How to Calculate Buffer Rate in NS2

To calculate the Buffer Rate in Network Simulator 2 (NS2), it means the rate at which the packets are buffered (queued) or dropped because of buffer overflow in a network node (like a router or switch). It is vital for knowing how much traffic is being delayed or dropped because of network blockage, which can significantly influence Quality of Service (QoS). Here in the below, we provide the approach to compute the buffer rate in ns2:

Steps to Calculate Buffer Rate in NS2

To measure the buffer rate in NS2, you need to:

  1. Configure a simulation that uses queues.
  2. Allow queue monitoring to log when packets are included to the buffer or dropped because of congestion.
  3. Assess the trace file to compute the buffer rate, which could attach the queue occupancy rate or the packet drop rate due to buffer overflow.

Key Metrics Related to Buffer Rate:

  • Queue Length (Buffer Occupancy): The amount of packets in the queue at a particular time.
  • Queue Utilization: The rate at which packets are attached to the queue compared to the increased queue size.
  • Packet Drop Rate: The rate at which packets are dropped due to the buffer being full (overflow).
  1. Set Up NS2 Simulation with a Queue:

Simulate buffering at network nodes (routers or switches) using ns2’s queue objects. By setting up a queue amongst two nodes, you can observe packet enqueuing (buffering) and dequeuing (transmission), as well as packet drops due to buffer overflow.

Example TCL Script with a Queue:

# Create the simulator

set ns [new Simulator]

# Create two nodes

set node_(0) [$ns node]

set node_(1) [$ns node]

# Create a duplex link between the two nodes with a queue

# Queue limit of 50 packets and bandwidth of 1 Mbps

$ns duplex-link $node_(0) $node_(1) 1Mb 10ms DropTail

# Create UDP agents and CBR traffic

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 CBR traffic (to simulate constant packet generation)

set cbr0 [new Application/Traffic/CBR]

$cbr0 attach-agent $udp0

$cbr0 set packetSize_ 512       ;# Packet size of 512 bytes

$cbr0 set rate_ 2Mb             ;# Higher than link bandwidth to cause congestion

# Start and stop the traffic

$ns at 1.0 “$cbr0 start”

$ns at 10.0 “$cbr0 stop”

# Enable queue monitoring

set qmon [$ns monitor-queue $node_(0) $node_(1) [open queue-monitor.tr w] 0.1]

# Enable trace to capture buffer-related events

set tracefile [open out.tr w]

$ns trace-all $tracefile

# Close trace file at the end

proc finish {} {

global ns tracefile

$ns flush-trace

close $tracefile

exit 0

}

# End simulation at 12 seconds

$ns at 12.0 “finish”

Explanation:

  • Queue Setup: The link amongst node_(0) and node_(1) uses a DropTail queue with a bound of 50 packets and bandwidth of 1 Mbps. This configuration can cause packet drops if more than 50 packets are in the buffer.
  • CBR Traffic: Constant Bit Rate (CBR) traffic is sent at a higher rate than the link’s bandwidth (2 Mbps vs. 1 Mbps), designing congestion and capably filling the queue.
  • Queue Monitoring: NS2’s monitor-queue command logs buffer-related events every 0.1 seconds in the file queue-monitor.tr.
  1. Monitor Buffering and Packet Drops:

The queue-monitor.tr file logs queue events including enqueuing (buffering), dequeuing (transmission), and packet drops. Here’s an example of what the trace might look like:

+ 1.000000000 0 50 51 0

– 1.001000000 0 49 51 0

d 1.002000000 1 50 51 0

In this trace:

  • + represents a packet enqueued (buffered).
  • – indicates a packet dequeued (transmitted).
  • d signifies a packet dropped due to buffer overflow.
  • The numbers after the event denotes the current queue length and the maximum queue length.
  1. Calculating Buffer Rate:
  2. a) Queue Occupancy (Buffer Utilization) Rate:

Measure the buffer utilization rate by evaluating how commonly the queue reaches particular lengths during the simulation. The queue occupancy rate is computed as the ratio of the amount of buffered packets to the maximum queue length.

AWK Script to Calculate Buffer Utilization:

BEGIN {

total_occupancy = 0;

occupancy_samples = 0;

}

# Process enqueuing events to track queue occupancy

$1 == “+” {

queue_length = $3;  # Current queue length

total_occupancy += queue_length;

occupancy_samples++;

}

END {

avg_occupancy = total_occupancy / occupancy_samples;

print “Average Queue Occupancy: ” avg_occupancy ” packets”;

}

This script estimates the average queue occupancy by processing + events, which indicate packets enqueued.

  1. b) Packet Drop Rate (Due to Buffer Overflow):

Calculate the packet drop rate by summing up the count of d (drop) events and divide it by the total amount of packets sent.

AWK Script to Calculate Packet Drop Rate:

BEGIN {

sent_packets = 0;

dropped_packets = 0;

}

# Count sent packets

$1 == “s” {

sent_packets++;

}

# Count dropped packets

$1 == “d” {

dropped_packets++;

}

END {

drop_rate = (dropped_packets / sent_packets) * 100;

print “Packet Drop Rate: ” drop_rate “%”;

}

This script measures the packet drop rate as the percentage of dropped packets compared to the total number of sent packets.

  1. Run the AWK Scripts:

Once the simulation is done, execute the AWK scripts on the trace files to compute the buffer consumption and packet drop rate.

awk -f buffer_utilization.awk queue-monitor.tr

awk -f packet_drop_rate.awk out.tr

  1. Interpreting Buffer Rate Results:
  • High Buffer Utilization: If the queue remains close its maximum size for much of the simulation, this represents that the buffer is heavily consumed, and the network might be close to congestion.
  • High Packet Drop Rate: A high packet drop rate because of buffer overflow signifies that the queue is often full, and packets are being discarded, which may affect network performance (such as increased latency or minimized throughput).
  1. Conclusion:

To measure the buffer rate in NS2:

  1. Build the simulation with a queue amongst nodes.
  2. Permit queue monitoring to log buffer-related events (enqueues, dequeues, drops).
  3. Assess the trace file using AWK scripts to compute key metrics like queue utilization and packet drop rate.

Through the given procedure, we have comprehensively delivered the entire simulation set up, the required formula to measure and the sample snippets for the calculation of the buffer rate of a queue using ns2 simulator tool. if you need any extra details regarding this manual, we will provide it for you.

To calculate the Buffer Rate in Network Simulator 2 (NS2) is really hard so stay in touch with us we will guide you with best results.