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RFC 3939 - Calling Line Identification for Voice Mail Messages


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Network Working Group                                         G. Parsons
Request for Comments: 3939                                   J. Maruszak
Category: Standards Track                                Nortel Networks
                                                           December 2004

          Calling Line Identification for Voice Mail Messages

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2004).

Abstract

   This document describes a method for identifying the originating
   calling party in the headers of a stored voice mail message.  Two new
   header fields are defined for this purpose: Caller_ID and
   Called_Name.  Caller_id is used to store sufficient information for
   the recipient to callback, or reply to, the sender of the message.
   Caller-name provides the name of the person sending the message.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
   2.  Conventions Used in this Document. . . . . . . . . . . . . . .  3
   3.  Calling Line Identification Field. . . . . . . . . . . . . . .  3
       3.1.  Internal Call. . . . . . . . . . . . . . . . . . . . . .  4
       3.2.  External Call. . . . . . . . . . . . . . . . . . . . . .  4
       3.3.  Numbering Plan . . . . . . . . . . . . . . . . . . . . .  4
       3.4.  Date Header. . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Caller Name Field. . . . . . . . . . . . . . . . . . . . . . .  5
   5.  Formal Syntax. . . . . . . . . . . . . . . . . . . . . . . . .  6
       5.1.  Calling Line Identification Syntax . . . . . . . . . . .  6
       5.2.  Caller Name Syntax . . . . . . . . . . . . . . . . . . .  6
       5.3.  Examples . . . . . . . . . . . . . . . . . . . . . . . .  6
   6.  Other Considerations . . . . . . . . . . . . . . . . . . . . .  6
   7.  Security Considerations. . . . . . . . . . . . . . . . . . . .  7
   8.  IANA Considerations. . . . . . . . . . . . . . . . . . . . . .  7
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  8
       9.1.  Normative References . . . . . . . . . . . . . . . . . .  8
       9.2.  Informative References . . . . . . . . . . . . . . . . .  8
   10. Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . .  9
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
   Full Copyright Statement . . . . . . . . . . . . . . . . . . . . . 11

1.  Introduction

   There is currently a need for a mechanism to identify the originating
   party of a voice mail message, outside of the "FROM" header
   information.  The telephone number and name of the caller are
   typically available from the telephone network, but there is no
   obvious header field to store this in an Internet Mail message.

   This information is intended for use when the VPIM message format is
   used for storing "Call Answer" voice messages in an Internet Mail
   message store, i.e., the calling party leaves a voice message for the
   recipient, who was unable to answer the call.  The implication is
   that there is no RFC 2822 address known for the originator.

   [VPIMV2R2] suggests the originating number be included as an Internet
   address, using the first method shown below.  There are several other
   ways to store this information, but they all involve some
   manipulation of the "From" field.  For example:

      1. From: "416 555 1234" <non-mail-user@host>
      2. From: "John Doe" <4165551234@host>
      3. From:  unknown:;

   Since any of these is a forced translation, it would be useful to
   store the calling party's name and number as presented by the
   telephone system to the called party without manipulation.  This
   would allow the calling party's information to be displayed to the
   recipient (similar to it appearing on the telephone) and also allow
   future determination of an Internet address for the originator (if
   one exists).  Note that there is no requirement to store meta-data
   (e.g., type of number, presentation restricted), as this information
   is not presented to the called party and is generally not available
   to voice mail systems.  The intent is to store the available
   information to an analog (non-ISDN) phone (e.g., per [T1.401] in
   North America).

   [RFC2076] currently lists "phone" as an Internet message header which
   would hold the originating party's telephone number, but it is listed
   as "non-standard", i.e., usage of this header is not generally
   recommended.  It also has no defined format, making the information
   unparsable.  There is no similar entry for the originator's name.

   It is proposed that two new message header fields be included to hold
   this information, namely the Calling Line Identification ("Caller-
   ID") and Caller Name ("Caller-Name").

2.  Conventions Used in this Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in BCP 14, [RFC2119].

3.  Calling Line Identification Field

   The Calling Line Identification header ("Caller-ID") holds sufficient
   information for the recipient's voice mail system to call back, or
   reply to, the sender of the message.  The number that is contained in
   this header is supplied by the telephone system.  The exact format of
   the data received depends on the type of call, that is -- internal or
   external call.

   Note that for both options, the number field MUST contain only the
   digits of the number and MUST be representable using the American
   Standard Code for Information Interchange [ASCII] character set; it
   does not include any separating character (e.g., "-").

   It is expected that default, likely to be the most common case, will
   not have any numbering plan semantic associated with the number.
   However, in the case that it is known, an optional "NumberingPlan"
   parameter MAY be used to indicate the semantic.

3.1.  Internal Call

   For an internal call (e.g., between two extensions within the same
   company), it is sufficient to relay only the extension of the calling
   party, based on the company dialing plan.

   However, the support of longer numbers may be supported by the
   enterprise phone system.

3.2.  External Call

   For an international call, the calling party's number must be the
   full international number as described in [E.164], i.e., Country Code
   (CC), National Destination Code (NDC), and Subscriber Number (SN).
   Other information, such as prefixes or symbols (e.g., "+"), MUST NOT
   be included.  [E.164] allows for numbers of up to 15 digits.

   For a call within North America, it is also suggested that 15 digits
   per [T1.625] be supported.  However, some service providers may only
   support 10 digits as described in [T1.401] and [GR-31-CORE].  Though
   it is desirable that an international number not be truncated to 10
   digits if it contains more, it is recognized that limitations of
   various systems will cause this to happen.

   Implementors of this specification should be aware that some phone
   systems are known to truncate international numbers, even though this
   behavior is undesirable.

   Note that the other defined fields available to non-analog systems
   (e.g., subaddress, redirecting number), as well as the meta-data, are
   not intended to be stored in this header.

3.3.  Numbering Plan

   In this baseline case (i.e., analog lines), no numbering plan
   information is known or implied.  However, in the case that a
   numbering plan is known, an optional "NumberingPlan" parameter MAY be
   used to indicate the semantic.  Only three semantics are defined:
   "unknown", "local", and "e164".  "unknown" is the default if no
   numbering plan semantic is known (and the default if the parameter is
   absent).  "local" has meaning only within the domain of the voice
   mail system that stored the message (i.e., the voice mail system
   knows that the number belongs to a local numbering plan).  "e164"
   indicates that the number is as described in [E.164].  "x-" may be
   used to indicate enterprise or service specific dialing plans.

3.4.  Date Header

   The date and time may be included by the telephone system with the
   calling party's telephone number per [T1.401].  This MAY be used, as
   there is an existing "Date" Internet header to hold this information.
   It is a local implementation decision whether this time or the local
   system time will be recorded in the "Date" header.

4.  Caller Name Field

   The name of the person sending the message is also important.
   Information about whether the call is internal or external may be
   included if it is available.  This information may not be available
   on international calls.

   Further, the exact format for this field is typically a service
   provider option per [T1.641].  It is possible for the caller's name
   to be sent in one of several character sets depending on the service
   provider signaling transport (e.g., ISDN-UP, SCCP, TCAP).  These
   include:

      1) International Reference Alphabet (IRA), formerly know as
         International Alphabet No.5 or IA5 [T.50]
      2) Latin Alphabet No. 1 [8859-1]
      3) American National Standard Code for Information Interchange
         [ASCII]
      4) Character Sets for the International Teletex Service [T.61]

   Of these, the IRA and T.61 character sets contain a number of options
   that help specify national and application oriented versions.  If
   there is no agreement between parties to use these options, then the
   7-bit character set in which the graphical characters of IRA, T.61,
   and ASCII are coded exactly the same, will be assumed.  Further, the
   7-bit graphical characters of [8859-1] are the same as in [ASCII].

   Note that for delivery to customer equipment in North America, the
   calling name MUST be presented in ASCII per [T1.401].

   As a result, for the caller name header defined in this document,
   characters are represented with ASCII characters.  However, if a name
   is received that cannot be represented in 7-bit ASCII, it MAY be
   stored using its native character set as defined in [RFC2047].

   In telephone networks, the length of the name field MUST NOT exceed
   50 characters, as defined in [T1.641].  However, service providers
   may choose to further limit this to 15 characters for delivery to
   customer equipment, e.g., [T1.401] and [GR-1188-CORE].

5.  Formal Syntax

   Both Calling Line Identification and Caller Name follow the syntax
   specification using the augmented Backus-Naur Form (BNF) as described
   in [RFC2234].  While the semantics of these headers are defined in
   sections 4 and 5, the syntax uses the 'unstructured' token defined in
   [RFC2822]:

      unstructured = *([FWS] utext) [FWS]

5.1.  Calling Line Identification Syntax

      "Caller-ID" ":" 1*DIGIT [ "," "NumberingPlan="
      ( "unknown" / "local" / "e164" / ietf-token / x-token ) ] CRLF

        ietf-token := <An extension token defined by a
                       standards-track RFC and registered
                       with IANA.>

        x-token := <The two characters "X-" or "x-" followed, with
                    no intervening white space, by any token>

5.2.  Caller Name Syntax

      "Caller-Name" ":" unstructured CRLF

5.3.  Examples

      To: +19725551212@vm1.example.com
      Caller-ID: 6137684087
      Caller-Name: Derrick Dunne

      To: 6137637582@example.com
      Caller-ID: 6139416900
      Caller-Name: Jean Chretien

6.  Other Considerations

6.1.  Compatibility with Other Internet Phone Numbers

   The intent of these headers are to record telephone number that is
   sent by the analog phone system with an incoming call without
   alteration or interpretation.  If sufficient semantic is known or can
   be inferred, this may be included in the NumberingPlan field.  This
   may allow it to be later translated into an addressable phone number.
   Addressable or dialable phone numbers (which this document does not
   define) are defined in other documents, such as GSTN address
   [RFC3191] or telephone URL [RFC2806].

6.2.  Usage

   There are a few scenarios of how this mechanism may fail that must be
   considered.  The first is mentioned in section 3.2 - the truncation
   of an international number to 10 digits.  This could result in a
   misinterpretation of the resulting number.  For instance, an
   international number (e.g., from Ireland) of the form "353 91 73
   3307" could be truncated to "53 91 73 3307" if received in North
   America, and interpreted as "539 917 3307" - a seemingly "North
   American" style number.  Thus, the recipient is left with incorrect
   information to reply to the message, possibly with an annoyed callee
   at the North American number.

   The second scenario is the possibility of sending an internal
   extension to an external recipient when a Call Answer message is
   forwarded.  This poses two problems, the recipient is given the wrong
   phone number, and the company's dialing plan could be exposed.

   The final concern deals with exercising character options that are
   available in coding the Calling Name field.  An international system
   may send a message with coding options that are not available on the
   receiving system, thus giving the recipient an incorrect Caller Name.

7.  Security Considerations

   Note that unlisted and restricted numbers are not a concern as these
   header fields are defined to contain what the called party would see
   (e.g., 'Private Name'), as opposed to the complete details exchanged
   between service providers.

   However, it must also be noted that this mechanism allows the
   explicit indication of phone numbers in the headers of an email
   message (used to store voice messages).  While the rationale for this
   is reviewed in section 1, the recipient of this message may not be
   aware that this information is contained in the headers unless the
   user's client presents the information.  Its use is intended to be
   informative as it is when it appears on a telephone screen.

8.  IANA Considerations

   This document defines an IANA-administered registration space for
   Caller-ID numbering plans in section 5.1.  Each registry entry
   consists of an identifying token and a short textual description of
   the entry.  There are three initial entries in this registry:

      unknown - The number's semantics are unknown.  This value is the
                default in the absence of this parameter.

      local   - The number only has meaning within the domain of the
                sending system identified by the RFC 2822 From field of
                the message.

      e164    - The number's semantics are described in [E.164].

   The only way to add additional entries (ietf-token in section 5.1) to
   this registry is with a standards-track RFC.

9.  References

9.1.  Normative References

   [VPIMV2R2]     Vaudreuil, G. and G. Parsons, "Voice Profile for
                  Internet Mail - version 2 (VPIMv2)", RFC 3801, June
                  2004.

   [RFC2047]      Moore, K., "MIME (Multipurpose Internet Mail
                  Extensions) Part Three: Message Header Extensions for
                  Non-ASCII Text ", RFC 2047, November 1996.

   [RFC2822]      Resnick, P., "Internet Message Format", RFC 2822,
                  April 2001.

   [RFC2234]      Crocker, D. and P. Overell, "Augmented BNF for Syntax
                  Specifications: ABNF", RFC 2234, November 1997.

   [RFC2119]      Bradner, S., "Key words for use in RFCs to Indicate
                  Requirement Levels", BCP 14, RFC 2119, March 1997.

9.2.  Informative References

   [RFC2076]      Palme, J., "Common Internet Message Headers", RFC
                  2076, February 1997.

   [E.164]        ITU-T Recommendation E.164 (1997), "The international
                  public telecommunication numbering plan"

   [T.50]         ITU-T Recommendation T.50 (1992), "International
                  Reference Alphabet (IRA)"

   [T.61]         CCITT Recommendation T.61 (1988) (Withdrawn),
                  "Character Repertoire and Coded Character Sets for the
                  International Teletex Service"

   [8859-1]       ISO/IEC International Standard 8859-1 (1998),
                  Information Technology _ 8-bit single-byte coded
                  graphic character sets _ Part 1: Latin Alphabet No. 1

   [ASCII]        American National Standards Institute (ANSI), Coded
                  Character Set - 7-Bit American National Standard Code
                  for Information Interchange, ANSI X3.4, 1986.

   [T1.401]       American National Standards Institute (ANSI),
                  Telecommunications _ Network-to-Customer Installation
                  Interfaces _ Analog Voicegrade Switched Access Lines
                  with Calling Number Delivery, Calling Name Delivery,
                  or Visual Message-Waiting Indicator Features, ANSI
                  T1.6401.03-1998

   [T1.625]       American National Standards Institute (ANSI),
                  Telecommunications - Integrated Services Digital
                  Network (ISDN) _ Calling Line identification
                  Presentation and Restriction Supplementary Services,
                  ANSI T1.625-1993

   [T1.641]       American National Standards Institute (ANSI),
                  Telecommunications - Calling Name Identification
                  Presentation, ANSI T1.641-1995

   [GR-1188-CORE] Telcordia Technologies, "CLASS Feature: Calling Name
                  Delivery Generic Requirements", GR-1188-CORE, Issue 2,
                  December 2000

   [GR-31-CORE]   Telcordia Technologies, "CLASS Feature: Calling Number
                  Delivery", GR-31-CORE, Issue 1, June 2000

   [RFC3191]      Allocchio, C., "Minimal GSTN address format in
                  Internet Mail", RFC 3191, October 2001.

   [RFC2806]      Vaha-Sipila, A., "URLs for Telephone Calls", RFC 2806,
                  April 2000.

10.  Acknowledgments

   The previous authors of versions of this document were Derrick Dunne
   and Jason Collins.  The current authors would like to thank Derrick
   and Jason for their contributions.

Authors' Addresses

   Glenn Parsons
   Nortel Networks
   P.O. Box 3511, Station C
   Ottawa, ON K1Y 4H7

   Phone: +1-613-763-7582
   EMail: gparsons@nortelnetworks.com

   Janusz Maruszak

   Phone: +1-416-885-0221
   EMail: jjmaruszak@sympatico.ca

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