AVTCORE Working Group S. Majali
Internet-Draft Nvidia
Intended status: Experimental 3 June 2024
Expires: 5 December 2024
RTCP feedback Message for Loss Notification
draft-majali-avtcore-lntf-feedback-message-00
Abstract
Real-time media streams that use RTP, use multiple mechanisms to
recover from packet and frame loss. Sender to recover frame loss
effectively, it can use information on the last frame receiver
successfully decoded and latest packet it received on network. This
document describes an RTP Control Protocol (RTCP) feedback message
intended to notify the sender with loss details.
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This Internet-Draft will expire on 5 December 2024.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2
2. LNTF Message . . . . . . . . . . . . . . . . . . . . . . . . 2
3. SDP Definitions . . . . . . . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
7.1. Normative References . . . . . . . . . . . . . . . . . . 4
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
This document proposes RTCP feedback message Loss Notification (LNTF)
during packet loss, containing information about the latest frame
decoded and latest packet received by the receiver. This feedback is
beneficial in video streaming; video encoder can use this information
to encode future frames by referencing successfully decoded frames.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. LNTF Message
LNTF message is identified by payload type defined as Payload-
Specific Feedback message (PSFB).
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V=2|P| FMT=15 | PT=206 | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SSRC of packet sender |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SSRC of media source |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Unique identifier 'L' 'N' 'T' 'F' |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Last Decoded Sequence Number | Last Received SeqNum Delta |D|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Figure 1
The fields V, P, FMT, PT, length and SSRC are defined in the RTP
specification Section 6.1 of [RFC4585], the respective meaning being
summarized below:
version (V): 2 bits
This field identifies the RTP version. The current version is 2
padding (P): 1 bit
If set, the padding bit indicates that the packet contains
additional padding octets at the end that are not part of the
control information but are included in the length field.
feedback message type (FMT): 5 bits
This field identifies the type of the FB message. It must have
the value 15, Application layer FB message
payload type (PT): 8 bits
This is the RTCP packet type that identifies the packet as being
an RTCP FB message. The value must be PT=206, Payload-specific
message (PSFB)
length: 16 bits
The length of this packet in 32-bit words minus one, including the
header and any padding. This is in line with the definition of
the length field used in RTCP sender and receiver reports
Section 6.4.1 of [RFC3550]
SSRC of packet sender: 32 bits
The synchronization source identifier for the originator of this
packet
SSRC of media source: 32 bits
The synchronization source identifier of the media source that
this piece of feedback information is related to.
Unique identifier: 32 bits
LNTF message is identified by ASCII characters ‘L’, ‘N’, ‘T’, ‘F’
(0x4C4E5446).
Last Decoded Sequence Number: 16 bits
RTP sequence number of last frame decoded, first packet sequence
number of the frame is chosen.
Last Received Sequence Number Delta: 15 bits
Delta between last received sequence number and last decoded
sequence number.
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Decodability flag (D): 1 bit
Decodability flag indicates if last packet received is part of the
frame which potentially can be decoded. D=true for key frame
without RTP sequence gaps in that keyframe or frame with all
dependencies decodable. Frame with sequence number gap has
D=false.
3. SDP Definitions
This section defines Session Description Protocol (SDP) signaling for
LNTF feedback that can be employed by applications.
rtcp-fb-syntax = "a=rtcp-fb:" rtcp-fb-pt SP rtcp-fb-val CRLF
rtcp-fb-pt = "*" ; wildcard: applies to all formats
= /fmt ; as defined in SDP
rtcp-fb-val =/ "lntf"
The literals of the above grammar have the following semantics:
Feedback type "lntf": This feedback type indicates loss notification.
4. IANA Considerations
Upon publication of this document as an RFC (if it is decided to
publish it), IANA is requested to register the string "lntf" in its
registry of "rtcp-fb" values in the SDP attribute registry group.
5. Security Considerations
This is not different from security considerations for any other RTCP
message.
6. Acknowledgements
The authors would like to thank Alfred Heggestad and Harald
Alvestrand for their reviews and valuable comments.
7. References
7.1. Normative References
[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>.
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[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey,
"Extended RTP Profile for Real-time Transport Control
Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585,
DOI 10.17487/RFC4585, July 2006,
<https://www.rfc-editor.org/info/rfc4585>.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,
July 2003, <https://www.rfc-editor.org/info/rfc3550>.
Author's Address
Shridhar Majali
Nvidia
2788 San Tomas Expressway
Santa Clara, CA 95051
United States of America
Email: smajali@nvidia.com
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