Ip Private Branch Exchange Architecture

Internet Protocol Private Branch Exchange (IP PBX) architecture varies somewhat among different manufacturers, but the servers for call processing and gateway functionality are common to all. The gateway converts Voice over Internet Protocol (VoIP) signals to those compatible with the Public Switched Telephone Network (PSTN). These are located in a separate gateway or in a router (see Figure 2-4). In addition, Layer 2 switches transmit calls to other devices connected to the switch and backbone switches.

Figure 2-4 An overview of the IP PBX architecture.

Communications Servers and Voice as an Application on the LAN

Communications servers perform call processing, sending instructions on how to set up calls. They send instructions for features such as three-party conferencing, speed dial, and transfer. Communications servers host the software for the system, trunking, and station features. These servers specify the trunks over which international, local, and interstate calls should be routed. They also have lists of user profiles with extension numbers and permissions. Permissions include specifying who is allowed to use particular features such as video conferencing and placing calls to international locations.