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S.R.P** 7TH- TERM- IT & IS FOR CONSTRUCTION MGMT Page 1

MCM 713 : IT & IS FOR CONSTRUCTION MANAGEMENT.

Que : What is Programming language ?

A vocabulary and set of grammatical rules for instructing a computer to perform specific tasks. Theterm programming language usually refers to high-level languages, such as BASIC, C, C++,

COBOL, FORTRAN, Ada, and Pascal. Each language has a unique set of keywords (words that it

understands) and a special syntax for organizing program instructions.

High-level programming languages, while simple compared to human languages, are more

complex than the languages the computer actually understands, calledmachine languages. Each

different type of CPU has its own unique machine language.

Lying between machine languages and high-level languages are languages called assembly

languages. Assembly languages are similar to machine languages, but they are much easier toprogram in because they allow a programmer to substitute names for numbers. Machine

languages consist of numbers only.

A programming language is a notation for writing programs, which are specifications of a

computation or algorithm.[1]Some, but not all, authors restrict the term "programming language" to

those languages that can express allpossible algorithms.[1][2]Traits often considered important for

what constitutes a programming language include:

Function and target: A computer programming language is a language[3] used to write

computer programs, which involve a computer performing some kind of computation[4] or

algorithm and possibly control external devices such as printers,disk drives,robots,[5]and

so on. For example PostScript programs are frequently created by another program to

control a computer printer or display. More generally, a programming language may

describe computation on some, possibly abstract, machine. It is generally accepted that a

complete specification for a programming language includes a description, possibly

idealized, of a machine or processor for that language.[6] In most practical contexts, a

programming language involves a computer; consequently programming languages are

usually defined and studied this way.[7] Programming languages differ from natural

languages in that natural languages are only used for interaction between people, whileprogramming languages also allow humans to communicate instructions to machines.

There are thousands of computer programming languages. These are listed in various ways:

Educational programming language

Generational list of programming languages

History of programming languages

List of object-oriented programming terms

List of programming languages

List of programming languages by category by general usage and context

List of programming languages for artificial intelligence

Non-English-based programming languages

Timeline of programming languages
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Introduction to C Programming Language

C is a general-purpose computer programming language developed in 1972 by Dennis Ritchie at

the Bell Telephone Laboratories for use with the Unix operating system.

Although C was designed for implementing system software, it is also widely used for developing

portable application software.

C is one of the most popular programming languages.It is widely used on many different software

platforms, and there are few computer architectures for which a C compiler does not exist. C has

greatly influenced many other popular programming languages, most notably C++, which

originally began as an extension to C.

Que : What is the concept of Operating system ?

The most important program that runs on a computer. Every general-purpose computer must have

an operating system to run other programs. Operating systems perform basic tasks, such as

recognizing input from the keyboard, sending output to the display screen, keeping track of files

and directories on the disk, and controlling peripheral devices such as disk drives and printers.

For large systems, the operating system has even greater responsibilities and powers. It is like a

traffic cop -- it makes sure that different programs and users running at the same time do not

interfere with each other. The operating system is also responsible for security, ensuring that

unauthorized users do not access the system.

Operating systems can be classified as follows:

multi-user : Allows two or more users to run programs at the same time. Some

operating systems permit hundreds or even thousands of concurrent users.

multiprocessing: Supports running a program on more than one CPU.

multitasking: Allows more than one program to run concurrently.

multithreading: Allows different parts of a single program to run concurrently.

real time: Responds to input instantly. General-purpose operating systems, such as

DOS and UNIX, are not real-time.

Operating systems provide a software platform on top of which other programs, calledapplicationprograms, can run. The application programs must be written to run on top of a particular

operating system. Your choice of operating system, therefore, determines to a great extent the

applications you can run. For PCs, the most popular operating systems are DOS, OS/2, and

Windows, but others are available, such as Linux.

As a user, you normally interact with the operating system through a set of commands. For

example, the DOS operating system contains commands such as COPY and RENAME for

copying files and changing the names of files, respectively. The commands are accepted and

executed by a part of the operating system called the command processor or command lineinterpreter. Graphical user interfaces allow you to enter commands by pointing and clicking at

objects that appear on the screen.
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Operating System Functions

At the simplest level, an operating system does two things:

1. It manages the hardware and software resources of the system. In a desktop computer,

these resources include such things as the processor, memory, disk space and more (On a

cell phone, they include the keypad, the screen, the address book, the phone dialer, the

battery and the network connection).

2. It provides a stable, consistent way for applications to deal with the hardware without

having to know all the details of the hardware.

The operating system's tasks, in the most general sense, fall into six categories:

Processor management

Memory management

Device management

Storage management Application interface

User interface

While there are some who argue that an operating system should do more than these six tasks,

and some operating-system vendors do build many more utility programs and auxiliary functions

into their operating systems, these six tasks define the core of nearly all operating systems. Next,

let's look at the tools the operating system uses to perform each of these functions.

Que : What is a digital computer ?

A device that processes numerical information; more generally, any device that manipulates

symbolic information according to specified computational procedures. The term digital

computeror simply, computerembraces calculators, computer workstations, control computers

(controllers) for applications such as domestic appliances and industrial processes, data-

processing systems, microcomputers, microcontrollers, multiprocessors, parallel computers,

personal computers, network servers, and supercomputers.

A digital computer is an electronic computing machine that uses the binary digits (bits) 0 and 1 to

represent all forms of information internally in digital form. Every computer has a set of instructions

that define the basic functions it can perform. Sequences of these instructions constitute machine-

language programs that can be stored in the computer and used to tailor it to an essentially

unlimited number of specialized applications. Calculators are small computers specialized for

mathematical computations. General-purpose computers range from pocket-sized personal digital

assistants (notepad computers), to medium-sized desktop computers (personal computers and

workstations), to large, powerful computers that are shared by many users via a computer

network. The vast majority of digital computers now in use are inexpensive, special-purposemicrocontrollers that are embedded, often invisibly, in such devices as toys, consumer electronic

equipment, and automobiles. See alsoBit; Computer programming; Embedded systems.
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The main data-processing elements of a computer reside in a small number of electronic

integrated circuits (ICs) that form a microprocessor or central processing unit (CPU). Electronic

technology allows a basic instruction such as add two numbers to be executed many millions of

times per second. Other electronic devices are used for program and data storage (memory

circuits) and for communication with external devices and human users (input-output circuits).

Nonelectronic (magnetic, optical, and mechanical) devices also appear in computers. They are

used to construct input-output devices such as keyboards, monitors (video screens), secondary

memories, printers, sensors, and mechanical actuators.

Functions of digital computer

A general purpose computer has four main components: the arithmetic logic unit (ALU), the control

unit, the memory, and the input and output devices (collectively termed I/O). These parts are

interconnected by busses, often made of groups of wires.

All digital computers, no matter what size or shape, have certain similarities in the way they are

organized. A computer must be able to read or accept instructions and data, remember the

problem solved and the data to use, perform arithmetical calculations and logical manipulations on

the data, read out the results, and control the entire operation.

Inside each of these parts are thousands to trillions of small electrical circuits which can be turned

off or on by means of an electronic switch. Each circuit represents a bit (binary digit) of information

so that when the circuit is on it represents a "1", and when off it represents a "0" (in positive logic

representation). The circuits are arranged in logic gates so that one or more of the circuits may

control the state of one or more of the other circuits.

The control unit, ALU, registers, and basic I/O (and often other hardware closely linked with these)

are collectively known as a central processing unit (CPU). Early CPUs were composed of many

separate components but since the mid-1970s CPUs have typically been constructed on a single

integrated circuit called amicroprocessor.

1.Control unitDiagram showing how a particular MIPS architecture instruction would be decoded by the control

system.

The control unit (often called a control system or central controller) manages the computer's

various components; it reads and interprets (decodes) the program instructions, transforming them

into a series of control signals which activate other parts of the computer.[24]Control systems in

advanced computers may change the order of some instructions so as to improve performance.

A key component common to all CPUs is the program counter, a special memory cell (a register)

that keeps track of which location in memory the next instruction is to be read from.
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The control system's functions is as followsnote that this is a simplified

description, and some of these steps may be performed concurrently or in a different

order depending on the type of CPU:

1. Read the code for the next instruction from the cell indicated by the program

counter.

2. Decode the numerical code for the instruction into a set of commands orsignals for each of the other systems.

3. Increment the program counter so it points to the next instruction.

4. Read whatever data the instruction requires from cells in memory (or perhaps

from an input device). The location of this required data is typically stored

within the instruction code.

5. Provide the necessary data to an ALU or register.

6. If the instruction requires an ALU or specialized hardware to complete, instruct

the hardware to perform the requested operation.7. Write the result from the ALU back to a memory location or to a register or

perhaps an output device.

8. Jump back to step (1).

2.Arithmetic/logic unit (ALU)

The ALU is capable of performing two classes of operations: arithmetic and logic.

The set of arithmetic operations that a particular ALU supports may be limited to adding and

subtracting or might include multiplying or dividing, trigonometry functions (sine, cosine, etc.) and

square roots. Some can only operate on whole numbers (integers) whilst others use floating point

to represent real numbersalbeit with limited precision. However, any computer that is capable of

performing just the simplest operations can be programmed to break down the more complex

operations into simple steps that it can perform. Therefore, any computer can be programmed to

perform any arithmetic operationalthough it will take more time to do so if its ALU does not

directly support the operation. An ALU may also compare numbers and return boolean truth

values (true or false) depending on whether one is equal to, greater than or less than the other ("is

64 greater than 65?").

3. MemoryMagnetic core memory was the computer memory of choice throughout the 1960s, until it was

replaced by semiconductor memory.

A computer's memory can be viewed as a list of cells into which numbers can be placed or read.

Each cell has a numbered "address" and can store a single number. The computer can be

instructed to "put the number 123 into the cell numbered 1357" or to "add the number that is in cell1357 to the number that is in cell 2468 and put the answer into cell 1595". The information stored

in memory may represent practically anything. Letters, numbers, even computer instructions can

be placed into memory with equal ease. Since the CPU does not differentiate between different
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types of information, it is the software's responsibility to give significance to what the memory sees

as nothing but a series of numbers.

The CPU contains a special set of memory cells called registers that can be read and written to

much more rapidly than the main memory area. There are typically between two and one hundred

registers depending on the type of CPU. Registers are used for the most frequently needed data

items to avoid having to access main memory every time data is needed. As data is constantly

being worked on, reducing the need to access main memory (which is often slow compared to theALU and control units) greatly increases the computer's speed.

Computer main memory comes in two principal varieties: random-access memory or RAM and

read-only memory or ROM. RAM can be read and written to anytime the CPU commands it, but

ROM is pre-loaded with data and software that never changes, so the CPU can only read from it.

ROM is typically used to store the computer's initial start-up instructions. In general, the contents

of RAM are erased when the power to the computer is turned off, but ROM retains its data

indefinitely. In a PC, the ROM contains a specialized program called the BIOS that orchestrates

loading the computer's operating system from the hard disk drive into RAM whenever thecomputer is turned on or reset. In embedded computers, which frequently do not have disk drives,

all of the required software may be stored in ROM. Software stored in ROM is often called

firmware, because it is notionally more like hardware than software. Flash memory blurs the

distinction between ROM and RAM, as it retains its data when turned off but is also rewritable. It is

typically much slower than conventional ROM and RAM however, so its use is restricted to

applications where high speed is unnecessary.

4.Input/output (I/O)

Hard disk drives are common storage devices used with computers.

I/O is the means by which a computer exchanges information with the outside

world.[29] Devices that provide input or output to the computer are called

peripherals.[30]On a typical personal computer, peripherals include input devices like

the keyboard and mouse, and output devices such as the display and printer. Hard

disk drives, floppy disk drives and optical disc drives serve as both input and output

devices. Computer networking is another form of I/O.

Often, I/O devices are complex computers in their own right with their own CPU and

memory. A graphics processing unit might contain fifty or more tiny computers that

perform the calculations necessary to display graphics, Modern desktop computers

contain many smaller computers that assist the main CPU in performing I/O.

Its ridiculous to live 100 years and only be able to remember 30 million bytes. You know, less than a compact disc. The human condition

is really becoming more obsolete every minute.
http://en.wikipedia.org/wiki/Processor_registerhttp://en.wikipedia.org/wiki/Random-access_memoryhttp://en.wikipedia.org/wiki/Read-only_memoryhttp://en.wikipedia.org/wiki/BIOShttp://en.wikipedia.org/wiki/Operating_systemhttp://en.wikipedia.org/wiki/Embedded_systemhttp://en.wikipedia.org/wiki/Firmwarehttp://en.wikipedia.org/wiki/Flash_memoryhttp://en.wikipedia.org/wiki/Hard_disk_drivehttp://en.wikipedia.org/wiki/Computer#cite_note-28http://en.wikipedia.org/wiki/Computer#cite_note-28http://en.wikipedia.org/wiki/Computer#cite_note-28http://en.wikipedia.org/wiki/Peripheralhttp://en.wikipedia.org/wiki/Computer#cite_note-29http://en.wikipedia.org/wiki/Computer#cite_note-29http://en.wikipedia.org/wiki/Computer#cite_note-29http://en.wikipedia.org/wiki/Personal_computerhttp://en.wikipedia.org/wiki/Mouse_%28computing%29http://en.wikipedia.org/wiki/Computer_monitorhttp://en.wikipedia.org/wiki/Printer_%28computing%29http://en.wikipedia.org/wiki/Hard_disk_drivehttp://en.wikipedia.org/wiki/Hard_disk_drivehttp://en.wikipedia.org/wiki/Floppy_diskhttp://en.wikipedia.org/wiki/Optical_disc_drivehttp://en.wikipedia.org/wiki/Computer_networkinghttp://en.wikipedia.org/wiki/Graphics_processing_unithttp://en.wikipedia.org/wiki/Desktop_computerhttp://en.wikipedia.org/wiki/Desktop_computerhttp://en.wikipedia.org/wiki/Graphics_processing_unithttp://en.wikipedia.org/wiki/Computer_networkinghttp://en.wikipedia.org/wiki/Optical_disc_drivehttp://en.wikipedia.org/wiki/Floppy_diskhttp://en.wikipedia.org/wiki/Hard_disk_drivehttp://en.wikipedia.org/wiki/Hard_disk_drivehttp://en.wikipedia.org/wiki/Printer_%28computing%29http://en.wikipedia.org/wiki/Computer_monitorhttp://en.wikipedia.org/wiki/Mouse_%28computing%29http://en.wikipedia.org/wiki/Personal_computerhttp://en.wikipedia.org/wiki/Computer#cite_note-29http://en.wikipedia.org/wiki/Peripheralhttp://en.wikipedia.org/wiki/Computer#cite_note-28http://en.wikipedia.org/wiki/Hard_disk_drivehttp://en.wikipedia.org/wiki/Flash_memoryhttp://en.wikipedia.org/wiki/Firmwarehttp://en.wikipedia.org/wiki/Embedded_systemhttp://en.wikipedia.org/wiki/Operating_systemhttp://en.wikipedia.org/wiki/BIOShttp://en.wikipedia.org/wiki/Read-only_memoryhttp://en.wikipedia.org/wiki/Random-access_memoryhttp://en.wikipedia.org/wiki/Processor_register


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Que : Types of Information Systems

Information systems differ in their business needs. Also depending upon different levels in

organization information systems differ. Three major information systems are

1. Transaction processing systems

2. Management information systems

3. Decision support systems

The information needs are different at different organizational levels. Accordingly the information

can be categorized as: strategic information, managerial information and operational information.

Strategic information is the information needed by top most management for decision making. For

example the trends in revenues earned by the organization are required by the top management

for setting the policies of the organization. This information is not required by the lower levels in

the organization. The information systems that provide these kinds of information are known as

Decision Support Systems.

The second category of information required by the middle management is known as managerial

information. The information required at this level is used for making short term decisions and

plans for the organization. Information like sales analysis for the past quarter or yearly production

details etc. fall under this category. Management information system (MIS) caters to such

information needs of the organization. Due to its capabilities to fulfill the managerial information

needs of the organization, Management Information Systems have become a necessity for all big

organizations. And due to its vastness, most of the big organizations have separate MIS

departments to look into the related issues and proper functioning of the system.

The third category of information is relating to the daily or short term information needs of the

organization such as attendance records of the employees. This kind of information is required at

the operational level for carrying out the day-to-day operational activities. Due to its capabilities to

provide information for processing transaction of the organization, the information system is known

as Transaction Processing System or Data Processing System. Some examples of information

provided by such systems areprocessing of orders, posting of entries in bank, evaluating overdue

purchaser orders etc.

Transaction Processing Systems

TPS processes business transaction of the organization. Transaction can be any activity of the

organization. Transactions differ from organization to organization. For example, take a railway

reservation system. Booking, canceling, etc are all transactions. Any query made to it is a

transaction. However, there are some transactions, which are common to almost all organizations.

Like employee new employee, maintaining their leave status, maintaining employees accounts,

etc.

This provides high speed and accurate processing of record keeping of basic operational

processes. These include calculation, storage and retrieval.

Transaction processing systems provide speed and accuracy, and can be programmed to follow

routines functions of the organization.
http://www.freetutes.com/systemanalysis/types-of-information-system.html#transaction-processing-systemshttp://www.freetutes.com/systemanalysis/types-of-information-system.html#management-information-systemshttp://www.freetutes.com/systemanalysis/types-of-information-system.html#decision-support-systemshttp://www.freetutes.com/systemanalysis/types-of-information-system.html#decision-support-systemshttp://www.freetutes.com/systemanalysis/types-of-information-system.html#management-information-systemshttp://www.freetutes.com/systemanalysis/types-of-information-system.html#transaction-processing-systems


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Management Information Systems

These systems assist lower management in problem solving and making decisions. They use the

results of transaction processing and some other information also. It is a set of information

processing functions. It should handle queries as quickly as they arrive. An important element of

MIS is database.

A database is a non-redundant collection of interrelated data items that can be processed throughapplication programs and available to many users.

Decision Support Systems

These systems assist higher management to make long term decisions. These type of systems

handle unstructured or semi structured decisions. A decision is considered unstructured if there

are no clear procedures for making the decision and if not all the factors to be considered in the

decision can be readily identified in advance.

These are not of recurring nature. Some recur infrequently or occur only once. A decision support

system must very flexible. The user should be able to produce customized reports by giving

particular data and format specific to particular situations.

Summary of Information Systems

Catagories of Information System Characteristices

Transaction Processing System Substitutes computer-based processing for manual

procedures.

Deals with well-structured processes. Includes

record keeping applications.

Management information system Provides input to be used in the managerial decision

process. Deals with supporting well structured

decision situations. Typical information requirements

can be anticipated.

Decision support system Provides information to managers who must make

judgements about particular situations. Supports

decision-makers in situations that are not well

structured.

Most software today is very much like an Egyptian pyramid with millions of bricks piled on top ofeach other, with no structural

integrity, but just done by brute force and thousands of slaves.


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What is DBMS ?(DATABASE MANAGEMENT SYSTEM)

As one of the oldest components associated with computers, the database management

system, or DBMS, is a computer software program that is designed as the means of

managing all databases that are currently installed on a system hard drive or network.

Different types of database management systems exist, with some of them designed for

the oversight and proper control of databases that are configured for specific purposes.

Here are some examples of the various incarnations of DBMS technology that are

currently in use, and some of the basic elements that are part of DBMS software

applications.

As the tool that is employed in the broad practice of managing databases, the DBMS is

marketed in many forms. Some of the more popular examples of DBMS solutions include

Microsoft Access, FileMaker, DB2, and Oracle. All these products provide for the creation

of a series of rights or privileges that can be associated with a specific user. This meansthat it is possible to designate one or more database administrators who may control each

function, as well as provide other users with various levels of administration rights. This

flexibility makes the task of using DBMS methods to oversee a system something that can

be centrally controlled, or allocated to several different people.

There are four essential elements that are found with just about every example of DBMS

currently on the market. The first is the implementation of a modeling language that serves

to define the language of each database that is hosted via the DBMS. There are several

approaches currently in use, with hierarchical, network, relational, and object examples.Essentially, the modeling language ensures the ability of the databases to communicate

with the DBMS and thus operate on the system.

Second, data structures also are administered by the DBMS. Examples of data that are

organized by this function are individual profiles or records, files, fields and their definitions,

and objects such as visual media. Data structures are what allows DBMS to interact with

the data without causing and damage to the integrity of the data itself.

A third component of DBMS software is the data query language. This element is involved

in maintaining the security of the database, by monitoring the use of login data, the

assignment of access rights and privileges, and the definition of the criteria that must be

employed to add data to the system. The data query language works with the data

structures to make sure it is harder to input irrelevant data into any of the databases in use

on the system.

Last, a mechanism that allows for transactions is an essential basic for any DBMS. This

helps to allow multiple and concurrent access to the database by multiple users, prevents

the manipulation of one record by two users at the same time, and preventing the creation

of duplicate records.
http://www.wisegeek.com/what-is-a-computer.htmhttp://www.wisegeek.com/what-is-a-hard-drive.htmhttp://www.wisegeek.com/what-is-a-query.htmhttp://www.wisegeek.com/what-is-a-query.htmhttp://www.wisegeek.com/what-is-a-hard-drive.htmhttp://www.wisegeek.com/what-is-a-computer.htm


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Que: APPROACHES TO SYSTEM DEVELOPMENT

Learning Objectives

Explain the purpose and various phases of the systems development life cycle

(SDLC)

Explain the differences between predictive SDLC and adaptive SDLC

Explain the differences between a model, a tool, a technique, and a methodology

Describe the two overall approaches used to develop information systems: the

traditional method and the object-oriented method

The Systems Development Lifecycle

u Systems development life cycle (SDLC)

l Provides overall framework for managing systems development process

u Two main approaches to SDLC

I. Predictive approach assumes project can be planned out in advance

II. Adaptive approach more flexible, assumes project cannot be planned out in

advance

uAll projects use some variation of SDLC

Choosing the Predictive vs. Adaptive Approach to the SDLC

I.Traditional PredictiveApproach to the SDLC

u Project planning initiate, ensure feasibility, plan schedule, obtain approval for project

u Analysis understand business needs and processing requirements

u Design define solution system based on requirements and analysis decisions

u Implementation construct, test, train users, and install new system

u Support keep system running and improve


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Waterfall model Approach to the SDLC

Basic Principles:

1. Project is divided into sequential phases, with some overlap and splashback acceptable

between phases.

2. Emphasis is on planning, time schedules, target dates, budgets and implementation of an

entire system at one time.

3. Tight control is maintained over the life of the project through the use of extensive written

documentation, as well as through formal reviews and approval/signoff by the user and

information technology management occurring at the end of most phases before eginning

the next phase.

Strengths:

1. Ideal for supporting less experienced project teams and project managers, or project teams

whose composition fluctuates.

2. The orderly sequence of development steps and strict controls for ensuring the adequacy of

documentation and design reviews helps ensure the quality, reliability, and maintainability

of the developed software.

3. Progress of system development is measurable.

4. Conserves resources.

Weaknesses:

1. Inflexible, slow, costly and cumbersome due to significant structure and tight controls.

2. Project progresses forward, with only slight movement backward.

3. Little room for use of iteration, which can reduce manageability if used.

4. Depends upon early identification and specification of requirements, yet users may not be

able to clearly define what they need early in the project.

5. Requirements inconsistencies, missing system components, and unexpected

developmentneeds are often discovered during design and coding.

6. Problems are often not discovered until system testing.

7. System performance cannot be tested until the system is almost fully coded, and under-

capacity may be difficult to correct.

8. Situations where most appropriate:


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9. Project is for development of a mainframe-based or transaction-oriented batch system.

10. Project is large, expensive, and complicated.

11. Project has clear objectives and solution.

12. Pressure does not exist for immediate implementation.

13. Project requirements can be stated unambiguously and comprehensively.

14. Project requirements are stable or unchanging during the system development life cycle.

15. User community is fully knowledgeable in the business and application.

II . Newer Adaptive Approaches to the SDLC Based on spiral model

o Project cycles through development activities over and over until project is complete

o Prototype created by end of each cycle

o Focuses on mitigating risk

Iteration Work activities are repeated

o

Each iteration refines previous resulto Approach assumes no one gets it right the first time

o There are a series of mini projects for each iteration

The Spiral Life Cycle Model

This is a recent model that has been proposed by Boehm. As the name suggests, the activities in

this model can be organized like a spiral. The spiral has many cycles. The radial dimension

represents the cumulative cost incurred in accomplishing the steps dome so far and the angular

dimension represents the progress made in completing each cycle of the spiral. The structure of

the spiral model is shown in the figure given below. Each cycle in the spiral begins with the

identification of objectives for that cycle and the different alternatives are possible for achieving the

objectives and the imposed constraints.

The next step in the spiral life cycle model is to evaluate these different alternatives based on the

objectives and constraints. This will also involve identifying uncertainties and risks involved. The

next step is to develop strategies that resolve the uncertainties and risks. This step may involve


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activities such as benchmarking, simulation and prototyping. Next, the software is developed by

keeping in mind the risks. Finally the next stage is planned.

The next step is determined by remaining risks. For example, its performance or user-interface

risks are considered more important than the program development risks. The next step may be

evolutionary development that involves developing a more detailed prototype for resolving the

risks. On the other hand, if the program development risks dominate and previous prototypes have

resolved all the user-interface and performance risks; the next step will follow the basic waterfallapproach.

The risk driven nature of the spiral model allows it to accommodate any mixture of specification-

oriented, prototype-oriented, simulation-oriented or some other approach. An important feature of

the model is that each cycle of the spiral is completed by a review, which covers all the products

developed during that cycle, including plans for the next cycle. The spiral model works for

developed as well as enhancement projects.

Spiral Model Description

The development spiral consists of four quadrants as shown in the figure above

Quadrant 1: Determine objectives, alternatives, and constraints.

Quadrant 2: Evaluate alternatives, identify, resolve risks.

Quadrant 3: Develop, verify, next-level product.

Quadrant 4: Plan next phases.

Although the spiral, as depicted, is oriented toward software development, the concept is equally

applicable to systems, hardware, and training, for example. To better understand the scope of

each spiral development quadrant, lets briefly address each one.

Quadrant 1: Determine Objectives, Alternatives, and Constraints

Activities performed in this quadrant include:

1. Establish an understanding of the system or product objectivesnamely performance,

functionality, and ability to accommodate change.

2. Investigate implementation alternativesnamely design, reuse, procure, and procure/

modify

3. Investigate constraints imposed on the alternativesnamely technology, cost, schedule,

support, and risk. Once the system or products objectives, alternatives, and constraints are

understood, Quadrant 2 (Evaluate alternatives, identify, and resolve risks) is performed.


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Quadrant 2: Evaluate Alternatives, Identify, Resolve Risks

Engineering activities performed in this quadrant select an alternative approach that best satisfies

technical, technology, cost, schedule, support, and risk constraints. The focus here is on risk

mitigation. Each alternative is investigated and prototyped to reduce the risk associated with the

development decisions. Boehm describes these activities as follows:

. . . This may involve prototyping, simulation, benchmarking, reference checking,

administering user

questionnaires, analytic modeling, or combinations of these and other risk resolution

techniques.

The outcome of the evaluation determines the next course of action. If critical operational

and/or technical issues (COIs/CTIs) such as performance and interoperability (i.e., external

and internal) risks remain, more detailed prototyping may need to be added beforeprogressing to the next quadrant. Dr. Boehm notes that if the alternative chosen is

operationally useful and robust enough to serve as a low-risk base for future product

evolution, the subsequent risk-driven steps would be the evolving series of evolutionary

prototypes going toward the right (hand side of the graphic) . . . the option of writing

specifications would be addressed but not exercised. This brings us to Quadrant 3.

Quadrant 3: Develop, Verify, Next-Level Product

If a determination is made that the previous prototyping efforts have resolved theCOIs/CTIs, activities to develop, verify, next-level product are performed. As a result, the

basic waterfall approach may be employedmeaning concept of operations, design,

development, integration, and test of the next system or product iteration. If appropriate,

incremental development approaches may also be applicable.

Quadrant 4: Plan Next Phases

The spiral development model has one characteristic that is common to all modelsthe

need for advanced technical planning and multidisciplinary reviews at critical staging orcontrol points. Each cycle of the model culminates with a technical review that assesses

the status, progress, maturity, merits, risk, of development efforts to date; resolves critical

operational and/or technical issues (COIs/CTIs); and reviews plans and identifies

COIs/CTIs to be resolved for the next iteration of the spiral.


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Que :ACTIVITIES OF EACH SDLC PHASE (SYSTEMS DEVELOPMENT LIFE CYCLE)

1. Predictive or adaptive approach use SDLC

2. Activities of each phase are similar

3. Phases are not always sequential

4. Phases can overlap

1. Activities of Planning Phase of SDLC

a. Define business problem and scope

b. Produce detailed project schedule

c. Confirm project feasibility

i. Economic, organizational, technical, resource, and schedule

d. Staff the project (resource management)

e. Launch project official announcement

2. Activities of Analysis Phase of SDLCa. Gather information to learn problem domain

b. Define system requirements

c. Build prototypes for discovery of requirements

d. Prioritize requirements

e. Generate and evaluate alternatives

f. Review recommendations with management

3. Activities of Design Phase of SDLC

a. Design and integrate the networkb. Design the application architecture

c. Design the user interfaces

d. Design the system interfaces

e. Design and integrate the database

f. Prototype for design details

g. Design and integrate system controls

4. Activities of Implementation Phase of SDLC

a. Construct software components

b. Verify and test

c. Convert data

d. Train users and document the system

e. Install the system

5. Activities of Support Phase of SDLC

a. Maintain system

i. Small patches, repairs, and updates

b. Enhance system

i. Small upgrades or enhancements to expand system capabilitiesii. Larger enhancements may require separate development project

c. Support users

i. Help desk and/or support team


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What are Methodologies?

Comprehensive guidelines to follow for completing every SDLC activity

Collection of models, tools, and techniques

What Are Models?

Representation of an important aspect of real world, but not the same as real thing

Abstraction used to

separate out aspect

Diagrams and charts

Project planning and

budgeting aids

Some Models Used in System

Development

What Are Tools?

Software support that helps create models or other required project components

Range from simple drawing

programs to complex CASE

tools to project managementsoftware

What Are Techniques?

Collection of guidelines that help analysts complete a system development activity or task

Can be step-by-step

instructions or just

general advice


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Two Approaches to System Development ?

u Traditional approach

l Also called structured system development

l Structured analysis and design technique (SADT)

l Includes information engineering (IE)

u Object-oriented approachl Also called OOA, OOD, and OOP

l Views information system as collection of interacting objects that work together to

accomplish tasks

TRADITIONAL APPROACH

1.Structured System Development

I. Structure Programming

II. Top-down Programming

III. Structured Design

IV. Structured Analysis

I. Structured Programming

a. Improves computer program quality

b. Allows other programmers to easily read and modify code

c. Each program module has one beginning and one ending

d. Three programming constructs (sequence, decision, repetition)

II. Top-Down Programming

a. Divides complex programs into hierarchy of modules

b. The module at top controls execution by calling lower level modules

c. Modular programming

i. Similar to top-down programming

d. One program calls other programs to work together as single system

III. Structured Design

a. What the set of programs should be

b. What each program should accomplish

c. How the programs should be organized into a hierarchy


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Object-Oriented Approach

1. Completely different approach to information systems

2. Views information system as collection of interacting objects that work together to accomplish

tasks

o Objects things in computer system that can respond to messages

o Conceptually, no processes, programs, data entities, or files are defined just objects3. OO languages: Java, C++, C# .NET, VB .NET

Terminologies of O-O Approach

1. Object-oriented analysis (OOA)

2. Object-oriented design (OOD)

3. Object-oriented programming (OOP)

1. Object-oriented analysis (OOA)

a. Defines types of objects users deal with

b. Shows use cases are required to complete tasks

2. Object-oriented design (OOD)

a. Defines object types needed to communicate with people and devices in system

b. Shows how objects interact to complete tasks

c. Refines each type of object for implementation with specific language of environment

3. Object-oriented programming (OOP)

Writing statements in programming language to define what each type of object does


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MANAGEMENT INFORMATION SYSTEM ( MIS) CONCEPT

The concept of the MIS has evolved over a period of time comprising many different facets of the

organizational function. MIS is a necessity of all the organizations.

The initial concept of MIS was to process data from the organization and present it in the for of

reports at regular intervals. The system was largely capable of handling the data from collectionto processing. It was more impersonal, requiring each individual to pick and choose the

processed data and use it for his requirements. This concept was further modified when a

distinction was made between data and information. The information is a product of an analysis of

data. This concept is similar to a raw material and the finished product. What are needed are

information and not a mass of data. However, the data can be analyzed in a number of ways,

producing different shades and specifications of the information as a product. It was,

therefore, demanded that the system concept be an individual- oriented, as each individual

may have a different orientation. Towards the information. This concept was further

modified, that the system should present information in such a form and format that it creates

an impact on its user, provoking a decision or an investigation. It was later realized then even

though such an impact was a welcome modification, some sort of selective approach was

necessary in the analysis and reporting. Hence, the concept of exception reporting was imbibed in

MIS.

MIS DEFINITION

The Management Information System (MIS) is a concept of the last decade or two. It has

been understood and described in a number ways. It is also known as the Information

System, the Information and Decision System, the Computer- based information System.

The MIS has more than one definition, some of which are give below.

1. The MIS is defined as a system which provides information support for decision making in

the organization.

2. The MIS is defined as an integrated system of man and machine for providing the information

to support the operations, the management and the decision making function in the

organization.

3. The MIS is defined as a system based on the database of the organization evolved for thepurpose of providing information to the people in the organization.

4. The MIS is defined as a Computer based Information System.

ROLE OF THE MANAGEMENT INFORMATION SYSTEM

The role of the MIS in an organization can be compared to the role of heart in the body. The

information is the blood and MIS is the heart. In the body the heart plays he role of supplying

pure blood to all the elements of the body including the brain. The heart works faster and

supplies more blood when needed. It regulates and controls the incoming impure blood,

processes it and sends it to the destination in the quantity needed. It fulfills the needs of blood

supply to human body in normal course and also in crisis.


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The MIS plays exactly the same role in the organization. The system ensures that an appropriate

data is collected from the various sources, processed, and sent further to all the needy

destinations. The system is expected to fulfill the information needs of an individual, a group

of individuals, the management functionaries: the managers and the top management.

The MIS satisfies the diverse needs through a variety of systems such as Query Systems,

Analysis Systems, Modeling Systems and Decision Support Systems the MIS helps in

Strategic Planning, Management Control, Operational Control and Transaction Processing.

The MIS helps the clerical personnel in the transaction processing and answers their queries

on the data pertaining to the transaction, the status of a particular record and references on a

variety of documents. The MIS helps the junior management personnel by providing the

operational data for planning, scheduling and control, and helps them further in decision making

at the operations level to correct an out of control situation. The MIS helps the middle

management in short them planning, target setting and controlling the business functions. It is

supported by the use of the management tools of planning and control. The MIS helps the top

management in goal setting,strategic planning and evolving the business plans and their implementation.

Implementation of MIS

The choice of the system or the sub-system depends on its position in the total MIS plan, the size

of the system, the user understands of the system and the complexity and its interface with other

systems.

The designer first develops systems independently and starts integrating them with other systems,

enlarging the system scope and meeting the varying information needs.

Determining the position of the system in the MIS is easy. The real problem in the degree of

structure, and formalization in the system and procedures which determine the timing and duration

of development of the system. Higher the degree of structured ness and formalization, greater is

the stabilization of the rules, the procedures, decision making and the understanding of the overall

business activity. Here, it is observed that the users and the designer interaction are smooth, and

each others need are clearly understood and respected mutually. The development becomes a

methodical approach with certainty in input-process and outputs.

MIS is generally used by medium and larger scale organizations. However, small organizations

are yet to understand its application. There is dire need to build up computer culture by properly

disseminating information about computer applications and its benefits.

Implementation of MIS can be achieved by using any of the methods such as direct, parallel,

modular or phase in.


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Direct Approach

Direct installation of the new system with immediate discontinuance of the old existing system is

reffered as cold turnkey approach. This approach becomes useful when these factors are

considered.

1. The new system does no replace the existing system.

2. Old system is regarded absolutely of no value

3. New system is compact and simple.

4. The design of the new system is inexpensive with more advantages and less risk involved.

Parallel Approach

The selected new system is installed and operated with current system. This method is expensive

because of duplicating facilities and personal to maintain both the systems. In this approach a

target date must be fixed when the operations of old system cease and new one will operate on its

own.

Modular Approach

This is generally recognized as Pilot approach, means the implementation of a system in the

Organization on a piece-meal basis.

This has few advantages / merits

1. The risk of systems failure is localized

2. The major problem can be easily identified and corrected before further implementation.

3. Operating personal can be trained before system is installed in a location.

Phase-in-Implementation

This approach is similar to modular method but it differs because of segmentation of system,

however, not the organization. It has advantages that the rate of changes in a given Organization

can be totally minimized and the data processing resource can be acquired gradually over a

period of time. System exhibits certain disadvantages such as limited applicability, more costs

incurred to develop interface with old system and a feeling in the Organization that system is never

completed.


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Implementation Procedures

Planning the Implementation

After designing the MIS it is essential that the organization should plan carefully for

implementation. The planning stage should invariably include the following:

1. Identification of tasks of Implementation

Planning the implementation activities, acquisition of facilities, procedures development,

generating files and forms, testing the system and evaluating and maintenance of the system.

2. Relationship establishment among the activity

Network diagram must be prepared to correlate concurrent and sequential activities.

3. Establishing of MIS

For monitoring the progress of implementation and for proper control of activities, efficient

information system should be developed.

4. Acquisition of Facilities

For installation of new system or to replace current system the manager should prepare a

proposal for approval from the management by considering space requirement movement ofpersonal and location for utility outlets and controls.

5. Procedure Development

This is an important stop for implementation of the system including various activities such as

evaluation selection of hardware, purchase or development of software, testing and

implementation strategies.

6. Generating Files and Forms

The MIS manager should generate files and formats for storing actual date. This requires checklist

data, format date storage forms and other remarks in data base.

7. Testing of the System

Test should be performed in accordance with the specifications at the implementation stage

consisting of component test sub system test and total system test.


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Evaluation and maintenance of MIS system

The performance should e evaluated in order to find out cost effectiveness and efficacy of the

system with minimum errors due to designs environmental changes or services.

Software Maintenances

The proper maintenance is the enigma of the system development and it holds software industry

captive lying up programming resources. There are some problems in maintenance such as

regarding it as non rewarding non availability of technicians and tools no cognizance of users

about maintenance problem and cost lack of standard procedures and guidelines. Most

programmers feel maintenance as low level drudgery. If proper attentions is paid over a period of

time eventually less maintenance is required.

Types of Maintenance

The maintenance of system are classified into corrective/adaptive/perfective. Corrective

maintenance means repairing process or performance failures. Adaptive maintenance means

changing the programming function whereas perfective maintenance deals with enhancing theperformance or modifying the program.

Primary Activities of a Maintenance Procedure

Documentation is major part of maintenance in system development. Maintenance staff receives

requests from the authorized user. Programming library should be maintained.

Reduction in Maintenance Costs

Several organizations having MIS generally go in for reducing maintenance costs and it consists of

three major phases.

1. Maintenance management audit through questionnaires and interviews.

2. Software system audit.

3. Software modification.

Evaluation Methods

Evaluation of the MIS in an organization is integral part of the control processes. There are severalevaluation approaches such as quality assurance review compliance of audits budget

performance review computer personal productivity assessment computer performance evaluation

service level monitoring user audit survey post installation review and cost benefit analysis.

Evaluation performance measurement can be classified into two classes as effectiveness and

efficiency. The relationship between effectiveness and efficiency is that the format is a measure of

goodness of out put and the latter is a measure of the resources required to achieve the output.


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ISO-OSI 7-Layer Network Architecture

This lecture introduces the ISO-OSI layered architecture of Networks. According to the ISO

standards, networks have been divided into 7 layers depending on the complexity of the

fucntionality each of these layers provide. The detailed description of each of these layers is given

in the notes below. We will first list the layers as defined by the standard in the increasing order of

function complexity:

1. Physical Layer

2. Data Link Layer

3. Network Layer

4. Transport Layer

5. Session Layer

6. Presentation Layer

7. Application Layer

Physical LayerThis layer is the lowest layer in the OSI model. It helps in the transmission of data between two machines

that are communicating through a physical medium, which can be optical fibres,copper wire or wireless etc.

The following are the main functions of the physical layer:

1. Hardware Specification: The details of the physical cables, network interface cards, wireless

radios, etc are a part of this layer.

Coaxial Cable Hybrid Cable Wireless Card Network Card

2. Encoding and Signalling: How are the bits encoded in the medium is also decided by this layer.For example, on the coppar wire medium, we can use differnet voltage levels for a certain time

interval to represent '0' and '1'. We may

use +5mV for 1nsec to represent '1' and -

5mV for 1nsec to represent '0'. All the

issues of modulation is dealt with in this

layer. eg, we may use Binary phase shift

keying for the representation of '1' and '0'

rather than using different volatage levels

if we have to transfer in RF waves.

Binary Phase Shift Keying
http://www.cse.iitk.ac.in/users/dheeraj/cs425/lec01.html#physicalhttp://www.cse.iitk.ac.in/users/dheeraj/cs425/lec01.html#physicalhttp://www.cse.iitk.ac.in/users/dheeraj/cs425/lec01.html#datalinkhttp://www.cse.iitk.ac.in/users/dheeraj/cs425/lec01.html#datalinkhttp://www.cse.iitk.ac.in/users/dheeraj/cs425/lec01.html#networkhttp://www.cse.iitk.ac.in/users/dheeraj/cs425/lec01.html#networkhttp://www.cse.iitk.ac.in/users/dheeraj/cs425/lec01.html#transporthttp://www.cse.iitk.ac.in/users/dheeraj/cs425/lec01.html#transporthttp://www.cse.iitk.ac.in/users/dheeraj/cs425/lec02.html#sessionhttp://www.cse.iitk.ac.in/users/dheeraj/cs425/lec02.html#sessionhttp://www.cse.iitk.ac.in/users/dheeraj/cs425/lec02.html#presentationhttp://www.cse.iitk.ac.in/users/dheeraj/cs425/lec02.html#presentationhttp://www.cse.iitk.ac.in/users/dheeraj/cs425/lec02.html#applicationhttp://www.cse.iitk.ac.in/users/dheeraj/cs425/lec02.html#applicationhttp://www.cse.iitk.ac.in/users/dheeraj/cs425/lec02.html#applicationhttp://www.cse.iitk.ac.in/users/dheeraj/cs425/lec02.html#presentationhttp://www.cse.iitk.ac.in/users/dheeraj/cs425/lec02.html#sessionhttp://www.cse.iitk.ac.in/users/dheeraj/cs425/lec01.html#transporthttp://www.cse.iitk.ac.in/users/dheeraj/cs425/lec01.html#networkhttp://www.cse.iitk.ac.in/users/dheeraj/cs425/lec01.html#datalinkhttp://www.cse.iitk.ac.in/users/dheeraj/cs425/lec01.html#physical


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3. Data Transmission and Reception: The transfer of each bit of data is the responsibility of this

layer. This layer assures the transmissoin of each bit with a high probability. The

transmission of the bits is not completely reliable as their is no error correction in this layer.

4. Topology and Network Design: The network design is the integral part of the physical

layer. Which part of the network is the router going to be placed, where the switches will be

used, where we will put the hubs, how many machines is each switch going to handle, what

server is going to be placed where, and many

such concerns are to be taken care of by the

physical layer. The variosu kinds of

netopologies that we decide to use may be

ring, bus, star or a hybrid of these topologies

depending on our requirements.

Data Link Layer

This layer provides reliable transmission of a packet by using the services of the physical layer

which transmits bits over the medium in an unreliable fashion. This layer is concerned with :

1. Framing: Breaking input data into frames (typically a few hundred bytes) and caring about

the frame boundaries and the size of each frame.

2. Acknowledgment : Sent by the receiving end to inform the source that the frame was

received without any error.

3. Sequence Numbering : To acknowledge which frame was received.

4. Error Detection : The frames may be damaged, lost or duplicated leading to errors.The

error control is on link to link basis.

5. Retransmission : The packet is retransmitted if the source fails to receive

acknowledgment.

6. Flow Control : Necessary for a fast

transmitter to keep pace with a slow

receiver.

Data Link Layer


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Network LayerIts basic functions are routing and congestion control.

Routing: This deals with determining how packets will be routed (transferred) from source to destination. It

can be of three types :

Static : Routes are based on static tables that are "wired into" the network and are rarely changed. Dynamic : All packets of one application can follow different routes depending upon the topology of

the network, the shortest path and the current

network load.

Semi-Dynamic : A route is chosen at the start of

each conversation and then all the packets of the

application follow the same route.

Routing

The services provided by the network can be of two

types :

Connection less service: Each packet of an application is treated as an independent

entity. On each packet of the application the destination address is provided and the packet

is routed.

Connection oriented service: Here, first a connection is established and then all packets

of the application follow the same route. To understand the above concept, we can also

draw an analogy from the real life. Connection oriented service is modeled after the

telephone system. All voice packets go on the same path after the connection isestablished till the connection is hung up. It acts like a tube ; the sender pushes the objects

in at one end and the receiver takes them out in the same order at the other end.

Connection less service is modeled after the postal system. Each letter carries the

destination address and is routed independent of all the others. Here, it is possible that the

letter sent first is delayed so that the second letter reaches the destination before the first

letter.

Congestion Control: A router can be connected to 4-5 networks. If all the networks send packet

at the same time with maximum rate possible then the router may not be able to handle all the

packets and may drop some/all packets. In this context the dropping of the packets should be

minimized and the source whose packet was dropped should be informed. The control of such

congestion is also a function of the network layer. Other issues related with this layer are

transmitting time, delays, jittering.

Internetworking: Internetworks are multiple networks that are connected in such a way that they

act as one large network, connecting multiple office or department networks. Internetworks are

connected by networking hardware such as routers, switches, and bridges.Internetworking is a

solution born of three networking problems: isolated LANs, duplication of resources, and the lack

of a centralized network management system. With connected LANs, companies no longer haveto duplicate programs or resources on each network. This in turn gives way to managing the

network from one central location instead of trying to manage each separate LAN. We should be


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able to transmit any packet from one network to any other network even if they follow different

protocols or use different addressing modes.

Network Layer does not guarantee that the packet will reach its intended destination. There are

no reliability guarantees.

Transport Layer

Its functions are :

Multiplexing / Demultiplexing : Normally the transport layer will create distinct network

connection for each transport connection required by the session layer. The transport layer

may either create multiple network connections (to improve throughput) or it may multiplex

several transport connections onto the same network connection (because creating and

maintaining networks may be expensive). In the latter case, demultiplexing will be required

at the receiving end. A point to note here is that communication is always carried out

between two processes and not between two machines. This is also known as process-to-

process communication.

Fragmentation and Re-assembly : The data accepted by the transport layer from the

session layer is split up into smaller units (fragmentation) if needed and then passed to the

network layer. Correspondingly, the data provided by the network layer to the transport

layer on the receiving side is re-assembled.

Types of service : The transport layer also decides the type of service that should be

provided to the session layer. The service may be perfectly reliable, or may be reliable

within certain tolerances or may not be reliable at all. The message may or may not be

received in the order in which it was sent. The decision regarding the type of service to be

provided is taken at the time when the connection is established.

Error Control : If reliable service is provided then error detection and error recovery

operations are also performed. It provides error control mechanism on end to end basis.

Flow Control : A fast host cannot keep pace with a slow one. Hence, this is a mechanism

to regulate the flow of information.

Connection Establishment / Release : The transport layer also establishes and releases

the connection across the network. This requires some sort of naming mechanism so that a

process on one machine can indicate with whom it wants to communicate.


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Session Layer

It deals with the concept of Sessions i.e. when a user logins to a remote server he should be

authenticated before getting access to the files and application programs. Another job of session

layer is to establish and maintain sessions. If during the transfer of data between two machines

the session breaks down, it is the session layer which re-establishes the connection. It also

ensures that the data transfer starts from where it breaks keeping it transparent to the end user.

e.g. In case of a session with a database server, this layer introduces check points at various

places so that in case the connectoin is broken and reestablished, the transition running on the

database is not lost even if the user has not committed. This activity is called Synchronization.

Another function of this layer is Dialogue Control which determines whose turn is it to speak in a

session. It is useful in video conferencing.

Presentation Layer

This layer is concerned with the syntax and semantics of the information transmitted. In order to

make it possible for computers with different data representations to communicate data structures

to be exchanged can be defined in abstract way alongwith standard encoding. It also manages

these abstract data structres and allows higher level of data structres to be defined an exchange.

It encodes the data in standard agreed way(network format). Suppose there are two machines A

and B one follows 'Big Endian' and other 'Little Endian' for data representation. This layer ensures

that the data transmitted by one gets converted in the form compatibale to othe machine. This

layer is concerned with the syntax and semantics of the information transmitted.In order to make it

possible for computers with different data representations to communicate data structures to be

exchanged canbe defined in abstract way alongwith standard encoding. It also manages these

abstract data structres and allows higher level of data structres to be defined an exchange. Other

functions include compression, encryption etc.

Application Layer

The seventh layer contains the application protocols with which the user gains access to the

network. The choice of which specific protocols and their associated functions are to be used at

the application level is up to the individual user. Thus the boundary between the presentation layer

and the application layer represents a separation of the protocols imposed by the network

designers from those being selected and implemented by the network users.For example

commonly used protocols are HTTP(for web browsing), FTP(for file transfer) etc.


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What is Network Layer?

The network layer is concerned with getting packets from the source all the way to the destination.

The packets may require to make many hops at the intermediate routers while reaching the

destination. This is the lowest layer that deals with end to end transmission. In order to achieve its

goals, the network layer must know about the topology of the communication network. It must also

take care to choose routes to avoid overloading of some of the communication lines while leavingothers idle. The network layer-transport layer interface frequently is the interface between the

carrier and the customer, that is the boundary of the subnet. The functions of this layer include :

1. Routing - The process of transferring packets received from the Data Link Layer of the

source network to the Data Link Layer of the correct destination network is called routing.

Involves decision making at each intermediate node on where to send the packet next so

that it eventually reaches its destination. The node which makes this choice is called a

router. For routing we require some mode of addressing which is recognized by the

Network Layer. This addressing is different from the MAC layer addressing.

2. Inter-networking - The network layer is the same across all physical networks (such as

Token-Ring and Ethernet). Thus, if two physically different networks have to communicate,

the packets that arrive at the Data Link Layer of the node which connects these two

physically different networks, would be stripped of their headers and passed to the Network

Layer. The network layer would then pass this data to the Data Link Layer of the other

physical network..

3. Congestion Control - If the incoming rate of the packets arriving at any router is more than

the outgoing rate, then congestion is said to occur. Congestion may be caused by many

factors. If suddenly, packets begin arriving on many input lines

7th term- it & is for construction management

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