How to Implement MAC Protocol in NS2

To implement Medium Access Control (MAC) protocol in ns2, we have to configure how nodes in the network interact over a common medium. NS2 help different in-built MAC protocols like IEEE 802.11 (used in wireless networks) and used in wired networks. We can execute custom MAC protocols or alter the available ones by generating or adjusting MAC layers in TCL scripts of ns2 and C++ source files.

Use the given procedure for the implementation of MAC protocol using ns2:

Steps to Implement a MAC Protocol in NS2

  1. Install NS2

Make certain that you have installed and configured the ns2 on your computer.

  1. Use an Existing MAC Protocol

NS2 comes with a built-in 802.11 MAC protocol, which can be easily used in wireless simulations. Below is an example of how to configure a simulation using the 802.11 MAC protocol.

Example: Using the Built-in 802.11 MAC Protocol in NS2

# 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

}

# Set up the topography for the simulation area

set topo [new Topography]

$topo load_flatgrid 1000 1000

# Define the wireless channel

set chan [new Channel/WirelessChannel]

# Configure mobile nodes with the IEEE 802.11 MAC protocol

$ns node-config -adhocRouting DSDV \

-llType LL \

-macType Mac/802_11 \

-ifqType Queue/DropTail/PriQueue \

-ifqLen 50 \

-antType Antenna/OmniAntenna \

-propType Propagation/TwoRayGround \

-phyType Phy/WirelessPhy \

-channel $chan

# Create nodes

set node1 [$ns node]

set node2 [$ns node]

# Set node positions

$node1 set X_ 200

$node1 set Y_ 200

$node1 set Z_ 0

$node2 set X_ 800

$node2 set Y_ 800

$node2 set Z_ 0

# Create a duplex wireless link between the nodes

$ns duplex-link $node1 $node2 2Mb 10ms DropTail

# Define TCP traffic between node1 and node2

set tcp [new Agent/TCP]

set sink [new Agent/TCPSink]

$ns attach-agent $node1 $tcp

$ns attach-agent $node2 $sink

$ns connect $tcp $sink

# Create FTP traffic over TCP

set ftp [new Application/FTP]

$ftp attach-agent $tcp

$ftp start 1.0

$ftp stop 4.5

# Schedule simulation end

$ns at 5.0 “finish”

# Run the simulation

$ns run

  1. Explanation of the Script
  • 802.11 MAC Protocol: The MAC protocol for wireless communication is set using -macType Mac/802_11.
  • Nodes and Links: Two mobile nodes (node1 and node2) interact through a wireless channel using the 802.11 MAC protocol.
  • Traffic: FTP traffic is created over TCP to replicate packet transmission.

This script utilize the default MAC protocol (802.11) provided by NS2, which is often used in wireless network simulations. Yet, if you want to alter or execute a custom MAC protocol, you need to work with NS2’s C++ source files.

  1. Modify or Implement a Custom MAC Protocol

Execute or alter a MAC protocol by adjusting the C++ files in NS2 that state the MAC layer. This involves:

  1. Modifying existing MAC layer code: You can alter the activities of available MAC protocols by modifying their source code.
  2. Creating a new MAC protocol: You can state your custom MAC protocol by generating new classes and integrating them into NS2.

NS2 MAC protocol implementations are found in the mac directory in the NS2 source code. The 802.11 MAC protocol is established in the mac-802_11.cc and mac-802_11.h files.

Example: Custom MAC Protocol Implementation

Here’s how to generate or alter a custom MAC protocol by editing the mac-802_11.cc file or creating new MAC protocol files.

  1. Navigate to NS2 Source Code: Open the mac directory in your NS2 source code folder:

cd ns-2.xx/mac/

  1. Edit the MAC Protocol Files: If you’re modifying the 802.11 MAC, you can start by editing the mac-802_11.cc file.
  2. Define a Custom MAC Class:
    • You can configure your custom MAC class by generating new .cc and .h files (for example: mac-custom.cc and mac-custom.h).
    • Within the custom MAC class, state the activities for medium access control as well as managing collisions, retransmissions, and backoff mechanisms.

Example Custom MAC Class Skeleton (C++)

#include “mac.h”

#include “packet.h”

#include “timer-handler.h”

class MacCustom : public Mac {

public:

MacCustom();

void recv(Packet *p, Handler *h);

void send(Packet *p, Handler *h);

protected:

void handleCollision();

void backoff();

};

MacCustom::MacCustom() {

// Constructor initialization (e.g., timers, backoff values)

}

void MacCustom::recv(Packet *p, Handler *h) {

// Handle packet reception

if (collisionDetected()) {

handleCollision();

} else {

// Normal packet processing

}

}

void MacCustom::send(Packet *p, Handler *h) {

// Handle packet transmission with custom logic

if (isMediumBusy()) {

backoff();

} else {

// Transmit packet

}

}

void MacCustom::handleCollision() {

// Handle collision (e.g., drop packet, retransmit, etc.)

}

void MacCustom::backoff() {

// Implement custom backoff strategy

}

  1. Integrate Your Custom MAC into NS2:
    • Include the new MAC class to NS2’s Makefile so that it is compiled:
      • Open Makefile.in in the NS2 root directory.
      • Attach your new MAC protocol files (mac-custom.o) to the list of objects to be compiled.
  2. Recompile NS2: After adding your custom MAC protocol to the source code, recompile NS2:

./configure

make clean

make

  1. Use Your Custom MAC Protocol in TCL:
    • Now, you can use your custom MAC protocol in your TCL script by stating the new MAC type in the set up.

# Configure nodes to use the custom MAC protocol

$ns node-config -macType Mac/Custom

  1. Testing and Validation

After executing your custom MAC protocol:

  • Execute the simulation and gather trace files to validate that your MAC protocol is functions as expected.
  • You can alter your custom MAC protocol to establish mechanisms like:
    • Collision detection and avoidance.
    • Backoff algorithms.
    • Priority-based medium access.

At the end of this set up, you can now obtain the usage of ns2 in the implementation of the examples relevant to the MAC (Medium Access Control) protocol. We also provide the sample snippet in C++, authentication and customization of the network simulation.

If you want to implement the MAC Protocol using the NS2 tool, ns2project.com is the perfect resource for you. We provide the latest ideas and topics to help you out. You can find guidance on MAC layers in TCL scripts and C++ source files for your projects.