Chapter 2 Business Information Business Data Communications 4

Chapter 2 : Business Information Business Data Communications, 4 e

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)

amplitude (volts) Analog Signaling phase difference 1 cycle 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 1 s and 0 s to represent everything Binary digits can be represented as voltage pulses

Basic Digital Terms Bit: digit in a binary number n n n 1 is a 1 -bit number (=1 in base 10) 10 is a 2 -bit number (=2 in base 10) 1001 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 (Nyquist Rate) Measured in samples per second, or smp/sec Telephone quality: 8000 smp/sec, each sample using 8 bits n 8 bits * 8000 smp/sec = 64 kbps to transmit CD audio quality: 44000 smp/sec, each sample using 16 bits n 16 bits * 44000 smp/sec = 1. 41 mbps to transmit clearly

CPE: Customer Premises Equipments

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 n n More units means more detail Displayed units generally called pixels

Image Quality Issues More pixels=better quality=larger size More compression=reduced quality=increased speed 1. 2. “Lossy” gives from 10: 1 to 20: 1 compression “Lossless” gives less than 5: 1 Format (vector vs bitmapped/raster) affects size and therefore bandwidth requirements 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

Response Time The time it takes a system to react to a given input. n n Computer processing power Competing requirements Response Time Ranges Table 2. 6 (p. 32) On-line transactions: n n User response time System response time Network transfer time Response Time Requirements Fig. 2. 6 (p. 34)

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”?