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MoQ relay for support of deadline-aware media transport
draft-ma-moq-relay-for-deadline-01

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This is an older version of an Internet-Draft whose latest revision state is "Active".
Authors Yong Cui , Chuan Ma , Yixin Liao , Hang Shi
Last updated 2023-09-11 (Latest revision 2023-03-12)
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draft-ma-moq-relay-for-deadline-01
Media Over QUIC                                                   Y. Cui
Internet-Draft                                                     C. Ma
Intended status: Standards Track                                 Y. Liao
Expires: 14 March 2024                               Tsinghua University
                                                                  H. Shi
                                                                  Huawei
                                                       11 September 2023

        MoQ relay for support of deadline-aware media transport
                   draft-ma-moq-relay-for-deadline-01

Abstract

   This draft specifies the behavior of MoQ relays for delivering media
   before the deadline to decrease end-to-end latency and save transport
   costs in media transmission.  To achieve this, the draft introduces
   deadline-aware actions prioritizing media streams with earlier
   deadlines, ensuring timely transmission while minimizing costs.

About This Document

   This note is to be removed before publishing as an RFC.

   Status information for this document may be found at
   https://datatracker.ietf.org/doc/draft-ma-moq-relay-for-deadline/.

   Source for this draft and an issue tracker can be found at
   https://github.com/STAR-Tsinghua/draft-moq-for-deadline.

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/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 14 March 2024.

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Copyright Notice

   Copyright (c) 2023 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 publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   3
   3.  Overview of Deadline-aware MoQ Architecture . . . . . . . . .   3
   4.  Deadline-aware Extension of MoQ . . . . . . . . . . . . . . .   5
     4.1.  Object Model: Block . . . . . . . . . . . . . . . . . . .   5
       4.1.1.  Metadata  . . . . . . . . . . . . . . . . . . . . . .   5
     4.2.  Deadline-aware Action . . . . . . . . . . . . . . . . . .   7
       4.2.1.  Deadline-aware Scheduling and Cancelling  . . . . . .   7
       4.2.2.  Deadline-aware Redundancy Coding  . . . . . . . . . .   7
   5.  Discussions . . . . . . . . . . . . . . . . . . . . . . . . .   7
     5.1.  Drop Notification . . . . . . . . . . . . . . . . . . . .   8
     5.2.  Data Buffer . . . . . . . . . . . . . . . . . . . . . . .   8
     5.3.  Clock Synchronization . . . . . . . . . . . . . . . . . .   8
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   Media over QUIC (MoQ) is a transport system designed to provide
   efficient media transport.  However, some use cases, such as live
   streaming, online meetings, and gaming, require the client to receive
   their media before a specific time, referred to as the 'deadline.'
   Exceeding the deadline results in dropped data, which can increase
   latency and negatively affect user experience.

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   To address this issue, a deliver-before-deadline transport service
   can be provided, which is the goal of the Deadline-aware Transport
   Protocol (DTP) proposed in [I-D.draft-shi-quic-dtp].  DTP leverages
   stream-level scheduling, active stream canceling, and redundancy
   coding to prioritize urgent data and prevent outdated data from
   blocking later data.

   This document proposes the behavior of deadline-aware actions on MoQ
   relay nodes, extending the basic MoQ relay to provide deliver-before-
   deadline transmission.  The relay design utilizes scheduling, data
   canceling, and redundancy coding to decrease queuing time, prevent
   unnecessary re-transmission of overdue data, and ultimately reduce
   end-to-end latency.  By providing better data delivery strategies,
   MoQ relays with deadline-aware actions can significantly enhance
   overall user experience in media transport.

2.  Conventions and Definitions

   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.

3.  Overview of Deadline-aware MoQ Architecture

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                         +===========================+
                         :             /=======\     :
                         :    Deadline :Block 1:     :
                         :     -aware  :DDL:xxx:     :
                         :   Canceling \=======/     :
               /-------\ :                 ^         :
               |Block 1| :                 :         :
               |DDL:xxx| :    +---------+  :         :
   +---------+ \-------/ :    |Deadline |  :         :
   |Publisher|-----------:--->| -aware  |==:         :
   +---------+ /-------\ :    |  Relay  |            :
               |Block 2| :    +---------+            :
               |DDL:yyy| :         |  /-----------\  :
               \-------/ :         |  | Block 2   |  :
                         :         |  | DDL:yyy   |  :
                         :         |  |-----------|  :
                         :         |  | Redundancy|  :
                         :         |  | Coding    |  :
                         :         v  \-----------/  :
                         :    +---------+            :
                         :    |Deadline |            :    +----------+
                         :    | -aware  |------------:--->|Subscriber|
                         :    |  Relay  |   /-------\:    +----------+
                         :    +---------+   |Block 2|:
                         :                  |DDL:yyy|:
                         :                  \-------/:
                         +===========================+
                         Deadline-aware MoQ Relay nodes

              Figure 1: The Architecture of Deadline-aware MoQ

   Figure 1 illustrates the fundamental architecture of Deadline-aware
   MoQ.  This architecture involves the extension of MoQ Publishers and
   Subscribers, which transport block-like data and add 'Deadline' as a
   component of Metadata within the header.  Relay nodes within this
   system are equipped with deadline-aware actions, including deadline-
   aware scheduling, canceling, and redundancy coding.  The relay may
   schedule the data blocks, cancel the overdue ones, and add redundancy
   code to avoid re-transmission.  The relays receive block-like data
   from the publisher, transfer between relays, make deadline-aware
   actions, and transmit it to the subscriber.

   The main focus of this draft is the extension of MoQ relays or the
   'Deadline-aware MoQ Relay.'  The Deadline-aware MoQ Relay SHOULD send
   data in a block-like style to enable deadline-aware actions.  A Block
   is a basic data unit in the MoQ system, like the Object in [MOQT].  A
   Block SHOULD contain, at a minimum, a Block ID field in the its
   header to distinguish it from others.

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   Depending on the MoQ implementation, the relay implementation may map
   the block transmission to different mechanisms of [QUIC], such as
   matching a Block to multiple QUIC datagrams or a single QUIC stream.
   Deadline-aware MoQ Relay SHOULD support various MoQ transport
   implementations.  When the relay receives data without any deadline-
   related information from the endpoint, it SHOULD forward it without
   utilizing any deadline-aware actions.

   The Deadline-aware MoQ Relay SHOULD support various relay topologies,
   as discussed in [I-D.draft-shi-moq-design-space-analysis-of-moq].
   Each relay topology may require a different MoQ architecture or
   implementation.  Therefore, the deadline-aware actions should act as
   a plugin that relays can quickly implement regardless of the topology
   and architecture.

4.  Deadline-aware Extension of MoQ

4.1.  Object Model: Block

   In this draft, we utilize the Block as the fundamental unit for data
   transmission.  A Block comprises two essential components: metadata
   and payload.  The payload of a Block is a sequence of bytes that
   carries the basic unit in media transport, such as a video frame.
   Meanwhile, a Block's metadata encompasses deadline-related
   information necessary for enabling Deadline-aware Actions(see
   Section 4.2).  It's worth noting that the metadata of a Block can
   remain unencrypted, whereas the payload of a Block SHOULD be
   encrypted.

   The Block serves as a model exclusively for data transmission within
   the MoQ framework.  Its purpose is to support the design principles
   of data units within MoQ, like the Object or the Group in MOQT.
   Importantly, it is crucial that the Block model does not supersede or
   alter the original data transmission model and should adapt to
   different designs in MoQ.

4.1.1.  Metadata

   For Deadline-aware MoQ Relay, data block metadata is required to
   enable deadline-aware actions.  Both the endpoint and the relay
   SHOULD attach the following metadata to each data block when using
   deadline-aware actions:

   *  block id: the identifier of each block

   *  size: the size of the payload in bytes

   *  priority: the block's relative priority in a single session

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   *  deadline: the expected completion time of the block.  The relay
      can drop overdue data.

   The relay SHOULD maintain track of the metadata of a block until the
   block misses its deadline.

   Additionally, if the endpoint does not offer metadata in the header
   of a data block, relays MAY implement other mechanisms to acquire and
   synchronize deadline-related metadata.

   e.x.  The specific methodology for encapsulating metadata needs to
   wait until the MoQ specification is standardized.

4.1.1.1.  Proirity

   TODO: At present, we set the priority as a relative value within a
   session.  However, the determination of object priority in MOQT
   remains a subject of ongoing discussion.  We are contemplating
   deferring this aspect until the Working Group reaches a consensus on
   the matter.

4.1.1.2.  Deadline

   Deadlines can be defined in two distinct manners: End-to-End Deadline
   and Hop-by-Hop Deadline.

   The End-to-End Deadline indicates the expected end-to-end delay of
   the application, beyond which a data block is considered obsolete.
   Conversely, the Hop-by-Hop Deadline represents the anticipated delay
   between two nodes within each hop.  It defines the tolerance for
   delay between relay nodes but does not convey the end-to-end latency
   requirement.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             Type (i)                        ...
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                   [Duration (i)/Timestamp (i)]              ...
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            Figure 2: A Prototype Design for the Deadline Field

   Figure 2 demonstrates a potential implementation of the Deadline
   field.  The Type field specifies the function of these two fields.
   The last bit of Type (0x1) indicates whether the Block uses Hop-by-
   Hop Deadline.  The least significant bit of Type (0x1) indicates
   whether the Block utilizes the Hop-by-Hop Deadline.  The second-to-

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   last bit of Type (0x2) indicates whether the Block employs a time
   duration as the maximum delay tolerance or a Unix timestamp as the
   expiration time for the data.  A Type value of 0x4 signifies that the
   Block has no Deadline requirement.

   The Deadline-aware MoQ Relay SHOULD implement stratergies to manage
   both End-to-End Deadline and Hop-by-Hop Deadline requirements.

4.2.  Deadline-aware Action

4.2.1.  Deadline-aware Scheduling and Cancelling

   When implementing deadline-aware actions, the Deadline-aware MoQ
   Relay can utilize the block metadata for scheduling blocks at the
   block-level.  The scheduler SHOULD minimize the total time of queuing
   and try to meet the deadline requirements of as many high-priority
   blocks as possible.

   If a block misses its deadline, Deadline-aware MoQ Relay MAY cancel
   it.  In such cases, the endpoints SHOULD be able to accept partially
   received data and not request for data re-transmission when a block
   is dropped.  Additionally, the relays MAY inform the endpoints and
   other relays about the cancellation of these blocks.

4.2.2.  Deadline-aware Redundancy Coding

   To improve reliability and decrease latency, Deadline-aware MoQ Relay
   MAY introduce redundancy data to blocks close to their deadline or
   transmitted over a network with a high loss rate.  This redundancy
   can help to prevent the need for re-transmission.  If the first relay
   adds redundancy coding to the data, other relay nodes in the network
   may benefit from it.

   When redundancy coding is enabled, at least two nodes SHOULD
   implement a pair of encoder and decoder that comply with the
   redundancy coding method.  The endpoint MAY also implement a
   redundancy encoder and decoder to utilize the relay's redundancy
   coding function fully.

   The first node that encodes the data with redundancy coding MUST add
   redundancy-related information to the metadata of the data block.

5.  Discussions

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5.1.  Drop Notification

   In situations where a data block is dropped by a relay due to a
   missed deadline or other reasons, sending an explicit dropping
   message to other relays and both endpoints can be helpful in
   notifying them of the data loss.  The dropping message may include
   information about the block, such as its ID and metadata.  However,
   the effective method for notifying other nodes and the decision
   regarding whether to send drop notifications to other relays are
   still pending discussion.  Broadcasting drop notifications could
   potentially lead to network flooding and requires further
   consideration.

5.2.  Data Buffer

   Further discussion is required to determine if the relay should
   implement a buffer for data blocks during forwarding and how such a
   buffer should be implemented.  This buffer may be used for re-
   transmission purposes and may benefit users with larger delay
   tolerance, among other potential uses.

5.3.  Clock Synchronization

   To enable accurate deadline-aware actions, it is recommended that all
   endpoints and relays perform clock synchronization.  Nevertheless,
   achieving high-precision clock synchronization over the Internet can
   be a formidable task, and it is also impractical to synchronize all
   devices in a single MoQ session.  The challenge then becomes how to
   carry out deadline-aware actions in the presence of imprecise clock
   accuracy, which is a critical question that needs to be addressed.

6.  Security Considerations

   Access to the metadata of the Deadline-aware MoQ Relay SHOULD be
   limited to selected relays.  The relay SHOULD NOT access the content
   of the data block.

7.  IANA Considerations

   This document has no IANA actions.

8.  References

8.1.  Normative References

   [I-D.draft-shi-quic-dtp]
              Cui, Y., Ma, C., Shi, H., Zheng, K., and W. Wang,
              "Deadline-aware Transport Protocol", Work in Progress,

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              Internet-Draft, draft-shi-quic-dtp-08, 28 July 2023,
              <https://datatracker.ietf.org/doc/html/draft-shi-quic-dtp-
              08>.

   [MOQT]     Curley, L., Pugin, K., Nandakumar, S., and V. Vasiliev,
              "Media over QUIC Transport", Work in Progress, Internet-
              Draft, draft-ietf-moq-transport-00, 5 July 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-moq-
              transport-00>.

   [QUIC]     Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
              Multiplexed and Secure Transport", RFC 9000,
              DOI 10.17487/RFC9000, May 2021,
              <https://www.rfc-editor.org/rfc/rfc9000>.

   [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/rfc/rfc2119>.

   [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/rfc/rfc8174>.

8.2.  Informative References

   [I-D.draft-shi-moq-design-space-analysis-of-moq]
              Shi, H., Cui, Y., and X. Yu, "Design Space Analysis of
              MoQ", Work in Progress, Internet-Draft, draft-shi-moq-
              design-space-analysis-of-moq-02, 11 September 2023,
              <https://datatracker.ietf.org/doc/html/draft-shi-moq-
              design-space-analysis-of-moq-02>.

Acknowledgments

   We sincerely thank Wei Cao for his advice and revisions to this
   draft.

Authors' Addresses

   Yong Cui
   Tsinghua University
   30 Shuangqing Rd
   Beijing
   China
   Email: cuiyong@tsinghua.edu.cn

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   Chuan Ma
   Tsinghua University
   30 Shuangqing Rd
   Beijing
   China
   Email: simonkorl0228@gmail.com

   Yixin Liao
   Tsinghua University
   30 Shuangqing Rd
   Beijing
   China
   Email: lyxceasar@outlook.com

   Hang Shi
   Huawei
   Email: shihang9@huawei.com

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