One document matched: draft-camarillo-mmusic-sdp-bfcp-00.txt
MMUSIC Working Group G. Camarillo
Internet-Draft Ericsson
Expires: April 15, 2005 October 15, 2004
Session Description Protocol (SDP) Format for Binary Floor Control
Protocol (BFCP) Streams
draft-camarillo-mmusic-sdp-bfcp-00.txt
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Copyright Notice
Copyright (C) The Internet Society (2004).
Abstract
This document specifies how to describe BFCP streams in a SDP session
description. User agents using the offer/answer model to establish
BFCP streams use this format in their offers and their answers.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Fields in the m Line . . . . . . . . . . . . . . . . . . . . . 3
4. The confid and userid SDP Parameters . . . . . . . . . . . . . 4
5. The k line . . . . . . . . . . . . . . . . . . . . . . . . . . 4
6. TCP Connection Management . . . . . . . . . . . . . . . . . . 4
7. Association between Streams and Floors . . . . . . . . . . . . 5
8. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
9. Security Considerations . . . . . . . . . . . . . . . . . . . 6
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
10.1 SDP Attributes Registration . . . . . . . . . . . . . . . 6
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
12.1 Normative References . . . . . . . . . . . . . . . . . . . . 6
12.2 Informational References . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 7
Intellectual Property and Copyright Statements . . . . . . . . 8
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1. Introduction
As discussed in the BFCP specification [5], a given BFCP client needs
a set of data in order to establish a BFCP connection to a floor
control server. These data include the transport address of the
server, the conference identifier, and the user identifier.
Clients can obtain this information in different ways, one of them
consisting of using an offer/answer [3] exchange. This document
specifies how to encode this information in the SDP session
descriptions which are part of an offer/answer exchange.
User agents typically use the offer/answer model to establish a
number of media streams of different types. Following this model, a
BFCP connection is described as any other media stream by using an
SDP 'm' line, possibly followed by a number of attributes encoded in
'a' lines.
2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
described in BCP 14, RFC 2119 [1] and indicate requirement levels for
compliant implementations.
3. Fields in the m Line
According to RFC 2327 [2], the 'm'line format is the following:
m=<media> <port> <transport> <fmt list>
The media field MUST have a value of "application". The port field
is not used by BFCP, and MAY be set to any value chosen by the
endpoint. A port field value of zero has the standard SDP meaning
(i.e., rejection of the media stream).
The port field is set following the rules in [4]. Depending on the
value of the setup attribute (disccused in Section 6), the port field
contains the port the remote endpoint will initiate its TCP
connection to, or is irrelevant (i.e., the endpoint will initiate the
connection towards the remote endpoint) and should be set to a value
of 9, which is the discard port. Since BFCP only runs on top of TCP,
the port is always a TCP port.
We define two new values for the transport field: TCP/BFCP and TCP/
TLS/BFCP.
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The fmt (format) list is ignored for BFCP. The fmt list of BFCP m
lines SHOULD contain a single "*" character.
The following is an example of an m line for a BFCP connection:
m=application 20000 TCP/BFCP *
4. The confid and userid SDP Parameters
We define the confid and the userid SDP media-level attributes.
Their syntax is:
confid-attribute = "a=confid: " conference-id
conference-id = token
userid-attribute = "a=userid: " user-id
user-id = token
The confid and the userid attributes carry the integer representation
of a conference ID and a user ID respectively.
Endpoints which use the offer/answer model to establish BFCP
connections MUST support the confid and the userid attributes. A
floor control server acting as an offerer or as an answerers SHOULD
include these attributes in its session descriptions.
5. The k line
If the offer/answer exchange is encrypted and integrity protected,
the offerer MAY use an SDP 'k' line to provide the answerer with a
shared secret to be used to calculate the value of the DIGEST TLVs.
The following is an example of a 'k' line:
k=base64:c2hhcmVkLXNlY3JldA==
6. TCP Connection Management
The management of the TCP connection used to transport BFCP is
performed using the setup and 'connection' attributes as defined in
[4].
The setup attribute indicates which of the endpoints (client or floor
control server) initiates the TCP connection. The 'connection'
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attribute handles TCP connection reestablishment.
Editor's note: need to address loss and re-establishment of TCP
connections.
7. Association between Streams and Floors
We define the floorid SDP media-level attribute. Its syntax is:
floor-id-attribute = "a=floorid:" token " mstream:" 1*(token)
The floorid attribute is used in BFCP m lines and associates a floor
ID with a media stream. The token representing the floor ID is the
integer representation of the 16-bit floorid to be used in BFCP. The
token representing the media stream is a pointer to the media stream,
which is identified by an SDP label attribute [6]
Endpoints which use the offer/answer model to establish BFCP
connections MUST support the floorid and the label attributes. A
floor control server acting as an offerer or as an answerers SHOULD
include these attributes in its session descriptions.
8. Example
The following is an example of an offer sent by a conference server
to a user. For the purpose of brevity, the main portion of the
session description is omitted in the examples, which only show m=
lines and their attributes.
m=application 20000 TCP/BFCP *
k=base64:c2hhcmVkLXNlY3JldA==
a=setup:passive
a=connection:new
a=confid:4321
a=userid:1234
a=floorid:1 m-stream:10
a=floorid:2 m-stream:11
m=audio 20000 RTP/AVP 0
a=label:10
m=video 30000 RTP/AVP 31
a=label:11
The following is the answer returned by the user.
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m=application 9 TCP/BFCP *
a=setup:active
a=connection:new
m=audio 25000 RTP/AVP 0
m=video 35000 RTP/AVP 31
9. Security Considerations
TBD.
10. IANA Considerations
TBD.
10.1 SDP Attributes Registration
TBD:
11. Acknowledgments
Joerg Ott, Keith Drage, and Alan Johnston provided useful ideas for
this document.
12. References
12.1 Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Handley, M. and V. Jacobson, "SDP: Session Description
Protocol", RFC 2327, April 1998.
[3] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
Session Description Protocol (SDP)", RFC 3264, June 2002.
[4] Yon, D., "Connection-Oriented Media Transport in the Session
Description Protocol (SDP)", draft-ietf-mmusic-sdp-comedia-08
(work in progress), July 2004.
[5] Camarillo, G., "The Binary Floor Control Protocol (BFCP)",
draft-ietf-xcon-bfcp-01 (work in progress), August 2004.
[6] Levin, O. and G. Camarillo, "The SDP (Session Description
Protocol) Label Attribute",
draft-levin-mmmusic-sdp-media-label-00 (work in progress), July
2004.
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12.2 Informational References
Author's Address
Gonzalo Camarillo
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
EMail: Gonzalo.Camarillo@ericsson.com
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