range from 0–4 kHz; that narrow band works well over long distances. (The
fact that POTS uses such a narrow band to carry voices is the reason phone
conversations sound relatively thin or tinny compared to face-to-face or FM
radio.) Standard dial-up modems modulate their signal into the same 4 kHz-wide
band. The advanced engineering behind DSL sends its signals in a fatter (and
higher) section of bandwidth on the copper wire, between 25 kHz and 1 MHz.The advantages of DSL include the fact that the connection between the
home/office and the phone company’s switching center is not shared by
other users; the speed you receive when your connection is installed should
not go down and could possibly go up if the phone company improves its
facilities. Another advantage is that users can continue to use their telephone
line for standard telephone conversations, removing the need for a separate
phone line for dial-up Internet service.On the downside, though, DSL may not be available in areas where the POTS
is very old. And the farther your home or office is from the phone company’s
central office, the higher the likelihood that DSL service may be slower or
unreliable. (In most instances, you want to be no farther than one or two
miles from the central office; that’s probably not a problem in an urban set-
ting, but out in the country the nearest phone company facility may be much
more distant.)And, just as I warned about cable modem providers, you need to make a
judgment about the quality of customer service you expect from your phone
company. If they don’t deliver decent quality and reliable POTS, don’t expect
them to be able to make you happy with higher-tech DSL.You may receive a free loan of a DSL modem when you contract with a phone
company for the service or you may be required to rent one from the com-
pany; it may be cheaper to buy your own DSL modem, although the phone
company may decline to offer support for something it did not provide.Pitting Internal versus External Connections...........................................
Dial-up modems are often offered as internal devices on laptops, built directly
into the motherboard as a Winmodem(a scheme that uses the CPU for some
of the functions of the device, sometimes also called a soft modem) or installed
in a mini-PCI slot in the case. Another option for internal installation is the
use of a PC Card slot. The other option for dial-up modems is as an external
device, attached to a serial port or a USB port. (More on USB in Chapter 16.)232 Part IV: Failing to Communicate