How to Begin Implement Open Shortest Path Protocol in NS3

To execute the Open Shortest Path First (OSPF) protocol using NS3 that comprises of designing a custom routing protocol according to the OSPF mechanism. While NS3 doesn’t provide inherent support for OSPF execution, we can make or prolong an Ipv4RoutingProtocol for managing the needs of OSPF like Link State Advertisements (LSAs), link state databases, and the Shortest Path First (SPF) method.

We will guide you on how we can start executing the OSPF in NS3:

Steps to Begin Implement OSPF Protocol in NS3

Step 1: Understand OSPF Concepts

1. OSPF Overview:
   • Link State Routing Protocol: Every single router sustains a map (link-state database) of the network topology.
   • Key Mechanisms:
     • Interchange of LSAs among the routers.
     • To construct a link-state database.
     • Determine the shortest path to utilize Dijkstra’s SPF algorithm.
2. Features to Implement:
   • Neighbor Discovery: Explore the neighbors using Hello messages.
   • Flooding of LSAs: Deliver network topology data.
   • Shortest Path Computation: Calculate the routing table uisng Dijkstra’s algorithm.

Step 2: Set Up NS3

1. Install NS3:
   • Clone the GitHub repository and construct 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:
   • Execute a basic instance simulation script to confirm the installation:

./ns3 run examples/tutorial/first

Step 3: Plan OSPF Implementation

1. Core Components:
   • Hello Protocol: Launching neighbor relationships.
   • Link State Advertisements (LSAs): Deliver the network topology data.
   • Link State Database (LSDB): It saves LSAs which are inherited from neighbors.
   • Shortest Path First Algorithm: Determines the best route using this method.
2. Message Types:
   • Hello Messages: It is used for neighbor discovery.
   • LSAs: Transmitting topology data.
   • Acknowledgments: Intended for reliable LSA transmission.

Step 4: Implement the OSPF Protocol

Step 4.1: Define the OSPF Protocol Class

Make a OSPF protocol class to prolong the Ipv4RoutingProtocol:

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

#include “ns3/node.h”

#include “ns3/socket.h”

using namespace ns3;

class OspfProtocol : public Ipv4RoutingProtocol {

public:

static TypeId GetTypeId(void);

OspfProtocol();

virtual ~OspfProtocol();

// Overrides for routing protocol

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;

virtual void NotifyInterfaceUp(uint32_t interface) override;

virtual void NotifyInterfaceDown(uint32_t interface) override;

virtual void NotifyAddAddress(uint32_t interface, Ipv4InterfaceAddress address) override;

virtual void NotifyRemoveAddress(uint32_t interface, Ipv4InterfaceAddress address) override;

private:

void SendHelloMessages();

void ProcessHelloMessages(Ptr<Packet> packet);

void FloodLsa();

void ProcessLsa(Ptr<Packet> packet);

void ComputeShortestPath();

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

Ptr<Socket> m_socket;

};

Step 4.2: Implement Protocol Logic

• Neighbor Discovery with Hello Messages:
  • Transmit the Hello messages periodically for determining the neighbors.

void OspfProtocol::SendHelloMessages() {

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

// Add Hello message data

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

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

}

void OspfProtocol::ProcessHelloMessages(Ptr<Packet> packet) {

// Process incoming Hello message and update neighbors

}

• Flooding of LSAs:
  • Distribute topology data to every neighbor.

void OspfProtocol::FloodLsa() {

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

// Add LSA data

for (auto &neighbor : m_neighbors) {

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

}

}

void OspfProtocol::ProcessLsa(Ptr<Packet> packet) {

// Update LSDB and trigger SPF computation if necessary

}

• Shortest Path Computation:
  • Determine the routing table to leverage Dijkstra’s algorithm.

void OspfProtocol::ComputeShortestPath() {

// Implement Dijkstra’s algorithm using m_lsdb

}

• Packet Forwarding:
  • According to the calculated shortest paths, we can transmit the packets.

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

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

// Lookup the route in the routing table

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

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

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

route->SetOutputDevice(oif);

return route;

}

Step 5: Integrate OSPF into NS3

Step 5.1: Register the Protocol

Record the protocol using NS3’s TypeId system:

TypeId OspfProtocol::GetTypeId(void) {

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

.SetParent<Ipv4RoutingProtocol>()

.SetGroupName(“Internet”)

.AddConstructor<OspfProtocol>();

return tid;

}

Step 5.2: Add OSPF to Nodes

Install OSPF on nodes with InternetStackHelper:

#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);  // Use your custom protocol

stack.Install(nodes);

Simulator::Run();

Simulator::Destroy();

return 0;

}

Step 6: Test and Validate

1. Simulation Setup:
   • Set up a simulation network including numerous nodes and links.
   • Make use of traffic generators such as UdpEchoClient and UdpEchoServer.
2. Enable Logging:
   • For debugging OSPF we need to utilize logging system of NS3:

export NS_LOG=”OspfProtocol=level_all|prefix_time”

./ns3 run my-simulation

1. Analyze Results:
   • Ensure route convergence, message overhead, and performance parameters for analyse.
   • Verify behaviour of routing with the support of FlowMonitor or packet tracing.

Step 7: Extend and Optimize

1. Enhancements:
   • Integrate support for areas such as backbone and non-backbone.
   • Execute the validation approaches.
2. Optimization:
   • For large networks, experiment the scalability.
   • Enhance the flooding method for minimizing overhead.

The above manual have aggregated the sufficient details that including snippet codes about how to implement and analyse the Open Shortest Path Protocol using NS3 environment. We will attach further information on this topic later.