How to Calculate Network Time Synchronization in NS2

To calculate Network time synchronization in NS2 has needs to follow the steps and it is defined to mimic and evaluating how well the clocks of numerous nodes in a network are synchronized. In distributed networks, time synchronization is vital for coordinated communication, accurate data logging, and make sure that network events are properly ordered via diverse devices. In NS2, we can mimic time synchronization protocols, evaluate clock offsets, and estimate synchronization accuracy among nodes.

Here is a brief procedure to calculate the Network time synchronization in NS2

Steps to Simulate and Calculate Network Time Synchronization in NS2

  1. Set up the NS2 Simulation for Time Synchronization

To mimic time synchronization, we can establish nodes that interacts timestamps to synchronize their clocks. The main goal is to evaluate on how much the clocks of the nodes deviate from each other and how synchronization protocols help in to minimize this deviation.

Example NS2 Script for Basic Time Synchronization

# Create NS2 simulator instance

set ns [new Simulator]

# Open trace file for logging network events

set tracefile [open time_sync_trace.tr w]

$ns trace-all $tracefile

# Define network nodes

set node1 [$ns node]  ;# Node 1 (reference clock)

set node2 [$ns node]  ;# Node 2 (node to be synchronized)

set node3 [$ns node]  ;# Node 3 (another node to be synchronized)

# Create duplex links between nodes

$ns duplex-link $node1 $node2 1Mb 10ms DropTail

$ns duplex-link $node1 $node3 1Mb 10ms DropTail

# Set up UDP agents to simulate time synchronization messages

set udp1 [new Agent/UDP]

$ns attach-agent $node1 $udp1

set udp2 [new Agent/UDP]

$ns attach-agent $node2 $udp2

$ns connect $udp1 $udp2

set udp3 [new Agent/UDP]

$ns attach-agent $node3 $udp3

$ns connect $udp1 $udp3

# Set up CBR traffic to simulate time messages being sent periodically

set cbr1 [new Application/Traffic/CBR]

$cbr1 set packetSize_ 500

$cbr1 set interval_ 1.0  ;# Time messages sent every second

$cbr1 attach-agent $udp1

# Start synchronization messages

$ns at 0.5 “$cbr1 start”

# Stop simulation at 10 seconds

$ns at 10.0 “finish”

proc finish {} {

global ns tracefile

$ns flush-trace

close $tracefile

exit 0

}

# Run the simulation

$ns run

Explanation:

  • Nodes: Three nodes are generated (node1, node2, and node3). Node1 behaves the reference clock, and node2 and node3 are synchronized to node1.
  • Traffic: UDP agents replicate the exchange of time synchronization messages among the nodes. These messages are sent intermittently every second using a Constant Bit Rate (CBR) traffic generator.
  • Synchronization: Time messages are sent from node1 (the reference node) to node2 and node3 to harmonised their clocks.
  1. Monitor and Log Synchronization Events

The trace file will log all events such as packet transmissions and receptions. These logs can be measured to estimate the time delay, clock offset, and synchronization accuracy.

  1. Calculate Clock Offset and Time Delay

Clock synchronization needs to evaluating the clock offset (the difference among two nodes’ clocks) and time delay (the time it takes for a message to travel among nodes).

Clock Offset Calculation

The clock offset is the difference among the timestamp of the message transferred by node1 (reference clock) and the timestamp when node2 or node3 receives the message. This can be estimated by comparing the timestamps of routed and received packets.

Here’s an AWK script to estimate clock offsets among node1 (reference) and node2:

awk ‘

{

if ($1 == “+”) {  # Message sent from node1

if ($3 == “node1”) {

send_time[$7] = $2;  # Record the time the message was sent

}

}

if ($1 == “r” && $3 == “node2”) {  # Message received at node2

if (send_time[$7] != “”) {

clock_offset = $2 – send_time[$7];  # Calculate the clock offset

print “Clock Offset between node1 and node2:”, clock_offset, “seconds”;

}

}

}’ time_sync_trace.tr

This script estimate the clock offset by subtracting the time the message was sent from node1 from the time the message was received at node2.

Time Delay Calculation

The time delay is the time it takes for a time synchronization message to travel from node1 to node2 or node3. This can be estimated similarly to the clock offset but without deliberating the nodes’ clocks.

Here’s an AWK script to estimate the time delay among node1 and node2:

awk ‘

{

if ($1 == “+”) {

if ($3 == “node1”) {

send_time[$7] = $2;  # Record the time the message was sent

}

}

if ($1 == “r” && $3 == “node2”) {  # Message received at node2

if (send_time[$7] != “”) {

time_delay = $2 – send_time[$7];  # Calculate the time delay

print “Time Delay between node1 and node2:”, time_delay, “seconds”;

}

}

}’ time_sync_trace.tr

This script estimates the time delay by subtracting the time the message was sent from the time the message was received, delivering the delay in transmission.

  1. Assess Synchronization Accuracy

Once we have estimated the clock offset and time delay, we can evaluate the accuracy of the synchronization among the nodes. Smaller clock offsets and time delays signify better synchronization.

To assess the synchronization accuracy:

  • Clock Offset: If the clock offset is close to zero, the clocks are well-synchronized.
  • Time Delay: The smaller the time delay, the more accurate the synchronization because messages arrive faster and the clocks can be adapted with lower latency.
  1. Simulate Time Synchronization Protocols

We can mimic time synchronization protocols such as Network Time Protocol (NTP) or Precision Time Protocol (PTP) by adding more sophisticated techniques to synchronize the clocks. In such cases, nodes would interchange multiple messages, compute round-trip delays, and modify their clocks accordingly.

For instance, to mimic NTP-like behaviour, nodes would exchange timestamps, estimate both forward and backward delays, and then adapt their clocks in terms of the average of these delays.

  1. Visualize Synchronization Results

We can utilize Python (matplotlib) to envision clock offsets or time delays among the nodes to better know the synchronization performance.

Example Python Plot for Clock Offset:

import matplotlib.pyplot as plt

# Example data for clock offset over time

time = [0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5]

clock_offset = [0.02, 0.015, 0.01, 0.005, 0.003, 0.001, 0.0015, 0.001, 0.0008]  # Example clock offset data in seconds

plt.plot(time, clock_offset, marker=’o’)

plt.title(‘Clock Offset Over Time’)

plt.xlabel(‘Time (seconds)’)

plt.ylabel(‘Clock Offset (seconds)’)

plt.grid(True)

plt.show()

Summary

To compute network time synchronization in NS2:

  1. Set up the simulation: Describe nodes and utilize UDP traffic to mimic the exchange of time synchronization messages.
  2. Log synchronization events: Capture all events in a trace file, has contained the sending and receiving of messages.
  3. Calculate clock offsets: Relate the timestamps of sent and received messages to estimate the clock offset among nodes.
  4. Calculate time delays: Evaluate the time it takes for synchronization messages to travel among nodes.
  5. Evaluate synchronization accuracy: Utilize the estimated clock offsets and time delays to evaluate the quality of synchronization.
  6. Visualize results: Plot clock offset and time delay to measure on how well the nodes are synchronized.

At the end, we thorough the manual and provide the valuable insights regarding how to calculate the Network time synchronization in ns2 tool. Further details regarding the implementation of the Network time synchronization in diverse simulations will be provided.

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