Indicates the number of minutes within the window in which
the availability of the line (network) is to be calculated. The
availability of the line is an indication of the percentage
of time the line has been in service.
It is calculated as follows:
(((wfDsuCsuCqmsLaWindow*60) - (wfDsuCsuCqmsLaErrCnt*wfDsuCsuCqmsLaPollRate))/
wfDsuCsuCqmsLaWindow*60)