Introduction to ns-2 and AI Prompting

Hello World ns-2 Script 

Here is a simple ns-2 script that creates a basic network with two nodes and a point-to-point link. This is a great "Hello World" equivalent for network simulation.

# --- 1. Simulation Setup ---
# Create a new simulator instance
set ns [new Simulator]

# Open a NAM trace file
set nam_file [open out.nam w]
$ns namtrace-all $nam_file

# --- 2. Network Topology ---
# Create two nodes
set n0 [$ns node]
set n1 [$ns node]

# Create a duplex-link between them
# Bandwidth: 1.5Mb, Delay: 10ms, Queue type: DropTail
$ns duplex-link $n0 $n1 1.5Mb 10ms DropTail

# --- 3. Traffic and Agents ---
# Create a UDP agent and attach it to n0
set udp [new Agent/UDP]
$ns attach-agent $n0 $udp

# Create a CBR traffic source and attach it to the UDP agent
set cbr [new Application/Traffic/CBR]
$cbr set packetSize_ 500
$cbr set interval_ 0.005
$cbr attach-agent $udp

# Create a Null agent (receiver) and attach it to n1
set null_agent [new Agent/Null]
$ns attach-agent $n1 $null_agent

# Connect the sender (n0's UDP) to the receiver (n1's Null)
$ns connect $udp $null_agent

# --- 4. Event Scheduling ---
# Schedule a traffic start event at 0.5s
$ns at 0.5 "$cbr start"

# Schedule a traffic stop event at 4.5s
$ns at 4.5 "$cbr stop"

# Stop the simulation at 5.0s
$ns at 5.0 "finish"

# --- 5. Finish Procedure ---
# This procedure closes files and launches NAM
proc finish {} {
    global ns nam_file
    $ns flush-trace
    close $nam_file
    exec nam out.nam &
    exit 0
}

# --- 6. Run the Simulation ---
$ns run

Explanation of the Code

1. Header Files and Namespace

• #include "ns3/...-module.h": These lines include the necessary header files for the ns-2 modules we will be using, such as the core, network, and point-to-point modules.

• using namespace ns3;: This line allows us to use ns-2 classes directly without the ns3:: prefix, making the code cleaner.

2. Main Function main()

• The main() function is the entry point of the program, just like in any other C++ application.

• int argc, char *argv[]: These are the standard command-line arguments that can be used to pass parameters to the simulation.

3. Creating Nodes

• NodeContainer nodes;: This creates an object to hold our nodes.

• nodes.Create(2);: This command creates two simulation nodes. In ns-2, a node is analogous to a computer or device.

4. Creating the Channel and Devices

• PointToPointHelper pointToPoint;: This is a "helper" class that simplifies the creation of a point-to-point link.

• SetDeviceAttribute(...) and SetChannelAttribute(...): These lines configure the link's properties, such as the data rate (5 Mbps) and propagation delay (2 ms).

• NetDeviceContainer devices;: This object will hold the network devices (e.g., network interface cards) for the nodes.

• devices = pointToPoint.Install(nodes);: This command creates the link and installs a network device on each of the two nodes.

5. Installing the Internet Stack

• InternetStackHelper stack;: This helper class simplifies the installation of the network stack (including TCP/IP, UDP, etc.) on the nodes.

• stack.Install(nodes);: This installs the full Internet protocol stack on both of our nodes, which is necessary for them to communicate.

6. Assigning IP Addresses

• Ipv4AddressHelper address;: This helper is used to assign IP addresses to the network devices.

• address.SetBase("10.1.1.0", "255.255.255.0");: This sets the network base and subnet mask for the IP addresses.

• Ipv4InterfaceContainer interfaces = address.Assign(devices);: This assigns IP addresses (e.g., 10.1.1.1 and 10.1.1.2) from the specified network to the two devices.

7. Running the Simulation

• Simulator::Run();: This is the most important command. It starts the discrete-event simulation, running all the scheduled events.

• Simulator::Destroy();: This cleans up all resources used by the simulation. It's good practice to call this at the end of every simulation.