How to Implement Network Offloading in NS2

To implement the Network offloading in NS2 has needs to replication the transfer of data traffic from one network to another to diminish the load on the primary network and enhance overall performance and this is a common approach in modern mobile networks in which traffic is offloaded from cellular networks like 4G/5G to Wi-Fi networks or other infrastructure to handles congestion and enhance network resources.

In NS2, we can mimic network offloading by describing diverse network types like cellular and Wi-Fi, classifying offloading triggers such as congestion, low bandwidth, and switching traffic from one network to another.

Here is the procedure to implement the network offloading in ns2:

Key Concepts for Simulating Network Offloading in NS2:

  1. Multi-homed Nodes: Nodes that is associated to multiple networks like cellular and Wi-Fi.
  2. Offloading Triggers: Conditions like congestion, low bandwidth, or high latency that leads traffic to be offloaded.
  3. Offloading Mechanism: Traffic is retransmitted from one network like cellular to another such as Wi-Fi to minimize congestion.

Steps to Implement Network Offloading in NS2

  1. Define Multiple Networks: generate different kinds of networks like cellular and Wi-Fi.
  2. Implement Offloading Logic: Describe conditions in which traffic should be offloaded from one network to another.
  3. Switch Traffic: Once offloading conditions are met, switch the traffic from the congested network to the less loaded one.

Example: Simulating Network Offloading in NS2

This sample will demonstrates how to mimic traffic offloading among a cellular network and a Wi-Fi network. Traffic initially uses the cellular network, and upon identifying congestion, it is offloaded to the Wi-Fi network.

Step 1: Create a Multi-homed Node Connected to Both Networks

The node can be associated to both a cellular network (simulated with a higher delay) and a Wi-Fi network (lower delay), and traffic can be switched among the networks.

# Define the simulator object

set ns [new Simulator]

# Define trace and nam files for output

set tracefile [open out.tr w]

set namfile [open out.nam w]

$ns trace-all $tracefile

$ns namtrace-all $namfile

# Define a ‘finish’ procedure to end the simulation and visualize in NAM

proc finish {} {

global ns tracefile namfile

$ns flush-trace

close $tracefile

close $namfile

exec nam out.nam &

exit 0

}

# Define the wireless channel

set chan [new Channel/WirelessChannel]

# Create two separate network types: cellular and Wi-Fi

# Wi-Fi network will have lower delay, while cellular will have higher delay

# Create Wi-Fi network

set wifi_base [$ns node]

set wifi_node [$ns node]

# Create Cellular network

set cellular_base [$ns node]

set cellular_node [$ns node]

# Set node positions (not necessary for functionality but useful for NAM visualization)

$wifi_base set X_ 100; $wifi_base set Y_ 100; $wifi_base set Z_ 0

$wifi_node set X_ 200; $wifi_node set Y_ 100; $wifi_node set Z_ 0

$cellular_base set X_ 300; $cellular_base set Y_ 300; $cellular_base set Z_ 0

$cellular_node set X_ 400; $cellular_node set Y_ 300; $cellular_node set Z_ 0

# Define a duplex link for the Wi-Fi network with lower delay

$ns duplex-link $wifi_base $wifi_node 2Mb 5ms DropTail

# Define a duplex link for the cellular network with higher delay (to simulate slower cellular connection)

$ns duplex-link $cellular_base $cellular_node 2Mb 50ms DropTail

# Step 2: Define TCP traffic over the cellular network initially

set tcp [new Agent/TCP]

set sink [new Agent/TCPSink]

$ns attach-agent $cellular_node $tcp

$ns attach-agent $cellular_base $sink

$ns connect $tcp $sink

# Create FTP traffic over TCP to simulate data transmission

set ftp [new Application/FTP]

$ftp attach-agent $tcp

$ftp start 1.0  ;# Start FTP traffic at 1 second

$ftp stop 3.0   ;# Stop FTP traffic at 3 seconds

# Step 3: Offload the traffic to the Wi-Fi network based on congestion (e.g., after 2 seconds)

proc offload_traffic_to_wifi {} {

global ns wifi_node wifi_base tcp sink

# Detach the current agents from the cellular network

$ns detach-agent $cellular_node $tcp

$ns detach-agent $cellular_base $sink

# Reattach TCP traffic to the Wi-Fi network

set new_tcp [new Agent/TCP]

set new_sink [new Agent/TCPSink]

$ns attach-agent $wifi_node $new_tcp

$ns attach-agent $wifi_base $new_sink

# Connect the TCP agent to the new sink (Wi-Fi base)

$ns connect $new_tcp $new_sink

# Restart the FTP traffic over the Wi-Fi network

set new_ftp [new Application/FTP]

$new_ftp attach-agent $new_tcp

$new_ftp start 3.5

}

# Schedule the offloading after congestion (e.g., after 2 seconds)

$ns at 3.0 “offload_traffic_to_wifi”

# Schedule the end of the simulation

$ns at 6.0 “finish”

# Run the simulation

$ns run

  1. Explanation of the Script
  • Two Networks: Two different network types are generated, denotes a Wi-Fi network (with lower delay) and a cellular network (with higher delay). These networks denote the primary network (cellular) and the offloading network (Wi-Fi).
  • Initial Traffic on Cellular Network: Traffic is initially transferred over the cellular network from cellular_node to cellular_base.
  • Offloading Condition: After 3 seconds, the traffic is unloaded to the Wi-Fi network by detaching the agents from the cellular network and reattaching them to the Wi-Fi network.
  • Offloading Traffic: The traffic is switched from the cellular network to the Wi-Fi network by using the offload_traffic_to_wifi procedure.
  1. Run the Simulation

Save the script as network_offloading.tcl and executed it using:

ns network_offloading.tcl

This will create a trace file (out.tr) and a NAM file (out.nam). The trace file logs the packet transmissions, and the NAM files permits to envision the offloading process.

  1. Visualize the Network in NAM

To envision the simulation in NAM, use the following command:

nam out.nam

In the NAM visualization, we can observe:

  • Traffic being started sent over the cellular network.
  • After 3 seconds, the traffic is offloaded to the Wi-Fi network.
  1. Advanced Offloading Strategies
  • Dynamic Offloading Based on Network Conditions: Rather than offloading traffic after a fixed time, we can offload traffic enthusiastically according to network conditions such as congestion, low bandwidth, or high delay. For instance, if the cellular network experiences high delay or packet loss, we can offload traffic to the Wi-Fi network.

Example:

proc check_network_conditions_and_offload {delay_threshold} {

global ns cellular_node wifi_node

# Measure delay (or other network metrics)

set current_delay [expr rand() * 100]  ;# Simulate random delay for demonstration

if { $current_delay > $delay_threshold } {

puts “Offloading traffic due to high delay on cellular network”

offload_traffic_to_wifi

} else {

puts “No offloading needed. Current delay: $current_delay ms”

}

}

# Schedule the network condition check at regular intervals

$ns at 2.0 “check_network_conditions_and_offload 30”

$ns at 3.0 “check_network_conditions_and_offload 30”

  • Selective Offloading: We can unload only particular kinds of traffic like video streaming while keeping other traffic on the cellular network.
  • Multi-path Offloading: Rather than fully offloading traffic, we can allocate traffic across both the cellular and Wi-Fi networks to balance the load.

We demonstrate how the Network offloading will simulate the network scenario and how to execute and analyse the outcomes using the ns2. Additional specific details about how the Network offloading will perform in other simulation scenarios.

For assistance with the implementation of Network Offloading in the NS2 tool, contact  ns2project.com. We offer comprehensive guidance to ensure high-quality results and also specialize in cellular networks, including 4G and 5G, as well as Wi-Fi networks relevant to your project.