**How to Calculate Network Number of Alive nodes in NS2**

To calculate the Network Number of Alive nodes in Network Simulator 2 (NS2), this indicates the nodes that have sufficient energy to continue performing in the network. It is particularly related in wireless networks includes Wireless Sensor Networks (WSNs), where nodes have restricted energy resources and a vital parameter is how many nodes stay “alive” at a certain point in time.

We can use energy model to record the energy utilization of each node and define if their remaining energy is greater than zero to compute the number of alive nodes in ns2. Nodes with energy remaining are considered “alive”.

In the following, we have given the steps to compute it using ns2:

**Steps to Calculate the Number of Alive Nodes in NS2:**

**Set Up the Energy Model**: Start by setting up an energy model for each node in the simulation which will track how much energy each node uses during transmission, receptions and indolent states.**Track the Remaining Energy of Each Node**: At each time step or at the end of the simulation, verify the remaining energy of each node to state if it is still alive.**Calculate the Number of Alive Nodes**: After executing the simulation, you can extract the remaining energy of each node from the trace file or by using NS2’s energy model functions. Nodes with remaining energy greater than zero are deliberated alive.

**Example Tcl Script to Set Up the Energy Model in NS2:**

Below is a sample NS2 script that mimics a wireless network with energy constraints. The script tracks the energy consumption of nodes, and at the end of the simulation, computes the number of alive nodes.

# 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

# Define energy model parameters

set val(initialEnergy) 100.0 ;# Initial energy in joules

set val(txPower) 0.5 ;# Transmission power in watts

set val(rxPower) 0.3 ;# Reception power in watts

set val(idlePower) 0.01 ;# Idle power in watts

# Create 5 nodes

for {set i 0} {$i < 5} {incr i} {

set node($i) [$ns node]

# Assign energy model to each node

$node($i) energy-model EnergyModel

$node($i) add-energy $val(initialEnergy)

}

# Set up wireless traffic between nodes

set udp0 [new Agent/UDP]

set null0 [new Agent/Null]

$ns attach-agent $node(0) $udp0

$ns attach-agent $node(4) $null0

$ns connect $udp0 $null0

# Create CBR traffic source

set cbr0 [new Application/Traffic/CBR]

$cbr0 attach-agent $udp0

$cbr0 set packetSize_ 512

$cbr0 set rate_ 1Mb

# Start and stop traffic

$ns at 1.0 “$cbr0 start”

$ns at 5.0 “$cbr0 stop”

# Define finish procedure to check remaining energy of each node

proc finish {} {

global ns node tracefile

set alive_nodes 0

for {set i 0} {$i < 5} {incr i} {

set remaining_energy [$node($i) energy]

puts “Node($i) remaining energy: $remaining_energy J”

if {$remaining_energy > 0} {

incr alive_nodes

}

}

puts “Number of alive nodes: $alive_nodes”

$ns flush-trace

close $tracefile

exit 0

}

# End simulation after 6 seconds

$ns at 6.0 “finish”

$ns run

**Explanation of the Script:**

**Energy Model Setup**: Each node is allocated an initial energy of 100 joules. The transmission power (txPower), reception power (rxPower), and idle power (idlePower) are also stated for the energy consumption model.**Traffic Generation**: A basic traffic flow is generated amongst node0 and node4 using UDP and CBR (Constant Bit Rate) traffic.**Finish Procedure**: At the end of the simulation, the finish procedure is called to certify the remaining energy of each node and define how many nodes are still “alive.” The remaining energy is printed for each node, and the amount of alive nodes is estimated by summing up nodes with energy greater than 0.

**Running the Simulation:**

When the simulation is executed, NS2 records the energy consumption for each node. As nodes send, receive, and stay idle, their energy is depleted in terms of the power utilization specified in the energy model.

**Trace File Analysis:**

If you want to verify the count of alive nodes at various times during the simulation, you can alter the script to validate the energy of each node at certain intervals rather than just at the end of the simulation. This will grant you to monitor how the number of alive nodes varies over time.

**Example Output:**

The output of the script will be similar to the following:

Node(0) remaining energy: 98.5 J

Node(1) remaining energy: 100.0 J

Node(2) remaining energy: 100.0 J

Node(3) remaining energy: 100.0 J

Node(4) remaining energy: 99.7 J

Number of alive nodes: 5

**Bash Script for Post-Simulation Analysis:**

If you have a huge amount of nodes and need to automate the computation of the number of alive nodes from the trace file, you can extract the remaining energy of each node from the trace or log file and estimate the number of alive nodes by using bash script.

Example:

# Extract remaining energy from trace file (assuming energy info is logged)

grep “Node” trace.log > energy_log.txt

# Calculate the number of alive nodes (energy > 0)

awk ‘{ if ($4 > 0) alive_nodes+=1 } END { print “Number of alive nodes: “, alive_nodes }’ energy_log.txt

**Summary of Steps:**

**Set Up the Energy Model**: Allocate an energy model to each node with initial energy and consumption rates for transmission, reception, and idle states.**Run the Simulation**: Produce traffic amongst nodes and permit NS2 to replicate energy consumption according to the specified energy model.**Calculate Alive Nodes**: At the end of the simulation or at certain intervals, verify the remaining energy of each node. Sums the number of nodes that still have energy greater than zero to state the number of alive nodes.**Automate the Process**: Optionally, automate the process using a script to estimate the count of alive nodes from the trace file.

We have comprehensively provided the expounded details that will help you to calculate the number of alive nodes in the network using ns2 tool by configuring an energy model to track the energy consumption of each nodes in the simulation network. You can refer the given guide and examples, if needed.

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