S-38.188 Computer Networks (Spring-04)

FAQ (22.4.2004)

If necessary a FAQ page will be created on this web page concerning the project works.

First always read the newsgroup discussion (for students that do not understand Finnish, I apologize for most material being in Finnish, ask in English in the newsgroup if you don't find an answer to your question or it is only in Finnish)

opinnot.sahko.s-38.tietoverkkotekniikka In an alternative web-interface form.

Part 3

Queue monitoring: set qmon and the questats() procedure before setting fmon AND flowstats procedure. If you have set fmon... before set qmon... you get queue sizes that are incorrect (you notice it by them being larger than the maximum)
Nam windows open to other peoples sessions. Markus gave advice on this, use nam with command "nam -a out.nam" I still advise not to use nam too much. It slows down the simulations and out.nam files take up too much memory. Only when you need to check something in the simulation that you don't understand, use nam.
Monitoring the congestion window according to my advice, does not always work. Set an extra parameter
"$tcp($i) set maxcwnd_ $maxwnd"
this controls the value of cwnd_ to always be below $maxwnd.
However not having this does not change results, as a TCP source never sends more than $maxwnd worth of packets. (So you can change "by hand" the large values to $maxwnd values in your .dat files)
There is a typo in the assignment: section 3.2 item 4. "Study the congestion window for two persistent TCP flows that you traced in part 2 and..." should be "...that you traced in section 3.1. item 5 and..."
Simulation time has to be long enough, in order for you the results to depict a stable situation. The congestion window of the flows behind the slow access links must go through a few cycles of additive increase/multiplicative decrease.
I propose using simulation times larger than 60 seconds. Preferably more!
For each simulation you have to monitor the congestion windows and calculate throughputs.

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Sivua on viimeksi päivitetty 22.04.2004 14:58.
URI: http://www.netlab.tkk.fi/opetus/s38188/2004/harj/FAQ.shtml
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