How to Implement Switched Mesh Topology in NS2

To implement a switched mesh topology in NS2 Network Simulator 2 has includes to configure a mesh topology in which the nodes are associated through switches. This encompasses to replicate switches and nodes in a way that implements on how switches handles traffic routing in a network. The following are the detailed procedures to implement the switched mesh topology in ns2:

Steps to Implement Switched Mesh Topology in NS2

Set up NS2

Make sure that NS2 is installed on system. You can install it using the following commands (on Linux/Ubuntu):

sudo apt-get update

sudo apt-get install ns2

Understanding Switched Mesh Topology

A switched mesh topology means that:

Switches behave like intermediaries among the nodes. Rather than nodes being directly associated, they send traffic via the switches.
Each node associates to a switch and switches may interconnect to other switches or nodes, relaying on the mesh arrangement.

Create a TCL Script for Switched Mesh Topology

Below is an example TCL script for a basic 2×2 switched mesh topology, in which each switch associates to two nodes and other switches.

Example TCL Script for Switched Mesh Topology:

# Define the simulator

set ns [new Simulator]

# Open trace files

set tracefile [open switch_mesh_out.tr w]

set namfile [open switch_mesh_out.nam w]

$ns trace-all $tracefile

$ns namtrace-all $namfile

# Define the topology

set topo [new Topography]

$topo load_flatgrid 500 500

# Create a channel for wired links

set chan [new Channel/WiredChannel]

# Define the switches in the switched mesh topology

set switch_0 [$ns node]

set switch_1 [$ns node]

set switch_2 [$ns node]

set switch_3 [$ns node]

# Define the end devices (nodes) connected to the switches

set node_0 [$ns node]

set node_1 [$ns node]

set node_2 [$ns node]

set node_3 [$ns node]

# Position the switches (for visualization purposes in NAM)

$switch_0 set X_ 100.0

$switch_0 set Y_ 200.0

$switch_1 set X_ 300.0

$switch_1 set Y_ 200.0

$switch_2 set X_ 100.0

$switch_2 set Y_ 400.0

$switch_3 set X_ 300.0

$switch_3 set Y_ 400.0

# Position the nodes connected to switches

$node_0 set X_ 50.0

$node_0 set Y_ 200.0

$node_1 set X_ 150.0

$node_1 set Y_ 200.0

$node_2 set X_ 50.0

$node_2 set Y_ 400.0

$node_3 set X_ 150.0

$node_3 set Y_ 400.0

# Connect the nodes to switches (simulating the switched network)

$ns duplex-link $node_0 $switch_0 100Mb 1ms DropTail

$ns duplex-link $node_1 $switch_0 100Mb 1ms DropTail

$ns duplex-link $node_2 $switch_2 100Mb 1ms DropTail

$ns duplex-link $node_3 $switch_2 100Mb 1ms DropTail

# Interconnect the switches (mesh topology)

$ns duplex-link $switch_0 $switch_1 100Mb 1ms DropTail

$ns duplex-link $switch_0 $switch_2 100Mb 1ms DropTail

$ns duplex-link $switch_1 $switch_3 100Mb 1ms DropTail

$ns duplex-link $switch_2 $switch_3 100Mb 1ms DropTail

# Add more inter-switch links if necessary for redundancy or different layouts

# Example: Full mesh between switches

# $ns duplex-link $switch_0 $switch_3 100Mb 1ms DropTail

# Setup traffic between nodes

# Traffic from node_0 to node_3 through the switched mesh

set udp0 [new Agent/UDP]

set null0 [new Agent/Null]

$ns attach-agent $node_0 $udp0

$ns attach-agent $node_3 $null0

$ns connect $udp0 $null0

# Create CBR (Constant Bit Rate) traffic

set cbr0 [new Application/Traffic/CBR]

$cbr0 set packetSize_ 512

$cbr0 set interval_ 0.01

$cbr0 attach-agent $udp0

# Start traffic at time 1.0 second

$ns at 1.0 “$cbr0 start”

# Schedule simulation end

$ns at 10.0 “finish”

# Finish procedure to close the simulation

proc finish {} {

global ns tracefile namfile

$ns flush-trace

close $tracefile

close $namfile

exec nam switch_mesh_out.nam &

exit 0

}

# Run the simulation

$ns run

Explanation of the Script:

Switches:
- We describe four switch nodes (switch_0, switch_1, switch_2, and switch_3) to mimic a small switched mesh network. These switches help as the intermediaries among the nodes.
Nodes:
- Four nodes (node_0, node_1, node_2, and node_3) are interconnected to the switches. Each switch in the mesh topology associates to multiple nodes.
Inter-Switch Links:
- Duplex links are generated among the switches to form a mesh topology. Each switch is associated to its neighbouring switches.
Traffic Setup:
- UDP traffic is configured to flow from node_0 to node_3. This traffic goes via the switches in the mesh.
- A CBR (Constant Bit Rate) application is used to create traffic among the nodes.
Visualization:
- The script creates a trace file (switch_mesh_out.tr) and a NAM file (switch_mesh_out.nam). We can envision the replication using NAM (Network Animator).

Run the Simulation

Save the script as switch_mesh.tcl and executed it in NS2:

ns switch_mesh.tcl

To view the network animation using NAM, use:

nam switch_mesh_out.nam

Customization:

Expanding the Mesh:
- Maximize the number of switches and nodes to generate larger mesh topologies. For example, we can generate a 3×3 or 4×4 switched mesh topology by adding more switches and nodes.
Traffic Flow:
- We can configure more complex traffic patterns by adding multiple UDP or TCP flows among diverse nodes in the mesh.
Redundant Links:
- For redundancy or enhanced performance, we can add more links among switches to generate a fully connected mesh or partial mesh topology.
Link Parameters:
- Modify the link bandwidth and latency to replicate diverse network conditions. For instance, we can lower the bandwidth or maximize the delay to replicate slower connections among switches.

We demonstrate and show how the switched mesh topologies will effectively manage the diverse routing network conditions among the nodes that were executed in ns2 tool. We plan to provide the detailed information regarding the switched mesh topologies implementation process in further scripts.

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