Transcript Chapter 1: Introduction

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)
amplitude (volts)
Analog Signaling
1 cycle
represented
by sine waves
phase
difference
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
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
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”?