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TCP/IP

What is TCP/IP?​

  • TCP/IP stands for Transmission Control Protocol / Internet Protocol.
  • It's the fundamental suite of communication protocols that powers the Internet and most modern networks.
  • Originally developed by the U.S. Department of Defense (ARPANET, 1970s), it became the standard networking model.

TCP/IP Layered Model​

TCP/IP is organized into four layers (similar to the OSI 7-layer model, but more practical):

  1. Link Layer (Network Interface)
  • Handles physical network hardware (Ethernet, Wi-Fi).
  • Defines how bits are transmitted over wires, fiber, or radio.
  • Examples: Ethernet, PPP, ARP.
  1. Internet Layer
  • Responsible for addressing and routing packets across networks.
  • Core protocol: IP (Internet Protocol).
  • Examples: IPv4, IPv6, ICMP.
  1. Transport Layer
  • Ensures end-to-end communication between applications.
  • Two main protocols:
    • TCP (Transmission Control Protocol) → reliable, connection-oriented (web, email).
    • UDP (User Datagram Protocol) → fast, connectionless (DNS, video streaming, gaming).
  1. Application Layer
  • Where actual user applications and services live.
  • Examples: HTTP, HTTPS, FTP, SMTP, DNS, SSH.

Key Features​

  • IP:
    • Provides addressing (IP addresses) and routing.
    • Doesn’t guarantee delivery (best-effort).
  • TCP:
    • Builds on IP to provide reliable, ordered, error-checked communication.
    • Ensures data arrives intact and in the right order.
    • Uses mechanisms like handshakes, acknowledgments, retransmissions.
  • UDP:
    • Lightweight, no guarantee of delivery or order.
    • Useful for real-time applications (gaming, VoIP, streaming).

Example Flow (Sending a Web Page)​

  1. You type http://example.com.
  2. Application Layer (HTTP): creates a request.
  3. Transport Layer (TCP): wraps the request in segments, ensures reliability.
  4. Internet Layer (IP): adds source/destination IP addresses, routes packets.
  5. Link Layer (Ethernet/Wi-Fi): sends packets as electrical signals/radio waves.
  6. Server responds with HTTP data: the process happens in reverse.

Why TCP/IP Matters​

  • Universal: used by the Internet, LANs, cloud systems.
  • Scalable: supports billions of devices.
  • Flexible: works across different physical networks (fiber, copper, wireless).
  • Robust: designed to withstand network failures.