CRESCENT INSTITUTE OF TECHNOLOGY AND MANAGEMENT

KALINGARAJAPURAM, KANJAMPURAM

KANYAKUMARI 629 154.

PAPER – I COMPUTER CONCEPTS AND INFORMATION TECHNOLOGY

UNIT – I Introduction to computers Generation – types and characteristics – Mini – mainframe – PC – work stations – Super computers – Network computers – Parts of computers: CPU, Control unit, ALU, Memory, Registers, Memory types, RAM & ROM – storage devices – Magnetic disk, Hard disk, Floppy Disks – CD ROM.

UNIT – II Input devices, key board – mouse – trackball – joystick – scanner – OCR – Touch screens – Light Pen. Output devices - Monitors – printers – Dot Matrix – ink jet – Laser Printers. Software – Operating Systems – Compiler – Programming languages – Word processions – spread sheets.

UNIT – III Computer Networks – Communication media – network types – LAN, MAN, WAN, Topologies: Ring, star and Bus topologies.

UNIT – IV Data processing : Data versus information – File processing – Database processing DBMS: Database Definition – Need for Database – Characteristics of a database – Database Management system services, Types of DBMS: Network, Relational, hierarchical and Object Oriented Models.

UNIT –V Internet and WWW – Reasons for internet internet connections direct and Dial-up, List of Uses of internet – internet Protocols such as FTP, HTTP, TCP/IP. Email, Browsing, Browser – Types Searching information and sending and receiving mails, Search engines Yahoo and Google.

UNIT – I What is a computer? A computer is a truly amazing electronic device that performs specified sequences of operations as per the set of instructions (known as programs) given on a set of data (input) to generate desired information (output). Being a machine, it will not perform independently or creatively. It will do only, what is instructed to do, in specific terms.

Generation of Computers

The evolution of computers has passed through a number of stages before it reached the present state. From the early 1950s, growth of the computers was very rapid but this development took distinct phases known as generation of computers. First Generation The first generation computers were the voluminous computers. These computers used electronic valves (vacuum tubes) and had the main limitations of very large electric power consumption and very little reliability. Second Generation The invention of transistor in 1948 (invented at Bell Laboratories, USA) led to the development of second-generation computers. Transistors replaced the valves (vacuum tubes) completely as they were far more

superior in performance on account of their miniature size, smaller power consumption and less expensive. Third Generation These computers use integrated circuits (ICs) in place of transistors and they were having higher speed, large storage capacities and less expensive. An integrated circuit arranges thousands of switches on circuit boards known as a chip. These machines used more versatile programmes like Multi Programming Techniques and Database Management. Fourth Generation Due to development of large scale integrated chips known as microprocessor chips in 1971 by Intel Corporation, another breed became popular as fourth generation computers. Fifth Generation: These machines will use parallel processing techniques and artificial intelligence techniques.

Therefore these computers will be able to think as human beings can think. Characteristics of Computers The interesting features of a computer are: • High Speed – Ability to perform tasks at a greater speed than human beings. – Perform complex calculations in seconds. • Accuracy – Perform tasks with accuracy. – Input given to the computer determines the output received. • Storage – Can store large amounts of information. – Retrieve information whenever required. • Automation – Can be instructed to perform tasks automatically. • Diligence – Can perform the same task repeatedly, without getting tired. – Can do the same job with the same accuracy for hours or longer. • Versatility – Can be used to perform simple as well as complex tasks. • Cost effective – Reduce the amount of paperwork and human effort, thereby reducing costs. Types of Computers

Digital – A Digital computer uses digital technology. It processes digital quantities that attain discrete values. Most computers used for information processing are of this type. Analog – An Analog computer is designed to process continuous physical quantities. Examples of analog computer usage include monitoring temperature, voltage and current reading in a power station. Each of these parameters can attain an infinite number of values, not just simple on and off. What is a mainframe computer?

• Mainframe computers are the big, powerful, expensive computers used in the background by most large organisations. The power of the mainframe can be distributed amongst many people accessing the mainframe via their own PC. Organisations such as large insurance companies would use the mainframe to keep track of their policyholders and send out renewal notices.

What is a PC?

• IBM invented the PC (Personal Computer) way back in 1981. All PCs released since then are in many ways compatible with the original design, though many extensions have been made. The term PC compatible relates to PCs manufactured by companies other than IBM which are compatible with the traditional PC specification. In the early days, most PCs ran an operating system called DOS (Disk Operating System). These days most PCs will be running a version of Microsoft Windows.

Workstation

Workstation is a computer used for engineering applications (CAD/CAM), desktop publishing, software development, and other such types of applications which require a moderate amount of computing power and relatively high quality graphics capabilities. Workstations generally come with a large, high-resolution graphics screen, large amount of RAM, inbuilt network support, and a graphical user interface. Most workstations also have a mass storage device such as a disk drive, but a special type of workstation, called a diskless workstation, comes without a disk drive. Common operating systems for workstations are UNIX and Windows NT. Like PC, Workstations are also single-user computers like PC but are typically linked together to form a local-area network, although they can also be used as stand-alone systems. Supercomputer Supercomputers are one of the fastest computers currently available. Supercomputers are very expensive and are employed for specialized applications that require immense amount of mathematical calculations (number crunching). For example, weather forecasting, scientific simulations, (animated) graphics, fluid dynamic calculations, nuclear energy research, electronic design, and analysis of geological data (e.g. in petrochemical prospecting).

What is a networked computer?

• A network allows you to connect two or more computers together. This allows data stored on one PC to be retrieved by other PCs connected to the network. It also allows the sharing of resources. Thus

instead of each PC requiring its own printer to be directly connected to it, you can have a single printer shared amongst many networked PCs. In the early days, to network PCs together was a complicated task, only to be attempted by qualified professionals. These days most people with a good working knowledge of Microsoft Windows can install and configure a Windows based network. However to get the best out of your network, in terms of performance and security, still requires a qualified, experienced technician.

Control Unit The Control Unit, as the very name implies, controls the movement and operates within the CPU. Based on the instructions given CPU ensures the operations as specified in the program are performed in the sequence. This operation may be receipt of data and storing them at specified locations, transfer of data from one address of memory to another, transfer of data from Memory to the Arithmetic Unit, controlling the Arithmetic Unit to memory from there on to the output. Arithmetic and Logic Unit: All the calculations are performed and all comparisons (decisions) are made in the Arithmetic and Logic Unit (ALU) of the CPU. No Processing occurs in the primary storage. Intermediate results generated are temporarily placed in a designated working storage area until needed at a later time. Data may thus move from one primary storage to the ALU and back again to store at many times before processing is finished. Once completed, the final results are released to an output storage section and from there to an output device. The type and number

of Arithmetic Logic operations a computer can perform are determined by the design of the CPU. Memory The data fed to the computer stays stored in the memory, as and when the data is required to be processed or operated upon, it is transferred to the Arithmetic Logic Unit which does all the computation work like addition, subtraction etc. After processing, the data is again brought back and stored in the memory. There are two types of memories: 1 MAIN MEMORY (RAM) – The main memory is Random Access Memory (RAM). The name derives from the fact that data can be stored in and retrieved at random, from anywhere. Main memory is in volatile state. When the computer is off, main memory is empty; when it is on, main memory is capable of receiving and holding a copy of the software instructions and data necessary for processing. Because main memory is a volatile form of storage and the users might lose any unsaved information, hence user often stores their work on devices such as floppy disks or hard disks.

2 READ ONLY MEMORY (ROM) – Instructions to perform such operations, which are critical to the operation of a computer, are stored permanently on a read-only memory

(ROM) chip installed by the manufacturer inside the computer. When the power in the computer is turned off, the instructions stored in ROM are not lost and the data cannot be changed.

Storage Devices

Hard disk drives are an internal, higher capacity drive which also stores the operating system which runs when you power on the computer. "Floppy" disk drives allow you to save work on small disks and take the data with you. Floppy disk

• Floppy disks are also known as diskettes. They are very slow compared to hard disks or CD-ROMs, and hold relatively small amounts of data (1.44 Mbytes). Sometimes people will backup (i.e. copy) important data from their hard disk to floppy disks. However, as diskettes are notoriously unreliable this is not the best way of backing up valuable data (but is better than nothing).

Hard (Fixed) Disk

• Hard disks are the main, large data storage area within your computer. Hard disks are used to store your operating system, your application programs (i.e. your word processor, games etc) and your data. They are much faster than CD-ROMs and floppy disks and can also hold much more data. The picture shows the inside of a hard disk (which you would not normally see). Hard disks are installed within the system unit of your computer.

CD-ROM Disks Speed: Much slower than hard disks. The original CD-ROM speciation is given a value of 1x speed, and later, faster CD-ROMs are quoted as a multiple of this value.

UNIT II INPUT DEVICES

The Mouse

• The mouse came into common use on a PC with the introduction of the Microsoft Windows operating system. Before this, the operating system (DOS) would normally be controlled via the keyboard. These days it is vital to be a competent mouse user. There are many different types of mice, a commonly used model now has a small wheel on it which when combined with the correct software allows additional functionality and fine control over the use of your applications.

The Keyboard

• The keyboard is still the commonest way of entering information into a computer. There are a number of different types, including those specially designed for use with Microsoft Windows. The quality of the keyboard is often overlooked when buying a PC; it should be robust and easy to use.

Tracker Balls

• A tracker ball is an alternative to the traditional mouse and favoured by graphic designers. Tracker balls often give much finer control over the movement of the items on the screen. They may take a while to get used to if you are used to the traditional mouse, but offer a lot in terms of added flexibility.

Joysticks

• Many games require a joystick for the proper playing of the game. There are many different types, the more sophisticated respond to movement in 3 axis directions, as well as having a number of configurable buttons. Like most things in life you get what you pay for with joysticks and it is worth investing in a good,

strongly constructed model, especially bearing in mind that children will hammer these devices whilst playing games.

Scanners

• A scanner allows you to scan printed material and convert it into a file format which may be used within the PC. You can scan pictures and then manipulate these inside the PC using a graphics application of your choice. In addition, you can scan printed text and convert this not just to a picture of the text but also to, actual text which can be manipulated and edited as text within your word-processor. There are a number of specialist programs, generically called OCR (Optical Character Recognition) programs which are specifically designed for converting printed text into editable text within your applications.

Optical Character Reader (OCR) OCR is an input device used to read a printed text. OCR scans text optically character by character, converts them into a machine readable code and stores the text on the system memory. The Optical Character Reader (OCR) can read alphabets, characters and numbers printed on paper. These characters can be either handwritten or typed. However special fonts are required to be used while typing. In case of handwritten data, the characters have to be of standard predefined size. The OCR reads each character as a collection of pixels. The light which is reflected from the page to be scanned is converted into binary data. OCRs are available in various sizes and speeds. These devices are expensive and are mainly used in processing where the data volumes are large.

Touch screen: A touch panel is a transparent plate which is fitted over the CRT. Input is registered when a finger or any other object comes in contact with the plate. There are two types of touch panels:

• Optical touch panels

• Electric touch panels

Light Pens

• A light pen is used to allow users to point to areas on a screen and is often used to select menu choices.

Output Devices After the computer has processed the data, the final result has to be brought out from the machine in some intelligent and readable form.

Monitor Monitor is an output device with the help of which a user can see the results produced by the computer. It is also called as Visual Display Unit (VDU) available in different sizes.

Printers Printers are very useful in day-to-day life to take a hardcopy of our work. There are different types of printers based on the quality and printing speed at which they print.

Dot Matrix printers

• Dot matrix printers work by firing a row of pins through an ink ribbon onto the paper. The more pins the print head has the higher the quality of the print, most modern dot matrix printers have 24 pins. Unfortunately, dot matrix printers can generate a lot of noise and do not produce a very high quality of print, especially when printing graphics. As a result, the inkjet printer has now largely replaced the dot matrix printer. Dot matrix printers are used for high volume / low quality printing, e.g. printing company pay slips.

Inkjet printers

• Inkjet printers work by using tiny jets to spray ink onto the paper. Inkjet printers are very quiet in operation and produce print quality comparable to that of laser

printers, though laser printers still have the edge in terms of speed. Inkjet printers are ideal for low volume printing where high quality print is required and speed is not a high priority, e.g. printing letters in a small office or in the home.

Laser printers

• Laser printers produce high print quality at high speed. They are called "laser printers" due to the fact that they contain a small laser within them. There is a wide range of laser printer manufacturers and one buzzword to be aware of is Postscript, a type of printer which is designed to give very high quality reproduction of pictures.

Software: The computer performs operations like addition, subtraction, multiplication and division only when the user instructs it to do so. The user issues instructions and the CPU acts in accordance with the instructions. The sets of instructions, which control the sequence of operations, are known as programs, and collectively programs are called software. The software can be broadly classified into two types. They are: a. System Software b. Application software

What is an Operating System?

The operating system is a special type of program which loads automatically when you start your computer. The operating system allows you to use the advanced features of a modern computer without having to learn all the details of how the hardware works. There are a number of different types of operating system in common use. The IBM PC (Personal Computer) was introduced way back in 1981and was originally supplied with an operating system called DOS (Disk Operating System). This operating system was very basic, and you had to be a bit of a computer expert just to understand how to use it.

Compiler: A compiler is a computer program that generates other programs. It translates an input program written in a high-level language that is easier for humans to create into a program in a machine-level language that can be executed by the computer.

Programming Languages For programming computers, we want simple, unambiguous, regular, and economical languages with powerful means of abstraction. A programming language is a language that is designed to be read and written by humans to create programming programs that can be executed by computers. Language Programming languages come in many flavors. It is difficult to simultaneously satisfy all desired properties since simplicity is often at odds with economy. Every feature that is added to a language to increase its expressiveness incurs a cost in reducing simplicity and regularity. For the first two parts of this book, we use the Scheme programming language which was designed primarily for simplicity. For the later parts of the book, we use the Python programming language, which provides more expressiveness but at the cost of some added complexity. Word processing

• A word processing program (such as Microsoft Word) allows you to produce letters, memos, etc., easily. You can easily mail merge a list of names and addresses to produce mass mailers, individually addressed to customers or subscribers.

Spreadsheets

• A spreadsheet program (such as Microsoft Excel) allows you to work out a company’s income, expenditure and then calculate the balance. It enables you to make 'what if' type projections of how the company will fair in the future and to forecast how changes in prices will affect profits.

UNIT III COMPUTER NETWORKS

INTRODUCTION With standardized hardware and software, the microcomputers provide user-friendly environment. It meets the computing requirements of most users. But, the need for interaction with other computer users and with other computer systems for exchange of data etc., has increased over the years. Networks are increasingly meeting this need. From the users’ point of view the networks may be of two types: Local area network and Wide area network.

Computer networking is the process of inter connecting two or more computers so that the users can communicate with each other, share resources and overcome other limitations of stand-alone systems. The network can be established with a variety of combinations of computers such as a net of only microcomputers, microcomputers and one or more minicomputers and a set of microcomputers connected to a mainframe computer. The computers in typical network are autonomous in the sense that they have processing capability independent of the network.

Importance of Networking Computer networks allow the user to access remote programs and remote databases either of the same organization or from other enterprises or public sources. Computer networks provide communication possibilities faster than other facilities. Because of these optimal information and communication possibilities, computer networks may increase the organizational learning rate there are other reasons why any organization should have a computer network. • cost reduction by sharing hardware and software resources • High reliability by having multiple sources of supply • cost reduction by downsizing to microcomputer-based networks instead of using mainframes

• Greater flexibility because of possibility to connect devices from various vendors. A network is two or more computers connected together to share information and files between them. Businesses aren't the only ones that can benefit from creating a network. Home users can enjoy sharing music, movies and printers from any computer. File Sharing: Computers connected to a network can share files and documents with each other. Personal computers connected to a business network can choose which files and folders are available to share on the network. Printers: Computers can print pages to another computer with a printer on the network. Additionally, printers can be connected using a print server, which allows direct printing from all computers. Computer Network Types of Networks A) Local Area Networks Local area networks (LANs) are used to connect networking devices that are in a very close geographic area, such as a floor of a building, a building itself, or a campus environment. B) Wide Area Networks

C) Wide area networks (WANs) are used to connect LANs together. Typically, WANs are used when the LANs that must be connected are separated by a large distance. D) Metropolitan Area Networks A metropolitan area network (MAN) is a hybrid between a LAN and a WAN. A computer network is an interconnection of various computer systems located at different places. In computer network two or more computers are linked together with a medium and data communication devices for the purpose of communicating data and sharing resources. The computer that provides resources to other computers on a network is known as server in the network the individual computers, which access shared network resources, are known as workstations or nodes. Computer Networks may be classified on the basis of geographical area in two broad categories. 1. Local Area Network (LAN) 2. Wide Area Network (WAN) I. Local Area Network: Networks used to interconnect computers in a single room, rooms within a building or buildings on one site are called Local Area Network (LAN). LAN links computers, i.e., software and hardware, in the same area for the purpose of sharing information. Usually LAN links computers within a limited geographical area because they must be connected by a cable, which is quite expensive.

Major Characteristics of LAN are as follows: 1 Every computer has the potential to communicate with any other computers of the network 2 High degree of interconnection between computers 3 Easy physical connections of computers in a network 4 Inexpensive medium of data transmission 5 High data transmission rate Advantages of LAN are as follows: • The reliability of network is high because the failure of one computer in the network does not effect the functioning for other computers. • Addition of new computer to network is easy. • High rate of data transmission is possible. • Peripheral devices like magnetic disk and printer can be shared by other computers. Disadvantages of LAN is • If the communication line fails, the entire network system breaks down. Use of LAN: Followings are the major areas where LAN is normally used • File transfers and Access • Word and text processing • Electronic message handling • Remote database access • Personal computing • Digital voice transmission and storage 4.4 Network Components 1) Hub

A hub works in the physical layer of the OSI model. It is basically a non-intelligent device, and has no decision making capability. What a Hub basically does is take the input data from one of the ports and broadcast the information to all the other ports connected to the network.

To demonstrate its working, consider a 4 port network as shown in Fig 1. There are 4 computers connected to the 4 ports. Suppose, if Computer A wants to send some data to Computer B using a Hub, then, Computer A broadcasts the data on the network, and Computer B, being connected to the network, has access to the data. But, in this case all the other ports connected to the network has access to the data that is being transmitted by Computer A. This happens because, the Hub works in the Physical Layer and hence it does not know about the MAC addresses of the ports connected to the network. So, there is a lack of security in the Hub.

USB Hub The picture shows a USB Hub, wherein the data is fed into the input port and is broadcasted to all the other 4 ports. The Network Hubs are outdated and are out of the market. 2) Switch A switch is an intelligent device that works in the data link layer. The term intelligent refers to the decision making capacity of the Switch. Since it works in the Data link layer, it has knowledge of the MAC addresses of the ports in the network.

Switch Hence, in the Fig 1, if data has to be sent from Computer A to Computer B, then, the data is transferred to the Computer B only, and not to any other computers connected on the network. Hence, it establishes a link between the sender and the receiver based on the MAC addresses. This also means that when data is being sent from A to B, Computer C can

establish a link with Computer D and communication can take place between them. So, simultaneous data transfer is possible in a switch. Also, Hub divides bandwidth, but a Switch does not. It is also to be noted that a switch is a secure device, because it sends information only to the desired destinations, and also certain security features such as firewalls can be implemented in the Switches. 3) Bridge A bridge is also a device which works in the Data Link Layer, but is more primitive when compared to a switch. Initial bridges were used to connect only 2 LAN’s, but the most recent ones perform similar operation as the switches. It also works on the principle of transfer of information using the MAC addresses of the ports.

Bridge It can be noted is that the normal ADSL modem can be connected via bridging also. The only difference is that, when bridging is used, each time the device has to be connected to the internet; it has to dial to the internet and establish a connection. Also, a bridge alone cannot be used to connect to the internet, because, the bridge works in the Data Link Layer, and has no knowledge of the IP Addresses, which are used in the Internet. 4) Router

Any computer can be connected to the internet via MODEM, which performs the Modulation and the Demodulation operations. But, when there is more than one computer at home or in an organization, and you have a single internet connection, you need a Router. Router is a device which is used when multiple devices need to connect to the Internet using the same IP. Any Internet Service Provider (ISP) provides a single IP, and especially for personal use, the IP address is assigned dynamically. This is done because, suppose, an ISP has 1000 IP addresses, it does not mean that it has 1000 customers. An ISP assumes that not all devices will be connected to the internet at the same time. Hence, when a user wants to access the internet, any IP address from the pool of IP addresses from the ISP will be assigned to connect the user to the internet.

Router Functionality: When a router receives the data, it determines the destination address by reading the header of the packet. Once the address is determined, it searches in its routing table to get know how to reach the destination and then forwards the packet to the higher hop on the route. The hop could be the final destination or another router.

Routing tables play a very pivotal role in letting the router makes a decision. Thus a routing table is ought to be updated and complete. The two ways through which a router can receive information are: • Static Routing: In static routing, the routing information is fed into the routing tables manually. It does not only become a time-taking task but gets prone to errors as well. The manual updating is also required in case of statically configured routers when change in the topology of the network or in the layout takes place. Thus static routing is feasible for tinniest environments with minimum of one or two routers. • Dynamic Routing: For larger environment dynamic routing proves to be the practical solution. The process involves use of peculiar routing protocols to hold communication. The purpose of these protocols is to enable the other routers to transfer information about to other routers, so that the other routers can build their own routing tables. 5) Gateway The Gateway devices work in the Transport layer and above, where the different network technologies are implemented. A gateway is necessary when there are different technologies implemented by the different LAN’s which are to be connected together.

Gateway function

The Fig shows the working of a gateway. Consider 2 networks, say in New York, and a network in London. If data has to be sent from one place to another, we need to ensure that the network technologies that are being used by both the networks are the same. If not, we need to use a Gateway. In the more common example, we use a telephone network and internet networks, which works on different technologies. The telephone network follows the ISDN, and the Internet follows the IP. Here, 2 different technologies are being used. In this case, the router fails to work, since the router cannot understand the functionalities of both the networks. Hence, we require a Gateway, which acts as a translator in communicating between the 2 networks. 6) Modems Modem is a device which converts the computer-generated digital signals of a computer into analog signals to enable their travelling via phone lines. The ‘modulator-demodulator’ or modem can be used as a dial up for LAN or to connect to an ISP. Modems can be both external, as in the device which connects to the USB or the serial port of a computer, or proprietary devices for handheld gadgets and other devices, as well as internal; in the form of add-in expansion cards for computers and PCMCIA cards for laptops.

Configuration of a modem differs for both the external and internal modem. For internal modems, IRQ – Interrupt request is used to configure the modem along with I/O, which is a memory address. Typically before the installation of built-in modem, integrated serial interfaces are disabled, simultaneously assigning them the COM2 resources. For external connection of a modem, the modem assigns and uses the resources itself. This is especially useful for the USB port and laptop users as the non-complex and simpler nature of the process renders it far much more beneficial for daily usage. Upon installation, the second step to ensure the proper working of a modem is the installation of drivers. The modem working speed and processing is dependent on two factors: • Speed of UART – Universal Asynchronous Receiver or Transmitter chip (installed in the computer to which the modem connection is made) • Speed of the modem itself. Network Topology Topology refers to the way in which the network of computers is connected. Each topology is suited to specific tasks and has its own advantages and disadvantages. The choice of topology is dependent upon type and number of equipment being used, planned applications and rate of data transfer required, response time, and cost. Topology can also be defined as the geometrically interconnection pattern by which the stations (nodes/computers) are connected using suitable transmission media (which can be point-to-point and broadcast). Think of a topology as a network's virtual shape or structure. This shape does not necessarily correspond to the actual physical layout of the devices on the network. For example, the computers on a home LAN may be arranged in a circle in a family room, but it would be highly

unlikely to find a ring topology there. Network topologies are categorized into the following basic types: • Bus • Ring • Star • Tree • mesh More complex networks can be built as hybrids of two or more of the above basic topologies. 1) Bus Topology Bus networks (not to be confused with the system bus of a computer) use a common backbone to connect all devices. A single cable, the backbone functions as a shared communication medium that devices attach or tap into with an interface connector. A device wanting to communicate with another device on the network sends a broadcast message onto the wire that all other devices see, but only the intended recipient actually accepts and processes the message. Bus networks work best with a limited number of Networking made it easy 2 Compiled by devices. If more than a few dozen computers are added to a network bus, performance problems will likely result. In addition, if the backbone cable fails, the entire network effectively becomes unusable. 2) Ring Topology In a ring network, every device has exactly two neighbors for communication purposes. All messages travel through a ring in the same direction (either "clockwise" or "counterclockwise"). A failure in any cable or device breaks the loop and can take down the entire network. To implement a ring network, one typically uses FDDI, SONET, or

Token Ring technology. Ring topologies are found in some office buildings or school campuses. Definition: Token Ring is a data link technology for local area networks (LANs). It operates at layer 2 of the OSI model. How Token Ring Works Unlike all other standard forms of LAN interconnects, Token Ring maintains one or more common data frames that continuously circulates through the network. These frames are shared by all connected devices on the network as follows: • A frame (packet) arrives at the next device in the ring sequence that device checks whether the frame contains a message addressed to it. If so, the device removes the message from the frame. If not, the frame is empty (called a token frame). • The device holding the frame decides whether to send a message. If so, it inserts message data into the token frame and issues it back onto the LAN. If not, the device releases the token frame for the next device in sequence to pick up • The above steps are repeated continuously for all devices in the token ring 3) Star Topology Many home networks use the star topology. A star network features a central connection point called a "hub" that may be a hub, switch or router. Devices typically connect to the hub with Unshielded Twisted Pair (UTP) Ethernet. Compared to the bus topology, a star network generally requires more cable, but a failure in any star network cable will only take down one computer's network access and not the entire LAN. (If the hub fails, however, the entire network also fails.)

4) Tree Topology Tree topologies integrate multiple star topologies together onto a bus. In its simplest form, only hub devices connect directly to the tree bus and each hub functions as the "root" of a tree of devices. This bus/star hybrid approach supports future expandability of the network much better than a bus (limited in the number of devices due to the broadcast traffic it generates) or a star (limited by the number of hub connection points) alone. 5) Mesh Topology Mesh topologies involve the concept of routes. Unlike each of the previous topologies, messages sent on a mesh network can take any of several possible paths from source to destination. (Recall that even in a ring, although two cable paths exist, messages can only travel in one direction.) Some WANs, most notably the Internet, employ mesh routing. A mesh network in which every device connects to every other is called a full mesh. As shown in the illustration below, partial mesh networks also exist in which some devices connect only indirectly to others. Wireless networking Wireless networking is a method by which homes, telecommunications networks and enterprise (business) installations avoid the costly process of introducing cables into a building, or as a connection between various equipment locations. • Do not require physical cabling • Particularly useful for remote access for laptop users • Eliminate cable faults and cable breaks. • Signal interference and security issue. Moving data through a wireless network involves three separate elements: the radio signals, the data format, and the network structure.

Each of these elements is independent of the other two. In terms of the OSI reference model, the radio signal operates at the physical layer, and the data format controls several of the higher layers. The network structure includes the wireless network interface adapters and base stations that send and receive the radio signals. In a wireless network, the network interface adapters in each computer and base station convert digital data to radio signals, which they transmit to other devices on the same network, and they receive and convert incoming radio signals from other network elements back to digital data. A wireless network enables people to communicate and access applications and information without wires. This provides freedom of movement and the ability to extend applications to different parts of a building, city, or nearly anywhere in the world. Wireless networks allow people to interact with e-mail or browse the Internet from a location that they prefer. Many types of wireless communication systems exist, but a distinguishing attribute of a wireless network is that communication takes place between computer devices. These devices include personal digital assistants (PDAs), laptops, personal computers (PCs), servers, and printers. Computer devices have processors, memory, and a means of interfacing with a particular type of network. Traditional cell phones don't fall within the definition of a computer device; however, newer phones and even audio headsets are beginning to incorporate computing power and network adapters. Eventually, most electronics will offer wireless network connections. As with networks based on wire, or optical fiber, wireless networks convey information between computer devices. The information can take the form of e-mail messages, web pages, and database records, streaming video or voice. In most cases, wireless networks transfer data, such as e-mail messages and files, but advancements in the performance of wireless networks is enabling support for video and voice communications as well.

Types of Wireless Networks WLANS: Wireless Local Area Networks WLANS allow users in a local area, such as a university campus or library, to form a network or gain access to the internet. A temporary network can be formed by a small number of users without the need of an access point; given that they do not need access to network resources. WPANS: Wireless Personal Area Networks The two current technologies for wireless personal area networks are Infra-Red (IR) and Bluetooth (IEEE 802.15). These will allow the connectivity of personal devices within an area of about 30 feet. However, IR requires a direct line of site and the range is less. WMANS: Wireless Metropolitan Area Networks This technology allows the connection of multiple networks in a metropolitan area such as different buildings in a city, which can be an alternative or backup to laying copper or fiber cabling. WWANS: Wireless Wide Area Networks These types of networks can be maintained over large areas, such as cities or countries, via multiple satellite systems or antenna sites looked after by an ISP. These types of systems are referred to as 2G (2nd Generation) systems. Comparison of Wireless Network Types.

UNIT IV

Data processing Data processing refers to the process of collecting and manipulating raw data to yield useful information. Data processing is also the conversion of raw data into machine-readable form and its subsequent processing by a computer. On BusinessDictionary.com, Web Finance gives a general definition of data processing as the operations performed on data to obtain useful information in the appropriate form. Data processing converts the otherwise unusable data into a useful form. It involves data storage, organization, modification and final presentation of the desired information. Processed data comes in the form of reports, diagrams and tables. In computing, processed data comes in audio, video, graphic, diagrammatic, text and numeric forms.

There are various techniques of data processing, including manual, automatic and electronic data processing. Manual data processing is a traditional form of data processing that involves manual data collection and collection, analysis and presentation, such as bookkeeping and census exercises. Automatic data processing is an almost obsolete data processing technique that was mainly done using electromagnetic devices, such as electric accounting machines and unit record equipment. Electronic data processing is the widespread, modern technique of collecting, manipulating, analyzing and presenting data and information. Electronic data processing is also known as computerized data processing.

Database is a collection of related data and data is a collection of facts and figures that can be processed to produce information. Mostly data represents recordable facts. Data aids in producing information, which is based on facts For example, if we have data about marks obtained by all students, we can then conclude about toppers and average marks. A database management system stores data in such a way that it becomes easier to retrieve, manipulate, and produce information.

Data base Databases and database technology have a major impact on the growing use of computers. It is fair to say that databases play a critical role in almost all areas where computers are used, including business, electronic commerce, engineering, medicine, genetics, law, education, and library science. The word database is so commonly used that we must begin by defining what a database is. Our initial definition is quite general.

A database is a collection of related data.1 By data, we mean known facts that can be recorded and that have implicit meaning. For example, consider the names, telephone numbers, and addresses of the people you know. You may have recorded this data in an indexed address book or you may have stored it on a hard drive, using a personal computer and software such as Microsoft Access or Excel. This collection of related data with an implicit meaning is a database.

The preceding definition of database is quite general; for example, we may consider the collection of words that make up this page of text to be related data and hence to constitute a database. However, the common use of the term database is usually more restricted. A database has the following implicit properties:

A database represents some aspect of the real world, sometimes called the miniworld or the universe of discourse (UoD). Changes to the mini world are reflected in the database.

■ A database is a logically coherent collection of data with some inherent meaning. A random assortment of data cannot correctly be referred to as a database.

■ A database is designed, built, and populated with data for a specific purpose. It has an intended group of users and some preconceived applications in which these users are interested. In other words, a database has some source

Characteristics of Database

Traditionally, data was organized in file formats. DBMS was a new concept then, and all the research was done to make it overcome the deficiencies in traditional style of data management. A modern DBMS has the following characteristics: Real-world entity: A modern DBMS is more realistic and uses real-world entities to design its architecture. It uses the behavior and attributes too. For example, a school database may use students as an entity and their age as an attribute. Relation-based tables: DBMS allows entities and relations among them to form tables. A user can understand the architecture of a database just by looking at the table names. Isolation of data and application: A database system is entirely different than its data. A database is an active entity, whereas data is said to be passive, on which the database works and organizes. DBMS also stores metadata, which is data about data, to ease its own process. Less redundancy: DBMS follows the rules of normalization, which splits a relation when any of its attributes is having redundancy in values. Normalization is a mathematically rich and scientific process that reduces data redundancy. Consistency: Consistency is a state where every relation in a database remains consistent. There exist methods and techniques, which can detect attempt of leaving database in inconsistent state. A DBMS can provide greater consistency as compared to earlier forms of data storing applications like file-processing systems. Query Language: DBMS is equipped with query language, which makes it more efficient to retrieve and manipulate data. A user can apply as many and as different filtering options as required to retrieve a set of data. Traditionally it was not possible where file-processing system was used. ACID Properties: DBMS follows the concepts of Atomicity, Consistency, Isolation, and Durability (normally shortened as ACID). These concepts are applied on transactions, which manipulate data in a database. ACID properties help the database stay healthy in multi-transactional environments and in case of failure. Multiuser and Concurrent Access: DBMS supports multi-user environment and allows them to access and manipulate data in parallel. Though there are restrictions

on transactions when users attempt to handle the same data item, but users are always unaware of them. Multiple views: DBMS offers multiple views for different users. A user who is in the Sales department will have a different view of database than a person working in the Production department. This feature enables the users to have a concentrate view of the database according to their requirements. Security: Features like multiple views offer security to some extent where users are unable to access data of other users and departments. DBMS offers methods to impose constraints while entering data into the database and retrieving the same at a later stage. DBMS offers many different levels of security features, which enables multiple users to have different views with different features. For example, a user in the Sales department cannot see the data that belongs to the Purchase department. Additionally, it can also be managed how much data of the Sales department should be displayed to the user. Since a DBMS is not saved on the disk as traditional file systems, it is very hard for miscreants to break the code.

Users A typical DBMS has users with different rights and permissions who use it for different purposes. Some users retrieve data and some back it up. The users of

a DBMS can be broadly categorized as follows:

Administrators: Administrators maintain the DBMS and are responsible for administrating the database. They are responsible to look after its usage and by whom it should be used. They create access profiles for users and apply limitations to maintain isolation and force security. Administrators also look after DBMS resources like system license, required tools, and other software and hardware related maintenance. Designers: Designers are the group of people who actually work on the designing part of the database. They keep a close watch on what data should be kept and in what format. They identify and design the whole set of entities, relations, constraints, and views. End Users: End users are those who actually reap the benefits of having a DBMS. End users can range from simple viewers who pay attention to the logs or market rates to sophisticated users such as business analysts. Files- a file is considered as a sequence of bytes, the operating system supplies routines that can read/write a specified number of bytes. file is a sequence of records of the same type.

UNIT V Overview of WWW The World-Wide Web is based on a simple protocol called HTTP that allows browser programs such as Netscape, kfm or internet explorer, to fetch files from remote server programs, for example apache, and to view them (the files are often called pages, which is odd because they are files!). WWW files are named by URIs which have a special format that includes the remote server name and the name of the file (note: A URI is sometimes called a URL). The files can be written in a special document description language called HTML that is interpreted by the browser to give an appealing visual effect on a graphical display. The HTML files can contain embedded URIs that refer to other WWW files, these are usually highlighted by the browser and if selected will cause retrieval of the named file. Such references are sometimes called hyper-links, it is the use of these that produce a “web” and give the web (HTTP, URIs, and HTML) its power. Interconnection Agreements At its most basic, an interconnection agreement says “You carry some traffic for me, in return for which I’ll do something—either carry traffic for you, or pay you, or some combination of the two.” Interconnection agreements are often tailored very carefully and minutely to the specific circumstances of the parties involved, particularly when those parties are large ISPs. The current environment is one in which a heterogeneous mix of network providers—large and small; local, national, and global; public and private—connect to each other’s networks under a variety of arrangements, which adhere to one of four basic models: 1) Bilateral settlements. Two operators interconnect. Each accepts traffic destined for its own customers and originating within the other’s network. Neither network delivers traffic to third parties on behalf of the other. Each charges for the volume of traffic it accepts from the other. ( It follows that if the value of traffic in both directions is equal, the net settlement amount would be zero)

2) Sender Keep All. As with bilateral settlements, two operators each accept traffic from the other, for delivery to the accepting network’s customers. But no charge is made. 3) Transit. One operator, the provider, accepts traffic originating within the other’s network, destined not only for its own customers but for third party networks with whom the provider in turn connects. The provider charges a fee for carrying the other network’s traffic. 4) Multilateral exchanges. An operator connects to an exchange, a (usually commercial) facility carrying connections from multiple operators. There, traffic is routed to other operators’ networks via equipment provided by the exchange and according to rules administered by the exchange; the operator settles through the exchange for traffic that others carry on its behalf and that it carries on behalf of others. Micro-economics of Interconnection Many economic and business-policy factors affect an individual ISP’s decision to peer or not to peer with another ISP, and in the case of a paid arrangement (bilateral settlement or transit), the pricing19 External, publicly-advertised factors include: • Geographic coverage of the two networks: either overlapping, such that a peering relationship would be symmetrical; or non-overlapping, such that a peering relationship would extend each network’s geographic reach. • Technical factors: networks may require certain technical standards, or preferentially choose interconnection partners where the peering relationship gives access to a desired technology. • Operational: networks may require a certain level of operational support. • Routing: networks may require specific routing policies and practices. • Size: networks may choose to peer only with similarly sized networks. • Anticipated traffic volumes.

Additional, idiosyncratic factors apply. For example, if one network’s specific geography or customer mix or traffic mix dovetails with an important element of the other network’s strategy, it would lead to a higher perceived value and price than otherwise. In any given case, the arrangement is made on the basis of a perceived equitable exchange of value between the two interconnecting parties, where the value of the arrangement to each of the parties is determined by a number of factors, some obvious (direct cash payment, cost-effective transit, or access to a large user community, for example); others entirely idiosyncratic . The argument has been made in the past, for example, that certain bilateral relationships between overseas and US-based networks are “unfair” on the grounds that the cost of the transatlantic or transpacific link was borne entirely by the overseas network, whereas the origination of traffic was split more evenly between the two. In some cases, European ISPs in one country were connecting to US backbones in order to send traffic back to a neighboring European country, bearing the cost in effect of two transatlantic hops. Macro-Economics of Interconnection In addition to examining the factors influencing a single interconnection arrangement, it is worth examining the overall characteristics of the market in which these arrangements happen. An essential characterization of a market is its liquidity. Does a buyer or a seller have a choice of many parties to deal with? Or is there a monopoly or oligopoly limiting choice? In some sense, choice is intrinsic to the Internet’s routed, connectionless architecture, as contrasted with the circuit-switched, connection-oriented public telephone networks. Just because ISP “X” can’t strike a satisfactory bargain with ISP “Y”, does not mean that X’s customers will be unable to reach Y’s customers: X always has the option of buying transit from some third party who is in turn connected to Y. (Y has a strong incentive not to make the terms of interconnection too onerous for at least some well-connected peers, at risk of cutting its customers off from regions of the Internet) In addition to the intrinsic choice, the overall economic environment in which interconnection agreements are negotiated can be characterized as a free market with a large number of players. Models of interconnection economics have been

developed by <<citations, including “Internet interconnection and the off-net cost pricing principle”: “The purpose of this article is to develop a framework for modeling the competition among interconnected Internet “backbone operators” or “networks.“>> Email Basics Email, short for Electronic Mail, consists of messages which are sent and received using the Internet. There are many different email services available that allow you to create an email account and send and receive email and attachments, many of which are free. Today we will focus on the services available through Yahoo! Mail because it is free and one of the more popular email services available, but we will also give hints, examples and advice for Gmail and the email software programs Outlook, Outlook Express, and Thunderbird. The Pros and Cons of Email The Pros • It's fast. Most messages are delivered within minutes – sometimes seconds – around the world without the inconvenience and cost of using s postal service. In fact, postal service is often referred to as "snail mail" by email users. • It's personal. While the nature of email is informal, its efficiency is an excellent Substitute for telephone conversations. • You can think through your response. Like a letter, you can type your reply and make changes before sending. • The sender and the receiver don't have to be working at the same time. Email avoids problems such as telephone tag or trying to contact someone in a different time zone. • Email makes it easy to keep a record of your communication. You can save and refer to later copies of the emails you send as well as those you receive. • You can reach a lot of people at once. It is possible to send one message to hundreds of recipients at once, or you can send a private message to one individual.

The Cons • Junk Mail (also known as Spam). This is as annoying in email as it is with traditional mail. Try not to send unnecessary messages. • Ads. The reason you can get free email services like Yahoo is because of advertisements. You pay the price of having to click around them to read your mail. • Misinterpretation. Email arrives without tone or hand gestures which can lead to Mis understandings. • Email messages can be passed on to others. You should always count on the possibility of your message ending up in the inbox of someone it wasn't intended for. • You can hide behind email. It's tempting to use email instead of facing a person when you have to deal with an unpleasant situation. It's best to talk to a person face-to-face under these circumstances. Don't use email for: • Long or complicated messages • Sometimes it’s more effective to speak to someone in person or on the phone. It can be difficult to effectively write down a complicated message in email format. • Questions that require a lot of clarification • If a message is going to require several exchanges back and forth to make sure it is understood, more direct communication is best. • Delivering indiscreet, sensitive, or private information • While your Email account is personal, keep in mind that, while rare, passwords have been stolen and there are ways for interested parties to intercept information. • Angry exchanges • Things you should say in person Setting up a Yahoo! Email Account Connect to the Internet by double-clicking the Internet Explorer desktop icon. Go to the Yahoo! Mail site by typing http://mail.yahoo.com into the address bar at the top of the screen. You should see a screen that looks like this: Click on the Sign Up link at the bottom of the box. Checking Your Email with Yahoo!

Once you have set up your email account, you can check your mail anywhere that you can access the Internet. This is how it is done: 1. Connect to the Internet by double-clicking the Internet Explorer desktop icon. 2. Go to the Yahoo! Mail site by typing http://mail.yahoo.com into the address bar at the top of the screen. 3. Type your Yahoo! ID and Password into the box at right. (Don’t forget the @yahoo.com at the end!) 4. The next page will show you the number of new messages in your Inbox Click on the Inbox link in the middle or on the Menu bar at left to retrieve your messages.

5. The Inbox is where all of your incoming messages are stored. Click

Composing and Sending Messages

To compose a message, click the New or Compose button at the top of any screen.

The compose screen (below) is a blank message form.

• From: is your email address, or the address sending the email. Usually this is already filled in with your address • To: is where you type the email address of the primary recipients. • Subject: is a concise indication of the subject of your message. It is important to include a subject line because it will benefit the recipient by allowing them see what your email is about before they open it. It is especially helpful if you are sending email to someone who might not recognize their address. This will help indicate to them that the email is not spam, or junk email. • Add CC / Add BCC: To add secondary addresses to your email, click on these links and additional boxes will appear. • Add CC: CC stands for “carbon copy.” This allows you to “copy” a person on an email that you are sending to someone else. • Add BCC: This is for “blind carbon copies.” If you send a copy of an email to someone by putting their address here, the recipients in the to: and CC: boxes will not be able to see that person’s address.

Composing and Sending Messages, continued The box where you actually type your message is easy to spot because it's the largest one in the window. Click inside to start typing. If you want to change the appearance of your text, you can use the formatting toolbar at the top of the box. The formatting options are similar to those used in Microsoft Word.

Once you have completed your message, send it by clicking on the Send button at the top of the window.

By default, Yahoo! Mail saves the messages you send in your Sent messages folder so you have a record of what you sent and when. You can find your Sent message folder from the main Mail tab in the Menu bar on the left in Yahoo! Mail and on the left side of each page.

Once you have read your message, you have several options. The buttons for each of these options is on or near the toolbar. Look around a little and you will find them!: Replying to the message: Selecting this option will include the original message you were sent and address the message automatically to the person who sent it to you. You can then add text to the existing message and delete portions of the text if you wish before returning your reply to the sender. Click on the Reply button to reply only to the sender. Or, click on the arrow on the Reply button and select “Reply to Everyone” if you prefer to send the message to all recipients of the original message.

Forwarding the Message: This feature copies the message you are viewing for delivery to another email address. You can't see the original message but you can add text at the beginning of the message before sending it. MovingmessagestootherfoldersUse folders to organize your email! Some are already made for you, can see these in the left menu bar on the main mail tab. If you want to create more folders - just click on “Add” at the top. A pop-up box will appear; type the name you want to use and click okay! Messages can be moved to folders by selecting the message from the Inbox by checking the boxes next to each message you want to move. Then click on the “Move” button and choose the desired folder. If you already have the message open, simply click “Move” from the message screen and choose the folder you want to put it in! When you receive a message with an attachment a paper clip appears next to the subject of the message in your inbox window. Click on the subject of the message to open it. At the bottom of the message “header” (aka where the to, from, and subject lines are and before the body of the message, you’ll see a list of the attachments:

Click on the attachment name, and Yahoo! Will scan the attachment for possible viruses and give you a report. Once the document has been determined clean, a box will pop up and you click on “Download Attachment” to download the document to your computer once you click on Download, a box will pop up and ask you if you would like to open the file, or if you would like to save it to a disk: To open the file, click the Open button, and the program that runs this type of file (such as Word) will open with the attached file.

To save the file to your computer, or a floppy disk or USB key: click the Save button. If you choose this option, you won't get to see the contents of the file first. Then you will have to “browse” to where you want to save the file.

What is a web browser? If you want to view web pages on different websites, you will need to use a program called a ‘browser’. This acts as your door to the internet. Browsers are all slightly different, but they all allow you to ‘surf’ the internet and access different websites. Types of browser If you have a Windows device, you’ll have a browser program called Internet Explorer. If you have an Apple product, then you’ll use a browser called Safari. There are also other browsers available, such as Google Chrome and Mozilla Firefox. To access the internet, you’ll firstly need to click or tap on your browser program’s icon. A browser window will open. There are several different functions within this window that allow you to do different things. Web address (or URL) To load a web page you want to view, just type in its web address - also known as it’s ‘URL’ - into the address bar (the space at the top of the window) and then press the ‘Enter’ button. As a shortcut, you can copy and paste a URL into the address bar. The BBC’s website can be found at the address www.bbc.co.uk - this address takes you to the BBC’s ‘homepage’. A homepage - which is a bit like the front page of a newspaper - is an entry point for a website and has links to lots of other web pages on the same site.

Make sure you get all of the words, numbers and punctuation in a web address exactly correct, otherwise it won’t load. If you don’t know the exact address, you can use a search engine (such as Google or Yahoo!) to help you look for it. Links (or hyperlinks) On any page of a website, you will see text links which may be underlined. An image on a web page may also contain a link. By clicking or tapping on a link, you might be taken to a different place on the same web page, a different page on the same website, or another website altogether. You can tell if a piece of text or an image is an active link as your cursor arrow will change in appearance as you hover over the link – for example, the cursor arrow might turn into the shape of a pointing hand. What is a web browser? Backwards, forwards and reloading There are two arrow symbols at the top of your browser window – one pointing left (which is the back icon) and the other pointing right (which is the forward icon). If you want to go back to a previous page, you can click or tap on the back icon. Similarly, you can use the forward icon to go forwards. You may also want to reload the same page - for example, if it’s a breaking news story that is being regularly updated. Some browsers refer to this function as ‘refreshing’ a page. Depending on your browser, the symbol for ‘reload’ or ‘refresh’ may appear as a circular arrow or arrows. Storing favorite’s pages As you browse various web pages, you’ll probably find ones you like and want to visit again. You can use your web browser to save and store links to these pages. Firefox, Chrome and Safari refer to these stored pages as ‘Bookmarks’, while Internet Explorer calls them ‘Favorites’ (spelt the American way). Find the Bookmark or Favorites symbol or tab at the top of the browser window and click on it. A link to your chosen page will either be saved automatically or

you’ll be offered the option of saving it. This function varies from browser to browser (and from device to device), but is usually pretty straightforward. Other features You can also set a ‘homepage’ which loads every time you open your browser program. Your chosen homepage could be the main page of a search engine, the BBC’s homepage, or anything you want. You can change your homepage by going to your browser preferences and changing the address in the relevant box. Your browser stores the address of every page you visit in its ‘History’. This is useful if you visited a page a few days ago and want to view it again, but can’t remember its address or find the website. You can easily delete your History if you want to. Parental controls and cookies You can use security settings to filter out inappropriate material such as violent or adult content. This can be useful if, for example, you have children and want them to browse safely. What is a web browser? Many internet service providers (ISPs) have free parental control software which you can activate at any time. See the UK Safer Internet Centre link at the end of this guide for more details. When you go to a new website you may see a notice about ‘cookies’ on the first page. Cookies are small pieces of data stored on your computer by the website, so the site can remember you the next time you return to it. The notice will tell you how the site uses the data. Finally, if the text on a page is too small for you to easily read, you can ‘zoom in’ to make it bigger. This useful function can be found in the ‘View’ menu.

Search Engine • A search engine is a tool that allows a user to enter keywords and retrieve information on websites Contained in its catalog or database. • Search engine tools like Google are run by search engine software that allows the database to be searched. Features of Search Engine • A true search engine is an automated software program that moves around the Web collecting Webpages to include in its catalog or database. • It searches when a user requests information from a search engine; not the entire Web. • Each search engine has its own catalog or database of collected Webpages, so you will get different Results/hits by using different search engines. Types of Search Engines • There are three main types of search engine tools: – Search directories or indexes – Hybrid search engines – Meta search engines • All of these tools are often referred to as search engines How Are These Tools Different? • A search engine type is determined by how the information contained in its catalog or database is collected the sites in the catalog or database of a search directory or index are compiled by humans; not an automated software program. The sites are submitted, and then assigned to the appropriate category. • Some search directories or indexes do not consider content when adding pages to their catalog. Others collect rate or rank materials. Some search directories include annotations that evaluate, review, or otherwise describe the content. • Yahoo and Look Smart are examples of search directories or indexes.

• Hybrid search engines will present both crawler-based results and human-powered listings. Usually, a hybrid search engine will favor one type of listings over another. • MSN Search is more likely to present human powered listings over its crawler-based results especially for more obscure queries. Multiple (Meta) Search Engines • A Meta search engine is a tool that helps to locate information available via the WWW. • It provides a single interface that enables users to search many different search engines, indexes and Data bases. • Thus Meta search engines are capable of searching several search engine databases at once. The Three Parts of a Search Engine • Spider, crawler or robot • Index, catalog or database • Search engine software • The first part of a search engine is called the spider. The spider (sometimes called a crawler or robot) is a program that moves around the World Wide Web visiting websites. • It reads the webpages it finds and follows the links further down into the website. • The spider returns from time to time and checks for changes. The pages that it finds are placed into the catalog. • The second part of a search engine is called the index, catalog, or database. • This index contains a copy of each page that was collected by the spider. • A spidered page must be indexed to become a search result.

• When a user requests keywords from a search engine, the search engine software sifts through all the indexed pages to find matching keywords, then returns the results/hits to the user. Successful Search Skills • Before you ever open your internet browser, prepare a list of keywords. This will help to eliminate being overwhelmed with millions of results/hits. • Follow these guidelines to create your list of keywords: 1. Identify the main concepts of your topic 2. List keywords for each concept 3. Include synonyms and alternate spellings 4. Determine the logical relationships between your keywords. Example: searching for the phrase “river boats” will bring you more relevant results/hits than searching for river AND boats or +river +boats • Use the advance search in which we can search information in a particular format. • Use image option for search only images about the specific topic. Use the Boolean Logic • AND – Requires all of the search terms to appear on a page • OR – Allows any of the search terms to appear on a page •NOT

– Requires a search term to not be present on a page Search Again in Different Search Engines • Each search engine has its own database of cataloged webpages • One search engine may return results/hits that another one doesn’t • No search engine covers the entire World Wide Web HTTP HTTP is the protocol used to communicate between a client and a server. HTTP defines what characters can be sent along the socket stream connection. The basic protocol is request and response. The server accepts a connection and the client sends a request command line, various optional MIME lines and then a blank. The server must then send a response line giving a success or failure code, followed by additional optional lines, then the blank line and finally, if a file was successfully requested, the file contents (whether HTML, GIF or whatever). That’s it. Except to look at a request and a response... Using a “dumb server” it is possible to capture and print the HTTP sent by clients. The program binds a high numbered port, says 8080, and accepts connections. It then just reads all the data from the socket and prints it on the standard output. Then it just closes the socket and causes the client to report an error. This is the HTTP request and options sent from net scape when it was given a URI

The standard output from the “dumb server” was: GET /abc.html HTTP/1.0 Connection: Keep-Alive User-Agent: Mozilla/4.7 [en] (X11; I; Linux 2.3.34 i686) Host: local host: 8080 Accept: image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, image/png, */*

Accept-Encoding: gzip Accept-Language: en Accept-Charset: iso-8859-1,*, utf-8

There are only 2 really essential parts: 1. The request line. It includes the command, in this case GET, the request file name, here /abc.html and the protocol version. 2. The other essential part is the blank line at the end. The other lines are optional. Some are very important and useful but are not obligatory. Similarly it is possible to examine the responses from servers by using a “dumb client” that sends a request to a server and prints out the complete response. This will show the HTTP response line with the status code, various optional lines, a blank line then the retrieved file if any. It is not possible to see the response from servers using a normal browser because they process the response lines and don’t show them. The example apache responded to:

The OSI and TCP/IP layers There is another (less used) view of layers called the ISO Open Systems Interconnection:

The TCP/IP can be seen as a simplification of the OSI levels: • The service level, 7–5 merged as the process or application layer. They provide FTP, Telnet, NFS, X11 and other higher level protocols.

• The transport layer, (the OSI layer 4) the link between different processes on different systems, the bit provided by TCP. • The network layer (OSI layer 3), that links systems across one or more networks, it provides internet working. The IP bit. • The data-link layer, (OSI layers 2 & 1). It is a network, for example Ethernet with its hardware and low-level protocols for moving data between 2 directly connected systems. Two very important concepts in understanding networking are protocols and service layers. Figure 1.1 is a simplified view of the layers of network service in TCP/IP.

Relationship between protocols and layers If a browser communicates with a web server they exchange messages (using the HTTP protocol), the messages are simple character strings: • In order for the browser to send the HTTP message it must request that the layer below it (the transport layer) opens a connection to the server on the remote machine.

• The transport layer has to communicate with its peer, (the transport layer software on the remote machine) to establish the connection to the web server. Peers at the transport layer use the TCP protocol. • In order for the transport layer to send its TCP messages it breaks them into “packets” and requests that the network layer below it sends these packets to the remote machine which will pass them up to the peer transport layer. • The network layer uses the IPv4 (and soon IPv6) protocol. It also uses a routing protocol to work out which machine to send to in order to get the remote end. and it must ask the data link layer . . . This is very similar to using the Post Office to convey letters. • You write to your friend, the letter is your message (what you say in the letter and how they respond is your “protocol”), you put it in an envelope, put the address on the front and pass it down to the next “layer”—the postal service, • The local postal service sorts the letters and puts them in bags for different destinations, these are labeled. The bags are then given to an airline or a railway that uses the labels to deliver them to the remote postal service, • The remote postal service unpacks the bags and delivers the letters. Notice that it is necessary to have a “protocol” that is understood by the lower layer (TCP, or postal service bag labels) in order for messages from a higher level to be delivered. Notice also that the layer below knows nothing about the higher level protocol (whether it is HTTP or the contents of your letter).