Network Working Group D. Crocker
Internet-Draft: Brandenburg InternetWorking
Expiration <7/2004> G. Klyne
Nine by Nine
January 29, 2004
Full-mode Fax Profile for Internet Mail: FFPIM
(draft-ietf-fax-ffpim-02.txt)
STATUS OF THIS MEMO
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COPYRIGHT NOTICE
Copyright (C) The Internet Society (2004). All Rights
Reserved.
TABLE OF CONTENTS
1. Introduction
2. Content Negotiation
2.1. UA-based content negotiation
2.2. ESMTP-based content negotiation
2.3. Interactions between UA and ESMTP negotiation
mechanisms
3. Content Format
4. Security Considerations
5. Acknowledgements
6. References
7. Full Copyright Statement
8. Contact
Appendix A û Direct Mode
ABSTRACT
Classic facsimile document exchange represents both a
set of technical specifications and a class of service.
Previous work has replicated some of that service class
as a profile within Internet mail. The current
specification defines ôfull modeö 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 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>.
COPYRIGHT NOTICE
Copyright (C) The Internet Society (2004). All Rights
Reserved.
1. INTRODUCTION
The current specification defines ôfull modeö carriage
of facsimile data over the Internet, building upon
previous work [RFC2305, RFC2532] and adding the
remaining functionality necessary for achieving
reliability and capability negotiation for Internet
mail that is 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 providing a level of service that closely
approximates the level of service currently enjoyed by
fax users.
Basic terminology is discussed in [RFC2542].
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 ôMUSTö, ôMUST NOTö, ôREQUIREDö, ôSHALLö,
ôSHALL NOTö, ôSHOULDö, SHOULD NOTö, ôRECOMMENDEDö,
ôMAYö, and ôOPTIONALö 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, RFC2879].
Implementations that are 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
[SMTNEG]. 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, RFC2532]. The details for these
enhancements are contained in [TIFFFX].
Implementations that are conformant to FFPIM MUST
support TIFF enhancements.
<< QUESTION: Shall we require FFPIM support for
TIFF-FX (MUST), or shall we recommend support for
it (SHOULD), or shall we define TIFF-FX only as an
option (MAY)? /dave >>
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] 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. 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.
6. REFERENCES
[RFC2305] Toyoda, K., Ohno, H., Murai, J. and D.
Wing, "A Simple Mode of Facsimile Using
Internet Mail", RFC 2305, March 1998. (Under
revision, as draft-ietf-fax-service-v2.)
[RFC2532] Masinter, L., Wing, D., ôExtended Facsimile
Using Internet Mailö, RFC 2532, March 1999.
[RFC2534] Masinter, L., Holtman, K., Mutz, A. and D.
Wing, " Media Features for Display, Print,
and Fax", RFC 2534, March 1999.
[RFC2542] L. Masinter, L, ôTerminology and Goals for
Internet Faxö, RFC2542, March 1999
[RFC2879] McIntyre, L. and G. Klyne, "Content Feature
Schema for Internet Fax", RFC 2531, August
2000
[RFC3297] G. Klyne, R. Iwazaki, D. Crocker,
ôContent Negotiation for Messaging Services
based on Email ô, RFC 3297
[SMTNEG] Toyoda, K., Crocker, D. " SMTP and MIME
Extensions For Content Conversion", draft-
ietf-fax-esmtp-conneg
[T.30] "Procedures for Document Facsimile
Transmission in the General Switched
Telephone Network", ITU-T (CCITT),
Recommendation T.30, July, 1996.
[TIFFFX] D. Venable, S. Zilles, L. McIntyre, G.
Parsons, J. Rafferty, R. Buckley, ôFile
Format for Internet Fax ô, draft-ietf-fax-
tiff-fx-06.txt
<< QUESTION: WHAT IS THE STATUS OF THE TIFF-FX
DOCUMENT??? /Dave >>
7. 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.
8. CONTACT
David H. Crocker Tel: +1.408.246.8253
Brandenburg InternetWorking Email:
675 Spruce Dr. dcrocker@brandenburg.com
Sunnyvale, CA 94086 USA
Graham Klyne Email: GK-
Nine by Nine IETF@ninebynine.org
UK http://www.ninebynine.net/
APPENDIX A û 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.