The IP PBX/ VoIP Phone System includes the following components:
one or more SIP/VoIP Phones
IP PBX server
VoIP Gateway (optional)
The IP PBX server is similar to a Proxy server. It is such a server that forwards the
requests of clients to other servers. SIP clients can be hardware of software phones.
These connect to the IP PBX server and they send a request to the IP PBX when they
want to initiate a call, and the IP PBX creates the connection. The server contains
the data of all the telephones and users with their SIP addresses, and that is how it
can execute external and internal calls with the help of the VoIP Gateway or
the VoIP porvider.
Figure 1 - An example for integrating the PBX into a network