Chapter 1: Introduction Business Data Communications, 4e

Information & Communication 8Generation and transfer of information is critical to today’s businesses 8Flow of information both mirror and shape organizational structures 8Networks are the enabling technology for this process

The “Manager’s Dilemma” 8Technology is necessary for competitiveness 8Cost of technology has decreased 8Reliance on technology has increased 8Number of choices have increased 8Choices are both more difficult and more important

Business Information Requirements 8Voice 8Data 8Image 8Video

Distributed Data Processing 8Centralized processing 8Distributed processing 8Hybrid systems

Transmission of Information 8Transmission and transmission media 8e.g. twisted pair, fiber, wireless, coax 8Communication Techniques 8encoding, interface, protocols 8Transmission efficiency 8multiplexing, compression

Networks 8Wide Area Networks 8Local Area Networks 8Wireless Networks

Communications Software 8TCP/IP 8Distributed Applications 8Client/Server Architectures & Intranets

Management Issues 8Doing Business on the Internet 8Network Management 8Network Security

Communications Standards 8Importance 8Process 8Organizations

Resources 8Web Sites 8Usenet Newsgroups 8Journals 8Business-oriented 8Technical

Telecommunication 8Uses electricity to transmit messages 8Speed of electricity dramatically extends reach 8Sound waves: ~670 mph 8Electricity: ~186,000 (speed of light) 8Bandwidth= information-carrying capacity of a channel

Data Communication 8Adding storage overcomes time constraints 8Store-and-forward communication 8 , voice mail, facsimile, file transfer, WWW

Analog Data 8Continuous signal 8Expressed as an oscillation (sine wave format) of frequency 8Example: Analog electrical signal generated by a microphone in response to continous changes in air pressure that make up sounds

Basic Analog Terms 8Wave frequency: Number of times a cycle occurs in given time period 8Wave amplitude: Height of a wave cycle 8Hertz: The number of times a wave cycle occurs in one second (commonly used measure of frequency)

Analog Signaling 8represented by sine waves time (sec) amplitude (volts) 1 cycle frequency (hertz) = cycles per second phase difference

Digital Data 8Represented as a sequence of discrete symbols from a finite “alphabet” of text and/or digits 8Rate and capacity of a digital channel measured in bits per second (bps) 8Digital data is binary: uses 1s and 0s to represent everything 8Binary digits can be represented as voltage pulses

Basic Digital Terms 8Bit: digit in a binary number 81 is a 1-bit number (=1 in base 10) 810 is a 2-bit number (=2 in base 10) is an 8-bit number (=153 in base 10) 8Byte: eight bits

VIViD Communication 8Voice 8Image 8Video 8Data

Converting Voice 8What makes sound? Vibration of air 8How can we record that vibration? 8How can we convert that to an electrical signal?

Analog Voice Communication 8Primarily used for transmission of human voice (telephony) 8Microphone captures voice vibrations, converts them to waves than can be expressed through variations of voltage 8Examples 8Telephone (3000Hz) 8Hi-Fi Sound (15,000Hz; approximate range of human ear) 8Compact Disc (20,000Hz for each of two channels)

Digital Voice Communication 8For good representation, must sample amplitude at a rate of at least twice the maximum frequency 8Measured in samples per second, or smp/sec 8Telephone quality: 8000smp/sec, each sample using 8 bits 88 bits * 8000smp/sec = 64kbps to transmit 8CD audio quality: 44000smp/sec, each sample using 16 bits 816 bits * 44000smp/sec = 1.41mbps to transmit clearly

Converting Images 8Break image up into small units 8More units means more detail 8Units called pixels 8Use photocell to read each unit, assign value 8How can we represent those units electrically? 8PACMAN example

Image Quality Issues 8More pixels=better quality 8More compression=reduced quality 8“Lossy” gives from 10:1 to 20:1 compression 8“Lossless” gives less than 5:1 8Less compression=reduced speed of transfer 8Choices in imaging technology, conversion, and communication all affect end-user’s satisfaction

Video Communication 8Sequences of images over time 8Same concept as image, but with the dimension of time added 8Significantly higher bandwidth requirements in order to send images (frames) quickly enough 8Similarity of adjacent frames allows for high compression rates

Data Communication 8In this context, we mean data stored on computers 8Already digital, so no conversion necessary 8Bandwidth usually affects speed, but not quality 8Examples?

Bandwidth Requirements 8Review chart on page 27 8What happens when bandwidth is insufficient? 8Poor quality or slow transmission 8How long does it take to become impatient? 8Is data communication ever “fast enough”?