How to Calculate Network Jitter in NS2
To calculate the Network Jitter in Network Simulator 2 (NS2) which means that the variation in packet delays when move over a network. In ns2, jitter can be computed by estimating the changes in the end-to-end delay amongst successive packets. It is a vital parameter for realistic applications like VoIP and video conferencing where reliable packet delivery times are important. The below guide will help you calculate the jitter in the ns2:
Steps to Calculate Network Jitter in NS2
- Set Up NS2 Simulation:
Start by developing a network simulation that contains data traffic amongst a source and destination node. The script below uses UDP with CBR (Constant Bit Rate) traffic.
Example TCL Script for Data Transmission:
# Create the simulator
set ns [new Simulator]
# Define the topology with two nodes: source and destination
set node_(0) [$ns node]
set node_(1) [$ns node]
# Create a duplex link between the nodes (1 Mbps bandwidth, 10ms delay)
$ns duplex-link $node_(0) $node_(1) 1Mb 10ms DropTail
# Attach UDP agents to nodes for sending and receiving data
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
# Set up Constant Bit Rate (CBR) traffic on the UDP agent
set cbr0 [new Application/Traffic/CBR]
$cbr0 attach-agent $udp0
$cbr0 set packetSize_ 512 ;# Packet size in bytes
$cbr0 set rate_ 1Mb ;# Transmission rate (1 Mbps)
# Start and stop the traffic
$ns at 1.0 “$cbr0 start”
$ns at 10.0 “$cbr0 stop”
# Set up tracing to capture packet transmission and reception events
set tracefile [open out.tr w]
$ns trace-all $tracefile
# Run the simulation
$ns run
- Run the Simulation:
After running the simulation using NS2, a trace file (out.tr) is produced, which contains events like packet transmission, reception, and other network behaviors.
- Analyze the Trace File:
Measure the jitter by focusing on the reception times of packets at the destination node. We can estimate the difference between the end-to-end delays of successive packets and use these changes to compute jitter.
Trace File Sample:
s 1.000000000 _0_ AGT — 512 cbr 0 0.0 1.0 1.0
r 1.010000000 _1_ AGT — 512 cbr 0 0.0 1.0 1.0
s 2.000000000 _0_ AGT — 512 cbr 1 0.0 2.0 2.0
r 2.015000000 _1_ AGT — 512 cbr 1 0.0 2.0 2.0
In this trace:
- s: Packet sent event.
- r: Packet received event.
- 1.010000000: Time at which the packet was acquired.
- Calculate Jitter Using AWK Script:
To calculate jitter, we need to estimate the alterations in delay amongst consecutive packets. The below AWK script does this:
AWK Script to Calculate Jitter:
BEGIN {
previous_delay = -1;
total_jitter = 0;
packet_count = 0;
}
# Capture the packet reception time and calculate the delay for each packet
$1 == “r” && $4 == “_1_” && $7 == “cbr” {
current_time = $2; # Current packet reception time
send_time = $10; # Packet send time (10th field)
delay = current_time – send_time; # End-to-end delay
# Calculate jitter if this is not the first packet
if (previous_delay >= 0) {
jitter = delay – previous_delay;
total_jitter += (jitter >= 0 ? jitter : -jitter); # Absolute jitter
}
previous_delay = delay; # Update previous delay for next packet comparison
packet_count++;
}
END {
if (packet_count > 1) {
average_jitter = total_jitter / (packet_count – 1); # Average jitter across all packets
print “Average Jitter: ” average_jitter ” seconds”;
} else {
print “Not enough packets to calculate jitter!”;
}
}
Explanation of the AWK Script:
- Previous delay: Tracks the delay of the previous packet.
- Current delay: The delay of the current packet, computed as the time difference amidst when the packet is obtained and when it was delivered.
- Jitter calculation: The changes amongst the delays of consecutive packets are estimated, and the absolute values are counted to get the entire jitter.
- Average jitter: The total jitter is divided by the amount of packets minus one (since jitter needs at least two packets) to get the average jitter.
- Run the AWK Script:
Store the AWK script like jitter.awk and execute it on the trace file (out.tr):
awk -f jitter.awk out.tr
- Interpreting the Results:
The output of the AWK script will offer the average jitter in seconds:
Example Output:
Average Jitter: 0.005 seconds
This output displays the average variation in delay amongst consecutive packets, which gives insight into the network’s stability for real-time applications.
- Conclusion:
To measure network jitter in NS2:
- Set up the simulation to produce traffic amongst nodes.
- Run the simulation to design a trace file with packet events.
- Analyze the trace file using an AWK script to calculate the end-to-end delays for successive packets.
- Calculate jitter as the variation in delays amidst consecutive packets and measure the average jitter over the entire simulation.
From this comprehensive guide, you can calculate the network jitter in the ns2 simulation with the help of the given aggregated set up that uses UDP and CBR traffic for the data transmission. We will provide you the additional details about this network jitter, if needed.
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