How to Calculate Network Stability Index in NS2

To calculate the Network Stability Index in NS2, we need to evaluate of how well a network sustains reliable communication over time, particular in dynamic conditions like mobility, node failures, or link failures. Stability can define to the consistency of network connectivity, packet delivery, and the parameters such as throughput and delay.

There is no built-in key parameter known as Network Stability Index in NS2, however we estimate a custom stability index based on numerous parameters like:

  • Packet Delivery Ratio (PDR): A measure of prosperous packet transmission.
  • Throughput: A measure of the data rate.
  • Link and Node Stability: A measure of how usually nodes or links fail and recover.
  • End-to-End Delay: Consistency in packet delivery times.

We can describe a Network Stability Index (NSI) according to this parameter, considering network failures, packet loss, and other performance degradations. The NSI can be stated as a function of these parameters in which a higher value signifies a more stable network.

Steps to Calculate Network Stability Index (NSI) in NS2

  1. Generate the Trace File

To compute numerous parameters, we want to create a trace file that records packet transmission, reception, and drop events:

set tracefile [open out.tr w]

$ns trace-all $tracefile

The trace file will log packet events such as:

  • +: Packet sent.
  • r: Packet received.
  • d: Packet dropped.
  1. Metrics to Include in the Stability Index

We can estimate the following parameter from the trace file to form the Network Stability Index (NSI):

  1. Packet Delivery Ratio (PDR):
    • Definition: The ratio of successfully delivered packets to the total packets sent.
    • A high PDR signifies the reliable communication that contributes to network stability.
  2. Throughput:
    • Definition: The rate at which data is efficiently routed over the network.
    • Consistent throughput over time refers a stable network.
  3. End-to-End Delay:
    • Definition: The time taken for a packet to move from the source to the destination.
    • A low and stable delay recommends good network performance.
  4. Node/Link Stability:
    • Definition: Evaluate of how usually nodes or links remain associated and operational over time.
    • Fewer node or link failures signify higher network stability.
  1. Calculate Packet Delivery Ratio (PDR)

The Packet Delivery Ratio (PDR) is key parameters for network stability. It demonstrated on how reliably packets are routed from source to destination.

AWK Script to Calculate PDR:

awk ‘{

if ($1 == “+” && $4 == “tcp”) {

sent_packets++;

}

if ($1 == “r” && $4 == “tcp”) {

received_packets++;

}

} END {

if (sent_packets > 0) {

pdr = (received_packets / sent_packets) * 100;

print “Packet Delivery Ratio (PDR): ” pdr “%”;

} else {

print “No packets were sent.”;

}

}’ out.tr

This script estimate the total number of packets sent and received and then calculate the PDR. A high PDR signify better network reliability and stability.

  1. Calculate Throughput

Throughput is a vital factor in network stability, as it represent on how much information is successfully transmitted over the network.

AWK Script to Calculate Throughput:

awk ‘{

if ($1 == “r” && $4 == “tcp”) {

total_bytes += $6;  # $6 is the packet size in bytes

}

} END {

simulation_time = 100.0;  # Replace with your actual simulation time in seconds

throughput = total_bytes * 8 / simulation_time;  # Convert bytes to bits

throughput_kbps = throughput / 1000;  # Convert to kilobits per second (Kbps)

throughput_mbps = throughput / 1000000;  # Convert to megabits per second (Mbps)

print “Throughput: ” throughput_kbps ” kbps (” throughput_mbps ” Mbps)”;

}’ out.tr

This script estimated the throughput in Kbps or Mbps. A higher and more consistent throughput signify better network stability.

  1. Calculate End-to-End Delay

The end-to-end delay is the time it takes for a packet to move from the source to the destination. Fluctuating in this delay can represent network instability.

AWK Script to Calculate Average End-to-End Delay:

awk ‘{

if ($1 == “+” && $4 == “tcp”) {

send_time[$6] = $2;  # Store the send time based on packet ID ($6)

}

if ($1 == “r” && $4 == “tcp”) {

if (send_time[$6] != “”) {

delay = $2 – send_time[$6];  # Calculate the delay for each packet

total_delay += delay;

packet_count++;

delete send_time[$6];  # Remove entry after calculating delay

}

}

} END {

if (packet_count > 0) {

avg_delay = total_delay / packet_count;

print “Average End-to-End Delay: ” avg_delay ” seconds”;

} else {

print “No packets were received.”;

}

}’ out.tr

This script estimates the average end-to-end delay. Lower delays with less variability signify better network performance and stability.

  1. Calculate Node/Link Stability

To evaluate node or link stability, we can log when nodes or links fail and recover in the course of the simulation. Fewer failures signifies higher network stability.

TCL Script to Monitor Node/Link Failures:

proc monitor_node {node_id} {

global ns node

set energy_level [$node($node_id) energy]

if { $energy_level <= 0.0 } {

puts “Node $node_id failed at time [$ns now]”

} else {

puts “Node $node_id is operational at time [$ns now]”

}

# Schedule the next energy check (e.g., every 10 seconds)

$ns at [expr [$ns now] + 10.0] “monitor_node $node_id”

}

# Schedule energy monitoring for each node

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

$ns at 0.0 “monitor_node $i”

}

This script monitors the uptime and downtime of nodes. We expand this to track link failures as well by resetting links among nodes if they fail.

  1. Define the Network Stability Index (NSI)

Once, we estimated the individual parameters such as PDR, throughput, delay, and node/link stability, we integrate them into a Network Stability Index (NSI). A simple formula for the NSI could be:

NSI=α×PDR+β×Throughput−γ×Delay−δ×Node/Link Failures\text{NSI} = \alpha \times \text{PDR} + \beta \times \text{Throughput} – \gamma \times \text{Delay} – \delta \times \text{Node/Link Failures}NSI=α×PDR+β×Throughput−γ×Delay−δ×Node/Link Failures

Where:

  • PDR: Packet Delivery Ratio (percentage).
  • Throughput: Data rate in Mbps or Kbps.
  • Delay: End-to-end delay (in seconds).
  • Node/Link Failures: Number of node or link failures in the course of the simulation.
  • α, β, γ, δ: Weighting factors that control the significance of each parameter in the overall index.

We can adapt the weights (α, β, γ, δ) based on the particular significance of each factor for network.

Example Calculation:

If you calculate:

  • PDR = 95%
  • Throughput = 400 Kbps
  • Delay = 0.2 seconds
  • Node Failures = 2

And assign weights:

  • α = 0.4
  • β = 0.3
  • γ = 0.2
  • δ = 0.1

Then the NSI might be calculated as:

NSI=0.4×95+0.3×400−0.2×0.2−0.1×2\text{NSI} = 0.4 \times 95 + 0.3 \times 400 – 0.2 \times 0.2 – 0.1 \times 2NSI=0.4×95+0.3×400−0.2×0.2−0.1×2 NSI=38+120−0.04−0.2=157.76\text{NSI} = 38 + 120 – 0.04 – 0.2 = 157.76NSI=38+120−0.04−0.2=157.76

A higher NSI represent a more stable network, although a lower NSI recommends more instability.

  1. Interpret the NSI
  • A high NSI means that the network is stable, with good packet delivery, high throughput, low delays, and few node/link failures.
  • A low NSI signifies that the network is unbalanced, with frequent packet losses, latency, and disruptions because of node or link failures.

Through this brief procedure, you can get to know more about the computational process and their techniques regarding the Network Stability Index including sample snippets using ns2 tool. We plan to deliver the more information regarding the Network Stability Index.

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