One document matched: draft-berger-avtext-framemarking-00.xml
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<rfc category="std" docName="draft-berger-avtext-framemarking-00" ipr="trust200902">
<front>
<title abbrev="Frame Marking">Frame Marking RTP Header Extension</title>
<author initials="E." surname="Berger" fullname="Espen Berger">
<organization>Cisco Systems</organization>
<address>
<phone>+47 98228179</phone>
<email>espeberg@cisco.com</email>
</address>
</author>
<author fullname="Suhas Nandakumar" initials="S" surname="Nandakumar">
<organization>Cisco Systems</organization>
<address>
<postal>
<street>170 West Tasman Drive</street>
<city>San Jose</city>
<region>CA</region>
<code>95134</code>
<country>US</country>
</postal>
<email>snandaku@cisco.com</email>
</address>
</author>
<author fullname="Mo Zanaty" initials="M" surname="Zanaty">
<organization>Cisco Systems</organization>
<address>
<postal>
<street>170 West Tasman Drive</street>
<city>San Jose</city>
<region>CA</region>
<code>95134</code>
<country>US</country>
</postal>
<email>mzanaty@cisco.com</email>
</address>
</author>
<date month="March" day="9" year="2015"/>
<area>Applications</area>
<keyword>Internet-Draft</keyword>
<abstract>
<t>This document describes a Frame Marking RTP header extension used to
convey information about video frames that is critical for error recovery
and packet forwarding in RTP middleboxes or network nodes. It is most
useful when media is encrypted, and essential when the middlebox or node
has no access to the media encryption keys. It is also useful for
codec-agnostic processing of encrypted or unencrypted media, while it also
supports extensions for codec-specific information.</t>
</abstract>
</front>
<middle>
<section title="Introduction" anchor="intro">
<t>Many widely deployed RTP topologies used in modern voice and video
conferencing systems include a centralized component that acts as an RTP switch.
It receives voice and video streams from each participant, which may be encrypted using
SRTP <xref target="RFC3711" />, or extensions that provide participants with
private media via end-to-end encryption that excludes the switch.
The goal is to provide a set of streams back to
the participants which enable them to render the right media content. In a
simple video configuration, for example, the goal will be that each participant
sees and hears just the active speaker. In that case, the goal of the switch is to
receive the voice and video streams from each participant, determine the active
speaker based on energy in the voice packets, possibly using the client-to-mixer
audio level RTP header extension, and select the corresponding video
stream for transmission to participants; see <xref target="rtpswitch" />.</t>
<t>In this document, an "RTP switch" is used as a common short term for the terms
"switching RTP mixer", "source projecting middlebox",
"source forwarding unit/middlebox" and "video switching MCU" as
discussed in <xref target="I-D.ietf-avtcore-rtp-topologies-update" />.</t>
<figure title="RTP switch" anchor="rtpswitch"><artwork><![CDATA[
+---+ +------------+ +---+
| A |<---->| |<---->| B |
+---+ | | +---+
| RTP |
+---+ | Switch | +---+
| C |<---->| |<---->| D |
+---+ +------------+ +---+
]]>
</artwork></figure>
<t>In order to properly support switching of video streams, the RTP switch typically needs
some critical information about video frames in order to start and stop forwarding streams.
<list style="symbols">
<t>Because of inter-frame dependencies, it should ideally switch video streams at a point
where the first frame from the new speaker can be decoded by recipients without prior
frames, e.g switch on an intra-frame. </t>
<t>In many cases, the switch may need to drop frames in order to realize congestion control
techniques, and needs to know which frames can be dropped with minimal impact to video quality.</t>
<t>Furthermore, it is highly desirable to do this in a way which is not specific to the
video codec. Nearly all modern video codecs share common concepts around frame types.</t>
<t>It is also desirable to be able to do this for SRTP without requiring the video switch to
decrypt the packets. SRTP will encrypt the RTP payload format contents and consequently this
data is not usable for the switching function without decryption, which may not even
be possible in the case of end-to-end encryption of private media.</t>
</list>
</t>
<t>By providing meta-information about the RTP streams outside the encrypted media payload an
RTP switch can do selective forwarding without decrypting the payload. This document provides a
solution to this problem.</t>
</section>
<section title="Solution">
<t>The solution uses RTP header extensions as defined in <xref target="RFC5285" />. A subset of
meta-information from the video stream is provided as an RTP header extension to allow a RTP switch
to do generic video switching handling of video streams encoded with different video codecs.</t>
<section title="Mandatory Extension" anchor="mandatory">
<t>The following information are extracted from the media payload:
<list style='symbols'>
<t>S: Start of Frame (1 bit) - MUST be 1 in the first packet in a frame
within a layer; otherwise MUST be 0.</t>
<t>E: End of Frame (1 bit) - MUST be 1 in the last packet in a frame
within a layer; otherwise MUST be 0. </t>
<t>I: Independent Frame (1 bit) - MUST be 1 for frames that can be
decoded indepedent of prior frames, e.g. intra-frame, VPx keyframe,
H.264 IDR <xref target="RFC6184" />, H.265 CRA/BLA; otherwise MUST be 0.</t>
<t>D: Discardable Frame (1 bit) - MUST be 1 for frames that can be dropped,
and still provide a decodable media stream; otherwise MUST be 0. </t>
<t>B: Base Layer Sync (1 bit) - MUST be 1 if this frame only depends
on the base layer; otherwise MUST be 0.</t>
<t>TID: Temporal ID (3 bits) - The base temporal quality starts with 0, and increases
with 1 for each temporal layer/sub-layer. </t>
</list>
</t>
<t>The values of frame information can be carried as RTP header extensions encoded
using the one-byte header as described in <xref target="RFC5285" /> as shown below.</t>
<figure>
<artwork><![CDATA[
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ID=2 | L=0 |S|E|I|D|B| TID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork></figure>
</section>
<section title="Optional Extensions">
<t>Optionally, video codec specific information MAY be provided
in addition to the mandatory information defined in the
<xref target="mandatory"/></t>
<t>The frame marking can be extended with codec specific information
using a longer length value in the one-byte header. The codec specific
information included in the header extension MUST match the SDP negotiated
payload format for the RTP stream.</t>
<figure>
<artwork><![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 2
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ID=2 | L=2 |S|E|I|D|B| TID | video codec specific information|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork></figure>
</section>
<section title="Examples">
<t> The following example shows H265 LayerID included as video codec
specific information. The length field is 1 to add another 1 byte of
data with the H265 LayerId (a 6-bit field) and a 2-bit PADding at the end.</t>
<figure>
<artwork><![CDATA[
0 1 2
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ID=2 | L=1 |S|E|I|D|B| TID |H265-LayerId |PAD|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork></figure>
<t>The following example shows VP8 15-bit running index of the frames
(pictureID) for representing the VP8 temporal layrer information.</t>
<figure>
<artwork><![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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ID=3 | L=2 |S|E|I|D|B| TID | PictureID |PAD|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork></figure>
</section>
<section title="Signaling information">
<t>The URI for declaring this header extension in an extmap attribute is
"urn:ietf:params:rtp-hdrext:framemarkinginfo". It does not contain any
extension attributes. </t>
<t>An example attribute line in SDP:</t>
<figure>
<artwork><![CDATA[
a=extmap:3 urn:ietf:params:rtp-hdrext:framemarkinginfo
]]></artwork></figure>
</section>
<section title="Considerations on use">
<t>The header extension values MUST represent what is already in the RTP payload.</t>
<t> When a RTP switch needs to discard a received video frame due to congestion control considerations,
it is RECOMMENDED that it preferably drop frames marked with the "discardable" bit.</t>
<t> When a RTP switch wants to forward a new video stream to a receiver, it is RECOMMENDED to
select the new video stream from the first switching point (I bit set) and forward the same.
A RTP switch can request a media source to generate a switching point for H.264 by sending
Full Intra Request (RTCP FIR) as defined in <xref target="RFC5104" />, for example. </t>
</section>
</section>
<section title="Security Considerations" >
<t>In the Secure Real-Time Transport Protocol (SRTP) <xref target="RFC3711" />, RTP header extensions are
authenticated but not encrypted. When header extensions are used some of the payload type information are
exposed and is visible to middle boxes. The encrypted media data is not exposed, so this is not seen as a
high risk exposure. </t>
</section>
<section title="IANA Considerations">
<t>This document defines a new extension URI to the RTP Compact HeaderExtensions sub-registry of the
Real-Time Transport Protocol (RTP) Parameters registry, according to the following data:</t>
<t>Extension URI: urn:ietf:params:rtp-hdrext:framemarkinginfo<vspace />
Description: Frame marking information for video streams<vspace />
Contact: espeberg@cisco.com<vspace />
Reference: RFC XXXX</t>
<t>Note to RFC Editor: please replace RFC XXXX with the number of this
RFC.</t>
</section>
</middle>
<back>
<references title="Normative References">
<reference anchor='KEYWORDS'>
<front>
<title abbrev='RFC Key Words'>Key words for use in RFCs to Indicate Requirement Levels</title>
<author initials='S.' surname='Bradner' fullname='Scott Bradner'>
<organization>Harvard University</organization>
<address>
<postal>
<street>1350 Mass. Ave.</street>
<street>Cambridge</street>
<street>MA 02138</street></postal>
<phone>- +1 617 495 3864</phone>
<email>sob@harvard.edu</email></address></author>
<date month='March' year='1997' />
<area>General</area>
<keyword>keyword</keyword>
<abstract>
<t>
In many standards track documents several words are used to signify
the requirements in the specification. These words are often
capitalized. This document defines these words as they should be
interpreted in IETF documents. Authors who follow these guidelines
should incorporate this phrase near the beginning of their document:
<list>
<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
RFC 2119.
</t></list></t>
<t>
Note that the force of these words is modified by the requirement
level of the document in which they are used.
</t></abstract></front>
<seriesInfo name='BCP' value='14' />
<seriesInfo name='RFC' value='2119' />
<format type='TXT' octets='4723' target='ftp://ftp.isi.edu/in-notes/rfc2119.txt' />
<format type='HTML' octets='14486' target='http://xml.resource.org/public/rfc/html/rfc2119.html' />
<format type='XML' octets='5661' target='http://xml.resource.org/public/rfc/xml/rfc2119.xml' />
</reference>
</references>
<references title="Informative References">
<!-- Here we use entities that we defined at the beginning. -->
<reference anchor='I-D.ietf-avtcore-rtp-topologies-update'>
<front>
<title abbrev='RTP Topologies'>RTP Topologies</title>
<author initials='M.' surname='Westerlund' fullname='M. Westerlund'>
<organization>Ericsson</organization></author>
<author initials='S.' surname='Wenger' fullname='S. Wenger'>
<organization>Vidyo</organization></author>
<date year='2013' day='22' month='April' /></front>
<seriesInfo name='Internet-Draft' value='draft-ietf-avtcore-rtp-topologies-update' />
<format type='HTML' target='http://tools.ietf.org/html/draft-ietf-avtcore-rtp-topologies-update-00' />
</reference>
&RFC3550;
&RFC3711;
&RFC5104;
&RFC5285;
&RFC6184;
</references>
</back>
</rfc>
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