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Telecommunications & Networking
Unit Subtitle: Modems
Copyright © Texas Education Agency, 2013. All rights reserved.
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Objectives
Describe the function of a modem
Identify considerations when choosing a
modem
Identify different types of modems
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Internal modem
External modem
K56 modem
Cable modem
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2
Overview Continued
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Describe how a modem works
List the steps to install/replace a modem
Identify testing and troubleshooting
techniques for a modem
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3
Modem Functions
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A modem is a device that lets computers
exchange information through telephone
lines
Modem stands for MOdulator/DEModulator
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4
Choosing a Modem
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1.
2.
When choosing a modem the following
features should be explored before buying:
Fax and Voice Capabilities - Most modem
have the capability to send and receive
faxes. You can create a document on your
computer and fax it to another computer.
Speed – The speed will indicate the amount
of information the modem can send and
receive.
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Choosing a Modem
3.
4.
Communications Program – A
communications program is a software that
manages the transmission of information
between two modems.
Upgrade – Look at the upgrade capabilities
of your modem. You may be able to
upgrade your current modem, such as
faster speed. The upgrade may be a
program you install or a chip you add to the
modem.
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6
Different types of Modems
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Most PCs have modems these days.
They can be internal or external.
External modems have LEDs (Light
Emitting Diode) that can be useful in
seeing whether the modem is
transmitting and receiving data
Internal modems don’t have this feature
but it is often simulated in software. It is
an expansion card that plugs into an
expansion slot inside a computer.
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Different types of Modems
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The K56 Modem will pull more data
faster from the Internet. This technology
allows a person at a home or office PC
to send data at normal analog modem
rates but get information back nearly
twice as fast.
The cable modem is a device that lets
computers access the Internet using
television cable.
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8
Different types of Modems
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Cable Modems are not really modems
because they work with digital signals
vs analog signals
DSL (digital subscriber line) and ISDN
(integrated services digital network)
modems send purely digital signals
over telephone lines. They offer
extremely fast Internet connections and
we can expect them to eventually
replace conventional modems.
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How a Modem Works
1
Communications software sends a
voltage along pin 20 of the serial port
of which the modem is connected
telling it that the PC is turned on. At
the same time the PC detects a
voltage from the modem on pin 6
telling it the modem is ready to
receive data or instructions.
2
A command is sent to the modem
over line 2, the Transmit Data line and
it tells your modem to go off hook-to
open a connection with the phone
line. The modem acknowledges the
command by replying to the PC on
line 3, the Receive Data line.
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3
When the modem on the other end of
the phone connection – the remote
modem- answers the call, your local
modem sends out a hailing tone to let
the remote modem know that it’s
being called by another modem. The
remote modem responds with a
higher-pitched tone,
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When your communications are
established, your modem sends your
PC a Carrier Detect (CD) on line 8.
The signal tells the communications
software that the modem is receiving
a carrier signal, which is a steady tone
of a certain frequency that later will be
modulated to transmit data.
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How a Modem Works Cont.
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The two modems exchange
information about how they’ll send
data to each other, a process called a
handshake. If the local and remote
systems do not use the same settings
during the handshake, either they’ll
wind up sending characters that make
no sense or they'll refuse to
communicate at all.
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When the communication software
wants to send data, it first sends data
to line 4 which will ask the modem
whether it is free to receive data from
your PC. If your PC is busy doing
something else, it will send a signal
to the modem telling it to stop
sending data until the PC finishes its
other work.
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At the other end of the phone line, the
remote modem hears incoming data
as a series of tones with different
frequencies. It demodulates these
tones back into digital signals and
sends them to the receiving computer.
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When you tell your communications
software to end a communications
session, the software sends a
command to the modem that causes it
to break the phone connection.
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Installing an External Modem
1.
2.
3.
Before installing a modem, turn off the
computer
If desired, connect the cable from your
telephone to the back of the modem.
This lets your telephone share the
telephone line with your computer
Connect the telephone line to the back
of the modem. Then connect the
telephone line to the telephone jack on
the wall.
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Installing an External Modem
4.
5.
Connect the serial cable to the back of
the modem. Then connect the serial
cable to a serial port at the back of the
computer.
Connect the power cable to the back of
the modem. Then plug the power cable
into an electrical outlet.
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13
Installing an Internal Modem
1.
2.
3.
An internal modem is an expansion
card that plugs into an expansion slot
inside the computer.
Place the expansion card in the slot.
Press down firmly and evenly across
the top of the card until it is securely
inserted in the expansion slot.
Secure the expansion card to the
computer case using a small screw.
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Installing an Internal Modem
4.
When you install an internal modem,
your computer thinks another serial port
has been added. Either adjust the
jumpers on the modem so it uses the
serial port or change the computer’s
settings to disable the existing serial
port.
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Installing an Internal Modem
5.
When you install an external or internal
modem the computer may automatically
detect and set up the modem, installing
the necessary driver for you. If the
computer does not automatically set up
the modem for you, you will need to
install the driver included with the
modem.
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Test and Troubleshoot
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A modem can be tested to make sure it
is communicating properly with a
computer. Simply use a program which
is included with your operating system
to test the modem. Try to make a
telephone call using the program. You
will hear the modem making a dialing
noise if it is communicating properly
with computer.
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Test and Troubleshoot
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If your modem is having problems
making a connection it may be features
on your telephone line such as call
waiting or voicemail that cause
connection problems. The voicemail
features changes the tone of the
telephone line to indicate a message is
waiting and it may prevent the modem
from establishing a connection.
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Test and Troubleshoot
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The call waiting feature generate a
beep to that indicates an incoming call
and the beep may cause some
modems to lose the connection. You
should disable these features before
using your modem.
If the modem is operating slowly, the
problem may be with the quality of the
telephone line. Contact your local
telephone company.
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Review
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What is the definition of a modem?
List the four features that should be explored
before buying a modem.
List some different types of modems.
Briefly explain how a modem works.
How is a modem tested?
List some troubleshooting techniques when a
modem is interrupted or disconnected by the
computer
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