What is a LAN? (Local Area Network)

A LAN connects devices like computers, printers, and switches within a limited area like a home, office, or school.

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Types of LANs:

1. Typical SOHO LANs (Small Office/Home Office):

• Few devices like PCs, a router, and a printer.

• Uses wireless and wired connections.

• Simple setup using Wi-Fi router or a small switch.
  Example: Your home internet setup.

2. Typical Enterprise LANs:

• Larger and more structured.

• Hundreds of devices connected using switches and routers.

• Includes multiple floors, departments, servers, etc.
  Example: LAN in a college campus or corporate office.

Ethernet Physical Layer Standards

Ethernet defines how data travels over wires. Some common standards:

• 10BASE-T: 10 Mbps, twisted pair cables

• 100BASE-T: 100 Mbps (Fast Ethernet)

• 1000BASE-T: 1 Gbps (Gigabit Ethernet)

All Ethernet standards use UTP cables, but support different speeds and pinouts.

Consistency with Ethernet Data Link Layer

No matter the speed (10/100/1000 Mbps), Ethernet works the same at the data link layer. This makes devices compatible and ensures smooth communication.

Building Physical Ethernet Networks with UTP Cables

UTP (Unshielded Twisted Pair) is the common cable used in LANs. It has 4 twisted wire pairs inside.

Transmitting Data Using Twisted Pairs

• Data is sent using electrical signals over these twisted wires.

• Twisting reduces interference and keeps the signal clean.

UTP Ethernet Link Breakdown:

A basic link includes:
Device → UTP Cable → Switch/Router

Cabling Pinouts (Wiring Standards)

10BASE-T & 100BASE-T (Both use 2 pairs):

1. Straight-Through Cable:

• Used to connect different devices (PC to Switch, Router to PC)

• Both ends follow the same color order (T568A or T568B)

2. Crossover Cable:

• Used to connect similar devices (PC to PC, Switch to Switch)

• One end T568A, the other T568B

Choosing the Right Cable:

Choosing the Right Cable:

Connection Type Cable Needed

PC to Switch Straight-Through

Switch to Switch Crossover

Router to Switch Straight-Through

PC to PC Crossover

1000BASE-T (Gigabit Ethernet):

• Uses all 4 pairs of wires

• Doesn't need crossover because it can auto-sense the connection

• Both ends can use the same wiring (straight)

How Ethernet Sends Data

• Ethernet divides data into frames

• Each frame has a source, destination, and actual data

• Frames travel through cables and reach the target device using MAC addresses