Bussiness data communications 4e chapter 2

Chapter 2 : Business Information
Business Data Communications, 4e


Analog Data
 Continuous signal
 Expressed as an oscillation (sine wave
format) of frequency
 Example: Analog electrical signal generated
by a microphone in response to continuous
changes in air pressure that make up sounds


Basic Analog Terms
 Wave frequency: Number of times a cycle
occurs in given time period
 Wave amplitude: Height of a wave cycle
 Hertz (Hz): The number of times a wave
cycle occurs in one second (commonly used
measure of frequency)


amplitude (volts)

Analog Signaling
phase
difference

1 cycle

time

(sec)
frequency (hertz)
= cycles per second


Digital Data
 Represented as a sequence of discrete symbols
from a finite “alphabet” of text and/or digits
 Rate and capacity of a digital channel measured in
bits per second (bps)
 Digital data is binary: uses 1s and 0s to represent
everything
 Binary digits can be represented as voltage pulses


Basic Digital Terms
 Bit: digit in a binary number
 1 is a 1-bit number (=1 in base 10)
 10 is a 2-bit number (=2 in base 10)
 10011001 is an 8-bit number (=153 in base 10)

 Byte: eight bits


Types of Information
 Audio
 Data
 Image
 Video

Understanding Audio
 What makes sound? Vibration of air
 How can we record that vibration?
 How can we convert that to an electrical
signal?


Digital Audio
 For good representation, must sample amplitude at a rate
of at least twice the maximum frequency
 Measured in samples per second, or smp/sec
 Telephone quality: 8000smp/sec, each sample using 8 bits
 8 bits * 8000smp/sec = 64kbps to transmit

 CD audio quality: 44000smp/sec, each sample using 16
bits
 16 bits * 44000smp/sec = 1.41mbps to transmit clearly


Data Communication
 In this context, we mean data already stored
on computers
 Already digital, so no conversion from analog
form necessary


Understanding Images
 to digitize and image, you must break it into
small units

 More units means more detail
 Displayed units generally called pixels


Image Quality Issues
 More pixels=better quality=larger size
 More compression=reduced quality=increased speed
 “Lossy” gives from 10:1 to 20:1 compression
 “Lossless” gives less than 5:1

 Format (vector vs bitmapped/raster) affects size and
therefore bandwidth requirements
 Choices in imaging technology, conversion, and
communication all affect end-user’s satisfaction


Video Communication
 Sequences of images over time
 Same concept as image, but with the dimension of
time added
 Significantly higher bandwidth requirements in
order to send images (frames) quickly enough
 Similarity of adjacent frames allows for high
compression rates


Response Time
 User response time
 System response time
 Network transfer time

Bandwidth Requirements
 Review Figure 2.7
 What happens when bandwidth is
insufficient?
 How long does it take to become impatient?
 Is data communication ever “fast enough”?