How to Calculate Network Resiliency in NS2

To calculate the Network resiliency refers using NS2 that to the ability of a network to maintain an acceptable level of service even in the face of challenges like node failures, attacks, or congestion. In the simulation tool NS2 (Network Simulator 2), network resiliency can estimate by calculating how successfully the network adjusts to adverse conditions and maintains connectivity, throughput, and overall performance of despite node or link failures. We provide brief step-by-step procedure to calculate the network resiliency in NS2:

Steps to Calculate Network Resiliency in NS2:

To compute the network resiliency, we can be replicated various failure situations like node failures, link failures, or congestion and then calculate the key performance indicators (KPIs) such as:

  1. Packet Delivery Ratio (PDR): The ratio of packets are effectively delivered to the end to the total packets sent.
  2. Throughput: The total data received at the end over time that indicates how successfully the network maintains performance after failures.
  3. Average End-to-End Delay: The time it takes for a packet to travel from the origin to the end. A sharp increase in delay may show the network degradation.
  4. Connectivity: The ability of the network to remain connected after failures.
  5. Recovery Time: The time taken by the network to recover or reroute traffic after a failure.
  6. Packet Loss: The number of packets are lost in the course of node or link failures.

General Approach to Simulate and Measure Resiliency:

  1. Simulate the Network: Describe a network topology within NS2 and also launch the failures (e.g., node or link failures) at particular times.
  2. Measure Pre- and Post-Failure Metrics: Calculate the performance metrics before and after the failure to estimate how the network reacts and recovers.
  3. Evaluate Resiliency: Compare the pre-failure and post-failure performance to assess the network’s ability to maintain service.

Example of Calculating Network Resiliency in NS2:

In this sample, we mimic a basic network with traffic among the nodes and introduce node failures at a particular time, and compute the key performance metrics to assess resiliency.

  1. Tcl Script to Simulate a Simple Network:

Given below is an example NS2 script, which configure a wireless network with five nodes, then makes a traffic among them, and introduces a node failure scenario.

# Create a new simulator instance

set ns [new Simulator]

# Open trace file to record events

set tracefile [open trace.tr w]

$ns trace-all $tracefile

# Create wireless nodes

set node0 [$ns node]

set node1 [$ns node]

set node2 [$ns node]

set node3 [$ns node]

set node4 [$ns node]

# Define network links (wired or wireless)

$ns duplex-link $node0 $node1 1Mb 10ms DropTail

$ns duplex-link $node1 $node2 1Mb 10ms DropTail

$ns duplex-link $node2 $node3 1Mb 10ms DropTail

$ns duplex-link $node3 $node4 1Mb 10ms DropTail

# Attach UDP agents and traffic

set udp0 [new Agent/UDP]

set null0 [new Agent/Null]

$ns attach-agent $node0 $udp0

$ns attach-agent $node4 $null0

$ns connect $udp0 $null0

# Create traffic source (CBR)

set cbr0 [new Application/Traffic/CBR]

$cbr0 attach-agent $udp0

$cbr0 set packetSize_ 512

$cbr0 set rate_ 1Mb

# Start traffic

$ns at 1.0 “$cbr0 start”

$ns at 5.0 “$cbr0 stop”

# Introduce a node failure at 3.0 seconds (disable node2)

$ns at 3.0 “$node2 reset”

# Define finish procedure to stop simulation

proc finish {} {

global ns tracefile

$ns flush-trace

close $tracefile

exit 0

}

# End simulation at 6 seconds

$ns at 6.0 “finish”

$ns run

Explanation of the Script:

  1. Network Setup: A simple linear network topology is made in which five nodes are connected through the links with 1 Mbps bandwidth and 10 ms delay. UDP traffic is generated from node0 to node4.
  2. Node Failure: At 3.0 seconds, we can replicate a failure at node2 utilising the reset command that well removes the node from the network.
  3. Metrics Collection: The trace file records all events, like packet transmissions, receptions, and drops. This trace file will use to estimate the resiliency metrics like packet delivery ratio, delay, throughput, and packet loss before and after the failure.
  1. Metrics to Measure Network Resiliency:

Packet Delivery Ratio (PDR):

The Packet Delivery Ratio (PDR) computes how many packets were effectively delivered to the end that compared to how many were transmitted. A drop in PDR after the node failure shows the effect of the failure.

PDR=Total Packets ReceivedTotal Packets Sent\text{PDR} = \frac{\text{Total Packets Received}}{\text{Total Packets Sent}}PDR=Total Packets SentTotal Packets Received​

Bash Script to Calculate PDR:

# Count the total number of packets sent

sent_packets=$(grep “^s” trace.tr | grep “_0_” | wc -l)

# Count the total number of packets received

received_packets=$(grep “^r” trace.tr | grep “_4_” | wc -l)

# Calculate PDR

if [ $sent_packets -gt 0 ]; then

pdr=$(echo “scale=2; $received_packets / $sent_packets * 100” | bc)

echo “Packet Delivery Ratio (PDR): $pdr%”

else

echo “No packets were sent.”

fi

Throughput:

Throughput is the rate at which data is effectively delivered to the end. It can compute as:

Throughput (bps)=Total Data Received (bits)Total Time\text{Throughput (bps)} = \frac{\text{Total Data Received (bits)}}{\text{Total Time}}Throughput (bps)=Total TimeTotal Data Received (bits)​

Bash Script to Calculate Throughput:

# Count the total number of packets received at node4

received_packets=$(grep “^r” trace.tr | grep “_4_” | wc -l)

# Packet size in bits (512 bytes = 4096 bits)

packet_size=4096

# Calculate total data received in bits

total_data_received=$(echo “$received_packets * $packet_size” | bc)

# Simulation time in seconds (example: 5 seconds)

simulation_time=5

# Calculate throughput in bits per second (bps)

throughput=$(echo “scale=2; $total_data_received / $simulation_time” | bc)

echo “Throughput: $throughput bps”

End-to-End Delay:

From the origin to the end, the end-to-end delay is the time taken for a packet to travel. A sharp increase in delay after a failure may be showed the routing issues.

Bash Script to Calculate End-to-End Delay:

# Extract send and receive times from the trace file

grep “^s” trace.tr > sent_packets.txt

grep “^r” trace.tr > received_packets.txt

# Calculate delay for each packet

awk ‘FNR==NR{sent[$6]=$2; next} {if ($6 in sent) print $2 – sent[$6]}’ sent_packets.txt received_packets.txt > delays.txt

# Calculate average end-to-end delay

awk ‘{sum+=$1; count+=1} END {if (count > 0) print “Average End-to-End Delay: “, sum/count, ” seconds”; else print “No packets received.”}’ delays.txt

Packet Loss:

Packet loss shows how many packets were dropped during the simulation, normally because of the buffer overflows, link failures, or node failures. An increase in packet loss after the failure shows the network degradation.

  1. Evaluate Network Resiliency:

When the metrics are estimated then we can be assessed the network resiliency by comparing the performance before and after the failure. A resilient network will have:

  • Minimal reduction in PDR.
  • Minor impact on throughput.
  • Limited increase in end-to-end delay.
  • Minimal packet loss.

Summary:

  1. Set up the Simulation: Describe a network topology then replicate the traffic, and launch the node or link failures at particular times.
  2. Analyse the Trace File: Evaluate the key performance metrics such as packet delivery ratio, throughput, end-to-end delay, and packet loss before and after the failure.
  3. Calculate Network Resiliency: Compare the pre-failure and post-failure performance to estimate how successfully the network maintains service under failure conditions.

In this setup, we had explained properly about the network resiliency that were calculated and analysed utilising the stepwise computation process in NS2 tool and we provided summary of this topic at the end. Additional specific insights will be offered based on your needs.

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