Internet DRAFT - draft-ietf-avtcore-rtp-over-quic
draft-ietf-avtcore-rtp-over-quic
Audio/Video Transport Core Maintenance J. Ott
Internet-Draft M. Engelbart
Intended status: Standards Track Technical University Munich
Expires: 24 August 2023 20 February 2023
RTP over QUIC
draft-ietf-avtcore-rtp-over-quic-02
Abstract
This document specifies a minimal mapping for encapsulating Real-time
Transport Protocol (RTP) and RTP Control Protocol (RTCP) packets
within the QUIC protocol. It also discusses how to leverage state
from the QUIC implementation in the endpoints, in order to reduce the
need to exchange RTCP packets and how to implement congestion control
and rate adaptation 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/.
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 August 2023.
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Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Background . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. What's in Scope for this Specification . . . . . . . . . 4
1.3. What's Out of Scope for this Specification . . . . . . . 5
2. Terminology and Notation . . . . . . . . . . . . . . . . . . 6
3. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 7
3.1. Supported RTP Topologies . . . . . . . . . . . . . . . . 8
4. Connection Establishment and ALPN . . . . . . . . . . . . . . 8
4.1. Draft version identification . . . . . . . . . . . . . . 9
5. Encapsulation . . . . . . . . . . . . . . . . . . . . . . . . 9
5.1. Multiplexing . . . . . . . . . . . . . . . . . . . . . . 9
5.2. QUIC Streams . . . . . . . . . . . . . . . . . . . . . . 10
5.3. QUIC Datagrams . . . . . . . . . . . . . . . . . . . . . 12
6. RTCP . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6.1. Transport Layer Feedback . . . . . . . . . . . . . . . . 13
6.2. Application Layer Repair and other Control Messages . . . 16
7. Congestion Control and Rate Adaptation . . . . . . . . . . . 17
7.1. Congestion Control at the QUIC layer . . . . . . . . . . 17
7.2. Congestion Control at the Application Layer . . . . . . . 18
7.3. Shared QUIC connections . . . . . . . . . . . . . . . . . 19
8. API Considerations . . . . . . . . . . . . . . . . . . . . . 19
8.1. Information to be exported from QUIC . . . . . . . . . . 19
8.2. Functions to be exposed by QUIC . . . . . . . . . . . . . 20
9. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 21
9.1. Flow Identifier . . . . . . . . . . . . . . . . . . . . . 21
9.2. Impact of Connection Migration . . . . . . . . . . . . . 21
9.3. 0-RTT considerations . . . . . . . . . . . . . . . . . . 22
10. Security Considerations . . . . . . . . . . . . . . . . . . . 22
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
11.1. Registration of a RTP over QUIC Identification String . 22
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 23
12.1. Normative References . . . . . . . . . . . . . . . . . . 23
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12.2. Informative References . . . . . . . . . . . . . . . . . 25
Appendix A. Experimental Results . . . . . . . . . . . . . . . . 27
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27
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]). It also
discusses how to leverage state from the QUIC implementation in the
endpoints, in order to reduce the need to exchange RTCP packets, and
how to implement congestion control and rate adaptation 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 been UDP, recently with DTLS on top to secure
the media exchange and occasionally TCP (and possibly TLS) as a
fallback.
This specification describes an application usage of QUIC
([RFC9308]). As a baseline, the specification does not expect more
than a standard QUIC implementation as defined in [RFC8999],
[RFC9000], [RFC9001], and [RFC9002], providing a secure end-to-end
transport that is also expected to work well through NATs and
firewalls. Beyond this baseline, real-time applications can benefit
from QUIC extensions such as unreliable QUIC datagrams [RFC9221],
which provides additional desirable properties for real-time traffic
(e.g., no unnecessary retransmissions, avoiding head-of-line
blocking).
Moreover, with QUIC's multiplexing capabilities, reliable and
unreliable transport connections as, e.g., needed for WebRTC, can be
established with only a single port used at either end of the
connection.
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1.2. What's in Scope for this Specification
This document defines a mapping for RTP and RTCP over QUIC (this
mapping is hereafter referred to as "RTP-over-QUIC"), and describes
ways to reduce the amount of RTCP traffic by leveraging state
information readily available within a QUIC endpoint. This document
also describes different options for implementing congestion control
and rate adaptation for RTP over QUIC.
This specification focuses on providing a secure encapsulation of RTP
packets for transmission over QUIC. The expected usage is wherever
RTP is used to carry media packets, allowing QUIC in place of other
transport protocols such as TCP, UDP, SCTP, DTLS, etc. That is, we
expect RTP-over-QUIC to be used in contexts in which a signaling
protocol is used to announce or negotiate a media encapsulation and
the associated transport parameters (such as IP address, port
number). RTP-over-QUIC is not intended as a stand-alone media
transport, although QUIC transport parameters could be statically
configured.
The above implies that RTP-over-QUIC is targeted at peer-to-peer
operation; but it may also be used in client-server-style settings,
e.g., when talking to a conference server as described in RFC 7667
([RFC7667]), or, if RTP-over-QUIC 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 RTP-over-QUIC
protocol operation.
RTP-over-QUIC does not impact the usage of RTP Audio Video Profiles
(AVP) ([RFC3551]), or any RTP-based mechanisms, even though it may
render some of them unnecessary, e.g., Secure Real-Time Transport
Prococol (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 RTP-over-
QUIC limit the use of RTCP-based mechanisms, even though some
information or functions obtained by using RTCP mechanisms may also
be available from the underlying QUIC implementation by other means.
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Between two (or more) endpoints, RTP-over-QUIC 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 may be established in
parallel using the same destination IP address, destination port
number, source IP address, source port number, protocol) 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 Specification
This document does not attempt to 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.
RTP-over-QUIC is designed for use with point-to-point connections,
because QUIC itself is not defined for multicast operation. The
scope of this document is limited to unicast RTP/RTCP, even though
nothing would or should prevent its use in multicast setups once QUIC
supports multicast.
RTP-over-QUIC does not define congestion control and rate adaptation
algorithms for use with media. However, Section 7 discusses options
for how congestion control and rate adaptation could be performed at
the QUIC and/or at the RTP layer, and how information available at
the QUIC layer could be exposed via an API for the benefit of RTP
layer implementation.
*Editor's note:* Need to check whether Section 7 will also
describe the QUIC interface that's being exposed, or if that ends
up somewhere else in the document.
RTP-over-QUIC 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 RTP-over-QUIC.
This document does not cover signaling for session setup. SDP for
RTP-over-QUIC 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]).
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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.
*Editor's note:* the list of terms below will almost certainly
grow in size as the specification matures.
The following terms are used:
Congestion Control: A mechanism to limit the aggregate amount of
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, causing some outstanding data to be discarded before the
receiver can receive the data and acknowledge it to the sender.
Datagram: Datagrams exist in UDP as well as in QUIC's unreliable
datagram extension. If not explicitly noted differently, the term
datagram in this document refers to a QUIC Datagram as defined in
[RFC9221].
Endpoint: A QUIC server or client that participates in an RTP over
QUIC session.
Frame: A QUIC frame as defined in [RFC9000].
Media Encoder: An entity that is used by an application to produce a
stream of encoded media, which can be packetized in RTP packets to
be transmitted over QUIC.
Rate Adaptation: A mechanism to help a sender determine and adjust
its sending rate, in order to maximize the amount of information
that is sent to a receiver, without causing queues to build beyond
a reasonable amount, causing "buffer bloat" and "jitter". Rate
adapation is one way to accomplish congestion control for realtime
media, especially when a sender has multiple media streams to the
receiver, because the sum of all sending rates for media streams
must not be high enough to cause congestion on the path these
media streams share between sender and receiver.
Receiver: An endpoint that receives media in RTP packets and may
send or receive RTCP packets.
Sender: An endpoint that sends media in RTP packets and may send or
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receive RTCP packets.
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. RTP over QUIC allows
the use of QUIC streams and QUIC datagrams to transport real-time
data, and thus, the QUIC implementation MUST support QUIC's datagram
extension, if RTP packets should be sent over QUIC datagrams. Since
datagram frames cannot be fragmented, the QUIC implementation MUST
also provide a way to query the maximum datagram size so that an
application can create RTP packets that always fit into a QUIC
datagram frame.
[RFC3550] specifies that RTP sessions need to be transmitted on
different transport addresses to allow multiplexing between them.
RTP over QUIC uses a different approach to leverage the advantages of
QUIC connections without managing a separate QUIC connection per RTP
session. QUIC 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
are flow identifiers prepended to each datagram frame as described in
Section 2.1 of [I-D.draft-ietf-masque-h3-datagram]. RTP over QUIC
uses a flow identifier to replace the network address and port number
to multiplex many RTP sessions over the same QUIC connection.
A rate adaptation algorithm can be plugged in to adapt the media
bitrate to the available bandwidth. This document does not mandate
any specific rate adaptation algorithm. Some examples include
Network-Assisted Dynamic Adaptation (NADA) [RFC8698] and Self-Clocked
Rate Adaptation for Multimedia (SCReAM) [RFC8298]. These rate
adaptation algorithms require some feedback about the network's
performance to calculate target bitrates. Traditionally this
feedback is generated at the receiver and sent back to the sender via
RTCP. Since QUIC also collects some metrics about the network's
performance, these metrics can be used to generate the required
feedback at the sender-side and provide it to the rate adaptation
algorithm to avoid the additional overhead of the RTCP stream.
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3.1. Supported RTP Topologies
RTP over QUIC only supports some of the RTP topologies described in
[RFC7667]. Most notably, due to QUIC being a purely unicast protocol
at the time of writing, RTP over QUIC cannot be used as a transport
protocol in any of the multicast topologies (e.g., _Topo-ASM_, _Topo-
SSM_, _Topo-SSM-RAMS_).
RTP supports different types of translators and mixers. Whenever a
middlebox such as a translator or a mixer needs to access the content
of RTP/RTCP-packets, the QUIC connection has to be terminated at that
middlebox.
Using RTP over QUIC 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 with transport translators which translate
from RTP over QUIC to RTP over a different transport protocol. A
similar problem can occur if a translator needs to translate from RTP
over UDP to RTP over QUIC datagrams, where the MTU of a QUIC datagram
may be smaller than the MTU of a UDP datagram. In both cases, the
translator may need to rewrite the RTP packets to fit into the
smaller MTU of the other protocol. Such a translator may need codec-
specific knowledge to packetize the payload of the incoming RTP
packets in smaller RTP packets.
4. Connection Establishment and ALPN
QUIC requires the use of ALPN [RFC7301] tokens during connection
setup. RTP over QUIC uses "rtp-mux-quic" as ALPN token in the TLS
handshake (see also Section 11.
Note that the use of a given RTP profile is not reflected in the ALPN
token even though it could be considered part of the application
usage. This is simply because different RTP sessions, which may use
different RTP profiles, may be carried within the same QUIC
connection.
*Editor's note:* "rtp-mux-quic" indicates that RTP and other
protocols may be multiplexed on the same QUIC connection using a
flow identifier as described in Section 5. Applications are
responsible for negotiation of protocols in use by appropriate use
of a signaling protocol such as SDP.
*Editor's note:* This implies that applications cannot use RTP
over QUIC as specified in this document over WebTransport.
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4.1. Draft version identification
*RFC Editor's note:* Please remove this section prior to
publication of a final version of this document.
RTP over QUIC uses the token "rtp-mux-quic" to identify itself in
ALPN.
Only implementations of the final, published RFC can identify
themselves as "rtp-mux-quic". 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-04 is identified using the
string "rtp-mux-quic-04".
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/RTCP packets in QUIC.
QUIC supports two transport methods: streams [RFC9000] and datagrams
[RFC9221]. This document specifies mappings of RTP to both of the
transport modes. Senders MAY combine both modes by sending some RTP/
RTCP packets over the same or different QUIC streams and others in
QUIC datagrams.
Section 5.1 introduces a multiplexing mechanism that supports
multiplexing RTP, RTCP, and, with some constraints, other non-RTP
protocols. Section 5.2 and Section 5.3 explain the specifics of
mapping RTP to QUIC streams and QUIC datagrams, respectively.
5.1. Multiplexing
RTP over QUIC uses flow identifiers to multiplex different RTP, RTCP,
and non-RTP data 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 a
stream of RTP packets, RTCP packets, or a data stream of a non-RTP
protocol.
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In a QUIC connection using the ALPN token defined in Section 4, every
QUIC datagram and every QUIC stream MUST start with a flow
identifier. A peer 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 and RTCP packets of different RTP sessions MUST use distinct flow
identifiers. If peers wish to send multiple types of media in a
single RTP session, they MAY do so by following [RFC8860].
A single RTP session MAY 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 MAY use the same flow
identifier (following the procedures defined in [RFC5761], or they
MAY use different flow identifiers.
The association between flow identifiers and data streams MUST be
negotiated using appropriate signaling. Applications MAY send data
using flow identifiers not associated with any RTP or RTCP stream.
If a receiver cannot associate a flow identifier with any RTP/RTCP or
non-RTP stream, it MAY drop the data stream.
There are different use cases for sharing the same QUIC connection
between RTP and non-RTP data streams. Peers might use the same
connection to exchange signaling messages or exchange data while
sending and receiving media streams. The semantics of non-RTP
datagrams or streams are not in the scope of this document. Peers
MAY use any protocol on top of the encapsulation described in this
document.
Flow identifiers introduce some overhead in addition to the header
overhead of RTP/RTCP and QUIC. QUIC variable-length integers require
between one and eight bytes depending on the number expressed. Thus,
it is advisable to use low numbers first and only use higher ones if
necessary due to an increased number of flows.
5.2. QUIC Streams
To send RTP/RTCP packets over QUIC streams, a sender MUST open a new
unidirectional QUIC stream. Streams are unidirectional because there
is no synchronous relationship between sent and received RTP/RTCP
packets. A sender MAY open new QUIC streams for different packets
using the same flow identifier, for example, to avoid head-of-line
blocking.
Figure 1 shows the encapsulation format for RTP over QUIC Streams.
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Payload {
Flow Identifier (i),
RTP/RTCP Payload(..) ...,
}
Figure 1: RTP over QUIC Streams Payload Format
Flow Identifier: Flow identifier to demultiplex different data flows
on the same QUIC connection.
RTP/RTCP Payload: Contains the RTP/RTCP payload; see Figure 2
The payload in a QUIC stream starts with the flow identifier followed
by one or more RTP/RTCP payloads. All RTP/RTCP 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/RTCP packet, followed by the packet itself, see Figure 2.
RTP/RTCP Payload {
Length(i),
RTP/RTCP Packet(..),
}
Figure 2: RTP/RTCP payload for QUIC streams
Length: A QUIC variable length integer Section 16 of [RFC9000]
describing the length of the following RTP/RTCP packets in bytes.
RTP/RTCP Packet: The RTP/RTCP packet to transmit.
If a sender knows that a packet, which was not yet successfully and
completely transmitted, is no longer needed, the sender MAY close the
stream by sending a RESET_STREAM frame.
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 on QUIC datagrams.
*Editor's Note:* It might be desired to also allow the receiver to
request cancellation of a stream by sending STOP_SENDING frame.
However, this might lead to unintended packet loss because the
receiver does not know which and how many packets follow on the
same stream. If this feature is required, a solution could be to
require senders to open new streams for each application data
unit, as described in a previous version of this document.
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Large RTP packets sent on a stream will be fragmented into smaller
QUIC frames. The QUIC frames are transmitted reliably and in order
such 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 QUIC frames lost in transit are retransmitted by QUIC.
Opening new streams for new packets MAY 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 have to 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 with
enough credit to open new streams for new packets at any time.
5.3. QUIC Datagrams
Senders can also transmit RTP packets in QUIC datagrams. QUIC
datagrams are an extension to QUIC described in [RFC9221]. QUIC
datagrams preserve frame boundaries. Thus, a single RTP packet can
be mapped to a single QUIC datagram without additional framing.
Senders SHOULD consider the header overhead associated with QUIC
datagrams and ensure that the RTP/RTCP packets, including their
payloads, flow identifier, QUIC, and IP headers, will fit into path
MTU.
Figure 3 shows the encapsulation format for RTP over QUIC Datagrams.
Payload {
Flow Identifier (i),
RTP/RTCP Packet (..),
}
Figure 3: RTP over QUIC Datagram Payload Format
Flow Identifier: Flow identifier to demultiplex different data flows
on the same QUIC connection.
RTP/RTCP Packet: The RTP/RTCP packet to transmit.
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Since QUIC datagrams are not retransmitted on loss (see also
Section 6.1 for loss signaling), if an application wishes to
retransmit lost RTP packets, the retransmission has to be implemented
by the application. RTP retransmissions can be done in the same RTP
session or a separate RTP session [RFC4588] and the flow identifier
MUST be set to the flow identifier of the RTP session in which the
retransmission happens.
6. RTCP
The RTP Control Protocol (RTCP) allows RTP senders and receivers to
exchange control information to monitor connection statistics and to
identify and synchronize streams. Many of the statistics contained
in RTCP packets overlap with the connection statistics collected by a
QUIC connection. To avoid using up bandwidth for duplicated control
information, the information SHOULD only be sent at one protocol
layer. QUIC relies on certain control frames to be sent.
In general, applications MAY send RTCP without any restrictions.
This document specifies a baseline for replacing some of the RTCP
packet types by mapping the contents to QUIC connection statistics.
Future documents can extend this mapping for other RTCP format types.
It is RECOMMENDED to expose relevant information from the QUIC layer
to the application instead of exchanging additional RTCP packets,
where applicable.
This section discusses what information can be exposed from the QUIC
connection layer to reduce the RTCP overhead and which type of RTCP
messages cannot be replaced by similar feedback from the transport
layer. The list of RTCP packets in this section is not exhaustive
and similar considerations SHOULD be taken into account before
exchanging any other type of RTCP control packets.
6.1. Transport Layer Feedback
This section explains how some of the RTCP packet types which 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.
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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. For RTP packets that are sent over QUIC streams, an
RTP packet can be considered acknowledged, when all frames which
carried fragments of the RTP packet were acknowledged.
When QUIC Streams are used, the application should be aware that the
direct mapping proposed below may 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 might be incorrect due to
retransmissions.
Some of the transport layer feedback that can be implemented in RTCP
contains information that is not included in QUIC by default, but can
be added via QUIC extensions. One important example are arrival
timestamps, which are not part of QUIC's default acknowledgment
frames, but can be added using [I-D.draft-smith-quic-receive-ts] or
[I-D.draft-huitema-quic-ts]. Another extension, that can improve the
precision of the feedback from QUIC is
[I-D.draft-ietf-quic-ack-frequency], which allows a sender to control
the delay of acknowledgments sent by the receiver.
The list of RTCP Receiver Reports that could be replaced by feedback
from QUIC follows:
* _Receiver Reports_ (PT=201, Name=RR, [RFC3550])
- _Fraction lost_: When RTP packets are carried in QUIC
datagrams, the fraction of lost packets can be directly
inferred from QUIC's acknowledgments. The calculation SHOULD
include all packets up to the acknowledged RTP packet with the
highest RTP sequence number. Later packets SHOULD be ignored,
since they may still be in flight, unless other QUIC packets
that were sent after the RTP packet, were already acknowledged.
- _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
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packets in QUIC 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 one of the extensions referenced above, senders
can infer from QUIC acks the interarrival jitter from the
arrival timestamps.
- _Last SR_: Similar to RTP arrival times, the arrival time of
RTCP Sender Reports can be inferred from QUIC acknowledgments,
if they include timestamps.
- _Delay since last SR_: This field is not required when the
receiver reports are entirely replaced by QUIC feedback.
* _Negative Acknowledgments_ (PT=205, FMT=1, Name=Generic NACK,
[RFC4585])
- The generic negative acknowledgment packet contains information
about packets which the receiver considered lost.
Section 6.2.1. of [RFC4585] recommends to use 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].
* _ECN Feedback_ (PT=205, FMT=8, Name=RTCP-ECN-FB, [RFC6679])
- ECN feedback 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 which are listed below. QUIC supports ECN reporting
through acknowledgments. If the connection supports ECN, the
reporting of ECN counts SHOULD be done using QUIC
acknowledgments, rather than RTCP ECN feedback reports.
* _Congestion Control Feedback_ (PT=205, FMT=11, Name=CCFB,
[RFC8888])
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- RTP Congestion Control Feedback 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].
* _Extended Reports_ (PT=207, Name=XR, [RFC3611])
- Extended Reports offer an extensible framework for a variety of
different control messages. Some of the standard report blocks
which can be implemented in extended reports such as loss RLE
or ECNs can be implemented in QUIC, too. For other report
blocks, it SHOULD be evaluated individually, if the contained
information can be transmitted using QUIC instead.
6.2. Application Layer Repair and other Control Messages
While the previous section presented some RTCP packet that can be
replaced by QUIC features, QUIC cannot replace all of the available
RTCP packet types. This mostly affects RTCP packet types which carry
control information that is to be interpreted by the application
layer instead of the transport itself.
_Sender Reports_ (PT=200, Name=SR, [RFC3550]) are similar to
_Receiver Reports_. They are sent by media senders and additionally
contain a NTP and a RTP timestamp and the number of packets and
octets transmitted by the sender. The timestamps can be used by a
receiver to synchronize streams. QUIC cannot provide a similar
control information, since it does not know about RTP timestamps.
Nor can a QUIC receiver calculate the packet or octet counts, since
it does not know about lost datagrams. Thus, sender reports are
required in RTP over QUIC to synchronize streams at the receiver.
The sender reports SHOULD not contain any receiver report blocks, as
the information can be inferred from the QUIC transport as explained
in the previous section.
Next to carrying transmission statistics, RTCP packets can contain
application layer control information, that cannot directly be mapped
to QUIC. This includes for example the _Source Description_ (PT=202,
Name=SDES), _Bye_ (PT=203, Name=BYE) and _Application_ (PT=204,
Name=APP) packet types from [RFC3550] or many of the payload specific
feedback messages (PT=206) defined in [RFC4585], which can for
example be used to control the codec behavior of the sender. Since
QUIC does not provide any kind of application layer control
messaging, these RTCP packet types SHOULD be used in the same way as
they would be used over any other transport protocol.
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7. Congestion Control and Rate Adaptation
Like any other application on the internet, RTP over QUIC needs to
perform congestion control to avoid overloading the network.
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].
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 accomoplish congestion control as
well. Various rate adaptation algorithms for real-time media are
defined in separate RFCs (e.g. SCReAM [RFC8298] and NADA [RFC8698]).
The rate adaptation algorithms for RTP are specifically tailored for
real-time transmissions at low latencies. The available rate
adaptation algorithms for RTP expose a target_bitrate that can be
used to dynamically reconfigure media codecs to produce media at a
rate that can be sent in real-time under the observed network
conditions.
This section defines two architectures for congestion control and
bandwidth estimation for RTP over QUIC, but it does not mandate any
specific rate adaptation algorithm to use. The section also
discusses congestion control implications of using shared or multiple
separate QUIC connections to send and receive multiple independent
data streams.
It is assumed that the congestion controller in use provides a pacing
mechanism to determine when a packet can be sent to avoid bursts.
The currently proposed congestion control algorithms for real-time
communications provide such pacing mechanisms. The use of congestion
controllers which don't provide a pacing mechanism is out of scope of
this document.
7.1. Congestion Control at the QUIC layer
If congestion control is to be applied at the transport layer, it is
RECOMMENDED that the QUIC Implementation uses a congestion controller
that keeps queueing delays short to keep the transmission latency for
RTP and RTCP packets as low as possible.
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Many low latency congestion control algorithms depend on detailed
arrival time feedback to estimate the current one-way delay between
sender and receiver. QUIC does not provide arrival timestamps in its
acknowledgments. The QUIC implementations of the sender and receiver
can use an extension to add this information to QUICs acknowledgment
frames, e.g. [I-D.draft-smith-quic-receive-ts] or
[I-D.draft-huitema-quic-ts].
If congestion control is done by the QUIC implementation, the
application needs a mechanism to query the currently available
bandwidth to adapt media codec configurations. The employed
congestion controller of the QUIC connection SHOULD expose such an
API to the application. If a current bandwidth estimate is not
available from the QUIC congestion controller, the sender can either
implement an alternative bandwidth estimation at the application
layer as described in Section 7.2 or a receiver can feedback the
observed bandwidth through RTCP, e.g., using
[I-D.draft-alvestrand-rmcat-remb].
7.2. Congestion Control at the Application Layer
If an application cannot access a bandwidth estimation from the QUIC
layer, or the QUIC implementation does not support a delay-based,
low-latency congestion control algorithm, the application can
alternatively implement a bandwidth estimation algorithm at the
application layer. Calculating a bandwidth estimation at the
application layer can be done using the same bandwidth estimation
algorithms as described in Section 7 (NADA, SCReAM). The bandwidth
estimation algorithm typically needs some feedback on the
transmission performance. This feedback can be collected following
the guidelines in Section 6.
If the application implements full congestion control rather than
just a bandwidth estimation at the application layer using a
congestion controller that satisfies the requirements of Section 7 of
[RFC9002], and the connection is only used to send real-time media
which is subject to the application layer congestion control, it is
RECOMMENDED to disable any other congestion control that is possibly
running at the QUIC layer. Disabling the additional congestion
controllers helps to avoid any interference between the different
congestion controllers.
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7.3. Shared QUIC connections
Two endpoints may want to 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. A straightforward solution is to
establish multiple QUIC connections, one for each channel. Or all
real-time channels are mapped to one QUIC connection, while a
separate QUIC connection is created for the non-real-time channels.
In both 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.
Alternatively, (all or a subset of) real-time and non-real-time
channels are multiplexed onto a single, shared QUIC connection, which
can be done by using the flow identifier described in Section 5.
Applications multiplexing multiple streams in one connection SHOULD
implement some form of stream prioritization or bandwidth allocation.
8. API Considerations
The mapping described in the previous sections poses some interface
requirements on the QUIC implementation. Although a basic mapping
should work without any of these requirements most of the
optimizations regarding rate adaptation and RTCP mapping require
certain functionalities to be exposed to the application. The
following to sections contain a list of information that is required
by an application to implement different optimizations (Section 8.1)
and functions that a QUIC implementation SHOULD expose to an
application (Section 8.2).
Each item in the following list can be considered individually. Any
exposed information or function can be used by RTP over QUIC
regardless of whether the other items are available. Thus, RTP over
QUIC 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.
8.1. Information to be exported from QUIC
This section provides a list of items that an application might want
to export from an underlying QUIC implementation. It is thus
RECOMMENDED that a QUIC implementation exports the listed items to
the application.
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* _Maximum Datagram Size_: The maximum datagram size that the QUIC
connection can transmit.
* _Datagram Acknowledgment and Loss_: Section 5.2 of [RFC9221]
allows QUIC implementations to notify the application that a QUIC
Datagram was acknowledged or that it believes a datagram was lost.
The exposed information SHOULD include enough information to allow
the application to maintain a mapping between the datagram that
was acknowledged/lost and the RTP packet that was sent in that
datagram.
* _Stream States_: The QUIC implementation SHOULD expose to a
sender, how much of the data that was sent on a stream was
successfully delivered and how much data is still outstanding to
be sent or retransmitted.
* _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 SHOULD be exposed to the application.
* _Bandwidth Estimation_: If congestion control is done at the
transport layer in the QUIC implementation, the QUIC
implementation SHOULD expose an estimation of the currently
available bandwidth to the application. Exposing the bandwidth
estimation avoids the implementation of an additional bandwidth
estimation algorithm in the application.
* _ECN_: If ECN marks are available, they SHOULD be exposed to the
application.
8.2. Functions to be exposed by QUIC
This sections lists functions that a QUIC implementation SHOULD
expose to an application to implement different features of the
mapping described in the previous sections of this document.
* _Cancel Streams_: To allow an application to cancel
(re)transmission of packets that are no longer needed, the QUIC
implementation MUST expose a way to cancel the corresponding QUIC
streams.
* _Configure Congestion Controller_: If congestion control is to be
implemented at the QUIC connection layer as described in
Section 7.1, the QUIC implementation SHOULD expose an API to allow
the application to configure the specifics of the congestion
controller.
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* _Disable Congestion Controller_: If congestion control is to be
implemented at the application layer as described in Section 7.2,
and the application layer is trusted to apply adequate congestion
control as described in Section 7 of [RFC9002] and Section 3.1 of
[RFC8085], it is RECOMMENDED to allow the application to disable
QUIC layer congestion control entirely.
9. Discussion
9.1. Flow Identifier
[RFC9221] suggests to use flow identifiers to multiplex different
streams on QUIC Datagrams, which is implemented in Section 5, but it
is unclear how applications can combine RTP over QUIC with other data
streams using the same QUIC connections. If the non-RTP data streams
use the same flow identifies, too and the application can make sure,
that flow identifiers are unique, there should be no problem. Flow
identifiers could be problematic, if different specifications for RTP
and non-RTP data streams over QUIC mandate different incompatible
flow identifiers.
9.2. Impact of Connection Migration
RTP sessions are characterized by a continuous flow of packets into
either or both directions. A connection migration may lead to
pausing media transmission until reachability of the peer under the
new address is validated. This may lead to short breaks in media
delivery in the order of RTT and, if RTCP is used for RTT
measurements, may cause spikes in observed delays. Application layer
congestion control mechanisms (and also packet repair schemes such as
retransmissions) need to be prepared to cope with such spikes.
If a QUIC connection is established via a signaling channel, this
signaling may have involved Interactive Connectivity Establishment
(ICE) exchanges to determine and choose suitable (IP address, port
number) pairs for the QUIC connection. Subsequent address change
events may be noticed by QUIC via its connection migration handling
and/or at the ICE or other application layer, e.g., by noticing
changing IP addresses at the network interface. This may imply that
the two signaling and data "layers" get (temporarily) out of sync.
*Editor's Note:* It may be desirable that the API provides an
indication of connection migration event for either case.
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9.3. 0-RTT considerations
For repeated connections between peers, the initiator of a QUIC
connection can use 0-RTT data for both QUIC streams and datagrams.
As such packets are subject to replay attacks, applications shall
carefully specify which data types and operations are allowed. 0-RTT
data may be beneficial for use with RTP over QUIC to reduce the risk
of media clipping, e.g., at the beginning of a conversation.
This specification defines carrying RTP on top of QUIC and thus does
not finally define what the actual application data are going to be.
RTP typically carries ephemeral media contents that is rendered and
possibly recorded but otherwise causes no side effects. Moreover,
the amount of data that can be carried as 0-RTT data is rather
limited. But it is the responsibility of the respective application
to determine if 0-RTT data is permissible.
*Editor's Note:* Since the QUIC connection will often be created
in the context of an existing signaling relationship (e.g., using
WebRTC or SIP), specific 0-RTT keying material could be exchanged
to prevent replays across sessions. Within the same connection,
replayed media packets would be discarded as duplicates by the
receiver.
10. Security Considerations
RTP over QUIC 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 RTP over QUIC.
11. IANA Considerations
11.1. Registration of a RTP over QUIC Identification String
This document creates a new registration for the identification of
RTP over QUIC in the "TLS Application-Layer Protocol Negotiation
(ALPN) Protocol IDs" registry [RFC7301].
The "rtp-mux-quic" string identifies RTP over QUIC:
Protocol: RTP over QUIC
Identification Sequence: 0x72 0x74 0x70 0x2D 0x6F 0x76 0x65 0x72
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0x2D 0x71 0x75 0x69 0x63 ("rtp-mux-quic")
Specification: This document
12. References
12.1. Normative References
[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-ietf-quic-ack-frequency]
Iyengar, J. and I. Swett, "QUIC Acknowledgement
Frequency", Work in Progress, Internet-Draft, draft-ietf-
quic-ack-frequency-02, 11 July 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-quic-
ack-frequency-02>.
[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>.
[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>.
[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>.
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[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>.
[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>.
[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>.
[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>.
[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>.
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[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>.
[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>.
12.2. Informative References
[I-D.draft-alvestrand-rmcat-remb]
Alvestrand, H. T., "RTCP message for Receiver Estimated
Maximum Bitrate", Work in Progress, Internet-Draft, draft-
alvestrand-rmcat-remb-03, 21 October 2013,
<https://datatracker.ietf.org/doc/html/draft-alvestrand-
rmcat-remb-03>.
[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-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>.
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[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-wish-whip]
Murillo, S. G. and A. Gouaillard, "WebRTC-HTTP ingestion
protocol (WHIP)", Work in Progress, Internet-Draft, draft-
ietf-wish-whip-06, 29 December 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-wish-
whip-06>.
[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>.
[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>.
[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>.
[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>.
[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>.
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Internet-Draft RTP over QUIC February 2023
[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>.
[RFC9308] Kühlewind, 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>.
Appendix A. Experimental Results
An experimental implementation of the mapping described in this
document can be found on Github (https://github.com/mengelbart/rtp-
over-quic). The application implements the RTP over QUIC Datagrams
mapping and implements SCReAM congestion control at the application
layer. It can optionally disable the builtin 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 6.1.
Experimental results of the implementation can be found on Github
(https://github.com/mengelbart/rtp-over-quic-mininet), too.
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.
The authors would like to thank Bernard Aboba, David Schinazi, Lucas
Pardue, Sergio Garcia Murillo, Spencer Dawkins, and Vidhi Goel for
their valuable comments and suggestions contributing to this
document.
Authors' Addresses
Jörg Ott
Technical University Munich
Email: ott@in.tum.de
Mathis Engelbart
Technical University Munich
Email: mathis.engelbart@gmail.com
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