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Thursday, September 21, 2017

Computer Networks and Internet

Unit – 4: Computer Network and Internet
Computer Network
A collection of computers and terminal devices connected together by a communication system is called a computer network. This collection of computers may include large-scale computers, medium-scale computers mini-computers and microcomputers. The set of terminal devices may include intelligent terminals, dumb terminals, work stations and communication hardware. The interweaving of computing and communication had led to information networks of great complexity and utility. Transmission lines can be used to connect a computer to another computer or a computer terminal to a computer. Networks have following prominent features such as:
(i) Multiple connection: Connecting a computer or terminal to any of a number of other computers at various locations.
(ii) Sharing: Permitting several terminals or computers to use the same transmission line alternatively.
(iii) Multiplexing: Permitting several terminals or computers to translate data over the same transmission line simultaneously.
(iv) Message Packing: Interleaving data into the line so that idle periods of one transmitter can be used to send data from another.
Advantages of Computer Network:
  1. A network provides the means to exchange data frequently on a daily basis.
  2. Network permits sharing of organization’s resources. For e.g. if there is too much work load at one site, the network allows the work to be transferred to another computer in the network.
  3. In case one computer fail, the network allows another computer in the network to take over the work load.
  4. Network can be used to provide a very flexible work environment and effective communication between organizations.
Hardware requirements for a computer network
Equipment that makes of the hardware of computer communication systems, are bridge, gateway, network interface card, terminals, modems or acoustic couplers, and hubs.
  1. Bridge: Consists of a computer with two or more network interface cards connecting two different types of networks.
  2. Gateway: Is used when simply transferring data between networks is not enough. Some network systems (in particular mainframe or minicomputers- based systems) require specific instructions on how data is to be managed once it is received onto the network. A gateway is also required when connecting two or more networks that are running on top of different Operating System (OS).
  3. Network Interface Card: It is the key component of the network workstation. Its chief purpose is to send data out onto the network and receive data sent to the workstation in which it resides. Each network card is manufactured with a unique, permanent electronics address.
  4. Terminals: A device that allows users to transmit data to, and receive data from computer or other information- processing machines. Terminals designed for interactive applications can be categorized in a number of ways. With respect to their electronic circuit, terminals can be categorized as dumb, smart, or intelligent.
  5. Modem: is an interface unit that enables a computer or a terminal to transmit and receives data using ordinary telephone lines. It stands for modulator demodulator. Two modems, one for each computer, are needed to computer communication over telephone lines. Modem changes computer or terminal generated digital signals to analog signals, so that the data can be transmitted over voice based telephone line. Electric signals generated by a terminal are modulated to make sounds similarly to those we hear on a voice telephone. After reaching its destination, the analog signal is demodulated by another modem to computer understandable digital signals. Modems are necessary only when an analog communication channel that is normal telephone lines are used.
  6. Hubs: Are used to interconnect the terminals and servers. All the networks (Except those using coaxial cable) requires a central location to bring media segments together. These central locations are called hubs. A hub organizes the cable and relays signals to the media segments.
Components of a network
A network consists of five basic components:
  1. The sending device.
  2. The communications interface devices.
  3. The communications channel.
  4. The receiving device.
  5. Communications software.
Different types of Networks
  1. Wide Area Network (WAN): Wide area network is a inter connected data communication network that covers a wide or large geographical area with various communication facilities. Such communication facilities can be long distance telephone service, satellite transmission and under-sea cables. It interconnects different sites, computer installation and user terminals spread over great distance (nationwide or even worldwide).
The WAN typically involves best computers and many different types of communication hardware and software, e.g. of WAN are interstate banking network, airline reservation system etc. Few features of WAN are:
  1. Multiple user computers connected together.
  2. Machines are spread over wide geographical region.
  3. Communication channels between the machines are usually furnished by a third party (e.g. The Telephone Company, a public data network, a satellite carrier).
  4. Channels are of relatively low capacity.
  5. Channels are relatively error prone.
  1. Local Area Network (LAN): Ans. Local area network or LAN is a network of interconnected data communication devices. LAN covers a limited geographical area; it can be within a department or division that belongs to the organization. LAN enables sharing of resources like hard disks, printers and also data created. LAN uses high-speed media and are mostly privately owned and operated. The main attributes of present day LAN are:
  1. Inexpensive transmission media.
  2. Inexpensive devices (modems, repeaters and trans-receiver) to interface to the media.
  3. Easy physical connection of devices to the media.
  4. High data transmission rates.
  5. A high degree of interconnection between devices.
  6. There is seldom a central controlling processor which polls the attached devices on the network.
A LAN should have the following requisite features:
  1. Compatibility: A layer of compatibility at the software level must be provided by local area network system so that software can be easily written and widely distributed. A LAN operating system must be flexible to support large variety of hardware e.g. Novell Netware.
  2. Internetworking: Bridging of different LANs together is one of the most important requirement of any LAN. Resources should be accessible from all workstation on the bridge network in a transparent way with no special commands requirements for crossing the bridge. Network operating system must be hardware independent providing the same user interface irrespective of the hardware.
  3. Growth Path and Modularity: One more essential feature of LAN is its modularity. It means a set of PCs should get easily converted into a LAN which can grow in size simply by adding additional workstations. For additional storage requirement, another hard disk should be easily added to another server.
  4. System Reliability and Maintenance: All computers are prone to system lockups, power failures and catastrophes. In case of centralized processing if central processor goes down, all users connected to it are left without a machine to work on. Such a situation can even arise in distributed or local area network. Hence, a LAN operating system should be powerful enough to withstand accidents.
  1. Metropolitan Area Network (MAN): MAN is a network spread over a city. It is somewhere between a LAN & a WAN. It sometimes refers to network of LAN within a metropolitan area. MANs are based on fiber optic transmission technology and provide high speed interconnection between site. Example: cable TV networks that are spread over a city can be termed as MANs.
  2. Virtual Private Network (VPN): A VPN is a private network that uses a public network (i.e. the internet) to connect remote sites or users together without paying the long-distance telecommunication charges that are levied for conventional network links. VPN provides a gateway between a corporate LAN and the internet and also allow access to a corporate network’s mail, shared files or intranet and also handles the security and privacy issues.
Distinction between LAN, MAN and WAN
Geographical Area
It covers small geographical distances.
Coverage within cities.
It covers very large geographical distances.
Coverage up to few kilometers.
Coverage upto hundreds of kilometers.
Global coverage.
Medium of Transmission
Guided medium of transmission is used. For example: Coaxial cables, twisted pair cables etc.
Guided as well as unguided medium of transmission is used.
Unguided medium of transmission is used. It uses wave transmission. For example, Radio waves, microwaves, satellite communication etc.
Setup cost is less.
Costlier than LAN.
Very costly. Huge infrastructure is required.
Supports a band width of 10 Mbps to 10 Gbps.
Supports a band width of 10 Mbps to 1 Gbps.
Supports a bandwidth from 15.4 Kbps to 2.4 Gbps.
Devices Used
Repeaters, Hubs, Routers.
Bridges, Routers.
WAN switches MODEMs.
Error Rate
Very low error rate.
Higher error rate.
More error rate as compared to LAN and MAN.

Network Topology
Network structure or network topology is the geometrical arrangement of computer resources, remote devices and communication facilities. It comprises 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. Term ‘circuit’ and ‘channel’ are synonyms for link.
This network structure decides which element in a computer network can communicate with each other. Basic network topologies are discussed as under:
  1. Star Network: In this network the communication channel emanates from a central computer system. It means that the processing nodes are directly connected with a central system. To transmit information from one node to another, it should be necessarily routed through the central computer.
  1. Easily expandable and shortened as it is easy to add or remove devices.
  2. Any single node failure does not bring down the entire network.
  3. Connection of additional computers does not increase the communication time between any two computers.
  4. It is easier to diagnose network problems though a central hub.
  1. Processing problem in the central computer (or hub) can paralyze the entire system.
  2. It costs more to cable a star configuration then other topologies.
  3. Maximum number of nodes expended depends upon the limits of expansion permitted by the hub.

  1. Bus Network: In this structure a single cable runs in the building or campus and all nodes are linked along with this communication line with two end points called the bus.
Most Appropriate for: Local Area Network (LAN)
  1. Reliable in very small networks as well as easy to use and understand.
  2. Highly reliable since any line breakdown does not affect the communication between two computers.
  3. Requires least amount of cable to connect and therefore less expensive.
  4. Easy to extend by joining cable with connector or repeater.
  1. Heavy Network traffic slows down the transmission rate.
  2. Only a single message can travel at a time.
  3. Each connection between two cables weakens the electrical signal.
  4. Troubleshooting is very difficult in bus configuration.

  1. Ring Network: In this network cable passes from one node to another node until all nodes are connected in the form of loop or ring.
Suitable for: LAN
  1. Offers high performance for small number of workstations or for longer networks where each station has a similar workload.
  2. Ring network can span longer distance than other type of networks.
  3. Reliable since communication between two computers is not dependent on a single computer like the host computer.
  4. Ring Networks are easily extendable.
  1. Relatively expensive & difficult to install.
  2. Failure of one computer on the network can affect the entire network.
  3. Difficult to troubleshoot a ring network.
  4. Adding or removing computer can disrupt the entire network.


  1. Mesh Network: Nodes under this network are randomly connected using communication lines. Mesh network can be fully connected or partially connected. In fully connected topology, each node is connected by a dedicated point to point link to every node. In partially connected topology, the computers are widely scattered.
  1. Reliability is very high since there exists an alternative path if the direct link between two node is down.
  2. It is easier to diagnose the network problems.
  3. Yields greater amount of redundancy in the event that one of the nodes fails where network traffic can be redirected to another node.
  1. The cost of installation & maintenance is high.
  2. If there are few cables in the network, the loss of even one cable or device may damage the network seriously.

Meaning of Internet, Intranet and Extranet
INTERNET: Internet is truncated version of internetworking, which refers to interconnecting two or more computer networks. A computer network is interconnection of autonomous computing systems through communicating systems through a communication media. The major goals of networking are to felicitate resource sharing and communication among users connected to hosts. Internet, being network of networks, has the same major goals and spans across the entire globe, compared to limited geophysical area covered by local area and wide area networks. Consequently, the Internet can be thought of as vast pool of computers, people and information spread across the entire world.
Intranet: Intranet can be designed as a network connecting an affiliated set of clients using standard Internet protocols, especially TCP/IP and HTTP. Another definition of an Intranet would be that an IP-based network of notes behind a firewall, or behind several firewalls connected by secure, possibly virtual, networks.
Extranet: Extranet is an acronym for .extended intranet. An extranet is a network that links business partners to each other over the internet by providing access to certain area of one another corporate intranets. It can be defined as a business to business intranet that allows limited, controlled, secure access between a company’ s intranet and designated, authenticated users from remote locations or in other word’s an intranet that allows controlled access by authenticated parties.
Differences between Internet and Intranet
Internet is a global network of interconnected computer networks formed by various educational, commercial, Governmental, non-profit and military organizations.
Intranet is a network of computers within an organization. It facilitates communication within the organization, among widely spread departments, divisions and regional locations.
These networks are individually owned and operated that are all interconnected.
Network owned by organizations or companies.
There are thousands of databases containing information of all sorts in addition to facilities like e-mail, chatting, games, messages boards and free software.
There are only few databases and that too only for business use and applications.
Browsers used
Access to information on internet can be through various browsers like Nets-cape Navigator, Internet Explorers etc.
Access to information on the Intranet can be through only one or same browser.
Internet used for business, educational, governmental, military, personal purposes.
Intranet used only for business purposes, like supplier management, inventory, distribution and channel management.

Role of Internet in Business
The internet plays a major role in every aspect of our modern life. Internet technologies play a major role in business. As a business owner, knowing the role of internet in business will help you take advantage of the powerful opportunities it offers to grow you business and make operations more effective. Here are different ways in which the internet has contributed to the success and growth of businesses.

1. Improved Communications and Networking: The global nature of the web makes the world a lot smaller, making it more efficient for companies to do business on the international realm. Through the Internet, companies can stay in touch with their partners, investors, clients, and customers, regardless of their locations. Email, web conferences, and VoIP make the transmission of important data more seamless. For instance, companies can quickly communicate with suppliers via chat or email to make sure deliveries and payments are covered. The Internet can save the company a lot of time and money as it reduces the need for additional paperwork.
2. Growth: The internet plays a big role in the growth of businesses. It gives businesses an opportunity to reach a wider global audience. Promoting through the internet is also a way to increase sales and reach the desired growth level. Business can also expand by having an online division.
3. Customer Contact: A company website keeps customers abreast of new products and services, 24/7. Profit also increases as their virtual store can cater to customers anytime, anywhere.

4. Market Research and Internet Advertising: Businesses can conduct market research through the Internet. They can use online surveys to study their market. They can directly ask consumers what they think about a particular product or service. It is a very cheap and effective way of doing market research.
The Internet offers a new medium for advertising. Mailings, newspapers ads, and fliers are slowly becoming obsolete as the Internet has become a more cost-effective way to reach consumers. E-newsletters can now be sent directly to the in-boxes of customers with just a few clicks of a mouse button.
5. Outsourcing services: The internet has helped cut costs by outsourcing services to countries where it is cheaper to provide these services. Apart from the cost reduction through the outsourcing role of internet in business, outsourcing enables businesses to concentrate on their core services and become more efficient.
6. Wider business networks: Companies can also maintain ties with other organizations and sister companies through the Internet. In real-time, they can all stay updated with new information about the business and other important matters.
7. Access to Data: The Internet is very rich in information. Anything you need, you can find on the web. For companies doing research in products, markets, industries, new ideas, and other topics, the Internet is an effective tool to use. Individuals can even join forums where they can interact with people from the same industry and exchange ideas.
8. Online Shopping Role: One role of internet in business is the birth of ecommerce websites and online payment solutions that allow people to shop online from the comfort of their own homes.
9. New Opportunities: The internet has opened up new business opportunities and giving rise to a group of successful online business owners. This is a powerful role as anyone can now start an online business.
The role of internet in business cannot be overstated. New businesses are taking advantage of the powerful role the internet plays in business to grow and succeed at a faster rate than was previously possible. Traditional businesses are also not being left behind as they are creating online divisions. A business owner can only ignore the role the internet plays in business at the peril of his or her business.

Role of Internet in Various sectors
  1. Government:
  1. It provides information to citizens concerning laws, statistics, timely information of issue about government agencies.
  2. Websites are being developed whereby citizens could log on their complaints to local police station through websites.
  1. Banks:
  1. Internet has made possible to make payments electronically on the web.
  2. It is possible to sell and purchase a script through our banker or merchant on the web.
  1. Insurance: In insurance sector, internet is useful to serve their policy details and information to users through various sites and current policy details.
  2. Taxation:
  1. Public can be aware of current tax laws through internet.
  2. Soon tax levied on assesses could also be paid through websites.
  1. Education:
  1. Information about admission to various courses, fee structure, scholarship details or any other relevant information are available through different websites.
  2. It also helps users to access libraries. Almost all major libraries are on the web.
Disadvantages/Issues of Internet
In spite of providing a wide-range of benefits, internet has some disadvantages.
  1. Theft of personal information: Culprit can hack and steal personal information like name, address, credit card number, etc. which brings financial loss to a person.
  2. Spamming: It refers to sending of huge unwanted e-mails intentionally to destroy the computer systems. Such activity is a harassment to the computer user.
  3. Virus threat: Virus is a program which damaged the functioning of computer systems. It comes through internet and can crash the total system on the sly.
  4. Hacking: Hacking is buzzword now a day. It is most significant threat of internet. A hacker can theft you personal document, picture, video or anything which you store in your computer and sometime it can be bigger.
  5. Wrong information: Though everyone can run website and there are many free blogging platform and document sharing site in the internet, so everyone can give information in internet as a result there often found wrong information, which is harmful to a user. It is one of the most important disadvantages of internet.
  6. Confusion to choose correct information: There are huge options to give information and anyone gives information to internet as a result there are many sites for the same topic. So, it is very confusing to choose correct website. This is another disadvantage of internet.
  7. Offensive material - fraudulent sites: No matter how careful you are when using the Internet, there is always the possibility that you will come across some sites that contain offensive or even illegal material. Use the 'safe search' option in your favourite search engine. Be assured, even adults use the 'safe search' just to reduce the time-wasting, inappropriate results of an innocent search term. The idea is to use the Internet as a tool to get on with the job in hand, whatever that may be.
  8. Information can be biased: No one owns the Internet and there is nothing to stop people posting their opinions and points of view on web pages, forums, blogs. Many people believe what they read on the Internet. You need to be careful and think about what you are reading. An awful lot of material and web sites are biased and only give you one point of view.
  9. Internet addiction: Sometime for some people use internet like addiction and that is really very harmful for health.
Meaning of Electronic Data Interchange
EDI or Electronic Data Interchange is the virtual exchange of data or business documents in electronic format between trading partners. This exchange of documents is generally between buyer and supplier and consists of transferring purchase orders, invoices, payments, shipping notices and various other documents and by nature eliminates paper trails, improves operational efficiency and enhances virtual exchanges with new trading partners. With EDI, any company can virtually interact with another organisation anywhere in the world without the hassle of waiting times and forecasting future procedures.
Merits of Electronic data interchange (EDI:
  1. Reduces cost: Reduces the overall costs of running a business, as the computer system carries out difficult and complicated tasks automatically. The cost of paper and paper processing is reduced due to electronic exchange of data.
  2. Overall monitoring of business activities: The computer system monitors and controls most aspects of the business. Stock levels, order levels, accounts and invoices are known immediately, without the need for labourious manual intervention and accounting. 
  3. Save time: EDI furthermore saves time over paper processing since the transfer of data from computer to computer is self-acting. There is no need to re key information with EDI. Efficiency levels are very high, as human error is minimised. The effective flow of business is assured.
  4. Improved Security: EDI systems enhance security for the customer and company.
    Improved communication between employees and branches, due to the use of standardised document and data formats.
  5. Improve clientele Service: The fast transfer of enterprise documents and assessed decline in mistakes helps to do business faster and more efficient.
  6. Elaborate Customer Base: Therefore with improved clientele service, we can finally elaborate our clientele base. Many large manufacturers and retailers are ordering their suppliers to institute an EDI program. So, when assessing a new product to carry or a new supplier to use, the ability to do EDI is a large-scale in addition to.
  7. Building long-term relationships EDI helps in building long term relationships with trading partners and hence helps in business growth.
Demerits or Barriers of Electronic data interchange (EDI):
  1. Too Many measures: There are too numerous measures bodies developing standard documents formats for EDI. Data Protection Laws, protecting customers and employees, must be applied and adhered to by employees and the company.
  2. Changing Standards: Each year, most measures bodies publish modifications to the measures. This increases difficulty for EDI users.
  3. EDI is Too Expensive: Some companies are only doing enterprise with others who use EDI. If a business likes to do enterprise with these associations, they have to apply an EDI program. This expense may be very huge for little companies.
  4. Chances of fraud and hacking: Systems need continual electronic protection, from viruses, hacking and potential fraud.
  5. Chances of System failure: EDI systems need regular software updates. In case of a systems failure, manual systems must also be in place to ensure that business continues.
  6. Huge investment of training: Staff must receive training, every time the EDI system is updated. This is a continuous investment. Companies relying on EDI must invest in backup systems, in case the primary system fails. Human input error is still potentially a problem, although the software being used should highlight most errors.
  7. Limit your trading partners: Some organization stops doing business which don’t use EDI. For instance, Wal-Mart prefers to do business only with those organization which uses EDI.
Techniques of EDI
Mainly EDI working technology involves two methods. They are:
  1. Direct method: Under this method, a dial-up or leased line is used by sending company to connect to trading partner’s computer and direct transmission occurs. On the receipt of information, for being used in local IT systems, trading partner’s EDI system translates standardized EDI data into local format. However, this method necessitates use of compatible hardware and communication software by two companies.

Business Translation Dial up or Translation Business
Partner 1 Software Leased Lines Software Partner 2

  1. Indirect method: Under this method, generally, data is transmitted over a Value Added Network (VAN). VAN refers to a system where for the purpose of transmission and storage of messages between business partners, telecommunication lines are linked to an electronic mailbox. A database facility which can be situated in computers of business partners can also be used with electronic mailbox. In database of receiver, messages are processed and updated through mailbox system with integration of electronic mailbox and database facility.

Business Partner A Business Partner B

       VAN Z

Business Partner C Business Partner D

Frequently used terms in Internet
Browser: Contains the basic software you need in order to find, retrieve, view, and send information over the Internet.
Download: To copy data from a remote computer to a local computer.
Upload: To send data from a local computer to a remote computer.
Email:  Email (electronic mail) is the exchange of computer stored messages by telecommunication. Email can be distributed to lists of people as well as to individuals. However, you can also send nontext files, such as graphic images and sound files, as attachments sent in binary streams.
Filter: Software that allows targeted sites to be blocked from view. Example: X_ Stop, AOL@School
Home Page: The beginning "page" of any site.
HTML (Hypertext Markup Language): The coding language used to create documents for use on the World Wide Web. There are three letter suffixes used in coding that help to identify the type location one is viewing
HTTP (Hypertext Transport Protocol): the set of rules for exchanging files (text, graphic images, sound, video, and other multimedia files) on the World Wide Web. Relative to the TCP/IP suite of protocols (which are the basis for information exchange on the Internet), HTTP is an application protocol. Hypertext Generally any text that contains "links" to other text.
Search Engine: A web server that collects data from other web servers and puts it into a database (much like an index), it provides links to pages that contain the object of your search.
TCP/IP: TCP/IP (Transmission Control Protocol/Internet Protocol) is the basic communication language or protocol of the Internet. It can also be used as a communications protocol in a private network (either an intranet or an extranet). When you are set up with direct access to the Internet, your computer is provided with a copy of the TCP/IP program just as every other computer that you may send messages to or get information from also has a copy of TCP/IP.
URL (Uniform Resource Locator): The Internet address. The prefix of a URL indicates which area of the Internet will be accessed. URLs look differently depending on the Internet resource you are seeking.
WWW (World Wide Web): A technical definition of the World Wide Web is all the resources and users on the Internet that are using the Hypertext Transfer Protocol (HTTP).
Firewall: A firewall is a hardware or software installed to provide security to the private networks connected to the internet. They can be implemented in both hardware and software, or a combination of both. All data entering or leaving the Intranet passes through the firewall which allows only the data meeting the administrators’ rules to pass through it.

World Wide Web  

The World Wide Web (WWW) is a client server based, distributed hypertext, and multimedia information system on the Internet. The concept of the web was born in European Particle Physics Libratory, where the web server software along with a character-based client was developed and made available on the Internet. WWW today has become the most popular information service and is associated with accessing and browsing information resources on the Internet. Web uses a protocol called Hypertext Transfer Protocol (HTTP). The web servers maintain information in the .web pages. which are simple ASCII files with all the text marked with Hypertext Mark-up Language (HTML) tags. It has tags for providing references to other web pages, which can be on the same server or any other server on the Internet irrespective of the geographical location. This facilitates hypertext links across the documents on the Internet. The clients or browsers access the web pages on the server’ s renders and formats them according to the HTML tags to display on the client’s system. When the user selects a hypertext link on a web-page, client can follow the link and fetch the referred document irrespective of the location of the document on the Internet. The Uniform Resource Locator (URL) specifies the location of the documents or web pages. It is a simple way of describing almost any information resource, using a standard format for locating information on the Internet, as: <Protocol> ://< Host. Domain> :< port>/<protocol-specific>