In order to transmit a large number of signals from one location to other, multiplexing is used.
Communication channels are costly so it is not economical to use separate channel per signal. Signals can be transmitted over a single communication channel by either dividing the time slots between various signals and transmitting it in turns time sharing or by assigning different bandwidth to each signal and transmitting at once frequency sharing.
In time division multiplexing TDM , a number of channels are interleaved in time into a single digital system. Each channel input is periodically sampled and assigned a certain time slot. At the transmitting end, input channels are sequentially sampled by a switch resulting in a train of amplitude samples.
The coder then sequentially converts each sample into a binary code using analogue to digital conversion techniques.
The Coder output is the string of binary digits representing channel 1, channel 2, and so on. The smallest group of bits containing at least one channel from each signal plus framing bit is known as a frame.
The framing bits forms a repetitive pattern i. DEMUX then successfully recognise the contents of framing pattern to distribute incoming bits to the proper channel. A buffer storage is necessary for word interleaving to accumulate a group of bits from each channel while waiting for transfer to the MUX.
This type of interleaving is used for word oriented data. If a fixed relationship exists between the Channel rates, the frame length is determined by a lowest common multiple of incoming channel width.
It Periodically generates the frame consisting of a constant number of time slots, each time slot of constant length. A starting delimiter flag is used for frame synchronisation which is needed to differentiate One Frame from next frame. Because of a flag, individual time slots can be identified by position within a frame.
When data from different channels is not available at fixed predetermined rates rather it is available at the rates which are statistically determined, then their multiplexing is known as asynchronous time division multiplexing or statistical time division multiplexing.
In this, data may send from a channel at any time and for different duration.
In this type of multiplexing, time slots are not fixed i. In asynchronous TDM, slots are not predefined, the slots are allocated to any of the channels that have data to send.
Why is sync pulse required in TDM? In order to identify the beginning of each frame, a sync pulse is added at the beginning of every frame. Share via:. It will be really helpful if u will also explain the reason behind the advantages and disadvantages.
Types of Multiplexing
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Synchronous Time Division Multiplexing 3 2. Asynchronous Time Division Multiplexing.
Types of Multiplexing Techniques: FDM WDM and TDM (Computer Science)
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