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

Cameron Byrne <cb.list6@gmail.com> Wed, 27 June 2012 16:19 UTC

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Date: Wed, 27 Jun 2012 09:19:00 -0700
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From: Cameron Byrne <cb.list6@gmail.com>
To: "Fabio Pietrosanti (naif)" <lists@infosecurity.ch>
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Subject: Re: [rtcweb] RTP Usage: Is RTP Retransmission REQUIRED or RECOMMENDED
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I think Bernard noted this as well, but it is not so much buffer
bloat... but the issue is indeed latency, not loss.  Consequently,
re-transmission not productive.

On Wed, Jun 27, 2012 at 12:42 AM, Fabio Pietrosanti (naif)
<lists@infosecurity.ch> wrote:
> If you use RTP over a Mobile Networks subject to strong packet loss
> (especially 3G or area plenty of many mobile devices), the RTP
> retransmission became a requirement.
>

Please cite the packet loss you are referring to.

Here is one imperfect data source,
http://pam2012.ftw.at/papers/PAM2012paper6.pdf.

I say it is imperfect because it relies on SACK, which can infer
packet loss, but frequently for mobile it just infers delay.  So, the
mobile packet loss is overstated.

Mobile (UMTS, ...) networks have extremely robust forward error
correct and re-transmission capabilities at layer 1 and layer 2, this
induces delay but ensure packet delivery.

See: http://en.wikipedia.org/wiki/Hybrid_automatic_repeat_request

Attempting to optimize for packet delivery at higher levels (RTP
re-transmission...)  leads to various counter productive race
conditions, since the RAN (radio access network) is designed for 100%
packet delivery.

CB

> If there is RTCP support within RTCWeb, we may define some "quality
> threshold" after that the RTP Retransmition became REQUIRED.
>
> Fabio
>
> On 6/27/12 9:36 AM, 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  +46 10 7148287
>> Färögatan 6                | Mobile +46 73 0949079
>> SE-164 80 Stockholm, Sweden| mailto: magnus.westerlund@ericsson.com
>> ----------------------------------------------------------------------
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