Media

Chapter 2

Two types of Cables

Baseband Broadband

Baseband Digital signaling over one wire

Electrical pulses or laser light Bi-directional – allows computers to

send and receive using one cable. Capable of multiplexing

Using TDM (Time Division Multiplexing) – method of putting multiple data streams in a single signal by separating the signal into many segments of short duration. Only changes the way data is transmitted.

Categories of Media

Coaxial Twisted pair Fiber Optic

Types of Media

Copper – coaxial cable, twisted pair

Glass – fiber optic

Interference EMI

Could come from fluorescent lights, ungrounded electronic equipment

Crosstalk There are 8 wires in twisted pair cable. When

electricity flows through a wire, it emanates a electromagnetic field. A pair of wires create a circuit for transmitting data via electrical current. If two wires are in the same electrical circuit, electrons flow from the negative voltage source to the destination along one wire and then the electrons flow from the destination to the positive voltage source along the other wire. If two wires within the cable are carrying a signal, energy from one wire can wind up in an adjacent wire. Thus, EMI within the cable is crosstalk.

Cancellation When two wires in an electrical circuit

are placed close together, their magnetic fields are the exact opposite of each other. These magnetic fields cancel out one another. The twisting of the wires improves the cancellation effect.

Attenuation

Cable length is specified because as a signal moves along the media it weakens (attenuates).

Coaxial Cable

Coaxial Cable Thin – 10Base2

Commonly called thinnet, thin wire, or thin Ethernet or cheapernet

BNC connector

Thick – 10Base5 Commonly called thicknet, thick wire,

or thick Ethernet Transceivers and Vampire Taps

Twisted Pair Shielded Twisted Pair (STP)

Contains eight copper wires covered in plastic The wires are twisted to reduce crosstalk.

Insulated Reduces EMI (electromagnetic interference) Fairly expensive Uses RJ45 connectors

Unshielded Twisted Pair (UTP) Commonly called Cat5 Contains eight copper wires covered in plastic The wires

are twisted to reduce crosstalk. Not insulated Inexpensive Uses RJ45 connectors

Twisted Pair Categories Cat 1 – Voice-grade UTP telephone cable. Cat 2 – Data grade – transmits up to 4Mbps Cat 3 – Data grade – transmits up to

10Mbps Cat 4 – Data grade – transmits up to

16Mbps (often used with Token Ring) Cat 5 – Data grade – transmits up to

100Mbps Cat 5e – Data grade – transmits up to 1000

Mbps

Thin Coaxial Cable (10Base2) Max speed: 10 Mbps Max length: 185 meters Max #nodes/segment: 30 Max #segments: 5 (only three can have

nodes connected) Min distance b/w nodes: .5 meter Transmission method: Baseband Connector: BNC

Thick Coaxial Cable (10Base5)

Max speed: 10 Mbps Max length: 500 meters Max #nodes/segment: 100 Min distance b/w nodes: 2.5 meters Transmission method: Baseband Connector: Vampire tap and

transceiver

Twisted Pair (10BaseT)

Max speed: 10 Mbps Max length: 100 meters Transmission method: Baseband Cable type: Cat 3, 4, 5 UTP or STP Connector: RJ45