[ns] CCN ethernet simulation.

[Devendra Goyal <dgoyal@ECECS.UC.EDU>]

Throughput thing sounds little weird. I checked everything I could. But
found no error.

I did another experiment, created a link between two nodes with following
specf.
$ns duplex-link $n1 $n2 10Mb 1ms DropTail

and a cbr with following specf.
$cbr0 set packetSize_ 1500
$cbr0 set rate_ 15Mb

on running this, I get following output:
For Packetsize= 1500 and Interval= 1.0 :
        Intended Throughput     = 29.739659045857014 Mbs
        Throughput              = 15.12356283864147 Mbs
        Avg. Plus Delay         = 0.03948850052429101 sec
        Avg. Minus Delay        = 0.001793289059769138 sec
        Packet Drop Prob        = 0.4914681834340562


The Throughput is more than the link bandwidth.
I cannot explain this.

The program is appended:

#Create a simulator object
set ns [new Simulator]

#Open the trace file
set nf [open out.ex2 w]
$ns trace-all $nf

#Define a 'finish' procedure
proc finish {} {
        global ns nf
        $ns flush-trace
        #Close the trace file
        close $nf
        exit 0
}

#Create four nodes
set n1 [$ns node]
set n2 [$ns node]

#Create links between the nodes
$ns duplex-link $n1 $n2 10Mb 1ms DropTail

#Create a UDP agent and attach it to node n0
set udp0 [new Agent/UDP]
$udp0 set class_ 1
$ns attach-agent $n1 $udp0

# Create a CBR traffic source and attach it to udp0
set cbr0 [new Application/Traffic/CBR]
$cbr0 set packetSize_ 1500
$cbr0 set rate_ 15Mb
$cbr0 attach-agent $udp0

#Create a Null agent (a traffic sink) and attach it to node n3
set null0 [new Agent/Null]
$ns attach-agent $n2 $null0

#Connect the traffic sources with the traffic sink
$ns connect $udp0 $null0

#Schedule events for the CBR agents
$ns at 0 "$cbr0 start"
$ns at 4.5 "$cbr0 stop"
#Call the finish procedure after 5 seconds of simulation time
$ns at 5.0 "finish"

#Run the simulation
$ns run

#end of program