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Versions: (draft-ejzak-mmusic-msrp-usage-data-channel) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 18

MMUSIC                                                     J. Recio, Ed.
Internet-Draft                                              Unaffiliated
Updates: RFC4975 (if approved)                               C. Holmberg
Intended status: Standards Track                                Ericsson
Expires: December 20, 2020                                 June 18, 2020


                        MSRP over Data Channels
              draft-ietf-mmusic-msrp-usage-data-channel-18

Abstract

   This document specifies how the Message Session Relay Protocol (MSRP)
   can be transported as a WebRTC data channel sub-protocol, using the
   SDP offer/answer generic data channel negotiation framework to
   establish such a channel.  Two network configurations are supported:
   connecting two MSRP over data channel endpoints; and a gateway
   configuration, connecting an MSRP over data channel endpoint with an
   MSRP over TCP or TLS endpoint.  This document updates RFC4975

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 https://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 December 20, 2020.

Copyright Notice

   Copyright (c) 2020 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
   (https://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.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  WebRTC Data Channel Considerations  . . . . . . . . . . . . .   4
     3.1.  MSRP Data Channel . . . . . . . . . . . . . . . . . . . .   4
   4.  SDP Considerations  . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  MSRP URI  . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.2.  msrp-scheme . . . . . . . . . . . . . . . . . . . . . . .   5
     4.3.  Use of the dcmap Attribute  . . . . . . . . . . . . . . .   5
     4.4.  Use of the dcsa Attribute . . . . . . . . . . . . . . . .   6
     4.5.  Use of the dcsa embedded setup Attribute  . . . . . . . .   7
     4.6.  Session Closing . . . . . . . . . . . . . . . . . . . . .   7
     4.7.  Support for MSRP File Transfer Function . . . . . . . . .   8
     4.8.  Example SDP Negotiation . . . . . . . . . . . . . . . . .   8
   5.  MSRP Considerations . . . . . . . . . . . . . . . . . . . . .   8
     5.1.  Session Mapping . . . . . . . . . . . . . . . . . . . . .   9
     5.2.  Session Opening . . . . . . . . . . . . . . . . . . . . .   9
     5.3.  Session Closing . . . . . . . . . . . . . . . . . . . . .   9
     5.4.  Data Framing  . . . . . . . . . . . . . . . . . . . . . .   9
     5.5.  Data Sending, Receiving and Reporting . . . . . . . . . .   9
     5.6.  Support for MSRP File Transfer Function . . . . . . . . .   9
   6.  Gateway Considerations  . . . . . . . . . . . . . . . . . . .  10
   7.  Updates to RFC4975  . . . . . . . . . . . . . . . . . . . . .  11
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
     9.1.  msrps URI scheme  . . . . . . . . . . . . . . . . . . . .  11
     9.2.  Subprotocol Identifier MSRP . . . . . . . . . . . . . . .  11
     9.3.  SDP Attributes  . . . . . . . . . . . . . . . . . . . . .  11
   10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  17
   11. CHANGE LOG  . . . . . . . . . . . . . . . . . . . . . . . . .  18
     11.1.  Changes against 'draft-ietf-mmusic-msrp-usage-data-
            channel-17'  . . . . . . . . . . . . . . . . . . . . . .  18
     11.2.  Changes against 'draft-ietf-mmusic-msrp-usage-data-
            channel-16'  . . . . . . . . . . . . . . . . . . . . . .  18
     11.3.  Changes against 'draft-ietf-mmusic-msrp-usage-data-
            channel-15'  . . . . . . . . . . . . . . . . . . . . . .  18
     11.4.  Changes against 'draft-ietf-mmusic-msrp-usage-data-
            channel-14'  . . . . . . . . . . . . . . . . . . . . . .  18
     11.5.  Changes against 'draft-ietf-mmusic-msrp-usage-data-
            channel-13'  . . . . . . . . . . . . . . . . . . . . . .  18
     11.6.  Changes against 'draft-ietf-mmusic-msrp-usage-data-
            channel-12'  . . . . . . . . . . . . . . . . . . . . . .  18
     11.7.  Changes against 'draft-ietf-mmusic-msrp-usage-data-



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            channel-11'  . . . . . . . . . . . . . . . . . . . . . .  19
     11.8.  Changes against 'draft-ietf-mmusic-msrp-usage-data-
            channel-10'  . . . . . . . . . . . . . . . . . . . . . .  19
     11.9.  Changes against 'draft-ietf-mmusic-msrp-usage-data-
            channel-09'  . . . . . . . . . . . . . . . . . . . . . .  19
     11.10. Changes against 'draft-ietf-mmusic-msrp-usage-data-
            channel-08'  . . . . . . . . . . . . . . . . . . . . . .  19
     11.11. Changes against 'draft-ietf-mmusic-msrp-usage-data-
            channel-07'  . . . . . . . . . . . . . . . . . . . . . .  19
     11.12. Changes against 'draft-ietf-mmusic-msrp-usage-data-
            channel-06'  . . . . . . . . . . . . . . . . . . . . . .  19
     11.13. Changes against 'draft-ietf-mmusic-msrp-usage-data-
            channel-05'  . . . . . . . . . . . . . . . . . . . . . .  20
     11.14. Changes against 'draft-ietf-mmusic-msrp-usage-data-
            channel-04'  . . . . . . . . . . . . . . . . . . . . . .  20
     11.15. Changes against 'draft-ietf-mmusic-msrp-usage-data-
            channel-03'  . . . . . . . . . . . . . . . . . . . . . .  20
     11.16. Changes against 'draft-ietf-mmusic-msrp-usage-data-
            channel-02'  . . . . . . . . . . . . . . . . . . . . . .  20
     11.17. Changes against 'draft-ietf-mmusic-msrp-usage-data-
            channel-01'  . . . . . . . . . . . . . . . . . . . . . .  21
     11.18. Changes against 'draft-ietf-mmusic-msrp-usage-data-
            channel-00'  . . . . . . . . . . . . . . . . . . . . . .  22
     11.19. Changes against 'draft-ejzak-mmusic-msrp-usage-data-
            channel-01'  . . . . . . . . . . . . . . . . . . . . . .  23
     11.20. Changes against '-00'  . . . . . . . . . . . . . . . . .  23
   12. Normative References  . . . . . . . . . . . . . . . . . . . .  23
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  24

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 was initially defined in
   [RFC4975] to work over TCP and TLS connections, and over a WebSocket
   subprotocol specified by [RFC7977].

   This document specifies the negotiation and transport of MSRP over a
   WebRTC data channel [I-D.ietf-rtcweb-data-channel].  Negotiation is
   carried out as specified in [I-D.ietf-mmusic-data-channel-sdpneg] and
   MSRP is transported as a sub-protocol of a WebRTC data channel,
   without the TCP and TLS layers.

   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



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   o  integrates those features with other WebRTC 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

   Compared to WebSockets, which provide a message passing protocol to
   applications with no direct access to TCP or TLS sockets, data
   channels provide a low latency transport, leverage NAT-aware
   connectivity and security features of WebRTC, and are increasingly
   available not only in modern browsers but in other applications that
   use WebRTC for media or other purposes, such as IoT or telemetry in
   general, non-media data exchange, and so on.

   Considering an MSRP endpoint as an MSRP application that uses a
   WebRTC data channel, 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.

   This document updates [RFC4975] as described in Section 7.

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.  WebRTC Data Channel Considerations

3.1.  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 channel is
   negotiated using the SDP-based external negotiation method defined in
   [I-D.ietf-mmusic-data-channel-sdpneg].

   The following WebRTC data channel property values
   [I-D.ietf-rtcweb-data-channel] apply to an MSRP data channel:










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      +--------------------------+---------------------------------+
      | Property                 | Value                           |
      +--------------------------+---------------------------------+
      | Subprotocol Identifier   | msrp                            |
      | Transmission reliability | reliable                        |
      | Transmission order       | in-order                        |
      | Label                    | See          Section 4.3        |
      +--------------------------+---------------------------------+

4.  SDP Considerations

   This section describes the SDP considerations which are specific to
   an MSRP data channel

4.1.  MSRP URI

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

     transport  /= "dc"
                   ; Add "dc" to existing transports per [RFC4975]

   MSRP design provides for new transport bindings, see Section 6 of
   [RFC4975], MSRP implementations are expected to allow unrecognized
   transports for which there is no need to establish a connection to
   the resource described by the URI, as it's the case of data channels
   (Section 4.4).

4.2.  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 as described in
   [I-D.ietf-rtcweb-data-channel].

4.3.  Use of the dcmap Attribute

   An offerer and answerer SHALL, in each offer and answer, include a
   dcmap attribute line ([I-D.ietf-mmusic-data-channel-sdpneg]) within
   the media description of 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"



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   The labelstring is set by the MSRP application according to
   [I-D.ietf-mmusic-data-channel-sdpneg].

   The offerer and answerer SHALL NOT include the max-retr and the max-
   time attribute parameters in the dcmap attribute.

   The offerer and answerer MAY include the ordered attribute parameter
   in the dcmap attribute.  If included, the attribute parameter value
   SHALL be set to "true".

   Below is an example of the dcmap attribute for an MSRP session to be
   negotiated with stream-id=2 and label="chat":

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

4.4.  Use of the dcsa Attribute

   An offerer and answerer SHALL, in each offer and answer, include a
   dcsa attribute line ([I-D.ietf-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.

   An offerer and answerer SHALL include a dcsa attribute for each of
   the following MSRP-specific SDP attributes:

   o  defined in [RFC4975]: "path".

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

   o  defined in [RFC6135]: "setup".  See Section 4.5

   It is considered a protocol error if one or more of the dcsa embedded
   attributes listed above are not included in an offer or answer.

   An offerer and answerer MAY include a dcsa attribute for any of the
   following MSRP-specific SDP attributes, following the procedures
   defined for each attributes:

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

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

   o  defined in [RFC5547]: all the parameters related to MSRP file
      transfer.  See Section 4.7.




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   A subsequent offer or answer MAY update the previously negotiated
   MSRP subprotocol attributes while keeping the same subprotocol
   a=dcmap description.  The semantics for newly negotiated MSRP
   subprotocol attributes are per [RFC4975].

   When MSRP messages are transported on a data channel, the "path"
   attribute is not used for routing of the messages.  The MSRP data
   channel is established using the SDP offer/answer procedures defined
   in [I-D.ietf-mmusic-data-channel-sdpneg], and the MSRP messages are
   then transported on that data channel.  This is different from legacy
   MSRP [RFC4975] but similar to MSRP CEMA [RFC6714].  However, when an
   endpoint receives an MSRP message over a data channel, it MUST still
   perform the MSRP-URI comparison procedures defined in [RFC4975].

4.5.  Use of the dcsa embedded setup Attribute

   As described in Section 4.4, the usage of a dsca embedded setup
   attribute is mandated for MSRP sessions over data channels.  It is
   used to negotiate which MSRP session endpoint assumes the active role
   as per Section 4.2.2 of [RFC6135] and Section 5.4 of [RFC4975].  It
   has no relationship with the DTLS connection establishment roles
   [I-D.ietf-mmusic-sctp-sdp].

   The dcsa embedded setup attribute is of the form "a=dcsa:x
   setup:<role>", with x being the data channel's SCTP stream
   identifier, so that such attribute is explicitly associated with an
   MSRP session over a specific data channel.

4.6.  Session Closing

   An MSRP session is closed by closing the associated data channel,
   following the procedures in [I-D.ietf-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.






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4.7.  Support for MSRP File Transfer Function

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

4.8.  Example SDP Negotiation

   The following is an example of an "m=" line for data channels 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 UDP/DTLS/SCTP webrtc-datachannel
      c=IN IP4 198.51.100.79
      a=max-message-size:100000
      a=sctp-port:5000
      a=setup:actpass
      a=fingerprint:SHA-1 \
          4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB
      a=tls-id:4a756565cddef001be82
      a=dcmap:0 label="chat";subprotocol="msrp"
      a=dcsa:0 msrp-cema
      a=dcsa:0 setup:active
      a=dcsa:0 accept-types:message/cpim text/plain
      a=dcsa:0 path:msrps://198.51.100.79:54111/si438dsaodes;dc
      a=dcmap:2 label="file transfer";subprotocol="msrp"
      a=dcsa:2 sendonly
      a=dcsa:2 msrp-cema
      a=dcsa:2 setup:active
      a=dcsa:2 accept-types:message/cpim
      a=dcsa:2 accept-wrapped-types:*
      a=dcsa:2 path:msrps://198.51.100.79:54111/jshA7we;dc
      a=dcsa:2 file-selector:name:"picture1.jpg" \
           type:image/jpeg size:1463440 hash:sha-1:\
           FF:27:0D:81:14:F1:8A:C3:35:3B:36:64:2A:62:C9:3E:D3:6B:51:B4
      a=dcsa:2 file-transfer-id:rjEtHAcYVZ7xKwGYpGGwyn5gqsSaU7Ep
      a=dcsa:2 file-disposition:attachment
      a=dcsa:2 file-date:creation:"Mon, 12 Jan 2018 15:01:31 +0800"
      a=dcsa:2 file-icon:cid:id2@bob.example.com
      a=dcsa:2 file-range:1-1463440

5.  MSRP Considerations

   The procedures specified in [RFC4975] apply except when this document
   specifies otherwise.  This section describes the MSRP considerations
   specific to an MSRP data channel.




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5.1.  Session Mapping

   In this document, each MSRP session maps to one data channel exactly.

5.2.  Session Opening

   Section 4.5 describes how the active MSRP session endpoint role is
   negotiated.  The active MSRP session endpoint uses the data channel
   established for this MSRP session by the generic data channel opening
   procedure defined in [I-D.ietf-mmusic-data-channel-sdpneg].

   As soon as the WebRTC data channel is opened, the MSRP session is
   actually opened by the active MSRP session endpoint.  In order to do
   this the active MSRP endpoint sends an MSRP SEND message (empty or
   not) to the other MSRP endpoint.

5.3.  Session Closing

   The closure of an MSRP session SHALL be signaled via SDP following
   the requirements in Section 4.6

   If the data channel used to transport the MSRP session fails and gets
   torn down, the endpoints SHALL consider the MSRP session failed.  An
   MSRP endpoint MAY, based on local policy, try to negotiate a new MSRP
   data channel.

5.4.  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.  Therefore all sent MSRP chunks including the MSRP chunk
   header SHALL have lengths of less than or equal to the value of the
   peer's "a=max-message-size" attribute, which is associated with the
   data channel's SCTP association.

5.5.  Data Sending, Receiving and Reporting

   Data sending, receiving and reporting procedures SHALL conform to
   [RFC4975].

5.6.  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 channels, 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 are negotiated as specified in Section 4.7.

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

6.  Gateway Considerations

   This section describes the network configuration where one MSRP
   endpoint uses an MSRP data channel as MSRP transport, the other MSRP
   endpoint uses TLS/TCP connections as MSRP transport, and the two MSRP
   endpoints interwork via a gateway.

   Specifically, a gateway can be configured to interwork an MSRP
   session over 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 an MSRP B2BUA to interwork all
   the procedures as necessary between the endpoints.  No further
   specification is needed for this model.

   Alternately, the gateway can provide transport level interworking
   between MSRP endpoints using different transport protocols.  In
   accordance with Section 4.4, path attributes SHALL NOT be used for
   transport level interworking.

   When the gateway performs transport level interworking between MSRP
   endpoints, all of the procedures in Section 5 and Section 4 apply to
   each peer, with the following additions:

   o  The gateway SHALL use CEMA towards the non-data channel endpoint.

   o  If the non-data channel endpoint does not support CEMA, transport
      level interworking mode is not possible, the gateway needs to act
      as an MSRP B2BUA.

   o  The gateway SHALL NOT modify the path attribute received from data
      channel or from non-data channel endpoints.

   o  The gateway SHALL NOT modify the setup value received from data
      channel or from non-data channel endpoints.

   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.




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7.  Updates to RFC4975

   This document updates [RFC4975], by allowing the usage of the "msrps"
   scheme when the underlying connection is protected with DTLS.

8.  Security Considerations

   MSRP traffic over data channels is secured, including
   confidentiality, integrity and source authentication, as specified by
   [I-D.ietf-rtcweb-data-channel]

   Note that discussion in [RFC4975] on MSRP message attribution to
   remote identities applies to data channel transport.

9.  IANA Considerations

   NOTE to RFC Editor: Please replace all instances of all instances of
   RFCXXXX with the number of this RFC.

9.1.  msrps URI scheme

   This document modifies the usage of the msrps URI scheme, registered
   by [RFC4975], adding DTLS as a protected transport indicated by the
   URI scheme.

   A reference to RFCXXXX is added to the URI scheme "msrps" in the
   Uniform Resource Identifier (URI) Schemes Registry.

9.2.  Subprotocol Identifier MSRP

   This document adds a reference to the subprotocol identifier "msrp"
   in the "WebSocket Subprotocol Name Registry"

9.3.  SDP Attributes

   This document modifies the usage of the SDP setup attribute, if this
   attribute is included in an SDP 'dcsa' attribute associated to an
   MSRP data channel.  The modified usage is described in Section 4.5.

   This document also adds a reference to the following attributes in
   the Session Description Protocol (SDP) Parameters registry, if these
   attributes are included in SDP 'dcsa' attributes associated to an
   MSRP data channel.  Usage of these attributes is described in section
   Section 4.4:

   o  "path"

   o  "msrp-cema"



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   o  "accept-types"

   o  "accept-wrapped-types"

   o  "max-size"

   o  "sendonly"

   o  "recvonly"

   o  "inactive"

   o  "sendrecv"

   o  "file-selector"

   o  "file-transfer-id"

   o  "file-disposition"

   o  "file-date"

   o  "file-icon"

   o  "file-range"

   The usage level "dcsa(msrp)" is added to the registration of the SDP
   'setup' attribute in the Session Description Protocol (SDP)
   Parameters registry as follows:

   +-----------------------+-------------------------------------------+
   | Contact name:         | IESG                                      |
   | Contact email:        | iesg@ietf.org                             |
   | Attribute name:       | setup                                     |
   | Usage level:          | dcsa(msrp)                                |
   | Purpose:              |  Negotiate the active role of an MSRP     |
   |                       | session over a data channel as per        |
   |                       | Section 4.5                               |
   | Reference:            | RFCXXXX                                   |
   +-----------------------+-------------------------------------------+

   The usage level "dcsa(msrp)" is added to the registration of the SDP
   'path' attribute in the Session Description Protocol (SDP) Parameters
   registry as follows:







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   +-----------------------+-------------------------------------------+
   | Contact name:         | IESG                                      |
   | Contact email:        | iesg@ietf.org                             |
   | Attribute name:       | path                                      |
   | Usage level:          | dcsa(msrp)                                |
   | Purpose:              | Indicate a series of MSRP devices visited |
   |                       | by messages sent in the MSRP session.     |
   | Reference:            | RFCXXXX                                   |
   +-----------------------+-------------------------------------------+

   The usage level "dcsa(msrp)" is added to the registration of the SDP
   'msrp-cema' attribute in the Session Description Protocol (SDP)
   Parameters registry as follows:

   +-----------------------+-------------------------------------------+
   | Contact name:         | IESG                                      |
   | Contact email:        | iesg@ietf.org                             |
   | Attribute name:       | msrp-cema                                 |
   | Usage level:          | dcsa(msrp)                                |
   | Purpose:              | Indicate that the routing of MSRP         |
   |                       | messages transported on a data channel is |
   |                       | more similar to the MSRP CEMA mechanism   |
   |                       | than the legacy MSRP routing mechanism.   |
   | Reference:            | RFCXXXX                                   |
   +-----------------------+-------------------------------------------+

   The usage level "dcsa(msrp)" is added to the registration of the SDP
   'accept-types' attribute in the Session Description Protocol (SDP)
   Parameters registry as follows:

   +-----------------------+-------------------------------------------+
   | Contact name:         | IESG                                      |
   | Contact email:        | iesg@ietf.org                             |
   | Attribute name:       | accept-types                              |
   | Usage level:          | dcsa(msrp)                                |
   | Purpose:              | Contain the list of media types that the  |
   |                       | endpoint is willing to receive.           |
   | Reference:            | RFCXXXX                                   |
   +-----------------------+-------------------------------------------+

   The usage level "dcsa(msrp)" is added to the registration of the SDP
   'accept-wrapped-types' attribute in the Session Description Protocol
   (SDP) Parameters registry as follows:








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   +-----------------------+-------------------------------------------+
   | Contact name:         | IESG                                      |
   | Contact email:        | iesg@ietf.org                             |
   | Attribute name:       | accept-wrapped-types                      |
   | Usage level:          | dcsa(msrp)                                |
   | Purpose:              | Contain the list of media types that the  |
   |                       | endpoint is willing to receive in an MSRP |
   |                       | message with multipart content.           |
   | Reference:            | RFCXXXX                                   |
   +-----------------------+-------------------------------------------+

   The usage level "dcsa(msrp)" is added to the registration of the SDP
   'max-size' attribute in the Session Description Protocol (SDP)
   Parameters registry as follows:

   +-----------------------+-------------------------------------------+
   | Contact name:         | IESG                                      |
   | Contact email:        | iesg@ietf.org                             |
   | Attribute name:       | max-size                                  |
   | Usage level:          | dcsa(msrp)                                |
   | Purpose:              | Indicate the largest message an MSRP      |
   |                       | endpoint wishes to accept.                |
   | Reference:            | RFCXXXX                                   |
   +-----------------------+-------------------------------------------+

   The usage level "dcsa(msrp)" is added to the registration of the SDP
   'sendonly' attribute in the Session Description Protocol (SDP)
   Parameters registry as follows:

   +-----------------------+-------------------------------------------+
   | Contact name:         | IESG                                      |
   | Contact email:        | iesg@ietf.org                             |
   | Attribute name:       | sendonly                                  |
   | Usage level:          | dcsa(msrp)                                |
   | Purpose:              | Negotiate the direction of the media flow |
   |                       | on an MSRP data channel.                  |
   | Reference:            | RFCXXXX                                   |
   +-----------------------+-------------------------------------------+

   The usage level "dcsa(msrp)" is added to the registration of the SDP
   'recvonly' attribute in the Session Description Protocol (SDP)
   Parameters registry as follows:









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   +-----------------------+-------------------------------------------+
   | Contact name:         | IESG                                      |
   | Contact email:        | iesg@ietf.org                             |
   | Attribute name:       | recvonly                                  |
   | Usage level:          | dcsa(msrp)                                |
   | Purpose:              | Negotiate the direction of the media flow |
   |                       | on an MSRP data channel.                  |
   | Reference:            | RFCXXXX                                   |
   +-----------------------+-------------------------------------------+

   The usage level "dcsa(msrp)" is added to the registration of the SDP
   'inactive' attribute in the Session Description Protocol (SDP)
   Parameters registry as follows:

   +-----------------------+-------------------------------------------+
   | Contact name:         | IESG                                      |
   | Contact email:        | iesg@ietf.org                             |
   | Attribute name:       | inactive                                  |
   | Usage level:          | dcsa(msrp)                                |
   | Purpose:              | Negotiate the direction of the media flow |
   |                       | on an MSRP data channel.                  |
   | Reference:            | RFCXXXX                                   |
   +-----------------------+-------------------------------------------+

   The usage level "dcsa(msrp)" is added to the registration of the SDP
   'sendrecv' attribute in the Session Description Protocol (SDP)
   Parameters registry as follows:

   +-----------------------+-------------------------------------------+
   | Contact name:         | IESG                                      |
   | Contact email:        | iesg@ietf.org                             |
   | Attribute name:       | sendrecv                                  |
   | Usage level:          | dcsa(msrp)                                |
   | Purpose:              | Negotiate the direction of the media flow |
   |                       | on an MSRP data channel.                  |
   | Reference:            | RFCXXXX                                   |
   +-----------------------+-------------------------------------------+

   The usage level "dcsa(msrp)" is added to the registration of the SDP
   'file-selector' attribute in the Session Description Protocol (SDP)
   Parameters registry as follows:










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   +-----------------------+-------------------------------------------+
   | Contact name:         | IESG                                      |
   | Contact email:        | iesg@ietf.org                             |
   | Attribute name:       | file-selector                             |
   | Usage level:          | dcsa(msrp)                                |
   | Purpose:              | Indicate a file in an MSRP file transfer  |
   |                       | negotiation.                              |
   | Reference:            | RFCXXXX                                   |
   +-----------------------+-------------------------------------------+

   The usage level "dcsa(msrp)" is added to the registration of the SDP
   'file-transfer-id' attribute in the Session Description Protocol
   (SDP) Parameters registry as follows:

   +-----------------------+-------------------------------------------+
   | Contact name:         | IESG                                      |
   | Contact email:        | iesg@ietf.org                             |
   | Attribute name:       | file-transfer-id                          |
   | Usage level:          | dcsa(msrp)                                |
   | Purpose:              | Indicate a unique identifier of the file  |
   |                       | transfer operation in an MSRP file        |
   |                       | transfer negotiation.                     |
   | Reference:            | RFCXXXX                                   |
   +-----------------------+-------------------------------------------+

   The usage level "dcsa(msrp)" is added to the registration of the SDP
   'file-disposition' attribute in the Session Description Protocol
   (SDP) Parameters registry as follows:

   +-----------------------+-------------------------------------------+
   | Contact name:         | IESG                                      |
   | Contact email:        | iesg@ietf.org                             |
   | Attribute name:       | file-disposition                          |
   | Usage level:          | dcsa(msrp)                                |
   | Purpose:              | Provide a suggestion to the other         |
   |                       | endpoint about the intended disposition   |
   |                       | of the file in an MSRP file transfer      |
   |                       | negotiation.                              |
   | Reference:            | RFCXXXX                                   |
   +-----------------------+-------------------------------------------+

   The usage level "dcsa(msrp)" is added to the registration of the SDP
   'file-date' attribute in the Session Description Protocol (SDP)
   Parameters registry as follows:







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   +-----------------------+-------------------------------------------+
   | Contact name:         | IESG                                      |
   | Contact email:        | iesg@ietf.org                             |
   | Attribute name:       | file-date                                 |
   | Usage level:          | dcsa(msrp)                                |
   | Purpose:              | Indicate a date related to the file in an |
   |                       | MSRP file transfer negotiation.           |
   | Reference:            | RFCXXXX                                   |
   +-----------------------+-------------------------------------------+

   The usage level "dcsa(msrp)" is added to the registration of the SDP
   'file-icon' attribute in the Session Description Protocol (SDP)
   Parameters registry as follows:

   +-----------------------+-------------------------------------------+
   | Contact name:         | IESG                                      |
   | Contact email:        | iesg@ietf.org                             |
   | Attribute name:       | file-icon                                 |
   | Usage level:          | dcsa(msrp)                                |
   | Purpose:              | Contain a pointer to a small preview icon |
   |                       | representing the contents of the file in  |
   |                       | an MSRP file transfer negotiation.        |
   | Reference:            | RFCXXXX                                   |
   +-----------------------+-------------------------------------------+

   The usage level "dcsa(msrp)" is added to the registration of the SDP
   'file-range' attribute in the Session Description Protocol (SDP)
   Parameters registry as follows:

   +-----------------------+-------------------------------------------+
   | Contact name:         | IESG                                      |
   | Contact email:        | iesg@ietf.org                             |
   | Attribute name:       | file-range                                |
   | Usage level:          | dcsa(msrp)                                |
   | Purpose:              | Contain the range of transferred octets   |
   |                       | of the file in an MSRP file transfer      |
   |                       | negotiation.                              |
   | Reference:            | RFCXXXX                                   |
   +-----------------------+-------------------------------------------+

10.  Acknowledgments

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




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   Richard Ejzak, Keith Drage and Juergen Stoetzer-Bradler contributed
   an earlier version, before the draft was re-adopted.

   Julien Maisonneuve helped with the re-adoption of the draft, and
   Maridi R.  Makaraju (Raju) contributed valuable comments after the
   draft was re-adopted.

11.  CHANGE LOG

11.1.  Changes against 'draft-ietf-mmusic-msrp-usage-data-channel-17'

   o  Shepherd's review: update to the file header, remove reference in
      abstract, mention update on introduction, reorder and complete
      IANA considerations.

   o  Editorial: a MSRP -> an MSRP; MSRP -> msrp for consistency; typos.

11.2.  Changes against 'draft-ietf-mmusic-msrp-usage-data-channel-16'

   o  WGLC review: draft updates RFC4975; clarify introduction; rewrite
      wording on path and transport negotiation; session closing
      clarifications; references cleanup.

   o  Editorial: consistent SHALL usage; reorder updates, security and
      IANA sections for consistency; typos; acknowledgements.

11.3.  Changes against 'draft-ietf-mmusic-msrp-usage-data-channel-15'

   o  More concise and clear introduction and section descriptions.

   o  Updates on author list, contributions and acknowledgements.

11.4.  Changes against 'draft-ietf-mmusic-msrp-usage-data-channel-14'

   o  Reorganization following t140-usage-data-channel structure.

11.5.  Changes against 'draft-ietf-mmusic-msrp-usage-data-channel-13'

   o  Clarify gateway procedures in accordance to mandatory use of CEMA.

11.6.  Changes against 'draft-ietf-mmusic-msrp-usage-data-channel-12'

   o  Make CEMA mandatory, clarify SDP procedures.








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11.7.  Changes against 'draft-ietf-mmusic-msrp-usage-data-channel-11'

   o  Additional clarifications on cema and path attribute after mail
      list feedback.

11.8.  Changes against 'draft-ietf-mmusic-msrp-usage-data-channel-10'

   o  Corrections and clarifications on cema and path attributes after
      mail list feedback.

11.9.  Changes against 'draft-ietf-mmusic-msrp-usage-data-channel-09'

   o  Corrected area to ART.

11.10.  Changes against 'draft-ietf-mmusic-msrp-usage-data-channel-08'

   o  Updated reference to 4566bis.

   o  Expanded motivation paragraphs in introduction.

11.11.  Changes against 'draft-ietf-mmusic-msrp-usage-data-channel-07'

   o  Move security considerations after IANA considerations, following
      RFC7322 suggested order.

   o  Update references to use xml.resource.org citation database.

   o  Reformat of the section discussing setup parameter

   o  Align examples with latest [I-D.ietf-mmusic-data-channel-sdpneg]
      draft.

   o  Edit section 6 for clarity.

   o  Security requirements.

   o  Clarify comment on unrecognized transports and session opening.

   o  Update year, add editor.

11.12.  Changes against 'draft-ietf-mmusic-msrp-usage-data-channel-06'

   o  Modification of Keith's address information.








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11.13.  Changes against 'draft-ietf-mmusic-msrp-usage-data-channel-05'

   o  Modification of Juergen's address information.

11.14.  Changes against 'draft-ietf-mmusic-msrp-usage-data-channel-04'

   o  Addition of "I-D.ietf-mmusic-rfc4566bis"/> to list of normative
      references.

   o  Addition of IANA considerations for setup attribute as per section
      8.2.4 of "I-D.ietf-mmusic-rfc4566bis"/>.

11.15.  Changes against 'draft-ietf-mmusic-msrp-usage-data-channel-03'

   o  Addition of IANA registration related Section 9.2.

11.16.  Changes against 'draft-ietf-mmusic-msrp-usage-data-channel-02'

   o  Addition of "a=setup:actpass", "a=connection:new",
      "a=fingerprint:..." and "a=dcsa:x setup=active" SDP attributes to
      the SDP example in Section 4.8.

   o  Addition of "RFC4145" and [I-D.ietf-mmusic-sctp-sdp] to list of
      normative references.

   o  Addition of new Section 4.5 describing how the active MSRP session
      endpoint role is negotiated.

   o  Extension of first paragraph of session-opening with new first
      sentence "Section 4.5 describes how the active MSRP session
      endpoint role is negotiated.".

   o  First sentence of second paragraph in session-opening was "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."  Replacement
      of this sentence with "As soon as this data channel is opened, the
      MSRP session is actually opened by the active MSRP endpoint.  In
      order to do this the active MSRP endpoint sends an MSRP SEND
      message (empty or not) to the other MSRP endpoint."

   o  Addition of setup attribute specific behavior descriptions of data
      channel to TCP or TLS interworking gateways in Section 6.








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11.17.  Changes against 'draft-ietf-mmusic-msrp-usage-data-channel-01'

   o  In the abstract replacement of the first sentence "This document
      specifies how the Message Session Relay Protocol (MSRP) can be
      instantiated as a data channel sub-protocol, using the SDP offer/
      answer exchange-based external negotiation defined in
      [I-D.ietf-mmusic-data-channel-sdpneg]" with "This document
      specifies how the Message Session Relay Protocol (MSRP) can be
      instantiated as a data channel sub-protocol, using the SDP offer/
      answer exchange-based generic data channel negotiation framework"
      in order to remove the reference from the abstract text.

   o  Addition of following sentence to the second paragraph in
      Section 1: "The MSRP protocol negotiation defined in this document
      is based on the generic SDP offer/answer exchange based data
      channel negotiation as specified in
      [I-D.ietf-mmusic-data-channel-sdpneg]".

   o  In Section 3.1 replacement of sub-protocol identifier "msrp" with
      "MSRP" in order to make this consistent with the formal
      specification in Section 4.3.

   o  Throughout the text replacement of "shall" with "SHALL" etc where
      appropriate as per [RFC2119].

   o  In Section 4.3 replacement of sentence 'The max-retr, max-time and
      ordered parameters shall not be used.' with 'Ordered and reliable
      data channels MUST always be used, such that the "max-retr" and
      "max-time" parameters SHALL NOT be used.  If the "ordered"
      parameter is used, then its value MUST be equal to "true".'.

   o  In Section 4.3 removal of "(on default SCTP port 5000)" from the
      sentence preceding the example "a=dcmap" attribute line.

   o  In Section 4.4 first paragraph was "The SDP offer shall also
      include a dcsa attribute line (defined in
      [I-D.ietf-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.".  Replacement of this paragraph with "The SDP offer
      SHALL also include within the media description for the SCTP
      association a dcsa attribute line (defined in
      [I-D.ietf-mmusic-data-channel-sdpneg]) for each MSRP-specific SDP
      attribute to be negotiated for each MSRP data channel being
      negotiated.".

   o  Appended following sentence at the end of the first paragraph of
      Section 5.4: "Therefore all sent MSRP chunks MUST have lengths of



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      less than or equal to the value of the peer's "a=max-message-size"
      attribute, which is associated with the data channel's SCTP
      association.".

   o  Addition of the previously missing colon to the "a=sctp-port"
      attribute line in Section 4.8.

   o  In Section 5.3 replacement of the first paragraph "Closing of an
      MSRP session is done using the generic data channel closing
      procedure defined in [I-D.ietf-mmusic-data-channel-sdpneg]." with
      'The closure of an MSRP session MUST be signaled via an SDP offer/
      answer exchange which removes the "a=dcmap:" and "a=dcsa:"
      attribute lines associated with the MSRP session from the
      associated DTLS/SCTP based media description.  This results in the
      associated data channel being closed as well as per
      [I-D.ietf-mmusic-data-channel-sdpneg], where the actual data
      channel closure procedure is typically initiated by the SDP
      answerer right after having accepted the SDP offer.'.

11.18.  Changes against 'draft-ietf-mmusic-msrp-usage-data-channel-00'

   o  Additional reference to [I-D.ietf-mmusic-data-channel-sdpneg] in
      list of normative references.

   o  Replacement of previous document title "MSRP over SCTP/DTLS data
      channels" with "MSRP over Data Channels" in order to align with
      the terminology used in [I-D.ietf-mmusic-data-channel-sdpneg].

   o  In "terminology", "WebRTC data channel" was defined as "A
      bidirectional channel consisting of paired SCTP outbound and
      inbound streams."  Replacement of this definition with "Data
      channel: A WebRTC data channel as specified in
      [I-D.ietf-rtcweb-data-channel]", and consistent usage of either
      "data channel" or "MSRP data channel" in the remainder of the
      document."

   o  In the introduction replacement of references to
      [I-D.ietf-rtcweb-data-protocol] with a reference to
      [I-D.ietf-rtcweb-data-channel].

   o  Consistent usage of '"m=" line' in whole document as per
      [RFC4566].

   o  In the gateway configuration section (Section 6) replacement of
      the first sentence "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



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      gateway" with "This section describes the network configuration
      where one MSRP endpoint uses data channels as MSRP transport, the
      other MSRP endpoint uses TLS/TCP connections as MSRP transport,
      and the two MSRP endpoints interwork via an MSRP gateway".

11.19.  Changes against 'draft-ejzak-mmusic-msrp-usage-data-channel-01'

   o  Removed empty spaces after ";" in the examples' "a=dcmap"
      attribute lines.

   o  In all examples, the "m=" line proto value "DTLS/SCTP" was
      replaced with "UDP/DTLS/SCTP" and the "a=fmtp" attribute lines
      were replaced with "a=max-message-size" attribute lines, as per
      draft-ietf-mmusic-sctp-sdp-12.

11.20.  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 draft-ejzak-mmusic-data-channel-
      sdpneg-02.

12.  Normative References

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

   [I-D.ietf-rtcweb-data-protocol]
              Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data Channel
              Establishment Protocol", draft-ietf-rtcweb-data-
              protocol-09 (work in progress), January 2015.

   [I-D.ietf-rtcweb-data-channel]
              Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data
              Channels", draft-ietf-rtcweb-data-channel-13 (work in
              progress), January 2015.

   [I-D.ietf-mmusic-data-channel-sdpneg]
              Drage, K., Makaraju, M., Ejzak, R., Marcon, J., and R.
              Even, "SDP-based Data Channel Negotiation", draft-ietf-
              mmusic-data-channel-sdpneg-28 (work in progress), May
              2019.






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   [I-D.ietf-mmusic-sctp-sdp]
              Holmberg, C., Shpount, R., Loreto, S., and G. Camarillo,
              "Session Description Protocol (SDP) Offer/Answer
              Procedures For Stream Control Transmission Protocol (SCTP)
              over Datagram Transport Layer Security (DTLS) Transport.",
              draft-ietf-mmusic-sctp-sdp-26 (work in progress), April
              2017.

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

   [RFC4975]  Campbell, B., Ed., Mahy, R., Ed., and C. Jennings, Ed.,
              "The Message Session Relay Protocol (MSRP)", RFC 4975,
              DOI 10.17487/RFC4975, September 2007,
              <https://www.rfc-editor.org/info/rfc4975>.

   [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,
              DOI 10.17487/RFC5547, May 2009,
              <https://www.rfc-editor.org/info/rfc5547>.

   [RFC6135]  Holmberg, C. and S. Blau, "An Alternative Connection Model
              for the Message Session Relay Protocol (MSRP)", RFC 6135,
              DOI 10.17487/RFC6135, February 2011,
              <https://www.rfc-editor.org/info/rfc6135>.

   [RFC6714]  Holmberg, C., Blau, S., and E. Burger, "Connection
              Establishment for Media Anchoring (CEMA) for the Message
              Session Relay Protocol (MSRP)", RFC 6714,
              DOI 10.17487/RFC6714, August 2012,
              <https://www.rfc-editor.org/info/rfc6714>.

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

Authors' Addresses

   Jose M. Recio (editor)
   Unaffiliated

   Email: jose@ch3m4.com





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   Christer Holmberg
   Ericsson
   Hirsalantie 11
   Jorvas 02420
   Finland

   Email: christer.holmberg@ericsson.com












































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