To simulate Dijkstra’s Link State projects utilizing NS2, we require setting up the routing behaviour rely on the Link-State Routing mechanism in which routers build a comprehensive map of the network and utilize Dijkstra’s algorithm to compute the shortest path among the nodes. The simulation environment NS2 contains support for link-state routing via static or dynamic routing protocols, however we can also modify it to explicitly replicate the behaviour of Dijkstra’s algorithm.
We deliver basic approach on how to simulate Dijkstra’s Link State Routing in NS2.
Steps to Simulate Dijkstra’s Link State Routing in NS2
- Set Up NS2 Environment
Make sure that NS2 is installed and running on the machine. We can check it by executing:
ns
If NS2 is installed then this will open the NS2 shell.
- Understanding Dijkstra’s Algorithm in Link-State Routing
Dijkstra’s Algorithm is utilized to compute the shortest path among the nodes in a network. In Link-State Routing, each node maintains a map of the whole network (i.e., all nodes and their links) and applies Dijkstra’s algorithm to discover the shortest paths.
- Writing a TCL Script for Dijkstra’s Link State Routing
Even though NS2 does not explicitly have a command for Dijkstra’s algorithm then it supports link-state routing utilizing protocols such as OSPF or Hierarchical routing. Following is an instance, which replicate link-state routing using Hierarchical Routing and applies Dijkstra’s algorithm implicitly to calculate the shortest paths.
# Create a simulator object
set ns [new Simulator]
# Open trace and NAM output files
set tracefile [open out.tr w]
set namfile [open out.nam w]
$ns trace-all $tracefile
$ns namtrace-all $namfile
# Enable hierarchical routing (Link-State type)
$ns node-config -addressType hierarchical
# Configure network address parameters
AddrParams set domain_num_ 2
lappend cluster_num 2 2 ;# Two clusters in each domain
AddrParams set cluster_num_ $cluster_num
# Define the network topology with nodes
set n0 [$ns node]
set n1 [$ns node]
set n2 [$ns node]
set n3 [$ns node]
set n4 [$ns node]
set n5 [$ns node]
# Create duplex links between nodes (simulating weights by adjusting delay)
$ns duplex-link $n0 $n1 1Mb 10ms DropTail
$ns duplex-link $n1 $n2 1Mb 20ms DropTail
$ns duplex-link $n1 $n3 1Mb 30ms DropTail
$ns duplex-link $n2 $n4 512Kb 50ms DropTail
$ns duplex-link $n3 $n5 1Mb 25ms DropTail
# Define the routing protocol (Link-State based, using hierarchical routing)
$ns rtproto LS
# Create a UDP agent and attach it to node n0 (source)
set udp0 [new Agent/UDP]
$ns attach-agent $n0 $udp0
# Create a Null agent and attach it to node n5 (destination)
set null0 [new Agent/Null]
$ns attach-agent $n5 $null0
# Connect the source and destination agents
$ns connect $udp0 $null0
# Create a CBR traffic generator and attach it to the UDP agent
set cbr [new Application/Traffic/CBR]
$cbr set packetSize_ 512
$cbr set interval_ 0.005
$cbr attach-agent $udp0
# Schedule the traffic generation
$ns at 1.0 “$cbr start”
$ns at 4.0 “$cbr stop”
$ns at 5.0 “finish”
# Define the finish procedure
proc finish {} {
global ns tracefile namfile
$ns flush-trace
close $tracefile
close $namfile
exec nam out.nam &
exit 0
}
# Run the simulation
$ns run
- Explanation of the Script
- Routing Protocol: The command $ns rtproto LS sets Link-State Routing for the simulation. This replicates the behaviour of routers utilizing Dijkstra’s algorithm to calculate the shortest paths.
- Network Topology: Six nodes are associated with duplex links. The delay parameter of each link replicates the link weights that will be utilized by the link-state routing algorithm to calculate the shortest paths.
- Traffic: Constant Bit Rate (CBR) traffic generator transmits traffic from node n0 to node n5 utilizing a UDP agent.
- Simulate Network Dynamics (Link Failures)
We can mimic link failures or topology changes in the course of the simulation to monitor how the link-state routing protocol actively adjusts. Insert the following commands to replicate a link failure:
# Simulate a link failure between n1 and n2 at 2.5 seconds
$ns rtmodel-at 2.5 down $n1 $n2
# Restore the link at 4.0 seconds
$ns rtmodel-at 4.0 up $n1 $n2
It will force the network to recomputed the shortest paths with the help of Dijkstra’s algorithm according to the new topology.
- Running the Simulation
To execute the simulation, save the script as dijkstra_linkstate.tcl and run it using the below command:
ns dijkstra_linkstate.tcl
It will make the output trace file (out.tr) and a NAM file (out.nam) for envisioning the network.
- Visualizing the Simulation
We can envision the network and routing decisions using NAM:
nam out.nam
The NAM tool will indicate how the link-state protocol (using Dijkstra’s algorithm) calculates the shortest paths among the nodes.
- Customizing the Simulation
We can further modify the simulation by:
- Inserting more nodes and links to make a larger network.
- Altering the link weights (by adjusting bandwidth or delay) to monitor diverse routing paths are calculated by Dijkstra’s algorithm.
- Testing with traffic patterns by utilizing distinct traffic generators like TCP or differing the traffic intervals.
- Analyzing the Trace File
The trace file (out.tr) encompasses detailed data regarding packet transmissions, routing updates, and network changes. We can be used awk or grep to extract key parameters like:
- Packet Delivery Ratio (PDR): Compute how successfully packets are delivered over the shortest paths.
- End-to-End Delay: Evaluate the time it takes for packets to travel from the origin to the destination.
- Routing Overhead: Calculate the amount of control messages are made by the link-state routing protocol to maintain the network map.
For instance, to assess the number of packets received at the destination:
grep “^r” out.tr | wc -l
- Performance Evaluation
Estimate the performance of Dijkstra’s link-state routing by:
- Scalability: Experiment the performance as minimize the amount of nodes in the network.
- Link Changes: Replicate frequent link failures and retrieves to observe how rapidly the routing protocol adjusts.
- Traffic Load: Differ the traffic intensity and monitor how the routing protocol performs under distinct load conditions.
From this manual, you can able to use Dijkstra’s algorithm to calculate the shortest path between the nodes to simulate the Dijkstra’s link state projects using NS2 tool and it has detailed simulation procedures with the sample codes, extension of this concepts and performance analysis. If you did like to know more details regarding this process we will provide it. For assistance with any Dijkstra’s Link State simulation, please provide us with the details of your project, and we will deliver optimal results. To enhance your network analysis, connect with phdprime.com, where we offer comprehensive explanations. We also provide guidance on link-state routing through both static and dynamic routing protocols relevant to your project.
