What is the difference between ip-pbx and traditional PBX?

The most important thing is that the switching principles are different. ippbx uses packet switching (main voice is c/c++), while pbx uses circuit switching (assembly).

Secondly, the access methods are also different. ippbx mainly uses the ip transmission method. The current mainstream one is the sip protocol. The traditional pbx uses the E1 transmission method or the analog relay transmission method.