Exercise 3: Analyze Bandwidth Share of TCP and UDP Traffic

It is equivalently important to understand the ns-2 output trace format and have some knowledge on how to extract relevant information. This exercise is dedicated to familiarize you with ns-2's output format, in particular by trace-all, and techniques to do trace post-processing.

Topology: Use the simple.tcl example discussed in class, but first swap the source/destination of udp1 i.e. make its source be n1 and destination n3.

As a result of running ns on the modified simple.tcl, we obtain an output file "simple.tr". It contains information of all packets enqueued (+), dequeued (-), received (r) and dropped (d).

a. Modify the simple.tcl (name this, say, simple1.tcl) so that

there is only one UDP/CBR flow (i.e. do not start the second UDP/CBR flow)

start the two flows (1 TCP and 1 UDP) at the same time 0.1 s

run the script for 6s.

Extract information from the "simple.tr" file and compute the total bytes of TCP (tcp) and UDP (cbr) traffic over link 2-3 for the duration of the simulation. Then, compute total TCP and UDP/CBR traffic in bytes and ratios of TCP and UDP/CBR to the total. Finally, comment on the bandwidth share of TCP vs. UDP/CBR.

b. Modify the simple1.tcl file (name this simple2.tcl) so that

there are two UDP/CBR flows

start the TCP and the 2 UDP flows at the same time 0.1 s

run the script for 6s.

Extract the information from the new simple.tr file and recompute the parameters above. What do you notice?

Note: Fill in the blanks according to your understanding of trace format in the following awk command for computing the total bytes of TCP or UDP traffic

awk '$1=="r" && ??==2 && ??==3 && $5=="??" {a += ??} END {print a}' simple1.tr

simple.tcl script

#create scheduler
set ns [new Simulator]

#choose colors
$ns color 0 blue
$ns color 1 red
$ns color 2 green

#turn tracing on
set f [open simple.tr w]
$ns trace-all $f
set nf [open simple.nam w]
$ns namtrace-all $nf

#create topology
set n0 [$ns node]
set n1 [$ns node]
set n2 [$ns node]
set n3 [$ns node]

$ns duplex-link $n0 $n2 5Mb 2ms DropTail
$ns duplex-link $n1 $n2 5Mb 2ms DropTail
$ns duplex-link $n2 $n3 1.5Mb 10ms DropTail
#limit queue size (otherwise unlimited)
#$ns queue-limit $n2 $n3 5

#adjust nam orientation
$ns duplex-link-op $n0 $n2 orient right-up
$ns duplex-link-op $n1 $n2 orient right-down
$ns duplex-link-op $n2 $n3 orient right

#turn nam visualization for n2-n3 queue
$ns duplex-link-op $n2 $n3 queuePos 0.5

#create udp agent
set udp0 [new Agent/UDP]
#attach agent to node
$ns attach-agent $n0 $udp0
#select packet color for nam
$udp0 set class_ 0
#create a cbr application
set cbr0 [new Application/Traffic/CBR]
#attach application to agent
$cbr0 attach-agent $udp0

#create another udp/cbr agent/application
set udp1 [new Agent/UDP]
$ns attach-agent $n3 $udp1
$udp1 set class_ 1
set cbr1 [new Application/Traffic/CBR]
$cbr1 attach-agent $udp1

#create and attach null agents
set null0 [new Agent/Null]
$ns attach-agent $n3 $null0

set null1 [new Agent/Null]
$ns attach-agent $n1 $null1

$ns connect $udp0 $null0
$ns connect $udp1 $null1

#schedule the start of cbr traffic
$ns at 1.0 "$cbr0 start"
$ns at 1.1 "$cbr1 start"

#create and attach a TCP agent source/sink
set tcp [new Agent/TCP]
$tcp set class_ 2
set sink [new Agent/TCPSink]
$ns attach-agent $n0 $tcp
$ns attach-agent $n3 $sink
$ns connect $tcp $sink

#attach an ftp application to the TCP agent
set ftp [new Application/FTP]
$ftp attach-agent $tcp

#schedule start of ftp application
$ns at 1.2 "$ftp start"

#schedule end of ftp application
$ns at 5.0 "$ftp stop"

#$ns at 5.0 "$ns detach-agent $n0 $tcp ; $ns detach-agent $n3 $sink"

#print the (default) cbr values
puts [$cbr0 set packetSize_]
puts [$cbr0 set interval_]

$ns at 6.0 "finish"

proc finish {} {
global ns f nf
$ns flush-trace
close $f
close $nf

#puts "running nam..."
#exec nam simple.nam &
exit 0
}

$ns run

** Refer to previous post on Network Simulator, Ns-2 Trace format