YouTube video: https://youtu.be/D26sUZ6DHNQ?si=V8x9Qm4yQzL_jhVZ

Sockets are fundamental to network communication in modern computing, yet many developers lack a clear understanding of what they truly are and how they function. This guide explains sockets in depth, their types, lifecycle, relevance to networking models, and importance in software architecture.

1. What is a Socket?

• Definition:

  A socket is an abstraction provided by the operating system that enables communication between different processes. These processes can be:

  • On the same machine
  • Across a network (e.g., internet or local network)

• Function:

  Sockets act as two-way communication endpoints. When two machines or applications need to communicate, each side creates a socket.

• Technical Composition:

  A socket wraps a combination of:

  • Protocol (TCP or UDP)
  • IP address
  • Port number

• Analogy:

  The socket is like the telephone, while the IP address and port number together represent the phone number and extension. Both parties must dial the right combination to establish communication.

2. Sockets in the OSI Model

• OSI Model Layers:

  Conceptual framework modeling how networks communicate.

• Socket's operating layer:

  Sockets operate primarily at the Transport Layer (Layer 4) of the OSI model.

• How it works:

  • Application layer (Layer 7) like browsers or services call the socket API for sending/receiving data.
  • The socket packages data into TCP or UDP segments.
  • Sends those segments to the Network Layer (Layer 3) which handles IP routing.

• Role:

  Provides a clean interface between application logic and underlying network stack, hiding complexities like routing, fragmentation, and retransmission.

3. TCP vs. UDP Sockets

TCP (Transmission Control Protocol) Sockets

• Connection-oriented: Require establishing a connection before data transfer.
• Reliable & Ordered: Guarantees ordered, error-checked delivery.