How to Calculate Stalling in NS2

To calculate stalling in ns2 has needs to follow a series of steps and it is usually defined to the situations in which a network application such as video streaming, file downloading, or real-time communication experiences disruptions because of insufficient data being received in time. This can happen when there is network congestion, packet loss, or insufficient bandwidth that mitigates the data from being delivered at the essential rate.

For instance, in video streaming, stalling occurs when the playback buffer is empty due to the video data is not being received rapidly enough. Stalling can rigorously affects the user experience and is a vital parameters for Quality of Service (QoS) in multimedia applications.

Below are the procedures to calculate the stalling in ns2:

Steps to Calculate Stalling in NS2

  1. Set Up a Simulation with Continuous Data Transmission:

Initially, we need to mimic a scenario that information such as video packets or real-time communication packets is being routed from a source to a destination. Stalling can happen when the receiver is unable to manage a steady flow of data because of difficulties like packet loss or insufficient throughput.

Example TCL Script for Data Transmission (e.g., Video Streaming):

# Create the simulator

set ns [new Simulator]

# Define the topology

set topo [new Topography]

$topo load_flatgrid 1000 1000

# Create two nodes: source and destination

set node_(0) [$ns node]

set node_(1) [$ns node]

# Create a duplex link with a queue between the nodes (buffer with 50 packets capacity)

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

# Attach UDP agents for video packet 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

# Set up CBR traffic (simulating a video stream)

set cbr0 [new Application/Traffic/CBR]

$cbr0 attach-agent $udp0

$cbr0 set packetSize_ 1024         ;# Video packet size (1024 bytes)

$cbr0 set rate_ 1Mb                ;# Streaming at 1 Mbps

# Start and stop the traffic

$ns at 1.0 “$cbr0 start”

$ns at 10.0 “$cbr0 stop”

# Enable tracing to capture packet reception

set tracefile [open out.tr w]

$ns trace-all $tracefile

# End the simulation after 12 seconds

proc finish {} {

global ns tracefile

$ns flush-trace

close $tracefile

exit 0

}

# End simulation at 12 seconds

$ns at 12.0 “finish”

  1. Identify Stalling Events:

In a usual scenario, stalling happens when the application doesn’t receive packets fast enough to keep up with its expected data rate. We can utilize the packet reception times in the trace file to estimate either stalling occurred by:

  • Inspection if the time among two packet receptions is too long.
  • Validating if the total data received over a given time is lower than the essential information rate.

For Instance, if a video stream needs 1 Mbps of information nevertheless the network delivers less than that, stalling might happen.

  1. Trace File Analysis for Stalling:

The NS2 trace file (out.tr) will includes details of packet transmissions and receptions. We can utilize this data to estimate uncertainty and when stalling happen.

Example Trace File Entries:

r 2.000000000 _1_ AGT  — 1024 cbr 0 0.0 1.0 1.0

r 3.000000000 _1_ AGT  — 1024 cbr 1 0.0 2.0 2.0

r 4.500000000 _1_ AGT  — 1024 cbr 2 0.0 3.0 3.0

r 6.000000000 _1_ AGT  — 1024 cbr 3 0.0 4.0 4.0

In this trace file:

  • r indicates a packet reception event.
  • 2.000000000 is the time of reception (in seconds).
  • 1024 is the packet size in bytes.

If the time among consecutive receptions is longer than expected, it can cause to stalling in a real-time application such  as video streaming.

  1. Calculating Stalling:

To estimate stalling, we need to validate whether the content is being offered at a sufficient rate. we can perform this by:

  • Tracking the inter-arrival time of packets: If the time among packet arrivals exceeds a specifics threshold, stalling has occurred.
  • Checking the throughput: If the received data is less than the essential rate over a given time window, stalling can be concluded.

AWK Script to Calculate Stalling Based on Packet Inter-arrival Time:

We can use the following AWK script to validate for stalling events according to packet inter-arrival times. If the gap among consecutive packets exceeds a threshold such as 1 second, it can be deliberated a stalling event.

BEGIN {

prev_time = 0;

stalling_events = 0;

stalling_threshold = 1.0;  # 1 second threshold for stalling

}

# Process received packets at the application layer

$1 == “r” && $4 == “_1_” && $7 == “cbr” {

if (prev_time > 0) {

inter_arrival_time = $2 – prev_time;

if (inter_arrival_time > stalling_threshold) {

stalling_events++;

print “Stalling event detected at time: ” $2;

}

}

prev_time = $2;

}

END {

print “Total stalling events: ” stalling_events;

}

This script validates the inter-arrival time among received packets at the destination node and counts the number of stalling events.

  1. Calculating Stalling Based on Throughput:

Otherwise, we can estimate stalling according to the throughput by comparing the actual received data rate to the essential data rate. For instance, if the application expects 1 Mbps however the received data rate is lower, stalling might occur.

AWK Script to Calculate Stalling Based on Throughput:

BEGIN {

required_rate = 1000000;  # 1 Mbps required rate in bits

received_data = 0;

stalling_time = 0;

window_start_time = 1.0;

window_end_time = 10.0;

}

# Process received packets at the application layer

$1 == “r” && $4 == “_1_” && $7 == “cbr” {

received_data += $8 * 8;  # Convert packet size to bits

}

END {

actual_rate = received_data / (window_end_time – window_start_time);

if (actual_rate < required_rate) {

stalling_time = window_end_time – window_start_time;

print “Stalling occurred. Actual rate: ” actual_rate ” bps”;

} else {

print “No stalling. Actual rate: ” actual_rate ” bps”;

}

}

This script estimates the actual throughput over a stated time window such as between 1.0 and 10.0 seconds and validates if it is lower than the required rate, representing stalling.

  1. Running the Scripts:

To execute the AWK scripts on trace file, use the following command:

awk -f stalling_time.awk out.tr

This will give the number of stalling events according to inter-arrival times or signify either the application experienced stalling according to the throughput.

  1. Conclusion:

To compute stalling in NS2:

  1. Set up a simulation in which data is routed continuously such as video streaming or real-time communication.
  2. Enable packet tracing to capture transmission and reception events.
  3. Analyze the trace file to compute inter-arrival times or throughput.
  4. Use AWK scripts to identify stalling events according to packet arrival times or insufficient throughput.

From the module, we understood how to calculate and mimic the scenario for stalling in ns2 tool that were calculate in real-time communication. If you have any doubts regarding the Stalling we will provide that in further works. For your project on calculating stalling in NS2, we invite you to reach out to us for exceptional support and clear insights. Our focus is on essential parameters that enhance the Quality of Service (QoS) in multimedia applications.