How to Begin Implement Global Routing in NS3

To implement Global Routing in NS3 which is talks about a protocol in which every node contain a global outlook of the entire network topology. This methodology utilises global data for determining the best routes that frequently used Dijkstra algorithm depends on the shortest routes. While NS3 already has a Global Routing Protocol, we will need to make a custom execution to discover or certain changes.

Below is a simple guide for implementing Global Routing using NS3:

Steps to Begin Implement Global Routing in NS3

Step 1: Understand Global Routing

1. Key Concepts:
   • All nodes distribute a general opinion of the whole network topology.
   • The routing table is centrally or distributedly determined with the support of global data.
   • It is normally exhausts the shortest-path mechanisms such as Dijkstra’s or Bellman-Ford.
2. Use Cases:
   • Its supports to replicate the centralized routing protocols such as OpenFlow.
   • According to the global parameters like latency, bandwidth to enhance the routes.

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 script to confirm set up:

./ns3 run examples/tutorial/first

Step 3: Plan Global Routing Protocol Design

1. Core Components:
   • Topology Discovery: Accumulate data regarding the network that contains nodes and links.
   • Routing Table Computation: Determine shortest paths depend on the global data.
   • Packet Forwarding: For packet forwarding we can utilize the computed routing table.
2. Workflow:
   • Collect the network topology that has links and nodes in initialization.
   • Calculate the routing table to leverage a shortest-path algorithm.
   • Rely on the computed routing table to transmit the packets.

Step 4: Implement Global Routing

Step 4.1: Define the Protocol Class

Prolong the Ipv4RoutingProtocol class to implement the functionality of Global Routing:

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

#include <map>

#include <vector>

#include <limits>

using namespace ns3;

class GlobalRouting : public Ipv4RoutingProtocol {

public:

static TypeId GetTypeId(void);

GlobalRouting();

virtual ~GlobalRouting();

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 BuildRoutingTable();

private:

void DiscoverTopology();

void ComputeShortestPaths(Ipv4Address source);

std::map<Ipv4Address, std::map<Ipv4Address, uint32_t>> m_topology; // Adjacency list

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

};

Step 4.2: Implement Core Functions

• Topology Discovery: Inhabit the adjacency list to denote the network for discover the topology.

void GlobalRouting::DiscoverTopology() {

m_topology.clear();

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

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

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

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

if (i != j) {

Ptr<NetDevice> neighborDevice = GetNode()->GetDevice(j);

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

uint32_t cost = 1; // Assign uniform cost or dynamic cost (e.g., delay)

m_topology[address][neighborAddress] = cost;

}

}

}

}

• Shortest Path Computation (Dijkstra): Determine the shortest routes from the source node to all other nodes.

void GlobalRouting::ComputeShortestPaths(Ipv4Address source) {

std::map<Ipv4Address, uint32_t> distances;

std::map<Ipv4Address, Ipv4Address> previous;

std::vector<Ipv4Address> nodes;

for (const auto &node : m_topology) {

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

previous[node.first] = Ipv4Address();

nodes.push_back(node.first);

}

distances[source] = 0;

while (!nodes.empty()) {

auto minNode = std::min_element(nodes.begin(), nodes.end(),

[&](const Ipv4Address &a, const Ipv4Address &b) {

return distances[a] < distances[b];

});

Ipv4Address current = *minNode;

nodes.erase(minNode);

for (const auto &neighbor : m_topology[current]) {

uint32_t alt = distances[current] + neighbor.second;

if (alt < distances[neighbor.first]) {

distances[neighbor.first] = alt;

previous[neighbor.first] = current;

}

}

}

m_routingTable.clear();

for (const auto &node : distances) {

if (node.second != std::numeric_limits<uint32_t>::max() && node.first != source) {

Ipv4Address nextHop = node.first;

while (previous[nextHop] != source) {

nextHop = previous[nextHop];

}

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

}

}

}

• Build Routing Table: Find the topology and calculate the build routing table.

void GlobalRouting::BuildRoutingTable() {

DiscoverTopology();

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

ComputeShortestPaths(localAddress);

}

• Packet Forwarding: For packet forwarding, we need to apply the routing table.

Ptr<Ipv4Route> GlobalRouting::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;

}

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

Ptr<const NetDevice> idev, UnicastForwardCallback ucb,

MulticastForwardCallback mcb, LocalDeliverCallback lcb,

ErrorCallback ecb) {

if (header.GetDestination() == GetNode()->GetObject<Ipv4>()->GetAddress(1, 0).GetLocal()) {

lcb(packet, header, idev); // Deliver locally

return true;

}

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

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

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

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

route->SetGateway(it->second.first); // Use next hop from routing table

ucb(route, packet, header);

return true;

}

return false;

}

Step 5: Register the Protocol

Enrol the protocol to include TypeId system in NS3:

TypeId GlobalRouting::GetTypeId(void) {

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

.SetParent<Ipv4RoutingProtocol>()

.SetGroupName(“Internet”)

.AddConstructor<GlobalRouting>();

return tid;

}

Step 6: Integrate into a Simulation

1. Simulation Script Example:

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

#include “ns3/global-routing.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<GlobalRouting> globalRouting = CreateObject<GlobalRouting>();

globalRouting->BuildRoutingTable();

stack.SetRoutingHelper(globalRouting);

stack.Install(nodes);

Simulator::Run();

Simulator::Destroy();

return 0;

}

Step 7: Test and Debug

1. Enable Logging:

export NS_LOG=”GlobalRouting=level_all|prefix_time”

./ns3 run my-simulation

1. Verify Behavior:
   • Confirm routing table items.
   • Verify packet forwarding for accuracy.

Step 8: Extend and Optimize

1. Enhancements:
   • Integrate the dynamic routing parameters such as bandwidth or delay.
   • It also assists for multipath routing.
2. Performance Testing:
   • Experiment the performance of global routing within large-scale networks.
   • Assess convergence time and scalability.

These projects focus on implementing and extending the Global Routing in the NS3 environment through above execution procedure with sample coding. Additional insights tailored to your needs can be delivered.