There is a SwyxWare installation with two servers, one in Dortmund and one in Berlin. The two SwyxServers are connected to each other over a SIP trunk.

A call comes in from the public network via the ISDN trunk group to the Dortmund number 0231 23456-888. This number is not assigned to a user within SwyxWare, but there is forwarding for the number range 0231 234567-88* via a SIP trunk group. In order for this call to be forwarded via this SIP trunk group, the corresponding permission must exist in the ISDN trunk group, which has received the call, i.e. the call that has been received by the trunk group must have the permission to leave the system via the SIP trunk: