Cis303a_chapt08.ppt Copyright© 2002 Morris Fulcher

Chapter 8Chapter 8Data and Network Communication TechnologyData and Network Communication Technology

Communications Protocols

Message

A unit of data or information transmitted from a sender to one or more recipients

Any number of bytes

TypesDataCommands

Control the communications process

Command and response sequences

Communications Protocol

A set of rules and conventions for communications(manners, etiquette , code of behavior , practice, set of rules, modus operandi, method)

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Cis303a_chapt08.ppt Copyright© 2002 Morris Fulcher

Encoding and Transmitting Bits

Carrier Waves

Travel as sine waves (Fig. 8-3, Pg. 279)Amplitude

Measure of the wave height (power)Distance between the wave peak and zero

PhaseSpecific time point within a wave’s cycleMeasured in degrees

Cycle

The time from the beginning of a wave and the end (or beginning of another wave)

Frequency

The number of cycles in one secondMeasured in Hertz (Hz)Amplitude is consistent

Modulation

Bits in a wave are encoded by manipulating Amplitude orFrequency orPhase

Signal

Specific data transmission event or group of events

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Cis303a_chapt08.ppt Copyright© 2002 Morris Fulcher

Modulation Methods

Multilevel coding

Embedding multiple bit values within a single wave characteristic (frequency or amplitude)

Wave characteristicsIn a given cycle

Various amplitude combinations(i.e. Binary 11 =

8 volt + ½ cycle and an 8 volt – ½ cycle

Binary 01 = 4 volt + ½ cycle and a 4 volt – ½ cycle

Binary 00 = 2 volt + ½ cycle and a 2 volt – ½ cycle

Binary 10 = 6 volt + ½ cycle and a 6 volt – ½ cycle

284 Fig. 8-9Error in chart

Cis303a_chapt08.ppt Copyright© 2002 Morris Fulcher

Modulation Methods

Amplitude Modulation (AM)

Bit values as specific wave amplitudes Amplitude is for one full wave cycleFrequency (cycles per second) is constantHigh interference factors

ObstructionsNoiseMagnetic interference

Lower power requirementsReference point (minimum absolute value) can be any

voltage: + or -Lower amplitudes travel through obstructionsi.e. 60 Hz cycle time, 10 volts = binary 1, 1 volt = binary 0

Frequency Modulation (FM)

Bit values as specific changes in frequency (cycles per second) in a time frame

Frequencies are consistent (x Hz for 0, y Hz for 1)Amplitude is consistentHigher power requirementsStatic time frames with frequency changesLess susceptible to

ObstructionsNoise

Higher frequencies travel through obstructions

Transmission/Reception considerationsLine of siteBounce

282 Fig 8-7