Bussiness data communications 4e chapter 2

Chapter : Business Information Business Data Communications, 4e 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 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 1s and 0s to represent everything  Binary digits can be represented as voltage pulses Basic Digital Terms  Bit: digit in a binary number  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 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  Measured in samples per second, or smp/sec  Telephone quality: 8000smp/sec, each sample using bits  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 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  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  “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  User response time  System response time  Network transfer time 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”? ... 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 Types of Information  Audio  Data  Image  Video Understanding... 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. .. sample using 16 bits  16 bits * 44000smp/sec = 1.41mbps to transmit clearly Data Communication  In this context, we mean data already stored on computers  Already digital, so no conversion from