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Versions: (draft-ibc-sipcore-sip-websocket) 00 01 02 03 04 05 06 07 08 09 10 RFC 7118

SIPCORE Working Group                                    I. Baz Castillo
Internet-Draft                                        J. Millan Villegas
Intended status: Standards Track                               Versatica
Expires: June 2, 2014                                         V. Pascual
                                                                  Quobis
                                                       November 29, 2013


    The WebSocket Protocol as a Transport for the Session Initiation
                             Protocol (SIP)
                  draft-ietf-sipcore-sip-websocket-10

Abstract

   The WebSocket protocol enables two-way realtime communication between
   clients and servers in web-based applications.  This document
   specifies a WebSocket sub-protocol as a reliable transport mechanism
   between SIP (Session Initiation Protocol) entities to enable usage of
   SIP in web-oriented deployments.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on June 2, 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
   (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



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   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  . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  The WebSocket Protocol . . . . . . . . . . . . . . . . . . . .  3
   4.  The WebSocket SIP Sub-Protocol . . . . . . . . . . . . . . . .  4
     4.1.  Handshake  . . . . . . . . . . . . . . . . . . . . . . . .  4
     4.2.  SIP Encoding . . . . . . . . . . . . . . . . . . . . . . .  5
   5.  SIP WebSocket Transport  . . . . . . . . . . . . . . . . . . .  6
     5.1.  Via Transport Parameter  . . . . . . . . . . . . . . . . .  6
     5.2.  SIP URI Transport Parameter  . . . . . . . . . . . . . . .  6
     5.3.  Via received Parameter . . . . . . . . . . . . . . . . . .  7
     5.4.  SIP Transport Implementation Requirements  . . . . . . . .  7
     5.5.  Locating a SIP Server  . . . . . . . . . . . . . . . . . .  8
   6.  Connection Keep-Alive  . . . . . . . . . . . . . . . . . . . .  8
   7.  Authentication . . . . . . . . . . . . . . . . . . . . . . . .  8
   8.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     8.1.  Registration . . . . . . . . . . . . . . . . . . . . . . . 10
     8.2.  INVITE Dialog through a Proxy  . . . . . . . . . . . . . . 11
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 15
     9.1.  Secure WebSocket Connection  . . . . . . . . . . . . . . . 15
     9.2.  Usage of SIPS Scheme . . . . . . . . . . . . . . . . . . . 16
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 16
     10.1. Registration of the WebSocket SIP Sub-Protocol . . . . . . 16
     10.2. Registration of new NAPTR Service Field Values . . . . . . 16
     10.3. SIP/SIPS URI Parameters Sub-Registry . . . . . . . . . . . 17
     10.4. Header Fields Sub-Registry . . . . . . . . . . . . . . . . 17
     10.5. Header Field Parameters and Parameter Values
           Sub-Registry . . . . . . . . . . . . . . . . . . . . . . . 17
     10.6. SIP Transport Sub-Registry . . . . . . . . . . . . . . . . 17
   11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 18
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
     12.1. Normative References . . . . . . . . . . . . . . . . . . . 18
     12.2. Informative References . . . . . . . . . . . . . . . . . . 19
   Appendix A.  Authentication Use Cases  . . . . . . . . . . . . . . 20
     A.1.  Just SIP Authentication  . . . . . . . . . . . . . . . . . 20
     A.2.  Just Web Authentication  . . . . . . . . . . . . . . . . . 20
     A.3.  Cookie Based Authentication  . . . . . . . . . . . . . . . 21
   Appendix B.  Implementation Guidelines . . . . . . . . . . . . . . 22
     B.1.  SIP WebSocket Client Considerations  . . . . . . . . . . . 23
     B.2.  SIP WebSocket Server Considerations  . . . . . . . . . . . 23
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23



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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 smartphones) will also make a WebSocket client
   stack available.  The specification in this document enables usage of
   SIP in these scenarios.

   This specification defines a WebSocket sub-protocol (as defined in
   section 1.9 in [RFC6455]) for transporting SIP messages between a
   WebSocket client and server, a reliable and message-boundary
   preserving transport for SIP, DNS NAPTR [RFC3403] service values and
   procedures for SIP entities implementing the WebSocket transport.
   Media transport is out of the scope of this document.

   Section 3 in this specification relaxes the requirement in [RFC3261]
   by which the SIP server transport MUST add a "received" parameter in
   the top Via header in certain circumstances.


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

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

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


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



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   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 (as the WebSocket SIP 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.

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

4.1.  Handshake

   The SIP WebSocket Client and SIP WebSocket Server negotiate usage of
   the WebSocket SIP sub-protocol during the WebSocket handshake
   procedure as defined in section 1.3 of [RFC6455].  The Client MUST



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   include the value "sip" in the Sec-WebSocket-Protocol header in its
   handshake request.  The 101 reply from the Server MUST contain "sip"
   in its corresponding Sec-WebSocket-Protocol header.

      The WebSocket Client initiates a WebSocket connection when
      attempting to send a SIP request (unless there is an already
      established WebSocket connection for sending the SIP request).  In
      case there is no HTTP 101 response during the WebSocket handshake
      it is considered a transaction error as per [RFC3261] section
      8.1.3.1 "Transaction Layer Errors".

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

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

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

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

   Once the negotiation has been completed, the WebSocket connection is
   established and can be used for the transport of SIP requests and
   responses.  Messages other than SIP requests and responses MUST NOT
   be transmitted over this connection.

4.2.  SIP Encoding

   WebSocket messages can be transported in either UTF-8 text frames or
   binary frames.  SIP [RFC3261] allows both text and binary bodies in
   SIP requests and responses.  Therefore SIP WebSocket Clients and SIP
   WebSocket Servers MUST accept both text and binary frames.

      If there is at least one non-UTF-8 symbol in the whole SIP message
      (including headers and body) then the whole message MUST be sent
      within a WebSocket binary message.  Given the nature of JavaScript
      and the WebSocket API it is RECOMMENDED to use UTF-8 encoding (or



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      ASCII which is a subset of UTF-8) for SIP messages carried over a
      WebSocket connection.


5.  SIP WebSocket Transport

   WebSocket [RFC6455] is a reliable protocol and therefore the SIP
   WebSocket sub-protocol defined by this document is a reliable SIP
   transport.  Thus, client and server transactions using WebSocket for
   transport MUST follow the procedures and timer values for reliable
   transports as defined in [RFC3261].

   Each SIP message MUST be carried within a single WebSocket message,
   and a WebSocket message MUST NOT contain more than one SIP message.
   Because the WebSocket transport preserves message boundaries, the use
   of the Content-Length header in SIP messages is not necessary when
   they are transported using the WebSocket sub-protocol.

      This simplifies parsing of SIP messages for both clients and
      servers.  There is no need to establish message boundaries using
      Content-Length headers between messages.  Other SIP transports,
      such as UDP and SCTP [RFC4168] also provide this benefit.

5.1.  Via Transport Parameter

   Via header fields in SIP messages carry a transport protocol
   identifier.  This document defines the value "WS" to be used for
   requests over plain WebSocket connections and "WSS" for requests over
   secure WebSocket connections (in which the WebSocket connection is
   established using TLS [RFC5246] with TCP 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 [RFC3261], which was then updated by [RFC4168]):

     transport  =/  "WS" / "WSS"

5.2.  SIP URI Transport Parameter

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

   The updated augmented BNF (Backus-Naur Form) for this parameter is
   the following (the original BNF for this parameter can be found in
   [RFC3261]):

     transport-param  =/  "transport=" "ws"



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5.3.  Via received Parameter

   [RFC3261] section 18.2.1 "Receiving Requests" states the following:

      When the server transport receives a request over any transport,
      it MUST examine the value of the "sent-by" parameter in the top
      Via header field value.  If the host portion of the "sent-by"
      field contains a domain name, or if it contains an IP address that
      differs from the packet source address, the server MUST add a
      "received" parameter to that Via header field value.  This
      parameter MUST contain the source address from which the packet
      was received.

   The requirement of adding the "received" parameter does not fit well
   into the WebSocket protocol design.  The WebSocket connection
   handshake reuses existing HTTP infrastructure in which there could be
   an unknown number of HTTP proxies and/or TCP load balancers between
   the SIP WebSocket Client and Server, so the source address the server
   would write into the Via "received" parameter would be the address of
   the HTTP/TCP intermediary in front of it.  This could reveal
   sensitive information about the internal topology of the Server's
   network to the Client.

   Given the fact that SIP responses can only be sent over the existing
   WebSocket connection, the Via "received" parameter is of little use.
   Therefore, in order to allow hiding possible sensitive information
   about the SIP WebSocket Server's network, this document updates
   [RFC3261] section 18.2.1 by stating:

      When a SIP WebSocket Server receives a request it MAY decide not
      to add a "received" parameter to the top Via header.  Therefore
      SIP WebSocket Clients MUST accept responses without such a
      parameter in the top Via header regardless of whether the Via
      "sent-by" field contains a domain name.

5.4.  SIP Transport Implementation Requirements

   [RFC3261] section 18 "Transport" states the following:

      All SIP elements MUST implement UDP and TCP.  SIP elements MAY
      implement other protocols.

   The specification of this transport enables SIP to be used as a
   session establishment protocol in scenarios where none of other
   transport protocols defined for SIP can be used.  Since some
   environments do not enable SIP elements to use UDP and TCP as SIP
   transport protocols, a SIP element acting as a SIP WebSocket Client
   is not mandated to implement support of UDP and TCP.



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5.5.  Locating a SIP Server

   [RFC3263] specifies the procedures which should be followed by SIP
   entities for locating SIP servers.  This specification defines the
   NAPTR service value "SIP+D2W" for SIP WebSocket Servers that support
   plain WebSocket connections and "SIPS+D2W" for SIP WebSocket Servers
   that support secure WebSocket connections.

      At the time this document was written, DNS NAPTR/SRV queries could
      not be performed by commonly available WebSocket client stacks (in
      JavaScript engines and web browsers).

   In the absence of DNS SRV resource records or an explicit port, the
   default port for a SIP URI using the "sip" scheme and the "ws"
   transport parameter is 80, and the default port for a SIP URI using
   the "sips" scheme and the "ws" transport parameter is 443.


6.  Connection Keep-Alive

   SIP WebSocket Clients and Servers may 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.

   The indication and use of the CRLF NAT keep-alive mechanism defined
   for SIP connection-oriented transports in [RFC5626] section 3.5.1 or
   [RFC6223] are, of course, usable over the transport defined in this
   specification.


7.  Authentication

   This section describes how authentication is achieved through the
   requirements in [RFC6455], [RFC6265], [RFC2617] and [RFC3261].

   WebSocket protocol [RFC6455] does not define an authentication
   mechanism, instead it exposes the following text in section 10.5
   "WebSocket Client Authentication":

      This protocol doesn't prescribe any particular way that servers
      can authenticate clients during the WebSocket handshake.  The



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      WebSocket server can use any client authentication mechanism
      available to a generic HTTP server, such as cookies, HTTP
      authentication, or TLS authentication.

   The following list exposes mandatory to implement and optional
   mechanisms for SIP WebSocket Clients and Servers in order to get
   interoperability at WebSocket authentication level:

   o  A SIP WebSocket Client MUST be ready to add a session Cookie when
      it runs in a web browser (or behaves like a browser navigating a
      website) and has previously retrieved a session Cookie from the
      web server whose URL domain matches the domain in the WebSocket
      URI.  This mechanism is defined by [RFC6265].

   o  A SIP WebSocket Client MUST be ready to be challenged with HTTP
      401 status code by the SIP WebSocket Server when performing the
      WebSocket handshake as stated in [RFC2617].

   o  A SIP WebSocket Client MAY use TLS client authentication (when in
      a secure WebSocket connection) as an optional authentication
      mechanism.

         Note however that TLS client authentication in WebSocket
         protocol is governed by the rules of HTTP protocol rather than
         the rules of SIP protocol.

   o  A SIP WebSocket Server MUST be ready to read session Cookies when
      present in the WebSocket handshake request, and use such a Cookie
      value for determining whether the WebSocket connection has been
      initiated by a HTTP client navigating a website in the same domain
      (or subdomain) as the SIP WebSocket Server.

   o  A SIP WebSocket Server SHOULD be able to reject a WebSocket
      handshake request with HTTP 401 status code by providing a Basic/
      Digest challenge as defined for HTTP protocol.

   Regardless of whether the SIP WebSocket Server requires
   authentication during the WebSocket handshake or not, authentication
   MAY be requested at SIP protocol level.

   Some authentication use cases are exposed in Appendix A.


8.  Examples







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8.1.  Registration


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

   Alice loads a web page using her web browser and retrieves JavaScript
   code implementing the WebSocket SIP sub-protocol defined in this
   document.  The JavaScript code (a SIP WebSocket Client) establishes a
   secure WebSocket connection with a SIP proxy/registrar (a SIP
   WebSocket Server) at proxy.example.com.  Upon WebSocket connection,
   Alice constructs and sends a SIP REGISTER request including Outbound
   and GRUU support.  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 Via header sent-by parameter and for the hostport of the URI
   in the Contact header (see Appendix B.1).

   Message details (authentication and SDP bodies are omitted for
   simplicity):


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

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


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

   HTTP/1.1 101 Switching Protocols
   Upgrade: websocket



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   Connection: Upgrade
   Sec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo=
   Sec-WebSocket-Protocol: sip


   F3 REGISTER  Alice -> proxy.example.com (transport WSS)

   REGISTER sip:proxy.example.com SIP/2.0
   Via: SIP/2.0/WSS df7jal23ls0d.invalid;branch=z9hG4bKasudf
   From: sip:alice@example.com;tag=65bnmj.34asd
   To: sip:alice@example.com
   Call-ID: aiuy7k9njasd
   CSeq: 1 REGISTER
   Max-Forwards: 70
   Supported: path, outbound, gruu
   Contact: <sip:alice@df7jal23ls0d.invalid;transport=ws>
     ;reg-id=1
     ;+sip.instance="<urn:uuid:f81-7dec-14a06cf1>"


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

   SIP/2.0 200 OK
   Via: SIP/2.0/WSS df7jal23ls0d.invalid;branch=z9hG4bKasudf
   From: sip:alice@example.com;tag=65bnmj.34asd
   To: sip:alice@example.com;tag=12isjljn8
   Call-ID: aiuy7k9njasd
   CSeq: 1 REGISTER
   Supported: outbound, gruu
   Contact: <sip:alice@df7jal23ls0d.invalid;transport=ws>
     ;reg-id=1
     ;+sip.instance="<urn:uuid:f81-7dec-14a06cf1>"
     ;pub-gruu="sip:alice@example.com;gr=urn:uuid:f81-7dec-14a06cf1"
     ;temp-gruu="sip:87ash54=3dd.98a@example.com;gr"
     ;expires=3600

8.2.  INVITE Dialog through a Proxy














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   Alice    (SIP WSS)    proxy.example.com    (SIP UDP)       Bob
   |                             |                             |
   |INVITE F1                    |                             |
   |---------------------------->|                             |
   |100 Trying F2                |                             |
   |<----------------------------|                             |
   |                             |INVITE F3                    |
   |                             |---------------------------->|
   |                             |200 OK F4                    |
   |                             |<----------------------------|
   |200 OK F5                    |                             |
   |<----------------------------|                             |
   |                             |                             |
   |ACK F6                       |                             |
   |---------------------------->|                             |
   |                             |ACK F7                       |
   |                             |---------------------------->|
   |                             |                             |
   |                 Bidirectional RTP Media                   |
   |<=========================================================>|
   |                             |                             |
   |                             |BYE F8                       |
   |                             |<----------------------------|
   |BYE F9                       |                             |
   |<----------------------------|                             |
   |200 OK F10                   |                             |
   |---------------------------->|                             |
   |                             |200 OK F11                   |
   |                             |---------------------------->|
   |                             |                             |

   In the same scenario Alice places a call to Bob's AoR (Address Of
   Record).  The SIP WebSocket Server at proxy.example.com acts as a SIP
   proxy, routing the INVITE to Bob's contact address (which happens to
   be using SIP transported over UDP).  Bob answers the call and then
   terminates it.

   Message details (authentication and SDP bodies are omitted for
   simplicity):


   F1 INVITE  Alice -> proxy.example.com (transport WSS)

   INVITE sip:bob@example.com SIP/2.0
   Via: SIP/2.0/WSS df7jal23ls0d.invalid;branch=z9hG4bK56sdasks
   From: sip:alice@example.com;tag=asdyka899
   To: sip:bob@example.com
   Call-ID: asidkj3ss



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   CSeq: 1 INVITE
   Max-Forwards: 70
   Supported: path, outbound, gruu
   Route: <sip:proxy.example.com:443;transport=ws;lr>
   Contact: <sip:alice@example.com
    ;gr=urn:uuid:f81-7dec-14a06cf1;ob>
   Content-Type: application/sdp


   F2 100 Trying  proxy.example.com -> Alice (transport WSS)

   SIP/2.0 100 Trying
   Via: SIP/2.0/WSS df7jal23ls0d.invalid;branch=z9hG4bK56sdasks
   From: sip:alice@example.com;tag=asdyka899
   To: sip:bob@example.com
   Call-ID: asidkj3ss
   CSeq: 1 INVITE


   F3 INVITE  proxy.example.com -> Bob (transport UDP)

   INVITE sip:bob@203.0.113.22:5060 SIP/2.0
   Via: SIP/2.0/UDP proxy.example.com;branch=z9hG4bKhjhjqw32c
   Via: SIP/2.0/WSS df7jal23ls0d.invalid;branch=z9hG4bK56sdasks
   Record-Route: <sip:proxy.example.com;transport=udp;lr>,
     <sip:h7kjh12s@proxy.example.com:443;transport=ws;lr>
   From: sip:alice@example.com;tag=asdyka899
   To: sip:bob@example.com
   Call-ID: asidkj3ss
   CSeq: 1 INVITE
   Max-Forwards: 69
   Supported: path, outbound, gruu
   Contact: <sip:alice@example.com
     ;gr=urn:uuid:f81-7dec-14a06cf1;ob>
   Content-Type: application/sdp


   F4 200 OK  Bob -> proxy.example.com (transport UDP)

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP proxy.example.com;branch=z9hG4bKhjhjqw32c
     ;received=192.0.2.10
   Via: SIP/2.0/WSS df7jal23ls0d.invalid;branch=z9hG4bK56sdasks
   Record-Route: <sip:proxy.example.com;transport=udp;lr>,
     <sip:h7kjh12s@proxy.example.com:443;transport=ws;lr>
   From: sip:alice@example.com;tag=asdyka899
   To: sip:bob@example.com;tag=bmqkjhsd
   Call-ID: asidkj3ss



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   CSeq: 1 INVITE
   Contact: <sip:bob@203.0.113.22:5060;transport=udp>
   Content-Type: application/sdp


   F5 200 OK  proxy.example.com -> Alice (transport WSS)

   SIP/2.0 200 OK
   Via: SIP/2.0/WSS df7jal23ls0d.invalid;branch=z9hG4bK56sdasks
   Record-Route: <sip:proxy.example.com;transport=udp;lr>,
     <sip:h7kjh12s@proxy.example.com:443;transport=ws;lr>
   From: sip:alice@example.com;tag=asdyka899
   To: sip:bob@example.com;tag=bmqkjhsd
   Call-ID: asidkj3ss
   CSeq: 1 INVITE
   Contact: <sip:bob@203.0.113.22:5060;transport=udp>
   Content-Type: application/sdp


   F6 ACK  Alice -> proxy.example.com (transport WSS)

   ACK sip:bob@203.0.113.22:5060;transport=udp SIP/2.0
   Via: SIP/2.0/WSS df7jal23ls0d.invalid;branch=z9hG4bKhgqqp090
   Route: <sip:h7kjh12s@proxy.example.com:443;transport=ws;lr>,
     <sip:proxy.example.com;transport=udp;lr>,
   From: sip:alice@example.com;tag=asdyka899
   To: sip:bob@example.com;tag=bmqkjhsd
   Call-ID: asidkj3ss
   CSeq: 1 ACK
   Max-Forwards: 70


   F7 ACK  proxy.example.com -> Bob (transport UDP)

   ACK sip:bob@203.0.113.22:5060;transport=udp SIP/2.0
   Via: SIP/2.0/UDP proxy.example.com;branch=z9hG4bKhwpoc80zzx
   Via: SIP/2.0/WSS df7jal23ls0d.invalid;branch=z9hG4bKhgqqp090
   From: sip:alice@example.com;tag=asdyka899
   To: sip:bob@example.com;tag=bmqkjhsd
   Call-ID: asidkj3ss
   CSeq: 1 ACK
   Max-Forwards: 69


   F8 BYE  Bob -> proxy.example.com (transport UDP)

   BYE sip:alice@example.com;gr=urn:uuid:f81-7dec-14a06cf1;ob SIP/2.0
   Via: SIP/2.0/UDP 203.0.113.22;branch=z9hG4bKbiuiansd001



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   Route: <sip:proxy.example.com;transport=udp;lr>,
     <sip:h7kjh12s@proxy.example.com:443;transport=ws;lr>
   From: sip:bob@example.com;tag=bmqkjhsd
   To: sip:alice@example.com;tag=asdyka899
   Call-ID: asidkj3ss
   CSeq: 1201 BYE
   Max-Forwards: 70


   F9 BYE  proxy.example.com -> Alice (transport WSS)

   BYE sip:alice@example.com;gr=urn:uuid:f81-7dec-14a06cf1;ob SIP/2.0
   Via: SIP/2.0/WSS proxy.example.com:443;branch=z9hG4bKmma01m3r5
   Via: SIP/2.0/UDP 203.0.113.22;branch=z9hG4bKbiuiansd001
   From: sip:bob@example.com;tag=bmqkjhsd
   To: sip:alice@example.com;tag=asdyka899
   Call-ID: asidkj3ss
   CSeq: 1201 BYE
   Max-Forwards: 69


   F10 200 OK  Alice -> proxy.example.com (transport WSS)

   SIP/2.0 200 OK
   Via: SIP/2.0/WSS proxy.example.com:443;branch=z9hG4bKmma01m3r5
   Via: SIP/2.0/UDP 203.0.113.22;branch=z9hG4bKbiuiansd001
   From: sip:bob@example.com;tag=bmqkjhsd
   To: sip:alice@example.com;tag=asdyka899
   Call-ID: asidkj3ss
   CSeq: 1201 BYE


   F11 200 OK  proxy.example.com -> Bob (transport UDP)

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP 203.0.113.22;branch=z9hG4bKbiuiansd001
   From: sip:bob@example.com;tag=bmqkjhsd
   To: sip:alice@example.com;tag=asdyka899
   Call-ID: asidkj3ss
   CSeq: 1201 BYE


9.  Security Considerations

9.1.  Secure WebSocket Connection

   It is RECOMMENDED that the SIP traffic transported over a WebSocket
   communication be protected by using a secure WebSocket connection



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   (using TLS [RFC5246] over TCP).

   When establishing a connection using SIP over secure WebSocket
   transport, the client MUST authenticate the server using the server's
   certificate according to the WebSocket validation procedure in
   [RFC6455].

      Server operators should note that this authentication procedure is
      different from the procedure for SIP Domain Certificates defined
      in [RFC5922].  Certificates that are appropriate for SIP over TLS
      over TCP will probably not be appropriate for SIP over secure
      WebSocket connections.

9.2.  Usage of SIPS Scheme

   The SIPS scheme in a SIP URI dictates that the entire request path to
   the target be secure.  If such a path includes a WebSocket connection
   it MUST be a secure WebSocket connection.


10.  IANA Considerations

   RFC Editor Note: Please set the RFC number assigned for this document
   in the sub-sections below and remove this note.

10.1.  Registration of the WebSocket SIP Sub-Protocol

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

   Subprotocol Identifier:  sip

   Subprotocol Common Name:  WebSocket Transport for SIP (Session
      Initiation Protocol)

   Subprotocol Definition:  TBD: this document

10.2.  Registration of new NAPTR Service Field Values

   This document defines two new NAPTR service field values (SIP+D2W and
   SIPS+D2W) and requests IANA to register these values under the
   "Registry for the Session Initiation Protocol (SIP) NAPTR Resource
   Record Services Field".  The resulting entries are as follows:

   Services Field   Protocol   Reference
   --------------   --------   ---------
   SIP+D2W          WS         TBD: this document



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   SIPS+D2W         WS         TBD: this document

10.3.  SIP/SIPS URI Parameters Sub-Registry

   This specification requests IANA to add a reference to this document
   under the "SIP/SIPS URI Parameters" Sub-Registry within the "Session
   Initiation Protocol (SIP) Parameters" Registry:

   Parameter Name   Predefined Values   Reference
   --------------   -----------------   ---------
   transport        Yes                 [RFC3261][TBD: this document]

10.4.  Header Fields Sub-Registry

   This specification requests IANA to add a reference to this document
   under the "Header Fields" Sub-Registry within the "Session Initiation
   Protocol (SIP) Parameters" Registry:

   Header Name   compact   Reference
   -----------   -------   ---------
   Via           v         [RFC3261][TBD: this document]

10.5.  Header Field Parameters and Parameter Values Sub-Registry

   This specification requests IANA to add a reference to this document
   under the "Header Field Parameters and Parameter Values" Sub-Registry
   within the "Session Initiation Protocol (SIP) Parameters" Registry:

                                 Predefined
   Header Field  Parameter Name  Values  Reference
   ------------  --------------  ------  ---------
   Via           received        No      [RFC3261][TBD: this document]

10.6.  SIP Transport Sub-Registry

   This document adds a new registry, "SIP Transport", to the "Session
   Initiation Protocol (SIP) Parameters" Registry.  Its format and
   initial values are as shown in the following table:













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   +------------+------------------------+
   | Transport  | Reference              |
   +------------+------------------------+
   | UDP        | [RFC 3261]             |
   | TCP        | [RFC 3261]             |
   | TLS        | [RFC 3261]             |
   | SCTP       | [RFC 3261], [RFC 4168] |
   | TLS-SCTP   | [RFC 4168]             |
   | WS         | [TBD: this document]   |
   | WSS        | [TBD: this document]   |
   +------------+------------------------+

   The policy for registration of values in this registry is "Standards
   Action", as that term is defined by [RFC5226].


11.  Acknowledgements

   Special thanks to the following people who participated in
   discussions on the SIPCORE and RTCWEB WG mailing lists and
   contributed ideas and/or provided detailed reviews (the list is
   likely to be incomplete): Hadriel Kaplan, Paul Kyzivat, Robert
   Sparks, Adam Roach, Ranjit Avasarala, Xavier Marjou, Nataraju A. B.,
   Martin Vopatek, Alexey Melnikov, Alan Johnston, Christer Holmberg,
   Salvatore Loreto, Kevin P. Fleming, Suresh Krishnan, Yaron Sheffer,
   Richard Barnes, Barry Leiba, Stephen Farrell, Ted Lemon, Benoit
   Claise, Pete Resnick, Binod, Saul Ibarra Corretge.


12.  References

12.1.  Normative References

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

   [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.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              June 2002.

   [RFC3263]  Rosenberg, J. and H. Schulzrinne, "Session Initiation
              Protocol (SIP): Locating SIP Servers", RFC 3263,



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              June 2002.

   [RFC3403]  Mealling, M., "Dynamic Delegation Discovery System (DDDS)
              Part Three: The Domain Name System (DNS) Database",
              RFC 3403, October 2002.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

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

   [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.

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

12.2.  Informative References

   [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.

   [RFC3327]  Willis, D. and B. Hoeneisen, "Session Initiation Protocol
              (SIP) Extension Header Field for Registering Non-Adjacent
              Contacts", RFC 3327, December 2002.

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

   [RFC4168]  Rosenberg, J., Schulzrinne, H., and G. Camarillo, "The
              Stream Control Transmission Protocol (SCTP) as a Transport
              for the Session Initiation Protocol (SIP)", RFC 4168,
              October 2005.

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




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   [RFC5627]  Rosenberg, J., "Obtaining and Using Globally Routable User
              Agent URIs (GRUUs) in the Session Initiation Protocol
              (SIP)", RFC 5627, October 2009.

   [RFC5922]  Gurbani, V., Lawrence, S., and A. Jeffrey, "Domain
              Certificates in the Session Initiation Protocol (SIP)",
              RFC 5922, June 2010.

   [RFC6223]  Holmberg, C., "Indication of Support for Keep-Alive",
              RFC 6223, April 2011.

   [WS-API]   W3C and I. Hickson, Ed., "The WebSocket API", April 2013.


Appendix A.  Authentication Use Cases

   Sections below briefly describe some SIP over WebSocket scenarios in
   which authentication take place in different ways.

A.1.  Just SIP Authentication

   SIP PBX model A implements the SIP WebSocket transport defined by
   this specification.  Its implementation is 100% website agnostic as
   it does not share information with the web server providing the HTML
   code to browsers, meaning that the SIP WebSocket Server (here the PBX
   model A) has no knowledge about web login activity within the
   website.

   In this simple scenario, the SIP WebSocket Server does not inspect
   fields in the WebSocket handshake HTTP GET request such as the
   request URL, the Origin header value, the Host header value or the
   Cookie header value (if present).  However some of those fields could
   be inspected for a minimal validation (i.e.  PBX model A could
   require that the Origin header value contains a specific URL so just
   users navigating such a website would be able to establish a
   WebSocket connection with PBX model A).

   Once the WebSocket connection has been established, SIP
   authentication is requested by PBX model A for each SIP request
   coming over that connection.  Therefore SIP WebSocket Clients must be
   provisioned with their corresponding SIP password.

A.2.  Just Web Authentication

   A SIP-to-PSTN provider offers telephony service for clients logged
   into its website.  The provider does not want to expose SIP passwords
   into the web for security/privacy reasons.




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   Once the user is logged into the web, the web server provides him
   with a SIP identity (SIP URI) and a session temporary token string
   (along with the SIP WebSocket Client JavaScript application and SIP
   settings).  The web server stores the SIP identity and session token
   into a database.

   The web application adds the SIP identity and session token as URL
   query parameters in the WebSocket handshake request and attempts the
   connection.  The SIP WebSocket Server inspects the handshake request
   and validates that the session token matches the value stored in the
   database for the given SIP identity.  In case the value matches, the
   WebSocket connection gets "authenticated" for that SIP identity.  The
   SIP WebSocket Client can then register and make calls.  The SIP
   WebSocket Server would however verify that the identity in those SIP
   requests (i.e. the From URI value) matches the SIP identity the
   WebSocket connection is associated to (otherwise the SIP request is
   rejected).

   When the user performs logout action in the web, the web server
   removes the SIP identity and session token tuple from the database
   and notifies it to the SIP WebSocket Server which revokes and closes
   the WebSocket connection.

   No SIP authentication takes place in this scenario.

A.3.  Cookie Based Authentication

   Apache web server comes with a new module mod_sip_websocket.  The web
   server is configured to listen in port 80 for both HTTP common
   requests and WebSocket handshake requests.  Therefore both the web
   server and the SIP WebSocket Server are co-located within the same
   host and same domain.

   Once the user is logged into the web, he is provided with the SIP
   WebSocket Client JavaScript application and SIP settings.  The HTTP
   200 response after the login procedure also contains a session Cookie
   [RFC6265].  The web application attempts then a WebSocket connection
   against the same URL/domain of the website and thus, the session
   Cookie is automatically added by the browser into the WebSocket
   handshake request (as the WebSocket protocol [RFC6455] states).

   The web server inspects the Cookie value (as it would do for a common
   HTTP request containing a session Cookie, so login procedure is not
   required again).  If the Cookie is valid the WebSocket connection is
   authorized and, as in the previous use case, the connection is also
   associated with a specific SIP identity which must be satisfied by
   every SIP request coming over that connection.




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   No SIP authentication takes place in this scenario but just common
   Cookie usage as widely deployed in the WWW.


Appendix B.  Implementation Guidelines

   Let us assume a scenario in which the users access with their web
   browsers (probably behind NAT) an application provided by a server on
   an intranet, login by entering their user identifier and credentials,
   and retrieve a JavaScript application (along with the HTML)
   implementing a SIP WebSocket Client.

   Such a SIP stack connects to a given SIP WebSocket Server (an
   outbound SIP proxy which also implements classic SIP transports such
   as UDP and TCP).  The HTTP GET method request sent by the web browser
   for the WebSocket handshake includes a Cookie [RFC6265] header with
   the value previously provided by the server after the successful
   login procedure.  The Cookie value is then inspected by the WebSocket
   server to authorize the connection.  Once the WebSocket connection is
   established, the SIP WebSocket Client performs a SIP registration to
   a SIP registrar server that is reachable through the proxy.  After
   registration, the SIP WebSocket Client and Server exchange SIP
   messages as would normally be expected.

   This scenario is quite similar to ones in which SIP UAs behind NATs
   connect to a proxy and must reuse the same TCP connection for
   incoming requests (because they are not directly reachable by the
   proxy otherwise).  In both cases, the SIP UAs are only reachable
   through the proxy they are connected to.

   The SIP Outbound extension [RFC5626] seems an appropriate solution
   for this scenario.  Therefore these SIP WebSocket Clients and the SIP
   registrar implement both the Outbound and Path [RFC3327] extensions,
   and the SIP proxy acts as an Outbound Edge Proxy (as defined in
   [RFC5626] section 3.4).

   SIP WebSocket Clients in this scenario receive incoming SIP requests
   via the SIP WebSocket Server they are connected to.  Therefore, in
   some call transfer cases the usage of GRUU [RFC5627] (which should be
   implemented in both the SIP WebSocket Clients and SIP registrar) is
   valuable.

      If a REFER request is sent to a third SIP user agent including the
      Contact URI of a SIP WebSocket Client as the target in its
      Refer-To header field, such a URI will be reachable by the third
      SIP UA only if it is a globally routable URI.  GRUU (Globally
      Routable User Agent URI) is a solution for those scenarios, and
      would cause the incoming request from the third SIP user agent to



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      be sent to the SIP registrar, which would route the request to the
      SIP WebSocket Client via the Outbound Edge Proxy.

B.1.  SIP 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.  A SIP WebSocket client running in such an environment
   can construct 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 Via and Contact headers.

      The Contact URI provided by SIP UAs requesting (and receiving)
      Outbound support is not used for routing requests to those UAs,
      thus it is safe to set a random domain in the Contact URI
      hostport.

   Both the Outbound and GRUU specifications require a SIP UA to include
   a Uniform Resource Name (URN) in a "+sip.instance" parameter of the
   Contact header they include their SIP REGISTER requests.  The client
   device is responsible for generating or collecting a suitable value
   for this purpose.

      In web browsers it is difficult to generate or collect a suitable
      value to be used as a URN value from the browser itself.  This
      scenario suggests that value is generated according to [RFC5626]
      section 4.1 by the web application running in the browser the
      first time it loads the JavaScript SIP stack code, and then it is
      stored as a Cookie within the browser.

B.2.  SIP WebSocket Server Considerations

   The SIP WebSocket Server in this scenario behaves as a SIP Outbound
   Edge Proxy, which involves support for Outbound [RFC5626] and Path
   [RFC3327].

   The proxy performs Loose Routing and remains in the path of dialogs
   as specified in [RFC3261].  If it did not do this, in-dialog requests
   would fail since SIP WebSocket Clients make use of their SIP
   WebSocket Server in order to send and receive SIP messages.











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Authors' Addresses

   Inaki Baz Castillo
   Versatica
   Barakaldo, Basque Country
   Spain

   Email: ibc@aliax.net


   Jose Luis Millan Villegas
   Versatica
   Bilbao, Basque Country
   Spain

   Email: jmillan@aliax.net


   Victor Pascual
   Quobis
   Spain

   Email: victor.pascual@quobis.com




























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