Analog Lines

Analog Lines

Using analog lines to dial out to other networks or to
the Internet—or to allow remote users to dial into your
network—is a straightforward solution. Most ordinary
phone lines are analog lines. Connect a modem to your
computer and to a wall jack and you’re in business. You
pay for a connection as you would pay for a phone call—
by the minute, or a set rate per local call (long distance
charges are the same as for a long distance telephone call).
At present, the fastest analog modems operate at
56 Kbps for transferring data. With today’s larger file sizes
and graphically sophisticated World Wide Web sites on the
Internet, you should look for modems that operate at a
minimum of 33.6 Kbps (also called V.34) and have
V.42 (error correction) and V.42bis (data compression)
capabilities for better performance.
While modems offer a simple solution for dialout
connections to other LANs and the Internet, they do not scale
well as your network grows. Each modem can support only
one remote “conversation” at a time, and each device that
wants to connect with the outside world needs a modem.
See the examples in the next section for ways to overcome
this limitation by installing a router for wide-area communications

and your Internet link.


Analog vs. Digital

The difference between analog and digital signals is very important
for data communications. The most familiar “analog”
communication is a phone call. Varying electrical voltage reflects
the variations in the volume and tone of the human voice. By
contrast, digital communications use a series of 1s and 0s to
carry information from point to point. Modems actually convert
the digital data of one computer into an analog signal for transmission
over the phone lines. On the receiving end, another
modem converts the analog signal back into a series of 1s and 0s,
so the receiving computer can interpret the transmission. Today,
phone companies can offer fully digital service between LANs
(leased lines such as 56 K, 384 K, and T1s are digital services), or
Integrated Services Digital Network (ISDN) which allows dialup
connections on an as-needed basis. When it comes to moving
data, digital communications are less susceptible to errors and
faster than analog signals because they are not susceptible to

problems such as electrical “noise” on transmission lines.