To simulate a Point-to-Multipoint Topology using OMNeT++ that contains configuring a network in which a single source (central node) communicates with several destination nodes (clients or leaf nodes). This type of topology is generally used in broadcasting, wireless communications, and telecommunications networks in which a single sender sends data to numerous receivers.
We will guide you through the simulation approach on how we can simulate a Point-to-Multipoint Topology in OMNeT++:
Steps to Simulate Point to Multipoint Topology Projects in OMNeT++
- Define the Network Structure (NED File)
In a Point-to-Multipoint topology, one node operates as the central point (source node), and it transmits messages to multiple other nodes (destination nodes). The NED file describes this structure.
Sample NED File (PointToMultipoint.ned)
network PointToMultipoint
{
submodules:
// Define the central node (the source or root)
source: Node {
@display(“p=300,100”); // Position at the top
}
// Define multiple destination nodes
destination[4]: Node {
@display(“p=100,200; p=200,200; p=400,200; p=500,200”);
}
connections allowunconnected:
// Connect the source node to each destination node
source.out++ –> destination[0].in++;
source.out++ –> destination[1].in++;
source.out++ –> destination[2].in++;
source.out++ –> destination[3].in++;
}
- Create Node Module (Node.ned)
To each node will be required an input and output gate to communicate with its neighbours. The Node.ned file describes these gates for each node (source and destination).
Sample Node Module (Node.ned)
simple Node
{
parameters:
@display(“i=device/laptop”); // Icon to represent the node
gates:
input in[]; // Input gate (to receive data)
output out[]; // Output gate (to send data)
}
- Implement Node Behavior (Node.cc)
In the Point-to-Multipoint topology, the source node transmits messages to several destination nodes. Each destination node will receive the message and process it. Here’s how we can execute this in C++:
Sample Node Behavior (Node.cc)
#include <omnetpp.h>
using namespace omnetpp;
class Node : public cSimpleModule
{
private:
bool isSource; // To check if the node is the source
protected:
virtual void initialize() override;
virtual void handleMessage(cMessage *msg) override;
void sendMessageToDestinations(); // Function to send messages to all destinations
};
Define_Module(Node);
void Node::initialize()
{
// Determine if this node is the source node based on its name
isSource = (strcmp(getName(), “source”) == 0);
if (isSource) {
// If the node is the source, schedule sending a message to the destination nodes
cMessage *msg = new cMessage(“Message from Source”);
scheduleAt(simTime() + 1.0, msg); // Send after 1 second
}
}
void Node::handleMessage(cMessage *msg)
{
if (isSource) {
// The source node sends a message to all connected destinations
sendMessageToDestinations();
delete msg; // Delete the original message after sending
} else {
// Destination nodes receive and process the message
EV << “Node ” << getName() << ” received: ” << msg->getName() << “\n”;
delete msg; // After processing, the message is deleted
}
}
void Node::sendMessageToDestinations()
{
// Send the message to all destination nodes
for (int i = 0; i < gateSize(“out”); i++) {
cMessage *msg = new cMessage(“Broadcast Message”);
EV << “Source sending message to destination node ” << i << “\n”;
send(msg, “out”, i); // Send to each destination node
}
}
- Run the Simulation
To run the simulation, describe the network parameters and simulation behaviour within the omnetpp.ini configuration file. This configuration file identifies how the simulation should perform and how long it should run.
Sample OMNeT++ Configuration (omnetpp.ini)
[General]
network = PointToMultipoint
sim-time-limit = 10s
# Node-specific configurations
*.source.numGates = 4 # The source node has 4 output gates to connect to destinations
*.destination[*].numGates = 1 # Each destination has 1 input gate
- Visualize and Analyze
- Message Flow: In this simulation, we should monitor the source node transmitting messages to all destination nodes concurrently, or one after the other based on the execution.
- Performance Metrics: We can be calculated the delay in message delivery from the source to the destination nodes. It can be helpful in applications such as broadcasting or multicasting in wireless networks.
- Enhance the Simulation
Here are a few ways to improve and extend the simulation:
- Bi-directional Communication
We can insert bi-directional communication in which the destination nodes are react to the source node. This would include changing the Node::handleMessage() function so as to destination nodes can transmit messages back to the source.
if (!isSource) {
// Destination nodes receive and process the message, then respond to the source
EV << “Node ” << getName() << ” received: ” << msg->getName() << “\n”;
cMessage *response = new cMessage(“Response from Destination”);
send(response, “out”, 0); // Send response back to the source node
delete msg;
}
- Traffic Load Simulation
We can replicate distinct traffic patterns by differing the frequency and size of the messages transmitted by the source node. For instance, we can transmit large bursts of traffic in a short period or mimic constant communication among the source and destinations.
- Multicast Group Simulation
We can replicate multicast groups by transmitting messages to only a subset of the destination nodes rather than broadcasting to all. Alter the sendMessageToDestinations() function to randomly choose which nodes are receive the message.
- Failure Scenarios
Replicate failures in the destination nodes in which specific nodes do not respond or cannot receive messages, permitting to monitor how this influences the overall communication in the network.
void Node::handleMessage(cMessage *msg)
{
if (!isSource && uniform(0, 1) < 0.1) { // 10% chance of failure
EV << “Node ” << getName() << ” failed to process the message.\n”;
delete msg;
} else {
// Process the message normally
…
}
}
- Use Case Example: Wireless Base Station and Clients
In a wireless network, a base station (source) communicates with numerous clients (destination nodes). This simulation can be utilized to model the communication behaviour among the base station and its clients. Here, the base station broadcasts data to the clients, and clients may respond or simply receive the data.
In this module, we indicated from how to define the network structure to how we can enhance and analyse the results regarding Point to Multipoint Topology projects through the above procedure using OMNeT++ analysis tool. If you know more about this projects, we will be presented it too.
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