Realtek High Definition Hd Audio Driver For Windows 10 But rather than going into an electrical outlet, the PBX system connects with a telephone service provider. Those extensions you use to call others within the same office work because of a PBX system. With a PBX system, however, those calls can be made by using simple three or four digit extensions. Siemens HiPath 3000 Service Manual pdf 1594 page Service Manual for the Siemens HiPath 3000 (v1. Think of it like a surge protector that plugs into an electrical outlet Multiple office phones are routed into the PBX, like multiple plugs are routed through a surge protector.