Internet DRAFT - draft-pascual-bfcpbis-bfcp-websocket
draft-pascual-bfcpbis-bfcp-websocket
BFCPBIS Working Group V. Pascual
Internet-Draft A. Roman
Updates: rfc4582bis, rfc4583bis (if approved) Quobis
Intended status: Standards Track S. Cazeaux
Expires: August 13, 2014 France Telecom Orange
G. Salgueiro
Cisco
S. Garcia Murillo
Medooze
February 9, 2014
The WebSocket Protocol as a Transport for the Binary Floor Control
Protocol (BFCP)
draft-pascual-bfcpbis-bfcp-websocket-00
Abstract
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
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This Internet-Draft will expire on August 13, 2014.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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
document.
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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
causes.
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
exchanges.
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
stack.
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
Host: bfcp-ws.example.com
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==
Origin: http://www.example.com
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
followed.
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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
[I-D.ietf-bfcpbis-rfc4583bis]
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/
WSS/BFCP.
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
[RFC4145]
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
connection
The following are examples of 'm' lines for BFCP connections:
Offer (browser):
m=application 9 TCP/WSS/BFCP *
a=setup:active
a=connection:new
a=floorctrl:c-only
m=audio 55000 RTP/AVP 0
m=video 55002 RTP/AVP 31
Answer (server):
m=application 50000 TCP/WSS/BFCP *
a=setup:passive
a=connection:new
a=ws-uri:wss://bfcp-ws.example.com?token=3170449312
a=floorctrl:s-only
a=confid:4321
a=userid:1234
a=floorid:1 m-stream:10
a=floorid:2 m-stream:11
m=audio 50002 RTP/AVP 0
a=label:10
m=video 50004 RTP/AVP 31
a=label:11
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
TCP).
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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'
Values
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
registry:
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
[I-D.ietf-bfcpbis-rfc4582bis]
Camarillo, G., Drage, K., Kristensen, T., Ott, J., and C.
Eckel, "The Binary Floor Control Protocol (BFCP)", draft-
ietf-bfcpbis-rfc4582bis-10 (work in progress), November
2013.
[I-D.ietf-bfcpbis-rfc4583bis]
Camarillo, G. and T. Kristensen, "Session Description
Protocol (SDP) Format for Binary Floor Control Protocol
(BFCP) Streams", draft-ietf-bfcpbis-rfc4583bis-08 (work in
progress), November 2013.
[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
Quobis
Email: victor.pascual@quobis.com
Anton Roman
Quobis
Email: anton.roman@quobis.com
Stephane Cazeaux
France Telecom Orange
Email: stephane.cazeaux@orange.com
Gonzalo Salgueiro
Cisco Systems, Inc.
7200-12 Kit Creek Road
Research Triangle Park, NC 27709
US
Email: gsalguei@cisco.com
Sergio Garcia Murillo
Medooze
Email: sergio.garcia.murillo@gmail.com
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