How to Start Physical Topology Projects Using NS2

To start a Physical Topology using NS2 (Network Simulator 2), we can create a network including real-world outlines and physical connections among the nodes. This topology deliberates the hardware-level network arrangement directly, to create it which is optimal for learning the network performance, fault tolerance, and protocol behavior. Following is a sequential methodology to get started Physical Topology project in NS2:

Steps to Start Physical Topology in NS2

  1. Understand Physical Topology
  • Structure:
    • Nodes are denoting the physical devices such as routers, switches, computers, and so on.
    • Links specifies real physical connections like wired or wireless.
  • Common Physical Topologies:
    • Star: Central hub associated to all devices.
    • Ring: Nodes are linked within a circular arrangement.
    • Mesh: Nodes are interrelated with redundancy.
    • Tree: It is hierarchical structure including a root and branches.
  1. Set Up NS2
  1. Install NS2:

sudo apt-get install ns2

  1. Verify Installation: Confirm installation including an example simulation script:

ns example.tcl

  1. Define Physical Topology
  • Make a physical topology type such as star, ring, mesh, tree, and so on.
  • We need to describe the nodes and its physical connections.
  1. TCL Script for Physical Topology

Here’s an instance tcl script to replicate a Star Topology like a physical network:

TCL Script Example (Star Topology)

# Initialize NS2 Simulator

set ns [new Simulator]

set tracefile [open physical_topology.tr w]

$ns trace-all $tracefile

# Create central hub node

set hub [$ns node]

# Create peripheral nodes

set num_nodes 5

for {set i 0} {$i < $num_nodes} {incr i} {

set n($i) [$ns node]

$ns duplex-link $hub $n($i) 1Mb 10ms DropTail

}

# Attach agents for traffic simulation

# Example: Traffic from Node 0 to Node 4 through the hub

set tcp0 [new Agent/TCP]

$ns attach-agent $n(0) $tcp0

set sink0 [new Agent/TCPSink]

$ns attach-agent $n(4) $sink0

$ns connect $tcp0 $sink0

# Add a traffic generator

set ftp [new Application/FTP]

$ftp attach-agent $tcp0

# Start traffic

$ns at 1.0 “$ftp start”

# End simulation

$ns at 5.0 “finish”

proc finish {} {

global ns tracefile

$ns flush-trace

close $tracefile

exit 0

}

$ns run

  1. Key Features to Simulate
  1. Traffic Flow:
    • We can experiment the interaction paths via physical outline.
    • Monitor the routing decisions and link consumption.
  2. Performance Metrics:
    • Throughput: Assess data delivery rates.
    • Latency: Examine the delays among source and destination end.
    • Packet Loss: Estimate the reliability of packets.
  1. Analyze Trace File
  • Examine the network performance to utilize the trace file as physical_topology.tr.
  • Obtain certain performance parameters:
    • Throughput:

grep “tcp” physical_topology.tr > throughput.log

    • Dropped Packets:

grep “drop” physical_topology.tr > dropped_packets.log

  1. Visualize Results

Make use of Gnuplot or another plotting tool for visualization:

  1. Throughput Graph:

set title “Physical Topology Throughput”

plot “throughput.log” using 1:2 with lines title “Throughput”

  1. Latency Graph:
    • Equate the delays through diverse paths.
  1. Extend the Simulation
  2. Simulate Other Physical Topologies
  • Ring Topology:
    • In a circular arrangement, associate the nodes.

for {set i 0} {$i < $num_nodes} {incr i} {

set next [expr ($i + 1) % $num_nodes]

$ns duplex-link $n($i) $n($next) 1Mb 10ms DropTail

}

  • Mesh Topology:
    • Link every single node to all other node in the mesh topology.

for {set i 0} {$i < $num_nodes} {incr i} {

for {set j [expr $i + 1]} {$j < $num_nodes} {incr j} {

$ns duplex-link $n($i) $n($j) 1Mb 10ms DropTail

}

}

  1. Introduce Node Failures
  • Replicate the link or node failures for learning the network resilience:

$ns at 3.0 “$ns reset-links $n(0) $hub”

  1. Test Protocol Performance
  • Test with performance of TCP, UDP, or routing protocols:

set udp [new Agent/UDP]

$ns attach-agent $n(1) $udp

set null [new Agent/Null]

$ns attach-agent $n(2) $null

$ns connect $udp $null

  1. Modify NS2 Core for Advanced Features
  1. Dynamic Topology Changes:
    • During simulation, we will dynamically integrate or eliminate the links:

$ns at 4.0 “$ns duplex-link $n(0) $n(3) 1Mb 10ms DropTail”

  1. Custom Node Logic:
    • Execute further routing or packet handling logic within the recv() mechanism.

In this approach, we can exhaustively know about how to simulate and analyse the Physical Topology projects and how to extend the simulation in NS2 environment. If you have any doubts about this simulation mechanism, we will support you.