Page 98 - Electronic Commerce

Technology Infrastructure: The Internet and the World Wide Web

SMTP and POP are two common protocols used for sending and retrieving e-mail.
Simple Mail Transfer Protocol (SMTP) specifies the format of a mail message and
describes how mail is to be administered on the e-mail server and transmitted on the 73
Internet. An e-mail client program running on a user’s computer can request mail from
the organization’s e-mail server using the Post Office Protocol (POP). A POP message can
tell the e-mail server to send mail to the user’s computer and delete it from the e-mail
server; send mail to the user’s computer and not delete it; or simply ask whether new mail
has arrived. POP provides support for Multipurpose Internet Mail Extensions (MIME),
which is a set of rules for handling binary files, such as word-processing documents,
spreadsheets, photos, or sound clips that are attached to e-mail messages.
The Interactive Mail Access Protocol (IMAP) performs the same basic functions as
POP, but includes additional features. For example, IMAP can instruct the e-mail server to
send only selected e-mail messages to the client instead of all messages. IMAP also allows
the user to view only the header and the e-mail sender’s name before deciding to
download the entire message, which avoids the POP requirement that users download
e-mail messages to their computers before they can search, read, forward, delete, or reply
to those messages. IMAP lets users create and manipulate e-mail folders (also called
mailboxes) and individual e-mail messages while the messages are still on the e-mail
server; that is, the user does not need to download e-mail before working with it.
IMAP lets users manipulate and store their e-mail on the e-mail server and access it
from any computer, which is important to people who access their email from different
computers at different times. The main drawback to IMAP is that e-mail messages are
stored on the server and, over time, can exceed the user’s space allowance on the server.
In general, server computers use faster (and thus, more expensive) disk drives than
desktop computers. Therefore, it is more expensive to provide disk storage space for large
quantities of e-mail on a server computer than to provide that same disk space on users’
desktop computers.

Web Page Request and Delivery Protocols
The Web is software that runs on computers that are connected to each other through the
Internet. Web client computers run software called Web client software or Web browser
software. Examples of popular Web browser software include Google Chrome, Microsoft
Internet Explorer, and Mozilla Firefox. Web browser software sends requests for Web page
files to other computers, which are called Web servers. A Web server computer runs
software called Web server software. Web server software receives requests from many
different Web clients and responds by sending files back to those Web client computers.
Each Web client computer’s Web client software renders those files into a Web page.
Thus, the purpose of a Web server is to respond to requests for Web pages from Web
clients. This combination of client computers running Web client software and server
computers running Web server software is an example of a client/server architecture.
The set of rules for delivering Web page files over the Internet is in a protocol called
the Hypertext Transfer Protocol (HTTP), which was developed by Tim Berners-Lee in
1991. When a user types a domain name (for example, www.yahoo.com) into a Web
browser’s address bar, the browser sends an HTTP-formatted message to a Web server

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