TCP/IP Model

1.1. The Four Layers of the TCP/IP Model

1. Link Layer

Function: Handles the physical transmission of data and node-to-node communication over a local network, combining the OSI model’s Physical and Data Link layers.

Key Responsibilities:

Transmits raw bits over physical media (e.g., cables, wireless signals).

Frames data for local delivery, adding headers and trailers (e.g., Ethernet frames).

Manages error detection (e.g., CRC - Cyclic Redundancy Check).

Controls access to the shared medium (e.g., CSMA/CD for Ethernet, CSMA/CA for Wi-Fi).

Uses physical addresses (e.g., MAC addresses) for device identification.

Examples:

Protocols: Ethernet (IEEE 802.3), Wi-Fi (IEEE 802.11), Point-to-Point Protocol (PPP), Address Resolution Protocol (ARP).

Technologies: MAC addressing, VLANs, Frame Relay.

Devices: Switches, bridges, Network Interface Cards (NICs), access points.

Example: MAC address (e.g., 00:1A:2B:3C:4D:5E), Ethernet cable (Cat6).

Analogy: The Link layer is like a local mail service, ensuring letters (data frames) are delivered between nearby addresses using the right roads (cables or wireless).