How to Calculate Sampling Interval in NS2

To calculate the sampling interval in ns2 has a series of steps to follow and it is specifically useful in Wireless Sensor Networks (WSNs) or other systems in which the information is intermittently gathered from sensors or nodes. The sampling interval defined to the time among consecutive data collection events or transmissions from a node. Since NS2 does not have a direct function for sampling interval, we can set up based on how often the data is sent or gathered by nodes in simulation.

Here is a guide on how to calculate the sampling interval in ns2:

Steps to Calculate Sampling Interval in NS2

  1. Understanding Sampling Interval:
  • The sampling interval is the time difference among consecutive data generation or collection events. In NS2, this can be emulated by controlling the traffic generation rate or the event scheduling frequency for data collection.
  • It is frequently described for sensor nodes that gather and transfer data periodically.
  • If we are using a CBR (Constant Bit Rate) application, the sampling interval can be determined by the inter-packet transmission time.
  1. Setting up the Network in NS2:

To estimate the sampling interval, we need to configure a network simulation in which nodes occasionally create and send data. Below is an example demonstrated on how to set up a CBR application to mimic periodic data collection.

Example TCL Script for Sampling Interval:

# Create the simulator

set ns [new Simulator]

# Define the topography (e.g., 1000m x 1000m area)

set topo [new Topography]

$topo load_flatgrid 1000 1000

# Create two nodes

set node_(0) [$ns node]

set node_(1) [$ns node]

# Define the wireless channel

set chan_ [new Channel/WirelessChannel]

$node_(0) set channel_ $chan_

$node_(1) set channel_ $chan_

# Attach traffic agents (UDP for constant data transmission)

set udp0 [new Agent/UDP]

set sink [new Agent/Null]

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

$ns attach-agent $node_(1) $sink

$ns connect $udp0 $sink

# Create a CBR traffic source

set cbr0 [new Application/Traffic/CBR]

$cbr0 attach-agent $udp0

# Set packet size and transmission rate

$cbr0 set packetSize_ 512        ;# Packet size in bytes

$cbr0 set interval_ 1.0          ;# Sampling interval of 1 second (1 packet per second)

# Start and stop the traffic

$ns at 1.0 “$cbr0 start”

$ns at 10.0 “$cbr0 stop”

# Enable tracing to monitor packet transmission and timing

set tracefile [open out.tr w]

$ns trace-all $tracefile

# Close the trace file at the end of the simulation

proc finish {} {

global ns tracefile

$ns flush-trace

close $tracefile

exit 0

}

# End the simulation at 20 seconds

$ns at 20.0 “finish”

  1. Calculating Sampling Interval from CBR Traffic:

In this sample, the sampling interval is set using the interval_ parameter in the CBR application. For example, interval_ 1.0 means the node sends one packet per second; replicate a sampling interval of 1 second.

  1. Analyzing the Trace File to Confirm Sampling Interval:

After the simulation, we can evaluate the trace file (out.tr) to validate the exact timing of packet transmissions. Each time a packet is routed, an event is recorded in the trace file, and we can estimate the time difference among consecutive packet transmissions to regulate the sampling interval.

Example Trace File Entry:

An sample trace file line for a packet transmission may look like this:

s 1.000000000 _0_ AGT  — 512 cbr 0 0.0 1.0 0 0

r 1.000123456 _1_ AGT  — 512 cbr 0 0.0 1.0 0 0

Here:

  • s 1.000000000: A packet was sent at 1.000 seconds by node 0.
  • r 1.000123456: A packet was received at 1.000123 seconds by node 1.

We can estimate the sampling interval by proving the time difference among consecutive s events.

AWK Script to Calculate Sampling Interval from Trace File:

We can utilize an AWK script to estimate the sampling interval from the trace file. The script below extracts the transmission times and computes the time difference among consecutive packet transmissions:

BEGIN {

last_time = 0;

}

# Process only “s” events for CBR packets sent from node 0

$1 == “s” && $4 == “_0_” && $7 == “cbr” {

if (last_time > 0) {

interval = $2 – last_time;

printf(“Sampling Interval: %f seconds\n”, interval);

}

last_time = $2;

}

To use the script, save it as calculate_interval.awk and execute it on the trace file:

awk -f calculate_interval.awk out.tr

This will output the sampling intervals for consecutive packet transmissions.

  1. Dynamic Sampling Interval:

If sampling interval alters dynamically in the course of the simulation such as, due to node mobility, congestion, or energy constraints, we can adapt the CBR or event scheduling enthusiastically during the simulation. This can be completed by updating the interval or event times in the course of runtime.

Example Dynamic Sampling Interval:

# Change sampling interval dynamically at time 5s

$ns at 5.0 “$cbr0 set interval_ 2.0”  ;# Change interval to 2 seconds

This will change the sampling interval from 1 second to 2 seconds through the simulation.

  1. Custom Sampling Logic:

If we are not using CBR or if we have a custom data collection mechanism, we can manually estimate the sampling interval by evaluating the time difference among successive data collection or transmission events.

For instance, we could use event scheduling to gather information at certain intervals and track the time differences among these events.

In this setup, we collect the innovative information regarding the sampling interval and how to calculate it to find the time taken for the transmission of gathered data over the wireless sensor network. We plan to deliver the more data regarding this process in further setup. To determine the sampling interval in NS2 for your project, connect with us for excellent guidance and concise explanations throughout your project.