Chapter 2 Business Information
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
Introduction • Information communication relates to business requirements. • 4 major forms of business Information (VIViD): • Voice or Audio • Image • Video • Data • Various types of Information communication will mostly take place in the form of Electrical Signals.
What is a Network • A transmission system that connect two or more applications running on different computers.
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
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
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
Digital Systems • Business information can be transmitted in digital or analog form • A digital system uses a sequence of discrete, discontinuous values or symbols to represent information • Discrete information has a finite “alphabet” • Examples include letters, numbers, icons, and binary data • The information rate and the capacity of a digital channel are measured in bits per second (bps)
Analog Systems • Use a continuous signal to represent either continuous or discrete information sources • Sources include sounds, music, and video • Expressed as an oscillation (sine wave format) of frequency • Information rate and channel capacity are measured in hertz (Hz) of bandwidth (1 Hz = 1 cycle per second)
Audio • Audio service support applications based on sound • It is mainly analog. • Bandwidth determines the quality of sound. Why? • Primary Application is Telephone Communication 3400 HZ bandwidth • Other applications: • Telemarketing • Voice mail • Audio teleconferencing (7000 Hz) • Entertainment radio (Hi-Fi 15,000, CD 20,000 per channel)
Digital Audio • Audio information can also be represented digitally. • To get a good representation of sound in digital format we need to sample its amplitude at a rate (samples per second, or smp/s) equal to at least twice the maximum frequency (in Hz) range of the analog signal (Nyquist Frequency)(Why?) • Telephone quality: 8000 smp/s, each sample using 8 bits • 8 bits * 8000 smp/s = 64 kbps to transmit • CD audio quality: 44,100 smp/s, each sample using 16 bits • 16 bits * 44,100 smp/s = 1.41mbps to transmit clearly • Quantization • The process after sampling that puts signal amplitudes in digital form
“Lossy” and “Lossless” • Audio compression algorithms can be used to reduce the bandwidth requirements for transmitting digital audio streams over communication lines • Lossless compression • Receivers can reproduce an exact digital duplicate of the original audio stream transmitted by the sender by expanding/decompressing the file that is received • Lossy compression • Irreversible changes are made to original file that diminishes the quality of the original audio stream when the receiver decompresses the file
Bandwidth (BW) • BW is the difference between the highest and lowest frequencies that an analog communications system can pass. • For example, a telephone accommodates with a BW of 3000 Hz: the difference between the lowest (300 Hz) and highest (3300 Hz) frequencies it can carry. • Therefore the BW measures the limits of these frequencies. • The higher the frequencies allowed, the more accurately a complex signal can be represented.
Analog to Digital • To convert analog signals to digital form a process : • Sampling • Quantization • Example: • For telephone quality sound: • Sampling rate: 8000 smp/s • Quantization: 8 bit/smp • Digitized telephone voice quality need: 8000x8=64000bps = 64kbs • For CD quality audio sterio • Sampling rate: 44000 smp/sec • Quantization: 16 bit/smp • Digitized CD quality need: 44000*16*2 = 1408000bps=1.41Mbps • Average length of telephone conversation is 1 to 5 minutes • Conversation in either direction is transmitted less than half the time (otherwise the two parties would be talking at once) • Speech takes place in bursts of 350 ms followed by 650 ms of silence
Frequency Spectrum • Any communication signal can be expressed as a combination of pure oscillations (Sine Waves) of various frequencies.
Audio • Networking Implications for Voice communication requires: • Intra-location facility • Access to outside telephone services provided by local telephone company and long distance carriers • These are provided either by: • PBX (Private Branch Exchange): also referred as in-house equipment, or called customer premises equipment. or • Centrex : performs the switching function in telephone company’s central office and all the telephone lines are routed from the customer site to the central switch.
Data Communication • In this context, we mean data stored on computers • Already digital, so no conversion necessary • Bandwidth usually affects speed, but not quality
Data • Consist of information that can be represented by a finite alphabet of symbols • Examples include text and numerical information • Symbols are represented by groups of 8 bits (octets or bytes) • Textual data convenient for human (Advantage) • Not easy to store and transmit by data processing and communications systems (Disadvantage). • Reason: Data processing & communications systems are designed for BINARY DATA • Solution: Use codes/standards to represent characters by sequence of bits • Textual data need to be converted to binary digits (bits) for data processing and communications systems • Examples: • Morse Code, • IRA (International Reference Alphabet) • ASCII (American Standard Code for Information Interchange)
Data • International Reference Alphabet (IRA) • Most commonly used text code • The U.S. national version of IRA is referred to as the American Standard Code for Information Interchange (ASCII) • Each character in this code is represented by a unique 7-bit pattern • Almost always stored and transmitted using 8 bits per character • Eighth bit is a parity bit used for error detection
Encoding Schemes UTF-8 Unicode Supported in numerous programming languages Also supported by the operating systems used on most computing and communication devices 16-bit code that is backward compatible with IRA/ASCII Used to represent characters for most of the writing systems used worldwide • UCS [Universal Character Set] Transformation Format – 8 • 8 bit code that is backward compatible with ASCII • Supports variable-length encoding • Capable of representing symbols and characters used in all the major languages spoken around the world • Became the dominant character-encoding scheme on the World Wide Web in 2007
IRA • IRA/ASCII: 7bits per Characters, i.e. 27=128 Characters
Data (Cont.) • Parity bit is the 8th bit in IRA or ASCII which is set such that the total number of binary 1s in each byte is always odd (odd parity) or always even (even parity). • Consequently a transmission error that changes 1 single bit (or odd number of bits) can be detected.
Data (Cont.) • Question: How many bits are approximately required to transmit a letter size page of text? • a Character use 1 byte or 8 bits • a page of 8.5x11 with 1in margin has 6.5x9 space • a double-space has 3-lines/in or 27-lines per page • a line has 65 characters (10 char per in) • (8bits)x(27lines)x(65char/line) = 14,040 bits p page. Or approximately, 10,000 bits per page
Data (Cont.) • How long it take to transmit a page by a modem? • A typical modem transmit 56K per sec is 56,000bps • A page takes 10,000 bits/56,000bps = 0.18sec • Experiment with a 84 page showed a total of 115,325 or 1373 char per page or 10,983 bits per page. • Using a Data Compression Technique data was reduced up to 40% , resulted in 4098 bits per page
Image • Information in the form of Pictures, Charts, or Drawings • Application: Fax, CAD, Publishing, Medical Imaging • Medical Imaging
Transfer Time for Digital Radiology Images Image (Cont.) Transmission Rate: DS-0 = 56 kbs DS-1= 1.544Mbps DS-3=44.736Mbps
Converting Images Image (Cont.) • digitize an image := Break image up into small units • More units means more detail • Units are called pixels • Use photocell to read each unit, assign value • How can we represent those units electrically?
Image Quality Issues Image (Cont.) • More pixels=better quality • More compression=reduced quality • “Lossy” gives from 10:1 to 20:1 compression • “Lossless” gives less than 5:1 • For medical imaging lossy compression is not allowed. So applications run below 5:1. • Less compression=reduced speed of transfer • Choices in imaging technology, conversion, and communication all affect end-user’s satisfaction
Image Representation • Vector graphics • Image is represented as a collection of straight and curved line segments • Simple objects and more complex objects are defined by the grouping of line segments • Binary codes are used to represent object type, size and orientation. • Raster graphics • Image is represented as a two-dimensional array of spots, called pixels • a “pixel” is the smallest single component of a digital image • in a simplest form (black & white image), a pixel is either black or white • Used for computer image processing and for facsimile
Image: Pixel: Abbreviation for picture element, is an individual dot in a dot-matrix representation of an image, it is the smallest element of a digital image.
Eight-Level Gray Scale Gray Scale Image: if each pixel is defined by more than1 bit. e.g. a 3-bit Gray Scale produces 8 shades of gray White Black Each pixel is defined 3-bit, i.e. 23=8. (000, 001, 010, 011, 100, 101, 110, 111)
Image and Document Formats • Common raster formats • JPEG (Joint Photographic Experts Group) • Most widely used • Designed to be general purpose • Appropriate for high-quality images • GIF (Graphics Interchange Format) • Generally useful for nonphotographic images with a fairly narrow range of color • Common document formats • PDF (Portable Document Format) used on the web • Postscript (page description language build into quality printers.
Comparison of Common Graphics File Formats Table 2.2 Comparison of Common Graphics File Formats
Networking Implication for Image Image (Cont.) • Fundamental difference between Image & Text: • Volume of Data • 1-page text: 13,000bits(300words)*(5.5Char/word)*(8bits) • 1-good quality computer screen image:300,000bits • 1-page fax with 200points resolution: 3,740,000bits • Using clustering black & white regions to compress image up to 8 - 16 times
Concerns: Response time Users need to be able to manipulate an image over communication lines in real time Throughput Communications infrastructure must have a capacity great enough to keep up with transmissions Security Some types of image transmissions must transfer over secure links and typically require encryption Networking Implications for Image Data • A tremendous number of bits is needed for representation in the computer • The number of bits needed can be reduced by the use of image compression techniques • Even with compression the number of bits to be transmitted is large, especially for color images
Video • Carries sequences of pictures in time • In essence makes use of a sequence of raster-scan images • 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 • Can be captured by either analog or digital video recorders • Significantly higher bandwidth requirements in order to send images (frames) quickly enough • Similarity of adjacent frames allows for high compression rates
Interlacing To produce a picture on the screen, an electron beam scans across the surface of the screen from left to right and top to bottom. Illumination is equal to intensity A to B is odd no. scan lines and C to D is even no. scan lines, that are scanned separately, with odd and even fields alternating on successive scans. 483 horizontal line of 30 scans per sec cause flickering effect. Hence, interlacing is used making 241.5 lines each and 60 scan per second
Digital VideoNetworking Implications • Video traffic on business networks is expanding at dramatic rates • Unless compressed, real-time video traffic requires extensive bandwidth • Lossy compression can be used • Discrete cosine transform (DCT) is the video compression algorithm that underlies JPEG, MPEG (Motion Pictures Expert Group), and H.263 video file formats • A key challenge for enterprise networks is scaling up IP networks to effectively support video transmission while also providing adequate quality of service to other business transmission requirements
Digital Television Formats Table 2.3 Digital Television Formats
Performance Measures • Data traffic is predicted to grow at a compound rate of 50% each year between 2012 and 2016 • The total annual volume is expected to exceed 60,000 petabytes by 2016 • With video and TV streaming exceeding all other forms of Web and Internet traffic • Wireless traffic for mobile connections is expected to grow at nearly the same annual rate • Key parameters related to performance: • Response time: The time it takes for a system to react to a request to perform a particular task. • Quality of experience • Throughput (Data Rate)
The shorter the RT the greater the cost • Computer Processing Power • The faster the computer the shorter the RT the more expensive equipment • Competing requirements • Providing rapid RT to some processes may penalize other processes • Therefore benefits of a given level of RT must be evaluated versus the cost of achieving that RT.