In case of TDM, time slots are allocated to channels, even if they have no information to transmit. This is just wastage of the bandwidth and to overcome this inefficiency of standard TDM, a technique known as STDM has been developed where time is allocated to lines only when it is required. This is achieved with the use of intelligent devices that are capable of identifying when a terminal is idle.
Because of the intelligent device statistically compensates for normal idle time, more lines can be connected to a transmission medium.
During the peak traffic period a buffer memory temporarily stores the data, so high-speed line time can be effectively utilized with active channels. It adopts a methodology where each transmission has an identification information (a channel identifier). This increases the overheads, which are handled by grouping a number of characters for each channel together for transmission. It is also referred as “Intelligent” TDM. In this case, data rate capacity is well below the sum of connected capacity of each channel because it utilizes the idle time very effectively. It is digital only and requires more complex framing of data.
It is widely used for remote communications with multiple terminals. The additional services such as data compression, line priority, mixed speed lines, host ports sharing; network port control, automatic speed detection etc are available with STDM techniques.