by Dinesh Thakur Category: Multiple Access

Multiplexing or (muxing) - To combine multiple signals (analog or digital) for transmission over a single line or media. A common type of multiplexing combines several low-speed signals for transmission over a single high-speed connection. In other words, we can say that Muxing is used for sharing of a medium and its link by two or more devices. It can provide both Efficiency and Privacy.

Multiplexing is done by using a device called multiplexer (MUX) that combines n input lines to generate one output line i.e. (many to one). Therefore multiplexer (MUX) has several inputs and one output.
At the receiving end, a device called demultiplexer (DEMUX) or (demuxing) is used that separates signal into its component signals. So DEMUX has one input and several outputs.

Concept of Multiplexing

As shown in fig multiplexer takes 4 input lines and diverts them to single output line. The signal from 4 different devices is combined and carried by this single line. At the receiving side, a demultiplexer takes this signal from a single line & breaks it into the original signals and passes them to the 4 different receivers.

                                 Multiplexing

Advantages of Multiplexing

If no multiplexing is used between the users at two different sites that are distance apart, then separate communication lines would be required as shown in fig.

This is not only costly but also become difficult to manage. If multiplexing is used then, only one line is required. This leads to the reduction in the line cost and also it would be easier to keep track of one line than several lines. Multiplexing efficient for utilization of bandwidth.

                                No Multiplexing Used

 

The following are several examples of different multiplexing methods:

Frequency Division Multiplexing (FDM) - Short for frequency division multiplexing, It is used in analog signal, a multiplexing technique that uses different frequencies to combine multiple streams of data for transmission over a communications medium. FDM assigns a different carrier frequency to each data stream and then combines many modulated carrier frequencies for transmission. For example, television transmitters use FDM to broadcast several channels at once. Band pass filter is used for separating channels and allows to pass a specific range of frequencies, During transmission of streams it blocks lower and higher frequencies. In Frequency Division Multiplexing, channels are separated by unused strips of guard bands to prevent Overlapping. Guard bands increase the bandwidth for FDM.

Time Division Multiplexing (TDM) - Short for Time Division Multiplexing, a type of multiplexing that combines data streams by assigning each stream a different time slot in a set. TDM is designed for digital signals, which combining several low-rate channels into high-rate one. TDM repeatedly transmits a fixed sequence of time slots over a single transmission channel. Within T-Carrier systems, such as T-1 and T-3, TDM combines Pulse Code Modulated (PCM) streams created for each conversation or data stream. TDM, slots are further divided into Frames. In order to separate channels AND gates are used in a TDM receiver.

Wavelength Division Multiplexing (WDM)  - Short for wavelength division multiplexing, It is used in analog signal, a type of multiplexing developed for use on optical fiber. WDM modulates each of several data streams onto a different part of the light spectrum. WDM is the optical equivalent of FDM.



About Dinesh Thakur

Dinesh ThakurDinesh Thakur holds an B.SC (Computer Science), MCSE, MCDBA, CCNA, CCNP, A+, SCJP certifications. Dinesh authors the hugely popular blog. Where he writes how-to guides around Computer fundamental , computer software, Computer programming, and web apps. For any type of query or something that you think is missing, please feel free to Contact us.