To simulate a Logical Topology in OMNeT++ has needs to design the logical connections among the nodes in a network that fluctuate from their physical connections. Since a physical topology denotes to the actual layout of devices and cables, a logical topology raises to how data flows among nodes that can be unalike from the physical arrangement.
In OMNeT++, we need to simulate numerous logical topologies over the same physical network structure. Logical topologies usually utilized to contain bus, star, ring, mesh, and hybrid topologies, among others. Send us all your research details to guide you with best simulation needs.
Here’s how you can simulate Logical Topology Projects in OMNeT++:
Steps to Simulate Logical Topology Projects in OMNeT++
- Understand Logical Topology
- Physical Topology: The actual arrangement of network devices.
- Logical Topology: The way data flows via the network. For instance, a network might be manually organized in a star (centralized), however logically the data might flow in a ring or mesh.
In OMNeT++, we need to design logical connections using different message-passing mechanisms, routing tables, and link configurations that fluctuate from the physical topology.
- Define the Physical and Logical Topologies
We can describe a physical topology that signify the actual arrangement of the nodes and then describe the logical topology via message passing and routing. For this instance, we will assume a physical star topology however replicate a logical ring topology.
- Define the Physical Topology in NED (Star Physical Topology)
The physical network will be configured as a star, in which all nodes are associated to a central switch. But, logically, we will make the data flow in a ring that will simulate in the message-passing behaviour.
Sample NED File (PhysicalStarTopology.ned)
network PhysicalStarTopology
{
submodules:
// Define the central switch that connects all nodes
switch: Switch {
@display(“p=300,100”);
}
// Define several nodes that are physically connected to the switch
node[5]: Node {
@display(“p=150,200; p=250,200; p=350,200; p=450,200; p=550,200”);
}
connections allowunconnected:
// Physically connect each node to the central switch
node[0].out++ –> switch.in++;
switch.out++ –> node[0].in++;
node[1].out++ –> switch.in++;
switch.out++ –> node[1].in++;
node[2].out++ –> switch.in++;
switch.out++ –> node[2].in++;
node[3].out++ –> switch.in++;
switch.out++ –> node[3].in++;
node[4].out++ –> switch.in++;
switch.out++ –> node[4].in++;
}
- Define the Node Behaviour for Logical Topology (Ring Logical Topology)
While the physical connections utilize a star, we will simulate a logical ring by controlling how messages flow among the nodes. The messages will follow a logical sequence from one node to the next, successfully forming a ring over the star physical topology.
Sample Node Module (Node.ned)
simple Node
{
parameters:
@display(“i=device/laptop”);
gates:
input in[];
output out[];
}
- Implement the Logical Ring Behavior (Node.cc)
In this step, we will implement a logical ring topology over the physical star. Each node will forward the message to the next logical node in the ring, while they are physically associated to the switch.
Sample Node Behavior (Node.cc)
#include <omnetpp.h>
using namespace omnetpp;
class Node : public cSimpleModule
{
private:
int nodeId;
int nextNodeId; // Logical next node in the ring
int totalNodes; // Total number of nodes in the logical topology
protected:
virtual void initialize() override;
virtual void handleMessage(cMessage *msg) override;
void forwardMessage(cMessage *msg); // Forward the message to the next logical node
};
Define_Module(Node);
void Node::initialize()
{
nodeId = getIndex(); // Assign the node’s index as its identifier
totalNodes = getParentModule()->par(“numNodes”);
nextNodeId = (nodeId + 1) % totalNodes; // Next node in the logical ring
// Only the first node initiates communication
if (nodeId == 0) {
cMessage *msg = new cMessage(“Start Message”);
scheduleAt(simTime() + 1.0, msg); // Initiate after 1 second
}
}
void Node::handleMessage(cMessage *msg)
{
EV << “Node ” << nodeId << ” received: ” << msg->getName() << “\n”;
// Forward the message to the next logical node in the ring
forwardMessage(msg);
}
void Node::forwardMessage(cMessage *msg)
{
// Forward the message to the next logical node in the ring
EV << “Node ” << nodeId << ” forwarding message to Node ” << nextNodeId << “\n”;
// Physically send the message through the switch
send(msg, “out”, 0);
}
Here’s what this code does:
- Node ID: Each node is allocated an ID based on its index in the simulation.
- Logical Ring: Each node forwards the message to the next logical node in the ring (calculated as nextNodeId).
- Message Passing: The message passes logically from node to node, even though they are physically associated via a switch.
- Simulate Logical Topology with Switch Forwarding
The switch will behave as an intermediary, simply forwarding messages among nodes, regardless of the logical connections. Here’s how we need to describe the switch behaviour.
Switch Behavior (Switch.cc)
#include <omnetpp.h>
using namespace omnetpp;
class Switch : public cSimpleModule
{
protected:
virtual void handleMessage(cMessage *msg) override;
};
Define_Module(Switch);
void Switch::handleMessage(cMessage *msg)
{
// The switch simply forwards the message to the intended destination
send(msg, “out”, 0); // Forward message to the appropriate output
}
- Run the Simulation
To execute the simulation, describe the number of nodes and set up simulation metrics in the omnetpp.ini file.
Sample OMNeT++ Configuration (omnetpp.ini)
network = PhysicalStarTopology
sim-time-limit = 10s
# Configure the number of nodes and gates
*.numNodes = 5
*.node[*].numGates = 1 # Each node has 1 connection to the switch
*.switch.numGates = 5 # Switch has 5 gates to connect to the 5 nodes
- Visualize and Analyse
- Message Flow: We will see that although the physical connections are in a star topology, the messages follow a logical ring pattern. The message initiate at Node 0, goes to Node 1, then Node 2, and so on, completing the logical ring.
- Logical vs Physical Topology: This replication illustrates how the logical topology (data flow) can differ from the physical topology (network layout). In this case, the physical star topology acts as logically as a ring topology.
- Enhancements to the Simulation
- Logical Bus Topology over Star
We need to replicate a logical bus topology by having each node broadcast the message to all other nodes through the switch, enabling any node to receive the broadcasted message.
void Node::broadcastMessage()
{
// Each node sends a broadcast message to all nodes via the switch
for (int i = 0; i < totalNodes; i++) {
if (i != nodeId) { // Avoid sending to itself
cMessage *msg = new cMessage(“Broadcast Message”);
send(msg, “out”, 0); // Send message to the switch for broadcasting
}
}
}
- Logical Mesh Topology over Star
We can simulate a mesh topology by enabling each node to transmit messages to any other node (not necessarily in a specific order) via the switch, related to fully connected logical topologies.
void Node::sendMessageToRandomPeer()
{
int targetPeer = intuniform(0, totalNodes – 1); // Randomly select a peer
if (targetPeer != nodeId) {
cMessage *msg = new cMessage(“Message to Peer”);
send(msg, “out”, 0); // Send message to the switch for forwarding
}
}
- Hybrid Logical Topologies
We can integrate different logical topologies over the same physical structure. For example, we could have a star topology in one part of the network and a ring topology in another part, with certain routing behaviour for each.
The given above is the fundamental approach that was illustrated with sample coding for Logical Topology project that were simulated across the OMNeT++ environment. We plan to deliver more information regarding this project in further manual.
