The TCP/IP Model

1. Physical Layer

Responsibilities

• Physical means of transmission
• Multiplexing techniques: https://www.geeksforgeeks.org/difference-between-tdm-and-fdm/
• Structured Cabling: https://en.wikipedia.org/wiki/ANSI/TIA-568
• Apropriately encoding bits for the specified mean of transmission
• Sending bits over the physical mean of transmission

2. Data Link Layer

Responsibilities

• Communication between neighbouring nodes on a network
• Error detection
• Error correction (except in fiber links)
• Controle de fluxo
• Congestion control (in fiber links)
• Physical addressing (ex: MAC)

Before fiber-optics:

• Error detection (BER ~10^-6) and correction
• Flow control
  • Start-Stop (feedback-based)
  • Sliding Window (rate-based)

After fiber-optics:

• Error detection (no correction, BER ~10^-9 to 10^-12)
• Congestion control
• Frame delimiting
• Sharing a physical medium: https://en.wikipedia.org/wiki/Carrier-sense_multiple_access_with_collision_detection

3. Internet Layer

Responsibilities

• Routing
• Segmentation based on Maximum Transmission Unit (MTU)
• Logical addressing (ex: IPv4)

4. Transport Layer

Responsibilities

• End-to-end communication
• Routing and congestion error detection and correction
• Flow control (sliding window)
• Congestion control
  • Avoid buffer overflows on routers
  • Performed by transmitter

5. Application Layer

Responsibilities

• User interface
• Authentication and authorization
• Generating data