This figure shows how a PBX system can be upgraded to use voice over IP (VoIP) telephone service without any significant changes to the PBX system. This example shows that a VoIP gateway is used to create addition lines for the PBX system. Because the VoIP gateway can produce standard telephone signals (standard telephone or T1/E1 lines), it can be directly connected to PBX system line cards. The PBX system administrator simply configures the PBX system to use the added lines through the same process that would be used when installing new telephone lines. The gateway is controlled to provide telephone services by a call server from a ITSP, IP Centrex or even another iPBX system.
Daniel casique EES seccion 1