How to Implement Routing Protocols in NS2

To design a routing protocol using the simulation tool NS2 (Network Simulator 2) which needs a solid understanding of network types such as ad-hoc networks, wireless sensor networks, or wired networks, NS2’s underlying architecture, and routing goals like minimizing delay, maximizing throughput, or ensuring reliability. These protocols are describe how packets are sent from source to end, and also they can be proactive, reactive, or hybrid in nature. Now, we provide comprehensive approach that helps to design a custom routing protocol in NS2.

Key Steps in Designing Routing Protocols in NS2

  1. Understand the Routing Goals: Describe the purpose of the routing protocol. It could concentrate on:
    • Minimizing latency: Minimize the time packets take to attain their end.
    • Maximizing throughput: Maximize the amount of data transmitted effectively.
    • Energy efficiency: Enhance an energy usage, particularly in wireless or sensor networks.
    • Scalability: Make sure the protocol works effectively in the large networks.
    • Reliability: Make certain that robust delivery in the existence of link failures or high mobility.
  2. Choose the Type of Routing Protocol:
    • Proactive (Table-Driven): These protocols such as DSDV maintain consistent current routing tables at every node. Routes are always obtainable, however there is overhead because of the periodic updates.
    • Reactive (On-Demand): This protocols like AODV find the routes only while required, decreasing control overhead however introducing route discovery delays.
    • Hybrid: Protocols such as ZRP (Zone Routing Protocol) associate proactive and reactive approaches for more scalable solutions.
  3. Define Packet Types:
    • Control Packets: This control packets used to handle routes such as Route Request (RREQ), Route Reply (RREP).
    • Data Packets: Encompass the actual payload like TCP or UDP packets.
    • Custom Packet Types: We can describe extra custom packets to handle special operations in the protocol.

Step-by-Step Guide to Designing a Routing Protocol in NS2

  1. Define Packet Structure

In the simulation NS2, we want to describe the structure of the packets that the protocol will be used. Packets can have headers including fields such as source address, destination address, sequence numbers, and so on.

Example: Define a Custom Packet Type for Your Protocol

Change the header file in C++ to describe custom packet types. For instance, to make a Route Request (RREQ) packet:

struct hdr_myprotocol {

int pkt_type;          // Packet type (RREQ, RREP, etc.)

int src_addr;          // Source address

int dest_addr;         // Destination address

int seq_num;           // Sequence number for avoiding loops

int hop_count;         // Number of hops

static int offset_;    // Offset for accessing the packet in the NS2 framework

inline static hdr_myprotocol* access(const Packet* p) {

return (hdr_myprotocol*) p->access(offset_);

}

};

// Set the offset for accessing the custom header

int hdr_myprotocol::offset_;

In the protocol, we can use hdr_myprotocol::access(p) to recover the header and alter the fields such as source, end, and hop count.

  1. Implement Routing Protocol Logic

Now, we will execute the core logic for the routing protocol, with how routes are discovered, maintained, and updated.

Example: Create a Routing Agent for Your Protocol

The routing agent manages incoming and outgoing packets, updating the routing table, and forwarding data.

class MyRoutingAgent : public Agent {

public:

MyRoutingAgent();

void recv(Packet* p, Handler* h);  // Override the receive function to process packets

void sendRREQ(int dest_addr);      // Function to send Route Request (RREQ)

void sendRREP(int src_addr);       // Function to send Route Reply (RREP)

protected:

map<int, int> routingTable;  // Simple routing table (destination -> next hop)

void forwardPacket(Packet* p);  // Forward data packets

};

// Constructor for the custom routing agent

MyRoutingAgent::MyRoutingAgent() : Agent(PT_UDP) {}

// Receive and process incoming packets

void MyRoutingAgent::recv(Packet* p, Handler* h) {

hdr_ip* iph = HDR_IP(p);

hdr_myprotocol* hdr = hdr_myprotocol::access(p);

// Process RREQ packets

if (hdr->pkt_type == RREQ) {

if (iph->dst() == node()->address()) {

sendRREP(iph->src());  // Destination found, send RREP

} else {

forwardPacket(p);  // Forward RREQ to the next node

}

}

// Process RREP packets

else if (hdr->pkt_type == RREP) {

// Add the route to the routing table

routingTable[hdr->src_addr] = hdr->hop_count;

forwardPacket(p);  // Forward RREP towards the source

}

// Process data packets

else {

forwardPacket(p);

}

}

// Send a Route Request (RREQ) to find a route

void MyRoutingAgent::sendRREQ(int dest_addr) {

Packet* p = allocpkt();

hdr_ip* iph = HDR_IP(p);

hdr_myprotocol* hdr = hdr_myprotocol::access(p);

hdr->pkt_type = RREQ;

hdr->src_addr = node()->address();

hdr->dest_addr = dest_addr;

send(p, 0);  // Send the packet

}

// Send a Route Reply (RREP) back to the source

void MyRoutingAgent::sendRREP(int src_addr) {

Packet* p = allocpkt();

hdr_ip* iph = HDR_IP(p);

hdr_myprotocol* hdr = hdr_myprotocol::access(p);

hdr->pkt_type = RREP;

hdr->src_addr = node()->address();

hdr->dest_addr = src_addr;

send(p, 0);

}

// Forward packets to the next hop

void MyRoutingAgent::forwardPacket(Packet* p) {

hdr_ip* iph = HDR_IP(p);

if (routingTable.find(iph->dst()) != routingTable.end()) {

int next_hop = routingTable[iph->dst()];

sendto(p, next_hop);  // Forward the packet to the next hop

} else {

// Route not found, drop the packet

Packet::free(p);

}

}

  1. Implement Routing Table Management

In a custom routing protocol, we will maintain a routing table to store paths to destinations and we can execute this as a basic map in C++ or a more difficult data structure based on the protocol’s requirements.

Example of a Simple Routing Table:

map<int, int> routingTable;  // Mapping destination -> next hop

void MyRoutingAgent::updateRoutingTable(int dest_addr, int next_hop) {

routingTable[dest_addr] = next_hop;

}

int MyRoutingAgent::lookupNextHop(int dest_addr) {

if (routingTable.find(dest_addr) != routingTable.end()) {

return routingTable[dest_addr];  // Return the next hop if route is found

} else {

return -1;  // Route not found

}

}

  1. Create Tcl Interface for NS2 Simulation

We will want to reveal the protocol to the NS2 simulator by making an interface for Tcl scripts, after defining your protocol in C++.

Example Tcl Interface:

extern “C” int Myprotocol_Init() {

// Create a new agent for the custom protocol

TclClass* tclClass = new TclClass(“Agent/MyRoutingProtocol”, createMyRoutingProtocol);

tclClass->bind();

return TCL_OK;

}

// Function to create a new instance of the routing protocol

Agent* createMyRoutingProtocol() {

return new MyRoutingAgent();

}

We also require to register this protocol in the ns-lib.tcl file thus it can be used in NS2 simulations.

  1. Simulate the Routing Protocol in NS2

Now the protocol is executed, we can replicate it using a Tcl script within the NS2. This script describes that the network topology, node placement, mobility, traffic patterns, and attaches the custom routing protocol to the nodes.

Example Tcl Script for Simulating Your Routing Protocol:

# Create a simulator instance

set ns [new Simulator]

# Define node configurations

set node1 [$ns node]

set node2 [$ns node]

set node3 [$ns node]

# Attach the custom routing protocol to the nodes

set ragent1 [new Agent/MyRoutingProtocol]

$ns attach-agent $node1 $ragent1

set ragent2 [new Agent/MyRoutingProtocol]

$ns attach-agent $node2 $ragent2

# Set up traffic between nodes

set udp0 [new Agent/UDP]

$ns attach-agent $node1 $udp0

$ns connect $udp0 $ragent2

set cbr0 [new Application/Traffic/CBR]

$cbr0 set packetSize_ 512

$cbr0 set interval_ 0.5

$cbr0 attach-agent $udp0

# Start traffic

$ns at 1.0 “$cbr0 start”

# Run the simulation

$ns run

  1. Evaluate Protocol Performance

We assess the performance of the routing protocol, after running the simulation which using metrics such as:

  • Packet Delivery Ratio (PDR): Estimate the percentage of effectively delivered packets.
  • Throughput: Shows the amount of data transmitted across the network.
  • Average Latency: Compute the delay among the packet transmission and reception.
  • Control Overhead: Calculate the amount of control traffic generated by the protocol like RREQ, RREP packets.
  • Energy Efficiency: In the wireless networks, assess the energy consumption of the nodes.

As shown above we elaborate on how to design a custom routing protocol, how to implement the routing table management, and how to evaluate this performance in NS2 with the support of stepwise methods.  We are prepared to share further informations as required.

For assistance in designing routing protocols using the NS2 tool, please feel free to contact us. We are prepared to provide you with a concise explanation and ensure timely delivery of our services.