How to Implement L3 Protocol in NS2

To implement the Layer 3 (L3) protocols in NS2, we have to generating or replicating network-layer protocols that manage routing and packet forwarding according to the IP addresses. It contains routing protocols like OSPF (Open Shortest Path First), RIP (Routing Information Protocol), and custom IP-based routing mechanisms.

We provided the implementation steps of L3 protocol using NS2:

Step-by-Step Implementation:

Step 1: Define the Protocol Requirements

Configure which L3 protocol you want to execute. This could be:

  • Routing Protocols: OSPF, RIP, or a custom routing algorithm.
  • IP Forwarding: Simple IP packet forwarding in terms of routing tables.
  • Address Resolution: Mechanisms like ARP (though technically Layer 2/3).

Step 2: Set Up NS2

Make certain that you have to install the NS2 on your computer. Authenticate the installation by execution a basic simulation. NS2 already has some basic L3 routing protocols (like AODV, DSDV) built-in, however for more modern protocols like OSPF, you would need to execute them or replicate their actions.

Step 3: Implement the L3 Protocol in C++

  1. Create the L3 Protocol Agent Class

Here’s a basic structure for executing a simple IP-based routing protocol. The sample offered below outlines the skeleton for a basic distance-vector routing protocol similar to RIP.

#include <agent.h>

#include <packet.h>

#include <trace.h>

#include <address.h>

#include <map>

class L3RoutingAgent : public Agent {

public:

L3RoutingAgent();

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

void sendRoutingUpdate();

void handleRoutingUpdate(Packet* p);

void forwardPacket(Packet* p);

protected:

std::map<int, int> routingTable_; // Destination -> Next Hop

std::map<int, int> distanceTable_; // Destination -> Distance

};

// Constructor

L3RoutingAgent::L3RoutingAgent() : Agent(PT_UDP) {

// Initialization code here

}

// Packet reception

void L3RoutingAgent::recv(Packet* p, Handler* h) {

hdr_ip* iph = hdr_ip::access(p);

int dest = iph->dst();

if (routingTable_.find(dest) != routingTable_.end()) {

forwardPacket(p);

} else {

handleRoutingUpdate(p);

}

}

// Send routing updates to neighbors

void L3RoutingAgent::sendRoutingUpdate() {

// Create and send routing update packet to neighbors

Packet* p = allocpkt();

hdr_ip* iph = hdr_ip::access(p);

// Fill in routing update data

send(p, 0);

}

// Handle incoming routing updates

void L3RoutingAgent::handleRoutingUpdate(Packet* p) {

// Process routing update and update routing tables

hdr_ip* iph = hdr_ip::access(p);

int src = iph->src();

// Update routing and distance tables based on received data

routingTable_[src] = src;  // Example: direct route

distanceTable_[src] = 1;   // Example: hop count

}

// Forward packet to the next hop

void L3RoutingAgent::forwardPacket(Packet* p) {

hdr_ip* iph = hdr_ip::access(p);

int nextHop = routingTable_[iph->dst()];

// Forward the packet to the next hop

send(p, 0);

}

  1. Integrate the Protocol into NS2
  1. Modify the Makefile: Include the new L3RoutingAgent class to the NS2 Makefile so that it gets compiled with the remains of the simulator.
  2. Recompile NS2:

make clean

make

Step 4: Create a Tcl Script to Simulate the L3 Protocol

Configure a Tcl script to recreate a network using your custom protocol, after the compilation is done.

Example Tcl Script:

# Create a simulator object

set ns [new Simulator]

# Define the topology

set val(chan)   Channel/WiredChannel

set val(ll)     LL

set val(ifq)    Queue/DropTail/PriQueue

set val(ifqlen) 50

set val(stop)   50.0

# Initialize the topology object

set topo [new Topography]

$topo load_flatgrid 500 500

# Create nodes representing routers

set router1 [$ns node]

set router2 [$ns node]

set router3 [$ns node]

# Establish links between routers

$ns duplex-link $router1 $router2 10Mb 10ms DropTail

$ns duplex-link $router2 $router3 10Mb 10ms DropTail

# Attach L3 routing agents to routers

set l3agent1 [new Agent/L3RoutingAgent]

set l3agent2 [new Agent/L3RoutingAgent]

set l3agent3 [new Agent/L3RoutingAgent]

$ns attach-agent $router1 $l3agent1

$ns attach-agent $router2 $l3agent2

$ns attach-agent $router3 $l3agent3

# Set up traffic sources and sinks

set src [new Agent/TCP]

set sink [new Agent/TCPSink]

$ns attach-agent $router1 $src

$ns attach-agent $router3 $sink

$ns connect $src $sink

# Start the simulation

$ns at 0.0 “$src start”

$ns at 0.5 “$l3agent1 sendRoutingUpdate”

$ns at 0.5 “$l3agent2 sendRoutingUpdate”

$ns at 0.5 “$l3agent3 sendRoutingUpdate”

$ns at $val(stop) “stop”

$ns at $val(stop) “exit 0”

proc stop {} {

global ns

$ns flush-trace

exit 0

}

# Run the simulation

$ns run

Step 5: Run the Simulation

  1. Save the Tcl script (l3_simulation.tcl).
  2. Open a terminal and direct to the directory where you stored the Tcl script.
  3. Execute the simulation using the following command:

ns l3_simulation.tcl

Step 6: Analyze the Results

  • Use trace files and the network animator (NAM) to evaluate the performance of your L3 protocol based on route convergence time, packet delivery ratio, and end-to-end delay.
  • Investigate how well your protocol manages several network topologies and traffic patterns.

Additional Considerations

  • Advanced Routing Protocols: For more modern L3 protocols like OSPF, consider accomplishing more detailed mechanisms like link-state advertisements, Dijkstra’s algorithm for shortest-path routing, and multi-area routing.
  • Scalability: Replicate the larger networks with more nodes and more advanced traffic scenarios to assess the scalability.
  • Integration with Existing Protocols: You can also incorporate the custom L3 protocol with available protocols in NS2 to configure hybrid or more classy routing mechanisms.

This guide will focus on generating a simplified version of a Layer 3 protocol and how to implement, execute them using ns2 simulation tool including samples. You can inquire about any added information of layer 3 protocol, we will send them.

The implementation of the L3 Protocol in NS2, along with relevant topic support, is facilitated by ns2project.com, consult us for optimal project outcomes.