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Versions: (draft-sandbakken-dispatch-bfcp-udp) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 Draft is active
In: MissingRef
BFCPbis Working Group                                 T. Kristensen, Ed.
Internet-Draft                                                  C. Eckel
Intended status: Standards Track                            A. Heggestad
Expires: July 27, 2012                                       M. Thompson
                                                           G. Sandbakken
                                                               E. McLeod
                                                                   Cisco
                                                        January 24, 2012


  Revision of the Binary Floor Control Protocol (BFCP) for use over an
                          unreliable transport
                    draft-ietf-bfcpbis-rfc4582bis-00

Abstract

   This draft describes how to extend the Binary Floor Control Protocol
   (BFCP) for use over an unreliable transport.  It details the
   differences from the BFCP protocol definition document and the
   Session Description Protocol (SDP) format specified for BFCP streams.

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 July 27, 2012.

Copyright Notice

   Copyright (c) 2012 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
   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 . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Motivation . . . . . . . . . . . . . . . . . . . . . . . . . .  4
     3.1.  Alternatives Considered  . . . . . . . . . . . . . . . . .  6
       3.1.1.  ICE TCP  . . . . . . . . . . . . . . . . . . . . . . .  6
       3.1.2.  Teredo . . . . . . . . . . . . . . . . . . . . . . . .  6
       3.1.3.  GUT  . . . . . . . . . . . . . . . . . . . . . . . . .  7
       3.1.4.  UPnP IGD . . . . . . . . . . . . . . . . . . . . . . .  7
       3.1.5.  NAT PMP  . . . . . . . . . . . . . . . . . . . . . . .  7
   4.  Difference from RFC4582  . . . . . . . . . . . . . . . . . . .  8
     4.1.  Overview of Operation (4)  . . . . . . . . . . . . . . . .  8
       4.1.1.  Floor Participant to Floor Control Server
               Interface (4.1)  . . . . . . . . . . . . . . . . . . .  8
     4.2.  COMMON-HEADER Format (5.1) . . . . . . . . . . . . . . . .  8
     4.3.  ERROR-CODE (5.2.6) . . . . . . . . . . . . . . . . . . . . 10
     4.4.  FloorRequestStatusAck (5.3.14) . . . . . . . . . . . . . . 10
     4.5.  ErrorAck (5.3.15)  . . . . . . . . . . . . . . . . . . . . 11
     4.6.  FloorStatusAck (5.3.16)  . . . . . . . . . . . . . . . . . 11
     4.7.  Goodbye (5.3.17) . . . . . . . . . . . . . . . . . . . . . 11
     4.8.  GoodbyeAck (5.3.18)  . . . . . . . . . . . . . . . . . . . 12
     4.9.  Transport (6)  . . . . . . . . . . . . . . . . . . . . . . 12
       4.9.1.  Reliable Transport (6.1) . . . . . . . . . . . . . . . 12
       4.9.2.  Unreliable Transport (6.2) . . . . . . . . . . . . . . 13
         4.9.2.1.  Congestion Control . . . . . . . . . . . . . . . . 15
         4.9.2.2.  ICMP Error Handling  . . . . . . . . . . . . . . . 15
       4.9.3.  Large Message Considerations . . . . . . . . . . . . . 15
     4.10. Lower-Layer Security (7) . . . . . . . . . . . . . . . . . 16
     4.11. Protocol Transactions (8)  . . . . . . . . . . . . . . . . 17
     4.12. Server Behavior (8.2)  . . . . . . . . . . . . . . . . . . 17
     4.13. Timers (8.3) . . . . . . . . . . . . . . . . . . . . . . . 17
     4.14. Request Retransmission Timer, T1 (8.3.1) . . . . . . . . . 17
     4.15. Response Retransmission Timer, T2 (8.3.2)  . . . . . . . . 18
     4.16. Timer Values (8.3.3) . . . . . . . . . . . . . . . . . . . 18
     4.17. Authentication and Authorization (9) . . . . . . . . . . . 18
       4.17.1. TLS Based Mutual Authentication (9.1)  . . . . . . . . 19
     4.18. Receiving a Response [to a FloorRequest Message]
           (10.1.2) . . . . . . . . . . . . . . . . . . . . . . . . . 19
     4.19. Receiving a Response [to a FloorRelease Message]
           (10.2.2) . . . . . . . . . . . . . . . . . . . . . . . . . 19
     4.20. Receiving a Response [to a ChairAction Message] (11.2) . . 19



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     4.21. Receiving a Response [to a FloorQuery Message] (12.1.2)  . 19
     4.22. Receiving a Response [to a FloorRequestQuery Message]
           (12.2.2) . . . . . . . . . . . . . . . . . . . . . . . . . 19
     4.23. Receiving a Response [to a UserQuery Message] (12.3.2) . . 20
     4.24. Receiving a Response [to a Hello Message] (12.4.2) . . . . 20
     4.25. Reception of a FloorRequestStatus Message (13.1.3) . . . . 20
     4.26. Reception of a FloorStatus Message (13.5.3)  . . . . . . . 20
     4.27. Reception of an Error Message (13.8.1) . . . . . . . . . . 20
     4.28. Security Considerations (14) . . . . . . . . . . . . . . . 21
     4.29. IANA Considerations - Primitive Subregistry (15.2) . . . . 21
     4.30. IANA Considerations - Error Code Subregistry (15.4)  . . . 21
     4.31. Example Call Flows for BFCP over Unreliable Transport
           (Appendix A) . . . . . . . . . . . . . . . . . . . . . . . 21
   5.  Revision of RFC4583  . . . . . . . . . . . . . . . . . . . . . 25
     5.1.  Fields in the 'm' Line (3) . . . . . . . . . . . . . . . . 25
     5.2.  Authentication (8) . . . . . . . . . . . . . . . . . . . . 25
     5.3.  Security Considerations (10) . . . . . . . . . . . . . . . 26
     5.4.  Registration of SDP 'proto' Values (11.1)  . . . . . . . . 26
   6.  NAT Traversal  . . . . . . . . . . . . . . . . . . . . . . . . 26
   7.  Future Work  . . . . . . . . . . . . . . . . . . . . . . . . . 26
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 27
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 27
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 27
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 28
   Appendix A.  Change History  . . . . . . . . . . . . . . . . . . . 29
     A.1.  draft-sandbakken-dispatch-bfcp-udp-03 to
           draft-ietf-bfcpbis-rfc4582bis-00 . . . . . . . . . . . . . 29
     A.2.  draft-sandbakken-dispatch-bfcp-udp-02 to -03 . . . . . . . 30
     A.3.  draft-sandbakken-dispatch-bfcp-udp-01 to -02 . . . . . . . 30
     A.4.  draft-sandbakken-dispatch-bfcp-udp-00 to -01 . . . . . . . 30
     A.5.  draft-sandbakken-xcon-bfcp-udp-02 to
           draft-sandbakken-dispatch-bfcp-udp-00  . . . . . . . . . . 31
     A.6.  draft-sandbakken-xcon-bfcp-udp-01 to -02 . . . . . . . . . 31
     A.7.  draft-sandbakken-xcon-bfcp-udp-00 to -01 . . . . . . . . . 32
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 32
















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1.  Introduction

   This draft describes how to extend the BFCP protocol to support
   unreliable transport.  Minor changes to the transaction model are
   introduced in that all requests now have an appropriate response to
   complete the transaction.  The requests are sent with a retransmit
   timer associated with the response to achieve reliability.

   This extension does not change the semantics of BFCP.  It permits UDP
   as an alternate transport.  Existing implementations, in the spirit
   of the approach detailed in earlier versions of this draft (see
   Appendix A), have demonstrated the approach to be feasible.  Initial
   compatibility among implementations has been achieved at previous
   interoperability events.  The purpose of this draft is to formalize
   and publish the extension from the standard specification to
   facilitate complete interoperability between implementations.

   The content of this draft relates to the BFCP protocol specification
   [RFC4582] and the SDP format for describing BFCP streams [RFC4583].
   This draft is written with the goal of identifying the extensions
   associated with adding support for UDP as an alternate transport to
   an existing BFCP implementation.


2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].


3.  Motivation

   In existing video conferencing deployments, BFCP is used to manage
   the floor for the content sharing associated with the conference.
   For peer to peer scenarios, including business to business
   conferences and point to point conferences in general, it is
   frequently the case that one or both endpoints exists behind a NAT/
   firewall.  BFCP roles are negotiated in the offer/answer exchange as
   specified in [RFC4583], resulting in one endpoint being responsible
   for opening the TCP connection used for the BFCP communication.










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                                +---------+
                                | Network |
                                +---------+
                         +-----+ /       \ +-----+
                         | NAT |/         \| NAT |
                         +-----+           +-----+
                   +----+ /                     \ +----+
                   |BFCP|/                       \|BFCP|
                   | UA |                         | UA |
                   +----+                         +----+

                            Figure 1: Use Case

   The communication session between the video conferencing endpoints
   typically consists of a number of RTP over UDP media streams, for
   audio and video, and a BFCP connection for floor control.  Existing
   deployments are most common in, but not limited to, enterprise
   networks.  In existing deployments, NAT/firewall traversal for the
   RTP streams works using ICE and/or other methods, including those
   described in [I-D.ietf-mmusic-media-path-middleboxes].

   When enhancing an existing SIP based video conferencing deployment
   with support for content sharing, the BFCP connection often poses a
   problem.  The reasons for this fall into two general classes.  First,
   there may be a strong preference for UDP based signaling in general.
   On high capacity endpoints (e.g.  PSTN gateways or SIP/H.323
   interworking gateways), TCP can suffer from head of line blocking,
   and it uses many kernel buffers.  Network operators view UDP as a way
   to avoid both of these.  Second, establishment and traversal of the
   TCP connection involving ephemeral ports, as is typically the case
   with BFCP over TCP, can be problematic, as described in Appendix A of
   [I-D.ietf-mmusic-ice-tcp].  A broad study of NAT behavior and peer-
   to-peer TCP establishment for a comprehensive set of TCP NAT
   traversal techniques over a wide range of commercial NAT products
   concluded it was not possible to establish a TCP connection in 11% of
   the cases [IMC05].  The results are worse when focusing on enterprise
   NATs.  A study of hole punching as a NAT traversal technique across a
   wide variety of deployed NATs reported consistently higher success
   rates when using UDP than when using TCP [P2PNAT].

   To overcome the problems with establishing TCP flows between BFCP
   entities, this draft defines UDP as an alternate transport for BFCP,
   leveraging the same mechanisms in place for the RTP over UDP media
   streams for the BFCP communication.  When using UDP as the transport,
   it is RECOMMENDED to follow the guidelines provided in [RFC5405].
   NAT traversal for BFCP over UDP entities is discussed in more detail
   in Section 6.




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   The authors view this extension as an admittedly non-ideal, but
   pragmatic, solution to an existing deployment challenge.

3.1.  Alternatives Considered

   In selecting the approach of defining UDP as an alternate transport
   for BFCP, several alternatives were considered and explored to some
   degree.  Each of these is discussed briefly in the following
   subsections.  In summary, while these alternatives work in a number
   of scenarios, they are not sufficient, in and of themselves, to
   address the use case targeted by this draft.

3.1.1.  ICE TCP

   ICE TCP [I-D.ietf-mmusic-ice-tcp] extends ICE to TCP based media,
   including the ability to offer a mix of TCP and UDP based candidates
   for a single stream.  ICE TCP has, in general, a lower success
   probability for enabling TCP connectivity without a relay if both of
   the hosts are behind a NAT (see Appendix A of
   [I-D.ietf-mmusic-ice-tcp]) than enabling UDP connectivity in the same
   scenarios.  The happens because many of the currently deployed NATs
   in video conferencing networks do not support the flow of TCP hand
   shake packets seen in case of TCP simultaneous-open, either because
   they do not allow incoming TCP SYN packets from an address to which a
   SYN packet has been sent to recently, or because they do not properly
   process the subsequent SYNACK.  Implementing various techniques
   advocated for candidate collection in [I-D.ietf-mmusic-ice-tcp]
   should increase the success probability, but many of these techniques
   require support from some network elements (e.g., from the NATs).
   Such support is not common in enterprise firewalls and NATs.

3.1.2.  Teredo

   Teredo [RFC4380] enables nodes located behind one or more IPv4 NATs
   to obtain IPv6 connectivity by tunneling packets over UDP.  Teredo
   extensions [RFC6081] provide additional capabilities to Teredo,
   including support for more types of NATs and support for more
   efficient communication.

   As defined, Teredo could be used to make BFCP work for the video
   conferencing use cases addressed in this draft.  However, running the
   service requires the help of "Teredo servers" and "Teredo relays"
   [RFC4380].  These servers and relays generally do not exist in the
   existing video conferencing deployments.  It also requires IPv6
   awareness on the endpoints.  It should also be noted that ICMP6, as
   used with Teredo to complete an initial protocol exchange and confirm
   that the appropriate NAT bindings have been set up, is not a
   conventional feature of IPv4 or even IPv6, and some currently



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   deployed IPv6 firewalls discard ICMP messages.  As these networks
   continue to evolve and tackle the transaction to IPv6, Teredo servers
   and relays may be deployed, making Teredo available as a suitable
   alternative to BFCP over UDP.

3.1.3.  GUT

   GUT [I-D.manner-tsvwg-gut] attempts to facilitate tunneling over UDP
   by encapsulating the native transport protocol and its payload (in
   general the whole IP payload) within a UDP packet destined to the
   well-known port GUT_P. Unfortunately, it requires user-space TCP, for
   which there is not a readily available implementation, and creating
   one is a large project in itself.  This draft has expired and its
   future is still not clear as it has not yet been adopted by a working
   group.

3.1.4.  UPnP IGD

   Universal Plug and Play Internet Gateway Devices (UPnP IGD) sit on
   the edge of the network, providing connectivity to the Internet for
   computers internal to the LAN, but do not allow Internet devices to
   connect to computers on the internal LAN.  IGDs enable a computer on
   an internal LAN to create port mappings on their NAT, through which
   hosts on the Internet can send data that will be forwarded to the
   computer on the internal LAN.  IGDs may be self-contained hardware
   devices or may be software components provided within an operating
   system.

   In considering UPnP IGD, several issues exist.  Not all NATs support
   UPnP, and many that do support it are configured with it turned off
   by default.  NATs are often multilayered, and UPnP does not work well
   with such NATs.  For example, a typical DSL modems acts as a NAT, and
   the user plugs in a wireless access point behind that, which adds
   another layer NAT.  The client can discover the first layer of NAT
   using multicast but it is harder to figure out how to discover and
   control NATs in the next layer up.

3.1.5.  NAT PMP

   The NAT Port Mapping Protocol (NAT PMP) allows a computer in a
   private network (behind a NAT router) to automatically configure the
   router to allow parties outside the private network to contact it.
   NAT PMP runs over UDP.  It essentially automates the process of port
   forwarding.  Included in the protocol is a method for retrieving the
   public IP address of a NAT gateway, thus allowing a client to make
   this public IP address and port number known to peers that may wish
   to communicate with it.




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   Many NATs do not support PMP.  In those that do support it, it has
   similar issues with negotiation of multilayer NATs as UPnP.  Video
   conferencing is used extensively in enterprise networks, and NAT PMP
   is not generally available in enterprise-class routers.


4.  Difference from RFC4582

   This section details the difference from [RFC4582], the base protocol
   specification of BFCP, required for use over an unreliable transport.
   The section numbers to which differences apply are indicated in
   parentheses in the titles of the sub-sections below.

4.1.  Overview of Operation (4)

   Fourth paragraph change:

      There are two types of transaction in BFCP: client-initiated
      transactions and server-initiated transactions.  Client-initiated
      transactions consist of a message from a client to the floor
      control server and a response from the floor control server to the
      client.  Correspondingly, server-initiated transactions consist of
      a message from the floor control server to a client and the
      associated acknowledgement message from the client to the floor
      control server.  Both messages can be related because they carry
      the same Transaction ID value in their common headers.

4.1.1.  Floor Participant to Floor Control Server Interface (4.1)

   Before seventh paragraph (page 9), insert:

      Figures 2 and 3 below show call flows for two sample BFCP
      interactions when used over reliable transport.  Appendix A
      (Editorial Note: here-in Section 4.31) shows the same sample
      interactions but over an unreliable transport.

4.2.  COMMON-HEADER Format (5.1)

   The figure below should replace Figure 5: COMMON-HEADER format.












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     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Ver |I|  Res  |  Primitive    |        Payload Length         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         Conference ID                         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |         Transaction ID        |            User ID            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 2: COMMON-HEADER format

   The following text precedes "Reserved" on page 15:

      I: The Transaction Initiator (I) flag-bit has relevance only for
      use of BFCP over unreliable transport.  When clear, it indicates
      that this message is a request initiating a new transaction, and
      the Transaction ID that follows has been generated for this
      transaction.  When set, it indicates that this message is a
      response to a previous request, and the Transaction ID that
      follows is the one associated with that request.  When BFCP is
      used over reliable transports, the flag has no significance and
      SHOULD be cleared.

   The Reserved field changes name to Res due to limited space in the
   ASCII graphic in Figure 2.  In the description of the Reserved field
   "the 5 bits" is changed to "the 4 bits".

   The description of Transaction ID should have the final clause
   deleted with the reference to Section 8 remaining.  The value used
   for server-initiated transactions MUST be non-zero when BFCP is used
   over unreliable transports, and this qualification shall be described
   in the updated Section 8.

   The values below should be appended to the end of Table 1: BFCP
   primitives.















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          +-------+-----------------------+--------------------+
          | Value | Primitive             | Direction          |
          +-------+-----------------------+--------------------+
          |   14  | FloorRequestStatusAck | P -> S ; Ch -> S   |
          |   15  | ErrorAck              | P -> S ; Ch -> S   |
          |   16  | FloorStatusAck        | P -> S ; Ch -> S   |
          |   17  | Goodbye               | P -> S ; Ch -> S ; |
          |       |                       | P <- S ; Ch <- S   |
          |   18  | GoodbyeAck            | P -> S ; Ch -> S ; |
          |       |                       | P <- S ; Ch <- S   |
          +-------+-----------------------+--------------------+

                         Table 1: BFCP primitives

4.3.  ERROR-CODE (5.2.6)

   The value below should be appended to the end of Table 5: Error Code
   meaning.

                    +-------+-------------------------+
                    | Value | Meaning                 |
                    +-------+-------------------------+
                    |   10  | Unable to parse message |
                    |   11  | Use DTLS                |
                    +-------+-------------------------+

                        Table 2: Error Code meaning

4.4.  FloorRequestStatusAck (5.3.14)

   This new subsection specifies the normative ABNF for the new
   primitive, FloorRequestStatusAck.

      Floor participants and chairs acknowledge the receipt of a
      FloorRequestStatus message from the floor control server when
      communicating over unreliable transport.  The following is the
      format of the FloorRequestStatusAck message:



   FloorRequestStatusAck          =    (COMMON-HEADER)
                                      *[EXTENSION-ATTRIBUTE]

                    Figure 3: FloorRequestStatusAck format







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4.5.  ErrorAck (5.3.15)

   This new subsection specifies the normative ABNF for the new
   primitive, ErrorAck.

      Floor participants and chairs acknowledge the receipt of an Error
      message from the floor control server when communicating over
      unreliable transport.  The following is the format of the ErrorAck
      message:



   ErrorAck                       =    (COMMON-HEADER)
                                      *[EXTENSION-ATTRIBUTE]

                          Figure 4: ErrorAck format

4.6.  FloorStatusAck (5.3.16)

   This new subsection specifies the normative ABNF for the new
   primitive, FloorStatusAck.

      Floor participants and chairs acknowledge the receipt of a
      FloorStatus message from the floor control server when
      communicating over unreliable transport.  The following is the
      format of the FloorStatusAck message:



   FloorStatusAck                 =    (COMMON-HEADER)
                                      *[EXTENSION-ATTRIBUTE]

                       Figure 5: FloorStatusAck format

4.7.  Goodbye (5.3.17)

   This new subsection specifies the normative ABNF for the new
   primitive, Goodbye.

      BFCP entities that wish to dissociate themselves from their remote
      participant do so through the transmission of a Goodbye.  The
      following is the format of the Goodbye message:



   Goodbye                        =    (COMMON-HEADER)
                                      *[EXTENSION-ATTRIBUTE]




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                           Figure 6: Goodbye format

4.8.  GoodbyeAck (5.3.18)

   This new subsection specifies the normative ABNF for the new
   primitive, GoodbyeAck.

      BFCP entities communicating over an unreliable transport should
      acknowledge the receipt of a Goodbye message from a peer.  The
      following is the format of the GoodbyeAck message:



   GoodbyeAck                     =    (COMMON-HEADER)
                                      *[EXTENSION-ATTRIBUTE]

                         Figure 7: GoodbyeAck format

4.9.  Transport (6)

   An additional behavior is recommended for entities participating in
   communication over an unreliable transport that either wish to leave
   or are asked to leave an established BFCP connection, as detailed in
   the revised section introduction text below.

      The transport over which BFCP entities exchange messages depends
      on how clients obtain information to contact the floor control
      server (e.g. using an SDP offer/answer exchange [RFC4583]).  Two
      transports are supported: TCP, appropriate where entities can be
      sure that their connectivity is not impeded by NAT devices, media
      relays or firewalls; and UDP for those deployments where TCP may
      not be applicable or appropriate.

      If a client wishes to end its BFCP association with a floor
      control server, it is RECOMMENDED that the client send a Goodbye
      message to dissociate itself from any allocated resources.  If a
      floor control server wishes to end its BFCP association with a
      client (e.g. the Focus of the conference informs the floor control
      server that the client has been kicked out from the conference),
      it is RECOMMENDED that the floor control server send a Goodbye
      message towards the client.

4.9.1.  Reliable Transport (6.1)

   BFCP entities may elect to exchange BFCP messages using TCP
   connections.  TCP provides an in-order reliable delivery of a stream
   of bytes.  Consequently, message framing is implemented in the
   application layer.  BFCP implements application-layer framing using



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   TLV-encoded attributes.

   A client MUST NOT use more than one TCP connection to communicate
   with a given floor control server within a conference.  Nevertheless,
   if the same physical box handles different clients (e.g. a floor
   chair and a floor participant), which are identified by different
   User IDs, a separate connection per client is allowed.

   If a BFCP entity (a client or a floor control server) receives data
   that cannot be parsed, the entity MUST close the TCP connection, and
   the connection SHOULD be reestablished.  Similarly, if a TCP
   connection cannot deliver a BFCP message and times out, the TCP
   connection SHOULD be reestablished.

   The way connection reestablishment is handled depends on how the
   client obtains information to contact the floor control server.  Once
   the TCP connection is reestablished, the client MAY resend those
   messages for which it did not get a response from the floor control
   server.

   If a floor control server detects that the TCP connection towards one
   of the floor participants is lost, it is up to the local policy of
   the floor control server what to do with the pending floor requests
   of the floor participant.  In any case, it is RECOMMENDED that the
   floor control server keep the floor requests (i.e., that it does not
   cancel them) while the TCP connection is reestablished.

   To maintain backwards compatibility with older implementations of
   [RFC4583], BFCP entities MUST interpret the graceful close of their
   TCP connection from their associated participant as an implicit
   Goodbye message.

4.9.2.  Unreliable Transport (6.2)

   BFCP entities may elect to exchange BFCP messages using UDP
   datagrams.  UDP is an unreliable transport where neither delivery nor
   order is assured.  Each BFCP UDP datagram MUST contain exactly one
   BFCP message.  In the event the size of a BFCP message exceeds the
   MTU size, the BFCP message will be fragmented at the IP layer.
   Considerations related to fragmentation are covered in Section 4.9.3.
   The message format for exchange of BFCP in UDP datagrams is the same
   as for a TCP stream above.

   Clients MUST announce their presence to the floor control server by
   transmission of a Hello message.  This Hello message MUST be
   responded to with a HelloAck message and only upon receipt can the
   client consider the floor control service as present and available.




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   As described in Section 8, each request sent by a floor participant
   or chair shall form a client transaction that expects an
   acknowledgement message back from the floor control server within a
   retransmission window.  Concordantly, messages sent by the floor
   control server that are not transaction-completing (e.g.  FloorStatus
   announcements as part of a FloorQuery subscription) are server-
   initiated transactions that require acknowledgement messages from the
   floor participant and chair entities to which they were sent.

   If a BFCP entity receives data that cannot be parsed, the receiving
   participant MAY send an Error message with parameter value 10
   indicating receipt of a malformed message.  If the message can be
   parsed to the extent that it is able to discern that it was a
   response to an outstanding request transaction, the client MAY
   discard the message and await retransmission.  BFCP entities
   receiving an Error message with value 10 SHOULD acknowledge the error
   and act accordingly.

   Transaction ID values are non-sequential and entities are at liberty
   to select values at random.  Entities MUST only have at most one
   outstanding request transaction at any one time.  Implicit
   subscriptions, such as FloorRequest messages that have multiple
   responses as the floor control server processes intermediate states
   until Granted or Denied terminal states attained, can be
   characterized by a client-initiated request transaction whose
   acknowledgement is implied by the first FloorRequestStatus response
   from the floor control server.  The subsequent changes in state for
   the request are new transactions whose Transaction ID is determined
   by the floor control server and whose receipt by the client
   participant shall be acknowledged with a FloorRequestStatusAck
   message.  [Editorial note: would it be more straightforward to have
   all FloorRequestStatus messages acknowledged with a
   FloorRequestStatusAck message?]

   By restricting entities to having at most one pending transaction
   open, both the out-of-order receipt of messages as well as the
   possibility for congestion are mitigated.  Additional details
   regarding congestion control are provided in Section 4.9.2.1.  A
   server-initiated request (e.g. a FloorStatus with an update from the
   floor control server) received by a participant before the initial
   FloorRequestStatus message that closes the client-initiated
   transaction that was instigated by the FloorRequest MUST be treated
   as superseding the information conveyed in any delinquent response.
   As the floor control server cannot send a second update to the
   implicit floor status subscription until the first is acknowledged,
   ordinality is maintained.





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4.9.2.1.  Congestion Control

   BFCP may be characterized to generate "low data-volume" traffic, per
   the classification in [RFC5405].  Nevertheless is it necessary to
   ensure suitable and necessary congestion control mechanisms are used
   for BFCP over UDP.  As described in previous paragraph every entity -
   client or server - is only allowed to send one request at a time, and
   await the acknowledging response.  This way at most one datagram is
   sent per RTT given the message is not lost during transmission.  In
   case the message is lost, the request retransmission timer T1
   specified in Section 4.14 will fire and the message is retransmitted
   up to three times.  The default initial interval is set to 500ms and
   the interval is doubled after each retransmission attempt, this is
   identical to the specification of the T1 timer in SIP as described in
   Section 17.1.1.2 of [RFC3261].

4.9.2.2.  ICMP Error Handling

   If a BFCP entity receives an ICMP port unreachable message mid-
   conversation, the entity SHOULD treat the conversation as closed
   (e.g. an implicit Goodbye message from the peer) and behave
   accordingly.  The entity MAY attempt to re-establish the conversation
   afresh.  The new connection will appear as a wholly new floor
   participant, chair or floor control server with all state previously
   held about that participant lost.

   Note: This is because the peer entities cannot rely on IP and port
   tuple to uniquely identify the participant, nor would extending Hello
   to include an attribute that advertised what the entity previously
   was assigned as a User ID be acceptable due to session hijacking.

   In deployments where NAT appliances, firewalls or other such devices
   are present and affecting port reachability for each entity, one
   possibility is to utilize the peer connectivity checks, relay use and
   NAT pinhole maintenance mechanisms defined in ICE [RFC5245].

4.9.3.  Large Message Considerations

   Large messages become a concern when using BFCP if the overall size
   of a single BFCP message exceeds that representable within the 16-bit
   Payload Length field of the COMMON-HEADER.  When using UDP, there is
   the added concern that a single BFCP message can be fragmented at the
   IP layer if its overall size exceeds the MTU threshold of the
   network.

   The target use cases for BFCP via UDP typically involve relatively
   small BFCP messages.  Combining that with the goal of minimizing
   differences to the standard BFCP specification, BFCP entities SHOULD



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   ensure that their messages are smaller than the recommended MTU size
   of 1300 bytes when encoded to minimize the likelihood of
   fragmentation in route to their peer entity.

      Note: While outside the scope of this document, the definition of
      additional mechanisms to further address BFCP message
      fragmentation are welcome.  Potential mechanisms mentioned
      previously include:



         - a mechanism for splitting a single large message into
         additive messages.  The mechanism defined for RELOAD in section
         5.7 of [I-D.ietf-p2psip-base] has been identified as a good
         candidate.

         - an applicability statement on those BFCP messages and/or
         attributes deemed as inappropriate for use over transports
         where fragmentation is a concern.

         - a SIP event package to deliver information to the endpoints.

4.10.  Lower-Layer Security (7)

   Expand the section to mandate support for DTLS when transport over
   UDP is used such that it reads as follows:

      BFCP relies on lower-layer security mechanisms to provide replay
      and integrity protection and confidentiality.  BFCP floor control
      servers and clients (which include both floor participants and
      floor chairs) MUST support TLS for transport over TCP and MUST
      support DTLS for transport over UDP [RFC5246].  Any BFCP entity
      MAY support other security mechanisms.

      BFCP entities MUST support, at a minimum, the
      TLS_RSA_WITH_AES_128_CBC_SHA ciphersuite [RFC5246].

      Which party, the client or the floor control server, acts as the
      TLS/DTLS server depends on how the underlying TCP/DTLS connection
      is established.  For example, when the TCP/DTLS connection is
      established using an SDP offer/answer exchange [RFC4583], the
      answerer (which may be the client or the floor control server)
      always acts as the TLS/DTLS server.








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4.11.  Protocol Transactions (8)

   The final clause of the introduction to section 8 should be read as:

      Since they do not trigger any response, their Transaction ID is
      set to 0 when used over reliable transports, but must be non-zero
      and unique in the context of outstanding transactions over
      unreliable transports.

      When using BFCP over unreliable transports, all requests will use
      retransmit timer T1 (see Section 4.13) until the transaction is
      completed.

4.12.  Server Behavior (8.2)

   The final clause of this section should be read as:

      Server-initiated transactions MUST contain a Transaction ID equal
      to 0 when BFCP is used over reliable transports.  Over unreliable
      transport, the Transaction ID shall have the same properties as
      for client-initiated transactions: the server MUST set the
      Transaction ID value in the common header to a number that is
      different from 0 and that MUST NOT be reused in another message
      from the server until the appropriate response from the client is
      received for the transaction.  The server uses the Transaction ID
      value to match this message with the response from the floor
      participant or floor chair.

4.13.  Timers (8.3)

   New section:

      When BFCP entities are communicating over an unreliable transport,
      two retransmission timers are employed to help mitigate against
      loss of datagrams.  Retransmission and response caching are not
      required when BFCP entities communicate over reliable transports.

4.14.  Request Retransmission Timer, T1 (8.3.1)

   T1 is a timer that schedules retransmission of a request until an
   appropriate response is received or until the maximum number of
   retransmissions have occurred.  The timer doubles on each re-
   transmit, failing after three unacknowledged transmission attempts.

   If a valid response is not received for a client- or server-initiated
   transaction, the implementation MUST consider the BFCP association as
   failed.  Implementations SHOULD follow the reestablishment procedure
   described in section 6 (e.g. initiate a new offer/answer [RFC3264]



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   exchange).  Alternatively, they MAY continue without BFCP and
   therefore not be participant in any floor control actions.

4.15.  Response Retransmission Timer, T2 (8.3.2)

   T2 is a timer that, when fires, signals that the BFCP entity can
   release knowledge of the transaction against which it is running.  It
   is started upon the first transmission of the response to a request
   and is the only mechanism by which that response is released by the
   BFCP entity.  Any subsequent retransmissions of the same request can
   be responded to by replaying the cached response, whilst that value
   is retained until the timer has fired.

   T2 shall be set such that it encompasses all legal retransmissions
   per T1 plus a factor to accommodate network latency between BFCP
   entities.

4.16.  Timer Values (8.3.3)

   The table below defines the different timers required when BFCP
   entities communicate over an unreliable transport.

        +-------+--------------------------------------+---------+
        | Timer | Description                          | Value/s |
        +-------+--------------------------------------+---------+
        |   T1  | Initial request retransmission timer |   0.5s  |
        |   T2  | Response retransmission timer        |   10s   |
        +-------+--------------------------------------+---------+

                              Table 3: Timers

   The default value for T1 is 500 ms, this is an estimate of the RTT
   for completing the transaction.  T1 MAY be chosen larger, and this is
   RECOMMENDED if it is known in advance that the RTT is larger.
   Regardless of the value of T1, the exponential backoffs on
   retransmissions described in Section 4.14 MUST be used.

4.17.  Authentication and Authorization (9)

   The first sentence of the second paragraph should be read as:

      BFCP supports TLS/DTLS mutual authentication between client and
      floor control servers, as specified in section 9.1.








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4.17.1.  TLS Based Mutual Authentication (9.1)

   Change each instance of "TLS" to "TLS/DTLS", and each instance of
   "TCP" to "TCP/UDP".

4.18.  Receiving a Response [to a FloorRequest Message] (10.1.2)

   Prepend the sentence below at the start of this subsection:

      When communicating over unreliable transport and upon receiving a
      FloorRequest from a participant, the floor control server MUST
      respond with a FloorRequestStatus message within the transaction
      failure window to complete the transaction.

4.19.  Receiving a Response [to a FloorRelease Message] (10.2.2)

   Prepend the sentence below at the start of this subsection:

      When communicating over unreliable transport and upon receiving a
      FloorRelease from a participant, the floor control server MUST
      respond with a FloorRequestStatus message within the transaction
      failure window to complete the transaction.

4.20.  Receiving a Response [to a ChairAction Message] (11.2)

   Prepend the sentence below at the start of this subsection:

      When communicating over unreliable transport and upon receiving a
      ChairAction from a participant, the floor control server MUST
      respond with a ChairActionAck message within the transaction
      failure window to complete the transaction.

4.21.  Receiving a Response [to a FloorQuery Message] (12.1.2)

   Prepend the sentence below at the start of this subsection:

      When communicating over unreliable transport and upon receiving a
      FloorQuery from a participant, the floor control server MUST
      respond with a FloorStatus message within the transaction failure
      window to complete the transaction.

4.22.  Receiving a Response [to a FloorRequestQuery Message] (12.2.2)

   Prepend the sentence below at the start of this subsection:

      When communicating over unreliable transport and upon receiving a
      FloorRequestQuery from a participant, the floor control server
      MUST respond with a FloorRequestStatus message within the



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      transaction failure window to complete the transaction.

4.23.  Receiving a Response [to a UserQuery Message] (12.3.2)

   Prepend the sentence below at the start of this subsection:

      When communicating over unreliable transport and upon receiving a
      UserQuery from a participant, the floor control server MUST
      respond with a UserStatus message within the transaction failure
      window to complete the transaction.

4.24.  Receiving a Response [to a Hello Message] (12.4.2)

   Prepend the sentence below at the start of this subsection:

      When communicating over unreliable transport and upon receiving a
      Hello from a participant, the floor control server MUST respond
      with a HelloAck message within the transaction failure window to
      complete the transaction.

4.25.  Reception of a FloorRequestStatus Message (13.1.3)

   The sentence below shall appear as a new subsection:

      When communicating over unreliable transport and upon receiving a
      FloorRequestStatus message from a floor control server, the
      participant MUST respond with a FloorRequestStatusAck message
      within the transaction failure window to complete the transaction.

4.26.  Reception of a FloorStatus Message (13.5.3)

   The sentence below shall appear as a new subsection:

      When communicating over unreliable transport and upon receiving a
      FloorStatus message from a floor control server, the participant
      MUST respond with a FloorStatusAck message within the transaction
      failure window to complete the transaction.

4.27.  Reception of an Error Message (13.8.1)

   The sentence below shall appear as a new subsection:

      When communicating over unreliable transport and upon receiving an
      Error message from a floor control server, the participant MUST
      respond with a ErrorAck message within the transaction failure
      window to complete the transaction.





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4.28.  Security Considerations (14)

   Change each instance of "TLS" to "TLS/DTLS", and each instance of
   "TCP" to "TCP/UDP".

4.29.  IANA Considerations - Primitive Subregistry (15.2)

   This section instructs the IANA to register the following new values
   for the BFCP primitive subregistry.

              +-------+-----------------------+-------------+
              | Value | Primitive             |  Reference  |
              +-------+-----------------------+-------------+
              |   14  | FloorRequestStatusAck | RFC 4582bis |
              |   15  | ErrorAck              | RFC 4582bis |
              |   16  | FloorStatusAck        | RFC 4582bis |
              |   17  | Goodbye               | RFC 4582bis |
              |   18  | GoodbyeAck            | RFC 4582bis |
              +-------+-----------------------+-------------+

                    Table 4: BFCP primitive subregistry

4.30.  IANA Considerations - Error Code Subregistry (15.4)

   This section instructs the IANA to register the following new values
   for the BFCP Error Code subregistry.

             +-------+-------------------------+-------------+
             | Value | Meaning                 |  Reference  |
             +-------+-------------------------+-------------+
             |   10  | Unable to parse message | RFC 4582bis |
             |   11  | Use DTLS                | RFC 4582bis |
             +-------+-------------------------+-------------+

                   Table 5: BFCP Error Code subregistry

4.31.  Example Call Flows for BFCP over Unreliable Transport (Appendix
       A)

   With reference to Section 4.1, the following figures show
   representative call-flows for requesting and releasing a floor, and
   obtaining status information about a floor when BFCP is deployed over
   an unreliable transport.  The figures here show a loss-less
   interaction.

   Editorial Note: A future version of this draft will show an example
   with lost packets due to unreliable transport, as well as examples on
   usage of DTLS and STUN in call the setup phase.



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         Floor Participant                                 Floor Control
                                                              Server
                 |(1) FloorRequest                               |
                 |Transaction ID: 123                            |
                 |User ID: 234                                   |
                 |FLOOR-ID: 543                                  |
                 |---------------------------------------------->|
                 |                                               |
                 |(2) FloorRequestStatus                         |
                 |Transaction ID: 123                            |
                 |User ID: 234                                   |
                 |FLOOR-REQUEST-INFORMATION                      |
                 |      Floor Request ID: 789                    |
                 |      OVERALL-REQUEST-STATUS                   |
                 |              Request Status: Pending          |
                 |      FLOOR-REQUEST-STATUS                     |
                 |            Floor ID: 543                      |
                 |<----------------------------------------------|
                 |                                               |
                 |(3) FloorRequestStatus                         |
                 |Transaction ID: 4098                           |
                 |User ID: 234                                   |
                 |FLOOR-REQUEST-INFORMATION                      |
                 |      Floor Request ID: 789                    |
                 |      OVERALL-REQUEST-STATUS                   |
                 |              Request Status: Accepted         |
                 |              Queue Position: 1st              |
                 |      FLOOR-REQUEST-STATUS                     |
                 |            Floor ID: 543                      |
                 |<----------------------------------------------|
                 |                                               |
                 |(4) FloorRequestStatusAck                      |
                 |Transaction ID: 4098                           |
                 |User ID: 234                                   |
                 |---------------------------------------------->|
                 |                                               |
                 |(5) FloorRequestStatus                         |
                 |Transaction ID: 4130                           |
                 |User ID: 234                                   |
                 |FLOOR-REQUEST-INFORMATION                      |
                 |      Floor Request ID: 789                    |
                 |      OVERALL-REQUEST-STATUS                   |
                 |              Request Status: Granted          |
                 |      FLOOR-REQUEST-STATUS                     |
                 |            Floor ID: 543                      |
                 |<----------------------------------------------|
                 |                                               |
                 |(6) FloorRequestStatusAck                      |



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                 |Transaction ID: 4130                           |
                 |User ID: 234                                   |
                 |---------------------------------------------->|
                 |                                               |
                 |(7) FloorRelease                               |
                 |Transaction ID: 154                            |
                 |User ID: 234                                   |
                 |FLOOR-REQUEST-ID: 789                          |
                 |---------------------------------------------->|
                 |                                               |
                 |(8) FloorRequestStatus                         |
                 |Transaction ID: 154                            |
                 |User ID: 234                                   |
                 |FLOOR-REQUEST-INFORMATION                      |
                 |      Floor Request ID: 789                    |
                 |      OVERALL-REQUEST-STATUS                   |
                 |              Request Status: Released         |
                 |      FLOOR-REQUEST-STATUS                     |
                 |            Floor ID: 543                      |
                 |<----------------------------------------------|

                Figure 8: Requesting and releasing a floor

   Note that in Figure 8, the FloorRequestStatus message from the floor
   control server to the floor participant is a transaction-closing
   message as a response to the client-initiated transaction with
   Transaction ID 154.  It does not and SHOULD NOT be followed by a
   FloorRequestStatusAck message from the floor participant to the floor
   control server.


         Floor Participant                                 Floor Control
                                                              Server
                 |(1) FloorQuery                                 |
                 |Transaction ID: 257                            |
                 |User ID: 234                                   |
                 |FLOOR-ID: 543                                  |
                 |---------------------------------------------->|
                 |                                               |
                 |(2) FloorStatus                                |
                 |Transaction ID: 257                            |
                 |User ID: 234                                   |
                 |FLOOR-ID:543                                   |
                 |FLOOR-REQUEST-INFORMATION                      |
                 |      Floor Request ID: 764                    |
                 |      OVERALL-REQUEST-STATUS                   |
                 |              Request Status: Accepted         |
                 |              Queue Position: 1st              |



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                 |      FLOOR-REQUEST-STATUS                     |
                 |            Floor ID: 543                      |
                 |      BENEFICIARY-INFORMATION                  |
                 |                  Beneficiary ID: 124          |
                 |FLOOR-REQUEST-INFORMATION                      |
                 |      Floor Request ID: 635                    |
                 |      OVERALL-REQUEST-STATUS                   |
                 |              Request Status: Accepted         |
                 |              Queue Position: 2nd              |
                 |      FLOOR-REQUEST-STATUS                     |
                 |            Floor ID: 543                      |
                 |      BENEFICIARY-INFORMATION                  |
                 |                  Beneficiary ID: 154          |
                 |<----------------------------------------------|
                 |                                               |
                 |(3) FloorStatus                                |
                 |Transaction ID: 4319                           |
                 |User ID: 234                                   |
                 |FLOOR-ID:543                                   |
                 |FLOOR-REQUEST-INFORMATION                      |
                 |      Floor Request ID: 764                    |
                 |      OVERALL-REQUEST-STATUS                   |
                 |              Request Status: Granted          |
                 |      FLOOR-REQUEST-STATUS                     |
                 |            Floor ID: 543                      |
                 |      BENEFICIARY-INFORMATION                  |
                 |                  Beneficiary ID: 124          |
                 |FLOOR-REQUEST-INFORMATION                      |
                 |      Floor Request ID: 635                    |
                 |      OVERALL-REQUEST-STATUS                   |
                 |              Request Status: Accepted         |
                 |              Queue Position: 1st              |
                 |      FLOOR-REQUEST-STATUS                     |
                 |            Floor ID: 543                      |
                 |      BENEFICIARY-INFORMATION                  |
                 |                  Beneficiary ID: 154          |
                 |<----------------------------------------------|
                 |                                               |
                 |(4) FloorStatusAck                             |
                 |Transaction ID: 4319                           |
                 |User ID: 234                                   |
                 |---------------------------------------------->|
                 |                                               |
                 |(5) FloorStatus                                |
                 |Transaction ID: 4392                           |
                 |User ID: 234                                   |
                 |FLOOR-ID:543                                   |
                 |FLOOR-REQUEST-INFORMATION                      |



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                 |      Floor Request ID: 635                    |
                 |      OVERALL-REQUEST-STATUS                   |
                 |              Request Status: Granted          |
                 |      FLOOR-REQUEST-STATUS                     |
                 |            Floor ID: 543                      |
                 |      BENEFICIARY-INFORMATION                  |
                 |                  Beneficiary ID: 154          |
                 |<----------------------------------------------|
                 |                                               |
                 |(6) FloorStatusAck                             |
                 |Transaction ID: 4392                           |
                 |User ID: 234                                   |
                 |---------------------------------------------->|

           Figure 9: Obtaining status information about a floor


5.  Revision of RFC4583

   This section details revisions to [RFC4583], the SDP format for
   specifying BFCP streams.  The section number to which updates apply
   are indicated in parentheses in the titles of the sub-sections below.

5.1.  Fields in the 'm' Line (3)

   The section shall be re-written to remove reference to the
   exclusivity of TCP as a transport for BFCP streams.

   1.  In paragraph four, "... will initiate its TCP connection ..."
       becomes "... will direct BFCP messages ..."

   2.  In paragraph four, delete "Since BFCP only runs on top of TCP,
       the port is always a TCP port."

   3.  Change paragraph five, "We define two new values ... ", to, "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, and 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 [RFC4347], which
       in turn runs on top of UDP."

5.2.  Authentication (8)

   In last paragraph, change "When TLS is used, once the underlaying TCP
   connection is established" to "When TLS is used with TCP, once the
   underlying connection is established".



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5.3.  Security Considerations (10)

   Append to the first paragraph, "Furthermore, when using DTLS over
   UDP, considerations for its use with RTP and RTCP are presented in
   [RFC5763].  The requirements for the offer/answer exchange, as listed
   in Section 5 of that document, MUST be followed."

5.4.  Registration of SDP 'proto' Values (11.1)

   This section should be renamed now that there are more values to
   register in the SDP parameters registry, with the following added to
   the table:

                      +--------------+-------------+
                      | Value        | Reference   |
                      +--------------+-------------+
                      | UDP/BFCP     | RFC 4583bis |
                      | UDP/TLS/BFCP | RFC 4583bis |
                      +--------------+-------------+

                 Table 6: Value for the SDP 'proto' field


6.  NAT Traversal

   One of the key benefits when using UDP for BFCP communication is the
   ability to leverage the existing NAT traversal infrastructure and
   strategies deployed to facilitate transport of the media associated
   with the video conferencing sessions.  Depending on the given
   deployment, this infrastructure typically includes some subset of ICE
   [RFC5245].

   In order to facilitate the initial establishment of NAT bindings, and
   to maintain those bindings once established, BFCP over UDP entities
   are RECOMMENDED to use STUN [RFC5389] for keep-alives, as described
   for SIP [RFC5626].  This results in each BFCP entity sending a
   packet, both to open the pinhole and to learn what IP/port the NAT
   assigned for the binding.

   In order to facilitate traversal of BFCP packets through NATs, BFCP
   over UDP entities are RECOMMENDED to use symmetric ports for sending
   and receiving BFCP packets, as recommended for RTP/RTCP [RFC4961].


7.  Future Work

   This draft reflects a work in progress, with at least the following
   items to be documented and/or revised:



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   DTLS usage:  Follow RFC 5763 recommendation for establishing DTLS, to
         remove incosistency in current description in the draft.

   Version number:  Define BFCP via UDP as version 2.  Whether or not
         version 2 applies when using TCP may require more discussion.

   Fragmentation scheme:  To be handled some way or another in upcoming
         version of this draft.

   Example signaling flows:  A later version of this draft will include
         further examples of signaling exchanges over unreliable
         transport as a visual aid and reference for implementers,
         including updated transactions, message retransmission, usage
         of DTLS during call setup, and combined usage of DTLS and STUN.

   Reformat and merge:  After figuring out the technical details in this
         draft, the "diff" will be merged to form proper bis-drafts to
         become RFC4582bis (in BFCPbis WG) and RFC4583bis (in MMUSIC
         WG).


8.  Acknowledgements

   We acknowledge substantial contributions to one or more previous
   versions of this draft from Trond G. Andersen, Alfred E. Heggestad,
   Gonzalo Camarillo, Roni Even, Lorenzo Miniero, Joerg Ott, Hadriel
   Kaplan, Dan Wing, Cullen Jennings, David Benham, and Alan Ford.


9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3264]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
              with Session Description Protocol (SDP)", RFC 3264,
              June 2002.

   [RFC4347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security", RFC 4347, April 2006.

   [RFC4582]  Camarillo, G., Ott, J., and K. Drage, "The Binary Floor
              Control Protocol (BFCP)", RFC 4582, November 2006.

   [RFC4583]  Camarillo, G., "Session Description Protocol (SDP) Format
              for Binary Floor Control Protocol (BFCP) Streams",



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              RFC 4583, November 2006.

   [RFC4961]  Wing, D., "Symmetric RTP / RTP Control Protocol (RTCP)",
              BCP 131, RFC 4961, July 2007.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

   [RFC5389]  Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
              "Session Traversal Utilities for NAT (STUN)", RFC 5389,
              October 2008.

   [RFC5626]  Jennings, C., Mahy, R., and F. Audet, "Managing Client-
              Initiated Connections in the Session Initiation Protocol
              (SIP)", RFC 5626, October 2009.

9.2.  Informative References

   [I-D.ietf-mmusic-ice-tcp]
              Rosenberg, J., Keranen, A., Lowekamp, B., and A. Roach,
              "TCP Candidates with Interactive Connectivity
              Establishment (ICE)", draft-ietf-mmusic-ice-tcp-16 (work
              in progress), November 2011.

   [I-D.ietf-mmusic-media-path-middleboxes]
              Stucker, B. and H. Tschofenig, "Analysis of Middlebox
              Interactions for Signaling Protocol Communication along
              the Media Path",
              draft-ietf-mmusic-media-path-middleboxes-03 (work in
              progress), July 2010.

   [I-D.ietf-p2psip-base]
              Jennings, C., Lowekamp, B., Rescorla, E., Baset, S., and
              H. Schulzrinne, "REsource LOcation And Discovery (RELOAD)
              Base Protocol", draft-ietf-p2psip-base-19 (work in
              progress), October 2011.

   [I-D.manner-tsvwg-gut]
              Manner, J., Varis, N., and B. Briscoe, "Generic UDP
              Tunnelling (GUT)", draft-manner-tsvwg-gut-02 (work in
              progress), July 2010.

   [IMC05]    Guha, S. and P. Francis, "Characterization and Measurement
              of TCP Traversal through NATs and Firewalls", 2005,
              <http://saikat.guha.cc/pub/imc05-tcpnat.pdf/>.

   [P2PNAT]   Ford, B., Srisuresh, P., and D. Kegel, "Peer-to-Peer
              Communication Across Network Address Translators",



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              April 2005,
              <http://www.brynosaurus.com/pub/net/p2pnat.pdf/>.

   [RFC3261]  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.

   [RFC4380]  Huitema, C., "Teredo: Tunneling IPv6 over UDP through
              Network Address Translations (NATs)", RFC 4380,
              February 2006.

   [RFC5245]  Rosenberg, J., "Interactive Connectivity Establishment
              (ICE): A Protocol for Network Address Translator (NAT)
              Traversal for Offer/Answer Protocols", RFC 5245,
              April 2010.

   [RFC5405]  Eggert, L. and G. Fairhurst, "Unicast UDP Usage Guidelines
              for Application Designers", BCP 145, RFC 5405,
              November 2008.

   [RFC5763]  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.

   [RFC6081]  Thaler, D., "Teredo Extensions", RFC 6081, January 2011.


Appendix A.  Change History

A.1.  draft-sandbakken-dispatch-bfcp-udp-03 to
      draft-ietf-bfcpbis-rfc4582bis-00

   1.  Draft name change.  Adopted as main work item in BFCPbis WG.

   2.  Switched from informational to standards track.

   3.  No conflict with IANA registries for BFCP, since the aim is a
       standards track RFC.  Removed text in Future work section.

   4.  Just editorial changes as requested by WG chairs; used as a
       starting point in the new WG.  Will add changes in upcoming
       version.  Also author list will be considered, for instance
       adding a contributors section in the draft.






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A.2.  draft-sandbakken-dispatch-bfcp-udp-02 to -03

   1.  Added fragmentation and reassembly mechanism defined for RELOAD
       as a candidate mechanism for consideration for BFCP when
       transported over UDP.

   2.  Added ERROR-CODE to indicate DTLS is required.

   3.  Added UDP/TLS/BFCP as 4th transport value for BFCP.

   4.  Added requirement to follow offer/answer procedure in [RFC5763]
       when using DTLS over UDP for BFCP.

A.3.  draft-sandbakken-dispatch-bfcp-udp-01 to -02

   1.  Switched from standards track to informational.

   2.  Added section on motivation, including alternatives considered,
       to address issues raised at IETF 79 and on various workgroup
       aliases.

   3.  Changed semantics of the Transaction Initiator (I) flag-bit.

   4.  Expanded transport section to more explicitly call out
       considerations regarding congestion control and ICMP errors, and
       add considerations for large messages.

   5.  Updated security related sections and added authentication
       section to address DTLS when using UDP.

   6.  Added section on NAT Traversal.

   7.  Some editorial changes.

A.4.  draft-sandbakken-dispatch-bfcp-udp-00 to -01

   1.  Decision made to not increase the protocol version number as a
       result of this extension.  Certain aspects of this draft require
       different behaviors depending on whether a reliable or unreliable
       transport is being used, e.g. server-initiated transactions
       having Transaction ID 0 over reliable transports without
       acknowledgements versus non-zero and active-unique with an
       acknowledgement message when entities communicate over unreliable
       transports.  As the graceful-close behavior of [RFC4582] is still
       allowed for TCP-based implementations without mandating the use
       of the new Goodbye message, there is no need to change the
       version number.




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   2.  Removed the - a bit too verbose - rationale/motivation text
       describing background and why other approaches where not chosen.
       Was OK for a -00 draft, not strictly needed.

   3.  Not mandate ICE as a SHALL, but leave it as a non-mandatory way
       of solving the potential need for NAT/FW traversal.

   4.  Emphasized that the reference to DTLS-SRTP are merely
       informational.

   5.  A dash of polish and nitpicking added, some typos fixed.

A.5.  draft-sandbakken-xcon-bfcp-udp-02 to
      draft-sandbakken-dispatch-bfcp-udp-00

   1.  Draft name change.  As XCON WG is closing this draft is submitted
       to Dispatch WG as the arena of discussion.

   2.  Moved Transaction Identifier bit (I) from the Transaction ID to
       one of the current 5 reserved bits.  Keep current Transaction ID
       syntax and semantics.  Avoid potential problems with existing TCP
       based implementations.

   3.  The way congestion control is taken care of is explained, with
       reference to [RFC5405].  One message per RTT.  Backoff and
       normative behavior for timer T1 clarified.

   4.  Mandated support for DTLS in case unreliable transport (i.e.
       UDP) is implemented.  Details and examples to be included.  Model
       after [RFC5763], details on how to adapt the SRTP associated
       details to BFCP and whether a reference or copying the text
       across and changing is needed.

   5.  Added the Rationale and Scope section to position and explain the
       motivation for this draft more in detail.

   6.  A number of typos and editorial changes.

A.6.  draft-sandbakken-xcon-bfcp-udp-01 to -02

   1.  Stepped away from changing semantics and directionality of Hello
       and HelloAck messages for pinhole establishment and keep-alive in
       favor of ICE toolset, particularly as this would have not
       resolved connectivity establishment as a precursor to deployment
       of DTLS [RFC4347] as a transport security mechanism.

   2.  Change to COMMON-HEADER to reserve bit-16 of Transaction ID to
       show originator of transaction such that request/response and



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       response/acknowledgement mapping can be maintained without
       colliding randomly chosen Transaction IDs.  This also avoids a
       three-way handshake scenario around FloorRequest where the
       implicit acknowledgement (in FloorRequestStatus) might also be
       interpreted as a transaction opening request on the part of the
       floor control server.

   3.  Defined additional timer (T2) to soak up lost responses without
       additional processing.

   4.  Restricted outstanding transactions to only one in-flight per
       direction at any one time to mitigate re-ordering issues.

   5.  Defined entity behavior when transactions timeout.

   6.  Specified initial suggestion for how to minimize fragmentation of
       messages.

   7.  Removed consideration of TCP-over-UDP after internal review.

   8.  Re-stated DTLS as likely preferred mechanism of securing
       transport, although this investigation is on-going.

A.7.  draft-sandbakken-xcon-bfcp-udp-00 to -01

   1.  Refactored to a format that represents explicit changes to base
       RFCs.

   2.  Introduction of issues currently under investigation that
       preclude adoption.

   3.  Specified retransmission timer for requests.


Authors' Addresses

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

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








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   Charles Eckel
   Cisco
   170 West Tasman Drive
   San Jose, CA 95134
   United States

   Email: eckelcu@cisco.com


   Alfred E. Heggestad
   Cisco
   Philip Pedersens vei 22
   N-1366 Lysaker
   Norway

   Email: aheggest@cisco.com


   Mark K. Thompson
   Cisco
   Ruscombe Business Park
   Ruscombe, England
   UK

   Email: markth2@cisco.com


   Geir A. Sandbakken
   Cisco
   Philip Pedersens vei 22
   N-1366 Lysaker
   Norway

   Email: geirsand@cisco.com


   Eoin McLeod
   Cisco
   Ruscombe Business Park
   Ruscombe, England
   UK

   Email: eoimcleo@cisco.com








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