How to Implement Overlay Topology in ns3

To implement an overlay topology in ns3, we need to create a virtual network on top of an existing network, where each overlay node can communicate directly with other overlay nodes, independent of the underlying physical network.

Here is a quick guide to implement this.

Steps for implementation

Step 1: Install ns-3

Make sure that ns3 is installed in the computer. If not, install it.

Step 2: Create a New Simulation Script

For your simulation, create a new C++ script.

Step 3: Include Necessary Headers

include the necessary ns3 headers in your script.

#include “ns3/core-module.h”

#include “ns3/network-module.h”

#include “ns3/internet-module.h”

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

#include “ns3/applications-module.h”

#include “ns3/csma-module.h”

Step 4: Set Up the Physical and Overlay Topology

Below is an example to set up an overlay topology on top of an physical network.

using namespace ns3;

NS_LOG_COMPONENT_DEFINE (“OverlayTopology”);

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

{

// Configure command line parameters

CommandLine cmd;

cmd.Parse (argc, argv);

// Create nodes

NodeContainer p2pNodes;

p2pNodes.Create (4); // Create 4 nodes for the physical network

// Create point-to-point links

PointToPointHelper pointToPoint;

pointToPoint.SetDeviceAttribute (“DataRate”, StringValue (“5Mbps”));

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

NetDeviceContainer p2pDevices;

for (uint32_t i = 0; i < p2pNodes.GetN (); ++i)

{

for (uint32_t j = i + 1; j < p2pNodes.GetN (); ++j)

{

NodeContainer pair (p2pNodes.Get (i), p2pNodes.Get (j));

NetDeviceContainer devicePair = pointToPoint.Install (pair);

p2pDevices.Add (devicePair);

}

}

// Install the internet stack

InternetStackHelper stack;

stack.Install (p2pNodes);

// Assign IP addresses

Ipv4AddressHelper address;

Ipv4InterfaceContainer p2pInterfaces;

for (uint32_t i = 0; i < p2pNodes.GetN (); ++i)

{

for (uint32_t j = i + 1; j < p2pNodes.GetN (); ++j)

{

std::ostringstream subnet;

subnet << “10.” << i << “.” << j << “.0”;

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

NetDeviceContainer devicePair = p2pDevices.Get (i * (p2pNodes.GetN () – 1) + (j – 1));

p2pInterfaces.Add (address.Assign (devicePair));

}

}

// Create overlay nodes

NodeContainer overlayNodes;

overlayNodes.Add (p2pNodes.Get (1)); // Using existing physical nodes

overlayNodes.Add (p2pNodes.Get (3));

// Create CSMA links for overlay network

CsmaHelper csma;

csma.SetChannelAttribute (“DataRate”, StringValue (“10Mbps”));

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

NetDeviceContainer overlayDevices;

overlayDevices = csma.Install (overlayNodes);

// Assign IP addresses to overlay network

address.SetBase (“10.1.3.0”, “255.255.255.0”);

Ipv4InterfaceContainer overlayInterfaces = address.Assign (overlayDevices);

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

uint16_t port = 9; // Port number for applications

// Install UDP Echo Server on overlay node 0

UdpEchoServerHelper echoServer (port);

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

serverApps.Start (Seconds (1.0));

serverApps.Stop (Seconds (10.0));

// Install UDP Echo Client on overlay node 1 to communicate with overlay node 0

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

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

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

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

ApplicationContainer clientApps = echoClient.Install (overlayNodes.Get (1));

clientApps.Start (Seconds (2.0));

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

Save the script as overlay-topology.cc and build the script using waf, then run the simulation.

./waf configure –enable-examples

./waf build

./waf –run scratch/overlay-topology

Explanation of the script

• Node Creation: For the base network and two overlay nodes, creates four physical nodes using existing physical nodes.
• Point-to-Point Links: For the physical network, configures point-to-point links.
• Network Configuration: To the physical network, assigns IP addresses.
• Overlay Network: For the overlay network, configures CSMA links and assigns IP addresses.
• Internet Stack: On all nodes, installs the internet stack.
• Applications: On one overlay node, sets up a UDP echo server and a UDP echo client on another overlay node to demonstrate communication.

Overall, we had a implementation on overlay topology by creating a virtual network on top of an existing network, where each overlay node can communicate directly with other overlay nodes, independent of the underlying physical network. Also, we provide a detailed explanation on Overlay Topology.

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