RTP over QUIC (RoQ)
draft-ietf-avtcore-rtp-over-quic-12
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Expired".
|
|
|---|---|---|---|
| Authors | Mathis Engelbart , Joerg Ott , Spencer Dawkins | ||
| Last updated | 2024-10-21 (Latest revision 2024-07-08) | ||
| Replaces | draft-engelbart-rtp-over-quic | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Associated WG milestone |
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||
| Document shepherd | Dr. Bernard D. Aboba | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | bernarda@microsoft.com |
draft-ietf-avtcore-rtp-over-quic-12
Audio/Video Transport Core Maintenance M. Engelbart
Internet-Draft J. Ott
Intended status: Experimental Technical University of Munich
Expires: 24 April 2025 S. Dawkins
Tencent America LLC
21 October 2024
RTP over QUIC (RoQ)
draft-ietf-avtcore-rtp-over-quic-12
Abstract
This document specifies a minimal mapping for encapsulating Real-time
Transport Protocol (RTP) and RTP Control Protocol (RTCP) packets
within the QUIC protocol. This mapping is called RTP over QUIC
(RoQ).
This document also discusses how to leverage state that is already
available from the QUIC implementation in the endpoints, in order to
reduce the need to exchange RTCP packets, and describes different
options for implementing congestion control and rate adaptation for
RTP without relying on RTCP feedback.
Discussion Venues
This note is to be removed before publishing as an RFC.
Discussion of this document takes place on the Audio/Video Transport
Core Maintenance Working Group mailing list (avt@ietf.org), which is
archived at https://mailarchive.ietf.org/arch/browse/avt/.
Source for this draft and an issue tracker can be found at
https://github.com/mengelbart/rtp-over-quic-draft.
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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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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 24 April 2025.
Copyright Notice
Copyright (c) 2024 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
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Background . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. What's in Scope for this Document . . . . . . . . . . . . 5
1.3. What's Out of Scope for this Document . . . . . . . . . . 6
2. Terminology and Notation . . . . . . . . . . . . . . . . . . 6
3. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 9
3.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 10
3.1.1. "Always-On" Transport-level Authentication and
Encryption . . . . . . . . . . . . . . . . . . . . . 10
3.1.2. "Always-On" Internet-Safe Congestion Control . . . . 11
3.1.3. RTP Rate Adaptation Based on QUIC Feedback . . . . . 12
3.1.4. Path MTU Discovery and RTP Media Coalescence . . . . 12
3.1.5. Multiplexing RTP, RTCP, and Non-RTP Flows on a Single
QUIC Connection . . . . . . . . . . . . . . . . . . . 13
3.1.6. Exploiting Multiple Paths . . . . . . . . . . . . . . 13
3.1.7. Exploiting New QUIC Capabilities . . . . . . . . . . 14
3.2. RTP with QUIC Streams, QUIC DATAGRAMs, and a Mixture of
Both . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.3. Supported RTP Topologies . . . . . . . . . . . . . . . . 16
4. Connection Establishment and Application-Layer Protocol
Negotiation . . . . . . . . . . . . . . . . . . . . . . . 19
4.1. Draft version identification . . . . . . . . . . . . . . 19
5. Encapsulation . . . . . . . . . . . . . . . . . . . . . . . . 19
5.1. Multiplexing . . . . . . . . . . . . . . . . . . . . . . 20
5.2. QUIC Streams . . . . . . . . . . . . . . . . . . . . . . 21
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5.2.1. Stream Encapsulation . . . . . . . . . . . . . . . . 22
5.2.2. Media Frame Cancellation . . . . . . . . . . . . . . 23
5.2.3. Flow control and MAX_STREAMS . . . . . . . . . . . . 24
5.3. QUIC DATAGRAMs . . . . . . . . . . . . . . . . . . . . . 25
6. Connection Shutdown . . . . . . . . . . . . . . . . . . . . . 26
7. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 26
8. Congestion Control and Rate Adaptation . . . . . . . . . . . 27
8.1. Congestion Control at the Transport Layer . . . . . . . . 28
8.2. Rate Adaptation at the Application Layer . . . . . . . . 29
8.3. Sharing QUIC connections . . . . . . . . . . . . . . . . 30
9. Guidance on Choosing QUIC Streams, QUIC DATAGRAMs, or a
Mixture . . . . . . . . . . . . . . . . . . . . . . . . . 31
9.1. RTP Considerations . . . . . . . . . . . . . . . . . . . 31
9.2. RTCP Considerations . . . . . . . . . . . . . . . . . . . 32
9.2.1. RTCP over QUIC datagrams . . . . . . . . . . . . . . 32
9.2.2. RTCP over QUIC streams . . . . . . . . . . . . . . . 33
9.2.3. Mixed operations . . . . . . . . . . . . . . . . . . 33
10. Replacing RTCP and RTP Header Extensions with QUIC
Feedback . . . . . . . . . . . . . . . . . . . . . . . . 34
10.1. RoQ Datagrams . . . . . . . . . . . . . . . . . . . . . 35
10.2. RoQ Streams . . . . . . . . . . . . . . . . . . . . . . 35
10.3. Multihop Topologies . . . . . . . . . . . . . . . . . . 36
10.4. Feedback Mappings . . . . . . . . . . . . . . . . . . . 36
10.4.1. Negative Acknowledgments ("NACK") . . . . . . . . . 37
10.4.2. ECN Feedback ("ECN") . . . . . . . . . . . . . . . . 37
10.4.3. Goodbye Packets ("BYE") . . . . . . . . . . . . . . 37
11. RoQ-QUIC and RoQ-RTP API Considerations . . . . . . . . . . . 37
12. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 39
12.1. Impact of Connection Migration . . . . . . . . . . . . . 39
12.2. 0-RTT and Early Data considerations . . . . . . . . . . 39
12.2.1. Effect of 0-RTT Rejection for RoQ using Early
Data . . . . . . . . . . . . . . . . . . . . . . . . 40
12.2.2. Effect of 0-RTT Replay Attacks for RoQ using Early
Data . . . . . . . . . . . . . . . . . . . . . . . . 40
12.3. Coalescing RTP packets in a single QUIC packet . . . . . 41
13. Directions for Future Work . . . . . . . . . . . . . . . . . 42
13.1. Future Work Resulting from Implementation and Deployment
Experience . . . . . . . . . . . . . . . . . . . . . . . 42
13.2. Future Work Resulting from New QUIC Extensions . . . . . 43
14. Implementation Status . . . . . . . . . . . . . . . . . . . . 43
14.1. mengelbart/roq . . . . . . . . . . . . . . . . . . . . . 44
14.2. bbc/gst-roq . . . . . . . . . . . . . . . . . . . . . . 45
14.3. mengelbart/rtp-over-quic . . . . . . . . . . . . . . . . 45
15. Security Considerations . . . . . . . . . . . . . . . . . . . 46
16. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 46
16.1. Registration of a RoQ Identification String . . . . . . 47
16.2. RoQ Error Codes Registry . . . . . . . . . . . . . . . . 47
17. References . . . . . . . . . . . . . . . . . . . . . . . . . 48
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17.1. Normative References . . . . . . . . . . . . . . . . . . 48
17.2. Informative References . . . . . . . . . . . . . . . . . 51
Appendix A. List of optional QUIC Extensions . . . . . . . . . . 61
Appendix B. Considered RTCP Packet Types and RTP Header
Extensions . . . . . . . . . . . . . . . . . . . . . . . 62
B.1. RTCP Control Packet Types . . . . . . . . . . . . . . . . 63
B.2. RTCP XR Block Type . . . . . . . . . . . . . . . . . . . 64
B.3. FMT Values for RTP Feedback (RTPFB) Payload Types . . . . 68
B.4. FMT Values for Payload-Specific Feedback (PSFB) Payload
Types . . . . . . . . . . . . . . . . . . . . . . . . . . 70
B.5. RTP Header extensions . . . . . . . . . . . . . . . . . . 71
B.5.1. RTP Compact Header Extensions . . . . . . . . . . . . 71
B.5.2. RTP SDES Compact Header Extensions . . . . . . . . . 73
B.6. Examples . . . . . . . . . . . . . . . . . . . . . . . . 74
B.6.1. Mapping QUIC Feedback to RTCP Receiver Reports
("RR") . . . . . . . . . . . . . . . . . . . . . . . 74
B.6.2. Congestion Control Feedback ("CCFB") . . . . . . . . 75
B.6.3. Extended Report ("XR") . . . . . . . . . . . . . . . 75
B.6.4. Application Layer Repair and other Control
Messages . . . . . . . . . . . . . . . . . . . . . . 75
Appendix C. Header overhead considerations . . . . . . . . . . . 76
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 77
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 78
1. Introduction
This document specifies a minimal mapping for encapsulating Real-time
Transport Protocol (RTP) [RFC3550] and RTP Control Protocol (RTCP)
[RFC3550] packets within the QUIC protocol ([RFC9000]). This mapping
is called RTP over QUIC (RoQ).
This document also discusses how to leverage state that is already
available from the QUIC implementation in the endpoints, in order to
reduce the need to exchange RTCP packets, and describes different
options for implementing congestion control and rate adaptation for
RTP without relying on RTCP feedback.
1.1. Background
The Real-time Transport Protocol (RTP) [RFC3550] is generally used to
carry real-time media for conversational media sessions, such as
video conferences, across the Internet. Since RTP requires real-time
delivery and is tolerant to packet losses, the default underlying
transport protocol has historically been UDP [RFC0768], but a large
variety of other underlying transport protocols have been defined for
various reasons (e.g., securing media exchange, or providing a
fallback when UDP is blocked along a network path). This document
describes RTP over QUIC, providing one more underlying transport
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protocol. The reasons for using QUIC as an underlying transport
protocol are given in Section 3.1.
This document describes an application usage of QUIC ([RFC9308]). As
a baseline, the document does not expect more than a standard QUIC
implementation as defined in [RFC8999], [RFC9000], [RFC9001], and
[RFC9002], providing a secure end-to-end transport. Beyond this
baseline, real-time applications can benefit from QUIC extensions
such as unreliable DATAGRAMs [RFC9221], which provides additional
desirable properties for real-time traffic (e.g., no unnecessary
retransmissions, avoiding head-of-line blocking).
1.2. What's in Scope for this Document
This document focuses on providing a secure encapsulation of RTP and
RTCP packets for transmission over QUIC. The expected usage is
wherever RTP is used to carry media packets, allowing QUIC in place
of other underlying transport protocols. We expect RoQ to be used in
contexts where a signaling protocol is used to announce or negotiate
a media encapsulation for RTP and the associated transport parameters
(such as IP address, port number). RoQ does not provide a stand-
alone media transport capability, because at a minimum, media
transport parameters would need to be statically configured.
RoQ can be used in many of the point-to-point and multi-endpoint RTP
topologies described in [RFC7667], and can be used with both
decentralized and centralized control topologies. When RoQ is used
in a decentralized topology, RTP packets are exchanged directly
between ultimate RTP endpoints. When RoQ is used in a centralized
topology, RTP packets transit one or more middleboxes which might
function as mixers or translators between ultimate RTP endpoints.
RoQ can also be used in RTP client-server-style settings, e.g., when
talking to a conference server as described in RFC 7667 ([RFC7667]),
or, if RoQ is used to replace RTSP ([RFC7826]), to a media server.
Moreover, this document describes how a QUIC implementation and its
API can be extended to improve efficiency of the RoQ protocol
operation.
RoQ does not limit the usage of RTP Audio Video Profiles (AVP)
([RFC3551]), or any RTP-based mechanisms, although it might render
some of them unnecessary, e.g., Secure Real-Time Transport Protocol
(SRTP) ([RFC3711]) might not be needed, because end-to-end security
is already provided by QUIC, and double encryption by QUIC and by
SRTP might have more costs than benefits. Nor does RoQ limit the use
of RTCP-based mechanisms, although some information or functions
provided by using RTCP mechanisms might also be available from the
underlying QUIC implementation.
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RoQ supports multiplexing multiple RTP-based media streams within a
single QUIC connection and thus using a single (destination IP
address, destination port number, source IP address, source port
number, protocol) 5-tuple. We note that multiple independent QUIC
connections can be established in parallel using the same 5-tuple.,
e.g. to carry different media channels. These connections would be
logically independent of one another.
1.3. What's Out of Scope for this Document
This document does not enhance QUIC for real-time media or define a
replacement for, or evolution of, RTP. Work to map other media
transport protocols to QUIC is under way elsewhere in the IETF.
This document does not specify RoQ for point-to-multipoint
applications, because QUIC itself is not defined for multicast
operation. The scope of this document is limited to unicast RTP,
even though nothing would prevent its use in multicast setups if
future QUIC extensions support multicast.
RoQ does not define new congestion control and rate adaptation
algorithms for use with RTP media, and does not specify the use of
particular congestion control and rate adaptation algorithms for use
with RTP media. However, Section 8 discusses multiple ways that
congestion control and rate adaptation could be performed at the QUIC
and/or at the RTP layer, and Section 11 describes information
available at the QUIC layer that could be exposed via an API for the
benefit of RTP layer implementation.
RoQ does not define prioritization mechanisms when handling different
media as those would be dependent on the media themselves and their
relationships. Prioritization is left to the application using RoQ.
This document does not cover signaling for session setup. SDP for
RoQ is defined in separate documents such as
[I-D.draft-dawkins-avtcore-sdp-rtp-quic], and can be carried in any
signaling protocol that can carry SDP, including the Session
Initiation Protocol (SIP) ([RFC3261]), Real-Time Protocols for
Browser-Based Applications (RTCWeb) ([RFC8825]), or WebRTC-HTTP
Ingestion Protocol (WHIP) ([I-D.draft-ietf-wish-whip]).
2. Terminology and Notation
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.
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*Note to the Reader:* [RFC3550] actually describes two closely-
related protocols - the RTP Data Transfer Protocol Section 5 of
[RFC3550], and the RTP Control Protocol Section 6 of [RFC3550].
In this document, the term "RTP" refers to the combination of RTP
Data Transfer Protocol and RTP Control Protocol, because the
distinction isn't relevant for encapsulation, and the term "RTCP"
always refers to the RTP Control Protocol.
*Note to the Reader:* the meaning of the terms "congestion
avoidance", "congestion control" and "rate adaptation" in the IETF
community have evolved over the decades since "slow start" and
"congestion avoidance" were added as mandatory to implement in
TCP, in Section 4.2.2.15 of [RFC1122]. Historically, "congestion
control" usually referred to "achieving network stability"
([VJMK88]), by protecting the network from senders who continue to
transmit packets that exceed the ability of the network to carry
them, even after packet loss occurs (called "congestion
collapse").
Modern general-purpose "congestion control" algorithms have moved
beyond avoiding congestion collapse, and work to avoid
"bufferbloat", which causes increasing round-trip delays, as
described in Section 8.2.
"Rate adaptation" more commonly refers to strategies intended to
guide senders on when to send "the next packet", so that one-way
delays along the network path remain minimal.
When RTP runs over QUIC, as described in this document, QUIC is
performing congestion control, and the RTP application is
responsible for performing rate adaptation.
In this document, these terms are used with the meanings listed
below, with the recognition that not all the references in this
document use these terms in the same way.
The following terms are used in this document:
Bandwidth Estimation: An algorithm to estimate the available
bandwidth of a link in a network. Such an estimation can be used
for rate adaptation, i.e., adapt the rate at which an application
transmits data.
Congestion Control: A mechanism to limit the aggregate amount of
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data that has been sent over a path to a receiver but has not been
acknowledged by the receiver. This prevents a sender from
overwhelming the capacity of a path between a sender and a
receiver, which might cause intermediaries on the path to drop
packets before they arrive at the receiver.
Datagram: The term "datagram" is ambiguous. Without a qualifier,
"datagram" could refer to a UDP packet, or a QUIC DATAGRAM frame,
as defined in QUIC's unreliable DATAGRAM extension [RFC9221], or
an RTP packet encapsulated in UDP, or an RTP packet capsulated in
QUIC DATAGRAM frame. This document uses the uppercase "DATAGRAM"
to refer to a QUIC DATAGRAM frame and the term RoQ datagram as a
short form of "RTP packet encapsulated in a QUIC DATAGRAM frame".
If not explicitly qualified, the term "datagram" in this document
refers to an RTP packet, and the uppercase "DATAGRAM" refers to a
QUIC DATAGRAM frame. This document also uses the term "RoQ datagram"
as a short form of "RTP packet encapsulated in a QUIC DATAGRAM
frame".
Endpoint: A QUIC client or QUIC server that participates in an RoQ
session. "A RoQ endpoint" is used in this document where that
seems clearer than "an endpoint" without qualification.
Early data: Application data carried in a QUIC 0-RTT packet payload,
as defined in [RFC9000]. In this document, the early data would
be an RTP packet.
Frame: A QUIC frame as defined in [RFC9000].
Peer: The term "peer" is ambiguous, and without a qualifier could be
understood to refer to an RTP endpoint, a RoQ endpoint, or a QUIC
endpoint. In this document, a "peer" is "the other RoQ endpoint
that a RoQ endpoint is communicating with", and does not have
anything to do with "peer-to-peer" operation versus "client-
server" operation.
Rate Adaptation: An application-level mechanism that adjusts the
sending rate of an application in response to changing path
conditions. For example, an application sending video might
respond to indications of congestion by adjusting the resolution
of the video it is sending.
Receiver: An endpoint that receives media in RTP packets and might
send or receive RTCP packets.
Sender: An endpoint that sends media in RTP packets and might send
or receive RTCP packets.
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Stream: The term "stream" is ambiguous. Without a qualifier,
"stream" could refer to a QUIC stream, as defined in [RFC9000], a
series of media samples, or a series of RTP packets. If not
explicitly qualified, the term "stream" in this document refers to
a QUIC stream and the term "STREAM" refers to a single QUIC STREAM
frame. This document also uses the term "RTP stream" or "RTCP
streams" as a short form of "a series of RTP packets" or "a series
of RTCP packets", the term "RoQ stream" as a short form of "one or
more RTP packets encapsulated in QUIC streams" and the term "media
stream" as a short form of "a series of one or more media
samples".
Packet diagrams in this document use the format defined in
Section 1.3 of [RFC9000] to illustrate the order and size of fields.
3. Protocol Overview
This document introduces a mapping of the Real-time Transport
Protocol (RTP) to the QUIC transport protocol. RoQ allows the use of
both QUIC streams and QUIC DATAGRAMs to transport real-time data, and
thus, if RTP packets are to be sent over QUIC DATAGRAMs, the QUIC
implementation MUST support QUIC's DATAGRAM extension.
[RFC3550] specifies that RTP sessions need to be transmitted on
different transport addresses to allow multiplexing between them.
RoQ uses a different approach to leverage the advantages of QUIC
connections without managing a separate QUIC connection per RTP
session. [RFC9221] does not provide demultiplexing between different
flows on DATAGRAMs but suggests that an application implement a
demultiplexing mechanism if required. An example of such a mechanism
would be flow identifiers prepended to each DATAGRAM frame as
described in Section 2.1 of [I-D.draft-ietf-masque-h3-datagram]. RoQ
uses a flow identifier to replace the network address and port number
to multiplex many RTP sessions over the same QUIC connection.
An RTP application is responsible for determining what to send in an
encoded media stream, and how to send that encoded media stream
within a targeted bitrate.
This document does not mandate how an application determines what to
send in an encoded media stream, because decisions about what to send
within a targeted bitrate, and how to adapt to changes in the
targeted bitrate, can depend on the application and on the codec in
use. For example, adjusting quantization in response to changing
network conditions might work well in many cases, but if what's being
shared is video that includes text, maintaining readability is
important.
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As of this writing, the IETF has produced two Experimental-track
congestion control documents for real-time media, Network-Assisted
Dynamic Adaptation (NADA) [RFC8698] and Self-Clocked Rate Adaptation
for Multimedia (SCReAM) [RFC8298]. These congestion control
algorithms use feedback about the network's performance to calculate
target bitrates. When these algorithms are used with RTP, the
necessary feedback is generated at the receiver and sent back to the
sender via RTCP.
Since QUIC itself collects some metrics about the network's
performance, these QUIC metrics can be used to generate the required
feedback at the sender-side and provide it to the congestion control
algorithm to avoid the additional overhead of the RTCP stream. This
is discussed in more detail in Section 10.
3.1. Motivation
From time to time, someone asks the reasonable question, "why would
anyone implement and deploy RoQ"? This reasonable question deserves
a better answer than "because we can". Upon reflection, the
following motivations seem useful to state.
The motivations in this section are in no particular order, and this
reflects the reality that not all implementers and deployers would
agree on "the most important motivations".
3.1.1. "Always-On" Transport-level Authentication and Encryption
Although application-level mechanisms to encrypt RTP payloads have
existed since the introduction of the Secure Real-time Transport
Protocol (SRTP) [RFC3711], the additional encryption of RTP header
fields and contributing sources has only been defined recently (in
Cryptex [RFC9335]), and both SRTP and Cryptex are optional
capabilities for RTP.
This is in sharp contrast to "always-on" transport-level encryption
in the QUIC protocol, using Transport Layer Security (TLS 1.3) as
described in [RFC9001]. QUIC implementations always authenticate the
entirety of each packet, and encrypt as much of each packet as is
practical, even switching from "long headers", which expose the QUIC
header fields needed to establish a connection, to "short headers",
which only expose the absolute minimum QUIC header fields needed to
identify an existing connection to the receiver, so that the QUIC
payload is presented to the correct QUIC application [RFC8999].
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3.1.2. "Always-On" Internet-Safe Congestion Control
When RTP is carried directly over UDP, as is commonly done, the
underlying UDP protocol provides multiplexing using UDP ports, but no
transport services beyond multiplexing are provided to the
application. All congestion control behavior is up to the RTP
application itself, and if anything goes wrong with the application
and this condition results in an RTP sender failing to recognize that
it is contributing to path congestion, the "worst case" response is
to invoke the RTP "circuit breaker" procedures [RFC8083]. These
procedures result in "ceasing transmission", as described in
Section 4.5 of [RFC8083]. Because RTCP-based circuit breakers only
detect long-lived congestion, a response based on these mechanisms
will not happen quickly.
In contrast, when RTP is carried over QUIC, QUIC implementations
maintain their own estimates of key transport parameters needed to
detect and respond to possible congestion, and these estimates are
independent of any measurements RTP senders and receivers are
maintaining. The result is that even if an RTP sender attempts to
"send" in the presence of persistent path congestion, QUIC congestion
control procedures (for example, the procedures defined in [RFC9002])
will cause the RTP packets to be buffered while QUIC responds to
detected packet loss. This happens without RTP senders taking any
action, but the RTP sender has no control over this QUIC mechanism.
Moreover, when a single QUIC connection is used to multiplex both RTP
and non-RTP packets as described in Section 3.1.5, the shared QUIC
connection will still be Internet-safe, with no coordination
required.
While QUIC's response to congestion ensures that RoQ will be
"Internet-safe", from the network's perspective, it is helpful to
remember that a QUIC sender responds to detected congestion by
delaying packets that are already available to send, to give the path
to the QUIC receiver time to recover from congestion.
* If the QUIC connection encapsulates RTP, this means that some RTP
packets will be delayed, arriving at the receiver later than a
consumer of the RTP flow might prefer.
* If the QUIC connection also encapsulates RTCP, this means that
these RTCP messages will also be delayed, and will not be sent in
a timely manner. This delay will impact RTT measurements using
RTCP and can interfere with a sender's ability to stabilize rate
control and achieve audio/video synchronization.
In summary,
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* Timely RTP stream-level rate adaptation will give a better user
experience by minimizing endpoint queuing delays and packet loss,
but
* in the presence of packet loss, QUIC connection-level congestion
control will respond more quickly and possibly more smoothly to
the end of congestion than RTP "circuit breakers".
3.1.3. RTP Rate Adaptation Based on QUIC Feedback
When RTP is carried directly over UDP, RTP makes use of a large
number of RTP-specific feedback mechanisms because there is no other
way to receive feedback. Some of these mechanisms are specific to
the type of media RTP is sending, but others can be mapped from
underlying QUIC implementations that are using this feedback to
perform congestion control for any QUIC connection, regardless of the
application reflected in the payload. This is described in (much)
more detail in Section 8 on rate adaptation, and in Section 10 on
replacing RTCP and RTP header extensions with QUIC feedback.
One word of caution is in order - RTP implementations might rely on
at least some minimal periodic RTCP feedback, in order to determine
that an RTP flow is still active, and is not causing sustained
congestion (as described in [RFC8083]. Because the necessary
"periodicity" is measured in seconds, the impact of this "duplicate"
feedback on path bandwidth utilization is likely close to zero.
3.1.4. Path MTU Discovery and RTP Media Coalescence
The minimum Path MTU (Maximum Transmission Unit) supported by
conformant QUIC implementations is 1200 bytes [RFC9000]. In
addition, QUIC implementations allow senders to use either DPLPMTUD
([RFC8899]) or PMTUD ([RFC1191], [RFC8201]) to determine the actual
Path MTU size that the receiver can accept, and that the path between
sender and receiver can support. The actual Path MTU can be larger
than the Minimum Path MTU.
This is especially useful in certain conferencing topologies, where
otherwise senders would have no choice but to use the lowest Path MTU
for all conference participants. Even in point-to-point RTP
sessions, this also allows senders to piggyback audio media in the
same UDP packet as video media, for example, and also allows QUIC
receivers to piggyback QUIC ACK frames on any QUIC packets being
transmitted in the other direction.
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3.1.5. Multiplexing RTP, RTCP, and Non-RTP Flows on a Single QUIC
Connection
This document defines a flow identifier for multiplexing multiple RTP
and RTCP ports on the same QUIC connection to conserve ports,
especially at NATs and firewalls. Section 5.1 describes the
multiplexing in more detail. Future extensions could further build
on the flow identifier to multiplex RTP with other protocols on the
same connection, as long as these protocols can co-exist with RTP
without interfering with the ability of this connection to carry
real-time media.
3.1.6. Exploiting Multiple Paths
Although there is much interest in multiplexing flows on a single
QUIC connection as described in Section 3.1.5, QUIC also provides the
capability of establishing and validating multiple paths for a single
QUIC connection as described in Section 9 of [RFC9000]. Once
multiple paths have been validated, a sender can migrate from one
path to another with no additional signaling, allowing an endpoint to
move from one endpoint address to another without interruption, as
long as only a single path is in active use at any point in time.
Connection migration could be desirable for a number of reasons, but
to give one example, this allows a QUIC connection to survive address
changes due to a middlebox allocating a new outgoing port, or even a
new outgoing IP address.
The Multipath Extension for QUIC [I-D.draft-ietf-quic-multipath]
would allow the application to actively use two or more paths
simultaneously, but in all other respects, this functionality is the
same as QUIC connection migration.
A sender can use these capabilities to more effectively exploit
multiple paths between sender and receiver with no action required
from the application, even if these paths have different path
characteristics. Examples of these different path characteristics
include senders handling paths differently if one path has higher
available bandwidth and the other has lower one-way latency, or if
one is a more costly cellular path and the other is a less costly
WiFi path.
Some of these differences can be detected by QUIC itself, while other
differences must be described to QUIC based on policy, etc. Possible
RTP implementation strategies for path selection and utilization are
not discussed in this document. Path scheduling APIs to let
applications control these mechanisms are a topic for future research
and might need further specification in future documents.
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3.1.7. Exploiting New QUIC Capabilities
The first version of the QUIC protocol described in [RFC9000] has
been completed, but extensions to QUIC are still under active
development in the IETF. Because of this, using QUIC as a transport
for a mature protocol like RTP allows developers to exploit new
transport capabilities as they become available.
3.2. RTP with QUIC Streams, QUIC DATAGRAMs, and a Mixture of Both
This document describes the use of QUIC streams and DATAGRAMs as RTP
encapsulations but does not take a position on which encapsulation an
application ought to use. Indeed, an application can use both QUIC
streams and DATAGRAM encapsulations on the same QUIC connection. The
choice of encapsulation is left to the application developer, but it
is worth noting differences that are relevant when making this
choice.
QUIC [RFC9000] was initially designed to carry HTTP [RFC9114] in QUIC
streams, and QUIC streams provide what HTTP application developers
need - for example, a stateful, connection-oriented, flow-controlled,
reliable, ordered stream of bytes to an application. QUIC streams
can be multiplexed over a single QUIC connection, using stream IDs to
demultiplex incoming messages.
QUIC DATAGRAMs [RFC9221] were developed as a QUIC extension, intended
to support applications that do not need reliable delivery of
application data. This extension defines two DATAGRAM frame types
(one including a length field, the other not including a length
field), and these DATAGRAM frames can co-exist with QUIC streams
within a single QUIC connection, sharing the connection's
cryptographic and authentication context, and congestion controller
context.
There is no default relative priority between DATAGRAM frames with
respect to each other, and there is no default priority between
DATAGRAM frames and QUIC STREAM frames. QUIC implementations can
present an API to allow applications to assign relative priorities
within a QUIC connection, but this is not mandated by the standard
and might not be present in all implementations.
Because DATAGRAMs are an extension to QUIC, they inherit a great deal
of functionality from QUIC (much of which is described in
Section 3.1); so much so that it is easier to explain what DATAGRAMs
do NOT inherit.
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* DATAGRAM frames do not provide any explicit flow control
signaling. This means that a QUIC receiver might not be able to
commit the necessary resources to process incoming frames, but the
purpose for DATAGRAM frames is to carry application-level
information that can be lost and will not be retransmitted.
* DATAGRAM frames cannot be fragmented. They are limited in size by
the max_datagram_frame_size transport parameter, and further
limited by the max_udp_payload_size transport parameter and the
Path MTU between endpoints.
* DATAGRAM frames belong to a QUIC connection as a whole. There is
no QUIC-level way to multiplex/demultiplex DATAGRAM frames within
a single QUIC connection. Any multiplexing identifiers must be
added, interpreted, and removed by an application, and they will
be sent as part of the payload of the DATAGRAM frame itself.
DATAGRAM frames do inherit the QUIC connection's congestion
controller. This means that although there is no frame-level flow
control, DATAGRAM frames can be delayed until the controller allows
them to be sent or dropped (with an optional notification to the
sending application). Implementations can also delay sending
DATAGRAM frames to maintain consistent packet pacing (as described in
Section 7.7 of [RFC9002]), and can allow an application to specify a
sending expiration time, but these capabilities are not mandated by
the standard and might not be present in all implementations.
Because DATAGRAMs are an extension to QUIC, a RoQ endpoint cannot
assume that its peer supports this extension. The RoQ endpoint might
discover that its peer does not support DATAGRAMs in one of two ways:
* as part of the signaling process to set up QUIC connections, or
* during negotiation of the DATAGRAM extension during the QUIC
handshake.
When either of these situations happen, the RoQ endpoint needs to
make a decision about what to do next.
* If the use of DATAGRAMs was critical for the application, the
endpoint can simply close the QUIC connection, allowing someone or
something to correct this mismatch, so that DATAGRAMs can be used.
* If the use of DATAGRAMs was not critical for the application, the
endpoint can negotiate the use of QUIC streams instead.
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3.3. Supported RTP Topologies
RoQ supports only some of the RTP topologies described in [RFC7667].
Most notably, due to QUIC [RFC9000] being a purely IP unicast
protocol at the time of writing, RoQ cannot be used as a transport
protocol for any of the paths that rely on IP multicast in several
multicast topologies (e.g., _Topo-ASM_, _Topo-SSM_, _Topo-SSM-RAMS_).
Some "multicast topologies" can include IP unicast paths (e.g.,
_Topo-SSM_, _Topo-SSM-RAMS_). In these cases, the unicast paths can
use RoQ.
RTP supports different types of translators and mixers. Whenever a
middlebox needs to access the content of QUIC frames (e.g., _Topo-
PtP-Translator_, _Topo-PtP-Relay_, _Topo-Trn-Translator_, _Topo-
Media-Translator_), the QUIC connection will be terminated at that
middlebox.
RoQ streams (see Section 5.2) can support much larger RTP packet
sizes than other transport protocols such as UDP can, which can lead
to problems when transport translators which translate from RoQ to
RTP over a different transport protocol. A similar problem can occur
if a translator needs to translate from RTP over UDP to RoQ over
DATAGRAMs, where the max_datagram_frame_size of a QUIC DATAGRAM can
be smaller than the MTU of a UDP datagram. In both cases, the
translator might need to rewrite the RTP packets to fit into the
smaller MTU of the other protocol. Such a translator might need
codec-specific knowledge to packetize the payload of the incoming RTP
packets in smaller RTP packets.
Additional details are provided in the following table.
+=======================================+============+========+==========+
|RFC 7667 Section |Shortcut |RTP over|Comments |
| |Name |QUIC? | |
+=======================================+============+========+==========+
|3.1 |Topo-Point- |yes | |
|(https://datatracker.ietf.org/doc/html/|to-Point | | |
|rfc7667#section-3.1) | | | |
+---------------------------------------+------------+--------+----------+
|3.2.1.1 |Topo-PtP- |yes |Note-NAT |
|(https://datatracker.ietf.org/doc/html/|Relay | | |
|rfc7667#section-3.2.1.1) | | | |
+---------------------------------------+------------+--------+----------+
|3.2.1.2 |Topo-Trn- |yes |Note-MTU |
|(https://datatracker.ietf.org/doc/html/|Translator | |Note-SEC |
|rfc7667#section-3.2.1.2) | | | |
+---------------------------------------+------------+--------+----------+
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|3.2.1.3 |Topo-Media- |yes |Note-MTU |
|(https://datatracker.ietf.org/doc/html/|Translator | | |
|rfc7667#section-3.2.1.3) | | | |
+---------------------------------------+------------+--------+----------+
|3.2.2 |Topo-Back- |yes |Note-SEC |
|(https://datatracker.ietf.org/doc/html/|To-Back | |Note-MTU |
|rfc7667#section-3.2.2) | | |Note-MCast|
+---------------------------------------+------------+--------+----------+
|3.3.1 |Topo-ASM |no |Note-MCast|
|(https://datatracker.ietf.org/doc/html/| | | |
|rfc7667#section-3.3.1) | | | |
+---------------------------------------+------------+--------+----------+
|3.3.2 |Topo-SSM |partly |Note-MCast|
|(https://datatracker.ietf.org/doc/html/| | |Note- |
|rfc7667#section-3.3.2) | | |UCast- |
| | | |MCast |
+---------------------------------------+------------+--------+----------+
|3.3.3 |Topo-SSM- |partly |Note-MCast|
|(https://datatracker.ietf.org/doc/html/|RAMS | |Note- |
|rfc7667#section-3.3.3) | | |MCast- |
| | | |UCast |
+---------------------------------------+------------+--------+----------+
|3.4 |Topo-Mesh |yes |Note-MCast|
|(https://datatracker.ietf.org/doc/html/| | | |
|rfc7667#section-3.4) | | | |
+---------------------------------------+------------+--------+----------+
|3.5.1 |Topo-PtM- |possibly|Note-MCast|
|(https://datatracker.ietf.org/doc/html/|Trn- | |Note-MTU |
|rfc7667#section-3.5.1) |Translator | |Note-Topo-|
| | | |PtM-Trn- |
| | | |Translator|
+---------------------------------------+------------+--------+----------+
|3.6 |Topo-Mixer |possibly|Note-MCast|
|(https://datatracker.ietf.org/doc/html/| | |Note-Topo-|
|rfc7667#section-3.6) | | |Mixer |
+---------------------------------------+------------+--------+----------+
|3.6.1 |Media- |partly |Note-Topo-|
|(https://datatracker.ietf.org/doc/html/|Mixing-Mixer| |Mixer |
|rfc7667#section-3.6.1) | | | |
+---------------------------------------+------------+--------+----------+
|3.6.2 |Media- |partly |Note-Topo-|
|(https://datatracker.ietf.org/doc/html/|Switching- | |Mixer |
|rfc7667#section-3.6.2) |Mixer | | |
+---------------------------------------+------------+--------+----------+
|3.7 |Selective |yes |Note-MCast|
|(https://datatracker.ietf.org/doc/html/|Forwarding | |Note-Topo-|
|rfc7667#section-3.7) |Middlebox | |Mixer |
+---------------------------------------+------------+--------+----------+
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|3.8 |Topo-Video- |yes |Note-MTU |
|(https://datatracker.ietf.org/doc/html/|switch-MCU | |Note-MCast|
|rfc7667#section-3.8) | | |Note-Topo-|
| | | |Mixer |
+---------------------------------------+------------+--------+----------+
|3.9 |Topo-RTCP- |yes |Note-MTU |
|(https://datatracker.ietf.org/doc/html/|terminating-| |Note-MCast|
|rfc7667#section-3.9) |MCU | |Note-Topo-|
| | | |Mixer |
+---------------------------------------+------------+--------+----------+
|3.10 |Topo-Split- |yes |Note-MCast|
|(https://datatracker.ietf.org/doc/html/|Terminal | | |
|rfc7667#section-3.10) | | | |
+---------------------------------------+------------+--------+----------+
|3.11 |Topo- |Possibly|Note-Warn,|
|(https://datatracker.ietf.org/doc/html/|Asymmetric | |Note- |
|rfc7667#section-3.11) | | |MCast, |
| | | |Note-MTU |
+---------------------------------------+------------+--------+----------+
Table 1
Note-NAT: Not supported, because QUIC [RFC9000] does not support NAT
traversal.
Note-MTU: Supported, but might require MTU adaptation.
Note-Sec: Note that because RoQ uses QUIC as its underlying
transport, and QUIC authenticates the entirety of each packet and
encrypts as much of each packet as is practical, RoQ secures both
RTP headers and RTP payloads, while other RTP transports do not.
Section 15 describes strategies to prevent the inadvertent
disclosure of RTP sessions to unintended third parties.
Note-MCast: Not supported, because QUIC [RFC9000] does not support
IP multicast.
Note-UCast-MCast: The topology refers to a _Distribution Source_,
which receives and relays RTP from a number of different media
senders via unicast before relaying it to the receivers via
multicast. QUIC can be used between the senders and the
_Distribution Source_.
Note-MCast-UCast: The topology refers to a _Burst Source_ or
_Retransmission Source_, which retransmits RTP to receivers via
unicast. QUIC can be used between the _Retransmission Source_ and
the receivers.
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Note-Topo-PtM-Trn-Translator: Supported for IP unicast paths between
RTP sources and translators.
Note-Topo-Mixer: Supported for IP unicast paths between RTP senders
and mixers.
Note-Warn: Quote from [RFC7667]: _This topology is so problematic
and it is so easy to get the RTCP processing wrong, that it is NOT
RECOMMENDED to implement this topology._
4. Connection Establishment and Application-Layer Protocol Negotiation
QUIC requires the use of Application-Layer Protocol Negotiation
(ALPN) [RFC7301] tokens during connection setup. RoQ uses "roq" as
the ALPN token, included as part of the TLS handshake (see also
Section 16).
Note that the "roq" ALPN token is not tied to a specific RTP profile,
even though the RTP profile could be considered part of the
application usage. This allows different RTP sessions, which might
use different RTP profiles, to be carried within the same QUIC
connection.
4.1. Draft version identification
*RFC Editor's note:* Please remove this section prior to
publication of a final version of this document.
RoQ uses the ALPN token "roq" to identify itself during QUIC
connection setup.
Only implementations of the final, published RFC can identify
themselves as "roq". Until such an RFC exists, implementations MUST
NOT identify themselves using this string.
Implementations of draft versions of the protocol MUST add the string
"-" and the corresponding draft number to the identifier. For
example, draft-ietf-avtcore-rtp-over-quic-09 is identified using the
string "roq-09".
Non-compatible experiments that are based on these draft versions
MUST append the string "-" and an experiment name to the identifier.
5. Encapsulation
This section describes the encapsulation of RTP packets in QUIC.
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QUIC supports two transport methods: QUIC streams [RFC9000] and
DATAGRAMs [RFC9221]. This document specifies mappings of RTP to both
transport modes. Senders MAY combine both modes by sending some RTP
packets over the same or different QUIC streams and others in
DATAGRAMs.
Section 5.1 introduces a multiplexing mechanism that supports
multiplexing multiple RTP sessions and RTCP. Section 5.2 and
Section 5.3 explain the specifics of mapping RTP to QUIC streams and
DATAGRAMs, respectively.
5.1. Multiplexing
RoQ uses flow identifiers to multiplex different RTP streams on a
single QUIC connection. A flow identifier is a QUIC variable-length
integer as described in Section 16 of [RFC9000]. Each flow
identifier is associated with an RTP stream.
In a QUIC connection using the ALPN token defined in Section 4, every
DATAGRAM and every QUIC stream MUST start with a flow identifier. An
endpoint MUST NOT send any data in a DATAGRAM or stream that is not
associated with the flow identifier which started the DATAGRAM or
stream.
RTP packets of different RTP sessions MUST use distinct flow
identifiers. If endpoints wish to send multiple types of media in a
single RTP session, they can do so by following the guidance
specified in [RFC8860].
A single RTP session can be associated with one or two flow
identifiers. Thus, it is possible to send RTP and RTCP packets
belonging to the same session using different flow identifiers. RTP
and RTCP packets of a single RTP session can use the same flow
identifier (following the procedures defined in [RFC5761]), or they
can use different flow identifiers.
Endpoints need to associate flow identifiers with RTP streams.
Depending on the context of the application, the association can be
statically configured, signaled using an out-of-band signaling
mechanism (e.g., SDP), or applications might be able to identify the
stream based on the RTP packets sent on the stream (e.g., by
inspecting the payload type).
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If an endpoint receives a flow identifier that it cannot associate
with an RTP stream, the endpoint MAY close the connection using the
ROQ_UNKNOWN_FLOW_ID error code. Closing the connection can be a
valid response if it is not expected that out of band signaling is
still ongoing and the application cannot handle unknown flow
identifiers.
If the association of flow identifiers with RTP streams depends on
out-of-band signaling, the signaling mechanism SHOULD be completed
before the exchange of RTP packets using the new flow identifiers
starts.
In cases where it cannot be guaranteed that signaling is completed
before RTP packets are transmitted, streams or DATAGRAMs with a given
flow identifer can arrive before the signaling finished. In that
case, an endpoint cannot associate the stream or DATAGRAM with the
corresponding RTP stream. The endpoint can buffer streams and
DATAGRAMs using an unknown flow identifier until they can be
associated with the corresponding RTP stream. To avoid resource
exhaustion, the buffering endpoint MUST limit the number of streams
and DATAGRAMs to buffer. If the number of buffered streams exceeds
the limit on buffered streams, the endpoint MUST send a STOP_SENDING
with the error code ROQ_UNKNOWN_FLOW_ID. It is an implementation's
choice on which stream to send STOP_SENDING. If the number of
buffered DATAGRAMs exceeds the limit on buffered DATAGRAMs, the
endpoint MUST drop a DATAGRAM. It is an implementation's choice
which DATAGRAMs to drop.
Flow identifiers introduce some overhead in addition to the header
overhead of RTP and QUIC. QUIC variable-length integers require
between one and eight bytes depending on the number expressed. Thus,
using low numbers as session identifiers first will minimize this
additional overhead.
5.2. QUIC Streams
To send RTP packets over QUIC streams, a sender MUST open at least
one new unidirectional QUIC stream. RoQ uses unidirectional streams,
because there is no synchronous relationship between sent and
received RTP packets. An endpoint that receives a bidirectional
stream with a flow identifier that is associated with an RTP stream,
MUST stop reading from the stream and send a CONNECTION_CLOSE frame
with the frame type set to APPLICATION_ERROR and the error code set
to ROQ_STREAM_CREATION_ERROR.
The underlying QUIC implementation might be acting as either a QUIC
client or QUIC server, so the unidirectional QUIC stream can be
either client-initiated or server-initiated, as described in
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Section 2.1 of [RFC9000], depending on the role. The QUIC
implementation's role is not controlled by RoQ, and can be negotiated
using a separate signaling protocol.
A RoQ sender can open new QUIC streams for different RTP packets
using the same flow identifier. This allows RoQ senders to use QUIC
streams while avoiding head-of-line blocking.
Because a sender can continue sending on a stream with a lower stream
identifier after starting packet transmission on a stream with a
higher stream identifier, a RoQ receiver MUST be prepared to receive
RoQ packets on any number of QUIC streams (subject to its limit on
parallel open streams) and MUST NOT make assumptions about which RTP
sequence numbers are carried in any particular stream.
5.2.1. Stream Encapsulation
Figure 1 shows the encapsulation format for RoQ Streams.
Payload {
Flow Identifier (i),
RTP Payload(..) ...,
}
Figure 1: RoQ Streams Payload Format
Flow Identifier: Flow identifier to demultiplex different data flows
on the same QUIC connection.
RTP Payload: Contains the RTP payload; see Figure 2
The payload in a QUIC stream starts with the flow identifier followed
by one or more RTP payloads. All RTP payloads sent on a stream MUST
belong to the RTP session with the same flow identifier.
Each payload begins with a length field indicating the length of the
RTP packet, followed by the packet itself, see Figure 2.
RTP Payload {
Length(i),
RTP Packet(..),
}
Figure 2: RTP payload for QUIC streams
Length: A QUIC variable length integer (see Section 16 of [RFC9000])
describing the length of the following RTP packets in bytes.
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RTP Packet: The RTP packet to transmit.
5.2.2. Media Frame Cancellation
QUIC uses RESET_STREAM and STOP_SENDING frames to terminate the
sending part of a stream and to request termination of an incoming
stream by the sending peer respectively.
A RoQ receiver that is no longer interested in reading a certain
portion of the media stream can signal this to the sending peer using
a STOP_SENDING frame.
If a RoQ sender discovers that a packet is no longer needed and knows
that the packet has not yet been successfully and completely
transmitted, it can use RESET_STREAM to tell the RoQ receiver that
the RoQ sender is discarding the packet.
In both cases, the error code of the RESET_STREAM frame or the
STOP_SENDING frame MUST be set to ROQ_FRAME_CANCELLED.
STOP_SENDING is not a request to the sender to stop sending RTP
media, only an indication that a RoQ receiver stopped reading the
QUIC stream being used to carry that RTP media. This can mean that
the RoQ receiver is no longer able to use the media frames being
received because they are "too old". A sender with additional media
frames to send can continue sending them on another QUIC stream.
Alternatively, new media frames can be sent as DATAGRAMs (see
Section 5.3). In either case, a RoQ sender resuming operation after
receiving STOP_SENDING can continue starting with the newest media
frames available for sending. This allows a RoQ receiver to "fast
forward" to media frames that are "new enough" to be used.
Any media frame that has already been sent on the QUIC stream that
received the STOP_SENDING frame, MUST NOT be sent again on the new
QUIC stream(s) or DATAGRAMs.
Note that an RTP receiver cannot request a reset of a particular
media frame because the sending QUIC implementation might already
have sent data for one or more following media frames on the same
stream. In that case, STOP_SENDING and the resulting RESET_STREAM
would also discard the following media frames and thus lead to
unintentionally skipping one or more media frames.
A translator that translates between two endpoints, both connected
via QUIC, MUST forward RESET_STREAM frames received from one end to
the other unless it forwards the RTP packets encapsulated in
DATAGRAMs.
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QUIC implementations will fragment large RTP packets into smaller
QUIC STREAM frames. The data carried in these QUIC STREAM frames is
transmitted reliably and is delivered to the receiving application in
order, so that a receiving application can read a complete RTP packet
from the stream as long as the stream is not closed with a
RESET_STREAM frame. No retransmission has to be implemented by the
application since data that was carried in QUIC frames that were lost
in transit is retransmitted by QUIC.
5.2.3. Flow control and MAX_STREAMS
In order to permit QUIC streams to open, a RoQ sender MUST configure
non-zero minimum values for the number of permitted streams and the
initial stream flow-control window. These minimum values control the
number of parallel, or simultaneously active, RTP flows. Endpoints
that excessively restrict the number of streams or the flow-control
window of these streams will increase the chance that the sending
peer reaches the limit early and becomes blocked.
Opening new streams for new packets can implicitly limit the number
of packets concurrently in transit because the QUIC receiver provides
an upper bound of parallel streams, which it can update using QUIC
MAX_STREAMS frames. The number of packets that can be transmitted
concurrently depends on several factors, such as the number of RTP
streams within a QUIC connection, the bitrate of the media streams,
and the maximum acceptable transmission delay of a given packet.
Receivers are responsible for providing senders enough credit to open
new streams for new packets at any time.
As an example, consider a conference scenario with 20 participants.
Each participant receives audio and video streams of every other
participant from a central RTP middlebox. If the sender opens a new
QUIC stream for every frame at 30 frames per second video and 50
frames per second audio, it will open 1520 new QUIC streams per
second. A receiver must provide at least that many credits for
opening new unidirectional streams to the RTP middlebox every second.
In addition, the receiver ought to also consider the requirements of
RTCP streams. These considerations can also be relevant when
implementing signaling since it can be necessary to inform the
receiver about how many stream credits it will have to provide to the
sending peer, and how rapidly it must provide these stream credits.
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5.3. QUIC DATAGRAMs
Senders can also transmit RTP packets in QUIC DATAGRAMs, using a QUIC
extension described in [RFC9221]. DATAGRAMs can only be used if the
use of the DATAGRAM extension was successfully negotiated during the
QUIC handshake. If the DATAGRAM extension was negotiated using a
signaling protocol, but was not also negotiated during the resulting
QUIC handshake, an endpoint can close the connection with the
ROQ_EXPECTATION_UNMET error code.
DATAGRAMs preserve application frame boundaries. Thus, a single RTP
packet can be mapped to a single DATAGRAM without additional framing.
Because QUIC DATAGRAMs cannot be IP-fragmented (Section 5 of
[RFC9221]), senders need to consider the header overhead associated
with DATAGRAMs, and ensure that the RTP packets, including their
payloads, flow identifier, QUIC, and IP headers, will fit into the
Path MTU.
Figure 3 shows the encapsulation format for RoQ Datagrams.
Payload {
Flow Identifier (i),
RTP Packet (..),
}
Figure 3: RoQ Datagram Payload Format
Flow Identifier: Flow identifier to demultiplex different data flows
on the same QUIC connection.
RTP Packet: The RTP packet to transmit.
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RoQ senders need to be aware that QUIC uses the concept of QUIC
frames, and QUIC connections use different kinds of QUIC frames to
carry different application and control data types. A single QUIC
packet can contain more than one QUIC frame, including, for example,
QUIC STREAM frames or DATAGRAM frames carrying application data and
ACK frames carrying QUIC acknowledgments, as long as the overall size
fits into the MTU. One implication is that the number of packets a
QUIC stack transmits depends on whether it can fit ACK and DATAGRAM
frames in the same QUIC packet. Suppose the application creates many
DATAGRAM frames that fill up the QUIC packet. In that case, the QUIC
stack would need to create additional packets for ACK frames, and
possibly other control frames. The additional overhead could, in
some cases, be reduced if the application creates smaller RTP
packets, such that the resulting DATAGRAM frame can fit into a QUIC
packet that can also carry ACK frames. Another implication is that
multiple RTP packets in either QUIC streams or QUIC DATAGRAMs might
be encapsulated in a single QUIC packet, which is discussed in more
detail in Section 12.3.
Since DATAGRAMs are not retransmitted on loss (see also Section 10.4
for loss signaling), if an application is using DATAGRAMs and wishes
to retransmit lost RTP packets, the application has to carry out that
retransmission. RTP retransmissions can be done in the same RTP
session or in a different RTP session [RFC4588] and the flow
identifier MUST be set to the flow identifier of the RTP session in
which the retransmission happens.
6. Connection Shutdown
Either endpoint can close the connection for any of a variety of
reasons. If one of the endpoints wants to close the RoQ connection,
the endpoint can use a QUIC CONNECTION_CLOSE frame with one of the
error codes defined in Section 7.
7. Error Handling
The following error codes are defined for use when abruptly
terminating RoQ streams, aborting reading of RoQ streams, or
immediately closing RoQ connections.
ROQ_NO_ERROR (0x00): No error. This is used when the connection or
stream needs to be closed, but there is no error to signal.
ROQ_GENERAL_ERROR (0x01): An error that does not match a more
specific error code occurred.
ROQ_INTERNAL_ERROR (0x02): An internal error has occurred in the RoQ
stack.
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ROQ_PACKET_ERROR (0x03): Invalid payload format, e.g., length does
not match packet, invalid flow id encoding, non-RTP on RTP-flow
ID, etc.
ROQ_STREAM_CREATION_ERROR (0x04): The endpoint detected that its
peer created a stream that violates the ROQ protocol, e.g., a
bidirectional stream, for sending RTP packets.
ROQ_FRAME_CANCELLED (0x05): A receiving endpoint is using
STOP_SENDING on the current stream to request new frames be sent
on new streams. Similarly, a sender notifies a receiver that
retransmissions of a frame were stopped using RESET_STREAM and new
frames will be sent on new streams.
ROQ_UNKNOWN_FLOW_ID (0x06): An endpoint was unable to handle a flow
identifier, e.g., because it was not signaled or because the
endpoint does not support multiplexing using arbitrary flow
identifiers.
ROQ_EXPECTATION_UNMET (0x07): RoQ out-of-band signaling set
expectations for QUIC transport, but the resulting QUIC connection
would not meet those expectations.
8. Congestion Control and Rate Adaptation
Like any other application on the Internet, RoQ applications need a
mechanism to perform congestion control to avoid overloading the
network. QUIC is a congestion-controlled transport protocol. RTP
does not mandate a single congestion control mechanism. RTP suggests
that the RTP profile defines congestion control according to the
expected properties of the application's environment.
This document discusses aspects of transport level congestion control
in Section 8.1 and application layer rate control in Section 8.2. It
does not mandate any specific congestion control algorithm for QUIC
or rate adaptation algorithm for RTP.
This document also gives guidance about avoiding problems with
_nested_ congestion controllers in Section 8.2.
This document also discusses congestion control implications of using
shared or multiple separate QUIC connections to send and receive
multiple independent RTP streams in Section 8.3.
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8.1. Congestion Control at the Transport Layer
QUIC is a congestion-controlled transport protocol. Senders are
required to employ some form of congestion control. The default
congestion control specified for QUIC in [RFC9002] is similar to TCP
NewReno [RFC6582], but senders are free to choose any congestion
control algorithm as long as they follow the guidelines specified in
Section 3 of [RFC8085], and QUIC implementors make use of this
freedom.
Congestion control mechanisms are often implemented at the transport
layer of the protocol stack, but can also be implemented at the
application layer.
A congestion control mechanism could respond to actual packet loss
(detected by timeouts), or to impending packet loss (signaled by
mechanisms such as Explicit Congestion Notification [RFC3168]).
For real-time traffic, it is best that the QUIC implementation uses a
congestion controller that aims at keeping queues at intermediary
network elements, and thus latency, as short as possible. Delay-
based congestion control algorithms might use, for example, an
increasing one-way delay as a signal of impending congestion, and
adjust the sending rate to prevent continued increases in one-way
delay.
A wide variety of congestion control algorithms for real-time media
have been developed (for example, "Google Congestion Controller"
[I-D.draft-ietf-rmcat-gcc]). The IETF has defined two such
algorithms in Experimental RFCs (SCReAM [RFC8298] and NADA
[RFC8698]). These algorithms for RTP are specifically tailored for
real-time transmission at low latencies, but the guidance in this
section would apply to any congestion control algorithm that meets
the requirements described in "Congestion Control Requirements for
Interactive Real-Time Media" [RFC8836].
Some low latency congestion control algorithms depend on detailed
arrival time feedback to estimate the current one-way delay between
sender and receiver, which is unavailable in QUIC [RFC9000] without
extensions. QUIC implementations can use an extension to add this
information to QUIC as described in Appendix A. In addition to these
dedicated real-time media congestion-control algorithms, QUIC
implementations could support the Low Latency, Low Loss, and Scalable
Throughput (L4S) Internet Service [RFC9330], which limits growth in
round-trip delays that result from increasing queuing delays. While
L4S does not rely on a QUIC protocol extension, L4S does rely on
support from network devices along the path from sender to receiver.
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The application needs a mechanism to query the available bandwidth to
adapt media codec configurations. If the employed congestion
controller of the QUIC connection keeps an estimate of the available
bandwidth, it could also expose an API to the application to query
the current estimate. If the congestion controller cannot provide a
current bandwidth estimate to the application, the sender can
implement an alternative bandwidth estimation at the application
layer as described in Section 8.2.
It is assumed that the congestion controller in use provides a pacing
mechanism to determine when a packet can be sent to avoid bursts and
minimize variation in inter-packet arrival times. The currently
proposed congestion control algorithms for real-time communications
(e.g., SCReAM and NADA) provide such pacing mechanisms, and the QUIC
exemplary congestion control algorithm (Section 7.7 of [RFC9002])
recommends pacing for senders.
8.2. Rate Adaptation at the Application Layer
RTP itself does not specify a congestion control algorithm, but
[RFC8888] defines an RTCP feedback message intended to enable rate
adaptation for interactive real-time traffic using RTP, and
successful rate adaptation will accomplish congestion control as
well.
If an application cannot access a bandwidth estimation from the QUIC
layer, the application can alternatively implement a bandwidth
estimation algorithm at the application layer. Congestion control
algorithms for real-time media such as GCC
[I-D.draft-ietf-rmcat-gcc], NADA [RFC8698], and SCReAM [RFC8298]
expose a target bitrate to dynamically reconfigure media codecs to
produce media at the rate of the observed available bandwidth.
Applications can use the same bandwidth estimation to adapt their
rate when using QUIC. However, running an additional congestion
control algorithm at the application layer can have unintended
effects due to the interaction of two _nested_ congestion
controllers.
If an RTP application paces its media transmission at a rate that
does not saturate path bandwidth, more heavy-handed congestion
control mechanisms (drastic reductions in the sending rate when loss
is detected, with much slower increases when losses are no longer
being detected) ought to rarely come into play. If an RTP
application chooses RoQ as its transport, sends enough media to
saturate the available path bandwidth, and does not adapt its sending
rate, these drastic measures will be required to avoid sustained or
oscillating congestion along the path.
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Thus, applications are advised to only use the bandwidth estimation
without running the complete congestion control algorithm at the
application layer before passing data to the QUIC layer.
The bandwidth estimation algorithm typically needs some feedback on
the transmission performance. This feedback can be collected via
RTCP or following the guidelines in Section 10 and Section 11.
8.3. Sharing QUIC connections
Two endpoints can establish channels to exchange more than one type
of data simultaneously. The channels can be intended to carry real-
time RTP data or other non-real-time data. This can be realized in
different ways.
* One straightforward solution is to establish multiple QUIC
connections, one for each channel, whether the channel is used for
real-time media or non-real-time data.
* Alternatively, all real-time channels are mapped to one QUIC
connection, while a separate QUIC connection is created for the
non-real-time channels.
* A third option is to multiplex all channels, whether real-time or
non-real-time, in a single QUIC connection via an extension to
RoQ.
In the first two cases, the congestion controllers can be chosen to
match the demands of the respective channels and the different QUIC
connections will compete for the same resources in the network. No
local prioritization of data across the different (types of) channels
would be necessary.
Although it is possible to multiplex (all or a subset of) real-time
and non-real-time channels onto a single, shared QUIC connection by
extending RoQ, the underlying QUIC implementation will likely use the
same congestion controller for all channels in the shared QUIC
connection. For this reason, applications multiplexing real-time and
non-real-time channels in one connection will need to implement some
form of prioritization or bandwidth allocation for the different
channels.
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9. Guidance on Choosing QUIC Streams, QUIC DATAGRAMs, or a Mixture
As noted in Section 3.2, this document does not take a position on
using QUIC streams, QUIC DATAGRAMs, or a mixture of both, for any
particular RoQ use case or application. It does seem useful to
include observations that might guide implementers who will need to
make choices about that.
9.1. RTP Considerations
One implementation goal might be to minimize processing overhead, for
applications that are migrating from RTP over UDP to RoQ. These
applications don't rely on any transport protocol behaviors beyond
UDP, which can be described as "IP plus multiplexing". The
implementers might be motivated by one or more of the advantages of
encapsulating RTP in QUIC that are described in Section 3.1, but they
do not need any of the advantages that would apply when encapsulating
RTP in QUIC streams. For these applications, simply placing each RTP
packet in a QUIC DATAGRAM frame when it becomes available would be
sufficient, using no QUIC streams at all.
Another implementation goal might be to prioritize specific types of
video frames over other types. For these applications, placing each
type of video frame in a separate QUIC stream would allow the RoQ
receiver to focus on the most important video frames more easily.
This also allows the implementer to rely on QUIC's "byte stream"
abstraction, freeing the application from dealing with MTU size
restrictions, in contrast to the need to fit RTP packets into QUIC
DATAGRAMs. The application might use QUIC streams for all of the RTP
packets carried over this specific QUIC connection, with no QUIC
DATAGRAMs at all.
Some applications might have implementation goals that don't fit
neatly into "QUIC streams only" or "QUIC DATAGRAMs only" categories.
For example, another implementation goal might be to use QUIC streams
to carry RTP video frames, but to use QUIC DATAGRAMs to carry RTP
audio frames, which are typically much smaller. Because humans tend
to tolerate inconsistent behavior in video better than inconsistent
behavior in audio, the application might add Forward Error Correction
[RFC6363] to RTP audio packets and encapsulate the result in QUIC
DATAGRAMs, while encapsulating RTP video packets in QUIC streams.
As noted in Section 5.1, all RoQ streams and RoQ datagrams begin with
a flow identifier. This allows a RoQ sender to begin by
encapsulating related RTP packets in QUIC streams and then switch to
carrying them in QUIC DATAGRAMs, or vice versa. RoQ receivers need
to be prepared to accept any valid RTP packet with a given flow
identifier, whether it started by being encapsulated in QUIC streams
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or in QUIC DATAGRAMs, and RoQ receivers need to be prepared to accept
RTP flows that switch from QUIC stream encapsulation to QUIC
DATAGRAMs, or vice versa.
Because QUIC provides a capability to migrate connections for various
reasons, including recovering from a path failure (Section 9 of
[RFC9000]), when a QUIC connection migrates, a RoQ sender has the
opportunity to revisit decisions about which RTP packets are
encapsulated in QUIC streams, and which RTP packets are encapsulated
in QUIC DATAGRAMs. Again, RoQ receivers need to be prepared for this
eventuality.
9.2. RTCP Considerations
RTCP was originally defined to be used with UDP, which implies (1)
the only buffering present would be at the IP interface level, so
that transmission timing is largely under the control of the
application, and (2) that the overhead, _avg_rtcp_size_, used to
compute the RTCP transmission interval could be deterministically
computed by adding the IP and UDP headers. Both change when carrying
RTCP over QUIC and they change in different ways when using QUIC
streams vs. QUIC datagrams.
9.2.1. RTCP over QUIC datagrams
When sending RTCP packets in QUIC datagrams this implies that a
packet may not be immediately transmitted as it is subject to queuing
and multiplexing with RTP packets and subject to QUIC congestion
control. This means that a sending timestamp added to an RTCP
packet, e.g., in an SR packet, may differ in unforeseeable ways from
the actual time when the packet gets sent into the network while
these are usually fairly close to each other for RTP-over-UDP.
Effectively, we have a application sending timestamp _t_a_ and the
network transmission timestamp _t_n_. Applications just have to be
aware that RTCP does not measure the network level RTT but rather the
application layer RTT.
Moreover, the true overhead per RTCP packet cannot easily be
determined: this is because, in addition to adding the IP and UDP
headers, the QUIC (short) header and the QUIC datagram frame header
are to be considered but their sizes vary and it is unknown which
other frames may be sent along in the same UDP packet. Any lower
bound that can be determined could be affected by the version of QUIC
being used. An example estimation of the overhead including IP, UDP
and QUIC headers is given in Appendix C.
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It is thus suggested that application developers recognize that per-
RTCP packet overhead will always be an estimate, and include IP, UDP,
QUIC, and DATAGRAM header sizes as a conservative heuristic. While
this value may not be precisely accurate, it follows the example of
RTP over UDP in [RFC3550], which includes the RTP and UDP header
sizes, and adding the additional QUIC and DATAGRAM header sizes
avoids the immediate problem of significantly understating
avg_rtcp_size, resulting in an underestimate of the cost of sending
additional RTCP reports.
9.2.2. RTCP over QUIC streams
The above considerations from Section 9.2.1 get even more complex
when transmitting RTCP reliably over QUIC streams: it is unknown if
(and how many) retransmissions occurred.
For RTT computations, again, this means that the application must
consider that it observes the application layer RTT including
retransmissions, where retransmissions also contribute to the
observed jitter.
For overhead computation, retransmissions are not explicitly
considered nor is the multiplexing with other streams.
To keep the complexity under control, it is again suggested that
application developers recognize that per-RTCP packet overhead will
always be an estimate, and these estimates should include plausible
values for IP, UDP, QUIC, and QUIC STREAM frame header sizes. While
this value may not be precisely accurate, it follows the example of
RoQ over DATAGRAMs in Section 9.2.1}, and again avoids the immediate
problem of significantly understating avg_rtcp_size, resulting in an
underestimate of the cost of sending additional RTCP reports.
9.2.3. Mixed operations
As noted in Section 9, applications may use QUIC streams, QUIC
DATAGRAMs, or a mixture, and this extends to choices for RTP and
RTCP. While applications may, in principle, mix sending RTP and RTCP
via QUIC streams and via QUIC DATAGRAMs, doing so has unforeseeable
implications on timing and reordering and overhead.
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Using the same QUIC primitives for both RTP and RTCP when
transporting a single media stream will be safer than mixing QUIC
primitives - for example, using QUIC streams to carry RTP media
payloads and QUIC DATAGRAMs to carry RTCP, or vice versa. If an
application uses both streams and datagrams to selectively obtain
reliable transmission for some RTP media payloads but not for others,
it is strongly suggested that the application developer knowingly
choose which RTT observations they are interested in, while remaining
aware of the advice included in Section 9.2.
Even this awareness may not be "safe enough" - for example, [RFC9221]
allows QUIC DATAGRAM frames to be coalesced with other QUIC frames,
and recommends, but does not require, QUIC DATAGRAMs to be sent as
soon as possible, or to be delivered to a receiving application
immediately. [RFC9221] also recommends, but does not require, a QUIC
implementation to provide an API for prioritization between QUIC
streams and QUIC DATAGRAMs.
10. Replacing RTCP and RTP Header Extensions with QUIC Feedback
Because RTP has so often used UDP as its underlying transport
protocol, receiving little or no transport feedback, existing RTP
implementations rely on feedback from the RTP Control Protocol (RTCP)
so that RTP senders and receivers can exchange control information to
monitor connection statistics and to identify and synchronize media
streams.
Because QUIC can provide transport-level feedback, it can replace at
least some RTP transport-level feedback with current QUIC feedback
[RFC9000]. In addition, RTP-level feedback that is not available in
QUIC by default can potentially be replaced with feedback provided by
useful QUIC extensions in the future as described in Appendix B.6.
When statistics contained in RTCP packets are also available from
QUIC or can be derived from statistics available from QUIC, it is
desirable to provide these statistics at only one protocol layer.
This avoids consumption of bandwidth to deliver equivalent control
information at more than one level of the protocol stack. QUIC and
RTCP both have rules describing when certain signals are to be sent.
This document does not change any of the rules described by either
protocol. Rather, it specifies a baseline for replacing some of the
RTCP packet types by mapping the contents to QUIC connection
statistics, and reducing the transmission frequency and bandwidth
requirements for some RTCP packet types that must be transmitted
periodically. Future documents can extend this mapping for other
RTCP format types and can make use of new QUIC extensions that become
available over time. The mechanisms described in this section can
enhance the statistics provided by RTCP and reduce the bandwidth
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overhead required by certain RTCP packets. Applications using RoQ
still need to adhere to the rules for RTCP feedback given by
[RFC3550] and the RTP profiles in use.
Most statements about "QUIC" in Section 10 are applicable to both RTP
packets encapsulated in QUIC streams and RTP packets encapsulated in
DATAGRAMs. The differences are described in Section 10.1 and
Section 10.2.
While RoQ places no restrictions on applications sending RTCP, this
document assumes that the reason an implementer chooses to support
RoQ is to obtain benefits beyond what's available when RTP uses UDP
as its underlying transport layer. Exposing relevant information
from the QUIC layer to the application instead of exchanging
additional RTCP packets, where applicable, will reduce processing and
bandwidth overhead for RoQ senders and receivers.
Section 10.4 discusses what information can be exposed from the QUIC
connection layer to reduce the RTCP overhead.
10.1. RoQ Datagrams
QUIC DATAGRAMs are ACK-eliciting packets, which means that an
acknowledgment is triggered when a DATAGRAM frame is received. Thus,
a sender can assume that an RTP packet arrived at the receiver or was
lost in transit, using the QUIC acknowledgments of QUIC DATAGRAM
frames. In the following, an RTP packet is regarded as acknowledged
when the QUIC DATAGRAM frame that carried the RTP packet was
acknowledged.
10.2. RoQ Streams
For RTP packets that are sent over QUIC streams, an RTP packet is
considered acknowledged after all STREAM frames that carried parts of
the RTP packet were acknowledged.
When QUIC streams are used, the implementer needs to be aware that
the direct mapping proposed below might not reflect the real
characteristics of the network. RTP packet loss can seem lower than
actual packet loss due to QUIC's automatic retransmissions.
Similarly, timing information can be incorrect due to retransmissions
or transmission delays introduced by the QUIC stack.
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10.3. Multihop Topologies
In some topologies, RoQ might only be used on some of the links
between multiple session participants. Other links might be using
RTP over UDP, or over some other supported RTP encapsulation
protocol, and some participants might be using RTP implementations
that don't support RoQ at all. These participants will not be able
to infer feedback from QUIC, and they might receive less RTCP
feedback than expected. This situation can arise when participants
using RoQ are not aware that other participants are not using RoQ and
minimize their use of RTCP, assuming their RoQ peer will be able to
infer statistics from QUIC. There are two ways to solve this
problem:
* If the middlebox translating between RoQ and RTP over other RTP
transport protocols such as UDP or TCP provides Back-to-Back RTP
sessions as described in Section 3.2.2 of [RFC7667], this
middlebox can add RTCP packets for the participants not using RoQ
by using the statistics the middlebox gets from QUIC and the
mappings described in the following sections.
* If the middlebox does not provide Back-to-Back RTP sessions,
participants can use additional signaling to let the RoQ
participants know what RTCP is required.
10.4. Feedback Mappings
This section explains how some of the RTCP packet types that are used
to signal reception statistics can be replaced by equivalent
statistics that are already collected by QUIC. The following list
explains how this mapping can be achieved for the individual fields
of different RTCP packet types.
The list of RTCP packets in this section is not exhaustive, and
similar considerations would apply when exchanging any other type of
RTCP control packets using RoQ.
A more thorough analysis including the information that cannot be
mapped from QUIC can be found in Appendix B: RTCP Control Packet
Types (in Appendix B.1), Generic RTP Feedback (RTPFB) (in
Appendix B.3), Payload-specific RTP Feedback (PSFB) (in
Appendix B.4), Extended Reports (in Appendix B.2), and RTP Header
Extensions (in Appendix B.5).
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10.4.1. Negative Acknowledgments ("NACK")
Generic _Negative Acknowledgments_ (PT=205, FMT=1, Name=Generic NACK,
[RFC4585]) contain information about RTP packets which the receiver
considered lost. Section 6.2.1. of [RFC4585] recommends using this
feature only if the underlying protocol cannot provide similar
feedback. QUIC does not provide negative acknowledgments but can
detect lost packets based on the Gap numbers contained in QUIC ACK
frames (Section 6 of [RFC9002]).
10.4.2. ECN Feedback ("ECN")
_ECN Feedback_ (PT=205, FMT=8, Name=RTCP-ECN-FB, [RFC6679]) packets
report the count of observed ECN-CE marks. [RFC6679] defines two
RTCP reports, one packet type (with PT=205 and FMT=8), and a new
report block for the extended reports. QUIC supports ECN reporting
through acknowledgments. If the QUIC connection supports ECN, using
QUIC acknowledgments to report ECN counts, rather than RTCP ECN
feedback reports, reduces bandwidth and processing demands on the
RTCP implementation.
10.4.3. Goodbye Packets ("BYE")
RTP session participants can use _Goodbye_ RTCP packets (PT=203,
Name=BYE, [RFC3550]), to indicate that a source is no longer active.
If the participant is also going to close the QUIC connection, the
_BYE_ packet can be replaced by a QUIC CONNECTION_CLOSE frame. In
this case, the reason for leaving can be transmitted in QUIC's
CONNECTION_CLOSE _Reason Phrase_. However, if the participant wishes
to use this QUIC connection for any other multiplexed traffic, the
participant has to use the BYE packet because the QUIC
CONNECTION_CLOSE would close the entire QUIC connection for all other
QUIC streams and DATAGRAMs.
11. RoQ-QUIC and RoQ-RTP API Considerations
The mapping described in the previous sections relies on the QUIC
implementation passing some information to the RoQ implementation.
Although RoQ will function without this information, some
optimizations regarding rate adaptation and RTCP mapping require
certain functionalities to be exposed to the application.
Each item in the following list can be considered individually. Any
exposed information or function can be used by RoQ regardless of
whether the other items are available. Thus, RoQ does not depend on
the availability of all of the listed features but can apply
different optimizations depending on the functionality exposed by the
QUIC implementation.
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* _initial_max_data transport_: If the QUIC receiver has indicated a
willingness to accept 0-RTT packets with early data, this is the
maximum size that the QUIC sender can use, as described in
Section 12.2.
* _Maximum Datagram Size_: The maximum DATAGRAM size that the QUIC
connection can transmit on the network path to the QUIC receiver.
If a RoQ sender using DATAGRAMs does not know the maximum DATAGRAM
size for the path to the RoQ receiver, there are only two choices
- either use heuristics to limit the size of RoQ messages, or be
prepared to lose RoQ messages that were too large to be carried
through the network path and delivered to the RoQ receiver.
* _Datagram Acknowledgment and Loss_: Section 5.2 of [RFC9221]
allows QUIC implementations to notify the application that a
DATAGRAM was acknowledged or that it believes a DATAGRAM was lost.
Given the DATAGRAM acknowledgments and losses, the application can
deduce which RTP packets arrived at the receiver and which were
lost (see also Section 10.1).
* _Stream States_: The stream states include which parts of the data
sent on a stream were successfully delivered and which are still
outstanding to be sent or retransmitted. If an application keeps
track of the RTP packets sent on a stream, their respective sizes,
and in which order they were transmitted, it can infer which RTP
packets were acknowledged according to the definition in
Section 10.2.
* _Arrival timestamps_: If the QUIC connection uses a timestamp
extension like [I-D.draft-smith-quic-receive-ts] or
[I-D.draft-huitema-quic-ts], the arrival timestamps or one-way
delays can support the application as described in Section 10 and
Section 8.
* _Bandwidth Estimation_: If a bandwidth estimate is available in
the QUIC implementation, exposing it avoids the overhead of
executing an additional bandwidth estimation algorithm in the
application.
* _ECN_: If ECN marks are available, they can support the bandwidth
estimation of the application.
* _RTT_: The RTT estimations as described in Section 5 of [RFC9002].
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One goal for the RoQ protocol is to shield RTP applications from the
details of QUIC encapsulation, so the RTP application doesn't need
much information about QUIC from RoQ, but some information will be
valuable. For example, it could be desirable that the RoQ
implementation provides an indication of connection migration to the
RTP application.
Because RTP applications do use the application timestamps contained
in RTCP packets in a variety of ways, a RoQ implementation that
provides and event-driven API can allow RoQ applications to generate
RTCP packets "at the last moment", when the RoQ application is able
to send the RTCP packet, and allow RoQ applications to notice that
QUIC congestion control is limiting the ability of the RoQ
application to send packets without this delay.
12. Discussion
This section contains topics that are worth mentioning, but don't fit
well into other sections of the document.
12.1. Impact of Connection Migration
RTP sessions are characterized by a continuous flow of packets in
either or both directions. A connection migration might lead to
pausing media transmission until reachability of the peer under the
new address is validated. This might lead to short breaks in media
delivery in the order of RTT and, if RTCP is used for RTT
measurements, might cause spikes in observed delays. Application
layer congestion control mechanisms (and packet repair schemes such
as retransmissions) need to be prepared to cope with such spikes. As
noted in Section 11, it could be desirable that the RoQ
implementation provides an indication of connection migration to the
RTP application, to assist in coping.
12.2. 0-RTT and Early Data considerations
RoQ applications, like any other RTP applications, want to establish
a media path quickly, reducing clipping at the beginning of a
conversation. For repeated connections between endpoints that have
previously carried out a full TLS handshake procedure, the initiator
of a QUIC connection can use 0-RTT packets with "early data" to
include application data in a packet that is used to establish a
connection.
As 0-RTT packets are subject to replay attacks, RoQ applications MUST
carefully specify which data types and operations are allowed.
Section 9.2 of [RFC9001] says
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Application protocols MUST either prohibit the use of extensions
that carry application semantics in 0-RTT or provide replay
mitigation strategies.
For the purposes of this discussion, RoQ is an application protocol
that allows the use of 0-RTT.
RoQ application developers ought to take the considerations described
in Section 12.2.1 and Section 12.2.2 into account when deciding
whether to use 0-RTT with early data for an application.
12.2.1. Effect of 0-RTT Rejection for RoQ using Early Data
If the goal for using early data is to reduce clipping, a QUIC
endpoint is relying on the other QUIC endpoint to accept the 0-RTT
packet carrying early data containing media.
A QUIC endpoint indicates its willingness to accept a 0-RTT packet
containing early data by sending the TLS early_data extension in the
NewSessionTicket message with the max_early_data_size parameter set
to the sentinel value 0xffffffff. The amount of data that a QUIC
client can send in QUIC 0-RTT is controlled by the initial_max_data
transport parameter supplied by the QUIC server. This is described
in more detail in Section 4.6.1 of [RFC9001].
If a QUIC endpoint is not willing to accept a 0-RTT packet containing
early data, but receives one anyway, the QUIC endpoint rejects the
0-RTT packet by sending EncryptedExtensions without an early_data
extension. This is described in more detail, in Section 4.6.2 of
[RFC9001]. This necessarily means that a QUIC endpoint attempting to
convey RoQ media is now subject to at least one additional RTT delay,
as it must send a QUIC Initial packet and perform a full QUIC
handshake before it can send RoQ media.
12.2.2. Effect of 0-RTT Replay Attacks for RoQ using Early Data
Including "early data" in the packet payload in any QUIC 0-RTT packet
exposes the application to an additional risk, of accepting "early
data" from a 0-RTT packet that has been replayed.
While it is true that
* RTP typically carries ephemeral media contents that is rendered
and possibly recorded but otherwise causes no side effects,
* the amount of data that can be carried as packet payload in a
0-RTT packet is rather limited, and
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* RTP implementations are likely to discard any replayed media
packets as duplicates,
it is still the responsibility of the RoQ application to determine
whether the benefits of using 0-RTT with early data outweigh the
risks.
Since the QUIC connection will often be created in the context of an
existing signaling relationship (e.g., using WebRTC or SIP), a
careful RoQ implementer can exchange specific 0-RTT keying material
to prevent replays across sessions.
12.3. Coalescing RTP packets in a single QUIC packet
Applications have some control over how the QUIC stack maps
application data to QUIC frames, but applications cannot control how
the QUIC stack maps STREAM and DATAGRAM frames to QUIC packets
Section 13 of [RFC9000] and Section 5 of [RFC9308].
* When RTP payloads are carried over QUIC streams, the RTP payload
is treated as an ordered byte stream that will be carried in QUIC
STREAM frames, with no effort to match application data
boundaries.
* When RTP payloads are carried over DATAGRAMs, each RTP payload
data unit is mapped into a DATAGRAM frame, but
* QUIC implementations can include multiple STREAM frames from
different streams and one or more DATAGRAM frames into a single
QUIC packet, and can include other QUIC frames as well.
QUIC stacks are allowed to wait for a short period of time if the
queued QUIC packet is shorter than the Path MTU, in order to optimize
for bandwidth utilization instead of latency, while real-time
applications usually prefer to optimize for latency rather than
bandwidth utilization. This waiting interval is under the QUIC
implementation's control, and could be based on knowledge about
application sending behavior or heuristics to determine whether and
for how long to wait.
When there are a lot of small DATAGRAM frames (e.g., an audio stream)
and a lot of large DATAGRAM frames (e.g., a video stream), it could
be a good idea to make sure the audio frames can be included in a
QUIC packet that also carries video frames (i.e., the video frames
don't fill the whole QUIC packet). Otherwise, the QUIC stack might
have to send additional small packets only carrying single audio
frames, which would waste some bandwidth.
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Application designers are advised to take these considerations into
account when selecting and configuring a QUIC stack for use with RoQ.
13. Directions for Future Work
This document describes RoQ in sufficient detail that an implementer
can build a RoQ application, but we recognize that additional work is
likely, after we have sufficient experience with RoQ to guide that
work (Section 13.1) and as new QUIC extensions become available
(Section 13.2).
13.1. Future Work Resulting from Implementation and Deployment
Experience
Possible directions would include
* More guidance on transport for RTCP (for example, when to use QUIC
streams vs. DATAGRAMs) including guidance on prioritization
between streams and DATAGRAMs for the performance of RTCP.
* More guidance on the use of real-time-friendly congestion control
algorithms (for example, Copa [Copa], L4S [RFC9330], etc.).
* More guidance for congestion control and rate adaptation for
multiple RoQ flows (whether streams or datagrams).
* Possible guidance for connection sharing between real-time and
non-real-time flows, including considerations for congestion
control and rate adaptation, scheduling, prioritization, and which
ALPNs to use.
* Investigation of the effects of delaying or dropping DATAGRAMs due
to congestion before they can be transmitted by the QUIC stack.
* Implementation of translating middleboxes for translating between
RoQ and RTP over UDP. As described in Section 3.3, RoQ can be
used to connect to some RTP middleboxes using some topologies, and
these middleboxes might be connecting RoQ endpoints and non-RoQ
endpoints, so will need to translate between RoQ and RTP over UDP.
For these reasons, publication of this document as a stable reference
for implementers to test with, and report results, seems useful.
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13.2. Future Work Resulting from New QUIC Extensions
In addition, as noted in Section 3.1.7, one of the motivations for
using QUIC as a transport for RTP is to exploit new QUIC extensions
as they become available. We noted several specific proposed QUIC
extensions in Appendix A, but these proposals are all solving
relevant problems, and those problems are worth solving for the QUIC
protocol, whether the listed proposals are used in the solution or
not.
* Guidance for using RoQ with QUIC connection migration and over
multiple paths. QUIC connection migration was already defined in
[RFC9000], and the Multipath Extension for QUIC
[I-D.draft-ietf-quic-multipath] has been adopted and is relatively
mature, so this is likely to be the first new QUIC extension we
address.
* Guidance for using RoQ with QUIC NAT traversal solutions. This
could use Interactive Connectivity Establishment (ICE) [RFC8445]
or other NAT traversal solutions.
* Guidance for improved jitter calculations to use with congestion
control and rate adaptation.
* Guidance for other aspects of QUIC performance optimization
relying on extensions.
Other QUIC extensions, not yet proposed, might also be useful with
RoQ.
14. Implementation Status
*RFC Editor's note:* Please remove this section prior to
publication of a final version of this document.
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC7942].
The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation
here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was
supplied by IETF contributors. This is not intended as, and must not
be construed to be, a catalog of available implementations or their
features. Readers are advised to note that other implementations may
exist.
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According to [RFC7942], "this will allow reviewers and working groups
to assign due consideration to documents that have the benefit of
running code, which may serve as evidence of valuable experimentation
and feedback that have made the implemented protocols more mature.
It is up to the individual working groups to use this information as
they see fit".
14.1. mengelbart/roq
Ogranization: Technical University of Munich
Implementation: [roq]
Description: _roq_ is a library implementing the basic encapsulation
described in Section 5. The library uses the Go programming
language and supports the [quic-go] QUIC implementation.
Level of Maturity: prototype
Coverage: : The library supports sending and receiving RTP and RTCP
packets using QUIC streams and QUIC DATAGRAMs, and supports
multiplexing using flow identifiers. Applications using the library
are responsible for appropriate signaling, setting up QUIC
connections, and managing RTP sessions. Applications choose whether
to send RTP and RTCP packets over streams or DATAGRAMs, and
applications also have control over the QUIC and RTP congestion
controllers in use since they control the QUIC connection setup and
can thus configure the QUIC stack they use to their preferences.
Version Compatibility: The library implements
[I-D.draft-ietf-avtcore-rtp-over-quic-10].
Licensing: MIT License
Implementation Experience: The implementer reports they have no
experience with the topics discussed in Section 13. RoQ relies on
out-of-band signaling for connection establishment, and since
there is currently no specification for SDP for RoQ, applications
using the library have to statically configure connection
information to allow testing
Contact Information: Mathis Engelbart (mathis.engelbart@gmail.com)
Last Updated: 25 May 2024
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14.2. bbc/gst-roq
Ogranization: BBC Research and Development
Implementation: RTP-over-QUIC elements for GStreamer [gst-roq]
Description: _gst-quic-transport_ provides a set of GStreamer
plugins implementing QUIC transport. _gst-roq_ provides a set of
GStreamer plugins implementing RoQ.
Level of Maturity: research
Coverage: The plugins support sending and receiving RTP and RTCP
packets using QUIC streams and QUIC DATAGRAMs, and supports
multiplexing using flow identifiers. GStreamer pipelines that use
the RoQ plugins found in the _gst-roq_ repository can make use of
the plugins found in the _gst-quic-transport_ repository to set up
QUIC connections. RTP sessions can be managed by existing
GStreamer plugins available in the standard GStreamer release.
GStreamer pipeline applications choose whether to send RTP and
RTCP packets over streams or DATAGRAMs.
Version Compatibility: The library implements
[I-D.draft-ietf-avtcore-rtp-over-quic-05].
Licensing: GNU Lesser General Public License v2.1
Implementation Experience: The implementer reports they have no
experience with the topics discussed in Section 13. Both in-band
and out-of-band signalling for RoQ media sessions is in active
development via an implementation of
[I-D.draft-hurst-sip-quic-00], which re-uses the GStreamer plugins
described above.
Contact Information: Sam Hurst (sam.hurst@bbc.co.uk)
Last Updated: 05 June 2024
14.3. mengelbart/rtp-over-quic
Ogranization: Technical University of Munich
Implementation: RTP over QUIC [RTP-over-QUIC]
Description: _RTP over QUIC_ is a experimental implementation of the
mapping described in an earlier version of this document.
Level of Maturity: research
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Coverage: The application implements the RoQ DATAGRAMs mapping and
implements SCReAM congestion control at the application layer. It
can optionally disable the built-in QUIC congestion control
(NewReno). The endpoints only use RTCP for congestion control
feedback, which can optionally be disabled and replaced by the
QUIC connection statistics as described in Section 10.4.
Experimental results of the implementation can be found in
[RoQ-Mininet].
Version Compatibility: [I-D.draft-ietf-avtcore-rtp-over-quic-00]
Licensing: MIT
Implementation Experience: See [RoQ-Mininet]
Contact Information: Mathis Engelbart (mathis.engelbart@gmail.com)
Last Updated: 25 May 2024
15. Security Considerations
RoQ is subject to the security considerations of RTP described in
Section 9 of [RFC3550] and the security considerations of any RTP
profile in use.
The security considerations for the QUIC protocol and DATAGRAM
extension described in Section 21 of [RFC9000], Section 9 of
[RFC9001], Section 8 of [RFC9002] and Section 6 of [RFC9221] also
apply to RoQ.
Note that RoQ provides mandatory security, and other RTP transports
do not. In order to prevent the inadvertent disclosure of RTP
sessions to unintended third parties, RTP topologies described in
Section 3.3 that include middleboxes supporting both RoQ and non-RoQ
paths MUST forward RTP packets on non-RoQ paths using a secure AVP
profile ([RFC3711], [RFC4585], or another AVP profile providing
equivalent RTP-level security), whether or not RoQ senders are using
a secure AVP profile for those RTP packets.
16. IANA Considerations
This document registers a new ALPN protocol ID (in Section 16.1) and
creates a new registry that manages the assignment of error code
points in RoQ (in Section 16.2).
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16.1. Registration of a RoQ Identification String
This document creates a new registration for the identification of
RoQ in the "TLS Application-Layer Protocol Negotiation (ALPN)
Protocol IDs" registry [RFC7301].
The "roq" string identifies RoQ:
Protocol: RTP over QUIC (RoQ)
Identification Sequence: 0x72 0x6F 0x71 ("roq")
Specification: This document
16.2. RoQ Error Codes Registry
This document establishes a registry for RoQ error codes. The "RTP
over QUIC (RoQ) Error Codes" registry manages a 62-bit space and is
listed under the "Real-Time Transport Protocol (RTP) Parameters"
heading.
The new error codes registry created in this document operates under
the QUIC registration policy documented in Section 22.1 of [RFC9000].
This registry includes the common set of fields listed in
Section 22.1.1 of [RFC9000].
Permanent registrations in this registry are assigned using the
Specification Required policy ([RFC8126]), except for values between
0x00 and 0x3f (in hexadecimal; inclusive), which are assigned using
Standards Action or IESG Approval as defined in Sections 4.9 and 4.10
of [RFC8126].
Registrations for error codes are required to include a description
of the error code. An expert reviewer is advised to examine new
registrations for possible duplication or interaction with existing
error codes.
In addition to common fields as described in Section Section 22.1 of
[RFC9000], this registry includes two additional fields. Permanent
registrations in this registry MUST include the following fields:
Name: A name for the error code.
Description: A brief description of the error code semantics, which
can be a summary if a specification reference is provided.
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The initial allocations in this registry are all assigned permanent
status and list a change controller of the IETF and a contact of the
AVTCORE working group (avt@ietf.org).
The entries in Table 2 are registered by this document.
+=======+===========================+=============+===============+
| Value | Name | Description | Specification |
+=======+===========================+=============+===============+
| 0x00 | ROQ_NO_ERROR | No Error | Section 7 |
+-------+---------------------------+-------------+---------------+
| 0x01 | ROQ_GENERAL_ERROR | General | Section 7 |
| | | error | |
+-------+---------------------------+-------------+---------------+
| 0x02 | ROQ_INTERNAL_ERROR | Internal | Section 7 |
| | | Error | |
+-------+---------------------------+-------------+---------------+
| 0x03 | ROQ_PACKET_ERROR | Invalid | Section 7 |
| | | payload | |
| | | format | |
+-------+---------------------------+-------------+---------------+
| 0x04 | ROQ_STREAM_CREATION_ERROR | Invalid | Section 7 |
| | | stream type | |
+-------+---------------------------+-------------+---------------+
| 0x05 | ROQ_FRAME_CANCELLED | Frame | Section 7 |
| | | cancelled | |
+-------+---------------------------+-------------+---------------+
| 0x06 | ROQ_UNKNOWN_FLOW_ID | Unknown | Section 7 |
| | | Flow ID | |
+-------+---------------------------+-------------+---------------+
| 0x07 | ROQ_EXPECTATION_UNMET | Externally | Section 7 |
| | | signaled | |
| | | requirement | |
| | | unmet | |
+-------+---------------------------+-------------+---------------+
Table 2: Initial RoQ Error Codes
17. References
17.1. 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/rfc/rfc2119>.
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[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/rfc/rfc3550>.
[RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and
Video Conferences with Minimal Control", STD 65, RFC 3551,
DOI 10.17487/RFC3551, July 2003,
<https://www.rfc-editor.org/rfc/rfc3551>.
[RFC3611] Friedman, T., Ed., Caceres, R., Ed., and A. Clark, Ed.,
"RTP Control Protocol Extended Reports (RTCP XR)",
RFC 3611, DOI 10.17487/RFC3611, November 2003,
<https://www.rfc-editor.org/rfc/rfc3611>.
[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/rfc/rfc4585>.
[RFC4588] Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R.
Hakenberg, "RTP Retransmission Payload Format", RFC 4588,
DOI 10.17487/RFC4588, July 2006,
<https://www.rfc-editor.org/rfc/rfc4588>.
[RFC6363] Watson, M., Begen, A., and V. Roca, "Forward Error
Correction (FEC) Framework", RFC 6363,
DOI 10.17487/RFC6363, October 2011,
<https://www.rfc-editor.org/rfc/rfc6363>.
[RFC6679] Westerlund, M., Johansson, I., Perkins, C., O'Hanlon, P.,
and K. Carlberg, "Explicit Congestion Notification (ECN)
for RTP over UDP", RFC 6679, DOI 10.17487/RFC6679, August
2012, <https://www.rfc-editor.org/rfc/rfc6679>.
[RFC7301] Friedl, S., Popov, A., Langley, A., and E. Stephan,
"Transport Layer Security (TLS) Application-Layer Protocol
Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301,
July 2014, <https://www.rfc-editor.org/rfc/rfc7301>.
[RFC7667] Westerlund, M. and S. Wenger, "RTP Topologies", RFC 7667,
DOI 10.17487/RFC7667, November 2015,
<https://www.rfc-editor.org/rfc/rfc7667>.
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[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/rfc/rfc8126>.
[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>.
[RFC8298] Johansson, I. and Z. Sarker, "Self-Clocked Rate Adaptation
for Multimedia", RFC 8298, DOI 10.17487/RFC8298, December
2017, <https://www.rfc-editor.org/rfc/rfc8298>.
[RFC8698] Zhu, X., Pan, R., Ramalho, M., and S. Mena, "Network-
Assisted Dynamic Adaptation (NADA): A Unified Congestion
Control Scheme for Real-Time Media", RFC 8698,
DOI 10.17487/RFC8698, February 2020,
<https://www.rfc-editor.org/rfc/rfc8698>.
[RFC8836] Jesup, R. and Z. Sarker, Ed., "Congestion Control
Requirements for Interactive Real-Time Media", RFC 8836,
DOI 10.17487/RFC8836, January 2021,
<https://www.rfc-editor.org/rfc/rfc8836>.
[RFC8888] Sarker, Z., Perkins, C., Singh, V., and M. Ramalho, "RTP
Control Protocol (RTCP) Feedback for Congestion Control",
RFC 8888, DOI 10.17487/RFC8888, January 2021,
<https://www.rfc-editor.org/rfc/rfc8888>.
[RFC8999] Thomson, M., "Version-Independent Properties of QUIC",
RFC 8999, DOI 10.17487/RFC8999, May 2021,
<https://www.rfc-editor.org/rfc/rfc8999>.
[RFC9000] 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>.
[RFC9001] Thomson, M., Ed. and S. Turner, Ed., "Using TLS to Secure
QUIC", RFC 9001, DOI 10.17487/RFC9001, May 2021,
<https://www.rfc-editor.org/rfc/rfc9001>.
[RFC9002] Iyengar, J., Ed. and I. Swett, Ed., "QUIC Loss Detection
and Congestion Control", RFC 9002, DOI 10.17487/RFC9002,
May 2021, <https://www.rfc-editor.org/rfc/rfc9002>.
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[RFC9221] Pauly, T., Kinnear, E., and D. Schinazi, "An Unreliable
Datagram Extension to QUIC", RFC 9221,
DOI 10.17487/RFC9221, March 2022,
<https://www.rfc-editor.org/rfc/rfc9221>.
17.2. Informative References
[Copa] "Copa: Practical Delay-Based Congestion Control for the
Internet", 2018, <https://web.mit.edu/copa/>.
[gst-roq] "RTP-over-QUIC elements for GStreamer", n.d.,
<https://github.com/bbc/gst-roq>.
[I-D.draft-dawkins-avtcore-sdp-rtp-quic]
Dawkins, S., "SDP Offer/Answer for RTP using QUIC as
Transport", Work in Progress, Internet-Draft, draft-
dawkins-avtcore-sdp-rtp-quic-00, 28 January 2022,
<https://datatracker.ietf.org/doc/html/draft-dawkins-
avtcore-sdp-rtp-quic-00>.
[I-D.draft-huitema-quic-ts]
Huitema, C., "Quic Timestamps For Measuring One-Way
Delays", Work in Progress, Internet-Draft, draft-huitema-
quic-ts-08, 28 August 2022,
<https://datatracker.ietf.org/doc/html/draft-huitema-quic-
ts-08>.
[I-D.draft-hurst-quic-rtp-tunnelling]
Hurst, S., "QRT: QUIC RTP Tunnelling", Work in Progress,
Internet-Draft, draft-hurst-quic-rtp-tunnelling-01, 28
January 2021, <https://datatracker.ietf.org/doc/html/
draft-hurst-quic-rtp-tunnelling-01>.
[I-D.draft-hurst-sip-quic-00]
Hurst, S., "SIP-over-QUIC: Session Initiation Protocol
over QUIC Transport", Work in Progress, Internet-Draft,
draft-hurst-sip-quic-00, 6 November 2022,
<https://datatracker.ietf.org/doc/html/draft-hurst-sip-
quic-00>.
[I-D.draft-ietf-avtcore-rtcp-green-metadata]
He, Y., Herglotz, C., and E. Francois, "RTP Control
Protocol (RTCP) Messages for Temporal-Spatial Resolution",
Work in Progress, Internet-Draft, draft-ietf-avtcore-rtcp-
green-metadata-04, 7 October 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-avtcore-
rtcp-green-metadata-04>.
Engelbart, et al. Expires 24 April 2025 [Page 51]
Internet-Draft RTP over QUIC (RoQ) October 2024
[I-D.draft-ietf-avtcore-rtp-over-quic-00]
Ott, J. and M. Engelbart, "RTP over QUIC", Work in
Progress, Internet-Draft, draft-ietf-avtcore-rtp-over-
quic-00, 26 July 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-avtcore-
rtp-over-quic-00>.
[I-D.draft-ietf-avtcore-rtp-over-quic-05]
Ott, J., Engelbart, M., and S. Dawkins, "RTP over QUIC
(RoQ)", Work in Progress, Internet-Draft, draft-ietf-
avtcore-rtp-over-quic-05, 26 July 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-avtcore-
rtp-over-quic-05>.
[I-D.draft-ietf-avtcore-rtp-over-quic-10]
Ott, J., Engelbart, M., and S. Dawkins, "RTP over QUIC
(RoQ)", Work in Progress, Internet-Draft, draft-ietf-
avtcore-rtp-over-quic-10, 8 May 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-avtcore-
rtp-over-quic-10>.
[I-D.draft-ietf-avtext-lrr-07]
Lennox, J., Hong, D., Uberti, J., Holmer, S., and M.
Flodman, "The Layer Refresh Request (LRR) RTCP Feedback
Message", Work in Progress, Internet-Draft, draft-ietf-
avtext-lrr-07, 2 July 2017,
<https://datatracker.ietf.org/doc/html/draft-ietf-avtext-
lrr-07>.
[I-D.draft-ietf-masque-h3-datagram]
Schinazi, D. and L. Pardue, "HTTP Datagrams and the
Capsule Protocol", Work in Progress, Internet-Draft,
draft-ietf-masque-h3-datagram-11, 17 June 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-masque-
h3-datagram-11>.
[I-D.draft-ietf-quic-ack-frequency]
Iyengar, J., Swett, I., and M. Kühlewind, "QUIC
Acknowledgment Frequency", Work in Progress, Internet-
Draft, draft-ietf-quic-ack-frequency-10, 29 August 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-quic-
ack-frequency-10>.
Engelbart, et al. Expires 24 April 2025 [Page 52]
Internet-Draft RTP over QUIC (RoQ) October 2024
[I-D.draft-ietf-quic-multipath]
Liu, Y., Ma, Y., De Coninck, Q., Bonaventure, O., Huitema,
C., and M. Kühlewind, "Multipath Extension for QUIC", Work
in Progress, Internet-Draft, draft-ietf-quic-multipath-11,
21 October 2024, <https://datatracker.ietf.org/doc/html/
draft-ietf-quic-multipath-11>.
[I-D.draft-ietf-quic-reliable-stream-reset]
Seemann, M. and K. Oku, "QUIC Stream Resets with Partial
Delivery", Work in Progress, Internet-Draft, draft-ietf-
quic-reliable-stream-reset-06, 28 February 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-quic-
reliable-stream-reset-06>.
[I-D.draft-ietf-rmcat-gcc]
Holmer, S., Lundin, H., Carlucci, G., De Cicco, L., and S.
Mascolo, "A Google Congestion Control Algorithm for Real-
Time Communication", Work in Progress, Internet-Draft,
draft-ietf-rmcat-gcc-02, 8 July 2016,
<https://datatracker.ietf.org/doc/html/draft-ietf-rmcat-
gcc-02>.
[I-D.draft-ietf-wish-whip]
Murillo, S. G. and A. Gouaillard, "WebRTC-HTTP ingestion
protocol (WHIP)", Work in Progress, Internet-Draft, draft-
ietf-wish-whip-16, 21 August 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-wish-
whip-16>.
[I-D.draft-smith-quic-receive-ts]
Smith, C. and I. Swett, "QUIC Extension for Reporting
Packet Receive Timestamps", Work in Progress, Internet-
Draft, draft-smith-quic-receive-ts-00, 25 October 2021,
<https://datatracker.ietf.org/doc/html/draft-smith-quic-
receive-ts-00>.
[I-D.draft-thomson-quic-enough]
Thomson, M., "Signaling That a QUIC Receiver Has Enough
Stream Data", Work in Progress, Internet-Draft, draft-
thomson-quic-enough-00, 30 March 2023,
<https://datatracker.ietf.org/doc/html/draft-thomson-quic-
enough-00>.
[IANA-RTCP-FMT-PSFB-PT]
"FMT Values for PSFB Payload Types", n.d.,
<https://www.iana.org/assignments/rtp-parameters/rtp-
parameters.xhtml#rtp-parameters-9>.
Engelbart, et al. Expires 24 April 2025 [Page 53]
Internet-Draft RTP over QUIC (RoQ) October 2024
[IANA-RTCP-FMT-RTPFB-PT]
"FMT Values for RTPFB Payload Types", n.d.,
<https://www.iana.org/assignments/rtp-parameters/rtp-
parameters.xhtml#rtp-parameters-8>.
[IANA-RTCP-PT]
"RTCP Control Packet Types (PT)", n.d.,
<https://www.iana.org/assignments/rtp-parameters/rtp-
parameters.xhtml#rtp-parameters-4>.
[IANA-RTCP-XR-BT]
"RTCP XR Block Type", n.d.,
<https://www.iana.org/assignments/rtcp-xr-block-types/
rtcp-xr-block-types.xhtml#rtcp-xr-block-types-1>.
[IANA-RTP-CHE]
"RTP Compact Header Extensions", n.d.,
<https://www.iana.org/assignments/rtp-parameters/rtp-
parameters.xhtml#rtp-parameters-10>.
[IANA-RTP-SDES-CHE]
"RTP SDES Compact Header Extensions", n.d.,
<https://www.iana.org/assignments/rtp-parameters/rtp-
parameters.xhtml#sdes-compact-header-extensions>.
[IEEE-1733-2011]
"IEEE 1733-2011 Standard for Layer 3 Transport Protocol
for Time-Sensitive Applications in Local Area Networks",
n.d., <https://standards.ieee.org/ieee/1733/4748/>.
[quic-go] "A QUIC implementation in pure Go", n.d.,
<https://github.com/quic-go/quic-go>.
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
DOI 10.17487/RFC0768, August 1980,
<https://www.rfc-editor.org/rfc/rfc768>.
[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122,
DOI 10.17487/RFC1122, October 1989,
<https://www.rfc-editor.org/rfc/rfc1122>.
[RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
DOI 10.17487/RFC1191, November 1990,
<https://www.rfc-editor.org/rfc/rfc1191>.
Engelbart, et al. Expires 24 April 2025 [Page 54]
Internet-Draft RTP over QUIC (RoQ) October 2024
[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP",
RFC 3168, DOI 10.17487/RFC3168, September 2001,
<https://www.rfc-editor.org/rfc/rfc3168>.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
DOI 10.17487/RFC3261, June 2002,
<https://www.rfc-editor.org/rfc/rfc3261>.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol (SRTP)",
RFC 3711, DOI 10.17487/RFC3711, March 2004,
<https://www.rfc-editor.org/rfc/rfc3711>.
[RFC5093] Hunt, G., "BT's eXtended Network Quality RTP Control
Protocol Extended Reports (RTCP XR XNQ)", RFC 5093,
DOI 10.17487/RFC5093, December 2007,
<https://www.rfc-editor.org/rfc/rfc5093>.
[RFC5104] Wenger, S., Chandra, U., Westerlund, M., and B. Burman,
"Codec Control Messages in the RTP Audio-Visual Profile
with Feedback (AVPF)", RFC 5104, DOI 10.17487/RFC5104,
February 2008, <https://www.rfc-editor.org/rfc/rfc5104>.
[RFC5450] Singer, D. and H. Desineni, "Transmission Time Offsets in
RTP Streams", RFC 5450, DOI 10.17487/RFC5450, March 2009,
<https://www.rfc-editor.org/rfc/rfc5450>.
[RFC5484] Singer, D., "Associating Time-Codes with RTP Streams",
RFC 5484, DOI 10.17487/RFC5484, March 2009,
<https://www.rfc-editor.org/rfc/rfc5484>.
[RFC5725] Begen, A., Hsu, D., and M. Lague, "Post-Repair Loss RLE
Report Block Type for RTP Control Protocol (RTCP) Extended
Reports (XRs)", RFC 5725, DOI 10.17487/RFC5725, February
2010, <https://www.rfc-editor.org/rfc/rfc5725>.
[RFC5760] Ott, J., Chesterfield, J., and E. Schooler, "RTP Control
Protocol (RTCP) Extensions for Single-Source Multicast
Sessions with Unicast Feedback", RFC 5760,
DOI 10.17487/RFC5760, February 2010,
<https://www.rfc-editor.org/rfc/rfc5760>.
Engelbart, et al. Expires 24 April 2025 [Page 55]
Internet-Draft RTP over QUIC (RoQ) October 2024
[RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and
Control Packets on a Single Port", RFC 5761,
DOI 10.17487/RFC5761, April 2010,
<https://www.rfc-editor.org/rfc/rfc5761>.
[RFC6051] Perkins, C. and T. Schierl, "Rapid Synchronisation of RTP
Flows", RFC 6051, DOI 10.17487/RFC6051, November 2010,
<https://www.rfc-editor.org/rfc/rfc6051>.
[RFC6284] Begen, A., Wing, D., and T. Van Caenegem, "Port Mapping
between Unicast and Multicast RTP Sessions", RFC 6284,
DOI 10.17487/RFC6284, June 2011,
<https://www.rfc-editor.org/rfc/rfc6284>.
[RFC6285] Ver Steeg, B., Begen, A., Van Caenegem, T., and Z. Vax,
"Unicast-Based Rapid Acquisition of Multicast RTP
Sessions", RFC 6285, DOI 10.17487/RFC6285, June 2011,
<https://www.rfc-editor.org/rfc/rfc6285>.
[RFC6332] Begen, A. and E. Friedrich, "Multicast Acquisition Report
Block Type for RTP Control Protocol (RTCP) Extended
Reports (XRs)", RFC 6332, DOI 10.17487/RFC6332, July 2011,
<https://www.rfc-editor.org/rfc/rfc6332>.
[RFC6464] Lennox, J., Ed., Ivov, E., and E. Marocco, "A Real-time
Transport Protocol (RTP) Header Extension for Client-to-
Mixer Audio Level Indication", RFC 6464,
DOI 10.17487/RFC6464, December 2011,
<https://www.rfc-editor.org/rfc/rfc6464>.
[RFC6465] Ivov, E., Ed., Marocco, E., Ed., and J. Lennox, "A Real-
time Transport Protocol (RTP) Header Extension for Mixer-
to-Client Audio Level Indication", RFC 6465,
DOI 10.17487/RFC6465, December 2011,
<https://www.rfc-editor.org/rfc/rfc6465>.
[RFC6582] Henderson, T., Floyd, S., Gurtov, A., and Y. Nishida, "The
NewReno Modification to TCP's Fast Recovery Algorithm",
RFC 6582, DOI 10.17487/RFC6582, April 2012,
<https://www.rfc-editor.org/rfc/rfc6582>.
[RFC6642] Wu, Q., Ed., Xia, F., and R. Even, "RTP Control Protocol
(RTCP) Extension for a Third-Party Loss Report", RFC 6642,
DOI 10.17487/RFC6642, June 2012,
<https://www.rfc-editor.org/rfc/rfc6642>.
Engelbart, et al. Expires 24 April 2025 [Page 56]
Internet-Draft RTP over QUIC (RoQ) October 2024
[RFC6776] Clark, A. and Q. Wu, "Measurement Identity and Information
Reporting Using a Source Description (SDES) Item and an
RTCP Extended Report (XR) Block", RFC 6776,
DOI 10.17487/RFC6776, October 2012,
<https://www.rfc-editor.org/rfc/rfc6776>.
[RFC6798] Clark, A. and Q. Wu, "RTP Control Protocol (RTCP) Extended
Report (XR) Block for Packet Delay Variation Metric
Reporting", RFC 6798, DOI 10.17487/RFC6798, November 2012,
<https://www.rfc-editor.org/rfc/rfc6798>.
[RFC6843] Clark, A., Gross, K., and Q. Wu, "RTP Control Protocol
(RTCP) Extended Report (XR) Block for Delay Metric
Reporting", RFC 6843, DOI 10.17487/RFC6843, January 2013,
<https://www.rfc-editor.org/rfc/rfc6843>.
[RFC6904] Lennox, J., "Encryption of Header Extensions in the Secure
Real-time Transport Protocol (SRTP)", RFC 6904,
DOI 10.17487/RFC6904, April 2013,
<https://www.rfc-editor.org/rfc/rfc6904>.
[RFC6958] Clark, A., Zhang, S., Zhao, J., and Q. Wu, Ed., "RTP
Control Protocol (RTCP) Extended Report (XR) Block for
Burst/Gap Loss Metric Reporting", RFC 6958,
DOI 10.17487/RFC6958, May 2013,
<https://www.rfc-editor.org/rfc/rfc6958>.
[RFC6990] Huang, R., Wu, Q., Asaeda, H., and G. Zorn, "RTP Control
Protocol (RTCP) Extended Report (XR) Block for MPEG-2
Transport Stream (TS) Program Specific Information (PSI)
Independent Decodability Statistics Metrics Reporting",
RFC 6990, DOI 10.17487/RFC6990, August 2013,
<https://www.rfc-editor.org/rfc/rfc6990>.
[RFC7002] Clark, A., Zorn, G., and Q. Wu, "RTP Control Protocol
(RTCP) Extended Report (XR) Block for Discard Count Metric
Reporting", RFC 7002, DOI 10.17487/RFC7002, September
2013, <https://www.rfc-editor.org/rfc/rfc7002>.
[RFC7003] Clark, A., Huang, R., and Q. Wu, Ed., "RTP Control
Protocol (RTCP) Extended Report (XR) Block for Burst/Gap
Discard Metric Reporting", RFC 7003, DOI 10.17487/RFC7003,
September 2013, <https://www.rfc-editor.org/rfc/rfc7003>.
Engelbart, et al. Expires 24 April 2025 [Page 57]
Internet-Draft RTP over QUIC (RoQ) October 2024
[RFC7004] Zorn, G., Schott, R., Wu, Q., Ed., and R. Huang, "RTP
Control Protocol (RTCP) Extended Report (XR) Blocks for
Summary Statistics Metrics Reporting", RFC 7004,
DOI 10.17487/RFC7004, September 2013,
<https://www.rfc-editor.org/rfc/rfc7004>.
[RFC7005] Clark, A., Singh, V., and Q. Wu, "RTP Control Protocol
(RTCP) Extended Report (XR) Block for De-Jitter Buffer
Metric Reporting", RFC 7005, DOI 10.17487/RFC7005,
September 2013, <https://www.rfc-editor.org/rfc/rfc7005>.
[RFC7097] Ott, J., Singh, V., Ed., and I. Curcio, "RTP Control
Protocol (RTCP) Extended Report (XR) for RLE of Discarded
Packets", RFC 7097, DOI 10.17487/RFC7097, January 2014,
<https://www.rfc-editor.org/rfc/rfc7097>.
[RFC7243] Singh, V., Ed., Ott, J., and I. Curcio, "RTP Control
Protocol (RTCP) Extended Report (XR) Block for the Bytes
Discarded Metric", RFC 7243, DOI 10.17487/RFC7243, May
2014, <https://www.rfc-editor.org/rfc/rfc7243>.
[RFC7244] Asaeda, H., Wu, Q., and R. Huang, "RTP Control Protocol
(RTCP) Extended Report (XR) Blocks for Synchronization
Delay and Offset Metrics Reporting", RFC 7244,
DOI 10.17487/RFC7244, May 2014,
<https://www.rfc-editor.org/rfc/rfc7244>.
[RFC7266] Clark, A., Wu, Q., Schott, R., and G. Zorn, "RTP Control
Protocol (RTCP) Extended Report (XR) Blocks for Mean
Opinion Score (MOS) Metric Reporting", RFC 7266,
DOI 10.17487/RFC7266, June 2014,
<https://www.rfc-editor.org/rfc/rfc7266>.
[RFC7272] van Brandenburg, R., Stokking, H., van Deventer, O.,
Boronat, F., Montagud, M., and K. Gross, "Inter-
Destination Media Synchronization (IDMS) Using the RTP
Control Protocol (RTCP)", RFC 7272, DOI 10.17487/RFC7272,
June 2014, <https://www.rfc-editor.org/rfc/rfc7272>.
[RFC7294] Clark, A., Zorn, G., Bi, C., and Q. Wu, "RTP Control
Protocol (RTCP) Extended Report (XR) Blocks for
Concealment Metrics Reporting on Audio Applications",
RFC 7294, DOI 10.17487/RFC7294, July 2014,
<https://www.rfc-editor.org/rfc/rfc7294>.
[RFC7380] Tong, J., Bi, C., Ed., Even, R., Wu, Q., Ed., and R.
Huang, "RTP Control Protocol (RTCP) Extended Report (XR)
Block for MPEG2 Transport Stream (TS) Program Specific
Engelbart, et al. Expires 24 April 2025 [Page 58]
Internet-Draft RTP over QUIC (RoQ) October 2024
Information (PSI) Decodability Statistics Metrics
Reporting", RFC 7380, DOI 10.17487/RFC7380, November 2014,
<https://www.rfc-editor.org/rfc/rfc7380>.
[RFC7509] Huang, R. and V. Singh, "RTP Control Protocol (RTCP)
Extended Report (XR) for Post-Repair Loss Count Metrics",
RFC 7509, DOI 10.17487/RFC7509, May 2015,
<https://www.rfc-editor.org/rfc/rfc7509>.
[RFC7728] Burman, B., Akram, A., Even, R., and M. Westerlund, "RTP
Stream Pause and Resume", RFC 7728, DOI 10.17487/RFC7728,
February 2016, <https://www.rfc-editor.org/rfc/rfc7728>.
[RFC7826] Schulzrinne, H., Rao, A., Lanphier, R., Westerlund, M.,
and M. Stiemerling, Ed., "Real-Time Streaming Protocol
Version 2.0", RFC 7826, DOI 10.17487/RFC7826, December
2016, <https://www.rfc-editor.org/rfc/rfc7826>.
[RFC7867] Huang, R., "RTP Control Protocol (RTCP) Extended Report
(XR) Block for Loss Concealment Metrics for Video
Applications", RFC 7867, DOI 10.17487/RFC7867, July 2016,
<https://www.rfc-editor.org/rfc/rfc7867>.
[RFC7941] Westerlund, M., Burman, B., Even, R., and M. Zanaty, "RTP
Header Extension for the RTP Control Protocol (RTCP)
Source Description Items", RFC 7941, DOI 10.17487/RFC7941,
August 2016, <https://www.rfc-editor.org/rfc/rfc7941>.
[RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", BCP 205,
RFC 7942, DOI 10.17487/RFC7942, July 2016,
<https://www.rfc-editor.org/rfc/rfc7942>.
[RFC8015] Singh, V., Perkins, C., Clark, A., and R. Huang, "RTP
Control Protocol (RTCP) Extended Report (XR) Block for
Independent Reporting of Burst/Gap Discard Metrics",
RFC 8015, DOI 10.17487/RFC8015, November 2016,
<https://www.rfc-editor.org/rfc/rfc8015>.
[RFC8083] Perkins, C. and V. Singh, "Multimedia Congestion Control:
Circuit Breakers for Unicast RTP Sessions", RFC 8083,
DOI 10.17487/RFC8083, March 2017,
<https://www.rfc-editor.org/rfc/rfc8083>.
[RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085,
March 2017, <https://www.rfc-editor.org/rfc/rfc8085>.
Engelbart, et al. Expires 24 April 2025 [Page 59]
Internet-Draft RTP over QUIC (RoQ) October 2024
[RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed.,
"Path MTU Discovery for IP version 6", STD 87, RFC 8201,
DOI 10.17487/RFC8201, July 2017,
<https://www.rfc-editor.org/rfc/rfc8201>.
[RFC8286] Xia, J., Even, R., Huang, R., and L. Deng, "RTP/RTCP
Extension for RTP Splicing Notification", RFC 8286,
DOI 10.17487/RFC8286, October 2017,
<https://www.rfc-editor.org/rfc/rfc8286>.
[RFC8445] Keranen, A., Holmberg, C., and J. Rosenberg, "Interactive
Connectivity Establishment (ICE): A Protocol for Network
Address Translator (NAT) Traversal", RFC 8445,
DOI 10.17487/RFC8445, July 2018,
<https://www.rfc-editor.org/rfc/rfc8445>.
[RFC8825] Alvestrand, H., "Overview: Real-Time Protocols for
Browser-Based Applications", RFC 8825,
DOI 10.17487/RFC8825, January 2021,
<https://www.rfc-editor.org/rfc/rfc8825>.
[RFC8849] Even, R. and J. Lennox, "Mapping RTP Streams to
Controlling Multiple Streams for Telepresence (CLUE) Media
Captures", RFC 8849, DOI 10.17487/RFC8849, January 2021,
<https://www.rfc-editor.org/rfc/rfc8849>.
[RFC8852] Roach, A.B., Nandakumar, S., and P. Thatcher, "RTP Stream
Identifier Source Description (SDES)", RFC 8852,
DOI 10.17487/RFC8852, January 2021,
<https://www.rfc-editor.org/rfc/rfc8852>.
[RFC8860] Westerlund, M., Perkins, C., and J. Lennox, "Sending
Multiple Types of Media in a Single RTP Session",
RFC 8860, DOI 10.17487/RFC8860, January 2021,
<https://www.rfc-editor.org/rfc/rfc8860>.
[RFC8861] Lennox, J., Westerlund, M., Wu, Q., and C. Perkins,
"Sending Multiple RTP Streams in a Single RTP Session:
Grouping RTP Control Protocol (RTCP) Reception Statistics
and Other Feedback", RFC 8861, DOI 10.17487/RFC8861,
January 2021, <https://www.rfc-editor.org/rfc/rfc8861>.
[RFC8899] Fairhurst, G., Jones, T., Tüxen, M., Rüngeler, I., and T.
Völker, "Packetization Layer Path MTU Discovery for
Datagram Transports", RFC 8899, DOI 10.17487/RFC8899,
September 2020, <https://www.rfc-editor.org/rfc/rfc8899>.
Engelbart, et al. Expires 24 April 2025 [Page 60]
Internet-Draft RTP over QUIC (RoQ) October 2024
[RFC9114] Bishop, M., Ed., "HTTP/3", RFC 9114, DOI 10.17487/RFC9114,
June 2022, <https://www.rfc-editor.org/rfc/rfc9114>.
[RFC9143] Holmberg, C., Alvestrand, H., and C. Jennings,
"Negotiating Media Multiplexing Using the Session
Description Protocol (SDP)", RFC 9143,
DOI 10.17487/RFC9143, February 2022,
<https://www.rfc-editor.org/rfc/rfc9143>.
[RFC9308] K��hlewind, M. and B. Trammell, "Applicability of the QUIC
Transport Protocol", RFC 9308, DOI 10.17487/RFC9308,
September 2022, <https://www.rfc-editor.org/rfc/rfc9308>.
[RFC9330] Briscoe, B., Ed., De Schepper, K., Bagnulo, M., and G.
White, "Low Latency, Low Loss, and Scalable Throughput
(L4S) Internet Service: Architecture", RFC 9330,
DOI 10.17487/RFC9330, January 2023,
<https://www.rfc-editor.org/rfc/rfc9330>.
[RFC9335] Uberti, J., Jennings, C., and S. Murillo, "Completely
Encrypting RTP Header Extensions and Contributing
Sources", RFC 9335, DOI 10.17487/RFC9335, January 2023,
<https://www.rfc-editor.org/rfc/rfc9335>.
[roq] "RTP over QUIC (RoQ)", n.d.,
<https://github.com/mengelbart/roq>.
[RoQ-Mininet]
"Congestion Control for RTP over QUIC Simulations", n.d.,
<https://github.com/mengelbart/rtp-over-quic-mininet>.
[RTP-over-QUIC]
"RTP over QUIC", n.d.,
<https://github.com/mengelbart/rtp-over-quic>.
[VJMK88] "Congestion Avoidance and Control", November 1988,
<https://ee.lbl.gov/papers/congavoid.pdf>.
[_3GPP-TS-26.114]
"IP Multimedia Subsystem (IMS); Multimedia telephony;
Media handling and interaction", 5 January 2023,
<https://portal.3gpp.org/desktopmodules/Specifications/
SpecificationDetails.aspx?specificationId=1404>.
Appendix A. List of optional QUIC Extensions
The following is a list of QUIC protocol extensions that could be
beneficial for RoQ, but are not required by RoQ.
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* _An Unreliable Datagram Extension to QUIC_ [RFC9221]. Without
support for unreliable DATAGRAMs, RoQ cannot use the encapsulation
specified in Section 5.3, but can still use QUIC streams as
specified in Section 5.2.
* A version of QUIC receive timestamps can be helpful for improved
jitter calculations and congestion control. If the QUIC
connection uses a timestamp extension such as _Quic Timestamps For
Measuring One-Way Delays_ [I-D.draft-huitema-quic-ts] or _QUIC
Extension for Reporting Packet Receive Timestamps_
[I-D.draft-smith-quic-receive-ts], the arrival timestamps or one-
way delays could be exposed to the application for improved
bandwidth estimation or RTCP mappings as described in Section 10
and Appendix B.
* _QUIC Acknowledgment Frequency_
[I-D.draft-ietf-quic-ack-frequency] can be used by a sender to
optimize the acknowledgment behavior of the receiver, e.g., to
optimize congestion control.
* _Signaling That a QUIC Receiver Has Enough Stream Data_
[I-D.draft-thomson-quic-enough] and _Reliable QUIC Stream Resets_
[I-D.draft-ietf-quic-reliable-stream-reset] would allow RoQ
senders and receivers to use versions of CLOSE_STREAM and
STOP_SENDING that contain offsets. The offset could be used to
reliably retransmit all frames up to a certain frame that ought to
be cancelled before resuming transmission of further frames on new
QUIC streams.
Appendix B. Considered RTCP Packet Types and RTP Header Extensions
This section lists all the RTCP packet types and RTP header
extensions that were considered in the analysis described in
Section 10.
Each subsection in Appendix B corresponds to an IANA registry, and
includes a reference pointing to that registry.
Several but not all of these control packets and their attributes can
be mapped from QUIC, as described in Section 10.4. _Mappable from
QUIC_ has one of four values: _yes_, _partly_, _QUIC extension
needed_, and _no_. _Partly_ is used for packet types for which some
fields can be mapped from QUIC, but not all. _QUIC extension needed_
describes packet types which could be mapped with help from one or
more QUIC extensions.
Examples of how certain packet types could be mapped with the help of
QUIC extensions follow in Appendix B.6.
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B.1. RTCP Control Packet Types
The IANA registry for this section is [IANA-RTCP-PT].
+============+========+===+==================+=========+============+
|Name |Shortcut|PT | Defining |Mappable |Comments |
| | | | Document |from QUIC| |
+============+========+===+==================+=========+============+
|SMPTE time- |SMPTETC |194| [RFC5484] |no | |
|code mapping| | | | | |
+------------+--------+---+------------------+---------+------------+
|Extended |IJ |195| [RFC5450] |no |Would |
|inter- | | | | |require |
|arrival | | | | |send- |
|jitter | | | | |timestamps, |
|report | | | | |which are |
| | | | | |not |
| | | | | |provided by |
| | | | | |any QUIC |
| | | | | |extension |
| | | | | |today |
+------------+--------+---+------------------+---------+------------+
|Sender |SR |200| [RFC3550] |QUIC |see |
|Reports | | | |extension|Appendix |
| | | | |needed / |B.6.4 and |
| | | | |partly |Appendix |
| | | | | |B.6.1 |
+------------+--------+---+------------------+---------+------------+
|Receiver |RR |201| [RFC3550] |QUIC |see |
|Reports | | | |extension|Appendix |
| | | | |needed |B.6.1 |
+------------+--------+---+------------------+---------+------------+
|Source |SDES |202| [RFC3550] |no | |
|description | | | | | |
+------------+--------+---+------------------+---------+------------+
|Goodbye |BYE |203| [RFC3550] |partly |see Section |
| | | | | |10.4.3 |
+------------+--------+---+------------------+---------+------------+
|Application-|APP |204| [RFC3550] |no | |
|defined | | | | | |
+------------+--------+---+------------------+---------+------------+
|Generic RTP |RTPFB |205| [RFC4585] |partly |see |
|Feedback | | | | |Appendix |
| | | | | |B.3 |
+------------+--------+---+------------------+---------+------------+
|Payload- |PSFB |206| [RFC4585] |partly |see |
|specific | | | | |Appendix |
| | | | | |B.4 |
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+------------+--------+---+------------------+---------+------------+
|extended |XR |207| [RFC3611] |partly |see |
|report | | | | |Appendix |
| | | | | |B.2 |
+------------+--------+---+------------------+---------+------------+
|AVB RTCP |AVB |208| [IEEE-1733-2011] |no | |
|packet | | | | | |
+------------+--------+---+------------------+---------+------------+
|Receiver |RSI |209| [RFC5760] |no | |
|Summary | | | | | |
|Information | | | | | |
+------------+--------+---+------------------+---------+------------+
|Port Mapping|TOKEN |210| [RFC6284] |no | |
+------------+--------+---+------------------+---------+------------+
|IDMS |IDMS |211| [RFC7272] |no | |
|Settings | | | | | |
+------------+--------+---+------------------+---------+------------+
|Reporting |RGRS |212| [RFC8861] |no | |
|Group | | | | | |
|Reporting | | | | | |
|Sources | | | | | |
+------------+--------+---+------------------+---------+------------+
|Splicing |SNM |213| [RFC8286] |no | |
|Notification| | | | | |
|Message | | | | | |
+------------+--------+---+------------------+---------+------------+
Table 3
B.2. RTCP XR Block Type
The IANA registry for this section is [IANA-RTCP-XR-BT].
+===============+==========+=========+==================================+
|Name |Document |Mappable |Comments |
| | |from QUIC| |
+===============+==========+=========+==================================+
|Loss RLE Report|[RFC3611] |yes |If only used for acknowledgment, |
|Block | | |could be replaced by QUIC |
| | | |acknowledgments, see Section 10.1 |
| | | |and Section 10.2 |
+---------------+----------+---------+----------------------------------+
|Duplicate RLE |[RFC3611] |no | |
|Report Block | | | |
+---------------+----------+---------+----------------------------------+
|Packet Receipt |[RFC3611] |QUIC |QUIC could provide packet receive |
|Times Report | |extension|timestamps when using a timestamp |
|Block | |needed / |extension that reports timestamp |
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| | |partly |for every received packet, such as|
| | | |[I-D.draft-smith-quic-receive-ts].|
| | | |However, QUIC does not provide |
| | | |feedback in RTP timestamp format. |
+---------------+----------+---------+----------------------------------+
|Receiver |[RFC3611] |QUIC |Used together with DLRR Report |
|Reference Time | |extension|Blocks to calculate RTTs of non- |
|Report Block | |needed |senders. RTT measurements can |
| | | |natively be provided by QUIC. |
+---------------+----------+---------+----------------------------------+
|DLRR Report |[RFC3611] |QUIC |Used together with Receiver |
|Block | |extension|Reference Time Report Blocks to |
| | |needed |calculate RTTs of non-senders. |
| | | |RTT can natively be provided by |
| | | |QUIC. |
+---------------+----------+---------+----------------------------------+
|Statistics |[RFC3611] |QUIC |Packet loss and jitter can be |
|Summary Report | |extension|inferred from QUIC |
|Block | |needed / |acknowledgments, if a timestamp |
| | |partly |extension is used (see |
| | | |[I-D.draft-smith-quic-receive-ts] |
| | | |or [I-D.draft-huitema-quic-ts]). |
| | | |The remaining fields cannot be |
| | | |mapped to QUIC. |
+---------------+----------+---------+----------------------------------+
|VoIP Metrics |[RFC3611] |no |as in other reports above, only |
|Report Block | | |loss and RTT available |
+---------------+----------+---------+----------------------------------+
|RTCP XR |[RFC5093] |no | |
+---------------+----------+---------+----------------------------------+
|Texas | | | |
|Instruments | | | |
|Extended VoIP | | | |
|Quality Block | | | |
+---------------+----------+---------+----------------------------------+
|Post-repair |[RFC5725] |no | |
|Loss RLE Report| | | |
|Block | | | |
+---------------+----------+---------+----------------------------------+
|Multicast |[RFC6332] |no | |
|Acquisition | | | |
|Report Block | | | |
+---------------+----------+---------+----------------------------------+
|IDMS Report |[RFC7272] |no | |
|Block | | | |
+---------------+----------+---------+----------------------------------+
|ECN Summary |[RFC6679] |partly |see Section 10.4.2 |
|Report | | | |
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+---------------+----------+---------+----------------------------------+
|Measurement |[RFC6776] |no | |
|Information | | | |
|Block | | | |
+---------------+----------+---------+----------------------------------+
|Packet Delay |[RFC6798] |no |QUIC timestamps can be used to |
|Variation | | |achieve the same goal |
|Metrics Block | | | |
+---------------+----------+---------+----------------------------------+
|Delay Metrics |[RFC6843] |no |QUIC has RTT and can provide |
|Block | | |timestamps for one-way delay, but |
| | | |QUIC timestamps cannot provide |
| | | |end-to-end statistics when QUIC is|
| | | |only used on one segment of the |
| | | |path. |
+---------------+----------+---------+----------------------------------+
|Burst/Gap Loss |[RFC7004] |no | |
|Summary | | | |
|Statistics | | | |
|Block | | | |
+---------------+----------+---------+----------------------------------+
|Burst/Gap |[RFC7004] |no | |
|Discard Summary| | | |
|Statistics | | | |
|Block | | | |
+---------------+----------+---------+----------------------------------+
|Frame |[RFC7004] |no | |
|Impairment | | | |
|Statistics | | | |
|Summary | | | |
+---------------+----------+---------+----------------------------------+
|Burst/Gap Loss |[RFC6958] | |no |
|Metrics Block | | | |
+---------------+----------+---------+----------------------------------+
|Burst/Gap |[RFC7003] |no | |
|Discard Metrics| | | |
|Block | | | |
+---------------+----------+---------+----------------------------------+
|MPEG2 Transport|[RFC6990] |no | |
|Stream PSI- | | | |
|Independent | | | |
|Decodability | | | |
|Statistics | | | |
|Metrics Block | | | |
+---------------+----------+---------+----------------------------------+
|De-Jitter |[RFC7005] |no | |
|Buffer Metrics | | | |
|Block | | | |
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+---------------+----------+---------+----------------------------------+
|Discard Count |[RFC7002] |no | |
|Metrics Block | | | |
+---------------+----------+---------+----------------------------------+
|DRLE (Discard |[RFC7097] |no | |
|RLE Report) | | | |
+---------------+----------+---------+----------------------------------+
|BDR (Bytes |[RFC7243] |no | |
|Discarded | | | |
|Report) | | | |
+---------------+----------+---------+----------------------------------+
|RFISD (RTP |[RFC7244] |no | |
|Flows Initial | | | |
|Synchronization| | | |
|Delay) | | | |
+---------------+----------+---------+----------------------------------+
|RFSO (RTP Flows|[RFC7244] |no | |
|Synchronization| | | |
|Offset Metrics | | | |
|Block) | | | |
+---------------+----------+---------+----------------------------------+
|MOS Metrics |[RFC7266] |no | |
|Block | | | |
+---------------+----------+---------+----------------------------------+
|LCB (Loss |[RFC7294],|no | |
|Concealment |Section | | |
|Metrics Block) |4.1 | | |
+---------------+----------+---------+----------------------------------+
|CSB (Concealed |[RFC7294],|no | |
|Seconds Metrics|Section | | |
|Block) |4.1 | | |
+---------------+----------+---------+----------------------------------+
|MPEG2 Transport|[RFC7380] |no | |
|Stream PSI | | | |
|Decodability | | | |
|Statistics | | | |
|Metrics Block | | | |
+---------------+----------+---------+----------------------------------+
|Post-Repair |[RFC7509] |no | |
|Loss Count | | | |
|Metrics Report | | | |
|Block | | | |
+---------------+----------+---------+----------------------------------+
|Video Loss |[RFC7867] |no | |
|Concealment | | | |
|Metric Report | | | |
|Block | | | |
+---------------+----------+---------+----------------------------------+
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|Independent |[RFC8015] |no | |
|Burst/Gap | | | |
|Discard Metrics| | | |
|Block | | | |
+---------------+----------+---------+----------------------------------+
Table 4: Extended Report Blocks
B.3. FMT Values for RTP Feedback (RTPFB) Payload Types
The IANA registry for this section is [IANA-RTCP-FMT-RTPFB-PT].
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+=======+=================+=================+=========+================+
|Name |Long Name |Document |Mappable |Comments |
| | | |from QUIC| |
+=======+=================+=================+=========+================+
|Generic|Generic negative |[RFC4585] |partly |see |
|NACK |acknowledgement | | |Section 10.4.1 |
+-------+-----------------+-----------------+---------+----------------+
|TMMBR |Temporary Maximum|[RFC5104] |no | |
| |Media Stream Bit | | | |
| |Rate Request | | | |
+-------+-----------------+-----------------+---------+----------------+
|TMMBN |Temporary Maximum|[RFC5104] |no | |
| |Media Stream Bit | | | |
| |Rate Notification| | | |
+-------+-----------------+-----------------+---------+----------------+
|RTCP- |RTCP Rapid |[RFC6051] |no | |
|SR-REQ |Resynchronisation| | | |
| |Request | | | |
+-------+-----------------+-----------------+---------+----------------+
|RAMS |Rapid Acquisition|[RFC6285] |no | |
| |of Multicast | | | |
| |Sessions | | | |
+-------+-----------------+-----------------+---------+----------------+
|TLLEI |Transport-Layer |[RFC6642] |no |There is no way |
| |Third-Party Loss | | |to tell a QUIC |
| |Early Indication | | |implementation |
| | | | |"don't ask for |
| | | | |retransmission".|
+-------+-----------------+-----------------+---------+----------------+
|RTCP- |RTCP ECN Feedback|[RFC6679] |partly |see |
|ECN-FB | | | |Section 10.4.2 |
+-------+-----------------+-----------------+---------+----------------+
|PAUSE- |Media Pause/ |[RFC7728] |no | |
|RESUME |Resume | | | |
+-------+-----------------+-----------------+---------+----------------+
|DBI |Delay Budget |[_3GPP-TS-26.114]| | |
| |Information (DBI)| | | |
+-------+-----------------+-----------------+---------+----------------+
|CCFB |RTP Congestion |[RFC8888] |QUIC |see |
| |Control Feedback | |extension|Appendix B.6.2 |
| | | |needed | |
+-------+-----------------+-----------------+---------+----------------+
Table 5
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B.4. FMT Values for Payload-Specific Feedback (PSFB) Payload Types
The IANA registry for this section is [IANA-RTCP-FMT-PSFB-PT].
Because QUIC is a generic transport protocol, QUIC feedback cannot
replace the following Payload-specific RTP Feedback (PSFB) feedback.
+=====+============+==============================================+
|Name |Long Name | Document |
+=====+============+==============================================+
|PLI |Picture Loss| [RFC4585] |
| |Indication | |
+-----+------------+----------------------------------------------+
|SLI |Slice Loss | [RFC4585] |
| |Indication | |
+-----+------------+----------------------------------------------+
|RPSI |Reference | [RFC4585] |
| |Picture | |
| |Selection | |
| |Indication | |
+-----+------------+----------------------------------------------+
|FIR |Full Intra | [RFC5104] |
| |Request | |
| |Command | |
+-----+------------+----------------------------------------------+
|TSTR |Temporal- | [RFC5104] |
| |Spatial | |
| |Trade-off | |
| |Request | |
+-----+------------+----------------------------------------------+
|TSTN |Temporal- | [RFC5104] |
| |Spatial | |
| |Trade-off | |
| |Notification| |
+-----+------------+----------------------------------------------+
|VBCM |Video Back | [RFC5104] |
| |Channel | |
| |Message | |
+-----+------------+----------------------------------------------+
|PSLEI|Payload- | [RFC6642] |
| |Specific | |
| |Third-Party | |
| |Loss Early | |
| |Indication | |
+-----+------------+----------------------------------------------+
|ROI |Video | [_3GPP-TS-26.114] |
| |region-of- | |
| |interest | |
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| |(ROI) | |
+-----+------------+----------------------------------------------+
|LRR |Layer | [I-D.draft-ietf-avtext-lrr-07] |
| |Refresh | |
| |Request | |
| |Command | |
+-----+------------+----------------------------------------------+
|VP |Viewport | [_3GPP-TS-26.114] |
| |(VP) | |
+-----+------------+----------------------------------------------+
|AFB |Application | [RFC4585] |
| |Layer | |
| |Feedback | |
+-----+------------+----------------------------------------------+
|TSRR |Temporal- | [I-D.draft-ietf-avtcore-rtcp-green-metadata] |
| |Spatial | |
| |Resolution | |
| |Request | |
+-----+------------+----------------------------------------------+
|TSRN |Temporal- | [I-D.draft-ietf-avtcore-rtcp-green-metadata] |
| |Spatial | |
| |Resolution | |
| |Notification| |
+-----+------------+----------------------------------------------+
Table 6
B.5. RTP Header extensions
Like the payload-specific feedback packets, QUIC cannot directly
replace the control information in the following header extensions.
RoQ does not place restrictions on sending any RTP header extensions.
However, some extensions, such as Transmission Time offsets [RFC5450]
are used to improve network jitter calculation, which can be done in
QUIC if a timestamp extension is used.
B.5.1. RTP Compact Header Extensions
The IANA registry for this section is [IANA-RTP-CHE].
+======================+=================+=================+========+
| Extension URI |Description |Reference |Mappable|
| | | |from |
| | | |QUIC |
+======================+=================+=================+========+
| urn:ietf:params:rtp- |Transmission |[RFC5450] |no |
| hdrext:toffset |Time offsets | | |
+----------------------+-----------------+-----------------+--------+
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| urn:ietf:params:rtp- |Audio Level |[RFC6464] |no |
| hdrext:ssrc-audio- | | | |
| level | | | |
+----------------------+-----------------+-----------------+--------+
| urn:ietf:params:rtp- |Splicing |[RFC8286] |no |
| hdrext:splicing- |Interval | | |
| interval | | | |
+----------------------+-----------------+-----------------+--------+
| urn:ietf:params:rtp- |SMPTE time-code |[RFC5484] |no |
| hdrext:smpte-tc |mapping | | |
+----------------------+-----------------+-----------------+--------+
| urn:ietf:params:rtp- |Reserved as base |[RFC7941] |no |
| hdrext:sdes |URN for RTCP | | |
| |SDES items that | | |
| |are also defined | | |
| |as RTP compact | | |
| |header | | |
| |extensions. | | |
+----------------------+-----------------+-----------------+--------+
| urn:ietf:params:rtp- |Synchronisation |[RFC6051] |no |
| hdrext:ntp-64 |metadata: 64-bit | | |
| |timestamp format | | |
+----------------------+-----------------+-----------------+--------+
| urn:ietf:params:rtp- |Synchronisation |[RFC6051] |no |
| hdrext:ntp-56 |metadata: 56-bit | | |
| |timestamp format | | |
+----------------------+-----------------+-----------------+--------+
| urn:ietf:params:rtp- |Encrypted |[RFC6904] |no |
| hdrext:encrypt |extension header | | |
| |element | | |
+----------------------+-----------------+-----------------+--------+
| urn:ietf:params:rtp- |Mixer-to-client |[RFC6465] |no |
| hdrext:csrc-audio- |audio level | | |
| level |indicators | | |
+----------------------+-----------------+-----------------+--------+
| urn:3gpp:video- |Higher |[_3GPP-TS-26.114]|probably|
| orientation:6 |granularity | |not(?) |
| |(6-bit) | | |
| |coordination of | | |
| |video | | |
| |orientation | | |
| |(CVO) feature, | | |
| |see clause 6.2.3 | | |
+----------------------+-----------------+-----------------+--------+
| urn:3gpp:video- |Coordination of |[_3GPP-TS-26.114]|probably|
| orientation |video | |not(?) |
| |orientation | | |
| |(CVO) feature, | | |
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| |see clause 6.2.3 | | |
+----------------------+-----------------+-----------------+--------+
| urn:3gpp:roi-sent |Signalling of |[_3GPP-TS-26.114]|probably|
| |the arbitrary | |not(?) |
| |region-of- | | |
| |interest (ROI) | | |
| |information for | | |
| |the sent video, | | |
| |see clause | | |
| |6.2.3.4 | | |
+----------------------+-----------------+-----------------+--------+
| urn:3gpp:predefined- |Signalling of |[_3GPP-TS-26.114]|probably|
| roi-sent |the predefined | |not(?) |
| |region-of- | | |
| |interest (ROI) | | |
| |information for | | |
| |the sent video, | | |
| |see clause | | |
| |6.2.3.4 | | |
+----------------------+-----------------+-----------------+--------+
Table 7
B.5.2. RTP SDES Compact Header Extensions
The IANA registry for this section is [IANA-RTP-SDES-CHE].
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+=======================+==================+===========+==========+
| Extension URI | Description | Reference | Mappable |
| | | | from |
| | | | QUIC |
+=======================+==================+===========+==========+
| urn:ietf:params:rtp- | Source | [RFC7941] | no |
| hdrext:sdes:cname | Description: | | |
| | Canonical End- | | |
| | Point Identifier | | |
| | (SDES CNAME) | | |
+-----------------------+------------------+-----------+----------+
| urn:ietf:params:rtp- | RTP Stream | [RFC8852] | no |
| hdrext:sdes:rtp- | Identifier | | |
| stream-id | | | |
+-----------------------+------------------+-----------+----------+
| urn:ietf:params:rtp- | RTP Repaired | [RFC8852] | no |
| hdrext:sdes:repaired- | Stream | | |
| rtp-stream-id | Identifier | | |
+-----------------------+------------------+-----------+----------+
| urn:ietf:params:rtp- | CLUE CaptId | [RFC8849] | no |
| hdrext:sdes:CaptId | | | |
+-----------------------+------------------+-----------+----------+
| urn:ietf:params:rtp- | Media | [RFC9143] | no |
| hdrext:sdes:mid | identification | | |
+-----------------------+------------------+-----------+----------+
Table 8
B.6. Examples
B.6.1. Mapping QUIC Feedback to RTCP Receiver Reports ("RR")
Considerations for mapping QUIC feedback into _Receiver Reports_
(PT=201, Name=RR, [RFC3550]) are:
* _Fraction lost_: When RTP packets are carried in DATAGRAMs, the
fraction of lost packets can be directly inferred from QUIC's
acknowledgments. The calculation includes all packets up to the
acknowledged RTP packet with the highest RTP sequence number.
* _Cumulative lost_: Similar to the fraction of lost packets, the
cumulative loss can be inferred from QUIC's acknowledgments,
including all packets up to the latest acknowledged packet.
* _Highest Sequence Number received_: In RTCP, this field is a
32-bit field that contains the highest sequence number a receiver
received in an RTP packet and the count of sequence number cycles
the receiver has observed. A sender sends RTP packets in QUIC
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packets and receives acknowledgments for the QUIC packets. By
keeping a mapping from a QUIC packet to the RTP packets
encapsulated in that QUIC packet, the sender can infer the highest
sequence number and number of cycles seen by the receiver from
QUIC acknowledgments.
* _Interarrival jitter_: If QUIC acknowledgments carry timestamps as
described in [I-D.draft-smith-quic-receive-ts], senders can infer
the interarrival jitter from the arrival timestamps in QUIC
acknowledgments.
* _Last SR_: Similar to lost packets, the NTP timestamp of the last
received sender report can be inferred from QUIC acknowledgments.
* _Delay since last SR_: This field is not required when the
receiver reports are entirely replaced by QUIC feedback.
B.6.2. Congestion Control Feedback ("CCFB")
RTP _Congestion Control Feedback_ (PT=205, FMT=11, Name=CCFB,
[RFC8888]) contains acknowledgments, arrival timestamps, and ECN
notifications for each received packet. Acknowledgments and ECNs can
be inferred from QUIC as described above. Arrival timestamps can be
added through extended acknowledgment frames as described in
[I-D.draft-smith-quic-receive-ts] or [I-D.draft-huitema-quic-ts].
B.6.3. Extended Report ("XR")
_Extended Reports_ (PT=207, Name=XR, [RFC3611]) offer an extensible
framework for a variety of different control messages. Some of the
statistics that are defined as extended report blocks can be derived
from QUIC, too. Other report blocks need to be evaluated
individually to determine whether the contained information can be
transmitted using QUIC instead. Table 4 in Appendix B.2 lists
considerations for mapping QUIC feedback to some of the _Extended
Reports_.
B.6.4. Application Layer Repair and other Control Messages
While Appendix B.6.1 presented some RTCP packets that can be replaced
by QUIC features, QUIC cannot replace all of the defined RTCP packet
types. This mostly affects RTCP packet types, which carry control
information that is to be interpreted by the RTP application layer
rather than the underlying transport protocol itself.
* _Sender Reports_ (PT=200, Name=SR, [RFC3550]) are similar to
_Receiver Reports_, as described in Appendix B.6.1. They are sent
by media senders and additionally contain an NTP and an RTP
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timestamp and the number of packets and octets transmitted by the
sender. The timestamps can be used by a receiver to synchronize
media streams. QUIC cannot provide similar control information
since it does not know about RTP timestamps. A QUIC receiver
cannot calculate the packet or octet counts since it does not know
about lost DATAGRAMs. Thus, sender reports are necessary in RoQ
to synchronize media streams at the receiver.
In addition to carrying transmission statistics, RTCP packets can
contain application layer control information that cannot directly be
mapped to QUIC. Examples of this information might include:
* _Source Description_ (PT=202, Name=SDES) and _Application_
(PT=204, Name=APP) packet types from [RFC3550], or
* many of the payload-specific feedback messages (PT=206) defined in
[RFC4585], used to control the codec behavior of the sender.
Since QUIC does not provide any kind of application layer control
messaging, QUIC feedback cannot be mapped into these RTCP packet
types. If the RTP application needs this information, the RTCP
packet types are used in the same way as they would be used over any
other transport protocol.
Appendix C. Header overhead considerations
As discussed in Section 9.2, the header overhead of an RTP packet
sent over RoQ cannot easily be determined. This section gives an
estimation of the minimum and maximum header overhead of different
combinations of STREAM and DATAGRAM frames using either IPv4 or IPv6.
However, even this estimation is not exactly correct, since it does
not take into account additional complications such as that RTP
packets may be fragmented over multiple STREAM frames and that QUIC
packets may contain more than a single FRAME, so that the RTCP
overhead could thus be the shared overhead of multiple RTP packets
being sent in different QUIC frames in the same QUIC packet.
* At least 20 Bytes (v4) or 40 Bytes (v6) IP header
* 8 Bytes UDP header
* 2-25 Bytes QUIC Short header packets
- 1 Byte fixed header
- 0-20 Bytes Connection ID
- 1-4 Bytes Packet Number
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* 2-25 Bytes STREAM frame header
- 1 Byte type
- 1-8 Bytes stream ID
- Optional 1-8 Bytes Offset
- Optional 1-8 Bytes Length
* 1-9 Bytes DATAGRAM frame header
- 1 Byte type
- Optional 1-8 Bytes length
* 1-8 Bytes RoQ Flow ID
* IPv4 with STREAM frames
- Minimum: 20+8+2+2+1=33 Bytes
- Maximum: 20+8+25+25+8=86 Bytes
* IPv6 with STREAM frames
- Minimum: 40+8+2+2+1=53 Bytes
- Maximum: 40+8+25+25+8=106 Bytes
* IPv4 with DATAGRAM frames
- Minimum: 20+8+2+1+1=32 Bytes
- Maximum: 20+8+25+9+8=70 Bytes
* IPv6 with DATAGRAM frames
- Minimum: 40+8+2+1+1=52 Bytes
- Maximum: 40+8+25+9+8=90 Bytes
Acknowledgments
Early versions of this document were similar in spirit to
[I-D.draft-hurst-quic-rtp-tunnelling], although many details differ.
The authors would like to thank Sam Hurst for providing his thoughts
about how QUIC could be used to carry RTP.
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The guidance in Section 5.2 about configuring the number of parallel
unidirectional QUIC streams is based on Section 6.2 of [RFC9114],
with obvious substitutions for RTP.
The authors would like to thank Bernard Aboba, David Schinazi, Gurtej
Singh Chandok, Lucas Pardue, Sam Hurst, Sergio Garcia Murillo, and
Vidhi Goel for their valuable comments and suggestions contributing
to this document.
Authors' Addresses
Mathis Engelbart
Technical University of Munich
Email: mathis.engelbart@gmail.com
Jörg Ott
Technical University of Munich
Email: ott@in.tum.de
Spencer Dawkins
Tencent America LLC
Email: spencerdawkins.ietf@gmail.com
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