Time Division Multiplexing (TDM)

TDM is a digital technique where multiple signals share one channel by occupying it in different time slots. The full bandwidth is used by one signal at a time.

Working

1. Each input gets a fixed time slot.
2. The multiplexer scans inputs in round-robin order, taking a small unit (bit/byte) from each.
3. One round of slots forms a frame; frames repeat continuously.
4. The demultiplexer, synchronized using framing bits, routes each slot to the correct output.

Types

• Synchronous TDM: slots are pre-assigned; an idle input wastes its slot.
• Statistical TDM: slots are assigned dynamically, only to active inputs; better utilization (needs addressing info).

Advantages

• Efficient use of link capacity
• No crosstalk or intermodulation distortion (unlike FDM)
• Simple, suited to digital data and voice (PCM, T1/E1)
• Easy to add or remove channels

Disadvantages

• Needs synchronization
• Wasted slots in synchronous TDM