This attribute indicates the current mode of the V.42bis decoder.
This mode can be either:
transparent: A mode of operation in which compression has been
selected but data is being transmitted in uncompressed form.
Transparent mode command sequences may be inserted into the
data stream.
compressed: A mode of operation in which data is transmitted in
codewords.
The encoder (at the mobile or PSTN) switches between the two
modes depending on whether the data coming from the Date
Terminal Equipment (DTE) is suitable for compression. The data
compression function periodically determines the compressibility of
the data based on a comparison of the number of bits required to
represent a segment of the data stream before and after
compression.