(Shelly Cashman Series) Gary B. Shelly, H. Albert Napier, Ollie N. Rivers-Web design_ introductory concepts and techniques -Cengage Learning (2008)
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12 Chapter 1 The Environment <strong>and</strong> the Tools<br />
satellite<br />
local<br />
access area<br />
local<br />
access area<br />
local<br />
telephone<br />
company<br />
analog<br />
signal<br />
longdistance<br />
telephone<br />
company<br />
microwave stations<br />
longdistance<br />
telephone<br />
company<br />
local<br />
telephone<br />
company<br />
analog<br />
signal<br />
telephone service<br />
customer<br />
telephone service<br />
customer<br />
Figure 1-15 The PSTN generally uses digital technology, with the exception of the final link from the local telephone company to a home<br />
or office, which usually is analog.<br />
DIAL-UP LINES A dial-up line is a temporary connection that uses one or more<br />
analog telephone lines for communications. Using a dial-up line to transmit data is similar<br />
to using the telephone to make a call. A modem at the sending end dials the telephone<br />
number of a modem at the receiving end. When the modem at the receiving end answers<br />
the call, a connection is established <strong>and</strong> data can be transmitted. Internet access using a<br />
dial-up line comes in two versions: regular dial-up <strong>and</strong> high-speed dial-up.<br />
The advantages of a dial-up line to connect to the Internet are low cost <strong>and</strong> easy<br />
access to existing telephone lines. The major disadvantage of dial-up line Internet access is<br />
slow access speed. Regular dial-up access is the slowest Internet access connection <strong>and</strong> is<br />
generally unsuitable for many of today’s online activities, such as sending large data files or<br />
viewing or listening to streaming media — video or sound that downloads to a computer<br />
continuously to be watched or listened to in real time — or online gaming. High-speed<br />
dial-up access, which combines the user’s dial-up line with the service provider’s acceleration<br />
servers that store frequently requested <strong>Web</strong> pages, can make dial-up Internet access<br />
up to seven times faster than regular dial-up. However, dial-up access is fast becoming the<br />
least popular Internet access method <strong>and</strong> is rarely used in business.<br />
DESIGN<br />
TIP<br />
Large images <strong>and</strong> multimedia elements on <strong>Web</strong> pages can degrade the<br />
audience’s viewing experiences at slower Internet access speeds.<br />
DIGITAL DEDICATED LINES Unlike a dial-up line in which the connection is<br />
reestablished each time it is used, a dedicated line is a constant connection between two<br />
communications devices. This constant connection provides a higher-quality connection<br />
than a dial-up line. Businesses often use dedicated lines to connect geographically distant<br />
offices. Dedicated lines either can be analog or digital; however, digital lines increasingly
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