Mr C JohnstonICT Teacher

www.computechedu.co.uk

G055 - Lecture 07

Signal Types and Transmission Media

Session Objectives Be able to describe different types of signal used to

transmit data on a network Know types of cable used to transmit data and the

correct connector type for each, Understand how fibre optical and wireless

transmission methods work.

Types of Signal Digital Signals are a series of pulses – either 1 or 0,

Computers operate using digital – therefore the signals generated are also digital,

To transmit them an interface card is needed to change the signals into a frequency which represents the 1s and 0s on the communication medium - this is known as modulation,

When a computer receives a signal it needs to be translated from the frequency into 1s and 0s which the computer can understand – this is known as demodulation.

Figure 1: A Digital Signal

Analogue Signals Analogue signals are a continuous wave pattern,

Some transmission medium can only carry analogue frequencies rather than digital, If digital data is going to be transmitted on a medium that can only carry analogue

signals, then it has to be converted into a set of analogue signals, The signals are modulated from digital to analogue and demodulated at the other

end, A device called a modem is responsible for this.

Figure 2: An Analogue Signal

Diagram Showing Modem Use

Email Compose

dAnd Sent

Modem

Computer In Coventry

Email ReceivedAnd Read

Modem

Computer In LondonPublic Telephone

System

Digital Signal Digital SignalAnalogue Signal

Newer digital phone lines don’t need a modem as they are able to accept digital frequencies

Common Cables1

4 sets of twisted pairs with an outer case, Twisted pairs reduce electrical interference, Cheap, easy to work with as its flexible fast with

data speeds up to 1000mb/s Still prone to electrical interference which

causes data to do missing.

RJ-45Unshielded Twisted Pair (UTP)

OverviewConnectorCable Type

4 sets of twisted pairs, covered with a layer of metal foil and an outer case,

Twisted pairs reduce electrical interference, Foil layer further reduces electrical interference

making it more reliable than UTP, Slightly nearer and less popular as UTP Cheap, easy to work with as its flexible fast with

data speeds up to 1000mb/s Still prone to electrical interference which

causes data to do missing.

RJ-45Shielded Twisted Pair (STP)

Common Cables2

Solid copper cable covered in an insulating plastic case. The case is then covered with a copper mesh which is all encased with another plastic sleeve,

Very little interference, Less flexible then UTP as thicker, Frequently used from road to box for cable broadband, Available in different thicknesses but thinner cables have

shorter cable runs.

BNC (Bayonet Neill-Concelman)

Coaxial cable

OverviewConnectorCable Type

Telephone cables also use twisted pairs with a smaller RJ-11 connector on – typically there are only 2 sets of pairs.

Telephone cables also use twisted pairs with a smaller RJ-11 connector on – typically there are only 2 sets of pairs.

Fibre Optics Uses pulses of light rather than electrical signals to

transmit the data – therefore is immune to electrical interference,

The light is pulsed down hollow glass or plastic tubes – main advantage is distance and speed - 14 Tera bits per second over a single 160 km long optical fiber is the current record. (http://www.ntt.co.jp/news/news06e/0609/060929a.html)

Hollow glass or plastic tube which light is pulsed down,

Has a protective cover to protect the light from interference and is immune to electrical interference,

Glass can carry longer than plastic, Can travel long distances and is fast Expensive over short distances but very

economical over long

SC (subscriber connector)

or

ST (straight tip)

Fibre Optic Cable

OverviewConnectorCable Type

Wireless Transmission Wireless networks uses radio signals to transmit data, so no wiring is required, Wireless Access Points are cabled to the main network and broadcast / receive

data via radio waves at a particular frequency, A wireless network card required in each client to receive / send the radio signal Radio waves are subject to interference from signals that just hang around in the

air, and it can be slow and unreliable. It is possible that signals can be received outside the area they are intended for,

causing some problems with security, Typical speeds 11 Mb/s to 54 Mb/s - 802.11n up to 600Mb/s,

RJ-45 Wiring Diagram

Topic Exercise Complete the following reading:

A2 Text Book Pages pg21-23 (start @ connections in a network heading)

AVCE Unit 08 Book pg44-46 Have a go at creating your own STP / UTP cable use

the wiring diagram to help and test with the cable tester,

Have a go at creating your own coax cable – we don’t have any BNC connectors but the TV ones are similar,

Download and complete this topics past exam paper questions – complete for next lesson.