How to Start Spanning Tree Protocol Projects Using NS2

To start a Spanning Tree Protocol (STP) project in Network Simulator 2 (NS2), we will replicate the STP behavior or execute the custom logic while NS2 doesn’t directly STP support. STP is normally utilised within Layer 2 Ethernet networks for avoiding loops and making sure that single dynamic path among the network nodes.

Below is a general approach to get started:

Steps to Start Spanning Tree Protocol Projects in NS2

Step 1: Set Up NS2 Environment

Install NS2:
- We should download and install the new version of NS2 on the system.
- Confirm installation by using below code:

ns -version

Understand NS2 Basics:
- Study on how to specify the nodes, links, and traffic to utilise Tcl scripts in NS2.
- Search examples through ns-allinone-2.x/examples/.

Step 2: Understand Spanning Tree Protocol

What is STP?
- A Layer 2 protocol, making a loop-free spanning tree topology which avoids loops within Ethernet networks.
- It inactivates the redundant links whereas maintaining one dynamic path to all network segments.
Core Components:
- Root Bridge: The central node of the spanning tree which is lowest bridge ID.
- Designated Bridge: This node responds for sending packets to a segment.
- Non-Designated Ports: Ports which is designed for avoiding loops.
Key Steps in STP:
- Root Election: Choose the root bridge according to the lowest bridge ID.
- Path Selection: It finds the shortest route to the root bridge.
- Port States: Then, allocate the ports like root, which is chosen, or obstructed.

Step 3: Design Network Topology

Define Nodes and Links:
- Make a network topology including potential loops.

set ns [new Simulator]

# Create nodes

set n1 [$ns node]

set n2 [$ns node]

set n3 [$ns node]

set n4 [$ns node]

# Define links

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

$ns duplex-link $n2 $n3 10Mb 10ms DropTail

$ns duplex-link $n3 $n4 10Mb 10ms DropTail

$ns duplex-link $n4 $n1 10Mb 10ms DropTail

$ns duplex-link $n1 $n3 10Mb 10ms DropTail

Simulate Loops:
- The network must contain several paths among the nodes for analysing the loop-prevention method of STP.

Step 4: Implement Spanning Tree Logic

Option 1: Simulate STP in Tcl

Root Bridge Election:
- We need to replicate the root bridge selection by way of allocating the bridge IDs and designating the lowest.

set bridges {n1 n2 n3 n4}

set rootBridge {}

set minID inf

foreach bridge $bridges {

set bridgeID [expr rand() * 1000] ;# Assign random bridge IDs

if {$bridgeID < $minID} {

set minID $bridgeID

set rootBridge $bridge

}

puts “Root Bridge: $rootBridge with ID $minID”

Port State Assignment:
- Depends on the shortest route to the root, discover the root, designated, and blocked ports.

proc assignPortStates {bridges root} {

foreach bridge $bridges {

if {$bridge != $root} {

# Determine port roles based on shortest path

puts “Bridge $bridge: Assign port roles”

}

assignPortStates $bridges $rootBridge

Option 2: Custom STP Implementation in C++

Create a Spanning Tree Protocol Agent:
- In NS2, prolong the Agent class for executing STP logic.
- Sustain a bridge ID, port states, and a topology database.

Example:

class STPAgent : public Agent {

public:

STPAgent();

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

void calculateSpanningTree();

private:

int bridgeID;

std::map<int, std::string> portStates; // Port ID -> State (Root, Designated, Blocked)

};

Implement Core Functions:
- Root Election: Transmit bridge IDs and find the root.
- Port State Assignment: Allocate the roles to ports rely on route cost.
Compile and Link:
- Change the NS2 Makefile with the custom STP agent.
- Recompile NS2 to utilise below command line:

make clean && make

Step 5: Add Traffic Sources

Define Traffic Flows:
- Connect agents to nodes and make a traffic flows.

set udp [new Agent/UDP]

$ns attach-agent $n1 $udp

set sink [new Agent/Null]

$ns attach-agent $n4 $sink

$ns connect $udp $sink

# Add CBR 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”

Monitor Traffic Flow:
- Monitor how STP removes loops and makes sure a single dynamic path.

Step 6: Simulate and Analyze

Run the Simulation:
- We need to store the script like stp_simulation.tcl and then run the simulation:

ns stp_simulation.tcl

Visualize in NAM:
- In NAM, monitor the spanning tree topology and traffic flow:

nam stp_simulation.nam

Analyze Trace File:
- Crucial performance parameters to estimate:
  - Duration to meet to a spanning tree.
  - Packet delivery ratio.
  - Redundant link deactivation.

Step 7: Enhance the Project

Dynamic Topology Changes:
- To replicate the link failures or additions depends on dynamic topology modifications and monitor how to STP meeting again.

$ns at 5.0 “$ns duplex-link-delete $n1 $n3”

Performance Comparison:
- We have to equate the STP including other loop-prevention approaches or spanning tree differences such as RSTP.
Scalability Testing:
- Experiment the scalability of STP as volume of nodes and links maximizes.

Example Script Outline

Below is an example NS2 Tcl script for an STP simulation: