How to Implement Network Collision Avoidance in NS2

To implement the Network Collision Avoidance within NS2 (Network Simulator 2), we will require to concentrate on minimising the likelihood of packet collisions at the MAC (Medium Access Control) layer. It is especially vital in the wireless networks that nodes are distribute a general medium for the communication. The simulation NS2 encompasses numerous MAC protocols such as CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) that is generally used to avoid the collisions in wireless networks. We deliver the stepwise process to executing this mechanisms within NS2:

Step-by-Step Implementation:

  1. Set up the Simulation Environment

The initial step is to configure the simple simulation environment in NS2. We will setup the wireless network and stipulate the MAC protocol, which supports collision avoidance.

Example TCL Script for Basic Setup:

# Create a simulator instance

set ns [new Simulator]

# Define network parameters

set val(chan) Channel/WirelessChannel         ;# Wireless channel type

set val(prop) Propagation/TwoRayGround        ;# Propagation model

set val(netif) Phy/WirelessPhy                ;# Network interface type

set val(mac) Mac/802_11                       ;# MAC protocol with collision avoidance (CSMA/CA)

set val(ifq) Queue/DropTail/PriQueue          ;# Interface queue type

set val(ll) LL                                ;# Link layer type

set val(ant) Antenna/OmniAntenna              ;# Antenna model

set val(x) 1000                               ;# X dimension of the topography

set val(y) 1000                               ;# Y dimension of the topography

# Create the topography

create-god 10                                 ;# Number of nodes in the network

This configure describes a wireless environment including MAC/802_11 that uses CSMA/CA to prevent the collisions by performing carrier sensing and forwarding RTS/CTS (Request to Send / Clear to Send) messages before data transmission.

  1. Create Wireless Nodes

Now, we describe the wireless nodes, which will communicate in the network. These nodes will configure to communicate using the MAC/802.11 protocol that automatically contains the collision avoidance features.

Example of Creating Nodes:

# Create 10 wireless nodes

for {set i 0} {$i < 10} {incr i} {

set node_($i) [$ns node]

}

# Assign node positions (static or mobile)

$node_(0) set X_ 100

$node_(0) set Y_ 200

$node_(1) set X_ 200

$node_(1) set Y_ 300

# Define positions for other nodes…

# Enable wireless communication for all nodes

for {set i 0} {$i < 10} {incr i} {

$node_($i) set X_ [expr rand() * $val(x)]

$node_($i) set Y_ [expr rand() * $val(y)]

}

This makes a nodes, which will communicate wirelessly and stipulates their first positions.

  1. Configure MAC/802.11 for Collision Avoidance

MAC/802.11 uses CSMA/CA to prevent the collisions. The key mechanism encompass using RTS/CTS handshakes before transmitting data to reserve the communication channel. If the channel is identified as busy, the node backs off and waits for a random amount of time before attempting to transmit again. In the simulation NS2, MAC/802.11 is the default protocol for wireless networks, also it previously contains these features. To allow or alter the collision avoidance parameters, we can change the below parameters:

  • RTS Threshold: Manages while RTS/CTS handshakes are used. If the packet size is above the threshold then RTS/CTS will be used.
  • Backoff Mechanism: The backoff mechanism avoids several nodes from transmitting at the similar time, so reducing collisions.

Example of Setting the RTS Threshold:

# Set the RTS threshold to enable RTS/CTS for packets larger than 1000 bytes

Mac/802_11 set RTSThresh_ 1000

By setting the RTS threshold, we can manage while RTS/CTS handshakes are started that supports to minimise the collisions, specifically when large packets are being transmitted.

  1. Set Up Traffic and Data Transmission

Next, replicate the transmission of data among the nodes are using UDP or TCP. We can make a CBR (Constant Bit Rate) traffic to mimic continuous data transmission. As the MAC protocol will manage the collision avoidance, we require only to aim on the describing the traffic patterns.

Example of Data Traffic Using UDP:

# Create UDP traffic from node 0 to node 1

set udp [new Agent/UDP]

$ns attach-agent $node_(0) $udp

# Create a traffic generator (CBR) for continuous data transmission

set cbr [new Application/Traffic/CBR]

$cbr set packet_size_ 512        ;# Size of each packet (bytes)

$cbr set rate_ 1Mb               ;# Transmission rate (1 Mbps)

$cbr attach-agent $udp

# Create a UDP sink (receiver) at node 1

set null [new Agent/Null]

$ns attach-agent $node_(1) $null

$ns connect $udp $null

# Start and stop the traffic

$ns at 1.0 “$cbr start”

$ns at 15.0 “$cbr stop”

In this situation, node 0 transfers data to node 1, and the MAC layer manages the collision avoidance.

  1. Implement Backoff Mechanism for Collision Avoidance

The backoff mechanism plays a critical role in CSMA/CA. Once a node senses, which the medium is busy, before retrying it waits for a random amount of time (backoff period). It is automatically managed by the MAC/802.11 protocol in NS2. But, we can modify the backoff parameters to enhance the collision avoidance.

Example of Modifying Backoff Parameters:

# Modify backoff parameters to reduce collisions

Mac/802_11 set CWMin_ 31       ;# Minimum contention window (default is 31)

Mac/802_11 set CWMax_ 1023     ;# Maximum contention window (default is 1023)

By altering the contention window (CW) parameters, we can control before retrying how long nodes are back off to access the medium. A larger contention window minimise the likelihood of collisions however increases the delay.

  1. Monitor Network Performance and Collision Avoidance

To estimate the efficiency of the collision avoidance strategy, allow tracing in NS2 to handle the events like packet transmission, reception, and collisions.

Enable Trace Files for Collision Monitoring:

# Enable tracing

set tracefile [open “collision_avoidance_trace.tr” w]

$ns trace-all $tracefile

# Run the simulation and monitor collisions

proc finish {} {

global ns tracefile

$ns flush-trace

close $tracefile

exit 0

}

The trace file will record all network events, with the packet collisions, transmission attempts, and backoff events. We can be used this information to estimate the efficiency of the collision avoidance strategy.

  1. Run the Simulation

At the end, set the simulation end time then run the simulation.

# Set the end time of the simulation

$ns at 20.0 “finish”

# Run the simulation

$ns run

We can evaluate the trace file, after the simulation to assess how successfully the collision avoidance mechanism operated, and how frequently collisions happened within the network.

Example Complete TCL Script for Collision Avoidance

# Create a simulator instance

set ns [new Simulator]

# Define wireless network parameters

set val(chan) Channel/WirelessChannel

set val(prop) Propagation/TwoRayGround

set val(netif) Phy/WirelessPhy

set val(mac) Mac/802_11

set val(ifq) Queue/DropTail/PriQueue

set val(ll) LL

t val(asent) Antenna/OmniAntenna

set val(x) 1000

set val(y) 1000

# Create nodes

for {set i 0} {$i < 10} {incr i} {

set node_($i) [$ns node]

}

# Set node positions (random or fixed)

$node_(0) set X_ 100

$node_(0) set Y_ 200

$node_(1) set X_ 200

$node_(1) set Y_ 300

# Set positions for other nodes…

# Modify RTS/CTS and backoff parameters

Mac/802_11 set RTSThresh_ 1000

Mac/802_11 set CWMin_ 31

Mac/802_11 set CWMax_ 1023

# Create UDP traffic between nodes

set udp [new Agent/UDP]

$ns attach-agent $node_(0) $udp

# Create a CBR traffic generator

set cbr [new Application/Traffic/CBR]

$cbr set packet_size_ 512

$cbr set rate_ 1Mb

$cbr attach-agent $udp

# Create a UDP sink at node 1

set null [new Agent/Null]

$ns attach-agent $node_(1) $null

$ns connect $udp $null

# Start and stop traffic

$ns at 1.0 “$cbr start”

$ns at 15.0 “$cbr stop”

# Enable tracing

set tracefile [open “collision_avoidance_trace.tr” w]

$ns trace-all $tracefile

# End simulation

$ns at 20.0 “finish”

proc finish {} {

global ns tracefile

$ns flush-trace

close $tracefile

exit 0

}

# Run the simulation

$ns run

As a result, we thoroughly offered the basic explanation with instances on how to approach the Network Collision Avoidance which is executed in NS2 simulation. We shall be offered more details through another manual, if required. Reach out to ns2project.com for top-notch Network Collision Avoidance solutions using the ns2 tool, where we share the best results for your projects. We concentrate on the latest research methods to ensure optimal outcomes, particularly in MAC protocols like CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance).