NEETU MARWAH

MBA (BANKING & INSURANCE)

INFORMATION TECHNOLOGY

ASSIGNMENT

The Five Generations of Computers

The history of computer development is often referred to in reference to the different generations of computing devices. Each of the five generations of computers is characterized by a major technological development that fundamentally changed the way computers operate.

The history of computer development is often referred to in reference to the different generations of computing devices. Each of the five generations of computers is characterized by a major technological development that fundamentally changed the way computers operate, resulting in increasingly smaller, cheaper, more powerful and more efficient and reliable computing devices.

First Generation (1940-1956) Vacuum Tubes

The first computers used vacuum tubes for circuitry and magnetic drums for memory, and were often enormous, taking up entire rooms. They were very expensive to operate and in addition to using a great deal of electricity, generated a lot of heat, which was often the cause of malfunctions. First generation computers relied on machine language, the lowest-level programming language understood by computers, to perform operations, and they could only solve one problem at a time. Input was based on punched cards and paper tape, and output was displayed on

printouts.The UNIVAC and ENIAC computers are examples of first-generation computing devices. The UNIVAC was the first commercial computer delivered to a business client, the U.S. Census Bureau in 1951.

Second Generation (1956-1963) Transistors

Transistors replaced vacuum tubes and ushered in the second generation of computers. The transistor was invented in 1947 but did not see widespread use in computers until the late 1950s. The transistor was far superior to the vacuum tube, allowing computers to become smaller, faster, cheaper, more energy-efficient and more reliable than their first-generation predecessors. Though the transistor still generated a great deal of heat that subjected the computer to damage, it was a vast improvement over the vacuum tube. Second-generation computers still relied on punched cards for input and printouts for output.

Second-generation computers moved from cryptic binary machine language to symbolic, or assembly, languages, which allowed programmers to specify instructions in words. High-level programming languages were also being developed at this time, such as early versions of COBOL and FORTRAN. These were also the first computers that stored their instructions in their memory, which moved from a magnetic drum to magnetic core technology.

The first computers of this generation were developed for the atomic energy industry.

Third Generation (1964-1971) Integrated Circuits

The development of the integrated circuit was the hallmark of the third generation of computers. Transistors were miniaturized and placed on silicon chips , called semiconductors, which drastically increased the speed and efficiency of computers.

Instead of punched cards and printouts, users interacted with third generation computers through keyboards and monitors and interfaced with an operating system, which allowed the device to run many different applications at one time with a central program that monitored the memory. Computers for the first time became accessible to a mass audience because they were smaller and cheaper than their predecessors.

Fourth Generation (1971-Present) Microprocessors

The microprocessor brought the fourth generation of computers, as thousands of integrated circuits were built onto a single silicon chip. What in the first generation filled an entire room could now fit in the palm of the hand. The Intel 4004 chip, developed in 1971, located all the components of the computer—from the central processing unit and memory to input/output controls—on a single chip.

In 1981 IBM introduced its first computer for the home user, and in 1984 Apple introduced the Macintosh. Microprocessors also moved out of the realm of desktop

computers and into many areas of life as more and more everyday products began to use microprocessors.

As these small computers became more powerful, they could be linked together to form networks, which eventually led to the development of the Internet. Fourth generation computers also saw the development of GUIs, the mouse and handheld devices.

Fifth Generation (Present and Beyond) Artificial Intelligence

Fifth generation computing devices, based on artificial intelligence, are still in development, though there are some applications, such as voice recognition, that are being used today. The use of parallel processing and superconductors is helping to make artificial intelligence a reality. Quantum computation and molecular and nanotechnology will radically change the face of computers in years to come. The goal of fifth-generation computing is to develop devices that respond to natural language input and are capable of learning and self-organization.

Basic levels of the Computer

1) Software2) Hardware3) Liveware - Person who operates it4) Firm- Computer Language (0 and 1)

HARDWARE

INPUT DEVICES OUTPUT DEVICES

1)KEYBOARD 1)MONITOR

2)MOUSE 2)PRINTER3)MICROPHONE 3)SPEAKERS4)WEBCAMERA 4)PROJECTOR5)SCANNER 5)SPEAK SYNTHERG6)JOYSTICK7)TOUCHPAD8)TRACKBALL

Hardware Components

The Motherboard

The motherboard, also called the logic board or main board, is a board with electrical circuits printed on it that holds many of the computer's essential components. The electrical circuits on the board allow the components to receive power and communicate with each other.

A desktop computer motherboard usually contains the CPU and the main memory, and you can attach graphics and sound cards, memory, and other peripherals to them with cards or cables. It's also very common for manufacturers to integrate some of these components directly onto the motherboard itself.

Integrated boards are usually less expensive and easier to manage since they come in a nice, tidy package. But they don’t offer the best performance, you can’t upgrade the components, and if something breaks on

an integrated board, you have to replace the whole board

The CPU

The CPU, or Central Processing Unit, is the brain of the computer. CPUs do two major things: performing mathematical and logical operations (in other words, making the computer do stuff), and retrieving and carrying out instructions from the computer's memory.

In personal computers, the CPU is a small, square chip with many little metallic pins sticking out of it called a microprocessor, and is attached directly to the motherboard. Since they create a lot of heat, modern CPUs have a heat sink and small fan attached to keep them cool.

If something goes wrong with your CPU, it can be replaced but it's a good idea to let a professional do it. They can be expensive, and it's easy to accidentally bend the pins when trying to install it.

COMPONENTS OF THE CPU

1)CONTROL UNIT

2)ARTHMETIC LOGIC UNIT

3)MEMORY UNIT

A computer can have more than one CPU; this is called multiprocessing. Some integrated circuits (ICs) can contain multiple CPUs on a single chip; those ICs are called multi-core processors.

Two typical components of a CPU are the arithmetic logic unit (ALU), which performs arithmetic and logical

operations, and the control unit (CU), which extracts instructions from memory and decodes and executes them, calling on the ALU when necessary.

Not all computational systems rely on a central processing unit. An array processor or vector processor has multiple parallel computing elements, with no one unit considered the "center". In the distributed computing model, problems are solved by a distributed interconnected set of processors.The abbreviation CPU is sometimes used incorrectly by people who are not computer specialists to refer to the cased main part of a desktop computer containing the motherboard, processor, disk drives, etc., i.e., not the display monitor or keyboard.

MEMORY OF THE COMPUTER

Primary memorySecondary memory

1) It is fixed.1) It is Movable.

2) Low capacity 2) It is high capacity.

3) It has More Speed.3) It has Less Speed

Eg; RAM- Random Access Memory,Eg: CD, Pendrive, Harddisk.

ROM- Read Only Memory.

MEMORY: In computing, memory refers to the physical devices used to store programs (sequences of

instructions) or data (e.g. program state information) on a temporary or permanent basis for use in a computer or other digital electronic device. The term primary memory is used for the information in physical systems which function at high-speed (i.e. RAM), as a distinction from secondary memory, which are physical devices for program and data storage which are slow to access but offer higher memory capacity. Primary memory stored on secondary memory is called "virtual memory". An archaic synonym for memory is store.[1]

PRIMARY MEMORY ; The term "memory", meaning primary memory is often associated with addressable semiconductor memory, i.e. integrated circuits consisting of silicon-based transistors, used for example as primary memory but also other purposes in computers and other digital electronic devices. There are two main types of semiconductor memory: volatile and non-volatile. Examples of non-volatile memory are flash memory (sometimes used as secondary, sometimes primary computer memory) and ROM/PROM/EPROM/EEPROM memory (used for firmware such as boot programs). Examples of volatile memory are primary memory (typically dynamic RAM, DRAM), and fast CPU cache memory (typically static RAM, SRAM, which is fast but energy-consuming and offer lower memory capacity per area unit than DRAM) .

SECONDARY MEMORY : The term storage is often used to describe secondary memorysuch as tape, magnetic disks and optical discs (CD-ROM and DVD-ROM).

In the early 1940s, memory technology mostly permitted a capacity of a few bytes. The first electronic programmable digital computer, the ENIAC, using thousands of octal-base radio vacuum tubes, could perform simple calculations involving 20 numbers of

ten decimal digits which were held in the vacuum tube accumulators.

The next significant advance in computer memory came with acoustic delay line memory, developed by J. Presper Eckert in the early 1940s. Through the construction of a glass tube filled with mercury and plugged at each end with a quartz crystal, delay lines could store bits of information within the quartz and transfer it through sound waves propagating through mercury. Delay line memory would be limited to a capacity of up to a few hundred thousand bits to remain efficient.

Two alternatives to the delay line, the Williams tube and Selectron tube, originated in 1946, both using electron beams in glass tubes as means of storage. Using cathode ray tubes, Fred Williams would invent the Williams tube, which would be the first random access computer memory. The Williams tube would prove more capacious than the Selectron tube (the Selectron was limited to 256 bits, while the Williams tube could store thousands) and less expensive. The Williams tube would nevertheless prove to be frustratingly sensitive to environmental disturbances.

Efforts began in the late 1940s to find non-volatile memory. Jay Forrester, Jan A. Rajchman and An Wang developed magnetic core memory, which allowed for recall of memory after power loss. Magnetic core memory would become the dominant form of memory until the development of transistor-based memory in the late 1960s.

Developments in technology and economies of scale have made possible so-called Very Large Memory (VLM) computers.The term "memory" when used with

reference to computers generally refers to Random Access Memory or RAM.

Volatile memoryis computer memory that requires power to maintain the stored information. Most modern semiconductor volatile memory is either Static RAM (see SRAM) or dynamic RAM (see DRAM). SRAM retains its contents as long as the power is connected and is easy to interface to but uses six transistors per bit. Dynamic RAM is more complicated to interface to and control and needs regular refresh cycles to prevent its contents being lost. However, DRAM uses only one transistor and a capacitor per bit, allowing it to reach much higher densities and, with more bits on a memory chip, be much cheaper per bit. SRAM is not worthwhile for desktop system memory, where DRAM dominates, but is used for their cache memories. SRAM is commonplace in small embedded systems, which might only need tens of kilobytes or less. Forthcoming volatile memory technologies that hope to replace or compete with SRAM and DRAM include Z-RAM, TTRAM, A-RAM and ETA RAM.

Non-volatile memory

Non-volatile memory is computer memory that can retain the stored information even when not powered. Examples of non-volatile memory include read-only memory (see ROM), flash memory, most types of magnetic computer storage devices (e.g. hard disks, floppy discs and magnetic tape), optical discs, and early computer storage methods such as paper tape and punched cards. Forthcoming non-volatile memory technologies include FeRAM, CBRAM, PRAM, SONOS, RRAM, Racetrack memory, NRAM and Millipede.

Virtual memory

Virtual memory is a system where all physical memory is controlled by the operating system. When a program needs memory, it requests it from the operating system. The operating system then decides what physical location to place the memory in.

This offers several advantages. Computer programmers no longer need to worry about where the memory is physically stored or whether the user's computer will have enough memory. It also allows multiple types of memory to be used. For example, some memory can be stored in physical RAM chips while other memory is stored on a hard drive. This drastically increases the amount of memory available to programs. The operating system will place actively used memory in physical RAM, which is much faster than hard disks. When the amount of RAM is not sufficient to run all the current programs, it can result in a situation where the computer spends more time moving memory from RAM to disk and back than it does accomplishing tasks; this is known as thrashing.

Virtual memory systems usually include protected memory, but this is not always the case.

Protected memory

Protected memory is a system where each program is given an area of memory to use and is not permitted to go outside that range. Use of protected memory greatly enhances both the reliability and security of a computer system.

Without protected memory, it is possible that a bug in one program will alter the memory used by another program. This will cause that other program to run off

of corrupted memory with unpredictable results. If the operating system's memory is corrupted, the entire computer system may crash and need to be rebooted. At times programs intentionally alter the memory used by other programs. This is done by viruses and malware to take over computers.

Protected memory assigns programs their own areas of memory. If the operating system detects that a program has tried to alter memory that does not belong to it, the program is terminated. This way, only the offending program crashes, and other programs are not affected by the error.

Protected memory systems almost always include virtual memory as well.

DIFFERENT CLASSES OF SOFTWARE OF THE COMPUTER

Types of softwares

A layer structure showing where the operating system software and application software are situated while running on a typical desktop computerSoftware encompasses a wide array of products that may be developed using different techniques such as ordinary programming languages, microcode, or an FPGAconfigurationOn virtually all computer platforms, software can be grouped into a few broad categories:

System softwareis computer software designed to operate the computer hardware, to provide basic functionality, and to provide a platform for running application software.System software includes device drivers, operating systems, servers, utilities, and window systems. System software also includes the boot firmware , which loads (or in some cases constitutes) the operating system. Firmware is software that has been permanently stored in hardware (specifically, in non-volatile memory). Thus, it has

qualities of both software and hardware, but it is still software.

Application softwareand scripts were historically defined as all the software that uses the computer system to perform useful work (or entertainment functions) beyond the basic operation of the computer itself. However, in practice the distinction between system software and application software is often blurred due to bundling of useful applications with the operating system.Application software includes desktop applications such as web browsers and Microsoft Office, as well as smartphone and tablet applications (called "apps").

Javascript scripts are pieces of software traditionally embedded in web pages that are run directly inside the web browser when a web page is loaded, without the need for a web browser plugin. Software written in other programming languages can also be run within the web browser if the software is either translated into Javascript, or if a web browser plugin that supports that language is installed; the most common example of the latter is ActionScript scripts, which are supported by the Adobe Flash .

Web applications usually run on the web server and output dynamically-generated web pages to web browsers, using e.g. PHP, Java or ASP.NET, or even Javascript that runs on the server; in modern times they commonly include some Javascript to be run in the web browser as well, in which case they typically run partly on the server, partly in the web browser.

Plugins and extensions are software that extends or modifies the functionality of another piece of software, and require that software be used in order to function;

Embedded software resides as firmware within embedded systems, devices dedicated to a single use or a few uses such as cars and televisions (although some embedded devices such as wireless chipsets can themselves be part of an ordinary, non-embedded computer system such as a PC or smartphone). In the embedded system context there is sometimes no clear distinction between the system software and the application software. However, some embedded systems run embedded operating systems, and these systems do retain the distinction between system software and application software (although typically there will only be one, fixed, application which is always ran).

Microcodeis a special, relatively obscure type of embedded software which tells the processor itself how to execute machine code, so it is actually a lower level than machine code. It is typically proprietary to the processor manufacturer, and any necessary correctional microcode software updates are supplied by them to users (which is much cheaper than shipping replacement processor hardware). Thus an ordinary programmer would not expect to ever have to deal with it.

NETWORKING

What is a Network?

A network consists of two or more computers that are linked in order to share resources (such as printers and CDs), exchange files, or allow electronic communications. The computers on a network may be linked through cables, telephone lines, radio waves, satellites, or infrared light beams.

Two very common types of networks include:

1. Local Area Network (LAN)2. Wide Area Network (WAN)

You may also see references to a Metropolitan Area Networks (MAN), a Wireless LAN (WLAN), or a Wireless WAN (WWAN).

Local Area Network

A Local Area Network (LAN) is a network that is confined to a relatively small area. It is generally limited to a geographic area such as a writing lab, school, or building.

Computers connected to a network are broadly categorized as servers or workstations. Servers are generally not used by humans directly, but rather run continuously to provide "services" to the other computers (and their human users) on the network. Services provided can include printing and faxing, software hosting, file storage and sharing, messaging, data storage and retrieval, complete access control (security) for the network's resources, and many others.

Workstations are called such because they typically do have a human user which interacts with the network through them. Workstations were traditionally

considered a desktop, consisting of a computer, keyboard, display, and mouse, or a laptop, with integrated keyboard, display, and touchpad. With the advent of the tablet computer, and the touch screen devices such as iPad and iPhone, our definition of workstation is quickly evolving to include those devices, because of their ability to interact with the network and utilize network services.

Servers tend to be more powerful than workstations, although configurations are guided by needs. For example, a group of servers might be located in a secure area, away from humans, and only accessed through the network. In such cases, it would be common for the servers to operate without a dedicated display or keyboard. However, the size and speed of the server's processor(s), hard drive, and main memory might add dramatically to the cost of the system. On the other hand, a workstation might not need as much storage or working memory, but might require an expensive display to accommodate the needs of its user. Every computer on a network should be appropriately configured for its use.

On a single LAN, computers and servers may be connected by cables or wirelessly. Wireless access to a wired network is made possible by wireless access points (WAPs). These WAP devices provide a bridge between computers and networks. A typical WAP might have the theoretical capacity to connect hundreds or even thousands of wireless users to a network, although practical capacity might be far less.

Nearly always servers will be connected by cables to the network, because the cable connections remain the fastest. Workstations which are stationary (desktops) are also usually connected by a cable to the network, although the cost of wireless adapters has dropped to

the point that, when installing workstations in an existing facility with inadequate wiring, it can be easier and less expensive to use wireless for a desktop.

See the Topology, Cabling, and Hardware sections of this tutorial for more information on the configuration of a LAN.

TYPES OF LAN

1)Client server network2)PEER to PEER network

SERVER:A computer or device on a network that manages network resources. There are many different types of servers. For example:

File server: A computer and storage device dedicated to storing files . Any user on the network can store files on the server.

Print server : A computer that manages one or more printers, and a network server is a computer that manages network traffic.

Database server: Acomputer system that processes database queries .

Servers are often dedicated, meaning that they perform no other tasks besides their server tasks. On multiprocessing operating systems , however, a single computer can execute several programs at once. A server in this case could refer to the program that is managing resources rather than the entire computer.

Client Server Network : Advantages and Disadvantages

The term client-server refers to a popular model for computer networking that utilizes client and server devices each designed for specific purposes. The client-server model can be used on the Internet as well as local area networks (LANs). Examples of client-server systems on the Internet include Web browsers and Web servers, FTP clients and servers, and the DNS.

Client and Server DevicesClient/server networking grew in popularity many years ago as personal computers (PCs) became the common alternative to older mainframe computers. Client devices are typically PCs with network software applications installed that request and receive information over the network. Mobile devices as well as desktop computers can both function as clients.

A server device typically stores files and databases including more complex applications like Web sites. Server devices often feature higher-powered central processors, more memory, and larger disk drives than clients.

Client-Server ApplicationsThe client-server model distinguishes between applications as well as devices. Network clients make requests to a server by sending messages, and servers respond to their clients by acting on each request and returning results. One server generally supports numerous clients, and multiple servers can be networked together in a pool to handle the increased processing load as the number of clients grows.

A client computer and a server computer are usually two separate devices, each customized for their designed purpose. For example, a Web client works best with a large screen display, while a Web server does not need any display at all and can be located anywhere in the world. However, in some cases a given device can function both as a client and a server for the same application. Likewise, a device that is a server for one application can simultaneously act as a client to other servers, for different applications.

[Some of the most popular applications on the Internet follow the client-server model including email, FTP and Web services. Each of these clients features a user interface (either graphic- or text-based) and a client application that allows the user to connect to servers. In the case of email and FTP, users enter a computer name (or sometimes an IP address) into the interface to set up connections to the server.

Local Client-Server Networks

Many home networks utilize client-server systems without even realizing it. Broadband routers, for example, contain DHCP servers that provide IP addresses to the home computers (DHCP clients). Other

types of network servers found in home include print servers and backup servers.

P2P - What is Peer-to-Peer ?

In its simplest form, a peer-to-peer (P2P) network is created when two or more PCs are connected and share resources without going through a separate server computer. A P2P network can be an ad hoc connection—a couple of computers connected via a Universal Serial Bus to transfer files. A P2P network also can be a permanent infrastructure that links a half-dozen computers in a small office over copper wires. Or a P2P network can be a network on a much grander scale in which special protocols and applications set up direct relationships among users over the Internet.

Figure : P2P network

A peer-to-peer (P2P) network is a type of decentralized and distributed network architecture in which individual nodes in the network (called "peers") act as both suppliers and consumers of resources, in contrast to the centralized client–server model where client nodes request access to resources provided by central servers.

In a peer-to-peer network, tasks (such as searching for files or streaming audio/video) are shared amongst multiple interconnected peers who each make a portion of their resources (such as processing power, disk storage or network bandwidth) directly available to other network participants, without the need for centralized coordination by servers.[

TYPES OF SERVERS

In a medium to large network, there can be many servers with each performing a different task:

Server Types

Proxy ServersA proxy server sits between a client program (typically a Web browser) and an external server (typically another server on the Web) to filter requests, improve performance, and share connections.

Mail ServersAlmost as ubiquitous and crucial as Web servers, mail servers move and store mail over corporate networks (via LANs and WANs) and across the Internet.

Server PlatformsA term often used synonymously with operating system, a platform is the underlying hardware or software for a system and is thus the engine that drives the server.

Web ServersAt its core, a Web server serves static content to a Web browser by loading a file from a disk and serving it across the network to a user's Web browser. This entire exchange is mediated by the browser and server talking to each other using HTTP.

Application ServersSometimes referred to as a type of middleware, application servers occupy a large chunk of computing territory between database servers and the end user, and they often connect the two.

Components of the server

Router (computing)

A Cisco ASM/2-32EM router deployed at CERN in 1987

A router is a device that forwards data packets between computer networks, creating an overlay internetwork. A

router is connected to two or more data lines from different networks. When a data packet comes in one of the lines, the router reads the address information in the packet to determine its ultimate destination. Then, using information in its routing table or routing policy, it directs the packet to the next network on its journey. Routers perform the "traffic directing" functions on the Internet. A data packet is typically forwarded from one router to another through the networks that constitute the internetwork until it reaches its destination node.[1]

The most familiar type of routers are home and small office routers that simply pass data, such as web pages, email, IM, and videos between the home computers and the Internet. An example of a router would be the owner's cable or DSL modem, which connects to the Internet through an ISP. More sophisticated routers, such as enterprise routers, connect large business or ISP networks up to the powerful core routers that forward data at high speed along the optical fiber lines of the Internet backbone. Though routers are typically dedicated hardware devices, use of software-based routers has grown increasingly common.

Bridge:-

Definition of the bridge:A bridge device filters data traffic at a network boundary. Bridges reduce the amount of traffic on a LAN by dividing it into two segments.

Bridges operate at the data link layer (Layer 2) of the OSI model. Bridges inspect incoming traffic and decide whether to forward or discard it. An Ethernet bridge, for example, inspects each incoming Ethernet frame -

including the source and destination MAC addresses, and sometimes the frame size - in making individual forwarding decisions.

Bridges serve a similar function as switches, that also operate at Layer 2. Traditional bridges, though, support one network boundary, whereas switches usually offer four or more hardware ports. Switches are sometimes called "multi-port bridges" for this reason.

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 packetarrives 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. So-called 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.

Introduction to Hubs

A special type of network device called the hub can be found in many home and small business networks. Though they've existed for many years, the popularity of hubs has exploded recently, especially among people relatively new to networking. Do you own a hub, or are you considering purchasing one? This article explains the purpose of hubs and some of the technology behind them...

General Characteristics of Hubs

A hub is a small rectangular box, often made of plastic, that receives its power from an ordinary wall outlet. A hub joins multiple computers (or other network devices) together to form a single network segment. On this network segment, all computers can communicate directly with each other. Ethernet hubs are by far the most common type, but hubs for other types of networks such as USB also exist.

A hub includes a series of ports that each accept a network cable. Small hubs network four computers. They contain four or sometimes five ports, the fifth port being reserved for "uplink" connections to another hub

or similar device. Larger hubs contain eight, 12, 16, and even 24 ports.

Key Features of Hubs

Hubs classify as Layer 1 devices in the OSI model. At the physical layer, hubs can support little in the way of sophisticated networking. Hubs do not read any of the data passing through them and are not aware of their source or destination. Essentially, a hub simply receives incoming packets, possibly amplifies the electrical signal, and broadcasts these packets out to all devices on the network - including the one that originally sent the packet!

Technically speaking, three different types of hubs exist:

Passive Active Intelligent

Passive hubs do not amplify the electrical signal of incoming packets before broadcasting them out to the network. Active hubs, on the other hand, do perform this amplification, as does a different type of dedicated network device called a repeater. Some people use the terms concentrator when referring to a passive hub and multiport repeater when referring to an active hub.

Intelligent hubs add extra features to an active hub that are of particular importance to businesses. An intelligent hub typically is stackable (built in such a way that multiple units can be placed one on top of the other to conserve space). It also typically includes remote management capabilities via SNMP and virtual LAN (VLAN) support.

Hubs remain a very popular device for small networks because of their low cost. A good five-port Ethernet hub can be purchased for less than $30 USD. USB hubs cost only a bit more.

Gateways

A gateway is a device used to connect networks using different protocols. Gateways operate at the network layer of the OSI model. In order to communicate with a host on another network, an IP host must be configured with a route to the destination network. If a configuration route is not found, the host uses the gateway (default IP router) to transmit the traffic to the destination host. The default t gateway is where the IP sends packets that are destined for remote networks. If no default gateway is specified, communication is limited to the local network. Gateways receive data from a network using one type of protocol stack, removes that protocol stack and repackages it with the protocol stack that the other network can use.

Examples

E-mail gateways-for example, a gateway that receives Simple Mail Transfer Protocol (SMTP) e-mail, translates it into a standard X.400 format, and forwards it to its destination

Gateway Service for NetWare (GSNW), which enables a machine running Microsoft Windows NT Server or Windows Server to be a gateway for Windows clients so that they can access file and print resources on a NetWare server

Gateways between a Systems Network Architecture (SNA) host and computers on a TCP/IP network, such as the one provided by Microsoft SNA Server

A packet assembler/disassemble (PAD) that provides connectivity between a local area network (LAN) and an X.25 packet-switching network

DIAL UP NETWORKING: Dial up networking technology provides PCs and other network devices access to a LAN or WAN via standard telephone lines. Dial up Internet service providers offer subscription plans for home computer users.

Types of dial up services include V.34 and V.90 modem as well as Integrated Services Digital Network (ISDN). Dial up systems utilize special-purpose network protocols like Point-to-Point Protocol (PPP).

To use a dial up Internet connection, a client modem calls another modem located at the Internet Service Provider (ISP). The modems transfer network information over the telephone until one modem or the other disconnects.

When the popularity of the Internet exploded in the 1990s, dial up was the most common form of Internet access due mainly to its low cost to setup. However, the performance of dial up networking is relatively poor due to the limitations of traditional modem technology. V.90 modem dial up supports less than 56 Kbps bandwidth and ISDN handles approximately 128Kbps.

Many home users are currently replacing their dial up services with high-speed broadband technologies that operate at much higher speeds.

Modulation and Demodulation( MODEM) : A modem (modulator-demodulator) is 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 with any means of transmitting analog signals, from light emitting diodes to radio. The most familiar example is a voice band modem that turns the digital data of a personal computer into modulated electrical signals in the voice frequency range of a telephone channel. These signals can be transmitted over telephone lines and demodulated by another modem at the receiver side to recover the digital data.

ISDN (Integrated Service Digital Network) :

ISDN stands for Integrated Services Digital Network. It is a design for a completely digital telephone/telecommunications network. It is designed to carry voice, data, images, video and everything you could ever need. It is also designed to provide a single interface (in terms of both hardware and communication protocols) for hooking up your phone, your fax machine, your computer, your videophone, your video-on-demand system (someday), and your microwave. ISDN is about what the future phone network, and information superhighway, will look like (or would have looked like).

ISDN was originally envisioned as a very fast service, but this was a long time ago when it was hoped to have fiber all the way to your house. It turned out that running all that fiber would be too expensive, so they designed ISDN to run on the copper wiring that you already have. Unfortunately, that slowed things down considerably - too slow for quality video, for instance.

ISDN has been very slow in coming. The standards organizations have taken their time in coming up with the standards. In fact, many people consider them to be out of date already. But on the other side of the coin, the phone companies (especially in the U.S.) have been very slow at designing products and services, or marketing them with ISDN in mind.

Things are starting to pick up, but still very slowly. ISDN is available now in many places, but it is not widely used. Further most of the products and services that people have forecast for ISDN still aren't available. For this reason many people say that ISDN also stands for "It Still Does Nothing".

Digital Subscriber Line (DSL):

When you connect to the Internet, you might connect through a regular modem, through a local-area network connection in your office, through a cable modem or through a digital subscriber line (DSL) connection. DSL is a very high-speed connection that uses the same wires as a regular telephone line.

Here are some advantages of DSL:

You can leave your Internet connection open and still use the phone line for voice calls.

The speed is much higher than a regular modem DSL doesn't necessarily require new wiring; it can

use the phone line you already have. The company that offers DSL will usually provide

the modem as part of the installation.

But there are disadvantages:

A DSL connection works better when you are closer to the provider's central office. The farther away you get from the central office, the weaker the signal becomes.

The connection is faster for receiving data than it is for sending data over the Internet.

The service is not available everywhere.

In this article, we explain how a DSL connection manages to squeeze more information through a standard phone line -- and lets you make regular telephone calls even when you're online.

Telephone Lines

If you have read How Telephones Work, then you know that a standard telephone installation in the United States consists of a pair of copper wires that the phone company installs in your home. The copper wires have lots of room for carrying more than your phone conversations -- they are capable of handling a much greater bandwidth, or range of frequencies, than that demanded for voice. DSL exploits this "extra capacity" to carry information on the wire without disturbing the line's ability to carry conversations. The entire plan is based on matching particular frequencies to specific tasks.

To understand DSL, you first need to know a couple of things about a normal telephone line -- the kind that telephone professionals call POTS, for Plain Old Telephone Service. One of the ways that POTS makes the most of the telephone company's wires and equipment is by limiting the frequencies that the

switches, telephones and other equipment will carry. Human voices, speaking in normal conversational tones, can be carried in a frequency range of 0 to 3,400 Hertz (cycles per second -- see How Telephones Work for a great demonstration of this). This range of frequencies is tiny. For example, compare this to the range of most stereo speakers, which cover from roughly 20 Hertz to 20,000 Hertz. And the wires themselves have the potential to handle frequencies up to several million Hertz in most cases.

The use of such a small portion of the wire's total bandwidth is historical -- remember that the telephone system has been in place, using a pair of copper wires to each home, for about a century. By limiting the frequencies carried over the lines, the telephone -system can pack lots of wires into a very small space without worrying about interference between lines. Modern equipment that sends digital rather than analog data can safely use much more of the telephone line's capacity. DSL does just that.

A DSL internet connection is one of many effective communication tools for keeping employees in touch with the office.

LEASED LINES:

What is Leased Line?

Permanent point to point connections

Ideal for linking two offices Always-on, uncontended symmetric data Fixed monthly charges Quality of Service network guarantee

A leased line is a permanent, always on connection between two locations. It is a dedicated, private line and only carries communications and traffic from your company, resulting in a guaranteed level of service. The line can be used for data, video and voice and is most effective when sharing bandwidth hungry applications between different offices. High speed connections up to 1Gig are available.

Benefits from a Leased Line?

Companies with separate office locations that regularly share a lot of data

Companies with separate office locations who want to use VoIP

What benefits would a Leased Line bring my business?

Cost effective for heavy Internet users. High speed data throughput. Private connection with no contention ratios. Fixed charges regardless of usage, allowing

accurate budgeting. A guaranteed high level of service with vastly

reduced latency and jitter.

NETWORK TOPOLOGY:-

Network topology is the study of arrangement are mapping of the elements (links, nodes) of the network. Especially physical (real) and logical (virtual ) interconnection between nodes.

A local Area network ( LAN) is one example of a network that exhibits both physical and logical topology.

Any particular network topology is determined only by the graphical mapping of the configuration of physical and /or logical connections between nodes.

BUS TOPOLOGY:

In a bus network all the computers or nodes are connected to a single communication cable which has two end points. A special device called transmission is not connected the network will start malfuhetioting.

When a device sends a packed of information and in the networks every oftain device sees and reads the packed. It some of those packed collects. The sending device waits and files tries to transmit again.

This topology is frequently used with LAM.

Advantage Of Bus Topology

1. Easy to implement and extend.2. Well suited for small networks and requiring high

speeds.3. Cost effective as only a single cable is used.4. Cable faults are easily identified can be organised as

a clients/severs as pees to pees network.

Disadvantages Of Bus Topology

1. An extra software is required to avoid collisions between date. If a connection is a Bus is broken the entire network may stop working.

2. Performance degrades as additional computers are added.

3. Proper termination is required ( loop must be in close path)

4. In is slower than other topologies.

RING TOPOLOGY:

A ring network is one in which all micro computers and other communication devices are connected in a continuous. Loop there are no. endpoints there is no. central server. The electronic messages are passed around the ring until they reach the right destination.

Advantages : The messages flow in only one dissection thus, there is no danger of collision.

Disadvantages : If a connection is broken the entire network stop.

STAR TOPOLOGY:

A star network is one in which all microcomputers and other communication devices are directly connected to a central through the central server to their destination .

Advantages :

Server prevents collision between massages.

If a connection between any communication device on the network will continue operating.

Disadvantages :

If the HUB stops the entire network stops.

MESH TOPOLOGY :

In mesh topology every node is connected to every other node in the network this type of topology is very expensive as there are many redundant connections. Therefore it is not mostly used in computer networks. It is commonly used in computer network. It is commonly used in wireless network.

TREE TOPOLOGY :

In tree topology the base of tree is formed by bus topology and its branches are formed by star topology because of BUS and STAR topology.

Alternatively referred to as a star bus topology, tree topology is one of the most common network setups that is similar to a bus topologyand a star topology. A tree topology connects multiple star networks to other star networks. Below is a visual example of asimple computer setup on a network using the star topology.