Fax                                                           D. Crocker
Internet-Draft                               Brandenburg InternetWorking
Expires: January 13, 2005                                       G. Klyne
                                                            Nine by Nine
                                                           July 15, 2004



            Full-mode Fax Profile for Internet Mail (FFPIM)
                        draft-ietf-fax-ffpim-06


Status of this Memo


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Copyright Notice


   Copyright (C) The Internet Society (2004). All Rights Reserved.


Abstract


   Classic facsimile document exchange represents both a set of
   technical specifications and a class of service.Ã Previous work has
   replicated some of that service class as a profile within Internet
   mail. The current specification defines "full mode" carriage of
   facsimile data over the Internet, building upon that previous work
   and adding the remaining functionality necessary for achieving
   reliability and capability negotiation for Internet mail, on a par
   with classic T.30 facsimile. These additional features are designed
   to provide the highest level of interoperability with the




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   standards-compliant email infrastructure and mail user agents, while
   providing a level of service that approximates what is currently
   enjoyed by fax users.


Table of Contents


   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Content Negotiation  . . . . . . . . . . . . . . . . . . . . .  3
   2.1 UA-based content negotiation . . . . . . . . . . . . . . . . .  4
   2.2 ESMTP-based content negotiation  . . . . . . . . . . . . . . .  4
   2.3 Interactions between UA and ESMTP negotiation mechanisms . . .  4
   3.  Content Format . . . . . . . . . . . . . . . . . . . . . . . .  4
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . .  5
   5.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   5.1 Normative References . . . . . . . . . . . . . . . . . . . . .  5
   5.2 Informative References . . . . . . . . . . . . . . . . . . . .  6
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . .  6
   A.  Direct Mode  . . . . . . . . . . . . . . . . . . . . . . . . .  7
   B.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  7
       Intellectual Property and Copyright Statements . . . . . . . .  9
































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1.  Introduction


   This specification defines "full mode" carriage of facsimile data
   over the Internet, building upon previous work in A Simple Mode of
   Facsimile Using Internet Mail [RFC2305] and Extended Facsimile Using
   Internet Mail [RFC2532], and adding the remaining functionality
   necessary for achieving reliability and capability negotiation for
   Internet mail that is on a par with classic [T30] facsimile. These
   additional features are designed to provide the highest level of
   interoperability with the standards-compliant email infrastructure
   and mail user agents, while providing a level of service that closely
   approximates the level of service currently enjoyed by fax users.


   Basic terminology is discussed in [RFC2542].Ã  Implementations which
   conform to this specification MUST also conform to [RFC2305] and
   [RFC2532].


   The new features are designed to be interoperable with the existing
   base of mail transfer agents (MTAs) and mail user agents (MUAs), and
   to take advantage of existing standards for optional functionality,
   such as positive delivery confirmation and disposition notification.
   Enhancements described in this document utilize the existing Internet
   email messaging infrastructure, where possible, instead of creating
   fax-specific features that are unlikely to be implemented in non-fax
   messaging software.


   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].


2.  Content Negotiation


   Classic facsimile service is interactive, so that a sending station
   can discover the capabilities of the receiving station, prior to
   sending a facsimile of a document. This permits the sender to
   transmit the best quality of facsimile that is supported by both the
   sending station and the receiving station. Internet mail is
   store-and-forward, with potentially long latency, so that
   before-the-fact negotiation is problematic.


   Use of a negotiation mechanism permits senders to transfer a richer
   document form than is permitted when using the safer-but-universal
   default form. Without this mechanism, the sender of a document cannot
   be certain that the receiving station will support be able to support
   the form.


   The capabilities that can be negotiated by an FFPIM participant are
   specified in [RFC2534] and [RFC2879]. Implementations that are




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   conformant to FFPIM MUST support content negotiation as described
   there.


2.1  UA-based content negotiation


   One method of exchanging capabilities information uses a post-hoc
   technique that permits an originator to send the best version known
   by the originator to be supported by the recipient and then to send a
   version that is better suited to the recipient if the recipient
   requests it. This mechanism is specified in [RFC3297]. FFPIM
   implementations MUST support this mechanism.


2.2  ESMTP-based content negotiation


   Another method uses an ESMTP option specified in [ID-Conneg]. It
   requires support for content negotiation along the entire path that
   the email travels. Using this mechanism, receiving ESMTP servers are
   able to report capabilities of the addresses (mailboxes) that they
   support [[and sending email clients are able to signal both
   permission and constraints on conversions.]]


   FFPIM participants MAY support this mechanism.


   NOTE: [[This specification provides for content conversion by
      unspecified intermediaries. Use of this mechanism carries
      significant risk. Although intermediaries always have the ability
      to perform damaging transformations, use of this specification
      could result in more exploitation of that potential and,
      therefore, more misbehavior. Use of intermediaries is discussed in
      [RFC3238].]]



2.3  Interactions between UA and ESMTP negotiation mechanisms


   FFPIM participants must ensure that their use of the UA and ESMTP
   methods for content negotiation is compatible. For example, the two
   mechanisms might consult two different repositories of capabilities
   information, and those repositories might contain different
   information. Presumably this means that at least one of the
   repositories is inaccurate, so the larger problem is one of
   correctness, rather than synchronization.


   This specification does not require a particular method of using the
   mechanisms together.


3.  Content Format


   FFPIM allows the transfer of enhanced TIFF data relative to [RFC2305]




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   and [RFC2532]. The details for these enhancements are contained in
   [ID-TIFF-FX]. Implementations that are conformant to FFPIM SHOULD
   support TIFF enhancements.


   It should also be noted that the content negotiation mechanism
   permits a sender to know the full range of content types that are
   supported by the recipient. Therefore, requirements for support of
   TIFF represent a functional minimum for FFPIM.


4.  Security Considerations


   As this document is an extension of [RFC2305] and [RFC2532], the
   Security Considerations sections of [RFC2305] and [RFC2532] apply to
   this document, including discussion of PGP and S/MIME use for
   authentication and privacy.


   It appears that the mechanisms added by this specification do not
   introduce new security considerations, however the concerns raised in
   [RFC2532] are particularly salient for these new mechanisms.


   Use of this specification should occur with particular attention to
   the following security concerns:


   * Negotiation can be used as a denial of service attack


   * Negotiating may lead to the use of an unsafe data format


   * Negotiation discloses information and therefore raises privacy
   concerns


   [[Content-based authentication and privacy techniques will not
   normally survive or permit content transformation efforts. Therefore,
   permission to convert SHOULD NOT normally be used with signed or
   sealed messages, unless the transforming intermediary participates in
   the protection mechanism and can assure its validity.]]


5.  References


5.1  Normative References


   [ID-Conneg]
              Toyoda, K. and D. Crocker, "SMTP and MIME Extensions For
              Content Conversion", draft-ietf-fax-esmtp-conneg-09 (work
              in progress), December 2003.


   [ID-TIFF-FX]
              Buckley, R., Venable, D., McIntyre, L., Parsons, G. and J.
              Rafferty, "File Format for Internet Fax",




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              draft-ietf-fax-tiff-fx-13 (work in progress), February
              2004.


   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.


   [RFC2305]  Toyoda, K., Ohno, H., Murai, J. and D. Wing, "A Simple
              Mode of Facsimile Using Internet Mail", RFC 2305, March
              1998.


   [RFC2532]  Masinter, L. and D. Wing, "Extended Facsimile Using
              Internet Mail", RFC 2532, March 1999.


   [RFC2534]  Masinter, L., Wing, D., Mutz, A. and K. Holtman, "Media
              Features for Display, Print, and Fax", RFC 2534, March
              1999.


   [RFC2542]  Masinter, L., "Terminology and Goals for Internet Fax",
              RFC 2542, March 1999.


   [RFC2879]  Klyne, G. and L. McIntyre, "Content Feature Schema for
              Internet Fax (V2)", RFC 2879, August 2000.


   [RFC3297]  Klyne, G., Iwazaki, R. and D. Crocker, "Content
              Negotiation for Messaging Services based on Email", RFC
              3297, July 2002.


5.2  Informative References


   [RFC3238]  Floyd, S. and L. Daigle, "IAB Architectural and Policy
              Considerations for Open Pluggable Edge Services", RFC
              3238, January 2002.


   [T30]      ITU-T (CCITT), "Procedures for Document Facsimile
              Transmission in the General Switched Telephone Network",
              Recommendation T.30, July 1996.



Authors' Addresses


   Dave Crocker
   Brandenburg InternetWorking
   675 Spruce Drive
   Sunnyvale, CA  94086
   USA


   Phone: +1.408.246.8253
   EMail: dcrocker@brandenburg.com




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   Graham Klyne
   Nine by Nine


   UK


   Phone:
   EMail: GK-IETF@ninebynine.org


Appendix A.  Direct Mode


   Email is a store-and-forward service, typically with delay between
   the time a message leaves the sender's realm and the time it arrives
   in the receiver's realm. The number of relays between sender and
   receiver is also unknown and variable. By contrast, facsimile is
   generally perceived as direct and immediate.


   An email profile that fully emulates facsimile must solve several
   different problems. One is to ensure that the document representation
   semantics are faithful. Another is that the interaction between
   sender and receiver is similar to that of telephony-based facsimile.
   In particular it must ensure the timeliness of the interaction. The
   specifications for FFPIM and its predecessors create the ability to
   have email emulate the information (semantics) activities of
   facsimile.


   The ESMTP CONNEG option sets the stage for achieving email-based
   facsimile transfer that has interactive negotiations that are on a
   par with telephony-based facsimile. The key, additional requirement
   is to achieve timeliness. Ultimately, this requires configuring
   sender and receiving email servers to interact directly. That is, the
   sender's MTA must directly contact the receiver's MTA. With typical
   email service configurations, the content and interaction semantics
   of facsimile can be emulated quite well, but the timeliness cannot be
   assured.


   To achieve direct sending, the originating MTA must be configured to
   do transmissions to hosts specified in email addresses, based on DNS
   queries. To achieve direct receiving, the target MTAs must have DNS A
   records without MX records. That is, they must be configured to use
   no intermediaries.


   The sender may then use ESMTP Conneg to determine the capabilities of
   the receiver. Afterwards the sender will use the capabilities
   information to tailor the TIFF message content that it sends.


Appendix B.  Acknowledgements


   The IETF Fax working group has diligently participated in a




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   multi-year effort to produce Internet-based emulation of classic
   facsimile via email profiles, as collaboration between the IETF and
   the ITU. The effort benefited from the group's willingness to provide
   an initial, minimal mechanism, and then grow the specification to
   include more facsimile features, as implementation and operations
   experience was gained.














































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Intellectual Property Statement


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Copyright Statement


   Copyright (C) The Internet Society (2004). This document is subject
   to the rights, licenses and restrictions contained in BCP 78, and
   except as set forth therein, the authors retain all their rights.






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Acknowledgment


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
















































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