1. Cis303a_chapt08.ppt Copyright© 2002 Morris Fulcher Chapter 8 Data 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 Types Data Commands 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) 276 277

2. 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 Phase Specific time point within a wave’s cycle Measured 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 second Measured in Hertz (Hz) Amplitude is consistent Modulation Bits in a wave are encoded by manipulating Amplitude or Frequency or Phase Signal Specific data transmission event or group of events 278 280 279

3. Cis303a_chapt08.ppt Copyright© 2002 Morris Fulcher Modulation Methods Multilevel coding Embedding multiple bit values within a single wave characteristic (frequency or amplitude) Wave characteristics In 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. 8-9 Error in chart

4. Cis303a_chapt08.ppt Copyright© 2002 Morris Fulcher Modulation Methods Amplitude Modulation (AM) Bit values as specific wave amplitudes Amplitude is for one full wave cycle Frequency (cycles per second) is constant High interference factors Obstructions Noise Magnetic interference Lower power requirements Reference point (minimum absolute value) can be any voltage: + or - Lower amplitudes travel through obstructions i.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 consistent Higher power requirements Static time frames with frequency changes Less susceptible to Obstructions Noise Higher frequencies travel through obstructions Transmission/Reception considerations Line of site Bounce 282 Fig 8-7