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Versions: (RFC 4583) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17

BFCPbis Working Group                                       G. Camarillo
Internet-Draft                                                  Ericsson
Obsoletes: 4583 (if approved)                              T. Kristensen
Intended status: Standards Track                                P. Jones
Expires: January 4, 2018                                           Cisco
                                                            July 3, 2017


   Session Description Protocol (SDP) Format for Binary Floor Control
                        Protocol (BFCP) Streams
                    draft-ietf-bfcpbis-rfc4583bis-17

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 14.

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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on January 4, 2018.

Copyright Notice

   Copyright (c) 2017 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
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents



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   carefully, as they describe your rights and restrictions with respect
   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Fields in the 'm' Line  . . . . . . . . . . . . . . . . . . .   3
   4.  Floor Control Server Determination  . . . . . . . . . . . . .   4
     4.1.  SDP 'floorctrl' Attribute . . . . . . . . . . . . . . . .   5
   5.  SDP 'confid' and 'userid' Attributes  . . . . . . . . . . . .   6
   6.  SDP 'floorid' Attribute . . . . . . . . . . . . . . . . . . .   7
   7.  SDP 'bfcpver' Attribute . . . . . . . . . . . . . . . . . . .   7
   8.  BFCP Connection Management  . . . . . . . . . . . . . . . . .   8
     8.1.  TCP Connection Management . . . . . . . . . . . . . . . .   8
   9.  Authentication  . . . . . . . . . . . . . . . . . . . . . . .   8
   10. ICE Considerations  . . . . . . . . . . . . . . . . . . . . .  10
   11. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . .  11
     11.1.  Generating the Initial SDP Offer . . . . . . . . . . . .  12
     11.2.  Generating the SDP Answer  . . . . . . . . . . . . . . .  13
     11.3.  Offerer Processing of the SDP Answer . . . . . . . . . .  14
     11.4.  Modifying the Session  . . . . . . . . . . . . . . . . .  14
   12. Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  14
   13. Security Considerations . . . . . . . . . . . . . . . . . . .  16
   14. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
     14.1.  Registration of SDP 'proto' Values . . . . . . . . . . .  17
     14.2.  Registration of the SDP 'floorctrl' Attribute  . . . . .  17
     14.3.  Registration of the SDP 'confid' Attribute . . . . . . .  18
     14.4.  Registration of the SDP 'userid' Attribute . . . . . . .  18
     14.5.  Registration of the SDP 'floorid' Attribute  . . . . . .  18
     14.6.  Registration of the SDP 'bfcpver' Attribute  . . . . . .  19
   15. Changes from RFC 4583 . . . . . . . . . . . . . . . . . . . .  19
   16. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  20
   17. References  . . . . . . . . . . . . . . . . . . . . . . . . .  20
     17.1.  Normative References . . . . . . . . . . . . . . . . . .  20
     17.2.  Informational References . . . . . . . . . . . . . . . .  22
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  23

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.  This data
   includes the transport address of the server, the conference
   identifier, and the user identifier.



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   One way for clients to obtain this information is to use an SDP
   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> <proto> <fmt> ...

   The media field MUST have a value of "application".

   The port field is set depending on the value of the proto 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 proto
   field.

      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 8.1), 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.





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   This document defines five values for the proto field: TCP/BFCP,
   TCP/DTLS/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.  TCP/DTLS/BFCP is used when running BFCP on top of DTLS [12], as
   described in this specification, which in turn runs on top of TCP
   using the framing method defined in [13] with DTLS packets being sent
   and received instead of RTP/RTCP packets using the shim defined in
   RFC4571 such that the length field defined in RFC4571 precedes each
   DTLS message.

   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, which in turn
   runs on top of UDP.

   The fmt (format) list is not applicable to BFCP.  The fmt list of 'm'
   lines in the case of any proto field value related to BFCP SHOULD
   contain a single "*" character.  If the the fmt list contains any
   other value it is ignored.

   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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4.1.  SDP 'floorctrl' Attribute

   This document defines the 'floorctrl' SDP media-level attribute to
   perform floor control server 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 a
   'floorctrl' attribute 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.  SDP 'confid' and 'userid' Attributes

   This document defines 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

   token-char            = %x21 / %x23-27 / %x2A-2B / %x2D-2E / %x30-39
                           / %x41-5A / %x5E-7E
   token                 = 1*(token-char)

   The 'confid' and the 'userid' attributes carry the decimal integer
   representation of a conference ID and a user ID, respectively.

   The token-char and token elements are defined in [11] but included
   here to provide support for the implementor of this SDP feature.

   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 MUST
   include these attributes in its session descriptions.







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6.  SDP 'floorid' Attribute

   This document defines the 'floorid' SDP media-level attribute.  This
   attribute is used to provide an association between media streams and
   floors.  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
   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 MUST
   include these attributes in its session descriptions.

      Note: In [18] 'm-stream' was erroneously used in Section 12.
      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.  SDP 'bfcpver' Attribute

   This document defines the 'bfcpver' SDP media-level attribute.  This
   attribute is used for BFCP version negotiation.  Its Augmented BNF
   syntax [2] is:

   bfcp-version-attribute = "a=bfcpver:" bfcp-version *(SP bfcp-version)
   bfcp-version           = token

   The 'bfcpver' attribute defines the list of the versions of BFCP
   supported by the endpoint.  Tokens representing versions MUST be
   integers matching the "Version" field that would be presented in the
   BFCP COMMON-HEADER [8].  The version of BFCP to be used will then be
   confirmed with a BFCP-level Hello/HelloAck.

   Endpoints that use the offer/answer model to establish BFCP
   connections SHOULD support the 'bfcpver' attribute.  A floor control
   server acting as an offerer or as an answerer SHOULD include this
   attribute in its session descriptions.  However, endpoints that
   support RFC XXXX, and not only the [18] subset, are REQUIRED to
   support and, when acting as a floor control server, to use the
   'bfcpver' attribute.



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   If a 'bfcpver' attribute is not present, default values are inferred
   from the transport specified in the 'm' line (Section 3).  In
   accordance with definition of the Version field in [8], when used
   over a reliable transport the default value is "1", and when used
   over an unreliable transport the default value is "2".

8.  BFCP Connection Management

   BFCP connections can use TCP or UDP as the underlying transport.
   BFCP entities exchanging BFCP messages over UDP 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.

8.1.  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 closed and reestablished
   following the rules in [8], the client MUST 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) MUST 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.

9.  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.  TLS/DTLS is the preferred mechanism, but
   other mechanisms are possible and outside the scope of this document.



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   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 SDP 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 MUST include it in their session
   descriptions.

   When TLS is used with TCP, once the underlying connection is
   established, the answerer which may be the client or the floor
   control server acts as the TLS server regardless of its role (passive
   or active) in the TCP establishment procedure.  If the TCP connection
   is lost, the active endpoint is responsible for re-establishing the
   TCP connection.  Unless a new TLS session is negotiated, subsequent
   SDP offers and answers will not impact the previously negotiated TLS
   roles.

   When DTLS is used with UDP, the requirements specified in Section 5
   of [16] MUST be followed.

      Informational note: How to determine which endpoint initiates the
      TLS/DTLS association depends on the selected underlying transport.
      It was decided to keep the original semantics in [18] for TCP to
      retain backwards compatibility.  When using UDP, the procedure
      above was preferred since it adheres to [16] as used for DTLS-
      SRTP, it does not overload offer/answer semantics, and it works
      for offerless INVITE in scenarios with B2BUAs.





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10.  ICE Considerations

   When BFCP is used with UDP based ICE candidates [14] then the
   procedures for UDP/TLS/BFCP are used.

   When BFCP is used with TCP based ICE candidates [15] then the
   procedures for TCP/DTLS/BFCP are used.

   In ICE environments, during the nomination process, endpoints go
   through multiple ICE candidate pairs, until the most preferred
   candidate pair is found.  During the nomination process, data can be
   sent as soon as the first working candidate pair is found, but the
   nomination process still continues and selected candidate pairs can
   still change while data is sent.

   Furthermore, if endpoints roam between networks, for instance when
   mobile endpoint switches from mobile connection to WiFi, endpoints
   will initiate an ICE restart, which will trigger a new nomination
   process between the new set of candidates and likely result in the
   new nominated candidate pair.

   Implementations MUST treat all ICE candidate pairs associated with an
   BFCP session on top of a DTLS association as part of the same DTLS
   association.  Thus, there will only be one BFCP session setup and one
   DTLS handshake even if there are multiple valid candidate pairs, and
   shifting from one candidate pair to another, including switching
   between UDP to TCP candidate pairs, will not impact the BFCP session
   or DTLS associations.  If new candidates are added, they will also be
   part of the same BFCP session and DTLS associations.  When
   transitioning between candidate pairs, different candidate pairs can
   be currently active in different directions and implementations MUST
   be ready to receive data on any of the candidates, even if this means
   sending and receiving data using UDP/TLS/BFCP and TCP/DTLS/BFCP at
   the same time in different directions.

   In order to maximize the likelihood of interoperability between the
   endpoints, all ICE enabled BFCP endpoints SHOULD implement support
   for UDP/TLS/BFCP.

   When an SDP offer or answer is sent with multiple ICE candidates
   during initial connection negotiation or after ICE restart, UDP based
   candidates SHOULD be included and default candidate SHOULD be chosen
   from one of those UDP candidates.  The proto value MUST match the
   transport protocol associated with the default candidate.  If UDP
   transport is used for the default candidate, then 'UDP/TLS/BFCP'
   proto value MUST be used.  If TCP transport is used for the default
   candidate, then 'TCP/DTLS/BFCP' proto value MUST be used.  Note that




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   under normal circumstances the proto value for offers and answers
   sent during ICE nomination SHOULD be 'UDP/TLS/BFCP'.

   When a subsequent SDP offer or answer is sent after ICE nomination is
   complete and does not initiate ICE restart, it will contain only the
   currently negotiated ICE candidate pair.  In this case, the proto
   value MUST match the transport protocol associated with the currently
   negotiated ICE candidate pair.  If UDP transport is used for the
   currently negotiated pair, then 'UDP/TLS/BFCP' proto value MUST be
   used.  If TCP transport is used for the currently negotiated pair,
   then 'TCP/DTLS/BFCP' proto value MUST be used.  Please note that if
   an endpoint switches between TCP-based and UDP-based candidates
   during the nomination process the endpoint is not required to send an
   SDP offer for the sole purpose of keeping the proto value of the
   associated 'm' line in sync.

      Note: The text in the paragraph above only applies when the usage
      of ICE has been negotiated.  If ICE is not used, the proto value
      MUST always reflect the transport protocol used at any given time.

      Note: Using ICE with protocols other then UDP/TLS/BFCP and
      TCP/DTLS/BFCP is outside of scope for this specification.

11.  SDP Offer/Answer Procedures

   This section defines the SDP offer/answer [4] procedures for
   negotiating and establishing a BFCP connection.  The generic
   procedures for DTLS are defined in [16], the specific BFCP parts are
   specified here.

   If the 'm' line 'proto' value is 'TCP/TLS/BFCP', 'TCP/DTLS/BFCP' or
   'UDP/TLS/BFCP', each endpoint MUST provide a certificate fingerprint,
   using the SDP 'fingerprint' attribute [7], if the endpoint supports,
   and is willing to use, a cipher suite with an associated certificate.

   The authentication certificates are interpreted and validated as
   defined in [10].  Self-signed certificates can be used securely,
   provided that the integrity of the SDP description is assured as
   defined in [10].

      Note: The procedures apply to a specific 'm' line describing a
      BFCP connection.  If an offer or answer contains multiple 'm'
      lines describing BFCP connections, the procedures are applied
      separately to each 'm' line.

      Informational note: The use of source-specific parameters in SDP,
      as defined in [19], is not applicable to BFCP.




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   Multiplexing of BFCP 'm' lines, as defined in BUNDLE [20], is not
   defined by this specification and MUST NOT be included in a BUNDLE
   group.  An analysis of the SDP attributes defined in [18], with
   regards to multiplexing of 'm' lines, is presented in Section 5.27 of
   [21].  The analysis for the 'bfcpver' SDP attribute, defined in this
   document is provided in Table 2.

        +---------+------------------------+-------+--------------+
        | Name    | Notes                  | Level | Mux Category |
        +---------+------------------------+-------+--------------+
        | bfcpver | Needs further analysis | M     | TBD          |
        +---------+------------------------+-------+--------------+

                 Table 2: Multiplexing Attribute Analysis

11.1.  Generating the Initial SDP Offer

   When the offerer creates an initial offer, the offerer:

   o  MUST, if the 'm' line proto value is 'TCP/BFCP', 'TCP/TLS/BFCP',
      'TCP/DTLS/TCP' or 'UDP/TLS/BFCP', associate an SDP setup
      attribute, with an 'actpass' value, with the 'm' line;

   o  MUST, if the 'm' line proto value is 'TCP/BFCP', 'TCP/TLS/BFCP' or
      'TCP/DTLS/BFCP', associate an SDP 'connection' attribute, with a
      'new' value, with the 'm' line; and

   In addition, if the offerer acts as the floor control server, the
   offerer:

   o  SHOULD associate an SDP 'floorctrl' attribute defined in
      Section 4.1, with the 'm' line;

   o  MUST associate an SDP 'confid' attribute defined in Section 5,
      with the 'm' line;

   o  MUST associate an SDP 'userid' attribute defined in Section 5,
      with the 'm' line;

   o  MUST associate an SDP 'floorid' attribute defined in Section 6,
      with the 'm' line;

   o  MUST associate an SDP 'label' attribute as described in Section 6,
      with the 'm' line; and

   o  SHOULD, if it supports only the RFC 4583 subset and MUST, if it
      supports RFC XXXX associate an SDP 'bfcpver' attribute defined in
      Section 7, with the 'm' line.



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11.2.  Generating the SDP Answer

   When the answerer receives an offer, which contains an 'm' line
   describing a BFCP connection, if the answerer accepts the 'm' line
   it:

   o  MUST insert a corresponding 'm' line in the answer, with an
      identical 'm' line proto value [4]; and

   o  MUST, if the 'm' line proto value is 'TCP/BFCP', 'TCP/DTLS/BFCP',
      'TCP/TLS/BFCP' or 'UDP/TLS/BFCP', associate an SDP setup
      attribute, with an 'active' or 'passive' value, with the 'm' line;

   In addition, if the answerer acts as the floor control server, the
   answerer:

   o  MUST, if the offer contains a 'floorctrl' attribute or else it
      SHOULD associate an SDP 'floorctrl' attribute defined in
      Section 4.1, with the 'm' line;

   o  MUST associate an SDP 'confid' attribute defined in Section 5,
      with the 'm' line;

   o  MUST associate an SDP 'userid' attribute defined in Section 5,
      with the 'm' line;

   o  MUST associate an SDP 'floorid' attribute defined in Section 6,
      with the 'm' line; and

   o  MUST associate an SDP 'label' attribute as described in Section 6,
      with the 'm' line.

   o  SHOULD, if it supports only the RFC 4583 subset and MUST, if it
      supports RFC XXXX associate an SDP 'bfcpver' attribute defined in
      Section 7, with the 'm' line.

   Once the answerer has sent the answer, the answerer:

   o  MUST, if the answerer is the 'active' endpoint, and if a TCP
      connection associated with the 'm' line is to be established (or
      re-established), initiate the establishing of the TCP connection;
      and

   o  MUST, if the answerer is the 'active' endpoint, and if an TLS/DTLS
      connection associated with the 'm' line is to be established (or
      re-established), initiate the establishing of the TLS/DTLS
      connection (by sending a ClientHello message).




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   If the answerer does not accept the 'm' line in the offer, it MUST
   assign a zero port value to the corresponding 'm' line in the answer.
   In addition, the answerer MUST NOT establish a TCP connection or a
   TLS/DTLS connection associated with the 'm' line.

11.3.  Offerer Processing of the SDP Answer

   When the offerer receives an answer, which contains an 'm' line with
   a non-zero port value, describing a BFCP connection, the offerer:

   o  MUST, if the offer is the 'active' endpoint, and if a TCP
      connection associated with the 'm' line is to be established (or
      re-established), initiate the establishing of the TCP connection;
      and

   o  MUST, if the offerer is the 'active' endpoint, and if an TLS/DTLS
      connection associated with the 'm' line is to be established (or
      re-established), initiate the establishing of the TLS/DTLS
      connection (by sending a ClientHello message).

   If the 'm' line in the answer contains a zero port value, the offerer
   MUST NOT establish a TCP connection or a TLS/DTLS connection
   associated with the 'm' line.

11.4.  Modifying the Session

   When an offerer sends an updated offer, in order to modify a
   previously established BFCP connection, it follows the procedures in
   Section 11.1, with the following exceptions:

   o  If the BFCP connection is carried on top of TCP, and unless the
      offerer wants to re-establish an existing TCP connection, the
      offerer MUST associate an SDP connection attribute, with an
      'existing' value, with the 'm' line; and

   o  If the offerer wants to disable a previously established BFCP
      connection, it MUST assign a zero port value to the 'm' line
      associated with the BFCP connection, following the procedures in
      [4].

12.  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.



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   m=application 50000 TCP/TLS/BFCP *
   a=setup:passive
   a=connection:new
   a=fingerprint:sha-256 \
        19:E2:1C:3B:4B:9F:81:E6:B8:5C:F4:A5:A8:D8:73:04: \
        BB:05:2F:70:9F:04:A9:0E:05:E9:26:33:E8:70:88:A2
   a=floorctrl:s-only
   a=confid:4321
   a=userid:1234
   a=floorid:1 mstrm:10
   a=floorid:2 mstrm:11
   a=bfcpver:1
   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-256 \
        6B:8B:F0:65:5F:78:E2:51:3B:AC:6F:F3:3F:46:1B:35: \
        DC:B8:5F:64:1A:24:C2:43:F0:A1:58:D0:A1:2C:19:08
   a=floorctrl:c-only
   a=bfcpver:1
   m=audio 55000 RTP/AVP 0
   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.













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   m=application 50000 UDP/TLS/BFCP *
   a=setup:actpass
   a=dtls-id:abc3dl
   a=fingerprint:sha-256 \
        19:E2:1C:3B:4B:9F:81:E6:B8:5C:F4:A5:A8:D8:73:04: \
        BB:05:2F:70:9F:04:A9:0E:05:E9:26:33:E8:70:88:A2
   a=floorctrl:c-only s-only
   a=confid:4321
   a=userid:1234
   a=floorid:1 mstrm:10
   a=floorid:2 mstrm:11
   a=bfcpver:2
   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=dtls-id:abc3dl
   a=fingerprint:sha-256 \
        6B:8B:F0:65:5F:78:E2:51:3B:AC:6F:F3:3F:46:1B:35: \
        DC:B8:5F:64:1A:24:C2:43:F0:A1:58:D0:A1:2C:19:08
   a=floorctrl:s-only
   a=confid:4321
   a=userid:1234
   a=floorid:1 mstrm:10
   a=floorid:2 mstrm:11
   a=bfcpver:2
   m=audio 55002 RTP/AVP 0
   m=video 55004 RTP/AVP 31

13.  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 [16].  The requirements for the
   offer/answer exchange, as listed in Section 5 of [16], MUST be
   followed.

   An initial integrity-protected channel is REQUIRED for BFCP to
   exchange self-signed certificates between a client and the floor




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   control server.  For session descriptions carried in SIP [3], S/MIME
   [6] is the natural choice to provide such a channel.

14.  IANA Considerations

      [Editorial note: The changes in Section 14.1 instruct the IANA to
      register the three new values TCP/DTLS/BFCP, UDP/BFCP and UDP/TLS/
      BFCP for the SDP 'proto' field.  The new section Section 14.6
      registers a new SDP "bfcpver" attribute.  The rest is unchanged
      from [17].]

14.1.  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/DTLS/BFCP | [RFC XXXX] |
                      | TCP/TLS/BFCP  | [RFC XXXX] |
                      | UDP/BFCP      | [RFC XXXX] |
                      | UDP/TLS/BFCP  | [RFC XXXX] |
                      +---------------+------------+

                 Table 3: Values for the SDP 'proto' field

14.2.  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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14.3.  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

14.4.  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

14.5.  Registration of the SDP 'floorid' 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:             floorid



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   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

14.6.  Registration of the SDP 'bfcpver' 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:             bfcpver

   Long-form attribute name:   BFCP Version

   Type of attribute:          Media level

   Subject to charset:         No

   Purpose of attribute:       The 'bfcpver' attribute lists supported
      BFCP versions.

   Allowed attribute values:   Tokens

15.  Changes from RFC 4583

   Following is the list of technical changes and other fixes from [18].

   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:

   1.  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 proto field values
       TCP/DTLS/BFCP, UDP/BFCP and UDP/TLS/BFCP added.

   2.  Authentication (Section 9):
       In last paragraph, made clear that a TCP connection was
       described.




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   3.  Security Considerations (Section 13):
       For the DTLS over UDP case, mention existing considerations and
       requirements for the offer/answer exchange in [16].

   4.  Registration of SDP 'proto' Values (Section 14.1):
       Register the three new values TCP/DTLS/BFCP, UDP/BFCP and
       UDP/TLS/BFCP in the SDP parameters registry.

   5.  BFCP Version Negotiation (Section 7):
       A new 'bfcpver' SDP media-level attribute is added in order to
       signal supported version number.

   Clarification and bug fixes:

   1.  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.

   2.  Fix typo in example (Section 12):
       Do not use 'm-stream' in the SDP example, use the correct 'mstrm'
       as specified in Section 12.  Recommend interpreting 'm-stream' if
       it is received, since it is present in some implementations.

   3.  Assorted clarifications (Across the document):
       Language clarifications as a result of reviews.  Also, the
       normative language where tightened where appropriate, i.e.
       changed from SHOULD strength to MUST in a number of places.

16.  Acknowledgements

   Joerg Ott, Keith Drage, Alan Johnston, Eric Rescorla, Roni Even, and
   Oscar Novo provided useful ideas for the original [18].  The authors
   also acknowledge contributions to the revision of BFCP for use over
   an unreliable transport from Geir Arne Sandbakken, Charles Eckel,
   Alan Ford, Eoin McLeod and Mark Thompson.  Useful and important final
   reviews were done by Ali C.  Begen, Mary Barnes and Charles Eckel.
   In the final stages, Roman Shpount made a considerable effort in
   adding proper ICE support and considerations.

17.  References

17.1.  Normative References

   [1]        Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.



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   [2]        Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <http://www.rfc-editor.org/info/rfc5234>.

   [3]        Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              DOI 10.17487/RFC3261, June 2002,
              <http://www.rfc-editor.org/info/rfc3261>.

   [4]        Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
              with Session Description Protocol (SDP)", RFC 3264,
              DOI 10.17487/RFC3264, June 2002,
              <http://www.rfc-editor.org/info/rfc3264>.

   [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, DOI 10.17487/RFC5280, May 2008,
              <http://www.rfc-editor.org/info/rfc5280>.

   [6]        Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
              Mail Extensions (S/MIME) Version 3.2 Certificate
              Handling", RFC 5750, DOI 10.17487/RFC5750, January 2010,
              <http://www.rfc-editor.org/info/rfc5750>.

   [7]        Yon, D. and G. Camarillo, "TCP-Based Media Transport in
              the Session Description Protocol (SDP)", RFC 4145,
              DOI 10.17487/RFC4145, September 2005,
              <http://www.rfc-editor.org/info/rfc4145>.

   [8]        Camarillo, G., Drage, K., Kristensen, T., Ott, J., and C.
              Eckel, "The Binary Floor Control Protocol (BFCP)", draft-
              ietf-bfcpbis-rfc4582bis-16 (work in progress), November
              2015.

   [9]        Levin, O. and G. Camarillo, "The Session Description
              Protocol (SDP) Label Attribute", RFC 4574,
              DOI 10.17487/RFC4574, August 2006,
              <http://www.rfc-editor.org/info/rfc4574>.

   [10]       Lennox, J. and C. Holmberg, "Connection-Oriented Media
              Transport over the Transport Layer Security (TLS) Protocol
              in the Session Description Protocol (SDP)", RFC 8122,
              DOI 10.17487/RFC8122, March 2017,
              <http://www.rfc-editor.org/info/rfc8122>.




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   [11]       Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, DOI 10.17487/RFC4566,
              July 2006, <http://www.rfc-editor.org/info/rfc4566>.

   [12]       Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
              January 2012, <http://www.rfc-editor.org/info/rfc6347>.

   [13]       Lazzaro, J., "Framing Real-time Transport Protocol (RTP)
              and RTP Control Protocol (RTCP) Packets over Connection-
              Oriented Transport", RFC 4571, DOI 10.17487/RFC4571, July
              2006, <http://www.rfc-editor.org/info/rfc4571>.

   [14]       Rosenberg, J., "Interactive Connectivity Establishment
              (ICE): A Protocol for Network Address Translator (NAT)
              Traversal for Offer/Answer Protocols", RFC 5245,
              DOI 10.17487/RFC5245, April 2010,
              <http://www.rfc-editor.org/info/rfc5245>.

   [15]       Rosenberg, J., Keranen, A., Lowekamp, B., and A. Roach,
              "TCP Candidates with Interactive Connectivity
              Establishment (ICE)", RFC 6544, DOI 10.17487/RFC6544,
              March 2012, <http://www.rfc-editor.org/info/rfc6544>.

   [16]       Holmberg, C. and R. Shpount, "Using the SDP Offer/Answer
              Mechanism for DTLS", draft-ietf-mmusic-dtls-sdp-26 (work
              in progress), June 2017.

   [17]       Camarillo, G., Ott, J., and K. Drage, "The Binary Floor
              Control Protocol (BFCP)", RFC 4582, DOI 10.17487/RFC4582,
              November 2006, <http://www.rfc-editor.org/info/rfc4582>.

   [18]       Camarillo, G., "Session Description Protocol (SDP) Format
              for Binary Floor Control Protocol (BFCP) Streams",
              RFC 4583, DOI 10.17487/RFC4583, November 2006,
              <http://www.rfc-editor.org/info/rfc4583>.

17.2.  Informational References

   [19]       Lennox, J., Ott, J., and T. Schierl, "Source-Specific
              Media Attributes in the Session Description Protocol
              (SDP)", RFC 5576, DOI 10.17487/RFC5576, June 2009,
              <http://www.rfc-editor.org/info/rfc5576>.

   [20]       Holmberg, C., Alvestrand, H., and C. Jennings,
              "Negotiating Media Multiplexing Using the Session
              Description Protocol (SDP)", draft-ietf-mmusic-sdp-bundle-
              negotiation-38 (work in progress), April 2017.



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   [21]       Nandakumar, S., "A Framework for SDP Attributes when
              Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-16
              (work in progress), December 2016.

Authors' Addresses

   Gonzalo Camarillo
   Ericsson
   Hirsalantie 11
   FI-02420 Jorvas
   Finland

   Email: Gonzalo.Camarillo@ericsson.com


   Tom Kristensen
   Cisco
   Philip Pedersens vei 1
   NO-1366 Lysaker
   Norway

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


   Paul E. Jones
   Cisco
   7025 Kit Creek Rd.
   Research Triangle Park, NC 27709
   USA

   Email: paulej@packetizer.com




















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