You might have noticed that many Internet sites include the letters HTTP in
the site address that appears in the address line of your web browser. HTTP
(another OSI Layer 7 protocol) defines the rules for transferring information,
files, and multimedia on web pages. Hypertext Markup Language (HTML) is
the language used within HTTP. HTML is actually a fairly simple, easy-tolearn
computer language that embeds symbols into a text file to specify visual
or functional characteristics such as font size, page boundaries, and application
usages (such as launching an e-mail tool when a user clicks certain links).
When the developer of an HTTP file (or web page) wants to allow for a jump
to a different place on the page, or even a jump to a new page, he or she simply
places the appropriate symbols into the file. People viewing the page just
see the link, which is most commonly specified with blue, underlined text. The
ease of jumping from site to site (called web surfing) is one of the reasons for
the proliferation of websites on, and growth of, the Internet.
Several free and commercial tools allow you to create a web page using
HTML without having to know all the rules.
One of the issues with HTML is that it is fairly limited as far as what it can do
given that it works only on text and still pictures. To achieve some of the really
cool moving graphics and web page features, other tools such as Flash,
XML, JavaScript, or other scripting languages are needed. 48
IT Certification CCIE,CCNP,CCIP,CCNA,CCSP,Cisco Network Optimization and Security Tips
Web Browsing
Browsing web pages on the Internet is another common network application.
Browsers run on a computer and allow a viewer to see website content.
Website content resides on a server, a powerful computer with a lot of disk
space and lots of computing cycles. The protocol that allows browsers and
servers to communicate is HTTP.
Browsers run on a computer and allow a viewer to see website content.
Website content resides on a server, a powerful computer with a lot of disk
space and lots of computing cycles. The protocol that allows browsers and
servers to communicate is HTTP.
Receiving E-Mails
E-mail is often received via a different server than the one that sends e-mail.
The type of server depends on which type of e-mail tool you use. For those
using an e-mail client, your e-mail is probably delivered to you via the most
common method, Post Office Protocol 3 (POP3) server. (We have no idea what
happened to the first two.) The POP3 server receives all its e-mails from SMTP
servers and sorts them into file spaces dedicated to each user (much the same
way mail is put into post office boxes at a local post office—thus the name).
When you open your e-mail client, it contacts the POP3 server to request all
the new e-mails. The e-mails are then transferred to your PC, and in most
cases the e-mails are erased from the POP3 server.
Another common method (or protocol) for mail retrieval is an Internet Mail
Access Protocol (IMAP) server. This is the protocol normally used by webbased
e-mail clients, and corporate e-mail systems such as Microsoft
Exchange. The IMAP server receives and sorts e-mail in much the same way as
a POP3 server. Unlike POP3, however, IMAP does not transfer the e-mails to
the machine of the account holder; instead, it keeps e-mail on the server. This
allows users to connect to use their e-mail account from multiple machines.
IMAP also allows for server-side filtering, a method of presorting e-mail based
on rules before it even gets to your PC. It’s kind of like having a friendly
postal worker who sorts all your bills to the top and magazines to the bottom.
Two main issues with IMAP servers are storage space and working offline.
Most Internet e-mail services put a limit on the amount of storage each subscriber
gets (some charge extra for additional storage space). In addition, these
services often limit the file size of attachments (such as photos). The other
issue is the ability to work offline or when not connected to the Internet. One
solution is called caching, which temporarily places the subscriber’s e-mail
information on whatever PC he or she wants to work offline with. When the
user reconnects, any e-mails created while offline are sent, and any new incoming
e-mails can be viewed.
The type of server depends on which type of e-mail tool you use. For those
using an e-mail client, your e-mail is probably delivered to you via the most
common method, Post Office Protocol 3 (POP3) server. (We have no idea what
happened to the first two.) The POP3 server receives all its e-mails from SMTP
servers and sorts them into file spaces dedicated to each user (much the same
way mail is put into post office boxes at a local post office—thus the name).
When you open your e-mail client, it contacts the POP3 server to request all
the new e-mails. The e-mails are then transferred to your PC, and in most
cases the e-mails are erased from the POP3 server.
Another common method (or protocol) for mail retrieval is an Internet Mail
Access Protocol (IMAP) server. This is the protocol normally used by webbased
e-mail clients, and corporate e-mail systems such as Microsoft
Exchange. The IMAP server receives and sorts e-mail in much the same way as
a POP3 server. Unlike POP3, however, IMAP does not transfer the e-mails to
the machine of the account holder; instead, it keeps e-mail on the server. This
allows users to connect to use their e-mail account from multiple machines.
IMAP also allows for server-side filtering, a method of presorting e-mail based
on rules before it even gets to your PC. It’s kind of like having a friendly
postal worker who sorts all your bills to the top and magazines to the bottom.
Two main issues with IMAP servers are storage space and working offline.
Most Internet e-mail services put a limit on the amount of storage each subscriber
gets (some charge extra for additional storage space). In addition, these
services often limit the file size of attachments (such as photos). The other
issue is the ability to work offline or when not connected to the Internet. One
solution is called caching, which temporarily places the subscriber’s e-mail
information on whatever PC he or she wants to work offline with. When the
user reconnects, any e-mails created while offline are sent, and any new incoming
e-mails can be viewed.
Sending E-Mails
E-mails are distributed using a (OSI Layer 7) protocol called Simple Mail
Transfer Protocol (SMTP). SMTP normally operates on powerful computers
dedicated to e-mail distribution, called SMTP servers. When you create and
send an e-mail, your e-mail client sends the file to the SMTP server. The server
pulls out the addresses from the message. (You can send e-mails to multiple
recipients.) For each domain name, the SMTP server must send a message to a
DNS to get the IP address of each recipient’s e-mail server. If the recipient is on
the same server as you (that is, if you send an e-mail to someone with the
same domain name), this step is unnecessary.
After your SMTP server knows the IP address of the recipient’s server, your
SMTP server transfers the e-mail message to the recipient’s SMTP server. If
there are multiple recipients in different e-mail domains, a separate copy of the
e-mail is transferred to each recipient’s SMTP server. According to the name of
the protocol, this is all pretty simple.
Transfer Protocol (SMTP). SMTP normally operates on powerful computers
dedicated to e-mail distribution, called SMTP servers. When you create and
send an e-mail, your e-mail client sends the file to the SMTP server. The server
pulls out the addresses from the message. (You can send e-mails to multiple
recipients.) For each domain name, the SMTP server must send a message to a
DNS to get the IP address of each recipient’s e-mail server. If the recipient is on
the same server as you (that is, if you send an e-mail to someone with the
same domain name), this step is unnecessary.
After your SMTP server knows the IP address of the recipient’s server, your
SMTP server transfers the e-mail message to the recipient’s SMTP server. If
there are multiple recipients in different e-mail domains, a separate copy of the
e-mail is transferred to each recipient’s SMTP server. According to the name of
the protocol, this is all pretty simple.
What’s Up with the @ Sign?
All e-mail addresses are made up of two parts: a recipient part and a domain
name. An @ symbol separates the two parts to denote that a recipient is
unique within a domain name. The domain name is usually the name of your
ISP (or your company if you have e-mail there), and, like a website, an e-mail
domain has an associated IP address. This allows (actually, requires) the use of
a DNS server to translate the domain name portion of an e-mail address to the
IP address of the server where the e-mail account resides.
The recipient part is the chosen identifier that you are known by within the email
domain. There are a lot of possibilities for choosing the recipient. Here
are a few popular styles:
Firstname.Lastname John.Brown
FirstinitialLastname JBrown
Nickname DowntownJohnnyBrown
Personalized license plate L8RG8R
Other obscure reference GrassyKnoll63
When picking an e-mail address, remember that sometimes you’ll have to verbally
tell someone your e-mail address, so “X3UT67B” is inadvisable.
name. An @ symbol separates the two parts to denote that a recipient is
unique within a domain name. The domain name is usually the name of your
ISP (or your company if you have e-mail there), and, like a website, an e-mail
domain has an associated IP address. This allows (actually, requires) the use of
a DNS server to translate the domain name portion of an e-mail address to the
IP address of the server where the e-mail account resides.
The recipient part is the chosen identifier that you are known by within the email
domain. There are a lot of possibilities for choosing the recipient. Here
are a few popular styles:
Firstname.Lastname John.Brown
FirstinitialLastname JBrown
Nickname DowntownJohnnyBrown
Personalized license plate L8RG8R
Other obscure reference GrassyKnoll63
When picking an e-mail address, remember that sometimes you’ll have to verbally
tell someone your e-mail address, so “X3UT67B” is inadvisable.
E-Mail Tools
There are two basic ways to create, send, and receive e-mails: with an e-mail
client and with a web-based e-mail tool:
• E-mail clients that are installed on individual machines are in wide use today.
The most popular are Microsoft Outlook/Outlook Express. E-mail clients
allow for the creation, distribution, retrieval, and storage of e-mails (as well as
some other useful features). These types of clients were originally designed so
that e-mails to and from an account could be accessed from a single machine.
E-mail clients physically move the e-mail from the e-mail server to your PC’s
hard drive. After the e-mail is downloaded, it no longer exists in the e-mail
provider’s network. The e-mail exists in your e-mail client program (on the
PC’s hard drive) until you delete it.
• Web-based e-mail tools, such as Google Mail, allow users to access their
e-mail from any machine connected to the Internet. Users log in to the website
with their registered name and password. Then they are given access to
a web-based e-mail client that has all the basic abilities of e-mail clients,
such as the ability to create, send, and receive e-mails. Many have more
advanced features, such as the ability to send and receive file attachments
and create and use address books.
Web-based e-mail tools differ from e-mail clients in that the e-mail is not
downloaded to your PC’s hard drive. It exists only on the e-mail provider’s
network until you delete it. Some people use a combination of web-based email
and e-mail clients. For example, you may use the web-based e-mail tool
to access your e-mail when you are away from home and not using your
home PC. When you are at home, you could then use your e-mail client.
client and with a web-based e-mail tool:
• E-mail clients that are installed on individual machines are in wide use today.
The most popular are Microsoft Outlook/Outlook Express. E-mail clients
allow for the creation, distribution, retrieval, and storage of e-mails (as well as
some other useful features). These types of clients were originally designed so
that e-mails to and from an account could be accessed from a single machine.
E-mail clients physically move the e-mail from the e-mail server to your PC’s
hard drive. After the e-mail is downloaded, it no longer exists in the e-mail
provider’s network. The e-mail exists in your e-mail client program (on the
PC’s hard drive) until you delete it.
• Web-based e-mail tools, such as Google Mail, allow users to access their
e-mail from any machine connected to the Internet. Users log in to the website
with their registered name and password. Then they are given access to
a web-based e-mail client that has all the basic abilities of e-mail clients,
such as the ability to create, send, and receive e-mails. Many have more
advanced features, such as the ability to send and receive file attachments
and create and use address books.
Web-based e-mail tools differ from e-mail clients in that the e-mail is not
downloaded to your PC’s hard drive. It exists only on the e-mail provider’s
network until you delete it. Some people use a combination of web-based email
and e-mail clients. For example, you may use the web-based e-mail tool
to access your e-mail when you are away from home and not using your
home PC. When you are at home, you could then use your e-mail client.
E-mail is one of the most common network applications in use today.
Although it might seem relatively new, e-mail was invented in the early 1970s.
Back then, of course, there was no Internet as we know it today, so having email
was a bit like owning a car before there was a highway system.
Today, e-mail is so widespread that ISPs just assume that you want an e-mail
address and automatically assign you one (or even several) when you begin
your service agreement.
Although it might seem relatively new, e-mail was invented in the early 1970s.
Back then, of course, there was no Internet as we know it today, so having email
was a bit like owning a car before there was a highway system.
Today, e-mail is so widespread that ISPs just assume that you want an e-mail
address and automatically assign you one (or even several) when you begin
your service agreement.
The Internet and Its Applications
What makes the Internet useful and interesting to the average person is not the
network, but rather the applications that operate on the network. The two
most common Internet applications in use today are e-mail and web browsers.
network, but rather the applications that operate on the network. The two
most common Internet applications in use today are e-mail and web browsers.
Subscribe to:
Posts (Atom)