How to Implement Network Troubleshooting in NS2
To implement Network Troubleshooting in NS2 has a series of steps those classifying and identifying difficulties like packet loss, excessive delays, link failures, or congestion, and defining the root leads of these issues. NS2 delivers a flexible framework to mimic these challenges and measure numerous network behaviours to support in troubleshooting.
Here’s a step-by-step guide on how to implement Network Troubleshooting in NS2:
Step-by-Step Guide to Implement Network Troubleshooting in NS2
- Set Up the Basic Network Topology:
- Initiate by configuring a network topology that contain multiple nodes and links in which potential network issues may arise, like packet loss, congestion, or link failures.
Example OTcl script to set up a simple wired network topology:
set ns [new Simulator]
set nf [open out.tr w]
$ns trace-all $nf
set namfile [open out.nam w]
$ns namtrace-all $namfile
# Create nodes
set node0 [$ns node]
set node1 [$ns node]
set node2 [$ns node]
# Create duplex links between nodes
$ns duplex-link $node0 $node1 1Mb 10ms DropTail
$ns duplex-link $node1 $node2 1Mb 10ms DropTail
# Define TCP communication between node0 and node2
set tcp [new Agent/TCP]
set sink [new Agent/TCPSink]
$ns attach-agent $node0 $tcp
$ns attach-agent $node2 $sink
$ns connect $tcp $sink
set ftp [new Application/FTP]
$ftp attach-agent $tcp
# Start FTP traffic at 1 second and stop at 5 seconds
$ns at 1.0 “$ftp start”
$ns at 5.0 “$ftp stop”
# Run the simulation
$ns at 6.0 “finish”
proc finish {} {
global ns nf namfile
$ns flush-trace
close $nf
close $namfile
exec nam out.nam &
exit 0
}
$ns run
- This script configures a basic three-node topology with TCP communication among node0 and node2 via node1.
- Simulate Common Network Issues:
- Packet loss, link failures, high delay, and congestion are common concerns that need troubleshooting. We can mimic these conditions to validate on how the network act as and responds to them.
2.1 Simulate Packet Loss:
- Packet loss can be replicated by manually dropping packets or by minimizing the link bandwidth that can lead to buffer overflows.
Example OTcl script to replicate packet loss by minimizing link bandwidth:
# simulate link congestion by reducing bandwidth at 3.0 seconds
$ns at 3.0 “$ns duplex-link-op $node1 $node2 bw 512Kb”
- This minimizes the bandwidth among node1 and node2 that could cause to packet drops due to congestion.
2.2 Simulate Link Failure:
- A link failure can be mimicked by turning off a link for a specific period during the simulation.
Example OTcl script to simulate a link failure and recovery:
# Simulate a link failure between node0 and node1 at 3.0 seconds
$ns at 3.0 “$ns link $node0 $node1 down”
# Simulate link recovery at 4.0 seconds
$ns at 4.0 “$ns link $node0 $node1 up”
- This leads the link among node0 and node1 to go down at 3.0 seconds and recover at 4.0 seconds.
2.3 Simulate High Delay:
- We can establish high delay on a link to mimic slow network performance and troubleshoot excessive latency issues.
Example OTcl script to simulate high delay:
# Increase the delay on the link between node1 and node2 at 3.5 seconds
$ns at 3.5 “$ns duplex-link-op $node1 $node2 delay 100ms”
- This adds a latency of 100ms to the link among node1 and node2 that mimics network slowness.
2.4 Simulate Congestion:
- Congestion can be replicated by sending a large volume of traffic via the network, which overwhelms the available bandwidth.
Example OTcl script to simulate congestion with an additional traffic flow:
# Create a UDP agent and CBR (Constant Bit Rate) traffic source
set udp [new Agent/UDP]
$ns attach-agent $node1 $udp
$ns connect $udp $sink
set cbr [new Application/Traffic/CBR]
$cbr attach-agent $udp
$cbr set rate_ 2Mb ;# High traffic rate to cause congestion
# Start the congestion at 2.0 seconds
$ns at 2.0 “$cbr start”
- This mimics the congestion by generating high-rate traffic from node1 to node2.
- Monitor and Analyse Network Issues:
- Once disputes are simulated, we need to observe the network to capture the issues like packet loss, excessive delays, or minimized throughput. NS2 trace files deliver detailed logs of all network events.
3.1 Packet Loss Monitoring:
- Use AWK scripts to observes and evaluate packet loss.
Example AWK script to calculate packet loss:
awk ‘{
if ($1 == “s” && $4 == “TCP”) {
sent_packets++
}
if ($1 == “r” && $4 == “TCP”) {
received_packets++
}
} END {
packet_loss = sent_packets – received_packets
print “Total Packet Loss: “, packet_loss
}’ out.tr
- This script estimates packet loss by comparing the number of packets sent and received.
3.2 Delay Monitoring:
- Use AWK to measure the latency among packets sent and received.
Example AWK script to calculate packet delay:
awk ‘{
if ($1 == “s” && $4 == “TCP”) {
start_time[$11] = $2
}
if ($1 == “r” && $4 == “TCP”) {
end_time[$11] = $2
total_delay += end_time[$11] – start_time[$11]
packet_count++
}
} END {
print “Average Delay: “, total_delay / packet_count, “seconds”
}’ out.tr
- This script estimates the average delay for packets in the network.
3.3 Throughput Monitoring:
- Throughput is an required metric to observe the performance of the network during troubleshooting.
Example AWK script to calculate throughput:
awk ‘{
if ($1 == “r” && $4 == “TCP”) {
total_bytes += $6
}
} END {
print “Throughput: “, total_bytes / 5, “bytes per second”
}’ out.tr
- This script estimates the throughput over the duration of the simulation.
- Implement Corrective Actions:
- According to the analysis, we can execute corrective actions, like increasing bandwidth, rerouting traffic, or adapting queue sizes.
Example OTcl script to adapt bandwidth:
# Increase the bandwidth between node1 and node2 at 4.5 seconds to alleviate congestion
$ns at 4.5 “$ns duplex-link-op $node1 $node2 bw 2Mb”
- This script upsurges the bandwidth among node1 and node2 to resolve congestion.
- Run the Simulation and Log Results:
- After replicating the difficulties and implementing corrective actions, execute the simulation to log all events. The trace file (out.tr) will contain eloborated information on packet transmission, drops, delays, and throughput.
To run the simulation:
ns your_script.tcl
- Visualize Network Problems in NAM:
- Use NAM (Network Animator) to envision network challenges like packet loss, latency, and congestion in real-time.
To launch NAM:
nam out.nam
- NAM enables to monitor packet drops, queue build-ups, and other network challenges visually, that supports you to identify and troubleshoot the issues.
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