How to Implement Network Mobility Management in NS2

To implement the Network mobility handoff within NS2 has requires to encompass, simulating the movement of mobile nodes among various network segments such as between various Access Points or Base Stations and managing the handoff of continuing connections. It is frequently used to replicate the situation in which the mobile nodes are alters its point of attachment as they transfer like in cellular networks or wireless LANs. We give the protocol on how we can execute the network mobility handoff in NS2:

Key Concepts:

  1. Mobile Nodes (MN): These nodes that move among the various points of attachment.
  2. Access Points (APs) or Base Stations (BSs): Set the nodes are delivering network access to the mobile nodes.
  3. Handoff: The procedure of transmitting an active connection from one AP or BS to another as the mobile node that transfers.

Steps to Implement Network Mobility Handoff in NS2

  1. Install NS2

Make sure that NS2 is installed on the computer and we can download NS2 from the NS2 webpage.

  1. Create a Basic TCL Script for Mobility and Handoff

To replicate the handoff, we will describe several access points or base stations, a mobile node, and a mobility model which transfers the mobile node among various APs. The handoff that happens while the mobile node transfer from the coverage area of the one AP to another.

Example: Simulating Network Mobility and Handoff between Access Points

# Define a 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

}

# Create two Access Points (AP1 and AP2)

set AP1 [$ns node]

set AP2 [$ns node]

# Create a mobile node (MN) that moves between AP1 and AP2

set MN [$ns node]

# Set the topography object to define the simulation area

set topo [new Topography]

$topo load_flatgrid 1000 1000

# Create a duplex link between each AP and the mobile node

$ns duplex-link $AP1 $MN 11Mb 10ms DropTail

$ns duplex-link $AP2 $MN 11Mb 10ms DropTail

# Define TCP traffic from AP1 to MN

set tcp [new Agent/TCP]

set sink [new Agent/TCPSink]

$ns attach-agent $AP1 $tcp

$ns attach-agent $MN $sink

$ns connect $tcp $sink

# Create FTP traffic over TCP

set ftp [new Application/FTP]

$ftp attach-agent $tcp

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

$ftp stop 4.5    ;# Stop FTP traffic at 4.5 seconds

# Set up mobility for the mobile node

$MN set X_ 100  ;# Initially near AP1

$MN set Y_ 100

$MN set Z_ 0

# Move the mobile node from AP1 to AP2’s coverage area

$ns at 2.0 “$MN set X_ 800; $MN set Y_ 800”  ;# Move MN toward AP2 at 2 seconds

# Simulate handoff by re-attaching traffic to AP2 after movement

proc handoff {} {

global ns MN tcp sink AP2

# Detach the current TCP agent from AP1 and reconnect to AP2

$ns detach-agent $MN $sink

$ns detach-agent $AP2 $tcp

# Create new sink at MN and reconnect to AP2 for handoff

set new_sink [new Agent/TCPSink]

$ns attach-agent $MN $new_sink

$ns connect $tcp $new_sink

puts “Handoff complete: Reconnected to AP2”

}

# Schedule handoff at 2.5 seconds

$ns at 2.5 “handoff”

# Schedule the end of the simulation

$ns at 5.0 “finish”

# Run the simulation

$ns run

  1. Explanation of the Script
  • Access Points (AP1 and AP2): These two access points like AP1 and AP2 are made to signify the fixed network setup. It can be connected to the mobile node (MN) through the wireless links.
  • Mobile Node (MN): The mobile node transfer among the coverage areas of AP1 and AP2. It begins near AP1 and moves to the  AP2.
  • Traffic Setup: TCP traffic (through FTP) is produced from the access point AP1 to the mobile node (MN). It denotes a continuing the connection which required to be handed off while the node transfers to the coverage of the access point AP2.
  • Mobility: The mobile node is primarily close to the access point AP1 and transfers to the AP2 at time 2.0 seconds.
  • Handoff Procedure: The handoff is replicated by removing the TCP connection from the access point AP1 and reattaching it to AP2 while the mobile node attains the AP2’s coverage area.
  1. Run the Simulation

We can save the script as mobility_handoff.tcl then run it using:

ns mobility_handoff.tcl

It will produce a trace file (out.tr) and a NAM file (out.nam) and we can open the NAM file to envision the mobility and handoff.

  1. Visualize the Handoff in NAM

We can use the NAM file to envision the node movement and handoff:

nam out.nam

We should monitor the mobile node moving among the AP1 and AP2, including the handoff happening around 2.5 seconds.

  1. Customize the Handoff Criteria

The specimen above executes the handoff rely on the node’s position. We can improve the emulation by considering other handoff criteria, like:

  • Signal Strength: Handoff happens according to the Received Signal Strength Indicator (RSSI) from the access points.
  • Load Balancing: Handoff occurs if one AP is overloaded then the other has more capacity.
  • Quality of Service (QoS): Handoff rely on the maintaining a less QoS level.

Given below is how we may change the handoff logic according to signal strength (RSSI):

proc handoff_based_on_rssi {} {

global ns MN tcp sink AP1 AP2

# Simulate signal strength for AP1 and AP2

set rssi_ap1 [expr 1000 – [$MN set X_]]   ;# Signal strength decreases as MN moves away from AP1

set rssi_ap2 [expr [$MN set X_] – 500]    ;# Signal strength increases as MN moves closer to AP2

if { $rssi_ap1 < $rssi_ap2 } {

puts “Handoff triggered based on RSSI: Connecting to AP2”

# Detach TCP from AP1 and reconnect to AP2

$ns detach-agent $MN $sink

$ns detach-agent $AP2 $tcp

set new_sink [new Agent/TCPSink]

$ns attach-agent $MN $new_sink

$ns connect $tcp $new_sink

}

}

# Check RSSI at regular intervals for handoff

$ns at 1.5 “handoff_based_on_rssi”

$ns at 2.0 “handoff_based_on_rssi”

$ns at 2.5 “handoff_based_on_rssi”

This logic verifies the RSSI values at intervals and activates a handoff while the mobile node is closer to the AP2.

  1. Analysing the Trace File

When the simulation runs, we can assess the trace file (out.tr) to monitor the packet transmissions before and after the handoff. Now, we can look for:

  • Throughput: Calculates the throughput before and after the handoff.
  • Packet Loss: Verify if any packets were dropped while the handoff.
  • Delay: Estimate any increase in delay because of the handoff process.

In conclusion, we were provide the details on how to setup basic Tcl script, and how to visualize and analyse the trace file for  implementing the Network Mobility Management in the Network simulation called ns2 including examples with codes. Additional details will be offered regarding this topic. We work on cellular networks or wireless LANs based on your projects , get best implementation assistance from us.