Overview

The first IP-PBX systems were based on a client/server design. When most telecommunications managers hear the term IP-PBX, they usually envision a client/server design, although the converged system design is gaining in popularity and likely will dominate the market for the next few years. An IP-PBX system based on client/server design fully uses and depends on a LAN/WAN switching network infrastructure for call control and communications signaling. Like converged IP-PBX systems, client/server designs are not standard or uniform across manufacturers, although the competing models share some common design elements.

The term client/server is borrowed from the world of data communications. It describes an IP-PBX system that does not use a traditional PBX common control complex and integrated circuit switched network or traditional common equipment hardware (port cabinets and port interface circuit cards). A client/server data communications design specifies a data processing topology in which a personal computer (client) depends on a centralized computer (server) for applications software and database management functions. For many years the traditional PBX system design was compared with a mainframe computer because all call control and switching functions were centralized and desktop terminals (teleprinters, CRTs) lacked processing functions of their own. As enterprise voice communications systems evolved toward distributed and dispersed modular design topologies, similar to the concurrent evolution of minicomputer and personal computer networks, the term client/server was used more and more to describe the improved PBX system design. The first IP-PBX systems more closely conformed to data communications and processing client/server design...