WebRTC-HTTP ingestion protocol (WHIP)
draft-ietf-wish-whip-09

wish                                                          S. Murillo
Internet-Draft                                                 Millicast
Intended status: Standards Track                           A. Gouaillard
Expires: 25 January 2024                                  CoSMo Software
                                                            24 July 2023

                 WebRTC-HTTP ingestion protocol (WHIP)
                        draft-ietf-wish-whip-09

Abstract

   This document describes a simple HTTP-based protocol that will allow
   WebRTC-based ingestion of content into streaming services and/or
   CDNs.

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
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   Drafts is at https://datatracker.ietf.org/drafts/current/.

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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 25 January 2024.

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/
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   Please review these documents carefully, as they describe your rights
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   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Protocol Operation  . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  ICE and NAT support . . . . . . . . . . . . . . . . . . .   8
     4.2.  WebRTC constraints  . . . . . . . . . . . . . . . . . . .  11
     4.3.  Load balancing and redirections . . . . . . . . . . . . .  12
     4.4.  STUN/TURN server configuration  . . . . . . . . . . . . .  12
     4.5.  Authentication and authorization  . . . . . . . . . . . .  14
     4.6.  Simulcast and scalable video coding . . . . . . . . . . .  15
     4.7.  Protocol extensions . . . . . . . . . . . . . . . . . . .  15
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  16
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
     6.1.  Link Relation Type: ice-server  . . . . . . . . . . . . .  17
     6.2.  Registration of WHIP URN Sub-namespace and WHIP
           Registry  . . . . . . . . . . . . . . . . . . . . . . . .  17
     6.3.  URN Sub-namespace for WHIP  . . . . . . . . . . . . . . .  18
       6.3.1.  Specification Template  . . . . . . . . . . . . . . .  18
     6.4.  Registering WHIP Protocol Extensions URIs . . . . . . . .  20
       6.4.1.  Registration Procedure  . . . . . . . . . . . . . . .  20
       6.4.2.  Guidance for Designated Experts . . . . . . . . . . .  21
       6.4.3.  WHIP Protocol Extension Registration Template . . . .  21
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  22
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  22
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  22
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  26
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  26

1.  Introduction

   The IETF RTCWEB working group standardized JSEP ([RFC8829]), a
   mechanism used to control the setup, management, and teardown of a
   multimedia session.  It also describes how to negotiate media flows
   using the Offer/Answer Model with the Session Description Protocol
   (SDP) [RFC3264] as well as the formats for data sent over the wire
   (e.g., media types, codec parameters, and encryption).  WebRTC
   intentionally does not specify a signaling transport protocol at
   application level.

   Unfortunately, the lack of a standardized signaling mechanism in
   WebRTC has been an obstacle to adoption as an ingestion protocol
   within the broadcast/streaming industry, where a streamlined
   production pipeline is taken for granted: plug in cables carrying raw
   media to hardware encoders, then push the encoded media to any
   streaming service or Content Delivery Network (CDN) ingest using an
   ingestion protocol.

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   While WebRTC can be integrated with standard signaling protocols like
   SIP [RFC3261] or XMPP [RFC6120], they are not designed to be used in
   broadcasting/streaming services, and there also is no sign of
   adoption in that industry.  RTSP [RFC7826], which is based on RTP, is
   not compatible with the SDP offer/answer model [RFC3264].

   This document proposes a simple protocol for supporting WebRTC as
   media ingestion method which:

   *  Is easy to implement,

   *  Is as easy to use as popular IP-based broadcast protocols

   *  Is fully compliant with WebRTC and RTCWEB specs

   *  Allows for ingest both in traditional media platforms and in
      WebRTC end-to-end platforms with the lowest possible latency.

   *  Lowers the requirements on both hardware encoders and broadcasting
      services to support WebRTC.

   *  Is usable both in web browsers and in native encoders.

2.  Terminology

   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.

   *  WHIP client: WebRTC media encoder or producer that acts as a
      client of the WHIP protocol by encoding and delivering the media
      to a remote Media Server.

   *  WHIP endpoint: Ingest server receiving the initial WHIP request.

   *  WHIP endpoint URL: URL of the WHIP endpoint that will create the
      WHIP resource.

   *  Media Server: WebRTC Media Server or consumer that establishes the
      media session with the WHIP client and receives the media produced
      by it.

   *  WHIP resource: Allocated resource by the WHIP endpoint for an
      ongoing ingest session that the WHIP client can send requests for
      altering the session (ICE operations or termination, for example).

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   *  WHIP resource URL: URL allocated to a specific media session by
      the WHIP endpoint which can be used to perform operations such as
      terminating the session or ICE restarts.

3.  Overview

   The WebRTC-HTTP Ingest Protocol (WHIP) uses an HTTP POST request to
   perform a single-shot SDP offer/answer so an ICE/DTLS session can be
   established between the encoder/media producer (WHIP client) and the
   broadcasting ingestion endpoint (Media Server).

   Once the ICE/DTLS session is set up, the media will flow
   unidirectionally from the encoder/media producer (WHIP client) to the
   broadcasting ingestion endpoint (Media Server).  In order to reduce
   complexity, no SDP renegotiation is supported, so no "m=" sections
   can be added once the initial SDP offer/answer over HTTP is
   completed.

 +-------------+    +---------------+ +--------------+ +---------------+
 | WHIP client |    | WHIP endpoint | | Media Server | | WHIP resource |
 +--+----------+    +---------+-----+ +------+-------+ +--------|------+
    |                         |              |                  |
    |                         |              |                  |
    |HTTP POST (SDP Offer)    |              |                  |
    +------------------------>+              |                  |
    |201 Created (SDP answer) |              |                  |
    +<------------------------+              |                  |
    |          ICE REQUEST                   |                  |
    +--------------------------------------->+                  |
    |          ICE RESPONSE                  |                  |
    |<---------------------------------------+                  |
    |          DTLS SETUP                    |                  |
    |<======================================>|                  |
    |          RTP/RTCP FLOW                 |                  |
    +<-------------------------------------->+                  |
    | HTTP DELETE                                               |
    +---------------------------------------------------------->+
    | 200 OK                                                    |
    <-----------------------------------------------------------x

              Figure 1: WHIP session setup and teardown

4.  Protocol Operation

   In order to set up an ingestion session, the WHIP client will
   generate an SDP offer according to the JSEP rules and perform an HTTP
   POST request to the configured WHIP endpoint URL.

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   The HTTP POST request will have a content type of "application/sdp"
   and contain the SDP offer as the body.  The WHIP endpoint will
   generate an SDP answer and return a "201 Created" response with a
   content type of "application/sdp", the SDP answer as the body, and a
   Location header field pointing to the newly created resource.

   The SDP offer SHOULD use the "sendonly" attribute and the SDP answer
   MUST use the "recvonly" attribute in any case.

POST /whip/endpoint HTTP/1.1
Host: whip.example.com
Content-Type: application/sdp
Content-Length: 1326

v=0
o=- 5228595038118931041 2 IN IP4 127.0.0.1
s=-
t=0 0
a=group:BUNDLE 0 1
a=extmap-allow-mixed
a=msid-semantic: WMS
m=audio 9 UDP/TLS/RTP/SAVPF 111
c=IN IP4 0.0.0.0
a=rtcp:9 IN IP4 0.0.0.0
a=ice-ufrag:EsAw
a=ice-pwd:bP+XJMM09aR8AiX1jdukzR6Y
a=ice-options:trickle
a=fingerprint:sha-256 DA:7B:57:DC:28:CE:04:4F:31:79:85:C4:31:67:EB:27:58:29:ED:77:2A:0D:24:AE:ED:AD:30:BC:BD:F1:9C:02
a=setup:actpass
a=mid:0
a=bundle-only
a=extmap:4 urn:ietf:params:rtp-hdrext:sdes:mid
a=sendonly
a=msid:- d46fb922-d52a-4e9c-aa87-444eadc1521b
a=rtcp-mux
a=rtpmap:111 opus/48000/2
a=fmtp:111 minptime=10;useinbandfec=1
m=video 9 UDP/TLS/RTP/SAVPF 96 97
c=IN IP4 0.0.0.0
a=rtcp:9 IN IP4 0.0.0.0
a=ice-ufrag:EsAw
a=ice-pwd:bP+XJMM09aR8AiX1jdukzR6Y
a=ice-options:trickle
a=fingerprint:sha-256 DA:7B:57:DC:28:CE:04:4F:31:79:85:C4:31:67:EB:27:58:29:ED:77:2A:0D:24:AE:ED:AD:30:BC:BD:F1:9C:02
a=setup:actpass
a=mid:1
a=bundle-only
a=extmap:4 urn:ietf:params:rtp-hdrext:sdes:mid

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a=extmap:10 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id
a=extmap:11 urn:ietf:params:rtp-hdrext:sdes:repaired-rtp-stream-id
a=sendonly
a=msid:- d46fb922-d52a-4e9c-aa87-444eadc1521b
a=rtcp-mux
a=rtcp-rsize
a=rtpmap:96 VP8/90000
a=rtcp-fb:96 ccm fir
a=rtcp-fb:96 nack
a=rtcp-fb:96 nack pli
a=rtpmap:97 rtx/90000
a=fmtp:97 apt=96

HTTP/1.1 201 Created
ETag: "xyzzy"
Content-Type: application/sdp
Content-Length: 1400
Location: https://whip.example.com/resource/id

v=0
o=- 1657793490019 1 IN IP4 127.0.0.1
s=-
t=0 0
a=group:BUNDLE 0 1
a=extmap-allow-mixed
a=ice-lite
a=msid-semantic: WMS *
m=audio 9 UDP/TLS/RTP/SAVPF 111
c=IN IP4 0.0.0.0
a=rtcp:9 IN IP4 0.0.0.0
a=ice-ufrag:38sdf4fdsf54
a=ice-pwd:2e13dde17c1cb009202f627fab90cbec358d766d049c9697
a=fingerprint:sha-256 F7:EB:F3:3E:AC:D2:EA:A7:C1:EC:79:D9:B3:8A:35:DA:70:86:4F:46:D9:2D:CC:D0:BC:81:9F:67:EF:34:2E:BD
a=candidate:1 1 UDP 2130706431 198.51.100.1 39132 typ host
a=setup:passive
a=mid:0
a=bundle-only
a=extmap:4 urn:ietf:params:rtp-hdrext:sdes:mid
a=recvonly
a=rtcp-mux
a=rtcp-rsize
a=rtpmap:111 opus/48000/2
a=fmtp:111 minptime=10;useinbandfec=1
m=video 9 UDP/TLS/RTP/SAVPF 96 97
c=IN IP4 0.0.0.0
a=rtcp:9 IN IP4 0.0.0.0
a=ice-ufrag:38sdf4fdsf54
a=ice-pwd:2e13dde17c1cb009202f627fab90cbec358d766d049c9697

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a=fingerprint:sha-256 F7:EB:F3:3E:AC:D2:EA:A7:C1:EC:79:D9:B3:8A:35:DA:70:86:4F:46:D9:2D:CC:D0:BC:81:9F:67:EF:34:2E:BD
a=candidate:1 1 UDP 2130706431 198.51.100.1 39132 typ host
a=setup:passive
a=mid:1
a=bundle-only
a=extmap:4 urn:ietf:params:rtp-hdrext:sdes:mid
a=extmap:10 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id
a=extmap:11 urn:ietf:params:rtp-hdrext:sdes:repaired-rtp-stream-id
a=recvonly
a=rtcp-mux
a=rtcp-rsize
a=rtpmap:96 VP8/90000
a=rtcp-fb:96 ccm fir
a=rtcp-fb:96 nack
a=rtcp-fb:96 nack pli
a=rtpmap:97 rtx/90000
a=fmtp:97 apt=96

              Figure 2: HTTP POST doing SDP O/A example

   Once a session is setup, ICE consent freshness [RFC7675] SHALL be
   used to detect non graceful disconnection and DTLS teardown for
   session termination by either side.

   To explicitly terminate a session, the WHIP client MUST perform an
   HTTP DELETE request to the resource URL returned in the Location
   header field of the initial HTTP POST.  Upon receiving the HTTP
   DELETE request, the WHIP resource will be removed and the resources
   freed on the Media Server, terminating the ICE and DTLS sessions.

   A Media Server terminating a session MUST follow the procedures in
   [RFC7675] Section 5.2 for immediate revocation of consent.

   The WHIP endpoints MUST return an "405 Method Not Allowed" response
   for any HTTP GET, HEAD or PUT requests on the endpoint URL in order
   to reserve its usage for future versions of this protocol
   specification.

   The WHIP endpoints MUST support OPTIONS requests for Cross-Origin
   Resource Sharing (CORS) as defined in [FETCH] and it SHOULD include
   an "Accept-Post" header with a mime type value of "application/sdp"
   on the "200 OK" response to any OPTIONS request received as per
   [W3C.REC-ldp-20150226].

   The WHIP resources MUST return an "405 Method Not Allowed" response
   for any HTTP GET, HEAD, POST or PUT requests on the resource URL in
   order to reserve its usage for future versions of this protocol
   specification.

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4.1.  ICE and NAT support

   The initial offer by the WHIP client MAY be sent after the full ICE
   gathering is complete with the full list of ICE candidates, or it MAY
   only contain local candidates (or even an empty list of candidates)
   as per [RFC8863].

   In order to simplify the protocol, there is no support for exchanging
   gathered trickle candidates from Media Server ICE candidates once the
   SDP answer is sent.  The WHIP Endpoint SHALL gather all the ICE
   candidates for the Media Server before responding to the client
   request and the SDP answer SHALL contain the full list of ICE
   candidates of the Media Server.  The Media Server MAY use ICE lite,
   while the WHIP client MUST implement full ICE.

   The WHIP client MAY perform trickle ICE or ICE restarts as per
   [RFC8838] by sending an HTTP PATCH request to the WHIP resource URL
   with a body containing a SDP fragment with MIME type "application/
   trickle-ice-sdpfrag" as specified in [RFC8840].  When used for
   trickle ICE, the body of this PATCH message will contain the new ICE
   candidate; when used for ICE restarts, it will contain a new ICE
   ufrag/pwd pair.

   Trickle ICE and ICE restart support is RECOMMENDED for a WHIP
   resource.

   If the WHIP resource supports either Trickle ICE or ICE restarts, but
   not both, it MUST return a "405 Not Implemented" response for the
   HTTP PATCH requests that are not supported.

   If the WHIP resource does not support the PATCH method for any
   purpose, it MUST return a "501 Not Implemented" response, as
   described in [RFC9110] Section 6.6.2.

   As the HTTP PATCH request sent by a WHIP client may be received out-
   of-order by the WHIP resource, the WHIP resource MUST generate a
   unique strong entity-tag identifying the ICE session as per [RFC9110]
   Section 2.3.  The initial value of the entity-tag identifying the
   initial ICE session MUST be returned in an ETag header field in the
   "201 Created" response to the initial POST request to the WHIP
   endpoint.  It MUST also be returned in the "200 OK" of any PATCH
   request that triggers an ICE restart.  Note that including the ETag
   in the original "201 Created" response is only REQUIRED if the WHIP
   resource supports ICE restarts and OPTIONAL otherwise.

   A WHIP client sending a PATCH request for performing trickle ICE MUST
   include an "If-Match" header field with the latest known entity-tag
   as per [RFC9110] Section 3.1.  When the PATCH request is received by

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   the WHIP resource, it MUST compare the indicated entity-tag value
   with the current entity-tag of the resource as per [RFC9110]
   Section 3.1 and return a "412 Precondition Failed" response if they
   do not match.

   WHIP clients SHOULD NOT use entity-tag validation when matching a
   specific ICE session is not required, such as for example when
   initiating a DELETE request to terminate a session.  WHIP resources
   MUST ignore any entity-tag value sent by the WHIP client when ICE
   session matching is not required, as in the HTTP DELETE request.

   A WHIP resource receiving a PATCH request with new ICE candidates,
   but which does not perform an ICE restart, MUST return a "204 No
   Content" response without body.  If the Media Server does not support
   a candidate transport or is not able to resolve the connection
   address, it MUST accept the HTTP request with the "204 No Content"
   response and silently discard the candidate.

PATCH /resource/id HTTP/1.1
Host: whip.example.com
If-Match: "xyzzy"
Content-Type: application/trickle-ice-sdpfrag
Content-Length: 548

a=ice-ufrag:EsAw
a=ice-pwd:P2uYro0UCOQ4zxjKXaWCBui1
m=audio 9 RTP/AVP 0
a=mid:0
a=candidate:1387637174 1 udp 2122260223 192.0.2.1 61764 typ host generation 0 ufrag EsAw network-id 1
a=candidate:3471623853 1 udp 2122194687 198.51.100.1 61765 typ host generation 0 ufrag EsAw network-id 2
a=candidate:473322822 1 tcp 1518280447 192.0.2.1 9 typ host tcptype active generation 0 ufrag EsAw network-id 1
a=candidate:2154773085 1 tcp 1518214911 198.51.100.2 9 typ host tcptype active generation 0 ufrag EsAw network-id 2
a=end-of-candidates

HTTP/1.1 204 No Content

                    Figure 3: Trickle ICE request

   A WHIP client sending a PATCH request for performing ICE restart MUST
   contain an "If-Match" header field with a field-value "*" as per
   [RFC9110] Section 3.1.

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   If the HTTP PATCH request results in an ICE restart, the WHIP
   resource SHALL return a "200 OK" with an "application/trickle-ice-
   sdpfrag" body containing the new ICE username fragment and password
   and OPTIONALLY a new set of ICE candidates for the WHIP client .
   Also, the "200 OK" response for a successful ICE restart MUST contain
   the new entity-tag corresponding to the new ICE session in an ETag
   response header field and MAY contain a new set of ICE candidates for
   the Media Server.

   If the ICE request cannot be satisfied by the WHIP resource, the
   resource MUST return an appropriate HTTP error code and MUST NOT
   terminate the session immediately.  The WHIP client MAY retry
   performing a new ICE restart or terminate the session by issuing an
   HTTP DELETE request instead.  In either case, the session MUST be
   terminated if the ICE consent expires as a consequence of the failed
   ICE restart as per [RFC7675] Section 5.1.

   PATCH /resource/id HTTP/1.1
   Host: whip.example.com
   If-Match: "*"
   Content-Type: application/trickle-ice-sdpfrag
   Content-Length: 54

   a=ice-ufrag:ysXw
   a=ice-pwd:vw5LmwG4y/e6dPP/zAP9Gp5k

   HTTP/1.1 200 OK
   ETag: "abccd"
   Content-Type: application/trickle-ice-sdpfrag
   Content-Length: 102

   a=ice-lite
   a=ice-ufrag:289b31b754eaa438
   a=ice-pwd:0b66f472495ef0ccac7bda653ab6be49ea13114472a5d10a

                       Figure 4: ICE restart request

   Because the WHIP client needs to know the entity-tag associated with
   the ICE session in order to send new ICE candidates, it MUST buffer
   any gathered candidates before it receives the HTTP response to the
   initial POST request or the PATCH request with the new entity-tag
   value.  Once it knows the entity-tag value, in order to lower the
   HTTP traffic and processing time required, the WHIP client SHOULD
   send a single aggregated HTTP PATCH request with all the ICE
   candidates it has buffered so far.

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   In case of unstable network conditions, the ICE restart HTTP PATCH
   requests and responses might be received out of order.  In order to
   mitigate this scenario, when the client performs an ICE restart, it
   MUST discard any previous ICE username and passwords fragments and
   ignore any further HTTP PATCH response received from a pending HTTP
   PATCH request.  WHIP clients MUST apply only the ICE information
   received in the response to the last sent request.  If there is a
   mismatch between the ICE information at the client and at the server
   (because of an out-of-order request), the STUN requests will contain
   invalid ICE information and will be rejected by the server.  When
   this situation is detected by the WHIP Client, it MUST send a new ICE
   restart request to the server.

4.2.  WebRTC constraints

   In the specific case of media ingestion into a streaming service,
   some assumptions can be made about the server-side which simplifies
   the WebRTC compliance burden, as detailed in WebRTC-gateway document
   [I-D.draft-ietf-rtcweb-gateways].

   In order to reduce the complexity of implementing WHIP in both
   clients and Media Servers, WHIP imposes the following restrictions
   regarding WebRTC usage:

   Both the WHIP client and the WHIP endpoint SHALL use SDP bundle
   [RFC9143].  Each "m=" section MUST be part of a single BUNDLE group.
   Hence, when a WHIP client sends an SDP offer, it MUST include a
   "bundle-only" attribute in each bundled "m=" section.  The WHIP
   client and the Media Server MUST support multiplexed media associated
   with the BUNDLE group as per [RFC9143] Section 9.  In addition, per
   [RFC9143] the WHIP client and Media Server will use RTP/RTCP
   multiplexing for all bundled media.  In order to reduce the network
   resources required at the Media Server, both The WHIP client and
   Media Server SHOULD include the "rtcp-mux-only" attribute in each
   bundled "m=" sections as per [RFC8858] i.

   This version of the specification only supports, at most, a single
   audio and video MediaStreamTrack in a single MediaStream as defined
   in [[!RFC8830]] and therefore, all "m=" sections MUST contain an
   "msid" attribute with the same value.  However, it would be possible
   for future revisions of this spec to allow more than a single
   MediaStream or MediaStreamTrack of each media kind, so in order to
   ensure forward compatibility, if the number of audio and or video
   tracks or number streams is not supported by the WHIP Endpoint, it
   MUST reject the HTTP POST request with a "406 Not Acceptable" error
   response.

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   Furthermore, the WHIP Endpoint SHOULD NOT reject individual "m="
   sections as per [RFC8829] Section 5.3.1 in case there is any error
   processing the "m=" section, but reject the HTTP POST request with a
   "406 Not Acceptable" error response to prevent having partially
   successful WHIP sessions which can be misleading to end users.

   When a WHIP client sends an SDP offer, it SHOULD insert an SDP
   "setup" attribute with an "actpass" attribute value, as defined in
   [RFC8842].  However, if the WHIP client only implements the DTLS
   client role, it MAY use an SDP "setup" attribute with an "active"
   attribute value.  If the WHIP endpoint does not support an SDP offer
   with an SDP "setup" attribute with an "active" attribute value, it
   SHOULD reject the request with a "422 Unprocessable Entity" response.

   NOTE: [RFC8842] defines that the offerer must insert an SDP "setup"
   attribute with an "actpass" attribute value.  However, the WHIP
   client will always communicate with a Media Server that is expected
   to support the DTLS server role, in which case the client might
   choose to only implement support for the DTLS client role.

   Trickle ICE and ICE restarts support is OPTIONAL for both the WHIP
   clients and Media Servers as explained in section 4.1.

4.3.  Load balancing and redirections

   WHIP endpoints and Media Servers might not be colocated on the same
   server, so it is possible to load balance incoming requests to
   different Media Servers.  WHIP clients SHALL support HTTP redirection
   via the "307 Temporary Redirect" response as described in [RFC9110]
   Section 6.4.7.  The WHIP resource URL MUST be a final one, and
   redirections are not required to be supported for the PATCH and
   DELETE requests sent to it.

   In case of high load, the WHIP endpoints MAY return a "503 Service
   Unavailable" response indicating that the server is currently unable
   to handle the request due to a temporary overload or scheduled
   maintenance, which will likely be alleviated after some delay.  The
   WHIP endpoint might send a Retry-After header field indicating the
   minimum time that the user agent ought to wait before making a
   follow-up request.

4.4.  STUN/TURN server configuration

   The WHIP endpoint MAY return STUN/TURN server configuration URLs and
   credentials usable by the client in the "201 Created" response to the
   HTTP POST request to the WHIP endpoint URL.

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   A reference to each STUN/TURN server will be returned using the
   "Link" header field [RFC8288] with a "rel" attribute value of "ice-
   server".  The Link target URI is the server URI as defined in
   [RFC7064] and [RFC7065].  The credentials are encoded in the Link
   target attributes as follows:

   *  username: If the Link header field represents a TURN server, and
      credential-type is "password", then this attribute specifies the
      username to use with that TURN server.

   *  credential: If the "credential-type" attribute is missing or has a
      "password" value, the credential attribute represents a long-term
      authentication password, as described in [RFC8489], Section 10.2.

   *  credential-type: If the Link header field represents a TURN
      server, then this attribute specifies how the credential attribute
      value should be used when that TURN server requests authorization.
      The default value if the attribute is not present is "password".

     Link: <stun:stun.example.net>; rel="ice-server"
     Link: <turn:turn.example.net?transport=udp>; rel="ice-server";
           username="user"; credential="myPassword"; credential-type="password"
     Link: <turn:turn.example.net?transport=tcp>; rel="ice-server";
           username="user"; credential="myPassword"; credential-type="password"
     Link: <turns:turn.example.net?transport=tcp>; rel="ice-server";
           username="user"; credential="myPassword"; credential-type="password"

              Figure 5: Example ICE server configuration

   NOTE: The naming of both the "rel" attribute value of "ice-server"
   and the target attributes follows the one used on the W3C WebRTC
   recommendation [W3C.REC-webrtc-20210126] RTCConfiguration dictionary
   in section 4.2.1. "rel" attribute value of "ice-server" is not
   prepended with the "urn:ietf:params:whip:" so it can be reused by
   other specifications which may use this mechanism to configure the
   usage of STUN/TURN servers.

   NOTE: Depending on the ICE Agent implementation, the WHIP client may
   need to call the setConfiguration method before calling the
   setLocalDescription method with the local SDP offer in order to avoid
   having to perform an ICE restart for applying the updated STUN/TURN
   server configuration on the next ICE gathering phase.

   There are some WebRTC implementations that do not support updating
   the STUN/TURN server configuration after the local offer has been
   created as specified in [RFC8829] Section 4.1.18.  In order to
   support these clients, the WHIP endpoint MAY also include the STUN/
   TURN server configuration on the responses to OPTIONS request sent to

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   the WHIP endpoint URL before the POST request is sent.  However, this
   method is not NOT RECOMMENDED and if supported by the underlying WHIP
   Client's webrtc implementation, the WHIP Client SHOULD wait for the
   information to be returned by the WHIP Endpoint on the response of
   the HTTP POST request instead.

   The generation of the TURN server credentials may require performing
   a request to an external provider, which can both add latency to the
   OPTIONS request processing and increase the processing required to
   handle that request.  In order to prevent this, the WHIP Endpoint
   SHOULD NOT return the STUN/TURN server configuration if the OPTIONS
   request is a preflight request for CORS, that is, if The OPTIONS
   request does not contain an Access-Control-Request-Method with "POST"
   value and the the Access-Control-Request-Headers HTTP header does not
   contain the "Link" value.

   It might be also possible to configure the STUN/TURN server URIs with
   long term credentials provided by either the broadcasting service or
   an external TURN provider on the WHIP client, overriding the values
   provided by the WHIP endpoint.

4.5.  Authentication and authorization

   WHIP endpoints and resources MAY require the HTTP request to be
   authenticated using an HTTP Authorization header field with a Bearer
   token as specified in [RFC6750] Section 2.1.  WHIP clients MUST
   implement this authentication and authorization mechanism and send
   the HTTP Authorization header field in all HTTP requests sent to
   either the WHIP endpoint or resource except the preflight OPTIONS
   requests for CORS.

   The nature, syntax, and semantics of the bearer token, as well as how
   to distribute it to the client, is outside the scope of this
   document.  Some examples of the kind of tokens that could be used
   are, but are not limited to, JWT tokens as per [RFC6750] and
   [RFC8725] or a shared secret stored on a database.  The tokens are
   typically made available to the end user alongside the WHIP endpoint
   URL and configured on the WHIP clients (similar to the way RTMP URLs
   and Stream Keys are distributed).

   WHIP endpoints and resources could perform the authentication and
   authorization by encoding an authentication token within the URLs for
   the WHIP endpoints or resources instead.  In case the WHIP client is
   not configured to use a bearer token, the HTTP Authorization header
   field must not be sent in any request.

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4.6.  Simulcast and scalable video coding

   Simulcast as per [RFC8853] MAY be supported by both the Media Servers
   and WHIP clients through negotiation in the SDP offer/answer.

   If the client supports simulcast and wants to enable it for
   publishing, it MUST negotiate the support in the SDP offer according
   to the procedures in [RFC8853] Section 5.3.  A server accepting a
   simulcast offer MUST create an answer according to the procedures
   [RFC8853] Section 5.3.2.

   It is possible for both Media Servers and WHIP clients to support
   Scalable Video Coding (SVC).  However, as there is no universal
   negotiation mechanism in SDP for SVC, the encoder must consider the
   negotiated codec(s), intended usage, and SVC support in available
   decoders when configuring SVC.

4.7.  Protocol extensions

   In order to support future extensions to be defined for the WHIP
   protocol, a common procedure for registering and announcing the new
   extensions is defined.

   Protocol extensions supported by the WHIP server MUST be advertised
   to the WHIP client in the "201 Created" response to the initial HTTP
   POST request sent to the WHIP endpoint.  The WHIP endpoint MUST
   return one "Link" header field for each extension, with the extension
   "rel" type attribute and the URI for the HTTP resource that will be
   available for receiving requests related to that extension.

   Protocol extensions are optional for both WHIP clients and servers.
   WHIP clients MUST ignore any Link attribute with an unknown "rel"
   attribute value and WHIP servers MUST NOT require the usage of any of
   the extensions.

   Each protocol extension MUST register a unique "rel" attribute value
   at IANA starting with the prefix: "urn:ietf:params:whip:ext" as
   defined in Section 6.3.

   For example, considering a potential extension of server-to-client
   communication using server-sent events as specified in
   https://html.spec.whatwg.org/multipage/server-sent-
   events.html#server-sent-events, the URL for connecting to the server
   side event resource for the published stream could be returned in the
   initial HTTP "201 Created" response with a "Link" header field and a
   "rel" attribute of "urn:ietf:params:whip:ext:example:server-sent-
   events".  (This document does not specify such an extension, and uses
   it only as an example.)

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   In this theoretical case, the "201 Created" response to the HTTP POST
   request would look like:

   HTTP/1.1 201 Created
   Content-Type: application/sdp
   Location: https://whip.example.com/resource/id
   Link: <https://whip.ietf.org/publications/213786HF/sse>;
         rel="urn:ietf:params:whip:ext:example:server-side-events"

5.  Security Considerations

   This document specifies a new protocol on top of HTTP and WebRTC,
   thus, security security protocols and considerations from related
   specifications apply to the WHIP specidifcation.  These include:

   *  WebRTC security considerations: [RFC8826].  HTTPS SHALL be used in
      order to preserve the WebRTC security model.

   *  Transport Layer Security (TLS): [RFC8446], [RFC8446], and
      [RFC9147].

   *  HTTP security: Section 11 of [RFC9112], Section 17 of [RFC9110],
      etc.

   *  URI security: Section 7 of [RFC3986].

   On top of that, the WHIP protocol exposes a thin new attack surface
   expecific of the REST API methods used within it:

   *  HTTP POST flooding and resource exhaustion: It would be possible
      for an attacker in possesion of authentication credentials valid
      to publish a WHIP stream to make multiple HTTP POST to the WHIP
      endpoint.  This will force the WHIP endpoint to process the
      incoming SDP and allocate resources for being able to setup the
      DTLS/ICE connection.  While the malicious client do not need to
      initiate the DTLS/ICE connection at all, the WHIP resource will
      have to wait for the DTLS/ICE connection timeout in order to
      release the associated resources.  If the connection rate is high
      enought, this could lead to a resource exhaustion on the WHIP
      server and it will not be able to process legit incoming
      publications.  In order to prevent this scenario, WHIP endpoints
      SHOULD implemement a rate limit and abalanche control mechanism
      for incoming initial HTTP POST requests.

   *  Insecure direct object references (IDOR) on the WHIP resource
      locations: If the URsL returned by the WHIP endpoint for the WHIP
      resources location are easy to guess, it would be possible for an
      attacker to send multiple HTTP DELETE requests and terminate all

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      the WHIP resources currentlyrunning in a a WHIP server.  In order
      to prevent this scenario, WHIP endpoints SHOULD generate URLs with
      enought randomness, using a cryptographically secure pseudorandom
      number generator and implemement a rate limit and abalanche
      control mechanism for HTTP DELETE requests.  The security
      considerations for Universally Unique IDentifier (UUID) [RFC4122]
      Section 6 are applicable for generating the WHIP resources
      location URL.

   *  HTTP PATCH flooding: Similar to the HTTP POST flooding, a
      malicious client could also create a resource exhaustion by
      sending multiple HTTP PATCH request to the WHIP resource, although
      the WHIP Resources can limit the impact by not allocating new ICE
      candaidates and reusing the existing ICE candidates when doing ICE
      restarts.  In order to prevent this scenario, WHIP endpoints
      SHOULD implemement a rate limit and abalanche control mechanism
      for incoming HTTP PATCH requests.

6.  IANA Considerations

   This specification adds a new link relation type and a registry for
   URN sub-namespaces for WHIP protocol extensions.

6.1.  Link Relation Type: ice-server

   The link relation type below has been registered by IANA per
   Section 4.2 of [RFC8288].

   Relation Name: ice-server

   Description: For the WHIP protocol, conveys the STUN and TURN servers
   that can be used by an ICE Agent to establish a connection with a
   peer.

   Reference: TBD

6.2.  Registration of WHIP URN Sub-namespace and WHIP Registry

   IANA is asked to add an entry to the "IETF URN Sub-namespace for
   Registered Protocol Parameter Identifiers" registry and create a sub-
   namespace for the Registered Parameter Identifier as per [RFC3553]:
   "urn:ietf:params:whip".

   To manage this sub-namespace, IANA is asked to created the "WebRTC-
   HTTP ingestion protocol (WHIP) URIs" registry, which is used to
   manage entries within the "urn:ietf:params:whip" namespace.  The
   registry description is as follows:

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   *  Registry name: WebRTC-HTTP ingestion protocol (WHIP) URIs

   *  Specification: this document (RFC TBD)

   *  Registration policy: Specification Required

   *  Repository: See Section Section 6.3

   *  Index value: See Section Section 6.3

6.3.  URN Sub-namespace for WHIP

   WHIP Endpoint utilizes URIs to identify the supported WHIP protocol
   extensions on the "rel" attribute of the Link header as defined in
   Section 4.7.

   This section creates and registers an IETF URN Sub-namespace for use
   in the WHIP specifications and future extensions.

6.3.1.  Specification Template

   Namespace ID:

   *  The Namespace ID "whip" has been assigned.

   Registration Information:

   *  Version: 1

   *  Date: TBD

   Declared registrant of the namespace:

   *  Registering organization: The Internet Engineering Task Force.

   *  Designated contact: A designated expert will monitor the WHIP
      public mailing list, "wish@ietf.org".

   Declaration of Syntactic Structure:

   *  The Namespace Specific String (NSS) of all URNs that use the
      "whip" Namespace ID shall have the following structure:
      urn:ietf:params:whip:{type}:{name}:{other}.

   *  The keywords have the following meaning:

      -  type: The entity type.  This specification only defines the
         "ext" type.

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      -  name: A required US-ASCII string that conforms to the URN
         syntax requirements (see [RFC8141]) and defines a major
         namespace of a WHIP protocol extension.  The value MAY also be
         an industry name or organization name.

      -  other: Any US-ASCII string that conforms to the URN syntax
         requirements (see [RFC8141]) and defines the sub-namespace
         (which MAY be further broken down in namespaces delimited by
         colons) as needed to uniquely identify an WHIP protocol
         extension.

   Relevant Ancillary Documentation:

   *  None

   Identifier Uniqueness Considerations:

   *  The designated contact shall be responsible for reviewing and
      enforcing uniqueness.

   Identifier Persistence Considerations:

   *  Once a name has been allocated, it MUST NOT be reallocated for a
      different purpose.

   *  The rules provided for assignments of values within a sub-
      namespace MUST be constructed so that the meanings of values
      cannot change.

   *  This registration mechanism is not appropriate for naming values
      whose meanings may change over time.

   Process of Identifier Assignment:

   *  Namespace with type "ext" (e.g., "urn:ietf:params:whip:ext") is
      reserved for IETF-approved WHIP specifications.

   Process of Identifier Resolution:

   *  None specified.

   Rules for Lexical Equivalence:

   *  No special considerations; the rules for lexical equivalence
      specified in [RFC8141] apply.

   Conformance with URN Syntax:

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   *  No special considerations.

   Validation Mechanism:

   *  None specified.

   Scope:

   *  Global.

6.4.  Registering WHIP Protocol Extensions URIs

   This section defines the process for registering new WHIP protocol
   extensions URIs with IANA in the "WebRTC-HTTP ingestion protocol
   (WHIP) URIs" registry (see Section 6.3).

   A WHIP Protocol Extension URI is used as a value in the "rel"
   attribute of the Link header as defined in Section 4.7 for the
   purpose of signaling the WHIP protocol extensions supported by the
   WHIP Endpoints.

   WHIP Protocol Extensions URIs have a "ext" type as defined in
   Section 6.3.

6.4.1.  Registration Procedure

   The IETF has created a mailing list, "wish@ietf.org", which can be
   used for public discussion of WHIP protocol extensions proposals
   prior to registration.  Use of the mailing list is strongly
   encouraged.  The IESG has appointed a designated expert RFC8126 who
   will monitor the wish@ietf.org mailing list and review registrations.

   Registration of new "ext" type URI (in the namespace
   "urn:ietf:params:whip:ext") belonging to a WHIP Protocol Extension
   MUST be documented in a permanent and readily available public
   specification, in sufficient detail so that interoperability between
   independent implementations is possible and reviewed by the
   designated expert as per [BCP26] Section 4.6.  An RFC is REQUIRED for
   the registration of new value data types that modify existing
   properties.  An RFC is also REQUIRED for registration of WHIP
   Protocol Extensions URIs that modify WHIP Protocol Extensions
   previously documented in an existing RFC.

   The registration procedure begins when a completed registration
   template, defined in the sections below, is sent to iana@iana.org.
   Decisions made by the designated expert can be appealed to an
   Applications and Real Time (ART) Area Director, then to the IESG.
   The normal appeals procedure described in [BCP9] is to be followed.

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   Once the registration procedure concludes successfully, IANA creates
   or modifies the corresponding record in the WHIP Protocol Extension
   registry.

   An RFC specifying one or more new WHIP Protocol Extension URIs MUST
   include the completed registration templates, which MAY be expanded
   with additional information.  These completed templates are intended
   to go in the body of the document, not in the IANA Considerations
   section.  The RFC SHOULD include any attributes defined.

6.4.2.  Guidance for Designated Experts

   The Designated Expert (DE) is expected to ascertain the existence of
   suitable documentation (a specification) as described in RFC8126 and
   to verify that the document is permanently and publicly available.

   The DE is also expected to check the clarity of purpose and use of
   the requested registration.

   Additionally, the DE must verify that any request for one of these
   registrations has been made available for review and comment within
   the IETF: the DE will post the request to the WebRTC Ingest Signaling
   over HTTPS (wish) Working Group mailing list (or a successor mailing
   list designated by the IESG).

   If the request comes from within the IETF, it should be documented in
   an Internet-Draft.  Lastly, the DE must ensure that any other request
   for a code point does not conflict with work that is active or
   already published within the IETF.

6.4.3.  WHIP Protocol Extension Registration Template

   A WHIP Protocol Extension URI is defined by completing the following
   template:

   *  URI: A unique URI for the WHIP Protocol Extension (e.g.,
      "urn:ietf:params:whip:ext:example:server-sent-events").

   *  Reference: A formal reference to the publicly available
      specification

   *  Name: A descriptive name of the WHIP Protocol Extension extension
      (e.g., "Sender Side events").

   *  Description: A brief description of the function of the extension,
      in a short paragraph or two

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   *  Contact information: Contact information for the organization or
      person making the registration

7.  Acknowledgements

   The authors wish to thank Lorenzo Miniero, Juliusz Chroboczek, Adam
   Roach, Nils Ohlmeier, Christer Holmberg, Cameron Elliott, Gustavo
   Garcia, Jonas Birme, Sandro Gauci and everyone else in the WebRTC
   community that have provided comments, feedback, text and improvement
   proposals on the document and contributed early implementations of
   the spec.

8.  References

8.1.  Normative References

   [BCP26]    Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, June 2017.

   [BCP9]     Bradner, S., "The Internet Standards Process -- Revision
              3", BCP 9, RFC 2026, October 1996.

              Dusseault, L. and R. Sparks, "Guidance on Interoperation
              and Implementation Reports for Advancement to Draft
              Standard", BCP 9, RFC 5657, September 2009.

              Housley, R., Crocker, D., and E. Burger, "Reducing the
              Standards Track to Two Maturity Levels", BCP 9, RFC 6410,
              October 2011.

              Resnick, P., "Retirement of the "Internet Official
              Protocol Standards" Summary Document", BCP 9, RFC 7100,
              December 2013.

              Kolkman, O., Bradner, S., and S. Turner, "Characterization
              of Proposed Standards", BCP 9, RFC 7127, January 2014.

              Dawkins, S., "Increasing the Number of Area Directors in
              an IETF Area", BCP 9, RFC 7475, March 2015.

              Halpern, J., Ed. and E. Rescorla, Ed., "IETF Stream
              Documents Require IETF Rough Consensus", BCP 9, RFC 8789,
              June 2020.

              Rosen, B., "Responsibility Change for the RFC Series",
              BCP 9, RFC 9282, June 2022.

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   [FETCH]    WHATWG, "Fetch - Living Standard", n.d.,
              <https://fetch.spec.whatwg.org>.

   [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>.

   [RFC3264]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
              with Session Description Protocol (SDP)", RFC 3264,
              DOI 10.17487/RFC3264, June 2002,
              <https://www.rfc-editor.org/rfc/rfc3264>.

   [RFC3553]  Mealling, M., Masinter, L., Hardie, T., and G. Klyne, "An
              IETF URN Sub-namespace for Registered Protocol
              Parameters", BCP 73, RFC 3553, DOI 10.17487/RFC3553, June
              2003, <https://www.rfc-editor.org/rfc/rfc3553>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <https://www.rfc-editor.org/rfc/rfc3986>.

   [RFC4122]  Leach, P., Mealling, M., and R. Salz, "A Universally
              Unique IDentifier (UUID) URN Namespace", RFC 4122,
              DOI 10.17487/RFC4122, July 2005,
              <https://www.rfc-editor.org/rfc/rfc4122>.

   [RFC6750]  Jones, M. and D. Hardt, "The OAuth 2.0 Authorization
              Framework: Bearer Token Usage", RFC 6750,
              DOI 10.17487/RFC6750, October 2012,
              <https://www.rfc-editor.org/rfc/rfc6750>.

   [RFC7064]  Nandakumar, S., Salgueiro, G., Jones, P., and M. Petit-
              Huguenin, "URI Scheme for the Session Traversal Utilities
              for NAT (STUN) Protocol", RFC 7064, DOI 10.17487/RFC7064,
              November 2013, <https://www.rfc-editor.org/rfc/rfc7064>.

   [RFC7065]  Petit-Huguenin, M., Nandakumar, S., Salgueiro, G., and P.
              Jones, "Traversal Using Relays around NAT (TURN) Uniform
              Resource Identifiers", RFC 7065, DOI 10.17487/RFC7065,
              November 2013, <https://www.rfc-editor.org/rfc/rfc7065>.

   [RFC7675]  Perumal, M., Wing, D., Ravindranath, R., Reddy, T., and M.
              Thomson, "Session Traversal Utilities for NAT (STUN) Usage
              for Consent Freshness", RFC 7675, DOI 10.17487/RFC7675,
              October 2015, <https://www.rfc-editor.org/rfc/rfc7675>.

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   [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>.

   [RFC8288]  Nottingham, M., "Web Linking", RFC 8288,
              DOI 10.17487/RFC8288, October 2017,
              <https://www.rfc-editor.org/rfc/rfc8288>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/rfc/rfc8446>.

   [RFC8489]  Petit-Huguenin, M., Salgueiro, G., Rosenberg, J., Wing,
              D., Mahy, R., and P. Matthews, "Session Traversal
              Utilities for NAT (STUN)", RFC 8489, DOI 10.17487/RFC8489,
              February 2020, <https://www.rfc-editor.org/rfc/rfc8489>.

   [RFC8725]  Sheffer, Y., Hardt, D., and M. Jones, "JSON Web Token Best
              Current Practices", BCP 225, RFC 8725,
              DOI 10.17487/RFC8725, February 2020,
              <https://www.rfc-editor.org/rfc/rfc8725>.

   [RFC8826]  Rescorla, E., "Security Considerations for WebRTC",
              RFC 8826, DOI 10.17487/RFC8826, January 2021,
              <https://www.rfc-editor.org/rfc/rfc8826>.

   [RFC8829]  Uberti, J., Jennings, C., and E. Rescorla, Ed.,
              "JavaScript Session Establishment Protocol (JSEP)",
              RFC 8829, DOI 10.17487/RFC8829, January 2021,
              <https://www.rfc-editor.org/rfc/rfc8829>.

   [RFC8838]  Ivov, E., Uberti, J., and P. Saint-Andre, "Trickle ICE:
              Incremental Provisioning of Candidates for the Interactive
              Connectivity Establishment (ICE) Protocol", RFC 8838,
              DOI 10.17487/RFC8838, January 2021,
              <https://www.rfc-editor.org/rfc/rfc8838>.

   [RFC8840]  Ivov, E., Stach, T., Marocco, E., and C. Holmberg, "A
              Session Initiation Protocol (SIP) Usage for Incremental
              Provisioning of Candidates for the Interactive
              Connectivity Establishment (Trickle ICE)", RFC 8840,
              DOI 10.17487/RFC8840, January 2021,
              <https://www.rfc-editor.org/rfc/rfc8840>.

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   [RFC8842]  Holmberg, C. and R. Shpount, "Session Description Protocol
              (SDP) Offer/Answer Considerations for Datagram Transport
              Layer Security (DTLS) and Transport Layer Security (TLS)",
              RFC 8842, DOI 10.17487/RFC8842, January 2021,
              <https://www.rfc-editor.org/rfc/rfc8842>.

   [RFC8853]  Burman, B., Westerlund, M., Nandakumar, S., and M. Zanaty,
              "Using Simulcast in Session Description Protocol (SDP) and
              RTP Sessions", RFC 8853, DOI 10.17487/RFC8853, January
              2021, <https://www.rfc-editor.org/rfc/rfc8853>.

   [RFC8858]  Holmberg, C., "Indicating Exclusive Support of RTP and RTP
              Control Protocol (RTCP) Multiplexing Using the Session
              Description Protocol (SDP)", RFC 8858,
              DOI 10.17487/RFC8858, January 2021,
              <https://www.rfc-editor.org/rfc/rfc8858>.

   [RFC8863]  Holmberg, C. and J. Uberti, "Interactive Connectivity
              Establishment Patiently Awaiting Connectivity (ICE PAC)",
              RFC 8863, DOI 10.17487/RFC8863, January 2021,
              <https://www.rfc-editor.org/rfc/rfc8863>.

   [RFC9110]  Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
              Ed., "HTTP Semantics", STD 97, RFC 9110,
              DOI 10.17487/RFC9110, June 2022,
              <https://www.rfc-editor.org/rfc/rfc9110>.

   [RFC9112]  Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
              Ed., "HTTP/1.1", STD 99, RFC 9112, DOI 10.17487/RFC9112,
              June 2022, <https://www.rfc-editor.org/rfc/rfc9112>.

   [RFC9143]  Holmberg, C., Alvestrand, H., and C. Jennings,
              "Negotiating Media Multiplexing Using the Session
              Description Protocol (SDP)", RFC 9143,
              DOI 10.17487/RFC9143, February 2022,
              <https://www.rfc-editor.org/rfc/rfc9143>.

   [RFC9147]  Rescorla, E., Tschofenig, H., and N. Modadugu, "The
              Datagram Transport Layer Security (DTLS) Protocol Version
              1.3", RFC 9147, DOI 10.17487/RFC9147, April 2022,
              <https://www.rfc-editor.org/rfc/rfc9147>.

   [W3C.REC-ldp-20150226]
              Malhotra, A., Ed., Arwe, J., Ed., and S. Speicher, Ed.,
              "Linked Data Platform 1.0", W3C REC REC-ldp-20150226, W3C 
              REC-ldp-20150226, 26 February 2015,
              <https://www.w3.org/TR/2015/REC-ldp-20150226/>.

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Internet-Draft                    whip                         July 2023

8.2.  Informative References

   [I-D.draft-ietf-rtcweb-gateways]
              Alvestrand, H. T. and U. Rauschenbach, "WebRTC Gateways",
              Work in Progress, Internet-Draft, draft-ietf-rtcweb-
              gateways-02, 21 January 2016,
              <https://datatracker.ietf.org/doc/html/draft-ietf-rtcweb-
              gateways-02>.

   [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>.

   [RFC6120]  Saint-Andre, P., "Extensible Messaging and Presence
              Protocol (XMPP): Core", RFC 6120, DOI 10.17487/RFC6120,
              March 2011, <https://www.rfc-editor.org/rfc/rfc6120>.

   [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>.

   [RFC8141]  Saint-Andre, P. and J. Klensin, "Uniform Resource Names
              (URNs)", RFC 8141, DOI 10.17487/RFC8141, April 2017,
              <https://www.rfc-editor.org/rfc/rfc8141>.

   [W3C.REC-webrtc-20210126]
              Jennings, C., Ed., Boström, H., Ed., and J. Bruaroey, Ed.,
              "WebRTC 1.0: Real-Time Communication Between Browsers",
              W3C REC REC-webrtc-20210126, W3C REC-webrtc-20210126, 26
              January 2021,
              <https://www.w3.org/TR/2021/REC-webrtc-20210126/>.

Authors' Addresses

   Sergio Garcia Murillo
   Millicast
   Email: sergio.garcia.murillo@cosmosoftware.io

   Alexandre Gouaillard
   CoSMo Software
   Email: alex.gouaillard@cosmosoftware.io

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