Multiplexing is a method of combining and transmitting numerous data streams over a single medium. Multiplexing is the process of combining data streams, and the hardware used for multiplexing is known as a multiplexer.

Multiplexing is accomplished through the use of a device known as a Multiplexer (MUX), which combines n input lines into a single output line. Many-to-one multiplexing is used, which means there are n input lines and one output line.

At the receiving end, a device called a Demultiplexer (DEMUX) is used to demultiplex the signal. DEMUX is a signal demultiplexer that splits a signal into its constituent signals (one input and n outputs). As a result, we can argue that demultiplexing is a one-to-many process.

Why Multiplexing?

• The signal is sent from the transmitter to the receiver via the transmission medium.
  There can only be one signal on the medium at a time.
• If several signals must share a single medium, the medium must be partitioned so that each signal receives a fraction of the available bandwidth.
  For example, if there are ten signals and the medium’s bandwidth is 100 units, each signal will share the 10 units.
• There is a risk of collision when numerous signals share the same medium.
  To avoid such a clash, the multiplexing notion is employed.
• Transmission services are extremely costly.

History of Multiplexing

Multiplexing is a telecommunications method that allows many phone conversations to be carried over a single line. In the early 1870s, telegraphy pioneered multiplexing, which is today widely utilized in communication. In 1910, George Owen Squier invented the telephone carrier multiplexing. telephone carrier multiplexing in 1910.

Concept of Multiplexing

A multiplexer transmits the ‘n’ input lines, and the multiplexer mixes the signals to generate a composite signal. A Demultiplexer divides a signal into component signals and transmits them to their proper destinations after passing the composite signal through it.

Advantages of Multiplexing:

• Over a single media, several signals can be delivered.
• A medium’s bandwidth can be appropriately utilized.

Multiplexing Techniques

The following are the several types of multiplexing techniques:

Frequency-division Multiplexing (FDM)

It’s a technique that uses analog technology. Division of Frequency Multiplexing is a technique for dividing a single transmission medium’s available bandwidth into many channels. A single transmission medium is divided into numerous frequency channels in the picture above, and each frequency channel is assigned to a distinct device. The frequency channel on Device 1 ranges from 1 to 5. Using modulation techniques, the input signals are converted into frequency bands, which are then mixed by a multiplexer to generate a composite signal. The FDM’s main goal is to divide the available bandwidth into distinct frequency channels and assign them to various devices. The input signals are divided into frequency bands and then merged to generate a composite signal using the modulation process. Sub-carriers are the carriers that are utilized for modulating the signals.
They are denoted by the letters f1,f2,..fn.

FDM is mostly utilized in radio and television transmissions.

Advantages Of FDM:

• For analog signals, FDM is employed.
• The FDM modulation procedure is relatively simple and straightforward.
• An FDM may send a large number of signals at the same time.
• It does not require any sender-to-receiver synchronization.

Disadvantages Of FDM:

• When low-speed channels are required, the FDM approach is utilised.
• It has a problem with crosstalk.
• It is required to use a large number of modulators.
• It requires a channel with a high bandwidth.

Applications Of FDM:

FDM is widely used in television networks. It is used in radio broadcasts on both FM and AM frequencies.
Different frequencies are used by each FM radio station, and they are multiplexed to generate a composite broadcast.
The multiplexed signal is broadcast over the airwaves.

Wavelength Division Multiplexing (WDM)

Wavelength Division Multiplexing (WDM) is similar to FDM, except that the optical signals are sent over a fibre optic connection. WDM is a technique for increasing the capacity of single fibre in fibre optics. It is utilised to take advantage of fibre optic cable’s high data rate capacity. It’s a technique for analogue multiplexing. With the help of a multiplexer, optical signals from many sources are merged to generate a larger range of light. The demultiplexer separates the signals at the receiving end so that they can be sent to their proper destinations. A prism can be used to multiplex and demultiplex signals. Prism can function as a multiplexer by combining numerous optical signals to generate a composite signal, which is then delivered across a fibre optic line. Prism also demultiplexes the signal, which is a reverse action.

Time Division Multiplexing

It’s a digital technique. All signals operate at the same time with different frequencies in Frequency Division Multiplexing, but all signals operate at the same frequency with different times in Time Division Multiplexing. The total time available in the channel is allocated among multiple users using the Time Division Multiplexing technology. As a result, each user is assigned a different time interval, known as a Time slot, during which the sender must deliver data. For a set period of time, a user takes control of the channel. Data is not delivered simultaneously with the Time Division Multiplexing technology, but rather one by one. The signal in TDM is sent in the form of frames. Frames comprise a cycle of time slots, with one or more slots devoted to each user in each frame. It may multiplex digital and analogue signals, however it is most commonly used to multiplex digital signals.

There are two types of TDM:

1. Synchronous TDM
2. Asynchronous TDM

Synchronous TDM

Synchronous TDM is a technique in which each device is allotted a time slot in advance. Regardless of whether the device carries data or not, each device in Synchronous TDM is assigned a time slot. The slot will remain empty if the device does not have any data. Signals are sent in the form of frames in Synchronous TDM. Frames are used to organise the time windows.
If a device does not have data for a specific time slot, it will send the empty slot. T-1 multiplexing, ISDN multiplexing, and SONET multiplexing are the most common Synchronous TDMs. There are n slots if there are n devices.

Concept Of Synchronous TDM

A time slot is assigned to each device. Regardless of whether or not the sender has data to deliver, the time slots are transmitted.

Disadvantages Of Synchronous TDM:

Because empty slots with no data are also transmitted, the channel’s capacity is not fully utilised. Although the first frame of the artwork is completely filled, some places in the second and third frames remain blank. As a result, we can deduce that the capacity of the channel is underutilised.

The transmission medium’s speed should be higher than the input lines’ total speed. Asynchronous Time Division Multiplexing is an alternative to Synchronous Time Division Multiplexing.

Asynchronous TDM

Statistical TDM is another name for an asynchronous TDM. Asynchronous TDM is a technology that differs from synchronous TDM in that time slots are not fixed. Only those devices with data to send have time periods assigned to them. As a result, the Asynchronous Time Division Multiplexor only sends data from active workstations. The time slots are dynamically allocated to the devices using an asynchronous TDM approach.In asynchronous TDM, the overall speed of the input lines can exceed the channel’s capacity. The incoming data streams are accepted by the asynchronous Time Division multiplexor, which constructs a frame with just data and no empty slots. Each slot in asynchronous TDM has an address portion that specifies the data source.

Asynchronous TDM differs from Synchronous TDM in that many slots in Synchronous TDM are underutilised, whereas slots in Asynchronous TDM are completely utilised. This results in a shorter transmission time and more efficient channel capacity usage. If there are n sending devices in Synchronous TDM, there are n time slots. If there are n sending devices in asynchronous TDM, there are m time slots where m is less than n (mn). The statistical analysis of the number of input lines determines the number of slots in a frame.

Concept Of Asynchronous TDM

Although there are four devices in the figure above, only two of them, A and C, are sending data. As a result, just the transmission line is used to transport the data of A and C.