How to Implement Hierarchical Star Topology in ns3

To implement a ring-mesh hybrid topology in ns3, we need to create a network in which the nodes are connected to both ring topology and mesh topology. Here we can use point-to-point link for Ring Topology and CSMA links for Mesh Topology.

The below given steps will guide on how to implement topology in ns3.

Step-by-step to implement the topology in ns3

Step 1: Install ns3

Make sure ns3 is installed on the system

Step 2: Create a New Simulation Script

Create a new C++ script for the simulation.

Step 3: Include Necessary Headers

In the script, include the necessary ns3 headers:

#include “ns3/core-module.h”

#include “ns3/network-module.h”

#include “ns3/internet-module.h”

#include “ns3/point-to-point-module.h”

#include “ns3/csma-module.h”

#include “ns3/mobility-module.h”

#include “ns3/applications-module.h”

Step 4: Set Up the Ring-Mesh Hybrid Topology

Below given example script guide to set up a ring-mesh hybrid topology with six nodes:

using namespace ns3;

NS_LOG_COMPONENT_DEFINE (“RingMeshHybridTopology”);

int main (int argc, char *argv[])

{

// Configure command line parameters

CommandLine cmd;

cmd.Parse (argc, argv);

// Create nodes

NodeContainer nodes;

nodes.Create (6); // Create 6 nodes for the ring-mesh hybrid network

// Create point-to-point links to form a ring topology

PointToPointHelper pointToPoint;

pointToPoint.SetDeviceAttribute (“DataRate”, StringValue (“1Gbps”));

pointToPoint.SetChannelAttribute (“Delay”, StringValue (“2ms”));

NetDeviceContainer devices;

Ipv4AddressHelper address;

Ipv4InterfaceContainer interfaces;

for (uint32_t i = 0; i < nodes.GetN (); ++i)

{

NodeContainer pair (nodes.Get (i), nodes.Get ((i + 1) % nodes.GetN ()));

NetDeviceContainer devicePair = pointToPoint.Install (pair);

devices.Add (devicePair);

 

std::ostringstream subnet;

subnet << “10.1.” << i << “.0”;

address.SetBase (subnet.str ().c_str (), “255.255.255.0”);

interfaces.Add (address.Assign (devicePair));

}

// Create CSMA links to form a mesh topology among the nodes

CsmaHelper csma;

csma.SetChannelAttribute (“DataRate”, StringValue (“1Gbps”));

csma.SetChannelAttribute (“Delay”, TimeValue (NanoSeconds (6560)));

NetDeviceContainer meshDevices;

for (uint32_t i = 0; i < nodes.GetN (); ++i)

{

for (uint32_t j = i + 1; j < nodes.GetN (); ++j)

{

NodeContainer pair (nodes.Get (i), nodes.Get (j));

NetDeviceContainer devicePair = csma.Install (pair);

meshDevices.Add (devicePair);

std::ostringstream subnet;

subnet << “10.2.” << i << “.” << j << “.0”;

address.SetBase (subnet.str ().c_str (), “255.255.255.0”);

interfaces.Add (address.Assign (devicePair));

}

}

// Install the internet stack

InternetStackHelper stack;

stack.Install (nodes);

// Assign IP addresses to the ring and mesh devices

for (uint32_t i = 0; i < devices.GetN (); i += 2)

{

Ipv4AddressHelper ipv4;

std::ostringstream subnet;

subnet << “10.1.” << (i / 2 + 1) << “.0”;

ipv4.SetBase (subnet.str ().c_str (), “255.255.255.0”);

ipv4.Assign (NetDeviceContainer (devices.Get (i), devices.Get (i + 1)));

}

for (uint32_t i = 0; i < meshDevices.GetN (); i += 2)

{

Ipv4AddressHelper ipv4;

std::ostringstream subnet;

subnet << “10.2.” << (i / 2 + 1) << “.0”;

ipv4.SetBase (subnet.str ().c_str (), “255.255.255.0”);

ipv4.Assign (NetDeviceContainer (meshDevices.Get (i), meshDevices.Get (i + 1)));

}

// Set up mobility model (optional)

MobilityHelper mobility;

Ptr<ListPositionAllocator> positionAlloc = CreateObject<ListPositionAllocator> ();

positionAlloc->Add (Vector (50.0, 50.0, 0.0)); // Node 0 position

positionAlloc->Add (Vector (100.0, 50.0, 0.0)); // Node 1 position

positionAlloc->Add (Vector (150.0, 50.0, 0.0)); // Node 2 position

positionAlloc->Add (Vector (150.0, 100.0, 0.0)); // Node 3 position

positionAlloc->Add (Vector (100.0, 100.0, 0.0)); // Node 4 position

positionAlloc->Add (Vector (50.0, 100.0, 0.0)); // Node 5 position

mobility.SetPositionAllocator (positionAlloc);

mobility.SetMobilityModel (“ns3::ConstantPositionMobilityModel”);

mobility.Install (nodes);

// Set up applications (e.g., UDP echo server and client)

uint16_t port = 9; // Port number for applications

// Install UDP Echo Server on node 0

UdpEchoServerHelper echoServer (port);

ApplicationContainer serverApps = echoServer.Install (nodes.Get (0));

serverApps.Start (Seconds (1.0));

serverApps.Stop (Seconds (10.0));

// Install UDP Echo Clients on other nodes to communicate with node 0

for (uint32_t i = 1; i < nodes.GetN (); ++i)

{

UdpEchoClientHelper echoClient (interfaces.GetAddress (0), port);

echoClient.SetAttribute (“MaxPackets”, UintegerValue (1));

echoClient.SetAttribute (“Interval”, TimeValue (Seconds (1.0)));

echoClient.SetAttribute (“PacketSize”, UintegerValue (1024));

ApplicationContainer clientApps = echoClient.Install (nodes.Get (i));

clientApps.Start (Seconds (2.0 + i)); // Stagger start times

clientApps.Stop (Seconds (10.0));

}

// Run simulation

Simulator::Stop (Seconds (10.0));

Simulator::Run ();

Simulator::Destroy ();

return 0;

}

Step 5: Build and Run the Simulation

1. Save the script as ring-mesh-hybrid-topology.cc.
2. Build the script using waf:

./waf configure –enable-examples

./waf build

1. Run the simulation:

./waf –run scratch/ring-mesh-hybrid-topology

Explanation of the Script

• Node Creation: Creates six nodes for the ring-mesh hybrid network.
• Point-to-Point Links (Ring Topology): Configures point-to-point links to form a ring topology among the nodes.
• CSMA Links (Mesh Topology): Uses CSMA links to interconnect the nodes in a mesh topology.
• Internet Stack: Installs the internet stack on all nodes.
• IP Addressing: Assigns IP addresses to both the ring and mesh devices using different subnets.
• Mobility Model: (Optional) Sets the position of nodes in a specific layout using ListPositionAllocator and ConstantPositionMobilityModel.
• Applications: Sets up a UDP echo server on node 0 and UDP echo clients on other nodes to demonstrate communication between nodes.

The basics instructions are provided above to set up a ring-mesh hybrid Topology in ns3 and the simulation process is explained elaborately.

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