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.