Fax D. Crocker
Internet-Draft Brandenburg InternetWorking
Expires: December 6, 2004 G. Klyne
Nine by Nine
June 7, 2004
Full-mode Fax Profile for Internet Mail:Ã FFPIM
draft-ietf-fax-ffpim-04
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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
standards-compliant email infrastructure and mail user agents, while
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providing a level of service that approximates what is currently
enjoyed by fax users.
The IETF has been notified of intellectual property rights claimed in
regard to some or all of the specification contained in this
document. For more information, consult the online list of claimed
rights in <http://www.ietf.org/ipr.html>.
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 References - Normative . . . . . . . . . . . . . . . . . . . . 5
5.2 References - Informative . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 6
A. Direct Mode . . . . . . . . . . . . . . . . . . . . . . . . . 6
B. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
Intellectual Property and Copyright Statements . . . . . . . . 8
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1. Introduction
The current 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.
FFPIM participants MAY support this mechanism.
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]
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.
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4. Security Considerations
As this document is an extension of [RFC2305] and [RFC2532], the
Security Considerations sections of [RFC2305] and [RFC2532] applies
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
5. References
5.1 References - Normative
[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",
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
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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 References - Informative
[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
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
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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
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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