Before learning about the Internet and to consider their applications, see the brief
Fascinating history of the Internet.
ARPANET
The network, which became known as the Internet began as a project of the American
Department of Defense. In 1969, the Department Advanced Research Projects Agency
(ARPA) was established in a wide area network with two nodes via dedicated lines are called
ARPANET, which was called the network, or network of networks, which was
reduced to race online. The nodes in this network were private universities and
research facilities under contract ARPA. The idea was that researchers
for better information sharing, if the communication is easier.
Initially, the network was a first data transfer speed of the device applications, users
now evident. Applications came later, out of necessity. In 1972, for example,
There are enough nodes that users need the ability to send text messages to the state
and the forthcoming enlargement of the network. It is therefore necessary, someone wrote a program
Text messages you send from one node to another. Electronic mail was born.
While the ARPANET quickly become common in academic circles and research, many of
Years passed before the public to know. This delay may have been
a good thing, because the network was created, in part, to test ideas Internetworking
and use them. The design and protocols of the network has gone through many
iterations, some of which were so fundamental as to cause a Flag Day, which the computer
scientific jargon is a change that is not backwards compatible, which requires that all users
to implement the change on the same day. Such changes do not trouble enough, when we
was only a few nodes on the network, but it would be almost impossible now.
Commercial Internet
ARPANET imitated, creating Internetworks for those who do not work for ARPA.
Soon it seemed that each group had its own Internet research. An Internet
For example, was devoted to magnetic fusion researchers working for the Ministry of US
Energy. Another new Internet was the NSFNET, which was founded in 1986 by the National Science
Foundation (NSF). The initial goal of this network to connect five
supercomputers, the Institute had ordered schools across the country, but
This goal was quickly modified to support all forms of school use. The NSFNET used
protocols for the ARPANET, but had a much greater extent. She finally reached all
major colleges and universities and became known to the public in a way never ARPANET.
These developments quickly attracted commercial interest. Even at this early stage, was
easy to see the possibilities of the technology beyond the use of the campus. The NSFNET
Paper, however, limited its use strictly academic pursuits. In response to the private
companies have developed their own networks to allow commercial traffic. When they arrived,
Internet, with a capital I was born. Current refers to the global Internet
network that has developed in the project NSFNET. The term Internet, with a lowercase i is a
generic term for a network that connects other networks.
Since these private networks, all captured by a thriving business, have
quickly grew in capacity to the point where the internets original that inspired them is
superfluous. Finally, both ARPANET and NSFNET dissolved, leaving all
circulation in the hands of the commercial networks.
The first applications of the Internet
What led to the popularity of the Internet was not the ability to transfer raw data through the
world, but new applications using this capability. Technology is always
Software drives hardware. Customers will not buy a DVD player, if some of their
favorite movies are not available on DVD. What we still need a new
The technology is the killer application, an application that will convince people to buy the technology.
When the Internet was still a cottage industry that lacked a killer app. E-mail has been useful
but not enough people have email accounts to make it exciting. What the Internet is necessary
is an application that allows users to publish documents and other files, so that
anyone who needs it can find and access. Then, the Internet can
become a giant directory information.
A first step in this direction was FTP, or File Transfer Protocol, which, as
name implies, is a mechanism for transferring files over the Internet. Users of FTP that allows
to publish files on one computer and allow others to copy these files to their
own equipment. Files can be available to all, or may be protected by a password.
But to access a file via FTP, users will need to know the address of the computer
where he lived. As with the RAM, each byte of memory address, each
computer on the Internet has an address. If users are not given the address where
particular file is found, they can not find the file. The situation would be similar to a library
whose books are arranged on shelves instead of ISBN and copyright issues. Not
one would be able to find any of this without the library catalog.
The next step was to create a catalog file FTP. In 1989, McGill University
in Montreal has developed a tool called "Archie", the name a pun on the word "archive"
and "archivist". This instrument will be in regular contact with all FTP sites, he knew
request their file directories, and create a list of files in a search index. Therefore,
Archie can be considered as the first Internet search engine. (A search engine is
program that allows users to find specific files or sections of a large collection.)
The tool does not solve all problems. He could go FTP address, it was
granted, it could not find new FTP sites on your own. Archie also has not been easy for
non-technical people to use. In addition, the program has been developed for UNIX systems,
and like most UNIX programs of that period, depends on the particular user to understand.
Another problem is that although Archie has to search for files, it was not possible
navigation. To continue the analogy with the library to search for Archie is like using paper
catalog to find titles on a particular subject, and the navigation is like around the batteries
see if any of the titles on the spines of interesting sound. In addition, libraries often
cartel-like "Books of fun at the Olympics," but no way equivalent to
group titles via FTP and Archie. In short, a true system of organization between
FTP files.
Then in 1991, Gopher introduced, so named because it was developed
University of Minnesota, whose mascot is a golden hamster. Instead of allowing users to
simply publish files, Gopher is a mechanism for the release of the two files and menus
the Internet. Instead of being presented with a list of files, the user accesses a Gopher
the site was a menu of options, such as: "1 file Prussian Military History." Menu
have sub-menus and submenus may still down there,
Gopher and easily used by non-technical and allowed easy navigation. This
the system also allows a site to reference another Gopher. Users who have published a list of
The archives of the Prussian military history may include menu items that would lead to other
Gopher sites, which were the files on the same subject.
As with FTP, search engines have been developed to Gopher, the first call
"Veronica". Officially, this was an acronym for "very easy rodent-oriented Netwide
Index of electronic files, "but clearly inspired by the name of the FTP Search
Motor Archie, Veronica had to play a cartoon character Archie.
(Other search engine introduced later called "Jughead").
Because Gopher sites referenced each other, it is possible to search engines to find new
Gopher sites on your own. A spider is a program that "crawls" through references to
Internet sites (such as rodents) to find new sites and material. Through
spiders, search engines may finally be indexed by all the rodents there.
All the pieces fall into place, but the Internet does not yet have final implementation. Well
Gopher was easier to use than FTP, which was still far from the mouse-based graphical interface
interfaces that users enjoy on Macintosh and Windows.
Although Gopher was developed, a researcher in physics, Tim Berners-Lee, led a team
that the organization has proposed using hypertext documents. Hypertext document contains
embedded links to other documents. This corresponds to the concept except that the Gopher
documents and references to other documents are integrated, not separated from the menus
and files. Please note that at this stage the documents were all in plain text, and links
The documents were selected using the keyboard, no mouse.
It came into place a piece of mosaic in 1993, he was a hyper-text program that
graphically documents, and where users selected links to other documents
the mouse.
Soon everyone was the creation of hypertext documents and their relationship to each other. The
relationships between these documents form a kind of spider web, and the whole collection
each other hypertext documents is now called the World Wide Web, or WWW, often only
called "web".
Web Killer App Internet. Although the Internet was a playground for a long time
researchers, students and computer enthusiasts of core was now a
goal that was so powerful and easier to use than the public could not help noticing. The
The popularity of the Web has caused the explosive growth of the Internet. Number
computers seemed to double overnight. Even today, for many people, "the
Internet "and" Web "is the same as it has no reason to
Internet without a Web
The future of Internet
Where does the Internet from here? While some researchers are looking for more
Killer applications are the Internet, others believe it is time for a new, faster Internet. A
To this end, a consortium of universities and government agencies working to develop
Internet2, the next version of the Internet.
In a way that history repeats itself, together with universities to try to
technologies that could one day be used by everyone. The current created by the Internet2 network
called "Abilene", named railhead in Abilene, Texas, which when built in 1860
was at the gates of the border. Abilene offers a higher throughput with low
delays in the current Internet. In a test of speed, the network was able to send
corresponds to a dozen CD-ROMs worth of data in less than a minute. While it is
same class as Gigabit Ethernet, believes that it was not on a LAN, but on the cables
that extended for thousands of miles. Internet2 Working Group considers important applications
There you can only work on a network.
One of the Internet is an eternal present real-time video, for example, take the camera in New
Video Transfer York for a user in Los Angeles. The current Internet is capable of
download the video, but due to various delays and the potential transmission problems,
more video data to accumulate before it can be transmitted to the user. This buffer
means that the video player waits until it is several seconds (or more) of receipts
images before playback begins. Period of time to recover small defects
transmission without interrupting video playback for users.
As the buffer is sometimes difficult to share. If you try
participate in a conversation that takes place across the network, you
need the ability to respond to what is happening now, not what happened 30 seconds
ago. In addition, to further reduce the problems, most of the video is sent over the Internet is a small
and use a couple of frames per second, resulting in rough play.
These problems have limited the development of video applications for the current
Internet. If technologies Abilene project is adopted by the entire community,
But how can people use the Internet to radically change again. Nobody knows
the killer applications might exist for the next Internet.
Internet Connection
Common ways to connect computers to the Internet through the T-lines, dial-up
technology and cable lines.
T-lines
Using the Internet, companies, schools and other organizations must first be connected to their
own computers together via a LAN technology such as Ethernet. One of the nodes
A LAN is a port. As described in the previous chapter, the gateway to translate
one network to another. In this case, the gateway translates via the Internet
protocols such as LAN.
Then the port is connected to the Internet. Since all computers
LAN is connected to the Internet through this one connection, the connection
needs a lot of bandwidth. A common solution is the T-line, leased lines
provider that is at different levels to the requirements of different bandwidth. (At first, the
provider was AT & T that created these names.)
A T1 line is typically a twisted pair and provides about 1.5 megabits per second, or about
190 kilobytes per second. This means you can transmit the contents of a CD-ROM
about an hour. Once the T1 line held fast, but that no longer exists.
A T3 line is a set of T1 lines and provides approximately 44 megabits per second, or 5,
megabytes per second. This means it could send the contents of the CD-ROM
two and half minutes.
Dial-up Connections
The home of origin of users connected to the Internet via ordinary phone lines, known as
audio line in the industry, and even more often. It is an analog phone system
Principles: As the talks at one end, the sound vibrates the coil microphone, which
produces a power level that varies vibrations vary. At the other extreme,
electricity is used for another speaker coil, which produces the same vibrations
the air at this point to reproduce the original sound of the voice. Unless you use
electricity, the process is the same as the children's game, with two cans are
associated with a leash. Because computers communicate digitally and telephone lines are
is an analog required.
A modem is a device that converts a digital signal into an analog signal, and vice versa.
The name comes from modulator / demodulator, digital-analog modulation
conversion, and demodulation is analog-digital conversion.
When someone is using dial-up connection, the modem is a computer system
and at the other end of the link. An Internet service provider, or ISP, in fact
provide an Internet connection. Each message sent through a dial-up connection is
digital modem until it reaches the sender, which is converted to analog, sent
telephone line to another modem, it becomes a numeric message,
reformats for the Internet Protocol and it starts its way to its final destination.
Telephone lines are not compatible with a wide frequency range, which explains why people have heard in a
phone rang again as if in a box. This results in low frequency low
bandwidth. Dial-up connections can not support a speed of 56 kilobits per second
that it would take more than a day to send the contents of the CD-ROM. Also
This rate is available only in one direction, from the Internet to the user's computer. In
the other direction, speed is only 33 kilobits per second. The term downstream refers
the Internet address of the user's computer, and refers to the upstream
the direction of the user's computer to the Internet. Many methods to communicate
with the Internet, the downstream bandwidth much higher than the upstream
bandwidth. In many applications this is not a problem, but some applications like video
Conferencing, require the same bandwidth in both directions.
DSL
Weakness of the dial-up connection will use an analog telephone, not
the son used to telephone lines. A DSL or digital subscriber line, digital data transmitted
on normal telephone lines and thus allows faster data transfer.
Unlike dial-up, which is available to anyone with a telephone line, ADSL
requires your phone company to install special equipment. A telephone line is a pair of
son of a leader in the home or office building is known as a central office or CO, and
each pair from the telephone CO known as the local network. You've probably seen these
windows of one or two-story buildings in the CO, is the name of the telephone company
do not check out or whatever. ADSL equipment must be installed in a CO
provide DSL service to all lines that connect the CO so that the line will never
by analog switches.
Performance of DSL is highly dependent on loop length. More
the wire, the more the signal degrades, and if speed is not lowered too many errors
occur for the connection to be useful. Therefore, the larger the home or business is a
CO, the better your DSL will perform.
Unlike a dial-up, DSL, because the use of a greater frequency range than that used
for voice communications, it does not block the telephone line. Can someone talk on the phone
while the DSL is in use without any interference between the two.
DSL comes in the events of the different bandwidth. DSL for home use are generally ADSL
where A stands for "asynchronous," which has a much higher bandwidth downstream
that the upstream bandwidth. (If bandwidth is the same in both directions, both
are synchronized;. are different, they are asynchronous) This
deal makes sense for home users and the home use of the most common
The Internet is the Internet, where a lot of data in the documents are sent to the user's computer
but there is little information will be sent back (often, only the name and location of the document
the user has selected). DSL service offers a classic 1.5 megabits per second
downstream (the equivalent in that direction for a T1 line), and 256 kilobits per second
upstream, which, although slower, is still about eight times faster than dial-up
upstream interface.
DSL services are for companies that also provide high-end prices, for example 3
megabits per second or more. At these speeds, they are a good alternative to a T1 line.
Cable
Another popular way to get a fast connection to the Internet through "cable
society ", the same company that provides cable TV at home. Access is
through the window is known as a cable modem, that even if the name does not have a modem at all,
because there is no digital to analog conversion. Instead, a cable modem is a gateway,
conversion between two different LAN protocols, so a computer can communicate
line cord.
The cable modem has two connections, a cable and a self-
connection to the user's computer. The computer and the modem cable in general
communicate over Ethernet is a LAN in miniature. Some cable modems are connected
Through the USB port (see Chapter 3) on your computer. Modem cable to communicate
with the cable company with another protocol, such as Ethernet, however, the connection
shared with other users. A device called a CMTS cable or modem termination system,
installed by the cable company to a group of subscribers in an area. The CMTS is another
Gateway, pulling the data cable to the line and to convert the Internet protocols, or
vice versa.
If you've used a cable modem, you may have noticed an "activity" light coming
the same when they are sent or received via Internet. This indicates
activities between the CMTS and cable modems, which is used not only the activity
involve your cable modem.
And 'this sharing of local cable, which limits the transfer rate. Cable Company
actually based transfer limits in the system. If a user could use 100 percent of
cable, the speed will far exceed the DSL, but because it is shared, it
speeds are "drowned" to something similar to DSL at a range of about 700 kilobits to 2
megabits per second or more. Because the "butterfly" is built into the system, the cable
company can offer service levels. Thus, users can pay only the bandwidth they need.
Both DSL and cable modem to the Internet is often referred to as
"Broadband," but this term is more about the advertisers that all you have technical
meaning. In a network, refers to "broadband" to a signal that uses a wide range (a large
band) frequencies. In the vernacular, but simply a means of broadband connection
is much faster than dial-up connection.
Internet Protocols
The protocols used by the Internet are called IP and TCP and operate at different levels.
IP, which simply means the Internet Protocol is a protocol to the lowest level and allows the raw
communication between two nodes on the Internet.
Internet nodes are identified by a numeric address called an IP address. This
the address is written as four numbers in the range from 0 to 255, 256 making it possible
(Remember the "two powers" in Chapter 2) separated by periods, such
170.171.1.150. Each node on the Internet at some point must have an IP address
other nodes to get it.
Because remember the IP address of another computer, it would be difficult for users
each node must also provide your own domain name. Node can not directly use the domain
name to send data, but can be used to obtain the IP address you need. A special
is called a name server or DNS, to return the IP address of a particular domain.
For example, typing a name like www.broadwaybooks.com in a web browser,
Before the browser can retrieve a web page, it must first check the DNS. If you write
a name does not exist in a browser error message indicating that the DNS
Research has failed.
Because so many computers using the Internet today, most home users do not receive a
permanent IP address in the way a site is. Instead, each time the computer
connected to the Internet, the computer is the user's ISP provides a temporary IP address
range of addresses assigned to that ISP.
IP is a low-level protocol, which contains only the so-called best delivery
service, which means it does not perform error checking, not following the message, and
does not guarantee delivery. Since this service is not sufficient for most
applications, higher-level protocol called TCP, or Transmission Control Protocol, is
used with IP to provide reliable transmission from sender to recipient. TCP provides
Follow-up messages, retransmission, and error checking.
WORLD WIDE WEB
As mentioned earlier in this chapter, the World Wide Web is the application of the Internet, which
makes the Internet so popular as it is. The Web is a success for several reasons.
First, compared to other ways of sharing information electronically, the website allows
Published a new material to decide how the material is organized and displayed. Just as
telephone directory is organized differently and has a different style of a treatise on the link
habits of penguins, various topics on the net will be organized and displayed in a
the most appropriate way for the material.
Second, Web publishing is cheap. Most ISP accounts give a certain amount of space on the web
no additional cost. This means that the majority of web users and web publishers have potential.
Even a contract for professional web hosting can be had for less than $ 100 a month.
Because Web publishing is so cheap compared to other ways of communicating
data, the total content of the web is growing rapidly.
Third, the Web is easy to use. No technical knowledge is required to find
or consult the information on any material. Even small children is not a problem
On the Web.
HTML
Atom the Web is a single document called a Web page, a text document
written in a special format called HTML. Groups of Web pages stored in the same
Internet domain called the site.
HTML (Hypertext Markup Language) is a combination of text and special
instructions that specify how the formatted text should appear. The term "labeled" refers
specific instructions. Just as barns or in the layout editor may notify the red
How to pen a block of text is formatted as a page, HTML describes how a network
page is formatted on the screen seen through a program called a Web browser, or
any browser.
A note on the capitalization
The term Wide Web or Web for short, refers to a single global entity, and should
adequately capitalized. Not all websites on the Internet, however. You can store a
copy to your own hard drive to watch, for example, and some companies are creating
groups of web pages for their LAN (corporate policies, for example), not for publication
On the Internet.
In summary, referring to an HTML document that may or may not be available in the
Internet "web" is fine, but when referring to the World Wide Web itself, or nothing
that, "Web" is the best.
HTML document is "marked" by using special instructions called tags, which are
distinguished from the document, using the symbols on the keyboard, and that in this context,
called "angle brackets". Here's a simple example of a marked in the HTML:
<b>I must</b> have <i>donuts, right now!</i>
When displayed, the text might look like:
I had donuts, right now!
<b>In the HTML tags to show "starts to display text in bold," and</b>
states that "the text shown in bold." Similarly, <i>and</i> enter
where to start and stop the display of text in italics.
HTML tags can be divided into four categories.
Keywords character formatting
Character formatting tags to change the appearance of the text itself. <b>And <i>the tags</i></b>
shown in the example above is an indication of formatting tags. This group includes most of
the same opportunities that appear on the "Font" menu in a normal word processor,
including fonts, font size, bold, italic, and so on.
The choice of a font is, however, the decision more complicated than a word processor.
When using a word processor that allows you to choose a font that is installed
computer. When designing a Web page, the designer can not know with certainty what
The fonts are installed on all computers that will see it. If a page describes the use of a
font does not have a computer, the browser will select the font you think is more like
or return to a default font. The text is still seen, but it may seem very different
than the designer. Because of these unknowns, designers tend to stick to a
few common fonts.
Tags last
Last tags determine how the text flows across the page. These labels tell where one
section ends and the next begins, and are used to divide the page into different
points, for example, make multicolumn layouts.
Web designers have problems with some of the same provision as they do with the sources. Users
are free to resize their browser window, and if the window is much narrower and
wider than that expect a designer, the layout can be bad.
Link Tags
Links are what makes hypertext. HTML can not be two kinds of references to material
outside the document.
A genus is a link to another web page or elsewhere on the same page, which is
is called an anchor tag. Anchors can be used to create a link to another page or to a
where others can link pages, or both. For example, a page that summarizes the
history of the Olympic Games could have a paragraph for each Olympic Games with an anchor
for each tag, so that part could be a direct link to the 1980 Olympics for example.
Moreover, the same side, some links at the top, so users can jump
directly to the part of the story, who cares without anchoring, other pages
can not link to the page itself, which means that the top of the page.
Another type of link to other media such as images. In addition to using photographs and other
graphics to better convey the material, Web designers use images to improve the design
and make up for other deficiencies. If a designer wants to use an unusual font for a title
at the top of the page, knowing that it is unlikely that the font is available for most users "
computers, the designer can create an image of the text in the chosen font. Because
images require more bytes to store an equivalent amount of text, although, as
techniques should be used sparingly.
Designers can also integrate other media such as audio or video. Finally, the page
link to other documents to HTML format is not appropriate. The IRS,
For example, the United States will do all the tax forms and instructions available on its website but does not
save in HTML format. Instead, use the Portable Document Format (PDF), which was
developed by Adobe Corporation to provide designers with the type of documents
control available in HTML. It avoids the problem by allowing police document
the designer to include the font data in the document. This makes very large files, but
means that it is not important, what fonts are installed on your computer. Avoid
configuration problems as well, then the document to be adjusted to the window of the user or
zoomed in on user request. PDF is an excellent choice for standardized forms
that can be printed to the user, such as the IRS provides.
Special Tags
Other tags are available for items that do not affect the site itself. For example, the web
to determine what is shown in the title bar of the browser. Other identifiers, called meta-tags
have nothing to do with the screen, but provide information about the content of the page.
This information can be useful for the indexing of pages and can also support in browsers
Displaying page properly.
HTML Tools
Web design is complicated work. It combines the skills of a graphic
with a programmer. Home HTML documents created with a text editor, the
The designer had to actually write all of these tags. This approach is cumbersome for large
pages because the text in the form of an HTML document looks very different than when
displayed in a browser. If you want to see how different, most browsers have an option
Internet Explorer is under the "View" menu, see "source", which is
HTML document as text. Do this for any large site on the net and you
quickly see that it is difficult.
Fortunately, the tools can now edit the HTML directly. These work programs, such as page
page layout program or word processor advanced. The designer can simply drag the text where
should define the font sizes and faces, the drops in the images, and so on, and the editor
creates an HTML designer, without even seeing it.
It is also useful for designers is the addition of style sheets to HTML. A style sheet is a
document and the HTML document can refer to how the text is displayed.
For example, a newspaper website have a style file that defines the
"Title", such as 20 point bold, Times New Roman ", subtitle" the 12-point Arial
font, italics, and a "history of the body" as an ordinary 12-point Arial font. And a web page
News story indicates that by using this style sheet states that Crusader "costume
Saves the city "is the title," Jimmy Dugan, Cub Reporter "is the signature, and the rest of
page is the body of the story. The browser formats the text according to the stylesheet.
If the website is only one page, style sheet does not save any time. But when the site is
tens or hundreds of pages with similar elements, a style sheet format allows text
be designated in one place, instead of over and over again on every page. If the designer later
decided that the titles of the 20 points are too big or not big enough, the only document
has changed is the style sheet. Without it, every page of the site is
changed.
Browsers
As mentioned earlier, web pages are displayed in a browser application called. Internet
Explorer, Netscape, Mozilla and Opera are just some of the many available browsers.
In addition to displaying the page, the browser is responsible for the recovery, usually through
Internet. The browser is also sometimes send the user information to trace the
Internet, which occurs when a user fills out a form.
Browsers also contains utility functions to improve the user experience, such as
keep a history of recently viewed pages. To improve performance, most browsers
They also have a cache. As noted in Chapter 3, the processors have caches recently used to maintain
The data so close that the request does not want to be the main memory if the data are
needed again soon. A web cache uses the same principle, keeping a copy of some
Web pages shown in the user's hard drive and display a copy of a page when the
user requests to view, instead of waiting to cross back to the Internet.
However, it is important in the browser just displays the page. In a perfect world, all
browsers display the same page, the same way. Unfortunately, there is
the case. Early in the history of the Web and HTML, the companies developing browsers
was in a hurry to introduce new features, moves faster than the organization responsible
the development of HTML itself. They created their own versions of HTML (add their own
Tag), and this tactic has encouraged designers to create pages that are not displayed correctly
except in the browser of this company.
VS exact layout. GUIDELINES
When Web and HTML was the first speed, a debate rages about how
specific tags should be marked. In essence, the debate is between those who
believed that the tags should specify as much as possible and those who thought they were
become more like guidelines.
For example, instead of using <i>a tag in italics, as the latter field, the best</i>
use a <em>tag, which is an abbreviation for "weight". In most browsers, text marked by</em>
<em>still appears in italics, but the browser could make bold or</em>
bright red, or any other method that clearly show the text. A label
is a logical tag that describes how the text relates to this document, rather than how it
actually appears.
It seems that the "exact design" camp won over the "logic of the guidelines" of the field. By
graphs, the exact layout is a good thing, because they are more precise control
than the appearance of each page, but for some users, this choice is a bad thing. Exact
requirements cause problems of accessibility, which refers to the ease of humans
persons with disabilities. For example, a designer who uses tags to highlight important segments
text in a different color does not help a viewer with color blindness.
The situation is not so bad today. It is rare to find a website showing correctly
a browser, but you can not read another. However, some differences remain, and are
enough to make a good setting wrong. Sometimes these differences can exist even
between older versions and newer of the same browser. These differences leave
designer two options. One possibility is to declare that the website is designed to
particular browser and all the problems with other browsers the user's problem. The
Another option is to check every page in the section of the popular browsers, and to avoid the tag
and models, which are known to cause problems.
Web Programming
Some websites that pages change so often, it is possible to execute each
with an HTML editor where changes are needed. A dynamic Web page is a web
page that appears when the user requests it, instead of creating time and
result simply copied to the user. Dynamic web pages can be separated to form
content to multiple style sheets. For example, the media,
template for a page can be created that basically says, "The main story is here," "Top
History of sport is here, '"the advertisement goes here," and so on. When a user wants
view the page, the site server meets the model with the stories in progress, a
randomly selected advertisements, and everything else.
Dynamic pages are an example of server-side scripting, which is a programming
made in the Web server using a scripting language (Perl, Chapter
5). Client-side scripting, however, incorporates fragments of program code on a network
page, which runs on the user's computer in response to user actions. When compiling
a form on a website, then click "Send", you make a piece of client
side scripting.
Server-side scripting is also used to manage user data when it reaches the server. For
For example, a Web site to pay an electricity bill, requires that the user enters an account
number. The server-side script to control the corporate database utilities
if the account number is valid and if so, retrieve account information, which
point, it generates a dynamic web page to return to the user.
Client-side script can not perform basic tasks. To perform a server-side script requires
a "return", ie, the data must travel to the user's computer to the Web server
return, which takes time. For user interaction faster and richer, some designers
contains embedded software running on the user's computer within the website. Two
common mechanisms to provide embedded applications is the Java programming
language (Chapter 5), to create "applets"-small
programs in a fully graphical user interface and the software Macromedia Flash, which allows
non-programmers to create animations and interactive programs in a style that is good
suitable for practice.
E-MAIL
E-mail means the messages, usually text, sent through the network from one user to one or
multiple users. Internet, e-mail usually achieved by using two
SMTP and POP3.
SMTP, which stands for Simple Mail Transfer Protocol, used in the program, which sends
message. POP3 is the third version of a protocol called POP or Post Office Protocol,
and is used by the program receiving the message. In addition to receiving
Message, the POP3 program is responsible for storage until the user is actually downloading
on his computer.
SMTP and POP3 programs do not reside on the computers of users who are
and receive mail. Instead, each user has an account on the SMTP server or POP3
by the provider of the user. If you look under the options to set up any mail program, such as
such as Outlook, you can see where the areas of the POP3 and SMTP servers specified.
Often, the fields have names like smtp.myISP.com mail.myISP.com or where
"MyISP" is the user's ISP.
When a user sends an e-mail, a chain of events takes place. Email Client User
communicates with the user specified SMTP server. The program locates SMTP
The IP address of the recipient of the email using a DNS server sends mail to the
POP3 server in that direction. The POP3 server receives the message and then stores the
server. In the end, the receiver checks the email using a mail program, and
POP3 server sends the message to the user, removing the copy.
This mechanism may seem to have more steps involved and computers as necessary
but the mail will not work so well that the fact no. Because the program is on POP3
a server that is always on behalf of a user may receive an e-mail at any time. If
POP3 program was on the recipient's computer, the user will receive e-mail
when the computer was on. Any other time, attempts to send an email to the user
fail.
When an e-mail does not reach its destination, which is known as a farewell, because one of the
email servers generally refers to e-mail to the sender with an explanation.
Rejected e-mails, why the program must be SMTP permanent running on its own server
well. Due to the problems of transition in the Internet, e-mail can be
temporarily unavailable. The SMTP server can be difficult trying to email several times
before calling it quits. Even after a sender has closed the computer, SMTP
The server can still groped to send the final installment of the e-mail users.
E-mail is a very economical way to communicate, but like all good things, can be
abuse. The most common abuse is spam, unsolicited e-mails, which are usually
commercial in nature in large quantities and sent to multiple addresses. Spammers harvest valid
e-mail addresses from different sources, or even legitimate businesses pay for their
mailing lists to customers. Spammers also "guess" email addresses, adding random
generated names to domain names. Spam is usually itself a bid for some
questionable (or illegal) of the product or service.
Spam is a growing problem. Once the spammers enough to start sending a person
address of spam is to replace the current e-mail when the account almost useless. A
to protect themselves, users should be very careful about releasing addresses
And they need to use the filters should eliminate spam before it hits the user in-boxes.
But none of the method is very effective. The only way spam will go away is if the user does not
never meet, which would make it unnecessary to send it to spammers.
Chat and IM
Chat refers to applications that allow a group of people to write text messages
to see every member of the group. IM allows companies and other organizations to exist
States, covering the globe.
Some cats are based on the Web and implement an integrated program written in a language
as Java. A user who has something to say, writing a message, press "Enter" and
Java applet sends the text to the Web server, which then relays it to all members of
group.
IRC or Internet Relay Chat, is an Internet-based protocol for instant messaging. IRC does
requires the user to enter a particular site, but instead of running the IRC client that
IRC works, such as e-mail program works. Just as e-mail programs, users
has a number of IRC clients to choose from.
The conversation is an example of how technology is a social side effects. People can connect with
ways they never could before. Suppose you enjoyed the collection of ceramics in figures
as the Mariachi band. Probably not enough people who think in your city, or
Every city, a sustainable Mariachi Ceramics Club. But there is probably sufficient
people in the world to support a club. With applications like chat, the club could
meets the network.
A similar application called instant messaging, in which two users can exchange text
messages and receive messages arrive instantly. Only one user can receive
messages of several users, but not for the cat, because each message
go to a user at a time. For this reason, it does not require a central location for
to share messages, requiring only two people with compatible messaging client. Immediate
Posts will also allow users to be notified when the users in their "buddy list" are
connected to the Internet.
SUMMARY
The Internet began with ARPANET, a Defense Department project.
ARPANET spawned the NSFNET, which, because it does not allow commercial traffic
was soon overshadowed by the private networks that operate under the same protocol. These private
Networks are the backbone of what is now called the Internet.
First file-sharing, such as File Transfer Protocol, Gopher, and was
popular on college campuses and research centers, but unknown to the general public.
The World Wide Web, linking users to a wide range of information through a
graphical, mouse interface, which has changed, and he grew, so did the Internet.
Users connect to the Internet via an ISP. Companies often
connected through a T1 line, a twisted pair or a set of lines called T1 T3
line. Business and home users, and to use the DSL that sends digital signals to the whole
existing phone lines. Dial-up connections also use the telephone, but must convert
digital signals into analog signals from the computer and back, which limits their effectiveness. Finally,
Cable TV providers also offer Internet access through their coaxial cables.
The Internet uses two protocols TCP and IP, to provide data transmission services. IP
provides quality service and reliable, while TCP offers superior service with error
correction and retransmission.
World Wide Web consists of interlinked documents called Web pages, which are text
messages in a special format called HTML. HTML specifies
Tags, text commands, enclosed in angle brackets, indicating how the text
should appear and how they should be placed on the page.
E-mail sent over the Internet using SMTP for sending messages and
POP3 to receive them. This arrangement allows the sender and the recipient of
message to the off-line when the message really cares.
Chat and instant messaging allow real-time business collaboration and socialization.
