How to Begin Implement Bellman Ford Routing in NS3

To execute the Bellman-Ford Routing using NS3 environment that requires to make a routing protocol in which nodes swap routing tables including its neighbors and determine the shortest paths to every destination using Bellman-Ford algorithm. Bellman-Ford is a distance-vector routing mechanism, which modernizes the routes according to the shortest distance from a node to their neighbors.

Below is a stepwise approach that supports to execute the Bellman-Ford routing in NS3:

Steps to Begin Implement Bellman Ford Routing in NS3

Step 1: Understand Bellman-Ford Basics

1. Key Concepts:
   • Every single node sustains a routing table including:
     • Destination: The victim node.
     • Next Hop: The intermediate node for the path.
     • Cost: The cost (distance) for attaining the destination.
   • Nodes swap routing tables including its neighbors.
   • The Bellman-Ford Algorithm is commonly utilized to modernize the routes according to the neighbors’ data.
2. Algorithm Workflow:
   • Every single node begins with their routing table.
   • Routing updates are periodically swapped.
   • The routing table is updated by leveraging the formula: d(u,v)=min⁡w∈neighbors(u){c(u,w)+d(w,v)}d(u, v) = \min_{w \in neighbors(u)} \{c(u, w) + d(w, v)\}d(u,v)=w∈neighbors(u)min​{c(u,w)+d(w,v)} where:
     • d(w,v)d(w, v)d(w,v) is the cost from www to vvv.
     • d(u,v)d(u, v)d(u,v) is the cost from node uuu to vvv.
     • c(u,w)c(u, w)c(u,w) is the cost from uuu to neighbor www.
3. Challenges:
   • Count-to-Infinity Problem: Endless loops by reason of routing updates.
   • Loop Prevention: Make use of mechanisms such as divided horizon or hold-down timers.

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: Execute a simple example simulation script by using:

./ns3 run examples/tutorial/first

Step 3: Plan Bellman-Ford Routing Design

1. Core Components:
   • Routing Table: It saves the cost for attaining each destination and the next hop.
   • Periodic Updates: Nodes are swapped its routing tables including neighbors.
   • Route Computation: Bellman-Ford mechanism supports to modernize routes.
2. Workflow:
   • Set routing tables including direct neighbors.
   • Transfer routing tables periodically to the neighbors.
   • Modernize routing tables utilizing Bellman-Ford method.

Step 4: Implement Bellman-Ford Routing

Step 4.1: Define the Protocol Class

We create a protocol class by prolonging the Ipv4RoutingProtocol class:

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

#include “ns3/socket.h”

#include <map>

using namespace ns3;

class BellmanFordRouting : public Ipv4RoutingProtocol {

public:

static TypeId GetTypeId(void);

BellmanFordRouting();

virtual ~BellmanFordRouting();

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;

void StartRouting();

private:

void InitializeRoutingTable();

void SendRoutingUpdates();

void ReceiveRoutingUpdates(Ptr<Socket> socket);

void UpdateRoutingTable(Ipv4Address neighbor, const std::map<Ipv4Address, uint32_t> &neighborTable);

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

Ptr<Socket> m_socket;

};

Step 4.2: Implement Core Functions

• Routing Table Initialization: Set the routing table including direct neighbors.

void BellmanFordRouting::InitializeRoutingTable() {

for (uint32_t i = 0; i < GetNode()->GetNDevices(); ++i) {

Ptr<NetDevice> device = GetNode()->GetDevice(i);

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

m_routingTable[address] = {address, 0}; // Cost to itself is 0

}

}

• Routing Updates: Transmit the routing update tables to neighbors periodically.

void BellmanFordRouting::SendRoutingUpdates() {

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

for (const auto &entry : m_routingTable) {

// Serialize routing table entries into packet

}

for (uint32_t i = 0; i < GetNode()->GetNDevices(); ++i) {

Ptr<NetDevice> device = GetNode()->GetDevice(i);

m_socket->SendTo(packet, 0, InetSocketAddress(Ipv4Address(“255.255.255.255”), 520));

}

Simulator::Schedule(Seconds(10.0), &BellmanFordRouting::SendRoutingUpdates, this);

}

• Routing Table Update Using Bellman-Ford: According to the received updates, modernize the routing table.

void BellmanFordRouting::UpdateRoutingTable(Ipv4Address neighbor,

const std::map<Ipv4Address, uint32_t> &neighborTable) {

for (const auto &entry : neighborTable) {

Ipv4Address dest = entry.first;

uint32_t costToDest = entry.second;

uint32_t newCost = m_routingTable[neighbor].second + costToDest;

if (m_routingTable.find(dest) == m_routingTable.end() || newCost < m_routingTable[dest].second) {

m_routingTable[dest] = {neighbor, newCost};

}

}

}

• Handle Received Updates: Execute the received routing updates from neighbors.

void BellmanFordRouting::ReceiveRoutingUpdates(Ptr<Socket> socket) {

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

std::map<Ipv4Address, uint32_t> neighborTable;

// Deserialize packet to extract neighbor’s routing table

Ipv4Address neighbor = …; // Extract neighbor address

UpdateRoutingTable(neighbor, neighborTable);

}

• Packet Forwarding: Send packets depending on the routing table.

Ptr<Ipv4Route> BellmanFordRouting::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 Bellman-Ford Routing into NS3

Register the Protocol:

Record the protocol that contains NS3’s TypeId system:

TypeId BellmanFordRouting::GetTypeId(void) {

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

.SetParent<Ipv4RoutingProtocol>()

.SetGroupName(“Internet”)

.AddConstructor<BellmanFordRouting>();

return tid;

}

Simulation Script:

Add the protocol to a simulation script:

#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<BellmanFordRouting> bfRouting = CreateObject<BellmanFordRouting>();

stack.SetRoutingHelper(bfRouting);

stack.Install(nodes);

Simulator::Run();

Simulator::Destroy();

return 0;

}

Step 6: Test and Debug

1. Enable Logging:

export NS_LOG=”BellmanFordRouting=level_all|prefix_time”

./ns3 run my-simulation

1. Verify Behavior:
   • Verify routing table updates.
   • Authenticate routing accuracy and packet delivery.

Step 7: Extend and Optimize

1. Enhancements:
   • Integrate the divided horizon for avoiding loops.
   • Execute hold-down timers to become stable routes.
2. Performance Testing:
   • Experiment the performance within large-scale networks.
   • Parse protocol scalability and convergence time.

This technique will guide you through the implementation process on how to start executing and analysing the Bellman Ford Routing using NS3 environment. We will also offer the extra information on relevant topic, if needed.