Bussiness data communications 4e chapter 2

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

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)

Analog Signaling

time (sec)

1 cycle

frequency (hertz)

= cycles per second

phase difference

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

 “Lossy” gives from 10:1 to 20:1 compression

 “Lossless” gives less than 5:1

therefore bandwidth requirements

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”?