| Internet-Draft | MoQ Use Cases and Requirements | November 2022 |
| Gruessing & Dawkins | Expires 11 May 2023 | [Page] |
This document describes use cases and requirements that guide the specification of a simple, low-latency media delivery solution for ingest and distribution, using either the QUIC protocol or WebTransport.¶
RFC Editor: please remove this section before publication¶
Source code and issues for this draft can be found at https://github.com/fiestajetsam/draft-gruessing-moq-requirements.¶
Discussion of this draft should take place on the IETF Media Over QUIC (MoQ) mailing list, at https://www.ietf.org/mailman/listinfo/moq.¶
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This document describes use cases and requirements that guide the specification of a simple, low-latency media delivery solution for ingest and distribution [MOQ-charter], using either the QUIC protocol [RFC9000] or WebTransport [WebTrans-charter].¶
This version of the document is intended to provide the MOQ working group with a starting point for work on the "Use Cases and Requirements document" milestone. The update implements the work plan described in [MOQ-ucr]. The authors intend to request MOQ working group adoption after IETF 115, so the working group can begin to focus on these topics in earnest.¶
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.¶
Our goal in this section is to understand the range of use cases that are in scope for "Media Over QUIC" [MOQ-charter].¶
For each use case in this section, we also describe¶
It is likely that we should add other characteristics, as we come to understand them.¶
The use cases described in this section have one particular attribute in common - the target latency for these cases are on the order of one or two RTTs. In order to meet those targets, it is not possible to rely on protocol mechanisms that require multiple RTTs to function effectively. For example,¶
This may help to explain why interactive use cases have typically relied on protocols such as RTP [RFC3550], which provide low-level control of packetization and transmission, and make no provision for retransmission.¶
| Attribute | Value |
|---|---|
| Senders/Receivers | One to One |
| Bi-directional | Yes |
| Latency | Ull-50 |
Where media is received, and user inputs are sent by the client. This may also include the client receiving other types of signaling, such as triggers for haptic feedback. This may also carry media from the client such as microphone audio for in-game chat with other players.¶
| Attribute | Value |
|---|---|
| Senders/Receivers | One to One |
| Bi-directional | Yes |
| Latency | Ull-50 |
Where media is received, and user inputs are sent by the client. Latency requirements with this use case are marginally different than the gaming use case. This may also include signalling and/or transmitting of files or devices connected to the user's computer.¶
| Attribute | Value |
|---|---|
| Senders/Receivers | Many to Many |
| Bi-directional | Yes |
| Latency | Ull-50 to Ull-200 |
Where media is both sent and received; This may include audio from both microphone(s) or other inputs, or may include "screen sharing" or inclusion of other content such as slide, document, or video presentation. This may be done as client/server, or peer to peer with a many to many relationship of both senders and receivers. The target for latency may be as large as Ull-200 for some media types such as audio, but other media types in this use case have much more stringent latency targets.¶
For the video conferencing/telephony use case, there can be additional scenarios where the audience greatly outnumbers the concurrent active participants, but any member of the audience could participate. As this has a much larger total number of participants - as many as Live Media Streaming Section 3.3.3, but with the bi-directionality of conferencing, this should be considered a "hybrid".¶
The use cases in this section, unlike the use cases described in Section 3.1, still have "humans in the loop", but these humans expect media to be "responsive", where the responsiveness is more on the order of 5 to 10 RTTs. This allows the use of protocol mechanisms that require more than one or two RTTs - as noted in Section 3.1, end-to-end recovery from packet loss and congestion avoidance are two such protocol mechanisms that can be used with Live Media.¶
To illustrate the difference, the responsiveness expected with videoconferencing is much greater than watching a video, even if the video is being produced "live" and sent to a platform for syndication and distribution.¶
| Attribute | Value |
|---|---|
| Senders/Receivers | One to One |
| Bi-directional | No |
| Latency | Ull-200 to Ultra-Low |
Where media is received from a source for onwards handling into a distribution platform. The media may comprise of multiple audio and/or video sources. Bitrates may either be static or set dynamically by signaling of connection information (bandwidth, latency) based on data sent by the receiver.¶
| Attribute | Value |
|---|---|
| Senders/Receivers | One to One |
| Bi-directional | No |
| Latency | Ull-200 to Ultra-Low |
Where media is sent onwards to another platform for further distribution. The media may be compressed down to a bitrate lower than source, but larger than final distribution output. Streams may be redundant with failover mechanisms in place.¶
| Attribute | Value |
|---|---|
| Senders/Receivers | One to Many |
| Bi-directional | No |
| Latency | Ull-200 to Ultra-Low |
Where media is received from a live broadcast or stream. This may comprise of multiple audio or video outputs with different codecs or bitrates. This may also include other types of media essence such as subtitles or timing signalling information (e.g. markers to indicate change of behaviour in client such as advertisement breaks). The use of "live rewind" where a window of media behind the live edge can be made available for clients to playback, either because the local player falls behind edge or because the viewer wishes to play back from a point in the past.¶
Our goal in this section is to understand the requirements that result from the use cases described in Section 3.¶
*Note: the initial high-level organization for this section is taken from Suhas Nandakumar's presentation, "Progressing MOQ" [Prog-MOQ], at the October 2022 MOQ virtual interim meeting, which was in turn taken from the MOQ working group charter [MOQ-charter]. We think this is a reasonable starting point. We won't be surprised to see the high-level structure change a bit as things develop, but we didn't want to have this section COMPLETELY blank when we request working group adoption.¶
TODO: Describe overall, high level requirements that we previously stated in earlier versions of this document.¶
Many of the use cases have bi-directional flows of media, with clients both sending and receiving media concurrently, thus the protocol should have a unified approach in connection negotiation and signalling to send and received media both at the start and ongoing in the lifetime of a session including describing when flow of media is unsupported (e.g. a live media server signalling it does not support receiving from a given client).¶
In the initiation of a session both client and server must perform negotiation in order to agree upon a variety of details before media can move in any direction:¶
Re-negotiation in an existing protocol should be supported to allow changes in what is being sent of received.¶
As multiple streams of media may be available for concurrent sending such as multiple camera views or audio tracks, a means of both identifying the technical properties of each resource (codec, bitrate, etc) as well as a useful identification for playback should be part of the protocol. A base level of optional metadata e.g. the known language of an audio track or name of participant's camera should be supported, but further extended metadata of the contents of the media or its ontology should not be supported.¶
Packaging of media describes how encapsulation of media to carry the raw media will work. There are at a high level two approaches to this:¶
The working group must agree on which approach should be taken to the packaging of media, taking into consideration the various technical trade offs that each provide.¶
End-to-end security describes the use of encryption of the media stream(s) to provide confidentiality in the presence of unauthorized intermediates or observers and prevent or restrict ability to decrypt the media without authorization. Generally, there are three aspects of end-to-end media security:¶
**Note: "Node-to-node" refers to a path segment connecting two MOQ nodes, that makes up part of the end-to-end path between the MOQ sender and ultimate MOQ receiver.¶
The working group must agree on a number of details here, and perhaps the first question is whether the MOQ protocol makes any provision for "node-to-node" media security, or simply treats authorized transcoders as MOQ receivers. If that's the decision all MOQ media security is "sender-to-receiver", but some "ends" may not be either senders or ultimate receivers, from a certain point of view.¶
This document makes no requests of IANA.¶
As this document is intended to guide discussion and consensus, it introduces no security considerations of its own.¶
The authors would like to thank several authors of individual drafts that fed into the "Media Over QUIC" charter process:¶
We would also like to thank Suhas Nandakumar for his presentation, "Progressing MOQ" [Prog-MOQ], at the October 2022 MOQ virtual interim meeting. We used his outline as a starting point for the Requirements section (Section 4).¶
James Gruessing would also like to thank Francesco Illy and Nicholas Book for their part in providing the needed motivation.¶