The value of sysUpTime when the call setup was started.
This will be useful for an NMS to sort the call history
entry with call setup time. Also, this object
can be useful in finding large delays between the time the
call was started and the time the call was connected.
For ISDN media, this will be the time when the setup
message was received from or sent to the network.
The value of this object is the same as callActiveSetupTime
in the callActiveTable