Reference:Administration/PBX/Objects/Trunk Line

The Trunk Line object is typically used to register gateways to external lines. Several registrations are accepted. Calls sent to the trunk object are sent to the registrations in a round-robin manor. If the call to a registration fails in a way that indicates a local problem the next registration is tried.

Some general diversions can be configured for incoming calls e.g. for calls to invalid numbers.

Trunk Object specific configuration

Loopback	Destination (Name or Number) to which calls are forwarded, which dialed the same Trunk object. This is typically used if the number of the Trunk object (e.g. 0) shall be used as extension number of the switchboard for incoming calls.
Incomplete	Destination (Name or Number) to which calls are forwarded, which dialed an incomplete number. If the incoming call is enblock this can be determined immediatelly. For overlap receiving calls a timeout of 4s is used. Sometimes it is desired that calls without extension number are sent to the switchboard. In this case the number of the switchboard should be configured here.
Invalid	Destination (Name or Number) to which calls are forwarded, which dialed an invalid number. Typically the number of the switchboard is configured here so that incoming calls whith an invalid extention are not lost.
Busy	If, in incoming calls via the exchange, a call number was dialled that is busy, call forwarding can be initiated by specifying a valid H.323 name (Name) or E.164 alias (Number).
No Answer Timeout	If, in incoming calls via the exchange, a call number was dialled and there is no answer, call forwarding can be initiated, after the specified time has elapsed (Timeout), by specifying a valid H.323 name (Name) or E.164 alias (Number).
Reroute supported	This check box determines wether Partial Rerouting will be performed while executing a diversion (CFU, CFNR).
Set Calling = Diverting No	Concerns calls that arrive on the PBX via the Trunk Line PBX object and are then forwarded by CFU, CFB or CFNR (Call Forwarding Unconditional, Call Forwarding Busy or Call Forwarding No Response) again via the Trunk Line object. For example: Subscriber A calls subscriber B. Subscriber B forwards the call from subscriber A to subscriber C. The CGPN (Calling Party Number) remains unchanged for a call diversion. Merely the DGPN (Diverting Party Number) is also sent as information, so that both call numbers are visible at the diversion destination (subscriber C). For an external call diversion to the PSTN, it is not permitted to use an external CGPN (subscriber A), however. Therefore, the CGPN must be replaced by an associated call number, in this case the DGPN (subscriber B). If this check box is not enabled, the local telephone office, in such as case, will automatically replace the CGPN through "screening". If you enable this check box, the diversion call is signalled as a normal outgoing call. The CGPN is then a number that belongs to the connection (subscriber B).
Outgoing Calls restricted	This check box allows you to suppress the display of the outgoing call number in general.
Outgoing Calls CGPN	The call number for outgoing calls (Calling Party Number) can be manipulated in general.