How to Calculate Network Path Latency in NS2
To calculate Network Path Latency in NS2, this is defined to the time it takes for a packet to traverse from the source node to the destination node beside a specified path. It involves the time spent in transmission, propagation, processing, and queuing delays and the Calculating path latency in NS2 has contain to measuring the trace file generated during the simulation.
Here’s how we can compute network path latency in NS2:
Steps to Calculate Network Path Latency
- Generate the Trace File
Make sure that TCL script creates a trace file that logs all events in the network that has when packets are sent and received. The trace file records timestamps, source and destination nodes, and packet IDs, all of which are necessary for estimating latency.
Here’s how we can permits trace generation in the NS2 script:
set tracefile [open out.tr w]
$ns trace-all $tracefile
This will log events in the trace file named out.tr.
- Understand the Trace File Format
Each line in the trace file denotes an event such as packet sent, packet received with information like the timestamp, node IDs, and packet type. A actual trace file line looks like this:
+ 0.123456 0 1 cbr 1040 ——- [0 0 1 0] ——- [1:0 0:0 32 0] [0] 0 0
r 0.234567 1 0 cbr 1040 ——- [0 1 0 0] ——- [0:0 1:0 32 0] [0] 0 0
- + specifies a packet sent event, and r shows a packet received event.
- The second field (0.123456, 0.234567) denotes the timestamp.
- The third and fourth fields (0, 1) denote the source and destination node IDs.
- The fifth field (cbr) denote the packet type like tcp, udp, cbr for constant bit rate.
In the above example:
- A packet was sent from node 0 at time 0.123456 and received at node 1 at time 0.234567.
- Identify Packet Events for Latency Calculation
To compute the network path latency, we need to:
- Find the timestamp of the sent event for a particular packet at the source node.
- Find the timestamp of the received event for the same packet at the destination node.
- Subtract the send time from the receive time to estimate the path latency.
For example:
- A packet was sent from node 0 at time 0.123456.
- The same packet was received at node 1 at time 0.234567.
- The path latency is:
Path Latency=0.234567−0.123456=0.111111 seconds\text{Path Latency} = 0.234567 – 0.123456 = 0.111111 \, \text{seconds}Path Latency=0.234567−0.123456=0.111111seconds
- Use AWK or Python to Automate Latency Calculation
For multiple packets, it’s easier to systematise the process of matching packet IDs and estimating latency. Here’s an AWK script that does this for all packets in the trace file:
AWK Script to Calculate Path Latency
awk ‘{
if ($1 == “+” && $4 == “tcp”) {
send_time[$6] = $2; # Store the send time based on packet ID
}
if ($1 == “r” && $4 == “tcp”) {
if (send_time[$6] != “”) {
latency = $2 – send_time[$6];
print “Packet ID: ” $6 “, Path Latency: ” latency ” seconds”;
delete send_time[$6]; # Remove entry after calculating latency
}
}
}’ out.tr
- $1 refers to the event (+ for sent, r for received).
- $2 is the timestamp.
- $4 is the packet type (tcp, udp, cbr, etc.).
- $6 is the packet ID.
This script fits the packets by their ID, estimates the time difference among the send and receive events, and prints the path latency for each packet.
- Calculate Average Path Latency
If we need to estimate the average latency for multiple packets, we can adjust the script to accumulate the latencies and calculate the average at the end:
awk ‘{
if ($1 == “+” && $4 == “tcp”) {
send_time[$6] = $2;
}
if ($1 == “r” && $4 == “tcp”) {
if (send_time[$6] != “”) {
latency = $2 – send_time[$6];
total_latency += latency;
packet_count++;
delete send_time[$6];
}
}
}
END {
if (packet_count > 0) {
print “Average Path Latency: ” total_latency / packet_count ” seconds”;
}
}’ out.tr
This script:
- Gathers the latencies for all packets.
- Divides the total latency by the number of packets to estimate the average latency.
- Calculate Path Latency for Specific Flows or Nodes
If we are intent in estimating the latency for packets among the particular nodes or flows, we can add further criteria in the AWK script to filter based on node IDs or other conditions.
For example, to estimate latency only for packets among nodes 0 and 1:
awk ‘{
if ($1 == “+” && $4 == “tcp” && $3 == 0 && $5 == 1) {
send_time[$6] = $2;
}
if ($1 == “r” && $4 == “tcp” && $3 == 1 && $5 == 0) {
if (send_time[$6] != “”) {
latency = $2 – send_time[$6];
print “Packet ID: ” $6 “, Path Latency: ” latency ” seconds”;
delete send_time[$6];
}
}
}’ out.tr
This script estimates the path latency only for packets routed among node 0 and node 1.
Example: Calculating Latency for a UDP Flow
If we need to estimate latency for UDP packets in its place of TCP, just replace “tcp” with “udp” in the above script. For example:
awk ‘{
if ($1 == “+” && $4 == “udp”) {
send_time[$6] = $2;
}
if ($1 == “r” && $4 == “udp”) {
if (send_time[$6] != “”) {
latency = $2 – send_time[$6];
print “Packet ID: ” $6 “, Path Latency: ” latency ” seconds”;
delete send_time[$6];
}
}
}’ out.tr
- Analyse the Results
Once we have calculated the latency for individual packets, we need to measure the outcomes for various kinds of traffic, routes, and network configurations to know the performance of network.
- Path latency is vital for measuring network performance based on delay-sensitive applications such as real-time video or voice.
- If the latency is high, we need to enhance routing protocols, bandwidth allocation, or node placements.
Within this module, we presented the entire demonstration about how to calculate and measure the performance regarding the Network Path Latency in the tool of ns2. Additional in depth details about the Network Path Latency will offer too.
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