How to Implement MAC protocol in OMNeT++
To implement a Medium Access Control (MAC) protocol in OMNeT++ has needs includes making a custom protocol that commands how network nodes access the communication medium, particularly in wireless networks where several nodes distribute the same channel. This protocol handles coordinates access, collisions, and make sure effective use of the network resources.
The following is a procedure to implementing a basic MAC protocol in OMNeT++ using the INET framework:
Step-by-Step Implementations:
- Set Up OMNeT++ and INET Framework:
- Install OMNeT++: Make sure that OMNeT++ is installed and configured on the system.
- Install INET Framework: Download and install the INET framework, which offers models for network protocols, with the MAC layer.
- Define the Network Topology:
Make a network topology where numerous nodes use the custom MAC protocol to communicate. This topology will contain nodes and possibly a central access point or router.
Example NED File (CustomMACNetwork.ned):
package mynetwork;
import inet.node.inet.StandardHost;
import inet.node.inet.Router;
network CustomMACNetwork
{
submodules:
nodeA: StandardHost {
@display(“p=100,200”);
wlan[0].typename = “CustomMac”;
}
nodeB: StandardHost {
@display(“p=300,200”);
wlan[0].typename = “CustomMac”;
}
nodeC: StandardHost {
@display(“p=200,300”);
wlan[0].typename = “CustomMac”;
}
router: Router {
@display(“p=200,100”);
}
connections allowunconnected:
nodeA.wlan[0] <–> wlan[0] <–> router.wlan[0];
nodeB.wlan[0] <–> wlan[0] <–> router.wlan[0];
nodeC.wlan[0] <–> wlan[0] <–> router.wlan[0];
}
In this example:
- nodeA, nodeB, nodeC: Denote the network nodes using the custom MAC protocol.
- router: Performances as a central router joining the nodes.
- Create a Custom MAC Protocol Module:
We want to make a new module that implements the MAC protocol. It includes describing the MAC protocol in C++ and incorporating it into the OMNeT++ simulation setting.
Example: Custom MAC Protocol (CustomMac.ned)
package mynetwork;
import inet.linklayer.contract.IMacProtocol;
simple CustomMac extends IMacProtocol
{
gates:
input upperLayerIn;
output upperLayerOut;
input lowerLayerIn;
output lowerLayerOut;
}
CustomMac.cc (Basic Implementation)
#include “CustomMac.h”
#include “inet/common/INETDefs.h”
#include “inet/linklayer/common/MacAddress.h”
#include “inet/linklayer/base/MacProtocolBase.h”
Define_Module(CustomMac);
void CustomMac::initialize(int stage) {
MacProtocolBase::initialize(stage);
if (stage == INITSTAGE_LOCAL) {
// Initialize your MAC protocol parameters here
txRate = par(“txRate”);
slotTime = par(“slotTime”);
EV << “Custom MAC initialized with txRate: ” << txRate << “, slotTime: ” << slotTime << endl;
}
}
void CustomMac::handleUpperPacket(cPacket *msg) {
// Handle packets from the upper layer (e.g., network layer)
EV << “Received packet from upper layer: ” << msg->getName() << endl;
sendDown(msg);
}
void CustomMac::handleLowerPacket(cPacket *msg) {
// Handle packets from the lower layer (e.g., physical layer)
EV << “Received packet from lower layer: ” << msg->getName() << endl;
sendUp(msg);
}
void CustomMac::handleSelfMessage(cMessage *msg) {
// Handle self-messages (e.g., timers for retransmissions)
EV << “Handling self-message: ” << msg->getName() << endl;
// Implement your MAC logic here
}
In this example:
- handleUpperPacket: Handles packets arriving from the upper layer that is network layer.
- handleLowerPacket: Controls packets arriving from the lower layer like physical layer.
- handleSelfMessage: Manages internal events, like timers or retransmission scheduling.
- Configure the Simulation:
We require to configure the simulation in the omnetpp.ini file to use the custom MAC protocol.
Example Configuration in omnetpp.ini:
[General]
network = CustomMACNetwork
**.nodeA.wlan[0].mac.typename = “CustomMac”
**.nodeB.wlan[0].mac.typename = “CustomMac”
**.nodeC.wlan[0].mac.typename = “CustomMac”
- Implement MAC Protocol Logic:
We can now implement the particular MAC protocol logic, like:
- Carrier Sense Multiple Access (CSMA): Before transmitting, Nodes sense the channel.
- Time Division Multiple Access (TDMA): Nodes are assigned particular time slots for transmission.
- Token Passing: A token is passed around nodes, and only the node keeping the token can transmit.
Example: Simple CSMA Implementation
void CustomMac::handleUpperPacket(cPacket *msg) {
if (channelIsIdle()) {
sendDown(msg); // Send packet if the channel is idle
} else {
scheduleAt(simTime() + slotTime, msg); // Wait for a slot time and retry
EV << “Channel busy, deferring transmission\n”;
}
}
bool CustomMac::channelIsIdle() {
// Implement logic to check if the channel is idle
return true; // Placeholder, always returns true in this example
}
In this simple CSMA execution, the node verify if the channel is idle before sending the packet. If the channel is busy, it waits for a slot time before redoing.
- Simulate and Monitor the MAC Protocol:
Run the simulation and observe the behaviour of the custom MAC protocol. We can analyse metrics like latency, collision rates, and throughput.
Example: Monitoring Throughput and Collision Rates
[General]
network = CustomMACNetwork
**.nodeA.wlan[0].mac.throughput.recordScalar = true
**.nodeA.wlan[0].mac.collisions.recordScalar = true
**.nodeB.wlan[0].mac.throughput.recordScalar = true
**.nodeB.wlan[0].mac.collisions.recordScalar = true
**.nodeC.wlan[0].mac.throughput.recordScalar = true
**.nodeC.wlan[0].mac.collisions.recordScalar = true
This configuration records the throughput and collision rates for each node, which we can analyse after the simulation.
- Extend the MAC Protocol:
We can extend the basic MAC protocol by adding aspects like:
- Retransmission mechanisms: Perform a backoff algorithm to manage collisions.
- Energy efficiency: Add power-saving modes to decrease energy consumption.
- QoS support: Prioritize traffic based on the kind of service or application.
Example: Backoff Algorithm
void CustomMac::handleCollision() {
// Implement a backoff algorithm when a collision is detected
int backoffTime = uniform(0, maxBackoffSlots) * slotTime;
scheduleAt(simTime() + backoffTime, msg);
EV << “Collision detected, backing off for ” << backoffTime << ” seconds\n”;
}
- Document and Report Findings:
After completing the simulations, record the MAC protocol’s performance, with metrics like throughput, collision rates, and delay. This will support in knowing the strengths and restrictions of the protocol.
We demonstrated intricate steps and methods for establishing MAC protocol using the OMNeT++tool. Contact us if you need any further assistance. Share with us your parameter details, and we will provide you with the best results of its network performance.