An Alternative Connection Model for the Message Session Relay Protocol (MSRP)
RFC 6135
Internet Engineering Task Force (IETF) C. Holmberg
Request for Comments: 6135 Ericsson
Category: Standards Track S. Blau
ISSN: 2070-1721 Ericsson AB
February 2011
An Alternative Connection Model for the
Message Session Relay Protocol (MSRP)
Abstract
This document defines an alternative connection model for Message
Session Relay Protocol (MSRP) User Agents (UAs); this model uses the
connection-oriented media (COMEDIA) mechanism in order to create the
MSRP transport connection. The model allows MSRP UAs behind Network
Address Translators (NATs) to negotiate which endpoint initiates the
establishment of the Transmission Control Protocol (TCP) connection,
in order for MSRP messages to traverse the NAT.
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 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6135.
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Holmberg & Blau Standards Track [Page 1]
RFC 6135 MSRP February 2011
Table of Contents
1. Introduction ....................................................2
2. Terminology .....................................................3
3. Applicability Statement .........................................3
4. COMEDIA for MSRP ................................................3
4.1. General ....................................................3
4.2. a=setup ....................................................3
4.2.1. General .............................................3
4.2.2. Attribute Usage .....................................4
4.3. TLS ........................................................5
4.4. a=connection ...............................................5
4.5. MSRP Relay Connection ......................................6
5. Interoperability with the Connection Model Defined in RFC 4975 ..6
6. Security Considerations .........................................6
7. Acknowledgements ................................................7
8. References ......................................................7
8.1. Normative References .......................................7
8.2. Informative References .....................................7
1. Introduction
The Message Session Relay Protocol (MSRP) core specification
[RFC4975] states that the MSRP User Agent (UA) that sends the Session
Description Protocol (SDP) offer is "active", and it is responsible
for creating the MSRP transport connection towards the remote UA if a
new connection is required. The core specification also allows, but
does not define, alternate mechanisms for MSRP UAs to create MSRP
transport connections.
[RFC4145] defines a connection-oriented media (COMEDIA) mechanism,
which endpoints can use to negotiate the endpoint that initiates the
creation of media transport connection.
COMEDIA is especially useful when one of the endpoints is located
behind a Network Address Translator (NAT). The endpoint can use the
mechanism to indicate that it will create the media transport
connection, in order for the media to traverse the NAT without the
usage of relays and without being required to support more complex
mechanisms (e.g., "TCP Candidates with Interactive Connectivity
Establishment (ICE)" [ICE-TCP]). In addition, COMEDIA allows the
usage of identical procedures in establishing Transmission Control
Protocol (TCP) [RFC0793] connections for different types of media.
An example is the Open Mobile Alliance (OMA)-defined "Instant Message
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