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Versions: 00 01 draft-ietf-mmusic-msrp-usage-data-channel

MMUSIC                                                     K. Drage, Ed.
Internet-Draft                                               M. Makaraju
Intended status: Standards Track                     J. Stoetzer-Bradler
Expires: April 30, 2015                                   Alcatel-Lucent
                                                                R. Ejzak
                                                               J. Marcon
                                                            Unaffiliated
                                                        October 27, 2014


                   MSRP over SCTP/DTLS data channels
             draft-ejzak-mmusic-msrp-usage-data-channel-01

Abstract

   This document specifies how the Message Session Relay Protocol (MSRP)
   can be instantiated as a data channel sub-protocol, using the the SDP
   offer/answer exchange-based external negotiation defined in
   [I-D.ejzak-mmusic-data-channel-sdpneg].  Two network configurations
   are documented: a WebRTC end-to-end configuration (connecting two
   MSRP over data channel endpoints), and a gateway configuration
   (connecting an MSRP over data channel endpoint with an MSRP over TCP
   endpoint).

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 April 30, 2015.

Copyright Notice

   Copyright (c) 2014 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
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Principles  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  MSRP data channel . . . . . . . . . . . . . . . . . . . .   4
     4.2.  Session mapping . . . . . . . . . . . . . . . . . . . . .   4
     4.3.  MSRP URI  . . . . . . . . . . . . . . . . . . . . . . . .   4
     4.4.  msrp-scheme . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  End-to-end configuration  . . . . . . . . . . . . . . . . . .   4
     5.1.  Basic MSRP support  . . . . . . . . . . . . . . . . . . .   4
       5.1.1.  Session negotiation . . . . . . . . . . . . . . . . .   5
         5.1.1.1.  Use of dcmap attribute  . . . . . . . . . . . . .   5
         5.1.1.2.  Use of dcsa attribute . . . . . . . . . . . . . .   5
         5.1.1.3.  Example SDP negotiation . . . . . . . . . . . . .   6
       5.1.2.  Session opening . . . . . . . . . . . . . . . . . . .   7
       5.1.3.  Data framing  . . . . . . . . . . . . . . . . . . . .   7
       5.1.4.  Data sending and reporting  . . . . . . . . . . . . .   7
       5.1.5.  Session closing . . . . . . . . . . . . . . . . . . .   7
     5.2.  Support for MSRP File Transfer function . . . . . . . . .   7
   6.  Gateway configuration . . . . . . . . . . . . . . . . . . . .   8
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   9
   10. CHANGE LOG  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     10.1.  Changes against '-00'  . . . . . . . . . . . . . . . . .   9
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     11.1.  Normative References . . . . . . . . . . . . . . . . . .   9
     11.2.  Informative References . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   The Message Session Relay Protocol (MSRP) [RFC4975] is a protocol for
   transmitting a series of related instant messages in the context of a
   session.  In addition to instant messaging, MSRP can also be used for
   image sharing or file transfer.  MSRP is currently defined to work
   over TCP and TLS connections.




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   This document defines the negotiation and transport of this MSRP
   protocol over WebRTC data channels, where a data channel is a bi-
   directional communication channel running on top of SCTP/DTLS (as per
   [I-D.ietf-rtcweb-data-protocol]) and where MSRP is instantiated as a
   sub-protocol of this data channel.

   Defining MSRP as a data channel sub-protocol has many benefits:

   o  provides to applications a proven protocol enabling instant
      messaging, file transfer, image sharing

   o  integrates those features with other RTCWeb voice, video and data
      features

   o  leverages the SDP-based negotiation already defined for MSRP

   o  allows the interworking with MSRP endpoints running on a TCP or
      TLS connection

   Considering an MSRP endpoint being an MSRP application that uses data
   channel from WebRTC specifications[I-D.ietf-rtcweb-data-protocol],
   this document describes two configurations where the other endpoint
   is respectively either another MSRP over data channel endpoint (e.g.,
   a WebRTC application) or an MSRP endpoint using either TCP or TLS
   transport.

2.  Conventions

   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].

3.  Terminology

   This document uses the following terms:

      Data channel: A bidirectional channel consisting of paired SCTP
      outbound and inbound streams.

      External negotiation: data channel negotiation based on out-of-
      band or in-band mechanisms other than the WebRTC data channel
      control protocol.

      In-band: transmission through the peer-to-peer SCTP association.

      Out-of-band: transmission through the call control signaling path,
      e.g., using JSEP [I-D.ietf-rtcweb-jsep] and the SDP Offer/Answer
      model [RFC3264].



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      MSRP data channel: A data channel specifically used to transport
      the messages of one MSRP session.

      Peer: From the perspective of one of the agents in a session, its
      peer is the other agent.  Specifically, from the perspective of
      the SDP offerer, the peer is the SDP answerer.  From the
      perspective of the SDP answerer, the peer is the SDP offerer.

4.  Principles

4.1.  MSRP data channel

   In this document, an MSRP data channel is a data channel for which
   the instantiated sub-protocol is "msrp", and where the MSRP-related
   negotiation is done as part of the SDP-based external negotiation
   method defined in [I-D.ejzak-mmusic-data-channel-sdpneg].

4.2.  Session mapping

   In this design, the MSRP connection maps to the SCTP association and
   the "SCTP stream pair" assigned to data channels, and each MSRP
   session maps to one data channel exactly.

4.3.  MSRP URI

   This document extends the MSRP URI syntax [RFC4975] by defining the
   new transport parameter value "dc":

   transport  /= "dc" / 1*ALPHANUM
              ; Add "dc" to existing transports per RFC4975

4.4.  msrp-scheme

   The msrp-scheme portion of the MSRP-URI that represents an MSRP data
   channel endpoint (used in the SDP path attribute and in the MSRP
   message headers) is always "msrps", which indicates that the MSRP
   data channel is always secured using DTLS.

5.  End-to-end configuration

   This section describes the network configuration where each MSRP
   endpoint is running MSRP over an SCTP/DTLS (data channel) connection.

5.1.  Basic MSRP support







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5.1.1.  Session negotiation

5.1.1.1.  Use of dcmap attribute

   The SDP offer shall include a dcmap attribute line (defined in
   [I-D.ejzak-mmusic-data-channel-sdpneg]), within the media description
   for the SCTP association for each MSRP data channel session to be
   negotiated.

   The attribute includes the following data channel parameters:

   o  "label=" labelstring

   o  "subprotocol=" "MSRP"

   The labelstring is set by the MSRP application according to
   [I-D.ejzak-mmusic-data-channel-sdpneg].  The max-retr, max-time and
   ordered parameters shall not be used.

   Rest of the SDP offer/answer procedures are per
   [I-D.ejzak-mmusic-data-channel-sdpneg]

   The following is an example of the dcmap attribute for an MSRP
   session to be negotiated (on default SCTP port 5000) with stream=2
   and label="chat":

   a=dcmap:2 label="chat"; subprotocol="MSRP"

5.1.1.2.  Use of dcsa attribute

   The SDP offer shall also include a dcsa attribute line (defined in
   [I-D.ejzak-mmusic-data-channel-sdpneg]) within the media description
   for the SCTP association for each MSRP-specific SDP attribute to be
   negotiated for each MSRP data channel being negotiated.

   The MSRP-specific items that can be negotiated include at least all
   of the following well-known attributes:

   o  defined in [RFC4975]: "path", "accept-types", "accept-wrapped-
      types", "max-size"

   o  defined in [RFC4566]: "sendonly", "recvonly", "inactive", and
      "sendrecv"

   o  defined in [RFC6135]: "setup"

   o  defined in [RFC6714]: "msrp-cema"




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   o  defined in [RFC5547]: all the parameters related to MSRP file
      transfer.  See Section 5.2.

   The msrp-cema attribute shall be assumed to be present for every MSRP
   session using data channel transport, so the inclusion of the msrp-
   cema attribute is optional.  This ensures that the data channel
   transport for the MSRP session is established without using the path
   attribute.

   The SDP answer shall include zero or more corresponding dcsa
   attribute lines for each negotiated MSRP session, according to the
   MSRP-specific attribute negotiation rules in the corresponding
   specifications.

   A new SDP offer/answer may update the MSRP subprotocol attributes
   while keeping the same subprotocol a=dcmap description.  The
   semantics for newly negotiated MSRP subprotocol attributes are per
   [RFC4975]

5.1.1.3.  Example SDP negotiation

   The following is an example of an m line for DataChannels in an SDP
   offer that includes the attributes needed to establish two MSRP
   sessions: one for chat and one for file transfer.  The example is
   derived from a combination of examples in [RFC4975] and [RFC5547].


      m=application 54111 DTLS/SCTP webrtc-datachannel
      c=IN IP4 79.97.215.79
      a=fmtp:webrtc-datachannel max-message-size=100000
      a=sctp-port 5000
      a=dcmap:1 label="chat"; subprotocol="MSRP"
      a=dcsa:1 accept-types:message/cpim text/plain
      a=dcsa:1 path:msrps://bob.example.com:54111/si438dsaodes;dc
      a=dcmap:2 label="file transfer"; \
           subprotocol="MSRP"
      a=dcsa::2 sendonly
      a=dcsa:2 accept-types:message/cpim
      a=dcsa:2 accept-wrapped-types:*
      a=dcsa:2 path:msrps://bob.example.com:54111/jshA7we;dc
      a=dcsa:2 file-selector:name:"My cool picture.jpg" \
           type:image/jpeg size:32349 hash:sha-1: \
           72:24:5F:E8:65:3D:DA:F3:71:36:2F:86:D4:71:91:3E:E4:A2:CE:2E
      a=dcsa:2 file-transfer-id:vBnG916bdberum2fFEABR1FR3ExZMUrd
      a=dcsa:2 file-disposition:attachment
      a=dcsa:2 file-date:creation:"Mon, 15 May 2006 15:01:31 +0300"
      a=dcsa:2 file-icon:cid:id2@bob.example.com
      a=dcsa:2 file-range:1-32349



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5.1.2.  Session opening

   The active MSRP endpoint does not use the path attribute to open a
   transport connection to its peer.  Instead, it uses the data channel
   established for this MSRP session by the generic data channel opening
   procedure defined in [I-D.ejzak-mmusic-data-channel-sdpneg].

   As soon as this data channel is opened, the MSRP session is actually
   opened by the active MSRP endpoint which sends an MSRP SEND message
   (empty or not) to the other MSRP endpoint.  The msrp-cema attribute
   is implicitly associated with every MSRP session using data channel
   transport.

5.1.3.  Data framing

   Each text-based MSRP message is sent on the corresponding SCTP stream
   using standard MSRP framing and chunking procedures, as defined in
   [RFC4975], with each MSRP chunk delivered in a single SCTP user
   message.

5.1.4.  Data sending and reporting

   Data sending and reporting procedures shall conform to RFC 4975.

5.1.5.  Session closing

   Closing of an MSRP session is done using the generic data channel
   closing procedure defined in [I-D.ejzak-mmusic-data-channel-sdpneg].

   The port value for the m line should not be changed (e.g., to zero)
   when closing an MSRP session (unless all data channels are being
   closed and the SCTP association is no longer needed), since this
   would close the SCTP association and impact all of the data channels.
   In all cases in [RFC4975] where the procedure calls for setting the
   port to zero for the MSRP m line in an SDP offer for TCP transport,
   the SDP offerer of an MSRP session with data channel transport shall
   remove the corresponding dcmap and dcsa attributes.

   The SDP answerer must ensure that no dcmap or dcsa attributes are
   present in the SDP answer if no corresponding attributes are present
   in the received SDP offer.

5.2.  Support for MSRP File Transfer function

   [RFC5547] defines an end-to-end file transfer method based on MSRP
   and the SDP offer/answer mechanism.  This file transfer method is
   also usable by MSRP endpoints using data channel, with the following
   considerations:



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   o  As an MSRP session maps to one data channel, a file transfer
      session maps also to one data channel.

   o  SDP attributes specified in [RFC5547] for a file transfer m-line
      are embedded as subprotocol-specific attributes using the syntax
      defined in [I-D.ejzak-mmusic-data-channel-sdpneg].

   o  Once the file transfer is complete, the same data channel MAY be
      reused for another file transfer.

6.  Gateway configuration

   This section describes the network configuration where one endpoint
   runs MSRP over a WebRTC SCTP/DTLS connection, the other MSRP endpoint
   runs MSRP over one or more TLS/TCP connections, and the two endpoints
   interwork via an MSRP gateway.

   Specifically, a gateway can be configured to interwork an MSRP
   session using a data channel with a peer that does not support data
   channel transport in one of two ways.  In one model, the gateway
   performs as a MSRP B2BUA to interwork all the procedures as necessary
   between the endpoints.  No further specification is needed for this
   model.

   Alternately, the gateway can use CEMA procedures to provide transport
   level interworking between MSRP endpoints using different transport
   protocols as follows.

   When the gateway performs transport level interworking between MSRP
   endpoints, all of the procedures in Section 5 apply to each peer,
   with the following additions:

   o  The endpoint establishing an MSRP session using data channel
      transport shall not request inclusion of any relays, although it
      may interoperate with a peer that signals the use of relays.

   o  The gateway receiving an SDP offer that includes a request to
      negotiate an MSRP session on a data channel can provide transport
      level interworking in the same manner as a CEMA SBC by forwarding
      TCP or TLS transport parameters in a new m line with the
      appropriate attributes within the forwarded SDP offer.

   o  Similarly, a gateway receiving an SDP offer to negotiate an MSRP
      session using TCP or TLS transport with an endpoint that only
      supports data channel transport for MSRP can provide transport
      level interworking in the same manner as a CEMA SBC by
      establishing a new data channel for the MSRP session with the
      target endpoint.



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7.  Security Considerations

   To be completed.

8.  IANA Considerations

   To be completed.

9.  Acknowledgments

   The authors wish to acknowledge the borrowing of ideas from another
   internet draft by Peter Dunkley and Gavin Llewellyn, and to thank
   Paul Kyzivat, Jonathan Lennox, Uwe Rauschenbach and Keith Drage for
   their invaluable comments.

10.  CHANGE LOG

10.1.  Changes against '-00'

   o  Transport parameter change for MSRP to allow MSRP RFC transports.

   o  Clarification on SDP offer/answer and removing duplicated
      procedures and refer them to
      [I-D.ejzak-mmusic-data-channel-sdpneg].

11.  References

11.1.  Normative References

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

   [I-D.ietf-rtcweb-jsep]
              Uberti, J., Jennings, C., and E. Rescorla, "Javascript
              Session Establishment Protocol", draft-ietf-rtcweb-jsep-07
              (work in progress), July 2014.

   [RFC3264]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
              with Session Description Protocol (SDP)", RFC 3264, June
              2002.

   [I-D.ietf-rtcweb-data-protocol]
              Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data Channel
              Establishment Protocol", draft-ietf-rtcweb-data-
              protocol-08 (work in progress), September 2014.






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   [I-D.ietf-rtcweb-data-channel]
              Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data
              Channels", draft-ietf-rtcweb-data-channel-12 (work in
              progress), September 2014.

   [I-D.ejzak-mmusic-data-channel-sdpneg]
              Drage, K., Ejzak, R., and J. Marcon, "SDP-based "SCTP over
              DTLS" data channel negotiation", draft-ejzak-mmusic-data-
              channel-sdpneg-01 (work in progress), October 2014.

   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, July 2006.

   [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.

   [RFC5547]  Garcia-Martin, M., Isomaki, M., Camarillo, G., Loreto, S.,
              and P. Kyzivat, "A Session Description Protocol (SDP)
              Offer/Answer Mechanism to Enable File Transfer", RFC 5547,
              May 2009.

   [RFC6135]  Holmberg, C. and S. Blau, "An Alternative Connection Model
              for the Message Session Relay Protocol (MSRP)", RFC 6135,
              February 2011.

   [RFC6714]  Holmberg, C., Blau, S., and E. Burger, "Connection
              Establishment for Media Anchoring (CEMA) for the Message
              Session Relay Protocol (MSRP)", RFC 6714, August 2012.

11.2.  Informative References

   [WebRtcAPI]
              Bergkvist, A., Burnett, D., Narayanan, A., and C.
              Jennings, "WebRTC 1.0: Real-time Communication Between
              Browsers", World Wide Web Consortium WD WD-webrtc-
              20120821, August 2012,
              <http://www.w3.org/TR/2012/WD-webrtc-20120821>.

Authors' Addresses








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   Keith Drage (editor)
   Alcatel-Lucent
   Quadrant, Stonehill Green, Westlea
   Swindon
   UK

   Email: keith.drage@alcatel-lucent.com


   Raju Makaraju
   Alcatel-Lucent
   2000 Lucent Lane
   Naperville, Illinois
   US

   Email: Raju.Makaraju@alcatel-lucent.com


   Juergen Stoetzer-Bradler
   Alcatel-Lucent
   Lorenzstrasse 10
   D-70435 Stuttgart
   Germany

   Email: Juergen.Stoetzer-Bradler@alcatel-lucent.com


   Richard Ejzak
   Unaffiliated

   Email: richard.ejzak@gmail.com


   Jerome Marcon
   Unaffiliated
















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