Two forms of call parking are provided: directed call park and nondirected call park. In directed call park, the application specifies the destination address where the call is to be parked. This roughly behaves like a call transfer to the destination address, but it doesn't alert or time out as a transfer would.
In nondirected call park, the switch returns to tapi32.dll the address where it parked the call. In either case, the TSPI_linePark function is used to park a given call at another address.A parked call can later be retrieved. The tapi32.dll specifies the park address to TSPI_lineUnpark, which returns a call handle to the unparked call (it retrieves a parked call). Appropriate LINE_CALLSTATE messages are sent to tapi32.dll as the call is reconnected.