Relay Extensions for the Message Sessions Relay Protocol (MSRP)
RFC 4976

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Network Working Group                                        C. Jennings
Request for Comments: 4976                           Cisco Systems, Inc.
Category: Standards Track                                        R. Mahy
                                                             Plantronics
                                                             A. B. Roach
                                                        Estacado Systems
                                                          September 2007

     Relay Extensions for the Message Session Relay Protocol (MSRP)

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Abstract

   Two separate models for conveying instant messages have been defined.
   Page-mode messages stand alone and are not part of a Session
   Initiation Protocol (SIP) session, whereas session-mode messages are
   set up as part of a session using SIP.  The Message Session Relay
   Protocol (MSRP) is a protocol for near real-time, peer-to-peer
   exchanges of binary content without intermediaries, which is designed
   to be signaled using a separate rendezvous protocol such as SIP.
   This document introduces the notion of message relay intermediaries
   to MSRP and describes the extensions necessary to use them.

Jennings, et al.            Standards Track                     [Page 1]
RFC 4976                      MSRP Relays                 September 2007

Table of Contents

   1. Introduction and Requirements ...................................3
   2. Conventions and Definitions .....................................4
   3. Protocol Overview ...............................................4
      3.1. Authorization Overview ....................................11
   4. New Protocol Elements ..........................................11
      4.1. The AUTH Method ...........................................11
      4.2. The Use-Path Header .......................................12
      4.3. The HTTP Authentication "WWW-Authenticate" Header .........12
      4.4. The HTTP Authentication "Authorization" Header ............12
      4.5. The HTTP Authentication "Authentication-Info" Header ......12
      4.6. Time-Related Headers ......................................12
   5. Client Behavior ................................................13
      5.1. Connecting to Relays Acting on Your Behalf ................13
      5.2. Sending Requests ..........................................18
      5.3. Receiving Requests ........................................18
      5.4. Managing Connections ......................................18
   6. Relay Behavior .................................................18
      6.1. Handling Incoming Connections .............................18
      6.2. Generic Request Behavior ..................................19
      6.3. Receiving AUTH Requests ...................................19
      6.4. Forwarding ................................................20
           6.4.1. Forwarding SEND Requests ...........................21
           6.4.2. Forwarding Non-SEND Requests .......................22
           6.4.3. Handling Responses .................................22
      6.5. Managing Connections ......................................23
   7. Formal Syntax ..................................................23
   8. Finding MSRP Relays ............................................24
   9. Security Considerations ........................................25
      9.1. Using HTTP Authentication .................................25
      9.2. Using TLS .................................................26
      9.3. Threat Model ..............................................27
      9.4. Security Mechanism ........................................29
   10. IANA Considerations ...........................................31
      10.1. New MSRP Method ..........................................31
      10.2. New MSRP Headers .........................................31
      10.3. New MSRP Response Codes ..................................31
   11. Example SDP with Multiple Hops ................................31
   12. Acknowledgments ...............................................32
   13. References ....................................................32
      13.1. Normative References .....................................32
      13.2. Informative References ...................................33
   Appendix A.  Implementation Considerations ........................34

Jennings, et al.            Standards Track                     [Page 2]
RFC 4976                      MSRP Relays                 September 2007