Modem.. How it works.. what is keen it that..

1. Modem
Presented by
Ravi Namboori

2. Index
 Introduction to modem
 Types of modem
 Modem Functions
 Modem purpose
 Modem security

3. Introduction
A modem is an electronic device that transforms computer's digital
information into analog carrier signals and vice versa. Computers use modems
to interconnect with each other over a network. The word modem is derived
from "modulator-demodulator" that defines the functions it performs.
Modulation is the process of changing the form of the signal carrying the
information. The demodulation process does the task of extracting information
from the signals that are modulated.
Modems are generally classified by the amount of data they can send in a
given unit of time, usually expressed in bits per second (bit/s or bps), or bytes
per second (B/s). Modems can also be classified by their symbol rate,
measured in baud. The baud unit denotes symbols per second, or the number
of times per second the modem sends a new signal.

4. The following characteristics distinguish one modem from another:
Bps : How fast the modem can transmit and receive data. At slow rates,
modems are measured in terms of baud rates. The slowest rate is 300 baud
(about 25 cps). At higher speeds, modems are measured in terms of bits per
second (bps). The fastest modems run at 57,600 bps, although they can achieve
even higher rates by compressing the data. Obviously, the faster the
transmission rate, the faster you can send and receive data.
Voice/data: Many modems support a switch to change between voice and
data modes. In data mode, the modem acts like a regular modem. In voice
mode, the modem acts like a regular telephone. Modems that support a
voice/data switch have a built-in loudspeaker and microphone for voice
communication.

5. Auto-answer: An auto-answer modem enables your computer to receive calls
in your absence. This is only necessary if you are offering some type of
computer service that people can call in to use.
Data compression: Some modems perform data compression, which enables
them to send data at faster rates. However, the modem at the receiving end
must be able to decompress the data using the same compression technique.
Flash memory : Some modems come with flash memory rather than
conventional ROM, which means that the protocols can be easily updated if
necessary.
Fax capability: Most modern modems are fax modems, which means that they
can send and receive faxes.

6. Different types of Modem are as follows:
Types of modem
Internal Modem
External Modem
PC Card Modem

7. It is the device installed in the desktop or laptop computer to communicate over a
network with other connected computers. These are cheaper than external
modems as they do not require a power supply or a chassis. There are two types of
internal modems: dial-up and Wi-Fi (wireless). Dial up works on the telephone
cables and requires a network access phone number and log on credentials to make
a connection and Wi-Fi modem comments to the network without filling these
credentials.
Internal Modem:

8. A modem that resides in a self-contained box outside the computer system.
Contrast with an internal modem, which resides on a printed circuit board inserted
into the computer. External modems are the simplest type of the modem to install
this kind of modem you didn’t open the computer. The telephone line plugs into a
socket on the rear panel of the modem. As external modems have their own power
supply you can turn off the modem quickly to break the connection. The examples
of these modems are the DSL modems which are used in the broadband
connections. External modems tend to be slightly more expensive than internal
modems.
External Modem:

9. These modems, designed for portable computers, are the size of a credit card and
fit into the PC Card slot on notebook and handheld computers. These modems are
removed when the modem is not needed. Except for their size, PC Card modems
are like a combination of external and internal modems. These devices are plugged
directly into an external slot in the portable computer. So no cable is required other
than the telephone line connection. The cards are powered by the computer, which
is fine unless the computer is battery-operated. Running a PC Card modem while
the portable computer is operating on battery power drastically decreases the life
of your batteries.
PC Card Modem:

10. Functions of Modem
 Error correction
 Flow control
 Compressing the data

11. Thank You