One document matched: draft-ietf-mmusic-sdp-bundle-negotiation-13.xml
<?xml version="1.0" encoding="iso-8859-1"?>
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<!DOCTYPE rfc SYSTEM "rfc2629.dtd"[]>
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<?rfc compact="yes" ?>
<?rfc sortrefs="no" ?>
<rfc ipr="trust200902" category="std" docName="draft-ietf-mmusic-sdp-bundle-negotiation-13.txt" updates="3264" submissionType="IETF" xml:lang="en">
<front>
<title abbrev="Bundled media">
Negotiating Media Multiplexing Using the Session Description Protocol (SDP)
</title>
<author initials="C.H." surname="Holmberg" fullname="Christer Holmberg">
<organization>Ericsson</organization>
<address>
<postal>
<street>Hirsalantie 11</street>
<code>02420</code>
<city>Jorvas</city>
<country>Finland</country>
</postal>
<email>christer.holmberg@ericsson.com</email>
</address>
</author>
<author fullname="Harald Tveit Alvestrand" surname="Alvestrand" initials="H. T.">
<organization>Google</organization>
<address>
<postal>
<street>Kungsbron 2</street>
<city>Stockholm</city>
<code>11122</code>
<country>Sweden</country>
</postal>
<email>harald@alvestrand.no</email>
</address>
</author>
<author fullname="Cullen Jennings" initials="C." surname="Jennings">
<organization>Cisco</organization>
<address>
<postal>
<street>400 3rd Avenue SW, Suite 350</street>
<city>Calgary</city>
<region>AB</region>
<code>T2P 4H2</code>
<country>Canada</country>
</postal>
<email>fluffy@iii.ca</email>
</address>
</author>
<date year="2014" />
<area>Transport</area>
<workgroup>MMUSIC Working Group</workgroup>
<keyword>RTP</keyword>
<keyword>SDP</keyword>
<keyword>Bundle</keyword>
<keyword>Multiplexing</keyword>
<keyword>RTCWEB</keyword>
<keyword>CLUE</keyword>
<keyword>RTCWEB</keyword>
<keyword>MMUSIC</keyword>
<keyword>AVT</keyword>
<keyword>WEB</keyword>
<keyword>Browser</keyword>
<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 address:port combination (BUNDLE address) for receiving media,
referred to as bundled media, associated with multiple
SDP media descriptions ("m=" lines).
</t>
<t>
To assist endpoints in negotiating the use of bundle this
specification defines a new SDP attribute, 'bundle-only',
which can be used to request that specific media is only
used if bundled. This specification also updates sections
5.1, 8.1 and 8.2 of RFC 3264 to allow an answerer to assign a
non-zero port value to an "m=" line in an SDP answer,
even if the "m=" line in the associated SDP offer
contained a zero port value.
</t>
<t>
There are multiple ways to correlate the bundled RTP
packets with the appropriate media descriptions. This
specification defines a new RTCP source description (SDES)
item and a new RTP header extension that provides an additional
way to do this correlation by using them to carry a value that
associates the RTP/RTCP packets with a specific media
description.
</t>
</abstract>
</front>
<middle>
<section title="Introduction" toc="default">
<t>
This specification defines a way to use a single address:port combination (BUNDLE address) for
receiving media associated with multiple SDP media descriptions ("m=" lines).
</t>
<t>
This specification defines a new SDP Grouping Framework <xref format="default" pageno="false"
target="RFC5888"/> extension called 'BUNDLE'. The extension can be used with the Session Description
Protocol (SDP) Offer/Answer mechanism <xref format="default" pageno="false" target="RFC3264"/>
to negotiate the usage of a BUNDLE group. Within the BUNDLE group, a BUNDLE address is used
for receiving media associated with multiple "m=" lines. This is referred to as bundled media.
</t>
<t>
The offerer and answerer <xref format="default" pageno="false" target="RFC3264"/> use
the BUNDLE extension to negotiate the BUNDLE addresses, one for the offerer (offerer BUNDLE
address) and one for the answerer (answerer BUNDLE address), to be used for receiving
the bundled media associated with a BUNDLE group. Once the offerer and the answerer have
negotiated a BUNDLE group, they assign their respective BUNDLE address to each "m=" line
in the BUNDLE group. The BUNDLE addresses are used to receive all media associated with
the BUNDLE group.
</t>
<t>
The use of a BUNDLE group and a BUNDLE address also allows the usage of a single set of
Interactive Connectivity Establishment (ICE) <xref format="default" pageno="false" target="RFC5245"/>
candidates for multiple "m=" lines.
</t>
<t>
This specification also defines a new SDP attribute, 'bundle-only', which can be used to
request that specific media is only used if kept within a BUNDLE group.
</t>
<t>
As defined in RFC 4566 <xref format="default" pageno="false" target="RFC4566"/>, the
semantics of assigning the same port value to multiple "m=" lines are undefined, and there is no
grouping defined by such means. Instead, an explicit grouping mechanism needs to be used to
express the intended semantics. This specification provides such an extension.
</t>
<t>
This specification also updates sections 5.1, 8.1 and 8.2 of RFC 3264 <xref format="default" pageno="false"
target="RFC3264"/>. The update allows an answerer to assign a non-zero port value to an "m=" line in an
SDP answer, even if the "m=" line in the associated SDP offer contained a zero port value.
</t>
<t>
This specification also defines a new Real-time Transport Protocol (RTP) <xref format="default"
pageno="false" target="RFC3550"/> SDES item and a new RTP header extension that
can be used to carry a value that associates RTP/RTCP packets with a specific media
description. This can be used to correlate a RTP packet with the correct media.
</t>
<t>
SDP bodies can contain multiple BUNDLE groups. A given BUNDLE address MUST only be associated
with a single BUNDLE group. The procedures in this specification apply independently to a given
BUNDLE group. All RTP based media flows associated with a single BUNDLE group belong to a single
RTP session <xref format="default" pageno="false" target="RFC3550"/>.
</t>
<t>
The BUNDLE extension is backward compatible. Endpoints that do not support the extension
are expected to generate offers and answers without an SDP 'group:BUNDLE' attribute, and
are expected to assign a unique address to each "m=" line within an offer and answer, according
to the procedures in <xref format="default" pageno="false" target="RFC4566"/> and
<xref format="default" pageno="false" target="RFC3264"/>
</t>
</section>
<section title="Terminology" toc="default">
<t>
5-tuple: A collection of the following values: source address, source port,
destination address, destination port, and transport-layer protocol.
</t>
<t>
Unique address: An IP address and port combination that is assigned to
only one "m=" line in an offer or answer.
</t>
<t>
Shared address: An IP address and port combination that is assigned to
multiple "m=" lines within an offer or answer.
</t>
<t>
Offerer BUNDLE-tag: The first identification-tag in a given
SDP 'group:BUNDLE' attribute identification-tag list in an offer.
</t>
<t>
Answerer BUNDLE-tag: The first identification-tag in a given
SDP 'group:BUNDLE' attribute identification-tag list in an answer.
</t>
<t>
Offerer BUNDLE address: Within a given BUNDLE group, an IP address and
port combination used by an offerer to receive all media associated
with each "m=" line within the BUNDLE group.
</t>
<t>
Answerer BUNDLE address: Within a given BUNDLE group, an IP address and
port combination used by an answerer to receive all media associated
with each "m=" line within the BUNDLE group.
</t>
<t>
BUNDLE group: A set of "m=" lines, created using an SDP Offer/Answer
exchange, which uses the same BUNDLE address for receiving media.
</t>
<t>
Bundled "m=" line: An "m=" line, whose identification-tag
is placed in an SDP 'group:BUNDLE' attribute identification-tag list
in an offer or answer.
</t>
<t>
Bundle-only "m=" line: A bundled "m=" line with an associated
SDP 'bundle-only' attribute.
</t>
<t>
Bundled media: All media associated with a given BUNDLE group.
</t>
<t>
Initial offer: The first offer, within an SDP session, in which
the offerer indicates that it wants to create a given BUNDLE group.
</t>
<t>
Subsequent offer: An offer which contains a BUNDLE group that
has been created as part of a previous SDP Offer/Answer exchange.
</t>
<t>
Identification-tag: A unique token value that is used to identify an
"m=" line. The SDP 'mid' attribute <xref format="default" pageno="false"
target="RFC5888" />, associated with an "m=" line, carries
an unique identification-tag. The session-level SDP 'group' attribute
<xref format="default" pageno="false" target="RFC5888" /> carries a list
of identification-tags, identifying the "m=" lines associated with that
particular 'group' attribute.
</t>
</section>
<section title="Conventions" toc="default">
<t>
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14, RFC 2119 <xref
format="default" pageno="false" target="RFC2119" />.
</t>
</section>
<section title="Applicability Statement" toc="default">
<t>
The mechanism in this specification only applies to the Session Description Protocol (SDP)
<xref format="default" pageno="false" target="RFC4566"/>, when used together with the
SDP Offer/Answer mechanism <xref format="default" pageno="false" target="RFC3264"/>.
</t>
</section>
<section title="SDP Grouping Framework BUNDLE Extension" anchor="sec-group" toc="default">
<section title="General" anchor="sec-group-gen" toc="default">
<t>
This section defines a new SDP Grouping Framework extension
<xref format="default" pageno="false" target="RFC5888"/>, 'BUNDLE'. The
BUNDLE extension can be used with the SDP Offer/Answer mechanism to negotiate
the usage of a single address:port combination (BUNDLE address) for receiving bundled media.
</t>
<t>
A single address:port combination is also used for sending bundled media. The address:port
combination used for sending bundled media MAY be the same as the BUNDLE address, used to receive
bundled media, depending on whether symmetric RTP is used. A given address:port combination MUST
NOT be used for sending media associated with multiple BUNDLE groups.
</t>
<t>
All media associated with a BUNDLE group share a single 5-tuple, i.e. in addition
to using a single address:port combination all bundled media MUST be transported using the same
transport-layer protocol.
</t>
<t>
The BUNDLE extension is indicated using an SDP 'group' attribute
with a "BUNDLE" semantics value <xref format="default" pageno="false"
target="RFC5888"/>. An identification-tag is assigned to each bundled
"m=" line, and each identification-tag is listed in the SDP 'group:BUNDLE'
attribute identification-tag list. Each "m=" line, whose identification-tag
is listed in the identification-tag list, is associated with a given
BUNDLE group.
</t>
<t>
SDP bodies can contain multiple BUNDLE groups. Any given bundled "m="
line MUST NOT be associated with more than one BUNDLE group.
</t>
<t>
<xref target="sec-sdp-oa" pageno="false" format="default"/> defines the
detailed SDP Offer/Answer procedures for the BUNDLE extension.
</t>
</section>
</section>
<section anchor="sec-bundle-only" title="SDP 'bundle-only' Attribute" toc="default">
<section anchor="sec-bundle-only-gen" title="General" toc="default">
<t>
This section defines a new SDP media-level attribute <xref target="RFC4566" pageno="false"
format="default"/>, 'bundle-only'.
</t>
</section>
<section anchor="sec-bundle-only-bo" title="bundle-only" toc="default">
<figure>
<preamble></preamble>
<artwork><![CDATA[
Name: bundle-only
Value:
Usage Level: media
Charset Dependent: no
Example:
a=bundle-only
]]></artwork>
</figure>
<t>
In order to ensure that an answerer that does not supports the BUNDLE extension always
rejects a bundled "m=" line, the offerer can assign a zero port value to the "m="
line. According to <xref target="RFC4566" pageno="false" format="default"/> an answerer
will reject such "m=" line.
By associating an SDP 'bundle-only' attribute with such "m=" line, the offerer can
request that the answerer accepts the "m=" line if the answerer supports the Bundle
extension, and if the answerer keeps the "m=" line within the associated BUNDLE group.
</t>
<t>
NOTE: Once an offerer BUNDLE address has been selected, the offerer can ensure that an
bundled "m=" line is accepted by the answerer only if the answerer keeps the "m=" line within
the associated BUNDLE group by assigning the offerer BUNDLE address to the "m=" line. If
the answerer does not keep that "m=" line within the BUNDLE group, the answerer will reject
it. Therefore, the SDP 'bundle-only' attribute is not needed in such cases
</t>
<t>
The usage of the 'bundle-only' attribute is only defined for a bundled "m=" line with
a zero port value, within an offer. Other usage is unspecified.
</t>
<t>
<xref target="sec-sdp-oa" pageno="false" format="default"/> defines the detailed SDP
Offer/Answer procedures for the 'bundle-only' attribute.
</t>
</section>
</section>
<section title="SDP Information Considerations" anchor="sec-sdp-cons" toc="default">
<section title="General" anchor="sec-sdp-cons-gen" toc="default">
<t>
This section describes restrictions associated with the usage of
SDP parameters within a BUNDLE group. It also describes, when parameter
and attribute values have been associated with each bundled "m=" line, how to
calculate a value for the whole BUNDLE group.
</t>
</section>
<section title="Connection Data (c=)" anchor="sec-sdp-cons-c" toc="default">
<t>
The "c=" line nettype value <xref format="default" pageno="false"
target="RFC4566"/> associated with a bundled "m=" line MUST be 'IN'.
</t>
<t>
The "c=" line addrtype value <xref format="default" pageno="false"
target="RFC4566"/> associated with a bundled "m=" line MUST be 'IP4' or
'IP6'. The same value MUST be associated with each "m=" line.
</t>
<t>
NOTE: Extensions to this specification can specify usage of the BUNDLE
mechanism for other nettype and addrtype values than the ones listed above.
</t>
</section>
<section title="Bandwidth (b=)" anchor="sec-sdp-cons-b" toc="default">
<t>
The proposed bandwidth for a bundled "m=" line SHOULD be calculated
in the same way as for a non-bundled "m=" line.
</t>
<t>
The total proposed bandwidth for a BUNDLE group is the sum of the
proposed bandwidth for each bundled "m=" line.
</t>
<t>
The total proposed bandwidth for an offer or answer is the sum of
the proposed bandwidth for each "m=" line (bundled and non-bundled)
within the offer or answer.
</t>
</section>
<section title="Attributes (a=)" anchor="sec-sdp-cons-a" toc="default">
<t>
An offerer and answerer MUST use the rules and restrictions defined
in <xref target="I-D.mmusic-sdp-mux-attributes" /> for when
associating SDP attributes with bundled "m=" lines.
</t>
</section>
</section>
<section title="SDP Offer/Answer Procedures" anchor="sec-sdp-oa" toc="default">
<section anchor="sec-sdp-oa-gen" title="General" toc="default">
<t>
This section describes the SDP Offer/Answer <xref format="default"
pageno="false" target="RFC3264"/> procedures for:
<list style="symbols">
<t>
Negotiating and creating of a BUNDLE group;
</t>
<t>
Selecting the BUNDLE addresses (offerer BUNDLE address and answerer BUNDLE address);
</t>
<t>
Adding an "m=" line to a BUNDLE group;
</t>
<t>
Moving an "m=" line out of a BUNDLE group; and
</t>
<t>
Disabling an "m=" line within a BUNDLE group.
</t>
</list>
</t>
<t>
The generic rules and procedures defined in <xref format="default" pageno="false"
target="RFC3264"/> and <xref format="default" pageno="false" target="RFC5888"/>
also apply to the BUNDLE extension. For example, if an offer is rejected
by the answerer, the previously negotiated SDP parameters and characteristics
(including those associated with a BUNDLE group) apply. Hence, if an offerer
generates an offer in which the offerer wants to create a BUNDLE group,
and the answerer rejects the offer, the BUNDLE group is not created.
</t>
<t>
The procedures in this section are independent of the media type or transport
protocol represented by a bundled "m=" line. <xref format="default" pageno="false"
target="sec-rtp"/> defines additional considerations for RTP based media.
<xref format="default" pageno="false" target="sec-bundle-only"/> defines
additional considerations for the usage of the SDP 'bundle-only' attribute.
<xref format="default" pageno="false" target="sec-ice"/> defines additional
considerations for the usage of Interactive Connectivity Establishment (ICE)
<xref format="default" pageno="false" target="RFC5245"/> mechanism .
</t>
<t>
The offerer and answerer MUST follow the rules and restrictions defined
in <xref format="default" pageno="false" target="sec-sdp-cons"/> when
creating offers and answers.
</t>
<t>
SDP bodies can contain multiple BUNDLE groups. The procedures in this
section apply independently to a given BUNDLE group.
</t>
</section>
<section anchor="sec-sdp-oa-ino" title="Generating the Initial SDP Offer" toc="default">
<section anchor="sec-sdp-oa-ino-gen" title="General" toc="default">
<t>
When an offerer generates an initial offer, in order to create a
BUNDLE group, it MUST:
<list style="symbols">
<t>
Assign a unique address to each "m=" line within the offer, following the
procedures in <xref target="RFC3264" pageno="false" format="default"/>;
</t>
<t>
Assign a unique address to each "m=" line within the offer, following the
procedures in <xref target="RFC3264" pageno="false" format="default"/>;
</t>
<t>
Add an SDP 'group:BUNDLE' attribute to the offer;
</t>
<t>
Place the identification-tag of each bundled "m=" line in the
SDP 'group:BUNDLE' attribute identification-tag list; and
</t>
<t>
Indicate which unique address the offerer suggests as the
offerer BUNDLE address [<xref target="sec-sdp-oa-ino-req" pageno="false"
format="default"/>].
</t>
</list>
</t>
<t>
If the offerer wants to request that the answerer accepts a given "m=" line only if
the answerer keeps the "m=" line within the BUNDLE group, the offerer MUST:
<list style="symbols">
<t>
Associate an SDP 'bundle-only' attribute [<xref target="sec-sdp-oa-ino-req" pageno="false"
format="default"/>] with the "m=" line; and
</t>
<t>
Assign a zero port value to the "m=" line.
</t>
</list>
</t>
<t>
NOTE: If the offerer assigns a zero port value to an "m=" line, but does not also associate an
SDP 'bundle-only' attribute with the "m=" line, it is an indication that the offerer wants
to disable the "m=" line [<xref target="sec-sdp-oa-mod-dis" pageno="false" format="default"/>].
</t>
<t>
[<xref target="sec-example-add" pageno="false" format="default"/>] shows
an example of an initial offer.
</t>
</section>
<section title="Suggesting the offerer BUNDLE address" anchor="sec-sdp-oa-ino-req" toc="default">
<t>
In the offer, the address assigned to the "m=" line associated with the
offerer BUNDLE-tag indicates the address that the offerer suggests as
the offerer BUNDLE address.
</t>
</section>
</section>
<section anchor="sec-sdp-oa-ans" title="Generating the SDP Answer" toc="default">
<section title="General" anchor="sec-sdp-oa-ans-gen" toc="default">
<t>
When an answerer generates an answer, which contains a BUNDLE group, the following general
SDP grouping framework restrictions, defined in <xref target="RFC5888" pageno="false"
format="default"/>, also apply to the BUNDLE group:
<list style="symbols">
<t>
The answerer MUST NOT include a BUNDLE group in the answer, unless the
offerer requested the BUNDLE group to be created in the associated offer; and
</t>
<t>
The answerer MUST NOT include an "m=" line within a BUNDLE group, unless
the offerer requested the "m=" line to be within that BUNDLE group in the
associated offer.
</t>
</list>
</t>
<t>
If the answer contains a BUNDLE group, the answerer MUST:
<list style="symbols">
<t>
Select an Offerer BUNDLE Address [<xref target="sec-sdp-oa-ans-off"
pageno="false" format="default"/>]; and
</t>
<t>
Select an Answerer BUNDLE Address [<xref target="sec-sdp-oa-ans-ans"
pageno="false" format="default"/>];
</t>
</list>
</t>
<t>
The answerer is allowed to select a new Answerer BUNDLE address each time it
generates an answer to an offer.
</t>
<t>
If the answerer does not want to keep an "m=" line within a BUNDLE group, it MUST:
<list style="symbols">
<t>
Move the "m=" line out of the BUNDLE group [<xref target="sec-sdp-oa-ans-mov"
pageno="false" format="default"/>]; or
</t>
<t>
Reject the "m=" line [<xref target="sec-sdp-oa-ans-rej" pageno="false"
format="default"/>];
</t>
</list>
</t>
<t>
If the answerer keeps a bundle-only "m=" line within the BUNDLE group,
it follows the procedures (assigns the answerer BUNDLE address to the "m="
line etc) for any other "m=" line kept within the BUNDLE group.
</t>
<t>
If the answerer does not want to keep a bundle-only "m=" line within the
BUNDLE group, it MUST reject the "m=" line [<xref target="sec-sdp-oa-ans-rej"
pageno="false" format="default"/>].
</t>
<t>
The answerer MUST NOT associate an SDP 'bundle-only' attribute with any
"m=" line in an answer.
</t>
<t>
NOTE: If a bundled "m=" line in an offer contains a zero port value, but the "m=" line does not contain
an SDP 'bundle-only' attribute, it is an indication that the offerer wants to disable the "m="
line [<xref target="sec-sdp-oa-mod-dis" pageno="false" format="default"/>].
</t>
</section>
<section title="Answerer Selection of Offerer Bundle Address" anchor="sec-sdp-oa-ans-off" toc="default">
<t>
In an offer, the address (unique or shared) assigned to the bundled "m=" line
associated with the offerer BUNDLE-tag indicates the address that
the offerer suggests as the offerer BUNDLE address
[<xref target="sec-sdp-oa-ino-req" pageno="false" format="default"/>]. The answerer
MUST check whether that "m=" line fulfills the following criteria:
<list style="symbols">
<t>
The answerer will not move the "m=" line out of the BUNDLE group
[<xref target="sec-sdp-oa-ans-mov" pageno="false" format="default"/>];
</t>
<t>
The answerer will not reject the "m=" line [<xref target="sec-sdp-oa-ans-rej"
pageno="false" format="default"/>]; and
</t>
<t>
The "m=" line does not contain a zero port value.
</t>
</list>
</t>
<t>
If all of the criteria above are fulfilled, the answerer MUST select the address
associated with the "m=" line as the offerer BUNDLE address. In the answer, the
answerer BUNDLE-tag represents the "m=" line, and the
address associated with the "m=" line in the offer becomes the offerer BUNDLE address.
</t>
<t>
If one or more of the criteria are not fulfilled, the answerer MUST select the next
identification-tag in the identification-tag list, and perform the same criteria
check for the "m=" line associated with that identification-tag. If there are no
more identification-tags in the identification-tag list, the answerer MUST NOT
create the BUNDLE group.
</t>
<t>
[<xref target="sec-example-add" pageno="false" format="default"/>] shows an
example of an offerer BUNDLE address selection.
</t>
</section>
<section title="Answerer Selection of Answerer BUNDLE Address" anchor="sec-sdp-oa-ans-ans" toc="default">
<t>
When the answerer selects a BUNDLE address for itself, referred to as the answerer
BUNDLE address, it MUST assign that address to each bundled "m=" line within the
created BUNDLE group in the answer.
</t>
<t>
The answerer MUST NOT assign the answerer BUNDLE address to an "m=" line that is
not within the BUNDLE group, or to an "m=" line that is within another BUNDLE group.
</t>
<t>
[<xref target="sec-example-add" pageno="false" format="default"/>] shows an example of an
answerer BUNDLE address selection.
</t>
</section>
<section title="Moving A Media Description Out Of A BUNDLE Group" anchor="sec-sdp-oa-ans-mov" toc="default">
<t>
When an answerer moves a "m=" line out of a BUNDLE group, it assigns an
address to the "m=" line in the answer based on the following rules:
<list style="symbols">
<t>
In the associated offer, if the "m=" line contains a shared address (e.g. a
previously selected offerer BUNDLE address), the answerer MUST reject the
moved "m=" line [<xref target="sec-sdp-oa-ans-rej" pageno="false"
format="default"/>];
</t>
<t>
In the associated offer, if the "m=" line contains a unique address, the
answerer MUST assign a unique address also to the "m=" line in the answer; or
</t>
<t>
In the associated offer, if an SDP 'bundle-only' attribute is associated with
the "m=" line, and if the "m=" line contains a zero port value, the answerer
MUST reject the "m=" line [<xref target="sec-sdp-oa-ans-rej" pageno="false"
format="default"/>].
</t>
</list>
</t>
<t>
In addition, in either case above, the answerer MUST NOT place the
identification-tag, associated with the moved "m=" line, in the
SDP 'group' attribute identification-tag list associated with the BUNDLE group.
</t>
</section>
<section title="Rejecting A Media Description In A BUNDLE Group" anchor="sec-sdp-oa-ans-rej" toc="default">
<t>
When an answerer rejects an "m=" line, it MUST assign an address with a zero port
value to the "m=" line in the answer, according to the procedures in <xref
target="RFC4566" pageno="false" format="default"/>.
</t>
<t>
In addition, the answerer MUST NOT place the identification-tag, associated with
the rejected "m=" line, in the SDP 'group' attribute identification-tag list
associated with the BUNDLE group.
</t>
</section>
</section>
<section anchor="sec-sdp-oa-off-ans" title="Offerer Processing of the SDP Answer" toc="default">
<section title="General" anchor="sec-sdp-oa-off-ans-gen" toc="default">
<t>
When an offerer receives an answer, if the answer contains a BUNDLE group, the offerer
MUST check that any bundled "m=" line in the answer was indicated as bundled in the
associated offer. If there is no mismatch, the offerer MUST use the offerer BUNDLE address,
selected by the answerer [<xref format="default" pageno="false" target="sec-sdp-oa-ans-off"/>],
as the address for each bundled "m=" line.
</t>
<t>
NOTE: As the answerer might reject one or more bundled "m=" lines, or move a bundled
"m=" line out of a BUNDLE group, each bundled "m=" line in the offer might not be
indicated as bundled in the answer.
</t>
<t>
If the answer does not contain a BUNDLE group, the offerer MUST process the answer
as a normal answer.
</t>
</section>
<section title="Bundle Address Synchronization (BAS)" anchor="sec-sdp-oa-off-ans-bas" toc="default">
<t>
When an offerer receives an answer, if the answer contains a BUNDLE group, the offerer MUST
check whether the offerer BUNDLE address, selected by the answerer [<xref format="default" pageno="false"
target="sec-sdp-oa-ans-off"/>], matches what was assigned to each bundled "m=" line (excluding any
bundled "m=" line that was rejected, or moved out of the BUNDLE group, by the answer)
in the associated offer. If there is a mismatch, the offerer SHOULD as soon as possible
generate a subsequent offer, in which it assigns the offerer BUNDLE address to each
bundled "m=" line. Such offer is referred to as a Bundle Address Synchronization (BAS) offer.
</t>
<t>
A BAS offer is typically sent in the following scenarios:
<list style="symbols">
<t>
The offerer receives an answer to an initial offer, as the bundled "m=" lines
in the initial offer always contain unique addresses [<xref target="sec-sdp-oa-ino"
pageno="false" format="default"/>]; or
</t>
<t>
The offerer receives an answer to an offer, in which a new bundled "m=" line has
been added to the BUNDLE group [<xref target="sec-sdp-oa-mod-add" pageno="false"
format="default"/>], and the offerer assigned a unique address to the bundled
"m=" line in the offer.
</t>
</list>
</t>
<t>
The offerer is allowed to modify any SDP parameter in the BAS offer.
</t>
<t>
NOTE: It is important that the BAS offer gets accepted by the
answerer. For that reason the offerer needs to consider the
necessity to modify SDP parameters in the BAS offer, in such a way
that could trigger the answerer to reject the BAS offer.
Disabling "m=" lines, or reducing the number of codecs, in a BAS
offer is considered to have a low risk of being rejected.
</t>
<t>
NOTE: The main purpose of the BAS offer is to ensure that
intermediaries, that might not support the BUNDLE extension, have
correct information regarding the address that is going to be used to
transport the bundled media.
</t>
<t>
[<xref target="sec-example-add" pageno="false" format="default"/>]
shows an example of a BAS offer.
</t>
</section>
</section>
<section title="Modifying the Session" anchor="sec-sdp-oa-mod" toc="default">
<section title="General" anchor="sec-sdp-oa-mod-gen" toc="default">
<t>
When an offerer generates a subsequent offer, it MUST assign
the previously selected offerer BUNDLE address [<xref format="default"
pageno="false" target="sec-sdp-oa-ans-off"/>], to each bundled "m=" line
(including any bundle-only "m=" line), except if:
<list style="symbols">
<t>
The offerer suggests a new offerer BUNDLE address
[<xref target="sec-sdp-oa-mod-req" pageno="false" format="default"/>];
</t>
<t>
The offerer wants to add a bundled "m=" line to the BUNDLE group
[<xref target="sec-sdp-oa-mod-add" pageno="false" format="default"/>];
</t>
<t>
The offerer wants to move a bundled "m=" line out of the BUNDLE group
[<xref target="sec-sdp-oa-mod-mov" pageno="false" format="default"/>]; or
</t>
<t>
The offerer wants to disable the bundled "m=" line [<xref format="default"
pageno="false" target="sec-sdp-oa-mod-dis"/>].
</t>
</list>
</t>
<t>
In addition, the offerer MUST select an offerer BUNDLE-tag
[<xref format="default" pageno="false" target="sec-sdp-oa-ino-req"/>], even
if the offerer does not suggest a new offerer BUNDLE address.
</t>
<t>
The offerer MUST NOT associate an SDP 'bundle-only' attribute with a
bundled "m=" line in a subsequent offer, unless the offerer also assigns
a zero port value to the "m=" line.
</t>
</section>
<section title="Request a new offerer BUNDLE address" anchor="sec-sdp-oa-mod-req" toc="default">
<t>
When an offerer generates an offer, in which it suggests a new
offerer BUNDLE address [<xref target="sec-sdp-oa-ino-req"
pageno="false" format="default"/>], the offerer MUST:
<list style="symbols">
<t>
Assign a unique address, which the offerer suggests as
the new offerer BUNDLE address, to a bundled "m=" line; and
</t>
<t>
Indicate that the offerer suggests the unique address as the
new offerer BUNDLE address [<xref format="default" pageno="false"
target="sec-sdp-oa-ino-req"/>]
</t>
</list>
</t>
<t>
NOTE: The offerer can assign a unique address to each bundled "m=" line
in the offer, or it can assign the previously selected offerer BUNDLE
address to each "m=" line (except to the "m=" line to which it assigns
the unique address that it suggests as the new offerer BUNDLE address).
</t>
</section>
<section title="Adding a media description to a BUNDLE group" anchor="sec-sdp-oa-mod-add" toc="default">
<t>
When an offerer generates an offer, in which it wants to add a bundled "m=" line
to a BUNDLE group, the offerer MUST:
<list style="symbols">
<t>
Assign a unique address, or the previously selected offerer BUNDLE address,
to the "m=" line; and
</t>
<t>
Extend the SDP 'group:BUNDLE' attribute identification-tag list with the
BUNDLE group [<xref format="default" pageno="false" target="sec-sdp-oa-ino-req"/>]
by adding the identification-tag associated with the added "m=" line to the list.
</t>
</list>
</t>
<t>
NOTE: Assigning a unique address to the "m=" line allows the answerer
to move the "m=" line out of the BUNDLE group [<xref format="default" pageno="false"
target="sec-sdp-oa-ans-mov"/>], without having to reject the "m=" line.
</t>
<t>
If the offerer suggests the address associated with the added "m=" line as
the new offerer BUNDLE address, the offerer BUNDLE-tag
MUST represent the added "m=" line [<xref format="default" pageno="false"
target="sec-sdp-oa-ino-req"/>].
</t>
<t>
[<xref target="sec-example-off-add" pageno="false" format="default"/>]
shows an example where an offerer sends an offer in order to
add a bundled "m=" line to a BUNDLE group.
</t>
</section>
<section title="Moving A Media Description Out Of A BUNDLE Group" anchor="sec-sdp-oa-mod-mov" toc="default">
<t>
When an offerer generates an offer, in which it wants to move a bundled "m=" line out
of a BUNDLE group it was added to in a previous offer/answer transaction, the offerer:
<list style="symbols">
<t>
MUST assign a unique address to the "m=" line; and
</t>
<t>
MUST NOT place the identification-tag associated with the "m=" line in
the SDP 'group:BUNDLE' attribute identification-tag list associated with
the BUNDLE group.
</t>
</list>
</t>
<t>
NOTE: If an "m=" line, when being moved out of a BUNDLE group, is added to
another BUNDLE group, the offerer applies the procedures in
[<xref target="sec-sdp-oa-mod-add" pageno="false" format="default"/>] to
the "m=" line.
</t>
<t>
[<xref target="sec-example-off-mov" pageno="false" format="default"/>]
shows an example of an offer for moving an "m=" line out of a BUNDLE group.
</t>
</section>
<section title="Disabling A Media Description In A BUNDLE Group" anchor="sec-sdp-oa-mod-dis" toc="default">
<t>
When an offerer generates an offer, in which it wants to disable a bundled "m=" line (added
to the BUNDLE group in a previous offer/answer transaction), the offerer:
<list style="symbols">
<t>
MUST assign an address with a zero port value to the "m=" line,
following the procedures in <xref target="RFC4566" pageno="false"
format="default"/>; and
</t>
<t>
MUST NOT place the identification-tag associated with the "m=" line in
the SDP 'group:BUNDLE' attribute identification-tag list associated with
the BUNDLE group.
</t>
</list>
</t>
<t>
[<xref target="sec-example-off-dis" pageno="false" format="default"/>]
shows an example of an offer for disabling an "m=" line within a
BUNDLE group.
</t>
</section>
</section>
</section>
<section title="Protocol Identification" anchor="sec-protocol-id" toc="default">
<section title="General" anchor="sec-protocol-id-gen" toc="default">
<t>
Each "m=" line within a BUNDLE group MUST use the same transport-layer protocol.
If bundled "m=" lines use different protocols on top of the transport-layer
protocol, there MUST exist a publicly available specification which describes
a mechanism, for this particular protocol combination, how to associate a
received packet with the correct protocol.
</t>
<t>
In addition, if a received packet can be associated with more than one
bundled "m=" line, there MUST exist a publically available specification which
describes a mechanism for associating the received packet with the correct "m=" line.
</t>
</section>
<section anchor="sec-packets-id-sds" title="STUN, DTLS, SRTP" toc="default">
<t>
Section 5.1.2 of <xref format="default" pageno="false" target="RFC5764"/> describes a
mechanism to identify the protocol of a received packet among the STUN, DTLS and SRTP protocols (in any combination).
If an offer or answer includes bundled "m=" lines that represent these protocols, the offerer
or answerer MUST support the mechanism described in <xref format="default" pageno="false"
target="RFC5764"/>, and no explicit negotiation is required in order to indicate support
and usage of the mechanism.
</t>
<t>
<xref format="default" pageno="false" target="RFC5764"/> does not describe how to identify
different protocols transported on DTLS, only how to identify the DTLS protocol itself. If
multiple protocols are transported on DTLS, there MUST exist a specification describing a
mechanism for identifying each individual protocol. In addition, if a received DTLS packet
can be associated with more than one "m=" line, there MUST exist a specification which
describes a mechanism for associating the received DTLS packet with the correct "m=" line.
</t>
<t>
[<xref format="default" pageno="false" target="sec-rtp-pt"/>] describes how to associate a received
(S)RTP packet with the correct "m=" line.
</t>
</section>
</section>
<section anchor="sec-rtp" title="RTP Considerations" toc="default">
<section anchor="sec-rtp-sessions" title="Single RTP Session" toc="default">
<section anchor="sec-rtp-sessions-gen" title="General" toc="default">
<t>
All RTP-based media within a single BUNDLE group belong to a
single RTP session <xref format="default" pageno="false"
target="RFC3550"/>. Disjoint BUNDLE groups will form multiple
RTP sessions, one per BUNDLE group.
</t>
<t>
Since a single RTP session is used for each bundle group, all
"m=" lines representing RTP-based media in a bundle group will
share a single SSRC numbering space <xref format="default"
pageno="false" target="RFC3550"/>.
</t>
<t>
The following rules and restrictions apply for a single RTP
session:
</t>
<t>
<list style="symbols">
<t>
A specific payload type value can be used in multiple bundled "m=" lines
if each codec associated with the payload type number shares an identical
codec configuration [<xref format="default" pageno="false"
target="sec-rtp-sessions-pt"/>].
</t>
<t>
The "proto" value in each bundled RTP-based "m=" line MUST be identical
(e.g. RTP/AVPF).
</t>
<t>
An SDP 'extmap' attribute <xref format="default" pageno="false"
target="RFC5285"/>, with a 'urn:ietf:params:rtp-hdrext:sdes:mid' URI value,
MUST, in every offer and answer, be associated with each bundled "m=" line
representing RTP-based media.
</t>
<t>
A given SSRC MUST NOT transmit RTP packets using payload types that
originate from different bundled "m=" lines.
</t>
</list>
</t>
<t>
NOTE: The last bullet above is to avoid sending multiple media types
from the same SSRC. If transmission of multiple media types are done
with time overlap, RTP and RTCP fail to function. Even if done in
proper sequence this causes RTP Timestamp rate switching issues
<xref format="default" pageno="false" target="RFC7160"/>. However,
once an SSRC has left the RTP session (by sending an RTCP BYE packet),
that SSRC value can later be reused by another source(possible associated
with a different bundled "m=" line.
</t>
</section>
<section anchor="sec-rtp-sessions-pt" title="Payload Type (PT) Value Reuse" toc="default">
<t>
Multiple bundled "m=" lines might represent RTP based media. As all RTP based
media associated with a BUNDLE group belong to the same RTP session, in order
for a given payload type value to be used inside more than one bundled "m=" line,
all codecs associated with the payload type number MUST share an identical codec
configuration. This means that the codecs MUST share the same media type,
encoding name, clock rate and any parameter that can affect the codec configuration
and packetization. <xref format="default" pageno="false"
target="I-D.mmusic-sdp-mux-attributes"/> lists SDP attributes, whose attribute
values must be identical for all codecs that use the same payload type value.
</t>
</section>
</section>
<section anchor="sec-rtp-pt" title="Associating RTP/RTCP Packets With Correct SDP Media Description" toc="default">
<t>
There are multiple mechanisms that can be used by an endpoint in
order to associate received RTP/RTCP packets with a bundled "m=" line.
Such mechanisms include using the payload type value carried inside the
RTP packets, the SSRC values carried inside the RTP packets, and other
"m=" line specific information carried inside the RTP packets.
</t>
<t>
As all RTP/RTCP packets associated with a BUNDLE group are received (and sent)
using single address:port combinations, the local address:port combination cannot
be used to associate received RTP packets with the correct "m=" line.
</t>
<t>
As described in [<xref format="default" pageno="false" target="sec-rtp-sessions-pt"/>],
the same payload type value might be used inside RTP packets described by
multiple "m=" lines. In such cases, the payload type value cannot be used to
associate received RTP packets with the correct "m=" line.
</t>
<t>
An offerer and answerer can in an offer and answer inform each other which
SSRC values they will use inside sent RTP/RTCP packets, by associating an SDP
'ssrc' attribute <xref format="default" pageno="false" target="RFC5576"/> with
each bundled "m=" line which contains a payload type value that is also used
inside another bundled "m=" line. As the SSRC values will be carried inside
the RTP/RTCP packets, the offerer and answerer can then use that information
to associate received RTP packets with the correct "m=" line. However, an
offerer will not know which SSRC values the answerer will use until it has
received the answer providing that information. Due to this, before the
offerer has received the answer, the offerer will not be able to associate
received RTP/RTCP packets with the correct "m=" line using the SSRC values.
</t>
<t>
In order for an offerer and answerer to always be able to associate received
RTP and RTCP packets with the correct "m=" line, an offerer and answerer using
the BUNDLE extension MUST support the mechanism defined in <xref format="default"
pageno="false" target="sec-receiver-id"/>, where the remote endpoint inserts the
identification-tag associated with an "m=" line in RTP and RTCP packets
associated with that "m=" line.
</t>
</section>
<section title="RTP/RTCP Multiplexing" anchor="sec-rtprtcp-mux" toc="default">
<section title="General" anchor="sec-rtprtcp-mux-gen" toc="default">
<t>
When a BUNDLE group, which contains RTP based media, is created, the offerer
and answerer MUST negotiate whether to enable RTP/RTCP multiplexing
for the RTP based media associated with the BUNDLE group <xref format="default"
pageno="false" target="RFC5761"/>.
</t>
<t>
If RTP/RTCP multiplexing is not enabled, separate address:port combinations will
be used for receiving (and sending) the RTP packets and the RTCP packets.
</t>
</section>
<section title="SDP Offer/Answer Procedures" anchor="sec-rtprtcp-mux-oa" toc="default">
<section title="General" anchor="sec-rtprtcp-mux-oa-gen" toc="default">
<t>
This section describes how an offerer and answerer can use the SDP 'rtcp-mux' attribute
<xref format="default" pageno="false" target="RFC5761"/> and the SDP 'rtcp' attribute
<xref format="default" pageno="false" target="RFC3605"/> to negotiate usage of RTP/RTCP
multiplexing for RTP based media associated with a BUNDLE group.
</t>
</section>
<section title="Generating the Initial SDP Offer" anchor="sec-rtprtcp-mux-oa-ino" toc="default">
<t>
When an offerer generates an initial offer, if the offerer wants to negotiate usage
of RTP/RTCP multiplexing within a BUNDLE group, the offerer MUST associate
an SDP 'rtcp-mux' attribute <xref format="default" pageno="false" target="RFC5761"/> with
each bundled RTP-based "m=" line (including any bundle-only "m=" line) in the offer. In addition, the offerer
MUST associate an SDP 'rtcp' attribute <xref format="default" pageno="false" target="RFC3605"/> with each
bundled RTP-based "m=" line (including any bundle-only "m=" line), with an attribute value that is identical to
the port value assigned to the "m=" line itself, in the offer.
</t>
<t>
If the offerer does not want to negotiate usage of RTP/RTCP multiplexing, it MUST
NOT associate the SDP attributes above with any bundled "m=" line.
</t>
</section>
<section title="Generating the SDP Answer" anchor="sec-rtprtcp-mux-oa-ans" toc="default">
<t>
When an answerer generates an answer, if the offerer indicated support of
RTP/RTCP multiplexing <xref format="default" pageno="false" target="RFC5761"/>
within a BUNDLE group in the associated offer, the answerer MUST either accept
or reject the usage of RTP/RTCP multiplexing in the answer.
</t>
<t>
If the answerer accepts usage of RTP/RTCP multiplexing within the BUNDLE group, it
MUST associate an SDP 'rtcp-mux' attribute with each bundled RTP-based "m=" line in the answer. The
answerer MUST NOT associate an SDP 'rtcp' attribute with any bundled "m=" line in the answer.
The answerer will use the port number of the selected offerer BUNDLE address for
sending RTP and RTCP packets associated with each bundled RTP-based "m=" line towards the offerer.
</t>
<t>
If the answerer rejects usage of RTP/RTCP multiplexing within the BUNDLE group, it
MUST NOT associate an SDP 'rtcp-mux' or SDP 'rtcp' attribute with any bundled "m=" line in
the answer. The answerer MUST, based on the port number of the selected offerer BUNDLE
address, use the next higher (odd) destination port number <xref format="default"
pageno="false" target="RFC3550"/> for sending RTCP packets associated with each bundled
RTP-based "m=" line towards the offerer.
</t>
<t>
NOTE: When the answerer rejects usage of RTP/RTCP multiplexing, the reason for mandating
usage of the next higher (odd) destination port number for RTCP is to allign the
procedures for the corresponding offer.
</t>
<t>
If the usage of RTP/RTCP multiplexing has been negotiated in a previous offer/answer
transaction, and the offerer indicates that it wants to continue using RTP/RTCP
multiplexing in a subsequent offer, the answerer MUST associate an SDP 'rtcp-mux' attribute
with each bundled "m=" line in the answer. I.e. the answerer MUST NOT disable the usage of
RTP/RTCP multiplexing.
</t>
</section>
<section title="Offerer Processing of the SDP Answer" anchor="sec-rtprtcp-mux-oa-pra" toc="default">
<t>
When the offerer receives an answer, if the answerer accepts the
usage of RTP/RTCP multiplexing, by including an SDP 'rtcp-mux' attribute
to each bundled "m=" line in the answer [<xref format="default" pageno="false"
target="sec-rtprtcp-mux-oa-ans"/>], the answerer follows the procedures
for RTP/RTCP multiplexing defined in <xref format="default" pageno="false"
target="RFC5761"/>. The offerer will use the port number of the answerer BUNDLE
address for sending RTP and RTCP packets associated with each bundled "m=" line
towards the answerer.
</t>
<t>
If the answerer does not accept the usage of RTP/RTCP multiplexing
[<xref format="default" pageno="false" target="sec-rtprtcp-mux-oa-ans"/>],
the offerer MUST use separate address:port combinations for RTP and RTCP.
The offerer will, based on the port number of the answerer BUNDLE address,
use the next higher (odd) destination port number <xref format="default" pageno="false"
target="RFC3550"/> for sending RTCP packets associated with a bundled "m="
line towards the answerer.
</t>
</section>
<section title="Modifying the Session" anchor="sec-rtprtcp-mux-oa-mod" toc="default">
<t>
When an offerer generates a subsequent offer, if it wants
to negotiate usage of RTP/RTCP multiplexing within a BUNDLE group, or
if it wants to continue usage of RTP/RTCP multiplexing (negotiated in
a previous offer/answer transaction), it MUST associate SDP 'rtcp-mux'
and 'rtcp' attributes with each bundled "m=" line (including any
bundled "m=" line that the offerer wants to add to the BUNDLE group),
unless the offerer wants to disable or remove the "m=" line from the
BUNDLE group.
</t>
<t>
If the offerer does not want to negotiate usage of RTP/RTCP multiplexing
within the BUNDLE group, or if it wants to disable usage of RTP/RTCP
multiplexing (negotiated in a previous offer/answer transaction), the
offerer MUST NOT associate SDP 'rtcp-mux' and 'rtcp' attributes with any
bundled "m=" line in the subsequent offer.
</t>
<t>
NOTE: It is RECOMMENDED that, once usage of RTP/RTCP multiplexing has been
negotiated within a BUNDLE group, that the usage is not disabled. Disabling
RTP/RTCP multiplexing means that the offerer and answerer need to
reserve new ports, to be used for sending and receiving RTCP packets.
</t>
</section>
</section>
</section>
</section>
<section title="ICE Considerations" anchor="sec-ice" toc="default">
<section title="General" anchor="sec-ice-gen" toc="default">
<t>
This section describes how to use the BUNDLE grouping extension together
with the Interactive Connectivity Establishment (ICE) mechanism <xref
format="default" pageno="false" target="RFC5245"/>.
</t>
<t>
The procedures defined in <xref format="default" pageno="false" target="RFC5245"/> also apply
to usage of ICE with BUNDLE, with the following exception:
</t>
<t>
<list style="symbols">
<t>
When BUNDLE addresses for a BUNDLE group have been selected for both endpoints, ICE
connectivity checks and keep-alives only need to be performed for the whole BUNDLE group,
instead of per bundled "m=" line.
</t>
</list>
</t>
<t>
Support and usage of ICE mechanism together with the BUNDLE extension is OPTIONAL.
</t>
</section>
<section title="SDP Offer/Answer Procedures" anchor="sec-ice-oa" toc="default">
<section title="General" anchor="sec-ice-oa-gen" toc="default">
<t>
When an offerer assigns a unique address to a bundled "m=" line (excluding
and bundle-only "m=" line), it MUST also associate unique ICE candidates <xref format="default"
pageno="false" target="RFC5245"/> to the "m=" line.
</t>
<t>
An offerer MUST NOT assign ICE candidates to a bundle-only "m=" line
with a zero port value.
</t>
<t>
NOTE: The bundle-only "m=" line, if accepted by the answerer, will inherit
the candidates associated with the selected offerer BUNDLE address. An answerer
that does not support BUNDLE would not accept a bundle-only "m=" line.
</t>
<t>
When an offerer or answerer assigns a shared address (i.e. a previously selected BUNDLE
address) to one or more bundled "m=" lines, it MUST associate identical ICE candidates
(referred to as shared ICE candidates) to each of those "m=" lines.
</t>
</section>
<section title="Generating the Initial SDP Offer" anchor="sec-ice-oa-ino" toc="default">
<t>
When an offerer generates an initial offer, it assigns unique or shared ICE candidates
to the bundled "m=" lines, according to <xref format="default" pageno="false"
target="sec-ice-gen"/>.
</t>
</section>
<section title="Generating the SDP Answer" anchor="sec-ice-oa-ans" toc="default">
<t>
When an answerer generates an answer, which contains a BUNDLE group,
the answerer MUST assign shared ICE candidates to each bundled "m=" line
(including "m=" lines that were indicated as bundle-only in the associated offer)
in the answer.
</t>
</section>
<section title="Offerer Processing of the SDP Answer" anchor="sec-ice-oa-pra" toc="default">
<t>
When an offerer receives an answer, if the answerer supports and uses the ICE
mechanism and the BUNDLE extension, the offerer MUST assign the same ICE candidates,
associated with the "m=" line representing the offerer BUNDLE address (selected by the
answerer), to each bundled "m=" line.
</t>
</section>
<section title="Modifying the Session" anchor="sec-ice-oa-mod" toc="default">
<t>
When an offerer generates a subsequent offer, it assigns unique or shared ICE
candidates to the bundled "m=" lines, according to (<xref format="default" pageno="false"
target="sec-ice-gen"/>).
</t>
</section>
</section>
</section>
<section anchor="sec-3264" title="Update to RFC 3264" toc="default">
<section anchor="sec-3264-gen" title="General" toc="default">
<t>
This section replaces the text of the following sections
of RFC 3264:
</t>
<t>
<list style="symbols">
<t>Section 5.1 (Unicast Streams).</t>
<t>Section 8.2 (Removing a Media Stream).</t>
<t>Section 8.4 (Putting a Unicast Media Stream on Hold).</t>
</list>
</t>
</section>
<section anchor="sec-3264-old-5_1" title="Original text of section 5.1 (2nd paragraph) of RFC 3264" toc="default">
<t>
For recvonly and sendrecv streams, the port number and address in the
offer indicate where the offerer would like to receive the media
stream. For sendonly RTP streams, the address and port number
indirectly indicate where the offerer wants to receive RTCP reports.
Unless there is an explicit indication otherwise, reports are sent to
the port number one higher than the number indicated. The IP address
and port present in the offer indicate nothing about the source IP
address and source port of RTP and RTCP packets that will be sent by
the offerer. A port number of zero in the offer indicates that the
stream is offered but MUST NOT be used. This has no useful semantics
in an initial offer, but is allowed for reasons of completeness,
since the answer can contain a zero port indicating a rejected stream
(Section 6). Furthermore, existing streams can be terminated by
setting the port to zero (Section 8). In general, a port number of
zero indicates that the media stream is not wanted.
</t>
</section>
<section anchor="sec-3264-new-5_1" title="New text replacing section 5.1 (2nd paragraph) of RFC 3264" toc="default">
<t>
For recvonly and sendrecv streams, the port number and address in the
offer indicate where the offerer would like to receive the media
stream. For sendonly RTP streams, the address and port number
indirectly indicate where the offerer wants to receive RTCP reports.
Unless there is an explicit indication otherwise, reports are sent to
the port number one higher than the number indicated. The IP address
and port present in the offer indicate nothing about the source IP
address and source port of RTP and RTCP packets that will be sent by
the offerer. A port number of zero in the offer by default indicates that the
stream is offered but MUST NOT be used, but an extension mechanism
might specify different semantics for the usage of a zero port value.
Furthermore, existing streams can be terminated by setting the port to
zero (Section 8). In general, a port number of zero by default indicates
that the media stream is not wanted.
</t>
</section>
<section anchor="sec-3264-old-8_2" title="Original text of section 8.2 (2nd paragraph) of RFC 3264" toc="default">
<t>
A stream that is offered with a port of zero MUST be marked with port
zero in the answer. Like the offer, the answer MAY omit all
attributes present previously, and MAY list just a single media
format from amongst those in the offer.
</t>
</section>
<section anchor="sec-3264-new-8_2" title="New text replacing section 8.2 (2nd paragraph) of RFC 3264" toc="default">
<t>
A stream that is offered with a port of zero MUST by default be
marked with port zero in the answer, unless an extension mechanism,
which specifies semantics for the usage of a non-zero port value, is
used. If the stream is marked with port zero in the answer, the answer
MAY omit all attributes present previously, and MAY list
just a single media format from amongst those in the offer."
</t>
</section>
<section anchor="sec-3264-old-8_4" title="Original text of section 8.4 (6th paragraph) of RFC 3264" toc="default">
<t>
RFC 2543 [10] specified that placing a user on hold was accomplished
by setting the connection address to 0.0.0.0. Its usage for putting
a call on hold is no longer recommended, since it doesn't allow for
RTCP to be used with held streams, doesn't work with IPv6, and breaks
with connection oriented media. However, it can be useful in an
initial offer when the offerer knows it wants to use a particular set
of media streams and formats, but doesn't know the addresses and
ports at the time of the offer. Of course, when used, the port
number MUST NOT be zero, which would specify that the stream has been
disabled. An agent MUST be capable of receiving SDP with a
connection address of 0.0.0.0, in which case it means that neither
RTP nor RTCP should be sent to the peer.
</t>
</section>
<section anchor="sec-3264-new-8_4" title="New text replacing section 8.4 (6th paragraph) of RFC 3264" toc="default">
<t>
RFC 2543 [10] specified that placing a user on hold was accomplished
by setting the connection address to 0.0.0.0. Its usage for putting
a call on hold is no longer recommended, since it doesn't allow for
RTCP to be used with held streams, doesn't work with IPv6, and breaks
with connection oriented media. However, it can be useful in an
initial offer when the offerer knows it wants to use a particular set
of media streams and formats, but doesn't know the addresses and
ports at the time of the offer. Of course, when used, the port
number MUST NOT be zero, if it would specify that the stream has been
disabled. However, an extension mechanism might specify different
semantics of the zero port number usage. An agent MUST be capable
of receiving SDP with a connection address of 0.0.0.0, in which case it
means that neither RTP nor RTCP should be sent to the peer.
</t>
</section>
</section>
<section title="RTP/RTCP extensions for identification-tag transport" anchor="sec-receiver-id" toc="default">
<section title="General" anchor="sec-receiver-id-gen" toc="default">
<t>
SDP Offerers and Answerers <xref format="default" pageno="false" target="RFC3264"/>
can associate identification-tags with "m=" lines within SDP Offers
and Answers, using the procedures in <xref format="default" pageno="false"
target="RFC5888"/>. Each identification-tag uniquely represents an "m=" line.
</t>
<t>
This section defines a new RTCP SDES item <xref format="default" pageno="false"
target="RFC3550"/>, 'MID', which is used to carry identification-tags within RTCP
SDES packets. This section also defines a new RTP header extension
<xref format="default" pageno="false" target="RFC5285"/>, which is used to carry
identification-tags in RTP packets.
</t>
<t>
The SDES item and RTP header extension make it possible for a receiver to associate
received RTCP- and RTP packets with a specific "m=" line, to which the receiver has
assigned an identification-tag, even if those "m=" lines are part of the same RTP session.
The endpoint informs the remote endpoint about the identification-tag using the
procedures in <xref format="default" pageno="false" target="RFC5888"/>, and the
remote endpoint then inserts the identification-tag in RTCP- and RTP packets sent
towards the other endpoint.
</t>
<t>
NOTE: This text above defines how identification-tags are carried in SDP Offers
and Answers. The usage of other signalling protocols for carrying identification-tags
is not prevented, but the usage of such protocols is outside the scope of this document.
</t>
<t>
<xref format="default" pageno="false" target="RFC3550"/> defines general procedures
regarding the RTCP transmission interval. The RTCP MID SDES item SHOULD be sent in
the first few RTCP packets sent on joining the session, and SHOULD be sent regularly
thereafter. The exact number of RTCP packets in which this SDES item is sent is
intentionally not specified here, as it will depend on the expected packet loss
rate, the RTCP reporting interval, and the allowable overhead.
</t>
<t>
The RTP MID header extension SHOULD be included in some RTP packets at the start of
the session and whenever the SSRC changes. It might also be useful to include the
header extension in RTP packets that comprise random access points in the media
(e.g., with video I-frames). The exact number of RTP packets in which this header
extension is sent is intentionally not specified here, as it will depend on expected
packet loss rate and loss patterns, the overhead the application can tolerate, and
the importance of immediate receipt of the identification-tag.
</t>
<t>
For robustness purpose, endpoints need to be prepared for situations where the
reception of the identification-tag is delayed, and SHOULD NOT terminate sessions
in such cases, as the identification-tag is likely to arrive soon.
</t>
</section>
<section title="RTCP MID SDES Item" anchor="sec-receiver-id-sdes-item" toc="default">
<figure>
<artwork align="left"><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MID=TBD | length | identification-tag ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t>
The identification-tag payload is UTF-8 encoded, as in SDP.
</t>
<t>
The identification-tag is not zero terminated.
</t>
<t>
[RFC EDITOR NOTE: Please replace TBD with the assigned SDES
identifier value.]
</t>
</section>
<section title="RTP MID Header Extension" anchor="sec-receiver-id-rtp-he" toc="default">
<t>
The payload, containing the mid value, of the RTP MID header extension element
can be encoded using either the one-byte or two-byte header <xref format="default"
pageno="false" target="RFC5285"/>. The identification-tag payload is UTF-8
encoded, as in SDP.
</t>
<t>
The identification-tag is not zero terminated. Note, however, that RTP header
extensions that are not a multiple of 32 bits in length MUST be padded to the
next 32-bit boundary using zero bytes; these padding bytes are not included in
the header length field <xref format="default" pageno="false" target="RFC3550"/>.
</t>
</section>
</section>
<section title="IANA Considerations" anchor="sec-receiver-id-iana" toc="default">
<section title="New SDES item" anchor="sec-receiver-id-iana-sdes-item" toc="default">
<t>
[RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number
of this document.]
</t>
<t>
[RFC EDITOR NOTE: Please replace TBD with the assigned SDES
identifier value.]
</t>
<t>
This document adds the MID SDES item to the IANA "RTCP SDES item
types" registry as follows:
</t>
<figure>
<artwork align="left"><![CDATA[
Value: TBD
Abbrev.: MID
Name: Media Identification
Reference: RFCXXXX
]]></artwork>
</figure>
</section>
<section title="New RTP Header Extension URI" anchor="sec-receiver-id-iana-rtp-uri" toc="default">
<t>
[RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number
of this document.]
</t>
<t>
This document defines a new extension URI in the RTP Compact Header
Extensions subregistry of the Real-Time Transport Protocol (RTP)
Parameters registry, according to the following data:
</t>
<figure>
<artwork align="left"><![CDATA[
Extension URI: urn:ietf:params:rtp-hdrext:sdes:mid
Description: Media identification
Contact: christer.holmberg@ericsson.com
Reference: RFCXXXX
]]></artwork>
</figure>
</section>
<section title="New SDP Attribute" anchor="sec-receiver-id-iana-sdp-attribute" toc="default">
<t>
[RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number
of this document.]
</t>
<t>
This document defines a new SDP media-level attribute,
'bundle-only', according to the following data:
</t>
<figure>
<artwork align="left"><![CDATA[
Attribute name: bundle-only
Type of attribute: media
Subject to charset: No
Purpose: Request a media description to be accepted
in the answer only if kept within a BUNDLE
group by the answerer.
Appropriate values: N/A
Contact name: Christer Holmberg
Contact e-mail: christer.holmberg@ericsson.com
Reference: RFCXXXX
]]></artwork>
</figure>
</section>
</section>
<section title="Security Considerations" anchor="sec-security" toc="default">
<t>
The security considerations defined in <xref format="default"
pageno="false" target="RFC3264"/> and <xref format="default"
pageno="false" target="RFC5888"/> apply to the BUNDLE
extension. Bundle does not change which information
flows over the network but only changes which ports that
information is flowing on and thus has very little
impact on the security of the RTP sessions.
</t>
<t>
When the BUNDLE extension is used, a single set of security credentials
might be used for all media streams associated with a BUNDLE group.
</t>
<t>
When the BUNDLE extension is used, the number of SSRC values within
a single RTP session increases, which increases the risk of SSRC
collision. <xref format="default" pageno="false" target="RFC4568"/>
describes how SSRC collision may weaken SRTP and SRTCP encryption
in certain situations.
</t>
</section>
<section title="Examples" anchor="sec-example-alt1" toc="default">
<section title="Example: Bundle Address Selection" anchor="sec-example-add" toc="default">
<t>
The example below shows:
<list style="symbols">
<t>1. An offer, in which the offerer assigns a unique address to each bundled "m=" line within the BUNDLE group.</t>
<t>2. An answer, in which the answerer selects the offerer BUNDLE address, and in which selects its own BUNDLE
address (the answerer BUNDLE address) and assigns it each bundled "m=" line within the BUNDLE group.</t>
<t>3. A subsequent offer (BAS offer), which is used to perform a Bundle Address Synchronization (BAS).</t>
</list>
</t>
<figure>
<artwork align="left" alt="" height="" name="" type="" width=""
xml:space="preserve"><![CDATA[
SDP Offer (1)
v=0
o=alice 2890844526 2890844526 IN IP4 atlanta.example.com
s=
c=IN IP4 atlanta.example.com
t=0 0
a=group:BUNDLE foo bar
m=audio 10000 RTP/AVP 0 8 97
b=AS:200
a=mid:foo
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:97 iLBC/8000
a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
m=video 10002 RTP/AVP 31 32
b=AS:1000
a=mid:bar
a=rtpmap:31 H261/90000
a=rtpmap:32 MPV/90000
a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
SDP Answer (2)
v=0
o=bob 2808844564 2808844564 IN IP4 biloxi.example.com
s=
c=IN IP4 biloxi.example.com
t=0 0
a=group:BUNDLE foo bar
m=audio 20000 RTP/AVP 0
b=AS:200
a=mid:foo
a=rtpmap:0 PCMU/8000
a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
m=video 20000 RTP/AVP 32
b=AS:1000
a=mid:bar
a=rtpmap:32 MPV/90000
a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
SDP Offer (3)
v=0
o=alice 2890844526 2890844526 IN IP4 atlanta.example.com
s=
c=IN IP4 atlanta.example.com
t=0 0
a=group:BUNDLE foo bar
m=audio 10000 RTP/AVP 0 8 97
b=AS:200
a=mid:foo
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:97 iLBC/8000
a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
m=video 10000 RTP/AVP 31 32
b=AS:1000
a=mid:bar
a=rtpmap:31 H261/90000
a=rtpmap:32 MPV/90000
a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
]]></artwork>
</figure>
</section>
<section title="Example: BUNDLE Extension Rejected" anchor="sec-example-bunrej" toc="default">
<t>
The example below shows:
<list style="symbols">
<t>1. An offer, in which the offerer assigns a unique address to each bundled "m=" line within the BUNDLE group.</t>
<t>2. An answer, in which the answerer rejects the offered BUNDLE group, and assigns a unique addresses
to each "m=" line (following normal RFC 3264 procedures).</t>
</list>
</t>
<figure>
<artwork align="left" alt="" height="" name="" type="" width=""
xml:space="preserve"><![CDATA[
SDP Offer (1)
v=0
o=alice 2890844526 2890844526 IN IP4 atlanta.example.com
s=
c=IN IP4 atlanta.example.com
t=0 0
a=group:BUNDLE foo bar
m=audio 10000 RTP/AVP 0 8 97
b=AS:200
a=mid:foo
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:97 iLBC/8000
a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
m=video 10002 RTP/AVP 31 32
b=AS:1000
a=mid:bar
a=rtpmap:31 H261/90000
a=rtpmap:32 MPV/90000
a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
SDP Answer (2)
v=0
o=bob 2808844564 2808844564 IN IP4 biloxi.example.com
s=
c=IN IP4 biloxi.example.com
t=0 0
m=audio 20000 RTP/AVP 0
b=AS:200
a=rtpmap:0 PCMU/8000
m=video 30000 RTP/AVP 32
b=AS:1000
a=rtpmap:32 MPV/90000
]]></artwork>
</figure>
</section>
<section title="Example: Offerer Adds A Media Description To A BUNDLE Group" anchor="sec-example-off-add" toc="default">
<t>
The example below shows:
<list style="symbols">
<t>1. A subsequent offer (the BUNDLE group has been created as part of a previous offer/answer
transaction), in which the offerer adds a new "m=" line, represented by the "zen"
identification-tag, to a previously negotiated BUNDLE group, assigns a unique address
to the added "m=" line, and assigns the previously selected offerer BUNDLE address to
each of the other bundled "m=" lines within the BUNDLE group.</t>
<t>2. An answer, in which the answerer assigns the answerer BUNDLE address to each
bundled "m=" line (including the newly added "m=" line) within the BUNDLE group.</t>
<t>3. A subsequent offer (BAS offer), which is used to perform a Bundle Address
Synchronization (BAS).</t>
</list>
</t>
<figure>
<artwork align="left" alt="" height="" name="" type="" width=""
xml:space="preserve"><![CDATA[
SDP Offer (1)
v=0
o=alice 2890844526 2890844526 IN IP4 atlanta.example.com
s=
c=IN IP4 atlanta.example.com
t=0 0
a=group:BUNDLE foo bar zen
m=audio 10000 RTP/AVP 0 8 97
b=AS:200
a=mid:foo
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:97 iLBC/8000
a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
m=video 10000 RTP/AVP 31 32
b=AS:1000
a=mid:bar
a=rtpmap:31 H261/90000
a=rtpmap:32 MPV/90000
a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
m=video 20000 RTP/AVP 66
b=AS:1000
a=mid:zen
a=rtpmap:66 H261/90000
a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
SDP Answer (2)
v=0
o=bob 2808844564 2808844564 IN IP4 biloxi.example.com
s=
c=IN IP4 biloxi.example.com
t=0 0
a=group:BUNDLE foo bar zen
m=audio 20000 RTP/AVP 0
b=AS:200
a=mid:foo
a=rtpmap:0 PCMU/8000
a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
m=video 20000 RTP/AVP 32
b=AS:1000
a=mid:bar
a=rtpmap:32 MPV/90000
a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
m=video 20000 RTP/AVP 66
b=AS:1000
a=mid:zen
a=rtpmap:66 H261/90000
a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
SDP Offer (3)
v=0
o=alice 2890844526 2890844526 IN IP4 atlanta.example.com
s=
c=IN IP4 atlanta.example.com
t=0 0
a=group:BUNDLE foo bar zen
m=audio 10000 RTP/AVP 0 8 97
b=AS:200
a=mid:foo
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:97 iLBC/8000
a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
m=video 10000 RTP/AVP 31 32
b=AS:1000
a=mid:bar
a=rtpmap:31 H261/90000
a=rtpmap:32 MPV/90000
a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
m=video 10000 RTP/AVP 66
b=AS:1000
a=mid:zen
a=rtpmap:66 H261/90000
a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
]]></artwork>
</figure>
</section>
<section title="Example: Offerer Moves A Media Description Out Of A BUNDLE Group" anchor="sec-example-off-mov" toc="default">
<t>
The example below shows:
<list style="symbols">
<t>1. A subsequent offer (the BUNDLE group has been created as part of a previous offer/answer
transaction), in which the offerer moves a bundled "m=" line out of a BUNDLE group, assigns a unique address to
the moved "m=" line, and assigns the offerer BUNDLE address to each other bundled "m=" line within the BUNDLE group.</t>
<t>2. An answer, in which the answerer moves the "m=" line out of the BUNDLE group, assigns unique address to
the moved "m=" line, and assigns the answerer BUNDLE address to each of the remaining bundled "m=" line within the BUNDLE group.</t>
</list>
</t>
<figure>
<artwork align="left" alt="" height="" name="" type="" width=""
xml:space="preserve"><![CDATA[
SDP Offer (1)
v=0
o=alice 2890844526 2890844526 IN IP4 atlanta.example.com
s=
c=IN IP4 atlanta.example.com
t=0 0
a=group:BUNDLE foo bar
m=audio 10000 RTP/AVP 0 8 97
b=AS:200
a=mid:foo
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:97 iLBC/8000
a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
m=video 10000 RTP/AVP 31 32
b=AS:1000
a=mid:bar
a=rtpmap:31 H261/90000
a=rtpmap:32 MPV/90000
a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
m=video 50000 RTP/AVP 66
b=AS:1000
a=mid:zen
a=rtpmap:66 H261/90000
SDP Answer (2)
v=0
o=bob 2808844564 2808844564 IN IP4 biloxi.example.com
s=
c=IN IP4 biloxi.example.com
t=0 0
a=group:BUNDLE foo bar
m=audio 20000 RTP/AVP 0
b=AS:200
a=mid:foo
a=rtpmap:0 PCMU/8000
a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
m=video 20000 RTP/AVP 32
b=AS:1000
a=mid:bar
a=rtpmap:32 MPV/90000
a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
m=video 60000 RTP/AVP 66
b=AS:1000
a=mid:zen
a=rtpmap:66 H261/90000
]]></artwork>
</figure>
</section>
<section title="Example: Offerer Disables A Media Description Within A BUNDLE Group" anchor="sec-example-off-dis" toc="default">
<t>
The example below shows:
<list style="symbols">
<t>1. A subsequent offer (the BUNDLE group has been created as part of a previous offer/answer
transaction), in which the offerer disables a bundled "m=" line within BUNDLE group, assigns a zero port number
to the disabled "m=" line, and assigns the offerer BUNDLE address to each of the other bundled
"m=" lines within the BUNDLE group.</t>
<t>2. An answer, in which the answerer moves the disabled "m=" line out of the BUNDLE group, assigns a zero port value
to the disabled "m=" line, and assigns the answerer BUNDLE address to each of the remaining bundled "m=" line within
the BUNDLE group.</t>
</list>
</t>
<figure>
<artwork align="left" alt="" height="" name="" type="" width=""
xml:space="preserve"><![CDATA[
SDP Offer (1)
v=0
o=alice 2890844526 2890844526 IN IP4 atlanta.example.com
s=
c=IN IP4 atlanta.example.com
t=0 0
a=group:BUNDLE foo bar
m=audio 10000 RTP/AVP 0 8 97
b=AS:200
a=mid:foo
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:97 iLBC/8000
a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
m=video 10000 RTP/AVP 31 32
b=AS:1000
a=mid:bar
a=rtpmap:31 H261/90000
a=rtpmap:32 MPV/90000
a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
m=video 0 RTP/AVP 66
a=mid:zen
a=rtpmap:66 H261/90000
SDP Answer (2)
v=0
o=bob 2808844564 2808844564 IN IP4 biloxi.example.com
s=
c=IN IP4 biloxi.example.com
t=0 0
a=group:BUNDLE foo bar
m=audio 20000 RTP/AVP 0
b=AS:200
a=mid:foo
a=rtpmap:0 PCMU/8000
a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
m=video 20000 RTP/AVP 32
b=AS:1000
a=mid:bar
a=rtpmap:32 MPV/90000
a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
m=video 0 RTP/AVP 66
a=mid:zen
a=rtpmap:66 H261/90000
]]></artwork>
</figure>
</section>
</section>
<section anchor="sec-acks" title="Acknowledgements" toc="default">
<t>
The usage of the SDP grouping extension for negotiating bundled media is
based on a similar alternatives proposed by Harald Alvestrand and Cullen
Jennings. The BUNDLE extension described in this document is based on
the different alternative proposals, and text (e.g. SDP examples)
have been borrowed (and, in some cases, modified) from those alternative
proposals.
</t>
<t>
The SDP examples are also modified versions from the ones in the Alvestrand
proposal.
</t>
<t>
Thanks to Paul Kyzivat, Martin Thomson, Flemming Andreasen, Thomas Stach and
Ari Keränen for taking the time to read the text along the way, and providing
useful feedback.
</t>
</section>
<section title="Change Log">
<t>[RFC EDITOR NOTE: Please remove this section when publishing]</t>
<t>Changes from draft-ietf-mmusic-sdp-bundle-negotiation-12
<list style="symbols">
<t>Usage of SDP 'extmap' attribute added</t>
<t>SDP 'bundle-only' attribute scoped with "m=" lines with a zero port value</t>
<t>Changes based on WGLC comments from Thomas Stach</t>
<t>- ICE candidates not assigned to bundle-only m- lines with a zero port value</t>
<t>- Editorial changes</t>
<t>Changes based on WGLC comments from Colin Perkins</t>
<t>- Editorial changes:</t>
<t>-- "RTP SDES item" -> "RTCP SDES item"</t>
<t>-- "RTP MID SDES item" -> "RTCP MID SDES item"</t>
<t>- Changes in section 10.1.1:</t>
<t>-- "SHOULD NOT" -> "MUST NOT"</t>
<t>-- Additional text added to the Note</t>
<t>- Change to section 13.2:</t>
<t>-- Clarify that mid value is not zero terminated</t>
<t>- Change to section 13.3:</t>
<t>-- Clarify that mid value is not zero terminated</t>
<t>-- Clarify padding</t>
<t>Changes based on WGLC comments from Paul Kyzivat</t>
<t>- Editorial changes:</t>
<t>Changes based on WGLC comments from Jonathan Lennox</t>
<t>- Editorial changes:</t>
<t>- Defintion of SDP bundle-only attribute alligned with
structure in 4566bis draft</t>
</list>
</t>
<t>Changes from draft-ietf-mmusic-sdp-bundle-negotiation-11
<list style="symbols">
<t>Editorial corrections based on comments from Harald Alvestrand.</t>
<t>Editorial corrections based on comments from Cullen Jennings.</t>
<t>Reference update (RFC 7160).</t>
<t>Clarification about RTCP packet sending when RTP/RTCP multiplexing
is not used (http://www.ietf.org/mail-archive/web/mmusic/current/msg13765.html).</t>
<t>Additional text added to the Security Considerations.</t>
</list>
</t>
<t>Changes from draft-ietf-mmusic-sdp-bundle-negotiation-10
<list style="symbols">
<t>SDP bundle-only attribute added to IANA Considerations.</t>
<t>SDES item and RTP header extension added to Abstract and Introduction.</t>
<t>Modification to text updating section 8.2 of RFC 3264.</t>
<t>Reference corrections.</t>
<t>Editorial corrections.</t>
</list>
</t>
<t>Changes from draft-ietf-mmusic-sdp-bundle-negotiation-09
<list style="symbols">
<t>Terminology change: "bundle-only attribute assigned to m= line" to
"bundle-only attribute associated with m= line".</t>
<t>Editorial corrections.</t>
</list>
</t>
<t>Changes from draft-ietf-mmusic-sdp-bundle-negotiation-08
<list style="symbols">
<t>Editorial corrections.</t>
<t>- "of"->"if" (8.3.2.5).</t>
<t>- "optional"->"OPTIONAL" (9.1).</t>
<t>- Syntax/ABNF for 'bundle-only' attribute added.</t>
<t>- SDP Offer/Answer sections merged.</t>
<t>- 'Request new offerer BUNDLE address' section added</t>
</list>
</t>
<t>Changes from draft-ietf-mmusic-sdp-bundle-negotiation-07
<list style="symbols">
<t>OPEN ISSUE regarding Receiver-ID closed.</t>
<t>- RTP MID SDES Item.</t>
<t>- RTP MID Header Extension.</t>
<t>OPEN ISSUE regarding insertion of SDP 'rtcp' attribute in answers closed.</t>
<t>- Indicating that, when rtcp-mux is used, the answerer MUST NOT include
an 'rtcp' attribute in the answer, based on the procedures in section 5.1.3 of
RFC 5761.</t>
</list>
</t>
<t>Changes from draft-ietf-mmusic-sdp-bundle-negotiation-06
<list style="symbols">
<t>Draft title changed.</t>
<t>Added "SDP" to section names containing "Offer" or "Answer".</t>
<t>Editorial fixes based on comments from Paul Kyzivat (http://www.ietf.org/mail-archive/web/mmusic/current/msg13314.html).</t>
<t>Editorial fixed based on comments from Colin Perkins (http://www.ietf.org/mail-archive/web/mmusic/current/msg13318.html).</t>
<t>- Removed text about extending BUNDLE to allow multiple RTP sessions within a BUNDLE group.</t>
</list>
</t>
<t>Changes from draft-ietf-mmusic-sdp-bundle-negotiation-05
<list style="symbols">
<t>Major re-structure of SDP Offer/Answer sections, to align with RFC 3264 structure.</t>
<t>Additional definitions added.</t>
<t>- Shared address.</t>
<t>- Bundled "m=" line.</t>
<t>- Bundle-only "m=" line.</t>
<t>- Offerer suggested BUNDLE mid.</t>
<t>- Answerer selected BUNDLE mid.</t>
<t>Q6 Closed (IETF#88): An Offerer MUST NOT assign a shared address to multiple "m=" lines until it has
received an SDP Answer indicating support of the BUNDLE extension.</t>
<t>Q8 Closed (IETF#88): An Offerer can, before it knows whether the Answerer supports the BUNDLE extension,
assign a zero port value to a 'bundle-only' "m=" line.</t>
<t>SDP 'bundle-only' attribute section added.</t>
<t>Connection data nettype/addrtype restrictions added.</t>
<t>RFC 3264 update section added.</t>
<t>Indicating that a specific payload type value can be used in multiple "m=" lines, if the value
represents the same codec configuration in each "m=" line.</t>
</list>
</t>
<t>Changes from draft-ietf-mmusic-sdp-bundle-negotiation-04
<list style="symbols">
<t>Updated Offerer procedures (http://www.ietf.org/mail-archive/web/mmusic/current/msg12293.html).</t>
<t>Updated Answerer procedures (http://www.ietf.org/mail-archive/web/mmusic/current/msg12333.html).</t>
<t>Usage of SDP 'bundle-only' attribute added.</t>
<t>Reference to Trickle ICE document added.</t>
</list>
</t>
<t>Changes from draft-ietf-mmusic-sdp-bundle-negotiation-02
<list style="symbols">
<t>Mechanism modified, to be based on usage of SDP Offers
with both different and identical port number values, depending
on whether it is known if the remote endpoint supports the
extension.</t>
<t>Cullen Jennings added as co-author.</t>
</list>
</t>
<t>Changes from draft-ietf-mmusic-sdp-bundle-negotiation-01
<list style="symbols">
<t>No changes. New version due to expiration.</t>
</list>
</t>
<t>Changes from draft-ietf-mmusic-sdp-bundle-negotiation-00
<list style="symbols">
<t>No changes. New version due to expiration.</t>
</list>
</t>
<t>Changes from draft-holmberg-mmusic-sdp-multiplex-negotiation-00
<list style="symbols">
<t>Draft name changed.</t>
<t>Harald Alvestrand added as co-author.</t>
<t>"Multiplex" terminology changed to "bundle".</t>
<t>Added text about single versus multiple RTP Sessions.</t>
<t>Added reference to RFC 3550.</t>
</list>
</t>
</section>
</middle>
<back>
<references title="Normative References">
<?rfc include="reference.RFC.2119"?>
<?rfc include="reference.RFC.3264"?>
<?rfc include="reference.RFC.4566"?>
<?rfc include="reference.RFC.5285"?>
<?rfc include="reference.RFC.5761"?>
<?rfc include="reference.RFC.5888"?>
<reference anchor="I-D.mmusic-sdp-mux-attributes">
<front>
<title abbrev="SDP Attribute Multiplexing">
A Framework for SDP Attributes when Multiplexing
</title>
<author fullname="Suhas Nandakumar" initials="S.N" surname="Nandakumar">
<organization>Cisco</organization>
<address>
</address>
</author>
<date day="26" month="November" year="2014" />
</front>
<seriesInfo name="Internet-Draft" value="draft-ietf-mmusic-sdp-mux-attributes-05" />
</reference>
</references>
<references title="Informative References">
<?rfc include="reference.RFC.3550"?>
<?rfc include="reference.RFC.3605"?>
<?rfc include="reference.RFC.4568"?>
<?rfc include="reference.RFC.5245"?>
<?rfc include="reference.RFC.5576"?>
<?rfc include="reference.RFC.5764"?>
<?rfc include="reference.RFC.7160"?>
<reference anchor="I-D.ietf-mmusic-trickle-ice">
<front>
<title abbrev="Trickle ICE">
Trickle ICE: Incremental Provisioning of Candidates
for the Interactive Connectivity Establishment (ICE) Protocol
</title>
<author fullname="Emil Ivov" initials="E.I" surname="Ivov">
<organization>Jitsi</organization>
</author>
<author fullname="Eric Rescorla" initials="E.R" surname="Rescorla">
<organization>RTFM, Inc</organization>
</author>
<author fullname="Justin Uberti" initials="J.U" surname="Uberti">
<organization>Google</organization>
</author>
<date day="7" month="February" year="2014" />
</front>
<seriesInfo name="Internet-Draft" value="draft-ietf-mmusic-trickle-ice-01" />
</reference>
</references>
<section title="Design Considerations" toc="default">
<section title="General" toc="default">
<t>
One of the main issues regarding the BUNDLE grouping extensions has been whether,
in SDP Offers and SDP Answers, the same port value should be inserted in "m="
lines associated with a BUNDLE group, as the purpose of the extension is to negotiate
the usage of a single address:port combination for media associated with the
"m=" lines. Issues with both approaches, discussed in the Appendix have been
raised. The outcome was to specify a mechanism which uses SDP Offers with both
different and identical port values.
</t>
<t>
Below are the primary issues that have been considered when defining the "BUNDLE"
grouping extension:
<list style="symbols">
<t>1) Interoperability with existing UAs.</t>
<t>2) Interoperability with intermediary B2BUA- and proxy entities.</t>
<t>3) Time to gather, and the number of, ICE candidates.</t>
<t>4) Different error scenarios, and when they occur.</t>
<t>5) SDP Offer/Answer impacts, including usage of port number value zero.</t>
</list>
</t>
<t>
NOTE: Before this document is published as an RFC, this Appendix might be removed.
</t>
</section>
<section title="UA Interoperability" toc="default">
<t>
Consider the following SDP Offer/Answer exchange, where Alice sends an SDP Offer to Bob:
</t>
<figure>
<artwork align="left" alt="" height="" name="" type="" width=""
xml:space="preserve"><![CDATA[
SDP Offer
v=0
o=alice 2890844526 2890844526 IN IP4 atlanta.example.com
s=
c=IN IP4 atlanta.example.com
t=0 0
m=audio 10000 RTP/AVP 97
a=rtpmap:97 iLBC/8000
m=video 10002 RTP/AVP 97
a=rtpmap:97 H261/90000
]]></artwork>
</figure>
<figure>
<artwork align="left" alt="" height="" name="" type="" width=""
xml:space="preserve"><![CDATA[
SDP Answer
v=0
o=bob 2808844564 2808844564 IN IP4 biloxi.example.com
s=
c=IN IP4 biloxi.example.com
t=0 0
m=audio 20000 RTP/AVP 97
a=rtpmap:97 iLBC/8000
m=video 20002 RTP/AVP 97
a=rtpmap:97 H261/90000
]]></artwork>
</figure>
<t>
RFC 4961 specifies a way of doing symmetric RTP but that is an a later
invention to RTP and Bob can not assume that Alice supports RFC 4961. This
means that Alice may be sending RTP from a different port than 10000 or
10002 - some implementation simply send the RTP from an ephemeral
port. When Bob's endpoint receives an RTP packet, the only way that Bob
know if it should be passed to the video or audio codec is by looking at
the port it was received on. This lead some SDP implementations to use the
fact that each "m=" line had a different port number to use that port
number as an index to find the correct m line in the SDP. As a result, some
implementations that do support symmetric RTP and ICE still use a SDP data
structure where SDP with "m=" lines with the same port such as:
</t>
<figure>
<artwork align="left" alt="" height="" name="" type="" width=""
xml:space="preserve"><![CDATA[
SDP Offer
v=0
o=alice 2890844526 2890844526 IN IP4 atlanta.example.com
s=
c=IN IP4 atlanta.example.com
t=0 0
m=audio 10000 RTP/AVP 97
a=rtpmap:97 iLBC/8000
m=video 10000 RTP/AVP 98
a=rtpmap:98 H261/90000
]]></artwork>
</figure>
<t>
will result in the second "m=" line being considered an SDP error
because it has the same port as the first line.
</t>
</section>
<section title="Usage of port number value zero" toc="default">
<t>
In an SDP Offer or SDP Answer, the media associated with an "m=" line can be
disabled/rejected by setting the port number value to zero. This is different
from e.g. using the SDP direction attributes, where RTCP traffic will
continue even if the SDP "inactive" attribute is indicated for the
associated "m=" line.
</t>
<t>
If each "m=" line associated with a BUNDLE group would contain different
port values, and one of those port values would be used for a BUNDLE address
associated with the BUNDLE group, problems would occur if an endpoint wants to
disable/reject the "m=" line associated with that port, by setting the port
value to zero. After that, no "m=" line would contain the port value which
is used for the BUNDLE address. In addition, it is unclear what would happen
to the ICE candidates associated with the "m=" line, as they are also used for
the BUNDLE address.
</t>
</section>
<section title="B2BUA And Proxy Interoperability" toc="default">
<t>
Some back to back user agents may be configured in a mode where if
the incoming call leg contains an SDP attribute the B2BUA does not
understand, the B2BUS still generates that SDP attribute in the Offer
for the outgoing call leg. Consider an B2BUA that did not understand
the SDP "rtcp" attribute, defined in RFC 3605, yet acted this way.
Further assume that the B2BUA was configured to tear down any call
where it did not see any RTCP for 5 minutes. In this cases, if the B2BUA
received an Offer like:
</t>
<figure>
<artwork align="left" alt="" height="" name="" type="" width=""
xml:space="preserve"><![CDATA[
SDP Offer
v=0
o=alice 2890844526 2890844526 IN IP4 atlanta.example.com
s=
c=IN IP4 atlanta.example.com
t=0 0
m=audio 49170 RTP/AVP 0
a=rtcp:53020
]]></artwork>
</figure>
<t>
It would be looking for RTCP on port 49172 but would not see any
because the RTCP would be on port 53020 and after five minutes, it would
tear down the call. Similarly, an SBC that did not understand BUNDLE yet
put BUNDLE in it's offer may be looking for media on the wrong port and
tear down the call. It is worth noting that a B2BUA that generated an
Offer with capabilities it does not understand is not compliant with the
specifications.
</t>
<section title="Traffic Policing" toc="default">
<t>
Sometimes intermediaries do not act as B2BUA, in the sense that
they don't modify SDP bodies, nor do they terminate SIP dialogs.
Still, however, they may use SDP information (e.g. IP address and
port) in order to control traffic gating functions, and to set
traffic policing rules. There might be rules which will trigger
a session to be terminated in case media is not sent or received
on the ports retrieved from the SDP. This typically occurs once the
session is already established and ongoing.
</t>
</section>
<section title="Bandwidth Allocation" toc="default">
<t>
Sometimes intermediaries do not act as B2BUA, in the sense that
they don't modify SDP bodies, nor do they terminate SIP dialogs.
Still, however, they may use SDP information (e.g. codecs and
media types) in order to control bandwidth allocation functions.
The bandwidth allocation is done per "m=" line, which means that
it might not be enough if media associated with all "m=" lines
try to use that bandwidth. That may either simply lead to bad
user experience, or to termination of the call.
</t>
</section>
</section>
<section title="Candidate Gathering" toc="default">
<t>
When using ICE, an candidate needs to be gathered for each port. This
takes approximately 20 ms extra for each extra "m=" line due to the NAT
pacing requirements. All of this gather can be overlapped with other
things while the page is loading to minimize the impact. If the client
only wants to generate TURN or STUN ICE candidates for one of the "m="
lines and then use trickle ICE <xref target="I-D.ietf-mmusic-trickle-ice" />
to get the non host ICE candidates for the rest of the "m=" lines, it MAY do
that and will not need any additional gathering time.
</t>
<t>
Some people have suggested a TURN extension to get a bunch of TURN
allocation at once. This would only provide a single STUN result so in
cases where the other end did not support BUNDLE, may cause more use of
the TURN server but would be quick in the cases where both sides
supported BUNDLE and would fall back to a successful call in the other
cases.
</t>
</section>
</section>
</back>
</rfc>
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