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1 Introduction to Internet

1.1 Introduction

By the turn of the century, information, including access to the Internet, will be the basis for personal, economic, and political advancement The popular name for the Internet is the information superhighway Whether you want to find the latest financial news, browse through library catalogs, exchange information with colleagues, or join in a lively political debate, the Internet is the tool that will take you beyond telephones, faxes, and isolated computers to a burgeoning networked information frontier The Internet supplements the traditional tools you use to gather information, Data Graphics, News and correspond with other people Used skillfully, the Internet shrinks the world and brings information, expertise, and knowledge on nearly every subject imaginable straight to your computer

1 2 What is the Internet?

The Internet links are computer networks all over the world so that users can share resources and communicate with each other Some computers have direct access to all the facilities on the Internet such as the universities And other computers, eg privately-owned ones, have indirect links through a commercial service provider, who offers some

or all of the Internet facilities In order to be connected to Internet, you must go through service suppliers Many options are offered with monthly rates Depending on the option chosen, access time may vary

The Internet is what we call a metanetwork, that is, a network of networks that spans the globe It's impossible to give an exact count of the number of networks or users that comprise the Internet, but it is easily in the thousands and millions respectively The Internet employs a set of standardized protocols which allow for the sharing of resources among different kinds of computers that communicate with each other on the network These standards, sometimes referred to as the Internet Protocol Suite, are the rules that developers adhere to when creating new functions for the Internet The Internet is also what we call a distributed system; there is no central archives Technically, no one runs the Internet Rather, the Internet is made up of thousands of smaller networks The Internet thrives and develops as its many users find new ways to create, display and retrieve the information that constitutes the Internet

1.3 History & Development of the Internet

In its infancy, the Internet was originally conceived by the Department of Defense

as a way to protect government communications systems in the event of a military strike The original network, dubbed ARPANet (for the Advanced Research Projects Agency that developed it) evolved into a communications channel among contractors, military personnel, and university researchers who were contributing to ARPA projects

The network employed a set of standard protocols to create an effective way for these people to communicate and share data with each other ARPAnet's popularity continued to spread among researchers and in the 1980 the National Science Foundation, whose NSFNet, linked several high speed computers, took charge of what had come to be known as the Internet

By the late 1980's, thousands of cooperating networks were participating in the Internet

In 1991, the U.S High Performance Computing Act established the NREN (National Research & Education Network) NREN's goal was to develop and maintain high-speed networks for research and education, and to investigate commercial uses for the Internet

The rest, as they say, is history in the making The Internet has been improved through the developments of such services as Gopher and the World Wide Web Even though the Internet is predominantly thought of as a research oriented network,

it continues to grow as an informational, creative, and commercial resource every day and all over the world

Birth of Internet - Key terms:

 1960 most universities and Government agencies had individual

mainframe computers, which were not interconnected

 1968 The national Physical Laboratory in Great Britain was the first to set up the test network

 1969 Pentagon’s Department of ARPA came out with the first infant network with four nodes

 Which was named as ARPANET

 1971 there were fifteen nodes in ARPANET

 1972 thirty seven nodes were added

 1980 NSF net (National Science Foundation)

1.4 Features of internet

a Key Web Features

b Key Usenet Newsgroups Features

c Key Email Features

d Key Mailing List Features

a) Key Web Features

 Ease Of Use

 Universal Access

 Search Capabilities

The web leverages the key features of the Internet and makes them widely accessible

to the public Key features of the web in particular are its ease of use, universal accessibility, and ability to be quickly searched:

• Ease of use The web can be immediately used by anyone already familiar with a computer window The only special features are links, which are as natural and intuitive to use as pressing a button This ease of use enabled the rapid adoption of the web in the 1990's, and led to the establishment of the Internet around the world

• Universal access The open design of the web makes it easy to build web browsers for a wide range of devices Web browsers have been deployed on cell phones and personal organizers, and the web is now the standard interface for providing access to information

• Search capabilities The development of search sites greatly multiplied the power and usefulness of the web by providing the capability to effectively search the content of millions of web pages in seconds Search sites significantly enabled the web to realize Vannevar Bush's vision of an automated library system

b) Key Usenet Newsgroups Features

Usenet messages are organized in newsgroups and threads that are stored

in Usenet archives indefinitely for later retrieval by anyone that wishes to access

them, even years later, connecting people across generations

Mailing lists, IRC, and MUD's also provide group communications, although on a lessor scale

• Common space The Usenet is the second largest common public space in existence, next to the Internet itself Anyone can post anything they wish to any newsgroup, and anyone can read any message they wish from any newsgroup

Like most common spaces, the Usenet therefore reflects the best and worst

of human nature, from community newsgroups where people are focused on selflessly helping each other, to less worthwhile groups where the postings are filled with pointless and counterproductive information

Like most common spaces, messages posted on the Usenet are public property

and can be freely copied and reused in other sources, although Usenet netiquette

mandates that credit should always be provided

c) Key Email Features

 Email Is A Push Technology

 Email Waits For You

 Email Is One-To-Many

 Email Is A Push Technology

Email is delivered to the recipient so they don't have to work to get it they just open their Inbox and there it is

Technologies are sometimes labeled push or pull as described below:

• Pull These technologies require the user to actively go and retrieve the information A library, the Web, and the Usenet are pull technologies, requiring active participation of a human being to retrieve the information

• Push These technologies deliver information to the user so all they have to do is receive it Radio, television, and email are push technologies

One of the reasons email has been such a big success is because it is a push technology The person that sends the email writes it, then POP3 and SMTP transmit it, and all the recipient has to do is open his email program and double-click on the email to read it

An advantage of push technologies is their ease of use they require a minimum of effort on the part of the recipient, which greatly supports adoption because they get used more often Partly because of this feature, the use of email has greatly outstripped all other Internet applications since its creation, even after the explosive development of the Web

 Email Waits For You

Email is particularly convenient because it is asynchronous; it waits for you and fits into your schedule instead of demanding that you structure your activities to synchronize with those you communicate with

For example, an email recipient doesn't have to be available when you compose and send an email you can send it at the time that is most convenient to you Similarly, you don't have to be available or even connected to the Internet when someone else sends you email it waits on your server until you log in and download it when most convenient to

Email provides the convenience that voice mail later provided for telephones except that voice mail is more ephemeral, cannot be conveniently edited, and is usually accompanied by a preference to talk to the other party in real time With email you know that the medium is inherently asynchronous, so you tend to write down all the information the addressee needs so they can respond when they are able.

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

• Receiving You can receive information that has been mailed to more than one person, for example 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 sending emails individually; you can save large amounts of time by sending one email to several people at once

Similarly, when you receive an email from an Internet mailing list you are getting information that would probably be impractical to receive any other way, since most organizations don't have the time or resources to send out paper based notices individually to hundreds or even thousands of people

e Key Mailing List Features

 One-to-many communication

Mailing lists enable powerful one-to-many communications

Because mailing lists are based on email, they share the key features of email

Mailing lists also build on that technology to create a new capability called many" functionality, enabling one person to communicate with many people at the same time This feature is a virtual Internet extension of the real-world communication power

"one-to-of a person speaking to a group, except that the members "one-to-of the audience may be located anywhere in the world

The reverse is also true: mailing lists can give one person unique access to the

informed opinion of a diverse group of people on various subjects with little effort the

email arrives from the groups they have subscribed to, and they then read the ones they want

Like so many of the Internet technologies, mailing lists are important primarily because of their power to bring people around the world together in a single communication setting

• Dial Up Connection (telephone line)

• DSL (Digital Subscriber Line) (broadband)

– Asymmetric digital Subscriber line (ADSL)

– Symmetric digital Subscriber line (SDSL)

– Depending upon the speed

• High-data-rate DSL (HDSL)

• Very high DSL (VDSL)

• RF Link (radio frequency)

• ISDN (Integrated Services Digital Network)

• A Cable modem.( cable TV line)

1.6 What makes the internet work?

The unique thing about the Internet is that it allows many different computers

to connect and talk to each other This is possible because of a set of standards, known as protocols that govern the transmission of data over the network: TCP/IP (Transmission Control Protocol/Internet Protocol) Most people who use the Internet aren't so interested in details related to these protocols They do, however, want to know what they can do on the Internet and how to do it effectively

1.7 The Client/Server Model

The most popular Internet tools operate as client/server systems You're running a program called a Web client This piece of software displays documents for you and

say, to set up a Telnet session, or to download a file your Web client will take care of this, too Your Web client connects (or "talks") to a Web server to ask for information on your behalf.

The Web server is a computer running another type of Web software which provides data, or "serves up" an information resource to your Web client

All of the basic Internet tools including Telnet, FTP, Gopher, and the World Wide Web are based upon the cooperation of a client and one or more servers In each case, you interact with the client program and it manages the details of how data is presented to you or the way in which you can look for resources In turn, the client interacts with one

or more servers where the information resides The server receives a request, processes it, and sends a result, without having to know the details of your computer system, because the client software on your computer system is handling those details The advantage of the client/server model lies in distributing the work so that each tool can focus or specialize on particular tasks: the server serves information to many users while the client software for each user handles the individual user's interface and other details of the requests and results

Characteristics of a client

• Initiates requests

• Waits for replies

• Receives replies

• Usually connects to a small number of servers at one time

• Typically interacts directly with end-users using a graphical user interface

Characteristics of a server

• Never initiates requests or activities

• Waits for and replies to requests from connected clients

• A server can remotely install/uninstall applications and transfer data to the intended clients

1.8 Electronic mail on the internet:

Electronic mail, or e-mail, is probably the most popular and widely used Internet function E-mail, email, or just mail, is a fast and efficient way to communicate with friends or colleagues You can communicate with one person at a time or thousands; you can receive and send files and other information You can even subscribe to electronic journals and newsletters You can send an e-mail message to a person in the same building or on the other side of the world

1.9 How does E-mail Work

E-mail is an asynchronous form of communication, meaning that the person whom you want to read your message doesn't have to be available at the precise moment you send your message This is a great convenience for both you and the recipient

On the other hand, the telephone, which is a synchronous communication medium, requires that both you and your listener be on the line at the same time in order for you to communicate (unless you leave a voice message) It will be impossible to discuss all the details of the many e-mail packages available to Internet users

Fortunately, however, most of these programs share basic functionality which allows you to:

 Send and receive mail messages

 save your messages in a file

 print mail messages

 reply to mail messages

 attach a file to a mail message

• WWW was found in the year 1989 by Tim Berners-Lee of CERN (the European Organization for Nuclear Research)

• He founded the basic HTML to use on the web

• In October 1994 Time Berners-Lee founded the World Wide Web consortium organization for developing nonproprietary

WWW (World Wide Web)-Key TermsWeb pages, Web Site, Portal, Web Servers,Mail Server, File Server, News Server, DNS

2 HTML 4 ProtocolsProtocols Introduction

• A protocol is a program written as per mutually accepted standard that two

computers use to communicate with each other

• Computers use protocols to format consistently their message so that other

computer can understand them

The Protocols determines the following:

• The type of error checking to be used

• Data compression method, if any

• How they sending device will indicate that it has finished sending a message

• How they receiving device will indicate that it has received a message

• There are varieties of standard protocols from which programmers can choose

• Each has particular advantages and disadvantages,

• Ex: Some are simpler than others Some are most reliable, and some are faster

Some standard protocols

• Simple Mail Transfer protocol (SMTP)

• Post Office Protocol version3 (POP3)

• Transmission Control Protocol/Internet Protocol (TCP/IP)

• Hyper Text Transfer Protocol (HTTP)

• File Transfer Protocol (FTP)

• Internet Mail Access Protocol (IMAP)

• Multipurpose Internet Mail Extensions (MIME)

• Network News Transfer Protocol (NNTP)

2.1 Hyper Text Transfer Protocol (HTTP).

HTTP is the network protocol of the Web It is both simple and powerful Knowing HTTP enables you to write Web browsers, Web servers, automatic page downloader’s, link-checkers, and other useful tools

2.1.1 What is HTTP

HTTP stands for Hypertext Transfer Protocol It's the network protocol used to deliver

virtually all files and other data (collectively called resources) on the World Wide Web,

whether they're HTML files, image files, query results, or anything else Usually, HTTP takes place through TCP/IP sockets (and this tutorial ignores other possibilities)

A browser is an HTTP client because it sends requests to an HTTP server (Web server),

which then sends responses back to the client The standard (and default) port for HTTP servers to listen on is 80, though they can use any port

2.1.2 What are "Resources"

HTTP is used to transmit resources, not just files A resource is some chunk of

information that can be identified by a URL (it's the R in URL) The most common kind

of resource is a file, but a resource may also be a dynamically-generated query result, the output of a CGI script, a document that is available in several languages, or something else

While learning HTTP, it may help to think of a resource as similar to a file, but more general As a practical matter, almost all HTTP resources are currently either files or server-side script output

2.1.3 Structure of HTTP Transactions

Like most network protocols, HTTP uses the client-server model: An HTTP client opens

a connection and sends a request message to an HTTP server; the server then returns a response message, usually containing the resource that was requested After delivering the response, the server closes the connection (making HTTP a stateless protocol, i.e not

maintaining any connection information between transactions)

The format of the request and response messages is similar, and English-oriented Both kinds of messages consist of:

• an initial line,

• zero or more header lines,

• a blank line (i.e a CRLF by itself), and

• an optional message body (e.g a file, or query data, or query output)

Put another way, the format of an HTTP message is:

<initial line, different for request vs response>

Header1: value1

Header2: value2

Header3: value3

<optional message body goes here, like file contents or query data;

it can be many lines long, or even binary data $&*%@!^$@>

Initial lines and headers should end in CRLF, though you should gracefully handle lines ending in just LF (More exactly, CR and LF here mean ASCII values 13 and 10, even though some platforms may use different characters.)

HTTP-Key Terms

• HTTP is the underlying protocol used by the WWW

• HTTP is stateless protocol (http is “stateless”

• server maintains no information about past client requests)

– Each visit as if the only visit so far

– Previous visits are not remembered by the server.

• HTTP Defines how messages are formatted and transmitted, and what action web servers and browsers should take in response to various commands

• HTTP is called a stateless protocol because each command is executed independently, without any knowledge of the commands that came before it

2.1.4 HTTP Versions: Past and Present

HTTP has evolved into multiple, mostly backwards-compatible protocol versions RFC

2145 describes the use of HTTP version numbers The client tells in the beginning of the request the version it uses, and the server uses the same or earlier version in the response

2.1.4.1 HTTP/0.9 (1991)

Deprecated Supports only one command, GET, which does not specify the HTTP version Does not support headers Since this version does not support POST, the information a client can pass to the server is limited by the URL length

Force PEP was originally intended to become a distinguishing feature of HTTP/1.2 In later PEP working drafts, however, the reference to HTTP/1.2 was removed The

experimental RFC 2774, HTTP Extension Framework, largely subsumed PEP It was

published in February 2000

The major changes between HTTP/1.0 and HTTP/1.1 include the way HTTP handles caching; how it optimizes bandwidth and network connections usage, manages error notifications; how it transmits messages over the network; how internet addresses are conserved; and how it maintains security and integrity

2.1.5 HTTP Methods

HTTP defines eight methods (sometimes referred to as "verbs") indicating the desired

action to be performed on the identified resource.

HEAD

Asks for the response identical to the one that would correspond to a GET request, but without the response body This is useful for retrieving meta-information written in response headers, without having to transport the entire content

GET

Requests a representation of the specified resource By far the most common method used on the Web today Should not be used for operations that cause side-effects (using it for actions in web applications is a common misuse) See safe methods below

POST

Submits data to be processed (e.g from an HTML form) to the identified resource The data is included in the body of the request This may result in the creation of a new resource or the updates of existing resources or both

Returns the HTTP methods that the server supports for specified URL This can

be used to check the functionality of a web server by requesting '*' instead of a specific resource

CONNECT

Converts the request connection to a transparent TCP/IP tunnel, usually to facilitate SSL-encrypted communication (HTTPS) through an unencrypted HTTP proxy

HTTP servers are required to implement at least the GET and HEAD methods and, whenever possible, also the OPTIONS method

2.1.6 Safe & Unsafe Methods

Some methods (e.g HEAD, GET, OPTIONS, and TRACE) are defined as safe,

which means they are intended only for information retrieval and should not change the state of the server (in other words, they should not have side effects) Repetition of the same GET request should therefore be harmless

Unsafe methods (such as POST, PUT and DELETE) should draw special attention, typically as a dialog box requesting confirmation of the action This is because repeated requests can cause side effects, such as unwanted duplication of a transaction

2.2 Simple Mail Transfer protocol (SMTP).

2.2.1 Introduction

The objective of the Simple Mail Transfer Protocol (SMTP) is to transfer mail reliably and efficiently

SMTP is independent of the particular transmission subsystem and requires only

a reliable ordered data stream channel While this document specifically discusses transport over TCP, other transports are possible

An important feature of SMTP is its capability to transport mail across networks, usually referred to as "SMTP mail relaying" A network consists of the mutually-TCP-accessible hosts on the public Internet, the mutually-TCP-accessible hosts

on a firewall-isolated TCP/IP Intranet, or hosts in some other LAN or WAN environment utilizing a non-TCP transport-level protocol

2.2.2 Structure of SMTP

The SMTP design is based on the following model of communication: as the result of a user mail request, the sender-SMTP establishes a two-way transmission channel to a receiver-SMTP The receiver-SMTP may be either the ultimate destination

or an intermediate SMTP commands are generated by the sender-SMTP and sent to the receiver-SMTP SMTP replies are sent from the receiver-SMTP to the sender-SMTP in response to the commands

Once the transmission channel is established, the SMTP-sender sends a MAIL command indicating the sender of the mail If the SMTP-receiver can accept mail it

responds with an OK reply The SMTP-sender then sends a RCPT command identifying

a recipient of the mail If the SMTP-receiver can accept mail for that recipient it responds with an OK reply; if not, it responds with a reply rejecting that recipient (but not the whole mail transaction) The SMTP-sender and SMTP-receiver may negotiate several recipients When the recipients have been negotiated the SMTP-sender sends the mail data, terminating with a special sequence If the SMTP-receiver successfully processes the mail data it responds with an OK reply The dialog is purposely lock-step, one-at-a-time

2.2.3 History of SMTP

The Mail Transfer Protocol (MTP) was first defined in RFC 772 in September

1980, and then updated in RFC 780 in May 1981 MTP describes a set of commands and procedures by which two devices can connect using TCP to exchange e-mail messages Its operation is described largely using elements borrowed from two early TCP/IP application protocols that were already in use at that time: Telnet and FTP The commands of MTP are in fact based directly on those of FTP

There wasn't anything inherently wrong with basing e-mail delivery on something like FTP, but defining it this way made MTP somewhat of a “hack” It was also restricted

to the capabilities defined by FTP, a general file transfer protocol, so it was not possible

to include features in the protocol that were specific to sending and receiving mail Due

to the importance of mail, a specific protocol designed for the purpose of delivering mail was warranted This protocol was first defined in RFC 788, published in November

e-1981: the Simple Mail Transfer Protocol (SMTP)

The name suggests that SMTP is “simpler” than the “non-simple” MTP that it replaced Whether this is true or not is somewhat a matter of opinion; I do note that RFC

788 is 61 pages long, while the earlier RFC 780 was only 43 pages What SMTP

definitely has over MTP is elegance; the protocol is designed specifically for the

transport of electronic mail While it retains certain similarities to FTP, it is an

“independent” protocol running over TCP So, from a conceptual standpoint, it can be considered simpler than MTP In terms of mechanics, the process SMTP uses to transfer

an e-mail message is indeed rather simple, especially compared to some other protocols

RFC 788 described the operation of SMTP carrying e-mail messages corresponding to the ARPAnet text message standard as described in RFC 733 Development of both e-mail messages and the SMTP protocol continued, of course In August 1982, a milestone in TCP/IP e-mail was achieved when RFCs 821 and 822 were published RFC 821 revised SMTP, and became the defining standard for the protocol for the next two decades RFC 822, its companion standard, became the standard for TCP/IP electronic mail messages carried by SMTP

HELO Hello The domain name of

the sender

The conventional instruction sent by an SMTP sender to an SMTP receiver to initiate the SMTP session

MAIL Initiate Mail Transaction

Must include a

“FROM:” parameter specifying the originator of the message, and may contain other parameters as well

Begins a mail transaction from the sender to the receiver

RCPT Recipient

Must include a “TO:”

parameter specifying the recipient mailbox, and may also

incorporate other optional parameters

Specifies one recipient of the e-mail message being conveyed in the current transaction

DATA

Mail Message

Tells the SMTP receiver that the SMTP sender is ready to transmit the e-mail message The receiver normally replies with an intermediate “go ahead”

message, and the sender then transmits the message one line at a time,

indicating the end of the message by a single period on a line by itself

Aborts a mail transaction in progress This may be used if an error is received

upon issuing a MAIL or RCPT

command, if the SMTP sender cannot continue the transfer as a result

VRFY Verify E-mail address of mailbox to be

verified

Asks the SMTP receiver to verify the validity of a mailbox

EXPN Expand E-mail address of mailing list.

Requests that the SMTP server confirm that the address specifies a mailing list, and return a list of the addresses on the list

name

Requests help information: general help

if no parameter is supplied, otherwise information specific to the command code supplied

The commands in the preceding table are the ones that are most commonly used

in SMTP today In addition to those, there are also certain commands that were originally defined in RFC 821 but have since become obsolete

SEND, SAML (“send and mail”) and SOML (“send or mail”): RFC 821 defined a

distinct mechanism for delivering mail directly to a user's terminal as opposed to a mailbox, optionally in combination with conventional e-mail delivery These were rarely implemented and obsoleted in RFC 2821

TURN: Reverses the role of the SMTP sender and receiver as described in the

SMTP special features topic This had a number of implementation and security issues and was removed from the standard in RFC 2821

Key Terms

• SMTP is used for sending e-mail messages

between servers

• Simple Mail Transport Protocol or SMTP is the

universal standard for moving mail over the Net

• Most e-mail systems that send mail over the internet

use SMTP to send messages from one server to another

• SMTP generally used to send messages from a mail

client to a mail server

2.3 Post Office Protocol version3 (POP3).

POP3 has made earlier versions of the protocol, informally called POP1 and

POP2, obsolete In contemporary usage, the less precise term POP almost always means POP3 in the context of e-mail protocols

2.3.1 Introduction

Post Office Protocol 3 (POP3) is a standard interface between an e-mail client program and the mail server, defined by IETF RFC 1939 The 3 at the end of the POP denotes that this is the third version of the mailbox access protocol POP3 and IMAP4 are the two common mailbox access protocols used for Internet e-mail POP3 provides a message store that holds incoming e-mail Users may log on and download their messages Most POP3 servers allow the downloading just the headers, the headers and a specified number of lines from the body of the message, or the entire message The mail client may automatically delete downloaded messages or offer the use the choise of leaving any or all of the messages on the server

2.3.2 POP3 Commands

USER user Username Provides username to the POP3 server Must be followed by a PASS command.

PASS pass Password Provides a password to the POP3 server Must follw a USER

DELE dele MessageNumber Marks the specified message for deletion

RSET rset Resets any messages which have been marked as read or deleted to the standard unread state.NOOP noop Returns a simple acknowledgement, without performing any

function

APOP apop Username EncryptedKey

Allows for a secure method of POP3 authentication, in which

a cleartext password does not have to be sent Instead, the client creates an MD5 encrypted string from the password, process id, and timestamp, and sends it to the POP3 server

2.3.3 Why POP 4

POP 3 is based on the principal of providing simple functionality on the server and putting all of the intelligence on the client This works well enough because most of the world is using POP 3 and its working just fine

POP 4 adds a few functions that allow the server to perform some more useful functionality while adding very little complexity to the server The design goal was to create a server protocol based on POP3 that had the minimum functionality required to operate a useful web-based mail client It was not intended to solve all of the

POP 4 is a superset of POP 3 and was styled around the interface that POP 3 currently supports To this end, the protocol is every bit as simple as POP 3, very little was added in terms of grammar to support the new commands So for example the usual dot-terminated-list is utilized as well as four letter command names Please note that below is the complete list of additions for the POP 4 protocol Some of them are mandatory, some are optional Please read the POP 4 spec in the link above for more details about each command

Key Terms

• POP is a protocol used to retrieve e-mail from a

mail server

• Provides centralized storage for e-mail messages

• POP does not allow users to store mail on the

server after they download it

• There are two versions of protocol

– POP2 requires SMTP

– POP3 Can be used with or without SMTP

2.4 Multipurpose Internet Mail Extensions (MIME).

In 1992, a new standard was defined by an Internet Engineering Task Force Working

2.4.1 Introduction

MIME is a specification for enhancing the capabilities of standard Internet electronic mail It offers a simple standardized way to represent and encode a wide variety of media types for transmission via Internet mail

When using the MIME standard, messages can contain the following types:

• Text messages in US-ASCII

• Character sets other than US-ASCII

• Multi-media: Image, Audio, and Video messages

• Multiple objects in a single message

2.4.2 What is MIME

On the Internet, data is sent as 8 bit bytes The receiving software collects these bytes and assembles them in the proper order Now the question becomes, "What do these bytes represent?" Are they text? Are they a picture? Are they a sound? How is it possible to know what they mean? Suppose, in addition to the bytes that contain whatever

it is, an additional few bytes are sent along saying what the data is If this is done, the recieving software or person knows what is in the bunch of bytes that make up the message This is what MIME does It tells what is in a message so that the message contents can be used in an appropriate way

2.4.3 History

The first steps to extend emails were defined 1985 in RFC 934 This document proposed a standard for message encapsulation when replying and forwarding messages After few years, in 1988 a content-type header for email was proposed in RFC 1049, which supported message contents like postscript and troff Two years later RFC 1154 proposed encoding header field to be used in email that permitted multi-structural messages This was highly experimental document at that time

In June 1992 were introduced RFCs 1341 and 1342 that can be considered the first version of MIME that we are today aware of They introduced extensions for images, audio and general application, encoding schemes that are used today and representation

of non-ascii data These documents were refined and expanded two years later in RFCs

1521, 1522 and 1523 The last RFC talked only about enriched text in MIME Two years ago, December 1996 MIME related RFCs were reworked once again and this time into a group of five RFCs 2045 through 2049 After these documents more extensions to MIME such as security has been proposed, but they have remained in separate documents

2.4.4 MIME message structure

MIME was designed to be in compliance with RFC 822 New introduces message headers are themselves consistent with message header syntax defined in RFC 822 In fact, RFC 822 specifically states that unrecognized message headers should be ignored Therefore Mail User Agent should be able to receive MIME messages, although some of data is not understood

MIME allows creating composite messages with one or more subparts, each of which can contain subparts There is no limit to number of nested message parts in message Each subpart is separated with a MIME boundary and has headers similar but not identical to the mail message headers MIME defines a number of new header fields in compliance with RFC822 header syntax They are used to describe the content of MIME message MIME specific header can occur in at least two contexts:

1 top level message headers

2.4.5 What are some common MIME types

text/plain as in the usual mail or news message

text/html HTML text as on the World Wide Web

image/jpeg a common image format

image/gif another common image format

application/octet-stream unknown type, any kind of data as bytes

audio/midi midi music format for synthesizers

audio/x-midi an alternate for the above

application/ps indicates PostScript document

Key Termes

• MIME protocol allows for the transmission of the

multimedia electronic mail

• MIME message generally consists of header fields

followed by data

• The header fields specify the MIME versions

• MIME is a protocol that allows you to send files as

attachments to e-mail easily

• Permits nontextual data to be sent in email

– Graphics image– Voice or video clip

2.5 Internet Mail Access Protocol (IMAP).

Short for Internet Message Access Protocol, a protocol for retrieving e-mail messages

The latest version, IMAP4, is similar to POP3 but supports some additional features For

example, with IMAP4, you can search through your e-mail messages for keywords while the messages are still on mail server You can then choose which messages to download

to your machine

2.5.1 History

IMAP was designed by Mark Crispin in 1986 as a remote mailbox protocol, in contrast to the widely used POP, a protocol for retrieving the contents of a mailbox IMAP was developed at Stanford University in 1986

Original IMAP

The original Interim Mail Access Protocol was implemented as a Xerox Lisp machine client and a TOPS-20 server

No copies of the original interim protocol or its software exist; all known installations of the original protocol were updated to IMAP2 Although some of its commands and responses were similar to IMAP2, the interim protocol lacked command/response tagging and thus its syntax was incompatible with all other versions

of IMAP

IMAP2

The interim protocol was quickly replaced by the Interactive Mail Access Protocol (IMAP2), defined in RFC 1064 and later updated by RFC 1176 IMAP2 introduced command/response tagging and was the first publicly distributed version

IMAP2bis

With the advent of MIME, IMAP2 was extended to support MIME body

structures and add mailbox management functionality (create, delete, rename, message upload) that was absent in IMAP2 This experimental revision was called IMAP2bis; its specification was never published in non-draft form Early versions of Pine were widely distributed with IMAP2bis support (Pine 4.00 and later supports IMAP4rev1)

IMAP4

An IMAP Working Group formed in the IETF in the early 1990s and took over responsibility for the IMAP2bis design The IMAP WG decided to rename IMAP2bis to IMAP4 to avoid confusion with a competing IMAP3 proposal from another group that never got off the ground The expansion of the IMAP acronym also changed to the Internet Message Access Protocol

Some design flaws in the original IMAP4 (defined by RFC 1730) that came out in implementation experience led to its revision and replacement by IMAP4rev1 two years later There were very few IMAP4 client or server implementations due to its short lifetime

IMAP4rev1

The current version of IMAP since 1996, IMAP version 4 revision 1

(IMAP4rev1), is defined by RFC 3501 which revised the earlier RFC 2060.

IMAP4rev1 is upwards compatible with IMAP2 and IMAP2bis; and is largely upwards-compatible with IMAP4 However, the older versions are either extinct or nearly so

Unlike many older Internet protocols, IMAP4 natively supports encrypted login mechanisms Plain-text transmission of passwords in IMAP4 is also possible Because the encryption mechanism to be used must be agreed between the server and client, plain-text passwords are used in some combinations of clients and servers (typically Microsoft Windows clients and non-Windows servers) It is also possible to encrypt IMAP4 traffic

using SSL, either by tunneling IMAP4 communications over SSL on port 993, or by

issuing STARTTLS within an established IMAP4 session (see RFC 2595).

IMAP4 works over a TCP/IP connection using network port 143

2.5.2 IMAP advantages

The functional areas where POP is weak, with respect to online/disconnected operation, are strengths for IMAP, since online access was its original design center Specific advantages of IMAP over POP (for online/disconnected use) include:

 Remote Folder Manipulation:

 Multiple folder support

 Online performance optimization

 In addition, IMAP has provision for negotiated extensions, and therefore its capabilities can grow incrementally

 Support for simultaneous update and update discovery in shared folders

2.5.3 Disadvantages of IMAP

IMAP has two disadvantages when compared to POP:

 The protocol is more complex, and requires more effort to implement

 There is currently less IMAP software available than POP software

While IMAP remedies many of the shortcomings of POP, this inherently introduces additional complexity Much of this complexity (e.g., multiple clients accessing the same mailbox at the same time) is compensated for by server-side workarounds such as maildir or database backends

Unless the mail store and searching algorithms on the server are carefully implemented, a client can potentially consume large amounts of server resources when searching massive mailboxes

IMAP4 clients need to explicitly request new email message content potentially causing additional delays on slow connections such as those commonly used by mobile devices A private proposal, push IMAP, would extend IMAP to implement push e-mail

by sending the entire message instead of just a notification However, push IMAP has not been generally accepted and current IETF work has addressed the problem in other ways (see the Lemonade Profile for more information)

Unlike some proprietary protocols which combine sending and retrieval operations, sending a message and saving a copy in a server-side folder with a base-level IMAP client requires transmitting the message content twice, once to SMTP for delivery and a second time to IMAP to store in a sent mail folder This is remedied by a set of extensions defined by the IETF LEMONADE Working Group for mobile devices:

URLAUTH (RFC 4467) and CATENATE (RFC 4469) in IMAP and BURL (RFC

4468) in SMTP-SUBMISSION POP3 servers don't support server-side folders so clients

have no choice but to store sent items on the client Many IMAP clients can be configured to store sent mail in a client-side folder In addition to the LEMONADE

"trio", Courier Mail Server offers a non-standard method of sending using IMAP by copying an outgoing message to a dedicated outbox folder

• The mail always stays on the server

3 Introduction to java script

JavaScript is a programming language that can be included on web pages to make them more interactive You can use it to check or modify the contents of forms, change

images, open new windows and write dynamic page content You can even use it with CSS to make DHTML (Dynamic Hyper Text Markup Language).

This allows you to make parts of your web pages appear or disappear or move around

on the page Java Scripts only execute on the page(s) that are on your browser window at any set time When the user stops viewing that page, any scripts that were running on it are immediately stopped The only exception is a cookie, which can be used by many pages to pass information between them, even after the pages have been closed

Before we go any further, let me say; JavaScript has nothing to do with Java If we are honest, JavaScript, originally nicknamed LiveWire and then LiveScript when it was created by Netscape, should in fact be called ECMAscript as it was renamed when Netscape passed it to the ECMA for standardization

JavaScript is a client side, interpreted, object oriented, high level scripting language, while Java is a client side, compiled, object oriented high level language

A scripting language developed by Netscape to enable Web authors to design interactive sites Although it shares many of the features and structures of the full Java language, it was developed independently Javascript can interact with HTML source code, enabling Web authors to spice up their sites with dynamic content JavaScript is endorsed by a number of software companies and is an open language that anyone can use without purchasing a license It is supported by recent browsers from Netscape and

Microsoft, though Internet Explorer supports only a subset, which Microsoft calls Jscript.

3.1 What is JavaScript

 JavaScript was designed to add interactivity to HTML pages

 JavaScript is a scripting language

 A scripting language is a lightweight programming language

 JavaScript is usually embedded directly into HTML pages

 JavaScript is an interpreted language (means that scripts execute without preliminary compilation)

 Everyone can use JavaScript without purchasing a license

3.2 What can a JavaScript Do

 JavaScript gives HTML designers a programming tool - HTML authors

are normally not programmers, but JavaScript is a scripting language with a very simple syntax! Almost anyone can put small "snippets" of code into their HTML pages

 JavaScript can put dynamic text into an HTML page - A JavaScript

statement like this: document write("<h1>" + name + "</h1>") can write a variable text into an HTML page

 JavaScript can react to events - A JavaScript can be set to execute when

something happens, like when a page has finished loading or when a user clicks on an HTML element

 JavaScript can read and write HTML elements - A JavaScript can read

and change the content of an HTML element

 JavaScript can be used to validate data - A JavaScript can be used to

validate form data before it is submitted to a server This saves the server from extra processing

 JavaScript can be used to detect the visitor's browser - A JavaScript can

be used to detect the visitor's browser, and - depending on the browser - load another page specifically designed for that browser

 JavaScript can be used to create cookies - A JavaScript can be used to

store and retrieve information on the visitor's computer

3.3 HTML – Java Script

3.3.1 How to Put a JavaScript Into an HTML Page

To insert a JavaScript into an HTML page, we use the <script> tag Inside the

<script> tag we use the type attribute to define the scripting language

So, the <script type="text/javascript"> and </script> tells where the JavaScript starts and ends:

3.3.2 Where to Put the JavaScript

JavaScript in a page will be executed immediately while the page loads into the browser This is not always what we want Sometimes we want to execute a script when a page loads, other times when a user triggers an event

Scripts in the head section: Scripts to be executed when they are called, or when

an event is triggered, go in the head section When you place a script in the head section, you will ensure that the script is loaded before anyone uses it

3.3.3 Where did it come from

 Originally called Live Script at Netscape

– started out to be a server side scripting language for providing database connectivity and dynamic HTML generation on Netscape Web Servers– Netscape decided it would be a good thing for their browsers and servers

to speak the same language so it got included in Navigator– Netscape in alliance w/Sun jointly announced the language and its new name Java Script

– Because of rapid acceptance by the web community Microsoft forced to include in IE Browser

3.3.4 What can it be used for

 Some pretty amazing things…

– Text animation

– graphic animation

– simple browser based application

– HTML forms submission

– client-side forms data validation (relieving the server of this task)

– web site navigation

3.4 Object based scripting

Objects refer to windows, documents, images, tables, forms, buttons or links, etc.Objects should be named Objects have properties that act as modifiers

3.4.1 Objects

• window - the current browser window

• window.history - the Netscape history list

• window.document - the html document currently in the browser client area

• window.location - the browser location field

• window.toolbar - the browser toolbar

• window.document.link - an array containing all of the links in the document

• window.document.anchor - an array of all the anchor points in the document

• Window.document.layer - a named document layer

• window.document.applet - a named java applet area

• window.document.image- a named image tag

• window.document.area - a named area

• window.document.form - a named form or the default form,ect

A few examples

• window.location = “http://www.yahoo.com”

– will take you to the specified URL (like a goto)

• window.history.back()

– back() is a method on history

– will be like clicking the back button in Nav 3

– in Nav 4 will take you back to prev window

alertblurcloseconfirmfocusopenpromptclearTimeoutsetTimeout

onLoadonUnloadonBluronFocus

Frame defaultStatus

framesopenerparentscrollselfstatustopwindow

alertblurcloseconfirmfocusopenpromptclearTimeoutsetTimeout

none (The onLoad and onUnload event handlers belong to the Window object)

Location hash

hosthostnamehrefpathnameporprotocolsearch

reloadreplace

None

History length

forwardgo

Navigator appCodeName

appNameappVersionmimeTypes

userAgentdocument alinkColor

anchorsappletsareabgColorcookiefgColorformsimageslastModifiedlinkColorlinkslocationreferrertitlevlinkColor

clearcloseopenwritewriteln

none (the onLoad and onUnload event handlers belong to the Window object

image

bordercompleteheighthspacelowsrcnamesrcvspacewidth

elementsencodingFileUploadmethodnametarget

submitreset

onSubmitonReset

text defaultValue

nametypevalue

focusblurselect

onBluronChargeonFocusonSelect

3.4.3 Object Model

 It is very important to understand the object model

 each object has its own properties, some of which are read only some of which you can set directly by assignment (as location)

 each object also has a set of behaviors called methods

3.4.4 Object Syntax

The following objects are also available in JavaScript:

B anchor (anchors array)

B form (forms array)

B frame (frames array)

 anchor ( anchors array)

A piece of text that can be the target of a hypertext link

A pushbutton on an HTML form

Syntax

To define a button:

<INPUT TYPE="button" NAME="buttonName" VALUE="buttonText"

[onClick="handlerText"]>

NAME="buttonName" specifies the name of the button object You can access

this value using the name property

VALUE="buttonText" specifies the label to display on the button face You can

access this value using the value property

NAME="checkboxName" specifies the name of the checkbox object You can

access this value using the name property

VALUE="checkboxValue" specifies a value that is returned to the server when the

checkbox is selected and the form is submitted This defaults to "on" You can access this value using the value property

CHECKED specifies that the checkbox is displayed as checked You can access

this value using the defaultChecked property

textToDisplay specifies the label to display beside the checkbox.

 Date Object

Lets you work with dates and times

Syntax

To create a Date object:

1 dateObjectName = new Date()

2 dateObjectName = new Date("month day, year hours:minutes:seconds")

3 dateObjectName = new Date(year, month, day)

4 dateObjectName = new Date(year, month, day, hours, minutes,

seconds)

dateObjectName is either the name of a new object or a property of an existing object month, day, year, hours, minutes, and seconds are string values for form 2 of the syntax

For forms 3 and 4, they are integer values

To use Date methods:

dateObjectName.methodName(parameters)

dateObjectName is either the name of an existing Date object or a property of an existing

object

methodName is one of the methods listed below

Exceptions: The Date object's parse and UTC methods are static methods that you use as follows:

Date.UTC(parameters)

Date.parse(parameters)

Methods:

<BODY BACKGROUND="backgroundImage" BGCOLOR="backgroundColor"

TEXT="foregroundColor"LINK="unfollowedLinkColor"

ALINK="activatedLinkColor"VLINK="followedLinkColor"

[onLoad="handlerText"][onUnload="handlerText"]>

</BODY>

BACKGROUND specifies an image that fills the background of the document

BGCOLOR, TEXT, LINK, ALINK, and VLINK are color specifications expressed

as a hexadecimal RGB triplet (in the format "rrggbb" or "#rrggbb") or as one of the string literals listed in Color Values

formName is either the name of a form or an element in the forms array

index is an integer representing an object on a form

 form ( forms array)

Lets users input text and make choices from form objects such as checkboxes, radio buttons, and selection lists You can also use a form to post data to a server

Syntax

To define a form, use standard HTML syntax with the addition of the onSubmit event handler:

<FORM NAME="formName" TARGET="windowName" ACTION="serverURL"

METHOD=GET | POST ENCTYPE="encodingType" [onSubmit="handlerText"]>

</FORM>

NAME="formName" specifies the name of the form object

TARGET="windowName" specifies the window that form responses go to When

you submit a form with a TARGET attribute, server responses are displayed in the

specified window instead of the window that contains the form windowName can be an

existing window; it can be a frame name specified in a <FRAMESET> tag; or it can be one of the literal frame names _top, _parent, _self, or _blank; it cannot be a JavaScript

expression (for example, it cannot be parent.frameName or windowName.frameName)

Some values for this attribute may require specific values for other attributes

ACTION="serverURL" specifies the URL of the server to which form field input

information is sent This attribute can specify a CGI or LiveWire application on the server; it can also be a mailto: URL if the form is to be mailed

METHOD=GET | POST specifies how information is sent to the server specified

by ACTION GET (the default) appends the input information to the URL which on most receiving systems becomes the value of the environment variable QUERY_STRING POST sends the input information in a data body which is available on stdin with the data length set in the environment variable CONTENT_LENGTH Some values for this

attribute may require specific values for other attributes

ENCTYPE="encodingType" specifies the MIME encoding of the data sent:

"application/x-www-form-urlencoded" (the default) or "multipart/form-data" Some values for this attribute may require specific values for other attributes

 frame ( frames array)

A window that can display multiple, independently scrollable frames on a single screen, each with its own distinct URL Frames can point to different URLs and be targeted by other URLs, all within the same screen A series of frames makes up a page

Syntax

To define a frame object, use standard HTML syntax The onLoad and onUnload event handlers are specified in the <FRAMESET> tag but are actually event handlers for the window object:

ROWS="rowHeightList" is a comma-separated list of values specifying the

row-height of the frame An optional suffix defines the units Default units are pixels

COLS="columnWidthList" is a comma-separated list of values specifying the

column-width of the frame An optional suffix defines the units Default units are pixels

<FRAME> defines a frame

SRC="locationOrURL" specifies the URL of the document to be displayed in the

frame The URL cannot include an anchor name; for example <FRAME SRC="doc2.html#colors" NAME="frame2"> is invalid

NAME="frameName" specifies a name to be used as a target of hyperlink jumps.

 hidden object

A text object that is suppressed from form display on an HTML form A hidden object is used for passing name/value pairs when a form submits

Syntax

To define a hidden object:

<INPUT TYPE="hidden" NAME="hiddenName" [VALUE="textValue"]>

NAME="hiddenName" specifies the name of the hidden object You can access

this value using the name property

VALUE="textValue" specifies the initial value of the hidden object.

propertyName is one of the properties

methodName is one of the methods.

o link object ( links array)

A piece of text or an image identified as a hypertext link When the user clicks the link text, the link hypertext reference is loaded into its target window

Syntax

To define a link, use standard HTML syntax with the addition of the onClick and

onMouseOver event handlers:

<A HREF=locationOrURL [NAME="anchorName"]

HREF=locationOrURL identifies a destination anchor or URL

NAME="anchorName" specifies a tag that becomes an available hypertext target

within the current document If this attribute is present, the link object is also an anchor object

TARGET="windowName" specifies the window that the link is loaded into windowName can be an existing window; it can be a frame name specified in a

<FRAMESET> tag; or it can be one of the literal frame names _top, _parent, _self, or

_blank; it cannot be a JavaScript expression (for example, it cannot be parent.frameName

windowReference is a variable windowVar from a window definition or one of

the synonyms top or parent

propertyName is one of the properties listed below.

A built-in object that has properties and methods for mathematical constants and

functions For example, the Math object's PI property has the value of pi

Syntax

To use a Math object:

1 Math.propertyName

2 Math.methodName(parameters)

propertyName is one of the properties.

methodName is one of the methods.

NAME="passwordName"

[VALUE="textValue"]

SIZE=integer>

NAME="passwordName" specifies the name of the password object You can

access this value using the name property

VALUE="textValue" specifies the initial value of the password object You can

access this value using the defaultValue property

SIZE=integer specifies the number of characters the password object can

accommodate without scrolling

radio object

A set of radio buttons on an HTML form A set of radio buttons lets the user choose one item from a list

To define a set of radio buttons, use standard HTML syntax with the addition of the onClick event handler:

<INPUT TYPE="radio" NAME="radioName" VALUE="buttonValue"

[CHECKED] [onClick="handlerText"]> textToDisplay

NAME="radioName" specifies the name of the radio object All radio buttons in a

group have the same NAME attribute You can access this value using the name property

VALUE="buttonValue" specifies a value that is returned to the server when the

radio button is selected and the form is submitted This defaults to "on" You can access this value using the value property

CHECKED specifies that the radio button is selected You can access this value

using the defaultChecked property

textToDisplay specifies the label to display beside the radio button.

NAME="resetName" specifies the name of the reset object You can access this

value using the name property

VALUE="buttonText" specifies the text to display on the button face You can

access this value using the value property

o select object ( options array)

A selection list or scrolling list on an HTML form A selection list lets the user choose one item from a list A scrolling list lets the user choose one or more items from a list

To define a select object, use standard HTML syntax with the addition of the onBlur, onChange, and onFocus event handlers:

<SELECT NAME="selectName" [SIZE="integer"] [MULTIPLE]

NAME="selectName" specifies the name of the select object You can access this

value using the name property

SIZE="integer" specifies the number of options visible when the form is

displayed

MULTIPLE specifies that the select object is a scrolling list (not a selection list) OPTION specifies a selection element in the list You can access the options using

the options array

VALUE="optionValue" specifies a value that is returned to the server when the

option is selected and the form is submitted You can access this value using the value property

SELECTED specifies that the option is selected by default You can access this

value using the defaultSelected property

textToDisplay specifies the text to display in the list You can access this value

using the text property

stringName is the name of a string variable

propertyName is one of the properties

methodName is one of the methods.

NAME="submitName" specifies the name of the submit object You can access

this value using the name property

VALUE="buttonText" specifies the label to display on the button face You can

access this value using the value property