Why Change to Client/Server Computing

Client/server is described as a `cost-reduction’ technology. This technology allows doing what one may be currently doing with computers much less expensively. These technologies include client/server computing, open systems, fourth generation languages, and relational databases. Cost reductions are usually quoted as the chief reasons for changing to client/server. However, the list of reasons has grown to include improved control, increased data integrity and security, increased performance, and better connectivity. The key business issues dividing adoption are:
􀂃 Improving the Flow of Management Information
􀂃 Better Service to End-User Departments.
􀂃 Lowering IT costs

What is Client/Server?

Client/Server (C/S) refers to computing technologies in which the hardware and software components (i.e., clients and servers) are distributed across a network. The client/server software architecture is a versatile, message-based and modular infrastructure that is intended to improve usability, flexibility, interoperability, and scalability as compared to centralised, mainframe, time sharing computing. This technology includes both the traditional database-oriented C/S technology, as well as more recent general distributed computing technologies. The use of LANs has made the client/server model even more attractive to organisations.

Need for Client Server Model

Client server technology, on the other hand, intelligently divides the processing work between the server and the workstation. The server handles all the global tasks while the workstation handles all the local tasks. The server only sends those records to the workstation that are needed to satisfy the information request. Network traffic is significantly reduced. The result of this system is that is fast, secure, reliable, efficient, inexpensive, and easy to use .

File sharing architecture

The original PC networks were based on file sharing architectures, where the server downloads files from the shared location to the desktop environment. The requested user job is then run in the desktop environment.
The traditional file server architecture has many disadvantages especially with the advent of less expensive but more powerful computer hardware. The server directs the data while the
workstation processes the directed data. Essentially this is a dumb server-smart workstation relationship. The server will send the entire file over the network even though the workstation only requires a few records in the file to satisfy the information request. In addition, an easy to use graphic user interface (GUI) added to this model simply adds to the network traffic, decreasing response time and limiting customer service.

Personal Computers

With introduction of the PC and its operating system, independent-computing workstations quickly became common. Disconnected, independent personal computing models allow processing loads to be removed from a central computer. Besides not being able to share data, disconnected personal workstation users cannot share expensive resources that mainframe system users can share: disk drives, printers, modems, and other peripheral computing devices. The data ( and peripheral) sharing problems of independent PCs and workstations, quickly led to the birth of the network/file server computing model, which links PCs and workstations together in a Local Area Network-LAN, so they can share data and peripherals.

Mainframe architecture

With mainframe software architectures, all intelligence is within the central host computer (processor) Users interact with the host through a dump terminal that captures keystrokes and sends that information to the host. Centralized host-based computing models allow many users to share a single computer’s applications, databases, and peripherals. Mainframe software architectures are not tied to a hardware platform. User interaction can be done using PCs and UNIX workstations.
A limitation of mainframe software architectures is that they do not easily support graphical user interfaces or access to multiple databases from geographically dispersed sites. They cost literally thousands of times more than PCs, but they sure don’t do thousands of times more work.

CLIENT / SERVER TECHNOLOGY

Recently, many organisations have been adopting a form of distributed processing called client / server computing. It can be defined as " a form of shared, or distributed, computing in which tasks and computing power are split between servers and clients (usually workstations or personal computers) Servers store and process data common to users across the enterprise, these data can then be accessed by client system. In this section we will discuss various aspects of client/server technology. But before that, let first look at the characteristics of the traditional computing models and various limitations that led to the client/ server computing.

Fiber Optic Cables

Many organisations are replacing the older, copper wire cables in their networks with fiber Optic cables. Fiber optic cables use light as the communications medium. To create the on-and-off bit code needed by computers, the light is rapidly turned on and off on the channel. Fiber optic channels are light weight, can handle many times the telephone conversation or volumes of data handled by copper wire cabling, and can be
installed in environments hostile to copper wire, such as wet areas or areas subject to a great deal of electromagnetic interference. Data is more secure in fiber optic networks.

Coaxial cable

It is a well established and long-used cabling system for terminals and computers. This cabling comes in a variety of sizes to suit different purposes. Coaxial cable is commonly used to connect computers and terminals in a local area such as an office, floor, building or campus .

Twisted-Pair wiring

Twisted-pair wiring or cabling is the same type of cabling system which is used for home and office telephone system. It is inexpensive and easy to install. Technological improvements over the last few years have increased the capacity of twisted-pair wires so that they can now handle data communications with speeds upto 10 mbps (million of bits per second) over limited distances.

Network Cabling

Once the server, workstations and network interface cards are in place, network cabling is used to connect everything together. The most popular type of network cable is the shielded twisted-pair, co-axial and fibre optic cabling as discussed below. Please note that cables and cards chosen should match each other.

Network interface card

As discussed earlier, every device connected to a LAN needs a Network interface card(NIC) to plug into the LAN. For example, a PC may have an Ethernet card installed in it to connect to an Ethernet LAN.

Workstations

Workstations are attached to the server through the network interface card and the cabling. The dumb terminals used on mainframes and minicomputer systems are not supported on networks because they are not capable of processing on their own. Workstations are normally intelligent systems, such as the IBM PC. The concept of distributed processing relies on the fact that personal computers attached to the networks perform their own processing after loading programs and data from the server. Hence, a workstation is called an Active Device on the network. After processing, files are stored back on the server where they can be used by other workstations.
The workstation can also be a diskless PC, wherein loading of operating system takes place from the file server. In short, a PC + a LAN card = a Workstation.

The network operating system

It is loaded into the server’s hard disk along with the system management tools and user utilities. When the system is restarted, NetWare boots and the server comes under its control. At this point, DOS or Windows is no longer valid on the network drive, since it is running the network operating system or NetWare; however most DOS/Windows programs can be run as normal. No processing is done on the server, and hence it is called a Passive Device. The choice of a dedicated or non-dedicated network server is basically a trade-off between the cost and performance, and operation of a network.

Components of a LAN

A typical local area network running under Novell NetWare has five basic components that make up the network. These are :
- File Servers
- Network operating system
- Personal Computers, Workstations or Nodes
- Network Interface Cards
- Cabling
(i) File Server - A network file server is a computer system used for the purpose of managing the file system, servicing the network printers, handling network communications, and other functions. A server may be dedicated in which case all of its processing power is allocated to network functions, or it may be non-dedicated which means that a part of the servers functions may be allocated as a workstation or DOS-based system.

LAN Requirements

There are certain features that every LAN should have and users would do well to keep note of these when they decide to implement their own network. These features essentially invoice hardware and software components. Broadly, these are :
(i) Compatibility - A local area network operating system must provide a layer of compatibility at the software level so that software can be easily written and widely distributed. A LAN operating system must be flexible, which means that it must support a large variety of hardware. Novell Net Ware is a network operating system that can provide these features, and has today, become an industry standard.
(ii) Internetworking - Bridging of different LANs together is one of the most important requirements of any LAN. Users should be able to access resources from all workstations on the bridge network in a transparent way; no special commands should be required to cross the bridge. A network operating system must be hardware independent, providing the same user interface irrespective of the hardware.

Why Lans ?

One of the original reasons for users going in for LANs was that such a distributed environment gave them the ability to have their own independent processing stations while sharing expensive computer resources like disk files, printers and plotters. Today, however, more critical reasons have emerged for users to increasingly move towards LAN solutions. These include :
(i) Security - Security for programs and data can be achieved using servers that are locked through both software and by physical means. Diskless nodes also offer security by not allowing users to download important data on floppies or upload unwanted software or virus.
(ii) Expanded PC usage through inexpensive workstation - Once a LAN has been set up, it actually costs less to automate additional employees through diskless PCs. Existing PCs can be easily converted into nodes by adding network interface cards.
(iii) Distributed processing - Many companies operate as if they had distributed system in place. If numerous PCs are installed around the office, these machines represent the basic platform for a LAN with inter-user communication and information exchange.

The Concept

While personal computers were becoming more powerful through the use of advanced processors and more sophisticated software, users of mainframes and minicomputers began to break with the tradition of having a centralized information systems division. PCs were easy to use and provided a better and more effective way of maintaining
data on a departmental level. In the mainframe and mini environment, the data required by individual departments was often controlled by the management information system department or some such similar department. Each user was connected to the main system through a dumb terminal that was unable to perform any of its own processing tasks. In the mainframe and minicomputer environment, processing and memory are centralized.

The Emergence of Local Area Networks

The advent of IBM PCs in the early 1980s set a whole new standard in both business and personal computing. Along with PCs came a new operating system called DOS. DOS provided an easy programming environment for software vendors developing and publishing software. The significance of the DOS standard is that it stimulates growth of new products by providing software and hardware vendors with an open development platform to build both accessories and software products. Since this brought in an abundance of software, the use of personal computers increased. As more and more people began to use computers, it became obvious that a way of connecting them together would provide many useful benefits, such as printer and hard disk sharing, especially when budgets became a constraint. This gave birth to the Local Area Network (LAN) concept.

Broad Band Networks (ISDN):

Integrated Services Digital Network (ISDN) is a system of digital phone connections to allow simultaneous voice and data transmission across the world. Such voice and data are carried by bearer channels (B channels) having a bandwidth of 64 kilobits per second. A data channel can carry signals at 16kbps or 64kbps, depending on the nature of service provided. There are two types of ISDN service – Basic Rate Interface (BRI) and Primary Rate Interface (PRI) BRI consists of two 64 kbps B channels and one 16kbps D channel for a total of 144kbps and is suitable for individual users. PRI consists of twenty three B channels and one 64kbps D channel for a total of 1536kbps and is suitable for users with higher capacity requirements. It is possible to support multiple primary PRI lines with one 64kbps D channel using Non Facility Associated Signaling (NFAS) .

OSI or the open System Interconnection

Has been outlined by International Organization for Standardization (ISO) to facilitate communication of heterogeneous hardware or software platforms with each other with the help of following seven layers of functions with their associated controls: -
Layer 1 or Physical Layer is a hardware layer which specifies mechanical features as well as electromagnetic features of the connection between the devices and the transmission. Network topology is a part of this layer.
Layer 2 or Data Link Layer is also a hardware layer which specifies channel access control method and ensures reliable transfer of data through the transmission medium.
Layer 3 or Network Layer makes a choice of the physical route of transmission of say, a message packet, creates a virtual circuit for upper layers to make them independent of data transmission and switching, establishes, maintains, terminates connections between the nodes, ensures proper routing of data.
Layer 4 or Transport Layer ensures reliable transfer of data between user processes, assembles and disassembles message packets, provides error recovery and flow control. Multiplexing and encryption are undertaken at this layer level.
Layer 5 or Session Layer establishes, maintains and terminates sessions (dialogues) between user processes. Identification and authentication are undertaken at this layer level.
Layer 6 or Presentation Layer controls on screen display of data, transforms data to a standard application interface. Encryption, data compression can also be undertaken at this layer level.

Transmission Protocols

For any network to exist , there must be connections between computers and agreements or what is termed as protocols about the communications language. However, setting up connections and agreements between dispersed computers (from PCs to mainframes) is complicated by the fact that over the last decade, systems have become increasingly heterogeneous in their software and hardware, as well as their intended functionality.
Protocols are software that performs a variety of actions necessary for data transmission between computers. Stated more precisely, protocols are a set of rules for inter-computer communication that have been agreed upon and implemented by many vendors, users and standards bodies. Ideally, a protocols standard allows heterogeneous computers to talk to each other.

Communications Software

Communications software manages the flow of data across a network. It performs the following functions:
• Access control: Linking and disconnecting the different devices; automatically dialing and answering telephones; restricting access to authorized users; and establishing parameters such as speed, mode, and direction of transmission.
• Network management: Polling devices to see whether they are ready to send or receive data; queuing input and output; determining system priorities; routing messages; and logging network activity, use, and errors.
• Data and file transmission: Controlling the transfer of data, files, and messages among the various devices.

Communication Services

Normally, an organization that wishes to transmit data uses one of the common carrier services to carry the messages from station to station. Following is a brief description of these services.
Narrow band Service - Usually, this service is used where data volume is relatively low ; the transmission rates usually range from 45 to 300 bits per second. Examples of this are the telephone companies’ typewriters exchange service (TWX) and Telex service.
Voice band Services - Voice band services use ordinary telephone lines to send data messages. Transmission rates vary from 300 to 4,800 bits per second, and higher.
Wide band Services - Wide band services provide data transmission rates from several thousands to several million bits per second. These services are limited to high-volume users. Such services generally use coaxial cable or microwave communication. Space satellites, a more exotic development, have been employed to rapidly transmit data from any part of the world to another part of the world.

Communications Channels

A communications channel is the medium that connects the sender and the receiver in the data communications network. Common communications channels include telephone lines, fiber optic cables, terrestrial microwaves, satellite, and cellular radios. A communications network often uses several different media to minimize the total data transmission costs. Thus, it is important to understand the basic characteristics, and costs, of different communications channels.

Packet switching

It is a sophisticated means of maximizing transmission capacity of networks. This is accomplished by breaking a message into transmission units, called packets, and routing them individually through the network depending on the availability of a channel for each packet. Passwords and all types of data can be included within the packet and the transmission cost is by packet and not by message, routes or distance. Sophisticated error and flow control procedures are applied on each link by the network.

Message Switching

Some organisations with a heavy volume of data to transmit use a special computer for the purpose of data message switching. The computer receives all transmitted data ; stores it ; and, when an outgoing communication line is available, forwards it to the receiving point.

Circuit switching

Circuit switching is what most of us encounter on our home phones. We place a call and either get our destination party or encounter a busy signal, we can not transmit any message. A single circuit is used for the duration of the call.

Transmission Modes

There are three different types of data communication modes :
(i) Simplex : A simplex communication mode permits data to flow in only one direction. A terminal connected to such a line is either a send-only or a receive only device. Simplex mode is seldom used because a return path is generally needed to send acknowledgements, control or error signals.
(ii) Half duplex : Under this mode, data can be transmitted back and forth between
two stations, but data can only go in one of the two directions at any given point of point.
(iii) Full duplex : A full duplex connection can simultaneously transmit and receive data between two stations. It is most commonly used communication mode. A full duplex line is faster, since it avoids the delay that occur in a half-duplex mode each time the direction of transmission is changed.

Asynchronous Transmission

In this transmission , each data word is accompanied by stop(1) and start (0) bits that identify the beginning and ending of the word. When no information is being transmitted (sender device is idle), the communication line is usually high (in binary 1), i.e., there is a continuous stream of 1.
Advantage: Reliable as the start and stop bits ensure that the sender and receiver remain in step with one another.
Disadvantage: Inefficient as the extra start and stop bits slow down the data transmission when there is a huge volume of information to be transmitted.

Synchronous Transmission

In this transmission ,bits are transmitted at fixed rate. The transmitter and receiver both use the same clock signals for synchronisation.
• Allows characters to be sent down the line without start-stop bits.
• Allows data to be send as a multi-word blocks.
• Uses a group of synchronisation bits, which is placed, at the beginning and at the end of each block to maintain synchronisation.
• Timing determined by a MODEM
Advantage: Transmission is faster because by removing the start and stop bits, many data words can be transmitted per second.
Disadvantage: The synchronous device is more expensive to build as it must be smart enough to differentiate between the actual data and the special synchronous characters.

Synchronous versus Asynchronous Transmission

Another aspect of data transmission is synchronization (relative timing) of the pulses when transmitted. When a computer sends the data bits and parity bit down the same communication channel, the data are grouped together in predetermined bit patterns for the receiving devices to recognize when each byte (character) has been transmitted. There are two basic ways of transmitting serial binary data: synchronous and asynchronous.

Serial versus Parallel Transmission

Data are transmitted along a communication either in serial or in parallel mode.
Serial Transmission: In serial transmission, the bits of each byte are sent along a single path one after another. An example is the serial port (RS-232) for the mouse or MODEM.
Advantages of serial transmission are :
It is a cheap mode of transferring data .
It is suitable to transmit data over long distance.
The disadvantage is :
This mode is not efficient (i.e. slow) as it transfers data in series .

Mesh network

In this structure, there is random connection of nodes using communication links. In real life, however, network connections are not made randomly. Network lines are expensive to install and maintain. Therefore, links are planned very carefully after serious thoughts, to minimize cost and maintain reliable and efficient traffic movement. A mesh network may be fully connected or connected with only partial links. In fully interconnected topology, each node is connected by a dedicated point to point link to every node. This means that there is no need of any routing function as nodes are directly connected. The reliability is very high as there are always alternate paths available if direct link between two nodes is down or dysfunctional.

Ring network

This is yet another structure for local area networks. In this topology, the network cable passes from one node to another until all nodes are connected in the form of a loop or ring. There is a direct point-to-point link between two neighboring nodes. These links are unidirectional which ensures that transmission by a node traverses the whole ring and comes back to the node, which made the transmission.

Bus network

This structure is very popular for local area networks. In this structure or topology, a single network cable runs in the building or campus and all nodes are linked along
with this communication line with two endpoints called the bus or backbone. Two ends of the cable are terminated with terminators.
Advantages:
• Reliable in very small networks as well as easy to use and understand.
• Requires the least amount of cable to connect the computers together and therefore is less expensive than other cabling arrangements.
• Is easy to extend. Two cables can be easily joined with a connector, making a longer cable for more computers to join the network.
• A repeater can also be used to extend a bus configuration.
Disadvantages:
• Heavy network traffic can slow a bus considerably. Because any computer can transmit at any time. But networks do not coordinate when information is sent. Computers interrupting each other can use a lot of bandwidth.

Star Network

That is, processing nodes in a star network interconnect directly with a central system. Each terminal, small computer, or large main frame can communicate only with the central site and not with other nodes in the network. If it is desired to transmit information from one node to another, it can be done only by sending the details to the central node, which in turn sends them to the destination.
A star network is particularly appropriate for organisations that require a centralized data base or a centralized processing facility. For example, a star network may be used in banking for centralized record keeping in an on-line branch office environment.

NETWORK STRUCTURE OR TOPOLOGY

The geometrical arrangement of computer resources, remote devices, and communication facilities is known as network structure or network topology. A compute network is comprised of nodes and links. A node is the end point of any branch in a computer, a terminal device, workstation or an interconnecting equipment facility. A link is a communication path between two nodes. The terms "circuit" and "channel" are frequently used as synonyms for link.

Remote Access Devices

Remote access devices are modem banks that serve as gateways to the Internet or to private corporate networks. Their function is to properly route all incoming and outgoing connections.

Protocol converters

Dissimilar devices can not communicate with each other unless a strict set of communication standards is followed. Such standards are commonly referred to as protocols. A protocol is a set of rules required to initiate and maintain communication between a sender and receiver device.
Because an organization’s network typically evolved over numerous years, it is often composed of a mixture of many types of computers, transmission channels, transmission modes, and data codes. To enable diverse systems components to communicate with one another and to operate as a functional unit, protocol conversion may be needed. For example, it may be necessary to convert from ASCII to EBCDIC. Protocol conversion can be accomplished via hardware, software, or a combination of hardware and software.

Front-end communication processors :

These are programmable devices which control the functions of communication system. They support the operations of a mainframe computer by performing functions, which it would otherwise be required to perform itself. These functions include code conversions, editing and verification of data, terminal recognition and control of transmission lines. The mainframe computer is then able to devote its time to data processing rather than data transmission.

Multiplexer :

This device enables several devices to share one communication line. The multiplexer scans each device to collect and transmit data on a single line to the CPU. It also communicates transmission from the CPU to the appropriate terminal linked to the Multiplexer. The devices are polled and periodically asked whether there is any data to transmit. This function may be very complex and on some systems, there is a separate computer processor devoted to this activity and this is called a "front-end-processor".

Modem :

Data communication discussed above could be achieved due to the development of encoding/decoding devices. These units covert the code format of computers to those of communication channels for transmission, then reverse the procedure when data are received. These communication channels include telephone lines, microwave links or satellite transmission. The coding/encoding device is called a modem.

Bridges, repeaters and gateways:

Workstations in one network often need access to computer resources in another network or another part of a WAN. For example, an office manager using a local area network might want to access an information service that is offered by a VAN over the public phone system. In order to accommodate this type of need, bridges and routers are often necessary.
Bridges: The main task of a bridge computer is to receive and pass data from one LAN to another. In order to transmit this data successfully, the bridge magnifies the data transmission signal. This means that the bridge can act as a repeater as well as a link.

Hubs

A hub is a hardware device that provides a common wiring point in a LAN. Each node is connected to the hub by means of simple twisted pair wires. The hub then provides a connection over a higher speed link to other LANs, the company’s WAN, or the Internet .

Switches and Routers

Are hardware devices used to direct messages across a network, switches create temporary point to point links between two nodes on a network and send all data along that link. Router computers are similar to bridges but have the added advantage of supplying the user with network management utilities. Routers help administer the data flow by such means as redirecting data traffic to various peripheral devices or other computers. In an
Internet work communication, routers not only pass on the data as necessary but also select appropriate routes in the event of possible network malfunctions or excessive use.

Network Interface Cards

Network interface cards (NIC) provide the connection for network cabling to servers and workstations. An NIC first of all, provides the connector to attach the network cable to a server or a workstation. The on-board circuitry then provides the protocols and commands required to support this type of network card. An NIC has additional memory for buffering incoming and outgoing data packets, thus improving the network throughput. A slot may also be available for remote boot PROM, permitting the board to be mounted in a diskless workstation. Network interface cards are available in 8-bit bus or in faster 16-bit bus standards.

COMPONENTS OF A NETWORK

There are five basic components in any network (whether it is the Internet, a LAN, a WAN, or a MAN):
1. The sending device
2. The communications interface devices
3. The communications channel
4. The receiving device
5. Communications software .

Peer to peer

In peer-to-peer architecture, there are no dedicated servers. All computers are equal, and therefore, are termed as peer. Normally, each of these machines functions both as a client and a server. This arrangement is suitable for environments with a limited number of users (usually ten or less) Moreover, the users are located in the same area and security is not an important issue while the network is envisaged to have a limited growth. At the same time, users need to freely access data and programs that reside on other computers across the network.

Client-Server

Client-Server networks are comprised servers -- typically powerful computers running advanced network operating systems -- and user workstations (clients) which access data or run applications located on the servers. Servers can host e-mail; store common data files and serve powerful network applications such as Microsoft's SQL Server. As a centerpiece of the network, the server validates logins to the network and can deny access to both networking resources as well as client software. Servers are typically the center of all backup and power protection schemas.

Site-to-Site VPN

Through the use of dedicated equipment and large-scale encryption, a company can connect multiple fixed sites over a public network such as the Internet. Site-to-site VPNs can be one of two types:
• Intranet-based - If a company has one or more remote locations that they wish to join in a single private network, they can create an intranet VPN to connect LAN to LAN.
• Extranet-based - When a company has a close relationship with another company (for example, a partner, supplier or customer), they can build an extranet VPN that connects LAN to LAN, and that allows all of the various companies to work in a shared environment.

VPN

A VPN is a private network that uses a public network (usually the Internet) to connect remote sites or users together. Instead of using a dedicated, real-world connection such as leased line, a VPN uses "virtual" connections routed through the Internet from the company's private network to the remote site or employee. There are two common types of VPN.

Wide Area Networks (WAN)

A WAN covers a large geographic area with various communication facilities such as long distance telephone service, satellite transmission, and under-sea cables. The WAN typically involves best computers and many different types of communication hardware and software. Examples of WANs are interstate banking networks and airline reservation systems. Wide area networks typically operate at lower link speeds ( about 1 Mbps) Following are the salient features of WAN:
• Multiple user computers connected together.
• Machines are spread over a wide geographic region
• Communications channels between the machines are usually furnished by a third party (for example, the Telephone Company, a public data network, a satellite carrier)
• Channels are of relatively low capacity (measuring through put in kilobits per second, k bits) .

Metropolitan Area Networks (MAN)

A metropolitan area network (MAN) is some where between a LAN and a WAN. The terms MAN is sometimes used to refer to networks which connect systems or local area networks within a metropolitan area (roughly 40 kms in length
from one point to another) MANs are based on fiber optic transmission technology and provide high speed (10 Mbps or so), interconnection between sites.
A MAN can support both data and voice, cable television networks are examples of MANs that distribute television signals. A MAN just has one or two cables and does not contain switching elements.

Local Area Networks (LAN)

A LAN covers a limited area. This distinction, however, is changing as the scope of LAN coverage becomes increasingly broad. A typical LAN connects as many as hundred or so microcomputers that are located in a relatively small area, such as a building or several adjacent buildings. Organizations have been attracted to LANs because they enable multiple users to share software, data, and devices. Unlike WAN which use point-to-point links between systems, LANs use a shared physical media which is routed in the whole campus to connect various systems. LANs use high-speed media (1 Mbps to 30 Mbps or more) and are mostly privately owned and operated.

Benefits of using networks

As the business grows, good communication between employees is needed. The organisations can improve efficiency by sharing information such as common files, databases and business application software over a computer network.
With improvements in network capacity and the ability to work wirelessly or remotely, successful businesses should regularly re-evaluate their needs and their IT infrastructure.
(i) Organisations can improve communication by connecting theirr computers and working on standardised systems, so that:
• Staff, suppliers and customers are able to share information and get in touch more easily
• More information sharing can make the business more efficient - eg networked access to a common database can avoid the same data being keyed multiple times, which would waste time and could result in errors.

Organization

A variety of network scheduling software is available that makes it possible to arrange meetings without constantly checking everyone's schedules. This software usually includes other helpful features, such as shared address books and to-do lists.

Communication and collaboration

It's hard for people to work together if no one knows what anyone else is doing. A network allows employees to share files, view other people's work, and exchange ideas more efficiently. In a larger office, one can use e-mail and instant messaging tools to communicate quickly and to store messages for future reference.

Internet Access and Security

When computers are connected via a network, they can share a common, network connection to the Internet. This facilitates email, document transfer and access to the resources available on the World Wide Web. Various levels of Internet service are available, depending on your organization's requirements. These range from a single dial-up connection (as you might have from your home computer) to 128K ISDN to 768K DSL or up to high-volume T-1 service. A.I. Technology Group strongly recommends the use of a firewall to any organization with any type of broadband Internet connection.

Fault Tolerance

Establishing Fault Tolerance is the process of making sure that there are several lines of defense against accidental data loss. An example of accidental data loss might be a hard drive failing, or someone deleting a file by mistake. Usually, the first line of defense is having redundant hardware, especially hard drives, so that if one fails, another can take its place without losing data. Tape backup should always be a secondary line of defense (never primary) While today's backup systems are good, they are not fail-safe. Additional measures include having the server attached to an uninterruptible power supply, so that power problems and blackouts do not unnecessarily harm the equipment.

Shared Databases

Shared databases are an important subset of file sharing. If the organization maintains an extensive database - for example, a membership, client, grants or financial accounting database - a network is the only effective way to make the database
available to multiple users at the same time. Sophisticated database server software ensures the integrity of the data while multiple users access it at the same time.

Remote Access

In our increasingly mobile world, staff often require access to their email, documents or other data from locations outside of the office. A highly desirable network function, remote access allows users to dial in to your organization's network via telephone and access all of the same network resources they can access when they're in the office. Through the use of Virtual Private Networking (VPN), which uses the Internet to provide remote access to your network, even the cost of long-distance telephone calls can be avoided.

Fax Sharing

Through the use of a shared modem(s) connected directly to the network server, fax sharing permits users to fax documents directly from their computers without ever having to print them out on paper. This reduces paper consumption and printer usage and is more convenient for staff. Network faxing applications can be integrated with email contact lists, and faxes can be sent to groups of recipients. Specialized hardware is available for high-volume faxing to large groups. Incoming faxes can also be handled by the network and forwarded directly to users' computers via email, again eliminating the need to print a hard copy of every fax - and leaving the fax machine free for jobs that require it.

E-Mail

Internal or "group" email enables staff in the office to communicate with each other quickly and effectively. Group email applications also provide capabilities for contact management, scheduling and task assignment. Designated contact lists can be shared by the whole organization instead of duplicated on each person's own rolodex; group events can be scheduled on shared calendars accessible by the entire staff or appropriate groups. Equally important is a network's ability to provide a simple organization-wide conduit for Internet email, so that the staff can send and receive email with recipients outside of the organization as easily as they do with fellow staff members. Where appropriate, attaching documents to Internet email is dramatically faster, cheaper and easier than faxing them.

Print Sharing

When printers are made available over the network, multiple users can print to the same printer. This can reduce the number of printers the organization must purchase, maintain and supply. Network printers are often faster and more capable than those connected directly to individual workstations, and often have accessories such as envelope feeders or multiple paper trays.

File Sharing

File sharing is the most common function provided by networks and consists of grouping all data files together on a server or servers. When all data files in an organization are concentrated in one place, it is much easier for staff to share documents and other data. It is also an excellent way for the entire office to keep files organized according to a consistent scheme. Network operating systems such as Windows 2000 allow the administrator to grant or deny groups of users access to certain files.

COMPUTER NETWORKS

A computer network is a collection of computers and terminal devices connected together by a communication system. The set of computers may include large-scale computers, medium scale computers, mini computers and microprocessors. The set of terminal devices may include intelligent terminals, "dumb" terminals, workstations of various kinds and miscellaneous devices such as the commonly used telephone instruments.
Many computer people feel that a computer network must include more than one computer system-otherwise, it is an ordinary on-line system. Others feel that the use of telecommunication facilities is of primary importance. Thus, there is no specific definition of a computer network.

Interpretation and evaluation

The patterns identified by the system are interpreted into knowledge which can then be used to support human decision-making e.g. prediction and classification tasks, summarizing the contents of a database or explaining observed phenomena.

Data mining

this stage is concerned with the extraction of patterns from the data. A pattern can be defined as given a set of facts(data) F, a language L, and some measure of certainty C a pattern is a statement S in L that describes relationships among a subset Fs of F with a certainty c such that S is simpler in some sense than the enumeration of all the facts in Fs.

Transformation

the data is not merely transferred across but transformed in that overlays may added such as the demographic overlays commonly used in market research. The data is made useable and navigable.

Preprocessing

this is the data cleansing stage where certain information is removed which is deemed unnecessary and may slow down queries for example unnecessary to note the sex of a patient when studying pregnancy. Also the data is reconfigured to ensure a consistent format as there is a possibility of inconsistent formats because the data is drawn from several sources e.g. sex may recorded as f or m and also as 1 or 0.

Selection

selecting or segmenting the data according to some criteria e.g. all those people who own a car, in this way subsets of the data can be determined.

DATA MINING

Data mining is concerned with the analysis of data and the use of software techniques for finding patterns and regularities in sets of data. It is the computer, which is responsible for finding the patterns by identifying the underlying rules and features in the data. The idea is that it is possible to strike gold in unexpected places as the data mining software extracts patterns not previously discernable or so obvious that no-one has noticed them before.
Data mining analysis tends to work from the data up and the best techniques are those developed with an orientation towards large volumes of data, making use of as much of the collected data as possible to arrive at reliable conclusions and decisions.

Concerns in using data warehouse

• Extracting, cleaning and loading data could be time consuming.
• Data warehousing project scope might increase.
• Problems with compatibility with systems already in place e.g. transaction processing system.
• Providing training to end-users, who end up not using the data warehouse.
• Security could develop into a serious issue, especially if the data warehouse is web accessible.
• A data warehouse is a HIGH maintenance system.

Advantages of using data warehouse

There are many advantages to using a data warehouse, some of them are:
• Enhances end-user access to a wide variety of data.
• Increases data consistency.
• Increases productivity and decreases computing costs.
• Is able to combine data from different sources, in one place.
• It provides an infrastructure that could support changes to data and replication of the changed data back into the operational systems.

Different methods of storing data in a data warehouse

All data warehouses store their data grouped together by subject areas that reflect the general usage of the data (Customer, Product, Finance etc.) The general principle used in the majority of data warehouses is that data is stored at its most elemental level for use in reporting and information analysis. Within this generic intent, there are two primary approaches to organising the data in a data warehouse.
The first is using a "dimensional" approach. In this style, information is stored as "facts" which are numeric or text data that capture specific data about a single transaction or event, and "dimensions" which contain reference information that allows each transaction or event to be classified in various ways. As an example, a sales transaction would be broken up into facts such as the number of products ordered, and the price paid, and dimensions such as date, customer, product, geographical location and sales person.

Optional Components

In addition, the following components also exist in some data warehouses:
1. Dependent Data Marts: A dependent data mart is a physical database (either on the same hardware as the data warehouse or on a separate hardware platform) that receives all its information from the data warehouse. The purpose of a Data Mart is to provide a sub-set of the data warehouse's data for a specific purpose or to a specific sub-group of the organisation.
2. Logical Data Marts: A logical data mart is a filtered view of the main data warehouse but does not physically exist as a separate data copy. This approach to data marts delivers the same benefits but has the additional advantages of not requiring additional (costly) disk space and it is always as current with data as the main data warehouse.

Operations

Data warehouse operations comprises of the processes of loading, manipulating and extracting data from the data warehouse. Operations also covers user management, security, capacity management and related functions.

Metadata

Metadata , or "data about data", is used to inform operators and users of the data warehouse about its status and the information held within the data warehouse. Examples of
data warehouse metadata include the most recent data load date, the business meaning of a data item and the number of users that are logged in currently.

Natural Language

It is difficult for a system to understand natural language due to its ambiguity in sentence structure, syntax, construction and meaning. Accordingly it is not possible to design an interface given this problem. However systems can be designed to understand a subset of a language which implies the use of natural language in a restricted domain.

STRUCTURED QUERY LANGUAGE AND OTHER QUERY LANGUAGES

A query language is a set of commands to create, update and access data from a database allowing users to raise adhoc queries / questions interactively without the help of programmers. A structured query language (SQL) is a set of thirty (30) English like commands which has since become an adoptable standard. The structured query language syntax use some set of commands regardless of the database management system software like ‘Select’, ‘From’, ‘Where’. For example, after ‘Select’ a user lists the fields, after ‘From’ the names of the files/group of records containing these fields are listed, after ‘Where’ conditions for search of the records are listed.