Not zero but one is realized by performer by using the DeliveryVerify
   operation.  When performer receives FAILURE.indication, it's
   responsible to resolve the case by using DeliveryVerify resulting in
   Not zero but one.

   Delivery procedure is as follows:

      o Deliver operation with 3-Way handshake is invoked.

      o If performer at User Agent (device) receives FAILURE.indication,
        it invokes DeliveryVerify.

   The semantic of DeliveryVerify operation is At Least Once.  This type
   of semantics corresponds to the case that invoker keeps trying over
   and over until it gets a proper reply.  This operation can be
   performed more than once without any harm.

   Implications:

      o A non-delivery report is sent by MTS only if the message is not
        delivered.

      o The UA is responsible for notifying the MTS (through an explicit
        deliveryVerify) to make sure that a delivery report is sent out.

4  DUPLICATE OPERATION DETECTION SUPPORT

4.1  Duplicate Operation Detection Support Overview

   Some operations are idempotent in nature, i.e.  they can be performed
   more than once without any harm.  However, some other operations are
   non-idempotent in nature, i.e.  they should be performed only once.
   In the case of non-idempotent operations, performer should be able to
   detect duplicate operations and perform each non-idempotent operation
   only once.

   Examples of non-idempotent operations are Submission and Delivery of
   messages which shouldn't be performed more than once.  Examples of
   idempotent operations are Submission-control and Delivery-control
   which can be performed more than once with no harm.

   ESRO Services don't detect duplicate invocation of operations.  As a
   result, the Duplicate Operation Detection Support Functional Unit is
   used to detect duplication when the same operation instance is
   invoked more than once.  Invoker assigns an Operation Instance
   Identifier to an operation and this Operation Instance Identifier is
   used at the peer performer entity to detect the duplicate invocation
   of the same operation.

   Using this support, non-idempotent operations can be repeated over
   and over with no harm because the duplicate invocations are detected
   by this functional unit.  This support helps the performer not to
   perform an operation more than once.

   Support for duplication detection is realized through allocating
   Operation Instance Id (see Section 4.1.2, "Operation Instance
   Identifier") to an operation by invoker.  When an operation is
   invoked using duplication detection support, performer logs the
   Operation Instance Identifier and checks the next operations against
   duplication.

   Operation value identifies whether performer should detect duplicate
   operations (see Section 4.1.1, "Operation Value") and Operation
   Instance Id is assigned by invoker and sent as the first byte of
   operation's parameter.

4.1.1  Operation Value

   Operation Values are divided into two groups.  Operation values from
   0 to 31 do not have Duplicate Operation Detection Support (0 to 31)
   and operation values from 32 to 63 have Duplicate Operation Detection
   Support.

   Duplicate Operation Detection Functional Unit checks for duplication
   only if Operation Value is in the range of 32 to 63.

   When invoker user uses an Operation Value in the range of 32 to 63
   which means operation with support for duplication detection, the
   user should specify an Operation Instance ID for the operation (see
   next section).

4.1.2  Operation Instance Identifier

   To support duplication detection, an Operation Instance Identifier is
   assigned by invoker user and sent as the first byte of the
   operation's parameter.  This identifier is used on performer side to
   detect duplicate invocation of the same operation.  Characteristics
   of Operation Instance Identifier is as follows:

      o Operation Instance Identifier is one byte and can have values
        from 0 to 255.

      o Operation Instance Identifier is sent as the first byte of the
        operations parameter (without encoding).

      o The length of Operation Instance Identifier is 8-bit, but
        depending on the performer capabilities, it might keep 0 to 127
        Operation Instance Identifiers for duplication detection.  The
        performer profile defines the number of outstanding Operation
        Instance Identifiers that are checked against duplication.  When
        a performer profile indicates support for 0 outstanding
        Operation Instance Identifier, it means it does not have support
        for Duplicate Operation Detection.  In this case, there should
        be only one outstanding operation at any point of time.

      o Instance ID check is not part of ESROS, per se.  Use of
        Duplicate Detection is determined by EMSD-P. Operation Instance
        ID for operations 32-63 is the first byte of the argument.
        Duplicate Detection suuport strips that byte.

      o The Instance ID is not subject to Basic Encoding Rules (BER).

      o The invoker user assigns the Operation Instance Identifier to
        the operation at the time of requesting the invoke service.  The
        Operation Value should be in the range of operation values with
        duplication detection support, i.e.  32 to 63.

      o It's the responsibility of the user to choose Operation Instance
        Identifier in a way that uniqely and unambiguously identifies
        the operation.

      o From the invoker's perspective, assumption is that two
        operations with the same operation Instance Identifier are
        totally identical which means they produce exact same results.

      o Operation Instance Identifier uniqely specifies a non-idempotent
        operation and multiple invocations of such an operation will
        eventually result in the same outcome because the duplicate
        instances are identified and the operation is not performed more
        than once.

      o From the performer's perspective, assumption is that two
        operations with the same Operation Instance Identifier should be
        executed once and once only.

      o If requested, the degree of duplication checked by Duplicate
        Operation Detection Support Functional Unit on the performer's
        side (i.e.  the total number of outstanding Operation Instance
        Identifier kept) can be communicated with the invoker to
        synchronize the invocations.

      o User of Duplicate Operation Detection Support is responsible to
        behave based on the performer profile and its limitations in
        this regard.  This behavior is defined based on the desired
        semantic of the operation which is to be implemented.

      o On the performer side, when an Operation Instance Identifier is
        received, a previous Operation Instance Identifier whose
        distance to this latest one is greater than or equal to half of
        the wrap-around range of the Operation Instance Identifier
        number is expired, i.e.  for an 8-bit Operation Instance
        Identifier, the distance of 128 causes an old Operation Instance
        Identifier to expire.

      o It's the responsibility of the invoker user to use consecutive
        Operation Instance Identifier numbers, or when it skips some
        Operation Instance Identifiers, it should remember that if there
        is an smaller Operation Instance Identifier on performer side
        with the distance explained above, it will be expired.

5  EMSD PROCEDURE FOR OPERATIONS

   The following sections shows the general procedures to be used in the
   implementation of the EMSD Message Transfer Server (MTS) and the EMSD
   User Agent (UA), with the option for 3-Way or 2-Way handshakes on
   operations which support them.  These procedures do not constitute
   complete behavior specifications for implementations.  The following
   sections contain information helpful to implementors.

   The MTS and the UA are event-driven.  Each waits for any of the
   possible event types, and, upon receiving an event, processes it.
   After processing the event, the next event is waited upon.

5.1  MTS Behavior

   The MTS is event-driven.

   If it received an event from ESROS, then it could be any of the
   following types:

      o Message submit indication;

      o Message submit confirm and failure indication;

      o Result and Error indication for a deliver operation;

      o DeliveryVerify indication;

      o Result and Error indication for a submissionVerify operation;

      o Result and Error indication for a submissionControl operation;

      o DeliveryControl indication.

   For an ESROS event responsibility is passed to the MTS performer
   (Section 5.1.1).

   If the MTS received an event:

      o for message delivery, from the RFC-822 mailer;

      o requesting submission controls upon the UA, or;

      o indicating an elapsed timer (meaning that it's time to re-
        attempt a message delivery)

   then responsibility is passed to the MTS invoker (Section 5.1.5).

5.1.1  MTS Performer

   The MTS performer is responsible for processing the following
   operations, received from ESROS:

      o Message-submission

      o Delivery-control

      o Delivery-verify

   The MTS performer should first make sure that it has received an
   INVOKE.indication.  Any other type of primitive shouldn't be
   occurring at this point, and should be ignored.

   If there's something wrong with the PDU or operation data, the MTS
   performer should send back an error to the proper invoker:

    1. Send an ESROS Error Request, then go wait for a response (either
       a confirmation or a failure indication).  The response is sent
       back on the same SAP type on which the event occurred.

    2. Keep track of the type of request that was issued.

   If there isn't anything wrong with the PDU or operation data, then
   the MTS performer has received a valid event from ESROS. This could
   be any of the defined Submission and Delivery Protocol operations.

5.1.2  Message-submission

    1. The Message-submission operation first checks to see which SAP
       this Submit Request came in on.

    2. The request could have arrived as 2-Way SAP (see #3) or a 3-Way
       SAP (see #7).

    3. If the event arrived on the 2-Way SAP, consider this a protocol
       violation and ignore it.

    4. Wait for a response to the request.  The response could be either
       an ERROR.confirm (see #5) or a FAILURE.indication (see #6).

    5. The ERROR.request has been confirmed.  The UA knows that the
       submitted message wasn't sent.  Since there was an error, there
       is nothing more to do, so return.

     6. If the result to the ErrorRequest is a Failure.indication, it
       can be assumed that either the UA has received nothing (the
       ERROR.request PDU was lost), which means failure for the UA; or
       that the 3-Way acknowledgment was lost, which means that the UA
       has in fact received the ERROR.request PDU and knows about the
       delivery failure.  Either way, the message can be ignored.  There
       is nothing more to do, so return.

    7. If the event was received on the 3-Way SAP, then this is the
       correct SAP on which to receive a Submit Request.  Send back a
       Result Request and keep track of the primitive which was issued.

    8. Now wait for a response to our request.  The response will be
       either a Result.confirm (see #9) or a Failure.indication (see
       #13).

    9. The RESULT.request has been confirmed.

    10. Submit the message to the RFC-822 mailer.

    11. Attempt, a number of times, to send the submitted message via
        the RFC-822 mailer.  If the send was successful, then return.

    12. If, after the maximum number of retries, the message was not
        able to be sent, consider it a failure.  Since the UA assumption
        has been that submission was successful, but now it has not been
        sent, a brand new message, a Non-Delivery message, must be
        generated and delivered to the UA. When this is completed, then
        return.

    13. A FAILURE.indication has occurred due to the previously issued
        RESULT.request.

    14. A Submission Verification is issued to the UA to see if the
        RESULT.request was received.  There are three possible results
        from sending the submission verification to the UA: Fail (see
        #15), Send Message (see #16) or Drop Message (see #20).

    15. Fail -- The Submission-verify request didn't reach the UA, or
        the Submission Verify response didn't get back.  Ignore the
        message and return.

    16. The Submission Verify operation succeeded, meaning that the UA
        received the request, and responded with a message stating that
        it wants the message to be sent.

    17. Attempt, a number of times, to send the submitted message via
        the RFC-822 mailer.

    18. If the message was submitted to the RFC-822 mailer successfully,
        then return.  If, after the maximum number of retries, the
        message was not able to send the message, consider it a failure.

    19. The UA already assumes that the Message-submission was
        successful.  Now since the submitted message has not been sent,
        a brand new message, a Non-Delivery message, must be generated
        and delivered to the UA. After this is accomplished, then
        return.

    20. The UA responded with a message stating that the message should
        be dropped.  This may occur if the UA never received the result
        from the MTS, meaning that it never received the Message Id, and
        had to therefore inform the user that the message couldn't be
        submitted.  This may also occur if the UA doesn't have the
        record of the message being verified.  It can be because the
        message record has been aged and expired, or because the EMSD-UA
        has not been able to keep the record of the received message
        because of storage or memory limitations.  There is nothing to
        do, so return.

5.1.3  Delivery-control

   This operation can be processed immediately.  After it is processed,
   the appropriate result is returned.

5.1.4  Delivery-verify

   This operation occurs when the UA doesn't think that the MTS has
   received the RESULT.indication from a previously delivered message.
   The UA wants to make sure that the MTS knows it has been delivered.
   The MTS will determine what it knows of the specified message, and
   send back a result.  This can be processed immediately, as it doesn't
   need to deal with duplicate detection.

5.1.5  MTS Invoker

   The MTS invoker is responsible for processing the following
   operations, received from ESROS:

      o Message-delivery

      o Submission-control

      o Submission-verify

   Submission-control

   Process the Submission Control request.

   Message-delivery

    1. Check the User Agent's profile to determine the SAP.

    2. Set the SAP to 3-Way.

    3. Issue the INVOKE.request on the appropriate SAP, with duplication
       detection enabled.  Since a local error is possible on issuing
       the INVOKE.request, a retry counter is needed.

    4. There are three possible events possible in result to the
       INVOKE.request:  an ERROR.indication (see #5), a
       RESULT.indication (see #9) or a FAILURE.indication (see #10).

    5. An ERROR.indication was received, which means that the UA can't
       accept the message right now.

    6. If the reason was one of a transient nature, wait for a while and
       then send the Deliver Request again.

    7. If the reason was one of a permanent nature, send back a non-
       delivery report to the originator.

    8. Since the error was one of a permanent nature, then the MTS must
       send back a non-delivery report, then log the unsuccessful
       delivery with error from UA and return.

    9. A RESULT.Indication was returned, which means that the Delivery
       was successful.  Send a delivery report to the originator if one
       was requested and log successful delivery and return.

       If the UA profile indicated that Complete mode was to be used,
       keep track of the fact that this message has been successfully
       delivered (as far as the MTS is concerned), so that if the UA
       sends us a Delivery Verify operation, we know that we consider
       the message to be delivered.

    10. A FAILURE.indication was returned, which means there was a
        problem getting the Deliver Request to the UA, or in getting the
        response back from the UA. In any case, a response was never
        received, so the request timed out.  Wait for a while, and then
        send the Deliver Request again.

        As long as a FAILURE.indication is returned and the number of
        retries has not been exceeded, keep trying to verify the
        delivery.

   Submission-verify

   The Submission-verify operation is always issued on the 2-Way SAP.
   The response is awaited.  If a response doesn't come, the request is
   queued and attempted again later.

    1. Issue the INVOKE.request on the 2-Way SAP, with duplication
       detection disabled.  Since a local error on issuing the invoke
       request is possible, a retry counter is needed.

    2. An INVOKE.Request has been issued and a response has been
       received.  The response will be either a a RESULT.indication (see
       #3) or a FAILURE.indication (see #4).  There are no defined
       errors to a Submission Verify operation, so an ERROR.indication
       should not be occurring here.

    3. A RESULT.indication was received.  Either ResponseSendMessage or
       ResponseDropMessage, as specified in the PDU, will be returned.

    4. A FAILURE.indication was received, which means that there was a
       problem getting the Submission Verify Request to the UA, or in
       getting the response back from the UA. In any case, the response
       was never received, so the request timed out.  Wait for a while,
       and then another attempt to send the Submission Verify request is
       needed.

   Non-Delivery Report

   Issue an INVOKE.request containing a Submit operation with a content
   type of Non-Delivery Report, to the UA. This operation is always
   issued on the 2-Way SAP. The response is awaited.  If a response
   doesn't come, the request is queued and attempted again later.

    1. Create a Submit operation.

    2. Issue the INVOKE.request on the 2-Way SAP, with duplication
       detection enabled.  Since a local error on issuing the invoke
       request is possible, a retry counter for is needed.

    3. A response to the INVOKE.Request has been received.  The response
       will be either a RESULT.indication (see #5), ERROR.indication
       (see #4), or a FAILURE indication (see #7).

    4. An ERROR.indication was received, which means that the UA doesn't
       know what to do with our non-delivery report.  That's the UAs
       problem, so just do nothing and return.

    5. A RESULT.indication was received, which means we delivered a
       successful non-delivery report.

    6. The result is logged.  Nothing more is needed, so return.

    7. A FAILURE.indication was received, which means there was a
       problem getting the Submit Request to the UA, or in getting the
       response back from the UA. In any case, the response was never,
       so the request timed out.  Wait for a while, and then send the
       Submission Verify request again.

5.2  UA Behavior

   The User Agent is event-driven.

   If it received an event from ESROS, then it could be any of the
   following types:

      o Message deliver indication;

      o Message deliver confirm and failure indication;

      o Result and Error indication for a submit operation;

      o Submission verify indication;

      o Result and Error indication for a delivery verify operation;

      o Result and Error indication for a delivery control operation;

      o Submission control indication.

   For an ESROS event responsibility is passed to the UA performer
   (Section 5.2.1).

   IF the UA received an event indicating that there's a message from
   the user, for submission, then responsibility is passed to the UA
   invoker (Section 5.2.2).

5.2.1  UA Performer

   The performer on the UA side is responsible for processing the
   following operations:

      o Message Delivery

      o Submission Verification

      o Submission Control

   Message-delivery

    1. A Message-delivery request is received.

    2. Check for the correctness of the PDU. If the PDU is bad the see
       #3.  If the PDU is good then see #8.

    3. Send an ESROS ERROR.request.  If the request arrived on a 3-Way
       SAP, use a 3-Way SAP for the result.  If the request arrived on a
       2-Way SAP, use a 2-Way SAP for the result.  Keep track of the
       type of request that was issued.

    4. Wait for the ESROS event.  The result could be an ERROR.confirm
       (see #5) or a FAILURE.indication (see #7).

    5. The ESROS event was an ERROR.confirm

    6. Log the message as the Non-Delivery was confirmed by the MTS and
       return.

    7. If the ESROS event was a FAILURE.indication, that means one of
       two things has occurred:

       A. The MTS has received nothing (the ERROR.request PDU was lost),
          which means that the MTS doesn't know that the message
          delivery has been rejected.  In this case, the MTS will
          eventually time out, and retransmit the message delivery
          request.

       B. The 3-Way acknowledgment was lost, which means that the MTS
          has in fact received the ERROR.request PDU and knows about the
          delivery failure.

       Either way, the message can now be ignored.

    8. Send an ESROS RESULT.request.  If the request arrived on a 3-Way
       SAP, use a 3-Way SAP for the result.  If the request arrived on a
       2-Way SAP, use a 2-Way SAP for the result.  Keep track of the
       type of request that was issued.

    9. Wait for the ESROS event.  The result could be an RESULT.confirm
       (see #10) or a FAILURE.indication (see #13).

    10. If the event is a RESULT.confirm, then the delivered message can
        now be given to the user.

    11. Deliver the message to the user.

    12. Log the message as Message Delivery Known to MTS.

    13. If the event is a FAILURE.indication, then, if the delivery was
        on a 3-Way SAP, a Delivery Verification request to the MTS can
        be issued to see if the MTS actually got the RSULT.request.  If
        the delivery was on a 2-Way SAP, then the message will delivered
        to the user and if the MTS has not received the RESULT.request,
        it will retransmit it later and the duplicate will be ignored.

    14. Deliver the message to the user.  Since a FAILRUE.indication was
        received in response to a RESULT.requst, it means that possible,
        the MTS didn't receive the RESULT.request.  The MTS could now
        time out, and send another copy of the same message.  Save the
        message for duplication detection.

    15. Log the fact that the message was delivered, but that the MTS
        might not be aware of it.

    16. If the UA supports Delivery Verification, and the Delivery
        Request was sent on the 3-Way SAP, then see #17.  If either of
        these conditions are not true, then return.

    17. Send a Delivery-verify request to see if the MTS got the
        RESULT.request.

        There are three possible results from sending the delivery
        verification to the MTS: Fail (see #18), ResponseNonDelivery
        (see #20) or ResponseDelivery (see #23).

    18. Fail -- Delivery Verify request didn't reach the MTS, or the
        Delivery Verify response didn't get back to the UA.

    19. Log this as delivering the message to the user, but the MTS
        having possibly sent a Non-Delivery report to the originator
        even though the UA did actually deliver the message to the user.
        Then return.

    20. ResponseNonDelivery -- Verify Response indicates that the MTS
        now knows (because of the Delivery Verify operation that the
        message has been delivered to the user, but had not received our
        RESULT.request nor a Delivery Verify operation in a timely
        manner, and had already sent out a Non-Delivery report to the
        originator.

    21. The MTS had not received, from the UA, in a timely manner, a
        RESULT.indication indicating that the message had been delivered
        to the user.  The MTS has already sent a Non-Delivery report to

        the originator.  The UA must let the user know about this.  Log
        the message as delivered to the user, but a Non-Delivery sent to
        the originator.

    22. Since the UA received a response to the Verify operation, it
        knows that the MTS knows about this message delivery, so the UA
        also knows that it won't be receiving a duplicate of it.  The UA
        can now remove this message's Message Id from the list of
        possible duplicates.

    23. ResponseDelivery -- Verify Response received from MTS.

    24. This means that the MTS knows (either because the MTS had
        received the RESULT.request that was sent by the UA or because
        the MTS has now received the UAs Delivery-verification message,
        informing that the UA received the message for delivery to the
        user.  The MTS is (or was) able to send a Delivery report to the
        originator if one was requested.  Log it as such.

    25. Since the UA received a response to the Verify operation, it
        knows that the MTS knows about this message delivery, so the UA
        also knows that it won't be receiving a duplicate of it.  The UA
        can now remove this message's Message Id from the list of
        possible duplicates and return.

   Submission-verify

   Process the Submission-verify request and return.

   Submission-control

   This operation can be processed immediately.  After it is processed,
   the appropriate result is returned.

5.2.2  UA Invoker

   The invoker on the UA side is responsible for processing the
   following operations:

      o Message-submission

      o Delivery-control

      o Delivery-verify

   Message-submission

   General procedures for UA's Message-submission mirror that of MTS's
   Message-delivery.

   Delivery-control

    1. Issue the INVOKE.request on the 3-Way SAP, with duplication
       detection enabled.  Since the UA can get a local error on issuing
       the invoke request, a retry counter is needed.

       If we got a local failure in issuing the Invoke Request, wait a
       while and then try again (up to the limit of the maximum number
       of retries).

    2. The UA has issued an INVOKE.Request.  Wait for a response from
       ESROS. The response will be either a RESULT.indication (see #5),
       ERROR.indication (see #3), or FAILURE.indication (see #7).

    3. A ERROR.indicaiton was received, meaning that the MTS told says
       that it cannot accept the message.

    4. Log the MTS rejection and return

    5. A RESULT.indication was received, which means that the Submission
       was successful.

    6. Log successful submission and return.

    7. a FAILURE.indication was received, meaning that there was a
       problem getting the Submit Request to the MTS, or in getting the
       response back from the MTS. In any case, the UA never received
       the response, so the request timed out.  Wait for a while, and
       then send the Submit Request again.

    8. The UA has exceeded the maximum number of retries.  Let the user
       know, log the failure and return.

   Delivery-verify

   General procedures for UA's Delivery-verify mirror that of MTS's
   Submission-verify.

6  EMSD FORMAT STANDARDS

6.1  Format Standard Overview

   EMSD Format Standard (EMSD-FS) is a non-textual form of compact
   encoding of Internet mail (RFC-822) messages which facilitates
   efficient transfer of messages.  EMSD-FS is used in conjunction with
   the EMSD-P but is not a general replacement for RFC-822.  EMSD-FS
   defines a method of representation of short interpersonal message.
   It defines the "Content" encoding (Header + Body).  Although EMSD-FS
   contains end-to-end information its scope is purely point-to-point.

   The "Efficient InterPersonal Message Format Standard" is defined in
   this section.  This standard is primarily intended for communication
   among people.

   The EMSD Format Standard is designed to be fully consistent with
   RFC-822 [3].  In many ways EMSD-FS can be considered to be an
   efficiency oriented encoder and decoder.  Through use of EMSD-FS an
   RFC-822 message is converted to a more compact binary encoding.  This
   more compact message is then transfered between an EMSD-SA and EMSD-
   UA. The compact message (represented in EMSD-FS) may then be
   converted back to RFC-822 intact.

   For messages that are originated (submitted) with EMSD protocol,
   certain fields (e.g., addresses, message-id) can have special forms
   that are specialized and produce more compact EMSD-FS encoding.
   These special forms are legitimate values of RFC-822 messages.

   This specification expresses information objects using ASN.1 [X.208].
   Encoding of ASN.1 shall be based on Basic Encoding Rules (BER) [5].
   Future revisions of this specification will use Packed Encoding Rules
   (PER) [4].

   The convention of (O) "OPTIONAL", (D) "DEFAULT", (C) "CONDITIONAL"
   and (M) "MANDATORY" which express requirements for presence of
   information is used in this section.

6.2  Interpersonal Messages

   An interpersonal message (IPM) consists of a heading and a body.

   IPM ::=   SEQUENCE

   {

     heading       Heading,

     body          Body OPTIONAL

   };

6.2.1  Heading fields

   The fields that may appear in the Heading of an IPM are defined and
   described below.

   Heading ::= SEQUENCE
   {
     -- Address of the sending agent (person, program, machine) of
     -- this message. This field is mandatory if the sender
     -- is different than the originator.
     sender                      [0]     EMSDORAddress OPTIONAL,

     -- Address of the originator of the message
     -- (not necessarily the sender)
     originator                          EMSDORAddress,

     -- List of recipients and flags associated with each.
     recipient-data                      SEQUENCE SIZE (1..ub-recipients)
                                         OF PerRecipientFields,

     -- Flags applying to this entire message
     per-message-flags           [1]     IMPLICIT BIT STRING

      {
      -- Priority values
      -- At most one of "non-urgent" and "urgent" may be specified
      -- concurrently.  If neither is specified, then a Priority
      -- level of "normal" is assumed.
      priority-non-urgent             (0),
      priority-urgent                 (1),

      -- Importance values

      -- At most one of "low" and "high" may be specified
      -- concurrently.  If neither is specified, then an
      -- Importance level of "normal" is  assumed.
      importance-low                  (2),
      importance-high                 (3),

      -- Indication of whether this message has been
         automatically forwarded
      auto-forwarded                  (4)
      } OPTIONAL,

     -- User-specified recipient who is to receive replies
        to this message.
     reply-to                    [2]     IMPLICIT SEQUENCE SIZE
                                         (1..ub-reply-to)
                                        OF EMSDORAddress OPTIONAL,

     -- Identifier of a previous message, for which this message
     -- is a reply
     replied-to-IPM                       EMSDMessageId OPTIONAL,

     -- Subject of the message.
     subject                     [3]     IMPLICIT AsciiPrintableString
                                         (SIZE (0..ub-subject-field))
                                                   OPTIONAL,

     -- RFC-822 header fields not explicitly provided for in
     -- this Heading. For messages incoming from the external
     -- world (i.e. in RFC-822 format), the Message-Id: field
     -- need not go here, as it is placed in the
     -- Envelope's EMSDMessageId (message-id) field.
     extensions        [4]  IMPLICIT  SEQUENCE
                            (SIZE (0..ub-header-extensions))
                            OF  IPMSExtension OPTIONAL,

     -- MIME Version (if other than 1.0)
     mime-version            [5]     IMPLICIT AsciiPrintableString
                                     (SIZE (0..ub-mime-version-length))
                                                  OPTIONAL,

     -- Top-level MIME Content Type
     mime-content-type       [6]     IMPLICIT AsciiPrintableString
                                     (SIZE (0..
                                      ub-mime-content-type-length))
                                               OPTIONAL,

     -- MIME Content Id
     mime-content-id         [7]     IMPLICIT AsciiPrintableString
                                     (SIZE (0..
                                      ub-mime-content-id-length))
                                               OPTIONAL,

     -- MIME Content Description
     mime-content-description [8]    IMPLICIT AsciiPrintableString
                                     (SIZE (0..ub-mime-content-
                                     description-length))
                                               OPTIONAL,
     -- Top-level MIME Content Type
     mime-content-transfer-encoding

                              [9]     IMPLICIT AsciiPrintableString
                                      (SIZE (0..ub-mime-content-
                                      transfer-encoding))
                                               OPTIONAL
   };

   Some fields have components and thus are composite, rather than
   indivisible.  A field component is called a sub-field.

   Sender

   This field is mandatory if the sender is different from the
   originator.

   Originator

   The Originator heading field (O) identifies the IPM's originator.

   Recipient-data

   PerRecipientFields ::= SEQUENCE
   {
     recipient-address                            EMSDORAddress,
     per-recipient-flags                          BIT STRING

     {
     -- Recipient Types.
     -- At most one of "copy" and "blind-copy" may be
     -- specified concurrently for a single recipient.  If
     -- neither is specified, than the recipient
     -- is assumed to be a "primary" recipient.
     recipient-type-copy                             (0),
     recipient-type-blind-copy                       (1),

     -- Notification Request Types.
     -- Only one of "rn" and "nrn" may be specified
     -- concurrently, \x110011 for a single recipient.
     -- "rn" implies "nrn" in addition.
     notification-request-rn                         (2),
     notification-request-nrn                        (3),

     notification-request-ipm-return                 (4),

     -- Report Request Types

     -- At most one of these should be set for a
     -- particular recipient. "delivery" implies "non-delivery"
     -- in addition.
     report-request-non-delivery                     (5),
     report-request-delivery                         (6),

     -- Originator-to-Recipient request for a reply.
     reply-requested                                 (7)
     } DEFAULT { report-request-non-delivery }

   };

   recipient-address

   The Primary Recipients heading field identifies the zero or more
   users who are the "primary recipients" of the IPM. The primary
   recipients might be those users who are expected to act upon the IPM.

   per-recipient-flags

   The Copy Recipients heading field identifies the zero or more users
   who are the "copy recipients" of the IPM. The copy recipients might
   be those users to whom the IPM is conveyed for information.

   recipient-type-copy

   This field is set if the recipient is on the Carbon Copy (CC) list.

   recipient-type-blind-copy

   This field is set if the recipient is on the Blind Carbon Copy (BCC)
   list.

   The Blind Copy Recipients heading field (C) identifies zero or more
   users who are the intended blind copy recipients of the IPM.

   The phrase "copy recipients" above has the same meaning as in "Copy
   Recipients" from Section 6.2.1 .  A blind copy recipient is one whose
   role as such is disclosed to neither primary nor copy recipients.

   In the instance of an IPM intended for a blind copy recipient, this
   conditional field shall be present and identify that user.  Whether
   it shall also identify the other blind copy recipients is a local
   matter.  In the instance of the IPM intended for a primary or copy
   recipient, the field shall be absent.

   notification-request-rn

   A receipt notification (rn) reports its originator's receipt, or his
   expected and arranged future receipt, of an IPM.

   notification-request-nrn

   A non-receipt notification (nrn) reports its originator's failure to
   receive, to accept, or his delay in receiving, an IPM.

   notification-request-ipm-return

   When this field is set, the contents of the message are returned
   along with the notification.

   report-request-non-delivery

   The report request enables the MTS to acknowledge to the MTS-user one
   or more outcomes of a previous invocation of the message-submission
   or probe-submission abstract-operations.

   A report is returned only in case of non-delivery.

   report-request-delivery

   For the message-submission, report-delivery indicates the delivery or
   non-delivery of the submitted message to one or more recipients.  For
   the probe-submission, the report-delivery indicates whether or not a
   message could be delivered if the message were to be submitted.

   reply-requested

   When set this field indicates that the originator requests that a
   recipient send a message in reply to the message which carries the
   request.

   per-message-Flags

   Priority

   The Priority field (default is normal) identifies the priority that
   the authorizing users attach to the IPM. It may assume any one of the
   following values:  urgent, normal, or non-urgent.

   At most one of either "non-urgent" or "urgent" may be specified
   concurrently.  If neither is specified, then a Priority level of
   "normal" is assumed.

   Importance

   The Importance heading field (default normal) identifies the
   importance that the authorizing users attach to the IPM. It may
   assume any one of the following values:  low, normal, or high.

   At most one of either "low" or "high" may be specified concurrently.
   If neither is specified, then a Importance level of "normal" is
   assumed.

   The values above are not defined by this specification; they are
   given meaning by users.

   auto-forwarded

   The Auto-forwarded heading field (default is false) indicates whether
   the IPM is the result of auto-forwarding.  It is a Boolean value.

   reply-to

   User-specified recipient or recipients who are to receive replies to
   this message.

   replied-to IPM

   The Replied-to IPM heading field (C) identifies the IPM to which the
   present IPM is a reply.  It comprises an IPM identifier.

   This conditional field shall be present if, and only if, the IPM is a
   reply.

   Note - In the context of forwarding, care should be taken to
   distinguish between the forwarding IPM and the forwarded IPM. This
   field should identify whichever of these two IPMs to which the reply
   responds.

   subject

   The Subject heading field (O) identifies the subject of the IPM. It
   corresponds to the "Subject:" field of RFC-822.

   extensions

   The Extensions heading field [D no extensions (i.e.  members)]
   conveys information accommodated by no other heading field.  It
   comprises a Set of zero or more IPMS extensions, each conveying one
   such information item.

   IPMSExtension ::= SEQUENCE
   {
       x-header-label                      AsciiPrintableString,
       x-header-value                      AsciiPrintableString
   };

6.2.2  Body part types

   The types of body parts that may appear in the Body of an IPM are
   structured using the MIME specification.

   Body ::= SEQUENCE
   {
     compression-method          [0]     IMPLICIT CompressionMethod
                                                  OPTIONAL,
     -- If compression method is not specified,
     -- "no-compression" is implied.

     message-body                        OCTET STRING
     -- See MIME for structure of the Body.
     -- If a compression method is specified, the entire text containing
     -- the Content-Type: element followed by the RFC-822 body are
     -- compressed using the specified method, and placed herein.
   };

   CompressionMethod ::= INTEGER
   {
     -- Compression Methods numbered 0 to 63 are reserved for
     -- assignment within this and associated specifications.

     no-compression                  (0),
     lempel-ziv                      (1)

     -- Compression Methods numbered between 64 and 127 may be
     --  used on a bilaterally-agreed basis between peers.
   } (0..127)

7  ACKNOWLEDGMENTS

   In the context of Limited Size Messaging (LSM) over CDPD and pACT
   over Narrowband PCS, AT&T Wireless Services (AWS), funded work which
   was relevant to the development of the EMSD protocols.

8  SECURITY CONSIDERATIONS

   This protocol supports simple authentication of the originator's
   address by the EMSD-SA and simple authentication of EMSD-SA by EMSD-
   UA.

   Mainstream Internet mail security mechanisms can be used in
   conjunction with the EMSD protocol.

9  AUTHOR'S ADDRESS

   Mohsen Banan
   Neda Communications, Inc.
   17005 SE 31st Place
   Bellevue, WA 98008

   EMail: mohsen@neda.com

A  EMSD-P ASN.1 MODULE

   This section compiles in one place the complete ASN.1 Module for EM
   Submission and Delivery Protocol.

   EMSD-SubmissionAndDeliveryProtocol DEFINITIONS ::=

   BEGIN

   EXPORTS EMSDORAddress, AsciiPrintableString, ContentType,
   DateTime, EMSDMessageId, EMSDORAddress, ProtocolVersionNumber;

   -- Upper bounds

   ub-recipients  INTEGER ::= 256;
   -- also defined in EMSD-InterpersonalMessaging1995
   ub-reply-to INTEGER ::= 256;
   -- also defined in EMSD-InterpersonalMessaging1995
   ub-subject-field INTEGER ::= 128;
   -- also defined in EMSD-InterpersonalMessaging1995
   ub-password-length INTEGER ::= 16;
   ub-content-length INTEGER ::= 65535;
   -- also defined in EMSD-Probe
   ub-content-types INTEGER ::= 128;
   ub-message-id-length INTEGER ::= 127;
   ub-total-number-of-segments INTEGER ::= 32;
   ub-header-extensions INTEGER ::= 64;
   -- also defined in EMSD-InterpersonalMessaging1995
   ub-emsd-name-length INTEGER ::= 64;
   ub-emsd-address-length INTEGER ::= 20;
   ub-rfc822-name-length INTEGER ::= 127;
   ub-mime-version-length INTEGER ::= 8;
   -- also defined in EMSD-InterpersonalMessaging1995
   ub-mime-content-type-length INTEGER ::= 127;
   -- also defined in EMSD-InterpersonalMessaging1995
   ub-mime-content-id-length INTEGER ::= 127;
   -- also defined in EMSD-InterpersonalMessaging1995
   ub-mime-content-description-length INTEGER ::= 127;
   -- also defined in EMSD-InterpersonalMessaging1995
   ub-mime-content-transfer-encoding INTEGER ::= 127;
   -- also defined in EMSD-InterpersonalMessaging1995
   ub-local-message-nu INTEGER ::= 4096;

   ----------------------
   -- SUBMIT Operation --
   ----------------------

   submit ES-OPERATION

       ARGUMENT SubmitArgument
       RESULT SubmitResult
       ERRORS
       {
           submissionControlViolated,
           securityError,
           resourceError,
           protocolViolation,
           messageError
       } ::= 33;

   SubmitArgument ::= SEQUENCE
   {
     -- Security features
     security           [0]    IMPLICIT SecurityElement
                               OPTIONAL,

     -- Segmentation features for efficient transport
     segment-info                  SegmentInfo OPTIONAL,

     -- Content type of the message
     content-type                            ContentType,

     --
     -- THE CONTENT --
     --

     -- The submission content
     content                       ANY DEFINED BY content-type

   };

   SubmitResult ::= SEQUENCE

   {

     -- Permanent identifier for this message.
     -- Also contains the message submission time.
     -- See comment regarding assignment of message
     -- identifiers, at the definition of EMSDLocalMessageId.
     message-id                        EMSDLocalMessageId
       };

   --------------------------------
   -- Delivery Control Operation --
   --------------------------------

   deliveryControl ES-OPERATION

       ARGUMENT DeliveryControlArgument
       RESULT DeliveryControlResult
       ERRORS
       {
           securityError,
           resourceError,
           protocolViolation
       } ::= 2;

   DeliveryControlArgument ::= SEQUENCE
   {
     -- Request an addition of or removal of a set of restrictions
     restrict             [0]     IMPLICIT Restrict DEFAULT update,

     -- Which operations are to be placed in the restriction set
     permissible-operations  [1]     IMPLICIT Operations OPTIONAL,

     -- What maximum content length should be allowed
     permissible-max-content-length
                             [2]     IMPLICIT INTEGER
                                     (0..ub-content-length) OPTIONAL,

     -- What is the lowest priority message which may be delivered
     permissible-lowest-priority
                             [3]     IMPLICIT ENUMERATED
                                     {
                                        non-urgent     (0),
                                        normal         (1),
                                        urgent         (2)
                                     } OPTIONAL,

     -- Security features
     security                  [4]     IMPLICIT SecurityElement
                                                     OPTIONAL,

     -- User Feature selection
     user-features             [5]     IMPLICIT OCTET STRING OPTIONAL
   };

   DeliveryControlResult ::= SEQUENCE
   {
     -- Operation types queued at the EMSD-SA due to existing
     -- restrictions.
     waiting-operations    [0]   IMPLICIT Operations DEFAULT { },

     -- Types of messages queued at the EMSD-SA due to
     -- existing restrictions

     waiting-messages      [1]   IMPLICIT WaitingMessages DEFAULT { },

     -- Content Types of messages queued at the EMSD-SA
     waiting-content-types   SEQUENCE SIZE (0..ub-content-types) OF
                                           ContentType DEFAULT { }
   };

   Restrict ::= ENUMERATED
   {
       update                                      (1),
       remove                                      (2)
   };

   Operations ::= BIT STRING
   {
       submission                                  (0),
       delivery                                    (1)
   };

   WaitingMessages ::= BIT STRING
   {
       long-content                                (0),
       low-priority                                (1)
   };

   -- Delivery Verify Operation

   deliveryVerify ES-OPERATION

       ARGUMENT DeliveryVerifyArgument
       RESULT DeliveryVerifyResult
       ERRORS
       {
           verifyError,
           resourceError,
           protocolViolation
       } ::= 5;

   DeliveryVerifyArgument ::= SEQUENCE
   {
     -- Identifier of this message. This is the same identifier that
     -- was provided to the originator in the Submission Result.
     -- See comment regarding assignment of message identifiers,
     -- at the definition of EMSDMessageId.
     message-id                                      EMSDMessageId
   };

   DeliveryVerifyResult ::= SEQUENCE
   {
                            status  DeliveryStatus
   };

    DeliveryStatus  ::= ENUMERATED
   {
           no-report-is-sent-out                   (1),
           delivery-report-is-sent-out             (2),
           non-delivery-report-is-sent-out         (3)
   };

   -----------------------
   -- DELIVER Operation --
   -----------------------

   deliver ES-OPERATION
       ARGUMENT DeliverArgument
       RESULT NULL
       ERRORS
       {
           deliveryControlViolated,
           securityError,
           resourceError,
           protocolViolation,
           messageError
       } ::= 35;

   DeliverArgument ::= SEQUENCE
   {
     -- Identifier of this message. This is the same identifier that
     -- was provided to the originator in the Submission Result.
     -- See comment regarding assignment of message identifiers,
     -- at the definition of EMSDMessageId.
     message-id                                      EMSDMessageId,

     -- Time the message was delivered to the recipient by EMSD-SA
     message-delivery-time                           DateTime,

     -- Time EMSD-SA originally took responsibility for processing
     -- of this message. This field shall be omitted if the message-id
     -- contains an EMSDLocalMessageId, because that field contains
     -- the submission time within it.
     message-submission-time [0]     IMPLICIT   DateTime OPTIONAL,

     -- Security features
     security                [1]     IMPLICIT   SecurityElement OPTIONAL,

     -- SegContentTypementation features for efficient transport
     segment-info                               SegmentInfo OPTIONAL,

     -- The type of the content
     content-type                               ContentType,

     --
     -- THE CONTENT --
     --

     -- The submitted (and now being delivered) content
     content                       ANY DEFINED BY content-type

   };

   -- Submission Control Operation

   submissionControl ES-OPERATION
       ARGUMENT SubmissionControlArgument
       RESULT SubmissionControlResult
       ERRORS
       {
           securityError,
           resourceError,
           protocolViolation
       } ::= 4;

   SubmissionControlArgument ::= SEQUENCE
   {
     -- Request an addition of or removal of a set of restrictions
     restrict               [0]     IMPLICIT Restrict DEFAULT update,

     -- Which operations are to be placed in the restriction set
     permissible-operations  [1]     IMPLICIT Operations OPTIONAL,

     -- What maximum content length should be allowed
     permissible-max-content-length
                             [2]     IMPLICIT INTEGER
                                     (0..ub-content-length) OPTIONAL,

     -- Security features
     security                [3]     IMPLICIT SecurityElement
                                                     OPTIONAL
   };

   SubmissionControlResult ::= SEQUENCE
   {
     -- Operation types queued at the EMSD-SA due to existing

     -- restrictions.
     waiting-operations    [0]   IMPLICIT Operations DEFAULT { }

   };

   ----------------------------------
   -- Submission Verify Operation --
   ----------------------------------

   submissionVerify  ES-OPERATION

       ARGUMENT SubmissionVerifyArgument
       RESULT SubmissionVerifyResult
       ERRORS
       {
           submissionVerifyError,
           resourceError,
           protocolViolation
       } ::= 6;

   SubmissionVerifyArgument ::= SEQUENCE
     -- Identifier of this message. This is the same identifier that
     -- was provided to the originator in the Submission Result.
     -- See comment regarding assignment of message identifiers,
     -- at the definition of EMSDMessageId.
     {
        message-id                       EMSDMessageId
     };

   SubmissionVerifyResult ::= SEQUENCE
       {
           status  SubmissionStatus
       };

   SubmissionStatus::= ENUMERATED
   {
           send-message            (1),
           drop-message            (2)
   };

   -- GetConfiguration Operation
   -- To be fully defined later. This will possibly include,
   -- but not be limited to:
   --      get-local-time-zone
   --      get-protocol-version
   --      etc.

   getConfiguration ES-OPERATION

           ARGUMENT NULL
           RESULT NULL
           ERRORS
           {
               resourceError,
               protocolViolation
           } ::= 7;

   -- SetConfiguration Operation
   -- To be fully defined later.

   setConfiguration ES-OPERATION

           ARGUMENT NULL
           RESULT NULL
           ERRORS
           {
               resourceError,
               protocolViolation
           } ::= 8;

   -- Security --

   SecurityElement ::= SEQUENCE

   {
     credentials                   Credentials,
     contentIntegrityCheck         ContentIntegrityCheck OPTIONAL
   };

   Credentials ::= CHOICE
   {
     simple                          [0]   IMPLICIT SimpleCredentials
     -- Strong Credentials are for future study
     -- strong                       [1]   IMPLICIT StrongCredentials
     -- externalProcedure            [2]   EXTERNAL
   };

   SimpleCredentials ::= SEQUENCE

   {
     eMSDAddress                         EMSDAddress OPTIONAL,
     password                    [0]     IMPLICIT OCTET STRING
                                 (SIZE (0..ub-password-length)) OPTIONAL
   };

   -- StrongCredentials ::= NULL
   -- for now.

   -- ContentIntegrityCheck is a 16-bit checksum of content
   ContentIntegrityCheck ::= INTEGER (0..65535);

   SegmentInfo ::= CHOICE

   {
     first           [APPLICATION 2]         IMPLICIT FirstSegment,
     other           [APPLICATION 3]         IMPLICIT OtherSegment
   };

   FirstSegment ::= SEQUENCE

   {
     sequence-id                             INTEGER,
     number-of-segments                      INTEGER
     -- number-of-segments must not exceed ub-total-number-of-segments

   };

   OtherSegment ::= SEQUENCE

   {
     sequence-id                             INTEGER,
     segment-number                          INTEGER
   };

   -----------
   -- Errors --
   ------------

   protocolVersionNotRecognized  ERROR PARAMETER NULL ::= 1;

   submissionControlViolated  ERROR PARAMETER NULL ::= 2;

   messageIdentifierInvalid  ERROR PARAMETER NULL ::= 3;

   securityError ERROR PARAMETER security-problem SecurityProblem ::= 4;

   deliveryControlViolated   ERROR PARAMETER NULL ::= 5;

   resourceError  ERROR PARAMETER NULL ::= 6;

   protocolViolation  ERROR PARAMETER NULL ::= 7;

   messageError  ERROR PARAMETER NULL ::= 8;

   SecurityProblem ::= INTEGER (0..127);

   --
   -- EXPORTED Definitions (for use by associated specifications) --
   --

   ContentType ::=  INTEGER
   {
     -- Content type 0 is reserved and shall never be transmitted.
     reserved                                 (0),
     -- Content types between 1 and 31 (inclusive) are for
     -- internal-use only
     probe                                    (1), -- reserved
     delivery-report                          (2), -- reserved

     -- Content types between 32 and 63 (inclusive) are for
     -- message types  defined within this specifications.
     emsd-interpersonal-messaging-1995        (32),
     voice-messaging                          (33) -- reserved

     -- Content types beyond and including 64 are for
     -- bilaterally-agreed use between peers.
   } (0..127);

   -- If this message was originated as an RFC-822 message, then this
   -- EMSDMessageId shall be the "Message-Id:" field from that message.
   -- If this message was originated within the EMSD domain,
   -- then this identifier shall be unique for the Message Center
   -- generating this id.

   EMSDMessageId ::= CHOICE
   {
     emsdLocalMessageId     [APPLICATION 4]  IMPLICIT
                            EMSDLocalMessageId,
     rfc822MessageId        [APPLICATION 5]  IMPLICIT
                            AsciiPrintableString
                            (SIZE (0..ub-message-id-length))

   };

   EMSDLocalMessageId ::= SEQUENCE
   {
     submissionTime                  DateTime,
     messageNumber                   INTEGER (0..ub-local-message-nu)
   };

   -- An Originator/Recipient Address in EMSD Environment

   EMSDORAddress ::= CHOICE
   {

     -- This is the local-format address
     emsd-local-address-format            EMSDAddress,

     -- This is a globally-unique RFC-822 Address
     rfc822DomainAddress                 AsciiPrintableString
   };

   EMSDAddress ::= SEQUENCE
   {
     emsd-address         OCTET STRING
                                    (SIZE (1..ub-emsd-address-length)),

     -- emsd-address is a decimal integer in BCD (Binary Encoded Decimal)
     -- format.
     -- If it had an odd number of digits, it is padded with 0 on
     -- the left.

     emsd-name                [0]     IMPLICIT OCTET STRING
                                      (SIZE (0..ub-emsd-name-length))
                                      OPTIONAL
   };

   DateTime ::= INTEGER;

   Iso8859String ::=  GeneralString;

   AsciiPrintableString ::= [ APPLICATION 0 ]
                            IMPLICIT Iso8859String (FROM

       (" "|"!"|"#"|"$"|"%"|"&"|"'"|"("|")"|"*"|"+"|","|"-"|"."|"/"|
        "0"|"1"|"2"|"3"|"4"|"5"|"6"|"7"|"8"|"9"|":"|";"|"<"|"="|">"|
        "?"|"@"|"A"|"B"|"C"|"D"|"E"|"F"|"G"|"H"|"I"|"J"|"K"|"L"|"M"|
        "N"|"O"|"P"|"Q"|"R"|"S"|"T"|"U"|"V"|"W"|"X"|"Y"|"Z"|"["|"]"|
        "^"|"_"|"`"|"a"|"b"|"c"|"d"|"e"|"f"|"g"|"h"|"i"|"j"|"k"|"l"|
        "m"|"n"|"o"|"p"|"q"|"r"|"s"|"t"|"u"|"v"|"w"|"x"|"y"|"z"|"{"|
        "|"|"}"|"~"|"\"|""""));

   ProtocolVersionNumber ::= [APPLICATION 1]    SEQUENCE
   {
     version-major                   INTEGER,
     version-minor           [0]     IMPLICIT INTEGER DEFAULT 0
   }
   END  -- end of EMSD-SubmissionAndDeliveryProtocol

B  EMSD-IPM ASN.1 MODULE

   This section compiles in one place the complete ASN.1 Module for
   EMSD-IPM.

   EMSD-InterpersonalMessaging1995 DEFINITIONS ::=

   BEGIN

   IMPORTS EMSDORAddress, EMSDMessageId, AsciiPrintableString
     FROM EMSD-SubmissionAndDeliveryProtocol;

   ub-recipients  INTEGER ::= 256;
   ub-reply-to INTEGER ::= 256;
   ub-subject-field INTEGER ::= 128;
   ub-header-extensions INTEGER ::= 64;
   ub-emsd-name-length INTEGER ::= 64;
   ub-mime-version-length INTEGER ::= 8;
   ub-mime-content-type-length INTEGER ::= 127;
   ub-mime-content-id-length INTEGER ::= 127;
   ub-mime-content-description-length INTEGER ::= 127;
   ub-mime-content-transfer-encoding INTEGER ::= 127;

   IPM ::=   SEQUENCE

   {
     heading                              Heading,
     body                                 Body OPTIONAL
   };

   Heading ::= SEQUENCE
   {
     -- Address of the sending agent (person, program, machine) of
     -- this message. This field is mandatory if the sender
     -- is different than the originator.
     sender                      [0]     EMSDORAddress OPTIONAL,

     -- Address of the originator of the message
     -- (not necessarily the sender)
     originator                          EMSDORAddress,

     -- List of recipients and flags associated with each.
     recipient-data                      SEQUENCE SIZE (1..ub-recipients)
                                         OF PerRecipientFields,

     -- Flags applying to this entire message
     per-message-flags           [1]     IMPLICIT BIT STRING

     {
        -- Priority values
        -- At most one of "non-urgent" and "urgent" may be specified
        -- concurrently.  If neither is specified, then a Priority
        -- level of "normal" is assumed.
        priority-non-urgent             (0),
        priority-urgent                 (1),

        -- Importance values
        -- At most one of "low" and "high" may be specified
        --  concurrently.  If neither is specified, then an
        -- Importance level of "normal" is  assumed.
        importance-low                  (2),
        importance-high                 (3),

        -- Indication of whether this message has been automatically
        -- forwarded
        auto-forwarded                  (4)
      }  OPTIONAL,

     -- User-specified recipient who is to receive replies to this
     -- message.
     reply-to                    [2]     IMPLICIT SEQUENCE SIZE
                                         (1..ub-reply-to)
                                         OF EMSDORAddress OPTIONAL,

     -- Identifier of a previous message, for which this message
     -- is a reply
     replied-to-IPM                       EMSDMessageId OPTIONAL,

     -- Subject of the message.
     subject                     [3]     IMPLICIT AsciiPrintableString
                                         (SIZE (0..ub-subject-field))
                                                   OPTIONAL,

     -- RFC-822 header fields not explicitly provided for in
     -- this Heading. For messages incoming from the external
     -- world (i.e. in RFC-822 format), the Message-Id: field
     -- need not go here, as it is placed in the
     -- Envelope's EMSDMessageId (message-id) field.
     extensions                [4]   IMPLICIT  SEQUENCE
                               (SIZE (0..ub-header-extensions))
                                     OF  IPMSExtension OPTIONAL,

     -- MIME Version (if other than 1.0)
     mime-version            [5]     IMPLICIT AsciiPrintableString
                                     (SIZE
                                     (0..ub-mime-version-length))

                                             OPTIONAL,

     -- Top-level MIME Content Type
     mime-content-type       [6]     IMPLICIT AsciiPrintableString
                                     (SIZE (0..
                                      ub-mime-content-type-length))
                                                OPTIONAL,

     -- MIME Content Id
     mime-content-id         [7]     IMPLICIT AsciiPrintableString
                                     (SIZE (0..
                                      ub-mime-content-id-length))
                                               OPTIONAL,

     -- MIME Content Description
     mime-content-description [8]    IMPLICIT AsciiPrintableString
                                     (SIZE (0..
                                  ub-mime-content-description-length))
                                               OPTIONAL,

     -- Top-level MIME Content Type
     mime-content-transfer-encoding
                              [9]     IMPLICIT AsciiPrintableString
                        (SIZE (0..ub-mime-content-transfer-encoding))
                                                  OPTIONAL
   };

   PerRecipientFields ::= SEQUENCE
   {
     recipient-address                            EMSDORAddress,
     per-recipient-flags                          BIT STRING

      {
         -- Recipient Types.
         -- At most one of "copy" and "blind-copy" may be
         -- specified concurrently for a single recipient.  If
         -- neither is specified, than the recipient
         -- is assumed to be a "primary" recipient.
         recipient-type-copy                             (0),
         recipient-type-blind-copy                       (1),

         -- Notification Request Types.
         -- Only one of "rn" and "nrn" may be specified
         -- concurrently, \x110011 for a single recipient.
         -- "rn" implies "nrn" in addition.
         notification-request-rn                         (2),
         notification-request-nrn                        (3),
         notification-request-ipm-return                 (4),

         -- Report Request Types
         -- At most one of these should be set for a
         -- particular recipient. "delivery" implies "non-delivery"
         -- in addition.
         report-request-non-delivery                     (5),
         report-request-delivery                         (6),

         -- Originator-to-Recipient request for a reply.
         reply-requested                                 (7)
      }  DEFAULT { report-request-non-delivery }

   };

   IPMSExtension ::= SEQUENCE
   {
     x-header-label                      AsciiPrintableString,
     x-header-value                      AsciiPrintableString
   };

   Body ::= SEQUENCE
   {
     compression-method          [0]     IMPLICIT CompressionMethod
                                                    OPTIONAL,
     -- If compression method is not specified,
     -- "no-compression" is implied.

     message-body                        OCTET STRING
     -- See MIME for structure of the Body.
     -- If a compression method is specified, the entire text containing
     -- the Content-Type: element followed by the RFC-822 body are
     -- compressed using the specified method, and placed herein.
   };

   CompressionMethod ::= INTEGER
   {
     -- Compression Methods numbered 0 to 63 are reserved for
     -- assignment within this and associated specifications.
     no-compression                  (0),
     lempel-ziv                      (1)

     -- Compression Methods numbered between 64 and 127 may be
     --  used on a bilaterally-agreed basis between peers.
   } (0..127)

   END  -- end of EMSD-InterpersonalMessaging1995

C  RATIONALE FOR KEY DESIGN DECISIONS

   This section summarizes the rationale behind key design decisions
   that were made while developing the EMSD Protocols.

C.1  Deviation From The SMTP Model

   SMTP is the main mail transport mechanism throughout the Internet.
   SMTP is widely deployed and well understood by many engineers who
   specialize in Internet email.  Because of these reasons, works based
   on SMTP or derived from it have a higher likelyhood of being widely
   deployed throughout the Internet.

   However, SMTP is highly inefficient for transfer of short messages.
   SMTP's inefficiency applies to both the number of transmissions and
   also to the number of bytes transmitted.

   Even when fully optimized with PIPELINING, SMTP is still quite
   inefficient.

   Submission of a short message with SMTP involves 15 transmissions.
   Submission of a short message with SMTP and PIPELINING involves 9
   transmissions.  Submission of a short message with EMSD (EMSD-P and
   ESRO) involves 3 transmissions (in typical cases).

   The key requirement driving the design of EMSD is efficiency.  It was
   determined that the at least 3 fold gains in efficiency justifies the
   deviation from the SMTP model.

C.1.1  Comparison of SMTP and EMSD Efficiency

   The table below illustrates the number of N-PDUs exchanged for
   transfer of a short Internet email when using SMTP, SMTP and
   PIPELINING, QMTP and EMSD. The names used for identifying the PDUs
   are informal names.

           SMTP      SMTP + pipelining   QMTP, QMQP,   EMSD
           -------   -----------------   ------------  -----------
   client: SYN       SYN                 SYN           Submit.Req
   server: SYN ok    SYN ok              SYN           Submit.Resp
   client: HELO      EHLO                message       ack
   server: ok        PIPELINING          accept close
   client: MAIL      MAIL RCPT DATA      close
   server: ok        ok
   client: RCPT      message QUIT
   server: ok        accept ok close
   client: DATA      close
   server: ok

   client: message
   server: accept
   client: QUIT
   server: ok close
   client: close

C.2  Use of ESRO Instead of TCP

   In order to provide the same level of reliability that the existing
   email protocols provide for short messages, it is clear that a
   reliable underlying service is needed.  UDP [6], by itself, is
   clearly not adequate.

   Use of TCP however, involves three phases:

      1. Connection Establishment

      2. Data Transfer

      3. Disconnect

   Reliable transfer of a short message using TCP at a minimum involves
   5 transmissions as it is the case with QMTP.

   The key requirement driving the design of EMSD is Efficiency.  It was
   determined that elimination of the extra 2 transmissions that are an
   inherent characteristic of TCP, justifies deviation from it.

   ESRO protocol, as specified in (RFC-2188 [1]), provides reliable
   connectionless remote operation services on top of UDP [6] with
   minimum overhead.  ESRO protocol supports segmentation and
   reassembly, concatenation and separation.

   Reliable transfer of a short message using ESRO involves 3
   transmissions as it is the case with EMSD-P.

C.3  Use Of Remote Procedure Call (RPC) Model

   Many Internet protocols are "text-based".  Few Internet protocols are
   RPC based.  Protocols designed around the "text-based" approach have
   a better track record of acceptance throughout the Internet.

   Considering that message submission and delivery in EMSD involve no
   more than two data exchanges, the text-based model becomes the same
   as an operation.  Furthermore, the RPC model is the natural way of
   using ESRO.

C.4  Use Of ASN.1

   In order to minimize the number of bytes transferred, efficient
   encoding mechanisms are needed.

   Amongst today's encoding mechanisms, ASN.1 has the unique feature of
   separating the abstract syntax from the encoding rules.  By selecting
   ASN.1 as the notation used for expressing EMSD's information objects,
   EMSD has the flexibility of using the most efficient encoding rules
   such as Packed Encoding Rules (PER) when they are available.

   Efficient encoding can always be better performed when the syntax of
   the information is known.  In general, encoding and compression
   techniques which use the knowledge of the syntax of the information
   produce better results than those compression techniques that work on
   arbitrary text.

D  FURTHER DEVELOPMENT

   Beyond this documentation of existing implementations, further
   development of EMSD protocol is anticipated.

   The following deficiencies and areas of improvement are identified.

      o Mapping of RFC-822 to EMSD-FS needs to be more explicit.

      o Mapping of EMSD-FS to RFC-822 needs to be more explicit.

      o Text of duplicate detection section needs more structure.

      o SubmissionControl operation needs more informative description.

      o Based on implementor's feedback the "EMSD PROCEDURE FOR
        OPERATIONS" section needs to be adjusted or re-done.

      o The EMSD protocol can be extended to also support transfer of
        raw RFC-822 text-based messages in addition to EMSD-FS. This
        would be a trade-off in favor of "ease of implementation"
        against "efficiency of bytes transfered".

      o Provide mechanisms to support fully automated initial
        provisioning of mail-boxes.

   Future development of the EMSD Protocol is anticipated to take place
   at http://www.emsd.org/.  Those interested in further development and
   maintenance of this protocol are invited to join the various mailing
   lists hosted at http://www.emsd.org/.

E. References

   [1] Banan, M., Cheng, J. and M. Taylor, "At&t/neda's efficient short
       remote operations (ESRO) protocol specification version 1.2.",
       RFC 2188, September 1997.

   [2] Bradner, S., "Key words for use in RFCs to indicate requirement
       levels", BCP 14, RFC 2119, March 1997.

   [3] Crocker, D., "Standard for the format of ARPA internet text
       messages", STD 11, RFC 822, August 1982.

   [4] Information Processing --- Open Systems Interconnection ---
       Specification of Packed Encoding Rules for Abstract Syntax
       Notation One (ASN.1). International Organization for
       Standardization and International Electrotechnical Committee.
       International Standard 8825-2.

   [5] Information Processing --- Open Systems Interconnection ---
       Specification of Basic Encoding Rules for Abstract Syntax
       Notation One (ASN.1). International Organization for
       Standardization and International Electrotechnical Committee,
       1987. International Standard 8825.

   [6] Postel, J., "User Datagram Protocol", STD 6, RFC 768, August
       1980.

F. Full Copyright Statement

   Copyright (C) The Internet Society (1999).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
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   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
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