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 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 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/ 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 Hurst Expires 1 August 2021 [Page 1] Internet-Draft QRT January 2021 extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are 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. Hurst Expires 1 August 2021 [Page 2] Internet-Draft QRT January 2021 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. Hurst Expires 1 August 2021 [Page 3] Internet-Draft QRT January 2021 * 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. Hurst Expires 1 August 2021 [Page 4] Internet-Draft QRT January 2021 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 Hurst Expires 1 August 2021 [Page 5] Internet-Draft QRT January 2021 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. Hurst Expires 1 August 2021 [Page 6] Internet-Draft QRT January 2021 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 Hurst Expires 1 August 2021 [Page 7] Internet-Draft QRT January 2021 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: Hurst Expires 1 August 2021 [Page 8] Internet-Draft QRT January 2021 * 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 Hurst Expires 1 August 2021 [Page 9] Internet-Draft QRT January 2021 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. Hurst Expires 1 August 2021 [Page 10] Internet-Draft QRT January 2021 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. Hurst Expires 1 August 2021 [Page 11] Internet-Draft QRT January 2021 * 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. Hurst Expires 1 August 2021 [Page 12] Internet-Draft QRT January 2021 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: Hurst Expires 1 August 2021 [Page 13] Internet-Draft QRT January 2021 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, . [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, . [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, . [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, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . Hurst Expires 1 August 2021 [Page 14] Internet-Draft QRT January 2021 [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, . [RFC3605] Huitema, C., "Real Time Control Protocol (RTCP) attribute in Session Description Protocol (SDP)", RFC 3605, DOI 10.17487/RFC3605, October 2003, . [RFC4588] Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R. Hakenberg, "RTP Retransmission Payload Format", RFC 4588, DOI 10.17487/RFC4588, July 2006, . [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/RFC5234, January 2008, . [RFC5888] Camarillo, G. and H. Schulzrinne, "The Session Description Protocol (SDP) Grouping Framework", RFC 5888, DOI 10.17487/RFC5888, June 2010, . [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, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8866] Begen, A., Kyzivat, P., Perkins, C., and M. Handley, "SDP: Session Description Protocol", RFC 8866, DOI 10.17487/RFC8866, January 2021, . 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, . Hurst Expires 1 August 2021 [Page 15] Internet-Draft QRT January 2021 [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, . [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, . [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, . [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, . 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 Hurst Expires 1 August 2021 [Page 16] Internet-Draft QRT January 2021 Sam Hurst BBC Research & Development Email: sam.hurst@bbc.co.uk Hurst Expires 1 August 2021 [Page 17]