IP Telecom Systems
The most attractive feature of VoIP is its cost saving potential. After the initial setup cost, significant net savings can be achieved by managing a single network rather than separate phone and data networks. As we move away from public switched telephone networks, calls, particularly long distance calls, become very inexpensive.
An IP PBX or IP telephone system consists of one or more IP phones, an IP PBX server and optionally a VoIP gateway to connect to existing PSTN lines. The IP PBX server functions in a similar manner to a proxy server: SIP clients, being either soft phones or hardware-based phones, register with the IP PBX server, and when they wish to make a call they ask the IP PBX to establish the connection.
The IP PBX has a directory of all phones/users and their corresponding SIP address and thus is able to connect an internal call or route an external call via either a VoIP gateway or a VoIP service provider.