Commutation (telemetry)

In telemetry, commutation is a process whereby multiple data streams ("measurands"), possibly with differing data rates, are combined into a single frame-based stream for transmission, before being separated again (decommutated) upon reception; it is a form of time-division multiplexing.

[1] Commutation is named by analogy with electric commutators, which engage multiple electrical contacts in sequence as they rotate; similarly, telemetry commutation involves sampling a sequence of data sources in turn, before returning to the first data source.

Measurands may be sampled multiple times within each minor frame (supercommutation), or they may only be sampled once in several frames (subcommutation), depending on the required data rate for each measurand.

[1] Commutated frames may also contain asynchronous data, which require further processing to extract.

Translators exist to allow support for equipment-specific database formats.

A sequence of minor frames (rows) including a subcommutated measurand ( word WD2, in blue, sampled at half the frame rate and transmitted in alternating minor frames) and a supercommutated measurand (word WD4, in orange, sampled at twice the frame rate and thus included twice in each minor frame)