sainik school kodagu jattingaray 081

7/31/2019 Sainik School Kodagu Jattingaray 081

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SAINIKSCHOOL

KODAGU

COMPUTER SCIENCEASSIGNMENT


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1. WHAT ARE WEB BROWSERS? PASTE FEW

PICTURES OF SOME WEB BROWSERS.

A web browser is a software application for retrieving,presenting, and traversing information resources on the WorldWide Web. An information resourceis identified by a UniformResource Identifier (URI) and may be a web page, image, video,or other piece of content.[2]Hyperlinks present in resourcesenable users easily to navigate their browsers to relatedresources. A web browser can also be defined as an applicationsoftware or program designed to enable users to access, retrieveand view documents and other resources on the Internet.

Although browsers are primarily intended to access the WorldWide Web, they can also be used to access information provided

by web servers in private networks or files in file systems. Themajor web browsers are Firefox, Google Chrome, InternetExplorer, Opera, and Safari
http://en.wikipedia.org/wiki/Software_applicationhttp://en.wikipedia.org/wiki/World_Wide_Webhttp://en.wikipedia.org/wiki/World_Wide_Webhttp://en.wikipedia.org/wiki/Uniform_Resource_Identifierhttp://en.wikipedia.org/wiki/Uniform_Resource_Identifierhttp://en.wikipedia.org/wiki/Web_pagehttp://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/Hyperlinkshttp://en.wikipedia.org/wiki/Application_softwarehttp://en.wikipedia.org/wiki/Application_softwarehttp://en.wikipedia.org/wiki/Internethttp://en.wikipedia.org/wiki/Web_servershttp://en.wikipedia.org/wiki/Private_networkshttp://en.wikipedia.org/wiki/File_systemshttp://en.wikipedia.org/wiki/Firefoxhttp://en.wikipedia.org/wiki/Google_Chromehttp://en.wikipedia.org/wiki/Internet_Explorerhttp://en.wikipedia.org/wiki/Internet_Explorerhttp://en.wikipedia.org/wiki/Opera_(web_browser)http://en.wikipedia.org/wiki/Safari_(web_browser)http://en.wikipedia.org/wiki/Safari_(web_browser)http://en.wikipedia.org/wiki/Opera_(web_browser)http://en.wikipedia.org/wiki/Internet_Explorerhttp://en.wikipedia.org/wiki/Internet_Explorerhttp://en.wikipedia.org/wiki/Google_Chromehttp://en.wikipedia.org/wiki/Firefoxhttp://en.wikipedia.org/wiki/File_systemshttp://en.wikipedia.org/wiki/Private_networkshttp://en.wikipedia.org/wiki/Web_servershttp://en.wikipedia.org/wiki/Internethttp://en.wikipedia.org/wiki/Application_softwarehttp://en.wikipedia.org/wiki/Application_softwarehttp://en.wikipedia.org/wiki/Hyperlinkshttp://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/Web_pagehttp://en.wikipedia.org/wiki/Uniform_Resource_Identifierhttp://en.wikipedia.org/wiki/Uniform_Resource_Identifierhttp://en.wikipedia.org/wiki/World_Wide_Webhttp://en.wikipedia.org/wiki/World_Wide_Webhttp://en.wikipedia.org/wiki/Software_application


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2.WHAT IS EMAIL? DISCUSS FEW FEATURES OF

EMAIL.

Electronic mail, commonly known as email or e-mail, is a method ofexchanging digital messages from an author to one or more recipients. Modernemail operates across the Internet or other computer networks. Some earlyemail systems required that the author and the recipient both be online at thesame time, in common with instant messaging. Today's email systems are basedon a store-and-forward model

. Email servers accept, forward, deliver and storemessages. Neither the users nor their computers are required to be online

simultaneously; they need connect only briefly, typically to an email server, for aslong as it takes to send or receive messages.

An email message consists of three components, the message envelope, themessage header, and the message body. The message header contains controlinformation, including, minimally, an originator's email address and one or morerecipient addresses. Usually descriptive information is also added, such as asubject header field and a message submission date/time stamp.

Originally a text-only (7-bit ASCII and others) communications medium, emailwas extended to carry multi-media content attachments, a process standardizedin RFC 2045 through 2049. Collectively, these RFCs have come to be calledMultipurpose Internet Mail Extensions (MIME).
http://en.wikipedia.org/wiki/Internethttp://en.wikipedia.org/wiki/Computer_networkhttp://en.wikipedia.org/wiki/Online_and_offlinehttp://en.wikipedia.org/wiki/Instant_messaginghttp://en.wikipedia.org/wiki/Store-and-forwardhttp://en.wikipedia.org/wiki/Computer_serverhttp://en.wikipedia.org/wiki/E-mail_serverhttp://en.wikipedia.org/wiki/Email_addresshttp://en.wikipedia.org/wiki/Request_for_Commentshttp://en.wikipedia.org/wiki/Multipurpose_Internet_Mail_Extensionshttp://en.wikipedia.org/wiki/Multipurpose_Internet_Mail_Extensionshttp://en.wikipedia.org/wiki/Request_for_Commentshttp://en.wikipedia.org/wiki/Email_addresshttp://en.wikipedia.org/wiki/E-mail_serverhttp://en.wikipedia.org/wiki/Computer_serverhttp://en.wikipedia.org/wiki/Store-and-forwardhttp://en.wikipedia.org/wiki/Store-and-forwardhttp://en.wikipedia.org/wiki/Store-and-forwardhttp://en.wikipedia.org/wiki/Store-and-forwardhttp://en.wikipedia.org/wiki/Store-and-forwardhttp://en.wikipedia.org/wiki/Instant_messaginghttp://en.wikipedia.org/wiki/Online_and_offlinehttp://en.wikipedia.org/wiki/Computer_networkhttp://en.wikipedia.org/wiki/Internet


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Electronic mail predates the inception of the Internet, and was in fact a crucial tool increating it,[2] but the history of modern, global Internet email services reaches back tothe early ARPANET. Standards for encoding email messages were proposed as earlyas 1973 (RFC 561). Conversion from ARPANET to the Internet in the early 1980sproduced the core of the current services. An email sent in the early 1970s looksquite similar to a basic text message sent on the Internet today.

Network-based email was initially exchanged on the ARPANET in extensions to theFile Transfer Protocol (FTP), but is now carried by the Simple Mail Transfer Protocol(SMTP), first published as Internet standard 10 (RFC 821) in 1982. In the process oftransporting email messages between systems, SMTP communicates deliveryparameters using a message envelopeseparate from the message (header andbody) itself.

In 1996, for the first time, more electronic mail was sent than postal mail in the U.S.Almost from its creation, email has been the most widely used Internetapplication,and in that respect can claim to be the most important. These same capabilities alsounderlie the technology of mailing lists. The following sections describe the keyfeatures of email.

Email Is A Push Technology

Email Waits For You Email Is One-To-Many

Email Is Almost Free.
http://en.wikipedia.org/wiki/Internethttp://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/ARPANEThttp://en.wikipedia.org/wiki/tools.ietf.org/html/rfc561http://en.wikipedia.org/wiki/File_Transfer_Protocolhttp://en.wikipedia.org/wiki/Simple_Mail_Transfer_Protocolhttp://en.wikipedia.org/wiki/Internet_standardhttp://en.wikipedia.org/wiki/tools.ietf.org/html/rfc821http://www.livinginternet.com/http://www.livinginternet.com/l/lp.htmhttp://www.livinginternet.com/e/ep_push.htmhttp://www.livinginternet.com/e/ep_wait.htmhttp://www.livinginternet.com/e/ep_many.htmhttp://www.livinginternet.com/e/ep_free.htmhttp://www.livinginternet.com/e/ep_free.htmhttp://www.livinginternet.com/e/ep_many.htmhttp://www.livinginternet.com/e/ep_many.htmhttp://www.livinginternet.com/e/ep_many.htmhttp://www.livinginternet.com/e/ep_many.htmhttp://www.livinginternet.com/e/ep_many.htmhttp://www.livinginternet.com/e/ep_wait.htmhttp://www.livinginternet.com/e/ep_push.htmhttp://www.livinginternet.com/l/lp.htmhttp://www.livinginternet.com/http://en.wikipedia.org/wiki/tools.ietf.org/html/rfc821http://en.wikipedia.org/wiki/Internet_standardhttp://en.wikipedia.org/wiki/Simple_Mail_Transfer_Protocolhttp://en.wikipedia.org/wiki/File_Transfer_Protocolhttp://en.wikipedia.org/wiki/tools.ietf.org/html/rfc561http://en.wikipedia.org/wiki/ARPANEThttp://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/Internet


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FEATURES OF EMAIL

Email Is A Push Technology

Email Waits For You

Email Is One-To-Many Email Is Almost Free
http://www.livinginternet.com/e/ep_push.htmhttp://www.livinginternet.com/e/ep_wait.htmhttp://www.livinginternet.com/e/ep_many.htmhttp://www.livinginternet.com/e/ep_free.htmhttp://www.livinginternet.com/e/ep_free.htmhttp://www.livinginternet.com/e/ep_many.htmhttp://www.livinginternet.com/e/ep_many.htmhttp://www.livinginternet.com/e/ep_many.htmhttp://www.livinginternet.com/e/ep_many.htmhttp://www.livinginternet.com/e/ep_many.htmhttp://www.livinginternet.com/e/ep_wait.htmhttp://www.livinginternet.com/e/ep_push.htm


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EMAIL IS A PUSH TECHNOLOGY

Electronic mail predates the inception of the Internet, and was in fact acrucial tool in creating it,

[2] but the history of modern, global Internet emailservices reaches back to the early ARPANET. Standards for encodingemail messages were proposed as early as 1973 (RFC 561). Conversionfrom ARPANET to the Internet in the early 1980s produced the core of thecurrent services. An email sent in the early 1970s looks quite similar to abasic text message sent on the Internet today.

Network-based email was initially exchanged on the ARPANET inextensions to the File Transfer Protocol (FTP), but is now carried by theSimple Mail Transfer Protocol (SMTP), first published as Internet standard10 (RFC 821) in 1982. In the process of transporting email messages

between systems, SMTP communicates delivery parameters using amessage envelopeseparate from the message (header and body) itself.

In 1996, for the first time, more electronic mail was sent than postal mail inthe U.S. Almost from its creation, email has been the most widely used

Internetapplication, and in that respect can claim to be the mostimportant. These same capabilities also underlie the technology of mailinglists. The following sections describe the key features of email.
http://www.livinginternet.com/e/ep_push.htmhttp://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/Internethttp://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/ARPANEThttp://en.wikipedia.org/wiki/tools.ietf.org/html/rfc561http://en.wikipedia.org/wiki/File_Transfer_Protocolhttp://en.wikipedia.org/wiki/Simple_Mail_Transfer_Protocolhttp://en.wikipedia.org/wiki/tools.ietf.org/html/rfc821http://en.wikipedia.org/wiki/Simple_Mail_Transfer_Protocolhttp://en.wikipedia.org/wiki/Internet_standardhttp://en.wikipedia.org/wiki/tools.ietf.org/html/rfc821http://www.livinginternet.com/http://www.livinginternet.com/l/lp.htmhttp://www.livinginternet.com/l/lp.htmhttp://www.livinginternet.com/l/lp.htmhttp://www.livinginternet.com/l/lp.htmhttp://www.livinginternet.com/l/lp.htmhttp://www.livinginternet.com/http://en.wikipedia.org/wiki/tools.ietf.org/html/rfc821http://en.wikipedia.org/wiki/Internet_standardhttp://en.wikipedia.org/wiki/Simple_Mail_Transfer_Protocolhttp://en.wikipedia.org/wiki/File_Transfer_Protocolhttp://en.wikipedia.org/wiki/tools.ietf.org/html/rfc561http://en.wikipedia.org/wiki/ARPANEThttp://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/Internethttp://www.livinginternet.com/e/ep_push.htm


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You can send an email to several people in one simple action. Communications can be dividedinto four types depending on the number of parties participating in the information transfer: (1)one-to-one, (2) one-to-many, (3) many-to-one, and (4)many-to-many.

Each type of communication has its own attributes and strengths. For example, the typical phonecall is one-to-one, and the typical meeting is many-to-many. Email is the most successful one-to-many technology, with respect to both sending and receiving:

Sending. You can send an email to more than one person at a time, for example to everyone inyour family, or to a group of friends.

Receiving. You can receive information that has been mailed to more than one person, forexample an announcement sent to hundreds of people on a mailing list.

The key advantage of this one-to-many communication is efficiency, since instead of sendingemails individually, you can save large amounts of time by sending one email to several peopleat once (also see address groups).

Similarly, when you receive an email from an Internetmailing list you are getting information thatwould probably be impractical to receive any other way, since most organizations don't have thetime or resources to send out paper based notices individually to hundreds or even thousands of

people. Email Is Almost Free
http://www.livinginternet.com/e/ea_addrgrp.htmhttp://www.livinginternet.com/http://www.livinginternet.com/http://www.livinginternet.com/e/ea_addrgrp.htm


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EMAIL IS ALMOST FREE

Email text takes up very little storage space or networkbandwidth and so is very inexpensive.

Email is by far the most inexpensive form ofcommunication across global distances. You can sendemail to anyone in the world, no matter how far away, atno extra cost to you. Use of regular paper mail,telephone, or telegram (while they existed) tocommunicate the same information would take muchlonger, and be much more expensive.

Based on a very conservative (inflated) cost of $10 agigabyte for Internetbandwidth, the table below showsthat it would take 50 thousand emails to cost $1 inbandwidth transfer. That is why the many choices foremail-only accounts are so inexpensive. In comparison,websurfing uses many times more bandwidth.
http://www.livinginternet.com/http://www.livinginternet.com/w/w.htmhttp://www.livinginternet.com/w/w.htmhttp://www.livinginternet.com/


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3. WHAT ARE THE ADVANTAGES OF USING EMAIL

. With the growing popularity of the Internet, e-mail has become the most popular communication method forthe internet users. Email is the fast and effective method of communication and it is probably the most preferredmethod for online communication. At present, thousands of users are using e-mails every day. Extensive use ofe-mail makes it so interesting and so versatile. If you want to send greetings to your grandfather or send somefiles to friends, you can easily use the e-mail to do so. There are a lot of advantages of email.

E-mail has come a long way since its introduction, but still, for the most part of the world it used as a secured,fast and easy way to communicate. Electronic communications policy is essentially a reference tool that ismuch more developed now, and you can do much more with it than other medium. With an ordinary file, youcan send text messages via e-mail address and send greeting cards, manage e-mail, duties or preventingunwanted emails by using a spam folder, and organize and manage tasks in their daily number of mail servers.You can send a heavy file within a minute by email.

However, this wonderful tool is not without fault. Some people use these advantages of email to send viruses

and worms through e-mail and in the process they send a lot of emails on your address. If you open and useany file that is infected, it can make a major damage to your computer. An e-mail virus may often be verydifficult to understand, especially for someone who have a little or limited knowledge about computer virusesand how they work. If you get an email with no name mentioned on it and if you open that mail, there are highchances for your computer to get infected by the virus and specious worm.

The privacy problems mentioned above is a big problem. Almost every e-mail goes through a series ofcomputers before it reaches the recipients inbox, and it is possible that individuals can access e-mail and readit. Therefore, it is important that you have a bullet-proof password. Thus you will be able to make your personalemails secured. Keep your security question and answer in a safe place. Do the best use of email and take thefull advantages of email. Do not use it to harass people, because it is the worst use of a good thing.


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ADVANTAGES OF EMAIL

I) E-mail is the most modern form of communication.2) Communication through e-mail is more relaxed.3) It is informal also.4) It is cheapest form of communication as today almost every individual hasinternet connection and thus, he/she

gets e-mail facility for free.5) Users of e-mail can send message to numerous recipients, read anddiscard message, file and retrieve

messages or forward it too. It is fastest as compared to other written means of communication. 4. To send an email log into your email provider. Type out your email and

address the email to who you would like to send it to. Click the send button andwait for your confirmation.


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Anemail client, email reader, or more formallymailuser agent(MUA), is acomputer programused toaccess and manage a user'semail.

The term can refer to any system capable of accessingthe user'semail mailbox, regardless of it being a mail useragent, a relaying server, or a human typing on a terminal.In addition, a web application that provides messagemanagement, composition, and reception functions issometimes also considered an email client, but morecommonly referred to aswebmail.

Popular email clients includeMicrosoft Outlook, IBMLotus Notes,Pegasus Mail, Mozilla'sThunderbird, andApple Inc.'sMail.
http://en.wikipedia.org/wiki/Computer_programhttp://en.wikipedia.org/wiki/Emailhttp://en.wikipedia.org/wiki/E-mail_Mailboxhttp://en.wikipedia.org/wiki/Webmailhttp://en.wikipedia.org/wiki/Microsoft_Outlookhttp://en.wikipedia.org/wiki/IBMhttp://en.wikipedia.org/wiki/Lotus_Noteshttp://en.wikipedia.org/wiki/Pegasus_Mailhttp://en.wikipedia.org/wiki/Mozilla_Foundationhttp://en.wikipedia.org/wiki/Mozilla_Thunderbirdhttp://en.wikipedia.org/wiki/Apple_Inc.http://en.wikipedia.org/wiki/Mail_(application)http://en.wikipedia.org/wiki/Mail_(application)http://en.wikipedia.org/wiki/Apple_Inc.http://en.wikipedia.org/wiki/Mozilla_Thunderbirdhttp://en.wikipedia.org/wiki/Mozilla_Foundationhttp://en.wikipedia.org/wiki/Pegasus_Mailhttp://en.wikipedia.org/wiki/Pegasus_Mailhttp://en.wikipedia.org/wiki/Pegasus_Mailhttp://en.wikipedia.org/wiki/Lotus_Noteshttp://en.wikipedia.org/wiki/Lotus_Noteshttp://en.wikipedia.org/wiki/IBMhttp://en.wikipedia.org/wiki/Microsoft_Outlookhttp://en.wikipedia.org/wiki/Webmailhttp://en.wikipedia.org/wiki/E-mail_Mailboxhttp://en.wikipedia.org/wiki/Emailhttp://en.wikipedia.org/wiki/Computer_program


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Like most client programs, an email client is only active when a user runs it. The most common arrangement isfor an email user (the client) to make an arrangement with a remote Mail Transfer Agent (MTA) server for thereceipt and storage of the client's emails. The MTA, using a suitable mail delivery agent (MDA), adds emailmessages to a client's storage as they arrive. The remote mail storage is referred to as the user's mailbox. Thedefault setting on many Unix systems is for the mail server to store formatted messages in mbox, within theuser's HOME directory. Of course, users of the system can log-in and run a mail client on the same computerthat hosts their mailboxes; in which case, the server is not actually remote, other than in a generic sense.

Emails are stored in the user's mailbox on the remote server until the user's email client requests them to bedownloaded to the user's computer, or can otherwise access the user's mailbox on the possibly remote server.The email client can be set up to connect to multiple mailboxes at the same time and to request the downloadof emails either automatically, such as at pre-set intervals, or the request can be manually initiated by the user.

A user's mailbox can be accessed in two dedicated ways. The Post Office Protocol (POP) allows the user todownload messages one at a time and only deletes them from the server after they have been successfullysaved on local storage. It is possible to leave messages on the server to permit another client to access them.However, there is no provision for flagging a specific message as seen, answered, or forwarded, thus POP isnot convenient for users who access the same mail from different machines.

Alternatively, the Internet Message Access Protocol (IMAP) allows users to keep messages on the server,flagging them as appropriate. IMAP provides folders and sub-folders, which can be shared among differentusers with possibly different access rights. Typically, the Sent, Drafts, and Trashfolders are created by default.

IMAP features an idleextension for real time updates, providing faster notification than polling, where longlasting connections are feasible. In addition, the mailbox storage can be accessed directly by programs running on the server or via shared

disks. Direct access can be more efficient but is less portable as it depends on the mailbox format; it is used bysome email clients, including some webmail applications.
http://en.wikipedia.org/wiki/Mail_Transfer_Agenthttp://en.wikipedia.org/wiki/Mail_delivery_agenthttp://en.wikipedia.org/wiki/E-mail_Mailboxhttp://en.wikipedia.org/wiki/Mboxhttp://en.wikipedia.org/wiki/Post_Office_Protocolhttp://en.wikipedia.org/wiki/Internet_Message_Access_Protocolhttp://en.wikipedia.org/wiki/IMAP_IDLEhttp://en.wikipedia.org/wiki/IMAP_IDLEhttp://en.wikipedia.org/wiki/Clustered_file_systemhttp://en.wikipedia.org/wiki/Clustered_file_systemhttp://en.wikipedia.org/wiki/Clustered_file_systemhttp://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/Clustered_file_systemhttp://en.wikipedia.org/wiki/Clustered_file_systemhttp://en.wikipedia.org/wiki/IMAP_IDLEhttp://en.wikipedia.org/wiki/IMAP_IDLEhttp://en.wikipedia.org/wiki/IMAP_IDLEhttp://en.wikipedia.org/wiki/Internet_Message_Access_Protocolhttp://en.wikipedia.org/wiki/Post_Office_Protocolhttp://en.wikipedia.org/wiki/Mboxhttp://en.wikipedia.org/wiki/E-mail_Mailboxhttp://en.wikipedia.org/wiki/Mail_delivery_agenthttp://en.wikipedia.org/wiki/Mail_Transfer_Agent


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Email clients usually contain user interfaces to display and edittext. Some applications permit the use of program-external editor.

The email clients will perform formatting according to RFC 5322for headers and body, and MIME for non-textual content andattachments. Headers include the destination fields, To, Cc, and

Bcc, and the originator fields Fromwhich is the message'sauthor(s), Senderin case there are more authors, and Reply-Toin case responses should be addressed to a different mailbox. Tobetter assist the user with destination fields, many clientsmaintain one or more address books and/or are able to connectto an LDAP directory server. For originator fields, clients may

support different identities. Client settings require the user's real nameand email addressfor

each user's identity, and possibly a list of LDAP servers.
http://en.wikipedia.org/wiki/Graphical_user_interfacehttp://en.wikipedia.org/w/index.php?title=RFC_5322&action=edit&redlink=1http://en.wikipedia.org/wiki/E-mailhttp://en.wikipedia.org/wiki/E-mailhttp://en.wikipedia.org/wiki/MIMEhttp://en.wikipedia.org/wiki/LDAPhttp://en.wikipedia.org/wiki/LDAPhttp://en.wikipedia.org/wiki/MIMEhttp://en.wikipedia.org/wiki/E-mailhttp://en.wikipedia.org/wiki/E-mailhttp://en.wikipedia.org/w/index.php?title=RFC_5322&action=edit&redlink=1http://en.wikipedia.org/wiki/Graphical_user_interface


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When a user wishes to create and send an email, the email clientwill handle the task. The email client is usually set upautomatically to connect to the user's mail server, which istypically either an MSA or an MTA, two variations of the SMTPprotocol. The email client which uses the SMTP protocol createsan authentication extension, which the mail server uses toauthenticate the sender. This method eases modularity andnomadic computing. The older method was for the mail server torecognize the client's IP address, e.g. because the client is on thesame machine and uses internal address 127.0.0.1, or becausethe client's IP address is controlled by the same internet serviceprovider that provides both internet access and mail services.

Client settings require the name or IP address of the preferredoutgoing mail server, the port number(25 for MTA, 587 for MSA),and the user nameand passwordfor the authentication, if any.There is a non-standard port 465 for SSL encrypted SMTPsessions, that many clients and servers support for backward

compatibility.
http://en.wikipedia.org/wiki/Mail_submission_agenthttp://en.wikipedia.org/wiki/Mail_transport_agenthttp://en.wikipedia.org/wiki/SMTPhttp://en.wikipedia.org/wiki/Internet_service_providerhttp://en.wikipedia.org/wiki/Internet_service_providerhttp://en.wikipedia.org/wiki/Transport_Layer_Securityhttp://en.wikipedia.org/wiki/Transport_Layer_Securityhttp://en.wikipedia.org/wiki/Internet_service_providerhttp://en.wikipedia.org/wiki/Internet_service_providerhttp://en.wikipedia.org/wiki/SMTPhttp://en.wikipedia.org/wiki/Mail_transport_agenthttp://en.wikipedia.org/wiki/Mail_submission_agent


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All relevant email protocols have an option to encrypt the wholesession, to prevent a user's nameand passwordfrom beingsniffed. They are strongly suggested for nomadic users andwhenever the internet access provider is not trusted.[1] Whensending mail, users can only control encryption at the first hopfrom a client to its configured outgoing mail server. At any furtherhop, messages may be transmitted with or without encryption,depending solely on the general configuration of the transmittingserver and the capabilities of the receiving one.

Encrypted mail sessions deliver messages in their original format,i.e. plain text or encrypted body, on a user's local mailbox and on

the destination server's. The latter server is operated by an emailhosting service provider, possibly a different entity than theinternet accessprovider currently at hand.
http://en.wikipedia.org/wiki/Packet_snifferhttp://en.wikipedia.org/wiki/Internet_access_providerhttp://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/Email_hosting_servicehttp://en.wikipedia.org/wiki/Email_hosting_servicehttp://en.wikipedia.org/wiki/Email_hosting_servicehttp://en.wikipedia.org/wiki/Email_hosting_servicehttp://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/Internet_access_providerhttp://en.wikipedia.org/wiki/Packet_sniffer


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There are two models for managing cryptographickeys. S/MIME employs a model based on a trustedcertificate authority (CA) that signs users' public keys.OpenPGP employs a somewhat more flexible web of

trustmechanism that allows users to sign oneanother's public keys. OpenPGP is also more flexiblein the format of the messages, in that it still supportsplain message encryption and signing as they used towork before MIME standardization.

In both cases, only the message body is encrypted.Header fields, including originator, recipients, andsubject, remain in plain text.
http://en.wikipedia.org/wiki/S/MIMEhttp://en.wikipedia.org/wiki/Certificate_authorityhttp://en.wikipedia.org/wiki/OpenPGPhttp://en.wikipedia.org/wiki/Web_of_trusthttp://en.wikipedia.org/wiki/Web_of_trusthttp://en.wikipedia.org/wiki/MIMEhttp://en.wikipedia.org/wiki/MIMEhttp://en.wikipedia.org/wiki/Web_of_trusthttp://en.wikipedia.org/wiki/Web_of_trusthttp://en.wikipedia.org/wiki/OpenPGPhttp://en.wikipedia.org/wiki/Certificate_authorityhttp://en.wikipedia.org/wiki/S/MIME


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In addition to the fat client email clients and small email clients, there are alsoWeb-based email applications called webmail. Webmail has several advantages,including an ability to send and receive email away from the user's normal baseusing a web browser, thus eliminating the need for an email client.

Some websites are dedicated to providing email services, including Hotmail,Gmail, AOL, and Yahoo; but there are many internet service providers whichprovide webmail services as part of their internet service package. The mainlimitations of webmail are that user interactions are subject to the website'soperating system and the general inability to download email messages andcompose or work on the messages offline, although Gmail does offer OfflineGmail through the installation of Gears and there are also other tools [2] tointegrate parts of the webmail functionality into the OS (e.g. creating messagesdirectly from third party applications via MAPI). The advantage of webmailprovided by a regular mail server is that email remains on the mail server until

the user can return to the base computer, when they can be downloaded. Usersmay be able to choose whether to leave a copy of the email on the server for abackup.
http://en.wikipedia.org/wiki/Fat_clienthttp://en.wikipedia.org/wiki/World_Wide_Webhttp://en.wikipedia.org/wiki/Webmailhttp://en.wikipedia.org/wiki/Web_browserhttp://en.wikipedia.org/wiki/Hotmailhttp://en.wikipedia.org/wiki/Gmailhttp://en.wikipedia.org/wiki/AOL_Mailhttp://en.wikipedia.org/wiki/Yahoo!_Mailhttp://en.wikipedia.org/wiki/Internet_service_providerhttp://en.wikipedia.org/wiki/Gears_(software)http://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/MAPIhttp://en.wikipedia.org/wiki/MAPIhttp://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/Gears_(software)http://en.wikipedia.org/wiki/Internet_service_providerhttp://en.wikipedia.org/wiki/Yahoo!_Mailhttp://en.wikipedia.org/wiki/AOL_Mailhttp://en.wikipedia.org/wiki/Gmailhttp://en.wikipedia.org/wiki/Hotmailhttp://en.wikipedia.org/wiki/Web_browserhttp://en.wikipedia.org/wiki/Webmailhttp://en.wikipedia.org/wiki/World_Wide_Webhttp://en.wikipedia.org/wiki/Fat_client


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WEB MAIL

A major disadvantage of webmail is that the hosting corporation orinstitution retains control over the individual's email as it is performing astorage function in addition to the service function. Since the solestorage location is hosted and controlled by the corporation or institutionthe individual does not "have" their email but only has "access" to it andthat access is under the sole control of the corporation or institution. This

becomes a problem when users loses their email account throughhacking or malice and are unable to retrieve the only copies of theirstored email. Webmail will also be affected by the speed and quality ofthe internet connection and this may be a problem for dial-up connectionusers. A major advantage of webmail is that the individual's email isavailable everywhere there is an internet connection and a browser andthe individual does not need a computer with their mail application

installed in it. With webmail the users' email is usually backed up withmultiple redundancy and corporations and institutions usually provideextremely reliable service as well as excellent spam filtering services.Privacy concerns have been raised about webmail as corporations arestoring large amounts of personal information.

4 WRITE THE PROCESS OF SENDING A MESSAGE


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4. WRITE THE PROCESS OF SENDING A MESSAGE

FROM ONE COMPUTER TO THE OTHER ON INTERNET.

WHAT IS THE ROLE OF CLIENT-SERVER TECHNOLOGY

AND TCP/IP IN IT? ]==Protocols== While popular protocols for retrieving mail include POP3and IMAP4, sending mail is usually done using the SMTP protocol.

Another important standard supported by most email clients is MIME,which is used to send binary fileemail attachments. Attachments arefiles that are not part of the email proper, but are sent with the email.

Most email clients use a User-Agent[4]header field to identify thesoftware used to send the message. According to RFC 2076, this is acommon but non-standard header field.

RFC 6409, Message Submission for Mail, details the role of the Mailsubmission agent.

RFC 5068, Email Submission Operations: Access and AccountabilityRequirements, provides a survey of the concepts of MTA, MSA, MDA,

and MUA. It mentions that "Access Providers MUST NOT block usersfrom accessing the external Internet using the SUBMISSION port 587"and that "MUAs SHOULD use the SUBMISSION port for messagesubmission.
http://en.wikipedia.org/wiki/POP3http://en.wikipedia.org/wiki/IMAP4http://en.wikipedia.org/wiki/SMTPhttp://en.wikipedia.org/wiki/MIMEhttp://en.wikipedia.org/wiki/Binary_filehttp://en.wikipedia.org/wiki/Email_attachmenthttp://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/Header_(information_technology)http://en.wikipedia.org/wiki/tools.ietf.org/html/rfc2076http://en.wikipedia.org/wiki/tools.ietf.org/html/rfc6409http://en.wikipedia.org/wiki/Mail_submission_agenthttp://en.wikipedia.org/wiki/Mail_submission_agenthttp://en.wikipedia.org/wiki/tools.ietf.org/html/rfc5068http://en.wikipedia.org/wiki/tools.ietf.org/html/rfc5068http://en.wikipedia.org/wiki/Mail_submission_agenthttp://en.wikipedia.org/wiki/Mail_submission_agenthttp://en.wikipedia.org/wiki/tools.ietf.org/html/rfc6409http://en.wikipedia.org/wiki/tools.ietf.org/html/rfc2076http://en.wikipedia.org/wiki/Header_(information_technology)http://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/Email_attachmenthttp://en.wikipedia.org/wiki/Binary_filehttp://en.wikipedia.org/wiki/MIMEhttp://en.wikipedia.org/wiki/SMTPhttp://en.wikipedia.org/wiki/IMAP4http://en.wikipedia.org/wiki/POP3


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Email servers and client use the following TCP portnumbers by convention, but customizedconfiguration exist:

protocol

use plain text or

encrypt sessions plain text

sessions only

encrypt sessionsonly

POP3 incoming mail 110
http://en.wikipedia.org/wiki/List_of_TCP_and_UDP_port_numbershttp://en.wikipedia.org/wiki/List_of_TCP_and_UDP_port_numbershttp://en.wikipedia.org/wiki/Post_Office_Protocolhttp://en.wikipedia.org/wiki/Post_Office_Protocolhttp://en.wikipedia.org/wiki/List_of_TCP_and_UDP_port_numbershttp://en.wikipedia.org/wiki/List_of_TCP_and_UDP_port_numbers


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POP3 incoming mail 110 995

IMAP4 incoming mail 143 993 SMTP

outgoing mail 25 (unofficial)[5] 465 MSA outgoing mail 587
http://en.wikipedia.org/wiki/Post_Office_Protocolhttp://en.wikipedia.org/wiki/Internet_Message_Access_Protocolhttp://en.wikipedia.org/wiki/Simple_mail_transfer_protocolhttp://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/Mail_submission_agenthttp://en.wikipedia.org/wiki/Mail_submission_agenthttp://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/Simple_mail_transfer_protocolhttp://en.wikipedia.org/wiki/Internet_Message_Access_Protocolhttp://en.wikipedia.org/wiki/Post_Office_Protocol


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MSAoutgoing mail587

HTTPwebmail

80443

Note that while webmail obeys the earlier HTTP disposition ofhaving separate ports for encrypt and plain text sessions, mailprotocols use the STARTTLS technique, thereby allowingencryption to start on an already established TCP connection.RFC 2595 discourages the use of the previously established ports995 and 993.
http://en.wikipedia.org/wiki/Mail_submission_agenthttp://en.wikipedia.org/wiki/HTTPhttp://en.wikipedia.org/wiki/STARTTLShttp://en.wikipedia.org/wiki/tools.ietf.org/html/rfc2595http://en.wikipedia.org/wiki/tools.ietf.org/html/rfc2595http://en.wikipedia.org/wiki/STARTTLShttp://en.wikipedia.org/wiki/HTTPhttp://en.wikipedia.org/wiki/Mail_submission_agent


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Microsoft mail systems define the proprietaryMessaging Application ProgrammingInterface (MAPI) that is used in client

applications, such as Microsoft Outlook, toaccess Microsoft Exchange electronic mailservers.
http://en.wikipedia.org/wiki/Microsofthttp://en.wikipedia.org/wiki/Proprietary_softwarehttp://en.wikipedia.org/wiki/Messaging_Application_Programming_Interfacehttp://en.wikipedia.org/wiki/Messaging_Application_Programming_Interfacehttp://en.wikipedia.org/wiki/Microsoft_Outlookhttp://en.wikipedia.org/wiki/Microsoft_Exchange_Serverhttp://en.wikipedia.org/wiki/Microsoft_Exchange_Serverhttp://en.wikipedia.org/wiki/Microsoft_Outlookhttp://en.wikipedia.org/wiki/Messaging_Application_Programming_Interfacehttp://en.wikipedia.org/wiki/Messaging_Application_Programming_Interfacehttp://en.wikipedia.org/wiki/Proprietary_softwarehttp://en.wikipedia.org/wiki/Microsoft


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TCP and IP were developed by a Department of Defense (DOD)research project to connect a number different networks designed bydifferent vendors into a network of networks (the "Internet"). It wasinitially successful because it delivered a few basic services thateveryone needs (file transfer, electronic mail, remote logon) across avery large number of client and server systems. Several computers in a

small department can use TCP/IP (along with other protocols) on asingle LAN. The IP component provides routing from the department tothe enterprise network, then to regional networks, and finally to theglobal Internet. On the battlefield a communications network will sustaindamage, so the DOD designed TCP/IP to be robust and automaticallyrecover from any node or phone line failure. This design allows theconstruction of very large networks with less central management.

However, because of the automatic recovery, network problems can goundiagnosed and uncorrected for long periods of time.

As with all other communications protocol, TCP/IP is composed oflayers:


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IP IP - is responsible for moving packet of data

from node to node. IP forwards each packetbased on a four byte destination address (the

IP number). The Internet authorities assignranges of numbers to different organizations.The organizations assign groups of theirnumbers to departments. IP operates on

gateway machines that move data fromdepartment to organization to region andthen around the world.


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-

TCP - is responsible for verifying the correctdelivery of data from client to server. Datacan be lost in the intermediate network. TCP

adds support to detect errors or lost data andto trigger retransmission until the data iscorrectly and completely received.


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Sockets - is a name givento the package ofsubroutines that provide

access to TCP/IP on mostsystems.


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The Army puts out a bid on a computer andDEC wins the bid. The Air Force puts out abid and IBM wins. The Navy bid is won by

Unisys. Then the President decides to invadeGrenada and the armed forces discover thattheir computers cannot talk to each other.

The DOD must build a "network" out ofsystems each of which, by law, was deliveredby the lowest bidder on a single contract.


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The Internet Protocol was developed to create a Network of Networks (the "Internet").Individual machines are first connected to a LAN (Ethernet or Token Ring). TCP/IP sharesthe LAN with other uses (a Novell file server, Windows for Workgroups peer systems). Onedevice provides the TCP/IP connection between the LAN and the rest of the world.

To insure that all types of systems from all vendors can communicate, TCP/IP is absolutelystandardized on the LAN. However, larger networks based on long distances and phonelines are more volatile. In the US, many large corporations would wish to reuse largeinternal networks based on IBM's SNA. In Europe, the national phone companies

traditionally standardize on X.25. However, the sudden explosion of high speedmicroprocessors, fiber optics, and digital phone systems has created a burst of newoptions: ISDN, frame relay, FDDI, Asynchronous Transfer Mode (ATM). New technologiesarise and become obsolete within a few years. With cable TV and phone companiescompeting to build the National Information Superhighway, no single standard can governcitywide, nationwide, or worldwide communications.

The original design of TCP/IP as a Network of Networks fits nicely within the currenttechnological uncertainty. TCP/IP data can be sent across a LAN, or it can be carried withinan internal corporate SNA network, or it can piggyback on the cable TV service.Furthermore, machines connected to any of these networks can communicate to any othernetwork through gateways supplied by the network vendor.


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Each technology has its own convention for transmittingmessages between two machines within the same network.On a LAN, messages are sent between machines bysupplying the six byte unique identifier (the "MAC" address).

In an SNA network, every machine has Logical Units withtheir own network address. DECNET, Appletalk, and NovellIPX all have a scheme for assigning numbers to each localnetwork and to each workstation attached to the network.


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On top of these local or vendor specific network addresses, TCP/IPassigns a unique number to every workstation in the world. This "IPnumber" is a four byte value that, by convention, is expressed byconverting each byte into a decimal number (0 to 255) andseparating the bytes with a period. For example, the PC Lube andTune server is 130.132.59.234.

An organization begins by sending electronic mail [email protected] requesting assignment of a networknumber. It is still possible for almost anyone to get assignment of anumber for a small "Class C" network in which the first three bytesidentify the network and the last byte identifies the individualcomputer. The author followed this procedure and was assigned thenumbers 192.35.91.* for a network of computers at his house.Larger organizations can get a "Class B" network where the first twobytes identify the network and the last two bytes identify each of upto 64 thousand individual workstations. Yale's Class B network is130.132, so all computers withIP address 130.132.*.* areconnected through Yale.


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The organization then connects to the Internet through one of adozen regional or specialized network suppliers. The networkvendor is given the subscriber network number and adds it to therouting configuration in its own machines and those of the othermajor network suppliers.

There is no mathematical formula that translates the numbers192.35.91 or 130.132 into "Yale University" or "New Haven, CT."The machines that manage large regional networks or the centralInternet routers managed by the National Science Foundation canonly locate these networks by looking each network number up in a

table. There are potentially thousands of Class B networks, andmillions of Class C networks, but computer memory costs are low,so the tables are reasonable. Customers that connect to theInternet, even customers as large as IBM, do not need to maintainany information on other networks. They send all external data to

the regional carrier to which they subscribe, and the regional carriermaintains the tables and does the a ro riate routin .


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New Haven is in a border state, split 50-50between the Yankees and the Red Sox. In thisspirit, Yale recently switched its connection fromthe Middle Atlantic regional network to the New

England carrier. When the switch occurred, tablesin the other regional areas and in the nationalspine had to be updated, so that traffic for 130.132was routed through Boston instead of New Jersey.The large network carriers handle the paperwork

and can perform such a switch given sufficientnotice. During a conversion period, the universitywas connected to both networks so that messagescould arrive through either path.


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Although the individual subscribers do not need to tabulate network numbers orprovide explicit routing, it is convenient for most Class B networks to beinternally managed as a much smaller and simpler version of the larger networkorganizations. It is common to subdivide the two bytes available for internalassignment into a one byte department number and a one byte workstation ID.

The enterprise network is built using commercially available TCP/IP routerboxes. Each router has small tables with 255 entries to translate the one byte

department number into selection of a destination Ethernet connected to one ofthe routers. Messages to the PC Lube and Tune server (130.132.59.234) aresent through the national and New England regional networks based on the130.132 part of the number. Arriving at Yale, the 59 department ID selects anEthernet connector in the C& IS building. The 234 selects a particularworkstation on that LAN. The Yale network must be updated as new Ethernetsand departments are added, but it is not effected by changes outside the

university or the movement of machines within the department. A Uncertain Path


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Every time a message arrives at an IP router, it makes anindividual decision about where to send it next. There is conceptof a session with a preselected path for all traffic. Consider acompany with facilities in New York, Los Angeles, Chicago andAtlanta. It could build a network from four phone lines forming aloop (NY to Chicago to LA to Atlanta to NY). A message arriving at

the NY router could go to LA via either Chicago or Atlanta. Thereply could come back the other way.

How does the router make a decision between routes? There isno correct answer. Traffic could be routed by the "clockwise"algorithm (go NY to Atlanta, LA to Chicago). The routers couldalternate, sending one message to Atlanta and the next toChicago. More sophisticated routing measures traffic patterns andsends data through the least busy link.


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If one phone line in this network breaks down, traffic can still reach itsdestination through a roundabout path. After losing the NY to Chicago line, datacan be sent NY to Atlanta to LA to Chicago. This provides continued servicethough with degraded performance. This kind of recovery is the primary designfeature of IP. The loss of the line is immediately detected by the routers in NYand Chicago, but somehow this information must be sent to the other nodes.Otherwise, LA could continue to send NY messages through Chicago, where

they arrive at a "dead end." Each network adopts some Router Protocol whichperiodically updates the routing tables throughout the network with informationabout changes in route status.

If the size of the network grows, then the complexity of the routing updates willincrease as will the cost of transmitting them. Building a single network thatcovers the entire US would be unreasonably complicated. Fortunately, theInternet is designed as a Network of Networks. This means that loops and

redundancy are built into each regional carrier. The regional network handles itsown problems and reroutes messages internally. Its Router Protocol updates thetables in its own routers, but no routing updates need to propagate from aregional carrier to the NSF spine or to the other regions (unless, of course, asubscriber switches permanently from one region to another).


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IBM designs its SNA networks to be centrally managed. If anyerror occurs, it is reported to the network authorities. By design,any error is a problem that should be corrected or repaired. IPnetworks, however, were designed to be robust. In battlefieldconditions, the loss of a node or line is a normal circumstance.Casualties can be sorted out later on, but the network must stay

up. So IP networks are robust. They automatically (and silently)reconfigure themselves when something goes wrong. If there isenough redundancy built into the system, then communication ismaintained.

In 1975 when SNA was designed, such redundancy would beprohibitively expensive, or it might have been argued that only theDefense Department could afford it. Today, however, simplerouters cost no more than a PC. However, the TCP/IP designthat, "Errors are normal and can be largely ignored," producesproblems of its own.


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Data traffic is frequently organized around "hubs," much like airline traffic.One could imagine an IP router in Atlanta routing messages for smallercities throughout the Southeast. The problem is that data arrives without areservation. Airline companies experience the problem around majorevents, like the Super Bowl. Just before the game, everyone wants to flyinto the city. After the game, everyone wants to fly out. Imbalance occurs onthe network when something new gets advertised. Adam Curry announced

the server at "mtv.com" and his regional carrier was swamped with trafficthe next day. The problem is that messages come in from the entire worldover high speed lines, but they go out to mtv.com over what was then aslow speed phone line.

Occasionally a snow storm cancels flights and airports fill up with strandedpassengers. Many go off to hotels in town. When data arrives at acongested router, there is no place to send the overflow. Excess packets

are simply discarded. It becomes the responsibility of the sender to retry thedata a few seconds later and to persist until it finally gets through. Thisrecovery is provided by the TCP component of the Internet protocol.


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TCP was designed to recover from node or line failures where thenetwork propagates routing table changes to all router nodes. Sincethe update takes some time, TCP is slow to initiate recovery. TheTCP algorithms are not tuned to optimally handle packet loss due totraffic congestion. Instead, the traditional Internet response to trafficproblems has been to increase the speed of lines and equipment in

order to say ahead of growth in demand. TCP treats the data as a stream of bytes. It logically assigns a

sequence number to each byte. The TCP packet has a header thatsays, in effect, "This packet starts with byte 379642 and contains200 bytes of data." The receiver can detect missing or incorrectlysequenced packets. TCP acknowledges data that has beenreceived and retransmits data that has been lost. The TCP designmeans that error recovery is done end-to-end between the Clientand Server machine. There is no formal standard for trackingproblems in the middle of the network, though each network hasadopted some ad hoc tools.


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NEED TO KNOW

There are three levels of TCP/IP knowledge. Those whoadminister a regional or national network must design a system oflong distance phone lines, dedicated routing devices, and verylarge configuration files. They must know the IP numbers andphysical locations of thousands of subscriber networks. Theymust also have a formal network monitor strategy to detect

problems and respond quickly. Each large company or university that subscribes to the Internet

must have an intermediate level of network organization andexpertise. A half dozen routers might be configured to connectseveral dozen departmental LANs in several buildings. All trafficoutside the organization would typically be routed to a singleconnection to a regional network provider.

However, the end user can install TCP/IP on a personal computerwithout any knowledge of either the corporate or regionalnetwork. Three pieces of information are required:


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The IP address assigned to this personal computer The part of the IP address (the subnet mask) that distinguishes

other machines on the same LAN (messages can be sent to themdirectly) from machines in other departments or elsewhere in theworld (which are sent to a router machine)

The IP address of the router machine that connects this LAN to therest of the world.

In the case of the PCLT server, the IP address is 130.132.59.234.Since the first three bytes designate this department, a "subnetmask" is defined as 255.255.255.0 (255 is the largest byte value andrepresents the number with all bits turned on). It is a Yale convention(which we recommend to everyone) that the router for each

department have station number 1 within the department network.Thus the PCLT router is 130.132.59.1. Thus the PCLT server isconfigured with the values:


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My IP address: 130.132.59.234 Subnet mask: 255.255.255.0 Default router: 130.132.59.1 The subnet mask tells the server that any other machine with

an IP address beginning 130.132.59.* is on the same

department LAN, so messages are sent to it directly. Any IPaddress beginning with a different value is accessed indirectlyby sending the message through the router at 130.132.59.1(which is on the departmental LAN).

Additional information is available in self-study courses fromSRA (1-800-SRA-1277)

TCP/IP [34610]


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5.WRITE NOTES ONWEB SERVER, WEB

PAGE, WEBSITE, WEB

CLIENT. EXPLAIN


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WEB SERVER

Web server can refer to either the hardware (the computer)or the software (the computer application) that helps todeliver Web content that can be accessed through theInternet.[1]

The most common use of web servers is to host websites,but there are other uses such as gaming, data storage orrunning enterprise applications.

The primary function of a web server is to deliver web pages

on the request to clients using the Hypertext TransferProtocol (HTTP). This means delivery of HTML documentsand any additional content that may be included by adocument, such as images, style sheets and scripts.
http://en.wikipedia.org/wiki/Computer_hardwarehttp://en.wikipedia.org/wiki/Softwarehttp://en.wikipedia.org/wiki/Web_contenthttp://en.wikipedia.org/wiki/Internethttp://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/Websitehttp://en.wikipedia.org/wiki/Online_gamehttp://en.wikipedia.org/wiki/Enterprise_softwarehttp://en.wikipedia.org/wiki/Web_pagehttp://en.wikipedia.org/wiki/Client_(computing)http://en.wikipedia.org/wiki/Hypertext_Transfer_Protocolhttp://en.wikipedia.org/wiki/Hypertext_Transfer_Protocolhttp://en.wikipedia.org/wiki/HTMLhttp://en.wikipedia.org/wiki/Imagehttp://en.wikipedia.org/wiki/Style_sheet_(web_development)http://en.wikipedia.org/wiki/Javascripthttp://en.wikipedia.org/wiki/Javascripthttp://en.wikipedia.org/wiki/Style_sheet_(web_development)http://en.wikipedia.org/wiki/Imagehttp://en.wikipedia.org/wiki/HTMLhttp://en.wikipedia.org/wiki/Hypertext_Transfer_Protocolhttp://en.wikipedia.org/wiki/Hypertext_Transfer_Protocolhttp://en.wikipedia.org/wiki/Client_(computing)http://en.wikipedia.org/wiki/Web_pagehttp://en.wikipedia.org/wiki/Enterprise_softwarehttp://en.wikipedia.org/wiki/Online_gamehttp://en.wikipedia.org/wiki/Websitehttp://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/Internethttp://en.wikipedia.org/wiki/Web_contenthttp://en.wikipedia.org/wiki/Softwarehttp://en.wikipedia.org/wiki/Computer_hardware


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A user agent, commonly a web browser orweb crawler, initiates communication bymaking a request for a specific resource

using HTTP and the server responds with thecontent of that resource or an error messageif unable to do so. The resource is typically a

real file on the server's secondary memory,but this is not necessarily the case anddepends on how the web server isimplemented.
http://en.wikipedia.org/wiki/User_agenthttp://en.wikipedia.org/wiki/Web_browserhttp://en.wikipedia.org/wiki/Web_crawlerhttp://en.wikipedia.org/wiki/Hypertext_Transfer_Protocolhttp://en.wikipedia.org/wiki/List_of_HTTP_status_codeshttp://en.wikipedia.org/wiki/Secondary_memoryhttp://en.wikipedia.org/wiki/Implementationhttp://en.wikipedia.org/wiki/Implementationhttp://en.wikipedia.org/wiki/Secondary_memoryhttp://en.wikipedia.org/wiki/List_of_HTTP_status_codeshttp://en.wikipedia.org/wiki/Hypertext_Transfer_Protocolhttp://en.wikipedia.org/wiki/Web_crawlerhttp://en.wikipedia.org/wiki/Web_browserhttp://en.wikipedia.org/wiki/User_agent


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While the primary function is to serve content, a fullimplementation of HTTP also includes ways of receivingcontent from clients. This feature is used for submittingweb forms, including uploading of files.

Many generic web servers also support server-side

scripting using Active Server Pages (ASP), PHP, or otherscripting languages. This means that the behaviour of theweb server can be scripted in separate files, while theactual server software remains unchanged. Usually, thisfunction is used to create HTML documents dynamically

("on-the-fly") as opposed to returning static documents.The former is primarily used for retrieving and/ormodifying information from databases. The latter istypically much faster and more easily cached.
http://en.wikipedia.org/wiki/Form_(web)http://en.wikipedia.org/wiki/Uploadhttp://en.wikipedia.org/wiki/Server-side_scriptinghttp://en.wikipedia.org/wiki/Server-side_scriptinghttp://en.wikipedia.org/wiki/Active_Server_Pageshttp://en.wikipedia.org/wiki/PHPhttp://en.wikipedia.org/wiki/Scripting_languagehttp://en.wikipedia.org/wiki/Dynamic_web_pagehttp://en.wikipedia.org/wiki/Static_web_pagehttp://en.wikipedia.org/wiki/Databasehttp://en.wikipedia.org/wiki/Web_cachehttp://en.wikipedia.org/wiki/Web_cachehttp://en.wikipedia.org/wiki/Databasehttp://en.wikipedia.org/wiki/Static_web_pagehttp://en.wikipedia.org/wiki/Dynamic_web_pagehttp://en.wikipedia.org/wiki/Scripting_languagehttp://en.wikipedia.org/wiki/PHPhttp://en.wikipedia.org/wiki/Active_Server_Pageshttp://en.wikipedia.org/wiki/Server-side_scriptinghttp://en.wikipedia.org/wiki/Server-side_scriptinghttp://en.wikipedia.org/wiki/Server-side_scriptinghttp://en.wikipedia.org/wiki/Server-side_scriptinghttp://en.wikipedia.org/wiki/Uploadhttp://en.wikipedia.org/wiki/Form_(web)


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Web servers are not always used for serving the World Wide Web.They can also be found embedded in devices such as printers,routers, webcams and serving only a local network. The web servermay then be used as a part of a system for monitoring and/oradministering the device in question. This usually means that no

additional software has to be installed on the client computer, sinceonly a web browser is required (which now is included with mostoperating systems).

In 1989 Tim Berners-Lee proposed a new project with the goal ofeasing the exchange of information between scientists by using a

hypertext system to his employer CERN. The project resulted inBerners-Lee writing two programs in 1990:

A browser called WorldWideWeb
http://en.wikipedia.org/wiki/World_Wide_Webhttp://en.wikipedia.org/wiki/Embedded_systemhttp://en.wikipedia.org/wiki/Printer_(computing)http://en.wikipedia.org/wiki/Router_(computing)http://en.wikipedia.org/wiki/Webcamhttp://en.wikipedia.org/wiki/Local_Area_Networkhttp://en.wikipedia.org/wiki/Operating_systemhttp://en.wikipedia.org/wiki/Tim_Berners-Leehttp://en.wikipedia.org/wiki/Hypertexthttp://en.wikipedia.org/wiki/CERNhttp://en.wikipedia.org/wiki/Web_browserhttp://en.wikipedia.org/wiki/WorldWideWebhttp://en.wikipedia.org/wiki/WorldWideWebhttp://en.wikipedia.org/wiki/Web_browserhttp://en.wikipedia.org/wiki/CERNhttp://en.wikipedia.org/wiki/Hypertexthttp://en.wikipedia.org/wiki/Tim_Berners-Leehttp://en.wikipedia.org/wiki/Tim_Berners-Leehttp://en.wikipedia.org/wiki/Tim_Berners-Leehttp://en.wikipedia.org/wiki/Operating_systemhttp://en.wikipedia.org/wiki/Local_Area_Networkhttp://en.wikipedia.org/wiki/Webcamhttp://en.wikipedia.org/wiki/Router_(computing)http://en.wikipedia.org/wiki/Printer_(computing)http://en.wikipedia.org/wiki/Embedded_systemhttp://en.wikipedia.org/wiki/World_Wide_Web


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The world's first web server, later known as CERNhttpd, which ran on NeXTSTEP

Between 1991 and 1994, the simplicity andeffectiveness of early technologies used to surf andexchange data through the World Wide Web helped toport them to many different operating systems andspread their use among scientific organizations anduniversities, and then to industry.

In 1994 Tim Berners-Lee decided to constitute theWorld Wide Web Consortium (W3C) to regulate thefurther development of the many technologies involved(HTTP, HTML, etc.) through a
http://en.wikipedia.org/wiki/CERN_httpdhttp://en.wikipedia.org/wiki/CERN_httpdhttp://en.wikipedia.org/wiki/NeXTSTEPhttp://en.wikipedia.org/wiki/World_Wide_Web_Consortiumhttp://en.wikipedia.org/wiki/HTTPhttp://en.wikipedia.org/wiki/HTMLhttp://en.wikipedia.org/wiki/HTMLhttp://en.wikipedia.org/wiki/HTTPhttp://en.wikipedia.org/wiki/World_Wide_Web_Consortiumhttp://en.wikipedia.org/wiki/NeXTSTEPhttp://en.wikipedia.org/wiki/CERN_httpdhttp://en.wikipedia.org/wiki/CERN_httpd


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Virtual hosting to serve many Web sites usingone IP address

Large file support to be able to serve files

whose size is greater than 2 GB on 32 bit OS Bandwidth throttling to limit the speed of

responses in order to not saturate the networkand to be able to serve more clients

Server-side scripting to generate dynamicWeb pages, still keeping web server andwebsite implementations sepa
http://en.wikipedia.org/wiki/Virtual_hostinghttp://en.wikipedia.org/wiki/IP_addresshttp://en.wikipedia.org/wiki/Large_file_supporthttp://en.wikipedia.org/wiki/Operating_systemhttp://en.wikipedia.org/wiki/Bandwidth_throttlinghttp://en.wikipedia.org/wiki/Server-side_scriptinghttp://en.wikipedia.org/wiki/Dynamic_Web_pagehttp://en.wikipedia.org/wiki/Dynamic_Web_pagehttp://en.wikipedia.org/wiki/Dynamic_Web_pagehttp://en.wikipedia.org/wiki/Dynamic_Web_pagehttp://en.wikipedia.org/wiki/Server-side_scriptinghttp://en.wikipedia.org/wiki/Server-side_scriptinghttp://en.wikipedia.org/wiki/Server-side_scriptinghttp://en.wikipedia.org/wiki/Bandwidth_throttlinghttp://en.wikipedia.org/wiki/Operating_systemhttp://en.wikipedia.org/wiki/Large_file_supporthttp://en.wikipedia.org/wiki/IP_addresshttp://en.wikipedia.org/wiki/Virtual_hosting


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Web servers are able to map the pathcomponent of a Uniform Resource Locator(URL) into:

A local file system resource (for static requests) An internal or external program name (for

dynamic requests)

For a static requestthe URL path specified by

the client is relative to the web server's rootdirectory.

Consider the following URL as it would berequested by a
http://en.wikipedia.org/wiki/Uniform_Resource_Locatorhttp://en.wikipedia.org/wiki/Uniform_Resource_Locator


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WEB PAGE A web page or webpage is a document or information resource that issuitable for the World Wide Web and can be accessed through a web

browser and displayed on a monitor or mobile device. This information isusually in HTML or XHTML format, and may provide navigation to otherweb pages via hypertextlinks. Web pages frequently subsume otherresources such as style sheets, scripts and images into their finalpresentation.

Web pages may be retrieved from a local computer or from a remoteweb server. The web server may restrict access only to a privatenetwork, e.g. a corporate intranet, or it may publish pages on the WorldWide Web. Web pages are requested and served from web serversusing Hypertext Transfer Protocol (HTTP).

Web pages may consist of files of static text and other content storedwithin the web server's file system (static web pages), or may beconstructed by server-side software when they are requested (dynamicweb pages). Client-side scripting can make web pages more responsiveto user input once on the client browser.
http://en.wikipedia.org/wiki/Documenthttp://en.wikipedia.org/wiki/Resource_(Web)http://en.wikipedia.org/wiki/World_Wide_Webhttp://en.wikipedia.org/wiki/Web_browserhttp://en.wikipedia.org/wiki/Web_browserhttp://en.wikipedia.org/wiki/Computer_displayhttp://en.wikipedia.org/wiki/Mobile_devicehttp://en.wikipedia.org/wiki/HTMLhttp://en.wikipedia.org/wiki/XHTMLhttp://en.wikipedia.org/wiki/Navigation_barhttp://en.wikipedia.org/wiki/Hypertexthttp://en.wikipedia.org/wiki/Hyperlinkhttp://en.wikipedia.org/wiki/Cascading_Style_Sheethttp://en.wikipedia.org/wiki/Client-side_scriptinghttp://en.wikipedia.org/wiki/Imageshttp://en.wikipedia.org/wiki/Web_serverhttp://en.wikipedia.org/wiki/Intranethttp://en.wikipedia.org/wiki/Server_(computing)http://en.wikipedia.org/wiki/Hypertext_Transfer_Protocolhttp://en.wikipedia.org/wiki/Web_contenthttp://en.wikipedia.org/wiki/Web_serverhttp://en.wikipedia.org/wiki/Static_Web_pagehttp://en.wikipedia.org/wiki/Server-side_scriptinghttp://en.wikipedia.org/wiki/Dynamic_web_pagehttp://en.wikipedia.org/wiki/Dynamic_web_pagehttp://en.wikipedia.org/wiki/Client-side_scriptinghttp://en.wikipedia.org/wiki/Client-side_scriptinghttp://en.wikipedia.org/wiki/Client-side_scriptinghttp://en.wikipedia.org/wiki/Client-side_scriptinghttp://en.wikipedia.org/wiki/Dynamic_web_pagehttp://en.wikipedia.org/wiki/Dynamic_web_pagehttp://en.wikipedia.org/wiki/Server-side_scriptinghttp://en.wikipedia.org/wiki/Server-side_scriptinghttp://en.wikipedia.org/wiki/Server-side_scriptinghttp://en.wikipedia.org/wiki/Static_Web_pagehttp://en.wikipedia.org/wiki/Web_serverhttp://en.wikipedia.org/wiki/Web_contenthttp://en.wikipedia.org/wiki/Hypertext_Transfer_Protocolhttp://en.wikipedia.org/wiki/Server_(computing)http://en.wikipedia.org/wiki/Intranethttp://en.wikipedia.org/wiki/Web_serverhttp://en.wikipedia.org/wiki/Imageshttp://en.wikipedia.org/wiki/Client-side_scriptinghttp://en.wikipedia.org/wiki/Cascading_Style_Sheethttp://en.wikipedia.org/wiki/Hyperlinkhttp://en.wikipedia.org/wiki/Hypertexthttp://en.wikipedia.org/wiki/Navigation_barhttp://en.wikipedia.org/wiki/XHTMLhttp://en.wikipedia.org/wiki/HTMLhttp://en.wikipedia.org/wiki/Mobile_devicehttp://en.wikipedia.org/wiki/Computer_displayhttp://en.wikipedia.org/wiki/Web_browserhttp://en.wikipedia.org/wiki/Web_browserhttp://en.wikipedia.org/wiki/World_Wide_Webhttp://en.wikipedia.org/wiki/Resource_(Web)http://en.wikipedia.org/wiki/Document


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Web pages usually include information as to the colours of text andbackgrounds and very often also contain links to images and sometimesother types of media to be included in the final view. Layout, typographicand color-scheme information is provided by Cascading Style Sheet(CSS) instructions, which can either be embedded in the HTML or canbe provided by a separate file, which is referenced from within theHTML. The latter case is especially relevant where one lengthystylesheet is relevant to a whole website: due to the way HTTP works,the browser will only download it once from the web server and use thecached copy for the whole site. Images are stored on the web server asseparate files, but again HTTP allows for the fact that once a web pageis downloaded to a browser, it is quite likely that related files such asimages and stylesheets will be requested as it is processed. An HTTP

1.1 web server will maintain a connection with the browser until allrelated resources have been requested and provided. Web browsersusually render images along with the text and other material on thedisplayed web page.
http://en.wikipedia.org/wiki/Hypermediahttp://en.wikipedia.org/wiki/Cascading_Style_Sheethttp://en.wikipedia.org/wiki/Websitehttp://en.wikipedia.org/wiki/Web_cachehttp://en.wikipedia.org/wiki/HTTP_persistent_connectionhttp://en.wikipedia.org/wiki/Web_browserhttp://en.wikipedia.org/wiki/Web_browserhttp://en.wikipedia.org/wiki/HTTP_persistent_connectionhttp://en.wikipedia.org/wiki/Web_cachehttp://en.wikipedia.org/wiki/Websitehttp://en.wikipedia.org/wiki/Cascading_Style_Sheethttp://en.wikipedia.org/wiki/Hypermedia


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Main article: dynamic web page

Client-side computer code such asJavaScript or code implementing Ajax

techniques can be provided either embeddedin the HTML of a web page or, like CSSstylesheets, as separate, linked downloads

specified in the HTML. These scripts may runon the client computer, if the user allows.
http://en.wikipedia.org/wiki/Dynamic_web_pagehttp://en.wikipedia.org/wiki/JavaScripthttp://en.wikipedia.org/wiki/Ajax_(programming)http://en.wikipedia.org/wiki/Ajax_(programming)http://en.wikipedia.org/wiki/JavaScripthttp://en.wikipedia.org/wiki/Dynamic_web_page


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A web browser can have a Graphical UserInterface, like Internet Explorer, MozillaFirefox, Chrome and Opera, or can be text-

based, like Lynx or Links.
http://en.wikipedia.org/wiki/Web_browserhttp://en.wikipedia.org/wiki/Graphical_User_Interfacehttp://en.wikipedia.org/wiki/Graphical_User_Interfacehttp://en.wikipedia.org/wiki/Internet_Explorerhttp://en.wikipedia.org/wiki/Mozilla_Firefoxhttp://en.wikipedia.org/wiki/Mozilla_Firefoxhttp://en.wikipedia.org/wiki/Google_Chromehttp://en.wikipedia.org/wiki/Opera_(web_browser)http://en.wikipedia.org/wiki/Command_Line_Interfacehttp://en.wikipedia.org/wiki/Command_Line_Interfacehttp://en.wikipedia.org/wiki/Lynx_(web_browser)http://en.wikipedia.org/wiki/Links_(web_browser)http://en.wikipedia.org/wiki/Links_(web_browser)http://en.wikipedia.org/wiki/Lynx_(web_browser)http://en.wikipedia.org/wiki/Command_Line_Interfacehttp://en.wikipedia.org/wiki/Command_Line_Interfacehttp://en.wikipedia.org/wiki/Command_Line_Interfacehttp://en.wikipedia.org/wiki/Opera_(web_browser)http://en.wikipedia.org/wiki/Google_Chromehttp://en.wikipedia.org/wiki/Mozilla_Firefoxhttp://en.wikipedia.org/wiki/Mozilla_Firefoxhttp://en.wikipedia.org/wiki/Internet_Explorerhttp://en.wikipedia.org/wiki/Graphical_User_Interfacehttp://en.wikipedia.org/wiki/Graphical_User_Interfacehttp://en.wikipedia.org/wiki/Web_browser


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Web users with disabilities often use assistive technologies andadaptive strategies to access web pages.[1] Users may be colorblind, may or may not want to use a mouse perhaps due to repetitivestress injury or motor-neurone problems, may be deaf and requireaudio to be captioned, may be blind and using a screen reader orbraille display, may need screen magnification, etc.

Disabled and able-bodied users may disable the download andviewing of images and other media, to save time, network bandwidthor merely to simplify their browsing experience. Users of mobiledevices often have restricted displays and bandwidth. Anyone mayprefer not to use the fonts, font sizes, styles and color schemesselected by the web page designer and may apply their own CSSstyling to the page.

The World Wide Web Consortium (W3C) and Web AccessibilityInitiative (WAI) recommend that all web pages should be designedwith all of these options in mind.
http://en.wikipedia.org/wiki/Web_accessibilityhttp://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/Screen_readerhttp://en.wikipedia.org/wiki/Braillehttp://en.wikipedia.org/wiki/World_Wide_Web_Consortiumhttp://en.wikipedia.org/wiki/Web_Accessibility_Initiativehttp://en.wikipedia.org/wiki/Web_Accessibility_Initiativehttp://en.wikipedia.org/wiki/Web_Accessibility_Initiativehttp://en.wikipedia.org/wiki/Web_Accessibility_Initiativehttp://en.wikipedia.org/wiki/World_Wide_Web_Consortiumhttp://en.wikipedia.org/wiki/Braillehttp://en.wikipedia.org/wiki/Screen_readerhttp://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/Web_accessibility


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A web page, as an information set, can contain numeroustypes of information, which is able to be seen, heard orinteract by the end user:

Perceived (rendered) information:

Textual information: with diverse render variations.

Non-textual information: Static imagesmay be raster graphics, typically GIF, JPEG or PNG; or vector

formats such as SVG or Flash.

Animated imagestypically Animated GIF and SVG, but also may be Flash,Shockwave, or Java applet.

Audio, typically MP3, ogg or various proprietary formats.

Video, WMV (Windows), RM (Real Media), FLV (Flash Video), MPG, MOV(QuickTime)

Interactive information: see interactive media." "
http://en.wikipedia.org/wiki/End-userhttp://en.wikipedia.org/wiki/Raster_graphicshttp://en.wikipedia.org/wiki/Graphics_Interchange_Formathttp://en.wikipedia.org/wiki/JPEGhttp://en.wikipedia.org/wiki/Portable_Network_Graphicshttp://en.wikipedia.org/wiki/Vector_graphicshttp://en.wikipedia.org/wiki/Vector_graphicshttp://en.wikipedia.org/wiki/Scalable_Vector_Graphicshttp://en.wikipedia.org/wiki/Adobe_Flashhttp://en.wikipedia.org/wiki/Animated_gifhttp://en.wikipedia.org/wiki/Scalable_Vector_Graphicshttp://en.wikipedia.org/wiki/Adobe_Flashhttp://en.wikipedia.org/wiki/Adobe_Shockwavehttp://en.wikipedia.org/wiki/Java_applethttp://en.wikipedia.org/wiki/Audio_frequencyhttp://en.wikipedia.org/wiki/MP3http://en.wikipedia.org/wiki/Ogghttp://en.wikipedia.org/wiki/Videohttp://en.wikipedia.org/wiki/Interactive_mediahttp://en.wikipedia.org/wiki/Interactive_mediahttp://en.wikipedia.org/wiki/Videohttp://en.wikipedia.org/wiki/Ogghttp://en.wikipedia.org/wiki/MP3http://en.wikipedia.org/wiki/Audio_frequencyhttp://en.wikipedia.org/wiki/Java_applethttp://en.wikipedia.org/wiki/Adobe_Shockwavehttp://en.wikipedia.org/wiki/Adobe_Flashhttp://en.wikipedia.org/wiki/Scalable_Vector_Graphicshttp://en.wikipedia.org/wiki/Animated_gifhttp://en.wikipedia.org/wiki/Adobe_Flashhttp://en.wikipedia.org/wiki/Scalable_Vector_Graphicshttp://en.wikipedia.org/wiki/Vector_graphicshttp://en.wikipedia.org/wiki/Vector_graphicshttp://en.wikipedia.org/wiki/Portable_Network_Graphicshttp://en.wikipedia.org/wiki/JPEGhttp://en.wikipedia.org/wiki/Graphics_Interchange_Formathttp://en.wikipedia.org/wiki/Raster_graphicshttp://en.wikipedia.org/wiki/End-user


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Interactive information: see interactive media. For "on page" interaction:

Interactive text: see DHTML.

Interactive illustrations: ranging from "click to play" images to games,typically using script orchestration, Flash, Java applets, SVG, or Shockwave.

Buttons: forms providing alternative interface, typically for use with scriptorchestrationand DHTML.

For "between pages" interaction:

Hyperlinks: standard "change page" reactivity.

Forms: providing more interaction with the server and server-sidedatabases.
http://en.wikipedia.org/wiki/Interactive_mediahttp://en.wikipedia.org/wiki/DHTMLhttp://en.wikipedia.org/wiki/Browser_gamehttp://en.wikipedia.org/wiki/Adobe_Flashhttp://en.wikipedia.org/wiki/Java_applethttp://en.wikipedia.org/wiki/Scalable_Vector_Graphicshttp://en.wikipedia.org/wiki/Adobe_Shockwavehttp://en.wikipedia.org/wiki/Adobe_Shockwavehttp://en.wikipedia.org/wiki/Scalable_Vector_Graphicshttp://en.wikipedia.org/wiki/Java_applethttp://en.wikipedia.org/wiki/Adobe_Flashhttp://en.wikipedia.org/wiki/Browser_gamehttp://en.wikipedia.org/wiki/DHTMLhttp://en.wikipedia.org/wiki/Interactive_media


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Internal (hidden) information: Comments Linked Files through Hyperlink (Like DOC,XLS,PDF,etc). Metadatawith semantic meta-information, Charset information, Document

Type Definition (DTD), etc. Diagramation and style information: information about rendered items (like

image size attributes) and visual specifications, as Cascading Style Sheets(CSS). Scripts, usually JavaScript, complement interactivity and functionality. Note: on server-side the web page may also have "Processing Instruction

Information Items". The web page can also contain dynamically adapted information elements,

dependent upon the rendering browser or end-user location (through theuse of IP address tracking and/or "cookie" information).

From a more general/wide point of view, some information (grouped)elements, like a navigation bar, are uniform for all website pages, like astandard. These kind of "website standard information" are supplied bytechnologies like web template systems.
http://en.wikipedia.org/wiki/Meta_tagshttp://en.wikipedia.org/wiki/Document_Type_Definitionhttp://en.wikipedia.org/wiki/Document_Type_Definitionhttp://en.wikipedia.org/wiki/Cascading_Style_Sheetshttp://en.wikipedia.org/wiki/JavaScripthttp://en.wikipedia.org/wiki/Navigation_barhttp://en.wikipedia.org/wiki/Web_template_systemhttp://en.wikipedia.org/wiki/Web_template_systemhttp://en.wikipedia.org/wiki/Navigation_barhttp://en.wikipedia.org/wiki/JavaScripthttp://en.wikipedia.org/wiki/Cascading_Style_Sheetshttp://en.wikipedia.org/wiki/Document_Type_Definitionhttp://en.wikipedia.org/wiki/Document_Type_Definitionhttp://en.wikipedia.org/wiki/Meta_tagshttp://en.wikipedia.org/wiki/Meta_tagshttp://en.wikipedia.org/wiki/Meta_tags


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Web pages will often require more screen space than is available for a particular displayresolution. Most modern browsers will place a scrollbar (a sliding tool at the side of thescreen that allows the user to move the page up or down, or side-to-side) in the window toallow the user to see all content. Scrolling horizontally is less prevalent than verticalscrolling, not only because such pages often do not print properly, but because itinconveniences the user more so than vertical scrolling would (because lines arehorizontal; scrolling back and forth for every line is much more inconvenient than scrollingafter reading a whole screen; also most computer keyboards have page up and down

keys, and many computer mice have vertical scroll wheels, but the horizontal scrollingequivalents are rare). When web pages are stored in a common directory of a web server, they become a

website. A website will typically contain a group of web pages that are linked together, orhave some other coherent method of navigation. The most important web page to have ona website is the index page. Depending on the web server settings, this index page canhave many different names, but the most common is index.html. When a browser visits thehomepage for a website, or any URL pointing to a directory rather than a specific file, the

web server will serve the index page to the requesting browser. If no index page is definedin the configuration, or no such file exists on the server, either an error or directory listingwill be served to the browser.
http://en.wikipedia.org/wiki/Display_resolutionhttp://en.wikipedia.org/wiki/Display_resolutionhttp://en.wikipedia.org/wiki/Scrollbarhttp://en.wikipedia.org/wiki/Computer_keyboardhttp://en.wikipedia.org/wiki/Mouse_(computing)http://en.wikipedia.org/wiki/Directory_(file_systems)http://en.wikipedia.org/wiki/Server_(computing)http://en.wikipedia.org/wiki/Websitehttp://en.wikipedia.org/wiki/Webserver_directory_indexhttp://en.wikipedia.org/wiki/Homepagehttp://en.wikipedia.org/wiki/Uniform_Resource_Locatorhttp://en.wikipedia.org/wiki/Uniform_Resource_Locatorhttp://en.wikipedia.org/wiki/Homepagehttp://en.wikipedia.org/wiki/Webserver_directory_indexhttp://en.wikipedia.org/wiki/Websitehttp://en.wikipedia.org/wiki/Server_(computing)http://en.wikipedia.org/wiki/Directory_(file_systems)http://en.wikipedia.org/wiki/Mouse_(computing)http://en.wikipedia.org/wiki/Computer_keyboardhttp://en.wikipedia.org/wiki/Scrollbarhttp://en.wikipedia.org/wiki/Display_resolutionhttp://en.wikipedia.org/wiki/Display_resolution


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A web page can either be a single HTML file, or made up of several HTML filesusing frames or Server Side Includes (SSIs). Frames have been known to causeproblems with web accessibility, copyright,[2] navigation, printing and searchengine rankings[3], and are now less often used than they were in the 1990s.[4][5]Both frames and SSIs allow certain content which appears on many pages, suchas page navigation or page headers, to be repeated without duplicating theHTML in many files. Frames and the W3C recommended alternative of 2000, the

tag,[4]

also allow some content to remain in one place while othercontent can be scrolled using conventional scrollbars. Modern CSS andJavaScript client-side techniques can also achieve all of these goals and more.

When creating a web page, it is important to ensure it conforms to the WorldWide Web Consortium (W3C) standards for HTML, CSS, XML and otherstandards. The W3C standards are in place to ensure all browsers whichconform to their standards can display identical content without any special

consideration for proprietary rendering techniques. A properly coded web page isgoing to be accessible to many different browsers old and new alike, displayresolutions, as well as those users with audio or visual impairments.
http://en.wikipedia.org/wiki/Framing_(World_Wide_Web)http://en.wikipedia.org/wiki/Server_Side_Includeshttp://en.wikipedia.org/wiki/Web_accessibilityhttp://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/HTML_elementhttp://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/Scrollbarhttp://en.wikipedia.org/wiki/JavaScripthttp://en.wikipedia.org/wiki/World_Wide_Web_Consortiumhttp://en.wikipedia.org/wiki/World_Wide_Web_Consortiumhttp://en.wikipedia.org/wiki/World_Wide_Web_Consortiumhttp://en.wikipedia.org/wiki/World_Wide_Web_Consortiumhttp://en.wikipedia.org/wiki/JavaScripthttp://en.wikipedia.org/wiki/Scrollbarhttp://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/HTML_elementhttp://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/Web_accessibilityhttp://en.wikipedia.org/wiki/Server_Side_Includeshttp://en.wikipedia.org/wiki/Framing_(World_Wide_Web)


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In order to graphically display a web page, aweb browser is needed. This is a type ofsoftware that can retrieve web pages from

the Internet. Most current web browsersinclude the ability to view the source code.Viewing a web page in a text editor will also

display the source code.
http://en.wikipedia.org/wiki/Application_softwarehttp://en.wikipedia.org/wiki/Internethttp://en.wikipedia.org/wiki/Source_codehttp://en.wikipedia.org/wiki/Source_codehttp://en.wikipedia.org/wiki/Internethttp://en.wikipedia.org/wiki/Application_software


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To create a web page, a text editor or a specialized HTML editoris needed. In order to upload the created web page to a webserver, traditionally an FTP client is needed.

The design of a web page is highly personal. A design can bemade according to one's own preference, or a premade webtemplate can be used. Web templates let web page designersedit the content of a web page without having to worry about theoverall aesthetics. Many people publish their own web pagesusing products like Tripod, or Angelfire. These web publishingtools offer free page creation and hosting up to a certain size limit.

Other ways of making a web page is to download specialized

software, like a Wiki, CMS, or forum. These options allow forquick and easy creation of a web page which is typically dynamic.
http://en.wikipedia.org/wiki/Text_editorhttp://en.wikipedia.org/wiki/HTML_editorhttp://en.wikipedia.org/wiki/File_Transfer_Protocolhttp://en.wikipedia.org/wiki/Web_templatehttp://en.wikipedia.org/wiki/Web_templatehttp://en.wikipedia.org/wiki/Wikihttp://en.wikipedia.org/wiki/Content_management_systemhttp://en.wikipedia.org/wiki/Internet_forumhttp://en.wikipedia.org/wiki/Dynamic_web_pagehttp://en.wikipedia.org/wiki/Dynamic_web_pagehttp://en.wikipedia.org/wiki/Internet_forumhttp://en.wikipedia.org/wiki/Content_management_systemhttp://en.wikipedia.org/wiki/Wikihttp://en.wikipedia.org/wiki/Web_templatehttp://en.wikipedia.org/wiki/Web_templatehttp://en.wikipedia.org/wiki/File_Transfer_Protocolhttp://en.wikipedia.org/wiki/HTML_editorhttp://en.wikipedia.org/wiki/Text_editor


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SAVING

While one is viewing a web page, a copy of it is saved locally; thisis what is being viewed. Depending on the browser settings, thiscopy may be deleted at any time, or stored indefinitely,sometimes without the user realizing it. Most GUI browsersprovide options for saving a web page more permanently. Thesemay include:

Save the rendered text without formatting or images, withhyperlinks reduced to plain text

Save the HTML as it was served Overall structure preserved,but some links may be broken

Save the HTML with relative links changed to absolute ones so

that hyperlinks are preserved Save the entire web page All images and other resources

including stylesheets and scripts are downloaded and saved in anew folder alongside the HTML, with links to them altered to referto the local copies. Other relative links changed to absolute


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Save the HTML as well as all images and other resources intoa single MHTML file. This is supported by Internet Explorerand Opera.[6] Other browsers may support this if a suitableplugin has been installed.

Most operating systems allow applications such as webbrowsers not only to print the currently viewed web page to aprinter, but optionally to "print" to a file that can be viewed orprinted later. Some web pages are designed, for example byuse of CSS, so that hyperlinks, menus and other navigationitems, which will be useless on paper, are rendered into printwith this in mind. Sometimes, the destination addresses ofhyperlinks may be shown explicitly, either within the body ofthe page or listed at the end of the printed version. Web pagedesigners may specify in CSS that non-functional menus,navigational blocks and other items may simply be absentfrom the printed version.

WEBSITE
http://en.wikipedia.org/wiki/MHTMLhttp://en.wikipedia.org/wiki/Internet_Explorerhttp://en.wikipedia.org/wiki/Opera_(web_browser)http://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/Opera_(web_browser)http://en.wikipedia.org/wiki/Internet_Explorerhttp://en.wikipedia.org/wiki/MHTML


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WEBSITE

A website, also written as Web site,[1]web site, orsimply site,[2] is a set of related web pages containingcontent (media) such as text, image, video, audio,etc. A website is hosted on at least one web server,accessible via a network such as the Internet

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