Dear All,
I am running Link State Protocol on a very simple three node topology.
having designed a topology with three nodes. I have also defined the link
cost between all the nodes. (Costs of the links are: n0-n1 : 1.5, n1-n2 :
1.5, n0-n2 : 10). When I run the simulation, according to the traffic goes
from node n0 to n2 directly. Although the total cost of node n0-n1-n2 is
less the total cost of n0-n2 directly. According to my knowledge, it should
not behave like this. If the accumulative cost of the links is less then the
direct link, traffic should traverse the lowest cost path.
I unable to grasp what is going on. I am pasting the script below for your
convenience, if you can see the script and tell me where am I wrong or if
there is anything missing in the script.
Also please tell me how should I write the script if I am wrong in the
script
#Create a simulator object
set ns [new Simulator]
#Open the nam trace file
set nf [open out.nam w]
$ns namtrace-all $nf
set f0 [open sp1.tr w]
$ns trace-all $f0
#Initialising Link-State routing Protocol
$ns rtproto LS
#Define a 'finish' procedure
proc finish {} {
global ns nf f0
$ns flush-trace
#Close the trace file
close $nf
close $f0
#Execute nam on the trace file
exec nam out.nam &
exit 0
}
#Create three nodes
set n0 [$ns node]
set n1 [$ns node]
set n2 [$ns node]
#Create links between the nodes
$ns duplex-link $n0 $n1 7Mb 10ms DropTail
#Giving cost to the link in both directions
$ns cost $n0 $n1 1.5
$ns cost $n1 $n0 1.5
$ns duplex-link $n1 $n2 7Mb 10ms DropTail
$ns cost $n1 $n2 1.5
$ns cost $n2 $n1 1.5
$ns duplex-link $n0 $n2 2Mb 10ms DropTail
$ns cost $n0 $n2 10
$ns cost $n2 $n0 10
#Create a UDP agent and attach it to node n0
set udp0 [new Agent/UDP]
$ns attach-agent $n0 $udp0
# Create a exponential traffic source and attach it to udp0
set expo [new Application/Traffic/Exponential]
$expo set packetSize_ 210
$expo set burst_time_ 500ms
$expo set idle_time_ 500ms
$expo set rate_ 100k
$expo attach-agent $udp0
#Create a Null agent (a traffic sink) and attach it to node n2
set null0 [new Agent/Null]
$ns attach-agent $n2 $null0
#Connect the traffic source with the traffic sink
$ns connect $udp0 $null0
#Schedule events for the expo agent and the network dynamics
$ns at 0.5 "$expo start"
#$ns rtmodel-at 1.0 down $n0 $n2
#$ns rtmodel-at 2.0 up $n0 $n2
$ns at 4.5 "$expo stop"
#Call the finish procedure after 5 seconds of simulation time
$ns at 5.0 "finish"
#Run the simulation
$ns run
-----
Regards,
Bilal A. Khan
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