This attribute specifies the time duration in seconds for which
signalOne is substituted into the appropriate signaling bits, when a
lineType that uses CAS has been defined. When signalOneDuration
has expired signalTwo is substituted into the appropriate signaling
bits.
If signalOneDuration is set to zero then only signalTwo is
substituted into the appropriate signaling bits during error
conditions.
signalOneDuration can be set to any integer value from 0 to 60
seconds.