To implement a logical topology in ns3, we need to follow several steps. Because, this logical topology shows that how the nodes logically interact, despite of their physical connections. So, we have to set up a virtual network but on the top it shows like an existing physical network. The following steps will guide on how to implement logical topology in ns3.
Step-by-step to implement logical 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 your 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/applications-module.h”
#include “ns3/csma-module.h”
Step 4: Set Up the Physical Topology
Here is an example of setting up a physical topology with point-to-point links:
using namespace ns3;
NS_LOG_COMPONENT_DEFINE (“LogicalTopology”);
int main (int argc, char *argv[])
{
// Configure command line parameters
CommandLine cmd;
cmd.Parse (argc, argv);
// Create nodes
NodeContainer nodes;
nodes.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 devices;
Ipv4AddressHelper address;
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 = pointToPoint.Install (pair);
devices.Add (devicePair);
std::ostringstream subnet;
subnet << “10.” << i << “.” << j << “.0”;
address.SetBase (subnet.str ().c_str (), “255.255.255.0”);
address.Assign (devicePair);
}
}
// Install the internet stack
InternetStackHelper stack;
stack.Install (nodes);
// Assign IP addresses
Ipv4AddressHelper ipv4;
for (uint32_t i = 0; i < nodes.GetN (); ++i)
{
for (uint32_t j = i + 1; j < nodes.GetN (); ++j)
{
std::ostringstream subnet;
subnet << “10.” << i << “.” << j << “.0”;
ipv4.SetBase (subnet.str ().c_str (), “255.255.255.0”);
ipv4.Assign (devices.Get (i * (nodes.GetN () – 1) + (j – 1)));
}
}
// Run simulation
Simulator::Stop (Seconds (10.0));
Simulator::Run ();
Simulator::Destroy ();
return 0;
}
Step 5: Build and Run the Simulation
- Save the script as logical-topology.cc.
- Build the script using waf:
./waf configure –enable-examples
./waf build
- Run the simulation:
./waf –run scratch/logical-topology
Explanation of the Script
- Node Creation: Creates four nodes for the physical network.
- Point-to-Point Links: Configures point-to-point links for the physical network.
- Network Configuration: Assigns IP addresses to the physical network.
Step 6: Implement Logical Topology
Here we need to define logical connections on top of the physical topology to implement logical topology. The given below example detaily explained about how to extend this using CSMA links for implementing logical topology.
#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”
using namespace ns3;
NS_LOG_COMPONENT_DEFINE (“LogicalTopology”);
int main (int argc, char *argv[])
{
// Configure command line parameters
CommandLine cmd;
cmd.Parse (argc, argv);
// Create nodes
NodeContainer nodes;
nodes.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;
Ipv4AddressHelper address;
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 = pointToPoint.Install (pair);
p2pDevices.Add (devicePair);
std::ostringstream subnet;
subnet << “10.” << i << “.” << j << “.0”;
address.SetBase (subnet.str ().c_str (), “255.255.255.0”);
address.Assign (devicePair);
}
}
// Install the internet stack
InternetStackHelper stack;
stack.Install (nodes);
// Assign IP addresses
Ipv4AddressHelper ipv4;
for (uint32_t i = 0; i < nodes.GetN (); ++i)
{
for (uint32_t j = i + 1; j < nodes.GetN (); ++j)
{
std::ostringstream subnet;
subnet << “10.” << i << “.” << j << “.0”;
ipv4.SetBase (subnet.str ().c_str (), “255.255.255.0”);
ipv4.Assign (p2pDevices.Get (i * (nodes.GetN () – 1) + (j – 1)));
}
}
// Create logical (overlay) topology using CSMA links
CsmaHelper csma;
csma.SetChannelAttribute (“DataRate”, StringValue (“10Mbps”));
csma.SetChannelAttribute (“Delay”, TimeValue (NanoSeconds (6560)));
NetDeviceContainer overlayDevices;
overlayDevices = csma.Install (nodes);
// Assign IP addresses to the overlay network
address.SetBase (“10.1.1.0”, “255.255.255.0”);
Ipv4InterfaceContainer overlayInterfaces = address.Assign (overlayDevices);
// Set up applications (e.g., UDP echo server and client) on overlay network
uint16_t port = 9; // Port number for applications
// Install UDP Echo Server on node 0 (overlay)
UdpEchoServerHelper echoServer (port);
ApplicationContainer serverApps = echoServer.Install (nodes.Get (0));
serverApps.Start (Seconds (1.0));
serverApps.Stop (Seconds (10.0));
// Install UDP Echo Client on node 1 (overlay) to communicate with 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 (nodes.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 7: Build and Run the Extended Simulation
- Save the extended script as logical-topology.cc.
- Build the script using waf:
./waf configure –enable-examples
./waf build
- Run the simulation:
./waf –run scratch/logical-topology
Explanation of the Extended Script
- Logical Topology: Uses CSMA links to create a logical overlay network on top of the physical point-to-point network.
- IP Addressing: Assigns a separate IP address space for the logical network.
- Applications: Sets up a UDP echo server and client on the logical network to demonstrate communication between overlay nodes.
The provided details completely covered the implementation process of logical topology and the example script guide to set up a simple logical topology using CSMA links.
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