A sub-subframe consists of a group of measurands that occurs at a slower data rate than measurands in a subframe. Using supercommutation and subcommutation, you can easily achieve a 1,000 to one difference in sampling rates. Sub-subframes can easily add another depth of 10, for a 10,000 to 1 sampling ratio. To maintain the major frame data rate, each time the major frame word reserved for the sub-subframe is encountered, the next major frame word's worth of the sub-subframe data bits are entered into the PCM data stream.

The sub-subframe counter provides the only sync required for the sub-subframe. It counts the number of words in the sub-subframe. A sub-subframe counter must be defined as a major frame measurand and be inserted into the major frame for each sub-subframe defined.

The following figure is a mechanical wheel analogy illustrating the relationship between major, super, and minor frame and subframe multiplexing.

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