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<rfc category="std" xmlns:xi="http://www.w3.org/2001/XInclude"
     docName="draft-ietf-mmusic-msrp-usage-data-channel-24"
     number="8873"
     ipr="trust200902" updates="4975">
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     updates="4975"
     obsoletes=""
     submissionType="IETF"
     category="std"
     consensus="true"
     xml:lang="en"
     tocInclude="true"
     tocDepth="4"
     symRefs="true"
     sortRefs="true"
     version="3">

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 <front>
  <!-- The abbreviated title is used in the page header - it is only necessary if the
       full title is longer than 39 characters -->
  <title abbrev="MSRP over Data Channels">
                 MSRP
                 Message Session Relay Protocol (MSRP) over Data Channels
    </title>

  <!-- add 'role="editor"' below for the editors if appropriate -->

  <!-- Another author who claims to be an editor -->
    <seriesInfo name="RFC" value="8873"/>

  <author initials="J. M." initials="JM." surname="Recio" fullname="Jose M. Recio" role="editor">
      <organization>Unaffiliated</organization>
      <address>
    <email>jose@ch3m4.com
    </email>
        <email>jose@ch3m4.com</email>
      </address>
    </author>
    <author initials="C." surname="Holmberg" fullname="Christer Holmberg">
      <organization>Ericsson</organization>
      <address>
        <postal>
          <street>Hirsalantie 11</street>
     <city>Jorvas 02420</city>
     <region/>
          <city>Jorvas</city>
	  <code> 02420</code>
          <country>Finland</country>
        </postal>
        <email>christer.holmberg@ericsson.com</email>
      </address>
    </author>
    <date year="2020"/>

  <!-- If the month and year are both specified and are the current ones,
   xml2rfc will fill
   in the current day for you. If only the current year is specified, xml2rfc will fill
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   necessary to specify at least a month (xml2rfc assumes day="1" if not specified for
   the purpose of calculating the expiry date).  With drafts it is normally sufficient
   to specify just the year. -->

  <!-- Meta-data Declarations --> year="2021" month="January" />

  <area>ART</area>
    <workgroup>MMUSIC</workgroup>

  <!-- WG name at the upperleft corner of the doc,
    IETF is fine for individual submissions.
    If this element is not present, the default is "Network Working Group",
    which is used by the RFC Editor as a nod to the history of the IETF. -->

  <!-- Keywords will be incorporated into HTML output
    files in a meta tag but they have no effect on text or nroff
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<keyword>webrtc</keyword>

  <abstract>
      <t>
      This document specifies how a Web Real-Time Communication (WebRTC)
      data channel can be used as a transport mechanism for the Message Session Relay Protocol (MSRP)
      and how the Session Description Protocol (SDP) offer/answer mechanism can be used to negotiate
      such a data channel, referred to as an MSRP data channel. Two network configurations are supported:
      connecting
      the connection of two MSRP data channel endpoints; and a gateway configuration, connecting which connects an MSRP data channel
      endpoint with an MSRP over endpoint that uses either TCP or TLS endpoint. TLS.  This document updates RFC4975. This document updates RFC4975. RFC 4975.
      </t>
    </abstract>
  </front>
  <middle>
    <section title="Introduction" anchor="introduction"> anchor="introduction" numbered="true" toc="default">
      <name>Introduction</name>
      <t>
      The Message Session Relay Protocol (MSRP) <xref target="RFC4975"/> target="RFC4975" format="default"/> 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 <xref target="RFC4975"/> target="RFC4975" format="default"/> to work over
      TCP and TLS connections, and over a WebSocket subprotocol specified by <xref target="RFC7977"/>. target="RFC7977" format="default"/>.
      </t>
      <t>
      This document specifies how a Web Real-Time Communication (WebRTC)
      data channel <xref target="I-D.ietf-rtcweb-data-channel"/> target="RFC8831" format="default"/> can be used as a transport mechanism for MSRP, MSRP
      without the TCP and TLS layers, and how the Session Description Protocol (SDP) offer/answer
      mechanism for data channels <xref target="I-D.ietf-mmusic-data-channel-sdpneg"/> target="RFC8864" format="default"/> can be used
      to negotiate such a data channel.
      </t>
      <t>
      In this document, an MSRP data channel refers to a WebRTC data
      channel for which the instantiated subprotocol is "msrp" and where
      the data channel is negotiated using the SDP offer/answer mechanism
      <xref target="I-D.ietf-mmusic-data-channel-sdpneg"/>. target="RFC8864" format="default"/>.
      </t>
      <t>Defining MSRP as a data channel subprotocol has many benefits:
      <list style="symbols">
        <t>provides
      </t>
      <ul spacing="normal">
        <li>provides to applications a proven protocol enabling instant messaging, file transfer, image sharing</t>
        <t>integrates sharing</li>
        <li>integrates those features with other WebRTC voice, video video, and data features</t>
        <t>leverages features</li>
        <li>leverages the SDP-based negotiation already defined for MSRP</t>
        <t>allows MSRP</li>
        <li>allows the interworking with MSRP endpoints running on a TCP or TLS connection</t>
      </list>
    </t> connection</li>
      </ul>
      <t>
      Compared to WebSockets, the WebSocket protocol, which provide provides a message passing message-passing protocol to applications with no direct access to
      TCP or TLS sockets, data channels provide a low latency transport, low-latency transport and leverage NAT-aware connectivity and
      the security features of WebRTC.
      </t>
      <t>
      Considering
   This document defines an MSRP data channel endpoint as an MSRP application that
   uses a WebRTC data channel, this channel for MSRP transport.  This document describes
      two
   configurations where the other for connecting such endpoint is respectively either to another MSRP over data channel endpoint
      (e.g., a WebRTC application) endpoint,
   or to an MSRP endpoint using that uses either TCP or TLS transport.
      </t>
      <t>
      This document updates <xref target="RFC4975"/> target="RFC4975" format="default"/> as described in <xref target="updates-to-rfc4975"/>. target="updates-to-rfc4975" format="default"/>.
      </t>
    </section>
    <section title="Conventions"> numbered="true" toc="default">
      <name>Conventions</name>
      <t>
      The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED",
      "NOT RECOMMENDED", "MAY", "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>",
"<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL NOT</bcp14>",
"<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>",
"<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
"<bcp14>MAY</bcp14>", and "OPTIONAL" "<bcp14>OPTIONAL</bcp14>" in this document are to be
interpreted as described in BCP 14 <xref target="RFC2119"/><xref target="RFC8174"/> target="RFC2119" format="default"/> <xref
target="RFC8174" format="default"/> when, and only when, they appear in all capitals, as
shown here.
      </t>
    </section>
    <section title="WebRTC numbered="true" toc="default">
      <name>WebRTC Data Channel Considerations"> Considerations</name>
      <section title="MSRP anchor="msrp-data-channel" numbered="true" toc="default">
        <name>MSRP Data Channel" anchor="msrp-data-channel"> Channel</name>
        <t>The following WebRTC data channel property values
<xref target="I-D.ietf-rtcweb-data-channel"/> target="RFC8831" format="default"/> apply to an MSRP data channel:</t>
    <texttable title="">
      <ttcol align="left">Property</ttcol>
      <ttcol align="left">Value</ttcol>
      <c>Subprotocol Identifier</c>
      <c>msrp</c>
      <c>Transmission reliability</c>
      <c>reliable</c>
      <c>Transmission order</c>
      <c>in-order</c>
      <c>Label</c>
      <c>See
        <xref target="use-of-dcmap-attribute"/>
      </c>
    </texttable>
        <table align="center">
          <thead>
            <tr>
              <th align="left">Property</th>
              <th align="left">Value</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td align="left">Subprotocol Identifier</td>
              <td align="left">msrp</td>
            </tr>
            <tr>
              <td align="left">Transmission reliability</td>
              <td align="left">reliable</td>
            </tr>
            <tr>
              <td align="left">Transmission order</td>
              <td align="left">in-order</td>
            </tr>
            <tr>
              <td align="left">Label</td>
              <td align="left">See
        <xref target="use-of-dcmap-attribute" format="default"/>
              </td>
            </tr>
          </tbody>
        </table>
      </section>
    </section>
    <section title="SDP Considerations" anchor="sdp-cons"> anchor="sdp-cons" numbered="true" toc="default">
      <name>SDP Considerations</name>
      <t>The generic SDP considerations, including the SDP offer/answer
        procedures <xref target="RFC3264"/>, target="RFC3264" format="default"/>, for negotiating a WebRTC data channel are
        defined in <xref target="I-D.ietf-mmusic-data-channel-sdpneg"/>. target="RFC8864" format="default"/>. This section, section
        and its subsections, subsections define the SDP considerations that are specific to an MSRP data channel,
        identified by the 'subprotocol' "subprotocol" attribute parameter, with a an "msrp" parameter value, value
        in the 'dcmap' attribute.</t>
      <section title="MSRP URI"> numbered="true" toc="default">
        <name>MSRP URI</name>
        <t>This document extends the MSRP URI syntax <xref target="RFC4975"/> target="RFC4975" format="default"/> by defining the new transport parameter value "dc" (an abbreviation of data channel):</t>
       <figure align="left" title="">
        <artwork align="left"><![CDATA[

        <sourcecode type="abnf"><![CDATA[
    transport  /= "dc"
    ; Add "dc" to existing transports per Section 9 of [RFC4975] ]]></artwork>
       </figure> ]]>
	</sourcecode>

        <t>MSRP design provides for new transport bindings (see Section 6 of <xref target="RFC4975"/>). target="RFC4975" section="6" sectionFormat="of"/>).
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 is the case of data channels (<xref target="use-of-dcsa-attribute"/>).</t> target="use-of-dcsa-attribute" format="default"/>).</t>
      </section>
      <section title="msrp-scheme"> numbered="true" toc="default">
        <name>MSRP URI msrp-scheme</name>
        <t>The msrp-scheme portion of the MSRP-URI MSRP URI that represents an MSRP data channel endpoint (used in the SDP path '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 <xref target="I-D.ietf-rtcweb-data-channel"/>.</t> target="RFC8831" format="default"/>.</t>
      </section>
      <section title="Use anchor="use-of-dcmap-attribute" numbered="true" toc="default">
        <name>Use of the dcmap Attribute" anchor="use-of-dcmap-attribute"> 'dcmap' Attribute</name>
        <t>An offerer and answerer SHALL, <bcp14>SHALL</bcp14>, in each offer and answer,
include a 'dcmap' attribute <xref target="I-D.ietf-mmusic-data-channel-sdpneg"/> target="RFC8864" format="default"/> in the SDP
media description (m= ("m=" section) <xref target="RFC4566"/> target="RFC4566" format="default"/> describing the SCTP association <xref target="RFC4960"/> target="RFC4960" format="default"/> used to realize the MSRP data channel.</t>
        <t>The attribute includes the following data channel parameters:
       <list style="symbols">
        <t>"label=" labelstring</t>
        <t>"subprotocol=" "msrp"</t>
       </list>
        </t>
        <ul spacing="normal">
          <li>"label=" labelstring</li>
          <li>"subprotocol=" "msrp"</li>
        </ul>
        <t>The labelstring is set by the MSRP application according to <xref target="I-D.ietf-mmusic-data-channel-sdpneg"/>.</t> target="RFC8864" format="default"/>.</t>
        <t>The offerer and answerer SHALL NOT <bcp14>SHALL NOT</bcp14> include the 'max-retr'
"max-retr" and the 'max-time' "max-time" attribute parameters in the 'dcmap' attribute.</t>
        <t>The offerer and answerer MAY <bcp14>MAY</bcp14> include the 'ordered' "ordered" attribute parameter in the 'dcmap' attribute. If included, the attribute parameter value SHALL <bcp14>SHALL</bcp14> be set to "true".</t>
        <t>Below is an example of a 'dcmap' attribute for an MSRP session to be
negotiated with stream-id=2 the "dcmap-stream-id" parameter set to 2 and label="chat":</t>

      <figure align="left" title="">
       <artwork align="left"><![CDATA[ the "label" parameter set to "chat":</t>

        <sourcecode type="sdp"><![CDATA[
a=dcmap:2 label="chat";subprotocol="msrp"
]]></artwork>
      </figure>
]]></sourcecode>

      </section>
      <section title="Use anchor="use-of-dcsa-attribute" numbered="true" toc="default">
        <name>Use of the dcsa Attribute" anchor="use-of-dcsa-attribute"> 'dcsa' Attribute</name>
        <t>
        An offerer and answerer can, in each offer and answer, include one or
        more 'dcsa' data channel subprotocol attributes ('dcsa' attributes) <xref target="I-D.ietf-mmusic-data-channel-sdpneg"/> target="RFC8864" format="default"/> in
        the m= "m=" section describing the SCTP association used to realize the
        MSPR
        MSRP data channel. An SDP attribute included in a 'dcsa' attribute is referred
        to as a dcsa embedded DCSA-embedded attribute.
        </t>
        <t>
        If an offerer or answerer receives a 'dcsa' attribute that contains
        an SDP attribute for which usage has not been defined for an MSRP data
        channel, the offerer or answerer should ignore the 'dcsa' attribute,
        following the rules in Section 6.7 of <xref target="I-D.ietf-mmusic-data-channel-sdpneg"/>. target="RFC8864" section="6.7" sectionFormat="of"/>.
        </t>
        <t>
        An offerer and answerer SHALL <bcp14>SHALL</bcp14> include a 'dcsa' attribute for each of the following MSRP-specific SDP attributes:
       <list style="symbols">
        <t>defined
        </t>
        <ul spacing="normal">
          <li>defined in <xref target="RFC4975"/>: "path".</t>
        <t>defined target="RFC4975" format="default"/>: 'path'.</li>
          <li>defined in <xref target="RFC6714"/>: "msrp-cema".</t>
        <t>defined target="RFC6714" format="default"/>: 'msrp-cema'.</li>
          <li>defined in <xref target="RFC6135"/>: "setup". target="RFC6135" format="default"/>: 'setup'.
              See <xref target="use-of-setup-attribute"/></t>
       </list>
      </t> target="use-of-setup-attribute" format="default"/>.</li>
        </ul>
        <t>
        It is considered a protocol error if one or more of the dcsa embedded DCSA-embedded attributes listed above are not included in an offer or answer.
        </t>
        <t>An offerer and answerer MAY <bcp14>MAY</bcp14> include a 'dcsa' attribute for any of the following MSRP-specific SDP attributes, following the procedures defined for each attribute:
       <list style="symbols">
        <t>defined
        </t>
        <ul spacing="normal">
          <li>defined in <xref target="RFC4975"/>: "accept-types", "accept-wrapped-types" target="RFC4975" format="default"/>: 'accept-types', 'accept-wrapped-types', and "max-size"</t>
        <t>defined 'max-size'.</li>
          <li>defined in <xref target="RFC4566"/>: "sendonly", "recvonly", "inactive" target="RFC4566" format="default"/>: 'sendonly', 'recvonly', 'inactive', and "sendrecv"</t>
        <t>defined 'sendrecv'.</li>
          <li>defined in <xref target="RFC5547"/>: target="RFC5547" format="default"/>: all the parameters related to MSRP file transfer. See <xref target="file_transfer_sdp"/>.</t>
       </list>
      </t> target="file_transfer_sdp" format="default"/>.</li>
        </ul>
        <t>
        A subsequent offer or answer MAY <bcp14>MAY</bcp14> update the previously negotiated MSRP subprotocol attributes
        while keeping the 'dcmap' attribute associated with the MSRP data channel unchanged. The semantics
        for newly negotiated MSRP subprotocol attributes are per <xref target="RFC4975"/>. target="RFC4975" format="default"/>.
        </t>
        <t>
        When MSRP messages are transported on a data channel, the 'path' attribute is not used for the routing
        of the messages. The MSRP data channel is established using the SDP offer/answer procedures defined
        in <xref target="I-D.ietf-mmusic-data-channel-sdpneg"/>, target="RFC8864" format="default"/>, and the MSRP messages are then transported
        on that data channel. This is different from legacy MSRP <xref target="RFC4975"/> target="RFC4975" format="default"/> but similar to
        MSRP CEMA Connection Establishment for Media Anchoring  (MSRP CEMA) <xref target="RFC6714"/>. target="RFC6714" format="default"/>.
        Because of this, a dcsa embedded DCSA-embedded 'msrp-cema' attribute is
        mandated for MSRP sessions over data channels. However, when an endpoint receives an MSRP message
        over a data channel, it MUST <bcp14>MUST</bcp14> still perform the MSRP-URI MSRP URI comparison procedures defined in
        <xref target="RFC4975"/>. target="RFC4975" format="default"/>.
        </t>
      </section>
      <section title="Use anchor="use-of-setup-attribute" numbered="true" toc="default">
        <name>Use of the dcsa embedded setup Attribute" anchor="use-of-setup-attribute"> DCSA-Embedded 'setup' Attribute</name>
        <t>
        As described in <xref target="use-of-dcsa-attribute"/>, target="use-of-dcsa-attribute" format="default"/>, the usage of a dsca embedded
DCSA-embedded 'setup' attribute is mandated for MSRP sessions over data channels.
        It is used to negotiate which MSRP session data channel endpoint assumes the active role as per Section 4.2.2 of
        <xref target="RFC6135"/> target="RFC6135" section="4.2.2" sectionFormat="of"/> and
        Section 5.4 of
        <xref target="RFC4975"/>. target="RFC4975" section="5.4" sectionFormat="of"/>. It has no relationship with the DTLS connection establishment roles <xref target="I-D.ietf-mmusic-sctp-sdp"/>. target="RFC8841" format="default"/>.
        </t>
        <t>
        The dcsa embedded setup DCSA-embedded 'setup' attribute is of the form
        "a=dcsa:x setup:&lt;role&gt;", with x being the data channel's SCTP stream identifier, so that
        such
        the 'setup' attribute is explicitly associated with an MSRP session over a specific data channel.
        </t>
      </section>
      <section title="Session Closing" anchor="session-closing-sdp"> anchor="session-closing-sdp" numbered="true" toc="default">
        <name>Session Closing</name>
        <t>An MSRP session is closed by closing the associated data channel, channel
following the procedures in <xref target="I-D.ietf-mmusic-data-channel-sdpneg"/>.</t> target="RFC8864" format="default"/>.</t>
        <t>The port value for the "m=" line SHOULD NOT <bcp14>SHOULD NOT</bcp14>
be changed (e.g. (e.g., to zero) when closing an MSRP session (unless all data
channels are being closed and the SCTP association is no longer needed), needed)
since this would close the SCTP association and impact all of the data channels.
In all cases in <xref target="RFC4975"/> target="RFC4975" format="default"/> where the procedure
calls for setting the port to zero for in the MSRP "m=" line in an SDP offer
for TCP transport, the SDP offerer of an MSRP session with data channel transport SHALL
<bcp14>SHALL</bcp14> remove the corresponding dcmap 'dcmap' and dcsa 'dcsa' attributes.</t>
      </section>
      <section title="Support anchor="file_transfer_sdp" numbered="true" toc="default">
        <name>Support for MSRP File Transfer Function" anchor="file_transfer_sdp"> Function</name>
        <t>SDP attributes specified in <xref target="RFC5547"/> target="RFC5547" format="default"/> for a file transfer "m=" line are embedded as subprotocol-specific attributes using the syntax defined in <xref target="I-D.ietf-mmusic-data-channel-sdpneg"/>.</t> target="RFC8864" format="default"/>.</t>
      </section>
      <section title="Example" anchor="example-sdp-negotiation"> anchor="example-sdp-negotiation" numbered="true" toc="default">
        <name>Example</name>
        <t>Below is an example of an offer and an answer that include 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 <xref target="RFC4975"/> target="RFC4975" format="default"/> and <xref target="RFC5547"/>.</t>

      <figure align="left" title="">
       <artwork align="left"><![CDATA[
Offer: target="RFC5547" format="default"/>.</t>

<t>Offer:</t>
 <sourcecode type="sdp"><![CDATA[

   m=application 54111 UDP/DTLS/SCTP webrtc-datachannel
   c=IN IP6 2001:db8::3
   a=max-message-size:100000
   a=sctp-port:5000
   a=setup:actpass
   a=fingerprint:SHA-256 12:DF:3E:5D:49:6B:19:E5:7C:AB:4A:AD:B9:B1:3F:\
      82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB:4A:AD 12:DF:3E:5D:49:6B:19:E5:7C:AB:4A:AD:B9:B1:\
      3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB:4A:AD
   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://2001:db8::3:54111/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://2001:db8::3:54111/jshA7we;dc
   a=dcsa:2 file-selector:name:"picture1.jpg" type:image/jpeg \
      size:1463440 hash:sha-256:7C:DF:3E:5D:49:6B:19:E5:12:AB:4A:AD: \ hash:sha-256:7C:DF:3E:5D:49:6B:19:E5:12:AB:4A:AD:\
      4A:B1:3F:82:3E:3B:54:12:02:5D:18:DF:49:6B:19:E5:7C:AB:B9:AD
   a=dcsa:2 file-transfer-id:rjEtHAcYVZ7xKwGYpGGwyn5gqsSaU7Ep
   a=dcsa:2 file-disposition:attachment
   a=dcsa:2 file-date:creation:"Tue, 11 Aug 2020 19:05:30 +0200"
   a=dcsa:2 file-icon:cid:id2@bob.example.com
   a=dcsa:2 file-range:1-1463440

Answer:

]]></sourcecode>

 <t>Answer:</t>

  <sourcecode type="sdp"><![CDATA[

   m=application 51444 UDP/DTLS/SCTP webrtc-datachannel
   c=IN IP6 IP6 2001:db8::1
   a=max-message-size:100000
   a=sctp-port:6000
   a=setup:passive
   a=fingerprint:SHA-256 5D:02:3E:AD:49:6B:19:E5:7C:AB:4A:AD:B9:B1: \
      3F:82:18:3B:54:DF:12:6B:3E:5D:49:DF:19:E5:7C:AB:4A:5D 5D:02:3E:AD:49:6B:19:E5:7C:AB:4A:AD:B9:\
      B1:3F:82:18:3B:54:DF:12:6B:3E:5D:49:DF:19:E5:7C:AB:4A:5D
   a=tls-id:65cd4a7565debe82f100
   a=dcmap:0 label="chat";subprotocol="msrp"
   a=dcsa:0 msrp-cema
   a=dcsa:0 setup:passive
   a=dcsa:0 accept-types:message/cpim text/plain
   a=dcsa:0 path:msrps://2001:db8::1:51444/di551fsaodes;dc
   a=dcmap:2 label="file transfer";subprotocol="msrp"
   a=dcsa:2 recvonly
   a=dcsa:2 msrp-cema
   a=dcsa:2 setup:passive
   a=dcsa:2 accept-types:message/cpim
   a=dcsa:2 accept-wrapped-types:*
   a=dcsa:2 path:msrps://2001:db8::1:51444/jksh7Bwc;dc
   a=dcsa:2 file-selector:name:"picture1.jpg" type:image/jpeg \
      size:1463440
   a=dcsa:2 file-transfer-id:rjEtHAcYVZ7xKwGYpGGwyn5gqsSaU7Ep
   a=dcsa:2 file-range:1-1463440

]]></artwork>
      </figure>

   ]]></sourcecode>

        <t>
   Note that due to RFC formatting conventions, this document splits
   SDP across lines whose content would exceed that exceeds 72 characters. A backslash character marks where characters across lines, marking this
   line folding
        has taken place. with a backslash character.  This backslash and its
   trailing CRLF and whitespace would not appear in actual SDP content.
        </t>
      </section>
    </section>
    <section title="MSRP Considerations" anchor="msrp-cons"> anchor="msrp-cons" numbered="true" toc="default">
      <name>MSRP Considerations</name>
      <t>The procedures specified in <xref target="RFC4975"/> target="RFC4975" format="default"/> apply except when this document specifies otherwise. This section describes the MSRP considerations specific to an MSRP data channel.</t>
      <section title="Session Mapping"> numbered="true" toc="default">
        <name>Session Mapping</name>
        <t>In this document, each MSRP session maps to one data channel exactly.</t>
      </section>
      <section title="Session Opening" anchor="session-opening-msrp"> anchor="session-opening-msrp" numbered="true" toc="default">
        <name>Session Opening</name>
        <t><xref target="use-of-setup-attribute"/> target="use-of-setup-attribute" format="default"/> describes how the active MSRP session data channel endpoint role is negotiated. The active MSRP session data channel endpoint uses the data channel established for this MSRP session by the generic data channel opening procedure defined in <xref target="I-D.ietf-mmusic-data-channel-sdpneg"/>.</t> target="RFC8864" format="default"/>.</t>
        <t>As soon as the WebRTC data channel is opened, the MSRP session is actually opened by the active MSRP session data channel endpoint.
In order to do this this, the active MSRP data channel endpoint sends an MSRP SEND message (empty or not) to the peer (passive) MSRP data channel endpoint.</t>
      </section>
      <section title="Session Closing" anchor="session-closing"> anchor="session-closing" numbered="true" toc="default">
        <name>Session Closing</name>
        <t>The closure of an MSRP session SHALL <bcp14>SHALL</bcp14> be signaled via
SDP following the requirements in <xref target="session-closing-sdp"/></t> target="session-closing-sdp" format="default"/>.</t>
        <t>If the data channel used to transport the MSRP session fails and gets is torn down, the MSRP data channel endpoints SHALL <bcp14>SHALL</bcp14> consider the MSRP session failed. An MSRP data channel endpoint MAY, <bcp14>MAY</bcp14>, based on local policy, try to negotiate a new MSRP data channel.</t>
      </section>
      <section title="Data Framing" anchor="data-framing"> anchor="data-framing" numbered="true" toc="default">
        <name>Data Framing</name>
        <t>Each text-based MSRP message is sent on the corresponding data channel using standard MSRP framing and chunking procedures, as defined in <xref target="RFC4975"/>, target="RFC4975" format="default"/>, with each MSRP chunk delivered in a single SCTP user message. Therefore all sent MSRP chunks SHALL <bcp14>SHALL</bcp14> have lengths of less than or equal to the value of the peer's "max-message-size" 'max-message-size' attribute <xref target="I-D.ietf-mmusic-sctp-sdp"/> target="RFC8841" format="default"/> associated with the SCTP association.</t>
      </section>
      <section title="Data numbered="true" toc="default">
        <name>Data Sending, Receiving Receiving, and Reporting"> Reporting</name>
        <t>Data sending, receiving receiving, and reporting procedures SHALL <bcp14>SHALL</bcp14> conform to <xref target="RFC4975"/>.</t> target="RFC4975" format="default"/>.</t>
      </section>
      <section title="Support anchor="file_transfer_msrp" numbered="true" toc="default">
        <name>Support for MSRP File Transfer Function" anchor="file_transfer_msrp"> Function</name>
        <t><xref target="RFC5547"/> target="RFC5547" format="default"/> 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, channel endpoints
with the following considerations:
      <list style="symbols">
       <t>As
        </t>
        <ul spacing="normal">
          <li>As an MSRP session maps to one data channel, a file transfer session maps also to one data channel.</t>
       <t>SDP channel.</li>
          <li>SDP attributes are negotiated as specified in <xref target="file_transfer_sdp"/>.</t>
       <t>Once target="file_transfer_sdp" format="default"/>.</li>
          <li>Once the file transfer is complete, the same data channel MAY <bcp14>MAY</bcp14> be reused for another file transfer.</t>
      </list>
     </t> transfer.</li>
        </ul>
      </section>
    </section>
    <section title="Gateway Considerations" anchor="gateway-cons"> anchor="gateway-cons" numbered="true" toc="default">
      <name>Gateway Considerations</name>
      <t>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.</t>
      <t>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.</t>
      <t>In one model, the gateway performs as an MSRP Back-to-Back User Agent (B2BUA) to interwork all the procedures as necessary between the endpoints.  No further specification is needed for this model.</t>
      <t>Alternately, the gateway can provide transport level transport-level interworking between MSRP endpoints using different transport protocols. In accordance with <xref target="use-of-dcsa-attribute"/>, path target="use-of-dcsa-attribute" format="default"/>,
'path' attributes SHALL NOT <bcp14>SHALL NOT</bcp14> be used for transport level transport-level interworking.</t>
      <t>When the gateway performs transport level transport-level interworking between
MSRP endpoints, all of the procedures in <xref target="msrp-cons"/> target="sdp-cons" format="default"/> and
<xref target="sdp-cons"/> target="msrp-cons" format="default"/> apply to each peer, with the following additions:

    <list style="symbols">
     <t>The

      </t>
      <ul spacing="normal">
        <li>The gateway SHALL <bcp14>SHALL</bcp14> use the MSRP CEMA mechanism <xref target="RFC6714"/> target="RFC6714" format="default"/> towards the non-data channel endpoint.</t>
     <t>If endpoint.</li>
        <li>If the non-data channel endpoint does not support MSRP CEMA, transport level
transport-level interworking mode is not possible, and the gateway needs to act as an MSRP B2BUA.</t>
     <t>The B2BUA.</li>
        <li>The gateway SHALL NOT <bcp14>SHALL NOT</bcp14> modify the path 'path' attribute received from data channel or from non-data channel endpoints.</t>
     <t>The endpoints.</li>
        <li>The gateway SHALL NOT <bcp14>SHALL NOT</bcp14> modify the setup 'setup' value
received from data channel or from non-data channel endpoints.</t>
     <t>The endpoints.</li>
        <li>The endpoint establishing an MSRP session using data channel transport SHALL NOT <bcp14>SHALL NOT</bcp14> request inclusion of any relays, although it MAY <bcp14>MAY</bcp14> interoperate with a peer that signals the use of relays.</t>
    </list>

   </t> relays.</li>
      </ul>
    </section>
    <section title="Updates anchor="updates-to-rfc4975" numbered="true" toc="default">
      <name>Updates to RFC4975" anchor="updates-to-rfc4975"> RFC 4975</name>
      <t>This document updates <xref target="RFC4975"/>, target="RFC4975" format="default"/>
by allowing the usage of the "msrps" scheme when the underlying connection is protected with DTLS.</t>
    </section>
    <section anchor="Security" title="Security Considerations"> numbered="true" toc="default">
      <name>Security Considerations</name>
      <t>MSRP traffic over data channels is secured, channels, including confidentiality, integrity integrity, and source authentication,
is secured as specified by by <xref target="I-D.ietf-rtcweb-data-channel"/>. target="RFC8831" format="default"/>.
      However, <xref target="RFC4975"/> target="RFC4975" format="default"/> allows transport of
MSRP traffic over non-secured nonsecured TCP connections, connections and does not provide a mechanism to guarantee usage of TLS end-to-end. end to end.
      As described in <xref target="RFC4975"/>, target="RFC4975" format="default"/>, even if TLS is used between some hops hops,
TCP might still be used between other hops.
      Operators need to ensure that establish proper policies are established
in order to ensure that the MSRP traffic is protected between endpoints.</t>
      <t><xref target="RFC5547"/> target="RFC5547" format="default"/> specifies security considerations related to the usage of MSRP for file transfer.</t>
      <t><xref target="RFC7092"/> target="RFC7092" format="default"/> specifies security considerations related to B2BUAs.</t>
      <t>Note that the discussion in Section 14.5 of <xref target="RFC4975"/> target="RFC4975" section="14.5" sectionFormat="of"/> on MSRP message attribution to remote identities applies to data channel transport.</t>
      <t>If the Session Initiation Protocol (SIP) <xref target="RFC3261"/> target="RFC3261" format="default"/> is used to implement the offer/answer transactions for establishing the MSRP data channel, the SIP security considerations specified in <xref target="RFC3261"/> target="RFC3261" format="default"/> apply.</t>
    </section>
    <section anchor="IANA" title="IANA Considerations">
   <t>NOTE to RFC Editor: Please replace all instances of all instances of RFCXXXX with the number of this RFC.</t> numbered="true" toc="default">
      <name>IANA Considerations</name>
      <section title="msrps anchor="IANA-reg-msrps" numbered="true" toc="default">
        <name>"msrps" URI scheme" anchor="IANA-reg-msrps"> scheme</name>
        <t>This document modifies the usage of the msrps "msrps" URI scheme,
registered by <xref target="RFC4975"/>, target="RFC4975" format="default"/>,
by adding DTLS as a protected transport indicated by the URI scheme.</t>
        <t>A reference to RFCXXXX is RFC 8873 has been added to the URI scheme "msrps"
in the Uniform "Uniform Resource Identifier (URI) Schemes Registry.</t> Schemes" registry.</t>
      </section>
      <section title="Subprotocol anchor="IANA-reg-MSRP" numbered="true" toc="default">
        <name>Subprotocol Identifier MSRP" anchor="IANA-reg-MSRP"> "msrp"</name>
        <t>A reference to RFCXXXX is RFC 8873 has been added to the subprotocol identifier
"msrp" in the "WebSocket Subprotocol Name Registry"</t> Registry".</t>
      </section>
      <section title="SDP Attributes" anchor="IANA-reg-other-sdp"> anchor="IANA-reg-other-sdp" numbered="true" toc="default">
        <name>SDP Attributes</name>
        <t>
      This document modifies the usage of a set of SDP attributes, attributes if any of those
      attributes is included in an SDP 'dsca' 'dcsa' attribute associated with an
      MSRP data channel. The modified usage of the SDP 'setup' attribute is
      described in <xref target="use-of-setup-attribute"/>. target="use-of-setup-attribute" format="default"/>. The usage of the other
      SDP attributes is described in <xref target="use-of-dcsa-attribute"/>.
    </t>
    <t>
    <list style="symbols">
      <t>"path"</t>
      <t>"msrp-cema"</t>
      <t>"accept-types"</t>
      <t>"accept-wrapped-types"</t>
      <t>"max-size"</t>
      <t>"sendonly"</t>
      <t>"recvonly"</t>
      <t>"inactive"</t>
      <t>"sendrecv"</t>
      <t>"file-selector"</t>
      <t>"file-transfer-id"</t>
      <t>"file-disposition"</t>
      <t>"file-date"</t>
      <t>"file-icon"</t>
      <t>"file-range"</t>
    </list> target="use-of-dcsa-attribute" format="default"/>.
        </t>
        <ul spacing="normal">
          <li>'accept-types'</li>
          <li>'accept-wrapped-types'</li>
          <li>'file-date'</li>
          <li>'file-disposition'</li>
          <li>'file-icon'</li>
          <li>'file-range'</li>
          <li>'file-selector'</li>
          <li>'file-transfer-id'</li>
          <li>'inactive'</li>
          <li>'max-size'</li>
          <li>'msrp-cema'</li>
          <li>'path'</li>
          <li>'recvonly'</li>
          <li>'sendonly'</li>
          <li>'sendrecv'</li>
        </ul>

        <t>The usage level "dcsa(msrp)" "dcsa (msrp)" has been added to the registration of the SDP
'accept-types' attribute in the Session Description Protocol (SDP) Parameters "att-field" subregistry as follows:</t>
         <dl spacing="compact" indent="18">

              <dt>Contact name:</dt>
              <dd>IESG</dd>

              <dt>Contact email:</dt>
              <dd>iesg@ietf.org</dd>

              <dt>Attribute name:</dt>
              <dd>accept-types</dd>

              <dt>Usage level:</dt>
              <dd>dcsa (msrp)</dd>

              <dt>Purpose:</dt>
              <dd>Contain the list of media types that the endpoint is willing to receive.</dd>

              <dt>Reference:</dt>
              <dd>RFC 8873</dd>

        </dl>

        <t>The usage level "dcsa (msrp)" has been added to the registration of the SDP 'setup'
'accept-wrapped-types' attribute in the Session Description Protocol (SDP) Parameters "att-field" sub-registry subregistry as follows:</t>

     <texttable title="">
       <ttcol align="left" width="35%"/>
       <ttcol align="left" width="65%"/>

       <c>Contact name:</c>
       <c>IESG</c>

       <c>Contact email:</c>
       <c>iesg@ietf.org</c>

       <c>Attribute name:</c>
       <c>setup</c>

       <c>Usage level:</c>
       <c>dcsa(msrp)</c>

       <c>Purpose:</c>
       <c>Negotiate
         <dl spacing="compact" indent="18">

              <dt>Contact name:</dt>
              <dd>IESG</dd>

              <dt>Contact email:</dt>
              <dd>iesg@ietf.org</dd>

              <dt>Attribute name:</dt>
              <dd>accept-wrapped-types</dd>

              <dt>Usage level:</dt>
              <dd>dcsa (msrp)</dd>

              <dt>Purpose:</dt>
              <dd>Contain the active role list of media types that the endpoint is willing to receive in an MSRP session over a data channel as per
       <xref target="use-of-setup-attribute"/>
       </c>

       <c>Reference:</c>
       <c>RFCXXXX</c>
     </texttable> message with multipart content.</dd>

              <dt>Reference:</dt>
              <dd>RFC 8873</dd>

        </dl>

        <t>The usage level "dcsa(msrp)" is "dcsa (msrp)" has been added to the registration of the SDP 'path'
'file-date' attribute in the Session Description Protocol (SDP) Parameters "att-field" sub-registry subregistry as follows:</t>

     <texttable title="">
       <ttcol align="left" width="35%"/>
       <ttcol align="left" width="65%"/>

       <c>Contact name:</c>
       <c>IESG</c>

       <c>Contact email:</c>
       <c>iesg@ietf.org</c>

       <c>Attribute name:</c>
       <c>path</c>

       <c>Usage level:</c>
       <c>dcsa(msrp)</c>

       <c>Purpose:</c>
       <c>Indicate an endpoint, but not used for routing, as described
         <dl spacing="compact" indent="18">

              <dt>Contact name:</dt>
              <dd>IESG</dd>

              <dt>Contact email:</dt>
              <dd>iesg@ietf.org</dd>

              <dt>Attribute name:</dt>
              <dd>file-date</dd>

              <dt>Usage level:</dt>
              <dd>dcsa (msrp)</dd>

              <dt>Purpose:</dt>
              <dd>Indicate one or more dates related to the file in <xref target="use-of-dcsa-attribute"/></c>
       <c>Reference:</c>
       <c>RFCXXXX</c>
     </texttable> an MSRP file transfer negotiation.</dd>

              <dt>Reference:</dt>
              <dd>RFC 8873</dd>

            </dl>

	        <t>The usage level "dcsa(msrp)" is "dcsa (msrp)" has been added to the registration of the SDP 'msrp-cema'
'file-disposition' attribute in the Session Description Protocol (SDP) Parameters "att-field" sub-registry subregistry as follows:</t>

     <texttable title="">
       <ttcol align="left" width="35%"/>
       <ttcol align="left" width="65%"/>

       <c>Contact name:</c>
       <c>IESG</c>

       <c>Contact email:</c>
       <c>iesg@ietf.org</c>

       <c>Attribute name:</c>
       <c>msrp-cema</c>

       <c>Usage level:</c>
       <c>dcsa(msrp)</c>

       <c>Purpose:</c>
       <c>Indicate that the routing of MSRP messages transported on
         <dl spacing="compact" indent="18">

              <dt>Contact name:</dt>
              <dd>IESG</dd>

              <dt>Contact email:</dt>
              <dd>iesg@ietf.org</dd>

              <dt>Attribute name:</dt>
              <dd>file-disposition</dd>

              <dt>Usage level:</dt>
              <dd>dcsa (msrp)</dd>

              <dt>Purpose:</dt>
              <dd>Provide a data channel is more similar suggestion to the MSRP CEMA mechanism than other endpoint about the legacy intended disposition of the file in an MSRP routing mechanism.</c>

       <c>Reference:</c>
       <c>RFCXXXX</c>
     </texttable> file transfer negotiation.</dd>

              <dt>Reference:</dt>
              <dd>RFC 8873</dd>

        </dl>

        <t>The usage level "dcsa(msrp)" is "dcsa (msrp)" has been added to the registration of the SDP 'accept-types'
'file-icon' attribute in the Session Description Protocol (SDP) Parameters "att-field" sub-registry subregistry as follows:</t>

     <texttable title="">
       <ttcol align="left" width="35%"/>
       <ttcol align="left" width="65%"/>

       <c>Contact name:</c>
       <c>IESG</c>

       <c>Contact email:</c>
       <c>iesg@ietf.org</c>

       <c>Attribute name:</c>
       <c>accept-types</c>

       <c>Usage level:</c>
       <c>dcsa(msrp)</c>

       <c>Purpose:</c>
       <c>Contain
         <dl spacing="compact" indent="18">

              <dt>Contact name:</dt>
              <dd>IESG</dd>

              <dt>Contact email:</dt>
              <dd>iesg@ietf.org</dd>

              <dt>Attribute name:</dt>
              <dd>file-icon</dd>

              <dt>Usage level:</dt>
              <dd>dcsa (msrp)</dd>

              <dt>Purpose:</dt>
              <dd>Contain a pointer to a small preview icon representing the list contents of media types that the endpoint is willing to receive.</c>

       <c>Reference:</c>
       <c>RFCXXXX</c>
     </texttable> file in an MSRP file transfer negotiation.</dd>

              <dt>Reference:</dt>
              <dd>RFC 8873</dd>

            </dl>

        <t>The usage level "dcsa(msrp)" is "dcsa (msrp)" has been added to the registration of the SDP 'accept-wrapped-types'
'file-range' attribute in the Session Description Protocol (SDP) Parameters "att-field" sub-registry subregistry as follows:</t>

     <texttable title="">
       <ttcol align="left" width="35%"/>
       <ttcol align="left" width="65%"/>

       <c>Contact name:</c>
       <c>IESG</c>

       <c>Contact email:</c>
       <c>iesg@ietf.org</c>

       <c>Attribute name:</c>
       <c>accept-wrapped-types</c>

       <c>Usage level:</c>
       <c>dcsa(msrp)</c>

       <c>Purpose:</c>
       <c>Contain
         <dl spacing="compact" indent="18">

              <dt>Contact name:</dt>
              <dd>IESG</dd>

              <dt>Contact email:</dt>
              <dd>iesg@ietf.org</dd>

              <dt>Attribute name:</dt>
              <dd>file-range</dd>

              <dt>Usage level:</dt>
              <dd>dcsa (msrp)</dd>

              <dt>Purpose:</dt>
              <dd>Contain the list range of transferred octets of media types that the endpoint is willing to receive file in an MSRP message with multipart content.</c>

       <c>Reference:</c>
       <c>RFCXXXX</c>
     </texttable> file transfer negotiation.</dd>

              <dt>Reference:</dt>
              <dd>RFC 8873</dd>

        </dl>

        <t>The usage level "dcsa(msrp)" is "dcsa (msrp)" has been added to the registration of the SDP 'max-size'
'file-selector' attribute in the Session Description Protocol (SDP) Parameters "att-field" sub-registry subregistry as follows:</t>

     <texttable title="">
       <ttcol align="left" width="35%"/>
       <ttcol align="left" width="65%"/>

       <c>Contact name:</c>
       <c>IESG</c>

       <c>Contact email:</c>
       <c>iesg@ietf.org</c>

       <c>Attribute name:</c>
       <c>max-size</c>

       <c>Usage level:</c>
       <c>dcsa(msrp)</c>

       <c>Purpose:</c>
       <c>Indicate the largest message
         <dl spacing="compact" indent="18">

              <dt>Contact name:</dt>
              <dd>IESG</dd>

              <dt>Contact email:</dt>
              <dd>iesg@ietf.org</dd>

              <dt>Attribute name:</dt>
              <dd>file-selector</dd>

              <dt>Usage level:</dt>
              <dd>dcsa (msrp)</dd>

              <dt>Purpose:</dt>
              <dd>Indicate a file in an MSRP endpoint wishes to accept.</c>

       <c>Reference:</c>
       <c>RFCXXXX</c>
     </texttable> file transfer negotiation.</dd>

              <dt>Reference:</dt>
              <dd>RFC 8873</dd>

        </dl>

        <t>The usage level "dcsa(msrp)" is "dcsa (msrp)" has been added to the registration of the SDP 'sendonly'
'file-transfer-id' attribute in the Session Description Protocol (SDP) Parameters "att-field" sub-registry subregistry as follows:</t>

     <texttable title="">
       <ttcol align="left" width="35%"/>
       <ttcol align="left" width="65%"/>

       <c>Contact name:</c>
       <c>IESG</c>

       <c>Contact email:</c>
       <c>iesg@ietf.org</c>

       <c>Attribute name:</c>
       <c>sendonly</c>

       <c>Usage level:</c>
       <c>dcsa(msrp)</c>

       <c>Purpose:</c>
       <c>Negotiate the direction
         <dl spacing="compact" indent="18">

              <dt>Contact name:</dt>
              <dd>IESG</dd>

              <dt>Contact email:</dt>
              <dd>iesg@ietf.org</dd>

              <dt>Attribute name:</dt>
              <dd>file-transfer-id</dd>

              <dt>Usage level:</dt>
              <dd>dcsa (msrp)</dd>

              <dt>Purpose:</dt>
              <dd>Indicate a unique identifier of the media flow on file transfer operation in an MSRP data channel.</c>

       <c>Reference:</c>
       <c>RFCXXXX</c>
     </texttable> file transfer negotiation.</dd>

              <dt>Reference:</dt>
              <dd>RFC 8873</dd>

        </dl>

        <t>The usage level "dcsa(msrp)" is "dcsa (msrp)" has been added to the registration of the SDP 'recvonly'
'inactive' attribute in the Session Description Protocol (SDP) Parameters "att-field" sub-registry subregistry as follows:</t>

     <texttable title="">
       <ttcol align="left" width="35%"/>
       <ttcol align="left" width="65%"/>

       <c>Contact name:</c>
       <c>IESG</c>

       <c>Contact email:</c>
       <c>iesg@ietf.org</c>

       <c>Attribute name:</c>
       <c>recvonly</c>

       <c>Usage level:</c>
       <c>dcsa(msrp)</c>

       <c>Purpose:</c>
       <c>Negotiate
         <dl spacing="compact" indent="18">

              <dt>Contact name:</dt>
              <dd>IESG</dd>

              <dt>Contact email:</dt>
              <dd>iesg@ietf.org</dd>

              <dt>Attribute name:</dt>
              <dd>inactive</dd>

              <dt>Usage level:</dt>
              <dd>dcsa (msrp)</dd>

              <dt>Purpose:</dt>
              <dd>Negotiate the direction of the media flow on an MSRP data channel.</c>

       <c>Reference:</c>
       <c>RFCXXXX</c>
     </texttable> channel.</dd>

              <dt>Reference:</dt>
              <dd>RFC 8873</dd>

        </dl>

        <t>The usage level "dcsa(msrp)" is "dcsa (msrp)" has been added to the registration of the SDP 'inactive'
'max-size' attribute in the Session Description Protocol (SDP) Parameters "att-field" sub-registry subregistry as follows:</t>

     <texttable title="">
       <ttcol align="left" width="35%"/>
       <ttcol align="left" width="65%"/>

       <c>Contact name:</c>
       <c>IESG</c>

       <c>Contact email:</c>
       <c>iesg@ietf.org</c>

       <c>Attribute name:</c>
       <c>inactive</c>

       <c>Usage level:</c>
       <c>dcsa(msrp)</c>

       <c>Purpose:</c>
       <c>Negotiate
         <dl spacing="compact" indent="18">

              <dt>Contact name:</dt>
              <dd>IESG</dd>

              <dt>Contact email:</dt>
              <dd>iesg@ietf.org</dd>

              <dt>Attribute name:</dt>
              <dd>max-size</dd>

              <dt>Usage level:</dt>
              <dd>dcsa (msrp)</dd>

              <dt>Purpose:</dt>
              <dd>Indicate the direction of the media flow on largest message an MSRP data channel.</c>

       <c>Reference:</c>
       <c>RFCXXXX</c>
     </texttable> endpoint wishes to accept.</dd>

              <dt>Reference:</dt>
              <dd>RFC 8873</dd>

        </dl>

        <t>The usage level "dcsa(msrp)" is "dcsa (msrp)" has been added to the registration of the SDP 'sendrecv'
'msrp-cema' attribute in the Session Description Protocol (SDP) Parameters "att-field" sub-registry subregistry as follows:</t>

     <texttable title="">
       <ttcol align="left" width="35%"/>
       <ttcol align="left" width="65%"/>

       <c>Contact name:</c>
       <c>IESG</c>

       <c>Contact email:</c>
       <c>iesg@ietf.org</c>

       <c>Attribute name:</c>
       <c>sendrecv</c>

       <c>Usage level:</c>
       <c>dcsa(msrp)</c>

       <c>Purpose:</c>
       <c>Negotiate
         <dl spacing="compact" indent="18">

              <dt>Contact name:</dt>
              <dd>IESG</dd>

              <dt>Contact email:</dt>
              <dd>iesg@ietf.org</dd>

              <dt>Attribute name:</dt>
              <dd>msrp-cema</dd>

              <dt>Usage level:</dt>
              <dd>dcsa (msrp)</dd>

              <dt>Purpose:</dt>
              <dd>Indicate that the direction routing of the media flow on an MSRP messages transported on a data channel.</c>

       <c>Reference:</c>
       <c>RFCXXXX</c>
     </texttable>

    <t>The usage level "dcsa(msrp)" channel is added more similar to the registration of the SDP 'file-selector' attribute in MSRP CEMA mechanism than the Session Description Protocol (SDP) Parameters "att-field" sub-registry as follows:</t>
     <texttable title="">
       <ttcol align="left" width="35%"/>
       <ttcol align="left" width="65%"/>

       <c>Contact name:</c>
       <c>IESG</c>

       <c>Contact email:</c>
       <c>iesg@ietf.org</c>

       <c>Attribute name:</c>
       <c>file-selector</c>

       <c>Usage level:</c>
       <c>dcsa(msrp)</c>

       <c>Purpose:</c>
       <c>Indicate a file in an legacy MSRP file transfer negotiation.</c>

       <c>Reference:</c>
       <c>RFCXXXX</c>
     </texttable> routing mechanism.</dd>

              <dt>Reference:</dt>
              <dd>RFC 8873</dd>

        </dl>

        <t>The usage level "dcsa(msrp)" is "dcsa (msrp)" has been added to the registration of the SDP 'file-transfer-id'
'path' attribute in the Session Description Protocol (SDP) Parameters "att-field" sub-registry subregistry as follows:</t>
     <texttable title="">
       <ttcol align="left" width="35%"/>
       <ttcol align="left" width="65%"/>

       <c>Contact name:</c>
       <c>IESG</c>

       <c>Contact email:</c>
       <c>iesg@ietf.org</c>

       <c>Attribute name:</c>
       <c>file-transfer-id</c>

       <c>Usage level:</c>
       <c>dcsa(msrp)</c>

       <c>Purpose:</c>
       <c>Indicate a unique identifier of the file transfer operation in
         <dl spacing="compact" indent="18">

              <dt>Contact name:</dt>
              <dd>IESG</dd>

              <dt>Contact email:</dt>
              <dd>iesg@ietf.org</dd>

              <dt>Attribute name:</dt>
              <dd>path</dd>

              <dt>Usage level:</dt>
              <dd>dcsa (msrp)</dd>

              <dt>Purpose:</dt>
              <dd>Indicate an MSRP file transfer negotiation.</c>

       <c>Reference:</c>
       <c>RFCXXXX</c>
     </texttable> endpoint, but not used for routing, as described in
<xref target="use-of-dcsa-attribute" format="default"/>.</dd>

              <dt>Reference:</dt>
              <dd>RFC 8873</dd>

        </dl>

        <t>The usage level "dcsa(msrp)" is "dcsa (msrp)" has been added to the registration of the SDP 'file-disposition'
'recvonly' attribute in the Session Description Protocol (SDP) Parameters "att-field" sub-registry subregistry as follows:</t>
     <texttable title="">
       <ttcol align="left" width="35%"/>
       <ttcol align="left" width="65%"/>

       <c>Contact name:</c>
       <c>IESG</c>

       <c>Contact email:</c>
       <c>iesg@ietf.org</c>

       <c>Attribute name:</c>
       <c>file-disposition</c>

       <c>Usage level:</c>
       <c>dcsa(msrp)</c>

       <c>Purpose:</c>
       <c>Provide a suggestion to the other endpoint about
         <dl spacing="compact" indent="18">

              <dt>Contact name:</dt>
              <dd>IESG</dd>

              <dt>Contact email:</dt>
              <dd>iesg@ietf.org</dd>

              <dt>Attribute name:</dt>
              <dd>recvonly</dd>

              <dt>Usage level:</dt>
              <dd>dcsa (msrp)</dd>

              <dt>Purpose:</dt>
              <dd>Negotiate the intended disposition direction of the file in media flow on an MSRP file transfer negotiation.</c>

       <c>Reference:</c>
       <c>RFCXXXX</c>
     </texttable> data channel.</dd>

              <dt>Reference:</dt>
              <dd>RFC 8873</dd>

        </dl>

        <t>The usage level "dcsa(msrp)" is "dcsa (msrp)" has been added to the registration of the SDP 'file-date'
'sendonly' attribute in the Session Description Protocol (SDP) Parameters "att-field" sub-registry subregistry as follows:</t>
     <texttable title="">
       <ttcol align="left" width="35%"/>
       <ttcol align="left" width="65%"/>

       <c>Contact name:</c>
       <c>IESG</c>

       <c>Contact email:</c>
       <c>iesg@ietf.org</c>

       <c>Attribute name:</c>
       <c>file-date</c>

       <c>Usage level:</c>
       <c>dcsa(msrp)</c>

       <c>Purpose:</c>
       <c>Indicate one or more dates related to
         <dl spacing="compact" indent="18">

              <dt>Contact name:</dt>
              <dd>IESG</dd>

              <dt>Contact email:</dt>
              <dd>iesg@ietf.org</dd>

              <dt>Attribute name:</dt>
              <dd>sendonly</dd>

              <dt>Usage level:</dt>
              <dd>dcsa (msrp)</dd>

              <dt>Purpose:</dt>
              <dd>Negotiate the file in direction of the media flow on an MSRP file transfer negotiation.</c>

       <c>Reference:</c>
       <c>RFCXXXX</c>
     </texttable> data channel.</dd>

              <dt>Reference:</dt>
              <dd>RFC 8873</dd>

        </dl>

        <t>The usage level "dcsa(msrp)" is "dcsa (msrp)" has been added to the registration of the SDP 'file-icon'
'setup' attribute in the Session Description Protocol (SDP) Parameters "att-field" sub-registry subregistry as follows:</t>
     <texttable title="">
       <ttcol align="left" width="35%"/>
       <ttcol align="left" width="65%"/>

       <c>Contact name:</c>
       <c>IESG</c>

       <c>Contact email:</c>
       <c>iesg@ietf.org</c>

       <c>Attribute name:</c>
       <c>file-icon</c>

       <c>Usage level:</c>
       <c>dcsa(msrp)</c>

       <c>Purpose:</c>
       <c>Contain a pointer to a small preview icon representing

         <dl spacing="compact" indent="18">

              <dt>Contact name:</dt>
              <dd>IESG</dd>

              <dt>Contact email:</dt>
              <dd>iesg@ietf.org</dd>

              <dt>Attribute name:</dt>
              <dd>setup</dd>

              <dt>Usage level:</dt>
              <dd>dcsa (msrp)</dd>

              <dt>Purpose:</dt>
              <dd>Negotiate the contents active role of the file in an MSRP file transfer negotiation.</c>

       <c>Reference:</c>
       <c>RFCXXXX</c>
     </texttable> session over a data channel as per
       <xref target="use-of-setup-attribute" format="default"/>.
              </dd>

              <dt>Reference:</dt>
              <dd>RFC 8873</dd>

         </dl>

        <t>The usage level "dcsa(msrp)" is "dcsa (msrp)" has been added to the registration of the SDP 'file-range'
'sendrecv' attribute in the Session Description Protocol (SDP) Parameters "att-field" sub-registry subregistry as follows:</t>
     <texttable title="">
       <ttcol align="left" width="35%"/>
       <ttcol align="left" width="65%"/>

       <c>Contact name:</c>
       <c>IESG</c>

       <c>Contact email:</c>
       <c>iesg@ietf.org</c>

       <c>Attribute name:</c>
       <c>file-range</c>

       <c>Usage level:</c>
       <c>dcsa(msrp)</c>

       <c>Purpose:</c>
       <c>Contain
         <dl spacing="compact" indent="18">

              <dt>Contact name:</dt>
              <dd>IESG</dd>

              <dt>Contact email:</dt>
              <dd>iesg@ietf.org</dd>

              <dt>Attribute name:</dt>
              <dd>sendrecv</dd>

              <dt>Usage level:</dt>
              <dd>dcsa (msrp)</dd>

              <dt>Purpose:</dt>
              <dd>Negotiate the range of transferred octets direction of the file in media flow on an MSRP file transfer negotiation.</c>

       <c>Reference:</c>
       <c>RFCXXXX</c>
     </texttable> data channel.</dd>

              <dt>Reference:</dt>
              <dd>RFC 8873</dd>

        </dl>
      </section>
    </section>
  </middle>

<back>

 <references>
      <name>References</name>
      <references>
        <name>Normative References</name>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"/>

<reference anchor="RFC8831" target="https://www.rfc-editor.org/info/rfc8831">
<front>
<title>WebRTC Data Channels</title>
<author initials="R" surname="Jesup" fullname="Randell Jesup">
  <organization/>
</author>
<author initials="S" surname="Loreto" fullname="Salvatore Loreto">
  <organization/>
</author>
<author initials="M" surname="Tüxen" fullname="Michael Tüxen">
  <organization/>
</author>
<date month='January' year='2021'/>
</front>
<seriesInfo name="RFC" value="8831"/>
<seriesInfo name="DOI" value="10.17487/RFC8831"/>
</reference>

  <reference anchor="RFC8864" target="https://www.rfc-editor.org/info/rfc8864">
    <front>
      <title>Negotiation Data Channels Using the Session Description
 Protocol (SDP)</title>
      <author fullname="Keith Drage" initials="K." surname="Drage">
        <organization>Unaffiliated</organization>
      </author>
      <author fullname="Raju Makaraju" initials="M." surname="Makaraju">
        <organization>Nokia</organization>
      </author>
      <author fullname="Richard Ejzak" initials="R." surname="Ejzak">
        <organization>Unaffiliated</organization>
      </author>
      <author fullname="Jerome Marcon" initials="J." surname="Marcon">
        <organization>Unaffiliated</organization>
      </author>
      <author fullname="Roni Even" initials="R." surname="Even" role="editor">
        <organization>Huawei</organization>
      </author>
      <date month="January" year="2021"/>
    </front>
    <seriesInfo name="RFC" value="8864"/>
    <seriesInfo name="DOI" value="10.17487/RFC8864"/>
  </reference>

<reference anchor="RFC8841" target="https://www.rfc-editor.org/info/rfc8841">

  <front>
    <title>Session Description Protocol (SDP) Offer/Answer Procedures for
    Stream Control Transmission Protocol (SCTP) over Datagram Transport Layer
    Security (DTLS) Transport</title>

    <author initials="C." surname="Holmberg" fullname="Christer Holmberg">
      <organization />
    </author>

    <author initials="R." surname="Shpount" fullname="Roman Shpount">
      <organization />
    </author>

    <author initials="S." surname="Loreto" fullname="Salvatore Loreto">
      <organization />
    </author>

    <author initials="G." surname="Camarillo" fullname="Gonzalo Camarillo">
      <organization />
    </author>

    <date month="January" year="2021" />
  </front>
  <seriesInfo name="RFC" value="8841" />
  <seriesInfo name="DOI" value="10.17487/RFC8841"/>

</reference>

        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.3264.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4566.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4960.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4975.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5547.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6135.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6714.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7977.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"/>
      </references>
      <references>
        <name>Informative References</name>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.3261.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7092.xml"/>
      </references>
    </references>

    <section title="Acknowledgments"> numbered="false" toc="default">
      <name>Acknowledgments</name>

      <t>The authors wish to acknowledge the borrowing of ideas from
      another internet draft Internet-Draft by Peter Dunkley and Gavin Llewellyn, <contact fullname="Peter Dunkley"/> and
      <contact fullname="Gavin Llewellyn"/>, and to thank Flemming Andreasen, Christian Groves, Paul Kyzivat, Jonathan Lennox, Uwe Rauschenbach, Albrecht Schwarz, and Keith Drage
      <contact fullname="Flemming Andreasen"/>, <contact fullname="Christian Groves"/>,
      <contact fullname="Paul Kyzivat"/>, <contact fullname="Jonathan Lennox"/>,
      <contact fullname="Uwe Rauschenbach"/>, <contact fullname="Albrecht Schwarz"/>, and
      <contact fullname="Keith Drage"/> for their invaluable comments.</t>
   <t>Richard Ejzak, Keith Drage and Juergen Stoetzer-Bradler
   <t><contact fullname="Richard Ejzak"/>, <contact fullname="Keith Drage"/>, and
      <contact fullname="Juergen Stoetzer-Bradler"/> contributed to an earlier version, draft version
      of this document before the draft was re-adopted.</t>
   <t>Julien Maisonneuve readopted.</t>
   <t><contact fullname="Julien Maisonneuve"/> helped with the re-adoption readoption of the draft, this document, and  Maridi
      <contact fullname="Maridi R. Makaraju (Raju) (Raju)"/> contributed valuable comments
      after the draft document was re-adopted.</t> readopted.</t>

    </section>

</middle>

<!--  *****BACK MATTER ***** -->

<back>
 <!-- References split into informative and normative -->

 <!-- There are 2 ways to insert reference entries from the citation libraries:
  1. define an ENTITY at the top, and use "ampersand character"RFC2629; here (as shown)
  2. simply use a PI "less than character"?rfc include="reference.RFC.2119.xml"?> here
  (for I-Ds: include="reference.I-D.narten-iana-considerations-rfc2434bis.xml")

  Both are cited textually in the same manner: by using xref elements.
  If you use the PI option, xml2rfc will, by default, try to find included files in the same
  directory as the including file. You can also define the XML_LIBRARY environment variable
  with a value containing a set of directories to search.  These can be either in the local
  filing system or remote ones accessed by http (http://domain/dir/... ).-->

 <references title="Normative References">

   &RFC2119;
   &DATAREQ;
   &DCSDPNEG;
   &SDPSCTP;
   &RFC3264;
   &RFC4566;
   &RFC4960;
   &RFC4975;
   &RFC5547;
   &RFC6135;
   &RFC6714;
   &RFC7977;
   &RFC8174;

 </references>
<references title="Informative References">

   &RFC3261;
   &RFC7092;

 </references>

  </back>
</rfc>