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How to Implement Data Link Layer in OMNeT++

To implement the Data Link Layer (DLL) in OMNeT++, we have to create a module that handles the data link features like framing, error detection, flow control, and possibly Medium Access Control (MAC). The Data Link Layer is accountable for node-to-node data transfer and operates amongst the physical layer and the network layer.

Here’s an entire implementation procedure of DLL:

Step-by-Step Implementation:

Step 1: Set Up OMNeT++ and INET Framework

  1. Install OMNeT++:
    • Make sure to install the  OMNeT++ on your system.
  2. Install the INET Framework:
    • Install the INET Framework, which offers multiple networking protocols and models, including existing data link and MAC layer models.

Step 2: Create a New OMNeT++ Project

  1. Create the Project:
    • Open OMNeT++ and create a new OMNeT++ project via File > New > OMNeT++ Project.
    • Name it (e.g., DataLinkLayerSimulation) and set up the project directory.
  2. Set Up Project Dependencies:
    • Make certain that the project references the INET Framework by right-clicking on the project in the Project Explorer, navigating to Properties > Project References, and checking the INET project.

Step 3: Define the Network Topology

  1. Create a NED File:
    • State the network topology using the NED language. This topology contains nodes that interact via the custom Data Link Layer.

Example:

network DataLinkLayerNetwork

{

parameters:

int numNodes = default(2); // Number of nodes in the network

submodules:

node[numNodes]: CustomNode {

@display(“i=device/laptop”);

}

connections allowunconnected:

node[0].linkLayer++ <–> node[1].linkLayer++;

}

  1. Configure Network Parameters:
    • Simulate a realistic network environment by set up necessary link parameters like bandwidth, delay, and packet loss.

Step 4: Implement the Custom Data Link Layer

  1. Create the Data Link Layer Module in NED

Example (in NED):

module CustomDataLinkLayer

{

parameters:

@display(“i=block/link”);

gates:

input upperLayerIn;  // From network layer (e.g., IP)

output upperLayerOut; // To network layer (e.g., IP)

input lowerLayerIn;  // From physical layer (e.g., Ethernet)

output lowerLayerOut; // To physical layer (e.g., Ethernet)

}

  1. Implement the Data Link Layer in C++

Here’s a basic structure for implementing a custom Data Link Layer in C++:

#include “inet/common/INETDefs.h”

#include “inet/common/packet/Packet.h”

#include “inet/linklayer/contract/ILinkLayer.h”

#include “inet/linklayer/common/MACAddress.h”

#include “inet/networklayer/contract/IInterfaceTable.h”

#include “inet/networklayer/common/L3Address.h”

#include “inet/networklayer/ipv4/IPv4InterfaceData.h”

#include “inet/networklayer/common/InterfaceTable.h”

#include “inet/linklayer/common/Ieee802Ctrl.h”

class CustomDataLinkLayer : public cSimpleModule, public inet::ILinkLayer

{

protected:

inet::MACAddress myMACAddress;

inet::InterfaceEntry *interfaceEntry;

inet::InterfaceTable *interfaceTable;

virtual void initialize(int stage) override;

virtual void handleMessage(cMessage *msg) override;

// Data Link Layer functionalities

void processUpperLayerPacket(Packet *packet);

void processLowerLayerPacket(Packet *packet);

void addMACHeader(Packet *packet);

void checkCRC(Packet *packet);

void handleCollisions(Packet *packet);

};

Define_Module(CustomDataLinkLayer);

void CustomDataLinkLayer::initialize(int stage) {

if (stage == inet::INITSTAGE_LOCAL) {

interfaceTable = getModuleFromPar<inet::InterfaceTable>(par(“interfaceTableModule”), this);

interfaceEntry = new inet::InterfaceEntry(this);

interfaceEntry->setMACAddress(myMACAddress);

interfaceEntry->setInterfaceName(“customLinkLayer”);

// Set up interface attributes (e.g., MTU, MAC address)

interfaceEntry->setMtu(1500);

interfaceEntry->setMacAddress(myMACAddress);

interfaceTable->addInterface(interfaceEntry);

}

}

void CustomDataLinkLayer::handleMessage(cMessage *msg) {

Packet *packet = check_and_cast<Packet *>(msg);

if (msg->arrivedOn(“upperLayerIn”)) {

processUpperLayerPacket(packet);

} else {

processLowerLayerPacket(packet);

}

}

void CustomDataLinkLayer::processUpperLayerPacket(Packet *packet) {

// Handle packet coming from the network layer

addMACHeader(packet);

send(packet, “lowerLayerOut”);

}

void CustomDataLinkLayer::processLowerLayerPacket(Packet *packet) {

// Handle packet received from the physical layer

checkCRC(packet);

send(packet, “upperLayerOut”);

}

void CustomDataLinkLayer::addMACHeader(Packet *packet) {

// Add MAC header to the packet

auto macHeader = makeShared<inet::Ieee802Ctrl>();

macHeader->setDest(inet::MACAddress::BROADCAST_ADDRESS);

macHeader->setSrc(myMACAddress);

packet->insertAtFront(macHeader);

}

void CustomDataLinkLayer::checkCRC(Packet *packet) {

// Implement CRC checking

// If CRC is invalid, drop the packet

bool crcValid = true; // Placeholder for CRC checking logic

if (!crcValid) {

delete packet;

return;

}

}

void CustomDataLinkLayer::handleCollisions(Packet *packet) {

// Handle packet collisions if necessary (e.g., for CSMA/CD)

// This function would contain logic for collision detection and resolution

}

Step 5: Integrate the Custom Data Link Layer into a Node

You need to incorporate the custom Data Link Layer into a node. For instance, you can create a CustomNode module that has the Data Link Layer together with the Network and Physical Layers.

Example (in NED):

module CustomNode

{

submodules:

linkLayer: CustomDataLinkLayer {

@display(“p=100,100;i=block/link”);

}

networkLayer: Ipv4NetworkLayer {

@display(“p=200,100;i=block/network”);

}

physicalLayer: PhysicalLayer {

@display(“p=300,100;i=block/phy”);

}

connections allowunconnected:

linkLayer.upperLayerOut –> networkLayer.lowerLayerIn;

networkLayer.lowerLayerOut –> linkLayer.upperLayerIn;

linkLayer.lowerLayerOut –> physicalLayer.upperLayerIn;

physicalLayer.upperLayerOut –> linkLayer.lowerLayerIn;

}

Step 6: Configure the Simulation

  1. Set Up the Simulation in omnetpp.ini:
    • State the simulation parameters like the network to use, simulation time, and custom Data Link Layer behavior.

Example:

network = DataLinkLayerNetwork

sim-time-limit = 100s

**.scalar-recording = true

**.vector-recording = true

  1. Compile and Run the Simulation:
    • Make sure, everything is properly executed and compiled. Run the simulation using OMNeT++’s IDE or command line.

Step 7: Analyze the Results

  1. Monitor Data Link Layer Behavior:
    • Witness how packets are processed at the Data Link Layer, including framing, CRC checking, and MAC address handling.
  2. Evaluate Performance:
    • Evaluate key performance metrics like packet delivery ratio, throughput, and error rates.
    • Scalars and Vectors: Use OMNeT++ tools to record and analyze scalar and vector data includes sum of frames transmitted, received, and dropped.

Step 8: Optimize and Extend the Data Link Layer

  1. Address Any Issues:
    • If the simulation reveals any issues (e.g., incorrect MAC header handling, packet loss), fine-tune the Data Link Layer logic or network configuration as needed.
  2. Extend the Data Link Layer:
    • Execute the additional Data link layer features like flow control, error correction mechanisms, or more advanced MAC protocols (e.g., CSMA/CD, CSMA/CA).

This procedure will walk you through the whole installation and implementation process of Data link layer in the OMNeT++ environment. We will also offer the extra information on data link layer or their framework execution for further references be in touch with us for best project performance results. If you want to execute Data link layer in the OMNeT++ tool then be in touch with us.

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