The WebSocket Protocol as a Transport for the Message Session Relay Protocol (MSRP)
draft-pd-dispatch-msrp-websocket-04

The information below is for an old version of the document
Document Type Active Internet-Draft (individual)
Authors Peter Dunkley  , Gavin Llewellyn  , Victor Pascual  , Anton Roman  , Gonzalo Salgueiro 
Last updated 2013-12-13
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Dispatch Working Group                                        P. Dunkley
Internet-Draft                                              G. Llewellyn
Updates: 4975, 4976 (if approved)                      Crocodile RCS Ltd
Intended status: Standards Track                              V. Pascual
Expires: June 16, 2014                                          A. Roman
                                                                  Quobis
                                                            G. Salgueiro
                                                                   Cisco
                                                       December 13, 2013

  The WebSocket Protocol as a Transport for the Message Session Relay
                            Protocol (MSRP)
                  draft-pd-dispatch-msrp-websocket-04

Abstract

   The WebSocket protocol enables two-way real-time communication
   between clients and servers.  This document specifies a new WebSocket
   sub-protocol as a reliable transport mechanism between MSRP (Message
   Session Relay Protocol) clients and relays to enable usage of MSRP in
   new scenarios.  This document normatively updates RFC 4975 and RFC
   4976.

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
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   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 June 16, 2014.

Copyright Notice

   Copyright (c) 2013 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

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   (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
   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  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  The WebSocket Protocol  . . . . . . . . . . . . . . . . . . .   4
   4.  The WebSocket MSRP Sub-Protocol . . . . . . . . . . . . . . .   5
     4.1.  Handshake . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.2.  MSRP Encoding . . . . . . . . . . . . . . . . . . . . . .   6
   5.  MSRP WebSocket Transport  . . . . . . . . . . . . . . . . . .   6
     5.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .   6
     5.2.  Updates to RFC 4975 . . . . . . . . . . . . . . . . . . .   6
       5.2.1.  MSRP URI Transport Parameter  . . . . . . . . . . . .   6
       5.2.2.  SDP Transport Protocol  . . . . . . . . . . . . . . .   7
     5.3.  Updates to RFC 4976 . . . . . . . . . . . . . . . . . . .   7
       5.3.1.  AUTH Request Authentication . . . . . . . . . . . . .   7
       5.3.2.  Use of TLS  . . . . . . . . . . . . . . . . . . . . .   7
   6.  Connection Keep-alive . . . . . . . . . . . . . . . . . . . .   7
   7.  Authentication  . . . . . . . . . . . . . . . . . . . . . . .   8
   8.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .   9
     8.1.  AUTH  . . . . . . . . . . . . . . . . . . . . . . . . . .   9
     8.2.  SDP Exchange (MSRP WebSocket Client to MSRP Client) . . .  10
     8.3.  SEND (MSRP WebSocket Client to MSRP Client) . . . . . . .  11
     8.4.  SEND (MSRP Client to MSRP WebSocket Client) . . . . . . .  13
     8.5.  SEND (MSRP WebSocket Client to MSRP WebSocket Client) . .  14
   9.  Implementation Status . . . . . . . . . . . . . . . . . . . .  16
     9.1.  Kamailio SIP Server . . . . . . . . . . . . . . . . . . .  17
     9.2.  Crocodile MSRP  . . . . . . . . . . . . . . . . . . . . .  18
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  18
     10.1.  Secure WebSocket Connection  . . . . . . . . . . . . . .  18
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  18
     11.1.  Registration of the WebSocket MSRP Sub-Protocol  . . . .  18
   12. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  19
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  19
     13.2.  Informative References . . . . . . . . . . . . . . . . .  20
   Appendix A.  Implementation Guidelines  . . . . . . . . . . . . .  21
     A.1.  MSRP WebSocket Client Considerations  . . . . . . . . . .  21
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  21

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1.  Introduction

   The WebSocket [RFC6455] protocol enables 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.

   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 smart-phones) will also make a WebSocket client
   stack available.  The specification in this document enables usage of
   MSRP in these scenarios.

   This specification defines a new WebSocket sub-protocol (as defined
   in section 1.9 in [RFC6455]) for transporting MSRP messages between a
   WebSocket client and MSRP relay [RFC4976] containing a WebSocket
   server, a new transport for MSRP, and procedures for MSRP clients and
   relays implementing the WebSocket transport.

   MSRP over WebSocket is well suited for MSRP interactions between
   clients and servers.  Common use cases for MSRP over WebSocket
   include:

   o  Human-to-machine messaging

   o  Client-to-server data exchange (for example, application control
      signalling)

   o  Human-to-human messaging where local policy requires
      authentication and/or logging

2.  Terminology

   All diagrams, examples, and notes in this specification are non-
   normative, as are all sections explicitly marked non-normative.
   Everything else in this specification is normative.

   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].

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2.1.  Definitions

   MSRP WebSocket Client:  An MSRP entity capable of opening outbound
         connections to MSRP relays which are WebSocket servers and
         communicating using the WebSocket MSRP sub-protocol as defined
         by this document.

   MSRP WebSocket Server:  An MSRP entity (specifically an MSRP relay
         [RFC4976]) capable of listening for inbound connections from
         WebSocket clients and communicating using the WebSocket MSRP
         sub-protocol as defined by this document.

3.  The WebSocket Protocol

   _This section is non-normative._

   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 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 (such as the WebSocket MSRP 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.

   WebSocket 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.

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      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 MSRP 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 MSRP sub-protocol for carrying MSRP requests
   and responses through a WebSocket connection.

4.1.  Handshake

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

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

     GET / HTTP/1.1
     Host: a.example.com
     Upgrade: websocket
     Connection: Upgrade
     Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==
     Origin: http://www.example.com
     Sec-WebSocket-Protocol: msrp
     Sec-WebSocket-Version: 13

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

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

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

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4.2.  MSRP Encoding

   WebSocket messages can be transported in either UTF-8 text frames or
   binary frames.  MSRP [RFC4975] allows both text and binary bodies in
   MSRP requests.  Therefore MSRP WebSocket Clients and Servers MUST
   accept both text and binary frames.

5.  MSRP WebSocket Transport

5.1.  General

   WebSocket clients cannot receive WebSocket connections initiated by
   other WebSocket clients or WebSocket servers.  This means that it is
   impossible for an MSRP client to communicate directly with other MSRP
   clients.  Therefore, all MSRP over WebSocket messages MUST be routed
   via an MSRP WebSocket Server.

   MSRP WebSocket Servers can be used to route MSRP messages between
   MSRP WebSocket Clients, and between MSRP WebSocket Clients and
   "normal" MSRP clients and relays.

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

      This simplifies parsing of MSRP messages for both clients and
      servers.  When large messages are sent MSRP chunking (as defined
      in section 5.1 of [RFC4975]) MUST be used to split the message
      into several smaller MSRP chunks.

5.2.  Updates to RFC 4975

5.2.1.  MSRP URI Transport Parameter

   This document defines the value "ws" as the transport parameter value
   for an MSRP URI [RFC3986] to be contacted using the MSRP WebSocket
   sub-protocol as transport.

   The updated augmented BNF (Backus-Naur Form) [RFC5234] for this
   parameter is the following (the original BNF for this parameter can
   be found in [RFC4975]):

     transport  =  "tcp" / "ws" / 1*ALPHANUM

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5.2.2.  SDP Transport Protocol

   This document does not define a new SDP transport protocol for MSRP
   over WebSockets.  As all MSRP over WebSocket messages MUST be routed
   via an MSRP WebSocket Server, it is acceptable for an MSRP WebSocket
   Client to specify the "TCP/MSRP" or "TCP/TLS/MSRP" protocols in the
   SDP m-line - that being the protocol used by non-WebSocket clients
   and between MSRP relays ([RFC4975] section 8.1).

   The "ws" transport parameter will appear in the endpoint URI in SDP
   "path" attribute ([RFC4975] section 8.2); compliant MSRP
   implementation should already allow unrecognised transports, provided
   that they do not have to establish a direct connection to the
   resource described by the URI.

5.3.  Updates to RFC 4976

5.3.1.  AUTH Request Authentication

   The MSRP relay specification [RFC4976] states that AUTH requests MUST
   be authenticated.  This document modifies this requirement to state
   that all connections between MSRP clients and relays MUST be
   authenticated.  In the case of the MSRP WebSocket Clients there are
   two possible authentication mechanisms:

   1.  HTTP Digest authentication in AUTH (as per [RFC4976]).

   2.  Cookie-based or HTTP Digest authentication in the WebSocket
       Handshake (see Section 7).

5.3.2.  Use of TLS

   The MSRP relay specification [RFC4976] mandates the use of TLS
   between MSRP clients and MSRP relays, and specifies the mechanisms
   that must be used for TLS authentication.  This document downgrades
   the MUSTs with respect to TLS to SHOULDs when using the MSRP
   WebSocket sub-protocol as transport.  Connections between MSRP
   WebSocket Clients and Servers SHOULD use secure WebSocket
   connections, but MAY use insecure WebSocket connections.  As the
   secure WebSocket connections are negotiated between the client's
   WebSocket stack and the WebSocket server, an MSRP WebSocket Client
   may have no knowledge of, or control over, the mechanisms used for
   TLS authentication.

6.  Connection Keep-alive

   _This section is non-normative._

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   It is RECOMMENDED that MSRP WebSocket Clients and Servers keep their
   WebSocket connections open by sending periodic WebSocket "Ping"
   frames as described in [RFC6455] section 5.5.2.

      The WebSocket API [WS-API] does not provide a mechanism for
      applications running in a web browser to control whether or not
      periodic WebSocket "Ping" frames are sent to the server.  The
      implementation of such a keep alive feature is the decision of
      each web browser manufacturer and may also depend on the
      configuration of the web browser.

   A future WebSocket protocol extension providing a similar keep alive
   mechanism could also be used.

   When MSRP WebSocket Clients or Servers cannot use WebSocket "Ping"
   frames to keep connections open an MSRP implementation MAY use
   bodiless SEND requests as described in [RFC4975] section 7.1.

7.  Authentication

   _This section is non-normative._

   Prior to sending MSRP requests, an MSRP WebSocket Client connects to
   an MSRP 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 MSRP WebSocket
   Server MAY inspect any HTTP headers present (for example, Cookie
   [RFC6265], Host [RFC2616], or Origin [RFC6454]) 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 MSRP 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.

   If the HTTP GET request contains an Origin header the MSRP WebSocket
   Server SHOULD indicate Cross-Origin Resource Sharing [CORS] by adding
   an Access-Control-Allow-Origin header to the 101 response.

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   Regardless of whether the MSRP WebSocket Server requires
   authentication during the WebSocket handshake, authentication MAY be
   requested at MSRP protocol level.  Therefore an MSRP WebSocket Client
   SHOULD support HTTP Digest [RFC2617] authentication as stated in
   [RFC4976].

8.  Examples

8.1.  AUTH

   Alice    (MSRP WSS)     a.example.com
   |                             |
   |HTTP GET (WS handshake) F1   |
   |---------------------------->|
   |101 Switching Protocols F2   |
   |<----------------------------|
   |                             |
   |AUTH F3                      |
   |---------------------------->|
   |200 OK F4                    |
   |<----------------------------|
   |                             |

   Alice loads a web page using her web browser and retrieves JavaScript
   code implementing the WebSocket MSRP sub-protocol defined in this
   document.  The JavaScript code (an MSRP WebSocket Client) establishes
   a secure WebSocket connection with an MSRP relay (an MSRP WebSocket
   Server) at a.example.com.  Upon WebSocket connection, Alice
   constructs and sends an MSRP AUTH request.  Since the JavaScript
   stack in a browser has no way to determine the local address from
   which the WebSocket connection was made, this implementation uses a
   random ".invalid" domain name for the hostpart of the From-Path URI
   (see Appendix A.1).

   Message details (authentication is omitted for simplicity):

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   F1 HTTP GET (WS handshake)  Alice -> a.example.com (TLS)

   GET / HTTP/1.1
   Host: a.example.com
   Upgrade: websocket
   Connection: Upgrade
   Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==
   Origin: https://www.example.com
   Sec-WebSocket-Protocol: msrp
   Sec-WebSocket-Version: 13

   F2 101 Switching Protocols  a.example.com -> Alice (TLS)

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

   F3 AUTH  Alice -> a.example.com (transport WSS)

   MSRP 49fi AUTH
   To-Path: msrps://alice@a.example.com:443;ws
   From-Path: msrps://df7jal23ls0d.invalid:2855/98cjs;ws
   -------49fi$

   F4 200 OK  a.example.com -> Alice (transport WSS)

   MSRP 49fi 200 OK
   To-Path: msrps://df7jal23ls0d.invalid:2855/98cjs;ws
   From-Path: msrps://alice@a.example.com:443;ws
   Use-Path: msrps://a.example.com:2855/jui787s2f;tcp
   Expires: 900
   -------49fi$

8.2.  SDP Exchange (MSRP WebSocket Client to MSRP Client)

   The following example shows SDP that could be included in a SIP
   message to set up an MSRP session between Alice and Bob where Alice
   uses a WebSocket MSRP relay.

   Note that SDP does not permit line folding.  A "\" in the examples
   shows a line continuation due to limitations in line length of this
   document.  Neither the backslash nor the extra CRLF is included in
   the actual SDP.

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   Alice makes an offer with a path including the relay:

   c=IN IP4 a.example.com
   m=message 1234 TCP/TLS/MSRP *
   a=accept-types:message/cpim text/plain text/html
   a=path:msrps://a.example.com:2855/jui787s2f;tcp \
          msrps://df7jal23ls0d.invalid:2855/98cjs;ws

   In this offer, Alice wishes to receive MSRP messages via the relay at
   a.example.com.  She wants to use TLS as the transport for the MSRP
   session (beyond the relay).  She can accept message/cpim, text/plain,
   and text/html message bodies in SEND requests.

   Bob's answer to this offer could look like:

   c=IN IP4 bob.example.com
   m=message 1234 TCP/TLS/MSRP *
   a=accept-types:message/cpim text/plain
   a=path:msrps://bob.example.com:8145/foo;tcp

   Here Bob wishes to receive the MSRP messages at bob.example.com.  He
   can accept only message/cpim and text/plain message bodies in SEND
   requests and has rejected the text/html content offered by Alice.  He
   does not need a relay to set up the MSRP session.

8.3.  SEND (MSRP WebSocket Client to MSRP Client)

   Alice    (MSRP WSS)     a.example.com      (MSRP TLS)     Bob
   |                             |                             |
   |SEND F1                      |                             |
   |---------------------------->|                             |
   |200 OK F2                    |                             |
   |<----------------------------|                             |
   |                             |SEND F3                      |
   |                             |---------------------------->|
   |                             |200 OK F4                    |
   |                             |<----------------------------|

   In the same scenario Alice sends an instant message to Bob (session
   details having been previously negotiated by some other mechanism -
   such as SDP [RFC4976]).  The MSRP WebSocket Server at a.example.com
   acts as an MSRP relay, routing the message to Bob over TLS.

   In this example Bob himself does not require an MSRP relay and has
   not authenticated with a.example.com but Alice does and has.

   Message details (note that MSRP does not permit line folding.  A "\"
   in the examples shows a line continuation due to limitations in line

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   length of this document.  Neither the backslash nor the extra CRLF is
   included in the actual request or response):

   F1 SEND  Alice -> a.example.com (transport WSS)

   MSRP 6aef SEND
   To-Path: msrps://a.example.com:2855/jui787s2f;tcp \
            msrps://bob.example.com:8145/foo;tcp
   From-Path: msrps://df7jal23ls0d.invalid:2855/98cjs;ws
   Success-Report: no
   Byte-Range: 1-*/*
   Message-ID: 87652
   Content-Type: text/plain

   Hi Bob, I'm about to send you file.mpeg
   -------6aef$

   F2 200 OK  a.example.com -> Alice (transport WSS)

   MSRP 6aef 200 OK
   To-Path: msrps://df7jal23ls0d.invalid:2855/98cjs;ws
   From-Path: msrps://a.example.com:2855/jui787s2f;tcp
   -------6aef$

   F3 SEND  a.example.com -> Bob (transport TLS)

   MSRP juh76 SEND
   To-Path: msrps://bob.example.com:8145/foo;tcp
   From-Path:  msrps://a.example.com:2855/jui787s2f;tcp \
               msrps://df7jal23ls0d.invalid:2855/98cjs;ws
   Success-Report: no
   Byte-Range: 1-*/*
   Message-ID: 87652
   Content-Type: text/plain

   Hi Bob, I'm about to send you file.mpeg
   -------juh76$

   F4 200 OK  Bob -> a.example.com (transport TLS)

   MSRP juh76 200 OK
   To-Path: msrps://a.example.com:2855/jui787s2f;tcp
   From-Path: msrps://bob.example.com:8145/foo;tcp
   -------juh76$

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8.4.  SEND (MSRP Client to MSRP WebSocket Client)

   Bob      (MSRP TLS)     a.example.com     (MSRP WSS)    Alice
   |                             |                             |
   |SEND F1                      |                             |
   |---------------------------->|                             |
   |200 OK F2                    |                             |
   |<----------------------------|                             |
   |                             |SEND F3                      |
   |                             |---------------------------->|
   |                             |200 OK F4                    |
   |                             |<----------------------------|

   In the same scenario Bob sends an instant message to Alice (session
   details having been previously negotiated by some other mechanism -
   such as SDP [RFC4976]).  The MSRP WebSocket Server at a.example.com
   acts as an MSRP relay, routing the message to Alice over secure
   WebSocket.

   In this example Bob himself does not require an MSRP relay and has
   not authenticated with a.example.com but Alice does and has.

   Message details (note that MSRP does not permit line folding.  A "\"
   in the examples shows a line continuation due to limitations in line
   length of this document.  Neither the backslash nor the extra CRLF is
   included in the actual request or response):

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   F1 SEND  Bob -> a.example.com (transport TLS)

   MSRP xght6 SEND
   To-Path: msrps://a.example.com:2855/jui787s2f;tcp \
            msrps://df7jal23ls0d.invalid:2855/98cjs;ws
   From-Path: msrps://bob.example.com:8145/foo;tcp
   Success-Report: no
   Byte-Range: 1-*/*
   Message-ID: 87652
   Content-Type: text/plain

   Thanks for the file.
   -------xght6$

   F2 200 OK  a.example.com -> Bob (transport TLS)

   MSRP xght6 200 OK
   To-Path: msrps://bob.example.com:8145/foo;tcp
   From-Path: msrps://a.example.com:2855/jui787s2f;tcp
   -------xght6$

   F3 SEND  a.example.com -> Alice (transport WSS)

   MSRP yh67 SEND
   To-Path:  msrps://df7jal23ls0d.invalid:2855/98cjs;ws
   From-Path:  msrps://a.example.com:2855/jui787s2f;tcp \
               msrps://bob.example.com:8145/foo;tcp
   Success-Report: no
   Byte-Range: 1-*/*
   Message-ID: 87652
   Content-Type: text/plain

   Hi Bob, I'm about to send you file.mpeg
   -------yh67$

   F4 200 OK  Bob -> a.example.com (transport TLS)

   MSRP yh67 200 OK
   To-Path:  msrps://a.example.com:2855/jui787s2f;tcp
   From-Path:  msrps://df7jal23ls0d.invalid:2855/98cjs;ws
   -------yh67$

8.5.  SEND (MSRP WebSocket Client to MSRP WebSocket Client)

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   Alice    (MSRP WSS)     a.example.com     (MSRP WSS)    Carol
   |                             |                             |
   |SEND F1                      |                             |
   |---------------------------->|                             |
   |200 OK F2                    |                             |
   |<----------------------------|                             |
   |                             |SEND F3                      |
   |                             |---------------------------->|
   |                             |200 OK F4                    |
   |                             |<----------------------------|

   In the same scenario Alice sends an instant message to Carol (session
   details having been previously negotiated by some other mechanism -
   such as SDP [RFC4976]).  The MSRP WebSocket Server at a.example.com
   acts as an MSRP relay, routing the message to Carol over secure
   WebSocket.

   In this example both Alice and Carol are using MSRP WebSocket Clients
   and an MSRP WebSocket Server.  This means that a.example.com will
   appear twice in the To-Path in F1. a.example.com can either handle
   this internally or loop the MSRP SEND request back to itself as if it
   were two, separate, MSRP relays.

   Message details (note that MSRP does not permit line folding.  A "\"
   in the examples shows a line continuation due to limitations in line
   length of this document.  Neither the backslash nor the extra CRLF is
   included in the actual request or response):

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   F1 SEND  Alice -> a.example.com (transport WSS)

   MSRP kjh6 SEND
   To-Path: msrps://a.example.com:2855/jui787s2f;tcp \
            msrps://a.example.com:2855/iwnslt;tcp \
            msrps://jk9awp14vj8x.invalid:2855/76qwe;ws
   From-Path: msrps://df7jal23ls0d.invalid:2855/98cjs;ws
   Success-Report: no
   Byte-Range: 1-*/*
   Message-ID: 87652
   Content-Type: text/plain

   Carol, here is the file Bob sent me.
   -------kjh6$

   F2 200 OK  a.example.com -> Alice (transport WSS)

   MSRP kjh6 200 OK
   To-Path: msrps://df7jal23ls0d.invalid:2855/98cjs;ws
   From-Path: msrps://a.example.com:2855/jui787s2f;tcp
   -------kjh6$

   F3 SEND  a.example.com -> Carol (transport WSS)

   MSRP re58 SEND
   To-Path: msrps://jk9awp14vj8x.invalid:2855/76qwe;ws
   From-Path: msrps://a.example.com:2855/iwnslt;tcp \
              msrps://a.example.com:2855/jui787s2f;tcp \
              msrps://df7jal23ls0d.invalid/98cjs;ws
   Success-Report: no
   Byte-Range: 1-*/*
   Content-Type: text/plain

   Carol, here is the file Bob sent me.
   -------re58$

   F4 200 OK  Carol -> a.example.com (transport WSS)

   MSRP re58 200 OK
   To-Path: msrps://a.example.com:2855/iwnslt;tcp
   From-Path: msrps://jk9awp14vj8x.invalid:2855/76qwe;ws
   -------re58$

9.  Implementation Status

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   Note to RFC Editor: Please remove this section and the reference to
   [RFC6982] before publication.

   This section records the status of known implementations of the
   protocol defined by this specification at the time of posting of this
   Internet-Draft, and is based on a proposal described in [RFC6982].
   The description of implementations in this section is intended to
   assist the IETF in its decision processes in progressing drafts to
   RFCs.  Please note that the listing of any individual implementation
   here does not imply endorsement by the IETF.  Furthermore, no effort
   has been spent to verify the information presented here that was
   supplied by IETF contributors.  This is not intended as, and must not
   be construed to be, a catalog of available implementations or their
   features.  Readers are advised to note that other implementations may
   exist.

   According to [RFC6982], "this will allow reviewers and working groups
   to assign due consideration to documents that have the benefit of
   running code, which may serve as evidence of valuable experimentation
   and feedback that have made the implemented protocols more mature.
   It is up to the individual working groups to use this information as
   they see fit".

9.1.  Kamailio SIP Server

   Organization:   Kamailio

   Name:   Kamailio v4.0.0 (4.0.0 http://www.kamailio.org/w/
      kamailio-v4-0-0-release-notes/)

   Description:   Kamailio (former OpenSER) is an Open Source SIP
      Server, able to handle thousands of call setups per second. (http:
      //www.kamailio.org)

   Level of maturity:   Beta

   Coverage:   This module implements a WebSocket (RFC 6455) server and
      provides connection establishment (handshaking), management
      (including connection keep-alive), and framing for the SIP and
      MSRP WebSocket sub-protocols (draft-ietf-sipcore-sip-websocket and
      draft-pd-dispatch-msrp-websocket).  The module supports WebSockets
      (ws) and secure WebSockets (wss).

   Licensing:   Open Source GPLv2

   Contact:   http://www.kamailio.org/w/contact-us/

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   URL:   http://git.sip-router.org/cgi-bin/
      gitweb.cgi?p=kamailio;a=tree;f=modules/
      websocket;h=e75c6cd28493f812a955eeff9e64905aee01bcbf;hb=HEAD

      http://git.sip-router.org/cgi-bin/
      gitweb.cgi?p=kamailio;a=tree;f=modules/
      msrp;h=0ffaeb57fb43a4d429680209262ad847f7ce6074;hb=HEAD

9.2.  Crocodile MSRP

   Organization:   Crocodile RCS Ltd.

   Name:   Crocodile MSRP (https://github.com/crocodilertc/crocodile-
      msrp)

   Description:   Crocodile MSRP is a Javascript MSRP over WebSocket
      stack.

   Level of maturity:   Beta

   Coverage:   Open source client implementation of draft-pd-dispatch-
      msrp-websocket.

   Licensing:   Released under the MIT license (http://
      www.opensource.org/licenses/mit-license.php).

   Contact:   Gavin Llewellyn (gavin.llewellyn@crocodilertc.net)

   URL:   https://github.com/crocodilertc/crocodile-msrp

10.  Security Considerations

10.1.  Secure WebSocket Connection

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

11.  IANA Considerations

11.1.  Registration of the WebSocket MSRP Sub-Protocol

   This specification requests IANA to register the WebSocket MSRP sub-
   protocol in the registry of WebSocket sub-protocols with the
   following data:

   Subprotocol Identifier:  msrp

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   Subprotocol Common Name:  WebSocket Transport for MSRP (Message
      Session Relay Protocol)

   Subprotocol Definition:  TBD, it should point to this document

12.  Acknowledgements

   Special thanks to Inaki Baz Castillo, Jose Luis Millan Villegas, and
   Victor Pascual, the authors of [I-D.ietf-sipcore-sip-websocket] which
   has inspired this draft.

   Additional thanks to Inaki Baz Castillo who pointed out that "web-
   browser" shouldn't be used all the time as this specification should
   be valid for smartphones and apps other than browsers and suggested
   clarifications to the SDP handling for MSRP over WebSocket.

   Special thanks to James Wyatt from Crocodile RCS Ltd for helping with
   the JavaScript MSRP over WebSockets prototyping.

   Thanks to Saul Ibarra Corretge for suggesting that the existing MSRP
   keep alive mechanism may be used when WebSocket pings are not
   available.

13.  References

13.1.  Normative References

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

   [RFC4975]  Campbell, B., Mahy, R., and C. Jennings, "The Message
              Session Relay Protocol (MSRP)", RFC 4975, September 2007.

   [RFC4976]  Jennings, C., Mahy, R., and A. Roach, "Relay Extensions
              for the Message Sessions Relay Protocol (MSRP)", RFC 4976,
              September 2007.

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

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

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13.2.  Informative References

   [CORS]     W3C and A. van Kesteren, Ed., "Cross-Origin Resource
              Sharing", January 2013.

   [I-D.ietf-sipcore-sip-websocket]
              Castillo, I., Millan, J., and V. Pascual, "The WebSocket
              Protocol as a Transport for the Session Initiation
              Protocol (SIP)", draft-ietf-sipcore-sip-websocket-09 (work
              in progress), June 2013.

   [RFC2606]  Eastlake, D. and A. Panitz, "Reserved Top Level DNS
              Names", BCP 32, RFC 2606, June 1999.

   [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.

   [RFC2617]  Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
              Leach, P., Luotonen, A., and L. Stewart, "HTTP
              Authentication: Basic and Digest Access Authentication",
              RFC 2617, June 1999.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66, RFC
              3986, January 2005.

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

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

   [RFC6454]  Barth, A., "The Web Origin Concept", RFC 6454, December
              2011.

   [RFC6982]  Sheffer, Y. and A. Farrel, "Improving Awareness of Running
              Code: The Implementation Status Section", RFC 6982, July
              2013.

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

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Appendix A.  Implementation Guidelines

   _This section is non-normative._

A.1.  MSRP WebSocket Client Considerations

   The JavaScript stack in web browsers does not have the ability to
   discover the local transport address used for originating WebSocket
   connections.  Therefore the MSRP WebSocket Client constructs a domain
   name consisting of a random token followed by the ".invalid" top-
   level domain name, as stated in [RFC2606], and uses it within its
   From-Path headers.

      The From-Path URI provided by MSRP clients which use an MSRP relay
      is not used for routing MSRP messages, thus it is safe to set a
      random domain in the hostpart of the From-Path URI.

Authors' Addresses

   Peter Dunkley
   Crocodile RCS Ltd
   Forum 3, Parkway
   Solent Business Park, Whiteley
   Fareham  PO15 7FH
   United Kingdom

   Email: peter.dunkley@crocodilertc.net

   Gavin Llewellyn
   Crocodile RCS Ltd
   Forum 3, Parkway
   Solent Business Park, Whiteley
   Fareham  PO15 7FH
   United Kingdom

   Email: gavin.llewellyn@crocodilertc.net

   Victor Pascual
   Quobis

   Email: victor.pascual@quobis.com

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   Anton Roman
   Quobis

   Email: anton.roman@quobis.com

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

   Email: gsalguei@cisco.com

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