Session Description Protocol (SDP) Format for Binary Floor Control Protocol (BFCP) Streams
draft-ietf-bfcpbis-rfc4583bis-06

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BFCPbis Working Group                                       G. Camarillo
Internet-Draft                                                  Ericsson
Obsoletes: 4583 (if approved)                              T. Kristensen
Intended status: Standards Track                                   Cisco
Expires: August 16, 2013                               February 12, 2013

   Session Description Protocol (SDP) Format for Binary Floor Control
                        Protocol (BFCP) Streams
                    draft-ietf-bfcpbis-rfc4583bis-06

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.

   This document obsoletes RFC 4583.  Changes from RFC 4583 are
   summarized in Section 12.

Status of this Memo

   This Internet-Draft is submitted 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 August 16, 2013.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   (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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   to this document.  Code Components extracted from this document must
   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 Simplified BSD License.

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.  BFCP Connection Management . . . . . . . . . . . . . . . . . .  7
     7.1.  TCP Connection Management  . . . . . . . . . . . . . . . .  7
   8.  Authentication . . . . . . . . . . . . . . . . . . . . . . . .  8
   9.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . .  9
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   11. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
     11.1. Registration of SDP 'proto' Values . . . . . . . . . . . . 11
     11.2. Registration of the SDP 'floorctrl' Attribute  . . . . . . 11
     11.3. Registration of the SDP 'confid' Attribute . . . . . . . . 12
     11.4. Registration of the SDP 'userid' Attribute . . . . . . . . 12
     11.5. Registration of the SDP 'floorid' Attribute  . . . . . . . 12
   12. Changes from RFC 4583  . . . . . . . . . . . . . . . . . . . . 13
   13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
   14. Normative References . . . . . . . . . . . . . . . . . . . . . 14
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15

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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 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

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document 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 depending on the value of the transport field,
   as explained below.  A port field value of zero has the standard SDP
   meaning (i.e., rejection of the media stream) regardless of the
   transport used.

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      When TCP is used as the transport, the port field is set following
      the rules in [7].  Depending on the value of the 'setup' attribute
      (discussed in Section 7.1), the port field contains the port to
      which the remote endpoint will direct BFCP messages 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.

      When UDP is used as the transport, the port field contains the
      port to which the remote endpoint will direct BFCP messages
      regardless of the value of the 'setup' attribute.

   We define four new values for the transport field: TCP/BFCP, TCP/TLS/
   BFCP, UDP/BFCP, and UDP/TLS/BFCP.  TCP/BFCP is used when BFCP runs
   directly on top of TCP, TCP/TLS/BFCP is used when BFCP runs on top of
   TLS, which in turn runs on top of TCP.  Similarly, UDP/BFCP is used
   when BFCP runs directly on top of UDP, and UDP/TLS/BFCP is used when
   BFCP runs on top of DTLS [12], which in turn runs on top of UDP.

   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.

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   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.

   c-s:  The offerer would be willing to act both as a floor control
      client and as a floor control server.

   If an SDP media description in an offer contains a 'floorctrl'
   attribute, the answerer accepting that media MUST include one in the
   corresponding media description of 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.

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   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-s

5.  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 decimal 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 the SDP media description for BFCP

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   media.  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.

   Note: In [15] 'm-stream' was erroneously used in Section 9.  Although
   the example was non-normative, it is implemented by some vendors and
   occurs in cases where the endpoint is willing to act as an server.
   Therefore, it is RECOMMENDED to support parsing and interpreting
   'm-stream' the same way as 'mstrm' when receiving.

7.  BFCP Connection Management

   BFCP connections may use TCP or UDP as the underlying transport.
   BFCP entities exchanging BFCP messages over UDP will direct the BFCP
   messages to the peer side connection address and port provided in the
   SDP 'm' line.  TCP connection management is more complicated and is
   described below.

7.1.  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 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

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   generate an offer in order to reestablish the TCP connection.

   Endpoints that use the offer/answer model to establish TCP
   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/DTLS 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-/DTLS-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/
   answer model to establish BFCP connections MUST support the
   'fingerprint' attribute and SHOULD include it in their session
   descriptions.

   When TLS is used with TCP, once the underlying connection is
   established, the answerer acts as the TLS server regardless of its
   role (passive or active) in the TCP establishment procedure.

   Endpoints that use the offer/answer model to establish a DTLS
   association MUST support the 'setup' attribute, as defined in [7].
   When DTLS is used with UDP, the 'setup' attribute indicates which of
   the endpoints (client or floor control server) initiates the DTLS
   association setup.  The requirements for the offer/answer exchange
   specified in [13], Section 5 MUST be followed when using DTLS.

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      Informational note: How to determine which endpoint to initiate
      the TLS/DTLS association depends on the selected underlying
      transport.  It was decided to keep the original semantics in [15]
      for TCP to retain backwards compatibility.  When using UDP, the
      procedure above was preferred since it adheres to [13] as used for
      DTLS-SRTP, it does not overload offer/answer semantics, and it
      works for offerless INVITE in scenarios with B2BUAs.

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 mstrm:10
   a=floorid:2 mstrm: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

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   m=video 55002 RTP/AVP 31

   A similar example using unreliable transport and DTLS is shown below,
   where the offer is sent from a client.

   m=application 50000 UDP/TLS/BFCP *
   a=setup:actpass
   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:c-only s-only
   a=confid:4321
   a=userid:1234
   a=floorid:1 mstrm:10
   a=floorid:2 mstrm:11
   m=audio 50002 RTP/AVP 0
   a=label:10
   m=video 50004 RTP/AVP 31
   a=label:11

   The following is the answer returned by the server.

   m=application 55000 UDP/TLS/BFCP *
   a=setup:active
   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:s-only
   a=confid:4321
   a=userid:1234
   a=floorid:1 mstrm:10
   a=floorid:2 mstrm:11
   m=audio 55002 RTP/AVP 0
   m=video 55004 RTP/AVP 31

10.  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.
   Furthermore, when using DTLS over UDP, considerations for its use
   with RTP and RTCP are presented in [13].  The requirements for the
   offer/answer exchange, as listed in Section 5 of that document, MUST
   be followed.

   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

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   [6] is the natural choice to provide such a channel.

11.  IANA Considerations

      [Editorial note: The changes in Section 11.1 instruct the IANA to
      register the two new values UDP/BFCP and UDP/TLS/BFCP for the SDP
      'proto' field, the rest is unchanged from [14].]

11.1.  Registration of SDP 'proto' Values

   The IANA has registered the following values for the SDP 'proto'
   field under the Session Description Protocol (SDP) Parameters
   registry:

                       +--------------+------------+
                       | Value        |  Reference |
                       +--------------+------------+
                       | TCP/BFCP     | [RFC XXXX] |
                       | TCP/TLS/BFCP | [RFC XXXX] |
                       | UDP/BFCP     | [RFC XXXX] |
                       | UDP/TLS/BFCP | [RFC XXXX] |
                       +--------------+------------+

                 Table 2: Values for the SDP 'proto' field

11.2.  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.

   Allowed attribute values:   1*("c-only" / "s-only" / "c-s")

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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 token

11.4.  Registration of the SDP 'userid' 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:   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

   The IANA has registered the following SDP att-field under the Session
   Description Protocol (SDP) Parameters registry:

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   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.  Changes from RFC 4583

   Following is the list of technical changes and other fixes from [15].

   Main purpose of this work was to add signaling support necessary to
   support BFCP over unreliable transport, as described in [8],
   resulting in the following changes:

   Fields in the 'm' Line  (Section 3):
         The section is re-written to remove reference to the
         exclusivity of TCP as a transport for BFCP streams.  The
         transport field values UDP/BFCP and UDP/TLS/BFCP added.

   Authentication  (Section 8):
         In last paragraph, made clear that a TCP connection was
         described.

   Security Considerations  (Section 10):
         For the DTLS over UDP case, mention existing considerations and
         requirements for the offer/answer exchange in [13].

   Registration of SDP 'proto' Values  (Section 11.1):
         Register the two new values UDP/BFCP and UDP/TLS/BFCP in the
         SDP parameters registry.

   The clarification and bug fixes:

   Errata ID: 712  (Section 4 and Section 6):
      Language clarification.  Don't use terms like an SDP attribute is
      "used in an 'm' line", instead make clear that the attribute is a
      media-level attribute.

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   Fix typo in example  (Section 9):
      Do not use 'm-stream' in the SDP example, use the correct 'mstrm'
      as specified in Section 9.  Recommend interpreting 'm-stream' if
      it is received, since it is present in some implementations.

13.  Acknowledgements

   Joerg Ott, Keith Drage, Alan Johnston, Eric Rescorla, Roni Even, and
   Oscar Novo provided useful ideas for the original [15].  The authors
   also acknowledge contributions to the revision of BFCP for use over
   an unreliable transport from Geir Arne Sandbakken, Charles Eckel,
   Eoin McLeod and Mark Thompson.

14.  Normative References

   [1]   Bradner, S., "Key words for use in RFCs to Indicate Requirement
         Levels", BCP 14, RFC 2119, March 1997.

   [2]   Crocker, D. and P. Overell, "Augmented BNF for Syntax
         Specifications: ABNF", STD 68, RFC 5234, January 2008.

   [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]   Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley,
         R., and W. Polk, "Internet X.509 Public Key Infrastructure
         Certificate and Certificate Revocation List (CRL) Profile",
         RFC 5280, May 2008.

   [6]   Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet Mail
         Extensions (S/MIME) Version 3.2 Certificate Handling",
         RFC 5750, January 2010.

   [7]   Yon, D. and G. Camarillo, "TCP-Based Media Transport in the
         Session Description Protocol (SDP)", RFC 4145, September 2005.

   [8]   Camarillo, G., Drage, K., Kristensen, T., Ott, J., and C.
         Eckel, "The Binary Floor Control Protocol (BFCP)",
         draft-ietf-bfcpbis-rfc4582bis-08 (work in progress),
         January 2013.

   [9]   Levin, O. and G. Camarillo, "The Session Description Protocol

Camarillo & Kristensen   Expires August 16, 2013               [Page 14]
Internet-Draft                    BFCP                     February 2013

         (SDP) Label Attribute", RFC 4574, August 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.

   [12]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
         Security Version 1.2", RFC 6347, January 2012.

   [13]  Fischl, J., Tschofenig, H., and E. Rescorla, "Framework for
         Establishing a Secure Real-time Transport Protocol (SRTP)
         Security Context Using Datagram Transport Layer Security
         (DTLS)", RFC 5763, May 2010.

   [14]  Camarillo, G., Ott, J., and K. Drage, "The Binary Floor Control
         Protocol (BFCP)", RFC 4582, November 2006.

   [15]  Camarillo, G., "Session Description Protocol (SDP) Format for
         Binary Floor Control Protocol (BFCP) Streams", RFC 4583,
         November 2006.

Authors' Addresses

   Gonzalo Camarillo
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   Email: Gonzalo.Camarillo@ericsson.com

   Tom Kristensen
   Cisco
   Philip Pedersens vei 22
   N-1366 Lysaker
   Norway

   Email: tomkrist@cisco.com, tomkri@ifi.uio.no

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