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
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”?