Intro to Computer Science, Lecture notes of Computer Science

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Chapter 8 Networks

Networking Basics

 The Uses of a Network

 Common Types of Networks

 Hybrid Networks

 How Networks Are Structured

 Network Topologies and Protocols

Sharing Data Anywhere, Anytime  (^) When PCs first appeared in businesses, software programs were designed for a single user. There were few obvious advantages to connecting PCs, and the technology was not adequate for doing so. As computers spread throughout business, developers began offering complex software designed for multiple users.  (^) Data communications—the electronic transfer of information between computers became a major focus of the computer industry.  (^) By interconnecting many individual networks into a massive single network, people around the world can share information as though they were across the hall from one another. The information they share can be much more than text documents.  (^) Many networks carry voice, audio, and video traffic, enabling videoconferencing and types of collaboration that were not possible just a few years ago. The Internet is an example of one such network and is possibly the single largest network in existence today.

Simultaneous Access

 There are moments in any business when several workers may need to use the same data at the same

time. A good example is a company’s quarterly sales report, which needs to be viewed and updated

by several managers. Without a network that allows workers to share files, workers must keep

separate copies of data stored on different disks by each worker who accesses the data.

 When the data is modified on one computer, data on the other computers becomes outdated. It

becomes difficult to determine which copy of the data is the most current.

 Companies can solve this problem by storing commonly used data at a central location, usually on a

network server (also called a server). A network server is a central computer with a large storage

device and other resources that all users can share.

Contd.

 If the server stores data files for users to access, it is commonly called a file server.

The business can store a single copy of a data file on the server that employees can

access whenever they want.

 Then, if one user makes a change to the file, other users will see the change when they

use the file, and no one needs to figure out who has the latest copy of the data.

Advanced software is needed to allow simultaneous access to the same file.

 In addition to using many of the same data files, most office workers also use the same

programs. In an environment where PCs are not networked, a separate copy of each

program must be installed on every computer. This setup can be costly for two

reasons.

 First, software can be expensive, especially when you must buy many dozens or

hundreds of copies.

 Second, installing and configuring a program on many different computers can take a

lot of time and labor, and maintaining many separate installations of a program is an

ongoi.ng expense

Shared Peripheral Devices  (^) The ability to share peripheral devices (especially expensive ones such as high volume laser printers, which can cost thousands of dollars) is one of the best reasons for small businesses to set up a network. Although printers are more affordable than they were a few years ago, it is still too expensive to provide every worker with a personal printer.  (^) Aside from the cost of buying multiple printers, maintenance contracts and supplies increase the total cost of ownership. When several people can share a printer on a network, printing becomes less expensive and easier to manage.  (^) There are two common ways to share a printer. A printer can connect directly to the network or it can be attached to a print server, which is a computer that manages one or more printers. Either way, users on desktop PCs will be able to submit documents across a network to a printer.

Personal Communications

 One of the most far-reaching applications of data communications is electronic mail (e-mail) ,

a system for exchanging written messages and, increasingly, voice and video messages)

through a network.

 In addition to e-mail, the spread of networking technology is adding to the popularity of

teleconferencing. A teleconference is any kind of multi way communication carried out in

real time using telecommunications or computer networks and equipment.

 In a teleconference, audio and video signals travel across a local area network through the use

of cables and switches or across the network’s Internet connections to remote sites located

throughout the world.

Easier Data Backup  (^) In business, data is extremely valuable, so it is important that employees back up their data. One way to assure that data is backed up is to keep it on a shared storage device that employees can access through a network. Often the network manager makes regular backups of the data on the shared storage device.  (^) Managers also can use special software to back up files stored on employees' hard drives from a central location. With this method, files do not have to be copied to the server before they can be backed up.

What are computer networks?

 A computer network can be defined as a communication system that links two or more

computers and peripheral devices and enables transfer of data between the components.

 Through doing this a company can order new raw materials more rapidly and cheaply

from its suppliers and can keep in touch with the needs of its customers.

 When computers and telecommunications are integrated, they can provide many

advantages. Take the simple example of a humble e-mail sent to a customer or colleague.

This costs only a few pence and can be sent to any location in the world immediately. As

well as the low cost and fast delivery, it can be integrated to work with the users’ other

information needs, perhaps by supplying a spreadsheet as an attachment.

Contd.  (^) Promote new ways of working. As well as the tangible benefits, introducing networks can facilitate a different approach to running a business. Setting up an internal network makes it possible to use group-working tools. Setting up a wide- area network makes electronic data interchange with suppliers possible.  (^) Operate geographically separate businesses as one. Through using wide-area communications technology, it is possible to rationalize the operations of a company that originally operated as separate business units in different geographic locations, perhaps with their own working practices, procedures and reporting mechanisms. Linked business units can use common ways of working facilitated by video conferencing as shown in the case study. Sharing of information on best practices can also occur.

Common Types of Networks

 If you want to understand the different types of networks and how they operate, you

need to know how networks are structured. There are two main types of networks:

 Local area networks (LANs) and

 Wide area networks (WANs).

Hybrid Networks

 Between the LAN and WAN structures, you will find hybrid networks such as

 Campus area networks (CANs)

 Metropolitan area networks (MANs).

 In addition, a new form of network type is emerging called home area networks (HANs).

The need to access corporate Web sites has created two classifications known as intranets

and extranets

Campus Area Networks (CANs )

 A campus area network (CAN) follows the same principles as a local

area network, only on a larger and more diversified scale. With a CAN,

different campus offices and organizations can be linked together.

 (^) Metropolitan Area Networks (MANs)

The metropolitan area network (MAN) b a large-scale network that

connects multiple corporate LANs together. MANs usually are not owned

by a single organization; their communication devices and equipment are

usually maintained by a group or single network provider that sells its

networking services to corporate customers.

 MANs often take the role of a high-speed network that allows for the

sharing of regional resources. MANs also can provide a shared

connection to other networks using a WAN link.

How Networks Are Structured  (^) Networks con be categorized by the roles the servers and PCs play in terms of hierarchical and security interaction. Some networks use servers  (^) Server-based networks  (^) Peer-to-peer networks

Server-based networks  (^) To understand a server-based network , it is important to know the meaning of the term node in a network. A node is a processing location that can be a PC or some other device such as a networked printer. Usually, server-based networks include many nodes and one or more servers, which control user access to the network's resources.  (^) As described earlier, this central computer is known as the file server, network server, application server; or just the server. Files and programs used by more than one user (at different nodes) are often stored on the server.