Cable Media

1. Twisted Pair Cable

Twisting is to cancel out the EMI (ElectroMagnetic Interference 電磁場干擾)

There are two types of twisted pair cable:

1. UTP (Unshielded twisted pair)
2. STP (Shielded twisted pair)

UTP

• consists of four twisted pair of copper wire
• UTP is specified in the EIA/TIA 568 Commercial Building Wiring Standard.
• maximum length 100m
• using RJ-45 connector like RJ-11 telephone connector

EIA/TIA stands for Electronic Industries Association and the Telecommunications Industries Association.

EIA/TIA defines UTP in:

1. category 1 ----- for voice only (telephone cable)
2. category 2 ----- 4Mbps
3. category 3 ----- 10Mbps
4. category 4 ----- 16 Mbps
5. category 5 ----- 100Mbps

STP

• consists of two twisted pair of copper wire
• use a foil warp around the wire pairs.
• 16 to 500 Mbps
• maximum length 100m
• using RJ-45 connector like RJ-11 telephone connector

Coaxial Cable

The copper wire mesh as a shielding that protects the transmitted data from EMI and more resistant to crosstalk and attenuation than twisted pair.

Crosstalk

Attenuation

• The weakening of a signal over distance
• Usually measured in decibels (分貝)
• Can be corrected with a repeater
  

There are two types of coaxial cable:

1. Thinnet
2. Thicknet

Thinnet

• about 0.25 inch in diameter
• maximum length 185m
• also called BNC (British Naval Connector) or RG-58
• requires 50-ohm terminators.
• 10Mbps
• using BNC connector

Thicknet

• about 0.5 inch diameter
• maximum length 500m
• also called RG-11 or Standard Ethernet
• using external transceivers
• 10Mbps
• using AUI (or called DIX or DB15) connector

Remark: Transceiver is used to convert parallel signals to serial signals and vice versa. Actually, every network adapter card must use a transceiver to transmit and receive data, Most network adapter card use built-in transceivers, except thicknet network adapter card.

Fiber-Optic Cable

carry digital signals in the form of light. Hence, fiber-optic cable is more secure than coaxial or twisted-pair cable form tapped.(勾線)

• diameter in unit of micron (微米)
• maximum length 2000m
• requires expertise to install (Polishing打磨)
• 100 Mbps to 2Gbps

Ethernet LAN Specification