How to Implement Network Congestion Control in NS2

To implement the Network Congestion Control using the NS2, which encompasses handling the flow of data packets to avoid the network from becoming overloaded, make sure that effective delivery and avoiding the packet loss because of the congestion. It can attain via numerous mechanisms like changing the packet transmission rates, managing queues, or employing algorithms such as TCP congestion control variants (e.g., Tahoe, Reno, Vegas). The following is a step-by-step implementation process to executing the Network Congestion Control in NS2:

Step-by-Step Guide to Implement Network Congestion Control in NS2

  1. Set Up the Basic Network Topology:
  • Initially, describe a network topology with several nodes in which the congestion can happen. The network should have necessary traffic flow to replicate the congestion, like several data sources transmitting to the similar end.

Instance OTcl script for a simple 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 network nodes

set node0 [$ns node]   ;# Source node 1

set node1 [$ns node]   ;# Intermediate node

set node2 [$ns node]   ;# Destination node

set node3 [$ns node]   ;# Source node 2

# Create duplex links between the nodes

$ns duplex-link $node0 $node1 1Mb 10ms DropTail

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

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

# Create two TCP agents for each source

set tcp0 [new Agent/TCP]

set tcp_sink0 [new Agent/TCPSink]

set tcp1 [new Agent/TCP]

set tcp_sink1 [new Agent/TCPSink]

# Attach agents to nodes

$ns attach-agent $node0 $tcp0

$ns attach-agent $node2 $tcp_sink0

$ns attach-agent $node3 $tcp1

$ns attach-agent $node2 $tcp_sink1

# Connect the TCP agents to the sinks

$ns connect $tcp0 $tcp_sink0

$ns connect $tcp1 $tcp_sink1

# FTP applications to generate traffic

set ftp0 [new Application/FTP]

set ftp1 [new Application/FTP]

$ftp0 attach-agent $tcp0

$ftp1 attach-agent $tcp1

# Start traffic at 1.0 seconds and stop at 5.0 seconds

$ns at 1.0 “$ftp0 start”

$ns at 1.5 “$ftp1 start”

$ns at 5.0 “$ftp0 stop”

$ns at 5.0 “$ftp1 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 configure describes two source nodes (node0 and node3) sending traffic via a general intermediate node (node1) to the end node (node2). It will generate congestion as both sources distribute the similar link.
  1. Implement Congestion Control Using TCP Variants:
  • The simulation platform NS2 supports numerous TCP congestion control algorithms like TCP Tahoe, TCP Reno, TCP Vegas, and more. We can be chosen various TCP variants to see how they manage the congestion.

Example OTcl script for TCP Tahoe:

# Set TCP variant to Tahoe

$tcp0 set class_ 1

$tcp1 set class_ 1

Example OTcl script for TCP Reno:

# Set TCP variant to Reno

$tcp0 set class_ 2

$tcp1 set class_ 2

Example OTcl script for TCP Vegas:

# Set TCP variant to Vegas

$tcp0 set class_ 3

$tcp1 set class_ 3

  • Above lines are set up the TCP agents to use particular variants of TCP, each with various congestion control mechanisms.
  1. Implement Active Queue Management (RED or DropTail):
  • Queue management shows a critical role in congestion control. By default, NS2 uses the DropTail queue management algorithm, however we also can be executed the Random Early Detection (RED) that supports to prevent the congestion by dropping packets before the queue becomes occupied.

RED Queue:

# Set up RED queue management at node1 (to manage congestion)

set red_q [new Queue/RED]

$ns queue-limit $node1 $node2 20  ;# Limit queue size to 20 packets

$ns link $node1 $node2 queue $red_q

DropTail Queue:

# Set up DropTail queue at node1

$ns queue-limit $node1 $node2 20  ;# Limit queue size to 20 packets

  • RED supports handle the congestion by probabilistically dropping packets before the queue overflows, signalling TCP sources to slow down.
  1. Monitor Congestion Metrics (Queue Size, Packet Drops):
  • To replicate the congestion control, it’s significant to observe the vital metrics queue size, packet drops, and throughput. We can print or record these values while the simulation.

Example OTcl script to monitor queue size and packet drops:

# Monitor the queue size at node1

proc monitor_queue_size {node1 node2} {

set queue_size [$node1 ifq-length]

puts “Queue size between $node1 and $node2: $queue_size”

return $queue_size

}

# Log queue size at intervals

$ns at 2.0 “monitor_queue_size $node1 $node2”

$ns at 3.0 “monitor_queue_size $node1 $node2”

  • This function records the size of the queue among the node1 and node2 that supporting to track congestion as the simulation runs.
  1. Simulate Congestion and Observe Behavior:
  • To replicate the congestion, we run the network with several traffic sources competing for the similar link. Monitor how various TCP variants manage the congestion by modifying its forwarding rates and handling packet losses.

Example of running the simulation:

ns your_script.tcl

  • The generated trace file (out.tr) will includes the informations regarding the transmission, queue sizes, packet drops, and other metrics that can examined to estimate the efficiency of congestion control mechanisms.
  1. Analyze Congestion Control Metrics:
  • Throughput: Estimate the amount of data effectively distributed to the end.
  • Packet Loss: Count the number of packets dropped because of the congestion.
  • Queue Size: Monitor how the queue length changes over time, indicating congestion levels.
  • End-to-End Delay: Estimate the delay experienced by packets from origin to end.

Example AWK script to analyze packet loss:

awk ‘{if ($1 == “d” && $4 == “TCP”) drop_count++;}

END { print “Total dropped TCP packets:”, drop_count }’ out.tr

  • This script counts the number of dropped TCP packets that helps to estimate the effect of congestion on the network.

Example AWK script to measure throughput:

awk ‘{if ($1 == “r” && $4 == “TCP”) received_packets++; total_data += $6;}

END { print “Throughput:”, total_data/received_packets, “bytes per packet”; }’ out.tr

  • This script measures the average throughput by estimating the count of received packets and the amount of data transferred.
  1. Visualize Congestion Control in NAM:
  • We can use the NAM (Network Animator) to envision how traffic flows over the network and how congestion happens. Also NAM can display how various TCP variants react to congestion.

nam out.nam

  • In NAM, we can monitor the packet drops, queue build up, and throughput changes as various TCP variants attempt to control congestion.

In the above informations, we had explained regarding the Network Congestion Control, which was executed and simulated within NS2 using the brief methods. Also we will provide additional details on this topic in various tools. Our team is committed to delivering timely support to guarantee that your comparison is carried out seamlessly. For assistance with the implementation of Network Congestion Control in NS2, please reach out to the ns2project.com team. We are here to help, offering outstanding project ideas tailored to your research needs.