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Multiplexing; synchronous vs asynchronous TDM
Short answer
Multiplexing combines several signals into one shared link using a MUX, with demultiplexing at the receiver (e.g., telephone T1 trunks). Synchronous TDM assigns fixed time slots, wasting capacity when sources are idle, and needs no addressing. Statistical TDM dynamically allocates slots only to active inputs, adding address overhead but greatly improving efficiency for bursty traffic.
Define multiplexing with example. Compare synchronous and asynchronous (statistical) TDM.
Multiplexing
Multiplexing is the technique of combining signals from several sources into one signal that is sent over a single shared link (channel), and separating them again at the receiver. A MUX at the sender and a DEMUX at the receiver do this.
A -->| | | |--> A
B -->| MUX |=== link ===|DEMUX|--> B
C -->| | | |--> C
Example: FM radio stations share the air using FDM; the telephone trunk network carries thousands of calls on one fibre using TDM. The main benefit is that a high-capacity link is shared, so cost is reduced.
Synchronous TDM
Each input is given a fixed time slot in every frame, whether or not it has data. If a source is idle, its slot goes empty.
Asynchronous (statistical) TDM
Slots are given only to inputs that have data. Because slots are not fixed, every slot carries an address (header) identifying its source.
| Point | Synchronous TDM | Asynchronous (statistical) TDM |
|---|---|---|
| Slot allocation | Fixed, one per input per frame | Dynamic, only for active inputs |
| Empty slots | Wasted when input idle | Almost none |
| Addressing | Not needed (position gives source) | Needed (address in each slot) |
| Link capacity | Sum of input rates | Less than sum of input rates |
| Efficiency | Low for bursty traffic | High for bursty traffic |
| Overhead | Only framing bits | Address bits per slot |
| Complexity / cost | Simple | Complex, needs buffers |
| Used in | T1/E1, SONET | ATM, frame relay, packet networks |
Example: with 4 inputs where only 2 are active, synchronous TDM sends 2 empty slots per frame; statistical TDM sends a frame of 2 slots only.
✓ Answer checked by Claude Sonnet 5.5
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