BSIT 1: Information Technology II1 Information Technology II Lecture 0 Uganda Christian University Faculty of Science and Technology Information Technology.

BSIT 1: Information Technology II 1

Uganda Christian UniversityFaculty of Science and Technology

Information Technology IIInformation Technology IILecture 0Lecture 0

BSIT 1, BES 1January Semester 2011Mr. Ronald Ssejjuuko

0781 457 [email protected]

Introduction

The growth and development of Information Technologies (IT) has led to the ignition and increase in their economic and social impact; a cause that has led many to crave and advance in areas of technology.

This course will enable students be part of this hi-tech epoch by building on the principles learnt in Information 1

Technology 1.

BSIT 1: Information Technology II

2

Introduction cont’d

So the principles and skills learnt from information technology 1 will highly be appreciated to underscore the need for this course.

This will enable the student to understand the need of information technology in keeping and manipulating information or data



Course description This course introduces the engineering behind a modern

information infrastructure which is the foundation for the revolution in Systems that we are currently experiencing including economic and social systems.

The course prepares students to take advantage of new information technologies that will as well influence their prospective careers and enhance their deeper study of computers and their use.

Students should and will be in position to make changes in their particular professions based on the continuing emergence of new information technologies and associated capabilities.


Course description It allows those who provide, interpret, manage and

otherwise use information to make fundamental changes in what they do and how they do it. These changes have created a need for a broad understanding of IT and the ways in which it can be applied.

►Understanding today’s IT is the basis for learning tomorrow’s IT and those who have the benefit of a broad understanding of the field will be better users of it than those to whom it remains vague and a bit of a mystery.


Learning objectives

The course seeks to provide knowledge regarding such concepts as the nature of information and all that it may entail, storage media and the fundamental principles governing information technology.

Exposure to hardware and software tools(advanced spreadsheets) for information capture, analysis, conversion, display and management will provide students with the knowledge needed to bring the appropriate information related technologies to bear in their disciplines.


Grading

3 tests will be administered of which a student has to do at least 2. (Best 2 tests will be considered)

Course Work (1) will be administered. Exercises will be done In order to receive a passing grade for this course, a

student should attain greater than 35% (17.5) of the entire course work and must receive a passing grade (greater than 35% [17.5]) in the final exam.


Grading Cont’d The basis for the final grade awarded is; Class attendance, participation & engagement 5% Tests 30% Assignments15% Final Exam 50%

• A student should receive a cumulative grade of greater than 50% marks to receive the normal progress attribute; implying that a student has to attain a grade greater than 50 as a result of the summation of the grades from both course work and the final exam.

• Students are expected to attend at least 85% of the total lectures.


Scheduled Dates for Tests & Course Work Assignment 1 Week 2 Test 1 Week 4 Assignment 2 Presentation Week 5 Test 2 Week 6 Test 3 Week 8 Final Exam Week 13

Dates may change depending on students progress or due to any other unpredicted events.

Exercises will be appended to students assessment


Classes Scheduled for:

Lecturer’s Office Hours:

Wednesday 11:00am - 4:00pmThursday 11:00am - 4:00pm

Day Time Room Course

Friday

Wednesday

4:00-6:00pm

5:00-7:00pm

K10

TP3

BES 1

Tuesday

Thursday

8:30-10:30am

8:30-10:30am

TP2

OV2

BSIT 1


Referential Material for this Course1. David Cyganski, John A. Orr with Richard F. Vaz (2001).

Information Technology Inside and Outside. Upper Saddle River, New Jersey: Prentice Hall.

2. Peter Norton (1999). Introduction to computers. Third Edition: Glencoe/McGraw-Hill

3. Peter Norton. Computing Fundamentals. Fifth Edition: Glencoe/McGraw-Hill

4. Introduction to information technology by Turban.Rainer.Potter5. E.S Waburoko Computers. An introduction to Information

Technology. 6. Beekman, George. Computer Confluence: Exploring Tomorrow's

Technology, Concise Edition. Edition 5.5. Upper Saddle River, NJ: Prentice Hall, 2003.Type: Textbook. ISBN: 978-0536-199690

Faith and Teaching Everyone should appreciate that God is the

beginning of all wisdoms. Nothing comes to us without God’s knowledge.

“Study to shew thyself approved unto God….” (2Tim 2:15)

And that ye study to be quiet, and to do your own business, and to work with your own hands, as we commanded you; (1Thes 4:11)


Faith and Teaching

2Thes3:10-12 For even when we were with you, we would give you this command: If anyone is not willing to work, let him not eat. For we hear that some among you walk in idleness, not busy at work, but busy bodies. Now such persons we command and encourage in the Lord Jesus Christ to do their work quietly and to earn their own living.

Faith and Teaching God gives you as much as you ask. Therefore ask

for more insight in whatever you learn so that you can be blessed with much knowledge.

Misuse of knowledge is abuse of God’s power -which not ethical in the Christian perspective.

Christians should view information technology as a tool to do God’s work, not for ungodly gains.


Faith and Teaching

Ethics: While more than just a list of “do’s” and “don’ts,” the

Bible does give us detailed instructions on how to live as a Christian should. The Bible is all we need to know about how to live that Christian life. However, the Bible does not explicitly cover every single situation we will face in our lives. How then is it sufficient? That is where Christian Ethics comes in.


Faith and Teaching Science defines ethics as “a set of moral principles, the

study of morality.” Therefore, Christian Ethics would be the principles, derived from the Christian faith, by which we act. God’s Word cover every situation we face throughout our lives, its principles give us the standards by which we must carry ourselves in those situations where there are no explicit instructions.

For example, the Bible does not say anything explicitly about the spreading pornographic contents, yet based on the principles we learn through Scripture, we can know that it is wrong.


Faith and Teaching For one thing, the Bible tells us that the body is a temple of

the Holy Spirit and that we should honor God with it (1 Corinthians 6:19-20). Knowing what these materials do to our bodies—the harm they cause to minds—we know that by viewing them we would be destroying the temple of the Holy Spirit. That is certainly not honoring to God.

The Bible also tells us that we are to follow the authorities that God Himself has put into place (Romans 13:1). Given the illegal nature of pornography, by spreading them we are not submitting to the authorities, but rather, rebelling against them.


By using the principles we find in Scripture, Christians can determine their course for any given situation. In some cases it will be simple, like the rules for Christian living we find in Colossians, chapter 3. In other cases, however, we need to do a little digging. The absolute best way to do that is to pray over God’s Word.

We need to rely on God. We must pray over His Word and open ourselves to His Spirit. The Spirit will teach us and guide us through the Bible to find the principle we need to stand on so we may walk and live as a Christian should.



Remember:

Work hard; success is a ladder you can not climb with your hands in your pockets!

You are not running the race alone otherwise you may crash

Faith and learning •Everyone should appreciate that God is the beginning of all wisdoms. Nothing comes to us without God’s knowledge.•God gives you as much as you ask. Therefore ask for more insight in whatever you learn so that you can be blessed with much knowledge.•Misuse of knowledge is abuse of God’s power -which not ethical in the Christian perspective.•Christians should view database system as a tool to do God’s work, not for unGodly gains.


Remember And lastly; obstacles don’t have to stop you. If you run

into a wall, don’t turn around and give up. Figure out how to climb it, go through it or walk around it. You don’t drown by falling in water. You drown by staying there. So please be encouraged to press on no matter what, for you know your goal. You may get weary, tired and knocked out, but get back up again and determinedly move on for what is ahead of you is surely a fortune. Let your friends into your circle for they will or may provide the strength needed for you to carry on.

All the best.


Course outline

This course will be administered in four main modules: Module 1- Introduction Information Revolution( A review on Information

Technology 1 Representing information in Bits The need and basis for data protocols Large Capacity Storage

Course outline Module 2- Fundamentals of Spreadsheets(advanced

• Importing and Exporting Data, Import from other applications

• Create, using, editing Templates

• What is a workspace? Using , Saving a workspace

• Link workbooks

• Formatting Numbers, conditional formatting

• Auditing a Worksheet, Printing Workbooks

• Use the Report Manager

• Working with Named Ranges

• Using Macros



Course outline cont’d Module 3- Graphics and visual information From the real world to Images and Video Computer Graphics and Virtual Reality Module 4- Data compression Compressing Information Image Compression Digital Video

Lecture 1

Module I- Introduction• Information Revolution( A review on Information

Technology 1

• Representing information in Bits

• The need and basis for data protocols

• Large Capacity Storage



Module I: What is the Information in the Information Revolution?

Objectives: Definition and explanation of what information

is and the important distinction among the terms information, message and signal

Components that make up an information System and their arrangement

Distinctions between analog and digital information and the rationale behind the quick replacement of analog systems by digital systems


In this module we will discuss what information is and the systems that surround us that store, manipulate and transmit this information. We will discuss some of the different forms that information can take - forms that are of much interest to artists, musicians, historians architects, salespersons, managers and public officials as they are to the scientists and engineers usually associated with Information Technology.

Information- Knowledge communicated or received concerning some fact or circumstance; news

The world is full of facts, some discovered, some remaining to be discovered. When used in some way, these facts become information.


Information, Messages and Signals Signal-This is actual entity (electrical, optical, mechanical etc)

that is transmitted from sender to receiver e.g. Human vocal cords send out audible signals such as speech. Animals like birds send out mating signals which are specific sound patterns they create. Similarly human vocal cords send out audible signals such as speech

Message- The knowledge that is transmitted e.g. in the case of birds might be “Its mating season, I’m available”. Whereas the signal is a specific sequence of sound waves, the message is the meaning conveyed by that sequence.

Another example are the kingdom drums that were used to communicate

Information

A message received and understood knowledge acquired through study or experience or instruction formal accusation of a crime data: a collection of facts from which conclusions may be drawn; "statistical data" (communication theory) a numerical measure of the uncertainty of an outcome; "the signal contained thousands of bits of information"



Process of Information generation

Conversion Manipulation Data Storage Capture Transmission Information Utilisation


Evolution

Oral Paintings Symbols Writings Printing Non Electronic Computation Telegraphy Telephone Radio TV


Forms of Data

Audio Graphics Text Audio-Visual Multimedia


Information Systems Examples: The phonograph The telephone The camera and other digital recording devices

Some Systems like the telephone System are transitioning from analog electronics to computer like electronics that are digital. (The meaning of analog and digital will be described in the subsequent sections)


Components of any communications system Generic Communication System

Input Transducer: Device that converts a physical signal from the source to an electrical, electromagnetic or mechanical signal more suitable for communication

Transmitter: Device that sends that transduced signal

Input Transducer

TransmitterTransmitting

ChannelReceiver

Out put Transducer


Transmission Channel: Physical medium on which the signal is carried

Receiver: Device that recovers the transmitted signal from the channel

Output Transducer: Device that converts the received signal back into a useful physical quantity


This type of representation is known as a block diagram that provides a model for many different communication systems and is a very useful tool for representing complex systems. Each block represents a subsystem which performs some function: the specific function determines the relationship between the signal entering the block and the signal leaving the block. (Signals are represented by arrows)


Representation and Quantifying Information. The fidelity and Information Content of Signals

Fidelity- A measure of the difference between the original and reproduced forms of the information. E.g., does the received voice sound the same as it would if the person were standing in the room? Probably not. Is the person recognizable? Quite possibly. Answering these questions may be quite different from determining the information content of the message.

Starts with encoding ( Codes)

Characteristics of Codeso Uniquenesso Standardizationo Compatibility


Representation and Quantifying Information.

NB: Faulting in any of the above leads to

Fidelity

The coding system determines the

Scheme For example the message “You have passed”.

Most of the information content is contained in the distinction between “passed” and “not passed”. As long as you have received that correctly, you do not care whether the message was high fidelity or not.


Analog and Digital Information Analog - Comes from the word analogy referring to the

relation that one thing has to another. It is used to refer to the natural world where time is continuous and most parameters like light and sound intensity, temperature, position etc can vary smoothly and continuously over some range, taking on an infinite number of possible values.

On the other hand, there are some parameters that change only in discrete steps e.g. days of the month, games won or lost and the squares on a check board.


The term digital is used to refer to information representation for which both time and the value being measured move in discrete steps, that is when there are a finite number of possible values.

Most modern communications and storage systems are built around the digital computer. Most of the information we deal with is analog, however it is possible to convert back and forth between analog and digital.


The Move toward digital Information Technology Classical information transmission and storage systems

developed over a period of decades or even longer. In contrast, some new Information Systems have sprung up and achieved widespread usage almost overnight. E.g. the phonograph invented in 1877 by Thomas Edison remained unchanged in principle until the CD was introduced in 1983. The phonographs which had been the sound recording norm for 100yrs essentially disappeared. How did this happen? Such fundamental changes happen as a result of two conditions:


1. The new System either enables some totally new capacity or is much better than the one it replaces

2. The cost of the new system is reasonably low compared to people’s willingness to pay.

The CD meets both criteria. Quality of the reproduction (as well as convenience of

use) is better Costs are low (manufacturing costs are very cheap) Digital electronics integrate small mechanical

components making them cheap and that is why analog systems that are large mechanical devices are tending to digital.


All other types of Information Systems in use (telephone, camera) have converted to and are in the process of converting to digital versions. (Telephone-VOIP, Cameras-Digital Cameras)

Digital information systems almost without exception have proven to be more reliable and less expensive than the analog systems they have replaced. This combination of better performance and lower cost devices further facilitated by the seemingly unending development of faster smaller and cheaper digital electronics has revolutionized the way in which we communicate and manage information.


Module I questions: Read about the following communication systems and

identify the five components shown in the block diagram (Input transducer, transmitter, the transmission channel, the receiver and the output transducer)

A doorbell Telephone System Cable TV Broadcast Radio

For each of the above systems, identify the signal, message and information that may be carried in the message.


Module I questions:

List as many information systems as you can that are found in your vicinity and identify as best as you can whether these systems are analog, digital or both. Briefly explain the analog and or digital aspects

Lecture 2

Fundamentals of Binary Representation



Fundamentals of Binary Representation Objectives: The concept of a code for information Binary numbering system and the means by

which all information can be represented by codes containing only zeroes and ones

Representation of numeric and text data with binary digits

Properties of signals that vary with time Means by which errors in stored or transmitted

information may be detected and corrected


The only reason that we can use the internet as a conduit for text, pictures, telephone conversations today and some day our regular TV viewing is that we can convert all these forms of information into the same form: Binary bits.

By the end of this module, you should have an understanding of how and why we use binary digits (bbinary digitsits) to represent information regardless of its original form. You should also have a grasp on the idea of protocols and become familiar with the details of a few simple binary protocols.

You will also become familiar with some of the terms and quantities used to refer to binary information.


Information and its Representation Can be traced back from cave drawings and stone

tablets, through scrolls and Gutenberg's revolutionary printing press into our current age of electronic Information Technology.

Before storing, manipulating or transmitting information we must first capture it and convert it into some representation that will facilitate our tasks.

Useful information and interesting data however appears to us in many different forms.

• Numeric• Voice messages• Pieces of Music• Photographs• Video


To carry out the above mentioned tasks (storing, manipulating or transmitting ) we require a process of encoding the information. The result of encoding will be a pattern or code representing the original information. We also require a process of decoding to convert the information back into its original form.

The encoding and decoding processes should be unique, each code must represent one thing so that information can be represented unambiguously and recreated correctly.


Whatever form we convert our information into must be well suited to the development of inexpensive and reliable equipment for handling it.

The technique for representing information must have the following requirements:• Unique- Uniquely represent information to recreate it

in its original form.• Standardized so that it can be used for many different

applications• Compatible with inexpensive and reliable technology

for handling information


The search for and appropriate code - Why binary Code? In our search for an appropriate code for

representing information, we will start by restricting ourselves to codes with a finite number of elements called an alphabet.

Such codes have a limited number of different symbols that can be used to represent information. This as we will see, leads to reliable means for storage and transmission.

But how many different symbols should the code have? We can gain some insight by looking at some familiar codes.


A look at written alphabets

The alphabet used for the English language is commonly thought to contain about 96 elements (26 lower case characters, 26 upper case characters, 10 numbers and 32 special characters such as space, the dollar sign-$, the ampersand-& etc)

We use this code daily to represent information for storage in books, and other documents; and transmission in form of letters and e-mail.


A more complex code is that used by the Chinese that has a total of as many as 40,000 characters. One complex character can convey an entire concept to the skilled reader. Because there are many different symbols, each one conveys much information, therefore fewer characters are needed to communicate a set of ideas than if we were to use the letters of written English.


This form of Chinese is thought of as one of the most difficult languages. There are so many characters, some quite similar to others, the task of distinguishing one from another is very challenging. On the other hand it is a relatively simple task to distinguish the few symbols of the English language from each other, making them less likely to cause misinterpretation.


The Need for a Robust Scheme We must consider the question of which is more

important:• That each symbol of code conveys a lot of information or

that• We should be able to readily distinguish the symbols from

each other Remember an information code must be unique,

compatible and standardized. Reliable manipulation of information depends upon

tolerance to errors. Because we must encode, store, manipulate, transmit and decode information using real equipment operating in the physical world, we will be subject to the laws of nature. Our equipment will not operate perfectly and will be subject to unpredictable disturbances.


The code therefore must represent information in a way that is robust or tolerant to errors or error resistant and in an unambiguous fashion. For this to take root, it would appear that we want as few different symbols as possible.

Remember the fewer symbols the code has, the easier it is to distinguish these symbols from each other and the more robust the code will be.

A code with just one symbol however would convey no useful information; only one character would be available and there would be no unique way to encode and decode information using this code.


A code with just two symbols called binary code might at first seem to be almost as useless. Certainly it should be a simple task to distinguish between only 2 characters; but it would seem as if each symbol would not be able to convey much information.

What good is a code that can only convey one of two symbols at any time?? The answer to this question will more or less extended over the rest of what we shall cover.


Bits as Building Blocks of Information

Binary code uses the first two integers 0 and 1. Another way of representing these is by “T” & “F” short for “True” and “False” respectively.

Because these are bbinary digitsits, (that can only take on one of two values), they are known as bits.

What happens when we begin to string together collections of these bits into longer structures or words?


A two bit word can be arranged in four patterns. 00, 01,10,11 We could therefore (by prior agreement between the

transmitter and receiver) use a pattern of two bits to represent any one of the four directions.

00-North 01-South 10-East 11-West We could transmit the bit pattern “10” to represent the

direction “East” if we wanted to send someone into that direction.


Note that the recipient of this message would need to know how the message was encoded so that it could be decoded from “10” to “East”.

Adding a third bit increases the representational power to eight patterns

000 100 001 101 010 110 011 111


Every time we add a bit, we double the number of possible combinations and so we double the number of different things these multi-bit codes or code words could be used to represent. This can be seen from the fact that each existing codeword can be changed into two new code words by adding another bit. Either a 0 or a 1 to the end of it.

In how many patterns can 4 bits be assembled?• Answer:

• 2*2*2*2=16 In how many patterns can 8 bits be assembled?


In general, given n bits in a code word; there are 2n different code words which can represent one of 2n different messages.

Convert these decimal integers to binary:• 16• 56• 100

From binary convert these back to decimal

Convert the following binary numbers to decimal.• 1011• 1001001• 100


BCD Representation An alternative representation of integers is simply to

represent the individual numbers that comprise them. For example the number 218 can be represented as three numerals.

2 representing 200 1 representing 10 8 representing 8 218 can then be converted to binary form by converting

each of the numerals, one at a time into binary code.

This scheme is referred to as the binary coded decimalbinary coded decimal form (BCD).

BCD Representation

In computing and electronic systems, binary-coded decimal (BCD) (sometimes called natural binary-coded decimal, NBCD) is an encoding for decimal numbers in which each digit is represented by its own binary sequence. Its main virtue is that it allows easy conversion to decimal digits for printing or display, and allows faster decimal calculations.


BCD Representation Its drawbacks are a small increase in the

complexity of circuits needed to implement mathematical operations. Uncompressed BCD is also a relatively inefficient encoding—it occupies more space than a purely binary representation.

In BCD, a digit is usually represented by four bits which, in general, represent the values/digits/characters 0–9. Other bit combinations are sometimes used for a sign or other indications.



BCD codes commonly used to represent numerals:

Numeral BCD Representation 0 0000 1 0001 2 0010 3 0011 4 0100 5 0101 6 0110 7 0111 8 1000 9 1001

►We can represent any integer by a string of binary digits. E.g..

► We can represent 328 as:

0011 0010 1000

► Space is inserted for convenience

Lecture 3

Representing Text with Bits



Representing Text with Bits In the previous slides, we saw how binary codes can be used to

represent the numerals 0-9. A similar approach called ASCII (Pronounced “ask-key”“ask-key” ) is commonly employed to represent text.

ASCII is an acronym for American Standard Code for Information Interchange.

It is used to encode text and in particular is useful for representing information which is entered via a computer keyboard. Therefore ASCII must be able to represent:• Numerals• Letters in both upper and lower case• Special printing symbols like @, $, *, &, %, (, ) etc • And commands that are commonly used by computers to represent

carriage returns, line feeds and other text-formatting directives.


Representing Text with Bits The commands being talked about here are referred to a

control characters, that can be generated from a keyboard by invoking functions like “backspace”, or “enter” or they can be created by special-purpose keys, such as “control”, “escape”, or numbered “function” keys.

The need for a code to represent all of these components of text motivated the development of ASCII and other similar codes.

When this code was developed, a decision was made that 128 different characters would suffice for representation of text (27=128), meaning that each text character or command is represented by a 7-bit word.


E.g.; the following piece of text consists of 16 letters, three spaces and an exclamation mark.

You are good students!

1011001 1101111 1110101 0100000 1100001 1110010 1100101 0100000 1100111 1101111 1101111 1100100 0100000 1110011 1110100 1110101 1100100 1100101 1101110 1110100 1110011 0100001

How would this text be represented in ASCII code? (Refer to the list appended to this set of notes)

You & I,


Convenient Forms for Binary CodesFor binary words - strings of ones and zeroes - often used to represent numbers, text characters and other quantities; to be conveniently and efficiently stored and manipulated by computers, they a typically used in sizes of 8, 16, 32 and 64 bits long.

Bits, bytes and Beyond.Bits, bytes and Beyond.Because the above sizes are all multiples of 8, a binary word of 8 8 bitsbits, known as a byte is a convenient measure of a binary word size in a computer. The amount of memory space-the number of binary digits that a computer can store is measured in bytes, each of which in turn represents 8 bits of storage. Because the architecture of computers makes it more practical for memory and other forms of information storage to be in sizes that are powers of 2, it is common to encounter memory sizes such as “64KB” and “8MB”.


Octal and Hexadecimal Representation

Octal (Base eight system) Uses 8 numerals: 0-7 The first 20 numbers in this system are:

0,1,2,3,4,5,6,7,10,11,12,13,14,15,16,17,20,21,22,23

From 23, What are the next 10 numbers in this system?

Each number can only take on one of 8 values and because 8 is a power of two (23), we can use and octal numeral to represent a grouping of bits. Specifically we can use an octal numeral to represent 3 bits:


Octal Numeral Bit Pattern

• 0 000

• 1 001

• 2 010

• 3 011

• 4 100

• 5 101

• 6 110

• 7 111

Because there are 8 numerals and also 8 Patterns that can be formed by three bits, we can use this table to represent groups of three bits by a single octal numeral. Thus if the following 12-bit pattern is stored in a computers memory:

0101100111012 (base two)-binary

We can represent these bits in octal form as

26358 (base eight) - Octal


Octal and Hexadecimal Representation Hexadecimal (Base sixteen system ) “Hex”-Uses 16 numerals But how? There are only 10 Arabic numerals? The letters A through F are used to fill out a set of 16

different numerals i.e.:

0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F

The first 20 numbers are therefore: 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,10,11,12,13


Because each numeral can take one of 16 values and because 16 is also a power of 2 (24), we can use a hex numeral to represent a grouping of four bits.

The table in the next slide shows the possible 4-bit patterns, along with their decimal, octal and hexadecimal representations.


Decimal Octal Hex Numeral Bit PatternDecimal Octal Hex Numeral Bit Pattern

• 0 0 0 0000• 1 1 1 0001• 2 2 2 0010• 3 3 3 0011• 4 4 4 0100• 5 5 5 0101• 6 6 6 0110• 7 7 7 0111• 8 10 8 1000• 9 11 9 1001• 10 12 A 1010• 11 13 B 1011• 12 14 C 1100• 13 15 D 1101• 14 16 E 1110• 15 17 F 1111

There are 16 hex There are 16 hex numerals and numerals and also 16 patterns also 16 patterns that can be that can be formed from four formed from four bits.bits.


Introduction to Error Detection and Correction Information once in binary form can be stored, transmitted

and retrieved with a great degree of convenience and reliability. However in any physical situation it is inevitable that problems might occur. In particular when binary information is sent across some physical channel- wires, coaxial cable, optical fiber or the airwaves; there always exists the possibility that some bits will be received in error due to interference and other unpredictable events.

Binary representation of information makes it possible to perform coding of information to ensure reliable performance.

Error Detection Methods The only way to do error detection and correction

is to send extra data with each message Two common error detection methods:

• Parity checking

• Simple parity

• Longitudinal parity or Longitudinal Redundancy Check (LRC)

• Polynomial Checking

• Cyclic Redundancy Checksum (CRC)-Read more on this


Coding involves changing the original information (pattern of bits) into a new encoded pattern that is usually longer but in some way more desirable.

Decoding involves recreating the original pattern.

One important function of coding is to enable the detection (and often correction) of errors that can occur in data transmission across a noisy channel.

This ability to detect and correct errors is one of the primary advantages of using digital transmission instead of analog.

A fundamental aspect of error control coding is redundancy. We may not want our information to have redundant information as this will consequently result in longer messages and a waste of transmission or storage resources.


However extra bits that are added to the transmitted data that repeat some of the previous information can be of importance in a way that this repetition helps the receiver detect errors

If an error is detected, the receiver can either request that the data be retransmitted or can possibly even correct the data itself.Error detection is the ability to detect the presence of errors caused by noise or other impairments during transmission from the transmitter to the receiver


7 bits of data(number of 1s)

8 bits including parity

even odd

0000000 (0) 00000000 10000000

1010001 (3) 11010001 01010001

1101001 (4) 01101001 11101001

1111111 (7) 11111111 01111111


Even Parity Example

Transmitted Character

Transmitted Information

Transmitted Parity

Received Information

Received Parity

Do We Detect an

error?

H

e

l

p

1001000

1100101

1101100

1110000

0

0

0

1

1000000

1100101

1101100

1110000

0

0

0

1

Yes

No

No

No


Simple Parity The number of ones in each data block is counted and a

zero or one is appended to that block to make the total number of ones even (for even parityeven parity) or odd (for odd parity).

By adding this additional bit (called a parity bit), we are ensuring that every block or coded word leaving the transmitter is known to have an even number of ones if even parity coding is used, or an odd number if odd parity coding us used.

If the number of ones does not match the parity (when the system is using even parity and a codeword with an odd number of ones is received), then we know that an error has occurred.


Simple Parity Analyze the table in slide 78. Because of a noisy

channel one character was impaired and hence that one bit is misinterpreted by the receiver. This message will therefore be decoded as “@elp”. (@ representing a received bit instead of H -misinterpretation). In this case, if the information includes a parity bit, the receiver can detect that the message contains an error and request a transmission.

What limitations can you deduce from this scheme?


Simple Parity What if the transmitted information was 1001000 and that

received is 1111000? The parity received will be correct but the bit sequence is

wrong! If you carefully note, the scheme does not detect which

actual bit has an error

So can we do better than this? Certainly; in fact, just about every system that uses digital

information employs a coding technique for detecting and correcting errors that is more complex and performs much better than the simple parity example we have seen.


Simple Parity As a good example, the information contained on a CD is

carefully encoded to allow the CD player to detect and correct errors that can occur during playback due to smudged or scratched discs or misalignment of the playback mechanism.

These high performance methods for error coding are based on more sophisticated approaches involving mathematical theories developed in support of information theory. These techniques all rely on the fundamental idea of adding structured redundancy to information before it is stored of transmitted.


Simple Parity This redundancy greatly improves the reliability of digital

information systems by allowing the detection and correction of errors. The more error-resistant we want our systems to be, the more redundancy we should add, while keeping in mind that this redundancy reduces the rate at which we are transmitting or storing actual information.

The tradeoff between error detection and correction capability and the desire to store or transmit as few bits as possible is one of the key areas of current research in data communication and must be carefully considered by system designers in light of the requirements of the systems they are designing.

Simple Parity Occasionally known as vertical redundancy check Add an additional bit to a string of bits:

• Even parity

• The 0 or 1 added to the string produces an even number of 1s (including the parity bit)

• Odd parity

• The 0 or 1 added … an odd number of 1s (including the parity bit)

0 1 0 1 0 1 01 Even parity

0 Odd parity

Example

1 0 0 0 1 0 0 1D

1 0 0 0 0 0 1 1A

1 0 1 0 1 0 0 0T

1 0 0 0 0 0 1 1A

Letter 7-bit ASCII Parity bit

Even Parity or Odd Parity?

90

Parity Examples - Using Even Parity

Parity

1 0 0 1 1 1 0 0

0 0 1 1 1 0 0 1

1 1 1 0 1 1 1 0

Data

VRC

1 0 0 1 1 1 0 0

0 0 1 1 1 0 0 1

1 1 1 0 1 1 1 0

1 1 1 0 1 1 1 0

0 0 1 1 1 0 0 1

0 0 1 0 1 0 1 1

0 0 1 1 1 0 0 1

1 0 0 0 1 1 1 0 LRC

Data

Even Parity of 1’s LRC/VRC

Reliability/Efficiency What happens if the character 10010101 is sent and

the first two 0s accidentally become two 1s? Thus, the following character is received: 11110101. Will there be a parity error? Problem: Simple parity only detects odd numbers of

bits in error• Isolated single-bit errors occur 50-60% of the time

• Error bursts occur 10-20% of the time

Efficiency: 1:7 (parity:data) w/ mediocre error-detection

Longitudinal Parity

Sometimes called LRC or Horizontal Parity Add Block Check Character (BCC) after a

block of characters:• Perform simple parity checking on each row of bits

• Then create a row of parity bits, or a BCC: each parity bit in this last row is a parity check for all the bits in the column

0 1 0 1 0 1 0 1

1 0 0 1 1 1 0 0

1 1 0 0 1 0 0 1BCC


Example

1 0 0 0 1 0 0 1D

1 0 0 0 0 0 1 1A

1 0 1 0 1 0 0 0T

1 0 0 0 0 0 1 1A

Letter 7-bit ASCII Parity bit

1 1 0 1 1 1 1 1BCC


Reliability/Efficiency Longitudinal parity is better at catching errors

• But requires too many check bits added to a block of data But still…

Efficiency: (n+8) : 7n (check bits: data) w/ a little bit better than mediocre error-detection

We need a better error detection method

Polynomial Checking Adds a character to the end of the data based on a

mathematical algorithm:• Checksum

• E.g., Sum the data values and divide the sum by 255. The remainder is the checksum

DA

TA

6865

8465

282

255= 1 remainder 27

0 0 1 1 0 1 1 1Checksum

27

Cyclical Redundancy Check (CRC) CRC error detection method treats packet of data to be transmitted as

a large polynomial Transmitter

• Using polynomial arithmetic, divides polynomial by a given generating polynomial

Quotient is discarded

• Remainder is “attached” to the end of data Data (with the remainder) is transmitted to the receiver Receiver divides the (data – remainder) by the same generating

polynomial If a remainder of zero results no error during transmission If a remainder not equal to zero results error during transmission

Example: CRC

0 0 1 1 0 1 1 1

01234567

Message polynomialx5+x4+x2+x1+x0 x5+x4+x2+x+1

Generating polynomialATM CRC x8 + x2 + x + 1CRC-16 x16 + x15 + x2 + 1

Error Control Once an error is detected, the receiver can:

1. Do nothingSome newer systems such as frame relay perform this

type of error control

2. Return an error message to the transmitterStop-and-wait ARQ (Automatic Repeat reQuest)

Go-back-N ARQ

Selective-reject ARQ

3. Fix the error with no further help from the transmitter

Stop-and-wait ARQ A transmitter sends

a frame then stops and waits for an acknowledgment

If a positive acknowledgment (ACK) is received, the next frame is sent

If a negative acknowledgment (NAK) is received, the same frame is transmitted again

Sliding Window Protocol Go-back-N ARQ and Selective-reject are more efficient

protocols• They assume that multiple frames are in transmission at one

time (sliding window)

A sliding window protocol allows transmitter to send up to the window size frames before receiving any acknowledgments

When a receiver does acknowledge receipt, the returned pack contains the number of the frame expected next

Example of Sliding Window

RR: Receive Ready

Go back-N ARQ If a frame arrives in error, the

receiver can ask transmitter to go back to the Nth frame, after Nth frame is retransmitted, sender resends all subsequent frames

Selective-reject ARQ Most efficient error

control protocol If a frame is received in

error, the receiver asks transmitter to resend ONLY the frame that was in error

Subsequent frames following the Nth frame are not retransmitted

Correct the Error For a receiver to correct the error with no further help

from the transmitter requires a large amount of redundant information accompanying original data

This redundant information allows the receiver to determine the error and make corrections

This type of error control is often called

Forward Error Correction

BSIT 1: Information Technology II1 Information Technology II Lecture 0 Uganda Christian University Faculty of Science and Technology Information Technology.

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