Chapter 2 : Business Information Business Data Communications, 4e

Analog Data 8Continuous signal 8Expressed as an oscillation (sine wave format) of frequency 8Example: Analog electrical signal generated by a microphone in response to continuous 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 (Hz): The number of times a wave cycle occurs in one second (commonly used measure of frequency)

Analog Signaling 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

Types of Information 8Audio 8Data 8Image 8Video

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

Digital Audio 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

Data Communication 8In this context, we mean data already stored on computers 8Already digital, so no conversion from analog form necessary

Understanding Images 8to digitize and image, you must break it into small units 8More units means more detail 8Displayed units generally called pixels

Image Quality Issues 8More pixels=better quality=larger size 8More compression=reduced quality=increased speed 8“Lossy” gives from 10:1 to 20:1 compression 8“Lossless” gives less than 5:1 8Format (vector vs bitmapped/raster) affects size and therefore bandwidth requirements 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

Response Time 8User response time 8System response time 8Network transfer time

Bandwidth Requirements 8Review Figure 2.7 8What happens when bandwidth is insufficient? 8How long does it take to become impatient? 8Is data communication ever “fast enough”?