To simulate Open Shortest Path First (OSPF) in NS2 has includes to execute or use the OSPF routing protocol functionality to enthusiastically identify the shortest path mong nodes in a network. Since NS2 supports numerous routing protocols, OSPF is not directly executed. but, OSPF can be replicated using either custom patches for NS2 or by approaching its characteristics using a similar proactive link-state routing protocol, such as OLSR (Optimized Link State Routing), that shares similarities with OSPF.
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If we need to simulate OSPF specifically, there are a few methods:
- Using OSPF Patch for NS2: we can patch NS2 with an OSPF implementation.
- Simulating OSPF Behaviour with OLSR: While OLSR and OSPF are both proactive link-state protocols, we can replicate OSPF’s shortest path functionality using OLSR in NS2.
Method 1: Using an OSPF Patch for NS2
If we need to identify an OSPF patch for NS2, we would follow these steps:
- Download the OSPF Patch: Look for an OSPF patch for NS2 (we need identify it through repositories or research papers).
- Patch NS2: Navigate to the NS2 root directory and implement the patch:
patch -p1 < ospf_ns2_patch.diff
- Rebuild NS2:
make clean
make
- Simulate OSPF: Once patched, we can set up OSPF in TCL scripts by choosing the OSPF routing protocol.
If we cannot identify a certain OSPF patch, we can proceed with Method 2 that approximates OSPF behaviour using OLSR.
Method 2: Simulating OSPF-like Behavior with OLSR
Optimized Link State Routing (OLSR) protocol is a proactive, link-state protocol, same as OSPF. OLSR can be utilized to replicate the behaviour of OSPF since it also floods link-state information to estimate the shortest path for routing traffic.
Here’s a step-by-step guide to simulate OSPF-like behaviour using OLSR in NS2:
- Install NS2
Ensure NS2 is installed on the system.
- TCL Script for OLSR-based Simulation
This script will replicate a simple network using the OLSR protocol that acts as similarly to OSPF by estimating the shortest path using link-state information.
Example TCL Script for OLSR-based OSPF Simulation
# Create a simulator object
set ns [new Simulator]
# Open files for tracing and NAM visualization
set tracefile [open ospf_simulation.tr w]
$ns trace-all $tracefile
set namfile [open ospf_simulation.nam w]
$ns namtrace-all $namfile
# Define network topology and setup links
set topo [new Topography]
$topo load_flatgrid 500 500
# Define link parameters: bandwidth, delay, and queue type
set bw 10Mb
set delay 10ms
set queue DropTail
# Create nodes for the network
set node_count 5
for {set i 0} {$i < $node_count} {incr i} {
set node($i) [$ns node]
}
# Create links between nodes (you can customize this part)
$ns duplex-link $node(0) $node(1) $bw $delay $queue
$ns duplex-link $node(1) $node(2) $bw $delay $queue
$ns duplex-link $node(2) $node(3) $bw $delay $queue
$ns duplex-link $node(3) $node(4) $bw $delay $queue
$ns duplex-link $node(4) $node(0) $bw $delay $queue
# Set routing protocol to OLSR (behaves like OSPF for shortest path routing)
$ns node-config -adhocRouting OLSR
# Node configuration (optional) to simulate mobility
$ns at 0.0 “$node(0) setdest 100 100 15”
$ns at 0.0 “$node(1) setdest 200 200 15”
$ns at 0.0 “$node(2) setdest 300 300 15”
$ns at 0.0 “$node(3) setdest 400 400 15”
$ns at 0.0 “$node(4) setdest 500 500 15”
# Attach TCP agent to node 0
set tcp0 [new Agent/TCP]
$ns attach-agent $node(0) $tcp0
# Attach TCP Sink agent to node 4
set sink [new Agent/TCPSink]
$ns attach-agent $node(4) $sink
# Connect TCP agent and Sink agent
$ns connect $tcp0 $sink
# Create an FTP application over TCP and start traffic
set ftp [new Application/FTP]
$ftp attach-agent $tcp0
$ns at 1.0 “$ftp start”
$ns at 10.0 “$ftp stop”
# End simulation after 15 seconds
$ns at 15.0 “finish”
# Define the finish procedure to close trace files and launch NAM
proc finish {} {
global ns tracefile namfile
$ns flush-trace
close $tracefile
close $namfile
exec nam ospf_simulation.nam &
exit 0
}
# Run the simulation
$ns run
- Explanation of the Script
- Simulator Object: Generates a simulator object and opens trace and NAM files for recording simulation events.
- Node Creation: Five nodes are created, and duplex links are configuring among them with 10Mbps bandwidth and 10ms delay.
- Routing Protocol: The OLSR protocol is set up for the nodes that act as similarly to OSPF by interchanging link-state information and estimate the shortest path.
- Traffic Generation: FTP traffic is created from node 0 (source) to node 4 (destination) using TCP as the transport protocol.
- Simulation End: The simulation executes for 15 seconds, and the FTP traffic terminate after 10 seconds.
- Running the Simulation
Save the above TCL script (e.g., ospf_simulation.tcl) and execute it using NS2 with the following command:
ns ospf_simulation.tcl
This will execute the simulation, create trace files, and generate a NAM visualization file.
- Analyzing the Results
- NAM Visualization: we can open the .nam file in NAM (Network Animator) to envision the network, traffic flow, and routing decisions made by the OLSR protocol.
nam ospf_simulation.nam
- Trace File Analysis: Utilize the .tr trace file to evaluate the performance of the routing protocol based on:
- End-to-End Delay: The time it takes for packets to traverse from the source to the destination.
- Packet Delivery Ratio (PDR): The ratio of successfully delivered packets to the total number of packets sent.
- Routing Overhead: The amount of control packets created by the routing protocol.
- Performance Metrics for OSPF-like Simulation
When replicating OSPF-like routing behaviour, we can evaluate the following parameter:
- Shortest Path Calculation: check that the protocol is prioritizing the shortest available path among nodes.
- End-to-End Delay: Evaluate the time taken for packets to traverse the network.
- Throughput: Estimate the rate of successful data delivery via the network.
- Packet Loss: monitor how many packets are lost in the course of the simulation.
- Routing Overhead: Track the overhead generated by the interchange of routing information (link-state advertisements).
- Extensions to the Simulation
We can expand this simulation to contain more complex OSPF characteristics or validate specific OSPF functionality:
- Dynamic Topology: establish node failures or link breakages to validate how the routing protocol adjusts to changes in the network.
- QoS Routing: Execute traffic engineering to replicate OSPF-TE (OSPF with Traffic Engineering) characteristics for enhancing network resource utilization.
- Scalability: Increase the number of nodes in the network to measure on how the protocol manages larger topologies.
The given above is the fundamental approach that was illustrated with sample coding for Open Shortest Path First project that were simulated across the ns2 environment. We deliver more information regarding this project in further manual.
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