rfc8864xml2.original.xml		rfc8864.xml
	<?xml version="1.0" encoding="UTF-8"?>		<?xml version='1.0' encoding='utf-8'?>
	<!DOCTYPE rfc SYSTEM "http://xml.resource.org/authoring/rfc2629.dtd" [		<!DOCTYPE rfc SYSTEM "rfc2629-xhtml.ent">
	<!ENTITY RFC2119 SYSTEM "http://xml.resource.org/public/rfc/bibxml/refere
	nce.RFC.2119.xml">		<rfc xmlns:xi="http://www.w3.org/2001/XInclude" category="std"
	<!ENTITY RFC3264 SYSTEM "http://xml.resource.org/public/rfc/bibxml/refere		submissionType="IETF" docName="draft-ietf-mmusic-data-channel-sdpneg-28"
	nce.RFC.3264.xml">		number="8864"
	<!ENTITY RFC3629 SYSTEM "http://xml.resource.org/public/rfc/bibxml/refere		consensus="true" ipr="trust200902" tocInclude="true" symRefs="true" sortRef
	nce.RFC.3629.xml">		s="true" version="3">
	<!ENTITY RFC3758 SYSTEM "http://xml.resource.org/public/rfc/bibxml/refere		<!-- xml2rfc v2v3 conversion 2.38.0 -->
	nce.RFC.3758.xml">		<front>
	<!ENTITY RFC4960 SYSTEM "http://xml.resource.org/public/rfc/bibxml/refere		<title abbrev="SDP-Based Data Channel Negotiation">
	nce.RFC.4960.xml">		Negotiation Data Channels Using the Session Description Protocol (SDP)</title>
	<!ENTITY RFC4582 SYSTEM "http://xml.resource.org/public/rfc/bibxml/refere		<seriesInfo name="RFC" value="8864"/>
	nce.RFC.4582.xml">		<author initials="K." surname="Drage" fullname="Keith Drage">
	<!ENTITY RFC4975 SYSTEM "http://xml.resource.org/public/rfc/bibxml/refere		<organization>Unaffiliated</organization>
	nce.RFC.4975.xml">		<address>
	<!ENTITY RFC5234 SYSTEM "http://xml.resource.org/public/rfc/bibxml/refere		<email>drageke@ntlworld.com</email>
	nce.RFC.5234.xml">		</address>
	<!ENTITY RFC6455 SYSTEM "http://xml.resource.org/public/rfc/bibxml/refere		</author>
	nce.RFC.6455.xml">		<author initials="M." surname="Makaraju" fullname="Maridi R. Makaraju (Raju)
	<!ENTITY RFC6525 SYSTEM "http://xml.resource.org/public/rfc/bibxml/refere		">
	nce.RFC.6525.xml">		<organization>Nokia</organization>
	<!ENTITY RFC8174 SYSTEM "http://xml.resource.org/public/rfc/bibxml/refere		<address>
	nce.RFC.8174.xml">		<postal>
	<!ENTITY DATAREQ SYSTEM "http://xml.resource.org/public/rfc/bibxml3/refer		<street>2000 Lucent Lane</street>
	ence.I-D.ietf-rtcweb-data-channel.xml">		<city>Naperville</city>
	<!ENTITY DATAPROTO SYSTEM "http://xml.resource.org/public/rfc/bibxml3/ref		<region>Illinois</region>
	erence.I-D.ietf-rtcweb-data-protocol.xml">		<country>United States of America</country>
	<!ENTITY SDPSCTP SYSTEM "http://xml.resource.org/public/rfc/bibxml3/refer		</postal>
	ence.I-D.ietf-mmusic-sctp-sdp.xml">		<email> Raju.Makaraju@nokia.com</email>
	<!ENTITY SDPBIS SYSTEM "http://xml.resource.org/public/rfc/bibxml3/refere		</address>
	nce.I-D.draft-ietf-mmusic-rfc4566bis-32.xml">		</author>
	<!ENTITY SDPMUXATTR SYSTEM "http://xml.resource.org/public/rfc/bibxml3/re
	ference.I-D.ietf-mmusic-sdp-mux-attributes.xml">		<author fullname="Richard Ejzak" initials="R." surname="Ejzak">
	<!ENTITY CLUEDATA SYSTEM "http://xml.resource.org/public/rfc/bibxml3/refe		<organization>Unaffiliated</organization>
	rence.I-D.ietf-clue-datachannel.xml">		<address>
	<!ENTITY MSRPDATA SYSTEM "http://xml.resource.org/public/rfc/bibxml3/refe		<email>richard.ejzak@gmail.com</email>
	rence.I-D.ietf-mmusic-msrp-usage-data-channel.xml">		</address>
	]>		</author>
	<?xml-stylesheet type='text/xsl' href='rfc2629.xslt' ?>		<author fullname="Jerome Marcon" initials="J." surname="Marcon">
	<?rfc toc="yes" ?>		<organization>Unaffiliated</organization>
	<?rfc symrefs="yes" ?>		<address>
	<?rfc iprnotified="no" ?>		<email>jeromee.marcon@free.fr</email>
	<?rfc strict="no" ?>		</address>
	<?rfc compact="yes" ?>		</author>
	<?rfc subcompact="no"?>		<author initials="R." surname="Even" fullname="Roni Even" role="editor">
	<?rfc sortrefs="yes" ?>		<organization></organization>
	<rfc category="std" docName="draft-ietf-mmusic-data-channel-sdpneg-28" ipr="trus		<address>
	t200902">		<email>ron.even.tlv@gmail.com</email>
	<front>		</address>
	<title abbrev="SDP-based Data Channel Negotiation">		</author>
	SDP-based Data Channel Negotiation
	</title>		<date month="September" year="2020"/>
	<author initials="K. E." surname="Drage" fullname="Keith Drage">
	<organization>Unaffiliated</organization>		<abstract>
	<address>		<t> Data channel setup can be done using either the in-band Data Channel
	<email>drageke@ntlworld.com</email>		Establishment Protocol (DCEP) or some out-of-band non-DCEP protocol. This docum
	</address>		ent specifies how the SDP (Session
	</author>
	<author initials="M. R." surname="Makaraju" fullname="Maridi R. M
	akaraju (Raju)">
	<organization>Nokia</organization>
	<address>
	<postal>
	<street>2000 Lucent Lane</street>
	<city>Naperville</city>
	<region>Illinois</region>
	<country>US</country>
	</postal>
	<email> Raju.Makaraju@nokia.com</email>
	</address>
	</author>
	<author fullname="Richard Ejzak" initials="R.P." surname="Ejzak">
	<organization>Unaffiliated</organization>
	<address>
	<email>richard.ejzak@gmail.com</email>
	</address>
	</author>
	<author fullname="Jerome Marcon" initials="J.M." surname="Marcon"
	>
	<organization>Unaffiliated</organization>
	<address>
	<email>jeromee.marcon@free.fr</email>
	</address>
	</author>
	<author initials="R. E." surname="Even" fullname="Roni Even" role
	="editor">
	<organization>Huawei</organization>
	<address>
	<email>roni.even@huawei.com</email>
	</address>
	</author>
	<date month="May" year="2019"/>
	<area>ART</area>
	<workgroup>MMUSIC</workgroup>
	<abstract>
	<t> Data channel setup can be done using either the in-b
	and Data Channel Establishment Protocol (DCEP) or using some out-of-band non-DCE
	P protocol. This document specifies how the SDP (Session
	Description Protocol) offer/answer exchange can be used to achieve		Description Protocol) offer/answer exchange can be used to achieve
	an out-of-band non-DCEP negotiation for establishing a data channel.		an out-of-band non-DCEP negotiation for establishing a data channel.
	</t>		</t>
	</abstract>		</abstract>
	</front>		</front>
	<middle>		<middle>
	<section title="Introduction" anchor="introduction">		<section anchor="introduction">
	<t> The concept of establishing a bi-directional		<name>Introduction</name>
			<t> The concept of establishing a bidirectional
	data channel running on top of the Stream Control Transmission		data channel running on top of the Stream Control Transmission
	Protocol (SCTP) is in		Protocol (SCTP) is discussed in
	<xref target="I-D.ietf-rtcweb-data-channel"/> allowing applications to use data		<xref target="RFC8831"/>, allowing applications to use data channels. An in-ban
	channels. An in-band Data		d Data
	Channel Establishment Protocol (DCEP) is in <xref target="I-D.ietf-rtcweb-dat		Channel Establishment Protocol (DCEP) is described in <xref target="RFC8832"/
	a-protocol"/>,		>;
	however other in-band or out-of-band		however, other in-band or out-of-band
	protocols may be used for establishing data channels. Each data		protocols may be used for establishing data channels. Each data
	channel consists of paired SCTP streams sharing the same SCTP Stream		channel consists of paired SCTP streams sharing the same SCTP Stream
	Identifier. Data channels are created by endpoint applications using		Identifier. Data channels are created by endpoint applications using
	the WebRTC API (Application Programming Interface), or other protocols		(1)&nbsp;the WebRTC API (Application Programming Interface) <xref
	like CLUE		target="WebRtcAPI"/> or (2)&nbsp; other protocols
	<xref target="I-D.ietf-clue-datachannel"/>. The protocols can be signaled		(e.g., Controlling Multiple Streams for Telepresence (CLUE)
	by the data channel "subprotocol" parameter, conceptually similar to		<xref target="RFC8850"/>). The protocols can be signaled
	the WebSocket <xref target="RFC5234"/> "subprotocol". However, apart from the		by the data channel 'subprotocol' parameter, conceptually similar to
			a WebSocket subprotocol as described in <xref target="RFC6455"/>.
			However, apart from the
	"subprotocol" value transmitted to the peer, an endpoint application can agre e on how to instantiate a given		"subprotocol" value transmitted to the peer, an endpoint application can agre e on how to instantiate a given
	subprotocol on a data channel, and whether it is signaled in-band		subprotocol on a data channel, and whether it is signaled in-band
	using DCEP or out-of-band using a non-DCEP protocol (or both). </t>		using DCEP or out-of-band using a non-DCEP protocol (or both).</t>
	<t>This document defines SDP offer/answer <xref target="R		<t>This document defines Session Description Protocol (SDP) offer/answer
	FC3264"/> procedures that enable out-of-band negotiation		procedures <xref target="RFC3264"/> that enable out-of-band negotiation
	for establishing data channels for transport of well-defined subprotocols.		for establishing data channels for transport of well-defined subprotocols.
	These procedures are based on generic SDP offer/answer negotiation rules for		These procedures are based on generic SDP offer/answer negotiation rules for
	SCTP		SCTP-based media transport as specified in <xref target="RFC8841"/> for
	based media transport as specified in <xref target="I-D.ietf-mmusic-sctp-sdp"		the SDP "m=" line proto values UDP/DTLS/SCTP and TCP/DTLS/SCTP.
	/> for		</t>
	the SDP "m" line proto values UDP/DTLS/SCTP and TCP/DTLS/SCTP.		<t>This document uses MSRP (the Message Session Relay Protocol) <xref targ
			et="RFC4975"/>
	</t>		and BFCP (the Binary Floor Control Protocol) <xref target="RFC4582"/> in seve
	<t>This document uses MSRP (Message Session Relay Protoco		ral examples. It does not provide a
	l) <xref target="RFC4975"/>
	and BFCP (Binary Floor Control Protocol) <xref target="RFC4582"/> in many of
	the examples. It does not provide a
	complete specification of how to negotiate the use of a data channel to trans port		complete specification of how to negotiate the use of a data channel to trans port
	MSRP. Procedures specific to each		MSRP. Procedures specific to each
	subprotocol would have to be documented elsewhere. For MSRP they are document ed in <xref target="I-D.ietf-mmusic-msrp-usage-data-channel"/> . The use of MSRP in some examples is only to show how the generic		subprotocol would have to be documented elsewhere. For MSRP, they are documen ted in <xref target="MSRP-over-Data-Channels"/>. The use of MSRP in some example s is only to show how the generic
	procedures described herein might apply to a specific subprotocol.		procedures described herein might apply to a specific subprotocol.
	</t>		</t>
	</section>		</section>
	<section title="Conventions">		<section>
	<t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL",		<name>Conventions</name>
	"SHALL NOT",		<t>The key words "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED","MAY", and "OPTIONAL		"<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>",
	" in this		"<bcp14>SHALL NOT</bcp14>", "<bcp14>SHOULD</bcp14>",
	document are to be interpreted as described in BCP14 <xref target="RFC2119"/		"<bcp14>SHOULD NOT</bcp14>",
	>		"<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
	<xref target="RFC8174"/> when, and only when, the		"<bcp14>MAY</bcp14>", and "<bcp14>OPTIONAL</bcp14>" in this document are
	y		to be interpreted as described in BCP&nbsp;14 <xref target="RFC2119"/>
	appear in all capitals, as shown here.		<xref target="RFC8174"/> when, and only when, they appear in all capitals,
			as shown here.</t>
	</t>		</section>
	</section>		<section anchor="terminology">
	<section title="Terminology" anchor="terminology">		<name>Terminology</name>
	<t>This document uses the following terms:		<t>This document uses the following terms:
	<list style="hanging">		</t>
	<t>Data channel: A WebRTC data channel as		<dl newline="false" spacing="normal">
	specified in		<dt>Data channel:</dt>
	<xref target="I-D.ietf-rtcweb-data-channel"/>.</t>		<dd>A WebRTC data channel as specified in
	<t>Data channel stack: An entity which, u		<xref target="RFC8831"/>.</dd>
	pon application request,		<dt>Data channel stack:</dt>
	runs the data channel protocol to keep track of states, sending and receivi		<dd>An entity that, upon application request,
	ng		runs the data channel protocol to keep track of states as well as the
	data. If the application is a browser based JavaScript application		sending and receiving of data. If the application is a browser-based JavaSc
			ript application,
	then this stack resides in the browser. If the application is a		then this stack resides in the browser. If the application is a
	native application then this stack resides in the application and is access		native application, then this stack resides in the application and is acces
	ible		sible
	via some sort of APIs.</t>		via some sort of API or APIs.</dd>
	<t>Data channel properties: Fixed propert		<dt>Data channel properties:</dt>
	ies assigned to a data		<dd>Fixed properties assigned to a data
	channel at the time of its creation. Some of these properties		channel at the time of its creation. Some of these properties
	determine the way the data channel stack transmits data on this		determine the way the data channel stack transmits data on this
	channel (e.g., stream identifier, reliability, order of delivery, etc.).</t		channel (e.g., stream identifier, reliability, order of delivery).</dd>
	>		<dt>Data channel subprotocol:</dt>
	<t>Data channel subprotocol: The applicat		<dd>The application protocol that is transported
	ion protocol which is transported
	over a single data channel. Data channel subprotocol messages are sent as d ata		over a single data channel. Data channel subprotocol messages are sent as d ata
	channel payload over an established data channel. SDP offer/answer exchange can be used		channel payload over an established data channel. An SDP offer/answer excha nge can be used
	as specified in this document to negotiate the establishment of data channe ls,		as specified in this document to negotiate the establishment of data channe ls,
	corresponding data channel properties, associated data channel subprotocols		corresponding data channel properties, associated data channel subprotocols
	and data		, and data
	channel subprotocol properties. In this case the data channel subprotocols		channel subprotocol properties. In this case, the data channel subprotocols
	may be identified		may be identified
	by the values of the "subprotocol" parameters of the SDP "a=dcmap" attribut		by the values of the 'subprotocol' parameters of the SDP "a=dcmap:" attribu
	e as		te as
	described in <xref target="subprotocol-parameter"/>. Within this document t		described in <xref target="subprotocol-parameter"/>. Within this document,
	he term		the term
	"data channel subprotocol" is often abbreviated as just "subprotocol".		"data channel subprotocol" is often abbreviated as just "subprotocol".
	</t>		</dd>
	<t>DCEP: Data Channel Establishment Proto		<dt>DCEP:</dt>
	col defined in		<dd>Data Channel Establishment Protocol, as defined in
	<xref target="I-D.ietf-rtcweb-data-protocol"/>.</t>		<xref target="RFC8832"/>.</dd>
	<t>In-band: Transmission through the peer		<dt>In-band:</dt>
	-to-peer SCTP association.</t>		<dd>Transmission through the peer-to-peer SCTP association.</dd>
	<t>Out-of-band: Transmission through the		<dt>Out-of-band:</dt>
	application signaling path.</t>		<dd>Transmission through the application signaling path.</dd>
	<t>Peer: From the perspective of one of t		<dt>Peer:</dt>
	he agents in a session, its		<dd>From the perspective of one of the agents in a session, its
	peer is the other agent. Specifically, from the perspective of the		peer is the other agent. Specifically, from the perspective of the
	SDP offerer, the peer is the SDP answerer. From the perspective of		SDP offerer, the peer is the SDP answerer. From the perspective of
	the SDP answerer, the peer is the SDP offerer.</t>		the SDP answerer, the peer is the SDP offerer.</dd>
	<t>SCTP Stream Sequence Number (SSN): the		<dt>SCTP Stream Sequence Number (SSN):</dt>
	SCTP stream sequence number as specified		<dd>The SCTP Stream Sequence Number, as specified
	in <xref target="RFC4960"/>.</t>		in <xref target="RFC4960"/>.</dd>
	<t>Stream identifier: The identifier of t		<dt>Stream identifier:</dt>
	he outbound and inbound		<dd>The identifier of the outbound and inbound
	SCTP streams composing a data channel.</t>		SCTP streams composing a data channel.</dd>
	</list>		</dl>
	</t>		</section>
	</section>		<section anchor="appl_statement">
	<section title=" Applicability Statement" anchor="appl_statement"		<name>Applicability Statement</name>
	>		<t> The mechanism described in this document only applies to SDP <xref tar
	<t> The mechanism in this document only applies to the Se		get="RFC8866"/> when used together with the SDP offer/answer
	ssion Description
	Protocol (SDP) <xref target="I-D.ietf-mmusic-rfc4566bis"/> when used together
	with the SDP offer/answer
	mechanism <xref target="RFC3264"/>. Declarative usage of SDP is out of scope for this		mechanism <xref target="RFC3264"/>. Declarative usage of SDP is out of scope for this
	document, and is thus undefined.</t>		document and is thus undefined.</t>
	</section>		</section>
	<section title="SDP Data Channel Attributes" anchor="sdp_synt">		<section anchor="sdp_synt">
	<t>This section defines two new SDP media-level attribute		<name>SDP Data Channel Attributes</name>
	s that can be used together with the SDP Offer/Answer mechanism to negotiate dat		<t>This section defines two new SDP media-level attributes that can be
	a channel-specific and subprotocol-specific parameters without the usage of DCEP		used together with the SDP Offer/Answer mechanism to negotiate
	<xref target="I-D.ietf-rtcweb-data-protocol"/>. The first attribute provides fo		data-channel-specific and subprotocol-specific parameters without the
	r negotiation of		usage of DCEP <xref target="RFC8832"/>. The first attribute (<xref
	channel-specific parameters. The second attribute provides for		target="subsec-sdp-attr-for-dc-par-neg"/>) provides for negotiation of
			channel-specific parameters. The second attribute (<xref target="prot_att"/
			>) provides for
	negotiation of subprotocol-specific parameters.</t>		negotiation of subprotocol-specific parameters.</t>
	<t>		<aside><t>
	Note: Appendix A provides information how data channels work in general and		Note: <xref target="generic-out-of-band-aspects"/> provides information
	especially summarizes some key aspects, which should be considered		regarding how data channels work in general. In particular, it
	for the negotiation of data channels if DCEP is not used.		summarizes some key aspects that should be considered
	</t>		for the negotiation of data channels if DCEP is not used.</t>
	<section title="SDP DCMAP Attribute " anchor="subsec-sdp-		</aside>
	attr-for-dc-par-neg">		<section anchor="subsec-sdp-attr-for-dc-par-neg">
	<t>This section defines a new media level attribu		<name>SDP DCMAP Attribute</name>
	te "a=dcmap:" that defines the data channel parameters for		<t>This section defines a new media-level attribute, "a=dcmap:", that de
			fines the data channel parameters for
	each data channel to be negotiated. </t>		each data channel to be negotiated. </t>
	<t>The attribute is used to create bi-directional SCTP data channels		<t>This attribute is used to create bidirectional SCTP data channels
	having the same set of attributes. The data channel properties		having the same set of attributes. The data channel properties
	(reliable/partially reliable, ordered/unordered) need to be suitable per the subprotocol transport requirements.		(reliable / partially reliable, ordered/unordered) need to be suitable per th e subprotocol transport requirements.
	</t>		</t>
	<section title="DCMAP Attribute Syntax" anchor="d		<section anchor="dcmap-attr-definition">
	cmap-attr-definition">		<name>DCMAP Attribute Syntax</name>
	<t>"a=dcmap:" is a media level attribute		<t>"a=dcmap:" is a media-level attribute having the following
	having the following ABNF		definition and ABNF (Augmented Backus-Naur Form) syntax <xref target="
	(Augmented Backus-Naur Form, <xref target="RFC5234"/>) syntax.		RFC5234"/>.
	<figure align="left" title="">
	<artwork align="left"><![
	CDATA[
	Formal Syntax:
	Name: dcmap
	Value: dcmap-value
	Usage Level: media
	Charset Dependent: no		</t>
			<table anchor="dcmap-attrib">
			<name>"a=dcmap:" Attribute Definition</name>
			<thead>
			<tr>
			<th colspan="2" align="center">"a=dcmap:" Attribute</th>
			</tr>
			</thead>
			<tbody>
			<tr>
			<td>Name</td>
			<td>dcmap</td>
			</tr>
			<tr>
			<td>Value</td>
			<td>dcmap-value</td>
			</tr>
			<tr>
			<td>Usage Level</td>
			<td>media</td>
			</tr>
			<tr>
			<td>Charset Dependent</td>
			<td>No</td>
			</tr>
			</tbody>
			</table>
	Syntax:		<t>Formal syntax:</t>
			<sourcecode name="abnf-1" type="abnf"><![CDATA[
	dcmap-value = dcmap-stream-id		dcmap-value = dcmap-stream-id
	[ SP dcmap-opt *(";" dcmap-opt) ]		[ SP dcmap-opt *(";" dcmap-opt) ]
	dcmap-opt = ordering-opt / subprotocol-opt / label-opt		dcmap-opt = ordering-opt / subprotocol-opt / label-opt
	/ maxretr-opt / maxtime-opt / priority-opt		/ maxretr-opt / maxtime-opt / priority-opt
	; maxretr-opt and maxtime-opt are mutually exclusive		; maxretr-opt and maxtime-opt are
	;		; mutually exclusive
	dcmap-stream-id = 1*5DIGIT		dcmap-stream-id = 1*5DIGIT
	ordering-opt = "ordered=" ordering-value		ordering-opt = "ordered=" ordering-value
	ordering-value = "true" / "false"		ordering-value = "true" / "false"
	subprotocol-opt = "subprotocol=" quoted-string		subprotocol-opt = "subprotocol=" quoted-string
	label-opt = "label=" quoted-string		label-opt = "label=" quoted-string
	maxretr-opt = "max-retr=" maxretr-value		maxretr-opt = "max-retr=" maxretr-value
	maxretr-value = "0" / integer		maxretr-value = "0" / integer
	; number of retransmissions,		; number of retransmissions,
	; less than 2^32,		; less than 2^32,
	; derived from 'Reliability Parameter' of		; derived from 'Reliability Parameter' [RFC8832]
	; [I-D.ietf-rtcweb-data-protocol]
	maxtime-opt = "max-time=" maxtime-value		maxtime-opt = "max-time=" maxtime-value
	maxtime-value = "0" / integer		maxtime-value = "0" / integer
	; milliseconds,		; milliseconds,
	; less than 2^32,		; less than 2^32,
	; derived from 'Reliability Parameter' of		; derived from 'Reliability Parameter' [RFC8832]
	; [I-D.ietf-rtcweb-data-protocol]
	priority-opt = "priority=" priority-value		priority-opt = "priority=" priority-value
	priority-value = "0" / integer		priority-value = "0" / integer
	; unsigned integer value indicating the priority of		; unsigned integer value indicating the priority of
	; the data channel,		; the data channel,
	; less than 2^16,		; less than 2^16,
	; derived from 'Priority' of		; derived from 'Priority' [RFC8832]
	; [I-D.ietf-rtcweb-data-protocol]
	quoted-string = DQUOTE *(quoted-char / escaped-char) DQUOTE		quoted-string = DQUOTE *(quoted-char / escaped-char) DQUOTE
	quoted-char = SP / quoted-visible		quoted-char = SP / quoted-visible
	quoted-visible = %x21 / %x23-24 / %x26-7E ; VCHAR without " or %		quoted-visible = %x21 / %x23-24 / %x26-7E ; VCHAR without " or %
	escaped-char = "%" HEXDIG HEXDIG		escaped-char = "%" HEXDIG HEXDIG
	DQUOTE = <from-RFC5234>		DQUOTE = <from RFC 5234>
	integer = <from-RFC4566>		integer = <from RFC 4566>]]></sourcecode>
	Examples:
			<t>Examples:</t>
			<sourcecode name="sdp-1" type="sdp"><![CDATA[
	a=dcmap:0		a=dcmap:0
	a=dcmap:1 subprotocol="bfcp";max-time=60000;priority=512		a=dcmap:1 subprotocol="bfcp";max-time=60000;priority=512
	a=dcmap:2 subprotocol="msrp";ordered=true;label="msrp"		a=dcmap:2 subprotocol="msrp";ordered=true;label="msrp"
	a=dcmap:3 label="Label 1";ordered=false;max-retr=5;priority=128		a=dcmap:3 label="Label 1";ordered=false;max-retr=5;priority=128
	a=dcmap:4 label="foo%09bar";ordered=true;max-time=15000		a=dcmap:4 label="foo%09bar";ordered=true;max-time=15000]]></sourcecode>
	]]></artwork>
	</figure>		<aside><t>Note: The last example (a=dcmap:4) shows a 'label' paramet
	</t>		er value
	<t>		that contains one nonprintable 'escaped-char' character
	<list style="hanging">		(the tabulator character).</t></aside>
	<t>Note: The last example
	(a=dcmap:4) shows a 'label' parameter value		<t>Within an "a=dcmap:" attribute line's 'dcmap-opt' value, only one
	which contains one non-printable 'escaped-char' character
	(the tabulator character).</t>
	</list>
	</t>
	<t>Within an 'a=dcmap:' attribute line's
	'dcmap-opt' value only one
	'maxretr-opt' parameter or one 'maxtime-opt' parameter may be present.		'maxretr-opt' parameter or one 'maxtime-opt' parameter may be present.
	Both MUST NOT be present.</t>		Both <bcp14>MUST NOT</bcp14> be present.</t>
	</section>		</section>
	<section title="Dcmap-stream-id Parameter" anchor		<section anchor="dcmap-stream-id-param-definition">
	="dcmap-stream-id-param-definition">		<name>&apos;dcmap-stream-id&apos; Parameter</name>
	<t>The 'dcmap-stream-id' parameter indica		<t>The 'dcmap-stream-id' parameter indicates the SCTP stream identifie
	tes the SCTP stream identifier		r
	within the SCTP association used to form the data channel.</t>		within the SCTP association used to form the data channel.</t>
	</section>		</section>
	<section title="Label Parameter">		<section>
	<t>The 'label' parameter indicates the na		<name>&apos;label&apos; Parameter</name>
	me of the		<t>The 'label' parameter indicates the name of the
	channel. It represents a label that can be used to distinguish,		channel. It represents a label that can be used to distinguish,
	in the context of the WebRTC API <xref target="WebRtcAPI"/>,		in the context of the WebRTC API <xref target="WebRtcAPI"/>,
	an RTCDataChannel object from other RTCDataChannel objects.		an RTCDataChannel object from other RTCDataChannel objects.
	This parameter maps to the 'Label' parameter defined in		This parameter maps to the 'Label' parameter defined in
	<xref target="I-D.ietf-rtcweb-data-protocol"/>.		<xref target="RFC8832"/>.
	The 'label' parameter is optional. If it is not		The 'label' parameter is optional. If it is not
	present, then its value defaults to the empty string.		present, then its value defaults to the empty string.
	</t>		</t>
	<t>In order to communicate with WEbRTC AP		<t>In order to communicate with the WebRTC API, the 'label' parameter
	I the label attribute should:		should
	<list style="symbols">		</t>
	<t>Serialize the WebRTC l		<ul spacing="normal">
	abel as a UTF-8 string <xref target="RFC3629"/>.</t>		<li>Serialize the WebRTC label as a UTF-8 string <xref target="RFC36
	<t>Treat the UTF-8 serial		29"/>.</li>
	ization as a series of bytes</t>		<li>Treat the UTF-8 serialization as a series of bytes.</li>
	<t>For each byte in the s		<li>
	erialization:		<t>For each byte in the serialization,
			</t>
	<list style="symb		<ul spacing="normal">
	ols">		<li>If the byte can be expressed as a 'quoted-char', do so.</li>
	<t>If the		<li>Otherwise, express the byte as an 'escaped-char'.</li>
	byte can be expressed as a `quoted-char`, do so</t>		</ul>
	<t>Otherw		</li>
	ise, express the byte as an `escaped-char`.</t>		</ul>
	</list>		<aside><t>Note: The empty string <bcp14>MAY</bcp14> also be explicitly
	</t>		used as a 'label' value,
	</list>
	</t>
	<t>Note: The empty string MAY also be exp
	licitly used as a 'label' value,
	such that 'label=""' is equivalent to the 'label' parameter not being		such that 'label=""' is equivalent to the 'label' parameter not being
	present at all.		present at all.
	<xref target="I-D.ietf-rtcweb-data-protocol"/> allows the DATA_CHANNEL_OP		<xref target="RFC8832"/> allows the DATA_CHANNEL_OPEN
	EN		message's 'Label' value to be an empty string.</t></aside>
	message's 'Label' value to be an empty string.</t>		</section>
	</section>		<section anchor="subprotocol-parameter">
	<section title="Subprotocol Parameter" anchor="su		<name>&apos;subprotocol&apos; Parameter</name>
	bprotocol-parameter">		<t>The 'subprotocol' parameter indicates which protocol the
	<t>The 'subprotocol' parameter indicates
	which protocol the
	client expects to exchange via the channel.		client expects to exchange via the channel.
	This parameter maps to the 'Protocol' parameter defined in		This parameter maps to the 'Protocol' parameter defined in
	<xref target="I-D.ietf-rtcweb-data-protocol"/>.		<xref target="RFC8832"/>.
	<xref target="IANA_subproto_ids"/> specifies how new subprotocol paramete		<xref target="IANA_subproto_ids"/> specifies how values for new subprotoc
	r		ol parameters are registered.
	values are registered.
	'subprotocol' is an optional parameter.		'subprotocol' is an optional parameter.
	If the 'subprotocol' parameter is not present, then its value		If the 'subprotocol' parameter is not present, then its value
	defaults to an empty string.</t>		defaults to an empty string.</t>
	<t> Note: The empty string MAY also be ex		<aside><t> Note: The empty string <bcp14>MAY</bcp14> also be
	plicitly used as 'subprotocol' value,		explicitly used as a 'subprotocol' value,
	such that 'subprotocol=""' is equivalent to the 'subprotocol' parameter n ot being		such that 'subprotocol=""' is equivalent to the 'subprotocol' parameter n ot being
	present at all. <xref target="I-D.ietf-rtcweb-data-protocol"/> allows the		present at all. <xref target="RFC8832"/> allows the
	DATA_CHANNEL_OPEN message's 'Subprotocol' value to be an empty string.		DATA_CHANNEL_OPEN message's 'Protocol' value to be an empty string.
	</t>		</t></aside>
	</section>		</section>
	<section title="Max-retr Parameter" anchor="max-r		<section anchor="max-retr-param-definition">
	etr-param-definition">		<name>&apos;max-retr&apos; Parameter</name>
	<t>This parameter indicates that the data		<t>This parameter indicates that the data channel is partially reliabl
	channel is partially reliable.		e.
	The 'max-retr' parameter indicates the maximal number of times a user mes sage will		The 'max-retr' parameter indicates the maximal number of times a user mes sage will
	be retransmitted. The max-retr parameter is optional. If		be retransmitted. The 'max-retr' parameter is optional. If
	the max-retr parameter and the max-time parameter are not present, then r		the 'max-retr' parameter and the 'max-time' parameter are not present, th
	eliable		en reliable
	transmission is performed as specified in <xref target="RFC4960"/>.		transmission is performed as specified in <xref target="RFC4960"/>.
	This parameter maps to the 'Number of RTX' parameter		This parameter maps to the 'Number of RTX' parameter
	defined in <xref target="I-D.ietf-rtcweb-data-protocol"/>.</t>		defined in <xref target="RFC8832"/>.</t>
	</section>		</section>
	<section title="Max-time Parameter">		<section>
	<t> This parameter indicates that the dat		<name>&apos;max-time&apos; Parameter</name>
	a channel is partially reliable.		<t> This parameter indicates that the data channel is partially reliab
			le.
	A user message will no longer be transmitted or retransmitted after		A user message will no longer be transmitted or retransmitted after
	a specified life-time given in milliseconds in the 'max-time'		a specified lifetime, given in milliseconds, in the 'max-time'
	parameter. The life-time starts when providing the user message to the pr		parameter. The lifetime starts when providing the user message to the pro
	otocol stack.		tocol stack.
	The max-time parameter is optional. If the max-retr parameter and the max-time		The 'max-time' parameter is optional. If the 'max-retr' parameter and the 'max-
	parameter are not present, then reliable		time' parameter are not present, then reliable
	transmission is performed as specified in <xref target="RFC4960"/>.		transmission is performed as specified in <xref target="RFC4960"/>.
	This parameter maps to the 'Lifetime in ms' parameter		This parameter maps to the 'Lifetime in ms' parameter
	defined in <xref target="I-D.ietf-rtcweb-data-protocol"/>.</t>		defined in <xref target="RFC8832"/>.</t>
	</section>		</section>
	<section title="Ordered Parameter" anchor="ordere		<section anchor="ordered-param-description">
	d-param-description">		<name>&apos;ordered&apos; Parameter</name>
	<t>The 'ordered' parameter with value "tr		<t>The 'ordered' parameter with value "true" indicates that the receiv
	ue" indicates that the receiver will		er will
	dispatch DATA chunks in the data channel to the upper layer		dispatch DATA chunks in the data channel to the upper layer
	while preserving the order. The ordered parameter is optional and		while preserving the order. The 'ordered' parameter is optional and
	takes two values: "true" for ordered and "false" for unordered delivery		takes two values -- "true" for ordered delivery and "false" for unordered
			delivery --
	with "true" as the default value.		with "true" as the default value.
	Any other value is ignored and default "ordered=true" is assumed.		Any other value is ignored, and the default "ordered=true" is assumed.
	In the absence of this parameter "ordered=true" is assumed.		In the absence of this parameter, "ordered=true" is assumed.
	This parameter maps to		This parameter maps to
	the ordered or unordered data channel types as defined in		the ordered or unordered data channel types as defined in
	<xref target="I-D.ietf-rtcweb-data-protocol"/>.</t>		<xref target="RFC8832"/>.</t>
	</section>		</section>
	<section title="Priority Parameter" anchor="prior		<section anchor="priority-param-description">
	ity-param-description">		<name>&apos;priority&apos; Parameter</name>
	<t>The 'priority' parameter indicates the		<t>The 'priority' parameter indicates the data channel's priority
	data channel's priority
	relative to the priorities of other data channels, which may		relative to the priorities of other data channels, which may
	additionally exist over the same SCTP association.		additionally exist over the same SCTP association.
	The 'priority' parameter maps to the 'Priority' parameter defined in		The 'priority' parameter maps to the 'Priority' parameter defined in
	<xref target="I-D.ietf-rtcweb-data-protocol"/>.		<xref target="RFC8832"/>.
	The 'priority' parameter is optional.		The 'priority' parameter is optional.
	In the absence of this parameter "priority=256" is assumed.		In the absence of this parameter, "priority=256" is assumed.
	</t>		</t>
	</section>		</section>
	<section title="DCMAP Multiplexing Category" anch		<section anchor="dcmap-mux-category">
	or="dcmap-mux-category">		<name>DCMAP Multiplexing Category</name>
	<t>The multiplexing category <xref target		<t>The multiplexing category <xref target="RFC8859"/> of the "a=dcmap:
	="I-D.ietf-mmusic-sdp-mux-attributes"/> of the "a=dcmap:" attribute is SPECIAL.		" attribute is SPECIAL.
	</t>		</t>
	<t>As the usage of multiple SCTP associat		<t>As the usage of multiple SCTP associations on top of a single DTLS
	ions on top of a single DTLS		association is outside the scope of <xref target="RFC8841"/>,
	association is outside the scope of <xref target="I-D.ietf-mmusic-sctp-sd
	p"/>,
	no "a=dcmap:" attribute multiplexing rules are specified for the UDP/DTLS /SCTP and		no "a=dcmap:" attribute multiplexing rules are specified for the UDP/DTLS /SCTP and
	TCP/DTLS/SCTP proto values.		TCP/DTLS/SCTP proto values.
	If future extensions of <xref target="I-D.ietf-mmusic-sctp-sdp"/> define how to		If future extensions of <xref target="RFC8841"/> define how to
	negotiate multiplexing of multiple SCTP associations on top of a single D TLS		negotiate multiplexing of multiple SCTP associations on top of a single D TLS
	association, or how to add multiple SCTP associations to one BUNDLE group , then		association or how to add multiple SCTP associations to one BUNDLE group, then
	multiplexing rules for the "a=dcmap:" attribute need to be		multiplexing rules for the "a=dcmap:" attribute need to be
	defined as well, for instance in an extension of this SDP offer/answer ba		defined as well -- for instance, in an extension of this specification.
	sed data channel		</t>
	negotiation specification.		</section>
	</t>		</section>
	</section>		<section anchor="prot_att">
	</section>		<name>SDP DCSA Attribute</name>
	<!-- subsec-sdp-attr-for-dc-par-neg -->		<t>In the SDP media description, each data channel declaration
	<section title="SDP DCSA Attribute" anchor="prot_att">		<bcp14>MAY</bcp14> also be followed by other SDP attributes, which
	<t>In the SDP media description, each data channe		apply to the corresponding data channel and its subprotocol. Each of
	l declaration MAY also be followed		these attributes is represented by one new "a=dcsa:" attribute line
	by other media level SDP attributes, which are either specifically defined		that references another SDP attribute defined for use with this data
	for or		channel's subprotocol. Instructions for registering attributes for use
	applied to the subprotocol in use.		with a data channel are given in <xref target="IANA-reg-data-channel-att
	Each of these attributes is represented by one new attribute line, and		ribs"/>.</t>
	it includes the contents of a media-level SDP attribute already		<t>Each SDP attribute that is related to the subprotocol and that would
	defined for use with this (sub)protocol in another IETF document.		normally
	Subprotocol specific attributes MAY also be defined for exclusive		be used to negotiate the subprotocol using the SDP offer/answer mechanism
	use with data channel transport, but MUST use the same syntax		is replaced with
	described here for other subprotocol related attributes.</t>		an attribute of the form "a=dcsa:stream-id original&nbhy;attribute",
	<t>Each SDP attribute, related to the subprotocol		where "dcsa" stands for "data channel subprotocol attribute",
	, that would normally		"stream-id" is the SCTP stream identifier assigned to this subprotocol
	be used to negotiate the subprotocol using SDP offer/answer is replaced wi		instance, and "original-attribute" represents the contents of the
	th		subprotocol-related attribute to be included.</t>
	an attribute of the form "a=dcsa:stream-id original-attribute",		<t>The same syntax applies to any other SDP attribute required for
	where dcsa stands for "data channel subprotocol attribute",
	stream-id is the SCTP stream identifier assigned to this subprotocol
	instance, and original-attribute represents the contents of the
	subprotocol related attribute to be included.</t>
	<t>The same syntax applies to any other SDP attri
	bute required for
	negotiation of this instance of the subprotocol.</t>		negotiation of this instance of the subprotocol.</t>
	<t>The detailed offer/answer procedures for the d		<t>The detailed offer/answer procedures for the dcsa attribute are
	csa attribute are dependent on the associated sub-protocol. If no offer/answer p		dependent on the associated subprotocol. If no offer/answer
	rocedures exist for the sub-protocol when used outside of the dcsa attribute, no		procedures exist for the subprotocol when used outside of the dcsa
	specification is needed for use with dcsa. The IANA registration procedures for		attribute, no specification is needed for use with dcsa. The IANA
	the WebSocket Subprotocol Name Registry (<xref target="IANA_subproto_ids"/>) do		(Internet Assigned Numbers Authority) registration procedures for the "W
	not strictly require a specification of the offer/answer procedures for the sub		ebSocket Subprotocol Name Registry" (<xref target="IANA_subproto_ids"/>) do not
	-protocol when used with dcsa. If the sub-protocol has defined offer/answer proc		strictly require a specification of the offer/answer procedures for the subproto
	edures when used outside of dcsa, such a specification is encouraged to ensure i		col when used with dcsa. If the subprotocol has defined offer/answer procedures
	nteroperability. If the sub-protocol has defined offer/answer procedures when us		when used outside of dcsa, such a specification is encouraged to ensure interope
	ed outside of dcsa, but no specification exists for the offer/answer procedures		rability. If the subprotocol has defined offer/answer procedures when used outsi
	for the sub-protocol when used with dcsa, implementations SHOULD assume the use		de of dcsa but no specification exists for the offer/answer procedures for the s
	of the default values for all otherwise-negotiable and applicable sub-protocol p		ubprotocol when used with dcsa, implementations <bcp14>SHOULD</bcp14> assume the
	arameters.		use of the default values for all otherwise-negotiable and applicable subprotoc
			ol parameters.
			</t>
			<section anchor="dcsa-attribute">
			<name>DCSA Attribute Syntax</name>
			<t>"a=dcsa:" is a media-level attribute having the following definition and
			ABNF (Augmented Backus-Naur Form) syntax <xref target="RFC5234"/>.
	</t>		</t>
	<section title="DCSA Syntax" anchor="dcsa-attribu
	te">
	<t>
	<figure align="left" title="">
	<artwork align="left"><![
	CDATA[
	Formal Syntax:
	Name: dcsa
	Value: dcsa-value
	Usage Level: media
	Charset Dependent: no
	Syntax:		<table anchor="dcsa-attrib">
			<name>"a=dcsa:" Attribute Definition</name>
			<thead>
			<tr>
			<th colspan="2" align="center">"a=dcsa:" Attribute</th>
			</tr>
			</thead>
			<tbody>
			<tr>
			<td>Name</td>
			<td>dcsa</td>
			</tr>
			<tr>
			<td>Value</td>
			<td>dcsa-value</td>
			</tr>
			<tr>
			<td>Usage Level</td>
			<td>media</td>
			</tr>
			<tr>
			<td>Charset Dependent</td>
			<td>No</td>
			</tr>
			</tbody>
			</table>
			<t>Formal syntax:</t>
			<sourcecode name="abnf-2" type="abnf"><![CDATA[
	dcsa-value = stream-id SP attribute		dcsa-value = stream-id SP attribute
	stream-id = 1*5DIGIT		stream-id = 1*5DIGIT
	attribute = <from-RFC4566>		attribute = <from RFC 4566>]]></sourcecode>
	Example:
			<t>Example:</t>
			<sourcecode name="sdp-2" type="sdp"><![CDATA[
	a=dcmap:2 subprotocol="msrp";ordered=true;label="msrp"		a=dcmap:2 subprotocol="msrp";ordered=true;label="msrp"
	a=dcsa:2 accept-types:text/plain		a=dcsa:2 accept-types:text/plain]]></sourcecode>
	]]></artwork>
	</figure>		<t>Note that the reference to <xref target="RFC8866"/> defines where t
	</t>		he
	<t>Note that the reference to <xref targe
	t="I-D.ietf-mmusic-rfc4566bis"/> defines where the
	attribute definition can be found;		attribute definition can be found;
	it does not provide any limitation on support of attributes		it does not provide any limitations on support of attributes
	defined in other documents in accordance with this attribute		defined in other documents in accordance with this attribute
	definition. Note however that not all SDP attributes are suitable		definition. Note, however, that not all SDP attributes are suitable
	as a "a=dcsa:" parameter. IANA SDP parameters contains		as an "a=dcsa:" parameter. The registry of IANA SDP parameters contains
	the lists of IANA (Internet Assigned Numbers Authority)		the lists of IANA-registered session-level and media-level or
	registered session and media level or		media-level-only SDP attributes.
	media level only SDP attributes.</t>		</t>
	<t>Thus in the example above, the origina		<t>Thus, in the example above, the original attribute line
	l attribute line		"a=accept&nbhy;types:text/plain" is represented by the attribute line
	"a=accept-types:text/plain" is represented by the attribute line
	"a=dcsa:2 accept-types:text/plain", which specifies that this		"a=dcsa:2 accept-types:text/plain", which specifies that this
	instance of the MSRP subprotocol being transported on the SCTP association using		instance of the MSRP subprotocol being transported on the SCTP association using
	the data channel with stream id 2 accepts		the data channel with stream id 2 accepts
	plain text files.</t>		plaintext files.</t>
	<t>As opposed to the data channel "a=dcma		<t>As opposed to the data channel "a=dcmap:" attribute parameters,
	p:" attribute parameters,
	these parameters		these parameters
	are subject to offer/answer negotiation following the procedures		are subject to offer/answer negotiation, following the procedures
	defined in the subprotocol specific documents.</t>		defined in the subprotocol-specific documents.</t>
	<t>It is assumed that in general the usag		<t>It is assumed that in general the usages of subprotocol-related
	es of subprotocol related media		media-level attributes are independent from the subprotocol's transport pr
	level attributes are independent from the subprotocol's transport protocol		otocol.
	.		Such transport-protocol-independent subprotocol-related attributes are
	Such transport protocol independent subprotocol related attributes are
	used in the same way as defined in the original subprotocol specification,		used in the same way as defined in the original subprotocol specification,
	also if the subprotocol is transported over a data channel and if the		also if the subprotocol is transported over a data channel and if the
	attribute is correspondingly embedded in a "a=dcsa" attribute.		attribute is correspondingly embedded in an "a=dcsa:" attribute.
	</t>		</t>
	<t>There may be cases, where the usage of		<t>There may be cases where the usage of a subprotocol-related
	a subprotocol related media level		media-level
	attribute depends on the subprotocol's transport protocol.		attribute depends on the subprotocol's transport protocol.
	In such cases the subprotocol related usage of the attribute is expected t		In such cases, the subprotocol-related usage of the attribute is expected
	o be		to be
	described for the data channel transport. A data channel specific usage of		described for the data channel transport. A data-channel-specific usage of
	a		a
	subprotocol attribute is expected to be specified in the same document tha t		subprotocol attribute is expected to be specified in the same document tha t
	registers the subprotocol's identifier for data channel usage as described in		registers the subprotocol's identifier for data channel usage as described in
	<xref target="IANA_subproto_ids"/>.		<xref target="IANA_subproto_ids"/>.
	</t>		</t>
	<t>SDP attributes that are only defined f		</section>
	or use at the		<section anchor="dcsa-mux-category">
	dcsa usage level, SHALL use the dcsa usage level when registering the		<name>DCSA Multiplexing Category</name>
	attribute. If existing media attributes are used in a datachannel		<t>The multiplexing category of the "a=dcsa:" attribute is SPECIAL.
	subprotocol specific way, then a new dcsa usage level		</t>
	MUST be defined for the existing media attribute. Where the SDP		<t>As the usage of multiple SCTP associations on top of a single DTLS
	attribute is applicable to a particular subprotocol/s this SHALL also		association is outside the scope of <xref target="RFC8841"/>,
	be registered by indicating the applicable subprotocol identifiers
	(see /<xref target="I-D.ietf-mmusic-rfc4566bis"/> section-8.5) along with the
	dcsa usage level.
	</t>
	</section>
	<section title="DCSA Multiplexing Category" ancho
	r="dcsa-mux-category">
	<t>The multiplexing category of the "a=dc
	sa:" attribute is SPECIAL.
	</t>
	<t>As the usage of multiple SCTP associat
	ions on top of a single DTLS
	association is outside the scope of <xref target="I-D.ietf-mmusic-sctp-sd
	p"/>,
	no "a=dcsa:" attribute multiplexing rules are specified for the UDP/DTLS/ SCTP and		no "a=dcsa:" attribute multiplexing rules are specified for the UDP/DTLS/ SCTP and
	TCP/DTLS/SCTP proto values.		TCP&wj;/DTLS&wj;/SCTP proto values.
	If future extensions of <xref target="I-D.ietf-mmusic-sctp-sdp"/> define		If future extensions of <xref target="RFC8841"/> define how to
	how to
	negotiate multiplexing of multiple SCTP associations on top of a single D TLS		negotiate multiplexing of multiple SCTP associations on top of a single D TLS
	association, or how to add multiple SCTP associations to one BUNDLE group , then		association or how to add multiple SCTP associations to one BUNDLE group, then
	multiplexing rules for the "a=dcsa:" attribute need to be		multiplexing rules for the "a=dcsa:" attribute need to be
	defined as well, for instance in an extension of this SDP based data chan		defined as well -- for instance, in an extension of this specification.
	nel		</t>
	negotiation specification.		</section>
	</t>		</section>
	</section>		</section>
	</section>		<section anchor="section_procedures">
	<!-- prot_att -->		<name>SDP Offer/Answer Procedures</name>
	</section>		<t>This section defines how data channels can be negotiated using the SDP
	<!-- sdp_sync -->
	<section title="SDP Offer/Answer Procedures" anchor="section_proc
	edures">
	<t>This section defines how data channels can be negotiat
	ed using the SDP
	offer/answer mechanism. A given media description can describe multiple		offer/answer mechanism. A given media description can describe multiple
	data channels (each represented by a separate SDP dcmap attribute) that		data channels (each represented by a separate SDP dcmap attribute) that
	can be created, modified and closed using different offer/answer exchange s.		can be created, modified, and closed using different offer/answer exchang es.
	The procedures in this section apply for a given data channel.		The procedures in this section apply for a given data channel.
	</t>		</t>
	<t>The generic offer/answer procedures for negotiating th		<t>The generic offer/answer procedures for negotiating the SCTP associatio
	e SCTP association used to realize data channels are defined in <xref target="I-		n used to realize data channels are defined in <xref target="RFC8841"/>. This se
	D.ietf-mmusic-sctp-sdp"/>. This section only defines the data channel specific p		ction only defines the data-channel-specific procedures.</t>
	rocedures.</t>		<t> "Initial offer" refers to the offer in which a data channel is
	<t> “Initial offer” refers to the offer in which a data c		opened. It can be either the initial offer or a subsequent offer of the as
	hannel is opened. It can be the initial offer, or a subsequent offer, of the ass		sociated SDP session.</t>
	ociated SDP session.</t>		<t>The detailed offer/answer procedures for the dcsa attribute are depende
	<t>The detailed offer/answer procedures for the dcsa attr		nt on the associated subprotocol; see <xref target="prot_att"/>.
	ibute are dependent on the associated sub-protocol see <xref target="prot_att"/>
	.
	</t>		</t>
	<section title="Managing Stream Identifiers" anchor="id_m		<section anchor="id_mgmt">
	ngt">		<name>Managing Stream Identifiers</name>
	<t>		<t>
			In order to avoid SCTP Stream identifier collisions, in alignment with
	In order to avoid SCTP Stream identifier collisio		<xref target="RFC8832"/>, the endpoint acting as a DTLS client (for
	ns, in alignment with <xref target="I-D.ietf-rtcweb-data-protocol"/>, the endpoi		the SCTP association used to realize data channels) <bcp14>MUST</bcp14> use even
	nt acting as DTLS client (for		identifier values,
	the SCTP association used to realize data channels) MUST use even identifier val		and the endpoint acting as a DTLS server <bcp14>MUST</bcp14> use odd identifier
	ues,		values. </t>
	and the endpoint acting as DTLS server MUST use odd identifier values. </t>		<t>SCTP stream identifiers associated with data channels that have been
	<t>SCTP stream identifiers associated with data c		negotiated using DCEP <bcp14>MUST NOT</bcp14> be included in SDP offers and answ
	hannels that have been negotiated using DCEP MUST NOT be included in SDP offers		ers.
	and answers.		</t>
	</t>		</section>
	</section>		<section anchor="param_negotiation">
	<!-- id_mngt -->		<name>Negotiating Data Channel Parameters</name>
	<section title="Negotiating Data Channel Parameters" anch		<t>
	or="param_negotiation">		The data channel types defined in <xref target="RFC8832"/> are
	<t>		mapped to the dcmap SDP attribute parameters in the following manner, where "
	The data channel types defined in <xref target="I-D.ietf-rtcweb-data-protocol		ordered=true" is the default and may be omitted:
	"/> are
	mapped to the dcmap SDP attribute parameters in the following manner where "o
	rdered=true" is the default and may be omitted:
	</t>		</t>
	<t>		<sourcecode name="data-channel-items" type="sdp"><![CDATA[
	<figure align="left" title="">
	<artwork align="left"><![CDATA[
	DATA_CHANNEL_RELIABLE		DATA_CHANNEL_RELIABLE
	ordered=true		ordered=true
	DATA_CHANNEL_RELIABLE_UNORDERED		DATA_CHANNEL_RELIABLE_UNORDERED
	ordered=false		ordered=false
	DATA_CHANNEL_PARTIAL_RELIABLE_REXMIT		DATA_CHANNEL_PARTIAL_RELIABLE_REXMIT
	ordered=true;max-retr=<number of retransmissions>		ordered=true;max-retr=<number of retransmissions>
	DATA_CHANNEL_PARTIAL_RELIABLE_REXMIT_UNORDERED		DATA_CHANNEL_PARTIAL_RELIABLE_REXMIT_UNORDERED
	ordered=false;max-retr=<number of retransmissions>		ordered=false;max-retr=<number of retransmissions>
	DATA_CHANNEL_PARTIAL_RELIABLE_TIMED		DATA_CHANNEL_PARTIAL_RELIABLE_TIMED
	ordered=true;max-time=<lifetime in milliseconds>		ordered=true;max-time=<lifetime in milliseconds>
	DATA_CHANNEL_PARTIAL_RELIABLE_TIMED_UNORDERED		DATA_CHANNEL_PARTIAL_RELIABLE_TIMED_UNORDERED
	ordered=false;max-time=<lifetime in milliseconds>		ordered=false;max-time=<lifetime in milliseconds>]]></sourcecode>
	]]></artwork>
	</figure>
	</t>
	<t>
	By definition max-retr and max-time are mutually exclusive,
	so both MUST NOT be present in the "a=dcmap:" attribute
	line. If an SDP offer contains both of these parameters then the
	receiver of such an SDP offer MUST reject the SDP offer. If an SDP
	answer contains both of these parameters then the offerer MUST treat
	the associated SDP offer/answer as failed. </t>
	</section>
	<!-- ="Negotiating Data Channel Parameters" -->
	<section title="Generating the Initial Offer for A Data C
	hannel" anchor="opendc">
	<t>When an offerer sends an initial offer, in ord
	er to negotiate an SCTP stream for a data channel, the offerer:
	<list style="symbols">		<t>
	<t>SHALL include an SDP dcmap att		By definition, 'max-retr' and 'max-time' are mutually exclusive,
	ribute (<xref target="sdp_synt"/> and <xref target="param_negotiation"/>) assoc		so both <bcp14>MUST NOT</bcp14> be present in the "a=dcmap:" attribute
	iated with the data channel in the “m=” section representing the SCTP associatio		line. If an SDP offer contains both of these parameters, then the
	n used to realize the data channel; and		receiver of such an SDP offer <bcp14>MUST</bcp14> reject the SDP offer. If a
	</t>		n SDP
	<t>MAY include one or more SDP dc		answer contains both of these parameters, then the offerer <bcp14>MUST</bcp14
	sa attributes (<xref target="prot_att"/>) associated with the		> treat
	data channel. The value of the stream-id part of each attribute SHALL matc		the associated SDP offer/answer as failed. </t>
	h the dcmap-stream-id value of the dcmap attribute.		</section>
	</t>		<section anchor="opendc">
	</list>		<name>Generating the Initial Offer for a Data Channel</name>
	</t>		<t>When an offerer sends an initial offer, in order to negotiate an SCTP
	</section>		stream for a data channel, the offerer
	<section title="Generating SDP Answer">
	<t>When an answerer receives an offer that includ
	es an “m=" section for an SCTP association, that describes an SCTP stream for a
	data channel, if the answerer accepts the data channel it:
	<list style="symbols">		</t>
	<t>SHALL include an SDP dcmap att		<ul spacing="normal">
	ribute (<xref target="sdp_synt"/> and <xref target="param_negotiation"/>)		<li><bcp14>SHALL</bcp14> include an SDP dcmap attribute
			(Sections&nbsp;<xref target="subsec-sdp-attr-for-dc-par-neg" format="c
			ounter"/> and <xref
			target="param_negotiation" format="counter"/>) associated with the dat
			a channel in the "m=" section representing the SCTP association used to realize
			the data channel, and
			</li>
			<li><bcp14>MAY</bcp14> include one or more SDP dcsa attributes (<xref
			target="prot_att"/>) associated with the
			data channel. The value of the 'stream-id' part of each attribute <bcp14>S
			HALL</bcp14> match the 'dcmap-stream-id' value of the dcmap attribute.
			</li>
			</ul>
			</section>
			<section>
			<name>Generating the SDP Answer</name>
			<t>When an answerer receives an offer that includes an "m=" section
			for an SCTP association, the offer describes an SCTP stream for a data c
			hannel, if the answerer accepts the data channel, it
			</t>
			<ul spacing="normal">
			<li><bcp14>SHALL</bcp14> include an SDP dcmap attribute
			(Sections&nbsp;<xref target="subsec-sdp-attr-for-dc-par-neg" format="c
			ounter"/> and <xref
			target="param_negotiation" format="counter"/>)
	associated		associated
	with the data channel in the "m=" section representing the SCTP association used		with the data channel in the "m=" section representing the SCTP association used
	to realize the data channel. The value of the dcmap-stream-id, max-retr and max-		to realize the data channel. The value of the 'dcmap-stream-id', 'max-retr', and
	time		'max-time'
	values of the dcmap attribute SHALL be identical to the value used for the data		values of the dcmap attribute <bcp14>SHALL</bcp14> be identical to the value use
	channel		d for the data channel
	in the offer; and		in the offer, and
			</li>
	</t>		<li><bcp14>MAY</bcp14> include one or more SDP dcsa attributes (<xref
	<t>MAY include one or more SDP dc		target="prot_att"/>) associated with the
	sa attributes (<xref target="prot_att"/>) associated with the
	data channel.		data channel.
	</t>		</li>
	</list>		</ul>
	</t>		</section>
	</section>		<section>
	<section title="Offerer Processing of the SDP Answer">		<name>Offerer Processing of the SDP Answer</name>
	<t>An offerer receiving an SDP answer performs th		<t>An offerer receiving an SDP answer performs the following:
	e following:
	<list style="symbols">		</t>
	<t>SHALL close any created data c		<ul spacing="normal">
	hannels as described in		<li>It <bcp14>SHALL</bcp14> close any created data channels as describ
			ed in
	<xref target="close-dc"/>		<xref target="close-dc"/>
	for which the expected "a=dcmap:" attributes are not		for which the expected "a=dcmap:" attributes are not
	present in the SDP answer. If the SDP answer has no "a=dcmap" attribute e		present in the SDP answer. If the SDP answer has no "a=dcmap:" attributes
	ither the peer does not support "a=dcmap:" attributes or		, either the peer does not support "a=dcmap:" attributes or
	it rejected all the data channels. In either case the offerer closes		it rejected all the data channels. In either case, the offerer
	all the SDP offered		closes all the data channels offered by SDP that were open at the ti
	data channels that were open at the time of offer.		me of the offer.
	The DTLS association and SCTP association will still be setup. At th		The DTLS association and SCTP association will still be set up. At t
	is		his
	point the offerer may use DCEP negotiation <xref target="I-D.ietf-rtcweb-data		point, the offerer may use DCEP negotiation <xref target="RFC8832"/> to open
	-protocol"/> to open data channels</t>		data channels.</li>
	</list>		</ul>
	</t>		<t>Each agent application <bcp14>MUST</bcp14> wait to send data until it
	<t>Each agent application MUST wait to send data		has
	until it has
	confirmation that the data channel at the peer is instantiated.		confirmation that the data channel at the peer is instantiated.
	For WebRTC, this is when both data channel stacks have channel		For WebRTC, this is when both data channel stacks have channel
	parameters instantiated. This occurs:		parameters instantiated and occurs as follows:
	<list style="symbols">		</t>
	<t>At both peers when a data chan		<ul spacing="normal">
	nel is created without a previously		<li>At both peers when a data channel is created without a previously
	established SCTP association, as soon as the SCTP association		established SCTP association, as soon as the SCTP association
	is successfully established.</t>		is successfully established.</li>
	<t>At the agent receiving an SDP		<li>At the agent receiving an SDP offer for which there is an
	offer for which there is an
	established SCTP association, as soon as it creates the		established SCTP association, as soon as it creates the
	negotiated data channel based on information		negotiated data channel based on information
	signaled in the SDP offer.</t>		signaled in the SDP offer.</li>
	<t>At the agent sending an SDP of		<li>At the agent sending an SDP offer to create a new data channel for
	fer to create a new data channel for which there is an established SCTP		which there is an established SCTP
	association, when it receives the SDP answer confirming acceptance		association, when it receives the SDP answer confirming acceptance
	of the data channel or when it begins to receive data on the		of the data channel or when it begins to receive data on the
	data channel from the peer, whichever occurs first.</t>		data channel from the peer, whichever occurs first.</li>
	</list>		</ul>
	</t>		</section>
	</section>		<section>
	<!-- opendc -->		<name>Modifying the Session</name>
	<section title="Modifying the Session">		<t>When an offerer sends a subsequent offer that includes information fo
	<t>When an offer sends a subsequent offer, that i		r
	ncludes information for
	a previously negotiated data channel, unless the offerer intends to		a previously negotiated data channel, unless the offerer intends to
	close the data channel (<xref target="close-dc"/>), the offerer SHALL include the		close the data channel (<xref target="close-dc"/>), the offerer <bcp14>SHALL< /bcp14> include the
	previously negotiated SDP attributes and attribute values associated with the		previously negotiated SDP attributes and attribute values associated with the
	data channel. The answerer may reject the offer. The means for rejecting an o ffer are dependent on		data channel. The answerer may reject the offer. The means for rejecting an o ffer are dependent on
	the higher layer protocol. The offer/answer exchange is atomic; if the answe r is rejected, the session reverts to the state prior to the		the higher-layer protocol. The offer/answer exchange is atomic; if the answe r is rejected, the session reverts to the state prior to the
	offer <xref target="RFC3264"/>.		offer <xref target="RFC3264"/>.
	</t>		</t>
	<section title="Closing a Data Channel" anchor="c		<section anchor="close-dc">
	lose-dc">		<name>Closing a Data Channel</name>
	<t>In order to close a data channel, the		<t>In order to close a data channel, the endpoint that wants to
	endpoint that wants to close		close the data channel
	SHALL send the SCTP SSN reset message <xref target="RFC6525"/>, following the		<bcp14>SHALL</bcp14> send an SCTP SSN Reset message <xref target="RFC6525"/>,
	procedures in section 6.7 of <xref target="I-D.ietf-rtcweb-data-channel"/>.		following the procedure in <xref target="RFC8831" sectionFormat="of" section="6
			.7"/>.
	In addition, if the closed data channel was negotiated using the offer/answer me		In addition, if the closed data channel was negotiated using the offer/answer
	chanism <xref target="opendc"/>, the endpoint that closed the data channel SHALL		mechanism (<xref target="opendc"/>), the endpoint that closed the data channel
	send a subsequent offer in which it either:		<bcp14>SHALL</bcp14> send a subsequent offer in which it does one of the followi
			ng:
	</t>		</t>
	<t>		<ul spacing="normal">
	<list style="symbols">		<li>Removes the SDP dcmap attribute and SDP dcsa attributes
	<t>		associated with the closed data channel. Once the endpoint
	removes the SDP dcmap attribute and SDP dcsa attributes associated with the c		receives a successful answer, the SCTP stream identifier value can
	losed data channel. Once the endpoint receives a successful answer, the SCTP str		later be used for a new data channel (negotiated using either SCTP
	eam identifier value can later be used for a new data channel (negotiated using		or the offer/answer mechanism), or
	DCTP or using the offer/answer mechanism); or</t>		</li>
	<t>after a reset has been		<li>After a reset has been performed, reuses the SCTP stream used fo
	performed re-uses the SCTP stream used for the closed data channel for a new da		r the closed data channel for a new data channel, following the procedure in <xr
	ta channel, using the procedures in <xref target="opendc"/>. The offerer SHALL u		ef target="opendc"/>. The offerer <bcp14>SHALL</bcp14> use a different SDP dcmap
	se a different SDP dcmap attribute value for the data channel using the same SCT		attribute value for the data channel using the same SCTP stream.
	P stream.		</li>
			</ul>
			</section>
			</section>
			<section anchor="various_SDP_OA_considerations">
			<name>Various SDP Offer/Answer Considerations</name>
			<t>An SDP offer or answer has no "a=dcmap:" attributes but has "a=dc
			sa:" attributes:
			</t>
			<ul spacing="normal">
			<li>This is considered an error case. In this case, the receiver o
			f such an
			SDP offer or answer <bcp14>MUST</bcp14> discard the "a=dcsa:" attrib
			utes.
			</li>
			</ul>
			<t>An SDP offer or answer has an "a=dcsa:" attribute whose subprotoc
			ol attribute
			is unknown:
			</t>
			<ul spacing="normal">
			<li>The receiver of such an SDP offer or answer <bcp14>SHOULD</bcp
			14> ignore this
			entire "a=dcsa:" attribute line.
			</li>
			</ul>
			<t>An SDP offer or answer has an "a=dcsa:" attribute whose subprotoc
			ol attribute
			is known but whose subprotocol attribute semantic is not known for the
			data channel transport case:
			</t>
			<ul spacing="normal">
			<li>The receiver of such an SDP offer or answer <bcp14>SHOULD</bcp
			14> ignore this
			entire "a=dcsa:" attribute line.
			</li>
			</ul>
			</section>
			</section>
			<section anchor="examples">
			<name>Examples</name>
	</t>		<t><xref target="example1"/> shows an example of an SDP offer and answer
	</list>		where the SDP answerer rejects the data channel
	</t>		with stream id 0 either for explicit reasons or because it does not
	</section>		understand the "a=dcmap:" attribute.
	<!-- Closing a Data Channel -->		As a result, the offerer will close the data channel created with the
	</section>		SDP offer/answer negotiation option.
	<section title="Various SDP Offer/Answer Considerations"		The SCTP association will still be set up over DTLS.
	anchor="various_SDP_OA_considerations">		At this point, the offerer or the answerer may use DCEP negotiation to open d
	<t>		ata
	<list>		channels.</t>
	<t>An SDP offer or answer has no
	"a=dcmap:" attributes but has "a=dcsa:" attributes.
	<list style="symbols">
	<t>This is consid
	ered an error case. In this case the receiver of such an
	SDP offer or answer MUST discard this "a=dcsa:" attributes.
	</t>
	</list>
	</t>
	<t>SDP offer or answer has an "a=
	dcsa" attribute, whose subprotocol attribute
	is unknown.
	<list style="symbols">
	<t>The receiver o
	f such an SDP offer or answer SHOULD ignore this
	entire "a=dcsa" attribute line.
	</t>
	</list>
	</t>
	<t>SDP offer or answer has an "a=
	dcsa" attribute, whose subprotocol attribute
	is known, but whose subprotocol attribute semantic is not known for the
	data channel transport case.
	<list style="symbols">
	<t>The receiver o
	f such an SDP offer or answer SHOULD ignore this
	entire "a=dcsa" attribute line.
	</t>
	</list>
	</t>
	</list>
	</t>
	</section>
	<!-- various SDP offer/answer ... -->
	</section>
	<!-- Procedures -->
	<section title="Examples" anchor="examples">
	<figure align="left" title="Example 1" anchor="example1">
	<artwork align="left"><![CDATA[
	SDP offer:
			<figure anchor="example1">
			<name>Example 1</name>
			<sourcecode name="example-1-sdp-offer" type="sdp"><![CDATA[
	m=application 10001 UDP/DTLS/SCTP webrtc-datachannel		m=application 10001 UDP/DTLS/SCTP webrtc-datachannel
	c=IN IP6 2001:db8::3		c=IN IP6 2001:db8::3
	a=max-message-size:100000		a=max-message-size:100000
	a=sctp-port:5000		a=sctp-port:5000
	a=setup:actpass		a=setup:actpass
	a=fingerprint:SHA-1 \		a=fingerprint:SHA-1 \
	4A:AD:B9:B1:3F:82:18:3B:54:02:12: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
	a=tls-id:abc3de65cddef001be82		a=tls-id:abc3de65cddef001be82
	a=dcmap:0 subprotocol="bfcp";label="bfcp"		a=dcmap:0 subprotocol="bfcp";label="bfcp"]]></sourcecode>
			<sourcecode name="example-1-sdp-answer" type="sdp"><![CDATA[
	SDP answer:
	m=application 10002 UDP/DTLS/SCTP webrtc-datachannel		m=application 10002 UDP/DTLS/SCTP webrtc-datachannel
	c=IN IP6 2001:db8::1		c=IN IP6 2001:db8::1
	a=max-message-size:100000		a=max-message-size:100000
	a=sctp-port:5002		a=sctp-port:5002
	a=setup:passive		a=setup:passive
	a=fingerprint:SHA-1 \		a=fingerprint:SHA-1 \
	5B:AD:67:B1:3E:82:AC:3B:90:02:B1:DF:12:5D:CA:6B:3F:E5:54:FA		5B:AD:67:B1:3E:82:AC:3B:90:02:B1:DF:12:5D:CA:6B:3F:E5:54:FA
	a=tls-id:dcb3ae65cddef0532d42		a=tls-id:dcb3ae65cddef0532d42]]></sourcecode> </figure>
	]]></artwork>
	</figure>
	<t>In the example in <xref target="example1"/> the SDP an
	swerer rejected the data channel
	with stream id 0 either for explicit reasons or because it does not
	understand the "a=dcmap:" attribute.
	As a result the offerer will close the data channel created with the
	SDP offer/answer negotiation option.
	The SCTP association will still be setup over DTLS.
	At this point the offerer or the answerer may use DCEP negotiation to open da
	ta
	channels.</t>
	<figure align="left" title="Example 2" anchor="example2">
	<artwork align="left"><![CDATA[
	SDP offer:
			<t><xref target="example2"/> shows an example of an SDP offer and answer
			where the SDP offer contains data channels for BFCP and
			MSRP subprotocols. The SDP answer rejects BFCP and accepts MSRP.
			So, the offerer closes the data channel for BFCP, and both the offerer
			and the answerer may start using the MSRP data channel
			(after the SCTP association is set&nbsp;up).
			The data channel with stream id 0 is free and can be used for future
			DCEP or SDP offer/answer negotiation.</t>
			<figure anchor="example2">
			<name>Example 2</name>
			<sourcecode name="example-2-sdp-offer" type="sdp"><![CDATA[
	m=application 10001 UDP/DTLS/SCTP webrtc-datachannel		m=application 10001 UDP/DTLS/SCTP webrtc-datachannel
	c=IN IP4 192.0.2.1		c=IN IP4 192.0.2.1
	a=max-message-size:100000		a=max-message-size:100000
	a=sctp-port:5000		a=sctp-port:5000
	a=setup:actpass		a=setup:actpass
	a=fingerprint:SHA-1 \		a=fingerprint:SHA-1 \
	4A:AD:B9:B1:3F:82:18:3B:54:02:12: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
	a=tls-id:abc3de65cddef001be82		a=tls-id:abc3de65cddef001be82
	a=dcmap:0 subprotocol="bfcp";label="bfcp"		a=dcmap:0 subprotocol="bfcp";label="bfcp"
	a=dcmap:2 subprotocol="msrp";label="msrp"		a=dcmap:2 subprotocol="msrp";label="msrp"
	a=dcsa:2 accept-types:message/cpim text/plain		a=dcsa:2 accept-types:message/cpim text/plain
	a=dcsa:2 path:msrp://alice.example.com:10001/2s93i93idj;dc		a=dcsa:2 path:msrp://alice.example.com:10001/2s93i93idj;dc]]></sourcecode>
			<sourcecode name="example-2-sdp-answer" type="sdp"><![CDATA[
	SDP answer:
	m=application 10002 UDP/DTLS/SCTP webrtc-datachannel		m=application 10002 UDP/DTLS/SCTP webrtc-datachannel
	c=IN IP4 192.0.2.2		c=IN IP4 192.0.2.2
	a=max-message-size:100000		a=max-message-size:100000
	a=sctp-port:5002		a=sctp-port:5002
	a=setup:passive		a=setup:passive
	a=fingerprint:SHA-1 \		a=fingerprint:SHA-1 \
	5B:AD:67:B1:3E:82:AC:3B:90:02:B1:DF:12:5D:CA:6B:3F:E5:54:FA		5B:AD:67:B1:3E:82:AC:3B:90:02:B1:DF:12:5D:CA:6B:3F:E5:54:FA
	a=tls-id:dcb3ae65cddef0532d42		a=tls-id:dcb3ae65cddef0532d42
	a=dcmap:2 subprotocol="msrp";label="msrp"		a=dcmap:2 subprotocol="msrp";label="msrp"
	a=dcsa:2 accept-types:message/cpim text/plain		a=dcsa:2 accept-types:message/cpim text/plain
	a=dcsa:2 path:msrp://bob.example.com:10002/si438dsaodes;dc		a=dcsa:2 path:msrp://bob.example.com:10002/si438dsaodes;dc]]></sourcecode> </f
	]]></artwork>		igure>
	</figure>
	<t>In the example in <xref target="example2"/> the SDP of		<t>The example in <xref target="example3"/> is a continuation of the examp
	fer contains data channels for BFCP		le in <xref target="example2"/>.
	(Binary Floor Control Protocol) and		The SDP offerer now removes the MSRP data channel with stream id 2
	MSRP subprotocols. The SDP answer rejected BFCP and accepted MSRP.		but opens a new MSRP data channel with stream id 4.
	So, the offerer closes the data channel for BFCP and both offerer		The answerer accepts the entire offer.
	and answerer may start using the MSRP data channel		As a result, the offerer closes the previously negotiated MSRP-related data c
	(after the SCTP association is set up).		hannel,
	The data channel with stream id 0 is free and can be used for future		and both the offerer and the answerer may start using the new MSRP-related da
	DCEP or SDP offer/answer negotiation.</t>		ta
	<t>Continuing the example in <xref target="example2"/>.</		channel.</t>
	t>
	<figure align="left" title="Example 3" anchor="example3">
	<artwork align="left"><![CDATA[
	Subsequent SDP offer:
			<figure anchor="example3">
			<name>Example 3</name>
			<sourcecode name="example-3-sdp-offer" type="sdp"><![CDATA[
	m=application 10001 UDP/DTLS/SCTP webrtc-datachannel		m=application 10001 UDP/DTLS/SCTP webrtc-datachannel
	c=IN IP4 192.0.2.1		c=IN IP4 192.0.2.1
	a=max-message-size:100000		a=max-message-size:100000
	a=sctp-port:5000		a=sctp-port:5000
	a=setup:actpass		a=setup:actpass
	a=fingerprint:SHA-1 \		a=fingerprint:SHA-1 \
	4A:AD:B9:B1:3F:82:18:3B:54:02:12: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
	a=tls-id:abc3de65cddef001be82		a=tls-id:abc3de65cddef001be82
	a=dcmap:4 subprotocol="msrp";label="msrp"		a=dcmap:4 subprotocol="msrp";label="msrp"
	a=dcsa:4 accept-types:message/cpim text/plain		a=dcsa:4 accept-types:message/cpim text/plain
	a=dcsa:4 path:msrp://alice.example.com:10001/2s93i93idj;dc		a=dcsa:4 path:msrp://alice.example.com:10001/2s93i93idj;dc]]></sourcecode>
			<sourcecode name="example-3-sdp-answer" type="sdp"><![CDATA[
	Subsequent SDP answer:
	m=application 10002 UDP/DTLS/SCTP webrtc-datachannel		m=application 10002 UDP/DTLS/SCTP webrtc-datachannel
	c=IN IP4 192.0.2.2		c=IN IP4 192.0.2.2
	a=max-message-size:100000		a=max-message-size:100000
	a=sctp-port:5002		a=sctp-port:5002
	a=setup:passive		a=setup:passive
	a=fingerprint:SHA-1 \		a=fingerprint:SHA-1 \
	5B:AD:67:B1:3E:82:AC:3B:90:02:B1:DF:12:5D:CA:6B:3F:E5:54:FA		5B:AD:67:B1:3E:82:AC:3B:90:02:B1:DF:12:5D:CA:6B:3F:E5:54:FA
	a=tls-id:dcb3ae65cddef0532d42		a=tls-id:dcb3ae65cddef0532d42
	a=dcmap:4 subprotocol="msrp";label="msrp"		a=dcmap:4 subprotocol="msrp";label="msrp"
	a=dcsa:4 accept-types:message/cpim text/plain		a=dcsa:4 accept-types:message/cpim text/plain
	a=dcsa:4 path:msrp://bob.example.com:10002/si438dsaodes;dc		a=dcsa:4 path:msrp://bob.example.com:10002/si438dsaodes;dc]]></sourcecode> </f
	]]></artwork>		igure>
	</figure>		</section>
	<t>The example in <xref target="example3"/> is a continua		<section anchor="sec-cons">
	tion of the example in <xref target="example2"/>.		<name>Security Considerations</name>
	The SDP offerer now removes the MSRP data channel with stream id 2,		<t>This document specifies new SDP attributes used in the negotiation of d
	but opens a new MSRP data channel with stream id 4.		ata channel parameters. </t>
	The answerer accepts the entire offer.		<t>
	As a result the offerer closes the earlier negotiated MSRP related data chann		These parameters are negotiated as part of opening an SCTP channel over DTLS as
	el		specified in <xref target="RFC8841"/>. Each
	and both offerer and answerer may start using new the MSRP related data chann		subprotocol may come with its own security considerations that need to be docume
	el.</t>		nted as part of the subprotocol definition.
	</section>		Otherwise, this document does not add any security considerations to those speci
	<!-- Examples -->		fied in <xref target="RFC8841"/>.
	<section title="Security Considerations" anchor="sec-cons">		</t>
	<t>This document specifies new SDP attributes used in the		<t>Such error cases as the use of unknown parameter values or violations
	negotiation of the DATA channel parameters. </t>		of the odd/even rule (<xref target="id_mgmt"/>) <bcp14>MUST</bcp14>
	<t>		be handled by closing the corresponding data channel.</t>
	These parameter are negotiated as part of opening a SCTP channel over DTLS as sp		</section>
	ecified in <xref target="I-D.ietf-mmusic-sctp-sdp"/>. Each		<section anchor="IANA">
	subprotocol may come with it’s own security considerations that need to be docum		<name>IANA Considerations</name>
	ented as part of the subprotocol definition.		<section anchor="IANA_subproto_ids">
	Otherwise this document does not add any security considerations to the ones spe		<name>Subprotocol Identifiers</name>
	cified in <xref target="I-D.ietf-mmusic-sctp-sdp"/>		<t>Registration of new subprotocol identifiers is performed using the ex
	</t>		isting IANA
	<t>Error cases like the use of unknown parameter values o
	r violation the odd/even rule MUST
	be handled by closing the corresponding Data Channel.</t>
	</section>
	<section title="IANA Considerations" anchor="IANA">
	<section title="Subprotocol Identifiers" anchor="IANA_sub
	proto_ids">
	<t>Registration of new subprotocol identifiers is
	performed using the existing IANA
	"WebSocket Subprotocol Name Registry" table.</t>		"WebSocket Subprotocol Name Registry" table.</t>
	<t>The following text should be added following t		<t>The following text has been added below the title of the table.</t>
	he title of the table.</t>		<t>"This table also includes subprotocol identifiers specified for usage
	<t>"This table also includes subprotocol identifi		within a
	ers specified for usage within a
	WebRTC data channel."</t>		WebRTC data channel."</t>
	<t>The following reference should be added to und		<t>This document (RFC 8864) has been added to the "Reference" list for
	er the heading reference:		the registry.</t>
	"RFC XXXX".</t>		<t>This document assigns no new values to this table.</t>
	<t>This document assigns no new values to this ta		<t>A subprotocol may simultaneously be defined for data channel transpor
	ble.</t>		t
	<t>A subprotocol may simultaneously be defined fo		and for WebSocket transport.
	r data channel transport		In such a case, the "Subprotocol Definition" and "Reference" cells in the
	and for Websocket transport.
	In such a case the "Subprotocol Definition" and "Reference" cells in the
	subprotocol's row of the IANA "WebSocket Subprotocol Name Registry" table sh ould		subprotocol's row of the IANA "WebSocket Subprotocol Name Registry" table sh ould
	contain two entries.		contain two entries.
	One entry in each of these cells should refer to the Websocket related		One entry in each of these cells should refer to the WebSocket-related
	subprotocol specification, and the other entry should refer to the data		subprotocol specification, and the other entry should refer to the
	channel related subprotocol specification.		data-channel-related subprotocol specification.
	</t>		</t>
	<t>NOTE to RFC Editor: Please replace "XXXX" with		</section>
	the number of this RFC.</t>		<section>
	</section>		<name>New SDP Attributes</name>
	<section title="New SDP Attributes">		<section anchor="IANA-reg-dcmap">
	<section title="dcmap" anchor="IANA-reg-dcmap">		<name>dcmap</name>
	<t>NOTE to RFC Editor: Please replace "XX		<t>This document defines a new SDP media-level attribute, "a=dcmap:",
	XX" with the number of this RFC.</t>		as follows:
	<t>This document defines a new SDP media-		</t>
	level attribute "a=dcmap:" as follows:		<table anchor="dcmap-iana">
	</t>		<name>New "a=dcmap:" Attribute</name>
	<texttable title="">		<thead>
	<ttcol align="left" width="35%"/>		<tr>
	<ttcol align="left" width="65%"/>		<th colspan="2" align="center">"a=dcmap:"</th>
	<c>Contact name:</c>		</tr>
	<c>IESG</c>		</thead>
	<c>Contact email:</c>		<tbody>
	<c>iesg@ietf.org</c>		<tr>
	<c>Attribute name:</c>		<td align="left">Contact name</td>
	<c>dcmap</c>		<td align="left">IESG</td>
	<c>Attribute syntax:</c>		</tr>
	<c>As per <xref target="dcmap-att		<tr>
	r-definition"/>		<td align="left">Contact email</td>
	</c>		<td align="left">iesg@ietf.org</td>
	<c>Attribute semantics:</c>		</tr>
	<c>As per <xref target="dcmap-att		<tr>
	r-definition"/>		<td align="left">Attribute name</td>
	</c>		<td align="left">dcmap</td>
	<c>Usage level:</c>		</tr>
	<c>media</c>		<tr>
	<c>Charset dependent:</c>		<td align="left">Attribute syntax</td>
	<c>No</c>		<td align="left">As per <xref target="dcmap-attr-definition"/>
	<c>Purpose:</c>		</td>
	<c>Define data channel specific p		</tr>
	arameters</c>		<tr>
	<c>Appropriate values:</c>		<td align="left">Attribute semantics</td>
	<c>As per <xref target="dcmap-att		<td align="left">As per <xref target="dcmap-attr-definition"/>
	r-definition"/>		</td>
	</c>		</tr>
	<c>O/A procedures:</c>		<tr>
	<c>As per <xref target="section_p		<td align="left">Usage level</td>
	rocedures"/>		<td align="left">media</td>
	</c>		</tr>
	<c>Mux category:</c>		<tr>
	<c>SPECIAL. See <xref target="dcm		<td align="left">Charset dependent</td>
	ap-mux-category"/>		<td align="left">No</td>
	</c>		</tr>
	<c>Reference:</c>		<tr>
	<c>RFCXXXX</c>		<td align="left">Purpose</td>
	</texttable>		<td align="left">To define data-channel-specific parameters</td>
	</section>		</tr>
	<section title="dcsa" anchor="IANA-reg-dcsa">		<tr>
	<t>NOTE to RFC Editor: Please replace "XX		<td align="left">Appropriate values</td>
	XX" with the number of this RFC.</t>		<td align="left">As per <xref target="dcmap-attr-definition"/>
	<t>This document defines a new SDP media-		</td>
	level attribute "a=dcsa:" as follows:		</tr>
	</t>		<tr>
	<texttable title="">		<td align="left">O/A procedures</td>
	<ttcol align="left" width="35%"/>		<td align="left">SDP offer/answer procedures as per <xref target
	<ttcol align="left" width="65%"/>		="section_procedures"/>
	<c>Contact name:</c>		</td>
	<c>IESG</c>		</tr>
	<c>Contact email:</c>		<tr>
	<c>iesg@ietf.org</c>		<td align="left">Mux category</td>
	<c>Attribute name:</c>		<td align="left">SPECIAL. See <xref target="dcmap-mux-category"/
	<c>dcsa</c>		>
	<c>Attribute syntax:</c>		</td>
	<c>As per <xref target="dcsa-attr		</tr>
	ibute"/>		<tr>
	</c>		<td align="left">Reference</td>
	<c>Attribute semantics:</c>		<td align="left">RFC 8864</td>
	<c>As per <xref target="dcsa-attr		</tr>
	ibute"/>		</tbody>
	</c>		</table>
	<c>Usage level:</c>		</section>
	<c>media</c>		<section anchor="IANA-reg-dcsa">
	<c>Charset dependent:</c>		<name>dcsa</name>
	<c>No</c>		<t>This document defines a new SDP media-level attribute, "a=dcsa:", a
	<c>Purpose:</c>		s follows:
	<c>Define data channel subprotoco		</t>
	l specific attributes</c>
	<c>Appropriate values:</c>
	<c>As per <xref target="dcsa-attr
	ibute"/>
	</c>
	<c>O/A procedures:</c>
	<c>As per <xref target="section_p
	rocedures"/>
	</c>
	<c>Mux category:</c>
	<c>SPECIAL. See <xref target="dcs
	a-mux-category"/>
	</c>
	<c>Reference:</c>
	<c>RFCXXXX</c>
	</texttable>
	</section>
	</section>
	</section>
	<section title="Contributors">
	<t>Juergen Stoetzer-Bradler co-authored this document.</t
	>
	</section>
	<section title="Acknowledgments">
	<t>The authors wish to acknowledge the borrowing of ideas
	from other
	internet drafts by Salvatore Loreto, Gonzalo Camarillo, Peter Dunkley
	and Gavin Llewellyn, and to thank Flemming Andreasen, Christian Groves,
	Gunnar Hellstrom, Paul Kyzivat, Jonathan Lennox,
	Uwe Rauschenbach and Roman Shpount for their invaluable comments.</t>
	<t>Special thanks to Christer Holmberg for helping finish
	the document and cleaning the SDP offer/answer section.</t>
	</section>
	<section title="CHANGE LOG">
	<section title="Changes against 'draft-ietf-mmusic-data-c
	hannel-sdpneg-15'">
	<t>
	<list style="symbols">
	<t>Editorial changes separate se
	ctions for offer/answer procedures.</t>
	<t>Update security section.</t>
	</list>
	</t>
	</section>
	<section title="Changes against 'draft-ietf-mmusic-data-c
	hannel-sdpneg-14'">
	<t>
	<list style="symbols">
	<t>Change "dtls-id" to "tls-id" a
	nd assign 20 octet long values</t>
	<t>Remove of RFC4566bis draft fro
	m list of normative references.
	</t>
	</list>
	</t>
	</section>
	<section title="Changes against 'draft-ietf-mmusic-data-c
	hannel-sdpneg-12'">
	<t>
	<list style="symbols">
	<t>Modification of Keith's addres
	s information.
	</t>
	</list>
	</t>
	</section>
	<section title="Changes against 'draft-ietf-mmusic-data-c
	hannel-sdpneg-11'">
	<t>
	<list style="symbols">
	<t>dcmap-stream-id syntax change
	to limit size to 5 digits.
	</t>
	<t>Add missing 'x' prefix to quot
	ed-visible syntax.
	</t>
	<t>Align SDP offerer and answerer
	handling when both max-retr and max-time are present.
	</t>
	<t>Use of TEST-NET-1 ip addresses
	in examples.
	</t>
	<t>Add missing a=dtls-id in one e
	xample.
	</t>
	</list>
	</t>
	</section>
	<section title="Changes against 'draft-ietf-mmusic-data-c
	hannel-sdpneg-10'">
	<t>
	<list style="symbols">
	<t>Removal of the "a=connection"
	attribute lines from all SDP examples.
	</t>
	</list>
	</t>
	</section>
	<section title="Changes against 'draft-ietf-mmusic-data-c
	hannel-sdpneg-09'">
	<t>
	<list style="symbols">
	<t>In the introduction:
	<list style="symbols">
	<t>Replacement of
	the sentence "The RTCWeb working group has defined the concept of
	bi-directional data channels running on top of SCTP/DTLS (SCTP over the Dat
	agram
	Transport Layer Security protocol)" with "The RTCWeb working group has defi
	ned the
	concept of bi-directional data channels running on top of the Stream Contro
	l
	Transmission Protocol (SCTP)".
	</t>
	<t>Addition of fo
	llowing sentences to the second paragraph: "These procedures are
	based on generic SDP offer/answer negotiation rules for SCTP
	based media transport as specified in <xref target="I-D.ietf-mmusic-sctp-sd
	p"/> for
	the SDP "m" line proto values UDP/DTLS/SCTP and TCP/DTLS/SCTP.
	In the future, data channels could be defined over other SCTP based protoco
	ls, such as
	SCTP over IP. However, corresponding potential other "m" line proto values
	are not
	considered in this document."
	</t>
	</list>
	</t>
	<t>Replacement of "DTLS connectio
	n" with "DTLS association" throughout the document.
	</t>
	<t>In sections <xref target="dcma
	p-mux-category"/> and
	<xref target="dcsa-mux-category"/> removal of the sentences "This document al
	so
	does not specify multiplexing rules for this attribute for SCTP or
	SCTP/DTLS proto values".
	</t>
	<t>In the text related to "Subseq
	uent SDP answer" in section
	<xref target="various_SDP_OA_considerations"/> replacement of "The DTLS/SCTP
	association remains open ..." with "The SCTP association remains open ...".
	</t>
	<t>In the text after the second S
	DP answer in section
	<xref target="examples"/> replacement of "... (after SCTP/DTLS association is
	setup)"
	with "... (after the SCTP association is set up)".
	</t>
	<t>Addition of draft-ietf-mmusic-
	dtls-sdp to the list of informative
	references.
	</t>
	<t>Addition of "a=dtls-id" attrib
	ute lines to the SDP offer/answer examples in
	<xref target="examples"/>.
	</t>
	</list>
	</t>
	</section>
	<section title="Changes against 'draft-ietf-mmusic-data-c
	hannel-sdpneg-08'">
	<t>
	<list style="symbols">
	<t>Addition of definition of "dat
	a channel subprotocol" to
	<xref target="terminology"/> as proposed on the MMUSIC list,
	https://www.ietf.org/mail-archive/web/mmusic/current/msg15827.html.
	</t>
	<t>Addition of RFC4566bis draft
	to list of normative references.
	</t>
	<t>Updates of tables in <xref tar
	get="IANA-reg-dcmap"/> and
	<xref target="IANA-reg-dcsa"/> as per section 8.2.4
	of RFC4566bis draft.
	</t>
	<t>Addition of new "new-usage-lev
	el">.
	</t>
	</list>
	</t>
	</section>
	<section title="Changes against 'draft-ietf-mmusic-data-c
	hannel-sdpneg-07'">
	<t>
	<list style="symbols">
	<t>Addition of two new paragraphs
	to <xref target="dcsa-attribute"/> regarding
	subprotocol attribute relationship with transport protocol.
	</t>
	<t>Addition of a note to <xref ta
	rget="IANA_subproto_ids"/> regarding subprotocols
	simultaneously defined for data channel and Websocket usage.
	</t>
	<t>Addition of two further SDP of
	fer/answer considerations to
	<xref target="various_SDP_OA_considerations"/> regarding unknown subprotocol
	attributes and known subprotocol attributes with unknown data channel transp
	ort
	related semantic.
	</t>
	</list>
	</t>
	</section>
	<section title="Changes against 'draft-ietf-mmusic-data-c
	hannel-sdpneg-06'">
	<t>
	<list style="symbols">
	<t>Changes addressing Christian G
	roves's WGLC review comments raised in
	http://www.ietf.org/mail-archive/web/mmusic/current/msg15357.html and
	http://www.ietf.org/mail-archive/web/mmusic/current/msg15359.html.
	</t>
	</list>
	</t>
	</section>
	<section title="Changes against 'draft-ietf-mmusic-data-c
	hannel-sdpneg-05'">
	<t>
	<list style="symbols">
	<t>In IANA registration <xref tar
	get="IANA-reg-dcmap"/> and
	<xref target="IANA-reg-dcsa"/> replacement of contact name and e-mail address
	with "MMUSIC Chairs" and "mmusic-chairs@ietf.org".
	</t>
	<t>In <xref target="dcsa-attribut
	e"/> replacement of "Thus in the example above, the
	original attribute line "a=accept-
	types:text/plain" is represented by the attribute line "a=dcsa:2
	accept-types:text/plain", which specifies that this instance of MSRP
	being transported on the SCTP association using the data channel with
	stream id 2 accepts plain text files." with "... which specifies that this
	instance of the MSRP subprotocol being transported ...".
	</t>
	<t>The last paragraph of <xref ta
	rget="dcsa-attribute"/> started with
	"Note: This document does not provide a complete specification ...".
	Removal of "Note:" and move of this paragraph to the introduction in
	<xref target="introduction"/> as last paragraph.
	</t>
	<t>
	<xref target="prot_att"/>
	's headline was "Subprotocol Specific Attributes".
	Change of this headline to "Other Media Level Attributes" and adaptations of
	the first
	paragraph of this section and the first paragraph of <xref target="dcsa-attri
	bute"/>
	in order to clarify that not only those attributes may be
	encapsulated in a "dcsa" attribute, which are specifically defined for the
	subprotocol, but that also other attributes may be encapsulated if
	they are related to the specific subprotocol instance.
	</t>
	<t>Move of the last but one parag
	raph of <xref target="dcsa-attribute"/> starting with
	"The same syntax applies to ..." right in front of the formal syntax definiti
	on of the
	"dcsa" attribute.
	</t>
	<t>Modifications of the text in <
	xref target="dcmap-mux-category"/> and
	<xref target="dcsa-mux-category"/> in order not to explicitly restrict usage
	of the
	"a=dcmap:" and "a=dcsa:" attributes to "m" lines with proto values "UDP/DTLS/
	SCTP"
	or "TCP/DTLS/SCTP".
	</t>
	</list>
	</t>
	</section>
	<section title="Changes against 'draft-ietf-mmusic-data-c
	hannel-sdpneg-04'">
	<t>
	<list style="symbols">
	<t>In <xref target="subprotocol-p
	arameter"/> the first (and only) paragraph was
	"The 'subprotocol' parameter indicates which protocol the
	client expects to exchange via the channel.
	'subprotocol' is an optional parameter.
	If the 'subprotocol' parameter is not present, then its value
	defaults to the empty string."
	Replacement of this paragraph with following two paragraphs:
	<list style="symbols">
	<t> The 'subproto
	col' parameter indicates which protocol the
	client expects to exchange via the channel.
	This parameter maps to the 'Protocol' parameter defined in
	<xref target="I-D.ietf-rtcweb-data-protocol"/>.
	<xref target="IANA_subproto_ids"/> specifies how new subprotocol parameter
	values are registered.
	'subprotocol' is an optional parameter.
	If the 'subprotocol' parameter is not present, then its value
	defaults to the empty string.
	</t>
	<t>Note: The empt
	y string MAY also be explicitly used as 'subprotocol' value,
	such that 'subprotocol=""' is equivalent to the 'subprotocol' parameter no
	t being
	present at all. <xref target="I-D.ietf-rtcweb-data-protocol"/> allows the
	DATA_CHANNEL_OPEN message's 'subprotocol' value to be an empty string.
	</t>
	</list>
	</t>
	<t>Addition of <xref target="I-D.
	ietf-mmusic-sdp-mux-attributes"/>
	to list the of normative references.
	</t>
	<t>Addition of dcmap attribute sp
	ecific IANA registration
	<xref target="IANA-reg-dcmap"/>.
	</t>
	<t>Addition of dcsa attribute spe
	cific IANA registration
	<xref target="IANA-reg-dcsa"/>.
	</t>
	<t>Addition of new <xref target="
	dcmap-mux-category"/> describing the mux category
	of the dcmap SDP attribute. This section and the new "a=dcsa:" attribute rel
	ated
	mux category section are similar to the "Mux Category" sections of
	the "a=sctp-port:" and "a=max-message-size:" attributes in
	<xref target="I-D.ietf-mmusic-sctp-sdp"/>.
	</t>
	<t>Addition of new <xref target="
	dcsa-mux-category"/> describing the mux category
	of the dcsa SDP attribute.
	</t>
	</list>
	</t>
	</section>
	<section title="Changes against 'draft-ietf-mmusic-data-c
	hannel-sdpneg-03'">
	<t>
	<list style="symbols">
	<t>In <xref target="introduction"
	/> replacement of
	"RTCWeb leaves it open for other applications to use data channels and its in
	-band
	DCEP or out-of-band non-DCEP protocols for creating them" with
	"... to use data channels and its in-band DCEP or other in-band or out-of-ban
	d
	protocols for creating them".
	Additionally replacement of
	"In particular, the SDP offer generated by the application
	includes no channel-specific information" with
	"... generated by the RTCweb data channel stack includes
	no channel-specific information".
	</t>
	<t>Move of former section 5 ("Dat
	a Channels") to new
	<xref target="generic-out-of-band-aspects"/> and removal of JavaScript API sp
	ecific
	discussions from this moved text (like mentioning of data channel stack speci
	fic
	states). Therefore former section 6 ("SDP Offer/Answer Negotiation") is now
	<xref target="sdp_synt"/>.
	</t>
	<t>In <xref target="sdp_synt"/>:
	<list style="symbols">
	<t>Relacement of
	<xref target="sdp_synt"/>'s
	first paragraph
	"This section defines a method of non-DCEP negotiation by which two
	clients can negotiate data channel-specific and subprotocol-specific
	parameters, using the out-of-band SDP offer/answer exchange. This
	SDP extension can only be used with the SDP offer/answer model." with
	"This section defines an SDP extension by which
	two clients can negotiate data channel-specific and subprotocol-specific
	parameters without using DCEP <xref target="I-D.ietf-rtcweb-data-protocol"/
	>.
	This SDP extension only defines usage in the context of SDP offer/answer."
	</t>
	<t>Addition of ne
	w paragraph:
	"<xref target="generic-out-of-band-aspects"/> provides information how data
	channels
	work in general and especially summarizes some key aspects, which should be
	considered for the negotiation of data channels if DCEP is not used."
	</t>
	</list>
	</t>
	<t>In <xref target="subsec-sdp-at
	tr-for-dc-par-neg"/> replacement of "The intention of
	exchanging these attributes is to create data channels on both the peers with
	the same
	set of attributes without actually using the DCEP
	<xref target="I-D.ietf-rtcweb-data-protocol"/>" with "The intention in exchan
	ging
	these attributes is to create, on two peers, without use of DCEP
	<xref target="I-D.ietf-rtcweb-data-protocol"/>,
	matched pairs of oppositely directed data channels having the same set of att
	ributes".
	</t>
	<t>In <xref target="max-retr-para
	m-definition"/> replacement of "The 'max-retr'
	parameter indicates the maximal number a user message will be retransmitted"
	with "The
	'max-retr' parameter indicates the maximal number of times a user message wil
	l
	be retransmitted".
	</t>
	<t>In <xref target="id_mngt"/> re
	placement of "However, an SDP offer/answer exchange
	MUST NOT be initiated if the associated SCTP stream is already negotiated via
	DCEP"
	with "However, an SCTP stream MUST NOT be referenced in a dcmap or dcsa
	attribute of an SDP offer/answer exchange if the associated SCTP stream has a
	lready
	been negotiated via DCEP".
	</t>
	<t>In the examples in <xref targe
	t="examples"/> addition of the previously missing
	colons to the "a=sctp-port" attribute lines.
	</t>
	</list>
	</t>
	</section>
	<section title="Changes against 'draft-ietf-mmusic-data-c
	hannel-sdpneg-02'">
	<t>
	<list style="symbols">
	<t>Move of reference draft-ietf-r
	tcweb-jsep from the list of normative
	references to the list of informative references. Remover in -07 since not ref
	erenced</t>
	<t>Addition of IANA SDP parameter
	s to the list of informative
	references
	and addition of following two sentences to the first paragraph after the ABNF
	definition: "Note however that not all SDP attributes are suitable
	as "a=dcsa:" parameter. IANA SDP parameters contains
	the lists of IANA registered session and media level or
	media level only SDP attributes."</t>
	<t>In the introduction replacemen
	t of last sentence
	"This document defines SDP-based out-of-band negotiation procedures
	to establish data channels for transport of well-defined subprotocols"
	with
	"This document defines SDP offer/answer negotiation procedures
	to establish data channels for transport of well-defined subprotocols,
	to enable out-of-band negotiation".
	</t>
	<t>Throughout the document replac
	ement of "external negotiation" with
	"SDP offer/answer negotiation" and removal of term "external negotiation" from
	the
	terminology list in <xref target="terminology"/>.</t>
	<t> Throughout the document repla
	cement of "internal negotiation" with
	"DCEP" and removal of terms "internal negotiation" and "in-band negotiation"
	from the terminology list in <xref target="terminology"/>.</t>
	<t>Addition of "SCTP Stream Seque
	nce Number (SSN)" to the list of terms.</t>
	<t>In <xref target="id_mngt"/> re
	placement of sentence
	"However, a single stream is managed using one method at a time." with
	"However, an SDP offer/answer exchange MUST NOT be initiated
	if the associated SCTP stream is already negotiated via DCEP".</t>
	<t>In <xref target="param_negotia
	tion"/> replacement of sentence
	"By definition max-retr and max-time are mutually exclusive, so only one of
	them can be present in a=dcmap" with
	"By definition max-retr and max-time are mutually exclusive,
	so aBoth MUST NOT be present in a=dcmap".</t>
	<t>Move of reference <xref target
	="WebRtcAPI"/> from list of normative references
	to list of informative references.</t>
	<t>Removal of almost all text par
	ts, which discussed JavaScript or other API specific
	aspects. Such API specific aspects were mainly discussed in sub-sections of Se
	ction 5
	and <xref target="sdp_synt"/>
	of draft-ietf-mmusic-data-channel-sdpneg-02.</t>
	</list>
	</t>
	</section>
	<section title="Changes against 'draft-ietf-mmusic-data-c
	hannel-sdpneg-01'">
	<t>
	<list style="symbols">
	<t>New <xref target="appl_stateme
	nt"/> regarding applicability to
	SDP offer/answer only.</t>
	<t>Addition of new <xref target="
	IANA_subproto_ids"/> "Subprotocol identifiers" as
	subsection of the "IANA Considerations" related <xref target="IANA"/>.
	Also removal of the temporary note
	"To be completed. As [I-D.ietf-rtcweb-data-protocol] this document should re
	fer to
	IANA's WebSocket Subprotocol Name Registry defined in <xref target="RFC6455"/
	>"</t>
	<t> In <xref target="param_negoti
	ation"/>:
	<list style="symbols">
	<t>In the first p
	aragraph
	replacement of the sentence "If an SDP offer
	contains both of these parameters then such an SDP offer will be rejected."
	with "If
	an SDP offer contains both of these parameters then the receiver of such an
	SDP
	offer MUST reject the SDP offer." </t>
	<t>In the second
	paragraph
	capitalization of "shall" and "may" such that both sentences now read:
	"The SDP answer SHALL echo the same subprotocol, max-retr, max-time,
	ordered parameters, if those were present in the offer, and MAY include
	a label parameter. They MAY appear in any order, which could be
	different from the SDP offer, in the SDP answer."</t>
	<t>In the third p
	aragraph
	replacement of the sentence
	"The same information MUST be replicated without changes in any subsequent
	offer or
	answer, as long as the data channel is still opened at the time of offer or
	answer
	generation." with
	"When sending a subsequent offer or an answer, and for as long as the data
	channel
	is still open, the sender MUST replicate the same information.".</t>
	</list>
	</t>
	<t>In <xref target="param_negotia
	tion"/> the mapping of data channel types defined in
	<xref target="I-D.ietf-rtcweb-data-protocol"/> to the SDP "a=dcmap" attribute
	parameters were illustrated using example "a=dcmap" attribute lines.
	Replacement of these example "a=dcmap" attribute lines with just the "a=dcmap
	"
	attribute parameters being relevant for the channel type.</t>
	<t>In <xref target="various_SDP_O
	A_considerations"/> the description of bullet
	point "SDP offer has no a=dcmap attributes - Initial SDP offer:" was
	"Initial SDP offer: No data channel negotiated yet."
	Replacement of this description with
	"Initial SDP offer: No data channel is negotiated yet.
	The DTLS connection and SCTP association is
	negotiated and, if agreed, established as per
	<xref target="I-D.ietf-mmusic-sctp-sdp"/>."</t>
	<t>In <xref target="various_SDP_O
	A_considerations"/> in both bullet points related to
	"Subsequent SDP offer" and "Subsequent SDP answer" replacement of
	"All the externally negotiated data channels must be closed now." with
	"All the externally negotiated data channels are expected to be closed now.".
	</t>
	<t>In <xref target="ext_open"/>'s
	sixth paragraph
	replacement of the two occurrences of "must" with "MUST".</t>
	<t>In <xref target="dcmap-attr-de
	finition"/> in the definition of the ABNF rule
	"dcmap-opt" there was a comment saying that
	"Only maxretr-opt or maxtime-opt is present. Both MUST NOT be present."
	Removal of the second normative sentence and instead addition of following ne
	w
	paragraph to the end of this section:
	"Within an 'a=dcmap' attribute line's 'dcmap-opt' value only one
	'maxretr-opt' parameter or one 'maxtime-opt' parameter is present.
	Both MUST NOT be present."</t>
	<t>In <xref target="ordered-param
	-description"/> replacement of the first sentence
	"The 'ordered' parameter with value "true" indicates that DATA chunks in the
	channel
	MUST be dispatched to the upper layer by the receiver while preserving the or
	der."
	with
	"The 'ordered' parameter with value "true" indicates that the receiver MUST d
	ispatch
	DATA chunks in the data channel to the upper layer while preserving the order
	.".</t>
	<t>In <xref target="opendc"/>'s f
	irst paragraph replacement of the one occurrence of
	"must" with "..., it MUST wait until ...".</t>
	<t>In <xref target="close-dc"/>:
	<list style="symbols">
	<t>In the second
	paragraph replacement of "must" with "... whether this closing MUST
	in addition ..."</t>
	<t>In the third p
	aragraph replacement of the sentence
	"The port value for the "m" line SHOULD NOT be changed (e.g., to zero)
	when closing a data channel ..." with
	"The offerer SHOULD NOT change the port value for the "m" line (e.g., to ze
	ro) when
	closing a data channel ...".</t>
	<t>In the last bu
	t two paragraph replacement of the sentence
	"... then an SDP offer which excludes this closed data channel SHOULD be ge
	nerated."
	with
	"... then the client SHOULD generate an SDP offer which excludes this close
	d data
	channel.".</t>
	<t>In the last bu
	t one paragraph replacement of "must" with
	"The application MUST also close...".</t>
	</list>
	</t>
	<t>In <xref target="prot_att"/> a
	ddition of following note after the formal definition
	of the 'a=dcsa' attribute:
	"Note that the above reference to RFC 4566 defines were the
	attribute definition can be found;
	it does not provide any limitation on support of attributes
	defined in other documents in accordance with this attribute
	definition."</t>
	</list>
	</t>
	</section>
	<section title="Changes against 'draft-ietf-mmusic-data-c
	hannel-sdpneg-00'">
	<t>
	<list style="symbols">
	<t>In <xref target="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
	<xref target="I-D.ietf-rtcweb-data-channel"/>", and consistent usage
	of "data channel" in the remainder of the document including the
	document's headline."</t>
	<t>In Section 5 removal of follow
	ing note:
	'OPEN ISSUE: The syntax in <xref target="I-D.ietf-mmusic-sctp-sdp"/> may
	change as that document progresses. In particular we expect
	"webrtc-datachannel" to become a more general term.'</t>
	<t>Consistent usage of '"m" line'
	in whole document as per RFC4566.</t>
	<t>In <xref target="subsec-sdp-at
	tr-for-dc-par-neg"/>
	removal of the example dcmap attribute line
	'a=dcmap:2 subprotocol="bfcp";label="channel 2' as there are already
	four examples right after the ABNF rules in
	<xref target="dcmap-attr-definition"/>.
	Corresponding removal of following related note:
	"Note: This document does not provide a complete specification
	of how to negotiate the use of a WebRTC data channel to transport BFCP.
	Procedures specific to each subprotocol such as BFCP will be
	documented elsewhere. The use of BFCP is only an example of how
	the generic procedures described herein might apply to a specific
	subprotocol."</t>
	<t>In <xref target="subsec-sdp-at
	tr-for-dc-par-neg"/>
	removal of following note:
	"Note: This attribute is derived from attribute "webrtc-DataChannel",
	which was defined in old version 03 of the
	following draft, but which was removed along with any support for SDP
	external negotiation in subsequent versions:
	<xref target="I-D.ietf-mmusic-sctp-sdp"/>."</t>
	<t>Insertion of following new sen
	tence to the beginning of
	<xref target="dcmap-attr-definition"/>:
	"dcmap is a media level attribute having following ABNF syntax:"</t>
	<t>Insertion of new <xref target=
	"dcmap-stream-id-param-definition"/>
	containing the dcmap-stream-id specifying sentence, which previously
	was placed right before the formal ABNF rules.
	Removal of the sentence 'Stream is a mandatory
	parameter and is noted directly after the "a=dcmap:" attribute's
	colon' as this information is part of the ABNF specification.</t>
	<t>In <xref target="dcmap-attr-de
	finition"/> modification of the
	'ordering-value' values from "0" or "1" to "true" or "false".
	Corresponding text modifications in <xref target="ordered-param-description"/
	>.</t>
	<t>In <xref target="dcmap-attr-de
	finition"/> the ABNF definition of "quoted-string"
	referred to rule name "escaped-char", which was not defined.
	Instead a rule with name "escaped" was defined. Renamed that rule's name
	to "escaped-char".</t>
	<t>Insertion of a dedicated note
	right after the "a=dcmap:4" attribute example
	in <xref target="dcmap-attr-definition"/> regarding the non-printable
	"escaped-char" character within the "label" value.</t>
	<t>In <xref target="prot_att"/>'s
	second paragraph replacement of
	"sctp stream identifier" with "SCTP stream identifier".</t>
	<t>In first paragraph of <xref ta
	rget="id_mngt"/> replacement of first two sentences
	'For the SDP-based external negotiation described in this document,
	the initial offerer based "SCTP over DTLS" owns by convention the
	even stream identifiers whereas the initial answerer owns the odd stream
	identifiers. This ownership is invariant for the whole
	lifetime of the signaling session, e.g. it does not change if the
	initial answerer sends a new offer to the initial offerer.'
	with
	'If an SDP offer/answer exchange
	(could be the initial or a subsequent one)
	results in a UDP/DTLS/SCTP or TCP/DTLS/SCTP based media description being
	accepted, and if this SDP offer/answer exchange results in the
	establishment of a new SCTP association, then the SDP offerer owns the
	even SCTP stream ids of this new SCTP association and the answerer owns
	the odd SCTP stream identifiers.
	If this "m" line is removed from the signaling session (its port number
	set to zero), and if usage of this or of a new UDP/DTLS/SCTP or
	TCP/DTLS/SCTP based "m" line is renegotiated later on,
	then the even and odd SCTP stream identifier
	ownership is redetermined as well as described above.'</t>
	<t>In <xref target="opendc"/> the
	first action of an SDP answerer,
	when receiving an SDP offer, was described as
	"Applies the SDP offer. Note that the browser ignores data channel
	specific attributes in the SDP."
	Replacement of these two sentences with
	"Parses and applies the SDP offer. Note that the typical parser
	normally ignores unknown SDP attributes, which includes data
	channel related attributes."</t>
	<t>In <xref target="opendc"/> the
	second sentence of the third
	SDP answerer action was
	"Note that the browser is asked to create data
	channels with stream identifiers not "owned" by the agent.".
	Replacement of this sentence with
	"Note that the agent is asked to
	create data channels with SCTP stream identifiers
	contained in the SDP offer if the SDP offer is accepted."</t>
	<t>In <xref target="close-dc"/> t
	he third paragraph began with
	"A data channel can be closed by sending a new SDP offer which
	excludes the dcmap and dcsa attribute lines for the data channel.
	The port value for the m line SHOULD NOT be changed (e.g., to zero)
	when closing a data channel (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.
	If the answerer accepts the SDP offer then it MUST also exclude the
	corresponding attribute lines in the answer. ..."
	Replacement of this part with
	"The intention to close a data channel can be signaled
	by sending a new SDP offer which
	excludes the "a=dcmap:" and "a=dcsa:" attribute lines for the data channel.
	The port value for the "m" line SHOULD NOT be changed (e.g., to zero)
	when closing a data channel (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.
	If the answerer accepts the SDP offer then it MUST close those data channels
	whose "a=dcmap:" and "a=dcsa:" attribute lines were excluded from the receive
	d
	SDP offer, unless those data channels were already closed,
	and it MUST also exclude the
	corresponding attribute lines in the answer."</t>
	<t>In <xref target="close-dc"/> t
	he hanging text after the third paragraph was
	"This delayed close is to handle cases where a successful SDP
	answer is not received, in which case the state of session should
	be kept per the last successful SDP offer/answer."
	Replacement of this sentence with
	"This delayed closure is RECOMMENDED in order
	to handle cases where a successful SDP answer is not received, in
	which case the state of the session SHOULD be kept per the last
	successful SDP offer/answer."</t>
	<t>Although dedicated to "a=dcmap
	" and "a=dcsa" SDP syntax aspects
	<xref target="subsec-sdp-attr-for-dc-par-neg"/> contained already
	procedural descriptions related to data channel reliability negotiation.
	Creation of new <xref target="param_negotiation"/> and moval of
	reliability negotiation related text to this new section.</t>
	</list>
	</t>
	</section>
	<section title="Changes against 'draft-ejzak-mmusic-data-
	channel-sdpneg-02'">
	<t>
	<list style="symbols">
	<t>Removal of note "ACTION ITEM"
	from section "subprotocol parameter".
	As <xref target="I-D.ietf-rtcweb-data-protocol"/> this document should refer
	to IANA's
	WebSocket Subprotocol Name Registry defined in <xref target="RFC6455"/>
	</t>
	<t>In whole document, replacement
	of "unreliable" with "partially reliable",
	which is used in <xref target="I-D.ietf-rtcweb-data-channel"/> and in
	<xref target="I-D.ietf-rtcweb-data-protocol"/> in most places.</t>
	<t>Clarification of the semantic
	if the "max-retr" parameter is not present in
	an "a=dcmap" attribute line. In section "max-retr parameter" the sentence
	"The max-retr parameter is optional with default value unbounded"
	was replaced with "The max-retr parameter is optional. If
	the max-retr parameter is not present, then the maximal number of
	retransmissions is determined as per the generic SCTP retransmission
	rules as specified in <xref target="RFC4960"/>".</t>
	<t>Clarification of the semantic
	if the "max-time" parameter is not present in
	an "a=dcmap" attribute line. In section "max-time parameter" the sentence
	"The max-time parameter is optional with default value unbounded"
	was replaced with "The max-time parameter is optional. If
	the max-time parameter is not present, then the generic SCTP
	retransmission timing rules apply as specified in <xref target="RFC4960"/>".<
	/t>
	<t>In section "label parameter" t
	he sentence "Label is a mandatory parameter."
	was removed and following new sentences (including the note) were added:
	"The 'label' parameter is optional. If it is not
	present, then its value defaults to the empty string.
	Note: The empty string may also be explicitly used as 'label' value,
	such that 'label=""' is equivalent to the 'label' parameter not being
	present at all.
	<xref target="I-D.ietf-rtcweb-data-protocol"/> allows the DATA_CHANNEL_OPEN
	message's 'Label' value to be an empty string."</t>
	<t>In section "subprotocol parame
	ter" the sentence
	"subprotocol is a mandatory parameter." was replaced with
	"'subprotocol' is an optional
	parameter. If the 'subprotocol' parameter is not present, then its
	value defaults to the empty string."</t>
	<t>In the "Examples" section, in
	the first two SDP offer examples in
	the "a=dcmap" attribute lines 'label="BGCP"' was replaced with 'label="bfcp"'
	.</t>
	<t>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.</
	t>
	</list>
	</t>
	</section>
	<section title="Changes against '-01'">
	<t>
	<list style="symbols">
	<t>Formal syntax for dcmap and dc
	sa attribute lines. </t>
	<t>Making subprotocol as an optio
	nal parameter in dcmap. </t>
	<t>Specifying disallowed paramete
	r combinations for max-time and max-retr. </t>
	<t>Clarifications on WebRTC data
	channel close procedures. </t>
	</list>
	</t>
	</section>
	<section title="Changes against '-00'">
	<t>
	<list style="symbols">
	<t> Revisions to identify differe
	nce between internal and external
	negotiation and their usage.</t>
	<t>Introduction of more generic t
	erminology, e.g. "application" instead of
	"browser".</t>
	<t>Clarification of how "max-retr
	and max-time affect the usage of
	unreliable and reliable WebRTC data channels.</t>
	<t>Updates of examples to take in
	to account the SDP syntax changes
	introduced with draft-ietf-mmusic-sctp-sdp-07.</t>
	<t>Removal of the SCTP port numbe
	r from the "a=dcmap" and "a=dcsa" attributes
	as this is now contained in the a=sctp-port attribute,
	and as draft-ietf-mmusic-sctp-sdp-07 supports only one SCTP association
	on top of the DTLS connection.</t>
	</list>
	</t>
	</section>
	</section>
	</middle>
	<back>
	<references title="Normative References">
	&RFC2119;
	&RFC4960;
	&RFC8174;
	&RFC3264;
	&RFC5234;
	&RFC6525;
	&RFC3629;
	&DATAREQ;
	&SDPBIS;
	&SDPSCTP;
	&SDPMUXATTR;
	&DATAPROTO;
	</references>
	<references title="Informative References">
	&RFC4582;		<table anchor="dcsa-iana">
	&RFC4975;		<name>New "a=dcsa:" Attribute</name>
	&RFC6455;		<thead>
	&CLUEDATA;		<tr>
	&MSRPDATA;		<th colspan="2" align="center">"a=dcsa:"</th>
			</tr>
			</thead>
			<tbody>
			<tr>
			<td align="left">Contact name</td>
			<td align="left">IESG</td>
			</tr>
			<tr>
			<td align="left">Contact email</td>
			<td align="left">iesg@ietf.org</td>
			</tr>
			<tr>
			<td align="left">Attribute name</td>
			<td align="left">dcsa</td>
			</tr>
			<tr>
			<td align="left">Attribute syntax</td>
			<td align="left">As per <xref target="dcsa-attribute"/>
			</td>
			</tr>
			<tr>
			<td align="left">Attribute semantics</td>
			<td align="left">As per <xref target="dcsa-attribute"/>
			</td>
			</tr>
			<tr>
			<td align="left">Usage level</td>
			<td align="left">media</td>
			</tr>
			<tr>
			<td align="left">Charset dependent</td>
			<td align="left">No</td>
			</tr>
			<tr>
			<td align="left">Purpose</td>
			<td align="left">To define attributes that are specific to data
			channel subprotocols</td>
			</tr>
			<tr>
			<td align="left">Appropriate values</td>
			<td align="left">As per <xref target="dcsa-attribute"/>
			</td>
			</tr>
			<tr>
			<td align="left">O/A procedures</td>
			<td align="left">SDP offer/answer procedures as per <xref target
			="section_procedures"/>
			</td>
			</tr>
			<tr>
			<td align="left">Mux category</td>
			<td align="left">SPECIAL. See <xref target="dcsa-mux-category"/>
			</td>
			</tr>
			<tr>
			<td align="left">Reference</td>
			<td align="left">RFC 8864</td>
			</tr>
			</tbody>
			</table>
			</section>
			</section>
			<section anchor="IANA-reg-data-channel-attribs">
			<name>Registering Attributes for Use with Data Channels</name>
			<t>When a subprotocol is defined for use over data channels with
			the SDP offer/answer mechanism, any SDP attributes that may be
			negotiated using the "a=dcsa:" attribute MUST be added to the IANA
			"attribute-name" registry (formerly "att-field"), as specified in
			<xref target="RFC8866" sectionFormat="comma" section="8.2.4"/>. This
			document specifies that new Usage Levels of the form "dcsa (foo)"
			(where "foo" is a placeholder for the subprotocol name) should be
			registered by documents that specify negotiation of particular
			subprotocols.</t>
			</section>
			</section>
			</middle>
			<back>
	<reference anchor="WebRtcAPI" target="https://www.w3.org/		<references>
	TR/2018/CR-webrtc-20180927/">		<name>References</name>
	<front>		<references>
	<title>		<name>Normative References</name>
	WebRTC 1.0: Real-time Communication Between Browsers		<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2119.
	</title>		xml"/>
	<author initials="A." surname="Bergkvist"		<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4960.
	fullname="Adam Bergkvist">		xml"/>
	<organization/>		<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8174.
	</author>		xml"/>
	<author initials="D." surname="Burnett" f		<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.3264.
	ullname="Daniel Burnett">		xml"/>
	<organization/>		<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5234.
	</author>		xml"/>
	<author initials="C." surname="Jennings"		<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6525.
	fullname="Cullen Jennings">		xml"/>
	<organization/>		<xi:include
	</author>		href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.3629.xml"/>
	<author initials="A." surname="Narayanan"
	fullname="Anant Narayanan">		<!-- draft-ietf-rtcweb-data-channel (RFC 8831) -->
	<organization/>		<reference anchor="RFC8831" target="https://www.rfc-editor.org/info/rfc8831">
	</author>		<front>
	<author initials="B." surname="Aboba" ful		<title>WebRTC Data Channels</title>
	lname="Bernard Aboba">		<author initials="R" surname="Jesup" fullname="Randell Jesup">
	<organization/>		<organization/>
	</author>		</author>
	<author initials="T." surname="Brandstett		<author initials="S" surname="Loreto" fullname="Salvatore Loreto">
	er" fullname="Taylor Brandstetter">		<organization/>
	<organization/>		</author>
	</author>		<author initials="M" surname="Tüxen" fullname="Michael Tüxen">
	<author initials="J." surname="Bruaroey"		<organization/>
	fullname="Jan-Ivar Bruaroey">		</author>
	<organization/>		<date month='September' year='2020'/>
	</author>		</front>
	<date month="September" day="27" year="20		<seriesInfo name="RFC" value="8831"/>
	18"/>		<seriesInfo name="DOI" value="10.17487/RFC8831"/>
	</front>		</reference>
	<seriesInfo name="World Wide Web Consortium CR" v
	alue="CR-webrtc-20180927"/>		<!-- draft-ietf-mmusic-rfc4566bis (RFC 8866) -->
	<format type="HTML" target="https://www.w3.org/TR		<reference anchor="RFC8866" target="https://www.rfc-editor.org/info/rfc8
	/2018/CR-webrtc-20180927"/>		866">
	</reference>		<front>
	</references>		<title>SDP: Session Description Protocol</title>
	<section title="Generic Data Channel Negotiation Aspects When Not		<author initials="A" surname="Begen" fullname="Ali Begen">
	Using DCEP" anchor="generic-out-of-band-aspects">		<organization/>
	<t>This appendix summarizes how data channels work in gen		</author>
	eral and discusses		<author initials="P" surname="Kyzivat" fullname="Paul Kyzivat">
	some key aspects, which should be considered for the out-of-band negotiation		<organization/>
	of data		</author>
			<author initials="C" surname="Perkins" fullname="Colin Perkins">
			<organization/>
			</author>
			<author initials="M" surname="Handley" fullname="Mark Handley">
			<organization/>
			</author>
			<date month="September" year="2020"/>
			</front>
			<seriesInfo name="RFC" value="8866"/>
			<seriesInfo name="DOI" value="10.17487/RFC8866"/>
			</reference>
			<!-- draft-ietf-mmusic-sctp-sdp (RFC 8841) -->
			<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="September" year="2020" />
			</front>
			<seriesInfo name="RFC" value="8841" />
			<seriesInfo name="DOI" value="10.17487/RFC8841"/>
			</reference>
			<!-- draft-ietf-mmusic-sdp-mux-attributes (RFC 8859) -->
			<reference anchor="RFC8859" target="https://www.rfc-editor.org/info/rfc8
			859">
			<front>
			<title>A Framework for Session Description Protocol (SDP)
			Attributes When Multiplexing</title>
			<author initials="S" surname="Nandakumar" fullname="Suhas Nandakumar
			">
			<organization/>
			</author>
			<date month="September" year="2020"/>
			</front>
			<seriesInfo name="RFC" value="8859"/>
			<seriesInfo name="DOI" value="10.17487/RFC8859"/>
			</reference>
			<!--draft-ietf-rtcweb-data-protocol (RFC 8832) -->
			<reference anchor="RFC8832" target="https://www.rfc-editor.org/info/rfc8832">
			<front>
			<title>WebRTC Data Channel Establishment Protocol</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='September' year='2020'/>
			</front>
			<seriesInfo name="RFC" value="8832"/>
			<seriesInfo name="DOI" value="10.17487/RFC8832"/>
			</reference>
			</references>
			<references>
			<name>Informative References</name>
			<!-- Watch to see if 4582bis gets published before this doc. -->
			<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4582.
			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.6455.
			xml"/>
			<!--draft-ietf-clue-datachannel (RFC 8850) -->
			<reference anchor='RFC8850' target='https://www.rfc-editor.org/info/rfc8850'>
			<front>
			<title>Controlling Multiple Streams for Telepresence (CLUE) Protocol Data Channe
			l</title>
			<author initials='C' surname='Holmberg' fullname='Christer Holmberg'>
			<organization />
			</author>
			<date month='September' year='2020' />
			</front>
			<seriesInfo name='RFC' value='8850' />
			<seriesInfo name='DOI' value='10.17487/RFC8850' />
			</reference>
			<!-- draft-ietf-mmusic-msrp-usage-data-channel (Submitted to IESG for Pub)
			Needs "long way" because Jose Recio is an editor -->
			<reference anchor='MSRP-over-Data-Channels'>
			<front>
			<title>MSRP over Data Channels</title>
			<author initials='J' surname='Recio' fullname='Jose Recio' role='editor'>
			<organization />
			</author>
			<author initials='C' surname='Holmberg' fullname='Christer Holmberg'>
			<organization />
			</author>
			<date month='August' day='18' year='2020' />
			</front>
			<seriesInfo name='Internet-Draft'
			value='draft-ietf-mmusic-msrp-usage-data-channel-24' />
			</reference>
			<reference anchor="WebRtcAPI" target="https://www.w3.org/TR/2019/CR-webr
			tc-20191213/">
			<front>
			<title>WebRTC 1.0: Real-time Communication Between Browsers</title>
			<author initials="C." surname="Jennings" fullname="Cullen Jennings">
			<organization/>
			</author>
			<author initials="H." surname="Boström" fullname="Henrik Boström">
			<organization/>
			</author>
			<author initials="J-I." surname="Bruaroey" fullname="Jan-Ivar Bruaro
			ey">
			<organization/>
			</author>
			<date year="2019" month="December" day="13"/>
			</front>
			<refcontent>W3C Candidate Recommendation</refcontent>
			</reference>
			<reference anchor="T38"
			target="https://www.itu.int/rec/T-REC-T.38-201511-I/en">
			<front>
			<title>Procedures for real-time Group 3 facsimile communication over IP netwo
			rks</title>
			<author>
			<organization>International Telecommunication Union</organization>
			</author>
			<date month="November" year="2015"/>
			</front>
			<seriesInfo name="ITU-T Recommendation" value="T.38"/>
			</reference>
			</references>
			</references>
			<section anchor="generic-out-of-band-aspects">
			<name>Generic Data Channel Negotiation Aspects when Not Using DCEP</name>
			<t>This appendix summarizes how data channels work in general and discusse
			s
			some key aspects that should be considered for the out-of-band negotiation of
			data
	channels if DCEP is not used.</t>		channels if DCEP is not used.</t>
	<t>A WebRTC application creates a data channel		<t>A WebRTC application creates a data channel
	by providing a number of setup parameters (subprotocol, label,		by providing a number of setup parameters (subprotocol, label,
	maximal number of retransmissions, maximal retransmission time, order of deli very,		maximal number of retransmissions, maximal retransmission time, order of deli very,
	priority). The application also specifies		priority). The application also specifies whether
	if it wants to make use of the negotiation using the DCEP		it wants to make use of the negotiation using DCEP
	<xref target="I-D.ietf-rtcweb-data-protocol"/>, or if the application		<xref target="RFC8832"/> or
	intends to negotiate data channels using the SDP offer/answer protocol.</t>		intends to negotiate data channels using the SDP offer/answer protocol.</t>
	<t>In any case, the SDP offer generated by the applicatio		<t>In any case, the SDP offer generated by the application is per
	n is per		<xref target="RFC8841"/>. In brief, it contains one
	<xref target="I-D.ietf-mmusic-sctp-sdp"/>. In brief, it contains one		"m=" line for the SCTP association on top of which the data channels will run
	"m" line for the SCTP association on top of which data channels will run:</t>		:
	<figure align="left" title="">		</t>
	<artwork align="left"><![CDATA[		<sourcecode name="app-a-sdp-example" type="sdp"><![CDATA[
	m=application 54111 UDP/DTLS/SCTP webrtc-datachannel		m=application 54111 UDP/DTLS/SCTP webrtc-datachannel
	c=IN IP4 192.0.2.1		c=IN IP4 192.0.2.1
	a=max-message-size:100000		a=max-message-size:100000
	a=sctp-port:5000		a=sctp-port:5000
	a=tls-id:abc3de65cddef001be82		a=tls-id:abc3de65cddef001be82
	a=setup:actpass		a=setup:actpass
	a=fingerprint:SHA-1 \		a=fingerprint:SHA-1 \
	4A:AD:B9:B1:3F:82:18:3B:54:02:12: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]]></sourcecode>
	]]></artwork>
	</figure>		<aside><t>Note: A WebRTC application will only use the "m=" line format "w
	<t>Note: A WebRTC application will only use "m" line form		ebrtc-datachannel"
	at "webrtc-datachannel",		and will not use other formats in the "m=" line for other protocols
	and will not use other formats in the "m" line for other protocols		such as T.38 <xref target="T38"/>.
	such as t38.		<xref target="RFC8841"/> supports only one SCTP
	<xref target="I-D.ietf-mmusic-sctp-sdp"/> supports only one SCTP
	association to be established on top of a DTLS association.		association to be established on top of a DTLS association.
	</t>		</t></aside>
	<t>Note: The above SDP media description does not contain		<aside><t>Note: The above SDP media description does not contain any chann
	any channel-specific		el-specific
	information.</t>		information.</t></aside>
	<section title="Stream Identifier Numbering" anchor="si_n		<section anchor="si_num">
	um">		<name>Stream Identifier Numbering</name>
	<t>Independently from the requested type of negot		<t>Independently from the requested type of negotiation, the application
	iation, the application		creating a data channel can either (1)&nbsp;pass the stream identifier to th
	creating a data channel can either pass the stream identifier to the data ch		e data channel stack to assign
	annel stack to assign		to the data channel or (2)&nbsp;let the data channel stack pick
	to the data channel or else let the data channel stack pick
	one identifier from the unused ones.</t>		one identifier from the unused ones.</t>
	<t>To avoid glare situations <xref target="RFC326 4"/>, each endpoint can moreover own an		<t>Moreover, to avoid glare situations <xref target="RFC3264"/>, each en dpoint can own an
	exclusive set of stream identifiers, in which case an endpoint can		exclusive set of stream identifiers, in which case an endpoint can
	only create a data channel with a stream identifier it owns.</t>		only create a data channel with a stream identifier it owns.</t>
	<t>Which set of stream identifiers is owned by wh ich endpoint is		<t>Which set of stream identifiers is owned by which endpoint is
	determined by convention or other means.		determined by convention or other means.
	<list style="hanging">		</t>
	<t>Note:For data channels negotia		<aside><t>Note: For data channels negotiated with DCEP, one endpoint o
	ted with the DCEP, one endpoint owns by		wns by
	convention the even stream identifiers, whereas the other owns the		convention the even stream identifiers, whereas the other owns the
	odd stream identifiers, as defined in		odd stream identifiers, as defined in
	<xref target="I-D.ietf-rtcweb-data-protocol"/>.</t>		<xref target="RFC8832"/>.</t></aside>
	<t>Note:For data channels negotia
	ted via different protocol from DCEP,		<aside><t>Note: For data channels negotiated via a protocol other than D
	no convention is defined by default.</t>		CEP,
	</list>		no convention is defined by default.</t></aside>
	</t>		</section>
	</section>		<section anchor="sec-gen-ext-neg">
	<section title="Generic Data Channel Negotiation Not Usin		<name>Generic Data Channel Negotiation Not Using DCEP</name>
	g DCEP" anchor="sec-gen-ext-neg">		<section>
	<section title="Overview">		<name>Overview</name>
	<t>DCEP negotiation only provides for neg		<t>DCEP negotiation only provides for negotiation of data channel
	otiation of data channel		transport parameters and does not provide for negotiation of
	transport parameters and does not provide for negotiation of subprotocol		subprotocol-specific parameters. Non-DCEP data channel negotiation can be d
	specific parameters. DCEP-less data channel negotiation can be defined to		efined to
	allow negotiation of parameters beyond those handled by DCEP,		allow negotiation of parameters beyond those handled by DCEP,
	e.g., parameters specific to the subprotocol instantiated on a		e.g., parameters specific to the subprotocol instantiated on a
	particular data channel.</t>		particular data channel.</t>
	<t>The following procedures are common to all methods of data channel		<t>The following procedures are common to all methods of data channel
	negotiation not using DCEP, whether in-band (communicated using proprietary means on		negotiation not using DCEP, whether in-band (communicated using proprietary means on
	an already established data channel) or out-of-band (using SDP offer/answer		an already-established data channel) or out-of-band (using the SDP
	or		offer/answer mechanism or
	some other protocol associated with the signaling channel).</t>		some other protocol associated with the signaling channel).</t>
	</section>		</section>
	<section title="Opening a Data Channel" anchor="e		<section anchor="ext_open">
	xt_open">		<name>Opening a Data Channel</name>
	<t>In the case of DCEP-less negotiation,		<t>In the case of non-DCEP negotiation, the endpoint application has t
	the endpoint application has the		he
	option to fully control the stream identifier assignments. However		option to fully control the stream identifier assignments. However,
	these assignments have to coexist with the assignments controlled by		these assignments have to coexist with the assignments controlled by
	the data channel stack for the DCEP negotiated data channels (if		the data channel stack for data channels negotiated using DCEP (if
	any). It is the responsibility of the application to ensure consistent		any). It is the responsibility of the application to ensure consistent
	assignment of stream identifiers.</t>		assignment of stream identifiers.</t>
	<t>When the application requests the crea		<t>When the application requests that the creation of a new data chann
	tion of a new data channel to		el
	be set up via DCEP-less negotiation, the data channel stack creates		be set up via non-DCEP negotiation, the data channel stack creates
	the data channel locally without sending any DATA_CHANNEL_OPEN message		the data channel locally without sending any DATA_CHANNEL_OPEN messages
	in-band.		in-band.
	However, even if the ICE (Interactive Connectivity Establishment),		However, even if the ICE (Interactive Connectivity Establishment),
	DTLS and SCTP procedures were already successfully		DTLS, and SCTP procedures were already successfully
	completed, the application can't send data on this data channel until the		completed, the application can't send data on this data channel until the
	negotiation is complete with the peer. This is because the peer needs		negotiation with the peer is complete. This is because the peer needs
	to be aware of and accept the usage of this data channel. The		to be aware of and accept the usage of this data channel. The
	peer, after accepting the data channel offer, can start sending data		peer, after accepting the data channel offer, can start sending data
	immediately. This implies that the offerer may receive data channel		immediately. This implies that the offerer may receive data channel
	subprotocol messages		subprotocol messages
	before the negotiation is complete and the application should be		before the negotiation is complete, and the application should be
	ready to handle it.</t>		ready to handle it.</t>
	<t>If the peer rejects the data channel p		<t>If the peer rejects the data channel part of the offer, then it
	art of the offer then it		doesn't have to do anything, as the data channel was not created using
	doesn't have to do anything as the data channel was not created using		the stack. The offerer, on the other hand, needs to close the data
	the stack. The offerer on the other hand needs to close the data
	channel that was opened by invoking relevant data channel stack API		channel that was opened by invoking relevant data channel stack API
	procedures.</t>		procedures.</t>
	<t>It is also worth noting that a data ch		<t>It is also worth noting that a data channel stack implementation ma
	annel stack implementation may		y
	not provide any API to create and close data channels; instead the		not provide any APIs to create and close data channels; instead, the
	data channels may be used on the fly as needed just by communicating		data channels may be used on the fly as needed, just by communicating
	via non-DCEP means or by even having some local configuration/assumptions		via non-DCEP means or even by having some local configuration/assumptions
	on both the peers.</t>		on both of the peers.</t>
	<t>The application then negotiates the da		<t>The application then negotiates the data channel
	ta channel
	properties and subprotocol properties with the peer's application		properties and subprotocol properties with the peer's application
	using a mechanism different from DCEP.</t>		using a mechanism different from DCEP.</t>
	<t>The peer then symmetrically creates a data channel		<t>The peer then symmetrically creates a data channel
	with these negotiated data channel properties. This is the only way		with these negotiated data channel properties. This is the only way
	for the peer's data channel stack to know which properties to apply		for the peer's data channel stack to know which properties to apply
	when transmitting data on this channel.		when transmitting data on this channel.
	The data channel stack must		The data channel stack must
	allow data channel creation with any non-conflicting stream identifier		allow data channel creation with any nonconflicting stream identifier
	so that both peers can create the data channel with the same		so that both peers can create the data channel with the same
	stream identifier.		stream identifier.
	</t>		</t>
	</section>		</section>
	<section title="Closing a Data Channel">		<section>
	<t>When the application requests the clos		<name>Closing a Data Channel</name>
	ing of a		<t>When the application requests the closing of a
	data channel negotiated without DCEP,		data channel negotiated without DCEP,
	the data channel stack always performs an SCTP SSN		the data channel stack always performs an SCTP SSN
	reset for this channel.</t>		Reset for this channel.</t>
	<t>Depending upon the method used for DCE		<t>Depending upon the method used for non-DCEP negotiation and the
	P-less negotiation and the		subprotocol associated with the data channel, the closing of the data chann
	subprotocol associated with the data channel, the closing might in		el might also be signaled to the peer via SDP offer/answer negotiation.</t>
	addition be signaled to the peer via SDP offer/answer negotiation.</t>		</section>
	</section>		</section>
	</section>		</section>
	<!-- sec-gen-ext-neg -->		<section anchor="acknowledgements" numbered="false">
	</section>		<name>Acknowledgements</name>
	<!-- generic-out-of-band-aspects -->		<t>The authors wish to acknowledge the borrowing of ideas from other
	</back>		draft documents by <contact fullname="Salvatore Loreto"/>, <contact
			fullname="Gonzalo Camarillo"/>, <contact fullname="Peter Dunkley"/>, and
			<contact fullname="Gavin Llewellyn"/>. The authors also wish to thank <contac
			t
			fullname="Flemming Andreasen"/>, <contact fullname="Christian Groves"/>,
			<contact fullname="Gunnar Hellström"/>, <contact fullname="Paul
			Kyzivat"/>, <contact fullname="Jonathan Lennox"/>,
			<contact fullname="Uwe Rauschenbach"/>, and <contact fullname="Roman Shpount"
			/> for their invaluable comments.</t>
			<t>Special thanks to <contact fullname="Christer Holmberg"/> for helping
			finish the document and cleaning up <xref target="section_procedures"/>.
			</t>
			</section>
			<section anchor="contributors" numbered="false">
			<name>Contributors</name>
			<t><contact fullname="Juergen Stoetzer-Bradler"/> made significant
			contributions to this document and should be considered a coauthor.</t>
			</section>
			</back>
	</rfc>		</rfc>
End of changes. 129 change blocks.
	1902 lines changed or deleted		1201 lines changed or added
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