This attribute counts the total number of times the Public Switched
Telephone Network (PSTN) modem enters a busy state (the IWF
has received a Receive Not Ready message) and asks the IWF V.42
not to send Information (I) frames to it until it is ready to receive
information frames again (indicated by receipt of a Receive Ready
message or a data message). The counter wraps when it exceeds the
maximum value.