This attribute indicates the most recent clear cause for the transport
connection.
This indicates the causes provided by the network.
A value of zero indicates that the transport connection has never
been cleared.
A value of 1000 indicates that the network has not provided a clear
cause for the transport connection clearing.
Section 5.4.5.15 of the ATMF UNI 3.1 specification lists the clear
causes provided by the network.