One document matched: draft-ietf-simple-msrp-acm-02.txt
Differences from draft-ietf-simple-msrp-acm-01.txt
SIMPLE Working Group C. Holmberg
Internet-Draft Ericsson
Expires: May 22, 2010 S. Blau
Ericsson AB
November 18, 2009
An Alternative Connection Model for the Message Session Relay Protocol
(MSRP)
draft-ietf-simple-msrp-acm-02.txt
Abstract
This document defines an alternative connection model for MSRP UAs,
which uses COMEDIA in order to create the MSRP transport connection.
The model allows MSRP UAs which are located behind NATs to indicate
that they want to initiate the establishment of the TCP connection
towards the remote MSRP UA, in order for MSRP messages to traverse
the NAT. The document also defines how an MSRP UA which is located
behind a NAT keeps the NAT binding alive.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on May 22, 2010.
Copyright Notice
Copyright (c) 2009 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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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 BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Applicability statement . . . . . . . . . . . . . . . . . . . . 3
4. COMEDIA for MSRP . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. General . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.2. a=setup . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.3. TLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.4. a=connection . . . . . . . . . . . . . . . . . . . . . . . 6
4.5. MSRP relay connection . . . . . . . . . . . . . . . . . . . 6
5. NAT keepalive . . . . . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
8. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 7
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
9.1. Normative References . . . . . . . . . . . . . . . . . . . 7
9.2. Informative References . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8
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1. Introduction
[RFC4975] defines that the MSRP UA which sends the SDP offer is
"active", and is this responsible to create the MSRP transport
connection towards the remote UA. [RFC4975] also allows, but does
not define, MSRP UAs to use other mechanisms in order to create the
MSRP transport connection.
[RFC4145] defines a mechanism, COMEDIA, which endpoints can use to
negotiate which endpoint will create the media transport connection.
COMEDIA is especially useful when an endpoint is located behind a
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.
An example is the OMA defined "Instant Message using SIMPLE" [OMA-TS-
SIMPLE_IM-V1_0-20090901-D], where one MSRP UA of every MSRP transport
connection represents a media server, and which is always located in
the network. The media server has a global address and handles
application specific policy control as well as NAT traversal. The
OMA IM uses COMEDIA for NAT traversal, and all IM MSRP clients
support COMEDIA.
This document defines how an MSRP UA uses COMEDIA in order to
negotiate which UA will create the MSRP transport TCP connection
towards the other UA. The document also defines how an MSRP UA can
establish an MSRP transport connection with a remote UA that does not
support COMEDIA.
2. 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 BCP 14, RFC 2119
[RFC2119].
3. Applicability statement
An MSRP UA SHOULD use the alternative connection model, defined in
this document, when the UA does not use an MSRP relay in order to
proxy its MSRP media.
An MSRP UA conformant to this document can interop with an [RFC4975]
conformant MSRP UA. However, if an MSRP UA conformant to this
document is located behind NAT, and does not proxy its MSRP
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communication via an MSRP-Relay node, and the UA receives an SDP
offer from an [RFC4975] conformant remote UA, NAT traversal can only
be achieved if the MSRP UA supports ICE and the network provides TURN
servers, or if the network supports SBC assisted NAT traversal for
TCP.
4. COMEDIA for MSRP
4.1. General
This section defines how an MSRP UA uses the COMEDIA SDP attributes
defined in [RFC4145], how an MSRP UA can use the COMEDIA TLS
extensions [RFC4572], and how an MSRP UA keeps a NAT binding alive.
4.2. a=setup
An MSRP UA MUST support the SDP a=setup attribute [RFC4145], in order
to negotiate which endpoint will create the MSRP transport connection
towards the other UA.
The a=setup attribute is particularly useful when one MSRP UA
represents a network media server, or any other entity which is not
located behind a NAT. The media server can ensure that the user MSRP
UAs will create the MSRP transport connections towards the server, so
that possible NATs at user premises will not interfere with the
connection creation.
An MSRP UA MUST always include an explicit a=setup attribute in its
SDP offers and answers, since it is sometimes useful for the other
endpoint, or for entities in the network, to know whether the UA
supports COMEDIA or not.
An MSRP UA MUST support the a=setup "active", "actpass" and "passive"
attribute values. An MSRP UA MUST NOT use the a=setup "holdcon"
attribute value.
When the a=setup attribute value is "actpass" or "passive", the IP
address:port value in the MSRP URI of the SDP a=path attribute MUST
contain the actual address:port on which the UA can receive a TCP
Open request for the MSRP transport connection.
If the a=setup attribute value is "active", the port number value
MUST either be the actual port number that the MSRP UA will use for
the TCP endpoint, or the port value 9.
If an MSRP UA can determine a valid WAN transport endpoint address:
port, i.e. an address:port that the other endpoint can use as
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destination for a TCP Open request, the UA MUST use the a=setup
"actpass" attribute value in SDP offers. This is in order to allow
the remote UA to send an SDP answer with an a=setup "active"
attribute value if the UA is located behind NAT, and in order to be
compatible with MSRP UAs that do not support COMEDIA and thus always
will always act as passive endpoints. If an MSRP UA cannot provide
the actual transport address, the UA MUST use the a=setup "active"
attribute value.
An MSRP UA can determine a valid WAN transport address:port if the UA
can determine that it is not located behind a NAT, or if the UA
relays its MSRP transport connections via a TURN server, or if the UA
through STUN signaling from the local port to be used for the
eventual transport connection has used STUN to retrieve NAT address:
port while also having determined that the NAT is not address
restricted.
If an MSRP UA is located behind a NAT, both SIP signaling and MSRP
media will pass trough the NAT, and a UA can determine whether the
media transport will be NATed by inspecting the SIP Via header in the
200 (OK) response if the initial REGISTER request, by comparing the
IP addresses in the Via sent-by and received parameters. If these
are not the same then the UA can determine that there is a NAT in the
path.
If an SDP offer includes an a=setup "actpass" attribute value, the
SDP answer MAY include an a=setup "active" attribute value, but
SHOULD include a=setup "passive" attribute value if the SDP answerer
knows that it is not located behind a NAT.
Once the active UA has established the MSRP transport connection, the
UA MUST immediately send an MSRP SEND request, as defined in
[RFC4975].
NOTE: According to [RFC4975] the initiating UA is always active, but
when COMEDIA is used the a=setup attribute is used to negotiate which
UA becomes active.
4.3. TLS
If MSRP UAs negotiate a TLS transport connection for MSRP, the client
and server TLS roles MUST negotiate the relevant parameter as defined
in COMEDIA-TLS [RFC4572], and in accordance with [RFC4975] the MSRP
URI scheme SHOULD be msrps and the m-line protocol indicator SHOULD
be TCP/TLS/MSRP.
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4.4. a=connection
MSRP UAs MUST NOT use the SDP a=connection attribute. [RFC4975]
defines connection reuse procedures for MSRP, and this document does
not modify those procedures.
If an MSRP UA receives an a=connection attribute, the UA MUST ignore
it.
NOTE: If an MSRP UA uses ICE [I.D.ietf-mmusic-ice] when it
establishes the MSRP transport connection, the UA needs to perform
the normal MSRP checks for possible reuse of an existing transport
connection before it sends any TCP Open requests.
4.5. MSRP relay connection
If an MSRP UA is located behind an MSRP relay [RFC4976], the UA MUST
always initiate a transport connection towards the relay, no matter
what value the client has provided in the a=setup attribute.
NOTE: Even if an MSRP UA initiates the TCP connection towards its
relay, the UA will only send a SEND request if the UA is active,
based on the COMEDIA negotiation.
5. NAT keepalive
If an MSRP UA is located behind a NAT the UA MUST keep the NAT
binding alive, in accordance with section 10 of [I.D.ietf-mmusic-
ice]. The UA SHOULD use the character string CR-LF as NAT keepalive.
However, if the NAT traversal method selected by ICE was based on
successful connectivity checks, using STUN, then the UA MAY
alternatively use STUN as defined in [I.D-ietf-mmusic-ice].
6. Security Considerations
The procedures define in this document do not impact the security
characteristics defined in [RFC4975].
7. Acknowledgements
Thanks to Ben Campbell, Remi Denis-Courmont, Nancy Greene, Hadriel
Kaplan, Adam Roach and Robert Sparks for their guidance and input in
order to produce this document.
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8. Change Log
[RFC EDITOR NOTE: Please remove this section when publishing]
Changes from draft-ietf-simple-acm-01
o Procedures for using SDP c/m for routing of MSRP messages removed.
o Procedures related to modification of MSRP address information by
intermediates moved to separate document.
o Solution to open issue on usage of the SDP a=connection
implemented.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2606] Eastlake, D. and A. Panitz, "Reserved Top Level DNS
Names", BCP 32, RFC 2606, June 1999.
[RFC3323] Peterson, J., "A Privacy Mechanism for the Session
Initiation Protocol (SIP)", RFC 3323, November 2002.
[RFC4145] Yon, D. and G. Camarillo, "TCP-Based Media Transport in
the Session Description Protocol (SDP)", RFC 4145,
September 2005.
[RFC4572] Lennox, J., "Connection-Oriented Media Transport over the
Transport Layer Security (TLS) Protocol in the Session
Description Protocol (SDP)", RFC 4572, July 2006.
[RFC4975] Campbell, B., Mahy, R., and C. Jennings, "The Message
Session Relay Protocol (MSRP)", RFC 4975, September 2007.
[RFC4976] Jennings, C., Mahy, R., and A. Roach, "Relay Extensions
for the Message Sessions Relay Protocol (MSRP)", RFC 4976,
September 2007.
[I-D.ietf-mmusic-ice]
Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols",
draft-ietf-mmusic-ice-19 (work in progress), October 2007.
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9.2. Informative References
Authors' Addresses
Christer Holmberg
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: christer.holmberg@ericsson.com
Staffan Blau
Ericsson AB
P.O Box 407
Sweden
Email: staffan.blau@ericsson.com
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