How to Begin Implement OSPF Algorithm in NS3

To start implementing the Open Shortest Path First (OSPF) protocol using NS3 which needs to design a custom routing protocol relies on the link-state routing principles of OSPF. OSPF applies Link-State Advertisements (LSAs) and Dijkstra’s Algorithm for determining the shortest paths in a network.

Below are structured steps on how to execute OSPF in NS3:

Steps to Begin Implement OSPF Algorithm in NS3

Step 1: Understand OSPF Basics

1. Key Components:
   • LSA (Link-State Advertisement): Nodes are transmitting data regarding tis connections to neighbors.
   • Link-State Database (LSDB): It sustains the network topology.
   • Dijkstra’s Algorithm: Determines the shortest paths according to the LSDB.
   • Areas: Hierarchical OSPF splits the network to zones for minimizing overhead.
2. Key Functions:
   • Neighbor Discovery: Launch neighbor relationships to leverage the Hello packets.
   • Topology Updates: Replace LSAs to construct and sustain the LSDB.
   • Path Calculation: Determine the routing table with the support of Dijkstra’s algorithm.

Step 2: Set Up NS3

1. Install NS3:

git clone https://gitlab.com/nsnam/ns-3-dev.git

cd ns-3-dev

./ns3 configure –enable-examples –enable-tests

./ns3 build

1. Verify Installation: Confirm the installation with executing an example simulation script:

./ns3 run examples/tutorial/first

Step 3: Plan OSPF Implementation

1. Workflow:
   • Discovery Phase: Start adjacencies utilising Hello packets.
   • Flooding Phase: Interchange LSAs to construct the LSDB.
   • Shortest Path Calculation: Make use of Dijkstra’s algorithm for calculating the shortest paths.
   • Forwarding Phase: Leverage computed routing table to transmit the packets.
2. Components:
   • Hello Protocol: Determine neighbors and launch the adjacencies.
   • LSA Generation and Flooding: Transmit the link-state data.
   • Routing Table Calculation: Estimate the routes to apply Dijkstra’s algorithm.

Step 4: Implement OSPF in NS3

Step 4.1: Define the OSPF Protocol Class

Prolong the Ipv4RoutingProtocol class to describe the OSPF Protocol:

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

#include “ns3/socket.h”

#include <map>

using namespace ns3;

class OspfProtocol : public Ipv4RoutingProtocol {

public:

static TypeId GetTypeId(void);

OspfProtocol();

virtual ~OspfProtocol();

virtual Ptr<Ipv4Route> RouteOutput(Ptr<Packet> packet, const Ipv4Header &header,

Ptr<NetDevice> oif, Socket::SocketErrno &sockerr) override;

virtual bool RouteInput(Ptr<const Packet> packet, const Ipv4Header &header,

Ptr<const NetDevice> idev, UnicastForwardCallback ucb,

MulticastForwardCallback mcb, LocalDeliverCallback lcb,

ErrorCallback ecb) override;

void NotifyInterfaceUp(uint32_t interface) override;

void NotifyInterfaceDown(uint32_t interface) override;

private:

void SendHelloPackets();

void ReceiveHelloPackets(Ptr<Socket> socket);

void FloodLsa();

void ReceiveLsa(Ptr<Socket> socket);

void ComputeRoutingTable();

std::map<Ipv4Address, std::pair<Ipv4Address, uint32_t>> m_routingTable; // Destination -> (NextHop, Cost)

std::map<Ipv4Address, std::map<Ipv4Address, uint32_t>> m_lsdb; // Link-State Database

Ptr<Socket> m_socket;

};

Step 4.2: Implement Key OSPF Features

• Hello Packets for Neighbor Discovery:

void OspfProtocol::SendHelloPackets() {

Ptr<Packet> packet = Create<Packet>();

m_socket->SendTo(packet, 0, InetSocketAddress(Ipv4Address(“224.0.0.5”), 520)); // OSPF multicast address

Simulator::Schedule(Seconds(10.0), &OspfProtocol::SendHelloPackets, this);

}

void OspfProtocol::ReceiveHelloPackets(Ptr<Socket> socket) {

Ptr<Packet> packet = socket->Recv();

// Process Hello packets to establish adjacencies

}

• LSA Flooding:

void OspfProtocol::FloodLsa() {

for (const auto &neighbor : m_lsdb) {

Ptr<Packet> packet = Create<Packet>();

// Serialize LSA information into packet

m_socket->SendTo(packet, 0, InetSocketAddress(neighbor.first, 520));

}

}

void OspfProtocol::ReceiveLsa(Ptr<Socket> socket) {

Ptr<Packet> packet = socket->Recv();

// Update the LSDB with the received LSA

}

• Routing Table Calculation Using Dijkstra’s Algorithm:

void OspfProtocol::ComputeRoutingTable() {

std::map<Ipv4Address, uint32_t> distance;

std::map<Ipv4Address, Ipv4Address> previous;

// Initialize distances

for (const auto &node : m_lsdb) {

distance[node.first] = UINT32_MAX;

}

Ipv4Address source = GetNode()->GetObject<Ipv4>()->GetAddress(1, 0).GetLocal();

distance[source] = 0;

// Dijkstra’s algorithm

while (!distance.empty()) {

auto it = std::min_element(distance.begin(), distance.end(),

[](const auto &a, const auto &b) { return a.second < b.second; });

Ipv4Address current = it->first;

uint32_t currentDist = it->second;

distance.erase(it);

for (auto &neighbor : m_lsdb[current]) {

uint32_t newDist = currentDist + neighbor.second;

if (newDist < distance[neighbor.first]) {

distance[neighbor.first] = newDist;

previous[neighbor.first] = current;

}

}

}

// Update routing table

for (auto &node : previous) {

m_routingTable[node.first] = {node.second, distance[node.first]};

}

}

• Packet Forwarding:

Ptr<Ipv4Route> OspfProtocol::RouteOutput(Ptr<Packet> packet, const Ipv4Header &header,

Ptr<NetDevice> oif, Socket::SocketErrno &sockerr) {

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

auto it = m_routingTable.find(header.GetDestination());

if (it != m_routingTable.end()) {

route->SetDestination(header.GetDestination());

route->SetGateway(it->second.first); // Next hop

route->SetOutputDevice(oif);

}

return route;

}

Step 5: Integrate the Protocol into NS3

Register the Protocol:

Record the OSPF protocol using TypeId system in NS3:

TypeId OspfProtocol::GetTypeId(void) {

static TypeId tid = TypeId(“ns3::OspfProtocol”)

.SetParent<Ipv4RoutingProtocol>()

.SetGroupName(“Internet”)

.AddConstructor<OspfProtocol>();

return tid;

}

Simulation Script:

Configure a network topology and set up the OSPF protocol:

#include “ns3/internet-stack-helper.h”

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

NodeContainer nodes;

nodes.Create(4);

PointToPointHelper p2p;

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

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

NetDeviceContainer devices = p2p.Install(nodes.Get(0), nodes.Get(1));

devices.Add(p2p.Install(nodes.Get(1), nodes.Get(2)));

devices.Add(p2p.Install(nodes.Get(2), nodes.Get(3)));

InternetStackHelper stack;

Ptr<OspfProtocol> ospf = CreateObject<OspfProtocol>();

stack.SetRoutingHelper(ospf);

stack.Install(nodes);

Simulator::Run();

Simulator::Destroy();

return 0;

}

Step 6: Test and Debug

1. Enable Logging: For debugging, we need to utilize NS3 logging:

export NS_LOG=”OspfProtocol=level_all|prefix_time”

./ns3 run my-ospf-simulation

1. Validate Behavior:
   • Verify LSDB synchronization and routing table accuracy.
   • Confirm the packet transmission with FlowMonitor.

Step 7: Extend and Optimize

1. Add Features:
   • It offers numerous areas and hierarchical OSPF.
   • Execute the timers for LSAs and Hello packets.
2. Performance Testing:
   • Replicate large-scale networks.
   • Examine the protocol scalability and convergence time.

Through this method, we had completed the implementation and extension of OSPF Algorithm that supports to determine the shortest path in the network using NS3 environment with coding snippets. We are able to offer further innovative information upon request.