Minimal PSTN address format in Internet Mail
RFC 2303

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Network Working Group                                      C. Allocchio
Request for Comments: 2303                                   GARR-Italy
Category: Standards Track                                    March 1998

              Minimal PSTN 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 (1998).  All Rights Reserved.

IESG NOTE

   This memo describes a simple method of encoding PSTN addresses 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 PSTN-based services.

   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 the MTA that is named on the right-hand-side
   (domain).

1. Introduction

   Since the very first e-mail to PSTN services gateway appeared, a
   number of different methods to specify a PSTN address as an e-mail
   address have been used by implementors. Two major objectives for this
   were

     - enable an e-mail user to access these services from his/her
       e-mail interface;

     - enable some kind of "PSTN over e-mail service" transport, to
       reduce the costs of PSTN long distance transmissions, and use the
       existing e-mail infrastructure.

Allocchio                   Standards Track                     [Page 1]
RFC 2303             Minimal PSTN in Internet Mail            March 1998

   This memo describes the MINIMAL addressing method to encode PSTN
   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 PSTN device user to
   access the e-mail transport service, is not discussed here.

   All implementations supporting this PSTN over e-mail service MUST
   support as a minimum the specification described in this document.
   The generic complex case of converting the whole PSTN addressing into
   e-mail is out of scope in this minimal specification: there is some
   work in progress in the field, where also a number of standard
   optional extensions are being defined.

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

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

   is defined in reference [6].

2. Minimal PSTN address

   The minimal specification of a PSTN address in e-mail address is as
   follows:

      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.

   Specifications adopting the "pstn-address" definition MUST define a
   unique case insensitive "service-selector" element to identify the
   specific messaging service involved.

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

   Implementations confirming to these minimal requirements
   specification are allowed to ingnore any other non-minimal extensions
   address element which can be present in the "pstn-address". However,

Allocchio                   Standards Track                     [Page 2]
RFC 2303             Minimal PSTN in Internet Mail            March 1998

   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" extensions elements MUST be defined in
   the "qualif-type1" form.

2.1 Minimal "global-phone" definition

   We now define the minimal supported syntax for global-phone:

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

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

   The use of other dialling schemas for PSTN numbers (like private
   numbering plans or local dialling conventions) is also allowed.