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Using the overlap_rcv feature of L4L3mENABLE_PROTOCOL
November 2009 330
How Overlap Receive Mode Changes
Call Control Events Presentation
Volume 5, Bfv API Reference Manual describes the normal call
control events associated with ISDN Call Processing and
Management. These events occur when incoming SETUP messages
contain all the appropriate CALLED_PARTY information elements
and SENDING_COMPLETE information elements.
When the overlap_rcv flag is enabled and the SETUP message arrives
with incomplete CALLED_PARTY information, the call control
events change as follows:
1. Network presents SETUP message to the module, with either
incomplete CALLED_PARTY information element present, or no
SENDING_COMPLETE info element present.
2. Instant ISDN activates the T302 timer, sends a SETUP_
ACKNOWLEDGE message to the Network, and enters the
Overlap Receive state. Instant ISDN also presents the initial call
information to the Host in an L3L4mSETUP_IND message.
Note: The T302 timer is under Host control (see IISDN_Q931_
TIMERS in the IISDN.H header file) with a default timer
value of 15 seconds.
3. The Network sends the remainder of the call information (if any)
in one or more INFORMATION messages. Each information
message arrives as an L3L4mINFO event to the Host application,
which contains CALLED_PARTY information elements, as well
as an indicator for SENDING_COMPLETE information
elements. Each time an INFORMATION message is received
without a SENDING_COMPLETE info element present in the
message, Instant ISDN restarts the T302 timer.
4. Presence of the SENDING_COMPLETE information element is
optional. Some ISDN switches and dialing plans will present all
of the CALLED_PARTY information and never send a
SENDING_COMPLETE info element in the final
INFORMATION or SETUP message.
5. When the final INFORMATION message has been received
(indicated by presence of the SENDING_COMPLETE
information element, or when the host has determined that the
CALLED_PARTY information is sufficient to complete the call),
the Host application issues an L4L3mCALL_PROCEEDING and
the call control events will then transpire normally.