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Md. Sayduzzaman Tuhin, Articled Student, S.F. Ahmed & Co. Mob:-01552-639307

Database Structure Database Structure:

The relation between many individual data elements stored in databases are based on one of several logical data structures or modes. DBMS are designed to use specific data structure to provide end users quick and easy access to stored info.

Classification of DB structures and file methods of Database: Five Fundamental Structure

Hierarchical structure Network structure Relational Structure Object oriented Structure Multidimensional Structure

Hierarchical structure:

This is the simplest type of database. The tree structure illustrates this concept.

Hierarchical Organization of a Family Structure

Hierarchical structure:

Information is accessed from the top to the bottom (top-down). Illustrates a parent-child relationship where each item relates only to the one above

and below it. Disadvantage – following the hierarchy is sometimes difficult, cumbersome, and time

consuming. Network Structure:

Very similar to hierarchical databases except that an element can have one or more superiors.

Network Structure permits the connection of the nodes multidirectionally.

Each node may have several owners (or elements) and may own any number of other data elements on the network

The database management software permits the extraction of needed information from such a structure to begin with any record in the file.

Father Mother

Parent

Family

Male Child Child

Children



Network Structure

Relational Structure:

They consist of one or more tables in which data are stored in the form of rows and columns.

Relational databases have many advantages over network and hierarchical databases.

The main advantage is that relationships between the data can be established whenever you (the user) request information.

Any relational database package normally uses an index of some sort for faster access to the data. Relational structures are a very popular database structuring approach for both mainframe and microcomputer database packages.

Relational Structure: Relational Operators

Join One to Many Many to Many

Multi- Dimensional Structure

Varity of Relational Model Multidimensional structure to organize and express relationships between data. Each dimension can represent data represent can represent different product

category like product type, region, sales channel and time. Object- Oriented Structure

Modern concept to handle new generation of multimedia and web application Entity Attribute Object Encapsulation Polymorphism Inheritance



Data & Information Data: Distinct pieces of information usually formatted in a special way. All software is divided into two general categories: data and programs. Programs are collections of instructions for manipulating data. Data can exist in a variety of forms -- as numbers or text on pieces of paper, as bits and bytes stored in electronic memory, or as facts stored in a person's mind. Information: Meaningful and usable arrangement of data is called Information. In general, raw data that (1) has been verified to be accurate and timely, (2) is specific and organized for a purpose, (3) is presented within a context that gives it meaning and relevance, and which (4) leads to increase in understanding and decrease in uncertainty. The value of information lies solely in its ability to affect a behavior, decision, or outcome. A piece of information is considered valueless if, after receiving it, things remain unchanged Characteristics of Information: � Timeliness: Should be soon enough to be meaningful � Sufficiency: Completeness, adequate enough for the purpose intended � Understandability: Practicality, Simplicity � Freedom from Bias � Reliability: Correct, Verifiability � Decision-Relevance: Relevance to subject matter, Significance � Comparability: Consistency of format, Consistency of fields. Information Systems: A set of interrelated components that collect, process, store and distribute information to support decision making and control in and organization.

IS more than computers: Activities in IS Three activities in an IS produce the information that organizes need to make decisions. Control operation, analyze problem, and create products and services. Information Systems Feedback Organization: Key elements of an organization are its people, structure, business processes, politics,

and culture

Input Process Output



Coordinates work through a structured hierarchy and through its business processes. The hierarchy arranges people in a pyramid structure of rising authority and responsibility Major Business Function:

Function Purpose Sales and marketing Selling the organization’s product and services Manufacturing and production Producing product or services Finance and accounting Managing the organization’s financial assets and

maintaining the organization’s financial records Human resources Attracting developing and maintaining the

organization’ labour forces; maintaining employee records

MANAGEMENT : Face challenges to run the organization Define strategy to face challenges Assign/ Allocate resources (Human, Finance) Do more than already exist in organization Create new product or service as using new knowledge and technology

TECHNOLOGY : Technology used to develop new product and services ► Use of Communication Internet Storage Data Processing E commerce Information need in various level of Organization:

Senior Management required information on Long term strategic decision about product and service Financial Performance

Mid level Management required information on Carries out Plan and Program of Senior management Face challenges and develop improvement ideas

Operational Management required information on Monitoring execution of activities as per plan Daily operational works

Information in Various Organizations: � Requirement of information varies from Organization to Organization � Sales and Marketing Systems � Market size for specific product � Customers behavior � Purchasing Habit/ Purchasing capacity � Cultural effect



Communication systems Wireless: Wireless communication is the transfer of information over a distance without the use of

electrical conductors or wires Terrestrial Microwave: � Transmission systems consisting of at least two radio transmitter/receivers (transceivers) connected to high gain antennas (directional antennas which concentrate electromagnetic or radio wave energy in narrow beams) focused in pairs on each other. � The operation is point point-to to-point point-communications are established between two and only two antennas with line line-of of-sight visibility. � This can be contrasted to point point-to to-multipoint systems like broadcast radio or television.

How Terrestrial Microwave Transfer and Receive Data: � Terrestrial microwave communication employs Earth Earth-based transmitters and receivers to transfer and receive data. � The frequencies used are in the low low-gigahertz range, which limits all communications to line line-of of-sight. � Example of terrestrial microwave equipment -telephone relay towers, which are placed every few miles to relay telephone signals cross country.

The Use of Microwave Link: A microwave link frequently is used to transmit signals in instances in which it would be

impractical to run cables. If you need to connect two networks separated by a public road, for example, you might find that regulations restrict you from running cables above or

below the road. In such a case, a microwave link is an ideal solution.

Satellite Communication: � Satellite is a microwave repeater in the space. � There are about 750 satellite in the space, most of them are used for communication. � They are: ►Wide area coverage of the earth earth’s surface. ►Transmission delay is about 0.3 sec. ► Transmission cost is independent of distance.

MAC(Media Access Control) protocols for satellite links � ALOHA: � Every station can transmit any time � Very low efficiency 18- 36 %. � FDMA (Frequency Division Multiple Access) � It is the oldest and most common. � the available satellite channel bandwidth is broken into frequency bands for different earth stations. Very Small Aperture Terminal (VSAT) Network: At the Very Small Aperture Terminal a lower performance microwave transceiver and

lower gain dish antenna (smaller size) is used. VSAT networks are arranged in a star based topology. Ideal for centralized networks with a central host (Banking institutions with branches all

over the country). Use the S ALOHA and TDMAS



Application: Telephony ►The first and historically most important application for communication satellites was

in intercontinental long distance telephony Satellite television Satellite radio Satellite Internet Military uses GPS

Cellular network : A cellular network is a radio network made up of a number of cells, each served by at

least one fixed served fixed--location transceiver known as a known cell site or base station. When joined together these cells provide radio coverage over a wide geographic area. This enables a large number of portable transceivers (mobile phones, pagers, etc) to communicate, with each other and with fixed transceivers and telephones anywhere in the network, via base stations, even if some of the transceivers are moving through more than one cell during transmission. Benefit of Cellular network: Cellular networks offer a number of advantages over alternative solutions: increased capacity reduced power usage larger coverage area reduced interference from other signals

Wireless LAN: A wireless local area local network (WLAN) links (devices via a wireless distribution

method and usually provides a connection through an access point to the wider internet. This gives users the mobility to move around within a local coverage area and still be connected to the network. Application of Wireless Network: Home network Network in Conference room Network in a floor of a office

Bluetooth: Bluetooth is a proprietary open wireless protocol for exchanging data over short distances (using short length radio waves) from fixed and mobile devices, creating personal area networks (PANs). It was originally conceived as a wireless alternative to RS--232 data cables. It can connect several devices, overcoming problems of synchronization. Bluetooth Application: � Wireless control of and communication between a mobile phone and a hands hands-free headset. This was one of the earliest applications to become popular. � Wireless networking between PCs in a confined space and where little bandwidth is required. � Wireless communication with PC input and output devices, the most common being the mouse, keyboard and printer. . � Transfer of files, contact details, calendar appointments, and reminders between devices with OBEX. � Replacement of traditional wired serial communications in test equipment, GPS receivers, medical equipment, bar code scanners, and traffic control devices. � For controls where infrared was traditionally used. � For low bandwidth applications where higher USB bandwidth is not required and cable -free connection desired.



� Sending small advertisements from Bluetooth enabled advertising hoardings to other, discoverable, Bluetooth devices. � Wireless bridge between two Industrial Ethernet networks. � Dial up internet access on personal computers or PDAs using a data capable mobile phone as a wireless modem � Short range transmission of health sensor data from medical devices to mobile phone, set set-top box or dedicated telehealth devices Wireless Web: Accessing internet web application without cables. PDA, Mobile devices using this technology WAP, GPRS (General packet radio service), 3G

Telecommunication Devices: Modem (modulator--demodulator): A device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data. Modems can be used over any means of transmitting analog signals, from driven diodes to radio. HUB: A common connection point for devices in a network. Hubs are commonly used to connect segments of a LAN. A hub contains multiple ports. When a packet arrives at one port, it is copied to the other ports so that all segments of the LAN can see all packets. � A passive hub serves simply as a conduit for the data, enabling it to go from one device (or segment) to another. � Intelligent hubs include additional features that enables an administrator to monitor the traffic passing through the hub and to configure each port in the hub. Intelligent hubs are also called manageable hubs. � A third type of hub, called a switching hub, actually reads the destination address of each packet and then forwards the packet to the correct port. Router: A device that forwards data packets along networks . A router is connected to at least two networks, commonly two LANs or WANs or a LAN and its ISP network. Routers are located at gateways , the places where two or more networks connect. Routers use headers and forwarding tables to determine the best path for forwarding the packets, and they use protocols to communicate with each other and configure the best route between any two hosts networks. ISP’s gateways, Gateway: The function of a gateway is to allow two or more dissimilar network to communicate as single logical entity. Port : An interface on a computer to which you can connect a device. Personal computers have various types of ports. Internally, there are several ports for connecting disk drives, display screens, and keyboards. Externally, personal computers have ports for connecting modems, printers, mice, and other peripheral devices. Almost all personal computers come with a serial RS RS-232C port or RS RS-422 port

for connecting a modem or mouse and a parallel port for connecting a printer. On PCs, the parallel port is a, Centronics interface that uses a 25 25-pin connector. SCSI (Small Computer System Interface) ports support higher transmission speeds than do conventional ports and enable you to attach up to seven devices to the same port. � In TCP/IP and UDP networks, an endpoint to a logical connection. The port number identifies what type of port it is. For example, port 80 is used for HTTP traffic. Also see Well-Known TCP Port Numbers in the Quick Reference section of Webopedia.



Telecommunication Software: TP: Short for transaction processing monitor, a program that monitors a transaction as it

passes from one stage in a process to another. The TP monitor's purpose is to ensure that the transaction processes completely or, if an error occurs, to take appropriate actions. TP monitors are especially important in three tier architectures that employ load balancing because a transaction may be forwarded to any of several servers. In fact, many TP monitors handle all the load balancing operations, forwarding transactions to different servers based on their availability transaction processing three-servers. CICS: Short for customer information control system, a TP monitor from IBM that was

originally developed to provide transaction processing for IBM mainframes. It controls the interaction between applications and users and lets programmers develop screen displays without detailed knowledge of the terminals being used. CICS is also available on non mainframe platforms including the RS/6000, AS/400 and OS/2 based PCs. Ping

Network management: � Network management refers to the activities, methods, procedures, and tools that pertain to the operation, administration, maintenance, and provisioning of networked systems � 4 Major issues � Traffic Management � Security Management � Monitoring � Capacity Planning Traffic / Bandwidth management: The process of measuring and controlling the communications (traffic, packets) on a

network link, to avoid filling the link to capacity or overfilling the link, which would result in network congestion and poor performance. Security Management: The specialist area of network security consists of the provisions made in an underlying computer network infrastructure, policies adopted by the network administrator to protect the network and the network accessible resources from unauthorized access, and consistent and continuous monitoring and measurement of its effectiveness (or lack) combined together. Monitoring The term network monitoring describes the use of a system that constantly

monitors a computer network for slow or failing components and that notifies the network administrator in case of outages via email, pager or other alarms For example, to determine the status of a web server, monitoring software may

periodically send an HTTP request to fetch a page; for email servers, a test message might be sent through SMTP and retrieved by IMAP or POP3 . Capacity planning Capacity planning is the process of determining the production capacity needed by an

organization to meet changing demands for its products. In the context of capacity planning, "capacity" is the maximum amount of work that an organization is capable of completing in a given period of time. The phrase is also used in business computing as a synonym for Capacity Management products.



Nature and Type of systems Nature and Type of systems: There are different interests, specialties, and levels in an organization, there are different

kinds of systems. No single system can provide all the information an organization needs Three main categories of information systems serve different organizational levels:

operational level systems, management level systems, and strategic level systems.

Three main categories of IS in Organization

Four Major Types of IS Type of System

Information Inputs

Processing Information Output Users

ESS Aggregate data; external, internal

Graphics; simulations interactive

Projection; responses to queries

Senior managers

DSS MIS TPS

TRANSACTION PROCESSING SYSTEMS (TS) Basic business systems that serve the operational level of the organization. A transaction processing system is a computerized system that performs and records the

daily routine transactions necessary to conduct business. Examples are sales order entry, hotel reservation systems, payroll, employee record keeping, and shipping.



Payroll TPS Five functional categories of TPS:



Five functional categories of TPS: Sales/marketing, Manufacturing/production, Finance/accounting, Human resources, and Other types of systems specific to a particular industry. Within each of these major

functions are sub functions TPS applications: � Transaction processing systems are often so central to a business that TPS failure for a few hours can lead to a firm firm’s demise and s perhaps that of other firms linked to it � Managers need TPS to monitor the status of internal operations and the firm firm’s relations s with the external environment. � TPS are also major producers of information for the other types of systems MANAGEMENT INFORMATION SYSTEMS (MIS): MIS primarily serve the functions of planning, controlling, and decision making at the

management level. Generally, they depend on underlying transaction processing systems for their data. Typically, MIS are oriented almost exclusively to internal, not environmental or external,

events. Depend on underlying transaction processing systems for their data

MIS



Characteristics of MIS: MIS usually serve managers primarily interested in weekly, monthly, and

yearly results MIS generally provide answers to routine questions that have been specified in

advance and have a predefined procedure for answering them. These systems are generally not flexible and have little analytical capability. Most MIS use simple routines such as summaries and comparisons, as opposed to

sophisticated mathematical models or statistical techniques. DECISION-SUPPORT SYSTEMS (DSS): DSS help managers make decisions that are unique, rapidly changing, and not easily

specified in advance DSS use internal information from TPS and MIS, they often bring in information from

external sources, such as current stock prices or product prices of competitors. Voyage-estimating decision-support system: Company carries bulk cargoes of coal, oil, ores and finished products for parent company Owns some ships, charters others Bids for shipping contracts in open market for general cargo

Voyage-estimating decision-support system What is the optimal speed at which a particular vessel can optimize its profit and still

meet its delivery schedule? What is the optimal loading pattern for a ship journeying from US W coast to Malaysia Given a customer delivery schedule and an offered freight rate, which vessel should be

assigned at what rate to maximize profits?

Voyage-estimating decision-support system



DSS Sometimes you ll hear DSS systems referred to as business intelligence systems because

they focus on helping users make better business decisions. Executive Support Systems (ESS): Senior managers use executive support systems (ESS) to help them make

decisions ESS are designed to incorporate data about external events, such as new tax laws or

competitors, but they also draw summarized information from internal MIS and DSS ESS employ the most advanced graphics software and can present graphs and data from

many sources. Often the information is delivered to senior executives through a portal, which uses a Web interface to present integrated personalized business content from a variety of sources. Unlike the other types of information systems, ESS are not designed primarily to

solve specific problems. ESS provide a generalized computing and communications capacity that can be applied to

a changing array of problems. Although many DSS are designed to be highly analytical, ESS tends to make less use of analytical models.

Executive Support Systems

Interrelationships among systems



IT Asset Management IT asset management (ITAM): IT asset management is the set of business practices that join financial, contractual and inventory functions to support life cycle management and strategic decision making for the IT environment. Assets include all elements of software and hardware that are found in the business environment.

Logic of asset management Systems:

• Asset Acquisition: – Usually begins with the departmental manager by recognizing the actual need – Managers have authority usually limited by materiality limit – Higher value needed to be approved by higher authority – After requisition approval and selection of supplier, asset purchased - Unlike expenditure this assed sends to direct department of custodian not central

inventory - Fixed asset department not inventory control, perform record keeping.

• Asset Maintenance: – Adjustment of asset subsidiary account balance as the asset depreciate (except

land) over the time or usages – Various depreciation method used

• Straight line • Double declining • Unit of production • Sum of the years digit

- Some time IFS specify the depreciation method e.g. for new office building straight –ling method with the period at least 40 years

- Depreciation value related to manufacturing charged as manufacturing overhead then WIP

- Other depreciation value charged as expense in current period.

• Disposal: – When asset reached at end of its useful life then it removed from asset

subsidiary ledger. – Firm can dispose it by scrap, donate or retire – Disposal report need to be sent to proper department for reporting

Computer Base Fixed Assed Systems:

• Acquisition Procedure: – Acquisition recognized in the systems when asset receiving report arrived and

cash disbursement required – At the time of registering fixed assed in the systems historical data used to

• Define residual value • Depreciation method • Useful life time • Location of the asset

– A fixed assed system automatically updates • Fixed asset control account in GL • Prepare Journal voucher as evidence of the entry • Prepare reports for accounting management



– Depending of depreciation parameters system prepare a depreciation schedule for each fixed asset.

• Maintenance: – Fixed asset system automatically doing

• Calculating the current period of depreciation • Updating the accumulated depreciation and book value in subsidiary

ledger • Posting the total amount of depreciation to affected GL accounts

(depreciation, expense, accumulated depreciation) • Asset routine services and maintenance

• Disposal: – After disposal authorization and entering in to systems, it automatically doing

• Post adjustment entry in the fixed asset control account of the GL • Records any loss or gain for disposal • Prepare journal voucher

Controlling Fixed Asset Systems:

• Authorization control: – Should be formal and explicitly authorized – Written approval is required – For high value items independent approval process required to evaluate merit

and cost-benefit analysis of the asset • Supervision:

– As widely distributed these have high scope of miss use. So super vision is important



Systems Development Life Cycle (SDLC) Topics to cover

• Portfolio/programme management • Business Case • Benefit realization techniques • Project management structure • Project organization forms • Project communication, culture, roles & responsibilities • Project management frameworks • Gantt Charts & PERT/CPM • Function Point Analysis • All software development projects • All software acquisition & implementation projects • All network development and extension projects

All kinds of IT projects are referred to as SDLC, in general.

System development approach, depending Upon the specific requirement of the organization in the total system may follow any one of the following models :

1. Waterfall model 2. Prototyping model 3. Spiral model

The combination of more than one of the Above model may be used for system Development, depending upon the nature and size of the project and the risk involved. This Is called hybrid approach of system Development



Waterfall Model – Typical Phases

PROPOSAL DEFINATION

FEASIBILITYSTUDY

SYSTEM DESIGN

IMPLEMENTATION

CODINGANDTESTING

SYSTEM MAINTENANCE

REQUIREMENTANALYSIS

Waterfall Model: Strength:

• Easy to understand, easy to use • Provides structure to inexperienced staff • Milestones are well understood • Sets requirements stability • Good for management control (plan, staff, track) • Works well when quality is more important than cost or schedule

Deficiencies: • All requirements must be known upfront • Deliverables created for each phase are considered frozen – inhibits flexibility • Can give a false impression of progress • Does not reflect problem-solving nature of software development – iterations of phases • Integration is one big bang at the end • Little opportunity for customer to preview the system (until it may be too late)

When to use Waterfall: • Requirements are very well known • Product definition is stable • Technology is understood • New version of an existing product • Porting an existing product to a new platform.

Prototype Model: Prototyping is the process of quickly putting together a working model in order to test various aspects of a design, illustrate ideas or features and gather early user feedback. Prototyping is often treated as an integral part of the system design process, where it is believed to reduce project risk and cost. Often one or more prototypes are made in a process of incremental development where each prototype is influenced by the performance of previous designs, in this way problems or deficiencies in design can be corrected.



Prototype Model:

REQUIREMENT ANALYSIS

REDEFINEPROTOTYPE

QUICKDESIGN

ENGINEER THEPRODUCT

PROTOTYPEBUILDING

USER EVALUATION

STOP

START

Advantages :

• Can be used when customer is not sure about what he wants • Faster way of finalizing the requirements • Useful for new technologies and domains

Disadvantage : • A prototype if used in a production environment, may lack quality • Overall maintainability may be overlooked • The customer may want the prototype delivered. • Process may continue forever (scope creep)

Spiral Model: The spiral model is a SDLC methodology that combines features of prototyping with the waterfall methodology. The spiral model is often favored for large, complex projects. Iterates cycles of these project phases: 1. Requirements definition 2. Risk analysis 3. Prototyping 4. Simulate, benchmark 5. Design, implement, test 6. Plan next cycle (if any)



Spiral Model – Steps:

• The new system requirements are defined. This usually involves interviewing a number of users representing all the end users of the system.

• A preliminary system design is created. • An initial prototype of the new system is constructed from the preliminary design. This is

usually a scaled-down system, and represents an approximation of the final product’s characteristics.

• After evaluating the strengths, weaknesses and risks of the first prototype, a second prototype is developed and tested.

• If the risk is considered to be too great, the client may choose to terminate the project at this point. Risk factors to be considered include development cost overruns, operating-cost miscalculation, etc.

• Subsequent prototypes are developed until the customer is satisfied that the latest prototype represents the desired product.

• The system is constructed, based on the final prototype. The final system is evaluated and tested. Routine maintenance is carried out continually to prevent large-scale failures and to minimize downtime. Advantages: 1. Avoidance of Risk is enhanced. 2. Strong approval and documentation control. 3. Implementation has priority over functionality. 4. Additional Functionality can be added at a later date.

• Adds risk analysis, and 4GL RAD prototyping to the waterfall model

• Each cycle involves

the same sequence of steps as the waterfall process model



Disadvantages: 1. Highly customized limiting re-usability 2. Applied differently for each application 3. Risk of not meeting budget or schedule 4. Possibility to end up implemented as the Waterfall framework When to use Spiral Model

When creation of a prototype is appropriate When costs and risk evaluation is important For medium to high-risk projects Long-term project commitment is unwise because of potential changes to economic

priorities Users are unsure of their needs Requirements are complex New product line Significant changes are expected (research and exploration)

Incremental SDLC Model:

Construct a partial implementation of a total system Then slowly add increased functionality The incremental model prioritizes requirements of the system and then implements

them in groups. Each subsequent release of the system adds function to the previous release, until all

designed functionality has been implemented. Incremental Model: Strengths:

Develops high-risk or major functions first Each release delivers an operational product Customer can respond to each build Uses “divide and conquer” breakdown of tasks Lowers initial delivery cost Initial product delivery is faster Customers get important functionality early Risk of changing requirements is reduced

Weaknesses: Requires good planning and design Requires early definition of a complete and fully functional system to allow for the

definition of increments Well-defined module interfaces are required (some will be developed long before

others) Total cost of the complete system is High



V-Shaped Model:

• A variant of the Waterfall that emphasizes the verification and validation of the

product. • Testing of the product is planned in parallel with a corresponding phase of

development. V-Shaped Model Steps:

• Project and Requirements Planning – allocate resources • Product Requirements and Specification Analysis – complete specification of the

software system • Architecture or High-Level Design – defines how software functions fulfill the design • Detailed Design – develop algorithms for each architectural component • Production, operation and maintenance – provide for enhancement and corrections • System and acceptance testing – check the entire software system in its environment • Integration and Testing – check that modules interconnect correctly • Unit testing – check that each module acts as expected • Coding – transform algorithms into software

Advantages:

• Emphasize planning for verification and validation of the product in early stages of product development

• Each deliverable must be testable • Project management can track progress by milestones • Easy to use

Disadvantages: • Does not easily handle concurrent events • Does not handle iterations or phases • Does not easily handle dynamic changes in requirements • Does not contain risk analysis activities

When to use V-Shaped Model • Excellent choice for systems requiring high reliability – hospital patient control

applications • All requirements are known up-front • When it can be modified to handle changing requirements beyond analysis phase

Solution and technology are known



Iterative SDLC Model:

DESIGN1 DESIGN2 DESIGN3 DESIGNn

IMPLEMENT1 IMPLEMENT2 IMPLEMENTn

ANALYSIS1 ANALYSIS2 ANALYSISn

Rapid Application Development (RAD) Model: • Requirements planning phase (a workshop utilizing structured discussion of business

problems) • User description phase – automated tools capture information from users • Construction phase – productivity tools, such as code generators, screen generators, etc. inside

a time-box. (“Do until done”) • Cutover phase -- installation of the system, user acceptance testing and user training

Strengths: • Reduced cycle time and improved productivity with fewer people means lower costs • Time-box approach mitigates cost and schedule risk • Customer involved throughout the complete cycle minimizes risk of not achieving customer

satisfaction and business needs • Focus moves from documentation to code (WYSIWYG). • Uses modeling concepts to capture information about business, data, and processes.

Weaknesses: • Accelerated development process must give quick responses to the user • Risk of never achieving closure • Hard to use with legacy systems • Requires a system that can be modularized • Developers and customers must be committed to rapid-fire activities in an abbreviated time frame.

When to use RAD: • Reasonably well-known requirements • User involved throughout the life cycle • Project can be time-boxed • Functionality delivered in increments • High performance not required • Low technical risks • System can be modularized

Agile Model Speed up or bypass one or more life cycle phases Usually less formal and reduced scope Used for time-critical applications Used in organizations that employ disciplined methods

Some Agile methods • Adaptive Software Development (ASD) • Feature Driven Development (FDD) • Crystal Clear • Dynamic Software Development Method (DSDM) • Rapid Application Development (RAD) • Scrum • Extreme Programming (XP) • Rational Unify Process (RUP)



SDLC Model Comparison Waterfall RAD Incremental Prototype Spiral Step by Step Approach. Next step can not start unless previous step is through

High speed adaptation of waterfall model. Development is done for independent components in parallel and then integrated

Successive enlargements and refinements of a system through multiple mini SDLCs. Customer’s requirements are gradually known

A simplified model of the system (prototype) is built fast to make the client have a feel of the system. While building prototype the minimum amount of coding is done without implementing coding standard, error management, normalization etc. It is a way of understanding requirements from the customer

Iterative nature of the Prototyping Model with the controlled and systematic approach of the Waterfall Model • Used in projects where risk factor is

high: military, research-oriented. • Performs risk evaluation in each

cycle. • Can be integrated with other life

cycles. • Multiple cycles performed. Each

cycle consists of: 1. Determine objectives, alternatives,

constraints 2. Evaluate alternatives, identify &

resolve risk (e.g. risk analysis, prototype, simulation)

3. Develop and verify product: prototype, product or other deliverable

4. Plan next phase: Review findings of this round and plan goals for next round

Waterfall RAD Incremental Prototype Spiral When the requirements are clear

When a system can be broken into independent sub systems

When the objectives of the system can be achieved by dividing the system into sub systems with a core system. The core system of sub system will serve the basic needs and the subsequent systems will serve the incremental needs. When there is a technical / resource risk

When Requirements are not completely known

When Risk is high

1.Requirements have to be fully understood to implement this model 2.As one phase depends on the other so it causes delay 3.Things keep coming in for a particular phase even after the phase is signed off 4.Rigid Model

1.Performance issue. 2.Technical issues are high 3.Interoperability issue with existing systems 4. Resource may be an issue

Difficulty in managing multiple concurrent increments

1.Does not work well for production system 2.Customer sees a 'working' model and gets impatient. 3.Developer may make implementation compromises to get prototype working quickly.

1.No scheduled project completion. 2.A dedicated team for risk analysis is required



Common Risks in SDLC:

1. Lack of management support 2. Functionality non-alignment with user departments 3. Scope variation, i.e., scope creeping (ineffective freezing of SRS) 4. Unfulfilling the requirements set in SRS by the vendor 5. Time over-run 6. Cost over-run 7. Insufficient or wrong identification of stakeholders and their participation 8. Insufficient breakdown of project activities and segregation of duties 9. Insufficient planning process 10. Insufficient or weak risk management 11. Improper cost estimation 12. Wrong selection of technology 13. Inappropriate or insufficient Test Cases in UAT 14. Insufficient participation user departments in UAT design and testing 15. Absence of Regression Testing (and fallback plan) and Sociability Testing (compatibility with

other related systems) 16. In sufficient Technical Testing, e.g., configuration testing, load testing, inter-operatibility of

system components, unhandled errors, automaticity of transactions, password encryption, etc 17. Erroneous data migration 18. Insufficient attention to security and controls (including validations and audit trails) in the

application system 19. Performance criteria not being met 20. Inappropriate resourcing 21. Insufficient documentation 22. Inadequate contractual protection 23. Inadequate adherence to chosen SDLC and/or development methodologies 24. Insufficient skill transfer by user training

Typical Audit Steps for SDLC: A. Control Objective #1 - SDLC Methodology

1. Determine the extent of the responsibilities of management, internal audit, users, quality assurance, and data processing during the system design, development, and maintenance.

2. Review SDLC workpapers to determine if the appropriate levels of authorization were obtained for each phase.

3. Obtain and review requests for DP services. Determine if the University's procedures are being followed.

B. Control Objective #2 - Needs Analysis 1. Review and evaluate the procedures for performing a needs analysis. 2. Review a needs analysis for a recent project and determine if it conforms to standards.

C. Control Objective #3 - Systems Design and Development 1. Review and evaluate the procedures for systems design and development. 2. Review design specifications schedules, look for written evidence of approval, and determine

if the design specifications comply with the standards. 3. Determine if an audit trail and programmed controls are incorporated in the design

specifications of a recent project. 4. Review samples of source documents used for data entry which are included in SDLC

workpapers of a recently developed application. Determine if they are designed to facilitate accurate gathering and entry of information.

5. Obtain and review programs to determine if they comply with the University's programming standards.

D. Control Objective #4 - Testing Procedures 1. Review and evaluate the procedures for system and program testing. 2. Review documented testing procedures, test data, and resulting output to determine if they

appear to be comprehensive and if they follow University standards. 3. Review the adequacy of testing performed on the manual phases of an application.



E. Control Objective #5 - Implementation Procedures 1. Review and evaluate procedures for program promotion and implementation. 2. Review documentation of the program promotion procedure. Determine if the standards are

followed and if documentation of compliance with the standards is available. Trace selected program and system software changes to the appropriate supporting records to determine if the changes have been properly approved.

3. Review documentation of the conversion/implementation of a newly developed application. Determine if the University's implementation procedures were followed.

F. Control Objective #6 - Post-implementation Review 1. Review and evaluate the procedures for performing post-implementation reviews. 2. Review program modifications, testing procedures, and the preparation of supporting

documentation to determine if the University's standards are being followed. G. Control Objective #7 - Maintenance of Applications

1. Review and evaluate the procedures for the maintenance of existing applications. 2. Review program modifications, testing procedures, and the preparation of supporting

documentation to determine if the University's standards are being followed. H. Control Objective #8 - Control over Systems Software

1. Review and evaluate the procedures for modifying systems software. 2. Review systems software modifications, testing procedures, and the preparation of supporting

documentation to determine if the University's standards are being followed. 3. Review and evaluate documentation of in-house developed systems software and the

features/options of proprietary systems software in use. I. Control Objective #9 - Documentation Standards

1. Obtain and review the documentation standards to determine if they are complete. EFFECT OF WEAKNESSES: Major portion of the cost of an application over its useful life is incurred for maintenance after the application becomes operational. If little attention is given to the SDLC in the creation of a system, excessive maintenance costs can be incurred, especially if it is necessary to put controls in after the application is already in production. Redesign is not only expensive, but also difficult to accomplish. If accurate and comprehensive documentation is not maintained, the auditor will have difficulty assessing controls without expending substantial effort to obtain an accurate description of significant applications and their relationships to one another. If modifications to application and system software are not adequately controlled, the integrity of the software may be compromised by unauthorized changes in programs, procedures, or data. When an application is properly designed, systems development and documentation controls can prevent or disclose the following types of errors:

1. implementation of applications that do not have adequate application controls; development of applications that either do not meet management objectives or do not operate in accordance with original specifications;

2. Implementation of applications that have not been adequately tested, and; 3. Implementation of applications that is susceptible to unauthorized modification.



Introduction to e-Business Learning Objectives

1. Explain what e-business is and how it affects organizations. 2. Discuss methods for increasing the likelihood of success and for minimizing the potential

risks associated with e-business. 3. Describe the networking and communications technologies that enable e-business.

Learning Objective 1: Explain what e-business is and how it affects organizations. Introduction: E-Business E-business refers to all uses of advances in information technology (IT), particularly networking and communications technology, to improve the ways in which an organization performs all of its business processes. E-business encompasses an organization’s external interactions with its:

Suppliers Customers Investors Creditors The government Media

E-business includes the use of IT to redesign its internal processes. For organizations in many industries, engaging in e-business is a necessity. Engaging in e-business in and of itself does not provide a competitive advantage. However, e-business can be used to more effectively implement its basic strategy and enhance

the effectiveness and efficiency of its value-chain activities. E-Business Models

Business to Consumers (B2C): Interactions between individuals and organizations. Business to Business (B2B): Interorganizational e-business.

Categories of E-Business

Type of E-Business Characteristics

B2C Organization-individual Smaller dollar value One-time or infrequent transactions Relatively simple

B2B B2G B2E

Interorganizational Larger dollar value Established, on-going relationships Extension of credit by seller to customer More complex

E-Business Effects on Business Processes

Electronic Data Interchange (EDI): Standard protocol, available since the 1970s, for electronically transferring information between organizations and across business processes.

EDI: Improves accuracy Cuts costs



Recent EDI Facilitators Traditional EDI was expensive. New developments that have removed this cost barrier are: The Internet: Eliminates the need for special proprietary third-party networks. XML: Extensible Markup Language – Set of standards for defining the content of data on

Web pages. ebXML:

Defines standards for coding common business documents. Eliminates need for complex software to translate documents created by different

companies. Integrated Electronic Data Interchange (EDI)

Reaping the full benefits of EDI requires that it be fully integrated with the company’s AIS.

Suppliers

Customers

AIS

Company

EDIPurchase orders

Customer orders

EDI

E-Business Effects on Value Chain Activities:

Value Chain – Primary Activities

E-Business Opportunity

Inbound logistics Acquisition of digitizable products Reduced inventory “buffers”

Operations Faster, more accurate production

Outbound logistics Distribution of digitizable products Continuous status tracking

Sales and Marketing Improved customer support Reduced advertising costs More effective advertising

Post-sale Support and Service Reduced costs 24/7 Service availability

Purchasing Human Resources Infrastructure

Source identification and reverse auctions

Employee self-service EFT, FEDI, other electronic payments

Purchasing and Inbound Logistics

The Internet improves the purchasing activity by making it easier for a business to identify potential suppliers and to compare prices.



Purchase data from different organizational subunits can be centralized. • This information can be used to negotiate better prices. • Number of suppliers can be reduced. • Reverse auctions can be held

For products that can be entirely digitized, the entire inbound logistics function can be performed electronically.

Internal Operations, Human Resources, and Infrastructure

Advanced communications technology can significantly improve: The efficiency of internal operations. Planning. The efficiency and effectiveness of the human resource support activity. The efficiency and effectiveness of customer payments.

Information Flows in Electronic Commerce

Buyer Seller1. Inquiries

2. Responses

3. Orders

4. Acknowledgment

5. Billing

6. Remittance data

7. PaymentsExplanations:

EDI = Steps 1-6

EFT = Step 7

FEDI = Steps 1-7 Financial Electronic Data Interchange (FEDI)

The use of EDI to exchange information is only part of the buyer-seller relationship in business-to-business electronic commerce.

Electronic funds transfer (EFT) refers to making cash payments electronically, rather than by check.

EFT is usually accomplished through the banking system’s Automated Clearing House (ACH) network.

An ACH credit is an instruction to your bank to transfer funds from your account to another account.

An ACH debit is an instruction to your bank to transfer funds from another account into yours.

Company A’sbank

Company B’sbank

Company A Company B

Remittance data and payment instruction

Remittance data and funds An Application Service Provider (ASPs):

An Application Service Provider (ASP) is a company that provides access to and use of application programs via the Internet.

The ASP owns and hosts the software; the contracting organization accesses the software via the Internet.

Factors to Consider When Evaluating ASPs



Advantages Lower costs Automatic upgrading to current version of software Need fewer in-house IT staff Reduced hardware needs Flexibility Knowledge support Security and privacy of data

Disadvantages Viability of ASP Security and privacy of data Availability and reliability of service Inadequate support or poor responsiveness to problems Standard software that may not meet all customized needs

Factors to Include in Service Level Agreements

Detailed specification of expected ASP performance Uptime Frequency of backups Use of encryption Data access controls

Remedies for failure of ASP to meet contracted service levels Ownership of data stored at ASP

Outbound Logistics: E-Business can improve the efficiency and effectiveness of sellers’ outbound logistical

activities. Timely and accurate access to detailed shipment information. Inventory optimization. For goods and services that can be digitized, the outbound logistics function can be

performed entirely electronically. Sales and Marketing:

Companies can create electronic catalogs to automate sales order entry. Significantly reduce staffing needs. Customization of advertisements

Post-Sale Support and Service: Consistent information to customers. Provide answers to frequently asked questions (FAQs)

Learning Objective 2: Discuss methods for increasing the likelihood of success and for minimizing the potential risks associated with E-Business. .E-Business Success Factors:

The degree to which e-business activities fit and support the organization’s overall business strategy.

The ability to guarantee that e-business processes satisfy the three key characteristics of any business transaction

Validity Integrity Privacy

Encryption: There are two principal types of encryption systems:

Single-key systems: Same key is used to encrypt and decrypt the message • Simple, fast, and efficient • Example: the Data Encryption Standard (DES) algorithm

Public Key Infrastructure (PKI): Uses two keys: • Public key is publicly available and usually used to encode message • Private key is kept secret and known only by the owner of that pair of keys.

Usually used to decode message



Advantages & Disadvantages of PKI: Advantages

No sharing of key necessary More secure than single-key systems

Disadvantages Much slower than single-key systems

Digital Signatures and Digests: Digital signature: An electronic message that uniquely identifies the sender of that message. Digest: The message that is used to create a digital signature or digital summary.

If any individual character in the original document changes, the value of the digest also changes. This ensures that the contents of a business document have not been altered or garbled during transmission

Digital Certificates & Certificate Authorities: Digital Certificate: Used to verify the identity of the public key’s owner.

A digital certificate identifies the owner of a particular private key and the corresponding public key, and the time period during which the certificate is valid.

Digital certificates are issued by a reliable third party, called a Certificate Authority, such as: Verisign Entrust Digital Signature Trust

The certificate authority’s digital signature is also included on the digital certificate so that the validity of the certificate can also be verified.

Learning Objective 3: Describe the networking and communications technologies that enable e-business. Types of Networks:

The global networks used by many companies to conduct electronic commerce and to manage internal operations consist of two components:

1 Private portion owned or leased by the company 2 The Internet

The private portion can be further divided into two subsets: 1 Local area network (LAN) — a system of computers and other devices, such as printers, that

are located in close proximity to each other. ■Wide area network (WAN) — covers a wide geographic area. 2 Companies typically own all the equipment that makes up their local area network (LAN). 2 They usually do not own the long-distance data communications connections of their wide

area network (WAN). 2 They either contract to use a value-added network (VAN) or use the Internet. 2 The Internet is an international network of computers (and smaller networks) all linked

together. 2 What is the Internet’s backbone?

2 the connections that link those computers together 2 Portions of the backbone are owned by the major Internet service providers (ISPs). 2 What is an Intranet? 2 The term Intranet refers to internal networks that connect to the main Internet. 2 They can be navigated with the same browser software, but are closed off from the general

public. 2 What are Extranets?

Companies build a virtual private network (VPN) to improve reliability and security, while

still taking advantage of the Internet.



Company A

AIS VPNequipmentISP

Internet

Data Communications System Components:

There are five basic components in any data communication network (whether it is the Internet, a LAN, a WAN, or a VAN):

1 The sending device 2 The communications interface device 3 The communications channel 4 The receiving device 5 Communication software

The following are components of the data communications model: – interface devices – communications software – communications channel

Interface Devices: There are six basic communication interface devices that are used in most networks:

1 Network interface cards 2 Modems 3 Remote access devices 4 Hubs 5 Switches 6 Routers

Company APC-1NIC

PC-2 PC-3NIC NIC

Switch

Router

Hub 1

Hub 1 OtherLANs

Internet service provider

Remote accessdevice

Frame relayswitch

Router



Home PCModem

Remote accessdevice

Frame relayswitch

Router

Home PCModem

Internet service provider

Communications Software:

Communications software manages the flow of data across a network. It performs the following functions:

– access control – network management – data and file transmission – error detection and control – data security

Communications Channels: A communications channel is the medium that connects the sender and the receiver.

– standard telephone lines – coaxial cables – fiber optics – microwave systems – communications satellites – cellular radios and telephones

SatelliteMicrowave stations

Topologies:

Local area networks (LANs) can be configured in one of three basic ways: 1 Star configuration 2 Ring configuration 3 Bus configuration

Network Configuration Options: A star configuration is a LAN configured as a star; each device is directly connected to the

central server. All communications between devices are controlled by and routed through the central server. Typically, the server polls each device to see if it wants to send a message.

Network Configuration Options (Star) The star configuration is the most expensive way to set up a LAN, because it requires the greatest amount of wiring.



Host computeror server

A B C

G F E

DH

Network Configuration Options (Ring) In a LAN configured as a ring, each node is directly linked to two other nodes

A

H

B

D

C

EGF

Network Configuration Options (Bus)

In a LAN configured as a bus, each device is connected to the main channel, or bus. Communication control is decentralized on bus networks.

A B C

GFE

D

H

Host computeror server

Bus channel

Network Configuration Options

Wide area networks (WANs) can be configured in one of three basic ways: 1 Centralized system 2 Decentralized system 3 Distributed data processing 3 In a centralized WAN, all terminals and other devices are connected to a central corporate

computer.

In a decentralized WAN, each departmental unit has its own computer and LAN. Decentralized systems usually are better able to meet individual department and user needs

than are centralized systems.



A distributed data processing system WAN is essentially a hybrid of the centralized and decentralized approaches

Many WANs, and most LANs, are set up as client/server systems. Each desktop computer is referred to as a client. The client sends requests for data to the servers. The servers perform preprocessing on the database and send only the relevant subset of data

to the client for local processing.



Programming language Objectives of this session

Introduction to Programming Language? Generation of Programming Language? Object Oriented Programming language. Visual Programming Steps in Programming Flowchart Pseudocode

Programming Language Set of rules that tell the computer what operations to perform. Can be classified in two levels

Lower level Higher Level

Lower Level: Closer to form to the language the computer itself uses[1,0]

Higher Level: Closer to the language people use. Compiler:

A compiler is a computer program (or set of programs) that transforms source code written in a computer language (the source language) into another computer language (the target language, often having a binary form known as object code). The most common reason for wanting to transform source code is to create an executable program.

Examples are C++, VB Interpreter:

An interpreter translates high-level instructions into an intermediate form, which it then executes.

In contrast, a compiler translates high-level instructions directly into machine language. Compiled programs generally run faster than interpreted programs.

The advantage of an interpreter, however, is that it does not need to go through the compilation stage during which machine instructions are generated. This process can be time-consuming if the program is long

OS independent Examples JAVA, Perl

Generation of Programming language Five Generations

1. First Generation language - Machine language - Basic language of the computer, representing instructions & data as binary digits. - Machine dependant. 2. Second Generation - Assembly Language -use symbols as abbreviations L for load.. - Easier and more efficient in software development.

First and Second Generation P.L More Technical More flexible Less user friendly Faster 3.Third Generation

High level languages, are very much like every day text & mathematical formula Run on different computers COBOL, FORTRAN, BASIC,C

Third Generation languages are Less technical Less flexible More user friendly Slower



4.Fourth Generation Language Nonprocedural languages, Not specify how. Need one-tenth number of statements of high-level language Easier

5.Fifth Generation Language Natural Language. No need to learn specific vocabulary, grammar, syntax. Very closely resembles human speech.

Expert systems, Computer-based collection of knowledge, Artificial Intelligence. Object Oriented Programming(OOP):

Object oriented programming combines data with instructions for processing that data to make a self-sufficient object that can be used in other programs.

An object is a block of preassembled programming code that is a self-contained module. Three Concepts of OOP Encapsulation: Means an object contains both data and instructions for processing. Inheritance: An object can be used as the foundation for similar objects. Polymorphism: Means a message produces different results based on the object that it is sent to. Visual Programming: Visual programming is a method of creating programs in which the programmer makes connections between objects by drawing, pointing, and clicking on diagrams and icon. Easier and graphical way. Steps in Programming: Five Steps Step -1:Define the problem: 1. Specify program objective and program users 2. Specify output requirements. 3. Specify input requirements 4. Specify processing requirements. 5. Study feasibility of implementing program 6. Document analysis and objective specification process. Step -2: Design a solution:

1. Map out the Program logic 2. Diagram a document program design. 3. Test design with structured walkthrough

Step -3: Code the program Write the program using high level language

Step –4: Test the program Test program with structured walkthrough, desk checking and sample data to try to break the program. Step –5: Finalize the Documentation

Assemble and finalize all documentation made during all previous steps. Algorithm:

An algorithm is a set of well-defined rules for the solution of a problem in a particular number of steps.

Pseudocode: • Pseudocode uses human-language stataements instead of symbols to represent program logic. • Precise • Does not follow a specific programming language

Flow chart: A program flowchart is a diagram that uses standard ANSI Symbols to show the step-by-step processing objectives and decision logic needed to solve a problem.



Standard flowchart Symbols:

Terminal, marks the beginning, end, or a part of interruption in a program Input/output

Processing, shows a group of instructions in located in order to perform a processing task. Decision, shows where alternative operation are performed based on the existence of certain

conditions.

Connector, shows movement to or from another part of the program. Predefined process, Indicate a group of operations not detailed in the particular flowchart.

The benefits of flowcharts:

Communication: Flowcharts are better way of communicating the logic of a system to all concerned;

Effective analysis: With the help of flowchart, problem can be analyzed in more effective way;

Proper documentation: Program flowcharts serve as a good program documentation, which is needed for various purposes;

Efficient Coding: The flowcharts act as a guide or blueprint during the systems analysis and program development phase;

Efficient Program Maintenance: The maintenance of operating program becomes easy with the help of flowchart. It helps the programmer to put efforts more efficiently on that part;

Flow chart to find the maximum

Start

READ N1, N2, N3

MAX=N1

2/11/2002

IF N2> MAX

MAX=N2

MAX=N3

PRINT MAX

NoYes

IF N3> MAXYes

No



Transaction Processing Processing Model:

• Batch Processing – Lag between the point of transaction (economic event) and reflect in firm’s

accounting systems – Data synchronized after fulfilling certain condition – Example : Salary of employees

• Real Time – Main accounting system updating immediate after transaction takes place. No lag,

no time gap. • Distributing Processing

- Transactions first up date with individual accounting system then update the main accounting system



Network and communication Network: A network is nothing more than two or more computers connected together so that they can exchange information. Types of Network: Local Area Network(LAN) Metropolitan Area Network(MAN) Wide Area Network(WAN) LAN: When computers located within a small geographical area such as office or a University Campus are connected together we call it a Local Area Network. MAN: The geographical range of MAN is bigger than LAN. It covers a small city. WAN: Wide area network span broad geographical distances, ranging from several miles to across entire continents. Wan may consist of a combination of switched and dedicated Lines, microwaves, and satellite communication. Uses of Computer Networks: Business Applications: 1. First goal is resource sharing to make all programs, equipment, and specially data available to anyone on the network without regard to the physical location of the resource and the user. 2. A computer network can provide a powerful communication medium among employees. 3. Many companies are doing business electronically with other companies, especially suppliers and customers. 4. Doing business with consumers over the Internet. Home Applications: Some of the popular uses of the Internet for home users are as follows: 1. Access to remote information 2. Person-to-person communication 3. Interactive entertainment 4. Electronic Commerce Mobile users: People on the road and sea may use their portable electronic equipment to send and receive telephone calls, faxes, electronic mail, surf the web, access remote files, and log on to the remote machines. Social issues: A popular feature of many networks is newsgroups or bulletin boards whereby people can exchange messages with like-minded individuals. Network Topology:

Network Topology refers to the physical data path that traffic takes across the network. Three basic types of topologies are bus, star and ring. Bus Topology: In a bus topology

Each node is connected to a common cable called a bus. Each node has a unique address. All nodes will receive a message, but only the addressed node is to respond. If one node is down, the network is still available. Fewer wires or lines are needed.

Fig: Bus topology



Star Topology: In a star topology a central host computer connected to a number of small computers or terminals. This topology is useful for applications where some processing must be centralized and some can be preformed locally. If the central host computer is down, the network will come to standstill. Ring Topology: In a ring topology all computers are connected by a closed loop in a manner that passes data in one direction from one computer to another. The main disadvantage of a ring is larger communication delays if the number of nodes increases. Model of Connectivity for networks:

Reference model: A reference model is a generic framework for thinking about a problem. Protocol: A protocol is a statement that explains how a specific task will be performed. Open system Interconnect (OSI) Model: OSI model is an international reference model developed by the International Standard Organization (ISO) for linking different types of computers and networks. The OSI model is made up of seven layers Application Layer Application Layer Presentation Network Presentation Layer Session Layer Session Layer Transport Layer Transport Layer Network Layer Network Layer Data Link Layer Data Link Layer Physical Layer Physical Layer

Physical Layer: This layer defines the electrical and mechanical aspects of interfacing to a physical medium for transmitting data. It also defines how physical links are setup, maintained and disconnected. Data Link Layer: This layer establishes an error-free communications path between computers over the physical channel. It gives the standard for framing messages, checking integrity of received messages, accessing and using channels and sequencing of transmitted data. Network Layer: The network layer handles the routing functions for data moving from one open system to another. This layer provides the addressing necessary to relay data through intermediate nodes or systems that provide the connectivity between nonadjacent open systems. Transport Layer: The transport layer is responsible for maintaining a specific class of service for the user. The transport layer provides communications flow control beyond the frame-level control provided in that data-link layer. To prevent congestion in a network, this layer segments data or block data to form smaller or larger packets. Session Layer: The session layer allows users on different machines to establish sessions between them. Session offers various services, including dialog control, token management and synchronization.



Presentation Layer: This layer is concerned with the syntax and semantics of the information transmitted. The presentation layer manages the abstract data structures and allows higher level data structures. It also provides ASCII-to-EBCDIC and EBCDIC-to-ASCII conversion. Application Layer: This provides services that directly support users such as file transfers, remote files access, and data base management, etc. Communication Media:

Physical communication media are the physical channels through which information is transmitted between computers in a network. A channel can utilize different kinds of telecommunication media: twisted wire, coaxial cable, fiber optics, terrestrial microwave, satellite, and wireless transmission. Twisted Wire: Twisted wire consists of stands of copper wire twisted in pairs and is the oldest transmission medium. Although it is low in cost, twisted pair is relatively slow for transmission data, and high-speed transmission causes interference called crosstalk. Coaxial Cable: Coaxial Cable consists of thickly insulated copper wire, which can transmit a larger volume of data than twisted wire can. It is faster, more interference-free transmission medium, with speeds up to 200 megabits per second. However, coaxial cable is thick, is hard to wire in many buildings, and cannot support analog phone conversations. Inner Outer Insulation Connector(wire) Conductor Insulation Fiber optics: Fiber optics cable consists of thousands of stands of clear glass fiber, the thickness of a human hair, which are bound into cables. Data are transformed into pulses of light, which are sent through the fiber optics cable by a laser device at a rate of 100 Mbps to 2Gbps. Light ray Cladding Core Optical fibers have several advantages. They are:

i) Very high bandwidth. ii) Protection against electromagnetic interface iii) More secure, as they cannot be trapped easily. iv) Light weight and no corrosion.

The major disadvantages of fibers are: i) It is more difficult to work with, more expensive, and hard to install ii) They are fragile and cannot have sharp bends.

Microwave: Microwave systems transmit high-frequency radio signals through the atmosphere and are widely used for high-volume, long-distance, point-to-point communication. The great advantage of microwaves is the large bandwidth of 40 to 200 MHz available which will permit data transmission rates in the range of 250 Mbps. The capital investment needed to install microwave link is very high.



Satellite A communication satellite is essentially a microwave relay station in the sky. Conventional communication satellites move in stationary orbits approximately 22000 miles above the earth. Communication satellites are cost effective for transmitting large quantities of data over long distances. Other communication Systems Gateway The function of a gateway is to allow two or more dissimilar network to communicate as single logical entity. Bridges A bridge is a device that’s used to connect two similar types of networks so that they act as if they’re one network. Router A router is similar to a super-intelligent bridge for big networks. Bridges know the address of all the computers on each side of the bridge and can be forwarded messages accordingly. Router not only knows the addresses of all computers but also other bridges and routers of the network, and can decide the most efficient path to send each message. Fire Wall A network fire wall is a gatekeeper computer system that protects a company’s networks from intrusion by serving as a filter and safe transfer point for access to and from the internet and other networks. It screens all network traffic for proper passwords or other security codes, and only allows authorized transmissions in and out of the network.

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