At the center we have, the IP PBX. Starting from the bottom, we see the Corporate Network. This is the company’s local network. Through that network, Computers running SIP clients, and IP Phones connect directly to the PBX. On the left, we see the company’s router/firewall connected to the internet. From there it can connect to remote extensions in the form of computers running the softphones, remote IP Phones, mobile devices running the Android and iOS apps, and Bridged PBX’s. Using a VoIP provider we can connect to the PSTN network. To the right a VoIP Gateway connects the PBX directly to the PSTN network.