Hi all, I've found, in the hard way, that "interval_" is a special pseudo-variable of Application/Traffic/CBR and has unexpecded and undocumented behaviour.
If the users sets the interval, followed by the packetsize, the specified interval is changed to make the __rate__ constant, which is not probably the user is trying to achieve. This is exemplified by this test script; note that the difference is the order of the lines setting interval and packetsize ##### set ns [new Simulator] set opt(CBR_interval) 0.1 ;# 100 packets per second set opt(packet_size) 1000 ;# 1000 bytes per packet set generator1 [new Application/Traffic/CBR] $generator1 set packetSize_ $opt(packet_size) $generator1 set interval_ $opt(CBR_interval) puts "Actual interval for generator 1: [$generator1 set interval_ ] Desired interval: $opt(CBR_interval) " set generator2 [new Application/Traffic/CBR] $generator2 set interval_ $opt(CBR_interval) $generator2 set packetSize_ $opt(packet_size) puts "Actual interval for generator 2: [$generator2 set interval_ ] Desired interval: $opt(CBR_interval) " exit ##### Which results, in ns2.29: Actual interval for generator 1: 0.1000000000001 Desired interval: 0.1 Actual interval for generator 2: 0.4761904761616 Desired interval: 0.1 The documentation is ambiguous: http://www.isi.edu/nsnam/ns/doc/node498.html "The setting of a CBR object's rate_ and interval_ are mutually exclusive" ... "In a simulation, either a rate or an interval (but not both) should be specified for a CBR object." ############## To solve this, either: a) make sure you specify the interval AFTER the packetsize; b) use my patch that solves this problem http://mailman.isi.edu/pipermail/ns-developers/2006-August/002375.html http://mailman.isi.edu/pipermail/ns-developers/2006-August/002377.html Pedro Vale Estrela
