Re: [rtcweb] RTP Usage: Is RTP Retransmission REQUIRED or RECOMMENDED

[Colin Perkins <[e-mail]>]

Roni,

I don't understand how you can say this is not practical. Magnus has an implementation, and he states it works well. That seems practical to me.

There are also self-evidently network paths with low enough RTT for RTP retransmission to be used for interactive calls, if the playout buffer code knows the RTT and adjusts the buffer to allow this. Not all paths, I agree, but that doesn't mean it's not useful in some environments. 

We're defining requirements for the RTP infrastructure in WebRTC clients here, not forcing all implementations to use every feature. My personal view is that retransmission should be REQUIRED. Given that the RTP/AVPF profile is REQUIRED, implementation of retransmission is straightforward. I see no benefit in leaving it out, and very little cost in requiring it.

Colin


On 28 Jun 2012, at 15:52, Roni Even wrote:
> Hi Magnus,
> So using retransmission is at the cost of losing lip synch which is very noticeable. I am not saying that it does not work to do retransmission, my claim that it is not practical and this is why I do not think it is required.
> Roni
> 
> -----Original Message-----
> From: [e-mail] [mailto:[e-mail]] On Behalf Of
> Magnus Westerlund
> Sent: 28 June, 2012 9:49 AM
> To: [e-mail]
> Subject: Re: [rtcweb] RTP Usage: Is RTP Retransmission REQUIRED or
> RECOMMENDED
> 
> Hi,
> 
> As Individual I like to state my position.
> 
> We have a video conference system developed by my colleagues used internally at Ericsson that uses RTP Retransmission for video, not for audio with great success. This is implemented such that we actually allow the video to fall behind the audio when packet loss and retransmission is not able to repair in a timely enough fashion. The benefit is minimal overhead and still no loss induced degradations in the video. Yes, we get degradation in form of frame display jittering and short freezes. But those events that are truly visible are rare over wired networks.
> 
> I am personally convinced that RTP Retransmission is great tool in the toolbox when it comes to improve media quality in many use cases. Yes there are scenarios where RTP retransmission is less efficient. Long RTTs (over 200-400 ms) is the primary source of degradations. Compared to FEC it so much more efficient from bandwidth consumption perspective.
> 
> I also think it is important that we have some mandatory to implement tool for making the transport more robust now that we have a consensus that we are not going for a FEC solution in the initial specification.
> 
> Thus my personal position is that RTP Retransmission should be REQUIRED to implement.
> 
> Cheers
> 
> Magnus
> 
> 
> On 2012-06-27 09:36, Magnus Westerlund wrote:
>> WG,
>> 
>> We had a discussion at the interim if RTP Retransmission is to be 
>> considered REQUIRED or RECOMMENDED to implement. I would like to see 
>> if we can first have some discussion on this topic before moving on to 
>> see if we can get a consensus here on the mailing list.
>> 
>> Please provide your views on this topic.
>> 
>> Cheers
>> 
>> Magnus Westerlund
>> (As Chair and document editor)
>> 
>> 
>> ----------------------------------------------------------------------
>> Multimedia Technologies, Ericsson Research EAB/TVM
>> ----------------------------------------------------------------------
>> Ericsson AB                | Phone  [phone]
>> Färögatan 6                | Mobile [phone]
>> SE-164 80 Stockholm, Sweden| mailto: [e-mail]
>> ----------------------------------------------------------------------
>> 
>> 
>> _______________________________________________
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>> https://www.ietf.org/mailman/listinfo/rtcweb
>> 
>> 
> 
> 
> -- 
> 
> Magnus Westerlund
> 
> ----------------------------------------------------------------------
> Multimedia Technologies, Ericsson Research EAB/TVM
> ----------------------------------------------------------------------
> Ericsson AB                | Phone  [phone]
> Färögatan 6                | Mobile [phone]
> SE-164 80 Stockholm, Sweden| mailto: [e-mail]
> ----------------------------------------------------------------------
> 
> 
> 
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-- 
Colin Perkins
http://csperkins.org/