[Day 1] 4. Ethernet

Ethernet Overview

Ethernet is a widely-used networking technology for connecting devices in a Local Area Network (LAN). Governed by IEEE standards, it supports speeds ranging from 10 Mbps to 100 Gbps.

Variants:

Metro Ethernet: Used for connecting businesses or regions, often spanning cities.
Point-to-Point Protocol over Ethernet (PPPoE): Commonly used for internet access in home broadband networks.

Token Ring

An older networking technology that operated at speeds of 4 Mbps and 16 Mbps.
It became obsolete due to its slower speeds and limited efficiency compared to Ethernet.

How Ethernet Works?

CSMA/CD (Carrier Sense Multiple Access / Collision Detection)

Older Ethernet used CSMA/CD to handle communication between devices.
Process:
- Carrier Sense: Each device checks if the network is free (no one else is sending data).
- Multiple Access: If the network is free, the device sends its data.
- Collision Detection: If two devices send data at the same time, a collision occurs.
- Back off: Both devices stop, wait for a random time, and then try again.
Modern Ethernet: Uses switches, which create separate collision domains, eliminating collisions entirely.

MAC Address

A Media Access Control (MAC) Address is a unique hardware identifier for devices in a network.
Structure:
- 48 bits, divided into two parts:
  - First 24 bits: Organizational Unique Identifier (OUI), assigned by IEEE to manufacturers.
  - Last 24 bits: Device-specific serial number.
Example MAC Address:
```
00:1A:2B:3C:4D:5E
```
.

Communication Methods

Unicast: One-to-one communication between devices.
Broadcast: One-to-all communication. A broadcast is sent to all devices using the special MAC address FF:FF:FF:FF:FF:FF.

Drawbacks of Older Ethernet

Increased Collisions: Devices shared the same medium, leading to frequent collisions.
Limited Media Availability: Shared media like hubs were inefficient.

How Modern Ethernet Works

Switches: Modern Ethernet uses network switches instead of hubs.
Dedicated Communication: Each device connected to a switch gets its own path to communicate, eliminating collisions.
Full-Duplex Mode: Data can be sent and received simultaneously between devices.
MAC Address Table: The switch learns the MAC addresses of connected devices and sends data directly to the correct destination.

This makes modern Ethernet faster, more reliable, and efficient compared to older methods!

NOTE: A hub simply broadcasts data to all connected devices, while a switch intelligently directs data packets to their intended recipient based on MAC addresses, and a router routes data packets between different networks by examining their IP addresses, essentially acting as a gateway between networks; in essence, hubs operate at the physical layer, switches at the data link layer, and routers at the network layer of the OSI model.