Chapter 2 - Part1: Business Information

1. Chapter 2 - Part1: Business Information Business Data Communications, 6e

2. Objectives • Information Sources • Types of Information • Communication requirements for each information type • Signal • Signal types: Analog/Digital • Need for Conversion of Signals • Errors in Signal Conversions • System response time

3. Introduction • Information communication relates to business requirements. • Various forms of business Information: • Audio • Data • Image • Video • Various types of Information communication will mostly take place in the form of Electrical Signals.

4. What is a Network • A transmission system that connect two or more applications running on different computers.

5. The Internet • The most famous network • The Internet is a global transmission network • Used by many applications: The Word Wide Web; Email; etc. Client/Server Applications • PC clients receive service from servers • Many applications need special clients • Many applications only need a browser

6. Data Communication Data Communications, as the name suggests, involves the transmission of data (text, numbers, pictures, and other information) • Adding storage overcomes time constraints • Store-and-forward communication • E-mail, voice mail, facsimile, file transfer, WWW

7. Telecommunication Telecommunications is the transmission of voice and video, including ordinary telephony and broadcast and cable television. • Uses electricity to transmit messages • Speed of electricity dramatically extends reach • Electricity: (Speed of light)~(670e6miph or 0.186e6mips) or (300e6 meter/s) • Sound waves: (Speed of Sound)~(670miph or 0.186mips) or (300meter/s) • Bandwidth= information-carrying capacity of a channel

8. Types of Information Information Source Discrete Continuous Rate/Capacity: Rate/Capacity: Cycle per sec (Hz) Bits per sec (bps) Analog Digital Example: Electrical Signal coming out of mic. representing the continuous acoustic changes in air pressure. Example: Text, Numerical Data, Binary Data

9. Analog Data • Also referred to as Continuous Signal • Expressed as an oscillation (sine wave format) or frequency • Example: Analog electrical signal generated by a microphone in response to continuous changes in air pressure that make up sounds

10. Sinusoidal Waveform V (Volt) • T := Time Period, Sec (1 Cycle) • F := Frequency (1/T)(Hz) • Vm:= Amplitude (Volt) •  :=2f=2 /T (Angular Velocity) Vm T t (sec)

11. Basic Analog Terms • Wave frequency: Number of times a cycle occurs in given time period (e.g. second) • Hertz: The number of times a wave cycle occurs in one second (commonly used as a measure of frequency) also known as Cycle/sec • Wave amplitude: Height of a wave cycle

12. B B C C A A A D D Cyclic Event

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

14. 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 is 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

15. Basic Digital Terms • Bit: digit in a binary number (i.e. base 2) • 1 in base 2 is a 1-bit number (is equivalent of 1 in base 10) • 12 = 110 • 10 in base 2 is a 2-bit number (is equivalent of 2 in base 10) • 102 = 210 • 10011001 in base 2 is an 8-bit number (=153 in base 10) • 100110012 = 15310 • Byte: eight bits

16. VIViD Communication 4 Major forms of business information are: • Voice or Audio • Image • Video • Data

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

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

19. Digitizing Analog Voice • Audio information can be converted to digital format. For doing this we need to sample its amplitude (sample per second, or smp/s) at a rate equal to at least twice the maximum frequency (Hz) of the analog signal. For voice of telephone quality this is 8000 smp/s. • After sampling, the signal amplitudes must be put in digital form, a process referred to as quantization. 8 bits per sample for telephone.

20. Digitalizing Audio Information • Digital Telephone Quality Voice: 8 bits/smp x 8000 smp/s = 64,000 bits per second (bps) • Compact Discs: for High quality CD 44,100 smps/ch is selected with 16 bit for each sample: (44,100 smp/s per channel) x (16 bits/smp) x 2 (channels) = 1,411,200 bits per second (bps) = 1.41 Mbps A CD contains 600 megabytes (MB) is equivalent of 1 hour of stereo sound.

21. Acquisition Basics Signal Conditioning Physical Phenomenon Computer Interface Card Transducer

22. Sources of Error • The fact that we are using a converter which has a finite number of bits introduces an error called “quantization error” • The fact that it takes a finite (non-zero) amount of time to perform the conversion introduces the possibility of an error called “aliasing”

23. Quantization Error V +5 +4 +3 +2 +1 0 -1 -2 -3 -4 -5 n+4 n+3 n+2 n+1 n n-1 n-2 n-3 n-4 V Analog to Digital Conversion

24. 2.44mV 1.22mV -1.22mV Quantization Error: The uncertainty introduced in D-A conversion • DAQ-12bit (i.e. 212 = 4096) • 10 volt input range • n digitized values range from 0-4095 • Uncertainty of 1.22 mV

25. Aliasing(An incorrect signal) • In communications, a false signal that results when an analog wave, such as voice or music, is digitized by periodic sampling. If the samples are too far apart in time (less than twice the highest frequency in the wave), the high-frequency components of the wave are not captured correctly, and the result is an alias— an incorrect signal— that appears when the original wave is reconstructed.

26. Aliasing

27. Aliasing Voltage vs Time

28. Aliasing

29. Aliasing

30. Aliasing

31. Aliasing

32. Aliasing Voltage vs Time

33. Aliasing (Continue) • Aliasing can lead to incorrect frequency information • Sampling Theorem - Maximum frequency component that can be correctly identified is that frequency which is 1/2 the sample frequency. This maximum frequency is called the Nyquist frequency.