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An IP PBX / VoIP PBX system consists of SIP phones, an IP PBX server and VoIP Gateway, WebRTC and offers offers unified communications features.
The SIP clients, being either mobile apps, soft phones or hardware based phones, register with the IP PBX server.The IP PBX server has a database of all SIP clients, with addresses and other details that are used to establish calls.
Broadly speaking, internal calls are directly routed to the SIP address of the destination party. There is no need for the call to pass through the IP PBX server once the initial connection has been established. This means all voice traffic travels directly between the two endpoints, ensuring that the server will not become overloaded as the number of concurrent calls increases.
External calls are redirected to the VoIP gateway or SIP trunks which connects the IP based system to the external PSTN. These gateways / trunks may be incorporated into the IP PBX and maintained by the organization or they may use one that is provided by an external vendor. The VoIP gateway / SIP Trunks itself can take many forms – it may be a standalone piece of hardware or an extension card that can simply be plugged into the server.
Many companies use IP PBX software to create a virtual server on an existing computer. This makes it very easy to test VoIP calls. Over the long-term, businesses can then upgrade their systems slowly for better reliability and integrity.