How to Implement Topology based Routing in OMNeT++

To implement topology-based routing in OMNeT++ has encompasses to generate the routing protocol that uses the network’s topology information to create the routing decisions. Topology-based routing protocols usually maintain the knowledge of the network’s layout, like the connections among the nodes, to regulate the best path for data transmission. Examples of topology-based routing protocols has involve Link State Routing (e.g., OSPF) and Distance Vector Routing (e.g., RIP). The below are the guide to implementing a basic topology-based routing protocol in OMNeT++, along with an example.

Steps to Implement Topology-Based Routing in OMNeT++

1. Install OMNeT++ and INET Framework:
   • Make certain that OMNeT++ and the INET framework are installed. The INET framework delivers the network models, components, and protocols that can be expanded for routing protocol design.
2. Define Network Topology:
   • Use a .ned file to define the network topology that contains nodes and their interconnections.
3. Design the Topology-Based Routing Algorithm:
   • Choose the type of topology-based routing algorithm we want to execute like  Link State, Distance Vector.
   • Execute the algorithm’s logic in a C++ class, where nodes exchange topology information and calculated the routes based on that information.
4. Implement the Routing Protocol in C++:
   • Generate a new C++ module in OMNeT++ that executes the topology-based routing logic.
   • The module should manage the tasks like to maintaining a routing table, updating it based on received topology information, and forwarding packets accordingly.
5. Integrate the Routing Protocol with Network Nodes:
   • Adjust the node modules to contain the topology-based routing protocol. This usually contains changing how nodes manages incoming and outgoing packets.
6. Simulation Configuration:
   • Setup the simulation in the .ini file. This contains to setting parameters such as routing update intervals, link costs, and node properties.
7. Run the Simulation and Analyse Results:
   • Implement the simulation and use OMNeT++’s tools to visualize and evaluate network behaviour, like routing table updates, packet flows, and performance metrics.

Example: Implementing a Simple Link State Routing Protocol

1. Define Network Topology in a .ned File

// TopologyNetwork.ned

package networkstructure;

import inet.node.ethernet.EtherSwitch;

import inet.node.inet.StandardHost;

network TopologyNetwork

{

submodules:

router1: StandardHost {

@display(“p=100,200”);

}

router2: StandardHost {

@display(“p=200,200”);

}

router3: StandardHost {

@display(“p=300,200”);

}

router4: StandardHost {

@display(“p=200,100”);

}

connections:

router1.ethg++ <–> Eth100m <–> router2.ethg++;

router2.ethg++ <–> Eth100m <–> router3.ethg++;

router2.ethg++ <–> Eth100m <–> router4.ethg++;

router3.ethg++ <–> Eth100m <–> router4.ethg++;

}

2. Implement the Link State Routing Protocol in C++

Generate a C++ class for the Link State Routing Protocol.

#include <omnetpp.h>

#include <map>

#include <vector>

#include <limits>

using namespace omnetpp;

class LinkStateRouting : public cSimpleModule

{

protected:

struct LinkState {

int node;

int cost;

};

struct RoutingTableEntry {

int nextHop;

int cost;

};

std::map<int, std::vector<LinkState>> topology;  // Map: Node -> List of Links

std::map<int, RoutingTableEntry> routingTable;   // Map: Destination -> Routing Table Entry

virtual void initialize() override;

virtual void handleMessage(cMessage *msg) override;

void updateTopology(int source, const std::vector<LinkState> &links);

void computeRoutingTable();

void forwardPacket(cPacket *packet);

public:

void sendLinkStateAdvertisements();

};

Define_Module(LinkStateRouting);

void LinkStateRouting::initialize()

{

// Initialize by sending link state advertisements to neighbors

sendLinkStateAdvertisements();

}

void LinkStateRouting::handleMessage(cMessage *msg)

{

if (cPacket *packet = dynamic_cast<cPacket *>(msg)) {

// Handle received packet (either a link state update or data packet)

if (strcmp(packet->getName(), “LinkStateUpdate”) == 0) {

// Process the received link state update

int source = packet->par(“source”).intValue();

std::vector<LinkState> links;

// Parse links from the packet

for (int i = 0; i < packet->par(“numLinks”).intValue(); i++) {

LinkState link = {packet->par(“linkNode” + std::to_string(i)).intValue(),

packet->par(“linkCost” + std::to_string(i)).intValue()};

links.push_back(link);

}

updateTopology(source, links);

computeRoutingTable();

} else {

forwardPacket(packet);

}

} else {

delete msg;  // Delete any other message

}

}

void LinkStateRouting::updateTopology(int source, const std::vector<LinkState> &links)

{

// Update the topology information for the given source node

topology[source] = links;

}

void LinkStateRouting::computeRoutingTable()

{

// Implement Dijkstra’s algorithm to compute the shortest paths

std::map<int, int> distances;

std::map<int, int> previous;

std::vector<int> nodes;

// Initialize distances to infinity and previous nodes to undefined

for (const auto &nodeLinks : topology) {

distances[nodeLinks.first] = std::numeric_limits<int>::max();

previous[nodeLinks.first] = -1;

nodes.push_back(nodeLinks.first);

}

// Assume the current node is the source

int source = getParentModule()->getId();

distances[source] = 0;

while (!nodes.empty()) {

// Select the node with the smallest distance

int minDist = std::numeric_limits<int>::max();

int u = -1;

for (int node : nodes) {

if (distances[node] < minDist) {

minDist = distances[node];

u = node;

}

}

// Remove u from the nodes list

nodes.erase(std::remove(nodes.begin(), nodes.end(), u), nodes.end());

// Update distances for neighbors of u

if (topology.find(u) != topology.end()) {

for (const auto &link : topology[u]) {

int v = link.node;

int alt = distances[u] + link.cost;

if (alt < distances[v]) {

distances[v] = alt;

previous[v] = u;

}

}

}

}

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

for (const auto &node : distances) {

int destination = node.first;

int cost = node.second;

if (destination != source) {

// Determine the next hop by backtracking from the destination

int nextHop = destination;

while (previous[nextHop] != source && previous[nextHop] != -1) {

nextHop = previous[nextHop];

}

routingTable[destination] = {nextHop, cost};

}

}

}

void LinkStateRouting::forwardPacket(cPacket *packet)

{

int destination = packet->par(“destination”).intValue();

if (routingTable.find(destination) != routingTable.end()) {

int nextHop = routingTable[destination].nextHop;

send(packet, “out”, nextHop);

} else {

delete packet;  // Drop the packet if no route is found

}

}

void LinkStateRouting::sendLinkStateAdvertisements()

{

// Send link state advertisements to all neighbors

int source = getParentModule()->getId();

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

cGate *outGate = gate(“out”, i);

int neighborId = outGate->getNextGate()->getOwnerModule()->getId();

int cost = outGate->getChannel()->par(“cost”).intValue();

// Create and send a Link State Update packet

cPacket *lsUpdate = new cPacket(“LinkStateUpdate”);

lsUpdate->addPar(“source”) = source;

lsUpdate->addPar(“numLinks”) = 1;

lsUpdate->addPar(“linkNode0”) = neighborId;

lsUpdate->addPar(“linkCost0”) = cost;

 

send(lsUpdate, “out”, i);

}

// Reschedule the next advertisement

scheduleAt(simTime() + 5, new cMessage(“sendLinkStateAdvertisements”));

}

3. Modify Node Modules to Use Link State Routing

Expand the node definition to involves the LinkStateRouting module.

simple LSNode

{

gates:

input radioIn;

output radioOut;

submodules:

radioModule: Radio {

@display(“p=50,50”);

}

routing: LinkStateRouting {

@display(“p=100,100”);

}

connections:

radioIn –> routing.in;

routing.out –> radioOut;

}

4. Configure the Simulation in .ini File

network = networkstructure.TopologyNetwork

sim-time-limit = 100s

# Routing configuration

**.router*.routing.updateInterval = 5s  # Time interval for sending link state advertisements

# Link cost configuration

**.router*.ethg*.channel.cost = 10  # Example link cost

Running the Simulation

• Compile the C++ code and execute the simulation in OMNeT++.
• Monitor how the Link State Routing protocol builds and updates the routing tables and how packets are forwarded via the network based on the computed paths.

Through the manual, we had got knowledge about how to execute and analyse the outcomes for topology based routing in OMNeT++ tool that provides the best path for transmission among the nodes.  We will provide the further details on how the topology-based routing performs in other simulation. The developers at omnet-manual.com are here to support you throughout your implementation of Topology-based Routing in the OMNeT++ tool. Stay connected with us to discover more about this subject and we also help you with comparison analysis.