How to Begin Implement Unicast Routing in NS3

To start implementing Unicast Routing using NS3, we will need to design a routing protocol, which manages unicast traffic. Unicast routing encompasses to transmit the packets from a single source to a single destination according to the routing table. NS3 environment offers a base class, Ipv4RoutingProtocol that we able to prolong execution of unicast routing protocol.

Below is a step-by-step guide on how to execute the unicast routing in NS3:

Steps to Begin Implement Unicast Routing in NS3

Step 1: Understand Unicast Routing

1. Core Concepts:
   • A unicast routing protocol determines the optimal route to transmit the packets to a certain destination.
   • Applies a routing table including entries within the form:

Destination -> Next Hop

1. • Instances of unicast routing protocols:
     • Dynamic Routing such as OSPF, AODV
     • Static Routing
2. Steps for Implementation:
   • Describe the routing protocol.
   • Make and sustain a routing table.
   • Execute the packet forwarding depends on routing table.
   • Manage route updates for dynamic protocols.

Step 2: Set Up NS3 Environment

1. Create a Protocol Directory:
   • Make a new protocol directory in src/, for example src/unicast-routing/.
2. Add Required Files:
   • unicast-routing-protocol.cc: Execution file.
   • unicast-routing-protocol.h: Header file for the unicast routing protocol.
   • unicast-routing-helper.h and unicast-routing-helper.cc: For incorporation, we can utilize Helper classes.
3. Update Build System:
   • Adjust the wscript using src/ with the new module for updating the system.

Step 3: Design the Unicast Routing Protocol

Define the Protocol Class

To execute unicast routing logic, we need to prolong the Ipv4RoutingProtocol class.

Header File (unicast-routing-protocol.h)

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

#include “ns3/socket.h”

#include “ns3/timer.h”

#include <map>

class UnicastRoutingProtocol : public ns3::Ipv4RoutingProtocol {

public:

static ns3::TypeId GetTypeId (void);

UnicastRoutingProtocol ();

virtual ~UnicastRoutingProtocol ();

// Override Ipv4RoutingProtocol methods

virtual ns3::Ptr<ns3::Ipv4Route> RouteOutput (

ns3::Ptr<const ns3::Packet> packet,

const ns3::Ipv4Header &header,

ns3::Ptr<ns3::NetDevice> oif,

ns3::Socket::SocketErrno &sockerr);

virtual bool RouteInput (

ns3::Ptr<const ns3::Packet> packet,

const ns3::Ipv4Header &header,

ns3::Ptr<const ns3::NetDevice> idev,

ns3::UnicastForwardCallback ucb,

ns3::MulticastForwardCallback mcb,

ns3::LocalDeliverCallback lcb,

ns3::ErrorCallback ecb);

void AddRoute (ns3::Ipv4Address destination, ns3::Ipv4Address nextHop, uint32_t interface);

void RemoveRoute (ns3::Ipv4Address destination);

private:

struct RouteEntry {

ns3::Ipv4Address nextHop;

uint32_t interface;

};

std::map<ns3::Ipv4Address, RouteEntry> m_routingTable; // Destination -> RouteEntry

};

Implement Core Functions

Add and Remove Routes

Enable the routing protocol for dynamically or statically integrating and eliminating the routes.

void UnicastRoutingProtocol::AddRoute (ns3::Ipv4Address destination, ns3::Ipv4Address nextHop, uint32_t interface) {

RouteEntry entry = {nextHop, interface};

m_routingTable[destination] = entry;

}

void UnicastRoutingProtocol::RemoveRoute (ns3::Ipv4Address destination) {

m_routingTable.erase(destination);

}

Route Output

Manage the route outgoing packets and compute the next hop.

ns3::Ptr<ns3::Ipv4Route> UnicastRoutingProtocol::RouteOutput (

ns3::Ptr<const ns3::Packet> packet,

const ns3::Ipv4Header &header,

ns3::Ptr<ns3::NetDevice> oif,

ns3::Socket::SocketErrno &sockerr) {

ns3::Ptr<ns3::Ipv4Route> route = ns3::Create<ns3::Ipv4Route> ();

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

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

route->SetGateway(it->second.nextHop);

route->SetOutputDevice(oif);

return route;

} else {

sockerr = ns3::Socket::ERROR_NOROUTETOHOST;

return nullptr;

}

}

Route Input

Find out whether transmitting or locally distributing and manage the route incoming packets.

bool UnicastRoutingProtocol::RouteInput (

ns3::Ptr<const ns3::Packet> packet,

const ns3::Ipv4Header &header,

ns3::Ptr<const ns3::NetDevice> idev,

ns3::UnicastForwardCallback ucb,

ns3::MulticastForwardCallback mcb,

ns3::LocalDeliverCallback lcb,

ns3::ErrorCallback ecb) {

if (header.GetDestination() == m_selfAddress) {

lcb(packet, header, 0); // Deliver locally

return true;

}

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

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

ucb(packet, header, it->second.nextHop, it->second.interface); // Forward

return true;

}

ecb(packet, header, ns3::Ipv4Header::DESTINATION_UNREACHABLE);

return false;

}

Step 4: Write a Helper Class

Make a helper class to make simpler incorporation into replications.

#include “unicast-routing-protocol.h”

class UnicastRoutingHelper {

public:

void Install (ns3::NodeContainer nodes) {

for (auto it = nodes.Begin(); it != nodes.End(); ++it) {

ns3::Ptr<UnicastRoutingProtocol> protocol = ns3::CreateObject<UnicastRoutingProtocol>();

(*it)->AggregateObject(protocol);

}

}

};

Step 5: Write a Simulation Script

Example Simulation Script

#include “ns3/core-module.h”

#include “ns3/network-module.h”

#include “ns3/internet-module.h”

#include “unicast-routing-helper.h”

using namespace ns3;

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

NodeContainer nodes;

nodes.Create (4);

InternetStackHelper stack;

stack.Install (nodes);

UnicastRoutingHelper unicastHelper;

unicastHelper.Install (nodes);

PointToPointHelper p2p;

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

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

p2p.Install (nodes.Get (0), nodes.Get (1));

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

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

Ipv4AddressHelper ipv4;

ipv4.SetBase (“10.1.1.0”, “255.255.255.0”);

ipv4.Assign (p2p.GetNetDeviceContainer());

// Add static routes

ns3::Ptr<UnicastRoutingProtocol> routingProtocol = nodes.Get(0)->GetObject<UnicastRoutingProtocol>();

routingProtocol->AddRoute(Ipv4Address(“10.1.1.3”), Ipv4Address(“10.1.1.2”), 1);

Simulator::Run ();

Simulator::Destroy ();

return 0;

}

Step 6: Compile and Run

1. Build the Protocol:

./waf configure

./waf build

1. Run the Simulation:

./waf –run your-script

Step 7: Analyze and Extend

1. Use Tracing Tools:
   • Allow tracing with the support of tools like AsciiTraceHelper or PcapHelper.
2. Enhancements:
   • Integrate assist for dynamic route updates.
   • Incorporate with performance parameters such as latency, bandwidth, or congestion.

We have provided a clear structure that helps for implementing and analyzing Unicast Routing using NS3 environment. We are prepared to expand it further for advanced understanding regarding this routing.