    Network Working Group                                       C. Allocchio
    Request for Comments: 3191                                    GARR-Italy
    Obsoletes: 2303                                             October 2001
    Updates: 2846
    Category: Standards Track

                  Minimal GSTN address format in Internet Mail

    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 (2001).  All Rights Reserved.

    Abstract

       This memo describes a simple method of encoding Global Switched
       Telephone Network (GSTN) addresses (commonly called "telephone
       numbers") in the local-part of Internet email addresses, along with
       an extension mechanism to allow encoding of additional standard
       attributes needed for email gateways to GSTN-based services.

    1. Introduction

       As with all Internet mail addresses, the left-hand-side (local-part)
       of an address generated according to this specification, is not to be
       interpreted except by an MTA that handles messages for the domain
       given in the right-hand-side.

       Since the very first e-mail to GSTN services gateway appeared, a
       number of different methods to specify a GSTN address as an e-mail
       address have been used by implementors.  Several objectives for this
       methods have been identified, like to enable an e-mail user to access
       GSTN services from his/her e-mail interface, to allow some kind of
       "GSTN over e-mail service" transport (possibly reducing the costs of
       GSTN long distance transmissions) while using the existing e-mail
       infrastructure.

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       This memo describes the MINIMAL addressing method to encode GSTN
       addresses into e-mail addresses and the standard extension mechanism
       to allow definition of further standard elements.  The opposite
       problem, i.e., to allow a traditional numeric-only GSTN device user
       to access the e-mail transport service, is not discussed here.

       The IANA registration templates which MUST be used to register any
       standard element defined according to this specification are given in
       the "IANA Considerations" chapter (section 7 of this document).

       All implementations supporting this GSTN over e-mail service MUST
       support as a minimum the specification described in this document.
       The generic complex case of converting the entirety of GTSN
       addressing into e-mail is out of scope in this minimal specification.

    1.1 Terminology and Syntax conventions

       In this document the formal definitions are described using ABNF
       syntax, as defined into [7].  This memo also uses some of the "CORE
       DEFINITIONS" defined in "APPENDIX A - CORE" of that document.  The
       exact meaning of the capitalized words

          "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",
          "SHOULD NOT", "RECOMMENDED", "MAY", "OPTIONAL"

       is defined in reference [6].

       In this document the following new terms are also defined:

          I-pstn device:
             a device which has an Internet domain name and it is able to
             communicate either directly or indirectly with the GSTN
             network;

          mta-I-pstn:
             the Internet domain name which identifies uniquely an I-pstn
             device over the Internet;

          pstn-email:
             the complete Internet e-mail address structure which is used to
             transport a GSTN address over the Internet e-mail service.

    2. Minimal GSTN address

       The minimal specification of a GSTN address within an e-mail address
       is as follows:

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          pstn-address = pstn-mbox  [ qualif-type1 ]

          pstn-mbox = service-selector "=" global-phone

          service-selector = 1*( DIGIT / ALPHA / "-" )
                             ; note that SP (space) is not allowed in
                             ; service-selector.
                             ; service-selector MUST be handled as a case
                             ; INSENSITIVE string by implementations.

       Other specifications adopting the "pstn-address" definition MUST
       define and register with IANA a unique case insensitive
       "service-selector" element to identify the specific messaging service
       involved.

       These specifications and registrations MUST also define which minimal
       "qualif-type1" extensions, if any, MUST be supported for the
       specified messaging service.

       Implementations confirming to this minimal requirements specification
       are allowed to ignore any other non-minimal extensions address
       element which is present in the "pstn-address".  However, conforming
       implementations MUST preserve all "qualif-type1" address elements
       they receive.

       The generic "qualif-type1" element is defined as:

          qualif-type1 = "/" keyword "=" string

          keyword = 1*( DIGIT / ALPHA / "-" )
                    ; note that SP (space) is not allowed in keyword

          string = PCHAR
                   ; note that printable characters are %x20-7E

       As such, all "pstn-address" extension elements MUST be defined in the
       "qualif-type1" form at the time of registration with IANA.

    2.1 Minimal "global-phone" definition

       The purpose of global-phone element is to represent standard E.164
       numeric addresses [10] within a syntax for electronic mail addressing
       that is compliant with standard e-mail specifications given in [1]
       and [2].

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       The minimal supported syntax for global-phone element is as follows:

          global-phone = "+" 1*( DIGIT / written-sep )

          written-sep = ( "-" / "." )

       The use of other dialing schemes for GSTN numbers (like private
       numbering plans or local dialing conventions) is also allowed.
       However, this does not preclude nor remove the mandatory requirement
       for support to the "global-phone" syntax within the minimal GSTN
       address format.

       Any other dialing schemes MUST NOT use the leading "+" defined here
       between the "=" sign and the dialing string.  The "+" sign is
       strictly reserved for the standard "global-phone" syntax.

       Note:

          The specification of alternate dialing schemas is out of scope for
          this minimal specification.

       This document also permits the use of written-sep elements in order
       to improve human readability of GSTN e-mail addresses.  The
       written-sep are elements which can be placed between dial elements
       such as digits etc.

       Implementors' note:

          Use of the written-sep elements is allowed, but not recommended
          for transmission.  Any occurrences of written-sep elements in a
          pstn-mbox MUST be ignored by all conformant implementations.

    2.2 The minimal "pstn-address" examples

       Some examples of minimal pstn-address are:

          VOICE=+3940226338

          FAX=+12027653000/T33S=6377

          SMS=+33-1-88335215

       Note:

          these examples are given as illustrations only; they do not
          necessarily represent valid pstn-addresses.

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    3. The e-mail address of the I-pstn device: mta-I-pstn

       An "I-pstn device" has, among its characteristics, a unique Internet
       domain name which identifies it on the Internet.  Within Internet
       mail, this is the Right Hand Side (RHS) part of the address, i.e.,
       the part on the right of the "@" sign.  For purposes of this document
       we will call this "mta-I-pstn"

          mta-I-pstn = domain

       For "domain" strings used in SMTP transmissions, the string MUST
       conform to the requirements of that standards <domain> specifications
       [1], [3].  For "domain" strings used in message content headers, the
       string MUST conform to the requirements of the relevant standards
       [2], [3].

       Note:

          the use of "domain names" or "domain literals" is permitted in
          addresses in both the SMTP envelope and message header fields.

    4. The pstn-email

       The complete structure used to transfer a minimal GSTN address over
       the Internet e-mail transport system is called "pstn-email".  This
       object is a an e-mail address which conforms to [2] and [3]
       "addr-spec" syntax, with structure refinements which allows the GSTN
       number to be identified.

          pstn-email =  ["""] ["/"] pstn-address ["/"] ["""] "@" mta-I-pstn

       Implementors' note:

          The optional "/" characters can result from translations from
          other transport gateways (such as some X.400 gateways) which have
          included the "/" as an optional element.  Implementations MUST
          accept the optional slashes but SHOULD NOT generate them.
          Gateways are allowed to strip them off when converting to Internet
          mail addressing.  The relevant standard [2], [3] define exactly
          when the optional "quotes" characters surrounding the entire local
          part (i.e., the part on the left of the "@" character into the
          pstn-email) MUST be added.

    4.1 Multiple subaddresses

       There are some instances in GSTN applications where multiple
       subaddresses are used.  On the other hand in e-mail practice a
       separate and unique e-mail address is always used for each recipient.

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       In the event a particular GSTN service requires multiple subaddresses
       (in any form defined by the standard specification for that GSTN
       service) that are associated with the same "pstn-mbox", then the use
       of multiple "pstn-email" elements is REQUIRED.

       Implementors' note:

          The UA may accept multiple subaddress elements for the same
          global-phone, but it MUST generate multiple "pstn-mbox" elements
          when submitting the message to the MTA.

    4.2 Some examples of minimal "pstn-email" addresses

       Some examples of minimal pstn-email addresses follows:

             VOICE=+3940226338@worldvoice.com

             FAX=+1.202.7653000/T33S=6377@faxserv.org

             /SMS=+33-1-88335215/@telecom.com

       Note:

          these examples are given as illustrations only; they do not
          necessarily represent valid pstn-addresses.

    5. Conclusions

       This proposal creates a minimal standard encoding for GSTN addresses
       within the global e-mail transport system.  It also defines the
       standard extension mechanism to be used to introduce new elements for
       GSTN addresses.

       The proposal is consistent with existing e-mail standards.  Each
       specific GSTN service using this proposal MUST define and register
       with IANA its own "service-selector" specification and MUST define
       and register the eventual other "qualif-type1" elements needed for
       its specific application.  An example of such an application is
       contained in reference [13].

    6. Security Considerations

       This document specifies a means by which GSTN addresses can be
       encoded into e-mail addresses.  Since e-mail routing is determined by
       Domain Name System (DNS) data, a successful attack to DNS could
       disseminate tampered information, which causes e-mail messages to be
       diverted via some MTA or Gateway where the security of the software
       has been compromised.

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       There are several means by which an attacker might be able to deliver
       incorrect mail routing information to a client.  These include: (a)
       compromise of a DNS server, (b) generating a counterfeit response to
       a client's DNS query, (c) returning incorrect "additional
       information" in response to an unrelated query.  Clients SHOULD
       ensure that mail routing is based only on authoritative answers.
       Once DNS Security mechanisms [5] become more widely deployed, clients
       SHOULD employ those mechanisms to verify the authenticity and
       integrity of mail routing records.

    7. IANA Considerations

       As the service-selector and qualif-type1 elements values are
       extensible, they MUST be registered with IANA.

       To register a service-selector or a qualif-type1 element, the
       registration form templates given in 7.1 and 7.2 MUST be used. Any
       new registration MUST fulfill the "Specification Required" criteria,
       as defined in RFC 2434, section 2 [16]:

         "Specification Required - Values and their meaning MUST be
          documented in an RFC or other permanent and readily available
          reference, in sufficient detail so that interoperability between
          independent implementations is possible."

       IANA MUST NOT accept registrations which are not supplemented by a
       Specification as defined above and which are not fully specified
       according to the template forms given in 7.1 and 7.2.  In case of
       need for further consultation about accepting a new registration,
       IANA SHOULD refer to the Application Area Director to be directed to
       the appropriate "expert" individual or IETF Working Group.

       After successful registration, IANA should publish the registered new
       element in the appropriate on-line IANA WEB site, and include it into
       the updates of the "Assigned Numbers" RFC series.

       This section (including 7.1 and 7.2) updates the ones contained in
       [15].

    7.1 IANA Registration form template for new values of GSTN
        address service-selector

       To: IANA@iana.org
       Subject: Registration of new values for the GSTN address
       service-selector specifier "foo"

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       service-selector name:

          foo

       Description of Use:

          foo - ("foo" is a fictional new service-selector used in this
          template as an example, it is to be replaced with the new value
          being registered.  Include a short description of the use of the
          new value here.  This MUST include reference to Standard Track
          RFCs and eventually to other Standard Bodies documents for the
          complete description; the use of the value must be defined
          completely enough for independent implementation).

       Security Considerations:

         (Any additional security considerations that may be introduced by
          use of the new service-selector parameter should be defined here
          or in the reference Standards Track RFCs)

       Person & email address to contact for further information:

          (fill in contact information)

       INFORMATION TO THE SUBMITTER:

          The accepted registrations will be listed in the "Assigned
          Numbers" series of RFCs.  The information in the registration form
          is freely distributable.

    7.2 IANA Registration form template for new values of GSTN
        address qualif-type1 keyword and value

       To: IANA@iana.org
       Subject: Registration of new values for the GSTN address
       qualif-type1 element "bar"

       qualif-type1 "keyword" name:

          bar

       qualif-type1 "value" ABNF definition:

          abnf - ("abnf" MUST define the ABNF form of the qualif-type1
          value.  The ABNF specification MUST be self-contained, using as
          basic elements the tokens given in specification [4].  To avoid
          any duplication (when appropriate), it MUST also use any already

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          registered non-basic token from other qualif-type1 elements, i.e.,
          it MUST use the same non-basic token name and then repeat its
          identical ABNF definition from basic tokens.

       Description of Use:

          bar - ("bar" is a fictional description for a new qualif-type1
          element used in this template as an example.  It is to be replaced
          by the real description of qualif-type1 element being registered.
          Include a short description of the use of the new qualif-type1
          here.  This MUST include reference to Standards Track RFCs and
          eventually to other Standard Bodies documents for the complete
          description; the use of the value MUST be defined completely
          enough for independent implementation.)

       Use Restriction:

          (If the new qualif-type1 elements is meaningful only for a
          specific set of service-element, you MUST specify here the list of
          allowed service-element types.  If there is no restriction, then
          specify the keyword "none")

       Security Considerations:

          (Any additional security considerations that may be introduced by
          use of the new service-selector parameter should be defined here
          or in the reference Standards Track RFCs)

       Person & email address to contact for further information:

          (fill in contact information)

       INFORMATION TO THE SUBMITTER:

          The accepted registrations will be listed in the "Assigned
          Numbers" series of RFCs.  The information in the registration form
          is freely distributable.

    8. Changes from RFC 2303 specification

       Although there are no technical or major changes from RFC 2303
       specification, this section briefly describes where updates and
       clarifications were introduced:

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       -  considering the case that telephony systems do not conform any
          more to the "single/few" Public Operator paradigm, the old
          definition "PSTN - Public Switched Telephone Network" was changed
          into the more adequate "GSTN - Global Switched Telephone Network"
          one.  However, in order to remain consistent with the previous
          specification, the ABNF variables names were not changed.

       -  it was made clear that "GSTN addresses" correspond, in common
          language, to "telephone numbers" and that the "global-phone" is a
          representation of E.164 numeric addresses;

       -  an explicit list of "new terms" with explanations was added to
          section 1.1;

       -  the fact that any other specification adopting the "pstn-address"
          definition MUST register with IANA the new "service-selector" and
          "qualif-type1" elements was made explicit throughout the document;
          the relevant mechanism to be used was added in section 7 "IANA
          considerations" (including the  IANA Registration form templates);
          this is also consistent with RFC 2846;

       -  in section 2.1 the use and meaning of "written-sep" was clarified;

       -  in section 4., the quoting rules of the "pstn-address" and their
          practical use was made explicit both in the definition of
          pstn-email" and in the Implementors' note;

       -  section 4.1 was updated to clarify how to generate "pstn-email"
          when more than one subaddress is used;

       -  the Author's Address was updated;

       -  the References list was updated to include RFC 2846 and RFC 2434.

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    9. Author's Address

          Claudio Allocchio
          INFN-GARR
          c/o Sincrotrone Trieste
          SS 14 Km 163.5 Basovizza
          I 34012 Trieste
          Italy

          RFC2822: Claudio.Allocchio@garr.it
          X.400:   C=it;A=garr;P=garr;S=Allocchio;G=Claudio;
          Phone:   +39 040 3758523
          Fax:     +39 040 3758565

    10. References

       [1]  Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC 821,
            August 1982.

       [2]  Crocker, D., "Standard for the Format of ARPA Internet Text
            Messages", STD 11, RFC 822, August 1982.

       [3]  Braden, R., "Requirements for Internet hosts - application and
            support", STD 3, RFC 1123, October 1989.

       [4]  Malamud, C. and M. Rose, "Principles of Operation for the
            TPC.INT Subdomain: Remote Printing -- Technical Procedures", RFC
            1528, October 1993.

       [5]  Eastlake, D. and C. Kaufman, "Domain Name System Security
            Extensions", RFC 2065, January 1997.

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

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

       [8]  ITU F.401 - Message Handling Services: Naming and Addressing for
            Public Message Handling Service; recommendation F.401 (August
            1992).

       [9]  ITU F.423 - Message Handling Services: Intercommunication
            Between the Interpersonal Messaging Service and the Telefax
            Service; recommendation F.423 (August 1992).

       [10] ITU E.164 - The International Public Telecommunication Numbering
            Plan E.164/I.331 (May 1997).

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       [11] ITU T.33 - Facsimile routing utilizing the subaddress;
            recommendation T.33 (July 1996).

       [12] ETSI I-ETS 300,380 - Universal Personal Telecommunication (UPT):
            Access Devices Dual Tone Multi Frequency (DTMF) sender for
            acoustical coupling to the microphone of a handset telephone
            (March 1995).

       [13] Allocchio, C., "Minimal FAX address format in Internet Mail",
            RFC 3192, October 2001.

       [14] Kille, S., "MIXER (Mime Internet X.400 Enhanced Relay): Mapping
            between X.400 and RFC 822/MIME", RFC 2156, January 1998.

       [15] Allocchio, C. "GSTN address element extensions in e-mail
            services", RFC 2846, June 2000.

       [16] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
            Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.

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    Full Copyright Statement

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    Acknowledgement

       Funding for the RFC Editor function is currently provided by the
       Internet Society.

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