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rfc:rfc3191

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.

Allocchio Standards Track [Page 1] RFC 3191 Minimal GSTN address format in Internet Mail October 2001

 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:

Allocchio Standards Track [Page 2] RFC 3191 Minimal GSTN address format in Internet Mail October 2001

    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].

Allocchio Standards Track [Page 3] RFC 3191 Minimal GSTN address format in Internet Mail October 2001

 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.

Allocchio Standards Track [Page 4] RFC 3191 Minimal GSTN address format in Internet Mail October 2001

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.

Allocchio Standards Track [Page 5] RFC 3191 Minimal GSTN address format in Internet Mail October 2001

 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.

Allocchio Standards Track [Page 6] RFC 3191 Minimal GSTN address format in Internet Mail October 2001

 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"

Allocchio Standards Track [Page 7] RFC 3191 Minimal GSTN address format in Internet Mail October 2001

 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

Allocchio Standards Track [Page 8] RFC 3191 Minimal GSTN address format in Internet Mail October 2001

    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:

Allocchio Standards Track [Page 9] RFC 3191 Minimal GSTN address format in Internet Mail October 2001

  1. 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.
  1. 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;
  1. an explicit list of "new terms" with explanations was added to

section 1.1;

  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;
  1. in section 2.1 the use and meaning of "written-sep" was clarified;
  1. 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;
  1. section 4.1 was updated to clarify how to generate "pstn-email"

when more than one subaddress is used;

  1. the Author's Address was updated;
  1. the References list was updated to include RFC 2846 and RFC 2434.

Allocchio Standards Track [Page 10] RFC 3191 Minimal GSTN address format in Internet Mail October 2001

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).

Allocchio Standards Track [Page 11] RFC 3191 Minimal GSTN address format in Internet Mail October 2001

 [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.

Allocchio Standards Track [Page 12] RFC 3191 Minimal GSTN address format in Internet Mail October 2001

Full Copyright Statement

 Copyright (C) The Internet Society (2001).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
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 or assist in its implementation may be prepared, copied, published
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 included on all such copies and derivative works.  However, this
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 The limited permissions granted above are perpetual and will not be
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Acknowledgement

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

Allocchio Standards Track [Page 13]

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