| Internet-Draft | SDP O/A for RTP over QUIC | January 2022 |
| Dawkins | Expires 1 August 2022 | [Page] |
This document describes these new SDP "proto" attribute values: "QUIC", "QUIC/RTP/SAVP", "QUIC/RTP/AVPF", and "QUIC/RTP/SAVPF", and describes how SDP Offer/Answer can be used to set up an RTP connection using QUIC as a transport protocol.¶
These proto values are necessary to allow the use of QUIC as an underlying transport protocol for applications such as SIP and WebRTC that commonly use SDP as a session signaling protocol to set up RTP connections.¶
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This document describes these new SDP "proto" attribute values: "QUIC", "QUIC/RTP/SAVP", "QUIC/RTP/AVPF", and "QUIC/RTP/SAVPF", and describes how SDP Offer/Answer ([RFC3264]) can be used to set up an RTP ([RFC3550]) connection using QUIC ([RFC9000] and related specifications) as a transport protocol.¶
These proto values are necessary to allow the use of QUIC as an underlying transport protocol for applications such as SIP ([RFC3261]) and WebRTC ([RFC8825]) that commonly use SDP as a session signaling protocol to set up RTP connections.¶
(Note to RFC Editor - if this document ever reaches you, please remove this section)¶
This document is intended for publication as a standards-track RFC in the IETF stream, but has not been adopted by any IETF working group, and does not carry any special status within the IETF.¶
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.¶
This document focuses on the IANA registration and description of the RTP sessions using SDP Offer/Answer, as would be the case for many current RTP applications in common use, such as SIP ([RFC3261]) and WebRTC ([RFC8825]).¶
This document is intended as complementary to drafts such as [I-D.engelbart-rtp-over-quic], which largely focus on RTP/RTCP encapsulation in QUIC, so that the SDP experts can focus on SDP offer/answer aspects, and the RTP experts can focus on RTP/RTCP encapsulation aspects.¶
(Note to RFC Editor - if this document ever reaches you, please remove this section)¶
With the concurrence of the AVTCORE and MMUSIC working group co-chairs, this document should be discussed in the AVTCORE working group, in the same venue where RTP over QUIC proposals are being discussed. When proposals for RTP over SIP have stablized in AVTCORE, this document will be sent to the MMUSIC working group for review by SDP experts, but SDP-specific comments are welcomed at any time.¶
Readers are also invited to open issues and send pull requests with contributed text for this document in the GitHub repository at https://github.com/SpencerDawkins/sdp-rtp-quic. The direct link to the list of issues is https://github.com/SpencerDawkins/sdp-rtp-quic/issues.¶
This document assumes that for RTP-over-QUIC, it is useful to register these AVP profiles using QUIC, in order to allow existing SIP and RTCWEB RTP applications to migrate more easily to QUIC:¶
This document assumes that any implementation adding support for RTP-over-QUIC could reasonably also add support for BUNDLE ([RFC8843]) and "rtcp-mux" ([RFC5761]), so these capabiilities are not mentioned further in this document.¶
Existing RTP implementations have the choice for any given RTP connection to exchange either unencrypted RTP streams (using AVP profiles such as RTP/AVPF) or encrypted RTP streams (using AVP profiles such as RTP/SAVPF).¶
An RTP implementation that uses QUIC as its underlying transport protocol will always send an RTP stream that is encrypted between the two QUIC endpoints, so some RTP implementations may be tempted to exchange unencrypted RTP as an encrypted QUIC payload, reasoning that QUIC protection will be sufficient.¶
One nuance here is that QUIC is heavily encrypted between two QUIC endpoints, with the very minimal exception of the invariant header fields described in [RFC8999], but as described in [RFC7667], many RTP applications use middleboxes for a variety of reasons, and some of these topologies (for example, media translation) require that the middlebox understand the RTP payload.¶
These middleboxes are explictly addressed, and the QUIC cryptographic handshake described in [RFC9001] takes place between the RTP endpoint and the RTP middlebox. After the QUIC cryptographic handshake has succeeded, the RTP middlebox has access to the RTP in the QUIC payload, and can perform whatever translations are appropriate before forwarding the RTP steam to another RTP endpoint. However, if the RTP sender uses one of the "insecure" AVPs, the middlebox does not have any indication that the RTP sender wants the translated RTP stream to be protected by encryption when the middlebox forwards it. That might be fine if the middlebox and RTP endpoint are both using RTP over QUIC, but if the middlebox is performing transport translation as well, the middlebox may also be translating an RTP-over-QUIC stream to RTP-over-UDP.¶
This specification tries to provide that indication by supporting both "secure" and "insecure" AVPs for RTP over QUIC, so the middlebox that is providing back-to-back RTP sessions as described in [RFC7667] can be aware of the sender's desire that a translated RTP stream is encypted regardless of the underlying transport protocol, without always requiring both SRTP and QUIC encryption between each pair of QUIC endpoints for all RTP traffic. That's one strategy, and it's certainly possible that other strategies might be safer, cleaner, and/or more useful.¶
The current contents of Section 2 and Section 3 would allow an existing RTP/RTCP implementation to make a relatively straightforward transition from "RTP over UDP" to "RTP over QUIC datagrams over UDP", and likewise from "RTCP over UDP" to "RTCP over QUIC datagrams over UDP".¶
Although it is still early days for RTP over QUIC, things may not be that straightforward. Just limiting our attention to various proposals for "RTP over QUIC" that have already been discussed on the Media Over QUIC IETF mailing list [MOQ] and in various IETF side meetings, we have seen¶
Changes to the SDP signaling in Section 2 and Section 3 may be (and likely would be) needed in order to support any of these desires (or other desires that may surface in the future).¶
As much as possible, these are reused from other specifications, with references to the original definitions.¶
The 'QUIC' protocol identifier is similar to the 'UDP' and 'TCP' protocol identifiers in that it only describes the transport protocol, and not the upper-layer protocol.¶
An 'm' line that specifies 'QUIC' MUST further qualify the application-layer protocol using an fmt identifier, such as "QUIC/RTP/AVPF". Media described using an 'm' line containing the 'QUIC' protocol identifier are carried using QUIC ([RFC9000]).¶
The following is an update to the ABNF for an 'm' line, as specified by [RFC8866], that defines a new value for the QUIC protocol.¶
media-field = %s"m" "=" media SP port \["/" integer\]
SP proto 1*(SP fmt) CRLF
m= line parameter parameter value(s)
------------------------------------------------------------------
<media>: (unchanged from {{RFC8866}})
<proto>: 'QUIC'
<port>: UDP port number
<fmt>: (unchanged from {{RFC8866}})
¶
The following is an update to the ABNF for an 'm' line, as specified by [RFC8866], that defines a new value for the QUIC/RTP/SAVP protocol.¶
media-field = %s"m" "=" media SP port \["/" integer\]
SP proto 1*(SP fmt) CRLF
m= line parameter parameter value(s)
------------------------------------------------------------------
<media>: (unchanged from {{RFC8866}})
<proto>: 'QUIC/RTP/SAVP'
<port>: UDP port number
<fmt>: (unchanged from {{RFC8866}})
¶
The following is an update to the ABNF for an 'm' line, as specified by [RFC8866], that defines a new value for the QUIC/RTP/AVPF protocol.¶
media-field = %s"m" "=" media SP port \["/" integer\]
SP proto 1*(SP fmt) CRLF
m= line parameter parameter value(s)
------------------------------------------------------------------
<media>: (unchanged from {{RFC8866}})
<proto>: 'QUIC/RTP/AVPF'
<port>: UDP port number
<fmt>: (unchanged from {{RFC8866}})
¶
The following is an update to the ABNF for an 'm' line, as specified by [RFC8866], that defines a new value for the QUIC/RTP/SAVPF protocol.¶
media-field = %s"m" "=" media SP port \["/" integer\]
SP proto 1*(SP fmt) CRLF
m= line parameter parameter value(s)
------------------------------------------------------------------
<media>: (unchanged from {{RFC8866}})
<proto>: 'QUIC/RTP/SAVPF'
<port>: UDP port number
<fmt>: (unchanged from {{RFC8866}})
¶
A complete example of an SDP offer using QUIC/RTP/AVPF might look like:¶
| SDP line | Notes |
|---|---|
| v=0 | Same as [RFC8866] |
| o=jdoe 3724394400 3724394405 IN IP4 198.51.100.1 | Same as [RFC8866] |
| s=Call to John Smith | Same as [RFC8866] |
| i=SDP Offer #1 | Same as [RFC8866] |
| u=http://www.jdoe.example.com/home.html | Same as [RFC8866] |
| e=Jane Doe jane@jdoe.example.com | Same as [RFC8866] |
| p=+1 617 555-6011 | Same as [RFC8866] |
| c=IN IP4 198.51.100.1 | Same as [RFC8866] |
| t=0 0 | Same as [RFC8866] |
| m=audio 49170 RTP/AVP 0 | Same as [RFC8866] |
| m=audio 49180 RTP/AVP 0 | Same as [RFC8866] |
| m=video 51372 QUIC/RTP/AVPF 99 | QUIC transport |
| a=setup:passive | will wait for QUIC handshake (setup attribute from [RFC4145]) |
| a=connection:new | don't want to reuse an existing QUIC connection (connection attribute from [RFC4145]) |
| c=IN IP6 2001:db8::2 | Same as [RFC8866] |
| a=rtpmap:99 h266/90000 | H.266 VVC codec [I-D.ietf-avtcore-rtp-vvc] |
This example is largely based on an example appearing in [RFC8866], Section 5, but is using QUIC/RTP/AVPF to support a newer codec.¶
Because QUIC uses connections for both streams and datagrams, we are reusing two session- and media-level SDP attributes from [SDP-attribute-name] that were defined in [RFC4145] for use with TCP: setup and connection.¶
This example SDP offer might be included in a SIP Invite.¶
This document registers these protocols in the proto registry ([SDP-parameters]).¶
IANA is requested to add these protocols to the Session Description Protocol (SDP) Parameters proto registry ([SDP-parameters]).¶
| Type | SDP Name | Reference |
|---|---|---|
| proto | QUIC | RFCXXXX |
| proto | QUIC/RTP/SAVP | RFCXXXX |
| proto | QUIC/RTP/AVPF | RFCXXXX |
| proto | QUIC/RTP/SAVPF | RFCXXXX |
Note to the RFC Editor¶
Please replace "RFCXXXX" with the assigned RFC number, when that is available, and remove this note.¶
Security considerations for the QUIC protocol are described in the corresponding section in [RFC9000].¶
Security considerations for the TLS handshake used to secure QUIC are described in [RFC9001].¶
Security considerations for SDP are described in the corresponding section in [RFC8866].¶
Security considerations for SDP offer/answer are described in the cooresponding section in [RFC3264].¶
My appreciation to the authors of [RFC4145], which served as a model for the initial structure of this document.¶
Thanks to these folks for helping to improve this draft:¶
(Your name also could appear here. Please comment and contribute, as per Section 1.4).¶