Time Division Multiplexing combines multiple signals into one channel by dividing time into slots. Each signal gets a recurring slot. They take turns. The channel carries one signal at a time, but so fast it seems simultaneous. TDM is used in telephone networks and digital transmission.

TDM is the digital counterpart of FDM. FDM divides frequency. TDM divides time. Both share a channel. TDM is used in T1 and E1 lines. It is used in SONET and SDH fiber networks. It is used in GSM. It is a foundational technique of digital communication.

TDM characteristics

• Time slots: recurring turns
• Synchronization: precise timing
• Fixed capacity: each signal gets a slot
• Efficient: no wasted frequency
• Used in: T1, E1, SONET, GSM

TDM is being replaced by packet switching. Packets are more flexible. They use bandwidth only when needed. TDM reserves a slot even when silent. But TDM is reliable and low-latency. It is still used in some networks. The old technique has not disappeared.