Network Working Group K. Toyoda, MGCS Internet Draft D. Crocker, Brandenburg draft-ietf-fax-esmtp-conneg-00.txt June 2001 Expires: <12/01> SMTP Service Extension for Content Negotiation of Internet Fax STATUS OF THIS MEMO This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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. COPYRIGHT NOTICE Copyright (C) The Internet Society (2001). All Rights Reserved. SUMMARY This document defines a content negotiation SMTP service extension [ESMTP1, ESMTP2] whereby an SMTP client may request information about content capabilities of the target device or system that is serviced by an SMTP server. The SMTP server may report the target's content capabilities back to the client. This process emulates a classic facsimile start-of- session capabilities negotiation. This service extension is primarily intended for "direct" SMTP transfers, although relayed scenarios are permitted. 1. CONVENTIONS In examples, "C:" and "S:" indicate lines sent by the client and server respectively. The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY" in this document are to be interpreted as defined in "Key words for use in RFCs to Indicate Requirement Levels" [KEYWORDS]. 2. CONTENT NEGOTIATION SERVICE EXTENSION (1) The name of the SMTP service extension is "Content_Negotiation" (2) The EHLO keyword value associated with this extension is "CONNEG" (3) A parameter using the keyword "CONNEG" is added to the RCPT-TO command (4) The server responds with a report of the content capabilities of the device or system that embodies the target RCPT-TO address. 3. CONNEG PARAMETER TO RCPT-TO Parameter: CONNEG Arguments: There are no arguments. Client Action: If the server issued a 250-CONNEG, as part of its EHLO response for the current session, the client MAY issue the CONNEG parameter with RCPT-TO. If the client issues the CONNEG parameter with RCPT-TO, then it MUST honor the capabilities specified in the CONNEG RCPT-TO reply, and transform data that is sent, so that the target can accept the data. The client SHOULD transform the data to the "highest" level of capability of the server. Server Action: If the client specifies CONNEG in the RCPT-TO, but the server does not support the CONNEG parameter, the server MUST reject the RCPT-TO command with a 504 reply. If the server does support the CONNEG parameter, then it MUST issue a 250 reply, followed by its capabilities of the target that is specified by the RCPT-TO address. The response to a CONNEG RCPT-TO request will be multi-line. For successful (250) responses, at least the first line of the response is for RCPT-TO information other than CONNEG. Additional response lines are for CONNEG. In order to avoid problems due to variations in line buffer sizes, the total parametric listing must be provided as a series of lines, each beginning with "250-CONNEG" except for the last line, which is "250 CONNEG". An alternative approach for lengthy CONNEG data would be to fit the entire parameter list into one, very long virtual line, using backslash ("\") escapes at the end of each physical line. This risks the buffer overflow problem, cited above. The contents of the capability listing MUST conform to the specifications in "Content Feature Schema for Internet Fax". [RFC2879] 4. SYNTAX Content_Negotiation = "CONNEG" Capability = <<as per [RFC2879]>> 5. EXAMPLE S: 220 ifax1.jp IFAX C: EHLO ifax1.jp S: 250-ifax1.jp S: 250-DSN S: 250 CONNEG C: MAIL FROM:<May@ifax2.jp> S: 250 <May@ifax2.jp> sender ok C: RCPT TO:<June@ifax1.jp> CONNEG S: 250-<June@ifax1.jp> recipient ok S: 250-CONNEG (&(image-file-structure=TIFF-minimal) S: 250-CONNEG (MRC-mode=0) S: 250-CONNEG (color=Binary) S: 250-CONNEG (|(&(dpi=204) S: 250-CONNEG (dpi-xyratio=[204/98,204/196]) ) S: 250-CONNEG (&(dpi=200) S: 250-CONNEG (dpi-xyratio=[200/100,1]) ) S: 250-CONNEG (&(dpi=400) S: 250-CONNEG (dpi-xyratio=1) ) ) S: 250-CONNEG (|(image-coding=[MH,MR,MMR]) S: 250-CONNEG (&(image-coding=JBIG) S: 250-CONNEG (image-coding-constraint=JBIG-T85) S: 250-CONNEG (JBIG-stripe-size=128) ) ) S: 250-CONNEG (paper-size=[letter,A4,B4]) S: 250 CONNEG (ua-media=stationery) ) C: DATA S: 354 okay, send data C: <<RFC 2822 message with MIME Content-Type:TIFF-FX Per: ( image-file-structure=TIFF-minimal dpi=400 image-coding=JBIG size-x=2150 ) >> S: 250 message accepted C: QUIT S: 221 goodbye 6. IANA CONSIDERATIONS This memo is not intended to create any new issues for IANA. 7. SECURITY CONSIDERATIONS This ESMTP option calls for a respondent to disclose its capabilities. Mechanisms for determining the requestor's authenticated identity are outside the scope of this specification. It is intended that this mechanism permit disclosure of public information; hence there is no particular need for security measures. However there is nothing to prevent disclosure of sensitive information that should receive restricted distribution. It is, therefore, the responsibility of the disclosing ESMTP server to determine whether additional security measures should be applied to the use of this ESMTP option. 8. ACKNOWLEDGEMENTS Graham Klyne provided useful suggestions to an earlier draft. 9. REFERENCES [ESMTP1] Klensin, J., Freed, N., Rose, M., Stefferud, E. and D. Crocker, "SMTP Service Extensions", RFC 1869, November 1995 [ESMTP2] Klensin, J., "Simple Mail Transfer Protocol", RFC 2821, April 2001. [RFC2879] McIntyre, L. and G. Klyne, "Content Feature Schema for Internet Fax", RFC 2531, August 2000 10. AUTHORS' ADDRESSES Kiyoshi Toyoda Matsushita Graphic Communication Systems,Inc 2-3-8 Shimomeguro, Meguro-Ku Tokyo 153 JAPAN +81.3.5434.7161 firstname.lastname@example.org Dave Crocker Brandenburg InternetWorking 675 Spruce Drive Sunnyvale, CA 94086 USA +1.408.246.8253 email@example.com 11. FULL COPYRIGHT STATEMENT Copyright (C) The Internet Society (2001). All Rights Reserved. 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