Chapter 2: Internet and its importance
In the previous unit, you read about history of computers and their characteristics. In the present
unit, you will learn about the various types of computer communication networks and their
nature.
A computer network, also referred as a network, is a group of computers and other specific
hardware components which are interconnected through communication channels allowing
sharing of resources and information. Typically, when more than one computer is interconnected
through a communication medium to interchange information then these computers are referred
as the computers functioning within a computer network. Networks are classified on the basis
of characteristics, such as the medium used to transport the data, communications protocol
used, scale, topology, etc. Networks are often classified by their physical or organizational extent
or their purpose, such as LAN, MAN and WAN.
• A Local Area Network (LAN) is a network that connects computers laboratory, office
building or closely positioned group of buildings. Each computer or device on the network
is a node.
• A Metropolitan Area Network (MAN) is a large computer network that usually spans a city
or a large campus.
• A Wide Area Network (WAN) is a computer network that covers a large geographic area,
such as a city, country or even international distances using a communications channel
to facilitate various types of media, such as telephone lines, cables and air waves. WAN
technologies generally function at the lower three layers of the OSI reference model: the
physical layer, the data link layer and the network layer.
The Transmission Control Protocol (TCP) is referred as the core protocols of the Internet
Protocol Suite. Out of the two original components of the suite, TCP is one which complements
the Internet Protocol (IP) and consequently the entire suite is universally referred to as TCP/IP.
TCP grants reliable, consistent and structured transmission of data from one computer to
another linked computer. Besides, TCP protocol is employed by key Internet applications, such
as the World Wide Web, e-mail, remote administration and file transfer. Computer network is a
collection of computers and intelligent peripheral equipment, such as automatic teller machines
and point-of-sale terminals.
This peripheral equipment is equipped with microprocessors that are interconnected by cables,
microwave relays and other high-speed communication links for the purpose of exchanging data
and sharing equipment.
Networking has been implemented on all levels from local to international in diverse sectors of
the society. Examples of computer networks are networks used by government organizations
for rapid retrieval of information from databases at central locations which are and those used
by banks and retail merchants for the transfer of funds or credit verification. If telephone lines
are adopted for a computer network, each computer in the network must be connected to a
telephone line via a modem (modulator/demodulator).
Need of Computer Networking
Earlier, transferring information from one computer to another could only be done through a
medium, such as a floppy disk or a tape. Resources, such as printers, scanners and CompactDisk Read Only Memory or CD-ROM drives could not be used to share information across the
computers because they had to be physically attached to the computer. Networking, which
means interconnecting the computer systems, came as a boon since it not only allowed sharing
equipment across connected computers but also a shared knowledge base, thereby helping
people to work collectively and taking advantage of the rich information. The following are the
features of computer networking:
•
File Sharing: Computer networking enables every computer in the network to share the
same file from a single computer on the network. It can also provide access rights, such
as read only or read write, for the shared files.
•
Printer Sharing: Computer networking also allows you to share a printer between
different computers in the network. Such a printer is called a network or a shared printer.
Using the network printer helps to cut down the printer expenses and it also provides
easier maintenance.
•
Program Sharing: Sometimes, it is best to put programs that everyone uses on a shared
disk rather in the separate copies of the programs on each user computer. For example,
if you have ten computer users who use Oracle, then you can install it on the server
machine and the users can access Oracle from the server machine.
•
Communication and Collaboration: Network communication enables communication
among the employees of an organization and helps the employees to work as a team. A
computer network allows employees to share files, view work of other employees and
exchange ideas more efficiently.
•
Internet: The Internet is a global system of interconnected computer networks that use
the standard Internet protocol suite (often called TCP/ IP, although not all applications
use TCP) to serve billions of users worldwide. A computer network helps to use the
Internet much easier by allowing several computers to share one modem for using the
same Internet connection.
Disadvantages of Networking
Though computer networking is very much helpful in data sharing and employee communication
within an organization, it also has various disadvantages. The various disadvantages of computer
networking are as follows:
•
Server Crash: This is the biggest disadvantage of networking in a server based network.
When the server crashes, work gets disrupted as all the network resources and its
benefits are lost. Unless proper precautions are taken to ensure regular backups, the
crash may result in the loss of critical data and time for days and even months.
•
Data Security: As all the data resources are pooled together, it is possible for
unauthorized personnel to access classified information if the network security is weak
or poorly implemented.
•
Privacy: In network the risk of loss of privacy is high as anyone with the network
privileges can read your private data.
Examples of Computer Networks
Since computers process data quickly, you can justifiably say that they ‘conquer time’. With a
computer, you can perform instant calculations that would have taken days, weeks or even years
by hand. Some examples of computer networks are as follows:
•
•
•
Researches at a small state university need a supercomputer to calculate the results of
a sophisticated bioinfromatic problem. But they do not have the money to travel to a
major supercomputer facility. In the past, these researchers would have given up. Today,
they can send their data to a supercomputer centre through the Internet. The next day,
they receive the results.
A Tokyo based insurance company has discovered a place where many young educated
employees live. These employees do not mind taking clerical jobs, such as processing
insurance claim forms. The company can send forms attached in e-mail messages from
Tokyo to Bhopal through a satellite network. Employees will fill these forms and mail back
to the insurance company through the same network.
You need some information from MIT, but do not have the time to visit their office. With
the aid of a program called Netscape Navigator, you can take a tour to several MIT
collections while sitting in front of your computer. You will find beautiful, full colour
graphic images of satellites, complex computer installations and research ware on the
company’s Website.
Network Applications
Computer network is a system that allows communication between two or more computers.
Computer networks have a wide scope of application, some of which are as follows:
• Resource sharing
• Home applications
• Mobile users
• Social issues
1. Resource Sharing
Resource sharing allows various resources, such as equipments and data available on the
network, to be shared among the end users. Computer network supports resource sharing
irrespective of physical location of resource and end user. For example, various employees of
an office can share a common printer attached to the network to take printouts of the information.
In addition, computer networks allow the sharing of information among various users connected
to the network. All large and medium-sized organizations are vitally dependent upon the
information stored over the network. For example, all organizations need to maintain information
about different business activities, such as maintaining customer’s records and supplier’s
records.
Different departments of the organization share information regarding business activities using
computer networks to run business. Computer networks support client-server model which allow
users to share resources. The client-server model supports computer network in which
numerous client computers can share the information with the help of the server computer.
When a client computer needs information, it sends a request for the required information to the
server computer. In turn, the server computer responds to that request by providing the required
information to the client computer.
2. Home Applications
Computer networks are used in various home applications, such as entertainment and word
processing. In addition, the Internet is a widely used home application, as people access the
Internet at home for various purposes, such as online shopping and communication.
3. Mobile Users
Computer networks connect mobile devices, such as notebook computers and Personal Digital
Assistants (PDA), using wireless technologies, such as Bluetooth and Wireless Application
Protocol (WAP). Bluetooth is used as Wireless Personal Area Networks or PANs. It connects and
exchanges the information between devices, such as mobile phones, laptops, personal
computers, printers, digital cameras and video game consoles via a secure, globally unlicensed
short-range radio frequency. The word ‘Bluetooth’ is derived from the cognomen of a 10th
century Danish King Harald Bluetooth who was the King of Denmark and Norway.
The Bluetooth technology has been designed to connect both mobile devices and peripherals
that require a wire. The services of Bluetooth are provided by wireless mode of communication
in which no setup is needed. The transfer speed of data rate is 1.0 Mbps or (Megabit per second).
It holds radio frequency chips, which are plugged into the devices. It maintains 2.45 GHz
frequency. It uses a technique called spread spectrum frequency hopping. A wireless solution
is given for the Bluetooth to reduce the cable networking in the peripherals.
It is a type of replacement for Infrared Data Association or IrDA. It is also considered
as complementary technology for Apple Airport and is valid for 802.11b, 802.11g and 802.11n.
People need to use wireless networks while travelling, as physical connections are not possible.
The various applications of wireless networks are:
• It is used in mobile computing.
• It is used in wireless parking meters.
• It is used in wireless meter reading for calculating water, electricity and gas bills.
• It is also used in Mobile Commerce (m-commerce).
4. Social Issues
The widespread application of computer networks has introduced new issues in the society.
These issues include social, ethical and political problems, as today the Internet is the prime
medium of communication and data transfer. The problems generated due to computer
networks are as follows:
•
Privacy of people is threatened as hackers can easily track personal information of the
Internet user. A small file called cookies that is stored on a user’s computer allows other
Internet users to access their personal information.
•
Newsgroups and bulletin boards do not care about speaking on sensitive topics, such as
politics and religion. Sometimes views posted on bulletin boards are offensive to some
people.
•
Hacking and other anti-social activities in computer networks are threats to the society.
2.3 Types of Computer Networks: LAN, MAN, WAN
Earlier, a computer network consisted of mainframes in an enclosure. You could see input in the
form of a punch card. These were read by card readers and output was in the form of printed
results via local printers. Local terminals were mostly used for control and programming input.
All processing was on a batch basis, rather than being interactive. In other words, the input was
transmitted in a batch from a card reader over a short circuit to the processor. The processor
processed the program in a batch and the output to the printer was also in a batch. The first true
mainframe was the IBM 360, introduced in 1964.
Over time, input to the mainframe was extended to multiple users at dumb terminals that were
connected to ports on the mainframe through terminal controllers, or cluster controllers. Terminal
controllers are those devices that first collect traffic from a set of terminals and then directs them
to a concentrator. Parallel to the development of data networking, computers also began to
change. Computers became more powerful as processor speeds increased with the
development of faster microprocessors on silicon chips. Memory became more available as chip
technology and hard drive technology improved.
Additionally, computers became smaller and less expensive, to the point that the typical desktop
PC is equivalent to an early mainframe that would have filled a moderate size office building. As
a result, all computing power and storage capability on all these desktops would lead to a need
to network with those devices within the workplace. It has been estimated that majority of data
transfer is confined to the workplace, while only a small percentage travels to remote places.
Hence, it is clear that PC users need to share access to hosts, databases, printers, etc. LANs
provide a solution to that requirement.
Robert M. Metcalfe and his associates at the Xerox Palo Alto Research Centre (Xerox PARC) first
conceived LAN technology. Later on, Xerox commercialized the technology and named it The
Xerox Wire. When Digital Equipment Corporation (DEC), Intel and Xerox corporation decided to
standardize the technology in 1979, they eventually named it to Ethernet. Ethernet quickly
became a de facto standard. Ethernet and LANs were officially recognized when the IEEE
established Project 802 at the request of its members. In the end of 1982, the first standard was
published and circulated. Ethernet, clearly, is still the most popular LAN standard.
Ethernet
The best alternative to high-speed and cost-effective LAN is called Ethernet. Data is transmitted
and received at the rate of 10 million bits per second. Heavy coaxial cable (thick net) or fiber
optic cable are used for transferring data between wiring closets. Thick net coaxial is made use
of for medium–long distances where the level of reliability needed is medium. At an upper cost,
the fiber has higher reliability and beyond. A light duty coaxial cable known as thin net is normally
used to connect workstations within the same room. These mirror a bigger picture of the
workstations in a laboratory surroundings.
Ethernet was first designed and installed by Xerox Corporation at its Palo Atto Research Center
(PARC) in the mid-1970. In the year 1980, DEC Intel and Xerox came out with a joint specification
which has become the de facto standard. Ethernet was named DIX from this period onwards. It
gained this name after its business sponsors Digital, Intel, and Xerox. Ethernet as the most
popular protocol for LAN technology
The Internet
The word Internet is a short form of a complete word Internetwork or interconnected network.
Therefore, it can be said that the Internet is not a single network, but a collection of networks.
The commonality between them in order to communicate with each other is TCP/IP. The Internet
consists of the following groups of networks:
• Backbones: These are large networks that exist primarily to interconnect other networks.
Some examples of backbones are NSFNET in the USA, EBONE in Europe and large
commercial backbones.
•
Regional Networks: These connect, for example, universities and colleges. ERNET
(Education and Research NETwork) is an example in the Indian context.
•
Commercial Networks: They provide access to the backbones to subscribers, and
networks owned by commercial organizations for internal use and also have connections
to the Internet. Mainly, Internet Service Providers come into this category.
•
Local Networks: These are campus wide university networks. The networks connect
users to the Internet using special devices that are called gateways or routers. These
devices provide connection and protocol conversion of dissimilar networks to the
Internet. Gateways or routers are responsible for routing data around the global network
until they reach their ultimate destination. The delivery of data to its final destination takes
place based on some routing table maintained by router or gateways. These are the
fundamental devices to connect similar or dissimilar networks together.
Over time, TCP/IP defined several protocol-sets for the exchange of routing information. Each
set pertains to a different historic phase in the evolution of architecture of the Internet backbone.
One of the utmost features about the Internet is that no one actually owns it. It is a global
collection of networks which includes both large and small networks. These networks link with
each other in various different modes to form the single entity termed as the Internet and the
design is based on the interconnected networks technology.
Nowadays, Internet access necessitates a broadband connection which is a high data rate
Internet access. The dial-up access deploys a 56K dial-up modem which uses a dedicated
telephone line and is limited to the bit rate of less than 56 Kbps. In contrast to this is the
broadband technology which provides more than double the dial-up bit rate and that too without
intervening with the telephone use. In other words, it means that the Internet access and voice
call can be carried out simultaneously.
The broadband connections are characterized by various minimum bandwidths ranging from 64
Kbps up to 2.0 Mbps. Some standards define the broadband connection as having download
data transfer rates equal to or faster than 256 Kbps, whereas others define it as having data
transmission speed exceeding 768 Kbps in either downstream or upstream direction. In general,
any connection of 256 Kbps or greater comes under broadband Internet.
Certain equipments which are required to access the Internet are as follows. Amongst these,
some of them are mandatory and some are optional.
•
Computer: A computer which is used to browse the Internet may either be a personal
computer with Pentium processor or a Macintosh. It should have enough power and
memory concomitant with multimedia features. Though 128 MB RAM is sufficient to
access the Internet but 512 MB RAM or more is recommended. Now-a-days, devices like
smart phones, mobile phones, pocket PCs, etc., are also used to browse the Internet.
•
Modem: It stands for Modulator/Demodulator. This may either be internally built in or
xternally connected. The modem is a device that converts data in binary code used by
the computer, to an analog signal that can be transmitted over the telephone network
and vice versa.
•
Internet Account with a Service Provider: An account with a service provider is
essential to create a link between the user’s computer and the Internet. A service provider
which is popularly referred to as ISP (Internet Service Provider), signifies phone or cable
companies that provide last mile connectivity. It may also refer to a cable line from the
subscriber’s home to his office and also to an exchange for long distance connectivity
based on monthly or annual charges.
•
Widely used Current Standard Broadband Technologies: These technologies are
DSLs digital Subscriber Line and cable modems. However, recent technologies like VDSL
and optical fiber connections are also gradually becoming popular in providing Internet
access in a much more cost-effective way than copper wire technology. Wi-Fi networks
are also used to provide the Internet connections. However, these are not served in the
areas by cable or ADSL symmetric Digital Subscriber Line). The WiMAX (Worldwide
Interoperability for Microwave Access) has been gaining popularity with regard to mobile
and stationary broadband access.
•
Internet Browser Software: It is the software tool which enables a user to browse the
Internet with the help of Web addresses or URLs. A few of the widely used browsers are
Internet Explorer (IE) version 7 or 8, Netscape, Mozilla Firefox, Chrome, AOL, Opera, etc
Technically, the Internet is known as ‘the network of networks’. It is like a phone system that
connects almost anywhere around the world. It exchanges information and acts as a global link
between small regional networks. The Internet services offer a gateway to a myriad of online
databases, library catalogues and collections, and software and document archives, in addition
to frequently used store-and-forward services, such as Usenet News and e-mail. The widely
used Internet services are as follows:
E-mail
E-mail is the prime Internet service that facilitates services to people or users across the world.
Full Internet connectivity is not required for this. For example, an electronic address provides
these services to FTP sites through which mail can be exchanged. Other Internet services, such
as IP address resolver, Archie Lookup, WHOIS service is done via e-mail.
The header and body of the message make an e-mail message. The header contains the
information where the message is to be sent and the complete path for reaching the destination,
date and return path. The body of the message is the actual message that has to be sent. The
syntax of an e-mail address is user @subdomain.domain, e.g., abc@gmail.com. A service
provider must be connected with leased line, dial-up or connection with any network for sending
e-mail.
File Transfer Protocol (FTP)
FTP is also prime Internet service that acts as protocol and transfers files over TCP/IP network
(the Internet). Once HTML page is developed on a local machine for a Website, it is first uploaded
to the Web server through FTP. Local machine is the machine on which you are initially logged
on. It includes functions to log on to the network, gives a list of directories and copy files.
FTP transfer is possible by entering URL preceded with ftp:// within address bar of a Web
browser. The FTP operations can be performed by issuing FTP commands at the command
prompt or by using FTP utility running under a graphical user interface on Windows OS.
FTP tasks can be performed through a browser. For example, type URL in IE address bar as
ftp:// to get FTP services, such as, ftp://YourLoginName@IPaddress.
The required steps used in connecting with FTP operations are as follows:
• The local machine is connected with remote machine by typing ‘ftp machinename’. The
machinename is the full name, written as aaa.cs.state.edu, of the remote machine to
which the local machine is to be connected. Basically, the machinename is the remote
machine’s full name.
• If the machinename is not available other option is taken as to type the ‘ftp
machinenumber’ that demands the Internet address of the remote machine, e.g.,
129.15.0.11.
• The FTP responds to the users to enter their loginname and password. The anonymous
ftp is used widely these days. Many computer systems provide this facility so that you
can access the information of specific machine without creating an account on that
particular machine. These types of services are provided by anonymous FTP. You need
not to be registered user of the system. The anonymous FTP server contains relevant
software, documents and files used to configure networks, graphics, images, songs,
lyrics and other useful information. An e-mail can be archived through the anonymous
FTP.
• The ready information is stored in machines for any user across the Internet who wants
to get the required information.
Telnet
Telnet is used to connect remote network computers. It is the Internet service that executes
commands on remote host as if you are logged in locally. For this, the machine name and valid
username are required to get connected.
World Wide Web (WWW)
WWW provides hypertext access to documents located anywhere on the Internet. It is a very
successful distributed information system. It is basically client-server data transfer protocol that
communicates via application level protocol. Its structural components are clients, browsers,
servers and caches.The Internet and semantic components include HyperText Transfer Protocol
(HTTP), HyperText Markup Language (HTML), eXtensible Markup Language (XML) and Uniform
Resource Identifiers (URIs). The clients who get various sites requested to the server via HTTP
determine the structure of WWW. Then Web pages constructs HTML consists of graphics and
sound embedded files.
For running the complete system, TCP/IP and DNS networking protocols are required.
The reason behind the evolution of Java programming language is to develop distributed
application. Distributed application means many CPUs are inter-connected through different
network topology so that each CPU can communicate with one another. Java introduced the
Remote Method Invocation (RMI) technique to implement distributed application. The java.net
package provides classes and methods to develop networking applications through different
network protocols.
A group of computers connected by cable to share information is popularly known as network.
A network is a set of computers and peripherals that are physically connected. Networking
enables sharing of resources and communication. Java applets can be downloaded from a
Website. This is one of the main attractions of Java. Networking in Java is possible through the
use of java.net package. The classes within this package encapsulate the socket model
developed by Berkeley software division. The network requires some components, such as:
• Server: Servers provide services to the client. If a server provides application services,
then it is treated as an application server.
• Client: The client accesses services from the server.
• Peer: Peer is a computer that works as a server as well as a client.
• Protocol: A protocol defines a specific set of communication rules that include the
syntax, semantics and synchronization of communication stream implemented between
different network computing systems.
• Physical media: Is the tangible medium with capabilities for storing or saving streams of
computer data, such as digital, audio or video content.
• Physical devices: Is a peripheral I/O device that extends the capabilities of the host
computer but is not used directly by the host computer.