One document matched: draft-ietf-mmusic-sdp-bundle-negotiation-06.xml
<?xml version="1.0" encoding="iso-8859-1"?>
<!-- comment -->
<!DOCTYPE rfc SYSTEM "rfc2629.dtd"[]>
<?rfc toc="yes" ?>
<?rfc compact="yes" ?>
<?rfc sortrefs="no" ?>
<rfc ipr="trust200902" category="std" docName="draft-ietf-mmusic-sdp-bundle-negotiation-06.txt" updates="3264" submissionType="IETF" xml:lang="en">
<front>
<title abbrev="Bundled media">
Multiplexing Negotiation Using Session Description Protocol (SDP) Port Numbers
</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 SDP Grouping Framework extension, "BUNDLE", that
can be used with the Session Description Protocol (SDP) Offer/Answer mechanism
to negotiate the usage of bundled media, which refers to the usage of a single 5-tuple for
sending and receiving media associated with multiple SDP media descriptions ("m=" lines).
</t>
<t>
This specification also updates sections 5.1, 8.1 and 8.2 of RFC 3264, in order to allow
an answerer to in an SDP answer assign a non-zero port value to an "m=" line, even if
the offerer in the associated SDP offer had assigned a zero port value to the "m=" line.
</t>
</abstract>
</front>
<middle>
<section title="Introduction" toc="default">
<t>
In the IETF RTCWEB WG, a need to use a single 5-tuple for sending and receiving media
associated with multiple SDP media descriptions ("m=" lines) has been identified. This
would e.g. allow the usage of a single set of Interactive Connectivity Establishment
(ICE) <xref format="default" pageno="false" target="RFC5245"/> candidates for multiple
media descriptions. Normally different media types (audio, video etc) will be described
using different media descriptions.
</t>
<t>
This specification defines a new SDP Grouping Framework <xref format="default" pageno="false"
target="RFC5888"/> extension, "BUNDLE", that can be used with the Session Description
Protocol (SDP) Offer/Answer mechanism <xref format="default" pageno="false" target="RFC3264"/>
to negotiate the usage of bundled media, which refers to the usage of a single 5-tuple for
sending and receiving media associated with multiple SDP media descriptions ("m=" lines).
</t>
<t>
The offerer and answerer <xref format="default" pageno="false" target="RFC3264"/> use
the BUNDLE mechanism to negotiate BUNDLE addresses, one for the offerer (offerer BUNDLE
address) and one for the answerer (answerer BUNDLE address) to be used for the bundled
media associated with a BUNDLE group.
</t>
<t>
Once it is known that both the offerer and the answerer supports the BUNDLE mechanism,
a BUNDLE group and the associated BUNDLE addresses have been negotiated, each endpoint can
assign its BUNDLE address to each "m=" line within, and use the address to send
and receive all media associated with, the BUNDLE group.
</t>
<t>
NOTE: 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>
SDP bodies can contain multiple BUNDLE groups. Each BUNDLE group MUST use a unique 5-tuple.
Any given "m=" line can only be associated with a single BUNDLE group.
</t>
<t>
The procedures in this specification apply to a given BUNDLE group.
</t>
<t>
The default assumption is that all Real-Time Protocol (RTP) <xref format="default"
pageno="false" target="RFC3550"/> based media flows associated with a BUNDLE group belong
to the same RTP Session <xref format="default" pageno="false" target="RFC3550"/>. Future
extensions can change that assumption.
</t>
<t>
The BUNDLE mechanism is backward compatible. Endpoints that do not support the BUNDLE mechanism
are expected to generate SDP offers and SDP answers without an SDP 'group:BUNDLE' attribute, and
are expected to assign a unique address to each "m=" line within an SDP offer and SDP answer, according
to the procedures in <xref format="default" pageno="false" target="RFC4566"/> and
<xref format="default" pageno="false" target="RFC3264"/>
</t>
<t>
This specification also updates sections 5.1, 8.1 and 8.2 of
<xref format="default" pageno="false" target="RFC3264"/>, in order to allow
an answerer to assign a non-zero port value to an "m=" line in an SDP answer, even if
the offerer in the associated SDP offer had assigned a zero port value to the "m=" line.
</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 protocol.
</t>
<t>
Unique address: An IP address and IP port combination that is assigned to
a single "m=" line in an SDP offer or SDP answer.
</t>
<t>
Shared address: An IP address and IP port combination that is assigned to
multiple "m=" lines in an SDP offer or SDP answer.
</t>
<t>
Offerer suggested BUNDLE mid: The first mid value in a given
SDP 'group:BUNDLE' attribute mid list in an SDP offer.
</t>
<t>
Answerer selected BUNDLE mid: The first mid value in a given
SDP 'group:BUNDLE' attribute mid list in an SDP answer.
</t>
<t>
Offerer BUNDLE address: Within a given BUNDLE group, an IP address and IP
port combination used by an offerer to send and 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 IP
port combination used by an answerer to send and 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,
for which a single 5-tuple is used to send and receive media. Each endpoint
uses its BUNDLE address, associated with the BUNDLE group, to send and receive
the media.
</t>
<t>
Bundled "m=" line: An "m=" line, in an SDP offer or SDP answer, associated with
a BUNDLE group.
</t>
<t>
Bundle-only "m=" line: An "m=" line, to which an SDP 'bundle-only' attribute
has been assigned.
</t>
<t>
Bundled media: All media associated with a BUNDLE group.
</t>
<t>
Initial SDP offer: The first SDP offer, in which
the offerer indicates that it wants to create a given BUNDLE group.
</t>
<t>
Subsequent SDP offer: An SDP offer which contains a BUNDLE group that
has been created as part of a previous SDP offer/answer exchange.
</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 Semantics" anchor="sec-group" toc="default">
<section title="General" anchor="sec-group-gen" toc="default">
<t>
This section defines a new SDP Grouping Framework extension, BUNDLE.
</t>
<t>
The BUNDLE extension can be indicated using an SDP session-level 'group'
attribute. Each SDP Media Description ("m=" line) that is grouped together,
using SDP media-level mid attributes, belongs to a given BUNDLE
group.
</t>
</section>
<section title="SDP Offer/Answer Procedures" anchor="sec-oa" toc="default">
<section title="General" anchor="sec-oa-gen" toc="default">
<t>
This section describes usage of the SDP offer/answer mechanism
<xref format="default" pageno="false" target="RFC3264"/> for negotiating
usage of the BUNDLE mechanism, for creating a BUNDLE group, for selecting the
BUNDLE addresses (offerer BUNDLE address and answerer BUNDLE address),
for adding an "m=" line to a BUNDLE group, for moving an "m=" line out of a
BUNDEL group, and for disabling an "m=" line within a BUNDLE group.
</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 mechanism. For example, if an SDP 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 SDP offer in which the offerer wants to create a BUNDLE group,
and the answerer rejects the SDP 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) mechanism <xref format="default"
pageno="false" target="RFC5245"/>.
</t>
</section>
<section title="SDP Information Considerations" anchor="sec-oa-sdp" toc="default">
<section title="General" anchor="sec-oa-sdp-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 assigned to each bundled "m=" line, how to
calculate a value for the whole BUNDLE group.
</t>
</section>
<section title="Connection Data (c=)" anchor="sec-oa-sdp-c" toc="default">
<t>
The "c=" line nettype value <xref format="default" pageno="false" target="RFC4566"/>
assigned to a bundled "m=" line MUST be 'IN'.
</t>
<t>
The "c=" line addrtype value <xref format="default" pageno="false" target="RFC4566"/>
assigned to a bundled "m=" line MUST be 'IP4' or 'IP6'. The same value MUST be assigned
to 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-oa-sdp-b" toc="default">
<t>
The total proposed bandwidth is the sum of the proposed bandwidth for each
bundled "m=" line.
</t>
</section>
<section title="Attributes (a=)" anchor="sec-oa-sdp-a" toc="default">
<t>
<xref target="I-D.nandakumar-mmusic-sdp-mux-attributes" /> defines
rules and restrictions for assigning different types of SDP attributes
to a bundled "m=" line.
</t>
</section>
</section>
<section title="Generating the Initial Offer" anchor="sec-oa-off" toc="default">
<section title="General" anchor="sec-oa-off-gen" toc="default">
<t>
When an offerer generates an initial SDP offer, in order to create a BUNDLE group,
the offerer MUST in the SDP offer assign a unique address to each "m=" line with
a non-zero port value, following the procedures in <xref target="RFC3264" pageno="false"
format="default"/>.
</t>
<t>
The offerer MUST in the SDP offer insert an SDP session level 'group:BUNDLE'
attribute, associated with the BUNDLE group, and assign an SDP 'mid'
attribute <xref target="RFC5888" pageno="false" format="default"/> to each
"m=" line that the offerer wants to be within the BUNDLE group,
and place the 'mid' attribute value in the 'group:BUNDLE' attribute mid list.
</t>
<t>
[<xref target="sec-example-add" pageno="false" format="default"/>] shows
an example of an initial SDP offer.
</t>
</section>
<section title="Request offerer BUNDLE address selection" anchor="sec-oa-off-req" toc="default">
<t>
When an offerer generates an initial SDP offer, in order to create a BUNDLE group,
the offerer MUST in the SDP offer indicate which unique address, associated with one of the
"m=" lines that the offerer wants to be within the BUNDLE group, that the offerer wants
the answerer to select as the offerer BUNDLE address [<xref format="default"
pageno="false" target="sec-oa-ans-off"/>]. In the SDP offer, the offerer BUNDLE
mid value represents that address.
</t>
</section>
</section>
<section title="Generating the Answer" anchor="sec-oa-ans" toc="default">
<section title="RFC 5888 restrictions" anchor="sec-oa-5888" toc="default">
<t>
When an answerer generates an SDP answer, the following restrictions, defined
in <xref target="RFC5888" pageno="false" format="default"/>, also apply a
BUNDLE group:
<list style="symbols">
<t>
1) The answerer MUST NOT in the SDP answer include a BUNDLE group, unless the
offerer in the associated SDP offer requested the BUNDLE group to be created; and
</t>
<t>
2) The answerer MUST NOT in the SDP answer include an "m=" line within a BUNDLE
group, unless the offerer in the associated SDP offer requested the "m=" line to
be within the BUNDLE group.
</t>
</list>
</t>
</section>
<section title="Answerer Selection of Offerer Bundle Address" anchor="sec-oa-ans-off" toc="default">
<t>
When an answerer generates an SDP answer, it MUST select a BUNDLE address for the offerer, referred to
as the offerer BUNDLE address. The answerer MUST select an address which the offerer
in the associated SDP answer requested to be within the BUNDLE group.
</t>
<t>
In the SDP offer, the offerer suggested BUNDLE mid represents the "m=" line
to which the offerer in the SDP offer has assigned the address that it wants
the answerer to select as the offerer BUNDLE address [<xref target="sec-oa-off-req"
pageno="false" format="default"/>]. The answerer MUST first select the "m=" line
associated with the offerer suggested BUNDLE mid, and check whether it fulfils the
following criteria:
<list style="symbols">
<t>
The answerer will in the SDP answer create the BUNDLE group;
</t>
<t>
The answerer will not in the SDP answer move the "m=" line out of the BUNDLE group
[<xref target="sec-oa-ans-mov" pageno="false" format="default"/>];
</t>
<t>
The answerer will not in the SDP answer reject the "m=" line [<xref target="sec-oa-ans-rej"
pageno="false" format="default"/>]; and
</t>
<t>
The offerer did not in the associated SDP offer assign a zero port value to the "m=" line.
</t>
</list>
</t>
<t>
If all of the criteria above is fulfilled, the answerer MUST select the address
associated with the "m=" line as the offerer BUNDLE address.
</t>
<t>
If all of the criteria is not fulfilled, the answerer MUST select the next mid
value in the mid list, and perform the same criteria check for the "m=" line
associated with the mid value.
</t>
<t>
In the SDP answer, the answerer selected BUNDLE mid value represents the "m=" line
which address (in the associated SDP offer) the answerer has selected as the offerer
BUNDLE address.
</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-oa-ans-ans" toc="default">
<t>
When an answerer generates an SDP answer, the answerer MUST select a BUNDLE address for itself,
referred to as the answerer BUNDLE address, and in the SDP answer assign the answerer
BUNDLE address to each "m=" line within the created BUNDLE group.
</t>
<t>
The answerer MUST NOT in the SDP answer assign the answerer BUNDLE address to an "m="
line that is not associated with the BUNDLE group, or to an "m=" line that is
associated with another BUNDLE group.
</t>
<t>
The answerer is allowed to select a new answerer BUNDLE address in every SDP answer that
the answerer generates.
</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-oa-ans-mov" toc="default">
<t>
When an answerer generates an SDP answer, in which the answerer moves a
bundled "m=" line out a BUNDLE group, the answerer assigns an address
to the moved "m=" line based on the type of address that the
offerer in the associated SDP offer assigned to the "m=" line.
<list style="symbols">
<t>
If the offerer in the SDP offer has assigned a shared address (e.g. a previously
selected offerer BUNDLE address) to the "m=" line, the answerer MUST in the SDP answer reject the moved
"m=" line, according to the procedures in [<xref target="sec-oa-ans-rej" pageno="false"
format="default"/>].
</t>
<t>
If the offerer in the SDP offer assigned an SDP 'bundle-only' attribute to the "m=" line,
the answerer MUST in the SDP answer reject the moved "m=" line, according to the procedures
in [<xref target="sec-oa-ans-rej" pageno="false" format="default"/>].
</t>
<t>
If the offerer in the SDP offer assigned a unique address to the "m=" line, the answerer
MUST in the SDP answer assign a unique address to the moved "m=" line.
</t>
</list>
</t>
<t>
In addition, in either case above, the answerer MUST NOT in the SDP answer
include a mid value, associated with the moved "m=" line, in the SDP
'group:BUNDLE' attribute mid list associated with the BUNDLE group.
</t>
</section>
<section title="Rejecting A Media Description In A BUNDLE Group" anchor="sec-oa-ans-rej" toc="default">
<t>
When an answerer generates an SDP answer, in which the answerer rejects
an "m=" line, the answerer MUST in the SDP answer assign an address with a zero port
value to the rejected "m=" line, according to the procedures in
<xref target="RFC4566" pageno="false" format="default"/>.
</t>
<t>
In addition, the answerer MUST NOT in the SDP answer
include a mid value, associated with the rejected "m=" line, in the SDP
'group:BUNDLE' attribute mid list associated with the BUNDLE group.
</t>
</section>
</section>
<section title="Offerer Processing of the Answer" anchor="sec-oa-off-ans" toc="default">
<section title="General" anchor="sec-oa-off-ans-gen" toc="default">
<t>
When an offerer receives an SDP answer, the offerer MUST apply the selected
offerer BUNDLE address to each bundled "m=" line. If the offerer generates
a subsequent SDP offer, the offerer MUST in the SDP offer assign the offerer
BUNDLE address to each bundled "m=" line (including any 'bundle-only' "m=" line)
[<xref format="default" pageno="false" target="sec-oa-mod"/>].
</t>
<t>
If the SDP answer does not contain a BUNDLE group, the offerer MUST cease
to use any procedure associated with the BUNDLE mechanism.
</t>
</section>
<section title="Bundle Address Synchronization (BAS)" anchor="sec-oa-off-ans-bas" toc="default">
<t>
If the selected offerer BUNDLE address is different than the address that the offerer
in the associated SDP offer assigned to a bundled "m=" line (including an "m=" line that the
offerer in the SDP offer added to an existing BUNDLE group [<xref format="default" pageno="false"
target="sec-oa-mod-add"/>]), and the bundled "m=" line was not rejected [<xref format="default" pageno="false"
target="sec-oa-ans-rej"/>], or moved out of the BUNDLE group [<xref format="default" pageno="false"
target="sec-oa-ans-mov"/>] by the answerer, the offerer SHOULD as soon as possible generate a
subsequent SDP offer, in which the offerer assigns the offerer BUNDLE address to each bundled "m=" line.
This procedure is referred to as Bundle Address Synchronization (BAS), and the SDP offer is referred
to as a BAS Offer.
</t>
<t>
The offerer MAY in the BAS offer modify any SDP parameter.
</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 in the BAS offer modify SDP parameters that could
get 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 mechanism, have
correct information regarding the address is going to be used to
transport the bundled media.
</t>
<t>
[<xref target="sec-example-add" pageno="false" format="default"/>]
shows an example where an offerer sends a BAS offer.
</t>
</section>
</section>
<section title="Modifying the Session" anchor="sec-oa-mod" toc="default">
<section title="General" anchor="sec-oa-mod-gen" toc="default">
<t>
When an offerer generates a subsequent SDP offer,
the offerer MUST in the SDP offer assign the previously
selected offerer BUNDLE address [<xref format="default" pageno="false"
target="sec-oa-ans-off"/>] to each bundled "m=" line (including any
bundle-only "m=" line), unless the offerer in the SDP offer
moves the "m=" line out of the BUNDLE group [<xref format="default"
pageno="false" target="sec-oa-mod-mov"/>], or disables the "m=" line
[<xref format="default" pageno="false" target="sec-oa-mod-dis"/>].
</t>
<t>
If the SDP offerer in the SDP offer adds an "m=" line to the
BUNDLE group [<xref format="default" pageno="false"
target="sec-oa-mod-add"/>], the offerer MAY assign the
previously selected offerer BUNDLE address to the added "m=" line.
</t>
<t>
In addition, the offerer MUST in the SDP offer indicate which
address (unique or previously selected offerer BUNDLE address)
it wants the answerer to select as the offerer BUNDLE
address, following the procedures in [<xref format="default"
pageno="false" target="sec-oa-off-req"/>]. The offerer MUST
do this even if the offerer in the SDP offer assigns a
previously selected offerer BUNDLE address to each bundled
"m=" line.
</t>
</section>
<section title="Adding a media description to a BUNDLE group" anchor="sec-oa-mod-add" toc="default">
<t>
When an offerer generates an SDP offer, in which the offerer wants to add an
"m=" line to a BUNDLE group, the offerer assigns in the SDP offer an address
(unique or previously selected offerer BUNDLE address) to the "m=" line, assigns an SDP 'mid'
attribute to the "m=" line, and places the mid value in the SDP 'group:BUNDLE' attribute mid
list associated with the BUNDLE group [<xref format="default" pageno="false" target="sec-oa-off-req"/>].
</t>
<t>
NOTE: If the offerer wants that the answerer selects the address
associated with the added "m=" as the offerer BUNDLE address, the
offerer suggested BUNDLE mid MUST represent the added "m=" line
[<xref format="default" pageno="false" target="sec-oa-off-req"/>].
</t>
<t>
[<xref target="sec-example-off-add" pageno="false" format="default"/>]
shows an example where an offerer sends an SDP offer in order to
add an "m=" line to a BUNDLE group.
</t>
</section>
<section title="Moving A Media Description Out Of A BUNDLE Group" anchor="sec-oa-mod-mov" toc="default">
<t>
When an offerer generates an SDP offer, in which the offerer wants to move
a bundled "m=" line out of a BUNDLE group, the offerer
MUST assign a unique address to the "m=" line.
In addition, the offerer MUST NOT place a mid value associated
with the "m=" line in the SDP 'group:BUNDLE' attribute mid
list associated with the BUNDLE group.
</t>
<t>
NOTE: The offerer MAY keep a previously assigned SDP 'mid' attribute in an "m=" line
that it wants to move out of a BUNDLE group, e.g. if the mid value is
used for some other SDP grouping extension than BUNDLE.
</t>
<t>
[<xref target="sec-example-off-mov" pageno="false" format="default"/>]
shows an example where an offerer sends an SDP offer in order to
move an "m=" line out of a BUNDLE group.
</t>
</section>
<section title="Disabling A Media Description In A BUNDLE Group" anchor="sec-oa-mod-dis" toc="default">
<t>
When an offerer generates an SDP offer, in which the offerer wants to
disable a bundled "m=" line, the offerer MUST assign an address with
a zero port alue to the "m=" line, following the procedures
in <xref target="RFC4566" pageno="false" format="default"/>.
In addition, the offerer MUST NOT place a mid value associated
with the "m=" line in the SDP 'group:BUNDLE' attribute mid
list associated with the BUNDLE group.
</t>
<t>
NOTE: The offerer MAY assign an SDP 'mid' attribute to an "m=" line
that it wants to disable, e.g. if the mid value is
used for some other SDP grouping extension than BUNDLE.
</t>
<t>
[<xref target="sec-example-off-dis" pageno="false" format="default"/>]
shows an example where an offerer sends an SDP offer in order to
disable an "m=" line within a BUNDLE group.
</t>
</section>
</section>
</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'. An offerer can in an SDP offer assign a 'bundle-only'
"m=" line to a bundled "m=" line (including an "m=" line that the offerer wants
to add to the BUNDLE group [<xref target="sec-oa-mod-add" pageno="false"
format="default"/>]), in order to ensure that the answerer only accepts the "m=" line
if the answerer supports the BUNDLE mechanism, and if the answerer in the SDP
answer keeps the "m=" line within the BUNDLE group.
</t>
</section>
<section anchor="sec-bundle-only-oa" title="SDP Offer/Answer Procedures" toc="default">
<section anchor="sec-bundle-only-ino" title="Generating the Initial Offer" toc="default">
<t>
When an offerer generates an initial SDP offer, in order to create a BUNDLE group, the offerer
can in the SDP offer assign an SDP 'bundle-only' attribute to an "m=" line
that the offerer wants to be within the BUNDLE group.
</t>
<t>
The offerer MUST in the SDP offer assign a zero port value the bundle-only "m="
line.
</t>
</section>
<section anchor="sec-bundle-only-ans" title="Generating the Answer" toc="default">
<t>
When the answerer selects the offerer BUNDLE address [<xref target="sec-oa-ans-off"
pageno="false" format="default"/>], the answerer MUST also take a bundle-only "m=" line
with a non-zero port value into consideration.
</t>
<t>
If the offerer in the SDP offer has assigned a zero port value to a bundle-only "m="
line, and if the answerer accepts the "m=" line, the answerer will treat the
"m=" line as any other bundle "m=" line when the answerer generates the SDP answer
[<xref target="sec-oa-ans" pageno="false" format="default"/>].
</t>
<t>
NOTE: If the offerer in the SDP offer has assigned a zero port value to a bundled "m=" line,
but the offerer has not assigned a 'bundle-only' SDP attribute to the "m=" line, it is an
indication that the offerer wants to disable the "m=" line
[<xref target="sec-oa-mod-dis" pageno="false" format="default"/>].
</t>
<t>
If the answerer in the SDP answer does not keep the bundle-only "m=" line within
the BUNDLE group, the answerer MUST in the SDP answer reject the "m=" line
[<xref target="sec-oa-ans-rej" pageno="false" format="default"/>].
</t>
<t>
The answerer MUST NOT in the SDP answer assign an SDP 'bundle-only' attribute to
an "m=" line (even if the offerer in the associated SDP offer has assigned a 'bundle-only'
attribute to the "m="line).
</t>
</section>
<section anchor="sec-bundle-only-opa" title="Offerer Processing of the Answer" toc="default">
<t>
When the offerer receives an SDP answer, the offerer follows the procedures in
[<xref target="sec-oa-off-ans" pageno="false" format="default"/>]. If the offerer
in the associated SDP offer assigned an SDP 'bundle-only' attribute to an "m=" line,
and the "m=" line was accepted (and was kept within the BUNDLE group) by the answerer,
the selected offerer BUNDLE address also applies to the "m=" line.
</t>
</section>
<section anchor="sec-bundle-only-mod" title="Modifying the Session " toc="default">
<t>
When an offerer creates a subsequent SDP offer, the offerer follows the
procedures in [<xref target="sec-oa-mod" pageno="false" format="default"/>].
If the offerer in the SDP offer assigns an SDP 'bundle-only' attribute to
a bundled "m=" line, in order to ensure that the answerer accepts the "m=" line
only if the answerer keeps the "m=" line within the BUNDLE group, the offerer
MUST NOT assign a zero port value to the "m=" line. Instead, the offerer MUST
in the SDP offer assign the offerer BUNDLE address or, if the "m=" line is added to the
BUNDLE group [<xref target="sec-oa-mod-add" pageno="false" format="default"/>],
either the offerer BUNDLE address or a unique address, to the "m=" line.
</t>
<t>
NOTE: The offerer can in a subsequent SDP offer assign an
SDP 'bundle-only' attribute to a bundled "m=" line even if the
offerer did not assign a 'bundle-only' attribute to the
"m=" line in a previous SDP offer.
</t>
<t>
If the offerer in the SDP offer wants to move a bundled
"m=" line out of a BUNDLE group [<xref target="sec-oa-mod-mov"
pageno="false" format="default"/>], the offerer MUST NOT in
the SDP offer assign a 'bundle-only' attribute to the "m=" line.
</t>
<t>
If the offerer in the SDP offer wants to disable a
bundled "m=" line [<xref target="sec-oa-mod-dis" pageno="false"
format="default"/>], the offerer MUST NOT in the SDP offer assign
a 'bundle-only' attribute to the "m=" line.
</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>
If bundled "m=" lines represent different transport protocols, there MUST
exist a specification which describes a mechanism, for this specific
transport protocol combination, how to associate a received packet with
the correct transport protocol.
</t>
<t>
In addition, if a received packet can be associated with more than one
bundled "m=" line, there MUST exist a specification which describes a mechanism
how to associated 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 how to identify the protocol among the STUN, DTLS and SRTP protocols (in any combination).
If an offer or answerer in SDP offers or answers include 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 how to identify 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 how to associate 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>
By default, all RTP based media within a BUNDLE group belong to a single RTP session
<xref format="default" pageno="false" target="RFC3550"/>. Multiple BUNDLE groups will form
multiple RTP Sessions.
</t>
<t>
NOTE: The usage of multiple RTP sessions within a BUNDLE group, or the usage of a single
RTP session that spans over multiple BUNDLE groups, is outside the scope of this specification.
Other specification needs to extend the BUNDLE mechanism in order to allow such usages.
</t>
<t>
When a single RTP session is used, all bundled "m=" lines representing RTP based media
share a single SSRC numbering space <xref format="default" pageno="false" target="RFC3550"/>.
</t>
<t>
In addition, 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 "m=" line MUST be identical (e.g. RTP/AVPF).</t>
<t>A given SSRC SHOULD NOT transmit RTP packets using payload types that
originates 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 fails
to function. Even if done in proper sequence this causes RTP Timestamp rate switching
issues [ref to draft-ietf-avtext-multiple-clock-rates].
</t>
</section>
<section anchor="sec-rtp-sessions-pt" title="Payload Type (PT) Value Re-usage" 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 used inside more than one bundled "m=" line, all codecs associated with the payload type
numbers 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.nandakumar-mmusic-sdp-mux-attributes"/> lists SDP
attributes, which 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 Packets With Correct SDP Media Description" toc="default">
<t>
In general, there are multiple mechanisms that can be used by an endpoint in order to associate received
RTP packets with the bundled "m=" line representing the RTP packets. Such mechanisms include using the local
address:port combination on which the RTP packets are received, 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 packets associated with a BUNDLE group are sent and received using the same 5-tuple, 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 SDP offer and answer inform each other which SSRC values they will use
inside sent RTP packets by, by assigning an SDP 'ssrc' attribute <xref format="default" pageno="false"
target="RFC5576"/> to 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 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 SDP answer
providing that information. Due to this, before the offerer has received the SDP answer, the offerer will
not be able to associate received RTP 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 packets with the correct
"m=" line, the offerer and answerer MUST in an SDP offer and answer assign an SDP "receiver-id" attribute
[receiver-id-reference-to-be-added] to each bundled "m=" line which contains a payload type value that
is also used inside another bundled "m=" line. If an answerer accepts such "m=" line, and keeps it within
the BNDLE group, the answerer MUST insert the 'receiver-id' attribute value in RTP packets, associated
with the "m=" line, sent towards the offerer.
</t>
<t>
OPEN ISSUE: We need a mechanism that implements the 'receiver-id' mechanism and the associated SDP attribute.
</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 5-tuples will be used for sending
and receiving 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 associated with a BUNDLE group.
</t>
</section>
<section title="Generating the Initial Offer" anchor="sec-rtprtcp-mux-oa-ino" toc="default">
<t>
When an offerer generates an initial SDP offer, if the offerer wants to negotiate usage
of RTP/RTCP multiplexing within a BUNDLE group, the offerer MUST in the SDP offer assign
an SDP 'rtcp-mux' attribute <xref format="default" pageno="false" target="RFC5761"/> to
each bundled "m=" line (including any bundle-only "m=" line). In addition, the offerer
MUST in the SDP offer assign an SDP 'rtcp' attribute <xref format="default"
pageno="false" target="RFC3605"/> to each bundled "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.
</t>
<t>
If the offerer does not want to negotiate usage of RTP/RTCP multiplexing, the offerer MUST
NOT assign the SDP attributes above to any bundled "m=" line.
</t>
</section>
<section title="Generating the Answer" anchor="sec-rtprtcp-mux-oa-ans" toc="default">
<section title="Generating the Answer to an Initial Offer" anchor="sec-rtprtcp-mux-oa-ans-ino" toc="default">
<t>
When the answerer generates an SDP answer to an initial SDP offer,
if the offerer in the associated SDP offer indicated support of RTP/RTCP
multiplexing <xref format="default" pageno="false" target="RFC5761"/> within
a BUNDLE group, the answerer MUST in the SDP answer either accept or reject usage
of RTP/RTCP multiplexing.
</t>
<t>
If the answerer accepts usage of RTP/RTCP multiplexing within the BUNDLE group, the answerer
MUST in the SDP answer assign an SDP 'rtcp-mux' attribute to each bundled "m=" line. The
answerer MUST NOT in the SDP answer assign an SDP 'rtcp' attribute to any bundled
"m=" line.
</t>
<t>
OPEN ISSUE: Do we want to include the SDP 'rtcp' attribute also in the SDP answer, eventhough it
is not needed?
</t>
<t>
If the answerer rejects usage of RTP/RTCP multiplexing within the BUNDLE group, the answerer
MUST NOT in the SDP answer assign an SDP 'rtcp-mux' or SDP 'rtcp' attribute to any bundled "m=" line.
</t>
</section>
<section title="Generating the Answer to a Subsequent Offer" anchor="sec-rtprtcp-mux-oa-ans-sub" toc="default">
<t>
When the answerer generates an SDP answer to a subsequent SDP offer, if the offerer in the associated SDP offer
indicated support of RTP/RTCP multiplexing <xref format="default" pageno="false" target="RFC5761"/> within
a BUNDLE group, the answerer MUST in the SDP answer assign an SDP 'rtcp-mux' attribute and SDP 'rtcp' attribute
to each bundled "m=" line.
</t>
<t>
NOTE: The BUNDLE mechanism does not allow the answerer to, in a subsequent SDP answer, disable
usage of RTP/RTCP multiplexing, if the offerer in the associated SDP offer indicates that it
wants to continue using RTP/RTCP multiplexing.
</t>
</section>
</section>
<section title="Offerer Processing of the Answer" anchor="sec-rtprtcp-mux-oa-pra" toc="default">
<t>
When the offerer receives an SDP answer, it follows the procedures
defined in <xref format="default" pageno="false" target="RFC5245"/>.
</t>
</section>
<section title="Modifying the Session" anchor="sec-rtprtcp-mux-oa-mod" toc="default">
<t>
When an offerer generates a subsequent SDP offer, if the offerer wants
to negotiate usage of RTP/RTCP multiplexing within a BUNDLE group, or
if the offerer wants to continue usage of previously negotiated RTP/RTCP
multiplexing within the BUNDLE group, the offerer MUST in the SDP offer
assign 'rtcp-mux' and 'rtcp' attributes to each bundled "m=" line (including
bundle-only "m=" lines), unless the "m=" line is disabled or removed 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 the offerer wants to disable previously
negotiated usage of RTP/RTCP multiplexing within a BUNDLE group, the offerer
MUST NOT in the SDP offer assign 'rtcp-mux' and 'rtcp' attributes to any
bundled "m=" line.
</t>
<t>
NOTE: It is RECOMMENDED that, once usage of RTP/RTCP multiplexing has been negotiated within a BUNDLE group,
that the usage of not disabled. Disabling RTP/RTCP multiplexing means that the offerer and answerer need to
reserve new IP 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>
Support and usage of ICE mechanism together with the BUNDLE mechanism is optional.
</t>
</section>
<section title="SDP Offer/Answer Procedures" anchor="sec-ice-oa" toc="default">
<section title="Generating the Initial Offer" anchor="sec-ice-ino" toc="default">
<t>
When an offerer generates an initial SDP offer, which contains a BUNDLE group, the
offerer MUST assign ICE candidates <xref format="default" pageno="false" target="RFC5245"/>
to each bundled "m=" line, except to an "m=" line to which the offerer assigns
a zero port value (e.g. a bundle-only "m=" line). The offerer MUST assign unique
ICE candidate values to each "m=" line.
</t>
</section>
<section title="Generating the Answer" anchor="sec-ice-ans" toc="default">
<t>
When an answerer generates and SDP Answer, which contains a BUNDLE group,
the answerer MUST assign ICE candidates to each bundled "m=" line. The answerer
MUST assign identical ICE candidate values to each bundled "m=" line.
</t>
</section>
<section title="Offerer Processing of the Answer" anchor="sec-ice-pra" toc="default">
<t>
When the offerer receives an SDP answer, it follows the procedures
defined in <xref format="default" pageno="false" target="RFC5245"/>.
</t>
</section>
<section title="Modifying the Session" anchor="sec-ice-mod" toc="default">
<t>
When an offerer generates a subsequent SDP offer, for each bundled
"m=" line to which the offerer assigns its BUNDLE address, the offerer
MUST assign identical ICE candidate values. The offerer MUST assign
the ICE candidate values associated with the "m=" line that was used
by the answerer to select the offerer BUNDLE address [ref-to-be-added].
</t>
</section>
<section title="Keep-alives" anchor="sec-ice-con-checks" toc="default">
<t>
Once it is known that both endpoints support, and accept to use, the BUNDLE grouping
extension, ICE connectivity checks and keep-alives only needs to be performed for the
whole BUNDLE group, instead of for each bundled "m=" line.
</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.
</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="Security Considerations" anchor="sec-security" toc="default">
<t>
This specification does not significantly change the security
considerations of SDP which can be found in Section X of TBD.
</t>
<t>
TODO: Think carefully about security analysis of reuse of same SDES
key on multiple "m=" lines when the far end does not use BUNDLE and
warn developers of any risks.
</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 SDP offer, in which the offerer assigns a unique address to each bundled "m=" line within the BUNDLE group.</t>
<t>2. An SDP 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 SDP 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
a=mid:foo
b=AS:200
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:97 iLBC/8000
m=video 10002 RTP/AVP 31 32
a=mid:bar
b=AS:1000
a=rtpmap:31 H261/90000
a=rtpmap:32 MPV/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
a=mid:foo
b=AS:200
a=rtpmap:0 PCMU/8000
m=video 20000 RTP/AVP 32
a=mid:bar
b=AS:1000
a=rtpmap:32 MPV/90000
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
a=mid:foo
b=AS:200
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:97 iLBC/8000
m=video 10000 RTP/AVP 31 32
a=mid:bar
b=AS:1000
a=rtpmap:31 H261/90000
a=rtpmap:32 MPV/90000
]]></artwork>
</figure>
</section>
<section title="Example: Bundle Mechanism Rejected" anchor="sec-example-bunrej" toc="default">
<t>
The example below shows:
<list style="symbols">
<t>1. An SDP offer, in which the offerer assigns a unique address to each bundled "m=" line within the BUNDLE group.</t>
<t>2. An SDP 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
a=mid:foo
b=AS:200
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:97 iLBC/8000
m=video 10002 RTP/AVP 31 32
a=mid:bar
b=AS:1000
a=rtpmap:31 H261/90000
a=rtpmap:32 MPV/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
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. An SDP offer, in which the offerer adds a new "m=" line, represented by the "zen" mid value,
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 SDP 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 SDP 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
a=mid:foo
b=AS:200
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:97 iLBC/8000
m=video 10000 RTP/AVP 31 32
a=mid:bar
b=AS:1000
a=rtpmap:31 H261/90000
a=rtpmap:32 MPV/90000
m=video 20000 RTP/AVP 66
a=mid:zen
b=AS:1000
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 zen
m=audio 20000 RTP/AVP 0
a=mid:foo
b=AS:200
a=rtpmap:0 PCMU/8000
m=video 20000 RTP/AVP 32
a=mid:bar
b=AS:1000
a=rtpmap:32 MPV/90000
m=video 20000 RTP/AVP 66
a=mid:zen
b=AS:1000
a=rtpmap:66 H261/90000
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
a=mid:foo
b=AS:200
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:97 iLBC/8000
m=video 10000 RTP/AVP 31 32
a=mid:bar
b=AS:1000
a=rtpmap:31 H261/90000
a=rtpmap:32 MPV/90000
m=video 10000 RTP/AVP 66
a=mid:zen
b=AS:1000
a=rtpmap:66 H261/90000
]]></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. An SDP offer, 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 SDP 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 other 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
a=mid:foo
b=AS:200
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:97 iLBC/8000
m=video 10000 RTP/AVP 31 32
a=mid:bar
b=AS:1000
a=rtpmap:31 H261/90000
a=rtpmap:32 MPV/90000
m=video 50000 RTP/AVP 66
b=AS:1000
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
a=mid:foo
b=AS:200
a=rtpmap:0 PCMU/8000
m=video 20000 RTP/AVP 32
a=mid:bar
b=AS:1000
a=rtpmap:32 MPV/90000
m=video 60000 RTP/AVP 66
b=AS:1000
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. An SDP offer, in which the offerer disables a bundled "m=" line within BUNDLE group, assigns a zero port number
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 SDP 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 other bundled "m=" lines 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
a=mid:foo
b=AS:200
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:97 iLBC/8000
m=video 10000 RTP/AVP 31 32
a=mid:bar
b=AS:1000
a=rtpmap:31 H261/90000
a=rtpmap:32 MPV/90000
m=video 0 RTP/AVP 66
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
a=mid:foo
b=AS:200
a=rtpmap:0 PCMU/8000
m=video 20000 RTP/AVP 32
a=mid:bar
b=AS:1000
a=rtpmap:32 MPV/90000
m=video 0 RTP/AVP 66
a=rtpmap:66 H261/90000
]]></artwork>
</figure>
</section>
</section>
<section title="IANA Considerations" toc="default">
<t>
This document requests IANA to register the new SDP Grouping semantic
extension called BUNDLE.
</t>
</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 mechanism 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 and Martin Thompson for taking the 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-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 mechanism.</t>
<t>Q8 Closed (IETF#88): An Offerer can, before it knows whether the Answerer supports the BUNDLE mechanism,
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.5761"?>
<?rfc include="reference.RFC.5888"?>
<reference anchor="I-D.nandakumar-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="14" month="February" year="2014" />
</front>
<seriesInfo name="Internet-Draft" value="draft-ietf-mmusic-sdp-mux-attributes-01" />
</reference>
</references>
<references title="Informative References">
<?rfc include="reference.RFC.3550"?>
<?rfc include="reference.RFC.3605"?>
<?rfc include="reference.RFC.5245"?>
<?rfc include="reference.RFC.5576"?>
<?rfc include="reference.RFC.5764"?>
<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 number 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 5-tuple 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 number 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 number values, and one of those port would be used for the 5-tuple,
problems would occur if an endpoint wants to disable/reject the "m=" line
associated with that port, by setting the port number value to zero. After that,
no "m=" line would contain the port number value which is used for the 5-tuple.
In addition, it is unclear what would happen to the ICE candidates associated
with the "m=" line, as they are also used for the 5-tuple.
</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>
| PAFTECH AB 2003-2026 | 2026-04-23 14:19:30 |