Internet DRAFT - draft-ietf-mmusic-sdp-bfcp
draft-ietf-mmusic-sdp-bfcp
MMUSIC Working Group G. Camarillo
Internet-Draft Ericsson
Expires: June 2, 2006 November 29, 2005
Session Description Protocol (SDP) Format for Binary Floor Control
Protocol (BFCP) Streams
draft-ietf-mmusic-sdp-bfcp-03.txt
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on June 2, 2006.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document specifies how to describe BFCP streams in SDP session
descriptions. User agents using the offer/answer model to establish
BFCP streams use this format in their offers and their answers.
Camarillo Expires June 2, 2006 [Page 1]
Internet-Draft BFCP November 2005
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Fields in the 'm' Line . . . . . . . . . . . . . . . . . . . . 3
4. Floor Control Server Determination . . . . . . . . . . . . . . 4
5. The 'confid' and 'userid' SDP Attributes . . . . . . . . . . . 6
6. Association between Streams and Floors . . . . . . . . . . . . 6
7. TCP Connection Management . . . . . . . . . . . . . . . . . . 7
8. Authentication . . . . . . . . . . . . . . . . . . . . . . . . 7
9. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
10. Security Considerations . . . . . . . . . . . . . . . . . . . 9
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
11.1. Registration of the 'TCP/BFCP' and 'TCP/TLS/BFCP' SDP
'proto' values . . . . . . . . . . . . . . . . . . . . . 9
11.2. Registration of the SDP 'floorctrl' Attribute . . . . . . 10
11.3. Registration of the SDP 'confid' Attribute . . . . . . . 10
11.4. Registration of the SDP 'userid' Attribute . . . . . . . 10
11.5. Registration of the SDP 'floorid' Attribute . . . . . . . 11
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11
13. Normative References . . . . . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 13
Intellectual Property and Copyright Statements . . . . . . . . . . 14
Camarillo Expires June 2, 2006 [Page 2]
Internet-Draft BFCP November 2005
1. Introduction
As discussed in the BFCP (Binary Floor Control Protocol)
specification [8], 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.
One way for clients to obtain this information consists of using an
offer/answer [4] exchange. This document specifies how to encode
this information in the SDP session descriptions which are part of
such 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
This Section describes how to generate an 'm' line for a BFCP stream.
According to the SDP specification [11], the 'm' line format is the
following:
m=<media> <port> <transport> <fmt> ...
The media field MUST have a value of "application".
The port field is set following the rules in [7]. Depending on the
value of the 'setup' attribute (disccused in Section 7), 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. A port field value of zero has the
standard SDP meaning (i.e., rejection of the media stream).
Camarillo Expires June 2, 2006 [Page 3]
Internet-Draft BFCP November 2005
We define two new values for the transport field: TCP/BFCP and TCP/
TLS/BFCP. The former is used when BFCP runs directly on top of TCP
and the latter is used when BFCP runs on top of TLS, which in turn
runs on top of TCP.
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 50000 TCP/TLS/BFCP *
4. Floor Control Server Determination
When two endpoints establish a BFCP stream, they need to determine
which of them acts as a floor control server. The most common
scenario consists of a client establishing a BFCP stream with
conference server that acts as the floor control server. Floor
control server determination is straight forward because one endpoint
can only act as a client and the other can only act as a floor
control server.
However, there are scenarios where both endpoints could act as a
floor control server. For example, is a two-party session that
involves an audio stream and a shared whiteboard, the endpoints need
to decide which party will be acting as the floor control server.
Furthermore, there are situations where both the offerer and the
answerer act as both clients and floor control servers in the same
session. For example, in a two-party session that involves an audio
stream and a shared whiteboard, one party acts as the floor control
server for the audio stream and the other acts as the floor control
server for the shared whiteboard.
We define the 'floorctrl' SDP media-level attribute to perform floor
control determination. Its Augmented BNF syntax [2] is:
floor-control-attribute = "a=floorctrl:" role *(SP role)
role = "c-only" / "s-only" / "c-s"
The offerer includes this attribute to state all the roles it would
be willing to perform:
Camarillo Expires June 2, 2006 [Page 4]
Internet-Draft BFCP November 2005
c-only: The offerer would be willing to only act as a floor control
client.
s-only: The offerer would be willing to only act as a floor control
server.
c-s: The offerer would be willing to act both as a floor control
client and as a floor control server.
If an 'm' line in an offer contains a 'floorctrl' attribute, the
answerer MUST include one in the corresponding 'm' line in the
answer. The answerer includes this attribute to state which role the
answerer will perform. That is, the answerer chooses one of the
roles the offerer is willing to perform and generates an answer with
the corresponding role for the answerer. Table 1 shows the
corresponding roles for an answerer depending on the offerer's role.
+---------+----------+
| Offerer | Answerer |
+---------+----------+
| c-only | s-only |
| s-only | c-only |
| c-s | c-s |
+---------+----------+
Table 1: Roles
The following are the description of the roles when chosen by an
answere:.
c-only: The answerer will act as a floor control client.
Consequently, the offerer will act as a floor control server.
s-only: The answerer will act as a floor control server.
Consequently, the offerer will act as a floor control client.
c-s: The answerer will act both as a floor control client and as a
floor control server. Consequently, the offerer will also act
both as a floor control client and as a floor control server as
well.
Endpoints which use the offer/answer model to establish BFCP
connections MUST support the 'floorctrl' attribute. A floor control
server acting as an offerer or as an answerers SHOULD include this
attribute in its session descriptions.
If the 'floorctrl' attribute is not used in an offer/answer exchange,
by default the offerer and the answerer will act as a floor control
client and as a floor control server respectively.
The following is an example of a 'floorctrl' attribute in an offer.
When this attribute appears in an answer, it only carries one role:
Camarillo Expires June 2, 2006 [Page 5]
Internet-Draft BFCP November 2005
a=floorctrl:c-only s-only c-s
5. The 'confid' and 'userid' SDP Attributes
We define the 'confid' and the 'userid' SDP media-level attributes.
These attributes attributes are used by a floor control server to
provide a client with a conference ID and a user ID respectively.
Their Augmented BNF syntax [2] 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.
6. Association between Streams and Floors
We define the floorid SDP media-level attribute. Its Augmented BNF
syntax [2] is:
floor-id-attribute = "a=floorid:" token [" mstrm:" token *(SP token)]
The floorid attribute is used in BFCP 'm' lines. It defines a floor
identifier and, possibly, associates it with one or more media
streams. The token representing the floor ID is the integer
representation of the Floor ID 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 [9]
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 answerer SHOULD
include these attributes in its session descriptions.
Camarillo Expires June 2, 2006 [Page 6]
Internet-Draft BFCP November 2005
7. TCP Connection Management
The management of the TCP connection used to transport BFCP is
performed using the 'setup' and 'connection' attributes as defined in
[7].
The 'setup' attribute indicates which of the endpoints (client or
floor control server) initiates the TCP connection. The 'connection'
attribute handles TCP connection reestablishment.
The BFCP specification [8] describes a number of situations when the
TCP connection between a client and the floor control server needs to
be reestablished. However, that specification does not describe the
reestablishment process because this process depends on how the
connection was established in the first place. BFCP entities using
the offer/answer model follow the following rules.
When the existing TCP connection is reseted following the rules in
[8], the client SHOULD generate an offer towards the floor control
server in order to reestablish the connection. If a TCP connection
cannot deliver a BFCP message and times out, the entity that
attempted to send the message (i.e., the one that detected the TCP
timeout) SHOULD generate an offer in order to reestablish the TCP
connection.
Endpoints which use the offer/answer model to establish BFCP
connections MUST support the 'setup' and the 'connection' attributes.
8. Authentication
When a BFCP connection is established using the offer/answer model,
it is assumed that the offerer and the answerer authenticate each
other using some mechanism. Once this mutual authentication takes
place, all the offerer and the answerer need to make sure is that the
entity they are receiving BFCP messages from is the same as the one
that generated the previous offer or answer.
When SIP is used to perform an offer/answer exchange, the initial
mutual authentication takes place at the SIP level. Additionally,
SIP uses S/MIME [6] to provide an integrity protected channel with
optional confidentiality for the offer/answer exchange. BFCP takes
advantage of this integrity protected offer/answer exchange to
perform authentication. Within the offer/answer exchange, the
offerer and the answerer exchange the fingerprints of their self-
signed certificates. These self-signed certificates are then used to
establish the TLS connection that will carry BFCP traffic between the
offerer and the answerer.
Camarillo Expires June 2, 2006 [Page 7]
Internet-Draft BFCP November 2005
BFCP clients and floor control servers follow the rules in [10]
regarding certificate choice and presentation. This implies that
unless a 'fingerprint' attribute is included in the session
description, the certificate provided at the TLS-level MUST either be
directly signed by one of the other party's trust anchors or be
validated using a certification path that terminates at one of the
other party's trust anchors [5]. Endpoints which use the offer/
answer model to establish BFCP connections MUST support the
'fingerprint' attribute and SHOULD include it in their session
descriptions.
When TLS is used, once the underlaying TCP connection is established,
the answerer acts as the TLS server regardless of its role (passive
or active) in the TCP establishment procedure.
9. Examples
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.
The following is an example of an offer sent by a conference server
to a client.
m=application 50000 TCP/TLS/BFCP *
a=setup:passive
a=connection:new
a=fingerprint:SHA-1 \
4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB
a=floorctrl:s-only
a=confid:4321
a=userid:1234
a=floorid:1 m-stream:10
a=floorid:2 m-stream:11
m=audio 50002 RTP/AVP 0
a=label:10
m=video 50004 RTP/AVP 31
a=label:11
Note that due to RFC formatting conventions, this document splits SDP
across lines whose content would exceed 72 characters. A backslash
character marks where this line folding has taken place. This
backslash and its trailing CRLF and whitespace would not appear in
actual SDP content.
The following is the answer returned by the client.
Camarillo Expires June 2, 2006 [Page 8]
Internet-Draft BFCP November 2005
m=application 9 TCP/TLS/BFCP *
a=setup:active
a=connection:new
a=fingerprint:SHA-1 \
3D:B4:7B:E3:CC:FC:0D:1B:5D:31:33:9E:48:9B:67:FE:68:40:E8:21
a=floorctrl:c-only
m=audio 55000 RTP/AVP 0
m=video 55002 RTP/AVP 31
10. Security Considerations
The BFCP [8], SDP [11], and the offer/answer [4] specifications
discuss security issues related to BFCP, SDP, and the offer/answer
respectively. In addition, [7] and [10] discuss security issues
related to the establishment of TCP and TLS connections using an
offer/answer model.
BFCP assumes an initial integrity-protected channel used to exchange
self-signed certificates between a client and the floor control
server. For session descriptions carried in SIP [3], S/MIME [6] is
the natural choice to provide such a channel.
11. IANA Considerations
The following sections instruct the IANA to perform a set of actions.
11.1. Registration of the 'TCP/BFCP' and 'TCP/TLS/BFCP' SDP 'proto'
values
This section instructs the IANA to register the following two new
values for the SDP 'proto' field under the Session Description
Protocol (SDP) Parameters registry:
+--------------+-----------+
| Value | Reference |
+--------------+-----------+
| TCP/BFCP | RFCxxxx |
| TCP/TLS/BFCP | RFCxxxx |
+--------------+-----------+
Table 2: Values for the SDP 'proto' field
[Note to the RFC editor: please, replace RFCxxxx with the RFC number
that this document will be assigned.]
Camarillo Expires June 2, 2006 [Page 9]
Internet-Draft BFCP November 2005
11.2. Registration of the SDP 'floorctrl' Attribute
This section instructs the IANA to register the following SDP att-
field under the Session Description Protocol (SDP) Parameters
registry:
Contact name: Gonzalo.Camarillo@ericsson.com
Attribute name: floorctrl
Long-form attribute name: Floor Control
Type of attribute Media level
Subject to charset: No
Purpose of attribute: The 'floorctrl' attribute is used to perform
floor control server determination.
Allowed attribute values: 1*("c-only" / "s-only" / "c-s")
11.3. Registration of the SDP 'confid' Attribute
This section instructs the IANA to register the following SDP att-
field under the Session Description Protocol (SDP) Parameters
registry:
Contact name: Gonzalo.Camarillo@ericsson.com
Attribute name: confid
Long-form attribute name: Conference Identifier
Type of attribute Media level
Subject to charset: No
Purpose of attribute: The 'confid' attribute carries the integer
representation of a Conference ID.
Allowed attribute values: A token
11.4. Registration of the SDP 'userid' Attribute
This section instructs the IANA to register the following SDP att-
field under the Session Description Protocol (SDP) Parameters
registry:
Camarillo Expires June 2, 2006 [Page 10]
Internet-Draft BFCP November 2005
Contact name: Gonzalo.Camarillo@ericsson.com
Attribute name: userid
Long-form attribute name: User Identifier
Type of attribute Media level
Subject to charset: No
Purpose of attribute: The 'userid' attribute carries the integer
representation of a User ID.
Allowed attribute values: A token
11.5. Registration of the SDP 'floorid' Attribute
This section instructs the IANA to register the following SDP att-
field under the Session Description Protocol (SDP) Parameters
registry:
Contact name: Gonzalo.Camarillo@ericsson.com
Attribute name: floorid
Long-form attribute name: Floor Identifier
Type of attribute Media level
Subject to charset: No
Purpose of attribute: The 'floorid' attribute associates a floor
with one or more media streams.
Allowed attribute values: Tokens
12. Acknowledgments
Joerg Ott, Keith Drage, Alan Johnston, Eric Rescorla, Roni Even, and
Oscar Novo provided useful ideas for this document.
13. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Camarillo Expires June 2, 2006 [Page 11]
Internet-Draft BFCP November 2005
Specifications: ABNF", RFC 2234, November 1997.
[3] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, June 2002.
[4] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
Session Description Protocol (SDP)", RFC 3264, June 2002.
[5] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet X.509
Public Key Infrastructure Certificate and Certificate
Revocation List (CRL) Profile", RFC 3280, April 2002.
[6] Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions
(S/MIME) Version 3.1 Certificate Handling", RFC 3850,
July 2004.
[7] Yon, D. and G. Camarillo, "TCP-Based Media Transport in the
Session Description Protocol (SDP)", RFC 4145, September 2005.
[8] Camarillo, G., "The Binary Floor Control Protocol (BFCP)",
draft-ietf-xcon-bfcp-05 (work in progress), July 2005.
[9] Levin, O. and G. Camarillo, "The SDP (Session Description
Protocol) Label Attribute",
draft-ietf-mmusic-sdp-media-label-01 (work in progress),
January 2005.
[10] Lennox, J., "Connection-Oriented Media Transport over the
Transport Layer Security (TLS) Protocol in the Session
Description Protocol (SDP)", draft-ietf-mmusic-comedia-tls-05
(work in progress), September 2005.
[11] Handley, M., "SDP: Session Description Protocol",
draft-ietf-mmusic-sdp-new-25 (work in progress), July 2005.
Camarillo Expires June 2, 2006 [Page 12]
Internet-Draft BFCP November 2005
Author's Address
Gonzalo Camarillo
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: Gonzalo.Camarillo@ericsson.com
Camarillo Expires June 2, 2006 [Page 13]
Internet-Draft BFCP November 2005
Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Disclaimer of Validity
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement
Copyright (C) The Internet Society (2005). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Camarillo Expires June 2, 2006 [Page 14]
