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. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. 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Majali Expires 5 December 2024 [Page 1] Internet-Draft RTCP LNTF June 2024 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| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Majali Expires 5 December 2024 [Page 2] Internet-Draft RTCP LNTF June 2024 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. Majali Expires 5 December 2024 [Page 3] Internet-Draft RTCP LNTF June 2024 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, . Majali Expires 5 December 2024 [Page 4] Internet-Draft RTCP LNTF June 2024 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [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, . [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, . Author's Address Shridhar Majali Nvidia 2788 San Tomas Expressway Santa Clara, CA 95051 United States of America Email: smajali@nvidia.com Majali Expires 5 December 2024 [Page 5]