How to start Bellman Ford Routing Projects using NS2

To create a Bellman-Ford Routing project using NS2, we require to observe for this procedure to execute and replicate the methods. Bellman-Ford is a distance vector routing algorithm that measure the minimum path from a source node to overall other nodes in the network. It can maintain the networks through various weights and supports negative edge weights such as if applicable.

Steps to start Bellman Ford Routing Projects using NS2

Step 1: Setup NS2 Environment

  1. Install NS2:
    • Download NS2 from the NS2 Official Website or use a precompiled package.
    • Install dependencies such as Tcl, OTcl, NAM and validate:

ns -version

  1. Understand NS2 Basics:
    • Examine the basic NS2 scripting we build a nodes, connection, and congestion flows.
    • Mention the sample scripts in ns-allinone-2.x/examples/.

Step 2: Understand Bellman-Ford Algorithm

  1. Bellman-Ford Overview:
    • Calculated the minimum paths iteratively through bring up-to-date distance vectors.
    • Every node has handled a distance table with:
      • Destination
      • Cost to reach the destination
      • Next-hop node
    • Bring up-to-date are shared by neighbours periodically.
  2. Key Features:
    • Maintain the dynamic topologies and connection for cost variations.
    • Finding the negative weight cycles.

Step 3: Design Network Topology

  1. Describe the nodes and connection in the network:

set ns [new Simulator]

# Define nodes

set n1 [$ns node]

set n2 [$ns node]

set n3 [$ns node]

set n4 [$ns node]

# Create links with bandwidth and delay

$ns duplex-link $n1 $n2 1Mb 10ms DropTail

$ns duplex-link $n2 $n3 1Mb 15ms DropTail

$ns duplex-link $n3 $n4 1Mb 20ms DropTail

$ns duplex-link $n1 $n4 1Mb 30ms DropTail

  1. Allocate the different costs to connection we replicate the real-world scenarios.

Step 4: Implement Bellman-Ford Algorithm

Option 1: Tcl Script Implementation

  1. Descirbe the procedure we measure the minimum path:

proc bellmanFord {nodes links src} {

set distances {}

set nextHop {}

# Initialize distances

foreach node $nodes {

if {$node == $src} {

set distances($node) 0

} else {

set distances($node) inf

}

set nextHop($node) -1

}

# Iterative relaxation

for {set i 1} {$i <= [llength $nodes]} {incr i} {

foreach {from to cost} $links {

if {$distances($from) + $cost < $distances($to)} {

set distances($to) [expr $distances($from) + $cost]

set nextHop($to) $from

}

}

}

# Print results

foreach node $nodes {

puts “Node $node: Distance = $distances($node), Next Hop = $nextHop($node)”

}

}

  1. Call the methods by your network’s nodes and connection:

set nodes {n1 n2 n3 n4}

set links {n1 n2 10 n2 n3 15 n3 n4 20 n1 n4 30}

bellmanFord $nodes $links n1

Option 2: Custom C++ Implementation

  1. Build a new routing agent for Bellman-Ford:
    • Spread the Agent class in NS2’s source code.

Example:

class BellmanFordAgent : public Agent {

public:

BellmanFordAgent();

void recv(Packet* p, Handler* h);

void calculateShortestPath();

private:

std::map<int, int> distanceTable; // Node -> Distance

std::map<int, int> nextHopTable; // Node -> Next Hop

};

  1. Execute the Bellman-Ford logic in the calculateShortestPath procedures:
    • Handle a distance vector and bring up-to-date it based on neighbours’ information.
  2. Recompile NS2 has include the modify agent:

make clean && make

Step 5: Define Traffic Flow

  1. Enhance the congestion sources and sinks to validate the procedures:

# Attach agents

set udp [new Agent/UDP]

$ns attach-agent $n1 $udp

set sink [new Agent/Null]

$ns attach-agent $n4 $sink

$ns connect $udp $sink

 

# Generate traffic

set cbr [new Application/Traffic/CBR]

$cbr attach-agent $udp

$cbr set packetSize_ 512

$cbr set interval_ 0.05

$ns at 1.0 “$cbr start”

  1. Monitor on how the packets are routed according to the Bellman-Ford algorithm.

Step 6: Simulate and Analyze

  1. Store the script as bellman_ford.tcl and replication for the process:

ns bellman_ford.tcl

  1. Envision the outcomes for NAM:

nam bellman_ford.nam

  1. Examine the trace file for:
    • Packet delivery ratio
    • Route convergence time
    • Path taken by packets

Step 7: Enhance the Project

  1. Dynamic Updates:
    • Replicate the connection failures and follow on how Bellman-Ford reacts.
  2. Performance Comparison:
    • Associate by Dijkstra’s procedures or other routing protocols.
  3. Scalability Testing:
    • Replicate a larger network by 20+ nodes.
  4. Cycle Detection:
    • Encompass the execution for finding and maintain the negative weight cycles.

Let me know if you need help with specific implementation steps or troubleshooting!

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