How to Implement Network Burst Loss in NS2

To implement the network burst loss using the NS2 (Network Simulator 2), which refers to a situation in which several packets are lost successively because of the network congestion, link failure, or other factors. Executing this network burst loss within NS2 can be complete by manually replicating the packet falls on network links or by set up the network parameters, which can trigger the packet loss, like queue management and congestion control.

To execute burst loss, we can make a network topology and launch bursty packet loss by either:

  1. Launching artificial packet drops at particular intervals on a link.
  2. Replicating congestion by limiting the queue size and overloading the link including traffic that will cause packet drops because of buffer overflow.

Steps to Implement Network Burst Loss in NS2:

  1. Set up the Network Topology

Initially, describe the network topology, which contains source and end nodes are connected via intermediate nodes (routers or switches). This topology will permit to replicate packet transmission among the nodes and also launch the burst loss on particular links.

Example TCL Script for Basic Setup:

# Create a simulator instance

set ns [new Simulator]

# Define link parameters (bandwidth and delay)

set bw 10Mb          ;# Bandwidth for each link

set delay 10ms       ;# Delay for each link

# Create network nodes

set node1 [$ns node]   ;# Source node

set node2 [$ns node]   ;# Intermediate router/switch

set node3 [$ns node]   ;# Destination node

# Create links between the nodes

$ns duplex-link $node1 $node2 $bw $delay DropTail

$ns duplex-link $node2 $node3 $bw $delay DropTail

It makes a basic network with three nodes are Node1 (source), Node2 (router/switch), and Node3 (destination).

  1. Configure Traffic for Packet Transmission

Then, configure the traffic among the source and end nodes using UDP or TCP agents. This traffic mimics data flows via the network that packet loss will happen.

Example of Configuring Traffic:

# Create a UDP agent for Node1 (source node)

set udp_src [new Agent/UDP]

$ns attach-agent $node1 $udp_src

# Create a CBR traffic generator to simulate constant packet flow

set cbr_src [new Application/Traffic/CBR]

$cbr_src set packet_size_ 1000      ;# Packet size in bytes

$cbr_src set rate_ 1Mb              ;# Data rate (e.g., 1 Mbps)

$cbr_src attach-agent $udp_src

# Create a UDP sink at Node3 (destination node)

set null_sink [new Agent/Null]

$ns attach-agent $node3 $null_sink

# Connect source node to destination node

$ns connect $udp_src $null_sink

# Start and stop the traffic

$ns at 1.0 “$cbr_src start”

$ns at 10.0 “$cbr_src stop”

  1. Simulate Burst Packet Loss

We can replicate burst packet loss by artificially introducing packet drops on a particular link at regular intervals or by triggering congestion via limited queue sizes.

Option 1: Manually Dropping Packets

We can force packet drops on a link by using the drop function within NS2. For sample, to drop packets on the link among the nodes are Node2 and Node3 at an exact time then we can be used the following:

# Schedule burst packet loss at time 5.0 seconds

proc drop_packets {} {

global ns node2 node3

$ns rtmodel-at 5.0 down $node2 $node3

$ns rtmodel-at 5.2 up $node2 $node3  ;# Restore the link after 0.2 seconds (simulating burst loss)

}

# Call the drop_packets procedure

drop_packets

The above code replicates a burst loss by disabling the link among Node2 and Node3 for a short time (e.g., 0.2 seconds). All packets are transmitted while this period will drop.

Option 2: Simulating Congestion

We can mimic packet loss as a result of congestion by set up a small queue size for the DropTail queue and making more traffic than the link can manage.

# Set a small queue size for the link to simulate congestion-based packet loss

$ns queue-limit $node2 $node3 5    ;# Limit the queue size to 5 packets

# Increase the data rate to overload the link, causing packet loss

$cbr_src set rate_ 5Mb             ;# Overload the link with higher traffic

In this setup:

  • The queue size is set to 5 packets. Once more packets arrive than the queue can hold, they will be dropped, replicating the congestion-based packet loss.
  • The data rate is maximized to 5 Mbps that exceeds the link capacity (10 Mbps with delay), leading to packet drops during the queue overflows.
  1. Enable Tracing and Monitor Burst Loss

The simulation platform NS2 delivers tracing capabilities, which permit to observe while packets are dropped and also we see how the network performs under the burst loss conditions.

Enable Trace Files:

# Enable tracing for the simulation

set tracefile [open “burst_loss_trace.tr” w]

$ns trace-all $tracefile

# Define a finish procedure to end the simulation and close the trace file

proc finish {} {

global ns tracefile

$ns flush-trace

close $tracefile

exit 0

}

# Set the simulation end time

$ns at 20.0 “finish”

The trace file will capture events like packet transmissions, packet drops, and routing decisions, that permitting to examine the network performance when burst loss periods.

  1. Run the Simulation

We can run the simulation to monitor how the network manages the burst loss and also observe the packet drops via the trace files.

# Run the simulation

$ns run

Example Complete TCL Script for Network Burst Loss Simulation

# Create a simulator instance

set ns [new Simulator]

# Define link parameters (bandwidth and delay)

set bw 10Mb

set delay 10ms

# Create network nodes

set node1 [$ns node]   ;# Source node

set node2 [$ns node]   ;# Intermediate router/switch

set node3 [$ns node]   ;# Destination node

# Create links between the nodes

$ns duplex-link $node1 $node2 $bw $delay DropTail

$ns duplex-link $node2 $node3 $bw $delay DropTail

# Create UDP agent for traffic from Node1 (source) to Node3 (destination)

set udp_src [new Agent/UDP]

$ns attach-agent $node1 $udp_src

# Create CBR traffic generator for UDP source

set cbr_src [new Application/Traffic/CBR]

$cbr_src set packet_size_ 1000

$cbr_src set rate_ 1Mb

$cbr_src attach-agent $udp_src

# Create UDP sink at Node3 (destination)

set null_sink [new Agent/Null]

$ns attach-agent $node3 $null_sink

# Connect source to destination

$ns connect $udp_src $null_sink

# Start and stop the traffic

$ns at 1.0 “$cbr_src start”

$ns at 10.0 “$cbr_src stop”

# Schedule burst packet loss at time 5.0 seconds

proc drop_packets {} {

global ns node2 node3

$ns rtmodel-at 5.0 down $node2 $node3

$ns rtmodel-at 5.2 up $node2 $node3   ;# Restore the link after 0.2 seconds (simulating burst loss)

}

# Call the drop_packets procedure

drop_packets

# Enable tracing

set tracefile [open “burst_loss_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

In this module, we dynamically explained on how to create a network topology, how to introduce bursty packet loss that were executed the Network Burst Loss in NS2. We will also provide more insights regarding this topic in various materials.

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