Thursday, October 7, 2010

Traffic Pattern Generation


Random traffic connections of TCP and CBR can be setup between mobilenodes using a traffic-scenario generator script. This traffic generator script is available under ~ns/indep-utils/cmu-scen-gen and is called cbrgen.tcl. It can be used to create CBR and TCP traffics connections between wireless mobilenodes. In order to create a traffic-connection file, we need to define the type of traffic connection (CBR or TCP), the number of nodes and maximum number of connections to be setup between them, a random seed and incase of CBR connections, a rate whose inverse value is used to compute the interval time between the CBR pkts. So the command line looks like the following:

ns cbrgen.tcl [-type cbr|tcp] [-nn nodes] [-seed seed] [-mc connections][-rate rate] >output.tcl

The start times for the TCP/CBR connections are randomly generated with a maximum value set at 180.0s, thus the simulation time is at least 180 seconds. And the number of nodes has no relationship to the maximum number of connections (mc), we can have 10 nodes, also 10 connections as one node could have multiple simultaneous connections to other nodes. The parameter "rate" means how many packets per second, thus, for CBR traffic, the packet intervel is the reversal of this parameter. And for TCP traffic, we don't have to specify rate, ftp connections are going to be used. the default packet size is 512B. Actully, we can change all this in the "output.tcl" file.Note that there is no guarantee that the number of connections are created and the actual nodes involved as source and sink. A typical generated CBR traffic file looks like:
# 2 connecting to 3 at time 82.557023746220864
set udp_(0) [new Agent/UDP]
$ns_ attach-agent $node_(2) $udp_(0)
set null_(0) [new Agent/Null]
$ns_ attach-agent $node_(3) $null_(0)
set cbr_(0) [new Application/Traffic/CBR]
$cbr_(0) set packetSize_ 512
$cbr_(0) set interval_ 0.25
$cbr_(0) set random_ 1
$cbr_(0) set maxpkts_ 10000
$cbr_(0) attach-agent $udp_(0)
$ns_ connect $udp_(0) $null_(0)
$ns_ at 82.557023746220864 "$cbr_(0) start"
#Total sources/connections: 4/6
The last lines shows how many actual connections are created and how many nodes are used for the source.

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