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@xxxxxxxxx] > 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 for VoIP > > Hi Arujna, > > I have a question concerning the following point: > > On 16/08/07, Arjuna Sathiaseelan <arjuna@xxxxxxxxxxxxxx> 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 > --- > "This email and any attachments are confidential. They may > contain legally privileged information or copyright material. > You should not read, copy, use or disclose them without > authorisation. If you are not an intended recipient, please > contact us at once by return email and then delete both > messages. We do not accept liability in connection with > computer virus, data corruption, delay, interruption, > unauthorised access or unauthorised amendment. This notice > should not be removed" >
