In computer networks, multiplexing is used to refer to a process where multiple channels are combined together to form a single bandwidth, and is transferred across the communication media. As we have cable in t.v. which gives plenty of channels in a single wire. This technique helps in making the transmission more inexpensive by transmitting the expensive signals. The device which perform this task is known as Multiplexer ( MUX ). So, it reveals that the multiplexing is a process of combining many channels in to one single bandwidth.
Now, this was the case of combining many signals into on bandwidth with different frequency. But, in end we have to retrieve the sent signal, that purpose is solved by De multiplexer ( DEMUX ). De multiplexer is present at the end (target/ destination) so that the transferred signals will be seen by the user. As it is necessary to convert the signal( because the signal is in bandwidth form and De multiplexer changes the bandwidth to different signals. So, in contrast with Multiplexing, De-multiplexing is a process of giving the plenty of channels (after Multiplexing) from a single bandwidth.
Therefore, it can be said that, Multiplexing is a process of taking multiple channels and resulting a single bandwidth, whereas De-multiplexing is a process of taking single input and giving multiple outputs.
TYPES OF MULTIPLEXING:-
FDM :- It stands for frequency division multiplexing. It is also called as Optical Communication that means, it uses light as the medium for the transmission of the data. It consists of a transmitter (which codes a message so that it can be transferred easily), the coded data is now known as signal, and a channel (which transfers the signal to the destination) and at the end we have receiver (which grabs the data which has been sent by the sender (transmitter).
WDM :- It stands for Wavelength Division Multiplexing. This is a form of Frequency Division Multiplexing. (FDM) but is commonly called wavelength division multiplexing. Here, multiple optical signals on a single optical fiber ( which is used to send the data in the form of light, and this is the superb technique for transferring the data because the optical fiber is thin as a human hair) by using different wavelengths of light to carry different signals. This allows for a multiplication in capacity, in addition to enables bi-directional communications over one strand of optical fiber.
TDM :- It stands for Time Division Multiplexing. Time-Division Multiplexing ( TDM ) is a type of multiplexing in which two or more signals or bit streams are transferred apparently simultaneously as sub-channels in one communication channel, but are physically they are not clubbed into one. The time domain is divided into several recurrent time slots of fixed length, one for every sub-channel. Taking an example that w have block of data in sub-channel A, which is transmitted during time slot A, sub-channel B during time slot B. One TDM frame( packet having a small part of the data) consists of one time slot per sub-channel. After the last sub-channel has delivered the data, this cycle starts again and again with a new frame.
CDM :- It stands for Code Division Multiplexing. Code division multiple access (CDMA) is a channel accessing method utilized by various radio communication technologies. CDM follows CDMA technique to access the particular data. One of the basic concepts in data communication is the idea of allowing several transmitters to send information simultaneously over a single communication channel. This allows several users to share a single bandwidth of frequencies. This concept is called multiplexing. CDMA follows spread spectrum technology and special codes to allow multiple users to be multiplexed over the same physical channel.