Simulation of Congestion Control Algorithms Using NS-2

 

Simulation of Congestion Control Algorithms Using NS-2

 

Aim

To study the Network Simulator (NS-2) and simulate TCP congestion control algorithms, namely TCP Reno and TCP Tahoe, and observe their congestion-window behavior.

 

Steps to execute

1.    Install NS-2 in Google Colab

a.   Open Google Colab and create a new notebook

b.   Check the Linux environment

o   !uname -a

c.   Update the package list

o   !apt-get update -qq

d.   Install NS-2

o   !apt-get install -y ns2

e.   Check the NS-2 installation and verify

o   !which ns

2.    TCP Reno congestion-control algorithm.

a.   Create the Reno TCL file

b.   Run the TCL program

c.   Check the generated files

d.   Plot the TCP Reno congestion window

3.   TCP Tahoe congestion-control algorithm

a.   Create the Tahoe TCL file

b.   Run the TCL program

c.   Check the generated files

d.   Plot the TCP Tahoe congestion window

 

 

TCP Reno congestion-control algorithm.

 

a.   Create the Reno TCL file

%%writefile reno_cwnd.tcl

 

# Create simulator

set ns [new Simulator]

 

# Create trace file

set tracefile [open reno.tr w]

$ns trace-all $tracefile

 

# Create congestion window file

set cwndfile [open reno_cwnd.tr w]

 

# Create nodes

set n0 [$ns node]

set n1 [$ns node]

set n2 [$ns node]

set n3 [$ns node]

 

# Create links

$ns duplex-link $n0 $n2 10Mb 10ms DropTail

$ns duplex-link $n1 $n2 10Mb 10ms DropTail

$ns duplex-link $n2 $n3 1Mb 20ms DropTail

 

# Queue size

$ns queue-limit $n2 $n3 10

 

# Create TCP Reno

set tcp [new Agent/TCP/Reno]

 

# Attach TCP to sender

$ns attach-agent $n0 $tcp

 

# Create TCP sink

set sink [new Agent/TCPSink]

 

# Attach sink to receiver

$ns attach-agent $n3 $sink

 

# Connect TCP and sink

$ns connect $tcp $sink

 

# Create FTP application

set ftp [new Application/FTP]

 

# Attach FTP to TCP

$ftp attach-agent $tcp

 

# Procedure to record congestion window

proc record {} {

    global ns tcp cwndfile

 

    set now [$ns now]

    set cwnd [$tcp set cwnd_]

 

    puts $cwndfile "$now $cwnd"

 

    $ns at [expr $now + 0.01] "record"

}

 

# Start recording

$ns at 0.0 "record"

 

# Start FTP

$ns at 0.5 "$ftp start"

 

# Stop FTP

$ns at 9.5 "$ftp stop"

 

# Finish simulation

$ns at 10.0 "finish"

 

proc finish {} {

    global ns tracefile cwndfile

 

    $ns flush-trace

 

    close $tracefile

    close $cwndfile

 

    exit 0

}

 

# Run simulation

$ns run

 

b.   Run the TCL program

!ns reno_cwnd.tcl

 

c.   Check the generated files

!ls -lh reno*

 

d.   Plot the TCP Reno congestion window

 

import matplotlib.pyplot as plt

 

time = []

cwnd = []

 

with open("reno_cwnd.tr", "r") as f:

    for line in f:

        t, c = line.split()

        time.append(float(t))

        cwnd.append(float(c))

 

plt.figure(figsize=(10,5))

plt.plot(time, cwnd)

 

plt.xlabel("Time (seconds)")

plt.ylabel("Congestion Window (packets)")

plt.title("TCP Reno Congestion Window")

plt.grid()

 

plt.show()

 

 

 

TCP Tahoe congestion-control algorithm

 

a.   Create the Tahoe TCL file

%%writefile tahoe_cwnd.tcl

 

# Create simulator

set ns [new Simulator]

 

# Create trace file

set tracefile [open tahoe.tr w]

$ns trace-all $tracefile

 

# Create congestion window file

set cwndfile [open tahoe_cwnd.tr w]

 

# Create nodes

set n0 [$ns node]

set n1 [$ns node]

set n2 [$ns node]

set n3 [$ns node]

 

# Create links

$ns duplex-link $n0 $n2 10Mb 10ms DropTail

$ns duplex-link $n1 $n2 10Mb 10ms DropTail

$ns duplex-link $n2 $n3 1Mb 20ms DropTail

 

# Queue size

$ns queue-limit $n2 $n3 10

 

# Create TCP Tahoe

set tcp [new Agent/TCP]

 

# Attach TCP to sender

$ns attach-agent $n0 $tcp

 

# Create TCP sink

set sink [new Agent/TCPSink]

 

# Attach sink to receiver

$ns attach-agent $n3 $sink

 

# Connect TCP and sink

$ns connect $tcp $sink

 

# Create FTP application

set ftp [new Application/FTP]

 

# Attach FTP to TCP

$ftp attach-agent $tcp

 

# Procedure to record congestion window

proc record {} {

    global ns tcp cwndfile

 

    set now [$ns now]

    set cwnd [$tcp set cwnd_]

 

    puts $cwndfile "$now $cwnd"

 

    $ns at [expr $now + 0.01] "record"

}

 

# Start recording

$ns at 0.0 "record"

 

# Start FTP

$ns at 0.5 "$ftp start"

 

# Stop FTP

$ns at 9.5 "$ftp stop"

 

# Finish simulation

$ns at 10.0 "finish"

 

proc finish {} {

    global ns tracefile cwndfile

 

    $ns flush-trace

 

    close $tracefile

    close $cwndfile

 

    exit 0

}

 

# Run simulation

$ns run

 

b.   Run the TCL program

!ns tahoe_cwnd.tcl

 

c.   Check the generated files

!ls -lh tahoe*

 

d.   Plot the TCP Tahoe congestion window

import matplotlib.pyplot as plt

 

time = []

cwnd = []

 

with open("tahoe_cwnd.tr", "r") as f:

    for line in f:

        t, c = line.split()

        time.append(float(t))

        cwnd.append(float(c))

 

plt.figure(figsize=(10,5))

 

plt.plot(time, cwnd)

 

plt.xlabel("Time (seconds)")

plt.ylabel("Congestion Window (packets)")

plt.title("TCP Tahoe Congestion Window")

 

plt.grid()

 

plt.show()