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Module 3: Physical & Data Link Layers

These layers are responsible for moving bits across the wire (or air) and organizing them into frames for local delivery.

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3.1 Layer 1: Physical Layer

The Physical Layer defines the hardware elements involved in transmitting data.

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Key Concepts

  • Media: Copper cables (Cat5e, Cat6), Fiber Optic, Wireless (Radio waves).
  • Signals: Digital (bits) vs Analog (waves).
  • Topologies: Bus, Star, Ring, Mesh.
The Data Link Layer ensures error-free transmission between two directly connected nodes.

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MAC Addresses

  • Media Access Control (MAC) address is a unique identifier assigned to a network interface controller (NIC).
  • Format: 00:1A:2B:3C:4D:5E (48-bit hex).

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Ethernet Frames

Data is packaged into frames.
  • Preamble: Synchronization.
  • Destination MAC: Where it’s going.
  • Source MAC: Where it came from.
  • Type: Protocol (e.g., IPv4).
  • Payload: The actual data (IP Packet).
  • FCS: Frame Check Sequence (Error detection).

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3.3 Switching

A Switch operates at Layer 2. It uses MAC addresses to forward frames to the correct port.
  1. Learning: Switch learns MAC addresses by inspecting Source MAC of incoming frames.
  2. Forwarding: Switch looks up Destination MAC in its MAC Table and forwards to the specific port.
  3. Flooding: If Destination MAC is unknown (or Broadcast), switch sends to all ports (except ingress).

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Next Module

Module 4: Network Layer

Dive into IP addressing and Routing.