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Network Working Group                                       G. CamarilloRequest for Comments: 4583                                      EricssonCategory: Standards Track                                  November 2006Session Description Protocol (SDP) Format forBinary Floor Control Protocol (BFCP) StreamsStatus of This Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The IETF Trust (2006).Abstract   This document specifies how to describe Binary Floor Control Protocol   (BFCP) streams in Session Description Protocol (SDP) descriptions.   User agents using the offer/answer model to establish BFCP streams   use this format in their offers and answers.Table of Contents1. Introduction ....................................................22. Terminology .....................................................23. Fields in the 'm' Line ..........................................24. Floor Control Server Determination ..............................35. The 'confid' and 'userid' SDP Attributes ........................56. Association between Streams and Floors ..........................57. TCP Connection Management .......................................58. Authentication ..................................................69. Examples ........................................................710. Security Considerations ........................................811. IANA Considerations ............................................8      11.1. Registration of the 'TCP/BFCP' and 'TCP/TLS/BFCP'            SDP 'proto' Values ........................................811.2. Registration of the SDP 'floorctrl' Attribute .............811.3. Registration of the SDP 'confid' Attribute ................911.4. Registration of the SDP 'userid' Attribute ................911.5. Registration of the SDP 'floorid' Attribute ..............1012. Acknowledgements ..............................................1013. Normative References ..........................................10Camarillo                   Standards Track                     [Page 1]

RFC 4583              SDP Format for BFCP Streams          November 20061.  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 is to use an   offer/answer [4] exchange.  This document specifies how to encode   this information in the SDP session descriptions that 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 inBCP 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 (discussed inSection 7), the port   field contains the port to which the remote endpoint will initiate   its TCP connection 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                   Standards Track                     [Page 2]

RFC 4583              SDP Format for BFCP Streams          November 2006   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.  In the most common   scenario, a client establishes a BFCP stream with a 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, in 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:   c-only:  The offerer would be willing to act as a floor control      client only.   s-only:  The offerer would be willing to act as a floor control      server only.Camarillo                   Standards Track                     [Page 3]

RFC 4583              SDP Format for BFCP Streams          November 2006   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 descriptions of the roles when they are chosen   by an answerer:   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.   Endpoints that 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 answerer 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:      a=floorctrl:c-only s-only c-sCamarillo                   Standards Track                     [Page 4]

RFC 4583              SDP Format for BFCP Streams          November 20065.  The 'confid' and 'userid' SDP Attributes   We define the 'confid' and the 'userid' SDP media-level attributes.   These 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 that 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 answerer 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 that 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.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].Camarillo                   Standards Track                     [Page 5]

RFC 4583              SDP Format for BFCP Streams          November 2006   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 reset 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 that use the offer/answer model to establish BFCP   connections MUST support the 'setup' and '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 ensure 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 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.   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 that use the offer/answerCamarillo                   Standards Track                     [Page 6]

RFC 4583              SDP Format for BFCP Streams          November 2006   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.   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 31Camarillo                   Standards Track                     [Page 7]

RFC 4583              SDP Format for BFCP Streams          November 200610.  Security Considerations   The BFCP [8], SDP [11], and offer/answer [4] specifications discuss   security issues related to BFCP, SDP, and 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 that an initial integrity-protected channel is 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 Considerations11.1.  Registration of the 'TCP/BFCP' and 'TCP/TLS/BFCP' SDP 'proto'       Values   The IANA has registered the following two new values for the SDP   'proto' field under the Session Description Protocol (SDP) Parameters   registry:                       +--------------+-----------+                       | Value        | Reference |                       +--------------+-----------+                       | TCP/BFCP     |RFC4583  |                       | TCP/TLS/BFCP |RFC4583  |                       +--------------+-----------+                 Table 2: Values for the SDP 'proto' field11.2.  Registration of the SDP 'floorctrl' Attribute   The IANA has registered 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.Camarillo                   Standards Track                     [Page 8]

RFC 4583              SDP Format for BFCP Streams          November 2006   Allowed attribute values:   1*("c-only" / "s-only" / "c-s")11.3.  Registration of the SDP 'confid' Attribute   The IANA has registered 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 token11.4.  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:   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 tokenCamarillo                   Standards Track                     [Page 9]

RFC 4583              SDP Format for BFCP Streams          November 200611.5.  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:   Tokens12.  Acknowledgements   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         Specifications: ABNF",RFC 4234, October 2005.   [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.Camarillo                   Standards Track                    [Page 10]

RFC 4583              SDP Format for BFCP Streams          November 2006   [7]   Yon, D. and G. Camarillo, "TCP-Based Media Transport in the         Session Description Protocol (SDP)",RFC 4145, September 2005.   [8]   Camarillo, G., Ott, J., and K. Drage, "The Binary Floor Control         Protocol (BFCP)",RFC 4582, November 2006.   [9]   Levin, O. and G. Camarillo, "The Session Description Protocol         (SDP) Label Attribute",RFC 4574, July 2006.   [10]  Lennox, J., "Connection-Oriented Media Transport over the         Transport Layer Security (TLS) Protocol in the Session         Description Protocol (SDP)",RFC 4572, July 2006.   [11]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session         Description Protocol",RFC 4566, July 2006.Author's Address   Gonzalo Camarillo   Ericsson   Hirsalantie 11   Jorvas  02420   Finland   EMail: Gonzalo.Camarillo@ericsson.comCamarillo                   Standards Track                    [Page 11]

RFC 4583              SDP Format for BFCP Streams          November 2006Full Copyright Statement   Copyright (C) The IETF Trust (2006).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   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, THE IETF TRUST,   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.Intellectual Property   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 inBCP 78 andBCP 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 athttp://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.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Camarillo                   Standards Track                    [Page 12]