How to Calculate Network Availability in NS2

To calculate the Network Availability in NS2 means the percentage of time that the network (or a subset of nodes and links) is operational and able to efficiently transfer data. It can be influenced by node failures, link failures or network congestion and it is vital for evaluating how resilient the network is to issues and failures.

To compute network availability in NS2, you normally need to consider metrics like uptime of nodes and links, packet delivery ratio (PDR), and connectivity status over time. The below process will guide you to calculate the availability in ns2:

Steps to Calculate Network Availability in NS2

  1. Define Network Availability

Network availability is frequently stated as:

Network Availability=Total UptimeTotal Simulation Time×100\text{Network Availability} = \frac{\text{Total Uptime}}{\text{Total Simulation Time}} \times 100Network Availability=Total Simulation TimeTotal Uptime​×100

Where:

  • Total Uptime: The number of time the network (or nodes/links) is operational.
  • Total Simulation Time: The duration of the simulation.

For a network with several nodes and links, you can configure availability as the average uptime of all nodes or links.

  1. Generate a Trace File

Make sure your NS2 simulation creates a trace file by attaching this line in your script:

set tracefile [open out.tr w]

$ns trace-all $tracefile

The trace file logs packet transmissions and receptions, which will help you assess when nodes or links are performing appropriately.

  1. Monitor Node and Link Uptime

Measure the network availability by observing the uptime and downtime of each node or link. If a node or link fails, it may stop delivering or receiving packets, which can be logged in the trace file.

You can mimic node failures in NS2 and log the time at which nodes fail or recover:

# Simulate node failure at time 50 seconds

$ns at 50.0 “$node(2) set energy 0”  ;# Node 2 fails at 50 seconds

# Simulate node recovery at time 100 seconds

$ns at 100.0 “$node(2) set energy 100”  ;# Node 2 recovers at 100 seconds

On the other hand, you can continuously see node status by verifying their energy level or connectivity status at regular intervals.

  1. Log Node Failures and Uptime

You can write a process in your TCL script to occasionally certify the status of each node (like by checking its energy level) and log when nodes go offline:

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 at the start of the simulation

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

$ns at 0.0 “monitor_node $i”

}

This script will log whether each node is operational or failed at regular intervals, permitting you to track uptime and downtime.

  1. Calculate Availability for Nodes

To estimate node availability, you can record when each node fails and when it recovers. For each node:

Node Availability=Node UptimeTotal Simulation Time×100\text{Node Availability} = \frac{\text{Node Uptime}}{\text{Total Simulation Time}} \times 100Node Availability=Total Simulation TimeNode Uptime​×100

You can then average the availability of all nodes to obtain the entire network availability:

Network Availability=∑i=1NNode AvailabilityiN\text{Network Availability} = \frac{\sum_{i=1}^{N} \text{Node Availability}_i}{N}Network Availability=N∑i=1N​Node Availabilityi​​

Where:

  • Node Availability_i is the availability of the i-th node.
  • N is the total count of nodes in the network.
  1. Use AWK or Python to Parse the Trace File

You can evaluate the trace file and track when nodes stop receiving packets, which can denote node or link failures by using AWK or Python script.

AWK Script to Calculate Node Uptime:

The given AWK script checks for packet transmissions (+) and receptions (r) and tracks when nodes stop receiving packets, which can signify a failure:

awk ‘{

if ($1 == “r” && $4 == “tcp”) {

node_status[$3] = “operational”;  # $3 is the node ID

if (!node_uptime[$3]) {

node_uptime[$3] = $2;  # $2 is the timestamp

}

}

} END {

total_uptime = 0;

for (node in node_status) {

uptime = node_uptime[node];

if (uptime > 0) {

total_uptime += uptime;

}

}

network_availability = (total_uptime / (10 * 100)) * 100;  # Assuming 10 nodes, simulation time 100s

print “Network Availability: ” network_availability “%”;

}’ out.tr

  • node_status[$3]: Keeps track of whether each node is operational.
  • node_uptime[$3]: Logs the time when a node becomes operational.
  • network_availability: calculate the average availability of the nodes.
  1. Packet Delivery Ratio (PDR) as a Proxy for Availability

Another technique to measure network availability is by computing the Packet Delivery Ratio (PDR). A high PDR means that most packets are being delivered successfully, representing high availability of the network.

Here’s an AWK script to calculate PDR, which can be an indicator of network availability:

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

If the PDR remains high throughout the simulation, it suggests that the network is highly available, as most packets are reaching their destination.

  1. Simulate Link Failures and Recoveries

You can simulate link failures by temporarily disconnecting links amongst nodes, and then check how the network manages these disruptions.

For instance, simulate link failure amidst node 1 and node 2 at 50 seconds and recovery at 100 seconds:

$ns at 50.0 “$ns reset-link $node(1) $node(2)”

$ns at 100.0 “$ns set-link $node(1) $node(2)”

Record the count of packets that were successfully transferred before and after the failure to analyze how link failures affect network availability.

  1. Calculate Overall Network Availability

Once you have logged the uptime and downtime of nodes or links, you can estimate the overall network availability as:

Network Availability=Total Uptime of Nodes or LinksTotal Simulation Time×100\text{Network Availability} = \frac{\text{Total Uptime of Nodes or Links}}{\text{Total Simulation Time}} \times 100Network Availability=Total Simulation TimeTotal Uptime of Nodes or Links​×100

For instance, if 10 nodes are operational for 90% of the time during a 100-second simulation, the network availability is:

Network Availability=10×9010×100×100=90%\text{Network Availability} = \frac{10 \times 90}{10 \times 100} \times 100 = 90\%Network Availability=10×10010×90​×100=90%

  1. Interpret the Results
  • High network availability refers to the network remains operational for a large portion of the simulation, and nodes and links can dependably transmit data.
  • Low network availability could be caused by frequent node or link failures, poor energy management, or network congestion.

By referring this detailed process, we grasped the concept on how to calculate the network availability in the ns2 and what are the techniques we can use to estimate it. We also provide some sample techniques with examples, formulas and snippets to help you.

To determine network availability using the NS2 tool, we’re here to assist you in achieving the best results. Simply provide us with your parameter details, and we’ll analyze and compare them to give you a comprehensive networking comparison for your project.