A VOIP telephone switchboard / IP switchboard consists of one or more SIP telephones / VOIP telephones, an IP switchboard server and optionally a VoIP Gateway. The IP PBX server is similar to a proxy server: SIP clients, whether they are virtual telephones or hardware-based telephones, register with the IP PBX server and when they want to make a call, they ask the switchboard IP that establishes the connection. The IP PBX has a directory of all the telephones / users and their corresponding SIP address and therefore can connect an internal call or route an external call through a VoIP Gateway or a VOIP service provider.
