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STUDY MATERIAL
B. Sc Computer Science
Subject : Internet and Java Programming
Unit : I
Semester : 6
Unit – I - Introduction to Internet
Definitions – Advantages – Browsers – Brief overview of servers – URL definition – Introduction to world wide web – uses of www – brief study of HTML tags – creation of simple HTML programs using tags – multimedia capabilities of www – commercial uses – client-server architecture in Internet- Domain name extension types – Internet services – Addressing scheme- Levels of HTML – features of Internet
INTRODUCTIONInternet is a network of networks that connects computers all over the world. Internet is a packet switched network that is modeled after the postal service. All correspondence is sent together and transferred to the Post office, where the packets are sorted and routed to their destinations. In computer networks, this is called packet switching where the data are divided into packets with headers that contain source and destination addresses. The format of the packets is specified by IP. These packets are called IP datagrams.
Evolution.Licklider of Massachusettes Institute of Technology envisioned a globally interconnected set of computers through which one can quickly access data and programs. He joined DARPA(Defence Advance Research Project Agency). The technological breakthrough came with packet switching. This technology enables systems to contact each other without the need of connecting one computer to another in the World. It enables a single line to be shared among an arbitrary number of uses. It enables systems to talk to each other without needing every computer to be connected to every other in the world. In 1966, DARPA finalised the first specification of their network called ARPANET(Advanced Research Project Agency Network). TCP/IP (Transmission Control Protocol/ Internet protocol )refers the set of protocols used in transmitting and receiving data over the network . An addressing logic would be built into Internet Protocol and it is carried out by specialised computers called routers. IP doesn’t guarantee error correction whereas TCP is responsible for reliable connectivity. The structure of the Internet can be understood in terms of host computers and nodes. Numerous branch lines are connected to computers called host. These hosts usually belong to large installations such as Universities and Internet Service Providers(ISP). Host computers always remain on to offer service to clients. ISP is a organization of business offfering public, the access to the InternetConnecting to InternetUsers can get connected to Internet via two ways1. Dail-up2. Dedicated or leased link
Dial-upMost users get connected to net through dial-up ie using telephone line and a modem. ISP provides the login name, password and telephone numbers using which the user dial-in and get connected to the net.Modem – It is a hardware device that acts as a interface between your system and the telephone line. Modem is the acronym for Modulation and Demodulationie The modem at the transmitting end converts the digital format to analog signals(which is modulation) and at the transmitting end conversion from analog to digital format (demodulation) takes place. Modem speeds are measured in bps.Internal and External modemsWe can have either internal or external modems. The external modems are easy to use and have maximum flexibility as they can be moved from one system to another. The external modems are easy to turn off or on. These modems requires a cable and must be plugged to a electrical lineInternal modem reside on an adaptor card which fits into an expansion slot inside your computer. If you want to switch on or off the modem you need to restart the system.
ISDNWith this dialup link ,speeds are limited to 33.6kbps on ordinary lines. Technologies such as ISDN can offer upto 128kbps.ISDN – is a type of telephone service which is an alternative to phone line. ISDN connections are digital and are faster. It allows us to connect to another computer at a speed much faster than even the fastest modem. In this case you need 2 interfaces, NT-1 (which is the interface between your equipment and the outside ISDN line)Terminal Adaptor – which converts signals from system or telephone to ISDN dataLeased lineIf your computer needs to be connected to the Internet all the time, u need to get a leased line. Leased lines come in various speeds including T1(1.5Mbps) and T3(44Mbps).If you don’t need that much speed, can go for fractional T1 lineTypes of Internet Accounts1. PPP account2. Shell accountWhen you use PPP account it lets you to connect your computer right to the Internet. ie for the duration of your Internet session, your computer is a part of the Net just like a computer is directly connected with a cable. In other words your computer temporarily becomes a Internet host. With this account it is possible to run any number of client programs simultaneously.
With the shell account the client programs run on the remote host not on your computer. Your computer acts as a terminal. You can only use text based programs. It is not possible to use multiple client programs simultaneously.
ADVANTAGESInternet has been perceived to be of several dimensions to users.
1. A medium of intercommunication between remote users2. a mechanism to share information and work collaboratively3. a means of publishing information globally4. a repository of informationGrowth and penetration of Internet has been achieved only with the convergence of underlying technologies of mass production of computer developments in networking, the growing availability and declining costs in telecom services and advancements in data compression and transmissionINTERNET SERVICES
EMAIL E-MAIL has revolutionized communications. It is cheaper, faster and more easier form of communications. E-mail is Cheaper, faster and more flexible than most other means of communication. E-mail involves transporting a file that contains a e-mail message from one computer to another. The system is based on the client-server paradigm, where one computer called the server provides the e-mail transport service while several other computers can avail of the services offered by the server. Each Internet user has an e-mail address of the form ork for example , which indicates that the user swetha has an account on the computer lycos.com. E-mail services use two protocols, the Simple Mail Transfer Protocol (SMTP), used to send the e-mail and Post Office Protocol(POP), to pickup the mail at the ISP’s mail box. Programmes used by the users to manage the mails are called e-mail clients, ex are Eudora, MS Outlook Express. With E-mail not only text messages can be transmitted but any type of information such as images, video sound or data can be sent as attachments. This is made possible by a technology called MIME (Multipurpose Internet Mail Extensions).A variation on the e-mail functionality is the mail servers(or list servers). List servers implement the concept of mailing lists, where a group of individuals onstitute a mailing list through appropriate software. The group is given an e-mail address. The mail is directed to every other member of the group as long as they are addressed to the group’s e-mail ID. TELNET Telnet is a protocol that allows a user to log on to a remote computer. Telnet assumes that the user has an account on a particular computer. After logging on, a user can work on a remote machine through telnet just as if she were working at a console of the machine. FILE TRANSFER PROTOCOL (FTP)FTP is used to transfer binary files between users. The Web is gradually replacing FTP. FTP servers make available files for download by clients. Clients can log on to a FTP server, locate the file to be downloaded and then download it to their machines. Windows come with an built in FTP client, but it is a text version. Graphics FTP clients are available on the Net so that we can download and use
.INTERNET RELAY CHAT (IRC)IRC or Chat is a real-time multi-user activity where several users geographically distributed, log into a common chat server and talk to one another through the keyboard. In order to organize large number of people chat sites are divided into channels or chat rooms and a user can join any one or more channels. Chatting requires the user of a chat client, and there are many clients available for free. Chat clients have several features such as private one to one chat, and file transfer between two users, some clients use animated images to represent various participants in a chat room. The popular chat servers are yahoo and MSN. Many web servers use web-based chat, which is implemented through a Java applet that appears in a small window. These chat clients cannot use the IRC chat servers, but require own servers.
One downside of the chat is there is no easy way to find whether the person you chat with is online or not. Personal Messenger provides solution for this problem. It used a small module downloaded from the service provider, which is installed in the user’s machine. As soon as the user’s machine goes online, the module gets activated. Each user can maintain a list of buddies and the pager can inform the user when any of them are online.
GOPHER
The gopher system is similar to the web, in that you use a client to connect to servers all over the world, one at a time. The totality of the information available via this system is called gopherspace. The difference between gopherspace and the web is in the way the information is organized. With gopher, information is presented as a series of menus. Each gopher server has a main menu, and a series of sub menus. To use a gopher, u need to select the menu item you want and your client will fetch it for you.
Menu items can point to a number of different types of resources : files, pictures, other Internet resources . When you select a file, your client will contact the gopher server containing the file and request a copy. When the file arrives, your client will display it for you on the screen.
USENET
USENET refers to User’s Network. It began as a sort of bulletin board where one can post a notice or seek a clarification. It is a large collection of discussion groups involving millions of people over the world. Each group is centered around a particular topic. Usenet consists of 30,000 newsgroups organised under several hierarchies. The main root hierarchies are biz- business comp -computer related, sci- science . alt – the alternate groups. Each root hierarchy has up to several thousand groups under it.
Usenet is a tremendously useful facility, as it enables users to post queries, and obtain answers from experts. A major obstacle in using this is the lack of servers.
Usenet discussion groups are referred to as Newsgroups. Within each group,
the individual contributions are called articles or postings. To read Usenet articles you use a program called a Newsreader. The actual articles are stored and managed by a program called a News server. Your newsreader acts as a News Client. The news server is sometimes called as NNTP(Network News Transfer Protocol) server. Each usenet site is run by a news administrator
INTERNET TELEPHONYTo a multimedia enabled computer, sound once it is digitized is only data and can be sent over any Internet connection. A user can talk in real time to another user on the Internet. Windows comes with built-in software for telephony (Microsoft Netmeeting). Video conferencing is only feasible at bandwidths higher than 28.6 kbps and requires a web camera. Software for this is available for free under the Windows environment.E-COMMERCEE-com refers to the application of the Internet in conducting commerce of any kind. It includes buying and selling of goods, services or information either between individuals or between corporations. E-com has been categorized into : Business-to-Business(B2B), Business-to-Consumer(B2C), Consumer-to-Consumer(C2C). B2C aims at direct contact with individual customer thereby reducing the dividing line between wholesaling and retailing. The B2C business cycle consists of an on-line store, which makes available a catalogue of products, with details such as specification, price and pictures through its web sites.
Specialized areas in B2B include Customer Relations Management(CRM) and Supply Chain Management(SCM). These services often sit atop a network that connects a company and their intermediate clients and suppliers(called an extranet). C2C is a smaller segment which involves direct client-to-client interaction where the users of a product or service share their information.The software used for Ecom varies widely . Java, Perl and C++ are used on the server side for scripting while coldfusion, Websphere are used for flexible development. A recent development has been the emergence of M-commerce or mobile commerce. M-commerce user use mobile devices such as cellular phones and Personal Digital Assistants (PDA) to conduct transactions over the Internet.The underlying transport-level technology is called the Wireless Application Protocol. Web is another service of Internet. This is discussed in detail.
INTRODUCTION TO WORLD WIDE WEBWeb and its Origin The web is a distributed document delivery system that runs on the Internet. It was developed by CERN(European Center for Nuclear Research). Its original purpose was to help physicists at different locations and colloborate and share research materials. Web has become an important medium for advertising and web addresses are now a common sight in magazines, newspapers and television ads. Web is the name given to a large collection of information , pictures and other data you can access over the Internet. This information has one important characteristic : one data item can contain a link to another data item. Millions of documents are published on the we, some servers are devoted to single topics. Others are open to any local new users who want to publish information for the audience. The web is also the application of choice for much of the E-Com that takes place on the net. A number of virtual stores have sprung up on the web allowing the shoppers to browse and buy from the comfort of home. WWW consortium administers further development of web protocols and software, and it is called as the home of the Web.Like all the Internet services, Web is based on a client-server system. This means you use a client program to contact a server program. ie you use a web client to communicate with a web server.