How to Calculate Network Response Time in NS2

To calculate the network response time using NS2 that normally refers to the time taken for a request to travel from a source to a destination and also receive a corresponding response (like in client-server or request-reply interactions). We can follow the simple procedure on how to calculate the network response time in NS2. The method contains examining the packet transmissions and receptions in the trace file made by NS2.

Steps to Calculate Network Response Time

  1. Generate the Trace File

Make certain that we are making a trace file during the simulation in NS2. Contain the following command in the TCL script:

set tracefile [open out.tr w]

$ns trace-all $tracefile

It will log all packet events, containing when packets are transmitted and received, with timestamps.

  1. Identify Packet Types

For a network response time calculation, we will require to observe the request and corresponding reply packets. Based on the simulation, these could be:

  • TCP segments (for TCP-based communication).
  • UDP packets (for UDP-based communication).
  • Application-level packets (such as HTTP request/response or ping requests).

For instance, if we are computing the response time for a ping request (ICMP) then we will look for:

  • The timestamp when the ICMP request packet is transmitted.
  • The timestamp when the ICMP reply packet is received.
  1. Understand Trace File Format

Every entry in the trace file delivers information such as:

  • Event type (+ for send, r for receive).
  • Time of event.
  • Node sending/receiving the packet.
  • Packet type (e.g., tcp, udp, cbr, ping).

An instance trace file line might look like this:

r 1.12345 2 3 tcp 1040 [0 2 3 0] ——- [2:0 3:0 32 0] [0] 0 0

Now, r means receive, 1.12345 is the time, 2 is the source node, 3 is the destination node, and tcp is the protocol type.

  1. Match Request and Response Packets

To estimate the network response time:

  • Discover the timestamp when the request packet is transmitted from the source (e.g., the client).
  • Find the timestamp when the corresponding response packet is received at the source.

For instance, if a TCP SYN packet is sent at time 0.5 and a TCP ACK packet is received at the time 1.5 then the network response time is:

Network Response Time=1.5−0.5=1 second\text{Network Response Time} = 1.5 – 0.5 = 1 \, \text{second}Network Response Time=1.5−0.5=1second

  1. Use AWK or Python to Automate the Process

If we have numerous request-reply interactions then we can be used a script to automate the computing of network response times. Given below is a basic AWK script example to calculate response times for TCP packets.

AWK Script to Calculate Network Response Time:

awk ‘{

# If the packet is sent (request), store its timestamp

if ($1 == “+” && $4 == “tcp”) {

sent_time[$6] = $2;

}

# If the packet is received (reply), calculate the response time

if ($1 == “r” && $4 == “tcp”) {

if (sent_time[$6] != “”) {

response_time = $2 – sent_time[$6];

print “Packet ID: ” $6 “, Response Time: ” response_time ” seconds”;

delete sent_time[$6];

}

}

}’ out.tr

  • $1 denotes to the event type (+ for sending, r for receiving).
  • $2 is the timestamp.
  • $4 refers to the packet type (tcp in this case).
  • $6 refers to the packet ID (unique identifier for each packet).

This script will:

  • Follow the sending time of a TCP packet.
  • Estimate the response time by discovering the corresponding received packet and then subtracting the send time from the receive time.
  1. Analyze Multiple Packets

If we are examining numerous request-response pairs then we can gather the response times and compute the average response time as follows:

awk ‘{

if ($1 == “+” && $4 == “tcp”) {

sent_time[$6] = $2;

}

if ($1 == “r” && $4 == “tcp”) {

if (sent_time[$6] != “”) {

response_time = $2 – sent_time[$6];

total_response_time += response_time;

count++;

delete sent_time[$6];

}

}

}

END {

if (count > 0) {

print “Average Response Time: ” total_response_time / count ” seconds”;

}

}’ out.tr

This script will:

  • Add all response times.
  • Compute the average response time after processing all packets.
  1. Interpret the Results

When the response times are estimated then we can be used them to examine the performance of the network, detect potential bottlenecks, or enhance the network configurations.

Example of Network Response Time Calculation

If we are simulating a TCP connection then we require to assess the response time among sending a TCP SYN and receiving the corresponding SYN-ACK, we will:

  • Detect the + event for the SYN packet (sent).
  • Detect the r event for the SYN-ACK packet (received).
  • Subtract the timestamp of the SYN from the timestamp of the SYN-ACK to obtain the network response time.

Network Response Time was delivered via simple technique, calculate and analyse with the help of the simulation tool NS2. Further exploration of this topic will be shared as required.

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