To simulate a Peer-to-Peer (P2P) Topology using OMNeT++ tool, which includes making a network in which nodes are communicate directly with each other without depending on a central server or a hierarchy. In a Peer-to-Peer network, every node (also known as a peer) serves as both a client and a server, meaning they can transmit and receive data.
Below is a step-by-step instruction to simulate a Peer-to-Peer Topology in OMNeT++:
Steps to Simulate Peer-to-Peer Topology Projects in OMNeT++
- Design the Peer-to-Peer Network Structure
In a Peer-to-Peer topology, each node (peer) is associated to other peers, and they exchange data directly. We can set up the P2P topology as:
- Fully Connected P2P: Every node is connected to every other node.
- Partially Connected P2P: Each node is associate to a subset of other nodes.
- Random P2P: Nodes are arbitrarily connected to other peers.
- Define the Network Structure (NED File)
For this instance, we will be made a Partially Connected P2P network in which each node is associated to a few random peers. The amount of connections can be modified based on the desired simulation configuration.
Sample NED File (P2PTopology.ned)
network P2PTopology
{
submodules:
// Define a set of peers (nodes) for the P2P network (e.g., 6 peers)
peer[6]: PeerNode {
@display(“p=100,100; p=200,150; p=300,200; p=400,250; p=500,300; p=600,350”);
}
connections allowunconnected:
// Define a partially connected P2P network
// Peer 0 connected to Peer 1 and Peer 2
peer[0].out++ –> peer[1].in++;
peer[1].out++ –> peer[0].in++;
peer[0].out++ –> peer[2].in++;
peer[2].out++ –> peer[0].in++;
// Peer 1 connected to Peer 3
peer[1].out++ –> peer[3].in++;
peer[3].out++ –> peer[1].in++;
// Peer 2 connected to Peer 4
peer[2].out++ –> peer[4].in++;
peer[4].out++ –> peer[2].in++;
// Peer 3 connected to Peer 5
peer[3].out++ –> peer[5].in++;
peer[5].out++ –> peer[3].in++;
// Peer 4 connected to Peer 5
peer[4].out++ –> peer[5].in++;
peer[5].out++ –> peer[4].in++;
}
In this structure:
- Six peers are partially connected to each other.
- Peers interchange messages directly with their connected peers.
- Define the Peer Node Module (NED File)
To each peer will have input and output gates to communicate with other peers. We will describe a PeerNode, which manages incoming and outgoing messages.
Sample PeerNode.ned (Node Structure)
simple PeerNode
{
parameters:
@display(“i=device/laptop”);
gates:
input in[];
output out[];
}
- Implement Peer Node Behavior (C++ Code)
Here, execute the behaviour of each peer. In a peer-to-peer system, nodes can transmit messages to their connected peers and also receive messages from them. Here’s how we can describe this performance.
Sample Peer Node Behavior (PeerNode.cc)
#include <omnetpp.h>
using namespace omnetpp;
class PeerNode : public cSimpleModule
{
private:
int peerId; // Unique identifier for each peer
protected:
virtual void initialize() override;
virtual void handleMessage(cMessage *msg) override;
void sendMessageToPeers(); // Function to send messages to connected peers
};
Define_Module(PeerNode);
void PeerNode::initialize()
{
peerId = getIndex(); // Assign the node’s index as its unique identifier
// Every peer starts by sending a message to its neighbors after a short delay
cMessage *msg = new cMessage(“Initial Message”);
scheduleAt(simTime() + uniform(1, 5), msg); // Random delay to simulate peer activity
}
void PeerNode::handleMessage(cMessage *msg)
{
EV << “Peer ” << peerId << ” received message: ” << msg->getName() << “\n”;
// After receiving a message, the peer forwards it to its connected peers
sendMessageToPeers();
delete msg; // Process and delete the incoming message
}
void PeerNode::sendMessageToPeers()
{
// Forward a message to all connected peers
for (int i = 0; i < gateSize(“out”); i++) {
cMessage *newMsg = new cMessage(“P2P Message”);
EV << “Peer ” << peerId << ” sending message to connected peer ” << i << “\n”;
send(newMsg, “out”, i); // Send to each connected peer
}
}
- Run the Simulation
To run the simulation, make an omnetpp.ini file to set up the simulation parameters.
Sample OMNeT++ Configuration (omnetpp.ini)
[General]
network = P2PTopology
sim-time-limit = 20s
# Each peer will have a different number of gates (connections)
*.peer[*].numGates = 2 # Default is 2 connections per peer, can be adjusted as needed
- Visualize and Analyze
- Message Flow: In this simulation, we can envision how messages are passed among the peers rely on their connections. The simulation will indicate the peers initiating communication with other peers, and the message flow will propagate via the network.
- Metrics: We can collect informations on parameters like message latency, hop count, and message propagation via the peer-to-peer network.
- Enhance the Simulation
Here are some ways to improve and prolong the peer-to-peer simulation:
- Randomized Peer Connections
We can randomize peer connections within the NED file or in the initialization phase to replicate dynamic peer-to-peer networks in which peers are connect to random subsets of other peers.
void PeerNode::initialize()
{
peerId = getIndex();
// Each peer connects to a random number of neighbors
int numConnections = intuniform(1, 3); // Randomly choose 1 to 3 connections
for (int i = 0; i < numConnections; i++) {
// Logic to connect this peer to random other peers
…
}
}
- Peer Failure Simulation
Replicate node failures in which specific peers stop reacting to messages after a particular period. It can useful in learning the robustness and fault tolerance of the peer-to-peer network.
void PeerNode::handleMessage(cMessage *msg)
{
if (uniform(0, 1) < 0.1) { // 10% chance of failure
EV << “Peer ” << peerId << ” failed to forward the message.\n”;
delete msg;
} else {
sendMessageToPeers(); // Normal message forwarding
}
}
- Multi-hop Communication
Execute multi-hop communication in which a message passes via numerous peers before attaining its destination. It can be mimicked by permitting the peers to forward messages they obtain to their own neighbours.
void PeerNode::handleMessage(cMessage *msg)
{
// Forward the message to other peers, but keep track of the message’s TTL (time-to-live)
int ttl = msg->par(“ttl”).intValue();
if (ttl > 0) {
cMessage *forwardedMsg = new cMessage(“Forwarded P2P Message”);
forwardedMsg->par(“ttl”) = ttl – 1; // Decrease TTL
sendMessageToPeers(forwardedMsg); // Forward the message
}
delete msg;
}
- File Sharing Simulation
Replicate a file-sharing system in which peers request and transfer files with other peers. We can be mimicked peer discovery, file searching, and file downloading via message passing.
void PeerNode::sendFileRequest()
{
cMessage *fileRequest = new cMessage(“File Request”);
send(fileRequest, “out”, randomGate()); // Send request to a random peer
}
- Dynamic Peer Addition/Removal
Replicate peers joining and exit the network dynamically to learn the behaviour of dynamic peer-to-peer networks.
- Use Case Example: BitTorrent-Like File Sharing
We can be used this peer-to-peer topology to replicate a BitTorrent-like file-sharing system, where:
- Peers search for certain files by querying other peers.
- Peers download parts of a file from numerous other peers.
- Peers can join or exit the network dynamically.
Throughout this manual, we shown detailed method with sample coding for Peer-to-Peer Topology projects, implemented and simulated with the help of simulation environment OMNeT++.
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