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1. Network Modems

2. Modem
• Is a short form for Modulator/Demodulator
• The process of converting binary information into
analog signals is called modulation and process of
converting analog signal back to binary information
is called demodulation
• Enables a computer to transfer data over the
telephone or cable lines

3. Features of a Modem
• Transmission speed – high data transmission rate can
be achieved by compressing the data
• Voice or Data communication
• Data compression – if the modem is trying to
compress data that is already compressed, the
compression will be less efficient
• Auto answering
• Fax capability

4. Working of a Modem
• Software in computer activates modem, which
listens for dial tone on phone line
• Modem dials a specified number
• Modem at receiving end answers call and sends out
a signal
• Modem at sending end converts digital signals to
analog signals
• Modem at receiving end converts analog signals
back to digital signals

5. Basic Types of Modems
• Internal - A modem card that
you can plug into an expansion
slot on the motherboard. It is
advisable to remove the
telephone line when not used
Internal
Modem
• External - Connected to the PC
through a cable, which is
plugged into serial port on the
back of the system unit. External Modem

6. Types of Modems
• X2 Modem – US robotics developed X2 technology
to transmit data at the speed of 56 Kbps over plian
old telephone service (POTS). Limitations: DTR is
40kbps from your computer to dial up server and ISP
modem must support V.90 standard
• V.90 Modem - Built with an assumption that one
end of a modem session has a pure digital
connection to the telephone line and DTR is 56 kbps

7. Type of Modems
• ISDN Modem - Enables to send data, voice, and
video over digital telephone lines or over an
ordinary telephone wire. DTR is 64 kbps and
requires ISDN adapter to perform conversion
between digital and analog signal

8. Types of Modems
• DSL Modem - Carries both voice and data at the
same time. It’s a high speed connection that allows
the phone wires to transmit modulated digital
content at high speed
• Cable Modem – Transfers data much faster than the
regular telephone modems, ISDN modems, and DSL
modems. External cable modem is connected to
either Ethernet card or USB port on the computer.
Communicates with a Cable Modem Termination
System (CMTS) at the local cable TV company office

9. EXTRA NOTE
• Best Practices
– Read the modem documentation before installing
a modem
• Precautions
– Wear an anti-static wristband
– Ensure the computer is switched off and unplug
the power cord from the wall socket
– Disconnect all the peripheral devices attached to
the computer