Message Session Relay Protocol (MSRP) over Data Channels
RFC 8873

Document Type RFC - Proposed Standard (January 2021; No errata)
Updates RFC 4975
Authors Jose Recio  , Christer Holmberg 
Last updated 2021-01-18
Replaces draft-ejzak-mmusic-msrp-usage-data-channel
Stream Internet Engineering Task Force (IETF)
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Internet Engineering Task Force (IETF)                    JM. Recio, Ed.
Request for Comments: 8873                                  Unaffiliated
Updates: 4975                                                C. Holmberg
Category: Standards Track                                       Ericsson
ISSN: 2070-1721                                             January 2021

        Message Session Relay Protocol (MSRP) over Data Channels


   This document specifies how a Web Real-Time Communication (WebRTC)
   data channel can be used as a transport mechanism for the Message
   Session Relay Protocol (MSRP) and how the Session Description
   Protocol (SDP) offer/answer mechanism can be used to negotiate such a
   data channel, referred to as an MSRP data channel.  Two network
   configurations are supported: the connection of two MSRP data channel
   endpoints; and a gateway configuration, which connects an MSRP data
   channel endpoint with an MSRP endpoint that uses either TCP or TLS.
   This document updates RFC 4975.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction
   2.  Conventions
   3.  WebRTC Data Channel Considerations
     3.1.  MSRP Data Channel
   4.  SDP Considerations
     4.1.  MSRP URI
     4.2.  MSRP URI msrp-scheme
     4.3.  Use of the 'dcmap' Attribute
     4.4.  Use of the 'dcsa' Attribute
     4.5.  Use of the DCSA-Embedded 'setup' Attribute
     4.6.  Session Closing
     4.7.  Support for MSRP File Transfer Function
     4.8.  Example
   5.  MSRP Considerations
     5.1.  Session Mapping
     5.2.  Session Opening
     5.3.  Session Closing
     5.4.  Data Framing
     5.5.  Data Sending, Receiving, and Reporting
     5.6.  Support for MSRP File Transfer Function
   6.  Gateway Considerations
   7.  Updates to RFC 4975
   8.  Security Considerations
   9.  IANA Considerations
     9.1.  "msrps" URI scheme
     9.2.  Subprotocol Identifier "msrp"
     9.3.  SDP Attributes
   10. References
     10.1.  Normative References
     10.2.  Informative References
   Authors' Addresses

1.  Introduction

   The Message Session Relay Protocol (MSRP) [RFC4975] is a protocol for
   transmitting a series of related instant messages in the context of a
   session.  In addition to instant messaging, MSRP can also be used for
   image sharing or file transfer.  MSRP was initially defined in
   [RFC4975] to work over TCP and TLS connections, and over a WebSocket
   subprotocol specified by [RFC7977].

   This document specifies how a Web Real-Time Communication (WebRTC)
   data channel [RFC8831] can be used as a transport mechanism for MSRP
   without the TCP and TLS layers, and how the Session Description
   Protocol (SDP) offer/answer mechanism for data channels [RFC8864] can
   be used to negotiate such a data channel.

   In this document, an MSRP data channel refers to a WebRTC data
   channel for which the instantiated subprotocol is "msrp" and the data
   channel is negotiated using the SDP offer/answer mechanism [RFC8864].

   Defining MSRP as a data channel subprotocol has many benefits:

   *  provides to applications a proven protocol enabling instant
      messaging, file transfer, image sharing

   *  integrates those features with other WebRTC voice, video, and data

   *  leverages the SDP-based negotiation already defined for MSRP

   *  allows the interworking with MSRP endpoints running on a TCP or
      TLS connection

   Compared to the WebSocket protocol, which provides a message-passing
   protocol to applications with no direct access to TCP or TLS sockets,
   data channels provide a low-latency transport and leverage NAT-aware
   connectivity and the security features of WebRTC.

   This document defines an MSRP data channel endpoint as an MSRP
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