What is Modem
The full form of modem is “modulator/demodulator”. It is a hardware component that allows computers or other devices to be connected to computers or other devices over the Internet.
It converts or “modulates” the analog signal from the phone or cable into a digital signal that can be easily recognized by a computer. Similarly, it converts digital data into analog signals on computers or other devices.
In 1962, the first commercial modem was made and sold by AT&T with the Bell 103. Previous modems used to be “dial-up”, meaning they had to dial a telephone number to connect to the ISP.
This modem operates in standard analog telephone lines and also uses the same frequency as telephone calls, limiting its data transfer rate to a maximum of 56 kbps.
Dial-up modems also require total bandwidth from local telephone lines, which means voice calls can interfere with your Internet connection.
At the same time, modern modems are usually DSL and cable modems, also known as “broadband” devices. DSL models operate over the standard telephone line, but they use a wider frequency range.
They
allow a higher data transfer rate if we compare it with a dial-up modem and it
does not interfere with phone calls.
How does the Modem work?
As we have just learned that the full form of Modem is Modulator – Demodulator. Modems are also used because it transfers data from one computer network to another computer network.
In this, the transfer of data is done through the lines of the telephone. By the way, computer networks work in digital mode, while analog signal technology is used to send messages across phone lines.
The
modulator converts the information in analog mode to end-to-end transmission
from digital mode and the demodulator converts the same information about the
same information from analog mode to end-to-end transmission.
Digitization is a process in which analog signals from computer networks are converted into digital signals in other computer networks.
When analog facilities are used, for data communication between two digital devices, they are called data terminal equipment (DTE), and modems are used at both ends. In such situations, the DTE can be a terminal or even a computer.
The modem presented at the end of the transmission, produced by DTE, converts it to an analog signal, as it is sufficient to modify the carrier. At the same time, the modem located on the receiving end transmits the display to the carrier and then the display digital signal arm ends up on the DTE.
The
transmission media between two modems may be in the form of special circuits or
telephone circuits. If telephone circuits are used, the modem is connected to
local telephone exchanges.
Use of Modem
Basic modulation techniques used by modems to convert digital data into analog signals:-
- Amplitude shift keying (ASK)
- Frequency shift keying (FSK)
- Phase shift keying (PSK)
- Differential PSK (DPSK)
These techniques are also called continuous binary
wave (CW) modulation.
Modems are always used in doubles. Any system,
whether it is simplex, half-duplex or full-duplex, requires a modem to transmit
and receive the tip
Hence we can say that a modem acts as an electronic bridge of action in two worlds – the first world which is a pure digital signal and the second world which is analog.
Function of modem
Modems are used to
connect users to the Internet and send faxes. But if this problem is gone now,
modems are now used in many applications in many businesses.
Many specialized
applications include Data Transfer, Long Distance Management, Broadband
Reserve, Sale of Points, Machine to Engine, and many more.
By the way, most of the solutions are located in the backend, so they are hidden from the users, but they work only with the backend and make our life easier every day.
Types of Computer Modems
There are many
different types of modems. They are also
classified through numerous ways. However, generally the classification is
based on the basic function of a modem. Some of the common types are –
On the basis of
directional capability, modems are divided into half duplex and full duplex types
Half duplex
- A half duplex modem permits transmission in one direction at a time.
- If a carrier is detected on the line by the modem, I gives an indication of the incoming carrier to the DTE through a control signal of its digital interface.
- As long as they camel’ IS being received; the modem does not give permission to the DTE to transmit data.
Full duplex
- A full duplex modem allows simultaneous transmission in both directions.
- Therefore, there are two carriers on the line, one outgoing and the other incoming. Wire and 4-wire Modems
- The line interface of the modem can have a 2-wire or a 4-wire connection to transmission medium. 4-wire Modem
- In a 4-wire connection, one pair of wires is used for the outgoing carrier and the other pair is used for incoming carrier.
- Full duplex and half duplex modes of data transmission are possible on a 4- wire connection.
- As the physical transmission path for each direction is separate, the same carrier frequency can be used for both the directions.
- 2-wire modems use the same pair of wires for outgoing and incoming carriers.
- A leased 2-wireconrlection is usually cheaper than a 4-wire connection as only one pair of wires is extended to the subscriber’s premises.
- The data connection established through telephone exchange is also a 2-wire connection.
- In 2-wire modems, half duplex mode of transmission that uses the same frequency for the incoming and outgoing carriers can be easily implemented.
- For full duplex mode of operation, it is necessary to have two transmission channels, one for transmit direction and the other for receive direction.
- This is achieved by frequency division multiplexing of two different carrier frequencies. These carriers are placed within the bandwidth of the speech channel.
Asynchronous &
Synchronous Modems
Asynchronous Modem
- Asynchronous modems can handle data bytes with start and stop bits.
- There is no separate timing signal or clock between the modem and the DTE.
- The internal timing pulses are synchronized repeatedly to the leading edge of the start pulse
Synchronous
Modem
- Synchronous modems can handle a continuous stream of data bits but requires a clock signal.
- The data bits are always synchronized to the clock signal.
- There are separate clocks for the data bits being transmitted and received.
- For synchronous transmission of data bits, the DTE can use its internal clock and supply the same to the modem.
