Ethernet Fundamentals

Origionally Ethernet was run over coaxial cables using BNC connectors and vampire taps 10Base2 and 10Base5 thinket and thicknet.

10BASE-T Ethernet allowe up to 10Mbps networks to be run over a twisted pair cable known as a category 3 or CAT 3.

could only go over 100 meters.

Deterministic - means the network access shoul be very organized and orderly. like each device has to raise it’s hand to send info.

Contention-based : used to determine who can get to use the network at a time. like a conversaton at a pub. you wait for your turn then you are able to speak. when doing this you may have collisions. conenton-based models can become extremely chaotiotic.

Ethernet is a contintion-based networkijng protocol. - lower overhead, don’t need to pass the token, and anyone can talk at any time.

CSMA/CD - Carrier sense multiple access. with collision detection. - you wait for the gap then send data, if there is a collision then you pause and resend.

CS - carrirer sensing - listen to the network to see if there is.a signal.

MA multiple access - many devices that are able to use the network at the same time.

CD collision detection - if a collision is detected they devices have to decide who goes first. if so they stop and both will resend at a reandom time to talk again.

Random backoff timer - allows devices to retransmit when the countdown is done.

so a device sends then has to wait for a random time to send it’s time.

the more devices communiction on a single network segment the more collisons that you will have.

Colision domain - each area of the netowrk that shares a single segment. Devices opperate in half duples when connected to a hub.

Keep collision domains small inside networks.

Ethernet swithc - increase the scaliblity of our networks. each switchport is it’s own collision domain.

Devices opperate in full-duplex mode when connected to a switch.

use switches instead of hubs.

Ethernet Standards & Access Methods (N10-009)

Early Ethernet

10BASE5 (Thicknet):
- Coaxial cable with vampire taps.
- Max segment: 500 m.
10BASE2 (Thinnet):
- Coaxial with BNC connectors.
- Max segment: 185 m.

10BASE-T

Introduced twisted pair (Cat3) cabling.
Speed: 10 Mbps.
Distance: 100 m per segment.
Became the foundation for modern Ethernet over twisted pair.

Deterministic vs. Contention

Deterministic Access (Token Ring, Token Bus):
- Orderly, “raise your hand to talk.”
- Uses tokens, no collisions.
Contention-Based Access (Ethernet):
- “Pub conversation” model.
- Anyone can speak, collisions possible.
- Lower overhead (no token passing).

CSMA/CD (Ethernet Legacy)

Carrier Sense Multiple Access with Collision Detection

CS (Carrier Sense): Device listens for quiet network before sending.
MA (Multiple Access): Many devices share the medium.
CD (Collision Detection): If collision occurs → stop, wait, and resend.
Random Backoff Timer: Devices wait a random time before retrying.
Issue: More devices = more collisions.

Collision Domains

Collision Domain: Segment where collisions can occur.
- On a hub, all devices share one collision domain.
- Devices operate in half-duplex.
Switches:
- Each switchport = its own collision domain.
- Devices operate in full-duplex → no collisions.
Best Practice: Use switches instead of hubs.

✅ Must-Know Exam Points

10BASE2 = BNC, 185 m.
10BASE5 = vampire taps, 500 m.
10BASE-T = Cat3, 100 m, 10 Mbps.
Ethernet = contention-based (CSMA/CD).
Switch = each port its own collision domain, full duplex.
Hub = one big collision domain, half duplex.

⚡ Flashcard Drill:

Q: Which Ethernet standard used vampire taps?

A: 10BASE5 (Thicknet).
Q: What replaced hubs to eliminate collisions?

A: Switches.
Q: What does CSMA/CD stand for?

A: Carrier Sense Multiple Access with Collision Detection.
Q: What duplex mode do switches support?

A: Full-duplex.