Internet DRAFT - draft-even-avtcore-priority-markings
draft-even-avtcore-priority-markings
AVTCore R. Even
Internet-Draft O. Idan
Intended status: Standards Track Huawei Technologies
Expires: June 26, 2019 December 23, 2018
Frame Priority Marking RTP Header Extension
draft-even-avtcore-priority-markings-03.txt
Abstract
This document updates the Frame Marking RTP header extension in
draft-ietf-avtext-framemarking-06 used to convey information about
video frames that is critical for error recovery and packet
forwarding in RTP middle-boxes or network nodes. The flags for frame
marking for non-scalable streams include the D bit to mark a frame
that can be discarded, and still provide a decodable media stream.
There is also the I bit for frames that can be decoded independent of
prior frames, e.g. intra-frame.
This memo adds priority values for the non-scalable streams
discardable frames
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on June 26, 2019.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
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publication of this document. Please review these documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Notation . . . . . . . . . . . . . . . . . . . . 3
3. Frame Priority . . . . . . . . . . . . . . . . . . . . . . . 3
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
5. Security considerations . . . . . . . . . . . . . . . . . . . 4
6. Normative References . . . . . . . . . . . . . . . . . . . . 4
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 4
1. Introduction
Frame Marking RTP Header Extension [I-D.ietf-avtext-framemarking]
provides a single bit for marking frames that may be discarded by a
middle box for non-scalable streams. Having one bit for marking a
discardable frame provides the same information to a middle box that
need to drop few frames or many frames. An encoder may want to mark
multiple frames as discardable but with different drop priority,
allowing the middle box to discard part or all the discardable
frames. The middle box can use the priority information for deciding
which frames to drop. By monitoring the RTP stream and the frame
marking a middle box can estimate how many RTP packets are in each
priority and use this information for the dropping decision.
A video stream is composed of Group of Pictures (GOP) where the GOP
includes I,P and B frames. A GOP is typically bound by I frames and
is 15-30,60 frames long but can vary with frame rate, content
complexity and encoder implementation. There are a couple of use
cases that can benefit if discard priority is available.
o When there are contiguous non referenced B frames dropping all of
them will reduce the actual frame rate. By providing different
priority to each of these B frames the middle box can affect the
actual frame rate. This information can be also deducted based on
the number of contiguous frames but having priority will make it
easier for the middle box for example when the frames are
interleaved.
o When there are referenced B frames, for example a non referenced B
frame (B1) followed by a B frame (B2) referenced by B1 only. If
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B1 is dropped then B2 can be dropped too. By using priority B1
can have lower priority than B2.
o Dropping a P frame that is close to the end of the GOP is also
possible comparing to a P frame in the beginning of the GOP. The
encoder can know when such P frame exist and mark is as
discardable with lowest priority.
2. Requirements Notation
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 [RFC2119].
3. Frame Priority
This memo adds two P bits to the RTP header extension defined in
[I-D.ietf-avtext-framemarking] section 3.1.
RTP Header Extension for non-scalable streams:
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ID=? | L=0 |S|E|I|D|P P 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
P: Priority bits (2 bits). If the D bit is set to zero these bits
MUST be zero. If the D bit is set to 1 the values 00 is the highest
drop priority (this will be the case when priority is not specified)
and 11 is the lowest drop priority.
The priority bits apply to a single RTP stream and a middle box MUST
NOT use this information to compare discardable frames from different
RTP streams.
Based on the use cases from the introduction, the priority of the non
referenced B frame will be 00, the priority of the referenced B
frames will be 01 and the priority of the discardable P frame will be
10. If the middle box drops the frames marked with priority 00 it
can now drop the frames marked with priority 01 since they are not
needed for decoding the stream.
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4. IANA Considerations
There are no IANA actions
5. Security considerations
This memo does not add any security information to the ones in
[I-D.ietf-avtext-framemarking]
6. Normative References
[I-D.ietf-avtext-framemarking]
Berger, E., Nandakumar, S., and M. Zanaty, "Frame Marking
RTP Header Extension", draft-ietf-avtext-framemarking-08
(work in progress), October 2018.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
Authors' Addresses
Roni Even
Huawei Technologies
Tel Aviv
Israel
Email: Roni.even@huawei.com
Ofer Idan
Huawei Technologies
Hod Hasharon
Israel
Email: ofer.idan@huawei.com
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