How to Implement link state routing in OMNeT++

To implement the Link State Routing in OMNeT++ has needs to contain making a simulation model where the routers change link state information to generate a whole map of the network. It allowing each router to independently evaluate the shortest paths to all ends using Dijkstra’s algorithm. This process is the basis for protocols such as OSPF (Open Shortest Path First).

Below is the step-by-step notes to implement Link State Routing in OMNeT++:

Step-by-Step Implementations:

Step 1: Set Up OMNeT++ and INET Framework

1. Install OMNeT++:
   • Make sure OMNeT++ is installed on the system. We can download it from the OMNeT++
2. Install the INET Framework:
   • The INET Framework offers a rich library of network models and protocols, containing some basic routing protocols that can extend. We can download INET from the INET GitHub repository.

Step 2: Create a New OMNeT++ Project

1. Create the Project:
   • Open OMNeT++ and construct a new OMNeT++ project through File > New > OMNeT++ Project.
   • Name the project like LinkStateRouting and set up the project directory.
2. Set Up Project Dependencies:
   • Make sure the project references the INET Framework by right-clicking on the project in the Project Explorer, navigating to Properties > Project References, and verifying the INET project.

Step 3: Define the Network Topology

1. Create a NED File:
   • Define the network topology using the NED language. This topology should contain routers and links where the routers will run the Link State Routing protocol.

Example:

network LinkStateNetwork

{

submodules:

router1: Router;

router2: Router;

router3: Router;

router4: Router;

connections:

router1.ethg++ <–> Eth10Mbps <–> router2.ethg++;

router2.ethg++ <–> Eth10Mbps <–> router3.ethg++;

router3.ethg++ <–> Eth10Mbps <–> router4.ethg++;

router4.ethg++ <–> Eth10Mbps <–> router1.ethg++;

}

1. Configure Network Parameters:
   • Set up the essential link parameters like bandwidth, delay, and packet loss to simulate a realistic network setting.

Step 4: Implement the Link State Routing Protocol

1. Define the Protocol Modules:
   • Generate a new module in NED for the Link State Routing protocol. This module will be part of the router’s network layer.

Example (in NED):

simple LinkStateRouting

{

parameters:

@display(“i=block/network2”);

gates:

inout lowerLayerIn;

inout lowerLayerOut;

}

1. Implement the Link State Algorithm in C++:
   • Implement the Link State Routing logic in a C++ class. It will include maintaining a link state database, flooding link state advertisements (LSAs), and computing the shortest paths using Dijkstra’s algorithm.

Example (C++ implementation):

#include <map>

#include <set>

#include “inet/common/INETDefs.h”

#include “inet/networklayer/ipv4/IPv4RoutingTable.h”

class LinkStateRouting : public cSimpleModule

{

private:

struct LinkState {

int cost;

std::string neighbor;

};

std::map<std::string, std::map<std::string, LinkState>> linkStateDatabase;  // Node -> (Neighbor -> LinkState)

std::map<std::string, int> routingTable;  // Destination -> Cost

std::string nodeId;  // Unique identifier for this router

protected:

virtual void initialize() override;

virtual void handleMessage(cMessage *msg) override;

void floodLinkState();

void processLinkState(cMessage *msg);

void calculateShortestPaths();

};

Define_Module(LinkStateRouting);

void LinkStateRouting::initialize() {

// Initialize the link state database with direct neighbors

nodeId = par(“nodeId”).stringValue();  // Assume each router has a unique nodeId parameter

for (int i = 0; i < gateSize(“lowerLayerOut”); i++) {

std::string neighbor = std::to_string(i + 1);

linkStateDatabase[nodeId][neighbor] = {1, neighbor};  // Cost to direct neighbors is 1

}

// Flood initial link state to neighbors

floodLinkState();

}

void LinkStateRouting::handleMessage(cMessage *msg) {

if (msg->arrivedOn(“lowerLayerIn”)) {

processLinkState(msg);

}

}

void LinkStateRouting::floodLinkState() {

// Send link state information to all neighbors

for (int i = 0; i < gateSize(“lowerLayerOut”); i++) {

cMessage *lsa = new cMessage(“LinkStateAdvertisement”);

// Package the link state information into the message

// Example: Add the link state entries to the message’s control info

for (auto &entry : linkStateDatabase[nodeId]) {

// Add each entry to the LSA message

// You may need a custom control info or message subclass

}

send(lsa, “lowerLayerOut”, i);

}

}

void LinkStateRouting::processLinkState(cMessage *msg) {

// Extract the link state information from the received message

// Update the link state database based on the received data

std::string neighbor = “some_neigh”;  // Extracted from msg

int cost = 1;  // Extracted from msg

for (auto &entry : linkStateDatabase[neighbor]) {

linkStateDatabase[entry.first][neighbor] = {cost, neighbor};

}

// Recalculate the shortest paths

calculateShortestPaths();

// Optionally, flood the updated link state if necessary

floodLinkState();

delete msg;

}

void LinkStateRouting::calculateShortestPaths() {

// Implement Dijkstra’s algorithm to calculate shortest paths based on the link state database

std::set<std::string> visited;

std::map<std::string, int> distances;  // Node -> Cost

for (const auto &entry : linkStateDatabase) {

distances[entry.first] = INT_MAX;

}

distances[nodeId] = 0;

while (!visited.empty()) {

std::string minNode;

int minDistance = INT_MAX;

for (const auto &entry : distances) {

if (visited.find(entry.first) == visited.end() && entry.second < minDistance) {

minDistance = entry.second;

minNode = entry.first;

}

}

visited.insert(minNode);

for (const auto &neighbor : linkStateDatabase[minNode]) {

int newDistance = minDistance + neighbor.second.cost;

if (newDistance < distances[neighbor.first]) {

distances[neighbor.first] = newDistance;

}

}

}

// Update the routing table based on the shortest paths found

routingTable = distances;

}

1. • Link State Database: Each router sustains a database of the network’s topology, with the cost of each link to its neighbours.
   • Flooding LSAs: To inform others of the state of their links the routers periodically flood the network with LSAs.
   • Shortest Path Calculation: To compute the shortest paths from the router to all other nodes in the network by using Dijkstra’s algorithm.
2. Integrate with the INET Framework:
   • Make sure the Link State Routing module interacts correctly with other layers in the protocol stack, especially the IP layer. We need to interface with the IPv4RoutingTable module to handle routes in the INET framework.

Step 5: Set Up the Simulation

1. Configure the Simulation in omnetpp.ini:

• Set up the simulation parameters, like traffic patterns, simulation time, and network settings.

Example:

[General]

network = LinkStateNetwork

sim-time-limit = 100s

# Enable scalar and vector recording for analysis

**.scalar-recording = true

**.vector-recording = true

# Application traffic configuration (if needed)

*.router1.numApps = 1

*.router1.app[0].typename = “UdpBasicApp”

*.router1.app[0].destAddress = “router4”

*.router1.app[0].destPort = 5000

*.router1.app[0].messageLength = 1024B

*.router1.app[0].sendInterval = uniform(1s, 2s)

1. Traffic Configuration:
   • Set up application-level traffic among the nodes to make network activity, which will trigger the exchange of link state information.

Step 6: Run the Simulation

1. Compile the Project:
   • Make sure everything is correctly implemented and compiled.
2. Run Simulations:
   • Perform the simulations using OMNeT++’s IDE or command line. Observe the behaviour of the routing protocol, particularly how it converges to a stable state and adapts to changes in the network.

Step 7: Analyze the Results

1. Monitor Convergence Time:
   • For the routing tables to measure the time it takes in all routers to stabilize that is converge to a consistent state.
2. Evaluate Protocol Performance:
   • Analyse key performance metrics like network utilization, update overhead, and route optimality.
   • Scalars and Vectors: To record and analyse scalar and vector data by using OMNeT++ tools. This can contain tracking the number of routing updates, the total number of hops, and the time taken to reach ends.
3. Check for Issues:
   • Check for issues like routing loops or instability, which are common concerns in dynamic networks.

Step 8: Refine and Optimize the Protocol

1. Address Any Bugs or Inefficiencies:
   • If the protocol exhibits problems like routing loops or slow convergence, consider applying improvements like faster LSA propagation or added efficient path recalculation.
2. Optimize for Performance:
   • Adjust parameters like update intervals or damping mechanisms to increase performance under several network conditions.
3. Re-Test:
   • Run the simulation again with the optimized protocol to prove improvements.

In this paper, we define network topology, implement link state algorithms in C++, and integrate with the INET framework to execute the Link State Routing in OMNeT++. We will give valid data about LSR in other tools as per requirements.

Stay connected with us for the simulation results on link state routing using the OMNeT++ tool in your projects. We will share the latest project ideas and provide support for executing them in this area.