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

["Roni Even" <[e-mail]>]

Hi Magnus,
The demo in the interim of what happens in retransmission was not in par
with my experience with any other recovery  methods including receiver based
repair without FEC.
Roni

-----Original Message-----
From: Magnus Westerlund [mailto:[e-mail]] 
Sent: 28 June, 2012 4:17 PM
To: Roni Even
Cc: [e-mail]
Subject: Re: [rtcweb] RTP Usage: Is RTP Retransmission REQUIRED or
RECOMMENDED

On 2012-06-28 16:52, 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.

My experience with using this system several times a week for the last two
years says that it is not that noticable. The type of video image
degradations you get from unrepaired burst losses are so much worse.

I also think it is important that we consider the goals. If your goal is a
really high quality telepresence system then this approach is most likely
not usable. But, most WebRTC applications doesn't have that quality
requirements nor the user expectancies to be significantly annoyed at a
short loss of lip sync. The bit-rate savings that RTP retransmission
provides compared to FEC is much more important in my mind.

I think the Google hangout session during the interim showed the importance
of having some video being much higher than having no video or requiring
video with perfect sync with audio. And Justin said, Google Hangout uses
Retransmission.

Cheers

Magnus


> 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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>> [e-mail]
>> https://www.ietf.org/mailman/listinfo/rtcweb
>>
>>
> 
> 


-- 

Magnus Westerlund

----------------------------------------------------------------------
Multimedia Technologies, Ericsson Research EAB/TVM
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Ericsson AB                | Phone  [phone]
Färögatan 6                | Mobile [phone]
SE-164 80 Stockholm, Sweden| mailto: [e-mail]
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