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TCP/IP Model Overview
The TCP/IP model, developed by the Department of Defense (DoD), is the foundation for communication on the internet. It consists of 5 layers, each responsible for different aspects of network communication.

1. Physical Layer

  • Purpose: Converts message bits into signals for transmission.
  • Medium: Electrical signals for copper, light for fiber optics, and radio waves for wireless.
  • Characteristics: Topology (bus, star, etc.), line configuration, transmission mode (simplex, duplex).

2. Data Link Layer (DLL)

  • Sub-layers:
    • MAC (Media Access Control): Adds headers and trailers to data for addressing and error-checking.
    • LLC (Logical Link Control): Handles flow control and error detection.
  • Functions: Encapsulates IP packets into frames for transmission, ensures error detection and flow control.

3. Network Layer

  • Purpose: Adds logical addresses (IP addresses) and finds the best path for data delivery.
  • Protocols:
    • IP (Internet Protocol): Routes packets based on destination IP addresses; does not ensure delivery.
    • ARP (Address Resolution Protocol): Maps IP addresses to MAC addresses.
    • ICMP (Internet Control Message Protocol): Used for error reporting.

4. Transport Layer

  • Purpose: Manages flow control, end-to-end communication, and error-free data transmission.
  • Protocols:
    • TCP (Transmission Control Protocol): Connection-oriented, reliable, ensures correct data order and retransmits lost packets.
    • UDP (User Datagram Protocol): Connectionless, faster, less reliable, no error checking.

5. Application Layer

  • Purpose: Provides network services to end users and applications.
  • Protocols:
    • HTTP (Hypertext Transfer Protocol): For accessing web pages.
    • DNS (Domain Name System): Translates domain names to IP addresses.
    • SMTP (Simple Mail Transfer Protocol): Used to send emails.
    • FTP (File Transfer Protocol): Transfers files between computers.
    • TELNET: Provides remote access to machines.

This model helps ensure proper communication across the internet by organizing how data is handled from the physical transmission to the application layer.