Fax D. Crocker Internet-Draft Brandenburg InternetWorking Expires: June 14, 2005 G. Klyne Nine by Nine December 14, 2004 Full-mode Fax Profile for Internet Mail (FFPIM) draft-ietf-fax-ffpim-07 Status of this Memo This document is an Internet-Draft and is subject to all provisions of section 3 of RFC 3667. By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she become aware will be disclosed, in accordance with RFC 3668. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on June 14, 2005. Copyright Notice Copyright (C) The Internet Society (2004). 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 Crocker & Klyne Expires June 14, 2005 [Page 1] Internet-Draft FFPIM December 2004 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. 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 . . . . . . . . . . . . . . . . . . . . . . 7 A. Direct Mode . . . . . . . . . . . . . . . . . . . . . . . . . 7 B. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8 Intellectual Property and Copyright Statements . . . . . . . . 9 Crocker & Klyne Expires June 14, 2005 [Page 2] Internet-Draft FFPIM December 2004 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 [RFC3965] 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 [RFC3965] 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 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 Crocker & Klyne Expires June 14, 2005 [Page 3] Internet-Draft FFPIM December 2004 conformant to FFPIM MUST support content negotiation as described there. 2.1 UA-based content negotiation One method for exchanging the 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 [RFC3965] Crocker & Klyne Expires June 14, 2005 [Page 4] Internet-Draft FFPIM December 2004 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 [RFC3965] and [RFC2532], the Security Considerations sections of [RFC3965] 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 Use of the ESMTP CONNEG option permits content transformation by an intermediary, along the mail transfer path. Ã When the contents are encrypted, the intermediary cannot perform the conversion, since it is not expected to have access to the relevant secret keying material. Ã When the contents are signed, but not encrypted, conversion will invalidate the signature. 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. Crocker & Klyne Expires June 14, 2005 [Page 5] Internet-Draft FFPIM December 2004 [ID-TIFF-FX] Buckley, R., Venable, D., McIntyre, L., Parsons, G. and J. Rafferty, "File Format for Internet Fax", draft-ietf-fax-tiff-fx-14 (work in progress), February 2004. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [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. [RFC3965] Toyoda, K., Ohno, H., Murai, J. and D. Wing, "A Simple Mode of Facsimile Using Internet Mail", RFC 3965, December 2004. 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. Crocker & Klyne Expires June 14, 2005 [Page 6] Internet-Draft FFPIM December 2004 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 highly variable 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 considered to be 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 former, the information (semantics) activities of facsimile. The ESMTP CONNEG option sets the stage for achieving the latter, with email-based facsimile transfer that has interactive negotiations, 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 not use Crocker & Klyne Expires June 14, 2005 [Page 7] Internet-Draft FFPIM December 2004 sending-side intermediaries such as outbound enterprise MTAs. Instead, it must be configured to do transmissions directly to hosts specified in email addresses, based on queries to the public DNS. To achieve direct receiving, the target MTAs must have DNS A records, without MX records. That is, they also 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. Crocker & Klyne Expires June 14, 2005 [Page 8] Internet-Draft FFPIM December 2004 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. 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Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM 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. 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. Crocker & Klyne Expires June 14, 2005 [Page 9] Internet-Draft FFPIM December 2004 Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Crocker & Klyne Expires June 14, 2005 [Page 10] 20