Re: [rtcweb] Draft proposal for updating Multiparty topologies in draft-ietf-rtcweb-rtp-usage
"Roni Even" <ron.even.tlv@gmail.com> Tue, 08 April 2014 15:04 UTC
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From: Roni Even <ron.even.tlv@gmail.com>
To: 'Magnus Westerlund' <magnus.westerlund@ericsson.com>, 'Harald Alvestrand' <harald@alvestrand.no>, rtcweb@ietf.org
References: <533E7A50.5040909@ericsson.com> <53425DDE.2030005@alvestrand.no> <534288C2.6010906@ericsson.com>
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Date: Tue, 08 Apr 2014 18:04:50 +0300
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Subject: Re: [rtcweb] Draft proposal for updating Multiparty topologies in draft-ietf-rtcweb-rtp-usage
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Hi, Inline Roni > -----Original Message----- > From: rtcweb [mailto:rtcweb-bounces@ietf.org] On Behalf Of Magnus > Westerlund > Sent: 07 April, 2014 2:15 PM > To: Harald Alvestrand; rtcweb@ietf.org > Subject: Re: [rtcweb] Draft proposal for updating Multiparty topologies in draft- > ietf-rtcweb-rtp-usage > > On 2014-04-07 10:12, Harald Alvestrand wrote: > > Thanks for the update! > > > > It does seem reasonably clear now - clear enough that I found one > > point that I violently disagree with (if I'm interpreting it > > correctly). See below. > > > > I don't have any negative comments on the rest of the section. > > > > On 04/04/2014 11:24 AM, Magnus Westerlund wrote: > >> WG, > >> (As Author) > >> > >> Colin and I have been working on resolving terminology usage and in > >> general giving the draft a polish over before the WG last call. One > >> section that has gotten quite some attention from us is the below one. > >> The changes are significantly from an editorial stand point. However, > >> the intended content has not been intended to be changed, although > >> clarified and better motivated. So please review it, we intended to > >> include this in the upcoming draft update. Feedback appreciated. > >> > >> 5.1. Conferencing Extensions and Topologies > >> > >> RTP is a protocol that inherently supports group communication. > >> Groups can be implemented by having each endpoint sending its RTP > >> packet streams to an RTP middlebox that redistributes the traffic, by > >> using a mesh of unicast RTP packet streams between endpoints, or by > >> using an IP multicast group to distribute the RTP packet streams. > >> These topologies can be implemented in a number of ways as discussed > >> in [I-D.ietf-avtcore-rtp-topologies-update]. > >> > >> While the use of IP multicast groups is popular in IPTV systems, the > >> topologies based on RTP middleboxes are dominant in interactive video > >> conferencing environments. Topologies based on a mesh of unicast > >> transport-layer flows to create a common RTP session have not seen > >> widespread deployment. Accordingly, WebRTC implementations are not > >> expected to support topologies based on IP multicast groups. WebRTC > >> implementations are also not expected to support mesh-based > >> topologies, such as a point-to-multipoint mesh configured as a single > >> RTP session (Topo-Mesh in the terminology of > >> [I-D.ietf-avtcore-rtp-topologies-update]). However, a point-to- > >> multipoint mesh constructed using several RTP sessions, in the WebRTC > >> context using independent RTCPeerConnections can be expected to be > >> utilised by WebRTC applications. > >> > >> WebRTC implementations of RTP endpoints implemented according to > this > >> memo are expected to support all the topologies described in > >> [I-D.ietf-avtcore-rtp-topologies-update] where the RTP endpoints send > >> and receive unicast RTP packet streams to some peer device, provided > >> that peer can participate in performing congestion control on the RTP > >> packet streams. The peer device could be another RTP endpoint, or it > >> could be an RTP middlebox that redistributes the RTP packet streams > >> to other RTP endpoints. This limitation means that some of the RTP > >> middlebox-based topologies are not suitable for use in the WebRTC > >> environment. Specifically: > >> > >> o Video switching MCUs (Topo-Video-switch-MCU) SHOULD NOT be used, > >> since they make the use of RTCP for congestion control and quality > >> of service reports problematic (see Section 3.6.2 of > >> [I-D.ietf-avtcore-rtp-topologies-update]). > >> > >> o Content modifying MCUs with RTCP termination (Topo-RTCP- > >> terminating-MCU) SHOULD NOT be used since they break RTP loop > >> detection, and prevent receivers from identifying active senders > >> (see section 3.8 of [I-D.ietf-avtcore-rtp-topologies-update]). > > > > In my (strong) opinion: This recommendation is wrong. > > > > All central conferencing units that use individual RTP sessions with > > clients fall into this category. This includes, I believe, every > > single multiuser video conferencing system based on WebRTC in > > existence (and there are many of them). > > Do they? The point of this topology is that it terminates the source > identification and hides when it is performing any type of mixing or switching > operation. You can perform this with a back to back RTP session style without > breaking this property. Just by correctly linking information between the > sessions. Which means that the individual RTP session is from the identification > part inseparable from an SFM or classic RTP mixer. Only the SSRC level loop > detection gets impacted. > > I do understand that people have implemented it this way. Implementation are > not necessarily equivalent to recommended practice. > [Roni Even] In this topology the source identification is done by the application layer and not the RTP layer (using for example conference event package or just the UI). So I think that "MAY" is strong enough and not "SHOULD NOT". I agree with Harald that it is widely used. > > > > I believe the recommendation should be: > > > > * Content modifying MCUs with RTCP termination > > (Topo-RTCP-terminating-MCU) MAY be used. Note that in this scenario, > > RTP loop detection and identification of active senders is the > > resposibility of the application; since the clients are isolated from > > each other at the RTP layer, RTP cannot assist with these functions. > > > > If this topology was without issues, then one would simply remove the bullet, > and let it fall under the general clause. However, it clearly needs that warning. > Which results in this topology being both positively and negatively treated in > regards to the other "you may encounter this topology". > > Cheers > > Magnus Westerlund > > ---------------------------------------------------------------------- > Services, Media and Network features, Ericsson Research EAB/TXM > ---------------------------------------------------------------------- > Ericsson AB | Phone +46 10 7148287 > Färögatan 6 | Mobile +46 73 0949079 > SE-164 80 Stockholm, Sweden | mailto: magnus.westerlund@ericsson.com > ---------------------------------------------------------------------- > > _______________________________________________ > rtcweb mailing list > rtcweb@ietf.org > https://www.ietf.org/mailman/listinfo/rtcweb
- [rtcweb] Draft proposal for updating Multiparty t… Magnus Westerlund
- Re: [rtcweb] Draft proposal for updating Multipar… Christian Groves
- Re: [rtcweb] Draft proposal for updating Multipar… Harald Alvestrand
- Re: [rtcweb] Draft proposal for updating Multipar… Magnus Westerlund
- Re: [rtcweb] Draft proposal for updating Multipar… Magnus Westerlund
- Re: [rtcweb] Draft proposal for updating Multipar… Harald Alvestrand
- Re: [rtcweb] Draft proposal for updating Multipar… Roni Even
- Re: [rtcweb] Draft proposal for updating Multipar… Roni Even
- Re: [rtcweb] Draft proposal for updating Multipar… Magnus Westerlund
- Re: [rtcweb] Draft proposal for updating Multipar… Magnus Westerlund
- Re: [rtcweb] Draft proposal for updating Multipar… Harald Alvestrand
- Re: [rtcweb] Draft proposal for updating Multipar… Magnus Westerlund
- Re: [rtcweb] Draft proposal for updating Multipar… Roni Even
- Re: [rtcweb] Draft proposal for updating Multipar… Cullen Jennings (fluffy)
- Re: [rtcweb] Draft proposal for updating Multipar… Magnus Westerlund
- Re: [rtcweb] Draft proposal for updating Multipar… Harald Alvestrand
- Re: [rtcweb] Draft proposal for updating Multipar… Cullen Jennings (fluffy)
- Re: [rtcweb] Draft proposal for updating Multipar… Harald Alvestrand
- Re: [rtcweb] Draft proposal for updating Multipar… Bernard Aboba