--- 1/draft-ietf-mmusic-sdp-simulcast-03.txt 2016-02-03 01:15:27.562064419 -0800 +++ 2/draft-ietf-mmusic-sdp-simulcast-04.txt 2016-02-03 01:15:27.618065813 -0800 @@ -1,56 +1,55 @@ Network Working Group B. Burman Internet-Draft M. Westerlund Intended status: Standards Track Ericsson -Expires: April 21, 2016 S. Nandakumar +Expires: August 6, 2016 S. Nandakumar M. Zanaty Cisco - October 19, 2015 + February 3, 2016 Using Simulcast in SDP and RTP Sessions - draft-ietf-mmusic-sdp-simulcast-03 + draft-ietf-mmusic-sdp-simulcast-04 Abstract In some application scenarios it may be desirable to send multiple differently encoded versions of the same media source in different - RTP streams. This is called simulcast. This document discusses the - best way of accomplishing simulcast in RTP and how to signal it in - SDP. A solution is defined by making an extension to SDP, and using - RTP/RTCP identification methods to relate RTP streams belonging to - the same media source. The SDP extension consists of a new media - level SDP attribute that expresses capability to send and/or receive - simulcast RTP streams. RTP/RTCP identification using either payload - types or a separately defined method for RTP stream configuration are - defined. + RTP streams. This is called simulcast. This document describes how + to accomplish simulcast in RTP and how to signal it in SDP. The + described solution uses an RTP/RTCP identification method to identify + RTP streams belonging to the same media source, and makes an + extension to SDP to relate those RTP streams as being different + simulcast formats of that media source. The SDP extension consists + of a new media level SDP attribute that expresses capability to send + and/or receive simulcast RTP streams. 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 http://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 April 21, 2016. + This Internet-Draft will expire on August 6, 2016. Copyright Notice - Copyright (c) 2015 IETF Trust and the persons identified as the + Copyright (c) 2016 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 (http://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 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 @@ -62,47 +61,47 @@ 2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 2.2. Requirements Language . . . . . . . . . . . . . . . . . . 4 3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.1. Reaching a Diverse Set of Receivers . . . . . . . . . . . 5 3.2. Application Specific Media Source Handling . . . . . . . 6 3.3. Receiver Media Source Preferences . . . . . . . . . . . . 7 4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 7 5. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 8 6. Detailed Description . . . . . . . . . . . . . . . . . . . . 9 - 6.1. Simulcast Capability . . . . . . . . . . . . . . . . . . 9 - 6.1.1. Declarative Use . . . . . . . . . . . . . . . . . . . 11 - 6.1.2. Offer/Answer Use . . . . . . . . . . . . . . . . . . 12 - 6.2. Relating Simulcast Streams . . . . . . . . . . . . . . . 14 - 6.3. Signaling Examples . . . . . . . . . . . . . . . . . . . 14 - 6.3.1. Unified Plan Client . . . . . . . . . . . . . . . . . 14 - 6.3.2. Multi-Source Client . . . . . . . . . . . . . . . . . 16 - 7. Network Aspects . . . . . . . . . . . . . . . . . . . . . . . 18 - 8. Limitations . . . . . . . . . . . . . . . . . . . . . . . . . 18 - 8.1. Single RTP Session . . . . . . . . . . . . . . . . . . . 18 - 8.2. SDP Format Identification . . . . . . . . . . . . . . . . 19 - 8.3. RID Identification . . . . . . . . . . . . . . . . . . . 19 - 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 - 10. Security Considerations . . . . . . . . . . . . . . . . . . . 20 - 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 20 - 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 20 - 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 20 - 13.1. Normative References . . . . . . . . . . . . . . . . . . 20 - 13.2. Informative References . . . . . . . . . . . . . . . . . 21 - Appendix A. Changes From Earlier Versions . . . . . . . . . . . 23 - A.1. Modifications Between WG Version -02 and -03 . . . . . . 23 - A.2. Modifications Between WG Version -01 and -02 . . . . . . 24 - A.3. Modifications Between WG Version -00 and -01 . . . . . . 24 - A.4. Modifications Between Individual Version -00 and WG - Version -00 . . . . . . . . . . . . . . . . . . . . . . . 24 - - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24 + 6.1. Simulcast Attribute . . . . . . . . . . . . . . . . . . . 9 + 6.2. Simulcast Capability . . . . . . . . . . . . . . . . . . 11 + 6.2.1. Declarative Use . . . . . . . . . . . . . . . . . . . 13 + 6.2.2. Offer/Answer Use . . . . . . . . . . . . . . . . . . 13 + 6.3. Relating Simulcast Streams . . . . . . . . . . . . . . . 15 + 6.4. Signaling Examples . . . . . . . . . . . . . . . . . . . 15 + 6.4.1. Single-Source Client . . . . . . . . . . . . . . . . 16 + 6.4.2. Multi-Source Client . . . . . . . . . . . . . . . . . 17 + 7. Network Aspects . . . . . . . . . . . . . . . . . . . . . . . 20 + 7.1. Bitrate Adaptation . . . . . . . . . . . . . . . . . . . 20 + 8. Limitations . . . . . . . . . . . . . . . . . . . . . . . . . 21 + 8.1. Single RTP Session . . . . . . . . . . . . . . . . . . . 21 + 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 + 10. Security Considerations . . . . . . . . . . . . . . . . . . . 21 + 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 22 + 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 22 + 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 22 + 13.1. Normative References . . . . . . . . . . . . . . . . . . 22 + 13.2. Informative References . . . . . . . . . . . . . . . . . 23 + Appendix A. Changes From Earlier Versions . . . . . . . . . . . 25 + A.1. Modifications Between WG Version -03 and -04 . . . . . . 25 + A.2. Modifications Between WG Version -02 and -03 . . . . . . 26 + A.3. Modifications Between WG Version -01 and -02 . . . . . . 26 + A.4. Modifications Between WG Version -00 and -01 . . . . . . 26 + A.5. Modifications Between Individual Version -00 and WG + Version -00 . . . . . . . . . . . . . . . . . . . . . . . 26 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26 1. Introduction Most of today's multiparty video conference solutions make use of centralized servers to reduce the bandwidth and CPU consumption in the endpoints. Those servers receive RTP streams from each participant and send some suitable set of possibly modified RTP streams to the rest of the participants, which usually have heterogeneous capabilities (screen size, CPU, bandwidth, codec, etc). One of the biggest issues is how to perform RTP stream adaptation to @@ -112,53 +111,50 @@ Simulcast is defined in this memo as the act of simultaneously sending multiple different encoded streams of the same media source, e.g. the same video source encoded with different video encoder types or image resolutions. This can be done in several ways and for different purposes. This document focuses on the case where it is desirable to provide a media source as multiple encoded streams over RTP [RFC3550] towards an intermediary so that the intermediary can provide the wanted functionality by selecting which RTP stream(s) to forward to other participants in the session, and more specifically how the identification and grouping of the involved RTP streams are - done. From an RTP perspective, simulcast is a specific application - of the aspects discussed in RTP Multiplexing Guidelines - [I-D.ietf-avtcore-multiplex-guidelines]. + done. This document describes a few scenarios where it is motivated to use - simulcast, and also defines the needed SDP signaling for it. + simulcast, and also defines the needed RTP/RTCP and SDP signaling for + it. 2. Definitions 2.1. Terminology This document makes use of the terminology defined in RTP Taxonomy - [I-D.ietf-avtext-rtp-grouping-taxonomy], RTP Topology [RFC5117] and - RTP Topologies Update [I-D.ietf-avtcore-rtp-topologies-update]. In - addition, the following terms are used: + [RFC7656], and RTP Topologies [RFC7667]. In addition, the following + terms are used: - RTP Mixer: An RTP middle node, defined in [RFC5117] (Section 3.4: - Topo-Mixer), further elaborated and extended with other topologies - in [I-D.ietf-avtcore-rtp-topologies-update] (Section 3.6 to 3.9). + RTP Mixer: An RTP middle node, defined in [RFC7667] (Section 3.6 to + 3.9). RTP Switch: A common short term for the terms "switching RTP mixer", "source projecting middlebox", and "video switching MCU" as - discussed in [I-D.ietf-avtcore-rtp-topologies-update]. + discussed in [RFC7667]. Simulcast Stream: One Encoded Stream or Dependent Stream from a set of concurrently transmitted Encoded Streams and optional Dependent Streams, all sharing a common Media Source, as defined in - [I-D.ietf-avtext-rtp-grouping-taxonomy]. Decoding a Dependent - Stream also requires the related (Dependent and) Encoded - Stream(s), but in the context of simulcast that is considered a - property of the Dependent Stream constituting the simulcast - stream. For example, HD and thumbnail video simulcast versions of - a single Media Source sent concurrently as separate RTP Streams. + [RFC7656]. Decoding a Dependent Stream also requires the related + (Dependent and) Encoded Stream(s), but in the context of simulcast + that is considered a property of the Dependent Stream constituting + the simulcast stream. For example, HD and thumbnail video + simulcast versions of a single Media Source sent concurrently as + separate RTP Streams. Simulcast Format: Different formats of a simulcast stream serve the same purpose as alternative RTP payload types in non-simulcast SDP, to allow multiple alternative media formats for a given RTP Stream. As for multiple RTP payload types on the m-line, any one of the alternative formats can be used at a given point in time, but not more than one (based on RTP timestamp), and what format is used can change dynamically from one RTP packet to another. For example, if all participants in a group video call can decode H.264 and H.265 video, but only some can encode H.265, both H.264 @@ -299,20 +294,26 @@ characteristics of the RTP stream they receive, for example in terms of the aspects listed in Section 3.1. Sending a simulcast of RTP streams is one way of accommodating receivers with conflicting or otherwise incompatible preferences. 4. Requirements The following requirements need to be met to support the use cases in previous sections: + Editor's note: Consider adding an explicit requirement that the + solution supports use of simulcast even when using multiple codecs + and multiple redundant RTP streams per defined codec (or something + similar), since this is really an existing requirement and should + also fully motivate the use of RID as identification mechanism. + REQ-1: Identification. It must be possible to identify a set of simulcasted RTP streams as originating from the same media source: REQ-1.1: In SDP signaling. REQ-1.2: On RTP/RTCP level. REQ-2: Transport usage. The solution must work when using: REQ-2.1: Legacy SDP with separate media transports per SDP media @@ -352,222 +353,280 @@ REQ-5.2: RTP Forward Error Correction [RFC5109]. REQ-5.3: Related payload types such as audio Comfort Noise and/or DTMF. REQ-6: Interoperability. The solution must be possible to use in: REQ-6.1: Interworking with non-simulcast legacy clients using a single media source per media type. - REQ-6.2: WebRTC "Unified Plan" environment with a single media - source per SDP media description. + REQ-6.2: WebRTC environment with a single media source per SDP + media description. 5. Overview As an overview, the above requirements are met by signaling simulcast capability and configurations in SDP [RFC4566]: o An offer or answer can contain a number of simulcast streams, separate for send and receive directions. o An offer or answer can contain multiple, alternative simulcast - streams in the same fashion as multiple, alternative codecs can be - offered in a media description. + stream formats in the same fashion as multiple, alternative codecs + can be offered in a media description. o A single media source per SDP media description is assumed, which - is aligned with the concepts defined in - [I-D.ietf-avtext-rtp-grouping-taxonomy] and will specifically work - in a WebRTC context, both with and without BUNDLE - [I-D.ietf-mmusic-sdp-bundle-negotiation] grouping. - - o The codec configuration for a simulcast stream can be expressed in - two alternative ways, with complementing drawbacks and benefits: - - * Through existing SDP formats (corresponding to RTP payload - types), enabling the use of simulcast with a minimum set of - additions to existing SDP specifications. + is aligned with the concepts defined in [RFC7656] and will + specifically work in a WebRTC context, both with and without + BUNDLE [I-D.ietf-mmusic-sdp-bundle-negotiation] grouping. - * Through use of a separately specified RTP-level identification - mechanism [I-D.pthatcher-mmusic-rid], which complements and - effectively extends the available simulcast stream - identification and configuration possibilities provided by - using SDP formats. + o The codec configuration for a simulcast stream is expressed + through use of a separately specified RTP-level identification + mechanism [I-D.ietf-mmusic-rid][I-D.roach-avtext-rid], which + complements and effectively extends the available simulcast stream + identification and configuration possibilities that could be + provided by using only SDP formats. o It is possible, but not required to use source-specific signaling [RFC5576] with the proposed solution. 6. Detailed Description - This section further details the overview above (Section 5). + This section further details the overview above (Section 5). First, + formal syntax is provided (Section 6.1), followed by the rest of the + SDP attribute definition in Section 6.2. Relating Simulcast Streams + (Section 6.3) provides the definition of the RTP/RTCP mechanisms + used. The section is concluded with a number of examples. -6.1. Simulcast Capability +6.1. Simulcast Attribute - Simulcast capability is expressed as a new media level SDP attribute, - "a=simulcast". For each desired direction (send/recv), the simulcast - attribute defines a list of simulcast streams (separated by - semicolons), each of which is a list of simulcast formats (separated - by commas). The meaning of the attribute on SDP session level is - undefined and MUST NOT be used. The ABNF [RFC5234] for this - attribute is: + Name: simulcast -sc-attr = "a=simulcast:" 1*2( WSP sc-str-list ) [WSP sc-pause-list] -sc-str-list = sc-dir WSP sc-id-type "=" sc-alt-list *( ";" sc-alt-list ) -sc-pause-list = "paused=" sc-alt-list + Value: sc-value + + Usage Level: media + + Charset Dependent: no + + Multiplex Category: NORMAL + + Syntax [RFC5234]: + + sc-attr = "a=simulcast:" sc-value + sc-value = sc-str-list [SP sc-str-list] + sc-str-list = sc-dir SP sc-alt-list *( ";" sc-alt-list ) sc-dir = "send" / "recv" -sc-id-type = "pt" / "rid" / token sc-alt-list = sc-id *( "," sc-id ) -sc-id = fmt / rid-identifier / token -; WSP defined in [RFC5234] -; fmt, token defined in [RFC4566] -; rid-identifier defined in [I-D.pthatcher-mmusic-rid] + sc-id-paused = "~" + sc-id = [sc-id-paused] rid-identifier / token + ; SP defined in [RFC5234] + ; token defined in [RFC4566] + ; rid-identifier defined in [I-D.ietf-mmusic-rid] Figure 1: ABNF for Simulcast - There are separate and independent sets of parameters for simulcast - in send and receive directions. When listing multiple directions, - each direction MUST NOT occur more than once on the same line. + The "a=simulcast" attribute has a parameter in the form of one or two + simulcast stream descriptions, each consisting of a direction ("send" + or "recv"), followed by a list of one or more simulcast streams. + Each simulcast stream in that list is separated by a semicolon (";"). + Each simulcast stream can in turn be offered in one or more + alternative formats, where each simulcast stream alternative is + separated by a comma (","). The simulcast stream alternative MUST be + described in the form of a RID, as described by + [I-D.ietf-mmusic-rid]. Each simulcast stream can be initially paused + [I-D.ietf-avtext-rtp-stream-pause], indicated by prepending a "~" to + the simulcast stream. In case there are simulcast stream + alternatives, pause can be specified individually for each + alternative. The reason to allow separate initial pause states for + each simulcast stream alternative is that pause capability can be + specified individually for each RTP payload type referenced by a RID, + which makes it infeasible to pause RID where any of the related RTP + payload type(s) do not have pause capability. - Two simulcast stream identification methods are defined; "pt" using - RTP payload type (SDP format), and "rid" using an additional RTP- - level identification mechanism [I-D.pthatcher-mmusic-rid]. Different - identification methods MUST NOT be used for different directions on a - single "a=simulcast" line. Implementations that support both - identification methods MAY include one "a=simulcast" line for each - identification method for the same "m="-line. Multiple "a=simulcast" - lines with the same identification method MUST NOT be used for a - single "m="-line. + Examples: + + a=simulcast:send 1,2,3;~4,~5 recv 1;~2,~5 + a=simulcast:recv 1;4,5 send 1;2 + + Figure 2: Simulcast Examples + + Above are two examples of different "a=simulcast" lines. + + The first line is an example offer to send two simulcast streams and + to receive two simulcast streams. The first simulcast stream in send + direction can be sent as three different alternatives (1, 2, 3), and + the second simulcast stream in send direction can be sent as two + different alternatives (4, 5). All second stream send alternatives + are offered as initially paused. The first simulcast stream in + receive direction has no alternatives (only 1). The second simulcast + stream in receive direction has two alternatives (2, 5) that are both + offered as initially paused. + + The second line is an example answer to the first line, accepting to + send and receive the two offered simulcast streams, however send and + receive directions are specified in opposite order compared to the + first line, which lets the answer keep the same order of simulcast + streams in the SDP as in the offer, even though directionality is + reversed. This example answer has removed all offered alternatives + for the first simulcast stream (keeping only 1), but kept alternative + formats for the second simulcast stream in receive direction (4, 5). + The answer accepts to send two simulcast streams, without + alternatives. The answer does not accept initial pause of any + simulcast streams, in either direction. More examples can be found + in Section 6.4. + +6.2. Simulcast Capability + + Simulcast capability is expressed as a new media level SDP attribute, + "a=simulcast" (Section 6.1), with multiplex category + [I-D.ietf-mmusic-sdp-mux-attributes] NORMAL. + + For each desired direction (send/recv), the simulcast attribute + defines a list of simulcast streams (separated by semicolons), each + of which is a list of simulcast formats (separated by commas). The + meaning of the attribute on SDP session level is undefined and MUST + NOT be used. + + The meaning of including multiple "a=simulcast" lines in a single SDP + media description is undefined and MUST NOT be used. There are + separate and independent sets of parameters for simulcast in send and + receive directions. When listing multiple directions, each direction + MUST NOT occur more than once on the same line. + + The different simulcast streams MUST be identified through the RTP- + level "RID" identification mechanism [I-D.ietf-mmusic-rid]. Attribute parameters are grouped by direction and consist of a listing of simulcast stream identifications to be used. The number of (non-alternative, see below) identifications in the list sets a limit to the number of supported simulcast streams in that direction. The order of the listed simulcast versions in the "send" direction suggests a proposed order of preference, in decreasing order: the stream listed first is the most preferred Section 3.1, and subsequent streams have progressively lower preference. The order of the listed simulcast streams in the "recv" direction expresses a preference which simulcast streams that are preferred, with the leftmost being most preferred. This can be of importance if the number of actually sent simulcast streams have to be reduced for some reason. Formats that have explicit dependencies [RFC5583] - [I-D.pthatcher-mmusic-rid] to other formats (even in the same media + [I-D.ietf-mmusic-rid] to other formats (even in the same media description) MAY be listed as different simulcast streams. Alternative simulcast formats MAY be specified as part of the attribute parameters by expressing each simulcast stream as a comma- - separated list of alternative format identifiers. In this case, - there MUST NOT be any capability restriction in what alternative - formats can be used across different simulcast streams, like - requiring all simulcast streams to use the same codec format - alternative. The order of the format alternatives within a simulcast - stream is significant; the alternatives are listed from (left) most - preferred to (right) least preferred. For the use of simulcast, this - overrides the normal codec preference as expressed by format type - ordering on the "m="-line, using regular SDP rules. This is to - enable a separation of general codec preferences and simulcast stream - configuration preferences. + separated list of alternative format identifiers. In this case, it + is not possible to align what alternative formats that are used + between different simulcast streams, like requiring all simulcast + streams to use alternatives with the same codec format. The order of + the format alternatives within a simulcast stream is significant; the + alternatives are listed from (left) most preferred to (right) least + preferred. For the use of simulcast, this overrides the normal codec + preference as expressed by format type ordering on the "m="-line, + using regular SDP rules. This is to enable a separation of general + codec preferences and simulcast stream configuration preferences. A simulcast stream can use a codec defined such that the same RTP SSRC can change RTP payload type multiple times during a session, possibly even on a per-packet basis. A typical example can be a speech codec that makes use of Comfort Noise [RFC3389] and/or DTMF [RFC4733] formats. In those cases, such "related" formats MUST NOT be listed explicitly in the attribute parameters, since they are not strictly simulcast streams of the media source, but rather a specific way of generating the RTP stream of a single simulcast stream with varying RTP payload type. Instead, only a single simulcast stream identification MUST be used per simulcast stream or alternative - simulcast format (if there are such) in the SDP. The used simulcast - stream identification SHOULD be the codec format most relevant to the - media description, if possible to identify, for example the audio - codec rather than the DTMF. What codec format to choose in the case - of switching between multiple equally "important" formats is left - open, but it is assumed that in the presence of such strong relation - it does not matter which is chosen. + simulcast format (if there are such) in the SDP. If RTP stream pause/resume [I-D.ietf-avtext-rtp-stream-pause] is - supported, the optional "paused=" parameter MAY be used in - conjunction with "rid" simulcast stream identification to specify - that a certain simulcast stream is initially paused already from - start of the RTP session. In this case, support for RTP stream - pause/resume MUST also be included under the same "m="-line listing - "a=simulcast". Initially paused simulcast streams MUST NOT be used - with "pt" identification. Initially paused simulcast streams are - resumed as described by the RTP pause/resume specification. + supported, any simulcast stream identification MAY be prefixed by a + "~" character to indicate that the corresponding simulcast stream is + initially paused already from start of the RTP session. In this + case, support for RTP stream pause/resume MUST also be included under + the same "m="-line listing "a=simulcast". If the simulcast stream is + specified as a list of alternative formats, the indication is + prepended to the first format of the list and applies to whatever + alternative that is eventually chosen. All RTP payload types related + to such initially paused simulcast stream MUST be listed in the SDP + as pause/resume capable as specified by + [I-D.ietf-avtext-rtp-stream-pause]. An initially paused simulcast stream in "send" direction MUST be considered equivalent to an unsolicited locally paused stream, and be - handled accordingly. + handled accordingly. Initially paused simulcast streams are resumed + as described by the RTP pause/resume specification. An RTP stream + receiver that wishes to resume an unsolicited locally paused stream + needs to know the SSRC of that stream. The SSRC of an initially + paused simulcast stream can be obtained from an RTP stream sender + RTCP Sender Report (SR) including both the desired SSRC as "SSRC of + sender", and the stream RID identification as an RID RTCP SDES item. - An initially paused simulcast stream in "recv" direction SHOULD cause - the remote RTP sender to put the stream as unsolicited locally - paused, unless there are other RTP stream receivers that do not mark - the simulcast stream as initially paused. The reason to require an - initially paused "recv" stream to be considered locally paused by the - remote RTP sender, instead of making it equivalent to implicitly - sending a pause request, is because the pausing RTP sender cannot - know which SSRC owns the restriction when TMMBR/TMMBN are used for - pause/resume signaling since the RTP receiver's SSRC in send - direction is not known yet. + Including an initially paused simulcast stream in "recv" direction in + an SDP towards an RTP sender, SHOULD cause the remote RTP sender to + put the stream as unsolicited locally paused, unless there are other + RTP stream receivers that do not mark the simulcast stream as + initially paused. The reason to require an initially paused "recv" + stream to be considered locally paused by the remote RTP sender, + instead of making it equivalent to implicitly sending a pause + request, is because the pausing RTP sender cannot know which SSRC + owns the restriction when TMMBR/TMMBN are used for pause/resume + signaling since the RTP receiver's SSRC in send direction is not + known yet. Use of the redundant audio data [RFC2198] format could be seen as a form of simulcast for loss protection purposes, but is not considered conflicting with the mechanisms described in this memo and MAY therefore be used as any other format. In this case the "red" format, rather than the carried formats, SHOULD be the one to list as a simulcast stream on the "a=simulcast" line. -6.1.1. Declarative Use + The media formats and corresponding characteristics of simulcast + streams SHOULD be chosen such that they are different. If this + difference is not required, RTP duplication [RFC7104] procedures + SHOULD be considered instead of simulcast. - When used as a declarative media description, a=simulcast "recv" - direction formats indicates the configured end point's required +6.2.1. Declarative Use + + When used as a declarative media description, "a=simulcast" line + "recv" direction formats indicate the configured end point's required capability to recognize and receive a specified set of RTP streams as - simulcast streams. In the same fashion, a=simulcast "send" direction - requests the end point to send a specified set of RTP streams as - simulcast streams. + simulcast streams. In the same fashion, "a=simulcast" line "send" + direction requests the end point to send a specified set of RTP + streams as simulcast streams. If multiple simulcast formats are listed, it means that the configured end point MUST be prepared to receive any of the "recv" formats, and MAY send any of the "send" formats for that simulcast stream. - Editor's note: The RID identification mechanism currently lacks a - declarative use definition. As declarative use may also not - follow unified plan with a single media source per '"m="-line, it - is uncertain if declarative can be defined for the mechanism in - its current shape. + Editor's note: It may not be beneficial for declarative use to be + limited to a single media source per "m=" line, as elaborated + further in Section 8. -6.1.2. Offer/Answer Use +6.2.2. Offer/Answer Use An offerer wanting to use simulcast SHALL include the "a=simulcast" attribute in the offer. An offerer that receives an answer without "a=simulcast" MUST NOT use simulcast towards the answerer. An - offerer that receives an answer with "a=simulcast" not listing a - direction or without any simulcast stream identifications in a - specified direction MUST NOT use simulcast in that direction. + offerer that receives an answer with "a=simulcast" without any + simulcast stream identifications in a specified direction MUST NOT + use simulcast in that direction. An answerer that does not understand the concept of simulcast will also not know the attribute and will remove it in the SDP answer, as defined in existing SDP Offer/Answer [RFC3264] procedures. An answerer that does understand the attribute and that wants to support simulcast in an indicated direction SHALL reverse directionality of the unidirectional direction parameters; "send" - becomes "recv" and vice versa, and include it in the answer. Note - that, like all other use of SDP format tags ("pt:") for the send - direction in Offer/Answer, format tags related to the simulcast - stream identification send direction in an offer are placeholders - that refer to information in the offer SDP, and the actual formats - that will be used on the wire (including RTP Payload Format numbers) - depends on information included in the SDP answer. + becomes "recv" and vice versa, and include it in the answer. An offerer listing a set of receive simulcast streams and/or alternative formats in the offer MUST be prepared to receive RTP streams for any of those simulcast streams and/or alternative formats from the answerer. An answerer that receives an offer with simulcast containing an "a=simulcast" attribute listing alternative formats for simulcast streams MAY keep all the alternatives in the answer, but it MAY also choose to remove any non-desirable alternatives per simulcast stream @@ -583,177 +642,184 @@ alternatives, and MAY send any of the kept receive direction alternatives from the answer. Similarly, the answerer MUST be prepared to receive any of the kept receive direction alternatives, and MAY send any of the kept send direction alternatives in the answer. The offerer and answerer MUST NOT send more than a single alternative format at a time (based on RTP timestamps) per simulcast stream, but MAY change format on a per-RTP packet basis. This corresponds to the existing (non-simulcast) SDP offer/answer case when multiple formats - are included on the "m="-line in the SDP answer. + are included on the "m=" line in the SDP answer. An offerer that receives an answer where some of the simulcast streams are removed MAY release the corresponding resources (codec, transport, etc) in its receive direction and MUST NOT send any RTP - streams corresponding to the removed simulcast streams. + packets corresponding to the removed simulcast streams. Simulcast streams or formats using undefined simulcast stream identifications MUST NOT be used as valid simulcast streams by an RTP stream receiver. - An offerer that is capable of using both simulcast stream - identification methods MAY include one "a=simulcast" line per - identification method in the offer. Note that it is in general not - expected that the "pt" identification method will provide feature - parity with the "rid" method, and the different "a=simulcast" lines - can therefore express different use of simulcast functionality. - However, for some configurations the different identification methods - can be equivalent. + An answerer that receives an offer without RTP stream pause/resume + capability MUST NOT mark any simulcast streams as initially paused in + the answer. - An answerer receiving an offer listing both simulcast stream - identification methods MUST choose only one and remove the other from - the answer. An answerer not supporting a simulcast stream - identification method in the offer MUST remove the non-supported - "a=simulcast" line from the answer, possibly falling back to not - using simulcast at all. + An answerer that receives an offer with RTP stream pause/resume + capability MAY mark any simulcast streams as initially paused in the + answer. - The media formats and corresponding characteristics of encoded - streams used in a simulcast SHOULD be chosen such that they are - different. If this difference is not required, RTP duplication - [RFC7104] procedures SHOULD be considered instead of simulcast. + An answerer that receives indication in an offer of a simulcast + stream being initially paused , SHOULD mark that simulcast stream as + initially paused also in the answer, regardless of direction, unless + it has good reason for the stream not being initially paused. + + An offerer that offered some of its simulcast streams as initially + paused and that receives an answer that does not indicate RTP stream + pause/resume capability, MUST NOT intially pause any simulcast + streams. + + An offerer with RTP stream pause/resume capability that receives an + answer where some simulcast streams are marked as initially paused, + SHOULD initially pause them regardless if they were marked as + initially paused also in the offer, unless it has good reason for + those streams not being initially paused. Note: The inclusion of "a=simulcast" or the use of simulcast does not change any of the interpretation or Offer/Answer procedures for other SDP attributes, like "a=fmtp" or "a=rid". -6.2. Relating Simulcast Streams - - As long as there is only a single media source per SDP media - description, simulcast RTP streams can be related on RTP level - through the RTP payload type and (optionally) RID - [I-D.pthatcher-mmusic-rid], as specified in the SDP "a=simulcast" - attribute (Section 6.1) parameters. When using BUNDLE - [I-D.ietf-mmusic-sdp-bundle-negotiation] with multiple SDP media - descriptions to specify a single RTP session, there is an - identification mechanism that allows relating RTP streams back to - individual media descriptions, after which the above RTP payload type - and RID relations can be used. +6.3. Relating Simulcast Streams - BUNDLE's MID is an RTCP source description (SDES) item. To ensure - rapid initial reception, required to correctly process the RTP - streams, it is also defined as an RTP header extension [RFC5285]. + Simulcast RTP streams MUST be related on RTP level through RID + [I-D.roach-avtext-rid], as specified in the SDP "a=simulcast" + attribute (Section 6.2) parameters. This is sufficient as long as + there is only a single media source per SDP media description. When + using BUNDLE [I-D.ietf-mmusic-sdp-bundle-negotiation], where multiple + SDP media descriptions jointly specify a single RTP session, the SDES + MID identification mechanism in BUNDLE allows relating RTP streams + back to individual media descriptions, after which the above + described RID relations can be used. Use of the RTP header extension + [RFC5285] for both MID and RID identifications can be important to + ensure rapid initial reception, required to correctly interpret and + process the RTP streams. Implementers of this specification MUST + support RTCP source description (SDES) item and SHOULD support RTP + header extension method to signal RID on RTP level. -6.3. Signaling Examples +6.4. Signaling Examples These examples describe a client to video conference service, using a centralized media topology with an RTP mixer. +---+ +-----------+ +---+ | A |<---->| |<---->| B | +---+ | | +---+ | Mixer | +---+ | | +---+ | F |<---->| |<---->| J | +---+ +-----------+ +---+ - Figure 2: Four-party Mixer-based Conference + Figure 3: Four-party Mixer-based Conference -6.3.1. Unified Plan Client +6.4.1. Single-Source Client - Alice is calling in to the mixer with a simulcast-enabled Unified - Plan client capable of a single media source per media type. The - client can send a simulcast of 2 video resolutions and frame rates: - HD 1280x720p 30fps and thumbnail 320x180p 15fps. This is defined - below using the "imageattr" [RFC6236]. Media formats (RTP payload - types) are used as simulcast stream identification. Alice's Offer: + Alice is calling in to the mixer with a simulcast-enabled client + capable of a single media source per media type. The client can send + a simulcast of 2 video resolutions and frame rates: HD 1280x720p + 30fps and thumbnail 320x180p 15fps. This is defined below using the + "imageattr" [RFC6236]. In this example, only the "pt" RID parameter + is used, effectively achieving a 1:1 mapping between RID and media + formats (RTP payload types), to describe simulcast stream formats. + Alice's Offer: v=0 o=alice 2362969037 2362969040 IN IP4 192.0.2.156 - s=Simulcast Enabled Unified Plan Client + s=Simulcast Enabled Client t=0 0 c=IN IP4 192.0.2.156 m=audio 49200 RTP/AVP 0 a=rtpmap:0 PCMU/8000 m=video 49300 RTP/AVP 97 98 a=rtpmap:97 H264/90000 a=rtpmap:98 H264/90000 a=fmtp:97 profile-level-id=42c01f; max-fs=3600; max-mbps=108000 a=fmtp:98 profile-level-id=42c00b; max-fs=240; max-mbps=3600 a=imageattr:97 send [x=1280,y=720] recv [x=1280,y=720] a=imageattr:98 send [x=320,y=180] recv [x=320,y=180] - a=simulcast: send pt=97;98 recv pt=97 + a=rid:1 pt=97 + a=rid:2 pt=98 + a=simulcast:send 1;2 recv 1 - Figure 3: Unified Plan Simulcast Offer + Figure 4: Single-Source Simulcast Offer The only thing in the SDP that indicates simulcast capability is the line in the video media description containing the "simulcast" attribute. The included format parameters indicates that sent simulcast streams can differ in video resolution. The Answer from the server indicates that it too is simulcast capable. Should it not have been simulcast capable, the "a=simulcast" line would not have been present and communication would have started with the media negotiated in the SDP. v=0 o=server 823479283 1209384938 IN IP4 192.0.2.2 - s=Answer to Simulcast Enabled Unified Plan Client + s=Answer to Simulcast Enabled Client t=0 0 c=IN IP4 192.0.2.43 m=audio 49672 RTP/AVP 0 a=rtpmap:0 PCMU/8000 m=video 49674 RTP/AVP 97 98 a=rtpmap:97 H264/90000 a=rtpmap:98 H264/90000 a=fmtp:97 profile-level-id=42c01f; max-fs=3600; max-mbps=108000 a=fmtp:98 profile-level-id=42c00b; max-fs=240; max-mbps=3600 a=imageattr:97 send [x=1280,y=720] recv [x=1280,y=720] a=imageattr:98 send [x=320,y=180] recv [x=320,y=180] - a=simulcast: recv pt=97;98 send pt=97 + a=rid:1 pt=97 + a=rid:2 pt=98 + a=simulcast:recv 1;2 send 1 - Figure 4: Unified Plan Simulcast Answer + Figure 5: Single-Source Simulcast Answer Since the server is the simulcast media receiver, it reverses the direction of the "simulcast" attribute parameters. -6.3.2. Multi-Source Client +6.4.2. Multi-Source Client Fred is calling in to the same conference as in the example above with a two-camera, two-display system, thus capable of handling two separate media sources in each direction, where each media source is simulcast-enabled in the send direction. Fred's client is restricted to a single media source per media description. The first two simulcast streams for the first media source use different codecs, H264-SVC [RFC6190] and H264 [RFC6184]. These two simulcast streams also have a temporal dependency. Two different video codecs, VP8 [I-D.ietf-payload-vp8] and H264, are offered as alternatives for the third simulcast stream for the first media - source. RID is used as simulcast stream identification, reducing the - number of media formats needed. Only the highest fidelity simulcast - stream are sent from start, the lower fidelity streams being - initially paused. + source. Only the highest fidelity simulcast stream are sent from + start, the lower fidelity streams being initially paused. The second media source is offered with three different simulcast streams. All video streams of this second media source are loss - protected by RTP retransmission [RFC4588]. RID is used as simulcast - stream identification. Also here, all but the highest fidelity - simulcast stream are initially paused. + protected by RTP retransmission [RFC4588]. Also here, all but the + highest fidelity simulcast stream are initially paused. Fred's client is also using BUNDLE to send all RTP streams from all media descriptions in the same RTP session on a single media transport. Although using many different simulcast streams in this - example, use of RID as simulcast stream identification enables use of - a low number of RTP payload types. Note that the use of both BUNDLE - and RID recommends using the RTP header extension [RFC5285] for - carrying these fields. + example, the use of RID as simulcast stream identification enables + use of a low number of RTP payload types. Note that the use of both + BUNDLE and RID recommends using the RTP header extension [RFC5285] + for carrying these fields, which is consequently also included in the + SDP. v=0 o=fred 238947129 823479223 IN IP4 192.0.2.125 s=Offer from Simulcast Enabled Multi-Source Client t=0 0 c=IN IP4 192.0.2.125 a=group:BUNDLE foo bar zen m=audio 49200 RTP/AVP 99 a=mid:foo @@ -767,39 +833,39 @@ a=fmtp:100 profile-level-id=42400d; max-fs=3600; max-mbps=108000; \ mst-mode=NI-TC a=fmtp:101 profile-level-id=42c00d; max-fs=3600; max-mbps=54000 a=fmtp:103 max-fs=900; max-fr=30 a=rid:1 send pt=100;max-width=1280;max-height=720;max-fr=60;depend=2 a=rid:2 send pt=101;max-width=1280;max-height=720;max-fr=30 a=rid:3 send pt=101;max-width=640;max-height=360 a=rid:4 send pt=103;max-width=640;max-height=360 a=depend:100 lay bar:101 a=extmap:1 urn:ietf:params:rtp-hdrext:sdes:mid - a=extmap:2 urn:ietf:params:rtp-hdrext:rid + a=extmap:2 urn:ietf:params:rtp-hdrext:sdes:rid a=rtcp-fb:* ccm pause nowait - a=simulcast: send rid=1;2;4,3 paused=2,3,4 + a=simulcast:send 1;2;~4,3 m=video 49602 RTP/AVPF 96 104 a=mid:zen a=rtpmap:96 VP8/90000 a=fmtp:96 max-fs=3600; max-fr=30 a=rtpmap:104 rtx/90000 a=fmtp:104 apt=96;rtx-time=200 a=rid:5 send pt=96;max-fs=921600;max-fr=30 a=rid:6 send pt=96;max-fs=614400;max-fr=15 a=rid:7 send pt=96;max-fs=230400;max-fr=30 a=extmap:1 urn:ietf:params:rtp-hdrext:sdes:mid - a=extmap:2 urn:ietf:params:rtp-hdrext:rid + a=extmap:2 urn:ietf:params:rtp-hdrext:sdes:rid a=rtcp-fb:* ccm pause nowait - a=simulcast: send rid=5;6;7 paused=6,7 + a=simulcast:send 5;~6;~7 - Figure 5: Fred's Multi-Source Simulcast Offer + Figure 6: Fred's Multi-Source Simulcast Offer Note: Empty lines in the SDP above are added only for readability and would not be present in an actual SDP. 7. Network Aspects Simulcast is in this memo defined as the act of sending multiple alternative encoded streams of the same underlying media source. When transmitting multiple independent streams that originate from the same source, it could potentially be done in several different @@ -810,145 +876,132 @@ clarification on how to handle multiple streams in an RTP session can be found in [I-D.ietf-avtcore-rtp-multi-stream]. The network aspects that are relevant for simulcast are: Quality of Service: When using simulcast it might be of interest to prioritize a particular simulcast stream, rather than applying equal treatment to all streams. For example, lower bit-rate streams may be prioritized over higher bit-rate streams to minimize congestion or packet losses in the low bit-rate streams. - Thus, there is a benefit to use a simulcast solution that supports - QoS as good as possible. + Thus, there is a benefit to use a simulcast solution with good QoS + support. NAT/FW Traversal: Using multiple RTP sessions incurs more cost for NAT/FW traversal unless they can re-use the same transport flow, which can be achieved by Multiplexing Negotiation Using SDP Port Numbers [I-D.ietf-mmusic-sdp-bundle-negotiation]. +7.1. Bitrate Adaptation + + Use of multiple simulcast streams can require a significant amount of + network resources. If the amount of available network resources + varies during an RTP session such that it does not match what is + negotiated in SDP, the bitrate used by the different simulcast + streams may have to be reduced dynamically. What simulcast streams + to prioritize when allocating available bitrate among the simulcast + streams in such adaptation SHOULD be taken from the simulcast stream + order on the "a=simulcast" line. Simulcast streams that have pause/ + resume capability and that would be given such low bitrate by the + adaptation process that they are considered not really useful can be + temporarily paused until the limiting condition clears. + 8. Limitations The chosen approach has a few limitations that are described in this - section. Some relate to the use of a single RTP session for all - simulcast formats of a media source, while others relate to the two - different simulcast stream identification methods. + section. The only one currently described relates to the use of a + single RTP session for all simulcast formats of a media source. 8.1. Single RTP Session The limitations in this section come from sending all simulcast streams related to a media source under the same SDP media description, which also means they are sent in the same RTP session. It is not possible to use different simulcast streams on different - transports, limiting the possibilities to apply different QoS to - different simulcast streams. When using unicast, QoS mechanisms + media transports, limiting the possibilities to apply different QoS + to different simulcast streams. When using unicast, QoS mechanisms based on individual packet marking are feasible, since they do not require separation of simulcast streams into different RTP sessions to apply different QoS. It is not possible to separate different simulcast streams into different multicast groups to allow a multicast receiver to pick the stream it wants, rather than receive all of them. In this case, the only reasonable implementation is to use different RTP sessions for each multicast group so that reporting and other RTCP functions operate as intended. -8.2. SDP Format Identification - - The limitations in this section come from and thus apply only when - using SDP format (RTP payload type) as simulcast stream - identification method. - - The available RTP payload type number space may not be sufficient - when many different media formats and/or simulcast streams are used - in the SDP. This can be particularly prominent when BUNDLE is used, - and for any technology that adds to the number of required RTP - payload types in a multiplicative way, such as for example adding RTP - retransmission [RFC4588] and Forward Error Correction [RFC5109]. - Flexible FEC Scheme [I-D.ietf-payload-flexible-fec-scheme] can be - used for RTP retransmissions and would avoid the double consumption - of the PT space that RTP Retransmission [RFC4588] causes. - - Only existing SDP attributes and parameters can be used to define - codec configuration for a simulcast format. Any codec that does not - define a sufficient set of codec parameters in "a=fmtp", or can make - use of other SDP attributes, may not be capable of expressing the - desired simulcast format dimensions (Section 3.1) with necessary - precision, or not at all. One example of this is the ability to - separate simulcast formats by bandwidth for codecs lacking a codec- - specific bandwidth parameter, since the SDP "b="-line covers all RTP - payload types listed on an "m="-line. - - A simulcast stream signaled as initially paused is not possible to - resume by a remote peer, because it cannot know which target SSRC to - use in the RESUME message [I-D.ietf-avtext-rtp-stream-pause]. - -8.3. RID Identification - - The limitations in this section come from and thus apply only when - using RID as simulcast stream identification method. - - Use of the additional "a=rid"-line in SDP and the corresponding RID - RTCP SDES item and RTP header extension requires some additional - implementation complexity, and incurs some extra bandwidth cost to - carry the RID RTCP SDES item and RTP header extension. - 9. IANA Considerations - This document requests to register a new SDP attribute, simulcast. - - Formal registrations to be written. + This document requests to register a new SDP attribute, simulcast, as + defined in Section 6.1. 10. Security Considerations - The simulcast capability, configuration attributes and parameters are - vulnerable to attacks in signaling. + The simulcast capability, configuration attributes, and parameters + are vulnerable to attacks in signaling. A false inclusion of the "a=simulcast" attribute may result in simultaneous transmission of multiple RTP streams that would otherwise not be generated. The impact is limited by the media description joint bandwidth, shared by all simulcast streams irrespective of their number. There may however be a large number of unwanted RTP streams that will impact the share of bandwidth allocated for the originally wanted RTP stream. A hostile removal of the "a=simulcast" attribute will result in simulcast not being used. Neither of the above will likely have any major consequences and can be mitigated by signaling that is at least integrity and source authenticated to prevent an attacker to change it. + Security considerations related to the use of RID is covered in + [I-D.ietf-mmusic-rid] and [I-D.roach-avtext-rid]. There are no + additional security concerns related to its use in this + specification. + 11. Contributors Morgan Lindqvist and Fredrik Jansson, both from Ericsson, have contributed with important material to the first versions of this - document. Robert Hansen and Cullen Jennings, from Cisco, and Peter - Thatcher, from Google, contributed significantly to subsequent - versions. + document. Robert Hansen and Cullen Jennings, from Cisco, Peter + Thatcher, from Google, and Adam Roach, from Mozilla, contributed + significantly to subsequent versions. 12. Acknowledgements 13. References 13.1. Normative References [I-D.ietf-avtext-rtp-stream-pause] Burman, B., Akram, A., Even, R., and M. Westerlund, "RTP Stream Pause and Resume", draft-ietf-avtext-rtp-stream- pause-10 (work in progress), September 2015. - [I-D.pthatcher-mmusic-rid] + [I-D.ietf-mmusic-rid] Thatcher, P., Zanaty, M., Nandakumar, S., Burman, B., Roach, A., and B. Campen, "RTP Payload Format - Constraints", draft-pthatcher-mmusic-rid-02 (work in - progress), October 2015. + Constraints", draft-ietf-mmusic-rid-01 (work in progress), + February 2016. + + [I-D.ietf-mmusic-sdp-mux-attributes] + Nandakumar, S., "A Framework for SDP Attributes when + Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-12 + (work in progress), January 2016. + + [I-D.roach-avtext-rid] + Roach, A., Nandakumar, S., and P. Thatcher, "RTP Payload + Format Constraints", draft-roach-avtext-rid-01 (work in + progress), February 2016. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [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, . @@ -973,42 +1026,30 @@ 13.2. Informative References [I-D.ietf-avtcore-multiplex-guidelines] Westerlund, M., Perkins, C., and H. Alvestrand, "Guidelines for using the Multiplexing Features of RTP to Support Multiple Media Streams", draft-ietf-avtcore- multiplex-guidelines-03 (work in progress), October 2014. [I-D.ietf-avtcore-rtp-multi-stream] - Lennox, J., Westerlund, M., Wu, W., and C. Perkins, - "Sending Multiple Media Streams in a Single RTP Session", - draft-ietf-avtcore-rtp-multi-stream-09 (work in progress), - September 2015. - - [I-D.ietf-avtcore-rtp-topologies-update] - Westerlund, M. and S. Wenger, "RTP Topologies", draft- - ietf-avtcore-rtp-topologies-update-10 (work in progress), - July 2015. - - [I-D.ietf-avtext-rtp-grouping-taxonomy] - Lennox, J., Gross, K., Nandakumar, S., Salgueiro, G., and - B. Burman, "A Taxonomy of Semantics and Mechanisms for - Real-Time Transport Protocol (RTP) Sources", draft-ietf- - avtext-rtp-grouping-taxonomy-08 (work in progress), July - 2015. + Lennox, J., Westerlund, M., Wu, Q., and C. Perkins, + "Sending Multiple RTP Streams in a Single RTP Session", + draft-ietf-avtcore-rtp-multi-stream-11 (work in progress), + December 2015. [I-D.ietf-mmusic-sdp-bundle-negotiation] Holmberg, C., Alvestrand, H., and C. Jennings, "Negotiating Media Multiplexing Using the Session Description Protocol (SDP)", draft-ietf-mmusic-sdp-bundle- - negotiation-23 (work in progress), July 2015. + negotiation-25 (work in progress), January 2016. [I-D.ietf-payload-flexible-fec-scheme] Singh, V., Begen, A., Zanaty, M., and G. Mandyam, "RTP Payload Format for Flexible Forward Error Correction (FEC)", draft-ietf-payload-flexible-fec-scheme-01 (work in progress), October 2015. [I-D.ietf-payload-vp8] Westin, P., Lundin, H., Glover, M., Uberti, J., and F. Galligan, "RTP Payload Format for VP8 Video", draft-ietf- @@ -1032,24 +1073,20 @@ [RFC4588] Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R. Hakenberg, "RTP Retransmission Payload Format", RFC 4588, DOI 10.17487/RFC4588, July 2006, . [RFC4733] Schulzrinne, H. and T. Taylor, "RTP Payload for DTMF Digits, Telephony Tones, and Telephony Signals", RFC 4733, DOI 10.17487/RFC4733, December 2006, . - [RFC5117] Westerlund, M. and S. Wenger, "RTP Topologies", RFC 5117, - DOI 10.17487/RFC5117, January 2008, - . - [RFC5285] Singer, D. and H. Desineni, "A General Mechanism for RTP Header Extensions", RFC 5285, DOI 10.17487/RFC5285, July 2008, . [RFC5576] Lennox, J., Ott, J., and T. Schierl, "Source-Specific Media Attributes in the Session Description Protocol (SDP)", RFC 5576, DOI 10.17487/RFC5576, June 2009, . [RFC5583] Schierl, T. and S. Wenger, "Signaling Media Decoding @@ -1065,76 +1102,107 @@ [RFC6190] Wenger, S., Wang, Y., Schierl, T., and A. Eleftheriadis, "RTP Payload Format for Scalable Video Coding", RFC 6190, DOI 10.17487/RFC6190, May 2011, . [RFC6236] Johansson, I. and K. Jung, "Negotiation of Generic Image Attributes in the Session Description Protocol (SDP)", RFC 6236, DOI 10.17487/RFC6236, May 2011, . + [RFC7656] Lennox, J., Gross, K., Nandakumar, S., Salgueiro, G., and + B. Burman, Ed., "A Taxonomy of Semantics and Mechanisms + for Real-Time Transport Protocol (RTP) Sources", RFC 7656, + DOI 10.17487/RFC7656, November 2015, + . + + [RFC7667] Westerlund, M. and S. Wenger, "RTP Topologies", RFC 7667, + DOI 10.17487/RFC7667, November 2015, + . + Appendix A. Changes From Earlier Versions NOTE TO RFC EDITOR: Please remove this section prior to publication. -A.1. Modifications Between WG Version -02 and -03 +A.1. Modifications Between WG Version -03 and -04 + + o Changed to only use RID identification, as was consensus during + IETF 94. + + o ABNF improvements. + + o Clarified offer-answer rules for initially paused streams. + + o Changed references for RTP topologies and RTP taxonomy documents + that are now published as RFC. + + o Added reference to the new RID draft in AVTEXT. + + o Re-structured section 6 to provide an easy reference by the + updated IANA section. + + o Added a sub-section 7.1 with a discussion of bitrate adaptation. + + o Editorial improvements. + +A.2. Modifications Between WG Version -02 and -03 o Removed text on multicast / broadcast from use cases, since it is not supported by the solution. o Removed explicit references to unified plan draft. o Added possibility to initiate simulcast streams in paused mode. o Enabled an offerer to offer multiple stream identification (pt or rid) methods and have the answerer choose which to use. o Added a preference indication also in send direction offers. o Added a section on limitations of the current proposal, including identification method specific limitations. -A.2. Modifications Between WG Version -01 and -02 +A.3. Modifications Between WG Version -01 and -02 o Relying on the new RID solution for codec constraints and configuration identification. This has resulted in changes in syntax to identify if pt or RID is used to describe the simulcast stream. o Renamed simulcast version and simulcast version alternative to simulcast stream and simulcast format respectively, and improved definitions for them. o Clarification that it is possible to switch between simulcast version alternatives, but that only a single one be used at any point in time. o Changed the definition so that ordering of simulcast formats for a specific simulcast stream do have a preference order. -A.3. Modifications Between WG Version -00 and -01 +A.4. Modifications Between WG Version -00 and -01 o No changes. Only preventing expiry. -A.4. Modifications Between Individual Version -00 and WG Version -00 +A.5. Modifications Between Individual Version -00 and WG Version -00 o Added this appendix. Authors' Addresses - Bo Burman Ericsson Kistavagen 25 SE-164 80 Stockholm Sweden Email: bo.burman@ericsson.com + Magnus Westerlund Ericsson Farogatan 2 SE-164 80 Stockholm Sweden Phone: +46 10 714 82 87 Email: magnus.westerlund@ericsson.com Suhas Nandakumar