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RE: [dccp] DCCP for VoIP
Hi
And thanks for the reponse sofar.
Regarding the RTT ws feedback issue below.
I recall that the RTT for satellite links is ~560ms, I would expect that
Wimax has a shorter RTT.
Do you have any indication (rule of thumb wise) at what levels of RTT it
may be necessary to send more than one feedback / RTT ?
Regards
Ingemar
> -----Original Message-----
> From: Emmanuel Lochin [mailto:emmanuel.lochin at gmail.com]
> Sent: den 16 augusti 2007 23:31
> To: Arjuna Sathiaseelan
> Cc: Ingemar Johansson S (LU/EAB); 'dccp' working group; Gorry
> Fairhurst; Golam Sarwar; Roksana Boreli; Sebastien Ardon;
> Guillaume Jourjon
> Subject: Re: [dccp] DCCP for VoIP
>
> Hi Arujna,
>
> I have a question concerning the following point:
>
> On 16/08/07, Arjuna Sathiaseelan <arjuna at erg.abdn.ac.uk> wrote:
> > > 2) How often is feedback sent? (sorry for a qu estion
> that I should
> > > probably answer myself by means of some RTFM) but if you could
> > > answer it I would really appreciate it.
> >
> > Usually CCIDs incorporating the TFRC or TFRC-SP protocol
> would send a
> > feedback once per RTT, unless there is a change in the loss
> event. If
> > there is a change in the loss event then the feedback would
> be sent immediately.
> > Alternatively these protocols could send multiple feedbacks per RTT
> > (when there is no change in the loss event) but it is not a common
> > practice in my opinion.
>
> I am wondering why this is not a common practice?
>
> We (Golam, Roksana and me, in copy of this email) are
> currently evaluating GNU/Linux DCCP/CCID3 over over live
> satellite and long range wireless links.
>
> As expected, DCCP/CCID3 obtains poor performance compared to TCP.
> In a logical way, on such long delay networks, the feedback
> loop is linked to the delay of the connection and thus,
> cannot update the transmitted rate as efficiently as over a
> low delay network.
>
> However, if we increase the number of feedback messages as a
> function of the RTT over these long delay networks,
> DCCP/CCID3 performance are really better. This has been
> verified in ns-2.30 and over satellite and Wimax networks. As
> a result, we are currently considering a dynamic algorithm
> for adjusting the amount of DCCP feedback based on RTT.
>
> Emmanuel
>
>
> --
> Emmanuel Lochin http://mobqos.ee.unsw.edu.au/~lochin/
> Networks and Pervasive Computing Research Program National
> ICT Australia Ltd Locked Bag 9013, Alexandria, NSW 1435 Australia
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