Re: [AVTCORE] Multi-party real-time text requiring new RTP payload type
Gunnar Hellström <gunnar.hellstrom@ghaccess.se> Wed, 22 April 2020 20:01 UTC
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To: Brian Rosen <br@brianrosen.net>
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From: Gunnar Hellström <gunnar.hellstrom@ghaccess.se>
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Date: Wed, 22 Apr 2020 22:01:27 +0200
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Subject: Re: [AVTCORE] Multi-party real-time text requiring new RTP payload type
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Thanks Brian, Den 2020-04-21 kl. 20:56, skrev Brian Rosen: > I’m okay with the new payload type. All of this would be new code, so > dealing with the new payload type wouldn’t be confusing or difficult. Right. And a lot from RFC 4103 is still valid with the new payload type, so that it can be an update to RFC 4103. > I’m not aware of any implementations of t140 without redundancy, but > I’m also not bothered by including rtt-mix. Right. No one using plain T.140 without redundancy currently. > > I’m also okay with James Hamlin’s proposal. I like the effect enough > that I’m not going to worry about bad implementations. I aim at including this new payload type in next version. I also intend to look at what sdp would look like if we include negotiation between RTP and SRTP. > Again, supporting this is new code, so if your implementation of T140 > and SDP in general is lacking, this would be a good time to fix that. > > Brian > Thanks, Gunnar > >> On Apr 21, 2020, at 5:18 AM, Gunnar Hellström >> <gunnar.hellstrom@ghaccess.se <mailto:gunnar.hellstrom@ghaccess.se>> >> wrote: >> >> Hi, >> >> I have got an off-list comment that the proposed use of the CSRC-list >> members to indicate source of the primary and the different >> redundancy generations of the T140blocks would require registration >> of a new payload type instead of saying that it is a refined use of >> text/red updated from RFC 4103. >> >> ( this is about >> https://www.ietf.org/id/draft-hellstrom-avtcore-multi-party-rtt-source-03.txt >> ) >> >> The purpose is to speed up the switch of source of text from the >> mixer so that every packet can have primary text from another source >> than the previous packet. Without the update, the mixer would need to >> send two packets with just redundant text before sending new text >> from another source. >> >> I am not yet totally convinced that we need to introduce a new >> payload type, but find it possible. >> >> Let us call it "text/rex" for "redundancy extended". >> >> It would cause a quite straightforward sdp negotiation of parties >> supporting both the traditional text/red format from RFC 4103, and >> the updated text/rex. >> >> Offer example : >> >> m=text 11000 RTP/AVP 101 100 98 >> a=rtpmap:98 t140/1000 >> a=rtpmap:100 red/1000 >> a=rtpmap:101 rex/1000 >> a=fmtp:100 98/98/98 >> a=fmtp:101 98/98/98 >> a=rtt-mix >> >> Answer example from a multi-party capable device >> m=text 11000 RTP/AVP 101 98 >> a=rtpmap:98 t140/1000 >> a=rtpmap:101 rex/1000 >> a=fmtp:101 98/98/98 >> a=rtt-mix >> >> Answer example from a multi-party unaware device: >> >> m=text 11000 RTP/AVP 100 98 >> a=rtpmap:98 t140/1000 >> a=rtpmap:100 red/1000 >> a=fmtp:100 98/98/98 >> >> >> >> It may look strange that the attribute a=rtt-mix is still there as an >> indication of multi-party capability when that already is implied in >> the "rex" payload type. But it is for the very rare case that the >> network conditions would allow use of bare t140 payload type without >> redundancy. Then there is a need to indicate multi-party awareness by >> a=rtt-mix . >> >> If we accept this move, we could also open for discussion if the >> format proposed by James Hamlin earlier in this list, where the >> maximum number of 16 members in the CSRC list allows transport of >> text from up to 16 sources in the same packet. That would make the >> mixing of real-time text as efficient and rapid as that of audio and >> video. A question is though if current implementations are well >> behaving and do not collapse by getting the combined sdp. >> >> If we do not accept this move and instead base the multi-party mixing >> on the current text/red format with short transmission intervals, we >> can claim that simultaneous typing is quite rare and that the >> introduced delay of the first few characters of about 200 ms from a >> second source when one is already sending is acceptable, knowing that >> most text conversations are at speeds of under 12 characters per >> second and that the transmissions from each source anyway comes in >> 300 ms intervals. Some jerkiness and delay will be noticable when >> there is more than two simultaneous senders. >> >> Regards >> >> Gunnar >> >> -- >> Gunnar Hellström >> GHAccess >> gunnar.hellstrom@ghaccess.se >> _______________________________________________ >> Audio/Video Transport Core Maintenance >> avt@ietf.org <mailto:avt@ietf.org> >> https://www.ietf.org/mailman/listinfo/avt > -- Gunnar Hellström GHAccess gunnar.hellstrom@ghaccess.se
- [AVTCORE] Multi-party real-time text requiring ne… Gunnar Hellström
- Re: [AVTCORE] Multi-party real-time text requirin… Brian Rosen
- Re: [AVTCORE] Multi-party real-time text requirin… Gunnar Hellström
- Re: [AVTCORE] Multi-party real-time text requirin… worley
- Re: [AVTCORE] Multi-party real-time text requirin… Gunnar Hellström
- Re: [AVTCORE] Multi-party real-time text requirin… Gunnar Hellström
- Re: [AVTCORE] Multi-party real-time text requirin… worley
- Re: [AVTCORE] Multi-party real-time text requirin… Gunnar Hellström
- Re: [AVTCORE] Multi-party real-time text requirin… Jonathan Lennox
- Re: [AVTCORE] Multi-party real-time text requirin… Gunnar Hellström
- Re: [AVTCORE] Multi-party real-time text requirin… Gunnar Hellström
- Re: [AVTCORE] Multi-party real-time text requirin… xthe.various.worley
- Re: [AVTCORE] Multi-party real-time text requirin… Gunnar Hellström
- Re: [AVTCORE] Multi-party real-time text requirin… worley
- Re: [AVTCORE] Multi-party real-time text Issue 4:… Gunnar Hellström