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Statistical time-division multiplexing (STDM) is a form of communication link sharing, which is almost identical to dynamic bandwidth allocation (DBA).
In STDM, a communication channel is split into a random range of variable bit-rate data streams or digital channels. The link sharing is tailored for the instantaneous traffic requirements of the data streams which are transmitted over every channel.
This type of multiplexing is a replacement for creating a fixed link sharing, such as in standard time division multiplexing (TDM) and frequency division multiplexing (FDM). Upon precise execution, STDM can offer an improvement in link utilization, referred to as the statistical multiplexing gain. STDM is facilitated by means of packet-mode or packet-oriented communication.
Techopedia Explains Statistical Time Division Multiplexing
STDM is more efficient than standard TDM. In standard TDM, time slots are allotted to channels even when there is no data to transmit. This leads to wasted bandwidth. STDM was originally developed to address this inefficiency, where the time allocation to lines happens only when it is actually required. This is attained through intelligent devices that are ideal for identifying an idle terminal.
STDM is same as TDM, with the exception that every signal is assigned a slot based on priority and demand. This indicates that STDM is an "on-demand" service as opposed to a fixed one. Standard TDM and various other circuit switchings are executed at the physical layer in the OSI and TCP/IP model, while STDM is executed at the data link layer and above.
Scenarios of statistical time-division multiplexing are:
- The MPEG transport stream used for digital TV transmission. STDM is used to permit multiple data, audio and video streams of different data rates to be broadcasted across a bandwidth-limited channel.
- The TCP and UDP protocols, in which data streams from various application processes are multiplexed together.
- The Frame relay packet-switching and X.25 protocols, in which the packets have different lengths.
- The Asynchronous Transfer Mode packet-switched protocol, in which the packets maintain a fixed length.
