One document matched: draft-jennings-sip-mime-01.txt

Differences from draft-jennings-sip-mime-00.txt

SIP WG                                                       C. Jennings
Internet-Draft                                             Cisco Systems
Expires: August 14, 2004                               February 14, 2004


            Recommendations for using MIME body parts in SIP
                       draft-jennings-sip-mime-01

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

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   This Internet-Draft will expire on August 14, 2004.

Copyright Notice

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

Abstract

   This document describes conventions for using MIME body parts in SIP
   messages. It recommends a transport encoding of "binary" since SIP
   messages are always passed over an 8bit clean transport.

   This work is being discussed on the sip@ietf.org mailing list.

1. Conventions

   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 RFC-2119 [2].

   This document adopts the terminology defined in RFC 2045 [1],



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   particularly for the terms "transport encoding" and "binary".

2. Introduction

   The Session Initiation Protocol (SIP) [3] protocol makes use of MIME
   [1] body parts. MIME provides several alternatives that were required
   given the characteristics of existing mail transport protocols and
   mail gateways that MIME operates through. SIP is always transported
   over an 8bit safe transport and thus does not need all the options
   available. This draft clarifies what should be used in the SIP
   context.

3. Discussion

   MIME offers several transport encoding options and any of them will
   work in SIP. However, having several options where one is needed does
   not contribute to interoperability. Binary encoding is faster to
   encode and decode, requires less code, and results in smaller
   messages than the other options. There has been a practice in the
   published SIP examples of using a base64 encoding due to the ease of
   displaying the examples in publication. Some SIP implementers have
   taken this to mean that this is the preferred encoding and as a
   result only work with base64. Given the need to improve
   interoperability, it is reasonable to suggest that SIP
   implementations send one type of encoding.

   There are situations in which the body from a SIP message might be
   passed to another non SIP transport that might expose additional
   limitations.  Currently the only example of this is the transfer of
   bodies from instant messaging messages to other instant messaging
   systems.  Since other instant messaging protocols are also 8bit
   clean, gateways from SIP instant messaging [5] to these other
   protocols do not have this problem.  Gateways to other protocols (for
   example SMTP [4]) need to modify the content of these messages
   anyway, regardless of the MIME encoding which is used on the original
   message.

4. Recommendations

   Devices MUST use a content transfer encoding of "binary" for MIME
   body parts in SIP messages they send.

5. Security Considerations

   This document limits options that exist in RFC 3261 so it does not
   introduce any additional security concerns beyond what is in RFC
   3261.




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Normative References

   [1]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
        Extensions (MIME) Part One: Format of Internet Message Bodies",
        RFC 2045, November 1996.

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

   [3]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
        Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP:
        Session Initiation Protocol", RFC 3261, June 2002.

Informative References

   [4]  Klensin, J., "Simple Mail Transfer Protocol", RFC 2821, April
        2001.

   [5]  Campbell, B., Rosenberg, J., Schulzrinne, H., Huitema, C. and D.
        Gurle, "Session Initiation Protocol (SIP) Extension for Instant
        Messaging", RFC 3428, December 2002.


Author's Address

   Cullen Jennings
   Cisco Systems
   170 West Tasman Drive
   MS: SJC-21/2
   San Jose, CA  95134
   USA

   Phone: +1 408 902-3341
   EMail: fluffy@cisco.com

















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