Chapter 1: Introduction

Business Data Communications, 4e

Information & Communication

Generation and transfer of information is critical to today’s businesses

Flow of information both mirror and shape organizational structures

Networks are the enabling technology for this process

The “Manager’s Dilemma”

Technology is necessary for competitiveness Cost of technology has decreased Reliance on technology has increased Number of choices have increased Choices are both more difficult and more

important

Business Information Requirements

Voice Data Image Video

Distributed Data Processing

Centralized processing Distributed processing Hybrid systems

Transmission of Information

Transmission and transmission media e.g. twisted pair, fiber, wireless, coax

Communication Techniques encoding, interface, protocols

Transmission efficiency multiplexing, compression

Networks

Wide Area Networks Local Area Networks Wireless Networks

Communications Software

TCP/IP Distributed Applications Client/Server Architectures & Intranets

Management Issues

Doing Business on the Internet Network Management Network Security

Communications Standards

Importance Process Organizations

Resources

Web Sites Usenet Newsgroups Journals

Business-oriented Technical

Telecommunication

Uses electricity to transmit messages Speed of electricity dramatically extends reach

Sound waves: ~670 mph Electricity: ~186,000 (speed of light)

Bandwidth= information-carrying capacity of a channel

Data Communication

Adding storage overcomes time constraints Store-and-forward communication

E-mail, voice mail, facsimile, file transfer, WWW

Analog Data

Continuous signal Expressed as an oscillation (sine wave

format) of frequency Example: Analog electrical signal generated

by a microphone in response to continous 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: The number of times a wave cycle

occurs in one second (commonly used measure of frequency)

Analog Signaling

represented by sine waves

time(sec)

amp

litu

de

(vo

lts)

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

VIViD Communication

Voice Image Video Data

Converting Voice

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

signal?

Analog Voice Communication Primarily used for transmission of human voice

(telephony) Microphone captures voice vibrations, converts them to

waves than can be expressed through variations of voltage Examples

Telephone (3000Hz) Hi-Fi Sound (15,000Hz; approximate range of human ear) Compact Disc (20,000Hz for each of two channels)

Digital Voice Communication 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

Converting Images

Break image up into small units More units means more detail Units called pixels

Use photocell to read each unit, assign value How can we represent those units electrically? PACMAN example

Image Quality Issues

More pixels=better quality More compression=reduced quality

“Lossy” gives from 10:1 to 20:1 compression “Lossless” gives less than 5:1

Less compression=reduced speed of transfer 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

Data Communication

In this context, we mean data stored on computers

Already digital, so no conversion necessary Bandwidth usually affects speed, but not

quality Examples?

Bandwidth Requirements

Review chart on page 27 What happens when bandwidth is

insufficient? Poor quality or slow transmission How long does it take to become impatient? Is data communication ever “fast enough”?