Computer World. Матросова Т.А. - 29 стр.

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speaker-to-speaker signal loss. It also opens the door to various speed and reliability
enhancements.
Even people familiar with modem technology can have trouble with the monthly
crop of new bells and whistles. Some software authors smooth the way by providing
automatic setup routines for many different modem brands.
Connecting Your Modem to a Phone Line
Telephone lines are wires, and all wires have resistance. Wires allow electrons
to flow from one point to another. The resistance in these wires helps to impede the
electron flow.
Impedance is an inherent physical property of wire. The amount of impedance
depends on the width of the wire in respect to how much current is flowing, and the
length of the wire. At the end of the wires, at the phone company office, are electrical
circuits and switches–all designed to permit transmission over these phone lines, but
all with limitations on their capabilities.
You can hook up to a phone line in two ways: acoustically or directly.
Direct-connect modems connect to telephone lines by means of the familiar
RJ11 modular telephone jack. They are less sensitive to noise, and are easy to
connect. Back in the old days, before modular phone jacks, you had to cut and splice
wires if you wanted a direct electrical connection between your modem and the
phone line. This wasn't too popular with the family, as it tended to render the
telephone useless.
Most modems are direct-connect. They've become so popular that hotels
catering to business travelers provide an extra RJ11 jack in their rooms. Electronics
stores sell special one-line adapter jacks.
Connecting Your Modem to a PC
After successfully connecting your modem to the telephone system, the next
step is to make the connection between the modem and your personal computer.
Free-standing (external) modems are connected by either a DB-25 or DB-9 cable to
the computer's RS-232 serial communications port. Board (internal) modems are con-
nected by plugging a card into one of the computer's expansion slots.
SUGGES TED AC TI VI TI ES
1. Explain what the word modem means.
2. Discuss the following with your partner:
What are the external and the internal types of modem?
Which type do you prefer? Why?
3. Write a short paragraph about modems.

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