How to Implement OSPF algorithm in ns3

To implement OSPF (Open Shortest Path First) routing in ns3, you have to incorporate these steps :

Steps for implementation

1. Set up your ns3 environment :

• Make sure that ns3 is installed in the computer. If not, install it from the official ns3 website.

2. Include necessary libraries :

• In your script, include the necessary libraries.

3. Define network topology :

• For your network topology, create the nodes and links.

4. Install Internet Stack :

• On your nodes, install the internet stack.

5. Configure OSPF Routing Protocol :

• Configure the OSPF routing protocol for your nodes.

6. Set Up Applications :

• To generate traffic and test the routing, install applications.

7. Run the Simulation :

• Define the simulation parameters and run it.

Example implementation in C++

ns3 does not support built-in OSPF implementation. Hence, we need to implement it by ourself. Here is a complete example on implementing a basic OSPF protocol in ns3:

Include libraries :

#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/ipv4-global-routing-helper.h”

#include “ns3/ospf-routing-helper.h” // This assumes you have an OSPF helper or equivalent

 

Define Network Topology:

using namespace ns3;

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

CommandLine cmd;

cmd.Parse(argc, argv);

NodeContainer nodes;

nodes.Create(4);

PointToPointHelper pointToPoint;

pointToPoint.SetDeviceAttribute(“DataRate”, StringValue(“5Mbps”));

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

NetDeviceContainer devices;

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

devices = pointToPoint.Install(nodes.Get(1), nodes.Get(2));

devices = pointToPoint.Install(nodes.Get(2), nodes.Get(3));

devices = pointToPoint.Install(nodes.Get(3), nodes.Get(0));

InternetStackHelper stack;

stack.Install(nodes);

Ipv4AddressHelper address;

address.SetBase(“10.1.1.0”, “255.255.255.0”);

Ipv4InterfaceContainer interfaces;

interfaces = address.Assign(devices);

Configure OSPF Routing:

// Assuming you have an OSPF helper

OspfRoutingHelper ospfRouting;

Ipv4ListRoutingHelper list;

list.Add(ospfRouting, 0);

InternetStackHelper stack;

stack.SetRoutingHelper(list);

stack.Install(nodes);

Set Up Applications:

uint16_t port = 9;

UdpEchoServerHelper server(port);

ApplicationContainer apps = server.Install(nodes.Get(3));

apps.Start(Seconds(1.0));

apps.Stop(Seconds(10.0));

UdpEchoClientHelper client(interfaces.GetAddress(3), port);

client.SetAttribute(“MaxPackets”, UintegerValue(1));

client.SetAttribute(“Interval”, TimeValue(Seconds(1.0)));

client.SetAttribute(“PacketSize”, UintegerValue(1024));

apps = client.Install(nodes.Get(0));

apps.Start(Seconds(2.0));

apps.Stop(Seconds(10.0));

Run the Simulation:

Simulator::Run();

Simulator::Destroy();

return 0;

}

Implementing OSPF

We need to create the OSPF implementation as ns3 does not support it. This includes significant work and requires implementing the OSPF protocol specifics, which involves :

• Link-state advertisements (LSAs)
• OSPF message exchanges (Hello, DBD, LSR, LSU, and LSAck)
• Shortest Path First (SPF) algorithm using Dijkstra’s algorithm

Example of an OSPF Helper Implementation Outline

Create an OSPF routing class that derives from Ipv4RoutingProtocol and implement the necessary methods.

1. Create a New Routing Protocol Class:

Create a new header file ospf-routing.h :

#ifndef OSPF_ROUTING_H

#define OSPF_ROUTING_H

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

#include “ns3/ipv4.h”

#include “ns3/net-device.h”

#include “ns3/ptr.h”

#include “ns3/socket.h”

namespace ns3 {

class OspfRouting : public Ipv4RoutingProtocol {

public:

static TypeId GetTypeId(void);

OspfRouting();

virtual ~OspfRouting();

virtual Ptr<Ipv4Route> RouteOutput(

Ptr<Packet> p, const Ipv4Header &header,

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

virtual bool RouteInput(

Ptr<const Packet> p, const Ipv4Header &header,

Ptr<const NetDevice> idev,

UnicastForwardCallback ucb, MulticastForwardCallback mcb,

LocalDeliverCallback lcb, ErrorCallback ecb);

virtual void NotifyInterfaceUp(uint32_t interface);

virtual void NotifyInterfaceDown(uint32_t interface);

virtual void NotifyAddAddress(uint32_t interface,

Ipv4InterfaceAddress address);

virtual void NotifyRemoveAddress(uint32_t interface,

Ipv4InterfaceAddress address);

virtual void SetIpv4(Ptr<Ipv4> ipv4);

private:

void SendHelloPackets();

void ReceiveHelloPackets(Ptr<Socket> socket);

void ProcessLinkStateAdvertisements();

void CalculateShortestPaths();

Ptr<Ipv4> m_ipv4;

std::map<Ipv4Address, Ptr<Socket>> m_socketMap;

// Other data structures for OSPF state

};

}

#endif // OSPF_ROUTING_H

Create the corresponding implementation file ospf-routing.cc:

#include “ospf-routing.h”

#include “ns3/log.h”

namespace ns3 {

NS_LOG_COMPONENT_DEFINE(“OspfRouting”);

NS_OBJECT_ENSURE_REGISTERED(OspfRouting);

TypeId OspfRouting::GetTypeId(void) {

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

.SetParent<Ipv4RoutingProtocol>()

.SetGroupName(“Internet”)

.AddConstructor<OspfRouting>();

return tid;

}

OspfRouting::OspfRouting() {

NS_LOG_FUNCTION(this);

}

OspfRouting::~OspfRouting() {

NS_LOG_FUNCTION(this);

}

void OspfRouting::SetIpv4(Ptr<Ipv4> ipv4) {

NS_LOG_FUNCTION(this << ipv4);

m_ipv4 = ipv4;

// Initialize OSPF state

}

void OspfRouting::SendHelloPackets() {

NS_LOG_FUNCTION(this);

// Implement OSPF Hello packet sending

}

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

NS_LOG_FUNCTION(this << socket);

// Implement OSPF Hello packet receiving

}

void OspfRouting::ProcessLinkStateAdvertisements() {

NS_LOG_FUNCTION(this);

// Implement processing of LSAs

}

void OspfRouting::CalculateShortestPaths() {

NS_LOG_FUNCTION(this);

// Implement Dijkstra’s algorithm for SPF calculation

}

Ptr<Ipv4Route> OspfRouting::RouteOutput(

Ptr<Packet> p, const Ipv4Header &header, Ptr<NetDevice> oif,

Socket::SocketErrno &sockerr) {

NS_LOG_FUNCTION(this << p << header << oif << sockerr);

// Implement route output logic

return 0;

}

bool OspfRouting::RouteInput(

Ptr<const Packet> p, const Ipv4Header &header,

Ptr<const NetDevice> idev, UnicastForwardCallback ucb,

MulticastForwardCallback mcb, LocalDeliverCallback lcb,

ErrorCallback ecb) {

NS_LOG_FUNCTION(this << p << header << idev << ucb << mcb

<< lcb << ecb);

// Implement route input logic

return false;

}

void OspfRouting::NotifyInterfaceUp(uint32_t interface) {

NS_LOG_FUNCTION(this << interface);

}

void OspfRouting::NotifyInterfaceDown(uint32_t interface) {

NS_LOG_FUNCTION(this << interface);

}

void OspfRouting::NotifyAddAddress(uint32_t interface,

Ipv4InterfaceAddress address) {

NS_LOG_FUNCTION(this << interface << address);

}

void OspfRouting::NotifyRemoveAddress(uint32_t interface,

Ipv4InterfaceAddress address) {

NS_LOG_FUNCTION(this << interface << address);

}

}

Running the Code :

Save your script to a file, for example, ospf-routing.cc and compile the script using the ns3 build system

./waf configure –enable-examples

./waf build

./waf –run scratch/ospf-routing

Overall, we had learned on implementing the OSPF (Open Shortest Path First) algorithm in ns3. Get more related projects on OSPF (Open Shortest Path First) algorithm.