How to Implement Network Traffic Offloading in NS2

To implement the Network traffic offloading in NS2 has series of steps to follow that contain to transfer the traffic from one network (usually cellular, like LTE or 5G) to another like Wi-Fi to balance the load and enhance the network performance. Traffic offloading is a idea in modern wireless networks to diminish the congestion in cellular networks, that enhance the user experience, and handles the network resources efficiently. This is usually used in scenarios in which the user devices are associated to both cellular and Wi-Fi networks and can effortlessly switch among them.

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To execute network traffic offloading in NS2 that can mimic a scenario in which the users are interconnected to both cellular (e.g., LTE) and Wi-Fi networks, and the traffic is offloaded to Wi-Fi when available. Here’s how to set it up:

Steps to Implement Network Traffic Offloading in NS2

  1. Set up NS2 Environment

If NS2 is not already installed, we can install it as follows:

wget https://sourceforge.net/projects/nsnam/files/latest/download -O ns-allinone-2.35.tar.gz

tar -xzvf ns-allinone-2.35.tar.gz

cd ns-allinone-2.35

./install

Make sure that NS2 is working properly by running a simple simulation.

  1. Understand Traffic Offloading Concept

Traffic offloading involves:

  • Primary network: Typically a cellular network (e.g., LTE or 5G).
  • Secondary network: A Wi-Fi network that can manage the offloaded traffic.
  • Decision point: A point at which traffic is offloaded from the primary network to the secondary network, according to the criteria such as congestion, signal strength, or bandwidth availability.

In NS2, we can mimic this by describing a topology with both cellular (LTE or 5G) and Wi-Fi networks, then dynamically switching traffic from cellular to Wi-Fi based on conditions.

  1. Design Network Topology

In this scenario, we will generate a basic network in which users are interconnected to both cellular and Wi-Fi networks. Traffic will be enthusiastically offloaded to Wi-Fi when available or when the cellular network becomes congested.

3.1 Create Nodes for Cellular and Wi-Fi Networks

# Create a simulator object

set ns [new Simulator]

# Open trace file for visualization

set nf [open out.nam w]

$ns namtrace-all $nf

# Create Base Stations and Access Points

set lte_bs [$ns node]    ;# LTE Base Station

set wifi_ap [$ns node]   ;# Wi-Fi Access Point

#Create User Devices

set ue1 [$ns node]       ;# User Device 1 (connected to LTE and Wi-Fi)

set ue2 [$ns node]       ;# User Device 2 (connected to LTE and Wi-Fi)

# Create Core Network

set core [$ns node]      ;# Core network

# Define Links (Cellular and Wi-Fi)

# Cellular Network (LTE)

$ns duplex-link $ue1 $lte_bs 10Mb 20ms DropTail   ;# UE1 to LTE Base Station

$ns duplex-link $ue2 $lte_bs 10Mb 20ms DropTail   ;# UE2 to LTE Base Station

# Wi-Fi Network

$ns duplex-link $ue1 $wifi_ap 100Mb 5ms DropTail  ;# UE1 to Wi-Fi AP

$ns duplex-link $ue2 $wifi_ap 100Mb 5ms DropTail  ;# UE2 to Wi-Fi AP

# Connect LTE Base Station and Wi-Fi Access Point to Core Network

$ns duplex-link $lte_bs $core 1Gb 10ms DropTail

$ns duplex-link $wifi_ap $core 1Gb 5ms DropTail

This generates two user devices (UE1 and UE2) associated to both an LTE Base Station and a Wi-Fi Access Point. Both networks are intetconnected to the core network.

  1. Simulate Traffic for Each User Device

We can emulate various traffic patterns for the user devices. Initially, traffic will flow across the LTE network, and later, traffic will be offloaded to the Wi-Fi network when it’s available.

4.1 Create Traffic Agents for LTE Network

Generate traffic for the user devices using UDP or TCP agents.

# Traffic over LTE (Initial Traffic)

set udp_lte1 [new Agent/UDP]         ;# UDP agent for UE1 (LTE)

$ns attach-agent $ue1 $udp_lte1

set sink_lte1 [new Agent/Null]       ;# Sink for LTE traffic

$ns attach-agent $lte_bs $sink_lte1

$ns connect $udp_lte1 $sink_lte1

# Create a CBR traffic for UE1 over LTE

set cbr_lte1 [new Application/Traffic/CBR]

$cbr_lte1 attach-agent $udp_lte1

$cbr_lte1 set packetSize_ 1000       ;# Packet size for LTE traffic

$cbr_lte1 set rate_ 2Mb              ;# Data rate for LTE traffic

# Start LTE traffic at 1.0 seconds

$ns at 1.0 “$cbr_lte1 start”

# Similar setup for UE2

set udp_lte2 [new Agent/UDP]         ;# UDP agent for UE2 (LTE)

$ns attach-agent $ue2 $udp_lte2

set sink_lte2 [new Agent/Null]       ;# Sink for LTE traffic

$ns attach-agent $lte_bs $sink_lte2

$ns connect $udp_lte2 $sink_lte2

# Create a CBR traffic for UE2 over LTE

set cbr_lte2 [new Application/Traffic/CBR]

$cbr_lte2 attach-agent $udp_lte2

$cbr_lte2 set packetSize_ 1000       ;# Packet size for LTE traffic

$cbr_lte2 set rate_ 2Mb              ;# Data rate for LTE traffic

# Start LTE traffic at 1.0 seconds

$ns at 1.0 “$cbr_lte2 start”

In this step, both user devices send traffic via the LTE network with a constant data rate of 2 Mbps.

  1. Implement Traffic Offloading to Wi-Fi

Traffic offloading can be emulated by dynamically switching traffic from the LTE network to the Wi-Fi network at a certain time or based on a network condition such as congestion or available bandwidth.

5.1 Offload Traffic to Wi-Fi

At a certain time (e.g., 5 seconds), the traffic from the LTE network will be offloaded to the Wi-Fi network.

# Traffic Offload to Wi-Fi (Dynamic Switching)

# At 5.0 seconds, switch UE1 traffic to Wi-Fi

set udp_wifi1 [new Agent/UDP]

$ns attach-agent $ue1 $udp_wifi1

set sink_wifi1 [new Agent/Null]

$ns attach-agent $wifi_ap $sink_wifi1

$ns connect $udp_wifi1 $sink_wifi1

# Create a CBR traffic for UE1 over Wi-Fi

set cbr_wifi1 [new Application/Traffic/CBR]

$cbr_wifi1 attach-agent $udp_wifi1

$cbr_wifi1 set packetSize_ 1000       ;# Packet size for Wi-Fi traffic

$cbr_wifi1 set rate_ 10Mb             ;# Higher data rate for Wi-Fi

# Offload traffic at time 5.0

$ns at 5.0 “$cbr_wifi1 start”

# Similarly offload UE2 traffic to Wi-Fi at time 5.5

set udp_wifi2 [new Agent/UDP]

$ns attach-agent $ue2 $udp_wifi2

set sink_wifi2 [new Agent/Null]

$ns attach-agent $wifi_ap $sink_wifi2

$ns connect $udp_wifi2 $sink_wifi2

# Create CBR traffic for UE2 over Wi-Fi

set cbr_wifi2 [new Application/Traffic/CBR]

$cbr_wifi2 attach-agent $udp_wifi2

$cbr_wifi2 set packetSize_ 1000       ;# Packet size for Wi-Fi traffic

$cbr_wifi2 set rate_ 10Mb             ;# Higher data rate for Wi-Fi

# Offload traffic at time 5.5

$ns at 5.5 “$cbr_wifi2 start”

In this setup:

  • UE1 offloads its traffic to the Wi-Fi network at 5.0 seconds.
  • UE2 offloads its traffic to the Wi-Fi network at 5.5 seconds.

After traffic is offloaded, the data rate for both users’ increases to 10 Mbps that signifies the higher capacity of the Wi-Fi network.

  1. Enable Trace Files and Visualization in NAM

We can enable trace files to capture the behaviour of the simulation and envision it in NAM (Network Animator).

6.1 Enable Trace Files:

# Enable trace file generation

set tracefile [open “out.tr” w]

$ns trace-all $tracefile

6.2 Run and Visualize the Simulation:

Execute the simulation and view it in NAM:

ns your_script.tcl

nam out.nam

In NAM, we can discern the traffic initially flowing across the LTE network, then being offloaded to the Wi-Fi network as per the offload schedule.

  1. End the Simulation

Describe when to end the simulation.

# End the simulation after 10 seconds

$ns at 10.0 “finish”

proc finish {} {

global ns nf

$ns flush-trace

close $nf

exit 0

}

$ns run

  1. Analyse the Results

Once the simulation is complete, we can evaluate the trace file to gather metrics such as:

  • Throughput: How much data was transmitted before and after offloading.
  • Latency: The delay before and after offloading.
  • Packet loss: If any packets were dropped during the offload process.

Tools such as AWK or Python scripts can be used to parse the trace file and extract the parameters.

In the end of the simulation, we should have some knowledge about how the network Traffic Offloading will perform dynamically from one network to another network in the scenarios like WiFi or manage the network congestion that were implemented by using ns2 tool. We will elaborate the further helpful information about the network traffic offloading.