MODEM INTERNAL AND EXTERNAL TYPES

1. GOHEL VISHAL. H
LECTURER OF COMPUTER DEPT.
GOVERNMENT POLYTECHNIC BHUJ
9638893297
Chapter 12 Slide 1 of 11

2. Modems
Chapter 12

3. Objectives
Identify the features of a modem
Discuss the working of a modem
Explain the different types of modems
Discuss about the modem standards and
protocols
Install and configure a modem
Test a modem
Troubleshoot a modem
Chapter 12 Slide 3 of 11

4. 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
Chapter 12 Slide 4 of 11

5. 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
Chapter 12 Slide 5 of 11

6. 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
Chapter 12 Slide 6 of 11

7. 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
 External - Connected to the
PC through a cable, which is
plugged into serial port on the
back of the system unit.
Internal Modem
External Modem
Chapter 12 Slide 7 of 11

8. Types of Modems - I
 56K Modem - A traditional modem is used to connect end users
from home or small businesses to an ISP. A development in the
modem is 56K modem (DTR is 56 Kbps) which uses the
existing telephone line. The subscriber is connected to the
switching station of the telephone company. The connection
from the switching station to the ISP computer (server) is used
by the subscriber.
 X2 Modem – US robotics developed X2 technology to transmit
data at the speed of 56 Kbps over plain 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
Chapter 12 Slide 8 of 11

9. Types of Modems - II
 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
 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
 ADSL Modem - ADSL (Asymmetric Digital Subscriber
Line) is a high speed data communication technology. It
allows you to transmit digital information at a high
bandwidth using existing copper telephone lines. ADSL is an
"always on" service (as long as your computer is powered
on); this allows you to leave the downloading of larger files
to continue without you. The data stream speed of ADSL is
from 512 kbps to 8 Mbps.
Chapter 12 Slide 9 of 11

10. Types of Modems - III
 USB Modem - The modem has USB connector at one end
and RJ-11 connector at other end or SIM card based. In
case of wireless, modern USB modem, it comes along with
a SIM card in your laptop/desktop (in USB Slot).
 Data Card - Now a days data cards are used with PCs and
Laptops to provide mobile wireless Internet access and
come with a SIM card. There are many companies which
provide this facility such as Airtel, Tata Indicom, BSNL
and, Reliance
 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
Chapter 12 Slide 10 of 11

11. LEDs on External Modem
AA – Auto Answer
CD – Carrier Detect
RD – Receive Data
SD – Send Data
TR – Terminal Ready (Same DTR)
CS – Clear to Send
ARQ – Error Control
OH – Off Hook
MR – Modem Ready
Chapter 12 Slide 11 of 11

12. Modem Modulation Standards
Two modems
communicating with
each other must
support same
modulation standards
Standard Description
V.32bis Supports full-duplex transmission at a speed of
up to 14,000 bps
V.34 Supports full-duplex transmission at a speed of
up to 28,800 bps
V.42 Regulates error-detection for high-speed modems.
This standard enables modems to work
with both, digital and analog phone lines.
V.42bis Used for data compression that enables to
transmit data at a speed of up to 34,000 bps
X2 Supports data transmission at a speed of up to 56
Kbps
V.90 Integrates both K56Flex and X2 standards into
one
V.92 Provides features such as:
 Modem on hold – Enables to suspend the
data call made by the user and answer to an
inbound call
 Quick connect – Enables to reduce the
connection time by remembering the line
conditions to the dial-up server
 V.PCM-Upstream – Enables faster
upstream communication at a speed of up
to 48,000 bps.
Chapter 12 Slide 12 of 11

13. Best practices and Precautions while installing
a Modem
 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
Chapter 12 Slide 14 of 11

14. Installing a Modem and Configuring the
Modem and show from CBT
Test Modem
Chapter 12 Slide 15 of 11

15. Troubleshooting Modems
The external modem is not working
The external modem is not receiving the
command
The modem dials but does not connect
The modem does not get a dial tone
Modem is busy or not responding
Chapter 12 Slide 16 of 11

16. Summary - I
 Modem is a communication device that enables a computer to
transfer data over the telephone or cable lines
 Data transmission speed, data compression, data or voice
communication, fax capability are the most common features
of a modem
 An internal modem is a modem card that you can plug into an
expansion slot on the motherboard
 An external modem is connected to the PC through a cable,
which is plugged into serial port on the back of the system
unit
Chapter 12 Slide 17 of 11

17. Summary - II
 X2 technology transmits data at the speed of 56 Kbps because
of the high-speed digital lines connected to most phone
switching stations
 V.90 technology was built with an assumption that one end of
a modem session has a pure digital connection to the
telephone line
 Integrated Services Digital Network (ISDN) is a set of
international communication standard for transmitting digital
data over a telephone line
 DSL needs a device called DSL modem to convert digital
signals to analog signals and analog signals back to the digital
signals
Chapter 12 Slide 18 of 11

18. Summary - III
A cable modem is a device that enables to connect
a PC to the cable TV line.
Modem protocols are used to transfer data over a
telephone line.
Configuring a modem helps to modify the
properties of the modem
AT commands are used to communicate directly
with the modem.
Troubleshooting modem enables to solve the
problems
Chapter 12 Slide 19 of 11