🌐 Developing TCP/IP Client and Server with Telnet (Java Networking)

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🔷 1. Definition

🔹 TCP/IP Client-Server Model

A TCP/IP client-server system is a network communication model where:

• Client sends request
• Server listens and responds
• Communication happens using TCP

👉 TCP ensures:

• Reliable communication
• Ordered data delivery
• Error checking

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🔹 Telnet

Telnet is a network protocol and tool used to:

• Connect to remote servers
• Test TCP connections manually
• Send simple text-based commands

👉 It works on port 23 (default)

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🔷 2. Purpose of TCP/IP Client-Server

• Build network applications
• Enable communication between systems
• Exchange data over internet or LAN
• Used in chat apps, file transfer, remote services

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🔷 3. TCP Client-Server Architecture

📊 Diagram Description:

Client → TCP Socket → Network → Server Socket → Server Process Response flows back similarly

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🔷 4. Key Classes in Java

Class	Purpose
Socket	Client-side connection
ServerSocket	Server-side listening
InputStream	Receive data
OutputStream	Send data

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🔷 5. Steps to Create TCP Server

✔ Step-by-step:

1. Create ServerSocket
2. Wait for client connection (accept())
3. Read data from client
4. Send response
5. Close connection

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🔹 TCP Server Example

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

public class TCPServer {
    public static void main(String[] args) throws Exception {

        ServerSocket serverSocket = new ServerSocket(5000);
        System.out.println("Server started... Waiting for client");

        Socket socket = serverSocket.accept();

        BufferedReader in = new BufferedReader(
            new InputStreamReader(socket.getInputStream()));

        String msg = in.readLine();
        System.out.println("Client says: " + msg);

        serverSocket.close();
    }
}

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🔷 6. Steps to Create TCP Client

✔ Step-by-step:

1. Create Socket
2. Connect to server
3. Send message
4. Close connection

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🔹 TCP Client Example

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

public class TCPClient {
    public static void main(String[] args) throws Exception {

        Socket socket = new Socket("localhost", 5000);

        PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
        out.println("Hello Server");

        socket.close();
    }
}

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🔷 7. Using Telnet for TCP Testing

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🔹 What Telnet Does

Telnet can act as a simple TCP client to:

• Connect to server
• Send raw text data
• Test port connectivity

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🔹 Command Example

telnet localhost 5000

👉 This connects to server running on port 5000

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🔹 What Happens:

1. Telnet opens TCP connection
2. User types message
3. Server receives message
4. Server responds (if programmed)

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🔷 8. TCP Communication Flow

📊 Flow:

1. Server starts (listening)
2. Client connects (Socket)
3. Data exchange happens
4. Connection closed

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🔷 9. Features of TCP

• Reliable communication
• Connection-oriented
• Error checking
• Data delivered in order

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🔷 10. TCP vs UDP (Important)

Feature	TCP	UDP
Reliability	High	Low
Speed	Slower	Faster
Connection	Yes	No
Example	Web, Telnet	Streaming

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🔷 11. Advantages of TCP Client-Server

• Reliable communication
• Easy to implement in Java
• Supports multiple clients
• Widely used in real systems

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🔷 12. Disadvantages

• Slower due to overhead
• Requires connection setup
• Not suitable for real-time systems

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🔷 13. Important Rules

• Server must run before client
• Ports must match
• Always close sockets
• Handle exceptions properly
• Use correct port numbers (>1024 recommended)

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🔷 14. Diagram Description (Exam Tip)

📊 TCP Client-Server Model:

Client (Socket) → Request → ServerSocket → Server processes request ← Response ← Client

Telnet can replace client in testing phase

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📝 Likely Exam Questions

1. What is TCP/IP client-server model?
2. Explain TCP server program in Java.
3. Write a TCP client program.
4. What is the role of ServerSocket?
5. What is Telnet used for?
6. Explain TCP communication flow.
7. Difference between TCP and UDP.
8. How does Telnet work with TCP?
9. Advantages of TCP programming.
10. Explain socket programming in Java.

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📌 Quick Revision Summary

• TCP = reliable connection-based protocol
• Client uses Socket
• Server uses ServerSocket
• Data is exchanged using streams
• Telnet = tool to test TCP connections
• Communication is bidirectional and reliable

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