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<rfc ipr="trust200902" docName="draft-ietf-mmusic-rid-15" category="std" updates <rfc xmlns:xi="http://www.w3.org/2001/XInclude" ipr="trust200902"
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<front> <front>
<title abbrev="RTP Restrictions">RTP Payload Format Restrictions</title> <title abbrev="RTP Restrictions">RTP Payload Format Restrictions</title>
<seriesInfo name="RFC" value="8851"/>
<author initials="A.B." surname="Roach (Editor)" fullname="Adam Roach"> <author initials="A.B." surname="Roach" fullname="Adam Roach" role="editor">
<organization>Mozilla</organization> <organization>Mozilla</organization>
<address> <address>
<email>adam@nostrum.com</email> <email>adam@nostrum.com</email>
</address> </address>
</author> </author>
<date month="May" year="2020"/>
<date year="2018" month="May" day="15"/> <keyword>WebRTC</keyword>
<keyword>Multiplexing</keyword>
<abstract> <abstract>
<t>In this specification, we define a framework for specifying restriction
<t>In this specification, we define a framework for specifying restrictions s
on RTP streams in the Session Description Protocol. on RTP streams in the Session Description Protocol (SDP).
This framework defines a new “rid” (“restriction identifier”) SDP attribute to u This framework defines a new "rid" ("restriction identifier") SDP attribute to
nambiguously unambiguously identify the RTP streams within an RTP session and restrict the
identify the RTP Streams within an RTP Session and restrict the streams’ payload streams' payload format parameters in a codec-agnostic way beyond what is
format parameters in a codec-agnostic way beyond what is provided with the provided with the regular payload types.</t>
regular Payload Types.</t> <t>This specification updates RFC 4855 to give additional guidance on choi
ce of
<t>This specification updates RFC4855 to give additional guidance on choice of Format Parameter (fmtp) names and their relation to the restrictions
Format Parameter (fmtp) names, and on their relation to the restrictions
defined by this document.</t> defined by this document.</t>
</abstract> </abstract>
</front> </front>
<middle> <middle>
<section anchor="terminology" numbered="true" toc="default">
<section anchor="terminology" title="Terminology"> <name>Terminology</name>
<t>The terms "source RTP stream", "endpoint", "RTP session", and "RTP stre
<t>The terms “Source RTP Stream”, “Endpoint”, “RTP Session”, and “RTP Stream” am"
are used as defined in <xref target="RFC7656"/>.</t> are used as defined in <xref target="RFC7656" format="default"/>.</t>
<t><xref target="RFC4566" format="default"/> and <xref target="RFC3264" fo
<t><xref target="RFC4566"/> and <xref target="RFC3264"/> terminology is also use rmat="default"/> terminology is also used where appropriate.</t>
d where appropriate.</t> </section>
<section anchor="sec-intro" numbered="true" toc="default">
</section> <name>Introduction</name>
<section anchor="sec-intro" title="Introduction"> <t>The payload type (PT) field in RTP provides a mapping between the RTP p
ayload
<t>The Payload Type (PT) field in RTP provides a mapping between the RTP payload format and the associated SDP media description. For a given PT, the SDP
format and the associated SDP media description. The SDP rtpmap and/or fmtp rtpmap and/or fmtp attributes are used to describe the properties of
attributes are used, for a given PT, to describe the properties of
the media that is carried in the RTP payload.</t> the media that is carried in the RTP payload.</t>
<t>Recent advances in standards have given rise to rich
<t>Recent advances in standards have given rise to rich multimedia applications requiring support for either multiple RTP streams within
multimedia applications requiring support for multiple RTP Streams within an an
RTP session <xref target="I-D.ietf-mmusic-sdp-bundle-negotiation"/>, RTP session <xref target="RFC8843" format="default"/> <xref target="RFC8853" for
<xref target="I-D.ietf-mmusic-sdp-simulcast"/> or having to support a large numb mat="default"/> or a
er of codecs. large number of codecs.
These demands have unearthed challenges inherent with:</t> These demands have unearthed challenges inherent with:</t>
<ul spacing="normal">
<t><list style="symbols"> <li>The restricted RTP PT space in specifying the various payload
<t>The restricted RTP PT space in specifying the various payload configurations</li>
configurations,</t> <li>The codec-specific constructs for the payload formats in SDP</li>
<t>The codec-specific constructs for the payload formats in SDP,</t> <li>Missing or underspecified payload format parameters</li>
<t>Missing or underspecified payload format parameters,</t> <li>Overloading of PTs to indicate not just codec configurations, but
<t>Overloading of PTs to indicate not just codec configurations, but individual streams within an RTP session</li>
individual streams within an RTP session.</t> </ul>
</list></t> <t>To expand on these points: <xref target="RFC3550" format="default"/>
assigns 7 bits for the PT in the RTP header. However, the assignment of
<t>To expand on these points: <xref target="RFC3550"/> assigns 7 bits for the PT static mapping of RTP payload type numbers to payload formats and
in the RTP multiplexing of RTP with other protocols (such as the RTP Control
header. However, the assignment of static mapping of RTP payload type numbers Protocol (RTCP)) could result in a limited number of payload type
to payload formats and multiplexing of RTP with other protocols (such as RTCP) numbers available for application usage. In scenarios where the number
could result in a limited number of payload type numbers available for of possible RTP payload configurations exceeds the available PT space
application usage. In scenarios where the number of possible RTP payload within an RTP session, there is a need for a way to represent the
configurations exceeds the available PT space within an RTP Session, there is additional restrictions on payload configurations and effectively map an
a need for a way to represent the additional restrictions on payload configurati RTP stream to its corresponding restrictions. This issue is exacerbated
ons by the increase in techniques -- such as simulcast and layered codecs --
and to effectively map an RTP Stream to its corresponding restrictions. This that introduce additional streams into RTP sessions.</t>
issue is exacerbated by the increase in techniques – such as simulcast and <t>This specification defines a new SDP framework for restricting source R
layered codecs – which introduce additional streams into RTP Sessions.</t> TP
streams (Section 2.1.10 of <xref target="RFC7656" format="default"/>), along wit
<t>This specification defines a new SDP framework for restricting Source RTP h
Streams (Section 2.1.10 <xref target="RFC7656"/>), along with
the SDP attributes to restrict payload formats in a codec-agnostic way. the SDP attributes to restrict payload formats in a codec-agnostic way.
This framework can be thought of as a complementary extension to the way This framework can be thought of as a complementary extension to the way
the media format parameters are specified in SDP today, via the “a=fmtp” the media format parameters are specified in SDP today, via the "a=fmtp"
attribute.</t> attribute.</t>
<t>The additional restrictions on individual streams are indicated with a
<t>The additional restrictions on individual streams are indicated with a new new
“a=rid” (“restriction identifier”) SDP attribute. Note that the restrictions com "a=rid" ("restriction identifier") SDP attribute. Note that the restrictions com
municated via this municated via this
attribute only serve to further restrict the parameters that are established attribute only serve to further restrict the parameters that are established
on a PT format. They do not relax any restrictions imposed by other mechanisms.< /t> on a PT format. They do not relax any restrictions imposed by other mechanisms.< /t>
<t>This specification makes use of the RTP Stream Identifier Source Descri
<t>This specification makes use of the RTP Stream Identifier Source Description ption
(SDES) RTCP item defined in <xref target="I-D.ietf-avtext-rid"/> to provide cor (SDES) RTCP item defined in <xref target="RFC8852" format="default"/> to provid
relation e correlation
between the RTP Packets and their format specification in the SDP.</t> between the RTP packets and their format specification in the SDP.</t>
<t>As described in <xref target="sec-rid_unaware" format="default"/>, this
<t>As described in <xref target="sec-rid_unaware"/>, this mechanism achieves bac mechanism achieves backwards
kwards compatibility via the normal SDP processing rules, which require unknown "a="
compatibility via the normal SDP processing rules, which require unknown a=
lines to be ignored. This means that implementations need to be prepared lines to be ignored. This means that implementations need to be prepared
to handle successful offers and answers from other implementations that to handle successful offers and answers from other implementations that
neither indicate nor honor the restrictions requested by this mechanism.</t> neither indicate nor honor the restrictions requested by this mechanism.</t>
<t>Further, as described in <xref target="sec-sdp_o_a" format="default"/>
<t>Further, as described in <xref target="sec-sdp_o_a"/> and its subsections, th and its subsections, this mechanism
is mechanism
achieves extensibility by: (a) having offerers include all supported achieves extensibility by: (a) having offerers include all supported
restrictions in their offer, and (b) having answerers ignore “a=rid” lines that restrictions in their offer, and (b) having answerers ignore "a=rid" lines that
specify unknown restrictions.</t> specify unknown restrictions.</t>
</section>
</section> <section anchor="key-words-for-requirements" numbered="true" toc="default">
<section anchor="key-words-for-requirements" title="Key Words for Requirements"> <name>Key Words for Requirements</name>
<t>
<t>The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL The key words "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>", "<bcp14>REQU
NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “NOT RECOMMENDED”, IRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL
“MAY”, and “OPTIONAL” in this document are to be interpreted as NOT</bcp14>", "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>", "<bcp14>
described in BCP 14 <xref target="RFC2119"/> <xref target="RFC8174"/> when, and RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
only when, they "<bcp14>MAY</bcp14>", and "<bcp14>OPTIONAL</bcp14>" in this document are to
appear in all capitals, as shown here.</t> be interpreted as
described in BCP&nbsp;14 <xref target="RFC2119" format="default"/> <xref tar
</section> get="RFC8174" format="default"/>
<section anchor="sec-rid_attribute" title="SDP “a=rid” Media Level Attribute"> when, and only when, they appear in all capitals, as shown here.
</t>
<t>This section defines new SDP media-level attribute <xref target="RFC4566"/>, </section>
“a=rid”, <section anchor="sec-rid_attribute" numbered="true" toc="default">
<name>SDP "a=rid" Media Level Attribute</name>
<t>This section defines new SDP media-level attribute <xref
target="RFC4566" format="default"/>, "a=rid",
used to communicate a set of restrictions to be used to communicate a set of restrictions to be
applied to an identified RTP Stream. Roughly speaking, this attribute takes the applied to an identified RTP stream. Roughly speaking, this attribute takes
following form (see <xref target="sec-abnf"/> for a formal definition).</t> the following form (see <xref target="sec-abnf" format="default"/> for a
formal definition):</t>
<figure><artwork><![CDATA[ <sourcecode type="sdp"><![CDATA[
a=rid:<rid-id> <direction> [pt=<fmt-list>;]<restriction>=<value>... a=rid:<rid-id> <direction> [pt=<fmt-list>;]<restriction>=<value>...
]]></sourcecode>
]]></artwork></figure> <t>An "a=rid" SDP media attribute specifies restrictions defining a unique
RTP payload configuration identified via the "rid-id" field. This
<t>An “a=rid” SDP media attribute specifies restrictions defining a unique value binds the restriction to the RTP stream identified by its RTP
RTP payload configuration identified via the “rid-id” field. This Stream Identifier Source Description (SDES) item <xref target="RFC8852" format="
value binds the restriction to the RTP Stream identified by its RTP default"/>.
Stream Identifier Source Description (SDES) item <xref target="I-D.ietf-avtext-r Implementations that use the "a=rid" parameter in SDP <bcp14>MUST</bcp14> suppor
id"/>. t
Implementations that use the “a=rid” parameter in SDP MUST support the RtpStreamId SDES item described in <xref target="RFC8852" format="default"/>
the RtpStreamId SDES item described in <xref target="I-D.ietf-avtext-rid"/>. Suc . Such
h implementations <bcp14>MUST</bcp14> send that SDES item for all streams in an SD
implementations MUST send that SDES item for all streams in an SDP media descrip P media description
tion ("m=") that have "a=rid" lines remaining after applying the rules in
(“m=”) that have “a=rid” lines remaining after applying the rules in <xref target="sec-sdp_o_a" format="default"/> and its subsections.</t>
<xref target="sec-sdp_o_a"/> and its subsections.</t> <t>Implementations that use the "a=rid" parameter in SDP and make use of
redundancy RTP streams <xref target="RFC7656" format="default"/> -- e.g., RTP RT
<t>Implementations that use the “a=rid” parameter in SDP and that X
make use of redundancy RTP streams <xref target="RFC7656"/>, e.g. RTP RTX <xref target="RFC4588" format="default"/> or Forward Error Correction (FEC) <xre
<xref target="RFC4588"/> or FEC <xref target="RFC5109"/>, f target="RFC5109" format="default"/> -- for any of the
for any of the source RTP streams that have “a=rid” lines remaining source RTP streams that have "a=rid" lines remaining
after applying the rules in <xref target="sec-sdp_o_a"/> and its subsections, MU after applying the rules in <xref target="sec-sdp_o_a" format="default"/> and it
ST s subsections <bcp14>MUST</bcp14>
support the RepairedRtpStreamId SDES item described in support the RepairedRtpStreamId SDES item described in
<xref target="I-D.ietf-avtext-rid"/> for those redundancy RTP streams. RepairedR <xref target="RFC8852" format="default"/> for those redundancy RTP streams. Repa
tpStreamId iredRtpStreamId
MUST be used for redundancy RTP streams to which it can be applied. <bcp14>MUST</bcp14> be used for redundancy RTP streams to which it can be applie
d.
Use of RepairedRtpStreamId is not applicable for Use of RepairedRtpStreamId is not applicable for
redundancy formats that directly associate RTP streams redundancy formats that directly associate RTP streams
through shared SSRCs (for example <xref target="I-D.ietf-payload-flexible-fec-sc through shared synchronization sources (SSRCs) -- for example, <xref
heme"/>) target="RFC8627" format="default"/> --
or other cases that RepairedRtpStreamId cannot support, such as referencing or other cases that RepairedRtpStreamId cannot support, such as referencing
multiple source streams.</t> multiple source streams.</t>
<t>RepairedRtpStreamId is used to provide the binding between the redundan
<t>RepairedRtpStreamId is used to provide the binding between the redundancy RTP cy RTP
stream and its source RTP stream, by setting the RepairedRtpStreamId value for stream and its source RTP stream by setting the RepairedRtpStreamId value for
the redundancy RTP stream to the RtpStreamId value of the source RTP stream. the redundancy RTP stream to the RtpStreamId value of the source RTP stream.
The redundancy RTP stream MAY (but need not) have an “a=rid” line of its own, The redundancy RTP stream <bcp14>MAY</bcp14> (but need not) have an "a=rid" line of its own,
in which case the RtpStreamId SDES item value will be different from the in which case the RtpStreamId SDES item value will be different from the
corresponding source RTP stream.</t> corresponding source RTP stream.</t>
<t>It is important to note that this indirection may result in the tempora
<t>It is important to note that this indirection may result in the temporary ry
inability to correctly associate source and redundancy data when the SSRC inability to correctly associate source and redundancy data when the SSRC
associated with the RtpStreamId or RepairedRtpStreamId is dynamically changed associated with the RtpStreamId or RepairedRtpStreamId is dynamically changed
during the RTP session. This can be avoided if all RTP packets, source and during the RTP session. This can be avoided if all RTP packets, source and
repair, after the change include their RtpStreamId or RepairedRtpStreamId, repair, include their RtpStreamId or RepairedRtpStreamId,
respectively. To maximize the probability of reception and utility of respectively, after the change. To maximize the probability of reception and ut
ility of
redundancy information after such a change, all the source packets referenced redundancy information after such a change, all the source packets referenced
by the first several repair packets SHOULD include such information. It is by the first several repair packets <bcp14>SHOULD</bcp14> include such informati
RECOMMENDED that the number of such packets is large enough to give a high on. It is
probability of actual updated association. Section 4.1.1 of <xref target="RFC828 <bcp14>RECOMMENDED</bcp14> that the number of such packets is large enough to gi
5"/> ve a high
probability of actual updated association. Section 4.1.1 of <xref target="RFC828
5" format="default"/>
provides relevant guidance for RTP header extension transmission provides relevant guidance for RTP header extension transmission
considerations. Alternatively, to avoid this issue, redundancy mechanisms considerations. Alternatively, to avoid this issue, redundancy mechanisms
that directly reference its source data may be used, such as that directly reference its source data may be used, such as
<xref target="I-D.ietf-payload-flexible-fec-scheme"/>.</t> <xref target="RFC8627" format="default"/>.</t>
<t>The "direction" field identifies the direction of the RTP stream packet
<t>The “direction” field identifies the direction of the RTP Stream packets to s to
which the indicated restrictions are applied. It may be either “send” or which the indicated restrictions are applied. It may be either "send" or
“recv”. Note that these restriction directions are expressed independently of "recv". Note that these restriction directions are expressed independently of
any “inactive”, “sendonly”, “recvonly”, or “sendrecv” attributes associated any "inactive", "sendonly", "recvonly", or "sendrecv" attributes associated
with the media section. It is, for example, valid to indicate “recv” with the media section. It is, for example, valid to indicate "recv"
restrictions on a “sendonly” stream; those restrictions would apply if, at a restrictions on a "sendonly" stream; those restrictions would apply if, at a
future point in time, the stream were changed to “sendrecv” or “recvonly”.</t> future point in time, the stream were changed to "sendrecv" or "recvonly".</t>
<t>The optional "pt=&lt;fmt-list&gt;" lists one or more PT values that can
<t>The optional “pt=&lt;fmt-list&gt;” lists one or more PT values that can be us be used
ed in the associated RTP stream. If the "a=rid" attribute contains
in the associated RTP Stream. If the “a=rid” attribute contains no "pt", then any of the PT values specified in the corresponding "m="
no “pt”, then any of the PT values specified in the corresponding “m=”
line may be used.</t> line may be used.</t>
<t>The list of zero or more codec-agnostic restrictions
<t>The list of zero or more codec-agnostic restrictions (<xref target="sec-rid_level_restrictions" format="default"/>) describes the res
(<xref target="sec-rid_level_restrictions"/>) describe the restrictions that the trictions that the
corresponding RTP Stream will conform to.</t> corresponding RTP stream will conform to.</t>
<t>This framework <bcp14>MAY</bcp14> be used in combination with the "a=fm
<t>This framework MAY be used in combination with the “a=fmtp” SDP attribute tp" SDP attribute
for describing the media format parameters for a given RTP Payload Type. In for describing the media format parameters for a given RTP payload type. In
such scenarios, the “a=rid” restrictions (<xref target="sec-rid_level_restrictio such scenarios, the "a=rid" restrictions (<xref target="sec-rid_level_restrictio
ns"/>) ns" format="default"/>)
further restrict the equivalent “a=fmtp” attributes.</t> further restrict the equivalent "a=fmtp" attributes.</t>
<t>A given SDP media description <bcp14>MAY</bcp14> have zero or more "a=r
<t>A given SDP media description MAY have zero or more “a=rid” lines describing id" lines describing
various possible RTP payload configurations. A given “rid-id” MUST NOT various possible RTP payload configurations. A given "rid-id" <bcp14>MUST NOT</b
be repeated in a given media description (“m=” section).</t> cp14>
be repeated in a given media description ("m=" section).</t>
<t>The “a=rid” media attribute MAY be used for any RTP-based media transport. I <t>The "a=rid" media attribute <bcp14>MAY</bcp14> be used for any RTP-base
t d media transport. It
is not defined for other transports, although other documents may extend its is not defined for other transports, although other documents may extend its
semantics for such transports.</t> semantics for such transports.</t>
<t>Though the restrictions specified by the "rid" restrictions follow a
<t>Though the restrictions specified by the “rid” restrictions follow a
syntax similar to session-level and media-level parameters, they are defined syntax similar to session-level and media-level parameters, they are defined
independently. All “rid” restrictions MUST be registered with IANA, using independently. All "rid" restrictions <bcp14>MUST</bcp14> be registered with IA
the registry defined in <xref target="sec-iana"/>.</t> NA, using
the registry defined in <xref target="sec-iana" format="default"/>.</t>
<t><xref target="sec-abnf"/> gives a formal Augmented Backus-Naur Form (ABNF) <x <t><xref target="sec-abnf" format="default"/> gives a formal Augmented Bac
ref target="RFC5234"/> kus-Naur Form (ABNF) <xref target="RFC5234" format="default"/>
grammar for the “rid” attribute. The “a=rid” media attribute is not dependent grammar for the "rid" attribute. The "a=rid" media attribute is not dependent
on charset.</t> on charset.</t>
</section>
<section anchor="sec-rid_level_restrictions" numbered="true" toc="default">
<name>"a=rid" Restrictions</name>
</section> <t>
<section anchor="sec-rid_level_restrictions" title="“a=rid” restrictions"> This section defines the "a=rid" restrictions that can be used to restrict the
RTP payload encoding format in a codec-agnostic way. Please also see
<t>This section defines the “a=rid” restrictions that can be used to restrict the preceding section for a description of how the "pt" parameter is used.
the RTP payload encoding format in a codec-agnostic way.</t> </t>
<t>The following restrictions are intended to apply to video codecs in a <t>The following restrictions are intended to apply to video codecs in a
codec-independent fashion.</t> codec-independent fashion.</t>
<ul spacing="normal">
<t><list style="symbols"> <li><strong>max-width</strong>, for spatial resolution in pixels. In th
<t>max-width, for spatial resolution in pixels. In the case that stream e case that
orientation signaling is used to modify the intended display orientation, stream-orientation signaling is used to modify the intended display
this attribute refers to the width of the stream when a rotation of zero orientation, this attribute refers to the width of the stream when a
degrees is encoded.</t> rotation of zero degrees is encoded.</li>
<t>max-height, for spatial resolution in pixels. In the case that stream <li><strong>max-height</strong>, for spatial resolution in pixels. In t
orientation signaling is used to modify the intended display orientation, he case that
stream-orientation signaling is used to modify the intended display
orientation,
this attribute refers to the height of the stream when a rotation of zero this attribute refers to the height of the stream when a rotation of zero
degrees is encoded.</t> degrees is encoded.</li>
<t>max-fps, for frame rate in frames per second. For encoders that do not use <li><strong>max-fps</strong>, for frame rate in frames per second. For
a fixed framerate for encoding, this value is used to restrict the minimum encoders that do not use
a fixed frame rate for encoding, this value is used to restrict the minimum
amount of time between frames: the time between any two consecutive frames amount of time between frames: the time between any two consecutive frames
SHOULD NOT be less than 1/max-fps seconds.</t> <bcp14>SHOULD NOT</bcp14> be less than 1/max-fps seconds.</li>
<t>max-fs, for frame size in pixels per frame. This is the product of frame <li><strong>max-fs</strong>, for frame size in pixels per frame. This is
width and frame height, in pixels, for rectangular frames.</t> the product of frame
<t>max-br, for bit rate in bits per second. The restriction applies to the width and frame height, in pixels, for rectangular frames.</li>
media payload only, and does not include overhead introduced by other layers <li><strong>max-br</strong>, for bitrate in bits per second. The restri
ction applies to the
media payload only and does not include overhead introduced by other layers
(e.g., RTP, UDP, IP, or Ethernet). The exact means of keeping within this (e.g., RTP, UDP, IP, or Ethernet). The exact means of keeping within this
limit are left up to the implementation, and instantaneous excursions limit are left up to the implementation, and instantaneous excursions
outside the limit are permissible. For any given one-second sliding window, outside the limit are permissible. For any given one-second sliding window,
however, the total number of bits in the payload portion of RTP SHOULD NOT however, the total number of bits in the payload portion of RTP <bcp14>SHOULD NO
exceed the value specified in “max-br.”</t> T</bcp14>
<t>max-pps, for pixel rate in pixels per second. This value SHOULD be handled exceed the value specified in "max-br."</li>
<li><strong>max-pps</strong>, for pixel rate in pixels per second. This
value <bcp14>SHOULD</bcp14> be handled
identically to max-fps, after performing the following conversion: max-fps = identically to max-fps, after performing the following conversion: max-fps =
max-pps / (width * height). If the stream resolution changes, this value is max-pps / (width * height). If the stream resolution changes, this value is
recalculated. Due to this recalculation, excursions outside the specified recalculated. Due to this recalculation, excursions outside the specified
maximum are possible near resolution change boundaries.</t> maximum are possible near resolution-change boundaries.</li>
<t>max-bpp, for maximum number of bits per pixel, calculated as an average of <li><strong>max-bpp</strong>, for maximum number of bits per pixel, calc
ulated as an average of
all samples of any given coded picture. This is expressed as all samples of any given coded picture. This is expressed as
a floating point value, with an allowed range of 0.0001 to 48.0. These a floating point value, with an allowed range of 0.0001 to 48.0. These
values MUST NOT be encoded with more than four digits to the right of the values <bcp14>MUST NOT</bcp14> be encoded with more than four digits to the righ
decimal point.</t> t of the
<t>depend, to identify other streams that the stream depends on. The value decimal point.</li>
<li><strong>depend</strong>, to identify other streams that the stream d
epends on. The value
is a comma-separated list of rid-ids. These rid-ids identify RTP streams is a comma-separated list of rid-ids. These rid-ids identify RTP streams
that this stream depends on in order to allow for proper interpretation. that this stream depends on in order to allow for proper interpretation.
The mechanism defined in this document allows for such dependencies The mechanism defined in this document allows for such dependencies
to be expressed only when the streams are in the same media section.</t> to be expressed only when the streams are in the same media section.</li>
</list></t> </ul>
<t>All the restrictions are optional and subject to negotiation based on t
<t>All the restrictions are optional and are subject to negotiation based on the he
SDP Offer/Answer rules described in <xref target="sec-sdp_o_a"/>.</t> SDP offer/answer rules described in <xref target="sec-sdp_o_a" format="default"/
>.</t>
<t>This list is intended to be an initial set of restrictions. Future documents <t>This list is intended to be an initial set of restrictions. Future docu
may define additional restrictions; see <xref target="sec-iana_rid"/>. While th ments
is document may define additional restrictions; see <xref target="sec-iana_rid" format="defa
ult"/>. While this document
does not define restrictions for audio codecs or any media types other than does not define restrictions for audio codecs or any media types other than
video, there is no reason such video, there is no reason such
restrictions should be precluded from definition and registration by other restrictions should be precluded from definition and registration by other
documents.</t> documents.</t>
<t><xref target="sec-abnf" format="default"/> provides formal Augmented Ba
<t><xref target="sec-abnf"/> provides formal Augmented Backus-Naur Form (ABNF) < ckus-Naur Form (ABNF) <xref target="RFC5234" format="default"/>
xref target="RFC5234"/> grammar for each of the "a=rid" restrictions defined in this section.</t>
grammar for each of the “a=rid” restrictions defined in this section.</t> </section>
<section anchor="sec-sdp_o_a" numbered="true" toc="default">
</section> <name>SDP Offer/Answer Procedures</name>
<section anchor="sec-sdp_o_a" title="SDP Offer/Answer Procedures"> <t>This section describes the SDP offer/answer procedures <xref target="RF
C3264" format="default"/> when
<t>This section describes the SDP Offer/Answer <xref target="RFC3264"/> procedur
es when
using this framework.</t> using this framework.</t>
<t>Note that "rid-id" values are only required to be unique within a
<t>Note that “rid-id” values are only required to be unique within a media section ("m=" line); they do not necessarily need to be unique within an
media section (“m-line”); they do not necessarily need to be unique within an
entire RTP session. In traditional usage, each media section is sent on its entire RTP session. In traditional usage, each media section is sent on its
own unique 5-tuple (that is: combination of sending address, sending port, own unique 5-tuple (that is: combination of sending address, sending port,
receiving address, receiving port, and transport protocol), which provides an receiving address, receiving port, and transport protocol), which provides an
unambiguous scope. Similarly, when using BUNDLE unambiguous scope.
<xref target="I-D.ietf-mmusic-sdp-bundle-negotiation"/>, MID values associate RT
P streams
uniquely to a single media description. When RID is used with the BUNDLE
mechanism, streams will be associated with both MID and RID SDES items.</t>
<section anchor="sec-gen_offer" title="Generating the Initial SDP Offer">
<t>For each RTP media description in the offer, the offerer MAY choose to includ Similarly, when using BUNDLE <xref target="RFC8843" format="default"/>,
e one Media Identification (MID) values associate RTP streams
or more “a=rid” lines to specify a configuration profile for the given set of uniquely to a single media description.
RTP Payload Types.</t>
<t>In order to construct a given “a=rid” line, the offerer must follow these When restriction identifier (RID) is used with the BUNDLE
mechanism, streams will be associated with both MID and RID SDES items.</t>
<section anchor="sec-gen_offer" numbered="true" toc="default">
<name>Generating the Initial SDP Offer</name>
<t>For each RTP media description in the offer, the offerer <bcp14>MAY</
bcp14> choose to include one
or more "a=rid" lines to specify a configuration profile for the given set of
RTP payload types.</t>
<t>In order to construct a given "a=rid" line, the offerer must follow t
hese
steps:</t> steps:</t>
<ol spacing="normal" type="1">
<t><list style="numbers"> <li>It <bcp14>MUST</bcp14> generate a "rid-id" that is unique within a
<t>It MUST generate a “rid-id” that is unique within a media media
description</t> description.</li>
<t>It MUST set the direction for the “rid-id” to one of <li>It <bcp14>MUST</bcp14> set the direction for the "rid-id" to one o
“send” or “recv”</t> f
<t>It MAY include a listing of SDP media formats (usually corresponding to RTP "send" or "recv".</li>
payload types) allowed to appear in the RTP Stream. Any Payload Types <li>It <bcp14>MAY</bcp14> include a listing of SDP media formats (usua
chosen MUST be a valid payload type for the media section (that is, it must lly corresponding to RTP
be listed on the “m=” line). The order of the listed formats is payload types) allowed to appear in the RTP stream. Any payload type
chosen <bcp14>MUST</bcp14> be a valid payload type for the media section (that i
s, it must
be listed on the "m=" line). The order of the listed formats is
significant; the alternatives are listed from (left) most preferred to significant; the alternatives are listed from (left) most preferred to
(right) least preferred. When using RID, this preference overrides the (right) least preferred. When using RID, this preference overrides the
normal codec preference as expressed by format type ordering on the normal codec preference as expressed by format type ordering on the
“m=”-line, using regular SDP rules.</t> "m=" line, using regular SDP rules.</li>
<t>The Offerer then chooses zero or more “a=rid” restrictions <li>The offerer then chooses zero or more "a=rid" restrictions
(<xref target="sec-rid_level_restrictions"/>) to be applied to the RTP Stream, a (<xref target="sec-rid_level_restrictions" format="default"/>) to be applied to
nd the RTP stream and
adds them to the “a=rid” line.</t> adds them to the "a=rid" line.</li>
<t>If the offerer wishes the answerer to have the ability to specify a <li>If the offerer wishes the answerer to have the ability to specify
restriction, but does not wish to set a value itself, it includes the a
name of the restriction in the “a=rid” line, but without any indicated restriction but does not wish to set a value itself, it includes the
value.</t> name of the restriction in the "a=rid" line, but without any indicated
</list></t> value.</li>
</ol>
<t>Note: If an “a=fmtp” attribute is also used to provide media-format-specific <t>Note: If an "a=fmtp" attribute is also used to provide media-format-s
parameters, then the “a=rid” restrictions will further restrict the pecific
equivalent “a=fmtp” parameters for the given Payload Type for the specified parameters, then the "a=rid" restrictions will further restrict the
RTP Stream.</t> equivalent "a=fmtp" parameters for the given payload type for the specified
RTP stream.</t>
<t>If a given codec would require an “a=fmtp” line when used without “a=rid” the <t>If a given codec would require an "a=fmtp" line when used without "a=
n rid", then
the offer MUST include a valid corresponding “a=fmtp” line even when using the offer <bcp14>MUST</bcp14> include a valid corresponding "a=fmtp" line even w
“a=rid”.</t> hen using
"a=rid".</t>
</section> </section>
<section anchor="answerer-processing-the-sdp-offer" title="Answerer processing t <section anchor="answerer-processing-the-sdp-offer" numbered="true" toc="d
he SDP Offer"> efault">
<name>Answerer Processing the SDP Offer</name>
<section anchor="sec-rid_unaware" title="“a=rid”-unaware Answerer"> <section anchor="sec-rid_unaware" numbered="true" toc="default">
<name>"a=rid"-Unaware Answerer</name>
<t>If the receiver doesn’t support the framework defined in this <t>If the receiver doesn't support the framework defined in this
specification, the entire “a=rid” line is ignored following the standard specification, the entire "a=rid" line is ignored following the standard
<xref target="RFC3264"/> Offer/Answer rules.</t> offer/answer rules <xref target="RFC3264" format="default"/>.</t>
<t><xref target="sec-gen_offer" format="default"/> requires the offer
<t><xref target="sec-gen_offer"/> requires the offer to include a valid “a=fmtp” to include a valid "a=fmtp" line
line for any media formats that otherwise require it (in other words, the "a=rid"
for any media formats that otherwise require it (in other words, the “a=rid” line cannot be used to replace "a=fmtp" configuration). As a result,
line cannot be used to replace “a=fmtp” configuration). As a result, ignoring the "a=rid" line is always guaranteed to result in a valid
ignoring the “a=rid” line is always guaranteed to result in a valid
session description.</t> session description.</t>
</section>
</section> <section anchor="sec-rid_offer_recv" numbered="true" toc="default">
<section anchor="sec-rid_offer_recv" title="“a=rid”-aware Answerer"> <name>"a=rid"-Aware Answerer</name>
<t>If the answerer supports the "a=rid" attribute, the following verif
<t>If the answerer supports the “a=rid” attribute, the following verification ication
steps are executed, in order, for each “a=rid” line in a received offer:</t> steps are executed, in order, for each "a=rid" line in a received offer:</t>
<ol spacing="normal" type="1">
<t><list style="numbers"> <li>The answerer ensures that the "a=rid" line is syntactically well
<t>The answerer ensures that the “a=rid” line is syntactically well formed. In the case of a syntax error, the "a=rid" line is discarded.</li>
formed. In the case of a syntax error, the “a=rid” line is discarded.</t> <li>The answerer extracts the rid-id from the "a=rid" line and verif
<t>The answerer extracts the rid-id from the “a=rid” line and verifies its ies its
uniqueness within a media section. In the case of a duplicate, the entire uniqueness within a media section. In the case of a duplicate, the entire
“a=rid” line, and all “a=rid” lines with rid-ids that duplicate this line, "a=rid" line, and all "a=rid" lines with rid-ids that duplicate this line,
are discarded and MUST NOT be included in the SDP Answer.</t> are discarded and <bcp14>MUST NOT</bcp14> be included in the SDP answer.</li>
<t>If the “a=rid” line contains a “pt=”, the list of payload types <li>If the "a=rid" line contains a "pt=", the list of payload types
is verified against the list of valid payload types for the media section is verified against the list of valid payload types for the media section
(that is, those listed on the “m=” line). Any PT missing from the “m=” line (that is, those listed on the "m=" line). Any PT missing from the "m=" line
is discarded from the set of values in the “pt=”. If no values are left is discarded from the set of values in the "pt=". If no values are left
in the “pt=” parameter after this processing, then the “a=rid” line is discarded in the "pt=" parameter after this processing, then the "a=rid" line is discarded
.</t> .</li>
<t>If the “direction” field is “recv”, the answerer ensures that the specified <li>If the "direction" field is "recv", the answerer ensures that th
“a=rid” restrictions are supported. In the case of an unsupported e specified
restriction, the “a=rid” line is discarded.</t> "a=rid" restrictions are supported. In the case of an unsupported
<t>If the “depend” restriction is included, the answerer MUST make restriction, the "a=rid" line is discarded.</li>
<li>If the "depend" restriction is included, the answerer <bcp14>MUS
T</bcp14> make
sure that the listed rid-ids unambiguously match the sure that the listed rid-ids unambiguously match the
rid-ids in the media description. Any “depend” “a=rid” lines that do not are rid-ids in the media description. Any "depend" "a=rid" lines that do not are
discarded.</t> discarded.</li>
<t>The answerer verifies that the restrictions are consistent <li>The answerer verifies that the restrictions are consistent
with at least one of the codecs to be used with the RTP Stream. If the with at least one of the codecs to be used with the RTP stream. If the
“a=rid” line contains a “pt=”, it contains the list of such "a=rid" line contains a "pt=", it contains the list of such
codecs; otherwise, the list of such codecs is taken from the associated codecs; otherwise, the list of such codecs is taken from the associated
“m=” line. See <xref target="sec-feature_interactions"/> for more detail. If th "m=" line. See <xref target="sec-feature_interactions" format="default"/> for m
e ore detail. If the
“a=rid” restrictions are incompatible with the other codec properties "a=rid" restrictions are incompatible with the other codec properties
for all codecs, then the “a=rid” line is discarded.</t> for all codecs, then the "a=rid" line is discarded.</li>
</list></t> </ol>
<t>Note that the answerer does not need to understand every restrictio
<t>Note that the answerer does not need to understand every restriction present n present
in a “send” line: if a stream sender restricts the stream in a way that the in a "send" line: if a stream sender restricts the stream in a way that the
receiver does not understand, this causes no issues with interoperability.</t> receiver does not understand, this causes no issues with interoperability.</t>
</section>
</section> </section>
</section> <section anchor="sec-rid_answer_send" numbered="true" toc="default">
<section anchor="sec-rid_answer_send" title="Generating the SDP Answer"> <name>Generating the SDP Answer</name>
<t>Having performed verification of the SDP offer as described in
<t>Having performed verification of the SDP offer as described in <xref target="sec-rid_offer_recv" format="default"/>, the answerer shall perform
<xref target="sec-rid_offer_recv"/>, the answerer shall perform the following st the following steps to
eps to
generate the SDP answer.</t> generate the SDP answer.</t>
<t>For each "a=rid" line that has not been discarded by previous process
<t>For each “a=rid” line that has not been discarded by previous processing:</t> ing:</t>
<ol spacing="normal" type="1">
<t><list style="numbers"> <li>The value of the "direction" field is reversed: "send" is changed
<t>The value of the “direction” field is reversed: “send” is changed to "recv", and "recv" is changed to "send".</li>
to “recv”, and “recv” is changed to “send”.</t> <li>The answerer <bcp14>MAY</bcp14> choose to modify specific "a=rid"
<t>The answerer MAY choose to modify specific “a=rid” restriction values in restriction values in
the answer SDP. In such a case, the modified value MUST be more restrictive the answer SDP. In such a case, the modified value <bcp14>MUST</bcp14> be more r
than the ones specified in the offer. The answer MUST NOT include any estrictive
restrictions that were not present in the offer.</t> than the ones specified in the offer. The answer <bcp14>MUST NOT</bcp14> includ
<t>The answerer MUST NOT modify the “rid-id” present in the offer.</t> e any
<t>If the “a=rid” line contains a “pt=”, the answerer is allowed to restrictions that were not present in the offer.</li>
discard one or more media formats from a given “a=rid” line. If the answerer <li>The answerer <bcp14>MUST NOT</bcp14> modify the "rid-id" present i
chooses to discard all the media formats from an “a=rid” line, the n the offer.</li>
answerer MUST discard the entire “a=rid” line. If the offer did not contain <li>If the "a=rid" line contains a "pt=", the answerer is allowed to
a “pt=” for a given “a=rid” line, then the answer MUST NOT discard one or more media formats from a given "a=rid" line. If the answerer
contain a “pt=” in the corresponding line.</t> chooses to discard all the media formats from an "a=rid" line, the
<t>In cases where the answerer is unable to support the payload configuration answerer <bcp14>MUST</bcp14> discard the entire "a=rid" line. If the offer did n
specified in a given “a=rid” line with a direction of “recv” in the offer, ot contain
the answerer MUST discard the corresponding “a=rid” line. This includes a "pt=" for a given "a=rid" line, then the answer <bcp14>MUST NOT</bcp14>
contain a "pt=" in the corresponding line.</li>
<li>In cases where the answerer is unable to support the payload confi
guration
specified in a given "a=rid" line with a direction of "recv" in the offer,
the answerer <bcp14>MUST</bcp14> discard the corresponding "a=rid" line. This i
ncludes
situations in which the answerer does not understand one or more of the situations in which the answerer does not understand one or more of the
restrictions in an “a=rid” line with a direction of “recv”.</t> restrictions in an "a=rid" line with a direction of "recv".</li>
</list></t> </ol>
<t>Note: In the case that the answerer uses different PT values to repre
<t>Note: in the case that the answerer uses different PT values to represent a sent a
codec than the offerer did, the “a=rid” values in the answer use the PT values codec than the offerer did, the "a=rid" values in the answer use the PT values
that are present in its answer.</t> that are present in its answer.</t>
</section>
</section> <section anchor="sec-rid_answer_recv" numbered="true" toc="default">
<section anchor="sec-rid_answer_recv" title="Offerer Processing of the SDP Answe <name>Offerer Processing of the SDP Answer</name>
r"> <t>The offerer <bcp14>SHALL</bcp14> follow these steps when processing t
he answer:</t>
<t>The offerer SHALL follow these steps when processing the answer:</t> <ol spacing="normal" type="1">
<li>The offerer matches the "a=rid" line in the answer to the "a=rid"
<t><list style="numbers"> line
<t>The offerer matches the “a=rid” line in the answer to the “a=rid” line in the offer using the "rid-id". If no matching line can be located
in the offer using the “rid-id”. If no matching line can be located in the offer, the "a=rid" line is ignored.</li>
in the offer, the “a=rid” line is ignored.</t> <li>If the answer contains any restrictions that were not present in t
<t>If the answer contains any restrictions that were not present in the offer, he offer,
then the offerer SHALL discard the “a=rid” line.</t> then the offerer <bcp14>SHALL</bcp14> discard the "a=rid" line.</li>
<t>If the restrictions have been changed between the offer and the <li>If the restrictions have been changed between the offer and the
answer, the offerer MUST ensure that the modifications are more restrictive answer, the offerer <bcp14>MUST</bcp14> ensure that the modifications are more r
than they were in the original offer, and that they can be supported; if estrictive
not, the offerer SHALL discard the “a=rid” line.</t> than they were in the original offer and that they can be supported; if
<t>If the “a=rid” line in the answer contains a “pt=” but the not, the offerer <bcp14>SHALL</bcp14> discard the "a=rid" line.</li>
offer did not, the offerer SHALL discard the “a=rid” line.</t> <li>If the "a=rid" line in the answer contains a "pt=" but the
<t>If the “a=rid” line in the answer contains a “pt=” and the offer did not, the offerer <bcp14>SHALL</bcp14> discard the "a=rid" line.</li>
<li>If the "a=rid" line in the answer contains a "pt=" and the
offer did as well, the offerer verifies that the list of payload types is a offer did as well, the offerer verifies that the list of payload types is a
subset of those sent in the corresponding “a=rid” line in the offer. Note subset of those sent in the corresponding "a=rid" line in the offer. Note
that this matching must be performed semantically rather than on literal PT that this matching must be performed semantically rather than on literal PT
values, as the remote end may not be using symmetric PTs. For the purpose values, as the remote end may not be using symmetric PTs. For the purpose
of this comparison: for each PT listed on the “a=rid” line in the answer, of this comparison: for each PT listed on the "a=rid" line in the answer,
the offerer looks up the corresponding “a=rtpmap” and “a=fmtp” lines in the the offerer looks up the corresponding "a=rtpmap" and "a=fmtp" lines in the
answer. It then searches the list of “pt=” values indicated in the offer, answer. It then searches the list of "pt=" values indicated in the offer
and attempts to find one with an equivalent set of “a=rtpmap” and “a=fmtp” and attempts to find one with an equivalent set of "a=rtpmap" and "a=fmtp"
lines in the offer. If all PTs in the answer can be matched, then the “pt=” lines in the offer. If all PTs in the answer can be matched, then the "pt="
values pass validation; otherwise, it fails. If this validation fails, the values pass validation; otherwise, it fails. If this validation fails, the
offerer SHALL discard the “a=rid” line. Note that this semantic comparison offerer <bcp14>SHALL</bcp14> discard the "a=rid" line. Note that this semantic c omparison
necessarily requires an understanding of the meaning of codec parameters, necessarily requires an understanding of the meaning of codec parameters,
rather than a rote byte-wise comparison of their values.</t> rather than a rote byte-wise comparison of their values.</li>
<t>If the “a=rid” line contains a “pt=”, the offerer verifies that <li>If the "a=rid" line contains a "pt=", the offerer verifies that
the attribute values provided in the “a=rid” attributes are consistent the attribute values provided in the "a=rid" attributes are consistent
with the corresponding codecs and their other parameters. See with the corresponding codecs and their other parameters. See
<xref target="sec-feature_interactions"/> for more detail. If the “a=rid” restri ctions <xref target="sec-feature_interactions" format="default"/> for more detail. If t he "a=rid" restrictions
are incompatible with the other codec properties, then the offerer are incompatible with the other codec properties, then the offerer
SHALL discard the “a=rid” line.</t> <bcp14>SHALL</bcp14> discard the "a=rid" line.</li>
<t>The offerer verifies that the restrictions are consistent <li>The offerer verifies that the restrictions are consistent
with at least one of the codecs to be used with the RTP Stream. If the with at least one of the codecs to be used with the RTP stream. If the
“a=rid” line contains a “pt=”, it contains the list of such "a=rid" line contains a "pt=", it contains the list of such
codecs; otherwise, the list of such codecs is taken from the associated codecs; otherwise, the list of such codecs is taken from the associated
“m=” line. See <xref target="sec-feature_interactions"/> for more detail. If th "m=" line. See <xref target="sec-feature_interactions" format="default"/> for m
e ore detail. If the
“a=rid” restrictions are incompatible with the other codec properties "a=rid" restrictions are incompatible with the other codec properties
for all codecs, then the offerer SHALL discard the “a=rid” line.</t> for all codecs, then the offerer <bcp14>SHALL</bcp14> discard the "a=rid" line.<
</list></t> /li>
</ol>
<t>Any “a=rid” line present in the offer that was not matched by step 1 above <t>Any "a=rid" line present in the offer that was not matched by step 1
has been discarded by the answerer, and does not form part of the negotiated above
restrictions on an RTP Stream. The offerer MAY still apply any restrictions has been discarded by the answerer and does not form part of the negotiated
it indicated in an “a=rid” line with a direction field of “send”, but restrictions on an RTP stream. The offerer <bcp14>MAY</bcp14> still apply any re
strictions
it indicated in an "a=rid" line with a direction field of "send", but
it is not required to do so.</t> it is not required to do so.</t>
<t>It is important to note that there are several ways in which an offer
<t>It is important to note that there are several ways in which an offer can can
contain a media section with “a=rid” lines, but the corresponding media contain a media section with "a=rid" lines, although the corresponding media
section in the response does not. This includes situations in which the section in the response does not. This includes situations in which the
answerer does not support “a=rid” at all, or does not support the indicated answerer does not support "a=rid" at all or does not support the indicated
restrictions. Under such circumstances, the offerer MUST be prepared to restrictions. Under such circumstances, the offerer <bcp14>MUST</bcp14> be prepa
red to
receive a media stream to which no restrictions have been applied.</t> receive a media stream to which no restrictions have been applied.</t>
</section>
</section> <section anchor="modifying-the-session" numbered="true" toc="default">
<section anchor="modifying-the-session" title="Modifying the Session"> <name>Modifying the Session</name>
<t>Offers and answers inside an existing session follow the rules for in
<t>Offers and answers inside an existing session follow the rules for initial itial
session negotiation. Such an offer MAY propose a change in the number of RIDs session negotiation. Such an offer <bcp14>MAY</bcp14> propose a change in the n
umber of RIDs
in use. To avoid race conditions with media, any RIDs with proposed changes in use. To avoid race conditions with media, any RIDs with proposed changes
SHOULD use a new ID, rather than re-using one from the previous offer/answer <bcp14>SHOULD</bcp14> use a new ID rather than reusing one from the previous off
exchange. RIDs without proposed changes SHOULD re-use the ID from the previous er/answer
exchange. RIDs without proposed changes <bcp14>SHOULD</bcp14> reuse the ID from
the previous
exchange.</t> exchange.</t>
</section>
</section> </section>
</section> <section anchor="sec-declarative_sdp" numbered="true" toc="default">
<section anchor="sec-declarative_sdp" title="Use with Declarative SDP"> <name>Use with Declarative SDP</name>
<t>This document does not define the use of a RID in declarative SDP. If
<t>This document does not define the use of RID in declarative SDP. If
concrete use cases for RID in declarative SDP use are identified concrete use cases for RID in declarative SDP use are identified
in the future, we expect that additional specifications will address in the future, we expect that additional specifications will address
such use.</t> such use.</t>
</section>
</section> <section anchor="sec-feature_interactions" numbered="true" toc="default">
<section anchor="sec-feature_interactions" title="Interaction with Other Techniq <name>Interaction with Other Techniques</name>
ues"> <t>Historically, a number of other approaches have been defined that allow
<t>Historically, a number of other approaches have been defined that allow
restricting media streams via SDP. These include:</t> restricting media streams via SDP. These include:</t>
<ul spacing="normal">
<li>Codec-specific configuration set via format parameters ("a=fmtp") --
for
example, the H.264 "max-fs" format parameter <xref target="RFC6184" format="defa
ult"/></li>
<t><list style="symbols"> <li>Size restrictions imposed by the "a=imageattr" attribute
<t>Codec-specific configuration set via format parameters (“a=fmtp”); for <xref target="RFC6236" format="default"/></li>
example, the H.264 “max-fs” format parameter <xref target="RFC6184"/></t> </ul>
<t>Size restrictions imposed by image attribute attributes (“a=imageattr”) <t>When the mechanism described in this document is used in conjunction wi
<xref target="RFC6236"/></t> th
</list></t>
<t>When the mechanism described in this document is used in conjunction with
these other restricting mechanisms, it is intended to impose additional these other restricting mechanisms, it is intended to impose additional
restrictions beyond those communicated in other techniques.</t> restrictions beyond those communicated in other techniques.</t>
<t>In an offer, this means that "a=rid" lines, when combined with other
<t>In an offer, this means that “a=rid” lines, when combined with other
restrictions on the media stream, are expected to result in a non-empty intersec tion. restrictions on the media stream, are expected to result in a non-empty intersec tion.
For example, if image attributes are used to indicate that a PT has a minimum For example, if image attributes are used to indicate that a PT has a minimum
width of 640, then specification of “max-width=320” in an “a=rid” line that is width of 640, then specification of "max-width=320" in an "a=rid" line that is
then applied to that PT is nonsensical. According to the rules of then applied to that PT is nonsensical. According to the rules of
<xref target="sec-rid_offer_recv"/>, this will result in the corresponding “a=ri d” line <xref target="sec-rid_offer_recv" format="default"/>, this will result in the co rresponding "a=rid" line
being ignored by the recipient.</t> being ignored by the recipient.</t>
<t>In an answer, the "a=rid" lines, when combined with the other
<t>In an answer, the “a=rid” lines, when combined with the other
restrictions on the media stream, are also expected to result in a non-empty restrictions on the media stream, are also expected to result in a non-empty
intersection. If the implementation generating an answer wishes to restrict a intersection. If the implementation generating an answer wishes to restrict a
property of the stream below that which would be allowed by other parameters property of the stream below that which would be allowed by other parameters
(e.g., those specified in “a=fmtp” or “a=imageattr”), its only recourse is to (e.g., those specified in "a=fmtp" or "a=imageattr"), its only recourse is to
discard the “a=rid” line altogether, as described in <xref target="sec-rid_answe discard the "a=rid" line altogether, as described in <xref target="sec-rid_answe
r_send"/>. r_send" format="default"/>.
If it instead attempts to restrict the stream beyond what is allowed by other If it instead attempts to restrict the stream beyond what is allowed by other
mechanisms, then the offerer will ignore the corresponding “a=rid” line, as mechanisms, then the offerer will ignore the corresponding "a=rid" line, as
described in <xref target="sec-rid_answer_recv"/>.</t> described in <xref target="sec-rid_answer_recv" format="default"/>.</t>
<t>The following subsections demonstrate these interactions using commonly
<t>The following subsections demonstrate these interactions using commonly-used used
video codecs. These descriptions are illustrative of the interaction principles video codecs. These descriptions are illustrative of the interaction principles
outlined above, and are not normative.</t> outlined above and are not normative.</t>
<section anchor="interaction-with-vp8-format-parameters" numbered="true" t
<section anchor="interaction-with-vp8-format-parameters" title="Interaction with oc="default">
VP8 Format Parameters"> <name>Interaction with VP8 Format Parameters</name>
<t><xref target="RFC7741" format="default"/> defines two format paramete
<t><xref target="RFC7741"/> defines two format parameters for the VP8 codec. rs for the VP8 codec.
Both correspond to restrictions on receiver capabilities, and never Both correspond to restrictions on receiver capabilities and never
indicate sending restrictions.</t> indicate sending restrictions.</t>
<section anchor="max-fr-maximum-framerate" numbered="true" toc="default"
<section anchor="max-fr-maximum-framerate" title="max-fr - Maximum Framerate"> >
<name>max-fr - Maximum Frame Rate</name>
<t>The VP8 “max-fr” format parameter corresponds to the “max-fps” restriction <t>The VP8 "max-fr" format parameter corresponds to the "max-fps" rest
riction
defined in this specification. If an RTP sender is generating a stream using defined in this specification. If an RTP sender is generating a stream using
a format defined with this format parameter, and the sending restrictions a format defined with this format parameter, and the sending restrictions
defined via “a=rid” include a “max-fps” parameter, then the sent stream defined via "a=rid" include a "max-fps" parameter, then the sent stream
will conform to the smaller of the two values.</t> will conform to the smaller of the two values.</t>
</section>
</section> <section anchor="max-fs-maximum-framesize-in-vp8-macroblocks" numbered="
<section anchor="max-fs-maximum-framesize-in-vp8-macroblocks" title="max-fs - Ma true" toc="default">
ximum Framesize, in VP8 Macroblocks"> <name>max-fs - Maximum Frame Size, in VP8 Macroblocks</name>
<t>The VP8 "max-fs" format parameter corresponds to the "max-fs"
<t>The VP8 “max-fs” format parameter corresponds to the “max-fs”
restriction defined in this document, by way of a conversion factor of the restriction defined in this document, by way of a conversion factor of the
number of pixels per macroblock (typically 256). If an RTP sender is number of pixels per macroblock (typically 256). If an RTP sender is
generating a stream using a format defined with this format parameter, and generating a stream using a format defined with this format parameter, and
the sending restrictions defined via “a=rid” include a “max-fs” parameter, the sending restrictions defined via "a=rid" include a "max-fs" parameter,
then the sent stream will conform to the smaller of the two values; then the sent stream will conform to the smaller of the two values;
that is, the number of pixels per frame will not exceed:</t> that is, the number of pixels per frame will not exceed:</t>
<figure><artwork><![CDATA[ <sourcecode>
min(rid_max_fs, fmtp_max_fs * macroblock_size) min(rid_max_fs, fmtp_max_fs * macroblock_size)
]]></artwork></figure> </sourcecode>
<t>This fmtp parameter also has bearing on the
max-height and max-width parameters.
<t>This fmtp parameter also has bearing on the <xref section="6.1" sectionFormat="of" target="RFC7741" format="default"/> requi
max-height and max-width parameters. Section 6.1 of res that the width and height of the frame in
<xref target="RFC7741"/> requires that the width and height of the frame in macroblocks be less than int(sqrt(fmtp_max_fs * 8)).
macroblocks are also required to be less than int(sqrt(fmtp_max_fs * 8)).
Accordingly, the maximum width of a transmitted stream will be limited to:</t> Accordingly, the maximum width of a transmitted stream will be limited to:</t>
<figure><artwork><![CDATA[ <sourcecode>
min(rid_max_width, int(sqrt(fmtp_max_fs * 8)) * macroblock_width) min(rid_max_width, int(sqrt(fmtp_max_fs * 8)) * macroblock_width)
]]></artwork></figure> </sourcecode>
<t>Similarly, the stream’s height will be limited to:</t> <t>Similarly, the stream's height will be limited to:</t>
<figure><artwork><![CDATA[ <sourcecode>
min(rid_max_height, int(sqrt(fmtp_max_fs * 8)) * macroblock_height) min(rid_max_height, int(sqrt(fmtp_max_fs * 8)) * macroblock_height)
]]></artwork></figure> </sourcecode>
</section>
</section> </section>
</section> <section anchor="interaction-with-h264-format-parameters" numbered="true"
<section anchor="interaction-with-h264-format-parameters" title="Interaction wit toc="default">
h H.264 Format Parameters"> <name>Interaction with H.264 Format Parameters</name>
<t><xref target="RFC6184" format="default"/> defines format parameters f
<t><xref target="RFC6184"/> defines format parameters for the H.264 video codec. or the H.264 video codec. The majority
The majority
of these parameters do not correspond to codec-independent restrictions:</t> of these parameters do not correspond to codec-independent restrictions:</t>
<ul spacing="normal">
<t><list style="symbols"> <li>deint-buf-cap</li>
<t>deint-buf-cap</t> <li>in-band-parameter-sets</li>
<t>in-band-parameter-sets</t> <li>level-asymmetry-allowed</li>
<t>level-asymmetry-allowed</t> <li>max-rcmd-nalu-size</li>
<t>max-rcmd-nalu-size</t> <li>max-cpb</li>
<t>max-cpb</t> <li>max-dpb</li>
<t>max-dpb</t> <li>packetization-mode</li>
<t>packetization-mode</t> <li>redundant-pic-cap</li>
<t>redundant-pic-cap</t> <li>sar-supported</li>
<t>sar-supported</t> <li>sar-understood</li>
<t>sar-understood</t> <li>sprop-deint-buf-req</li>
<t>sprop-deint-buf-req</t> <li>sprop-init-buf-time</li>
<t>sprop-init-buf-time</t> <li>sprop-interleaving-depth</li>
<t>sprop-interleaving-depth</t> <li>sprop-level-parameter-sets</li>
<t>sprop-level-parameter-sets</t> <li>sprop-max-don-diff</li>
<t>sprop-max-don-diff</t> <li>sprop-parameter-sets</li>
<t>sprop-parameter-sets</t> <li>use-level-src-parameter-sets</li>
<t>use-level-src-parameter-sets</t> </ul>
</list></t> <t>Note that the max-cpb and max-dpb format parameters for H.264 corresp
ond to
<t>Note that the max-cpb and max-dpb format parameters for H.264 correspond to
restrictions on the stream, but they are specific to the way the H.264 codec restrictions on the stream, but they are specific to the way the H.264 codec
operates, and do not have codec-independent equivalents.</t> operates, and do not have codec-independent equivalents.</t>
<t>The <xref target="RFC6184" format="default"/> codec format parameters
<t>The <xref target="RFC6184"/> codec format parameters covered in the following covered in the following sections
sections correspond to restrictions on receiver capabilities and never indicate
correspond to restrictions on receiver capabilities, and never indicate
sending restrictions.</t> sending restrictions.</t>
<section anchor="profile-level-id-and-max-recv-level-negotiated-sub-prof
<section anchor="profile-level-id-and-max-recv-level-negotiated-sub-profile" tit ile" numbered="true" toc="default">
le="profile-level-id and max-recv-level - Negotiated Sub-Profile"> <name>profile-level-id and max-recv-level - Negotiated Subprofile</nam
e>
<t>These parameters include a “level” indicator, which acts as an index <t>These parameters include a "level" indicator, which acts as an inde
into Table A-1 of <xref target="H264"/>. This table contains a number of paramet x
ers, into Table A-1 of <xref target="H264" format="default"/>. This table contains a
number of parameters,
several of which correspond to the restrictions defined in this several of which correspond to the restrictions defined in this
document. <xref target="RFC6184"/> also defines format parameters for the H.264 document. <xref target="RFC6184" format="default"/> also defines format paramete rs for the H.264
codec that may increase the maximum values indicated by the negotiated codec that may increase the maximum values indicated by the negotiated
level. The following sections describe the interaction between these level. The following sections describe the interaction between these
parameters and the restrictions defined by this document. In all cases, parameters and the restrictions defined by this document. In all cases,
the H.264 parameters being discussed are the maximum of those indicated the H.264 parameters being discussed are the maximum of those indicated
by <xref target="H264"></xref> Table A-1 and those indicated in the correspondin by <xref target="H264" format="default"/> Table A-1 and those indicated in the c
g “a=fmtp” line.</t> orresponding "a=fmtp" line.</t>
</section>
</section> <section anchor="max-br-maxbr-maximum-video-bitrate" numbered="true" toc
<section anchor="max-br-maxbr-maximum-video-bitrate" title="max-br / MaxBR - Max ="default">
imum Video Bitrate"> <name>max-br / MaxBR - Maximum Video Bitrate</name>
<t>The H.264 "MaxBR" parameter (and its equivalent "max-br" format
<t>The H.264 “MaxBR” parameter (and its equivalent “max-br” format parameter) corresponds to the "max-bps" restriction
parameter) corresponds to the “max-bps” restriction
defined in this specification, by way of a conversion factor of 1000 defined in this specification, by way of a conversion factor of 1000
or 1200; see <xref target="RFC6184"/> for details regarding which factor gets or 1200; see <xref target="RFC6184" format="default"/> for details regarding whi ch factor gets
used under differing circumstances.</t> used under differing circumstances.</t>
<t>If an RTP sender is generating a stream using
<t>If an RTP sender is generating a stream using
a format defined with this format parameter, and the sending restrictions a format defined with this format parameter, and the sending restrictions
defined via “a=rid” include a “max-fps” parameter, then the sent stream defined via "a=rid" include a "max-fps" parameter, then the sent stream
will conform to the smaller of the two values – that is:</t> will conform to the smaller of the two values -- that is:</t>
<figure><artwork><![CDATA[ <sourcecode>
min(rid_max_br, h264_MaxBR * conversion_factor) min(rid_max_br, h264_MaxBR * conversion_factor)
]]></artwork></figure> </sourcecode>
</section>
</section> <section anchor="max-fs-maxfs-maximum-framesize-in-h264-macroblocks" num
<section anchor="max-fs-maxfs-maximum-framesize-in-h264-macroblocks" title="max- bered="true" toc="default">
fs / MaxFS - Maximum Framesize, in H.264 Macroblocks"> <name>max-fs / MaxFS - Maximum Frame Size, in H.264 Macroblocks</name>
<t>The H.264 "MaxFs" parameter (and its equivalent "max-fs"
<t>The H.264 “MaxFs” parameter (and its equivalent “max-fs” format parameter) corresponds roughly to the "max-fs" restriction
format parameter) corresponds roughly to the “max-fs” restriction
defined in this document, by way of a conversion factor of 256 defined in this document, by way of a conversion factor of 256
(the number of pixels per macroblock).</t> (the number of pixels per macroblock).</t>
<t>If an RTP sender is generating a stream using
<t>If an RTP sender is generating a stream using
a format defined with this format parameter, and the sending restrictions a format defined with this format parameter, and the sending restrictions
defined via “a=rid” include a “max-fs” parameter, then the sent stream defined via "a=rid" include a "max-fs" parameter, then the sent stream
will conform to the smaller of the two values – that is:</t> will conform to the smaller of the two values -- that is:</t>
<sourcecode>
<figure><artwork><![CDATA[
min(rid_max_fs, h264_MaxFs * 256) min(rid_max_fs, h264_MaxFs * 256)
]]></artwork></figure> </sourcecode>
</section>
</section> <section anchor="sec-h264_max_mbps" numbered="true" toc="default">
<section anchor="sec-h264_max_mbps" title="max-mbps / MaxMBPS - Maximum Macroblo <name>max-mbps / MaxMBPS - Maximum Macroblock Processing Rate</name>
ck Processing Rate"> <t>The H.264 "MaxMBPS" parameter (and its equivalent "max-mbps"
format parameter) corresponds roughly to the "max-pps" restriction
<t>The H.264 “MaxMBPS” parameter (and its equivalent “max-mbps”
format parameter) corresponds roughly to the “max-pps” restriction
defined in this document, by way of a conversion factor of 256 defined in this document, by way of a conversion factor of 256
(the number of pixels per macroblock).</t> (the number of pixels per macroblock).</t>
<t>If an RTP sender is generating a stream using
<t>If an RTP sender is generating a stream using
a format defined with this format parameter, and the sending restrictions a format defined with this format parameter, and the sending restrictions
defined via “a=rid” include a “max-pps” parameter, then the sent stream defined via "a=rid" include a "max-pps" parameter, then the sent stream
will conform to the smaller of the two values – that is:</t> will conform to the smaller of the two values -- that is:</t>
<sourcecode>
<figure><artwork><![CDATA[
min(rid_max_pps, h264_MaxMBPS * 256) min(rid_max_pps, h264_MaxMBPS * 256)
]]></artwork></figure> </sourcecode>
</section>
</section> <section anchor="max-smbps-maximum-decoded-picture-buffer" numbered="tru
<section anchor="max-smbps-maximum-decoded-picture-buffer" title="max-smbps - Ma e" toc="default">
ximum Decoded Picture Buffer"> <name>max-smbps - Maximum Decoded Picture Buffer</name>
<t>The H.264 "max-smbps" format parameter operates the same way as the
<t>The H.264 “max-smbps” format parameter operates the same way as the "max-mbps" format parameter, under the hypothetical assumption that all
“max-mpbs” format parameter, under the hypothetical assumption that all
macroblocks are static macroblocks. It is handled by applying the macroblocks are static macroblocks. It is handled by applying the
conversion factor described in Section 8.1 of <xref target="RFC6184"/>, and the conversion factor described in Section 8.1 of <xref target="RFC6184" format="def ault"/>, and the
result of this conversion is applied as described in result of this conversion is applied as described in
<xref target="sec-h264_max_mbps"/>.</t> <xref target="sec-h264_max_mbps" format="default"/>.</t>
</section>
</section> </section>
</section> <section anchor="redundancy-formats-and-payload-type-restrictions" numbere
<section anchor="redundancy-formats-and-payload-type-restrictions" title="Redund d="true" toc="default">
ancy Formats and Payload Type Restrictions"> <name>Redundancy Formats and Payload Type Restrictions</name>
<t><xref target="sec-rid_attribute" format="default"/> specifies that re
<t><xref target="sec-rid_attribute"/> specifies that redundancy formats using re dundancy formats using redundancy RTP streams bind
dundancy RTP streams bind
the redundancy RTP stream to the source RTP stream with either the the redundancy RTP stream to the source RTP stream with either the
RepairedRtpStreamId SDES item, or other mechanisms. However, there exist RepairedRtpStreamId SDES item or other mechanisms. However, there exist
redundancy RTP payload formats that result in the redundancy being included in redundancy RTP payload formats that result in the redundancy being included in
the source RTP stream. An example of this is “RTP Payload for Redundant Audio the source RTP stream. An example of this is "RTP Payload for Redundant Audio
Data” <xref target="RFC2198"/>, which encapsulates one source stream with one or Data" <xref target="RFC2198" format="default"/>, which encapsulates one source s
more tream with one or more
redundancy streams in the same RTP payload. Formats defining the source and redundancy streams in the same RTP payload. Formats defining the source and
redundancy encodings as regular RTP payload types require some consideration redundancy encodings as regular RTP payload types require some consideration
for how the “a=rid” restrictions are defined. The “a=rid” line “pt=” parameter for how the "a=rid" restrictions are defined. The "a=rid" line "pt=" parameter
can be used to indicate whether the redundancy RTP payload type and/or the can be used to indicate whether the redundancy RTP payload type and/or the
individual source RTP payload type(s) are part of the restriction.</t> individual source RTP payload type(s) are part of the restriction.</t>
<t>Example (SDP excerpt):</t>
<t>Example (SDP Excerpt):</t> <sourcecode type="sdp">
<figure><artwork><![CDATA[
m=audio 49200 RTP/AVP 97 98 99 100 101 102 m=audio 49200 RTP/AVP 97 98 99 100 101 102
a=mid:foo a=mid:foo
a=rtpmap:97 G711/8000 a=rtpmap:97 G711/8000
a=rtpmap:98 LPC/8000 a=rtpmap:98 LPC/8000
a=rtpmap:99 OPUS/48000/1 a=rtpmap:99 OPUS/48000/1
a=rtpmap:100 RED/8000/1 a=rtpmap:100 RED/8000/1
a=rtpmap:101 CN/8000 a=rtpmap:101 CN/8000
a=rtpmap:102 telephone-event/8000 a=rtpmap:102 telephone-event/8000
a=fmtp:99 useinbandfec=1; usedtx=0 a=fmtp:99 useinbandfec=1; usedtx=0
a=fmtp:100 97/98 a=fmtp:100 97/98
a=fmtp:102 0-15 a=fmtp:102 0-15
a=ptime:20 a=ptime:20
a=maxptime:40 a=maxptime:40
a=rid:5 send pt=99,102;max-br=64000 a=rid:5 send pt=99,102;max-br=64000
a=rid:6 send pt=100,97,101,102 a=rid:6 send pt=100,97,101,102
</sourcecode>
]]></artwork></figure> <t>The RID with ID=6 restricts the payload types for this RID to 100
(the redundancy format), 97 (G.711), 101 (Comfort Noise), and 102
<t>The RID with ID=6 restricts the payload types for this RID to 100 (the redund (dual-tone multi-frequency (DTMF) tones). This means that RID 6 can
ancy either contain the Redundant Audio Data (RED) format, encapsulating
format), 97 (G.711), 101 (Comfort Noise) and 102 (DTMF tones). This means that encodings of the source media stream using payload type 97 and 98, 97
RID 6 can either contain the RED format, encapsulating encodings of the source without RED encapsulation, Comfort noise, or DTMF tones. Payload type
media stream using payload type 97 and 98, 97 without RED encapsulation, 98 is not included in the RID, and can thus not be sent except as
Comfort noise, or DTMF tones. Payload type 98 is not included in the RID, and redundancy information in RED encapsulation. If 97 were to be excluded
can thus not be sent except as redundancy information in RED encapsulation. If from the pt parameter, it would instead mean that payload types 97 and
97 were to be excluded from the pt parameter, it would instead mean that 98 are only allowed via RED encapsulation.</t>
payload types 97 and 98 are only allowed via RED encapsulation.</t> </section>
</section>
</section> <section anchor="format-parameters-for-future-payloads" numbered="true" toc=
</section> "default">
<section anchor="format-parameters-for-future-payloads" title="Format Parameters <name>Format Parameters for Future Payloads</name>
for Future Payloads"> <t>Registrations of future RTP payload format specifications that define m
edia
<t>Registrations of future RTP payload format specifications that define media
types that have parameters matching the RID restrictions specified in this memo types that have parameters matching the RID restrictions specified in this memo
SHOULD name those parameters in a manner that matches the names of those RID <bcp14>SHOULD</bcp14> name those parameters in a manner that matches the names o
restrictions, and SHOULD explicitly state what media type parameters are f those RID
restrictions and <bcp14>SHOULD</bcp14> explicitly state what media-type paramete
rs are
restricted by what RID restrictions.</t> restricted by what RID restrictions.</t>
</section>
<section anchor="sec-abnf" numbered="true" toc="default">
<name>Formal Grammar</name>
<t>This section gives a formal Augmented Backus-Naur Form (ABNF) <xref tar
get="RFC5234" format="default"/>
grammar, with the case-sensitive extensions described in <xref target="RFC7405"
format="default"/>, for each
of the new media and "a=rid" attributes defined in this document.</t>
</section> <sourcecode type="abnf"><![CDATA[
<section anchor="sec-abnf" title="Formal Grammar">
<t>This section gives a formal Augmented Backus-Naur Form (ABNF) <xref target="R
FC5234"/>
grammar, with the case-sensitive extensions described in <xref target="RFC7405"/
>, for each
of the new media and “a=rid” attributes defined in this document.</t>
<figure><artwork><![CDATA[
rid-syntax = %s"a=rid:" rid-id SP rid-dir rid-syntax = %s"a=rid:" rid-id SP rid-dir
[ rid-pt-param-list / rid-param-list ] [ rid-pt-param-list / rid-param-list ]
rid-id = 1*(alpha-numeric / "-" / "_") rid-id = 1*(alpha-numeric / "-" / "_")
alpha-numeric = < as defined in {{RFC4566}} > alpha-numeric = < as defined in [RFC4566] >
rid-dir = %s"send" / %s"recv" rid-dir = %s"send" / %s"recv"
rid-pt-param-list = SP rid-fmt-list *(";" rid-param) rid-pt-param-list = SP rid-fmt-list *(";" rid-param)
rid-param-list = SP rid-param *(";" rid-param) rid-param-list = SP rid-param *(";" rid-param)
rid-fmt-list = %s"pt=" fmt *( "," fmt ) rid-fmt-list = %s"pt=" fmt *( "," fmt )
fmt = < as defined in {{RFC4566}} > fmt = < as defined in [RFC4566] >
rid-param = rid-width-param rid-param = rid-width-param
/ rid-height-param / rid-height-param
/ rid-fps-param / rid-fps-param
/ rid-fs-param / rid-fs-param
/ rid-br-param / rid-br-param
/ rid-pps-param / rid-pps-param
/ rid-bpp-param / rid-bpp-param
/ rid-depend-param / rid-depend-param
/ rid-param-other / rid-param-other
skipping to change at line 811 skipping to change at line 744
rid-depend-param = %s"depend=" rid-list rid-depend-param = %s"depend=" rid-list
rid-param-other = 1*(alpha-numeric / "-") [ "=" param-val ] rid-param-other = 1*(alpha-numeric / "-") [ "=" param-val ]
rid-list = rid-id *( "," rid-id ) rid-list = rid-id *( "," rid-id )
int-param-val = 1*DIGIT int-param-val = 1*DIGIT
float-param-val = 1*DIGIT "." 1*DIGIT float-param-val = 1*DIGIT "." 1*DIGIT
param-val = *( %x20-58 / %x60-7E ) param-val = *(%x20-3A / %x3C-7E)
; Any printable character except semicolon ; Any printable character except semicolon
]]></sourcecode>
]]></artwork></figure> </section>
<section anchor="sdp-examples" numbered="true" toc="default">
</section> <name>SDP Examples</name>
<section anchor="sdp-examples" title="SDP Examples"> <t>Note: See <xref target="RFC8853" format="default"/> for examples of RID
used
<t>Note: see <xref target="I-D.ietf-mmusic-sdp-simulcast"/> for examples of RID
used
in simulcast scenarios.</t> in simulcast scenarios.</t>
<section anchor="many-bundled-streams-using-many-codecs" numbered="true" t
<section anchor="many-bundled-streams-using-many-codecs" title="Many Bundled Str oc="default">
eams using Many Codecs"> <name>Many Bundled Streams Using Many Codecs</name>
<t>In this scenario, the offerer supports the Opus, G.722, G.711, and DT
<t>In this scenario, the offerer supports the Opus, G.722, G.711 and DTMF audio MF audio
codecs, and VP8, VP9, H.264 (CBP/CHP, mode 0/1), H.264-SVC (SCBP/SCHP) and codecs and VP8, VP9, H.264 (CBP/CHP, mode 0/1), H.264-SVC (SCBP/SCHP), and
H.265 (MP/M10P) for video. An 8-way video call (to a mixer) is supported (send H.265 (MP/M10P) for video. An 8-way video call (to a mixer) is supported (send
1 and receive 7 video streams) by offering 7 video media sections (1 sendrecv 1 and receive 7 video streams) by offering 7 video media sections (1 sendrecv
at max resolution and 6 recvonly at smaller resolutions), all bundled on the at max resolution and 6 recvonly at smaller resolutions), all bundled on the
same port, using 3 different resolutions. The resolutions include:</t> same port, using 3 different resolutions. The resolutions include:</t>
<ul spacing="normal">
<li>1 receive stream of 720p resolution is offered for the active spea
ker.</li>
<li>2 receive streams of 360p resolution are offered for the prior 2 a
ctive
speakers.</li>
<li>4 receive streams of 180p resolution are offered for others in the
call.</li>
</ul>
<t><list style="symbols"> <t>NOTE: The SDP given below skips a few lines to
<t>1 receive stream of 720p resolution is offered for the active speaker.</t> keep the example short and focused, as indicated by either the "..."
<t>2 receive streams of 360p resolution are offered for the prior 2 active or the comments inserted.</t>
speakers.</t> <t>The offer for this scenario is shown
<t>4 receive streams of 180p resolution are offered for others in the call.</t below.</t>
>
</list></t>
<t>NOTE: The SDP given below skips a few lines to keep the example short and
focused, as indicated by either the “…” or the comments inserted.</t>
<t>The offer for this scenario is shown below.</t>
<figure><artwork><![CDATA[ <sourcecode type="sdp">
... ...
m=audio 10000 RTP/SAVPF 96 9 8 0 123 m=audio 10000 RTP/SAVPF 96 9 8 0 123
a=rtpmap:96 OPUS/48000 a=rtpmap:96 OPUS/48000
a=rtpmap:9 G722/8000 a=rtpmap:9 G722/8000
a=rtpmap:8 PCMA/8000 a=rtpmap:8 PCMA/8000
a=rtpmap:0 PCMU/8000 a=rtpmap:0 PCMU/8000
a=rtpmap:123 telephone-event/8000 a=rtpmap:123 telephone-event/8000
a=mid:a1 a=mid:a1
... ...
m=video 10000 RTP/SAVPF 98 99 100 101 102 103 104 105 106 107 m=video 10000 RTP/SAVPF 98 99 100 101 102 103 104 105 106 107
skipping to change at line 906 skipping to change at line 837
...same rtpmap/fmtp as above... ...same rtpmap/fmtp as above...
a=recvonly a=recvonly
a=mid:v4 (small resolution) a=mid:v4 (small resolution)
a=rid:4 recv max-width=320;max-height=180;max-fps=15 a=rid:4 recv max-width=320;max-height=180;max-fps=15
... ...
m=video 10000 RTP/SAVPF 98 99 100 101 102 103 104 105 106 107 m=video 10000 RTP/SAVPF 98 99 100 101 102 103 104 105 106 107
a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id
...same rtpmap/fmtp as above... ...same rtpmap/fmtp as above...
...same rid:4 as above for mid:v5,v6,v7 (small resolution)... ...same rid:4 as above for mid:v5,v6,v7 (small resolution)...
... ...
</sourcecode>
]]></artwork></figure> </section>
<section anchor="scalable-layers" numbered="true" toc="default">
</section> <name>Scalable Layers</name>
<section anchor="scalable-layers" title="Scalable Layers"> <t>Adding scalable layers to a session within a multiparty conference gi
ves a
<t>Adding scalable layers to a session within a multiparty conference gives a
selective forwarding unit (SFU) further flexibility to selectively forward selective forwarding unit (SFU) further flexibility to selectively forward
packets from a source that best match the bandwidth and capabilities of packets from a source that best match the bandwidth and capabilities of
diverse receivers. Scalable encodings have dependencies between layers, unlike diverse receivers. Scalable encodings have dependencies between layers, unlike
independent simulcast streams. RIDs can be used to express these dependencies independent simulcast streams. RIDs can be used to express these dependencies
using the “depend” restriction. In the example below, the highest resolution is using the "depend" restriction. In the example below, the highest resolution is
offered to be sent as 2 scalable temporal layers (using MRST). offered to be sent as 2 scalable temporal layers (using
See <xref target="I-D.ietf-mmusic-sdp-simulcast"/> for additional detail about s Multiple RTP Streams on a Single Media Transport (MRST)).
imulcast usage.</t> See <xref target="RFC8853" format="default"/> for additional detail about simulc
ast usage.</t>
<figure><artwork><![CDATA[ <sourcecode type="sdp">
Offer: Offer:
... ...
m=audio ...same as previous example ... m=audio ...same as previous example ...
... ...
m=video ...same as previous example ... m=video ...same as previous example ...
...same rtpmap/fmtp as previous example ... ...same rtpmap/fmtp as previous example ...
a=sendrecv a=sendrecv
a=mid:v1 (max resolution) a=mid:v1 (max resolution)
a=rid:0 send max-width=1280;max-height=720;max-fps=15 a=rid:0 send max-width=1280;max-height=720;max-fps=15
a=rid:1 send max-width=1280;max-height=720;max-fps=30;depend=0 a=rid:1 send max-width=1280;max-height=720;max-fps=30;depend=0
a=rid:2 recv max-width=1280;max-height=720;max-fps=30 a=rid:2 recv max-width=1280;max-height=720;max-fps=30
a=rid:5 send max-width=640;max-height=360;max-fps=15 a=rid:5 send max-width=640;max-height=360;max-fps=15
a=rid:6 send max-width=320;max-height=180;max-fps=15 a=rid:6 send max-width=320;max-height=180;max-fps=15
a=simulcast: send rid=0;1;5;6 recv rid=2 a=simulcast: send rid=0;1;5;6 recv rid=2
... ...
...same m=video sections as previous example for mid:v2-v7... ...same m=video sections as previous example for mid:v2-v7...
... ...
</sourcecode>
</section>
</section>
<section anchor="sec-iana" numbered="true" toc="default">
<name>IANA Considerations</name>
]]></artwork></figure> <t>This specification updates <xref target="RFC4855" format="default"/>
to give additional guidance on choice of Format Parameter (fmtp) names
</section> and their relation to RID restrictions.</t>
</section>
<section anchor="sec-iana" title="IANA Considerations">
<t>This specification updates <xref target="RFC4855"/> to give additional guidan
ce on choice
of Format Parameter (fmtp) names, and on their relation to RID restrictions.</t>
<section anchor="new-sdp-media-level-attribute" title="New SDP Media-Level attri
bute">
<t>This document defines “rid” as SDP media-level attribute. This attribute must
be registered by IANA under “Session Description Protocol (SDP) Parameters”
under “att-field (media level only)”.</t>
<t>The “rid” attribute is used to identify properties of RTP stream with in
an RTP Session. Its format is defined in <xref target="sec-abnf"/>.</t>
<t>The formal registration information for this attribute follows.</t>
<figure><artwork><![CDATA[
Contact name, email address, and telephone number
IETF MMUSIC Working Group
mmusic@ietf.org
+1 510 492 4080
Attribute name (as it will appear in SDP)
rid
Long-form attribute name in English
Restriction Identifier
Type of attribute (session level, media level, or both)
Media Level
Whether the attribute value is subject to the charset attribute
The attribute is not dependent on charset.
A one-paragraph explanation of the purpose of the attribute
The "rid" SDP attribute is used to to unambiguously identify
the RTP Streams within an RTP Session and restrict the
streams' payload format parameters in a codec-agnostic way
beyond what is provided with the regular Payload Types.
A specification of appropriate attribute values for this attribute
Valid values are defined by the ABNF in [RFCXXXXX]
Multiplexing (Mux) Category <section anchor="new-sdp-media-level-attribute" numbered="true" toc="defau
lt">
<name>New SDP Media-Level Attribute</name>
SPECIAL <t>This document defines "rid" as an SDP media-level attribute. This
]]></artwork></figure> attribute has been registered by IANA under "Session Description Protocol
(SDP) Parameters" under "att-field (media level only)".</t>
<t>The "rid" attribute is used to identify the properties of an RTP
stream within an RTP session. Its format is defined in <xref
target="sec-abnf" format="default"/>.</t>
<t>The formal registration information for this attribute follows.</t>
</section> <dl newline="true">
<section anchor="sec-iana_rid" title="Registry for RID-Level Parameters"> <dt>
Contact name, email address, and telephone number
</dt>
<dd>
<artwork>
IETF MMUSIC Working Group
mmusic@ietf.org
+1 510 492 4080
</artwork>
</dd>
<dt>
Attribute name (as it will appear in SDP)
</dt>
<dd>
rid
</dd>
<dt>
Long-form attribute name in English
</dt>
<dd>
Restriction Identifier
</dd>
<dt>
Type of attribute (session level, media level, or both)
</dt>
<dd>
Media Level
</dd>
<dt>
Whether the attribute value is subject to the charset attribute
</dt>
<dd>
The attribute is not dependent on charset.
</dd>
<dt>
A one-paragraph explanation of the purpose of the attribute
</dt>
<dd>
The "rid" SDP attribute is used to unambiguously identify
the RTP streams within an RTP session and restrict the
streams' payload format parameters in a codec-agnostic way
beyond what is provided with the regular payload types.
</dd>
<dt>
A specification of appropriate attribute values for this attribute
</dt>
<dd>
Valid values are defined by the ABNF in RFC 8851
</dd>
<dt>
Multiplexing (Mux) Category
</dt>
<dd>
SPECIAL
</dd>
</dl>
<t>This specification creates a new IANA registry named “rid attribute parameter </section>
s” <section anchor="sec-iana_rid" numbered="true" toc="default">
within the SDP parameters registry. The “a=rid” restrictions MUST be <name>Registry for RID-Level Parameters</name>
<t>This specification creates a new IANA registry named "RID Attribute P
arameters"
within the SDP parameters registry. The "a=rid" restrictions <bcp14>MUST</bcp14
> be
registered with IANA and documented under the same rules as for SDP registered with IANA and documented under the same rules as for SDP
session-level and media-level attributes as specified in <xref target="RFC4566"/ session-level and media-level attributes as specified in <xref target="RFC4566"
>.</t> format="default"/>.</t>
<t>Parameters for "a=rid" lines that modify the nature of encoded media
<t>Parameters for “a=rid” lines that modify the nature of encoded media MUST be <bcp14>MUST</bcp14> be
of the form that the result of applying the modification to the stream results of the form that the result of applying the modification to the stream results
in a stream that still complies with the other parameters that affect the in a stream that still complies with the other parameters that affect the
media. In other words, restrictions always have to restrict the definition to be media. In other words, restrictions always have to restrict the definition to be
a subset of what is otherwise allowable, and never expand it.</t> a subset of what is otherwise allowable, and never expand it.</t>
<t>New restriction registrations are accepted according to the “Specification <t>New restriction registrations are accepted according to the "Specific
Required” policy of <xref target="RFC5226"/>. The registration MUST contain the ation
RID Required" policy of <xref target="RFC8126" format="default"/>. The registration
<bcp14>MUST</bcp14> contain the RID
parameter name and a reference to the corresponding specification. The parameter name and a reference to the corresponding specification. The
specification itself must contain the following information (not all of which specification itself must contain the following information (not all of which
appears in the registry):</t> appears in the registry):</t>
<ul spacing="normal">
<li>restriction name (as it will appear in SDP)</li>
<li>an explanation of the purpose of the restriction</li>
<li>a specification of appropriate attribute values for this restricti
on</li>
<li>an ABNF definition of the restriction</li>
</ul>
<t><list style="symbols"> <t>The initial set of "a=rid" restriction names, with definitions in
<t>restriction name (as it will appear in SDP)</t> <xref target="sec-rid_level_restrictions" format="default"/> of this document,
<t>an explanation of the purpose of the restriction</t> is given below:</t>
<t>a specification of appropriate attribute values for this restriction</t>
<t>an ABNF definition of the restriction</t>
</list></t>
<t>The initial set of “a=rid” restriction names, with definitions in
<xref target="sec-rid_level_restrictions"/> of this document, is given below:</t
>
<figure><artwork><![CDATA[
RID Parameter Name Reference
------------------ ---------
max-width [RFCXXXX]
max-height [RFCXXXX]
max-fps [RFCXXXX]
max-fs [RFCXXXX]
max-br [RFCXXXX]
max-pps [RFCXXXX]
max-bpp [RFCXXXX]
depend [RFCXXXX]
]]></artwork></figure> <table anchor="RID-params">
<name>"a=rid" restriction names</name>
<thead>
<tr>
<th>RID Parameter Name</th>
<th>Reference</th>
</tr>
</thead>
<tbody>
<tr>
<td>pt</td>
<td>RFC 8851</td>
</tr>
<tr>
<td>max-width</td>
<td>RFC 8851</td>
</tr>
<tr>
<td>max-height</td>
<td>RFC 8851</td>
</tr>
<tr>
<td>max-fps</td>
<td>RFC 8851</td>
</tr>
<tr>
<td>max-fs</td>
<td>RFC 8851</td>
</tr>
<tr>
<td>max-br</td>
<td>RFC 8851</td>
</tr>
<tr>
<td>max-pps</td>
<td>RFC 8851</td>
</tr>
<tr>
<td>max-bpp</td>
<td>RFC 8851</td>
</tr>
<tr>
<td>depend</td>
<td>RFC 8851</td>
</tr>
</tbody>
</table>
<t>It is conceivable that a future document wants to define a RID-level <t>It is conceivable that a future document will want to define RID-leve l
restrictions that contain string values. These extensions need to take care to restrictions that contain string values. These extensions need to take care to
conform to the ABNF defined for rid-param-other. In particular, this means conform to the ABNF defined for rid-param-other. In particular, this means
that such extensions will need to define escaping mechanisms if they that such extensions will need to define escaping mechanisms if they
want to allow semicolons, unprintable characters, or byte values want to allow semicolons, unprintable characters, or byte values
greater than 127 in the string.</t> greater than 127 in the string.</t>
</section>
</section>
<section anchor="security-considerations" numbered="true" toc="default">
<name>Security Considerations</name>
</section> <t>As with most SDP parameters, a failure to provide integrity protection
</section> over
<section anchor="security-considerations" title="Security Considerations"> the "a=rid" attributes gives attackers a way to modify the session in
<t>As with most SDP parameters, a failure to provide integrity protection over
the “a=rid” attributes provides attackers a way to modify the session in
potentially unwanted ways. This could result in an implementation sending potentially unwanted ways. This could result in an implementation sending
greater amounts of data than a recipient wishes to receive. In general, greater amounts of data than a recipient wishes to receive. In general,
however, since the “a=rid” attribute can only restrict a stream to be a subset however, since the "a=rid" attribute can only restrict a stream to be a subset
of what is otherwise allowable, modification of the value cannot result in a of what is otherwise allowable, modification of the value cannot result in a
stream that is of higher bandwidth than would be sent to an implementation stream that is of higher bandwidth than would be sent to an implementation
that does not support this mechanism.</t> that does not support this mechanism.</t>
<t>The actual identifiers used for RIDs are expected to be opaque. As such
<t>The actual identifiers used for RIDs are expected to be opaque. As such, they , they
are not expected to contain information that would be sensitive, were it are not expected to contain information that would be sensitive, were it
observed by third-parties.</t> observed by third parties.</t>
</section>
</section>
<section anchor="acknowledgements" title="Acknowledgements">
<t>Many thanks to review from Cullen Jennings, Magnus Westerlund, and Paul
Kyzivat. Thanks to Colin Perkins for input on future payload type handing.</t>
</section>
</middle> </middle>
<back> <back>
<references>
<references title='Normative References'> <name>References</name>
<references>
<reference anchor="I-D.ietf-avtext-rid"> <name>Normative References</name>
<front> <reference anchor="RFC8852" target="https://www.rfc-editor.org/info/rfc8852">
<title>RTP Stream Identifier Source Description (SDES)</title> <front>
<title>RTP Stream Identifier Source Description (SDES)</title>
<author initials='A' surname='Roach' fullname='Adam Roach'> <author initials="A.B." surname="Roach" fullname="Adam Roach"/>
<organization /> <author initials="S" surname="Nandakumar" fullname="Suhas Nandakumar"/>
</author> <author initials="P" surname="Thatcher" fullname="Peter Thatcher"/>
<date month="May" year="2020"/>
<author initials='S' surname='Nandakumar' fullname='Suhas Nandakumar'> </front>
<organization /> <seriesInfo name="DOI" value="10.17487/RFC8852"/>
</author> <seriesInfo name="RFC" value="8852"/>
<author initials='P' surname='Thatcher' fullname='Peter Thatcher'>
<organization />
</author>
<date month='October' day='6' year='2016' />
<abstract><t>This document defines and registers two new RTCP Stream Identifier
Source Description (SDES) items. One, named RtpStreamId, is used for unique ide
ntification of RTP streams. The other, RepairedRtpStreamId, can be used to iden
tify which stream a redundancy RTP stream is to be used to repair.</t></abstract
>
</front>
<seriesInfo name='Internet-Draft' value='draft-ietf-avtext-rid-09' />
<format type='TXT'
target='http://www.ietf.org/internet-drafts/draft-ietf-avtext-rid-09.txt
' />
</reference>
<reference anchor="RFC2119" target='https://www.rfc-editor.org/info/rfc2119'>
<front>
<title>Key words for use in RFCs to Indicate Requirement Levels</title>
<author initials='S.' surname='Bradner' fullname='S. Bradner'><organization /></
author>
<date year='1997' month='March' />
<abstract><t>In many standards track documents several words are used to signify
the requirements in the specification. These words are often capitalized. This
document defines these words as they should be interpreted in IETF documents.
This document specifies an Internet Best Current Practices for the Internet Comm
unity, and requests discussion and suggestions for improvements.</t></abstract>
</front>
<seriesInfo name='BCP' value='14'/>
<seriesInfo name='RFC' value='2119'/>
<seriesInfo name='DOI' value='10.17487/RFC2119'/>
</reference>
<reference anchor="RFC3264" target='https://www.rfc-editor.org/info/rfc3264'>
<front>
<title>An Offer/Answer Model with Session Description Protocol (SDP)</title>
<author initials='J.' surname='Rosenberg' fullname='J. Rosenberg'><organization
/></author>
<author initials='H.' surname='Schulzrinne' fullname='H. Schulzrinne'><organizat
ion /></author>
<date year='2002' month='June' />
<abstract><t>This document defines a mechanism by which two entities can make us
e of the Session Description Protocol (SDP) to arrive at a common view of a mult
imedia session between them. In the model, one participant offers the other a d
escription of the desired session from their perspective, and the other particip
ant answers with the desired session from their perspective. This offer/answer
model is most useful in unicast sessions where information from both participant
s is needed for the complete view of the session. The offer/answer model is use
d by protocols like the Session Initiation Protocol (SIP). [STANDARDS-TRACK]</t
></abstract>
</front>
<seriesInfo name='RFC' value='3264'/>
<seriesInfo name='DOI' value='10.17487/RFC3264'/>
</reference>
<reference anchor="RFC3550" target='https://www.rfc-editor.org/info/rfc3550'>
<front>
<title>RTP: A Transport Protocol for Real-Time Applications</title>
<author initials='H.' surname='Schulzrinne' fullname='H. Schulzrinne'><organizat
ion /></author>
<author initials='S.' surname='Casner' fullname='S. Casner'><organization /></au
thor>
<author initials='R.' surname='Frederick' fullname='R. Frederick'><organization
/></author>
<author initials='V.' surname='Jacobson' fullname='V. Jacobson'><organization />
</author>
<date year='2003' month='July' />
<abstract><t>This memorandum describes RTP, the real-time transport protocol. R
TP provides end-to-end network transport functions suitable for applications tra
nsmitting real-time data, such as audio, video or simulation data, over multicas
t or unicast network services. RTP does not address resource reservation and do
es not guarantee quality-of- service for real-time services. The data transport
is augmented by a control protocol (RTCP) to allow monitoring of the data deliv
ery in a manner scalable to large multicast networks, and to provide minimal con
trol and identification functionality. RTP and RTCP are designed to be independ
ent of the underlying transport and network layers. The protocol supports the u
se of RTP-level translators and mixers. Most of the text in this memorandum is i
dentical to RFC 1889 which it obsoletes. There are no changes in the packet for
mats on the wire, only changes to the rules and algorithms governing how the pro
tocol is used. The biggest change is an enhancement to the scalable timer algori
thm for calculating when to send RTCP packets in order to minimize transmission
in excess of the intended rate when many participants join a session simultaneou
sly. [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='STD' value='64'/>
<seriesInfo name='RFC' value='3550'/>
<seriesInfo name='DOI' value='10.17487/RFC3550'/>
</reference>
<reference anchor="RFC4566" target='https://www.rfc-editor.org/info/rfc4566'>
<front>
<title>SDP: Session Description Protocol</title>
<author initials='M.' surname='Handley' fullname='M. Handley'><organization /></
author>
<author initials='V.' surname='Jacobson' fullname='V. Jacobson'><organization />
</author>
<author initials='C.' surname='Perkins' fullname='C. Perkins'><organization /></
author>
<date year='2006' month='July' />
<abstract><t>This memo defines the Session Description Protocol (SDP). SDP is i
ntended for describing multimedia sessions for the purposes of session announcem
ent, session invitation, and other forms of multimedia session initiation. [STA
NDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='4566'/>
<seriesInfo name='DOI' value='10.17487/RFC4566'/>
</reference>
<reference anchor="RFC4855" target='https://www.rfc-editor.org/info/rfc4855'>
<front>
<title>Media Type Registration of RTP Payload Formats</title>
<author initials='S.' surname='Casner' fullname='S. Casner'><organization /></au
thor>
<date year='2007' month='February' />
<abstract><t>This document specifies the procedure to register RTP payload forma
ts as audio, video, or other media subtype names. This is useful in a text-base
d format description or control protocol to identify the type of an RTP transmis
sion. [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='4855'/>
<seriesInfo name='DOI' value='10.17487/RFC4855'/>
</reference>
<reference anchor="RFC5234" target='https://www.rfc-editor.org/info/rfc5234'>
<front>
<title>Augmented BNF for Syntax Specifications: ABNF</title>
<author initials='D.' surname='Crocker' fullname='D. Crocker' role='editor'><org
anization /></author>
<author initials='P.' surname='Overell' fullname='P. Overell'><organization /></
author>
<date year='2008' month='January' />
<abstract><t>Internet technical specifications often need to define a formal syn
tax. Over the years, a modified version of Backus-Naur Form (BNF), called Augme
nted BNF (ABNF), has been popular among many Internet specifications. The curre
nt specification documents ABNF. It balances compactness and simplicity with rea
sonable representational power. The differences between standard BNF and ABNF i
nvolve naming rules, repetition, alternatives, order-independence, and value ran
ges. This specification also supplies additional rule definitions and encoding
for a core lexical analyzer of the type common to several Internet specification
s. [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='STD' value='68'/>
<seriesInfo name='RFC' value='5234'/>
<seriesInfo name='DOI' value='10.17487/RFC5234'/>
</reference>
<reference anchor="RFC7405" target='https://www.rfc-editor.org/info/rfc7405'>
<front>
<title>Case-Sensitive String Support in ABNF</title>
<author initials='P.' surname='Kyzivat' fullname='P. Kyzivat'><organization /></
author>
<date year='2014' month='December' />
<abstract><t>This document extends the base definition of ABNF (Augmented Backus
-Naur Form) to include a way to specify US-ASCII string literals that are matche
d in a case-sensitive manner.</t></abstract>
</front>
<seriesInfo name='RFC' value='7405'/>
<seriesInfo name='DOI' value='10.17487/RFC7405'/>
</reference>
<reference anchor="RFC8174" target='https://www.rfc-editor.org/info/rfc8174'>
<front>
<title>Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words</title>
<author initials='B.' surname='Leiba' fullname='B. Leiba'><organization /></auth
or>
<date year='2017' month='May' />
<abstract><t>RFC 2119 specifies common key words that may be used in protocol s
pecifications. This document aims to reduce the ambiguity by clarifying that on
ly UPPERCASE usage of the key words have the defined special meanings.</t></abs
tract>
</front>
<seriesInfo name='BCP' value='14'/>
<seriesInfo name='RFC' value='8174'/>
<seriesInfo name='DOI' value='10.17487/RFC8174'/>
</reference>
</references>
<references title='Informative References'>
<reference anchor="I-D.ietf-mmusic-sdp-bundle-negotiation">
<front>
<title>Negotiating Media Multiplexing Using the Session Description Protocol (SD
P)</title>
<author initials='C' surname='Holmberg' fullname='Christer Holmberg'>
<organization />
</author>
<author initials='H' surname='Alvestrand' fullname='Harald Alvestrand'>
<organization />
</author>
<author initials='C' surname='Jennings' fullname='Cullen Jennings'>
<organization />
</author>
<date month='December' day='14' year='2018' />
<abstract><t>This specification defines a new Session Description Protocol (SDP)
Grouping Framework extension, 'BUNDLE'. The extension can be used with the SDP
Offer/Answer mechanism to negotiate the usage of a single transport (5-tuple) f
or sending and receiving media described by multiple SDP media descriptions ("m=
" sections). Such transport is referred to as a BUNDLE transport, and the media
is referred to as bundled media. The "m=" sections that use the BUNDLE transpo
rt form a BUNDLE group. This specification updates RFC 3264, to also allow assi
gning a zero port value to a "m=" section in cases where the media described by
the "m=" section is not disabled or rejected. This specification updates RFC 58
88, to also allow an SDP 'group' attribute to contain an identification-tag that
identifies a "m=" section with the port set to zero. This specification define
s a new RTP Control Protocol (RTCP) source description (SDES) item and a new RTP
header extension that can be used to correlate bundled RTP/RTCP packets with th
eir appropriate "m=" section. This specification updates RFC 7941, by adding an
exception, for the MID RTP header extension, to the requirement regarding prote
ction of an SDES RTP header extension carrying an SDES item for the MID RTP head
er extension.</t></abstract>
</front>
<seriesInfo name='Internet-Draft' value='draft-ietf-mmusic-sdp-bundle-negotiatio
n-54' />
<format type='TXT'
target='http://www.ietf.org/internet-drafts/draft-ietf-mmusic-sdp-bundle
-negotiation-54.txt' />
</reference>
<reference anchor="I-D.ietf-mmusic-sdp-simulcast">
<front>
<title>Using Simulcast in SDP and RTP Sessions</title>
<author initials='B' surname='Burman' fullname='Bo Burman'>
<organization />
</author>
<author initials='M' surname='Westerlund' fullname='Magnus Westerlund'>
<organization />
</author>
<author initials='S' surname='Nandakumar' fullname='Suhas Nandakumar'>
<organization />
</author>
<author initials='M' surname='Zanaty' fullname='Mo Zanaty'>
<organization />
</author>
<date month='June' day='27' year='2018' />
<abstract><t>In some application scenarios it may be desirable to send multiple
differently encoded versions of the same media source in different RTP streams.
This is called simulcast. This document describes how to accomplish simulcast
in RTP and how to signal it in SDP. The described solution uses an RTP/RTCP ide
ntification method to identify RTP streams belonging to the same media source, a
nd makes an extension to SDP to relate those RTP streams as being different simu
lcast formats of that media source. The SDP extension consists of a new media l
evel SDP attribute that expresses capability to send and/or receive simulcast RT
P streams.</t></abstract>
</front>
<seriesInfo name='Internet-Draft' value='draft-ietf-mmusic-sdp-simulcast-13' />
<format type='TXT'
target='http://www.ietf.org/internet-drafts/draft-ietf-mmusic-sdp-simulc
ast-13.txt' />
</reference>
<reference anchor="I-D.ietf-payload-flexible-fec-scheme">
<front>
<title>RTP Payload Format for Flexible Forward Error Correction (FEC)</title>
<author initials='M' surname='Zanaty' fullname='Mo Zanaty'>
<organization />
</author>
<author initials='V' surname='Singh' fullname='Varun Singh'>
<organization />
</author>
<author initials='A' surname='Begen' fullname='Ali Begen'>
<organization />
</author>
<author initials='G' surname='Mandyam' fullname='Giridhar Mandyam'>
<organization />
</author>
<date month='December' day='11' year='2018' />
<abstract><t>This document defines new RTP payload formats for the Forward Error
Correction (FEC) packets that are generated by the non-interleaved and interlea
ved parity codes from source media encapsulated in RTP. These parity codes are s
ystematic codes, where a number of FEC repair packets are generated from a set o
f source packets from one or more source RTP streams. These FEC repair packets
are sent in a redundancy RTP stream separate from the source RTP stream(s) that
carries the source packets. RTP source packets that were lost in transmission c
an be reconstructed using the source and repair packets that were received. The
non-interleaved and interleaved parity codes which are defined in this specific
ation offer a good protection against random and bursty packet losses, respectiv
ely, at a cost of decent complexity. The RTP payload formats that are defined i
n this document address scalability issues experienced with the earlier specific
ations, and offer several improvements. Due to these changes, the new payload f
ormats are not backward compatible with earlier specifications, but endpoints th
at do not implement this specification can still work by simply ignoring the FEC
repair packets.</t></abstract>
</front>
<seriesInfo name='Internet-Draft' value='draft-ietf-payload-flexible-fec-scheme-
13' />
<format type='TXT'
target='http://www.ietf.org/internet-drafts/draft-ietf-payload-flexible-
fec-scheme-13.txt' />
<format type='PDF'
target='http://www.ietf.org/internet-drafts/draft-ietf-payload-flexible-
fec-scheme-13.pdf' />
</reference>
<reference anchor="RFC2198" target='https://www.rfc-editor.org/info/rfc2198'>
<front>
<title>RTP Payload for Redundant Audio Data</title>
<author initials='C.' surname='Perkins' fullname='C. Perkins'><organization /></
author>
<author initials='I.' surname='Kouvelas' fullname='I. Kouvelas'><organization />
</author>
<author initials='O.' surname='Hodson' fullname='O. Hodson'><organization /></au
thor>
<author initials='V.' surname='Hardman' fullname='V. Hardman'><organization /></
author>
<author initials='M.' surname='Handley' fullname='M. Handley'><organization /></
author>
<author initials='J.C.' surname='Bolot' fullname='J.C. Bolot'><organization /></
author>
<author initials='A.' surname='Vega-Garcia' fullname='A. Vega-Garcia'><organizat
ion /></author>
<author initials='S.' surname='Fosse-Parisis' fullname='S. Fosse-Parisis'><organ
ization /></author>
<date year='1997' month='September' />
<abstract><t>This document describes a payload format for use with the real-time
transport protocol (RTP), version 2, for encoding redundant audio data. [STANDA
RDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='2198'/>
<seriesInfo name='DOI' value='10.17487/RFC2198'/>
</reference>
<reference anchor="RFC4588" target='https://www.rfc-editor.org/info/rfc4588'>
<front>
<title>RTP Retransmission Payload Format</title>
<author initials='J.' surname='Rey' fullname='J. Rey'><organization /></author>
<author initials='D.' surname='Leon' fullname='D. Leon'><organization /></author
>
<author initials='A.' surname='Miyazaki' fullname='A. Miyazaki'><organization />
</author>
<author initials='V.' surname='Varsa' fullname='V. Varsa'><organization /></auth
or>
<author initials='R.' surname='Hakenberg' fullname='R. Hakenberg'><organization
/></author>
<date year='2006' month='July' />
<abstract><t>RTP retransmission is an effective packet loss recovery technique f
or real-time applications with relaxed delay bounds. This document describes an
RTP payload format for performing retransmissions. Retransmitted RTP packets ar
e sent in a separate stream from the original RTP stream. It is assumed that fe
edback from receivers to senders is available. In particular, it is assumed tha
t Real-time Transport Control Protocol (RTCP) feedback as defined in the extende
d RTP profile for RTCP-based feedback (denoted RTP/AVPF) is available in this me
mo. [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='4588'/>
<seriesInfo name='DOI' value='10.17487/RFC4588'/>
</reference>
<reference anchor="RFC5109" target='https://www.rfc-editor.org/info/rfc5109'>
<front>
<title>RTP Payload Format for Generic Forward Error Correction</title>
<author initials='A.' surname='Li' fullname='A. Li' role='editor'><organization
/></author>
<date year='2007' month='December' />
<abstract><t>This document specifies a payload format for generic Forward Error
Correction (FEC) for media data encapsulated in RTP. It is based on the exclusi
ve-or (parity) operation. The payload format described in this document allows
end systems to apply protection using various protection lengths and levels, in
addition to using various protection group sizes to adapt to different media and
channel characteristics. It enables complete recovery of the protected packets
or partial recovery of the critical parts of the payload depending on the packet
loss situation. This scheme is completely compatible with non-FEC-capable host
s, so the receivers in a multicast group that do not implement FEC can still wor
k by simply ignoring the protection data. This specification obsoletes RFC 2733
and RFC 3009. The FEC specified in this document is not backward compatible wi
th RFC 2733 and RFC 3009. [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='5109'/>
<seriesInfo name='DOI' value='10.17487/RFC5109'/>
</reference> </reference>
<reference anchor="RFC5226" target='https://www.rfc-editor.org/info/rfc5226'> <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
<front> ence.RFC.2119.xml"/>
<title>Guidelines for Writing an IANA Considerations Section in RFCs</title> <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
<author initials='T.' surname='Narten' fullname='T. Narten'><organization /></au ence.RFC.3264.xml"/>
thor> <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
<author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'><organizatio ence.RFC.3550.xml"/>
n /></author> <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
<date year='2008' month='May' /> ence.RFC.4566.xml"/>
<abstract><t>Many protocols make use of identifiers consisting of constants and <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
other well-known values. Even after a protocol has been defined and deployment ence.RFC.4855.xml"/>
has begun, new values may need to be assigned (e.g., for a new option type in DH <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
CP, or a new encryption or authentication transform for IPsec). To ensure that ence.RFC.5234.xml"/>
such quantities have consistent values and interpretations across all implementa <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
tions, their assignment must be administered by a central authority. For IETF p ence.RFC.7405.xml"/>
rotocols, that role is provided by the Internet Assigned Numbers Authority (IANA <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
).</t><t>In order for IANA to manage a given namespace prudently, it needs guide ence.RFC.8174.xml"/>
lines describing the conditions under which new values can be assigned or when m </references>
odifications to existing values can be made. If IANA is expected to play a role <references>
in the management of a namespace, IANA must be given clear and concise instruct <name>Informative References</name>
ions describing that role. This document discusses issues that should be consid
ered in formulating a policy for assigning values to a namespace and provides gu
idelines for authors on the specific text that must be included in documents tha
t place demands on IANA.</t><t>This document obsoletes RFC 2434. This document
specifies an Internet Best Current Practices for the Internet Community, and re
quests discussion and suggestions for improvements.</t></abstract>
</front>
<seriesInfo name='RFC' value='5226'/>
<seriesInfo name='DOI' value='10.17487/RFC5226'/>
</reference>
<reference anchor="RFC6184" target='https://www.rfc-editor.org/info/rfc6184'> <!-- draft-ietf-mmusic-sdp-bundle-negotiation in C238 -->
<front>
<title>RTP Payload Format for H.264 Video</title>
<author initials='Y.-K.' surname='Wang' fullname='Y.-K. Wang'><organization /></
author>
<author initials='R.' surname='Even' fullname='R. Even'><organization /></author
>
<author initials='T.' surname='Kristensen' fullname='T. Kristensen'><organizatio
n /></author>
<author initials='R.' surname='Jesup' fullname='R. Jesup'><organization /></auth
or>
<date year='2011' month='May' />
<abstract><t>This memo describes an RTP Payload format for the ITU-T Recommendat
ion H.264 video codec and the technically identical ISO/IEC International Standa
rd 14496-10 video codec, excluding the Scalable Video Coding (SVC) extension and
the Multiview Video Coding extension, for which the RTP payload formats are def
ined elsewhere. The RTP payload format allows for packetization of one or more N
etwork Abstraction Layer Units (NALUs), produced by an H.264 video encoder, in e
ach RTP payload. The payload format has wide applicability, as it supports appl
ications from simple low bitrate conversational usage, to Internet video streami
ng with interleaved transmission, to high bitrate video-on-demand.</t><t>This me
mo obsoletes RFC 3984. Changes from RFC 3984 are summarized in Section 14. Iss
ues on backward compatibility to RFC 3984 are discussed in Section 15. [STANDAR
DS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='6184'/>
<seriesInfo name='DOI' value='10.17487/RFC6184'/>
</reference>
<reference anchor="RFC6236" target='https://www.rfc-editor.org/info/rfc6236'> <reference anchor="RFC8843" target="https://www.rfc-editor.org/info/rfc8
<front> 843">
<title>Negotiation of Generic Image Attributes in the Session Description Protoc <front>
ol (SDP)</title> <title>Negotiating Media Multiplexing Using the Session Description
<author initials='I.' surname='Johansson' fullname='I. Johansson'><organization Protocol (SDP)</title>
/></author>
<author initials='K.' surname='Jung' fullname='K. Jung'><organization /></author
>
<date year='2011' month='May' />
<abstract><t>This document proposes a new generic session setup attribute to mak
e it possible to negotiate different image attributes such as image size. A pos
sible use case is to make it possible for a \%low-end \%hand- held terminal to d
isplay video without the need to rescale the image, something that may consume l
arge amounts of memory and processing power. The document also helps to maintai
n an optimal bitrate for video as only the image size that is desired by the rec
eiver is transmitted. [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='6236'/>
<seriesInfo name='DOI' value='10.17487/RFC6236'/>
</reference>
<reference anchor="RFC7656" target='https://www.rfc-editor.org/info/rfc7656'> <author initials="C" surname="Holmberg" fullname="Christer Holmberg"
<front> >
<title>A Taxonomy of Semantics and Mechanisms for Real-Time Transport Protocol ( <organization/>
RTP) Sources</title> </author>
<author initials='J.' surname='Lennox' fullname='J. Lennox'><organization /></au <author initials="H" surname="Alvestrand" fullname="Harald Alvestran
thor> d">
<author initials='K.' surname='Gross' fullname='K. Gross'><organization /></auth <organization/>
or> </author>
<author initials='S.' surname='Nandakumar' fullname='S. Nandakumar'><organizatio <author initials="C" surname="Jennings" fullname="Cullen Jennings">
n /></author> <organization/>
<author initials='G.' surname='Salgueiro' fullname='G. Salgueiro'><organization </author>
/></author> <date month="May" year="2020"/>
<author initials='B.' surname='Burman' fullname='B. Burman' role='editor'><organ </front>
ization /></author> <seriesInfo name="DOI" value="10.17487/RFC8843"/>
<date year='2015' month='November' /> <seriesInfo name="RFC" value="8843"/>
<abstract><t>The terminology about, and associations among, Real-time Transport </reference>
Protocol (RTP) sources can be complex and somewhat opaque. This document descri
bes a number of existing and proposed properties and relationships among RTP sou
rces and defines common terminology for discussing protocol entities and their r
elationships.</t></abstract>
</front>
<seriesInfo name='RFC' value='7656'/>
<seriesInfo name='DOI' value='10.17487/RFC7656'/>
</reference>
<reference anchor="RFC7741" target='https://www.rfc-editor.org/info/rfc7741'> <!-- draft-ietf-mmusic-sdp-simulcast in C238 -->
<front> <reference anchor="RFC8853" target="https://www.rfc-editor.org/info/rfc8
<title>RTP Payload Format for VP8 Video</title> 853">
<author initials='P.' surname='Westin' fullname='P. Westin'><organization /></au <front>
thor> <title>Using Simulcast in SDP and RTP Sessions</title>
<author initials='H.' surname='Lundin' fullname='H. Lundin'><organization /></au
thor>
<author initials='M.' surname='Glover' fullname='M. Glover'><organization /></au
thor>
<author initials='J.' surname='Uberti' fullname='J. Uberti'><organization /></au
thor>
<author initials='F.' surname='Galligan' fullname='F. Galligan'><organization />
</author>
<date year='2016' month='March' />
<abstract><t>This memo describes an RTP payload format for the VP8 video codec.
The payload format has wide applicability, as it supports applications from low-
bitrate peer-to-peer usage to high-bitrate video conferences.</t></abstract>
</front>
<seriesInfo name='RFC' value='7741'/>
<seriesInfo name='DOI' value='10.17487/RFC7741'/>
</reference>
<reference anchor="RFC8285" target='https://www.rfc-editor.org/info/rfc8285'> <author initials="B" surname="Burman" fullname="Bo Burman">
<front> <organization/>
<title>A General Mechanism for RTP Header Extensions</title> </author>
<author initials='D.' surname='Singer' fullname='D. Singer'><organization /></au <author initials="M" surname="Westerlund" fullname="Magnus Westerlun
thor> d">
<author initials='H.' surname='Desineni' fullname='H. Desineni'><organization /> <organization/>
</author> </author>
<author initials='R.' surname='Even' fullname='R. Even' role='editor'><organizat <author initials="S" surname="Nandakumar" fullname="Suhas Nandakumar
ion /></author> ">
<date year='2017' month='October' /> <organization/>
<abstract><t>This document provides a general mechanism to use the header extens </author>
ion feature of RTP (the Real-time Transport Protocol). It provides the option t <author initials="M" surname="Zanaty" fullname="Mo Zanaty">
o use a small number of small extensions in each RTP packet, where the universe <organization/>
of possible extensions is large and registration is decentralized. The actual e </author>
xtensions in use in a session are signaled in the setup information for that ses <date month="May" year="2020"/>
sion. This document obsoletes RFC 5285.</t></abstract> </front>
</front> <seriesInfo name="DOI" value="10.17487/RFC8853"/>
<seriesInfo name='RFC' value='8285'/> <seriesInfo name="RFC" value="8853"/>
<seriesInfo name='DOI' value='10.17487/RFC8285'/> </reference>
</reference>
<reference anchor="H264" target="http://www.itu.int/rec/T-REC-H.264-201304-I"> <xi:include
<front> href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.
<title>Advanced video coding for generic audiovisual services (V9)</title> 8627.xml"/>
<author > <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
<organization>ITU-T Recommendation H.264</organization> ence.RFC.2198.xml"/>
</author> <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
<date year="2014" month="February"/> ence.RFC.4588.xml"/>
</front> <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
</reference> ence.RFC.5109.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.8126.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.6184.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.6236.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.7656.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.7741.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.8285.xml"/>
<reference anchor="H264" target="https://www.itu.int/rec/T-REC-H.264">
<front>
<title>Advanced video coding for generic audiovisual services</title
>
<seriesInfo name="ITU-T Recommendation" value="H.264"/>
<author>
<organization>International Telecommunication Union</organization>
</author>
<date year="2019" month="June"/>
</front>
</reference>
</references>
</references> </references>
<section anchor="acknowledgements" numbered="false" toc="default">
<name>Acknowledgements</name>
<section anchor="contributors" title="Contributors"> <t>Many thanks to <contact fullname="Cullen Jennings"/>, <contact
fullname="Magnus Westerlund"/>, and <contact fullname="Paul Kyzivat"/>
<t>The following individuals have contributed significant text to this document. for reviewing. Thanks to <contact fullname="Colin Perkins"/> for input
</t> on future payload type handling.</t>
</section>
<figure><artwork><![CDATA[ <section anchor="contributors" numbered="false" toc="default">
Peter Thatcher <name>Contributors</name>
Google <t>The following individuals have contributed significant text to this doc
Email: pthatcher@google.com ument.</t>
Mo Zanaty
Cisco Systems
Email: mzanaty@cisco.com
Suhas Nandakumar <contact fullname="Peter Thatcher">
Cisco Systems <organization>Google</organization>
Email: snandaku@cisco.com <address>
<email>pthatcher@google.com</email>
</address>
</contact>
Bo Burman <contact fullname="Mo Zanaty">
Ericsson <organization>Cisco Systems</organization>
Email: bo.burman@ericsson.com <address>
<email>mzanaty@cisco.com</email>
</address>
</contact>
Byron Campen <contact fullname="Suhas Nandakumar">
Mozilla <organization>Cisco Systems</organization>
Email: bcampen@mozilla.com <address>
]]></artwork></figure> <email>snandaku@cisco.com</email>
</address>
</contact>
</section> <contact fullname="Bo Burman">
<organization>Ericsson</organization>
<address>
<email>bo.burman@ericsson.com
</email>
</address>
</contact>
<contact fullname="Byron Campen">
<organization>Mozilla</organization>
<address>
<email>bcampen@mozilla.com</email>
</address>
</contact>
</section>
</back> </back>
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