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.
AbstractThis 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.
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. 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 . 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.
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. 10] within a syntax for electronic mail addressing that is compliant with standard e-mail specifications given in  and .
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.
1], . For "domain" strings used in message content headers, the string MUST conform to the requirements of the relevant standards , . Note: the use of "domain names" or "domain literals" is permitted in addresses in both the SMTP envelope and message header fields. 2] and  "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 ,  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.
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. 13].
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  become more widely deployed, clients SHOULD employ those mechanisms to verify the authenticity and integrity of mail routing records. RFC 2434, section 2 : "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 .
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. 4]. To avoid any duplication (when appropriate), it MUST also use any already
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. RFC 2303 specification, this section briefly describes where updates and clarifications were introduced:
- 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.
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  Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC 821, August 1982.  Crocker, D., "Standard for the Format of ARPA Internet Text Messages", STD 11, RFC 822, August 1982.  Braden, R., "Requirements for Internet hosts - application and support", STD 3, RFC 1123, October 1989.  Malamud, C. and M. Rose, "Principles of Operation for the TPC.INT Subdomain: Remote Printing -- Technical Procedures", RFC 1528, October 1993.  Eastlake, D. and C. Kaufman, "Domain Name System Security Extensions", RFC 2065, January 1997.  Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.  Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications", RFC 2234, November 1997.  ITU F.401 - Message Handling Services: Naming and Addressing for Public Message Handling Service; recommendation F.401 (August 1992).  ITU F.423 - Message Handling Services: Intercommunication Between the Interpersonal Messaging Service and the Telefax Service; recommendation F.423 (August 1992).  ITU E.164 - The International Public Telecommunication Numbering Plan E.164/I.331 (May 1997).
 ITU T.33 - Facsimile routing utilizing the subaddress; recommendation T.33 (July 1996).  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).  Allocchio, C., "Minimal FAX address format in Internet Mail", RFC 3192, October 2001.  Kille, S., "MIXER (Mime Internet X.400 Enhanced Relay): Mapping between X.400 and RFC 822/MIME", RFC 2156, January 1998.  Allocchio, C. "GSTN address element extensions in e-mail services", RFC 2846, June 2000.  Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.
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