CSCD 218 : DATA COMMUNICATIONS AND NETWORKING 1

LECTURE 4INTRODUCTION AND BASIC CONCEPTS

TRANSMISSION MEDIA AND TRANSMISSION TECHNOLOGIES

LECTURER : FERDINAND KATSRIKU (PhD)

TRANSMISSSION MEDIARefers to the physical pathways that connect

computers, other devices, and people on a network—the highways and byways that comprise the information superhighway.

CLASSIFICATION OF TRANSMISSSION MEDIA

Guided Media (Wired)– Twisted-Pair Cable– Coaxial Cable– Fiber-Optic Cable

Unguided Media (Wireless)– Radio Waves– Microwaves– Infrared

CLASSIFICATION OF TRANSMISSSION MEDIA

TRANSMISSION MEDIA CHARACTERISTICSCostInstallation requirementsBandwidthBand Usage

– Baseband : Devotes the entire capacity of the medium to one communication channel. Mostly used in LANs

– Broadband : Enables two or more communicating channels to share the bandwidth of the medium. Eg;TV

AttenuationImmunity from electromagnetic interference

Cable Media – Primary cable typesThree main types :

Coaxial cable, Twisted-Pair cable and Fibre-Optic cable

The Coaxial Cable

Cable Media – Primary cable typesThe Coaxial Cable

Types of Coaxial CableTwo main types : The thinnet and the thicknetThe ThinnetA light and flexible cabling medium that is inexpensive and very easy to install. It can reliably transmit a signal for 185metres(about 610 feet).

The ThicknetThicker than thinnet. It is harder to work with compared to the thinnet. It can transmit a signal approximately 500metres (1,650 feet)

Connectors for Coaxial CablesCoaxial cables are used on bus topologies and the most common connector used for coaxial cables is the British Naval Connector (BNC).A BNC T-connector connects the network board in the PC to the network.

BNC Connectors

BNC Connectors BNC = Bayone-Neill-

Concelman BNC Connector is used to

connect the end of the cable to a device

BNC T is used in networks to branch out a cable for connection to a computer or other device

BNC Terminator is used at the end of the cable to prevent the reflection of signal.

Twisted – Pair Cable

Twisted – Pair Cable• One of the wires carries

signal, the other is used only as a ground reference.

• The receiver uses the difference b/w the two levels.

• Twisting increases the probability that both wires are effected by the noise in the same manner, thus the difference at the receiver remains same.

• Therefore, number of twists per unit length determines the quality of the cable.

Twisted Pair - Transmission Characteristics• analog

– needs amplifiers every 5km to 6km• digital

– can use either analog or digital signals– needs a repeater every 2-3km

• limited distance• limited bandwidth (1MHz)• limited data rate (100MHz)• susceptible to interference and noise

Unshielded vrs Shielded Twisted pair cable

UTP and STP cables

Unshielded Twisted Pair (UTP)• Ordinary telephone

wire• Cheapest• Easiest to install• Suffers from external

EM interference

Shielded Twisted Pair (UTP)• Metal braid or

sheathing that reduces

• More expensive• Harder to handle

(thick, heavy)

Grades or Categories of UTP

Categories of UTP

Connectors of UTP

Applications (UTP): Telephone lines connecting subscribers to the central office DSL lines LAN – 10Base-T and 100Base-T

Applications (STP):Most common mediumTelephone networkWithin buildingsFor local area networks (LAN)

Fibre – Optic Cable