How to Implement Network Topology Routing in NS2
To implement network topology-based routing in NS2 has a series of steps to follow that contain to model a routing protocol that takes the network topology into account when making routing decisions. In topology-based routing, the structure of the network on how nodes are interconnected is used to enhance the routes among nodes. This can contain parameters like hop count, node degree, or even geographic positions in some cases.
Here’s a detailed process on how to implement network topology-based routing in NS2:
Key Steps for Implementing Topology-Based Routing in NS2
- Define the Network Topology
The first step is to describe the network topology that involves to generating nodes, describing their positions, and establishing connections between them.
Example: Creating a Basic Topology (Wired or Wireless)
For wired or wireless networks, the topology can be generated using the node and duplex-link or wireless channel commands.
Wired Topology Example:
# Create the simulator instance
set ns [new Simulator]
# Create nodes
set node1 [$ns node]
set node2 [$ns node]
set node3 [$ns node]
# Create duplex links between nodes
$ns duplex-link $node1 $node2 1Mb 10ms DropTail # Link between node1 and node2
$ns duplex-link $node2 $node3 1Mb 10ms DropTail # Link between node2 and node3
# Optionally, you can also set up queue limits or error models on the links
$ns queue-limit $node1 $node2 50
Wireless Topology Example:
# Create a wireless channel
set channel [new Channel/WirelessChannel]
# Define the propagation and topography for wireless communication
set prop [new Propagation/TwoRayGround]
set topo [new Topography]
$topo load_flatgrid 500 500 # Set a 500×500 area for the network
# Create wireless nodes
for {set i 0} {$i < 10} {incr i} {
set node($i) [$ns node]
}
# Position nodes
$node(0) set X_ 100; $node(0) set Y_ 100; $node(0) set Z_ 0
$node(1) set X_ 200; $node(1) set Y_ 200; $node(1) set Z_ 0
$node(2) set X_ 300; $node(2) set Y_ 300; $node(2) set Z_ 0
- Wired networks: Use duplex-link to describe links among nodes.
- Wireless networks: Use WirelessChannel to configure interaction via a shared medium, and TwoRayGround for signal propagation.
- Choose or Implement a Topology-Based Routing Protocol
Topology-based routing protocols depend on how the network is connected. We can select an existing protocol such as DSDV, AODV, or DSR, or execute a custom topology-based routing algorithm that leverages node degree, link quality, or specific topological characteristics.
Option 1: Use an Existing Topology-Based Protocol
NS2 already deliver protocols such as DSDV (Destination-Sequenced Distance Vector) that is a proactive topology-based routing protocol that uses a routing table to sustain paths for all destinations.
Example of Configuring DSDV Routing:
# Enable DSDV for the wireless nodes
$ns node-config -adhocRouting DSDV -llType LL -macType Mac/802_11 -ifqType Queue/DropTail/PriQueue \
-ifqLen 50 -antType Antenna/OmniAntenna -propType Propagation/TwoRayGround -phyType Phy/WirelessPhy \
-channelType Channel/WirelessChannel
# Create a wireless node and configure it to use DSDV
set node1 [$ns node]
set node2 [$ns node]
# Start the simulation
$ns run
Option 2: Implement a Custom Topology-Based Routing Protocol
We can also execute a custom routing protocol in which the routing decisions are based on the network topology. For instance, we can generate a Shortest Path First (SPF) protocol or use a node degree-based metric.
Example: Custom Topology-Based Routing Agent (C++ Code):
Generate a new routing agent in C++ that will calculate the shortest path or use other topological parameters to prioritize the best route.
class TopologyRoutingAgent : public Agent {
public:
TopologyRoutingAgent();
void recv(Packet* p, Handler* h); // Receive and process incoming packets
void sendRREQ(int dest_addr); // Send Route Request (RREQ)
void sendRREP(int src_addr); // Send Route Reply (RREP)
protected:
map<int, vector<int>> topologyTable; // Topology information (e.g., neighbors)
map<int, int> routingTable; // Routing table storing best next hops
void calculateShortestPath(); // Calculate the shortest path based on topology
};
// Constructor
TopologyRoutingAgent::TopologyRoutingAgent() : Agent(PT_UDP) {
// Initialize the agent
}
// Process received packets
void TopologyRoutingAgent::recv(Packet* p, Handler* h) {
hdr_ip* iph = HDR_IP(p);
hdr_myprotocol* hdr = hdr_myprotocol::access(p);
// Process Route Request (RREQ) or Route Reply (RREP)
if (hdr->pkt_type == RREQ) {
if (iph->dst() == node()->address()) {
sendRREP(iph->src()); // If destination is reached, send back RREP
} else {
// Forward the RREQ based on topology
forwardPacket(p);
}
} else if (hdr->pkt_type == RREP) {
routingTable[hdr->src_addr] = hdr->hop_count; // Update routing table
forwardPacket(p); // Forward the RREP
}
}
// Send a Route Request (RREQ)
void TopologyRoutingAgent::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 a Route Reply (RREP)
void TopologyRoutingAgent::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);
}
// Calculate shortest path using the topology table
void TopologyRoutingAgent::calculateShortestPath() {
// Implement shortest path algorithm (e.g., Dijkstra’s Algorithm) here
// Update routingTable with the best next hop based on the calculated paths
}
This sample demonstrates a simple structure for a custom TopologyRoutingAgent that uses the network topology to route packets. We can add characteristics such as shortest path computation using Dijkstra’s Algorithm or other routing metrics.
- Create a Tcl Interface for the Routing Protocol
Once custom routing protocol is defined in C++, generate a Tcl interface to use it in NS2 simulations.
Example Tcl Interface:
extern “C” int TopologyRouting_Init() {
TclClass* tclClass = new TclClass(“Agent/TopologyRoutingAgent”, createTopologyRoutingAgent);
tclClass->bind();
return TCL_OK;
}
Agent* createTopologyRoutingAgent() {
return new TopologyRoutingAgent();
}
This interface guarantees that the new routing protocol can be used in NS2 simulation scripts.
- Simulate the Network with the Custom Routing Protocol
In simulation Tcl script, we can now attach the custom routing protocol to nodes.
Example Tcl Script for Simulating Custom Topology-Based Routing:
# Create a simulator instance
set ns [new Simulator]
# Create nodes
set node1 [$ns node]
set node2 [$ns node]
set node3 [$ns node]
# Attach the custom topology-based routing agent to the nodes
set tAgent1 [new Agent/TopologyRoutingAgent]
set tAgent2 [new Agent/TopologyRoutingAgent]
$ns attach-agent $node1 $tAgent1
$ns attach-agent $node2 $tAgent2
# Set up traffic between nodes
set udp0 [new Agent/UDP]
$ns attach-agent $node1 $udp0
$ns connect $udp0 $tAgent2
set cbr0 [new Application/Traffic/CBR]
$cbr0 set packetSize_ 512
$cbr0 set interval_ 0.5
$cbr0 attach-agent $udp0
# Start the traffic
$ns at 1.0 “$cbr0 start”
# Run the simulation
$ns run
- Analyze the Performance
Once the simulation is done, we can evaluate the performance of the topology-based routing protocol. The trace files created by NS2 will permits to evaluate performance metrics such as:
- Packet Delivery Ratio (PDR): The percentage of successfully delivered packets.
- Average Latency: The time it takes for packets to reach their destination.
- Routing Overhead: The amount of control traffic created by the routing protocol.
- Path Optimality: How optimal the selected routes are based on topology information.
We can use tools such as AWK, Perl, or Python to process the trace files and estimate these parameters.
Example of a Simple AWK Script to Calculate Packet Delivery Ratio:
awk ‘{
if ($1 == “r” && $4 == “AGT”) received++;
if ($1 == “s” && $4 == “AGT”) sent++;
} END { print “Packet Delivery Ratio = ” received/sent * 100 “%” }’ tracefile.tr
The above following demonstration will clearly show how to replicate and enforce the network topology-based routing in ns2 tool that is used to enhance the routes among nodes. More information will be shared regarding the network topology-based routing.
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