A count of Protection Switch Byte Failure conditions.
This condition occurs when either an inconsistent APS
byte or an invalid code is detected. An inconsistent
APS byte occurs when no three consecutive K1 bytes of
the last 12 successive frames are identical, starting
with the last frame containing a previously consistent
byte. An invalid code occurs when the incoming K1 byte
contains an unused code or a code irrelevant for the
specific switching operation (e.g., Reverse Request
while no switching request is outstanding) in three
consecutive frames. An invalid code also occurs when
the incoming K1 byte contains an invalid channel number
in three consecutive frames.