How to Begin Implement Centralized Routing in NS3

To begin the Centralized Routing in NS-3 tool has involves the routing protocol in which all routing decisions are create through a centralized controller or node. The various distributed routing protocols for centralized the routing manage a global view for the network topology and calculates the routes for all nodes.

Here’s a step-by-step guide to begin implementing centralized routing in NS-3:

Steps to Begin Implement Centralized Routing in NS3

Step 1: Understand Centralized Routing

1. Key Characteristics:
   • The central controller has calculates the routes for all nodes in a network.
   • Nodes are sending the packets according to the routing decisions are delivered through the controller.
   • The gathers the data for controller network topology from the nodes.
2. Applications:
   • Software Defined Networking (SDN).
   • Data center networks.
   • Wireless sensor networks by a base station.
3. Steps:
   • Report the nodes in network topology information for sample neighbor, connection costs for the controller.
   • The controller calculates the optimal routes for sample shortest path, load balancing.
   • Nodes are install a route has delivered through the controller.

Step 2: Set Up NS-3 Environment

1. Create a Protocol Directory:
   • Make a new directory below src/, for sample src/centralized-routing/.
2. Add Required Files:
   • centralized-routing-protocol.h: Header file has a centralized routing protocol.
   • centralized-routing-protocol.cc: estimate the needed file.
   • centralized-routing-helper.h and centralized-routing-helper.cc: Helper classes.
3. Update Build System:
   • Change the new module wscript in src/.

Step 3: Design Centralized Routing Protocol

Define the Protocol Class

Encompass the Ipv4RoutingProtocol for execute the centralized routing logic.

Header File (centralized-routing-protocol.h)

#include “ns3/ipv4-routing-protocol.h”

#include “ns3/socket.h”

#include “ns3/timer.h”

#include <map>

#include <vector>

class CentralizedRoutingProtocol : public ns3::Ipv4RoutingProtocol {

public:

static ns3::TypeId GetTypeId (void);

CentralizedRoutingProtocol ();

virtual ~CentralizedRoutingProtocol ();

// Override Ipv4RoutingProtocol methods

virtual ns3::Ptr<ns3::Ipv4Route> RouteOutput (

ns3::Ptr<const ns3::Packet> packet,

const ns3::Ipv4Header &header,

ns3::Ptr<ns3::NetDevice> oif,

ns3::Socket::SocketErrno &sockerr);

virtual bool RouteInput (

ns3::Ptr<const ns3::Packet> packet,

const ns3::Ipv4Header &header,

ns3::Ptr<const ns3::NetDevice> idev,

ns3::UnicastForwardCallback ucb,

ns3::MulticastForwardCallback mcb,

ns3::LocalDeliverCallback lcb,

ns3::ErrorCallback ecb);

void ReceiveTopologyInfo (ns3::Ptr<const ns3::Packet> packet);

void ComputeRoutes ();

void DistributeRoutes ();

private:

struct LinkInfo {

ns3::Ipv4Address neighbor;

uint32_t cost;

};

ns3::Ipv4Address m_controllerAddress;

std::map<ns3::Ipv4Address, std::vector<LinkInfo>> m_topologyDatabase; // Node -> Neighbors

std::map<ns3::Ipv4Address, ns3::Ipv4Address> m_routingTable; // Destination -> Next Hop

ns3::Timer m_computeTimer; // Timer for periodic route computation

};

Implement Core Functions

Topology Information Collection

Nodes are forwarding the network topology information such as neighbors and connection costs for the controller.

void CentralizedRoutingProtocol::ReceiveTopologyInfo (ns3::Ptr<const ns3::Packet> packet) {

// Deserialize topology information

ns3::Ipv4Address nodeAddress = …; // Extract node address

std::vector<LinkInfo> links = …;  // Extract link information

// Update topology database

m_topologyDatabase[nodeAddress] = links;

// Schedule route computation

m_computeTimer.Schedule (ns3::MilliSeconds (100));

}

Route Computation

The controller computes the minimum paths using an procedures such as Dijkstra’s.

void CentralizedRoutingProtocol::ComputeRoutes () {

// Dijkstra’s algorithm

std::map<ns3::Ipv4Address, uint32_t> distances;

std::map<ns3::Ipv4Address, ns3::Ipv4Address> previous;

for (const auto &entry : m_topologyDatabase) {

distances[entry.first] = std::numeric_limits<uint32_t>::max();

}

distances[m_controllerAddress] = 0;

std::set<ns3::Ipv4Address> visited;

while (visited.size() < m_topologyDatabase.size()) {

ns3::Ipv4Address currentNode = …; // Find the node with the smallest distance

for (const auto &link : m_topologyDatabase[currentNode]) {

uint32_t newDistance = distances[currentNode] + link.cost;

if (newDistance < distances[link.neighbor]) {

distances[link.neighbor] = newDistance;

previous[link.neighbor] = currentNode;

}

}

visited.insert(currentNode);

}

// Build routing table

for (const auto &entry : previous) {

m_routingTable[entry.first] = entry.second;

}

}

Route Distribution

Allocate the routes for all nodes are calculated.

void CentralizedRoutingProtocol::DistributeRoutes () {

for (const auto &entry : m_routingTable) {

ns3::Ipv4Address destination = entry.first;

ns3::Ipv4Address nextHop = entry.second;

// Send routing updates to nodes

ns3::Ptr<ns3::Packet> updatePacket = ns3::Create<ns3::Packet> ();

// Serialize routing update information

// …

m_socket->SendTo(updatePacket, 0, ns3::InetSocketAddress(destination, 9999));

}

}

Packet Forwarding

Nodes are sending the packets according to the routing table provided through the controller.

ns3::Ptr<ns3::Ipv4Route> CentralizedRoutingProtocol::RouteOutput (

ns3::Ptr<const ns3::Packet> packet,

const ns3::Ipv4Header &header,

ns3::Ptr<ns3::NetDevice> oif,

ns3::Socket::SocketErrno &sockerr) {

ns3::Ptr<ns3::Ipv4Route> route = ns3::Create<ns3::Ipv4Route> ();

if (m_routingTable.find(header.GetDestination()) != m_routingTable.end()) {

route->SetGateway(m_routingTable[header.GetDestination()]);

} else {

sockerr = ns3::Socket::ERROR_NOROUTETOHOST;

return nullptr;

}

return route;

}

Step 4: Write a Helper Class

Facilitate the incorporate for centralized routing in replication scripts.

#include “centralized-routing-protocol.h”

class CentralizedRoutingHelper {

public:

void Install (ns3::NodeContainer nodes, ns3::NodeContainer controller) {

for (auto it = nodes.Begin(); it != nodes.End(); ++it) {

ns3::Ptr<CentralizedRoutingProtocol> protocol = ns3::CreateObject<CentralizedRoutingProtocol>();

(*it)->AggregateObject(protocol);

}

// Set the controller for all nodes

}

};

Step 5: Write a Simulation Script

Example Simulation Script

#include “ns3/core-module.h”

#include “ns3/network-module.h”

#include “ns3/internet-module.h”

#include “centralized-routing-helper.h”

using namespace ns3;

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

NodeContainer nodes;

nodes.Create (5);

NodeContainer controller;

controller.Create (1);

InternetStackHelper stack;

stack.Install (nodes);

stack.Install (controller);

CentralizedRoutingHelper centralizedHelper;

centralizedHelper.Install(nodes, controller);

// Configure links and addresses

PointToPointHelper p2p;

p2p.SetDeviceAttribute (“DataRate”, StringValue (“10Mbps”));

p2p.SetChannelAttribute (“Delay”, StringValue (“2ms”));

p2p.Install (nodes.Get (0), controller.Get (0));

p2p.Install (nodes.Get (1), controller.Get (0));

// Additional links…

Simulator::Run ();

Simulator::Destroy ();

return 0;

}

Step 6: Compile and Run

1. Build the Protocol:

./waf configure

./waf build

1. Run the Simulation:

./waf –run your-script

Step 7: Analyze and Extend

1. Analyze with Tracing:
   • AsciiTraceHelper and PcapHelper use to authorize the routing behavior.
2. Enhance the Protocol:
   • Enhance the fault tolerance for controller failures.
   • Apply further advanced optimization procedures for route calculation.

We had learned here about how the centralized routing protocol will implemented and executed in ns3 environment. If you have concerns or queries, they will be addressed in a separate manual.