TCPLab — Java Socket Visualizer

TCPLabJava Socket Visualizer

idle

UTF-8 · Java

import java.net.*;
import java.io.*;

public class Server {
    private static final int PORT = 8080;

public static void main(String[] args) throws IOException {
        // Step 1: Create server socket (BIND + LISTEN)
        ServerSocket serverSocket = new ServerSocket(PORT);
        System.out.println("[SERVER] Socket created and bound to port " + PORT);
        System.out.println("[SERVER] Listening for incoming connections...");

// Step 2: ACCEPT - blocks until client connects
        Socket clientSocket = serverSocket.accept();
        System.out.println("[SERVER] Client connected: " + clientSocket.getInetAddress());

// Step 3: Set up I/O streams
        BufferedReader in = new BufferedReader(
            new InputStreamReader(clientSocket.getInputStream()));
        PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);

// Step 4: Read message from client
        String message = in.readLine();
        System.out.println("[SERVER] Received: " + message);

// Step 5: Send response (ACK with data)
        out.println("Hello from Server! Got your message: " + message);
        System.out.println("[SERVER] Response sent.");

// Step 6: Close connection (FIN)
        clientSocket.close();
        serverSocket.close();
        System.out.println("[SERVER] Connection closed.");
    }
}

import java.net.*;
import java.io.*;

public class Client {
    private static final String HOST = "localhost";
    private static final int PORT = 8080;

public static void main(String[] args) throws IOException {
        // Step 1: CREATE socket and CONNECT (3-way handshake)
        System.out.println("[CLIENT] Initiating connection to " + HOST + ":" + PORT);
        Socket socket = new Socket(HOST, PORT);
        System.out.println("[CLIENT] Connected! 3-way handshake complete.");

// Step 2: Set up I/O streams
        PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
        BufferedReader in = new BufferedReader(
            new InputStreamReader(socket.getInputStream()));

// Step 3: Send message to server
        String message = "Hello, Server! I am the TCP Client.";
        out.println(message);
        System.out.println("[CLIENT] Sent: " + message);

// Step 4: Read response from server
        String response = in.readLine();
        System.out.println("[CLIENT] Received: " + response);

// Step 5: Close connection (FIN)
        socket.close();
        System.out.println("[CLIENT] Connection closed.");
    }
}

Console Output

Press Run to execute the simulation

TCP LifecycleBasic TCP

Server

Client

Socket Created

Bind & Listen

SYN

SYN-ACK

ACK

Connected

DATA

ACK+DATA

FIN

FIN-ACK

Closed

Press Run to start the animated TCP walkthrough

Scenario: Basic TCP

Standard 3-way handshake & data transfer

Key Concepts

TCP uses a 3-way handshake (SYN -> SYN-ACK -> ACK) to establish connections

Each socket has an Initial Sequence Number (ISN) for reliable ordering

ServerSocket.accept() blocks until a client connects

4-way FIN handshake gracefully terminates connections

Ananya Addisu|BDU1600957