Value of sysUpTime when the physical layer for the call
achieved a steady state and the call is ready for higher
protocol layers to begin.
In the case of modem calls, the physical layer for the
call achieves a steady state when the data rates,
modulations, and error correcting protocols have been
negotiated between the originating and answering modems.
This is primarily intended for calls which connect to a
processing resource identified by cctHistoryResourceSlot
and cctHistoryResourcePort.
It also applies to digital calls using adaptive rate
technologies such as V.110 and V.120.