How to Simulate OSI Layer Protocol Projects Using NS2

To simulate an Open Systems Interconnection (OSI) layer protocols utilizing NS2 that contains designing network components and communication processes, which align with the distinct layers of the OSI model. NS2 (Network Simulator 2) primarily concentrates on the lower layers (Physical, Data Link, and Network layers), however with extra scripts and custom modules, we can replicate functionalities for higher layers (Transport, Session, Presentation, and Application).

We will walk you through step-by-step guide to simulate OSI layer protocols using NS2:

Steps to Simulate OSI Layer Protocol Projects in NS2

1. Understand the OSI Model and its Layers

• The OSI model contains seven layers:
  1. Physical Layer
  2. Data Link Layer
  3. Network Layer
  4. Transport Layer
  5. Session Layer
  6. Presentation Layer
  7. Application Layer

Each layer has its certain protocols, like Ethernet for Data Link Layer, IP for Network Layer, TCP/UDP for Transport Layer, and numerous application protocols (HTTP, FTP) for the Application Layer.

2. Set Up NS2

If not already done then we install NS2 on the system. The installation guidelines vary relying on the platform (Linux, Windows with Cygwin, or MacOS). Make sure we have a functional NS2 configuration:

• Download: NS2 Official Site

3. Choose the Protocol and Layer

Decide which layer and protocol we need to replicate. For instance:

• Data Link Layer: We might function with MAC protocols like IEEE 802.11.
• Network Layer: We can be used routing protocols such as AODV, DSR, or TCP/IP.
• Transport Layer: Utilize TCP or UDP protocols.
• Application Layer: Replicate protocols such as HTTP, FTP, or any custom application protocol.

4. NS2 Structure and Simulation Scripts

NS2 uses TCL scripts for running simulations. Each protocol is described in its corresponding C++ module that we can incorporate into the simulation script.

• Creating a TCL Script: A TCL script describes the network topology, type of protocols, and nodes to be replicated.

# Example: Simple OSI Layer Simulation (Transport Layer)

set ns [new Simulator]

set nf [open out.nam w]

$ns namtrace-all $nf

# Creating Nodes

set n1 [$ns node]

set n2 [$ns node]

# Creating a duplex link

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

# Define a TCP agent and attach it to n1 (Transport Layer)

set tcp [new Agent/TCP]

$ns attach-agent $n1 $tcp

# Define a Sink (Application Layer) and attach it to n2

set sink [new Agent/TCPSink]

$ns attach-agent $n2 $sink

# Establish connection between TCP and Sink

$ns connect $tcp $sink

# Simulate traffic at Application Layer

set ftp [new Application/FTP]

$ftp attach-agent $tcp

$ftp set type_ FTP

# Start and stop the simulation

$ns at 0.1 “$ftp start”

$ns at 4.5 “$ftp stop”

$ns at 5.0 “finish”

proc finish {} {

global ns nf

$ns flush-trace

close $nf

exit 0

}

$ns run

5. Protocol Implementation

In NS2, few OSI layer protocols are pre-built, even though others require extra modules or custom code. Here’s how we can replicate general protocols:

• Physical Layer: NS2 supports numerous wireless physical layers like 802.11.
• Data Link Layer: Utilize MAC protocols such as CSMA, TDMA, or IEEE 802.11 MAC for wireless simulations.
• Network Layer: AODV, DSR, and DSDV routing protocols are obtainable for mobile ad-hoc networks.
• Transport Layer: TCP and UDP protocols are readily available in NS2.
• Application Layer: Application-level simulations like FTP, CBR (Constant Bit Rate), and HTTP are built-in.

6. Running the Simulation

• We can save the TCL script (e.g., osi_simulation.tcl).
• Run the script in NS2 with the below command:

ns osi_simulation.tcl

7. Analyse Results

After running the simulation then NS2 generates outcomes files (trace files and NAM visualization files). We can utilize these for analysis:

• NAM (Network Animator): To envision the network traffic and the interaction among distinct OSI layers.
• Trace File: We can parse this file to investigate packet flows, delays, throughput, and so on.

8. Extending to Other Layers

If we require to replicate more advanced functionality for other OSI layers:

• Session, Presentation, Application Layers: These can be mimicked by inserting more custom application logic or scripts in the TCL code or using other libraries, which offer these functionalities.

9. Modify or Add Custom Protocols (Optional)

If we are watching to replicate a particular protocol not contained in NS2 then we require to:

• Write or alter C++ code for that protocol and recompile NS2.
• For instance, if replicating a custom routing protocol at the Network Layer, we might want to make or change classes in the ns-2.35/ directory.

10. Visualization and Debugging

• NAM: We can utilize the NAM graphical interface to monitor the simulation in action and visualize packet flows through distinct layers.
• AWK or Python: Examine the trace files are made in the course of simulation for performance parameters (delay, throughput, packet loss).

Example Simulation for Each Layer:

• Physical Layer: Wireless communications utilizing 802.11 protocols.
• Data Link Layer: MAC protocol simulations like TDMA, CSMA, or 802.11.
• Network Layer: Routing simulations using AODV, DSR, OSPF, and so on.
• Transport Layer: TCP/UDP protocol simulations.
• Application Layer: FTP, HTTP traffic simulations.

By using the detailed approach with example on how to replicate the OSI Layer Protocol projects and visualize its outcomes using NS2 virtual environment. If you obtain any query on this projects, feel free to ask!

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