(Layered Architecture) Learn communication in layered environment OMNet

Computer Networks Lab · OMNeT++ · The LNMIIT

Lab Assignment 7 — Layered Network Architecture

Network Layer Data Link Layer PDU Encapsulation OMNeT++ Simulation

Objective

Learn communication in a layered environment — create a 2-node network where each node has a Network Layer and Data Link Layer, and both layers communicate via Protocol Data Units (PDUs).

Task 1 — Network Design

Task 1.1

Create a network named Comp_network with two nodes, each having two layers: Network Layer and Data Link Layer. Both nodes connected with a 100ms delay channel.

Task 1.2

Each layer communicates through PDUs — Network Layer uses Nl_pkt, Data Link Layer uses Dll_pkt.

Task 1.3

Communication starts from Network Layer of Source Node → passed down to DLL → transferred to Destination Node via the channel.

Solution Files Overview

NED

Nl_node.ned

Network Layer module

NED

Dll_node.ned

Data Link Layer module

NED

Comp.ned

Compound node module

NED

Comp_network.ned

Full network definition

MSG

Nl_pkt.msg

Network layer PDU

MSG

Dll_pkt.msg

Data link layer PDU

C++

nl_node.h / .cpp

NL logic

C++

dll_node.h / .cpp

DLL logic

INI

omnetpp.ini

Simulation config

Bugs Fixed — Summary

✓ memory leak fixed ✓ decapsulate() return used ✓ 200ms time unit fixed ✓ off-by-one fixed ✓ unused variables removed

File	Bug / Issue	Fix Applied
nl_node.h	cGate* in — never used	Removed from header
nl_node.cpp	in = gate("nl_in") — dead code	Removed
nl_node.cpp	Self-message never deleted (memory leak)	delete msg added first
nl_node.cpp	remaining_packets-- inline — off-by-one	Set id first, then decrement
nl_node.cpp	scheduleAt(+200) — 200 seconds not ms	Changed to 0.2 (200ms)
dll_node.cpp	decapsulate() return discarded	Captured as cPacket* inner
dll_node.cpp	Sent outer Dll_pkt instead of inner Nl_pkt	send(inner, out_n)
dll_node.cpp	Outer Dll_pkt never deleted	delete message added
Comp_network.ned	source & dest declared but unused	parameters block removed
omnetpp.ini	**.dest = 2 — no module reads it	Removed

Source Code

NED Nl_node.ned

simple Nl_node
{
    parameters:
        int nl_id;
        int remaining_packets;
        int source;

    gates:
        input  nl_in;
        output nl_out;
}

NED Dll_node.ned

simple Dll_node
{
    parameters:
        int dll_id;

    gates:
        input  dlln_in;
        output dlln_out;
        input  dllc_in;
        output dllc_out;
}

NED Comp.ned

module Comp
{
    parameters:
        int c_id;

    gates:
        input  c_in;
        output c_out;

    submodules:
        Nl:  Nl_node  { nl_id  = c_id; }
        Dll: Dll_node { dll_id = c_id; }

    connections:
        Nl.nl_in   <-- Dll.dlln_out;
        Nl.nl_out  --> Dll.dlln_in;
        Dll.dllc_in  <-- c_in;
        Dll.dllc_out --> c_out;
}

NED Comp_network.ned

network Comp_network
{
    // unused parameters (source, dest) removed

    submodules:
        C1: Comp { c_id = 1; }
        C2: Comp { c_id = 2; }

    connections:
        C1.c_in  <-- { delay = 100ms; } <-- C2.c_out;
        C1.c_out --> { delay = 100ms; } --> C2.c_in;
}

MSG nl_pkt.msg & dll_pkt.msg

// ── nl_pkt.msg ──
packet Nl_pkt {
    int Nl_pkt_id;
    int Nl_pkt_type;
}

// ── dll_pkt.msg ──
packet Dll_pkt {
    int Dll_pkt_id;
    int Dll_pkt_type;
}

C++ nl_node.h

#ifndef __NLDLL_NL_NODE_H_
#define __NLDLL_NL_NODE_H_

#include <omnetpp.h>
#include <nl_pkt_m.h>

using namespace omnetpp;

class Nl_node : public cSimpleModule
{
  protected:
    int    id;
    int    remaining_packets;
    int    source;
    cGate* out;   // cGate* in removed (unused)
    virtual void initialize();
    virtual void handleMessage(cMessage *msg);
};

#endif

C++ dll_node.h

#ifndef __NLDLL_DLL_NODE_H_
#define __NLDLL_DLL_NODE_H_

#include <omnetpp.h>
#include <dll_pkt_m.h>
#include <nl_pkt_m.h>

using namespace omnetpp;

class Dll_node : public cSimpleModule
{
  protected:
    int    id;
    cGate* in_n;
    cGate* out_n;
    cGate* in_c;
    cGate* out_c;
    virtual void initialize();
    virtual void handleMessage(cMessage *msg);
};

#endif

C++ nl_node.cpp

#include "nl_node.h"

Define_Module(Nl_node);

void Nl_node::initialize()
{
    id                = par("nl_id");
    remaining_packets = par("remaining_packets");
    source            = par("source");
    // in = gate("nl_in") removed — cGate* in was unused
    out = gate("nl_out");

    if (id == source) {
        cMessage* event = new cMessage();
        scheduleAt(0, event);
    }
}

void Nl_node::handleMessage(cMessage *msg)
{
    if (msg->isSelfMessage()) {
        delete msg;   // memory leak fixed

        if (remaining_packets == 0)
            return;

        Nl_pkt* data = new Nl_pkt();
        data->setNl_pkt_id(remaining_packets);  // set first
        remaining_packets--;                     // then decrement
        data->setNl_pkt_type(1);
        send(data, out);

        cMessage* event = new cMessage();
        scheduleAt(simTime() + 0.2, event);   // 200ms = 0.2s
    }
    else {
        delete msg;
    }
}

C++ dll_node.cpp

#include "dll_node.h"

Define_Module(Dll_node);

void Dll_node::initialize()
{
    id    = par("dll_id");
    in_n  = gate("dlln_in");
    out_n = gate("dlln_out");
    in_c  = gate("dllc_in");
    out_c = gate("dllc_out");
}

void Dll_node::handleMessage(cMessage *msg)
{
    if (msg->getArrivalGate() == in_n)
    {
        Nl_pkt* data_to_encapsulate = check_and_cast<Nl_pkt*>(msg);
        Dll_pkt* data = new Dll_pkt();
        data->encapsulate(data_to_encapsulate);
        data->setDll_pkt_type(1);
        send(data, out_c);
    }
    else if (msg->getArrivalGate() == in_c)
    {
        Dll_pkt* message = check_and_cast<Dll_pkt*>(msg);
        if (message->getDll_pkt_type() == 1)
        {
            cPacket* inner = message->decapsulate(); // return value captured
            send(inner, out_n);                       // NL pkt forwarded

            Dll_pkt* ack = new Dll_pkt();
            ack->setDll_pkt_type(0);
            send(ack, out_c);

            delete message;   // outer DLL packet deleted
        }
        else {
            delete msg;
        }
    }
}

INI omnetpp.ini

[General]
network = Comp_network
**.remaining_packets = 10
**.source = 1
# **.dest = 2 removed — no module uses it