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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