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The WebSocket Protocol as a Transport for the Binary Floor Control Protocol (BFCP)

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This is an older version of an Internet-Draft that was ultimately published as RFC 8857.
Authors Victor Pascual , Anton Roman , Stephane Cazeaux , Gonzalo Salgueiro , Sergio Garcia Murillo
Last updated 2014-03-26
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BFCPBIS Working Group                                         V. Pascual
Internet-Draft                                                  A. Roman
Updates: rfc4582bis, rfc4583bis (if approved)                     Quobis
Intended status: Standards Track                              S. Cazeaux
Expires: September 27, 2014                        France Telecom Orange
                                                            G. Salgueiro
                                                       S. Garcia Murillo
                                                          March 26, 2014

   The WebSocket Protocol as a Transport for the Binary Floor Control
                            Protocol (BFCP)


   The WebSocket protocol enables two-way realtime communication between
   clients and servers.  This document specifies a new WebSocket sub-
   protocol as a reliable transport mechanism between Binary Floor
   Control Protocol (BFCP) entities to enable usage of BFCP in new
   scenarios.  This document normatively updates [I-D.draft-ietf-
   bfcpbis-rfc4582bis] and [I-D.draft-ietf-bfcpbis-rfc4583bis]

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

   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 September 27, 2014.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( in effect on the date of
   publication of this document.  Please review these documents
   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
     2.1.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  The WebSocket Protocol  . . . . . . . . . . . . . . . . . . .   4
   4.  The WebSocket BFCP Sub-Protocol . . . . . . . . . . . . . . .   4
     4.1.  Handshake . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.2.  BFCP encoding . . . . . . . . . . . . . . . . . . . . . .   5
   5.  BFCP WebSocket Transport  . . . . . . . . . . . . . . . . . .   6
   6.  Fields in the 'm' Line  . . . . . . . . . . . . . . . . . . .   6
   7.  Authentication  . . . . . . . . . . . . . . . . . . . . . . .   7
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
     9.1.  Registration of the WebSocket BFCP Sub-Protocol . . . . .   9
     9.2.  Registration of the 'TCP/WS/BFCP' and 'TCP/WSS/BFCP' SDP
           'proto' Values  . . . . . . . . . . . . . . . . . . . . .   9
     9.3.  Registration of the 'ws-uri' SDP media attribute  . . . .   9
     9.4.  Acknowledgements  . . . . . . . . . . . . . . . . . . . .  10
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  10
     10.2.  Informative References . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   The WebSocket [RFC6455] protocol enables two-way message exchange
   between clients and servers on top of a persistent TCP connection
   (optionally secured with TLS [RFC5246]).  The initial protocol
   handshake makes use of HTTP [RFC2616] semantics, allowing the
   WebSocket protocol to reuse existing HTTP infrastructure.

   The Binary Floor Control Protocol (BFCP) is a protocol to coordinate
   access to shared resources in a conference.  It is defined in
   [I-D.ietf-bfcpbis-rfc4582bis] and is used between floor participants
   and floor control servers, and between floor chairs (i.e.,
   moderators) and floor control servers.

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   Modern web browsers include a WebSocket client stack complying with
   the WebSocket API [WS-API] as specified by the W3C. It is expected
   that other client applications (those running in personal computers
   and devices such as smartphones) will also make a WebSocket client
   stack available.  This document updates [I-D.ietf-bfcpbis-rfc4582bis]
   and [I-D.ietf-bfcpbis-rfc4583bis] in order to enable the usage of
   BFCP in these scenarios.

   The transport over which BFCP entities exchange messages depends on
   how the clients obtain information to contact the floor control
   server (e.g. using an SDP offer/answer exchange per
   [I-D.ietf-bfcpbis-rfc4583bis] or the procedure described in RFC5018
   [RFC5018]).  [I-D.ietf-bfcpbis-rfc4582bis] defines two transports for
   BFCP: TCP and UDP.  This specification defines a new WebSocket sub-
   protocol (as defined in section 1.9 in [RFC6455]) for transporting
   BFCP messages between a WebSocket client and server, a new reliable
   and message boundary transport for BFCP.  In order to enable this,
   this document also defines two new SDP 'proto' values.

   This document does not restrict the selection nor prevent the usage
   of other transport mechanisms for the BFCP protocol.  Transport
   selection is entirely at the discretion of the application.  As an
   example, an RTCWeb applications may choose to use either DataChannel
   or WebSocket transport for BFCP, while non-RTCWeb applications could
   still benefit from the ubiquity of the WebSocket protocol and make
   use of the transport for BFCP defined in this document.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

2.1.  Definitions

   BFCP WebSocket Client:  A BFCP entity capable of opening outbound
         connections to WebSocket servers and communicating using the
         WebSocket BFCP sub-protocol as defined by this document.

   BFCP WebSocket Server:  A BFCP entity capable of listening for
         inbound connections from WebSocket clients and communicating
         using the WebSocket BFCP sub-protocol as defined by this

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3.  The WebSocket Protocol

   The WebSocket protocol [RFC6455] is a transport layer on top of TCP
   (optionally secured with TLS [RFC5246]) in which both client and
   server exchange message units in both directions.  The protocol
   defines a connection handshake, WebSocket sub-protocol and extensions
   negotiation, a frame format for sending application and control data,
   a masking mechanism, and status codes for indicating disconnection

   The WebSocket connection handshake is based on HTTP [RFC2616] and
   utilizes the HTTP GET method with an "Upgrade" request.  This is sent
   by the client and then answered by the server (if the negotiation
   succeeded) with an HTTP 101 status code.  Once the handshake is
   completed the connection upgrades from HTTP to the WebSocket
   protocol.  This handshake procedure is designed to reuse the existing
   HTTP infrastructure.  During the connection handshake, client and
   server agree on the application protocol to use on top of the
   WebSocket transport.  Such an application protocol (also known as a
   "WebSocket sub-protocol") defines the format and semantics of the
   messages exchanged by the endpoints.  This could be a custom protocol
   or a standardized one (as the WebSocket BFCP sub-protocol defined in
   this document).  Once the HTTP 101 response is processed both client
   and server reuse the underlying TCP connection for sending WebSocket
   messages and control frames to each other.  Unlike plain HTTP, this
   connection is persistent and can be used for multiple message

   The WebSocket protocol defines message units to be used by
   applications for the exchange of data, so it provides a message
   boundary-preserving transport layer.  These message units can contain
   either UTF-8 text or binary data, and can be split into multiple
   WebSocket text/binary transport frames as needed by the WebSocket

      The WebSocket API [WS-API] for web browsers only defines callbacks
      to be invoked upon receipt of an entire message unit, regardless
      of whether it was received in a single Websocket frame or split
      across multiple frames.

4.  The WebSocket BFCP Sub-Protocol

   The term WebSocket sub-protocol refers to an application-level
   protocol layered on top of a WebSocket connection.  This document
   specifies the WebSocket BFCP sub-protocol for carrying BFCP messages
   through a WebSocket connection.

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4.1.  Handshake

   The BFCP WebSocket Client and BFCP WebSocket Server negotiate usage
   of the WebSocket BFCP sub-protocol during the WebSocket handshake
   procedure as defined in section 1.3 of [RFC6455].  The Client MUST
   include the value "bfcp" in the Sec-WebSocket-Protocol header in its
   handshake request.  The 101 reply from the Server MUST contain "bfcp"
   in its corresponding Sec-WebSocket-Protocol header.

   Below is an example of a WebSocket handshake in which the Client
   requests the WebSocket BFCP sub-protocol support from the Server:

     GET / HTTP/1.1
     Upgrade: websocket
     Connection: Upgrade
     Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==
     Sec-WebSocket-Protocol: bfcp
     Sec-WebSocket-Version: 13

   The handshake response from the Server accepting the WebSocket BFCP
   sub-protocol would look as follows:

     HTTP/1.1 101 Switching Protocols
     Upgrade: websocket
     Connection: Upgrade
     Sec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo=
     Sec-WebSocket-Protocol: bfcp

   Once the negotiation has been completed, the WebSocket connection is
   established and can be used for the transport of BFCP messages.  The
   WebSocket messages transmitted over this connection MUST conform to
   the negotiated WebSocket sub-protocol.

4.2.  BFCP encoding

   BFCP messages use a TLV (Type-Length-Value) binary encoding,
   therefore BFCP WebSocket Clients and BFCP WebSocket Servers MUST be
   transported in unfragmented binary WebSocket frames
   (FIN:1,opcode:%x2) to exchange BFCP messages.  The WebSocket frame
   data MUST be a valid BCFP message, so the length of the payload of
   the WebSocket frame MUST be lower than the maximum size allowed (2^16
   +12 bytes) for a BCFP message as described in
   [I-D.ietf-bfcpbis-rfc4582bis].  In addition, the encoding rules for
   reliable protocols defined in [I-D.ietf-bfcpbis-rfc4582bis] MUST be

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5.  BFCP WebSocket Transport

   WebSocket [RFC6455] is a reliable protocol and therefore the BFCP
   WebSocket sub-protocol defined by this document is a reliable BFCP
   transport.  Thus, client and server transactions using WebSocket for
   transport MUST follow the procedures for reliable transports as
   defined in [I-D.ietf-bfcpbis-rfc4582bis] and

   BFCP WebSocket clients cannot receive incoming WebSocket connections
   initiated by any other peer.  This means that a BFCP Websocket client
   MUST actively initiate a connection towards a BFCP Websocket server

   Each BFCP message MUST be carried within a single WebSocket message,
   and a WebSocket message MUST NOT contain more than one BFCP message.

6.  Fields in the 'm' Line

   Rules to generate an 'm' line for a BFCP stream are described in
   [I-D.ietf-bfcpbis-rfc4583bis], Section 3

   New values are defined for the transport field: TCP/WS/BFCP and TCP/

      TCP/WS/BFCP is used when BFCP runs on top of WS, which in turn
      runs on top of TCP.

      TCP/WSS/BFCP is used when BFCP runs on top of WSS, which in turn
      runs on top of TLS and TCP.

   When TCP is used as the transport, the port field is set following
   the rules in Section 7 of [I-D.ietf-bfcpbis-rfc4582bis].  Depending
   on the value of the 'setup' attribute, 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.  Connection attribute and port MUST follow the rules of

   Some web browsers do not allow non-secure Websocket connections to be
   made.  So, while the recommendation to use Secure WebSockets (i.e.
   TCP/WSS) is for security reasons, it is also to achieve maximum
   compatiblity among clients.

   When using Secure Websockets the CNAME of the SSL certificate must
   match the WebSocket connection URI host, and while it is possible to
   generate self signed certificates with IPs as CNAME, it will not be
   viable in most cases for certificates signed by well known

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   authorities.  So, a new attribute 'ws-uri' is defined in this
   specification to indicate the connection uri for the WebSocket
   Client.  The Augmented BNF syntax as described in [RFC4234] is:

      ws-uri      = "a=ws-uri:" ws-URI

   Where ws-URI is defined in [RFC6455]

   When the 'ws-uri' attribute is present in the BCFP media section of
   the SDP, the IP and port provided in the 'c' lines SHALL be ignored
   and the full uri SHALL be used instead to open the WebSocket

   The following are examples of 'm' lines for BFCP connections:

   Offer (browser):
   m=application 9 TCP/WSS/BFCP *
   m=audio 55000 RTP/AVP 0
   m=video 55002 RTP/AVP 31

   Answer (server):
   m=application 50000 TCP/WSS/BFCP *
   a=floorid:1 m-stream:10
   a=floorid:2 m-stream:11
   m=audio 50002 RTP/AVP 0
   m=video 50004 RTP/AVP 31

7.  Authentication

   Section 9 of [I-D.ietf-bfcpbis-rfc4582bis] states that BFCP clients
   and floor control servers SHOULD authenticate each other prior to
   accepting messages, and RECOMMENDS that mutual TLS/DTLS
   authentication be used.  However, browser-based WebSocket clients
   have no control over the use of TLS in the WebSocket API [WS-API], so
   it is RECOMMENDED that standard Web-based methods for client and
   server authentication are used, as follows.

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   When a BFCP WebSocket client connects to a BFCP WebSocket server, it
   SHOULD use TCP/WSS as its transport.  The WebSocket client SHOULD
   inspect the TLS certificate offered by the server and verify that it
   is valid.

      Since the WebSocket API does not distinguish between certificate
      errors and other kinds of failure to establish a connection, it is
      expected that browser vendors will warn end users directly of any
      kind of problem with the server certificate.

   A floor control server that receives a message over TCP/WS can
   request the use of TCP/WSS by generating an Error message, as
   described in Section 13.8 of [I-D.ietf-bfcpbis-rfc4582bis], with an
   Error code with a value of 9 (use TLS).

   Prior to sending BFCP requests, a BFCP WebSocket client connects to a
   BFCP WebSocket server and performs the connection handshake.  As
   described in Section 3 the handshake procedure involves a HTTP GET
   method request from the client and a response from the server
   including an HTTP 101 status code.

   In order to authorize the WebSocket connection, the BFCP WebSocket
   server MAY inspect any cookie [RFC6265] headers present in the HTTP
   GET request.  For many web applications the value of such a cookie is
   provided by the web server once the user has authenticated themselves
   to the web server, which could be done by many existing mechanisms.
   As an alternative method, the BFCP WebSocket Server could request
   HTTP authentication by replying to the Client's GET method request
   with a HTTP 401 status code.  The WebSocket protocol [RFC6455] covers
   this usage in section 4.1:

      If the status code received from the server is not 101, the
      WebSocket client stack handles the response per HTTP [RFC2616]
      procedures, in particular the client might perform authentication
      if it receives 401 status code.

8.  Security Considerations

   Considerations from [I-D.ietf-bfcpbis-rfc4582bis],
   [I-D.ietf-bfcpbis-rfc4583bis] and RFC5018 [RFC5018] apply.

   BFCP relies on lower-layer security mechanisms to provide replay and
   integrity protection and confidentiality.  It is RECOMMENDED that the
   BFCP traffic transported over a WebSocket communication be protected
   by using a secure WebSocket connection (using TLS [RFC5246] over

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9.  IANA Considerations

9.1.  Registration of the WebSocket BFCP Sub-Protocol

   This specification requests IANA to register the WebSocket BFCP sub-
   protocol under the "WebSocket Subprotocol Name" Registry with the
   following data:

   Subprotocol Identifier:  bfcp

   Subprotocol Common Name:  WebSocket Transport for BFCP (Binary Floor
      Control Protocol)

   Subprotocol Definition:  TBD: this document

9.2.  Registration of the 'TCP/WS/BFCP' and 'TCP/WSS/BFCP' SDP 'proto'

   This document defines two new values for the SDP 'proto' field under
   the Session Description Protocol (SDP) Parameters registry.  The
   resulting entries are shown in Figure 1 below:

   Value           Reference
   --------------       ---------
   TCP/WS/BFCP             [TBD: this document]
   TCP/WSS/BFCP            [TBD: this document]

                Figure 1: Values for the SDP 'proto' field

9.3.  Registration of the 'ws-uri' SDP media attribute

   This section instructs the IANA to register the following SDP att-
   field under the Session Description Protocol (SDP) Parameters

   Contact name  TBD

   Attribute name  ws-uri

   Long-form attribute name  Websocket Connection URI

   Type of attribute  Media level

   Subject to charset  No

   Purpose of attribute  The 'ws-uri' attribute is intended to be used
      as connection URI for opening the WebSocket.

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   Allowed attribute values  A ws-URI as defined in [RFC6455]

9.4.  Acknowledgements

   The authors want to thank Robert Welboun, from Acme Packet, who made
   significant contributions to the first version of this document.

10.  References

10.1.  Normative References

              Camarillo, G., Drage, K., Kristensen, T., Ott, J., and C.
              Eckel, "The Binary Floor Control Protocol (BFCP)", draft-
              ietf-bfcpbis-rfc4582bis-11 (work in progress), February

              Camarillo, G. and T. Kristensen, "Session Description
              Protocol (SDP) Format for Binary Floor Control Protocol
              (BFCP) Streams", draft-ietf-bfcpbis-rfc4583bis-09 (work in
              progress), February 2014.

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

   [RFC4145]  Yon, D. and G. Camarillo, "TCP-Based Media Transport in
              the Session Description Protocol (SDP)", RFC 4145,
              September 2005.

   [RFC4234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", RFC 4234, October 2005.

   [RFC5018]  Camarillo, G., "Connection Establishment in the Binary
              Floor Control Protocol (BFCP)", RFC 5018, September 2007.

   [RFC6455]  Fette, I. and A. Melnikov, "The WebSocket Protocol", RFC
              6455, December 2011.

10.2.  Informative References

   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

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

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   [RFC6265]  Barth, A., "HTTP State Management Mechanism", RFC 6265,
              April 2011.

   [WS-API]   W3C and I. Hickson, Ed., "The WebSocket API", May 2012.

Authors' Addresses

   Victor Pascual


   Anton Roman


   Stephane Cazeaux
   France Telecom Orange


   Gonzalo Salgueiro
   Cisco Systems, Inc.
   7200-12 Kit Creek Road
   Research Triangle Park, NC  27709


   Sergio Garcia Murillo


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