CCC - Course on Computer Concept - Introduction to Internet and www (CHAPTER-6)

                             

Chapter – 6 Introduction to Internet and www

Basic of Computer Networks

Information and communication are two of the most important strategic issues for the success of every enterprise.

While today nearly every organization uses a number of computers and communication tools (like telephone or fax), they are often still isolated. While managers today are able to use applications like word processors or spreadsheets, not very many of them use computer-based tools to communicate with other departments or information retrieval programs.

To overcome these obstacles in an effective usage of information technology, computer networks are necessary. They are a new kind of organization of computer systems produced by the need to merge computers and communications. Computer networks can manage to put down the barriers between information held on several systems. Only with the help of computer networks can a borderless communication and information environment be built.

Importance of Networking

Computer networks allow the user to access remote programs and remote databases either of the same organization or from other enterprises or public sources. Computer networks provide communication possibilities faster than other facilities. Because of these optimal information and communication possibilities, computer networks may increase the organizational learning rate

there are other reasons why any organization should have a computer network

·         cost reduction by sharing hardware and software resources

·         high reliability by having multiple sources of supply

·         cost reduction by downsizing to microcomputer-based networks instead of using mainframes

·         greater flexibility because of possibility to connect devices from various vendors

A network is two or more computers connected together to share information and files between them. Businesses aren't the only ones that can benefit from creating a network. Home users can enjoy sharing music, movies and printers from any computer.

File Sharing : Computers connected to a network can share files and documents with each other. Personal computers connected to a business network can choose which files and folders are available to share on the network.

Printers : Computers can print pages to another computer with a printer on the network. Additionally, printers can be connected using a print server, which allows direct printing from all computers.

Types of Networks

A) Local Area Networks (LAN)

B) Metropolitan Area Network (MAN)

C) Wide area network (WAN)

 

Network Components

1) Hub

A hub works in the physical layer of the OSI model. It is basically a non-intelligent device, and has no decision making capability. What a Hub basically does is take the input data from one of the ports and broadcast the information to all the other ports connected to the network.

To demonstrate its working, consider a 4 port network as shown in Fig 1. There are 4 computers connected to the 4 ports. Suppose, if Computer A wants to send some data to Computer B using a Hub, then, Computer A broadcasts the data on the network, and Computer B, being connected to the network, has access to the data. But, in this case all the other ports connected to the network has access to the data that is being transmitted by Computer A. This happens because, the Hub works in the Physical Layer and hence it does not know about the MAC addresses of the ports connected to the network. So, there is a lack of security in the Hub.

2) Switch

A switch is an intelligent device that works in the data link layer. The term intelligent refers to the decision making capacity of the Switch. Since it works in the Data link layer, it has knowledge of the MAC addresses of the ports in the network.

 

3)Bridge

A bridge is also a device which works in the Data Link Layer, but is more primitive when compared to a switch. Initial bridges were used to connect only 2 LAN’s, but the most recent ones perform similar operation as the switches. It also works on the principle of transfer of information using the MAC addresses of the ports.

 

4)Router

Any computer can be connected to the internet via MODEM, which performs the MODulation and the DEModulation operations. But, when there are more than one computer at home or in an organization, and you have a single internet connection, you need a Router. Router is a device which is used when multiple devices need to connect to the Internet using the same IP.

 

5)Gateway

The Gateway devices work in the Transport layer and above, where the different network technologies are implemented. A gateway is necessary when there are different technologies implemented by the different LAN’s which are to be connected together.

6)Modems

Modem is a device which converts the computer-generated digital signals of a computer into analog signals to enable their travelling via phone lines. The ‘modulator-demodulator’ or modem can be used as a dial up for LAN or to connect to an ISP. Modems can be both external, as in the device which connects to the USB or the serial port of a computer, or proprietary devices for handheld gadgets and other devices, as well as internal; in the form of add-in expansion cards for computers and PCMCIA cards for laptops. 

Local Area Network (LAN)

Networks used to interconnect computers in a single room, rooms within a building or buildings on one site are called Local Area Network (LAN).

LAN links computers, i.e., software and hardware, in the same area for the purpose of sharing information. Usually LAN links computers within a limited geographical area because they must be connected by a cable, which is quite expensive.

Characteristics of LAN :

1.     Every computer has the potential to communicate with any other computers of the network

2.     High degree of interconnection between computers

3.     Easy physical connection of computers in a network

4.     Inexpensive medium of data transmission

5.     High data transmission rate

Advantages of LAN

·         The reliability of network is high because the failure of one computer in the network does not effect the functioning for other computers.

·         Addition of new computer to network is easy.

·         High rate of data transmission is possible.

·         Peripheral devices like magnetic disk and printer can be shared by other computers.

Disadvantages of LAN

·         If the communication line fails, the entire network system breaks down.

Use of LAN

·         File transfers and Access

·         Word and text processing

·         Electronic message handling

·         Remote database access

·         Personal computing

·         Digital voice transmission and storage

Network Topology

Topology refers to the way in which the network of computers is connected. Each topology is suited to specific tasks and has its own advantages and disadvantages. The choice of topology is dependent upon type and number of equipment being used, planned applications and rate of data transfer required, response time, and cost. Topology can also be defined as the geometrically interconnection pattern by which the stations (nodes/computers) are connected using suitable transmission media (which can be point-to-point and broadcast).

Think of a topology as a network's virtual shape or structure. This shape does not necessarily correspond to the actual physical layout of the devices on the network. For example, the computers on a home LAN may be arranged in a circle in a family room, but it would be highly unlikely to find a ring topology there. Network topologies are categorized into the following basic types:

·         bus

·         ring

·         star

·         tree

·         mesh

1)Bus Topology

Bus networks (not to be confused with the system bus of a computer) use a common backbone to connect all devices. A single cable, the backbone functions as a shared communication medium that devices attach or tap into with an interface connector. A device wanting to communicate with another device on the network sends a broadcast message onto the wire that all other devices but only the intended recipient actually accepts and processes the message.

bus networks work best with a limited number of Networking made it easy 2 Compiled by devices. If more than a few dozen computers are added to a network bus, performance problems will likely result. In addition, if the backbone cable fails, the entire network effectively becomes unusable.

2)Ring Topology

In a ring network, every device has exactly two neighbors for communication purposes. All messages travel through a ring in the same direction (either "clockwise" or "counterclockwise"). A failure in any cable or device breaks the loop and can take down the entire network. To implement a ring network, one typically uses FDDI, SONET, or Token Ring technology. Ring topologies are found in some office buildings or school campuses. 

3)Star Topology

Many home networks use the star topology. A star network features a central connection point called a "hub" that may be a hub, switch or router. Devices typically connect to the hub with Unshielded Twisted Pair (UTP) Ethernet. Compared to the bus topology, a star network generally requires more cable, but a failure in any star network cable will only take down one computer's network access and not the entire LAN. (If the hub fails, however, the entire network also fails.)

4)Tree Topology

Tree topologies integrate multiple star topologies together onto a bus. In its simplest form, only hub devices connect directly to the tree bus, and each hub functions as the "root" of a tree of devices. This bus/star hybrid approach supports future expandability of the network much better than a bus (limited in the number of devices due to the broadcast traffic it generates) or a star (limited by the number of hub connection points) alone.

5) Mesh Topology

Mesh topologies involve the concept of routes. Unlike each of the previous topologies, messages sent on a mesh network can take any of several possible paths from source to destination. (Recall that even in a ring, although two cable paths exist, messages can only travel in one direction.) Some WANs, most notably the Internet, employ mesh routing. A mesh network in which every device connects to every other is called a full mesh. As shown in the illustration below, partial mesh networks also exist in which some devices connect only indirectly to others.

Internet

It is a worldwide system which has the following characteristics:

• Internet is a world-wide / global system of interconnected computer networks.

• Internet uses the standard Internet Protocol (TCP/IP)

• Every computer in internet is identified by a unique IP address.

• IP Address is a unique set of numbers (such as 110.22.33.114) which identifies a computer’s location.

• A special computer DNS (Domain Name Server) is used to give name to the IP Address so that user can locate a computer by a name.

• For example, a DNS server will resolve a name http://www.tutorialspoint.com to a particular IP address to uniquely identify the computer on which this website is hosted.

• Internet is accessible to every user all over the world.

Evolution of the Internet

The structure and makeup of the Internet has adapted as the needs of its community have changed. Today's Internet serves the largest and most diverse community of network users in the computing world. A brief chronology and summary of significant components are provided in this chapter to set the stage for understanding the challenges of interfacing the Internet and the steps to build scalable internetworks.

Origins of the Internet

The Internet started as an experiment in the late 1960s by the Advanced Research Projects Agency (ARPA, now called DARPA) of the U.S. Department of Defense. DARPA experimented with the connection of computer networks by giving grants to multiple universities and private companies to get them involved in the research.

Applications of Internet

The Internet is extensively used for a wide variety of purposes. Some of these are mentioned below:

SEARCH FOR INFORMATION

A number of programs called search engines are available to search for the information on any topic. Some famous search engines are provided by: www.google.com, wikipedia.com, webopedia.com, MSN.com, Yahoo.com, etc.

E-MAIL (ELECTRONIC MAIL) SERVICES

The Internet is commonly used for sending and receiving e-mails. We can send a message electronically to any person on the globe, provided that person has an e-mail-id. This service is fast and economical.

CHATTING

Chatting involves textual exchange of message in real time. Chat servers provide facility to create virtual chat rooms and only the members associated with these rooms are allowed to share messages. Chat works best if the time is scheduled by both the parties who are willing to chat – as both the parties must be connected to the Internet while chatting. Some common chat engines are : Yahoo Messenger, Google Talk, Rediff Bol, etc.

INSTANT MESSENGER SERVICES

These tools can be used to send messages instantly. It also allows us to talk to anyone anywhere in the world. This is a cheaper and quicker method compared to other services. Unlike chatting, it is not necessary to have an account with the same provider. Additionally, both the users need not be connected while sending messages. We can easily download the messenger software from Internet e.g. MSN Messenger, Yahoo Messenger, etc.

NEWSGROUP

Newsgroup is an e-service hosted by many newsgroup organisations. One can become a member of a newsgroup and read and share current affairs and messages. Newsgroups cover a broad domain of interests including education, science and technology, medicine, arts, sports, etc. USENET is one such example.

TELECONFERENCING

People can have a conference or meeting sitting at different locations with a microphone attached to their computers.

VIDEO-CONFERENCING

In teleconferencing we are able to talk to each other sitting at different places but in video-conferencing we can also see what is happening at the other side. We have observed that the anchor, panelists and experts sitting at different locations across the globe communicate and share their views in many news channels. For this, we need a web-camera and a microphone connected to the computer system, high bandwidth connection, and video-conferencing software.

E-COMMERCE

E-commerce or Electronic-Commerce means online transactions of business. In this, the vendor and customer conduct a transaction sitting at different geographical locations, connected through the Internet. The customer need not strain himself by visiting a number of shops outside in scorching heat or heavy rains. He can do shopping by sitting at home, visiting the desired e-commerce site and placing an order online. E.g. http://shopping.indiatimes.com, http://ebay.com, http://shopping.rediff.com, etc.

M-COMMERCE

It is an acronym for mobile commerce. It is an upcoming technology after e-commerce. It involves buying and selling of goods and services electronically through wireless handheld devices at any place. We can do transactions through our mobile phones also.

Popular Web Browsers

The web is a collection of a huge amount of information. Every single web page consists of some information and also a number of links, which connects us to other related web pages. To visit the linked web pages, just click over the linked text and the next web page opens up.

Just like a word processing application is needed to open a word processor document, an application is needed to view an HTML document. To view a web page we need special software called web browser. Mosaic was the first web browser developed by National Centre for Supercomputing Application (NCSA). This browser didn’t have any special features like present day web browsers. It was not possible to view pictures or use any present day font formatting features in the web pages. Initially, the browsers were designed to show plain text, without any formatting.

With the increasing use, the need to incorporate additional features like text formatting, viewing images, playing sound, etc. was felt. Most modern day browsers incorporate all these features. Some other commonly used browsers are Netscape Navigator, Mozilla FireFox, Opera, Safari, MSIE (Microsoft Internet Explorer), etc. Almost all of these support a common set of rules of the language.

Popular Browsers

1)Firefox

Firefox is a very popular web browser. One of the great things about Firefox is that it is supported on all different OSs. Firefox is also open source which makes its support group a very large community of open source developers. Firefox is also known for its vast range of plugins/add-ons that let the user customize in a variety of ways. Firefox is a product of the Mozilla Foundation. The latest version of Firefox is Firefox 3.

Some of Firefox’s most prominant features include: tabbed browsing, a spell checker, incremental find, live bookmarking, a download manager, and an integrated search system that uses the user’s favorite search engine. Like mentioned before, one of the best things about Firefox is its vast amount of plugins/add-ons. Some of the most popular include NoScript (script blocker), FoxyTunes (controls music players), Adblock Plus (ad blocker), StumbleUpon (website discovery), DownThemAll! (download functions), and Web Developer (web tools).

2)Internet Explorer

Internet Explorer (IE - created by Microsoft) is a very prominant web browser for the Windows OS. IE is the most popular web browser. It comes pre-installed on all Windows computers. The latest version of IE is IE7 with IE8 in beta. IE was designed to view a broad range of web pages and to provide certain features within the OS.

IE almost fully supports HTML 4.01, CSS Level 1, XML 1.0, and DOM Level 1. It has introduced a number of proprietary extensions to many of the standards. This has resulted in a number of web pages that can only be viewed properly using IE. It has been subject to many security vulnerabilities just like Windows has. Much of the spyware, adware, and viruses across the Internet are made possible by exploitable bugs and flaws in the security architecture of IE. These are were drive-by downloads come into play (see computer security lesson for more details on that).

3) Safari

Safari (created by Apple) is a very popular web browser among Apple computers. Safari is also the native browser on the iPhone and iPod touch. Safari is available for Windows, but has not reached a very high level of Windows users since. In May 2008 Safari controlled 6.25% of marketshare among all web browsers.

4) Opera

Opera (created by the Opera Software company) is another fairly popular web browser. It handles common Internet-related tasks. Opera also includes features such as tabbed browsing, page zooming, mouse gestures, and an integrated download manager. Its security features include phishing and malware protection, strong encryption when browsing secure web sites, and the ability to easily delete private data such as cookies and browsing history. Opera runs on Windows, OS X, and Linux.

Popular Search Engines

A search engine is a software system that is designed to search for information on the World Wide Web. The search results are generally presented in a line of results often referred to as search engine results pages (SERPs). The information may be a mix of web pages, images, and other types of files. Some search engines also mine data available in databases or open directories. Unlike web directories, which are maintained only by human editors, search engines also maintain real-time information by running an algorithm on a web crawler.

1) Web Crawling

Matthew Gray’s World Wide Web Wanderer (1993) was one of the first efforts to automate the discovery of web pages Gray’s web crawler would download a web page, examine it for links to other pages, and continue downloading links it discovered until there were no more links left to be discovered. This is how web crawlers, also called spiders, generally operate today.

2)Indexing and Ranking

When a web crawler has downloaded a web page, the search engine will index its content. Often the stop words, words that occur very frequently like a, and, the, and to, are ignored. Other words might be stemmed. Stemming is a technique that removes suffixes from a word to improve the content of the index. For example, eating, eats, and eaten may all be stemmed to eat so that a search for eat will match all its variants.

3) Rank Optimization

Search engines guard their weighting formulas as a trade secret since it differentiates their service from other search engines, and they do not want content-producers (the public who produces web pages) to “unfairly” manipulate their rankings. However, many companies rely heavily on search engines for recommendations and customers, and their ranking on a search engine results page (SERP) is very important. Most search engine users only examine the first screen of results, and they view the first few results more often than the results at the bottom of the page. This naturally pits content-producers in an adversarial role against search engines since the producers have an economic incentive to rank highly in SERPs. Competition for certain terms (e.g., Hawaii vacation and flight to New York) is particularly fierce. Because of this, most search engines provide paid-inclusion or sponsored results along with regular (organic) results. This allows companies to purchase space on a SERP for certain terms.

Searching on Internet

A number of programs called search engines are available to search for the information on any topic. Some famous search engines are provided by: www.google.com, wikipedia.com, webopedia.com, MSN.com, Yahoo.com, etc.

Downloading Web Pages

The term downloading is distinguished from the related concept of streaming, which indicates the receiving of data that is used nearly immediately as it is received, while the transmission is still in progress and which may not be stored long-term, whereas in a process described using the term downloading, this would imply that the data is only usable when it has been received in its entirety.

Downloading is the transmission of a file from one computer system to another, usually smaller computer system. From the Internet user's point-of-view, to download a file is to request it from another computer (or from a Web page on another computer) and to receive it.