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Calling Line Identification for Voice Mail Messages

The information below is for an old version of the document that is already published as an RFC.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 3939.
Authors Glenn Parsons , Janusz Maruszak
Last updated 2020-01-21 (Latest revision 2004-06-14)
RFC stream Internet Engineering Task Force (IETF)
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IESG IESG state RFC 3939 (Proposed Standard)
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VPIM Working Group                                        Glenn Parsons
Internet Draft                                          Janusz Maruszak
Document: <draft-ema-vpim-clid-09.txt>                  Nortel Networks
Category: Standards Track                                      May 2004
          Calling Line Identification for Voice Mail Messages 
Status of this Memo 
   This document is an Internet-Draft and is in full conformance with 
   all provisions of Section 10 of RFC2026.  
   Internet-Drafts are working documents of the Internet Engineering 
   Task Force (IETF), its areas, and its working groups. Note that 
   other groups may also distribute working documents as Internet-
   Drafts. Internet-Drafts are draft documents valid for a maximum of 
   six months and may be updated, replaced, or obsoleted by other 
   documents at any time. It is inappropriate to use Internet-Drafts as
   reference material or to cite them other than as "work in progress."
   The list of current Internet-Drafts can be accessed at  
   The list of Internet-Draft Shadow Directories can be accessed at 
   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.
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Table of Contents 
 1. Introduction ....................................................3
 2. Conventions used in this document ...............................3
 3. Calling Line Identification Field ...............................4
 3.1 Internal Call ..................................................4
 3.2 External Call ..................................................4
 3.3 Numbering Plan .................................................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 ............................................7
 7. Security Considerations .........................................7
 8.   IANA Considerations ...........................................7
 9. References ......................................................8
 9.1 Normative References ...........................................8
 9.2 Informative References .........................................8
 10. Acknowledgments ................................................9
 11. Author's Addresses .............................................9
 11. Full Copyright Statement .......................................10
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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 no RFC 2822 address is 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 display of the calling party's information 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 information 
   available to an analog (non-ISDN) phone (e.g., per [T1.401] in North
   [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"). 
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2. Conventions used in this document 
   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 
   this document are to be interpreted as described in RFC-2119. 
3. Calling Line Identification Field 
   The Calling Line Identification header ("Caller-ID") is to hold 
   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, and likely 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 for up to 15 digits. 
   For a call within North America, it is also suggested to support 15
   digits per [T1.625].  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 this will happen
   due to limitations of various systems. 
   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. 

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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.  That is, for example, 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
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 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 
      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
      4) Character Sets for the International Teletex Service [T.61] 
   Of these, the IRA and T.61 character set contains 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].  
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   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 chose to limit this further 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 
       Caller-ID: 6137684087 
       Caller-Name: Derrick Dunne 
       Caller-ID: 6139416900  
       Caller-Name: Jean Chretien

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6. Other Considerations 

6.1 Compatibility with other Internet phone numbers

   The intent of these headers are to record without alteration or
   interpretation the telephone number that is sent by the analog 
   phone system with an incoming call.  If sufficient semantic is
   known or can be infered, this may be included in the NumberingPlan
   field.  This may allow it to be later be translated into an
   addressable phone number.  Addressabe or dialable phone numbers
   (which this document does not define) are defined in other 
   documents, such as GSTN address [RFC 3191] or telephone URL
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 leaving the recipient with the
   incorrect information to reply to the message _ and 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 
 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. 

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   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 would appear 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, Greg, Parsons, Glenn, "Voice Profile for 
   Internet Mail, version 2", RFC 3801, June 2004.   
   [RFC2047] K. Moore, "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,  June 
   [RFC2234] Crocker, D. and Overell, P.(Editors), "Augmented BNF for 
   Syntax Specifications: ABNF", RFC 2234, Internet Mail Consortium and
   Demon Internet Ltd., November 1997 
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9.2 Informative References 
   [RFC2076] Palme, "Common Internet Message Headers", RFC 2076, 
        May 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 Chaacter Sets for the International Teletex 
   [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 
   [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 
   [RFC 3191] Minimal GSTN address format in Internet Mail, RFC 3191,
   Oct 2001  
   [RFC 2806] URL for Telephone Calls, RFC 2806, April 2000  
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10. Acknowledgments 
   The previous authors of drafts of this document were Derrick Dunne 
   and Jason Collins. The current authors would like to thank Derrick 
   and Jason for their contributions.  
11. Author's Addresses 
   Glenn Parsons 
   Nortel Networks 
   P.O. Box 3511, Station C 
   Ottawa, ON K1Y 4H7  
   Phone: +1-613-763-7582 
   Janusz Maruszak 
   Phone: +1-416-885-0221
12. Full Copyright Statement 
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