The full form of modem is “modulator-demodulator”

What is Modem?

modem full form is Modulator and demodulator

Modem is a very familiar word to all of us. It is used for connecting a computer to a telephone line.

The telephone lines are designed to carry analog signals, and their bandwidth is also limited, so they cannot be used for digital data transmission.

A Modulates and demodulates converts digital data from computers to analog signals and puts it on the telephone lines.

It is a bi-directional device that converts the analog signals on telephone lines into digital data when it is used for data reception.

The modem is a combination of two words modulator and demodulator. The standard modulation techniques used in the Modulates and demodulates.

1. Amplitude shift keying (ASK)

2. Frequency shift keying (FSK)

3. Phase shift keying (PSK)

Role of Modem

The term ‘MODEM’ is derived from the words modulator and demodulator. Modulates and demodulates contain a modulator as well as a demodulator.

The normal digital signal cannot be put directly on the telephone lines.

This is because the bandwidth of the telephone lines is not sufficient to transfer digital data without distortion.

Therefore, the digital data is first converted to a signal that is compatible with the telephone lines.

This conversion is done by a special communications box called “MODEM”. It is the box that makes a digital data signal compatible with any non-digital system and medium besides the phone system.

An example is a Modulator and demodulator, which makes the data bits compatible with a microwave radio system.

The role of MODEM can be better understood by referring to the picture

The modem is a DCE (Data Communication Equipment), which is designed to operate with the DTE (Data Terminal Equipment). DTE is nothing else but computers.

The key idea behind Modulates and demodulates is to use tones (sine waves) of various frequencies, phases, or amplitudes to represent the binary data

Thus, the binary data is converted into a corresponding analog signal using a Modulates and demodulates on the sending side.

On the receiving side, the Modulator and demodulator convert these analog signals into corresponding digital data.

Thus, a MODEM converts digital data to be transmitted as a signal and the received analog signal into a digital signal

Modulation techniques used for modem:

The basic modulation techniques used by a modem to convert digital data to analog signals are

Amplitude Shift Keying (ASK)

Frequency Shift Keying (FSK)

Phase Shift Keying (PSK) and

Differential PSK (DPSK)

Quadrature Phase Shift Keying (QPSK)

Quadrature Amplitude Modulation (QAM)

In ASK the digital signal is represented by the presence and absence ( 1 and 0), respectively, of a sinusoidal carrier

Modulation techniques used for modem:

In PSK, the phase shift of a sinusoidal carrier will take two different values, corresponding to 0 and 1.

In FSK, the carrier frequency is switched between two values, i.e., f and f, corresponding to inputs 0 or 1, respectively.

QPSK is a multilevel modulation in which four phase shifts are used to represent four different symbols.

At high bit rates, a combination of ASK and PSK is employed to minimize the errors in the received data.

This method is known as “Quadrature Amplitude Modulation (QAM)”. Let us discuss these methods one by one.

Shown in the diagram is the classification of digital to analog modulation systems.

Need of Modulation

The Modulates and demodulates will modulate the digital data signal from the DTE (computer) into an analog signal.

This analog signal is then transmitted on the telephone lines.

The question is, why can’t we send the digital signal as it is on the telephone lines? Why should we modulate it?

Here is the answer to it. The digital data consists of binary Os and Is; therefore, the waveform changes its value abruptly from high to low or low to high

To carry such a signal without any distortion being introduced, the communication medium needs to have a large bandwidth.

Unfortunately, telephone lines do not have high bandwidth. Therefore, we have to convert the digital signal first into an analog signal, which needs a lower bandwidth, utilizing the modulation process.

Advantages and Disadvantages of CW Modulation

The advantage of CW modulation techniques such as ASK, PSK, FSK, etc. used for the transmission of data is that we can use telephone lines for the transmission of high-speed data. Due to the use of CW modulation, the BW requirement is reduced.

The disadvantage of CW modulation is that we need to use a Modulator and demodulator with every computer. This makes the system costly and complex

Functions to be performed at the transmitting end

Take the data from the RS-232 interface

Convert the data (Os and Is) into appropriate analog signals (modulation process)

Perform the line control and signaling at the other end of the phone line.

Send dialing signals if this Modulates and demodulates is designed to dial without the presence of the user.

Have protection against line overload and other problems.

Functions of receiving modems

Receive the analog signals and demodulate them into Is and Os.

Put the demodulated signal into RS-232 format and connect to the RS-232 interface

Perform line control and signaling.

Have protection against line overload and other problems.

Recover data with the minimum number of errors from the received signal corrupted by noise.

Functional Blocks of a Modem:

A simplified block diagram of a modem used with RS-232 interconnection This Modulates and demodulates is designed to interface data signals to the telephone lines.

A Modulates and demodulates consists of a transmitter or modulator, a receiver or demodulator, two interfaces, tone generation and receiving circuitry, and timing and line control circuits.

The digital signal to be transmitted is applied to the transmitter. The modulator converts it into a suitable modulated analog signal (ASK, FSK, or PSK) and puts it on the telephone line through a line interface block.

If the Modulates and demodulates are on the receiving end, then the modulated analog signal, which is received from a distance, is applied to the demodulator or receiver.

The receiver converts this signal into corresponding digital data and connects to the computer through a digital interface, which is usually an RS-232 interface.

The line interface connects the Modulates and demodulates to the transmission channel (telephone line) for transmission and reception of the modulated signals.

Modulates and demodulates connected to telephone exchanges have an additional provision for connecting a telephone instrument. The telephone instrument enables the establishment of a telephone connection.

Operation of a Modem

After knowing what the functional blocks of a modem are, let us now understand the operation of a modulator and demodulator.

We assume that the Modulator and demodulator are being used at the sending end and that it uses the “binary FSK” technique of modulation. The operation is as follows:

The computer generates a stream of data bits, like 1001101, and connects it to the transmitter (modulator) through the digital interface block.

The transmitter converts this bit stream into a corresponding binary FSK signal Thus, information is transmitted in terms of change in frequency.

This Modulator and demodulator use two frequencies to represent the two binary values, i.e., 0 and 1. Assume that a frequency of 1000 Hz is being used to represent a binary “0” and a frequency of 2000 Hz is being used to represent a binary “I.”. A stream of bits is thus converted into 1000 and 2000 Hz tones

These tones will be connected to the telephone line through the line interface block. By design, the telephone lines can handle these tones reasonably well compared to putting the digital data directly on the lines.

This modem uses the BFSK technique of modulation, but Modulates and demodulates can use other techniques such as BASK, BPSK, or QPSK

Rate of signaling (baud):

The rate at which the digital data is transmitted is called the sig rate, which is measured in “baud”, For example, if 300 bits are being sent per second, the signaling rate becomes 300 baud.

A low-performance modem is intended for use up to 300 or 600 b A mid-range modulator and demodulates can operate reliably from 1200 to 4800 MHz.

Best-performance Modulates and Demodulates can cover up to 19.6 kbps. With an increasing baud rate, the time taken for data transfer reduces, but at the cost of increased technical difficulties in receiving and recovering the signal from the received noise-corrupted signal.

Telephone Modem Bandwidth

Traditional telephone lines can carry frequencies between 300 and 3300 Hz Thus, the bandwidth is 3000 Hz
This entire range is used for transmitting voice.
The range used for data transmission is, however, restricted to 2400 H, from 600 Hz to 3000 Hz.
Thus, a bandwidth of 2400 Hz is allotted for data transmission.

Airtel Modem

What is it: An Airtel modem is a device provided by the telecommunications company Airtel that connects to the internet using mobile data or fixed-line connections.
Internet Access: It allows you to access the internet by receiving and transmitting data signals, either through a SIM card (mobile data) or via a wired connection.
Wireless or Wired: Airtel Modulator and demodulator come in both wireless (Wi-Fi) and wired versions. The wireless modem lets you connect multiple devices through Wi-Fi.
Home or Portable: Some Airtel modems are designed for home use, while others are portable, allowing you to access the internet on the go.
Subscription Service: To use Airtel Modulates and demodulates, you typically need a subscription plan from Airtel, which provides you with a data connection.
Benefits: Airtel modems offer convenience and flexibility, allowing you to get online from various locations, whether at home, in the office, or while traveling.
Speed and Coverage: The quality of your internet connection with an Airtel Modulates and demodulates depends on factors like signal strength and network coverage in your area.

JIO Modem

Internet Connection: A JIO modem is a device provided by the telecommunications company JIO to connect to the internet.
Various Types: JIO offers different types of modulators and demodulators, including fixed-line modems and portable devices for on-the-go connectivity.
Wireless Option: Many JIO modems are wireless, enabling multiple devices to connect to the internet through Wi-Fi.
Mobile Data: JIO modems can use JIO’s mobile data network to provide internet access, which can be especially convenient when you’re not at home.
Home and Travel: You can use a JIO modem at home for a stable internet connection, or take it with you when you travel to stay connected on the road.
Subscription Needed: To use a JIO modem, you typically need a subscription plan from JIO, which provides you with internet access.

Types of Modems:

Modems can be of several types, and they can be categorized in some ways. The classification is based on the following basic features of a modem:

Directional capability: half-duplex and full-duplex modems

Connection to the telephone line: 2-wire modem or 4-wire modem.

Transmission mode: Asynchronous modem or synchronous Modulates and demodulates.

Half-duplex modem:

A half-duplex modem will allow data transmission in only one direction at a time. The Modulates and demodulates operation explained in Section 3.12.3 is for a half-duplex modem.

In half-duplex modems, if a carrier is detected on the telephone line by the modem, it indicates the incoming carrier to the computer through the control signal of its digital interface.

So long as the carrier is being received, the Modulates and demodulates do not give clearance to the computer to transmit.

Thus, in a half-duplex Modulates and demodulates, simultaneous transmission and reception in both directions are not possible.

Full duplex modem:

A full duplex Modulates and demodulates will allow simultaneous transmission in both directions.

Thus, there are two carriers (analog signals) simultaneously present on the line, one outgoing and the other incoming.

Synchronous and Asynchronous Modems:

Asynchronous modem:

An asynchronous modem can only handle the data bytes with “start” and “stop” bits. There is no separate timing signal or clock between the computer and Modulates and demodulates.

This is the internal timing pulses are synchronized repeatedly to the leading edge of the “start” pulse.

The synchronous type of modem, on the other hand, can handle a continuous train of data bits, but it requires a clock signal.

The data bits are always synchronized to the clock signal. There are separate clock signals for the data bits being transmitted and received

For the synchronous transmission of data, the internal clock of the DTE is used and also supplied to the modem. Or it can take the clock from the Modulates and demodulates and sends the data bits corresponding to each clock pulse.

At the receiver, the clock signal is recovered from the received signal by the Modulates and demodulates and supplied to the DTE. The synchronous modem.

Synchronous modem

Modem Standards:

There are two modem standards

1. Bell modem standard

2. The International Telecommunication Union (ITU) standard Table shows the ITU and Bell standard compatibility.

Bell standard	ITU standard	Baud rate	Bit rate	Modulation
103	V.21	300	300	FSK
212	V.22	600	1200	4 – PSK
202	V.23	1200	120	FSK
201	V.26	1200	2400	4 – PSK
208	V.27	1600	4800	8 – PSK
209	V.29	2400	9600	16 – QAM

56 k modems:

Traditional modems have a limitation on the data rate of 33.6 kbps; however, new modulators and demodulators have a bit rate of 56 kbps.

56 kbps modems are used when only one party is using digital signaling, such as an Internet Service Provider (ISP).

They have asymmetrical data rates; when the flow of data is from the ISP to the client, the data rate is 56 kbps, and when it is from the client to the ISP, ISP the data rate is 33.6 kbps.

The connection using a 56 K modem

The traditional modules and demodulates have a data rate of 33.6 kbps in both directions because the switching station analog data is converted to digital using PCM at both ends.

Since the analog signal is quantized to create the digital signal, the quantizing noise resulting from the process of quantizing limits the data rate to 33.6 kbps.

Quantization limits the uploading rate.

The concept of a cable modem is the splitter directs the TV bands to the TV set and the Internet access bands to the PC.

The cable Modulates and demodulates supports a data rate from the ISP to client in the range of 3 to 10 Mbps and from client to ISP in the range of 500 kbps to 1 Mbps

The two most popular techniques used for modulation demodulation are 64 QAM (6 bits at a time) and Quarternary PS (4 bits at a time).

Cable Network for Data Transmission

To utilize the cable network for data transmission, we have to use two devices, namely the CM (Cable Modem) and the CMTS (Cable Modem Transmission System).

Cable Modem (CM):

The block schematic of the cable Modulates and demodulates. It is similar to an ADSL modem, and it is installed on the user’s premises.

The filter separates video and data in the incoming signal from the cable.

The video signal is applied to the TV whereas the data signal is applied to the computer via cable Modulates and demodulates.

Cable Modem Transmission System (CMTS):

The cable companies install the CMTS inside the distribution hub.

The data from the Internet is passed through the CMTS to the combiner The video signal from the head is also applied to the combiner.

The combiner output contains video as well as data from the internet. This signal is put on the optical fiber for routing to the subscribers.

The data from the subscribers coming via the optical fiber is applied to the CMTS, and the CMTS passes it to the internet.

Null Modem

If an observer stands between the DTE and DCE to observe the RS 232 interface, it is seen that a signal that comes out of a particular pin of the DTE port goes toward DCE on the same pin.

That means in any pair of corresponding pins of the DTE and DCE ports, one is the output pin and the other is the input pin.

Hence, to use RS 232 to interconnect any two devices, a DTE must think that it is connected to a DCE, irrespective of whether the other device is a DCE or not.

Thus, we can connect a computer and a terminal directly using the RS 232 interface if one of them has a DCE port and the other has a DTE port.

However, if both the devices that are to be interconnected have only the DTE ports, then one of the devices has to “look like” a DCE

A null modem does this job. It converts a DTE port to a DCE port and vice versa.

Thus we can connect two DTES using Null Modulates and demodulates.

Difference between Modem and Router

Modem Vs. Router

Aspect	Modem	Router
Full Form	Modulator-Demodulator	NA (Router is an abbreviation)
Function	Modulates and demodulates data for internet transmission over analog lines (e.g., DSL or cable).	Routes data between devices within a network and manages data traffic.
Primary Purpose	Connects your home network to the internet service provider (ISP).	Manages traffic between devices on your local network and directs data to the appropriate device.
Hardware Type	Hardware device	Hardware device
Internet Connectivity	Provides access to the internet from the ISP to your home network.	Does not provide internet access on its own but manages network traffic.
Public vs. Private IP	Connect your home network to the internet service provider (ISP).	Typically, the router assigns private IP addresses to devices within the local network.
Network Segmentation	Does not provide network segmentation but connects to a single device or a router.	Provides network segmentation, allowing multiple devices to connect to a single internet connection.
Security Features	Basic security features, such as a firewall, to protect the connection to the internet.	Offers advanced security features, including firewall, access control, and VPN support, to protect devices within the network.
Wi-Fi Connectivity	Some Modulators and demodulators have built-in Wi-Fi, but this feature is more commonly found in routers.	Routers often have built-in Wi-Fi, providing wireless connectivity to devices in the local network.
Standalone or Combo	Can be a standalone device or part of a combo unit (modem-router combination).	Standalone device or part of a combo unit (router-modem combination).
Examples	Cable modem, DSL Modulates and demodulates, fiber optic modem.	Wireless router, wired router, dual-band router.

Modem Vs. Router

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