A communications process that has been transmitting two or more than two digital signals over a single and common channel is known as Time division multiplexing or TDM. In this process the incoming signals are generally divided into the equal and fixed time slots. Once the multiplexing is done there are signals which are transmitted via a common shared medium which gets reassembled to their original version after de-multiplexing.
Time division multiplexing is also known by the name of digital circuit switched. It was developed long back in the 1870s due to the introduction of large scale telegram networks. Network of packet switching is used for telecommunication links which are the packets that are divided into stable and fixed lengths and also assigned to fixed time slots as well. Each of these signal packet is divided and transmitted to their allocated time slot and then reassembled for a complete signal at the required destination.
Time division multiplexing can be seperate into two different categories of systems – one is the TDM and the other is synchronous time division multiplexing (sync TDM). TDM is popularly used for the communications over long distances and Sync TDM is generally used for the requirement of higher speed of transmission.
How does Time division multiplexing works?
During each of the time slot of the TDM frame, there is a sample of the signal that helps for the given sub-channel. The frame for the Time division multiplexing is also consisted of the synchronisation channel and along with the error correction channel as well.
Once the first sample of the sub-channel is taken the process gets repeated for a second sample and then repeated once again for the third time. The frames keep getting looped one after the other. As the time slot expires it gets carry forwarded to the next sub-channel.
Best example of using the TDM includes the use of digitally transmitting several conversations over telephone on the same four wire cable made od copper or also the modern fiber optical cable in a time division multiplexing telephone.
These systems are of pulse code modulation or PCM or also from the plesiochronous digital hierarchy (PDH) systems. Moreover the synchronous Digital Hierarchy (SDH) and the synchronous optical network transmission (SONET) standards have also used TDM.
Within the time division multiple access, Time division multiplexing can be effectively used and this is where stations sharing the identical frequency channel is able to communicate with each other.