Internet DRAFT - draft-hurst-quic-rtp-tunnelling
draft-hurst-quic-rtp-tunnelling
Network Working Group S. Hurst
Internet-Draft BBC Research & Development
Intended status: Informational 28 January 2021
Expires: 1 August 2021
QRT: QUIC RTP Tunnelling
draft-hurst-quic-rtp-tunnelling-01
Abstract
QUIC is a UDP-based transport protocol for stream-orientated,
congestion-controlled, secure, multiplexed data transfer. RTP
carries real-time data between endpoints, and the accompanying
control protocol RTCP allows monitoring and control of the transfer
of such data. With RTP and RTCP being agnostic to the underlying
transport protocol, it is possible to multiplex both the RTP and
associated RTCP flows into a single QUIC connection to take advantage
of QUIC features such as low-latency setup and strong TLS-based
security.
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
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 1 August 2021.
Copyright Notice
Copyright (c) 2021 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/
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Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
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extracted from this document must include Simplified BSD License text
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provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions and Definitions . . . . . . . . . . . . . . . 3
1.2. Definitions . . . . . . . . . . . . . . . . . . . . . . . 3
2. Use Cases for an RTP Mapping over QUIC . . . . . . . . . . . 4
2.1. Live Event Contribution Feed . . . . . . . . . . . . . . 4
2.2. Audio and Video Conference via a Central Server . . . . . 5
3. QRT Sessions . . . . . . . . . . . . . . . . . . . . . . . . 5
4. RTP Sessions . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. QRT Flow Identifier . . . . . . . . . . . . . . . . . . . 6
4.2. RTCP Mapping . . . . . . . . . . . . . . . . . . . . . . 8
4.2.1. Restricted RTCP Packet Types . . . . . . . . . . . . 8
5. Loss Recovery and Retransmission . . . . . . . . . . . . . . 9
6. Using the Session Description Protocol to Advertise QRT
Sessions . . . . . . . . . . . . . . . . . . . . . . . . 9
6.1. Using the Session Description Protocol to Advertise QRT
Sessions using RTP Retransmission . . . . . . . . . . . . 10
7. Exposing Round-Trip Time to RTP applications . . . . . . . . 11
8. Application Interface Expectations . . . . . . . . . . . . . 11
9. Protocol Identifier . . . . . . . . . . . . . . . . . . . . . 12
9.1. Draft Version Identification . . . . . . . . . . . . . . 12
10. Security Considerations . . . . . . . . . . . . . . . . . . . 13
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
11.1. Registration of Protocol Identification String . . . . . 13
11.2. Registration of SDP Protocol Identifier . . . . . . . . 13
11.3. Registration of SDP Attribute Field . . . . . . . . . . 14
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
12.1. Normative References . . . . . . . . . . . . . . . . . . 14
12.2. Informative References . . . . . . . . . . . . . . . . . 15
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 16
Appendix B. Changelog . . . . . . . . . . . . . . . . . . . . . 16
B.1. Since draft-hurst-quic-rtp-tunnelling-00 . . . . . . . . 16
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction
The Real-time Transport Protocol (RTP) [RFC3550] provides end-to-end
network transport functions suitable for applications transmitting
data, such as audio and video, over multicast or unicast network
services for the purposes of telephony, video streaming, conferencing
and other real-time applications.
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The QUIC transport protocol is a UDP-based stream-orientated and
encrypted transport protocol aimed at offering improvements over the
common combination of TCP and TLS for web applications. Compared
with TCP+TLS, QUIC offers much reduced connection set-up times,
improved stream multiplexing aware congestion control, and the
ability to perform connection migration. QUIC offers two modes of
data transfer:
* Reliable transfer using STREAM frames, as specified in
[QUIC-TRANSPORT], [QUIC-RECOVERY], etc.
* Unreliable transfer using DATAGRAM extension frames, as specified
in [QUIC-DATAGRAM].
RTP has traditionally been run over UDP or DTLS to achieve timely but
unreliable data transfer. For use cases such as real-time audio and
video transmission, the underlying media codecs can be considered in
part fault-tolerant to an unreliable transport mechanism, with
missing data from the stream resulting in glitches in the media
presentation, such as missing video frames or gaps in audio playback.
By purposely using an unreliable transport mechanism, applications
can minimise the added latency that would otherwise result from
managing the large packet reception buffers needed to account for
network reordering or transport protocol retransmission.
1.1. Conventions and Definitions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Packet and frame diagrams in this document use the format described
in [QUIC-TRANSPORT].
1.2. Definitions
* Endpoint: host capable of being a participant in a QRT session.
* QRT session: A QUIC connection carrying one or more RTP sessions,
each with or without an accompanying RTCP channel.
* RTP layer: The logical entity which manages the RTP sessions
carried in the QRT session.
* Client: The endpoint which initiates the QUIC connection.
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* Server: The endpoint which accepts the incoming QUIC connection.
2. Use Cases for an RTP Mapping over QUIC
The following sections describe some possible use cases for an RTP
and RTCP mapping over QUIC, hereafter QRT. The examples were chosen
to illustrate some basic concepts, and are neither an exhaustive list
of possible use cases nor a limitation on what QRT may be used for.
2.1. Live Event Contribution Feed
A news organisation wishes to provide a two-way link to a live event
for distribution as part of an item in a news programme hosted in a
studio with a news anchor. The single camera remote production crew
will include a camera operator, sound technician and the reporter.
In order to deliver this experience, the following media flows are
required:
* A high-quality video feed from the remote camera to the news
organisation's gallery;
* One or more audio feeds for microphones at the event, including an
ambient microphone attached to the camera, a lapel microphone for
the reporter, and a handheld microphone to conduct interviews, all
synchronized;
* A video feed of the programme output from the gallery, after
mixing for local monitoring and for use on a comfort monitor;
* An audio feed from the anchor in the studio to the reporter;
* A two-way audio feed from the gallery to the remote production
crew for talkback communication;
* A tally light feed for the remote camera.
These media flows may be realised as a group of RTP sessions, some of
which must be synchronised together. The talkback streams do not
require any tight synchronisation with other streams in the group,
whereas the camera video feed and various microphone feeds need to be
tightly synchronised together.
At the event, a production machine running a software package that
includes a QRT client has two connections to the Internet; a high-
speed fibre link and a bonded cellular network link for backup.
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In order to prevent a bad actor on the network path being able to
tamper with the contribution, all communication between the news
organisation's gallery and the remote production need to be
encrypted. Because all the data is flowing between the same two
endpoints, only a single QRT session is required, and the various RTP
sessions that are encapsulated by the QRT session are (de)multiplexed
at each end.
During the live contribution, an accident cuts the fibre connection
to the remote production crew. Using the QUIC connection migration
mechanism presented in Section 9 of [QUIC-TRANSPORT], the QRT session
migrates from the fibre link onto the backup cellular link. This
preserves the state of the RTP sessions across a network migration
event, and all sessions continue.
2.2. Audio and Video Conference via a Central Server
A teleconference is taking place across multiple sites using a
centralised server. All participants connect to this single server,
and the server acts as an RTP mixer to reduce the number of RTP
sessions being sent to all participants, as well as re-encoding the
streams for efficiency reasons.
One participant of this conference has connected via mobile phone.
However, when the participant enters the range of a previously-
associated WiFi network, the mobile phone switches its network
connection across to this new network. The QRT session can then
migrate across, and the participant is able to continue the call with
minimal interruption.
3. QRT Sessions
A QRT session is defined as a QUIC connection which carries one or
more RTP sessions (including any associated RTCP flows) using
"DATAGRAM" frames, as specified in Section 4. Those RTP sessions may
be part of one or more RTP multimedia sessions, and a multimedia
session may be comprised of RTP sessions carried in one or more QRT
sessions.
A QRT session may be established using an existing or new QUIC
transport connection as specified in section 5 of [QUIC-TRANSPORT].
For a given QUIC transport connection, QRT MUST be the only protocol
using "DATAGRAM" frames. QRT MAY coexist on the same QUIC connection
with applications using other frame types, such as "STREAM" frames.
*Author's Note:* When [QUIC-DATAGRAM] or an equivalent extension
draft specifies a generic manner for multiplexing traffic destined
for different applications over "DATAGRAM" frames, then this draft
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SHOULD adopt such a mechanism and loosen or remove the restriction
on QRT being the only protocol using "DATAGRAM" frames on a QUIC
connection.
4. RTP Sessions
QRT allows multiple RTP sessions to be carried in a single QRT
session. Each RTP session is operated independently of all the
others, and individually discriminated by an QRT Flow Identifier, as
described below in Section 4.1.
RTP and RTCP packets are carried in QUIC "DATAGRAM" frames, as
described in [QUIC-DATAGRAM]. QUIC allows multiple QUIC frames to be
carried within a single QUIC packet, so multiple RTP/RTCP packets for
one (or more) RTP sessions may therefore be carried in a single QUIC
packet, subject to the network path MTU. If multiple RTP packets are
to be carried within a single QUIC packet, then all but the final
"DATAGRAM" frame must specify the length of the datagram, since the
RTP packet header does not provide its own length field.
[QUIC-DATAGRAM] specifies that if a "DATAGRAM" frame is received
without a Length field, then this "DATAGRAM" frame extends to the end
of the QUIC packet.
4.1. QRT Flow Identifier
[RFC3550] specifies that RTP sessions are distinguished by pairs of
transport addresses, with a separate pair of ports for the RTP and
RTCP packet flows comprising the RTP session. However, since QUIC
allows for connections to migrate between transport address
associations, and because we wish to multiplex multiple RTP sessions
over a single QRT session, this profile of RTP amends this statement
and instead introduces a QRT Flow Identifier to identify packet flows
belonging to different RTP sessions within the QRT session. A
matched pair of these QRT Flow Identifiers distinguishes the RTP
packet flow and RTCP packet flow of each RTP session. The QRT Flow
Identifier is a 62-bit unsigned integer between 0 and 2^62 - 1.
This specification does not mandate a means by which QRT Flow
Identifiers are allocated for use within QRT sessions. An example
mapping for this is discussed in Section 6 below. Implementations
SHOULD allocate flow identifiers that make the most efficient use of
the variable length integer packing mechanism, by not using flow
identifiers greater than can be expressed in the smallest variable
length integer field until all available flow identifiers have been
used.
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The scope of a QRT Flow Identifier is specific to the QRT session
that it is used on. An RTP flow carried over multiple QRT sessions
may have different flow identifiers on each QRT session that it
passes through. For example, there could be two QRT endpoints (A, B)
each sending a set of RTP flows to a third QRT endpoint which is
acting as an RTP mixer (M), which itself is then forwarding some or
all of the flows on to a fourth QRT endpoint (C) which consumes the
flows. As it's likely that the QRT Flow Identifiers for the
connections A->M and B->M will collide, the flow identifiers used on
the connection M->C will use different flow identifiers. The
allocation of identifiers to use is, again, not defined by this
document.
The flow of packets belonging to an RTP session is identified using
an RTP Session Flow Identifier header carried in the "DATAGRAM" frame
payload before each RTP/RTCP packet. This flow identifier is encoded
as a variable-length integer, as defined in [QUIC-TRANSPORT].
QRT Datagram Payload {
QRT Flow Identifier (i),
RTP/RTCP Packet (..)
}
Figure 1: QRT Datagram Payload
Similar to QUIC stream IDs, the least significant bit (0x1) of the
QRT Flow Identifier distinguishes between an RTP and an RTCP packet
flow. "DATAGRAM" frames which carry RTP packet flows set this bit to
0, and "DATAGRAM" frames which carry RTCP packet flows set this bit
to 1. As a consequence, RTP packet flows have even numbered QRT Flow
Identifiers, and RTCP packet flows have odd-numbered QRT Flow
Identifiers. Carriage of RTCP packets is discussed further in
Section 4.2.
+=======================+=====================================+
| Least significant bit | Flow identifier category |
+=======================+=====================================+
| 0x0 | RTP packet flow for an RTP session |
+-----------------------+-------------------------------------+
| 0x1 | RTCP packet flow for an RTP session |
+-----------------------+-------------------------------------+
Table 1: RTP session flow identifer categories
*Author's Note:* The author welcomes comments on whether a state
model of RTP session flows would be beneficial. Currently, once
an RTP session has been used by an endpoint, it is then considered
an extant RTP session and implementations would have to keep any
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resources allocated to that RTP session until the QRT session is
complete. In addition, how should endpoints react to receiving
packets for unknown QRT Flow Identifiers?
4.2. RTCP Mapping
An RTP session may have RTCP packet flows associated with it. These
flows are carried with different QRT Flow Identifiers, as described
in Section 4.1. The QRT Flow Identifier of the RTCP packet flow is
always the value of the RTP packet flow QRT Flow Identifier + 1. For
example, for an RTP packet flow using flow identifier 18, the RTCP
packet flow would use flow identifier 19.
Since RTCP packets contain a length field in their header,
implementations MAY combine several RTCP packets pertaining to the
same RTP session into a single "DATAGRAM" frame. Alternatively,
implementations MAY choose to carry these RTCP packets each in their
own "DATAGRAM" frame.
4.2.1. Restricted RTCP Packet Types
*Author's Note:* I have specifically avoided calling this section
"Prohibited RTCP packet types" for the time being, so as to not
unnecessarily exclude the carriage of these packet types for the
purposes of experimentation. Similarly, most statements below use
SHOULD NOT instead of MUST NOT. The author welcomes comments on
whether the document should prohibit the sending of some or all of
these packet types.
[QUIC-TRANSPORT] implements many transport features that RTP/RTCP has
also implemented in order to manage transmission on unreliable
transport protocols. In order to reduce duplication between QUIC
transport and RTP/RTCP, if QUIC transport or the QRT session exposes
a transport feature to the RTP layer then it takes precedence over
the same feature in RTP/RTCP.
In addition, some RTP/RTCP packets that relate to specific features
or capabilities of the transport protocol that are not explicitly
relevant to QRT SHOULD NOT be sent on a QRT session unless they
relate to some part of an RTP multimedia session outside of the scope
of the QRT session. Any and all QRT-specific messages should be
implemented at the "DATAGRAM" or "STREAM" level in QRT, and not
carried as RTP/RTCP packets.
The following is a non-exhaustive list of RTCP packet types that
SHOULD NOT be sent in a QRT session:
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* The "Generic NACK" packet. [RFC4585] states that Generic NACK
feedback SHOULD NOT be used if the underlying transport protocol
is capable of providing similar feedback information to the
sender. In order to fulfil this requirement, QRT implementations
MUST provide data about "DATAGRAM" acknowledgement, or lack
thereof, to the RTP layer.
* The "Loss RLE" Extended Report (XR) packet defined in [RFC3611]
contains information that should already be known to both ends of
the QUIC connection by means of the loss detection mechanism
specified in [QUIC-RECOVERY].
* The "Port Mapping" packet type defined in [RFC6284] is used to
negotiate UDP port pairs for the carriage of RTP and RTCP packets
to peers. This does not apply in a QRT session, because the QUIC
endpoints manage the UDP port association(s) for the QUIC
connection as a whole.
5. Loss Recovery and Retransmission
*Author's Note:* Do we want to mandate (make a MUST) doing
session-multiplexing instead of SSRC-multiplexing for RTP
retransmission?
[RFC4588] specifies two schemes to support retransmission in the case
of RTP packet loss. Since QRT natively supports RTP session
multiplexing on a single QUIC connection, endpoints choosing to
implement retransmission SHOULD do so using the session-multiplexing
scheme.
The selection of a new QRT Flow Identifier to use for the
retransmission RTP session is implementation-specific. Section 6.1
specifies how the mapping between original and retransmission RTP
sessions is expressed using the Session Description Protocol (SDP).
6. Using the Session Description Protocol to Advertise QRT Sessions
[RFC8866] describes a format for advertising multimedia sessions,
which is used by protocols such as [RFC3261].
This specification introduces a new SDP value attribute ""qrtflow""
as a means of assigning QRT Flow Identifiers to RTP and RTCP packet
flows. Its formatting in SDP is described by the following ABNF
[RFC5234]:
qrtflow-attribute = "a=qrtflow:" qrt-flow-id
qrt-flow-id = 1*DIGIT ; unsigned 62-bit integer
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Per Section 4.1 the value of the "qrt-flow-id" is required to be an
even number. (The odd-numbered RTCP flow associated with the RTP
session is not explicitly signalled in the SDP object.)
The example in Figure 2 below shows a hypothetical QRT server
advertising an endpoint to use for live contribution. It instructs a
prospective client to send a VC2-encoded video stream and a Vorbis-
encoded audio stream on two separate RTP sessions. In addition, it
uses the SDP grouping framework described in [RFC5888] to ensure lip
synchronisation between both of those RTP sessions.
v=0
o=gfreeman 1594130940 1594135167 IN IP6 qrt.example.org
s=Live Event Contribution
c=IN IP6 2001:db8::7361:6d68
t=1594130980 1594388466
a=group:LS 1 2
m=video 443 RTP/QRT 96
a=qrtflow:0
a=rtpmap:96 vc2
a=mid:1
a=sendonly
m=audio 443 RTP/QRT 97
a=qrtflow:2
a=rtpmap:97 vorbis
a=mid:2
a=sendonly
Figure 2: SDP object describing a QRT session
Since the value of a QRT Flow Identifier for an associated RTCP flow
is specified in Section 4.2, SDP advertisements containing the
"a=qrtflow:" attribute MUST NOT contain an instance of the "a=rtcp:"
attribute as defined in [RFC3605].
6.1. Using the Session Description Protocol to Advertise QRT Sessions
using RTP Retransmission
The example in Figure 3 below shows a hypothetical QRT session
advertisement for a bidirectional RTP session carrying an MPEG-2
Transport Stream in each direction on QRT Flow Identifier 0, and a
corresponding pair of retransmission flows on QRT Flow Identifier 2.
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v=0
o=gfreeman 1594130940 1594135167 IN IP6 qrt.example.org
s=Live Event Contribution
c=IN IP6 2001:db8::4242:4351:5254
t=1594130980 1594388466
m=video 443 RTP/QRT 33
a=qrtflow:0
m=video 443 RTP/QRT 96
a=rtpmap:97 rtx/90000
a=fmtp:96 apt=33;rtx-time=4000
a=qrtflow:2
Figure 3: SDP object describing a QRT session with RTP retransmission
7. Exposing Round-Trip Time to RTP applications
Section 5 of [QUIC-RECOVERY] specifies a mechanism for QUIC endpoints
to estimate the rount-trip time (RTT) of a connection. QRT
implementations SHOULD expose the values of "min_rtt", "smoothed_rtt"
and "rttvar" for each network path to the RTP layer, and they MAY use
these values either alone or in combination with RTCP messages to
discern the round-trip time of the QRT session.
*Author's Note:* The author welcomes comments on how appropriate
these QUIC RTT measurements are to the RTP layer.
8. Application Interface Expectations
The QRT implementation described in this document assumes that it is
a simple mapping layer between an RTP implementation and a QUIC
transport implementation. A QRT implementation MAY incorporate one
or both of the RTP and QUIC implementations into the same library or
application, or they MAY be separate and linked at runtime.
* The QRT implementation MUST provide an interface that consumes and
produces RTP and RTCP flows (as applicable). RTP and RTCP packets
in an RTP flow are expected to be carried with no modification,
and thus the QRT implementation should reject RTP/RTCP packets
which would not fit wholly within a single "DATAGRAM" frame, as
this specification does not permit fragmentation. QRT
implementations MUST expose the maximum RTP/RTCP packet size
permitted for the current network path.
*Author's Note:* Future versions of this specification may provide
additional guidance on the allocation of QRT Flow Identifiers.
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* The QUIC transport implementation MUST provide an implementation
of the [QUIC-DATAGRAM] extension frame type. A single QRT session
MUST be the only application using a "DATAGRAM" frame in any QUIC
connection.
* The QUIC transport implementation MUST provide an interface to the
QRT implementation to either query or push (via a callback)
details about whether a previously sent "DATAGRAM" has been
acknowledged by the remote peer as discussed in Section 5. The
QRT implementation will then forward that information to the RTP
implementation.
* The QUIC transport implementation SHOULD provide an interface to
the QRT implementation to either query or push (via a callback)
the QUIC round-trip time calculations as discussed in Section 7.
If provided, then the QRT implementation MUST expose that
information to the RTP implementation. Some conversion or
adaptation of that data to make it more applicable to a given RTP
implementation's expected format is permitted.
* The QRT implementation should indicate errors at any of its
interfaces at the soonest possible opportunity.
*Author's Note:* Future versions of this specification may specify
interfaces for handling prioritisation of individual RTP flows, or
multiplexing QRT with another "DATAGRAM"-using application
protocol. Ideally, these would be implemented generically at the
"DATAGRAM" frame level or via another generic draft, but may be
implemented directly in QRT if no generic implementation exists.
Experiments to this effect are encouraged.
9. Protocol Identifier
The QRT protocol specified in this document is identified by the
Application-Layer Protocol Negotiation (ALPN) [RFC7301] identifier
"qrt".
9.1. Draft Version Identification
*RFC Editor's Note:* Please remove this section prior to
publication of a final version of this document.
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Only implementations of the final, published RFC can identify
themselves as "qrt". Until such an RFC exists, implementations MUST
NOT identify themselves using this string. Implementations of draft
versions of the protocol MUST add the string "-h" and the
corresponding draft number to the identifier. For example, draft-
hurst-quic-rtp-tunnelling-00 is identified using the string "qrt-
h00".
Non-compatible experiments that are based on these draft versions
MUST append the string "-" and an experiment name to the identifier.
For example, an experimental implementation based on draft-hurst-
quic-rtp-tunnelling-00 which uses extension features not registered
with the appropriate IANA registry might identify itself as "qrt-h00-
extension-foo". Note that any label MUST conform to the "token"
syntax defined in Section 5.6.2 of [HTTP-SEMANTICS]. Experimenters
are encouraged to coordinate their experiments.
10. Security Considerations
Implementations of the protocol defined in this specification are
subject to the security considerations discussed in [QUIC-TRANSPORT]
and [QUIC-TLS].
11. IANA Considerations
11.1. Registration of Protocol Identification String
This document creates a new registration for the identification of
the QUIC RTP Tunnelling protocol in the "Application-Layer Protocol
Negotiation (ALPN) Protocol IDs" registry established by [RFC7301].
The "qrt" string identifies RTP sessions multiplexed and carried over
a QUIC transport layer:
Protocol: QUIC RTP Tunnelling
Identification Sequence: 0x71 0x72 0x74 ("qrt")
Specification: This document, Section 9
11.2. Registration of SDP Protocol Identifier
This document creates a new registration for the SDP Protocol
Identifier ("proto") "RTP/QRT" in the SDP Protocol Identifiers
("proto") registry established by [RFC8866].
The "RTP/QRT" string identifies a profile of RTP where sessions are
multiplexed and carried over a QUIC transport layer:
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SDP Protocol Name: RTP/QRT
Reference: This document, Section 6
11.3. Registration of SDP Attribute Field
This document creates a new registration for the SDP Attribute Field
("att-field") "qrtflow" in the SDP Attribute Field registry
established by [RFC8866].
SDP Attribute Field: "qrtflow"
Reference: This document, Section 6
12. References
12.1. Normative References
[HTTP-SEMANTICS]
Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", Work in Progress, Internet-Draft,
draft-ietf-httpbis-semantics-14,
<https://tools.ietf.org/html/draft-ietf-httpbis-semantics-
14>.
[QUIC-DATAGRAM]
Pauly, T., Ed., Kinnear, E., Ed., and D. Schinazi, Ed.,
"An Unreliable Datagram Extension to QUIC", Work in
Progress, Internet-Draft, draft-ietf-quic-datagram-01,
<https://tools.ietf.org/html/draft-ietf-quic-datagram-01>.
[QUIC-RECOVERY]
Iyengar, J., Ed. and I. Swett, Ed., "QUIC Loss Detection
and Congestion Control", Work in Progress, Internet-Draft,
draft-ietf-quic-recovery-34,
<https://tools.ietf.org/html/draft-ietf-quic-recovery-34>.
[QUIC-TRANSPORT]
Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", Work in Progress,
Internet-Draft, draft-ietf-quic-transport-34,
<https://tools.ietf.org/html/draft-ietf-quic-transport-
34>.
[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/info/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/info/rfc3550>.
[RFC3605] Huitema, C., "Real Time Control Protocol (RTCP) attribute
in Session Description Protocol (SDP)", RFC 3605,
DOI 10.17487/RFC3605, October 2003,
<https://www.rfc-editor.org/info/rfc3605>.
[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/info/rfc4588>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>.
[RFC5888] Camarillo, G. and H. Schulzrinne, "The Session Description
Protocol (SDP) Grouping Framework", RFC 5888,
DOI 10.17487/RFC5888, June 2010,
<https://www.rfc-editor.org/info/rfc5888>.
[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/info/rfc7301>.
[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/info/rfc8174>.
[RFC8866] Begen, A., Kyzivat, P., Perkins, C., and M. Handley, "SDP:
Session Description Protocol", RFC 8866,
DOI 10.17487/RFC8866, January 2021,
<https://www.rfc-editor.org/info/rfc8866>.
12.2. Informative References
[QUIC-TLS] Thomson, M., Ed. and S. Turner, Ed., "Using Transport
Layer Security (TLS) to Secure QUIC", Work in Progress,
Internet-Draft, draft-ietf-quic-tls-34,
<https://tools.ietf.org/html/draft-ietf-quic-tls-34>.
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[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/info/rfc3261>.
[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/info/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/info/rfc4585>.
[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/info/rfc6284>.
Appendix A. Acknowledgments
The author would like to thank Richard Bradbury, David Waring, Colin
Perkins, Joerg Ott, Lucas Pardue and Piers O'Hanlon for their helpful
comments on both the design and review of this document.
Appendix B. Changelog
B.1. Since draft-hurst-quic-rtp-tunnelling-00
* Specify that QRT cannot coexist with other applications using
"DATAGRAM" frames on a single QUIC connection
* Specify the principles which define which RTCP packet types can be
replaced with QUIC transport features
* Add an API expectations section
* Scope of the QRT Flow Identifier has been clarified
* Specify that the network path MTU should be exposed to help with
PMTUD
Author's Address
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Sam Hurst
BBC Research & Development
Email: sam.hurst@bbc.co.uk
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