Lecture Notes on Sockets

Overview

• Focus on fundamentals of sockets.
• Discuss client-server architecture, IP addresses, protocols, and coding in Python.
• Build a basic client-server system in Python.

Key Concepts

Client and Server

• Client: Requests services from a server.
• Server: Provides services to clients.
• Client-Server Architecture:
  • Structure programs with clients (computers, phones, etc.) connecting to a server.
  • Example: PC1 sends a message to PC2 through the server, not directly.
  • Server can act as a chat room, gaming server, etc.

IP Addresses

• Local IP Address: An address within a local area network (LAN).
  • Example: 192.168.0.15
• Public IP Address: Unique address used for internet connectivity.
  • Example: 76.28.44.211 (not a real address).
• Local IP addresses are not routable from outside the network.

Ports

• Ports serve as "doors" to access services on an IP address.
• Example: Connecting to 192.168.0.15:9090.
• Server must listen on the specified port to accept connections.

Sockets

• Definition: Communication endpoints for exchanging data.
• Types of Sockets:
  • AF_INET: Internet sockets using IPv4.
  • AF_INET6: Internet sockets using IPv6.
  • Other types include Bluetooth and infrared sockets.
• Socket Types:
  • SOCK_STREAM: TCP protocol (connection-based).
  • SOCK_DGRAM: UDP protocol (datagram-based).

TCP vs. UDP

• TCP (Transmission Control Protocol):

  • Reliable, connection-based.
  • Detects packet loss and maintains order.
  • Suitable for applications requiring full data integrity (e.g., file transfer).

• UDP (User Datagram Protocol):

  • Unreliable, datagram-based.
  • Allows packets to arrive out of order; no delivery guarantees.
  • Faster, suitable for real-time applications (e.g., video streaming, gaming).

When to Use

• Use TCP when data loss cannot be tolerated (e.g., file transfers).
• Use UDP when speed is critical and some data loss is acceptable (e.g., live video calls).

Implementation in Python

Server Implementation

1. Import socket module.
2. Create a socket and bind it to local IP and port.
3. Use listen() to accept incoming connections.
4. Use a loop to accept connections and handle communication.
5. Example code snippet for server: import socket server = socket.socket(socket.AF_INET, socket.SOCK_STREAM) server.bind((host, port)) server.listen(5) while True: comm_socket, addr = server.accept() print(f'Connected to {addr}') message = comm_socket.recv(1024).decode('utf-8') print(f'Message from client: {message}') comm_socket.send('Got your message, thank you'.encode('utf-8')) comm_socket.close()

Client Implementation

1. Import socket module.
2. Create a socket and connect to the server's IP and port.
3. Send a message to the server and receive a response.
4. Example code snippet for client: import socket client = socket.socket(socket.AF_INET, socket.SOCK_STREAM) client.connect((host, port)) client.send('Hello, World!'.encode('utf-8')) response = client.recv(1024).decode('utf-8') print(response) client.close()

Summary

• Understanding sockets is crucial for building networking applications.
• TCP ensures reliable communication, while UDP focuses on speed and efficiency.
• Implementation in Python is straightforward and can be adapted for various applications.