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

[Magnus Westerlund <[e-mail]>]

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]
>> ----------------------------------------------------------------------
>>
>>
>> _______________________________________________
>> rtcweb mailing list
>> [e-mail]
>> 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]
----------------------------------------------------------------------