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= ... 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. 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