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rfc:rfc3192

Network Working Group C. Allocchio Request for Comments: 3192 GARR-Italy Obsoletes: 2304 October 2001 Updates: 2846 Category: Standards Track

            Minimal FAX 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 of facsimile devices in the
 local-part of Internet email addresses.

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 the MTA that is named on the right-hand-side
 (domain).
 Since the very first e-mail to fax gateway objects appeared, a number
 of different methods to specify a fax 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 send and
 receive faxes from his/her e-mail interface, to allow some kind of
 "fax over e-mail service" transport (possibly reducing the costs of
 GSTN long distance transmissions) while using the existing e-mail
 infrastructure.
 This memo describes the MINIMAL addressing method and standard
 extensions to encode FAX addresses into e-mail addresses, as required
 in reference [13].  The opposite problem, i.e., to allow a
 traditional numeric-only fax device user to access the e-mail
 transport service, is not discussed here.

Allocchio Standards Track [Page 1] RFC 3192 Minimal FAX address format in Internet Mail October 2001

 These IANA forms used to register the standard elements defined here
 are given in the "IANA Considerations" chapter (section 7 of this
 document).
 All implementations supporting FAX over e-mail address format MUST
 support this minimal specification.

1.1 Terminology and Syntax conventions

 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 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-fax device:
       an I-pstn device type [13] which is able to communicate either
       directly or indirectly with the traditional FAX over GSTN
       service;
    mta-I-fax:
       the Internet domain name which identifies uniquely an I-fax
       device over the Internet (see also mta-I-pstn in [13]);
    fax-email:
       the complete Internet e-mail address structure which is used to
       transport a FAX address over the Internet e-mail service (see
       also pstn-email in [13]).

2. Minimal Fax address

 The minimal fax address within e-mail has been defined for
 consistency with reference [13] and it contains two elements: the
 fax-mbox and an optional qualif-type1 element.
 More precisely the GSTN minimal address specification requires the
 use of a unique service-selector for each specific application
 (section 2 in [13]).
 The "service-selector" defined for the fax service is as follows:
    service-selector = "FAX"

Allocchio Standards Track [Page 2] RFC 3192 Minimal FAX address format in Internet Mail October 2001

 In the syntax for the fax address a qualif-type1 element has been
 defined for support of T.30/T.33 subaddresses (see section 2 of
 [13]).  The use of this element is OPTIONAL, but compliant
 implementations MUST be able to support and correctly interpret it
 when present.  Its definition is as follows:
    qualif-type1 = "/" t33-sep "=" sub-addr
 where
    t33-sep = "T33S"
    sub-addr = 1*( DIGIT )
 Thus, the minimal specification of a fax in e-mail address is:
    fax-address = fax-mbox [ "/T33S=" sub-addr ]
    fax-mbox = "FAX=" global-phone
 Notes:
    For the case of a single subaddress, only numbers are allowed in
    <sub-addr> which is consistent with T.30, T.33, and this document.
    While T.30 and T.33 use SPACE to pad its field, padding isn't
    necessary in the <sub-addr> field defined by this document.
    For the case of multiple subaddresses, T.33 specifies the "#"
    character be used to specify multiple subaddreses.  However, only
    digits are permitted in the <sub-addr> field defined by this
    document.  Refer to section 4.1 in case multiple <sub-addr> per
    per <fax-mbox> need to be specified.
 The Minimal supported syntax for global-phone (as described in
 section 2.1 of reference [13]) is:
 global-phone = "+" 1*( DIGIT / written-sep )
 written-sep = ( "-" / "." )
 Refer to section 2.1 in [13] for other important considerations about
 the global-phone element.

2.2 Some examples of a minimal "fax-address"

 Some examples of minimal fax-address follows:

Allocchio Standards Track [Page 3] RFC 3192 Minimal FAX address format in Internet Mail October 2001

    FAX=+3940226338
    FAX=+12027653000/T33S=1387
    FAX=+33-1-88335215
 Note:
    the examples shown are just for illustration purposes.

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

 An "I-fax 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-fax"
    mta-I-fax = 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 fax-email

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

Allocchio Standards Track [Page 4] RFC 3192 Minimal FAX address format in Internet Mail October 2001

    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
    fax-email) MUST be added.

4.1 Multiple subaddresses

 There are some instances in GSTN applications where multiple
 subaddresses are used: T.33 subaddresses in fax service are one of
 these cases.  In e-mail practice a separate and unique e-mail address
 is always used for each recipient; as such, if multiple T.33
 subaddresses are present, the use of multiple "fax-email" elements is
 REQUIRED.
 Implementors' note:
    The UA MAY accept multiple subaddress elements for the same
    global-phone, but it MUST generate multiple "fax-mbox" elements
    when submitting the message to the MTA.

4.2 Some examples of minimal "fax-email"

    Some examples of minimal fax-email addresses follows:
    FAX=+3940226338@faxworld.org
    FAX=+12027653000/T33S=1387@faxworld.org
    /FAX=+33-1-88335215/@faxworld.org
 Note:
    the examples shown are just for illustration purposes.

5. Conclusion

 This proposal creates a minimal standard encoding for FAX addresses
 within the global e-mail transport system.  The proposal is
 consistent with existing e-mail standards.

6. Security Considerations

 This document specifies a means by which FAX 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 5] RFC 3192 Minimal FAX 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

 The IANA registration forms for "FAX" service-selector and "T33S"
 qualif-type1 elements are defined here.  These forms update the
 previous registration forms defined in [15].

7.1 IANA Registration form for updated value of GSTN

  address service-selector "FAX"
 To: IANA@iana.org
 Subject: Registration of updated values for the GSTN address
 service-selector specifier "FAX"
 service-selector name:
    FAX
 Description of Use:
    FAX - specify that the GSTN address refers either to an
    Internet Fax device, or an onramp/offramp Fax gateway.
    For a complete description refer to RFC 3192 and RFC 3191.
 Security Considerations:
    See the Security Consideration section of RFC 3192.
 Person & email address to contact for further information:
 Claudio Allocchio
 INFN-GARR
 c/o Sincrotrone Trieste
 SS 14 Km 163.5 Basovizza
 I 34012 Trieste
 Italy

Allocchio Standards Track [Page 6] RFC 3192 Minimal FAX address format in Internet Mail October 2001

 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

7.2 IANA Registration form for updated value of GSTN

  address qualit-type1 keyword "T33S" and value
 To: IANA@iana.org
 Subject: Registration of updated values for the GSTN address
 qualif-type1 element "T33S"
 qualif-type1 "keyword" name:
    T33S
 qualif-type1 "value" ABNF definition:
    sub-addr = 1*( DIGIT )
 Description of Use:
    T33S is used to specify the numeric only optional fax sub-address
    element described in "ITU T.33 - Facsimile routing utilizing the
    subaddress; recommendation T.33 (July, 1996)".  Further detailed
    description is available in RFC 3192.
 Use Restriction:
    The use of "T33S" is restricted to "FAX" service-selector, is it
    has no meaning outside the fax service.
 Security Considerations:
    See the Security Consideration section of RFC 3192.
 Person & email address to contact for further information:
    Claudio Allocchio
    INFN-GARR
    c/o Sincrotrone Trieste
    SS 14 Km 163.5 Basovizza
    I 34012 Trieste
    Italy

Allocchio Standards Track [Page 7] RFC 3192 Minimal FAX address format in Internet Mail October 2001

    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

8. Changes since RFC 2304 specification

 Although there are no major or technical changes from RFC 2304
 specification, this section briefly describes where updates and
 clarifications were introduced:
  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. section 7 "IANA Considerations" and the IANA registration forms

for the "FAX" "service-selector" and for the "T33S" "qualif-type1"

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

section 1.1;

  1. the case when multiple T.33 subaddresses are present was described

more explicitly in order to clarify how to handle them (section

    4.1);
  1. in section 3 the language describing "mta-I-fax" was updated to

better describe its relationship with an Internet Mail address;

  1. in section 4., the quoting rules of the "fax-address" and their

practical use was made explicit both in the definition of "fax-

    email" and in the Implementors' note;
  1. the Author's Address was updated;
  1. the References list was updates to substitute ITU E.164 (1991)

with ITU E.164 (1997).

Allocchio Standards Track [Page 8] RFC 3192 Minimal FAX 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 9] RFC 3192 Minimal FAX 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 GSTN address format in Internet Mail",
      RFC 3191, 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.

Allocchio Standards Track [Page 10] RFC 3192 Minimal FAX 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
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

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

Allocchio Standards Track [Page 11]

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