ITS Telecom CGW-D, Installation And Operation Manual, Page: 12 / 59

CGW-D
1-5
Incoming cellular calls can be forwarded to the PBX trunk or to the PSTN (and paid by the
organization, rather than by the cellular caller). The last operation is called "public call thru" or DISA
(Direct Inward System Access).
Figure 1-5. Office Trunk Gateway Configuration
This configuration is mainly used for Callback and Call-thru applications from external cellular users.
A Callback remote cellular user can call the PBX, and (if authorized) the call is disconnected and
reversed. The CGW-D calls back the remote user and sends a dial tone. The remote user becomes
now a local PBX member, and can (if authorized):
Call any internal PBX station.
Call any PSTN external number.
This application is primarily used by company employees situated out of the country.
A Call-thru remote cellular user calls the PBX and (if authorized) is forwarded to the PSTN. The user
pays for the local cellular call and the company pays for the PSTN extended call.