This object describes last cause of disconnection.
In hh3cQ931IsdnCallClear trap, the value of this node is
the reason of disconnection, this node is only valid
for hh3cQ931IsdnCallClear trap, the value of this node
is unknown in other situation.
unknown: unknown error.
normCallClr: normal call clearing.
noRouteToTransNet: no route to specified transit network.
noRouteToDest: no route to destination.
switchEquCongest: switching equipment congestion.
netOutofOrder: network out of order.