How to Calculate Network Queue time in NS2
To calculate the queue time in NS2 (Network Simulator 2) has includes to evaluate how long packets spend in the queue of a network node before they are processed or progressed. Queue time is significant parameters for measuring network performance, as it directly affects latency and overall throughput.
Here’s a step-by-step guide on how to calculate the network queue time in NS2:
Step-by-Step Implementation:
- Understand Queue Time
Queue time defined the time a packet waits in the queue of a network node before being transmitted. This metric can be estimated by subtracting the packet’s arrival time at the queue from the time it leaves the queue (whether for transmission or because of being dropped).
- Set Up the Simulation in NS2
Initially, make sure the NS2 simulation has queueing behaviour. By default, NS2 uses DropTail queues, nevertheless we can require other queue types such as RED (Random Early Detection). Here’s a simple sample of a simulation setup in which nodes are associated by links, and queues are generated at each node:
# Create NS2 simulator instance
set ns [new Simulator]
# Open trace file for output
set tracefile [open out.tr w]
$ns trace-all $tracefile
# Define nodes
set n0 [$ns node]
set n1 [$ns node]
set n2 [$ns node]
# Create links with queues between nodes (DropTail or RED)
$ns duplex-link $n0 $n1 1Mb 10ms DropTail
$ns queue-limit $n0 $n1 50 ;# Set queue size for link 0-1
$ns duplex-link $n1 $n2 1Mb 10ms RED
# Set up traffic (CBR traffic)
set udp0 [new Agent/UDP]
$ns attach-agent $n0 $udp0
set null0 [new Agent/Null]
$ns attach-agent $n2 $null0
$ns connect $udp0 $null0
set cbr0 [new Application/Traffic/CBR]
$cbr0 set packetSize_ 500
$cbr0 set interval_ 0.005
$cbr0 attach-agent $udp0
# Start and stop traffic
$ns at 0.5 “$cbr0 start”
$ns at 4.5 “$cbr0 stop”
$ns at 5.0 “finish”
proc finish {} {
global ns tracefile
$ns flush-trace
close $tracefile
exit 0
}
# Run simulation
$ns run
- Enable Queue Monitoring in NS2
We can clearly allow queue monitoring to collect queue-related statistics. For instance, we can permit queue monitoring on the link like this:
# Enable queue monitoring
$ns queue-monitor $n0 $n1 [open “queue-monitor.tr” w] # Monitor the queue at link n0-n1
This command will create a isolated trace file (queue-monitor.tr) that logs queue events, has packet enqueue and dequeue times.
- Examine the Trace File
NS2 trace files encompass information about packet enqueue (+ event), dequeue (- event), and drop (d event) events. The trace file format typically includes:
- +: Packet enqueued (arrival at queue)
- –: Packet dequeued (departure from queue for transmission)
- d: Packet dropped from the queue
A usual trace file line might look like this:
+ 0.123456 0 1 cbr 1000 ——- 1 0.0 0.0 1.0
– 0.123789 0 1 cbr 1000 ——- 1 0.0 0.0 1.0
Where:
- + indicates the packet is enqueued at time 0.123456.
- – indicates the packet is dequeued at time 0.123789.
The difference among these two times gives you the queue time for the packet.
- Extract Queue Time Using AWK
We can utilize an AWK script to process the trace file and estimate the queue time for each packet.
Here’s an AWK script that fits enqueue and dequeue events for packets and estimate the queue time:
awk ‘
{
if ($1 == “+”) {
enqueue_time[$7] = $2; # Record enqueue time using packet ID ($7)
}
if ($1 == “-“) {
dequeue_time = $2;
if (enqueue_time[$7] != “”) {
queue_time = dequeue_time – enqueue_time[$7]; # Calculate queue time
print “Packet ID: ” $7 “, Queue Time: ” queue_time ” seconds”;
delete enqueue_time[$7]; # Remove entry after calculation
}
}
}’ out.tr
This script:
- Records the enqueue time (+) for each packet.
- When the packet is dequeued (-), it estimate the time spent in the queue by subtracting the enqueue time from the dequeue time.
- Prints the queue time for each packet.
- Post-Process Queue Time Data
Once we have extracted the queue times for all packets, we can calculate:
- Average Queue Time: The mean of all queue times.
- Maximum Queue Time: The highest queue time observed.
- Queue Time Distribution: The spread of queue times to understand how long packets usually wait in the queue.
Here’s how you can calculate the average queue time:
awk ‘
{
if ($1 == “+”) {
enqueue_time[$7] = $2; # Record enqueue time using packet ID ($7)
}
if ($1 == “-“) {
dequeue_time = $2;
if (enqueue_time[$7] != “”) {
queue_time = dequeue_time – enqueue_time[$7]; # Calculate queue time
total_queue_time += queue_time; # Sum queue times
packet_count++; # Count packets
delete enqueue_time[$7]; # Remove entry after calculation
}
}
}
END {
if (packet_count > 0) {
avg_queue_time = total_queue_time / packet_count;
print “Average Queue Time: ” avg_queue_time ” seconds”;
} else {
print “No packets found”;
}
}’ out.tr
This script estimate the total queue time for all packets and divides it by the number of packets to acquire the average queue time.
- Analyse Queue Time Data
Once we have extracted queue time data:
- High queue times can signify congestion or inadequate bandwidth.
- Low queue times can recommend that the network is not heavily loaded.
We can further measure the queue time by plotting it using tools such as Python (matplotlib) or Excel for visual inspection.
Example Python Plot:
import matplotlib.pyplot as plt
# Example queue times
packet_ids = [1, 2, 3, 4, 5]
queue_times = [0.002, 0.003, 0.004, 0.005, 0.006]
plt.plot(packet_ids, queue_times, marker=’o’)
plt.title(‘Queue Time for Each Packet’)
plt.xlabel(‘Packet ID’)
plt.ylabel(‘Queue Time (seconds)’)
plt.grid(True)
plt.show()
Summary
To compute network queue time in NS2:
- Set up the simulation and make sure queueing behavior is permitted on the links.
- Monitor the queue using NS2’s built-in trace mechanisms.
- Process the trace file to extract enqueue and dequeue procedures.
- Calculate the queue time by subtracting enqueue times from dequeue times.
- Analyze the data to know the network performance in terms of queuing delay.
From this page, we had learned and get the knowledge on how to measure the queue times in the network to handle the enhanced transmission using the ns2 tool. We deliver the additional information on how the network queue time will perform in other simulation time.
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