Session Description Protocol (SDP) WebSocket Connection URI Attribute
draft-ietf-bfcpbis-sdp-ws-uri-08

BFCPBIS Working Group                                  Ram. Ravindranath
Internet-Draft                                              G. Salgueiro
Intended status: Standards Track                                   Cisco
Expires: July 17, 2017                                  January 13, 2017

 Session Description Protocol (SDP) WebSocket Connection URI Attribute
                    draft-ietf-bfcpbis-sdp-ws-uri-08

Abstract

   The WebSocket protocol enables bidirectional real-time communication
   between clients and servers in web-based applications.  This document
   specifies extensions to Session Description Protocol (SDP) for
   application protocols using WebSocket as a transport.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on July 17, 2017.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  SDP Considerations  . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.2.  ws-uri SDP Attribute  . . . . . . . . . . . . . . . . . .   3
     3.3.  wss-uri SDP Attribute . . . . . . . . . . . . . . . . . .   4
     3.4.  ws-uri and wss-uri Multiplexing Considerations  . . . . .   4
   4.  SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . .   5
     4.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.2.  Generating the Initial Offer  . . . . . . . . . . . . . .   5
     4.3.  Generating the Answer . . . . . . . . . . . . . . . . . .   6
     4.4.  Offerer Processing of the Answer  . . . . . . . . . . . .   7
     4.5.  Modifying the Session . . . . . . . . . . . . . . . . . .   7
     4.6.  Offerless INVITE Scenarios  . . . . . . . . . . . . . . .   7
   5.  Procedures at WebSocket Client  . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
     7.1.  Registration of the 'ws-uri' SDP Media Attribute  . . . .   8
     7.2.  Registration of the 'wss-uri' SDP Media Attribute . . . .   9
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   The WebSocket protocol [RFC6455] enables bidirectional message
   exchange between clients and servers on top of a persistent TCP
   connection (optionally secured with Transport Layer Security (TLS)
   [RFC5246]).  The initial protocol handshake makes use of Hypertext
   Transfer Protocol (HTTP) [RFC7230] semantics, allowing the WebSocket
   protocol to reuse existing HTTP infrastructure.

   Modern web browsers include a WebSocket client stack compliant with
   the WebSocket API [WS-API] as specified by the W3C.  It is expected
   that other client applications (e.g., those running on personal
   computers, mobile devices, etc.) will also make a WebSocket client
   stack available.  Several specifications have been written that
   define how different applications can use a WebSocket subprotocol as
   a reliable transport mechanism.

   For example, [RFC7118] defines WebSocket subprotocol as a reliable
   transport mechanism between Session Initiation Protocol
   (SIP)[RFC3261] entities to enable use of SIP in web-oriented
   deployments.  Additionally, [RFC7977] defines a new WebSocket sub-

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   protocol as a reliable transport mechanism between Message Session
   Relay Protocol (MSRP) clients and relays.  [RFC7395] defines a
   WebSocket subprotocol for the Extensible Messaging and Presence
   Protocol (XMPP).  Similarly, [I-D.ietf-bfcpbis-bfcp-websocket]
   defines a WebSocket sub-protocol as a reliable transport mechanism
   between Binary Floor Control Protocol (BFCP)
   [I-D.ietf-bfcpbis-rfc4582bis] entities to enable usage of BFCP in new
   scenarios.

   When WebSocket sub-protocol is used as a transport mechanism between
   a server and client, there needs to be a way to indicate the
   connection URI from the Server to the WebSocket Client.  For
   applications that use Session Description Protocol (SDP) [RFC4566] to
   negotiate, the connection URI can be indicated by means of an SDP
   attribute.  This specification defines new SDP attributes to indicate
   the connection URI for the WebSocket client.  Applications that use
   SDP for negotiation and WebSocket as a transport protocol can use
   this specification to advertise the WebSocket client connection URI.

2.  Terminology

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

3.  SDP Considerations

3.1.  General

   Applications that use the SDP Offer/Answer mechanism [RFC3264] for
   negotiating media and also use WebSocket as a transport protocol MAY
   indicate the connection URI for the WebSocket Client via a new SDP a=
   media-level attribute defined in Section 3.2.

   Applications that use SDP for negotiation and also use secure
   WebSocket as a transport protocol TLS MAY indicate the connection URI
   for the WebSocket Client via a new SDP a= media-level attribute
   defined in Section 3.3.

3.2.  ws-uri SDP Attribute

   This section defines a new SDP media-level attribute, 'ws-uri' which
   can appear in any of the media sections.

   Example:

      a=ws-uri:ws://example.com/chat

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   Where "ws://example.com/chat" is the ws-URI defined in Section 3 of
   [RFC6455].

   When the 'ws-uri' attribute is present in the media section of the
   SDP, the IP address in 'c= ' line SHALL be ignored and the full URI
   SHALL be used instead to open the WebSocket connection.  The clients
   MUST ensure that they use the URI to open the webSocket connection
   and ignore the IP address in 'c=' line and port in m= line.

3.3.  wss-uri SDP Attribute

   This section defines a new SDP media-level attribute, 'wss-uri' which
   can appear in any of the media sections.

   Example:

      a=wss-uri:wss://example.com/chat

   Here "wss://example.com/chat" is the wss-URI defined in Section 3 of
   [RFC6455].

   When the 'wss-uri' attribute is present in the media section of the
   SDP, the IP address in 'c= ' line SHALL be ignored and the full URI
   SHALL be used instead to open the WebSocket connection.  The clients
   MUST ensure that they use the URI to open the webSocket connection
   and ignore the IP address in 'c=' line and port in m= line.

3.4.  ws-uri and wss-uri Multiplexing Considerations

   Multiplexing characteristics of SDP attributes are described in
   [I-D.ietf-mmusic-sdp-mux-attributes].  Various SDP attribute
   multiplexing categories are introduced there.

   o  The multiplexing category of the "a=ws-uri:" attribute is CAUTION.

   o  The multiplexing category of the "a=wss-uri:" attribute is
      CAUTION.

   There are no multiplexing rules specified for the ws-uri and wss-uri
   SDP media-level attributes.  Additionally, the specification of
   multiplexing rules for the ws-uri and wss-uri attributes is outside
   the scope of this document.

   While it is technically possible to bundle WebSocket, there are a
   variety of reasons that make it impractical and it is thus considered
   unlikely to be used in practice.  Therefore, the ws-uri and wss-uri
   SDP media-level attributes defined in Section 3.2 and Section 3.3 for
   using WebSocket as a transport protocol are not likely to be used

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   with SDP bundle and are consequently categorized as CAUTION for
   multiplexing.

   If future extensions define how to bundle WebSocket then multiplexing
   rules for the "a=ws-uri:" and "a=wss-uri:" attributes need to be
   defined as well, for instance in an extension of this SDP based
   WebSocket negotiation specification.

4.  SDP Offer/Answer Procedures

4.1.  General

   An endpoint (i.e., both the offerer and the answerer) that wishes to
   negotiate WebSocket as transport protocol MUST indicate that it
   wishes to use WebSocket or secure WebSocket in the "proto" field of
   the "m=" line.  Furthermore, the server side, which could be either
   the offerer or answerer, MUST add an "a=ws-uri" or "a=wss-uri"
   attribute in the media section depending on whether it wishes to use
   WebSocket or secure WebSocket.  This new attribute MUST follow the
   syntax defined in Section 3.  The procedures in this section apply to
   an "m=" line associated with any media stream that uses WebSocket or
   secure WebSocket as transport.

4.2.  Generating the Initial Offer

   An SDP offerer in order to negotiate WebSocket as a transport MUST
   indicate the same in the "proto" field of the "m=" line.  For
   example, to negotiate BFCP-over-WebSocket the "proto" value in the
   "m=" line MUST be TCP/WSS/BFCP if WebSocket is over TLS, else it MUST
   be TCP/WS/BFCP.

   The offerer SHOULD assign the SDP "setup" attribute with a value of
   "active" (the offerer will be the initiator of the outgoing TCP
   connection), unless the offerer insists on being a receiver of an
   incoming connection, in which case the offerer SHOULD use a value of
   "passive".  The offerer MUST NOT assign an SDP "setup" attribute with
   a "holdconn" value.  If the "setup" attribute has a value "passive"
   it MUST have a URI in the "a=ws-uri" or "a=wss-uri" attribute.

   The following is an example of an "m=" line for a BFCP connection:

   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

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   In the above example, the client is intending to setup the TLS /TCP
   connection and hence the port is set to a value of 9, which is the
   discard port.

4.3.  Generating the Answer

   If the answerer accepts the offered WebSocket transport connection,
   in the associated SDP answer, the answerer MUST assign an SDP "setup"
   attribute with a value of either "active" or "passive", according to
   the procedures in [RFC4145].  The answerer MUST NOT assign an SDP
   "setup" attribute with a value of "holdconn".

   If the answerer assigns an SDP "setup" attribute with a value of
   "active", the answerer MUST initiate the WebSocket connection
   handshake by acting as client on the negotiated media stream, towards
   the URI specified in "a=ws-uri" or "a=wss-uri" using the procedures
   described in [RFC6455].

   If the answers assigns SDP "setup" attribute with "passive", then it
   MUST have a URI in either "a=ws-uri" or "a=wss-uri" attribute
   depending on whether the application uses WebSocket or
   secureWebSocket.  This attribute MUST follow the syntax defined in
   Section 3.  For BFCP application, the "proto" value in the "m=" line
   MUST be TCP/WSS/BFCP if WebSocket is run on TLS, else it MUST be
   TCP/WS/BFCP.

   The following example shows a case where the server responds with a
   BFCP media stream over a WebSocket connection running TLS.  It shows
   an answer "m=" line for the BFCP connection.  In this example since
   WebSockets is running over TLS, the server answers back with "a=wss-
   uri" attribute in the media section of SDP indicating the connection
   URI:

   Answer (server):
   m=application 50000 TCP/WSS/BFCP *
   a=setup:passive
   a=connection:new
   a=wss-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

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4.4.  Offerer Processing of the Answer

   When the offerer receives an SDP answer, if the offerer ends up being
   active it MUST follow the procedures in Section 5.

4.5.  Modifying the Session

   Once an offer/answer exchange has been completed, either endpoint MAY
   send a new offer in order to modify the session.  The endpoints can
   reuse the existing WebSocket connection by adding
   "a=connection:existing" attribute in the media section of SDP
   following the rules mentioned in [RFC4145] if the ws-uri values and
   the transport parameters indicated by each endpoint are unchanged.
   Otherwise, following the rules for the initial offer/answer exchange,
   the endpoints can negotiate and create a new WebSocket connection on
   top of TLS/TCP or TCP.

4.6.  Offerless INVITE Scenarios

   In some scenarios an endpoint (e.g., a browser) originating the call
   (UAC) can send an offerless INVITE to the server.  The server will
   generate an offer in response to the INVITE.  In such cases the
   server MUST send an offer with setup attribute as "passive" so as to
   accept incoming connection and MUST include "a=wss-uri" or "a=ws-uri"
   attribute in the media section depending on whether the server wishes
   to use WebSocket or secure WebSocket.  The SDP offer sent by the
   server will look like the example in Section 4.3.

5.  Procedures at WebSocket Client

   The webSocket client MUST always initiate the outgoing TCP connection
   and hence the SDP a=setup attribute MUST be always "active" for the
   WebSocket client in its SDP offer/answer.  In the below example, the
   WebSocket client is the offerer and hence assigns "setup" attribute
   with a value of "active".

   The WebSocket server is a server on the Internet and hence MUST
   always assign SDP "setup" attribute with a value of "passive".  This
   also avoids the need to use ICE between WebSocket Client and
   WebSocket Server as the connection model here would be a typical
   client to server web connection.

   Once the offer/answer is complete the client MUST initiate the
   WebSocket connection handshake by sending a GET message on the
   negotiated media stream, towards the URI specified in "a=ws-uri" or
   "a=wss-uri" as per the procedures described in [RFC6455].  When no
   port is passed in the "a=wss-uri" or "a=ws-uri" attribute, the
   default port (80 or 443) is used.

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6.  Security Considerations

   An attacker may attempt to add, modify, or remove 'a=ws-uri' or
   'a=wss-uri' attribute from a session description.  This could result
   in an application behaving undesirably.  Consequently, it is
   RECOMMENDED that integrity protection be applied to the SDP session
   descriptions.  For session descriptions carried in SIP [RFC3261], S/
   MIME is available to provide such end-to-end integrity protection.

   It is also RECOMMENDED that the application signaling traffic being
   transported over a WebSocket communication session be protected by
   using a secure WebSocket connection (using TLS [RFC5246] over TCP).

   The WebSocket clients have to initiate the TCP connection to the
   WebSocket server identified by the FQDN in a=ws/a=wss-uri.  Further
   as with any other web connection, the clients will verify the servers
   certificate.  The WebSocket client MUST follow the procedures in
   [RFC7525] while setting up TLS connection with webSocket server.

7.  IANA Considerations

7.1.  Registration of the 'ws-uri' SDP Media Attribute

   NOTE to RFC Editor: Please replace "XXXX" with the number of this
   RFC.

   This document defines a new SDP media-level attribute "ws-uri" in
   Section 3.2 and requests that IANA to register the following SDP att-
   field under the Session Description Protocol (SDP) Parameters
   registry as follows:

   +---------------------+---------------------------------------------+
   | Attribute name:     | ws-uri                                      |
   | Long-form attribute | Websocket Connection URI                    |
   | name:               |                                             |
   | Type of attribute:  | media                                       |
   | Mux category:       | CAUTION                                     |
   | Charset Dependent:  | No                                          |
   | Purpose:            | The 'ws-uri' attribute is intended to be    |
   |                     | used as a connection URI for opening the    |
   |                     | WebSocket connection.                       |
   | Appropriate values: | A ws-URI as defined in [RFC6455]            |
   | Contact name:       | Gonzalo Salgueiro                           |
   | Contact e-mail:     | gsalguei@cisco.com                          |
   | Reference:          | RFCXXXX                                     |
   +---------------------+---------------------------------------------+

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7.2.  Registration of the 'wss-uri' SDP Media Attribute

   NOTE to RFC Editor: Please replace "XXXX" with the number of this
   RFC.

   This document defines a new SDP media-level attribute "wss-uri" in
   Section 3.3 and requests that IANA to register the following SDP att-
   field under the Session Description Protocol (SDP) Parameters
   registry as follows:

   +---------------------+---------------------------------------------+
   | Attribute name:     | wss-uri                                     |
   | Long-form attribute | Websocket Connection URI over Secure        |
   | name:               | Transport                                   |
   | Type of attribute:  | media                                       |
   | Mux category:       | CAUTION                                     |
   | Charset Dependent:  | No                                          |
   | Purpose:            | The 'wss-uri' attribute is intended to be   |
   |                     | used as a connection URI for opening the    |
   |                     | WebSocket connection over a secure          |
   |                     | transport.                                  |
   | Appropriate values: | A wss-URI as defined in [RFC6455]           |
   | Contact name:       | Gonzalo Salgueiro                           |
   | Contact e-mail:     | gsalguei@cisco.com                          |
   | Reference:          | RFCXXXX                                     |
   +---------------------+---------------------------------------------+

8.  Acknowledgements

   Thanks to Christer Holmberg for raising the need for a BFCP-
   independent SDP attribute for WebSocket Connection URI.

   The authors wish to acknowledge Paul Kyzivat, Suhas Nandakumar,
   Christer Holmberg, Charles Eckel, Dan Wing, Alissa Cooper and Joel
   Halpern for their invaluable suggestions and review comments.

9.  References

9.1.  Normative References

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

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

   [RFC6455]  Fette, I. and A. Melnikov, "The WebSocket Protocol",
              RFC 6455, DOI 10.17487/RFC6455, December 2011,
              <http://www.rfc-editor.org/info/rfc6455>.

9.2.  Informative References

   [I-D.ietf-bfcpbis-bfcp-websocket]
              Pascual, V., Roman, A., Cazeaux, S., Salgueiro, G., R, R.,
              and S. Murillo, "The WebSocket Protocol as a Transport for
              the Binary Floor Control Protocol (BFCP)", draft-ietf-
              bfcpbis-bfcp-websocket-13 (work in progress), December
              2016.

   [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-16 (work in progress), November
              2015.

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

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

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

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

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <http://www.rfc-editor.org/info/rfc5246>.

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   [RFC7118]  Baz Castillo, I., Millan Villegas, J., and V. Pascual,
              "The WebSocket Protocol as a Transport for the Session
              Initiation Protocol (SIP)", RFC 7118,
              DOI 10.17487/RFC7118, January 2014,
              <http://www.rfc-editor.org/info/rfc7118>.

   [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Message Syntax and Routing",
              RFC 7230, DOI 10.17487/RFC7230, June 2014,
              <http://www.rfc-editor.org/info/rfc7230>.

   [RFC7395]  Stout, L., Ed., Moffitt, J., and E. Cestari, "An
              Extensible Messaging and Presence Protocol (XMPP)
              Subprotocol for WebSocket", RFC 7395,
              DOI 10.17487/RFC7395, October 2014,
              <http://www.rfc-editor.org/info/rfc7395>.

   [RFC7525]  Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
              2015, <http://www.rfc-editor.org/info/rfc7525>.

   [RFC7977]  Dunkley, P., Llewellyn, G., Pascual, V., Salgueiro, G.,
              and R. Ravindranath, "The WebSocket Protocol as a
              Transport for the Message Session Relay Protocol (MSRP)",
              RFC 7977, DOI 10.17487/RFC7977, September 2016,
              <http://www.rfc-editor.org/info/rfc7977>.

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

Authors' Addresses

   Ram Mohan Ravindranath
   Cisco Systems, Inc.
   Cessna Business Park,
   Kadabeesanahalli Village, Varthur Hobli,
   Sarjapur-Marathahalli Outer Ring Road
   Bangalore, Karnataka  560103
   India

   Email: rmohanr@cisco.com

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

   Email: gsalguei@cisco.com

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