Modems are used to transport data from a single machine network to another via telephone lines. The computer network operates in digital mode, whereas analog technology is utilized to send messages over phone lines.

At the sending end, a modulator changes information from digital to analog mode, and at the receiving end, a demodulator turns it from analog to digital. Digitizing is the act of transforming analog signals from a single computer network to digital signals from another network of computers so that they may be handled by a receiving computer.

Modems are used at both ends of an analog facility for data transfer between two digital devices known as Data Terminal Equipment (DTE). DTE might be a computer or a terminal.

At the receiving end, the modem modulates a carrier to transform the digital signal created by DTE into a signal that is analog. At the receiving end, this modem breaks down the carrier and sends the demodulate digital data to the DTE.

A dedicated circuit or a switched telephone line can be used to connect the two modems. If a switched phone circuit is utilized, the modems are linked to the local exchanges. When data transfer is necessary, a telephone connection is established between the modems.

What is the purpose of a modem?

Modems are devices that allow you to connect your house to the provider of your Internet service. They usually plug into an outlet, although they can also be in the shape of dongles. They enable Internet connectivity for your computer, iPad, or other devices. Routers aid in the distribution of Internet connections across devices on the household network. However, getting to the Internet is impossible without a modem.

Working of Modem

Modulation and demodulation are the two primary components of a modem. Where the modem can execute two functions at the same time. The modem's operation is described in detail below:

Data Generation: Data is created before it is transferred. As a result, the computer system created data in the form of 0s and 1s.
Modulation: Modulation involves the process of transforming digital data impulses from a machine into analog data signals that may travel over the internet. A carrier wave is used to encode digital data.
Transmission: The modulated data that is the product of the modulation is transferred via the line of communication to the receiver that is receiving it.
Demonstration: Demodulation is described as the process of converting analog messages from the internet into digital information signals that computer systems can understand. The electrical information that comes from the signalling element of the wave is decoded during the demodulation process.
Decoding: The output of demodulation, demodulated data, is delivered to computer systems for further processing.

Prepared to Send

To begin, the Data Interface Equipment or DTE (a computer) transmits a Preparing To send or RTS message to the Data Transmission Equipment or DCE (a modem). This is referred to as a wakeup call, and it causes the modem to send a Data Carrier Detect or DCD message to the receiving modem. A series of signals are then exchanged among the two until a communication channel is created. This is known as handshaking, and it explains why, even today, certain organizations, like as CompuServe, use the sign of two hands gripping each other to indicate that they are online. After then, all the second modem has to do is send a Data Terminal Set Ready or DSR message to its CPU and wait for a Data Termination Ready or DTR response. When this occurs, the first modem transmits a Clean to Send or CTS message to the machine that initiated the entire process, allowing data to be transferred. That's all there is to it.

Alternatively, if you're perplexed by what the Internet business refers to as TLAs (Three Letter Acronyms), the graphic below should assist.

It just appears to be perplexing. Take a second look, and everything will become clear.

To be thorough, the signals in question are all delivered through distinct pins in the plug, that's why the manuals for all modem and printers include a pin diagrams somewhere in the troubleshooting section. They are also standardised as a result of a meeting of industry experts to agree on standards for a wide variety of peripheral devices.

The Suggested Standard of cable was 232, which explains one technical phrase that almost everyone has heard of: RS 232.

Of course, there still leaves the matter of how data gets moved from a single machine to another, which is more difficult than it appears, owing to the fact that phone connections are analog while PCs are digital. To put it simply, a cell phone signal is always changing. Consider a sine wave produced by an oscilloscope to understand this. The signal may be continuous, but it alternates between positive and negative states in a sequence of smooth curves. Because computers can only grasp information provided as an array of binary digits, the goal is to transfer the digital result onto an analog signal.

Without delving into technical specifics, this is accomplished by superimposing multiple frequencies over the analog signal (which is then referred to as a carrier wave). distinct frequencies can then be used to represent distinct groups of binary digits, a process known as modulation when sent and demodulation when decoded at the point of reception. Naturally, two-way communication is accomplished by using a single device capable of both demodulating as well as modulating, which gives rise to the unit's name: the modem.

It follows that the higher the number of frequencies which can be overlaid on the carrier wave, the faster data may be conveyed. To put it another way, the more data that has to be transferred, the fewer frequencies are required.

Unfortunately, it is only able to convey just a handful of frequency at one time, which means transmission takes significantly longer as the quantity of the signals grows. With the regular transmission of images, music, and even videos via the Internet, and all of these requiring enormous data files, the quantity of accessible bandwidth is going to be a concern for some time.

Finally, because the entire operation boils down to delivering bits, or binary digits, across a phone line, the system's speed is represented in Bit Per Second or BPS, a rate stated by all modem manufacturers.

Unfortunately, there's a lot more to data connections than how quickly bits can be transferred down a telephone line. There's also the question about what those bits imply and how they'll be combined into something understandable at the other end. A wide range of concerns must be handled here, so let's take a quick look at just one of them, which are the communication methods.

Types of Modems

Modems are classified into several categories. Each modem has unique characteristics and offers distinct advantages.

The following are the different types of modems:

Optical Modem

Different types of media are utilized in modem to convey signals. The term "Optical Modem" refers to a modem that uses optical cables rather than other types of metallic media. The digital information is transformed into a light pulse that is transferred over optical fiber in the optic Modem.

Digital Modem

A digital modem is a type of modem that converts digital data into digital signals. Digital data is represented by 0s and 1s. It does this through the modulation process. For transmission, digital modem modifies digital data on digital carrier signals.

Cable Modem

Cable modems are a form of modem that is used to communicate between computers and Internet Service Providers. A cable modem enables high-speed data access over cable TV networks. These modems are often attached to desktops or computers and function as external devices.

Modem Satellite

Satellite modems are a kind of modem that delivers an internet connection via satellite dishes. This modem operates by converting incoming bytes into output radio waves and vice versa. When contrasted with other types of modems, such modems give a more dependable and efficient internet network.

Dialing Modem

A dialing modem is a modem that transfers data from a telephone to data from a computer. In a nutshell, a dial modem transforms analog to digital signals. All of the networking equipment linked to the machine are at one end, while the connection to the phone system is at the other. This modem transfers data at a rate of 56000 bits per second.

Full-duplex and half-duplex modems

Half duplex

A half duplex modem allows just one direction of transmission at a time.
If the modem detects a carrier on the line, it sends an indicator of the coming carrier through the DTE via a control signal on its digital interface.
The modem fails to allow the DTE to transfer data as long as the camel' IS being received.

Full duplex

A full duplex modem may transmit data in both directions at the same time.
As a result, the line has two carriers, one outgoing and one incoming. Modems with two and four wires
The modem's line interface can connect to the transmission medium via a 2-wire or 4-wire connection. Modem with four wires
A 4-wire connection uses one pair of wires to connect the out carrier and another pair for the incoming carrier.
A four-wire connection supports both full duplex & half duplex data transfer modes.
Because the actual transmission line for each direction is distinct, the same frequency for carriers may be utilized for both.

Modem with two wires

Outgoing and incoming carriers are carried on the same pair of wires in 2-wire modems.
Because just one pair of wires is stretched to the subscriber's home, a leased 2-wire connection is often less expensive than a 4-wire connection.
The data link formed via phone exchange is likewise a two-wire connection.
Half duplex transmission using the same frequency for both the incoming and outgoing carrier is simply done in 2-wire modems.
Full duplex functioning necessitates the use of two broadcast channels, one for transmitting and the other for receiving.
This is accomplished by multiplexing the frequency division of two distinct carrier frequencies. These carriers are put within the speech channel's bandwidth.

Modem Asynchronous

Data bytes having start and stop bits can be handled by asynchronous modems.
From the modem and the DTE, there is no independent timing signal or clock.
The internal timed pulses are repeatedly synced to the forefront of the start pulse.

Modem Synchronous

A clock signal is required for synchronous modems to manage a constant stream of data bits.
The data bits are constantly in sync with the clock signal.
There are different clocks for transmitting and receiving data bits.
The DTE may utilize its own internal clock and provide it to the modem for synchronous data bit transfer.

Modulation methods employed in Modem

Amplitude shift keying (ASK) is one of the primary modulation methods used by modems to transfer electronic data to analog signals.

FSK stands for frequency shift keying.
PSK stands for phase shift keying.
Differential PSK (DPSK) is a kind of PSK.

These methods are referred to as binary continuous waves (CW) modulation.

Modems are constantly utilized in groups of two. A modem is required at both the sending and receiving ends of any system, whether simplex, half duplex, or full duplex.
As a result, a modem serves as an electrical link between two worlds: the world of pure digital transmissions and the current analog world.

Modem Features

They have fast upload and connection speeds. An X2 modem has an upload bandwidth ranging from 28.1 to 56 Kbps.
They may be upgraded to meet practically any global standard with a software patch.
They allow high-speed downstream transmission of data by digitally encrypting all down data while maintaining upstream speeds of 33.6 kbps.
Some modems provide dual simultaneous voice and data (DSVD), which means they can transport both analog sounds and computer data.
They can detect the caller's originating phone number and so function as caller ID.
Some modems have extensive voice mail functionality and can function as intelligent telephones or electronic information systems.

Modem Advantages

A modem is a device that translates digital signals into analog signals.
The price of a modem rises in direct proportion to its features.
The modem facilitates the connection of the Ethernet to the internet.
A modem does both modulation and demodulation at the same time.

Modem Disadvantages

When linked to the hub, the modem's operation slows.
The modem is unable to monitor traffic between the Network and the internet.
A modem can only connect a limited number more network devices to the internet.
Modems are vulnerable to security-related attacks.
The modem does not carry out traffic maintenance.

Computer Network Tutorial

Model

Physical Layer

Data Link Layer

Network Layer

Transport Layer

Application Layer

Misc