Operating System Platform

The first PBX call processing system designs were based on proprietary operating systems before commonly used platforms such as Windows were developed. The operating system required to support a circuit switched PBX system must meet stringent, real-time, multitasking demands. A PBX system may need to support hundreds, maybe thousands, of simulta- neous conversations, with each station user potentially activating a variety of features before or during a call. The real-time nature of PBX-based voice communications requires an operating system designed for its unique operations and features. An operating system such as Windows is not ideally suited for circuit switched, real-time call processing applications. Even today, many years after Windows has become the most popular server operating system for enterprise system applications, most PBX systems use a proprietary operating system. A few small PBX system models designed for customers with fewer than 200 stations are based on a Windows NT or Windows 2000 operating system platform, but there are no announced plans to use a Windows operating system for a large system model based on a circuit switching design.

AT&T was the first PBX manufacturer to use a version of an industry standard operating system, UNIX, when it introduced its System 85 family in 1983. The proprietary operating system developed by AT&T in the early 1980s, known as Oryx/Pecos, is still used by Avaya, the AT&T/Lucent Technologies spin-off, in its current intermediate/large Definity PBX models. In keeping with the company’s tradition of innovative operating system platforms, Avaya’s small system Definity One and IP600 models were the first circuit-switched PBXs to run on a Windows 2000 operating system. The Avaya PBX system platform will be based on a client/server platform using a version of Linux as its operating system and targeted at customers with significant IP telephony requirements.

Alcatel used a version of the UNIX V operating system, known as Chorus, for its 4200/4400 PBX models during the mid-1990s and continues to use it as the foundation for its new OmniPCX 4400. Nortel Networks began using a UNIX derivative, VX Works, for its Meridian 1 system in the early 1990s, and has successfully migrated its software and operating system to its new Succession CSE 1000 client/server IP-PBX system design.

Mitel was the first traditional PBX system manufacturer to use Windows NT server for a circuit switched system design, but recently changed to a VX Works platform for the Ipera 3000, the latest upgrade of its server-based call processing design that supports the traditional circuit switched SX-2000 peripheral equipment cabinets.

The operating system of a traditional PBX system provides services and system resource allocation to the call processing, feature/function, administration, and maintenance software programs. The operating system coordinates all system processing elements and controls CPU bus activities. An operating system program passes signaling and information between high-level programs running on the Main System Processor and lower-level programs running on localized processors (cabinet carrier and/or port circuit level). Other important operating system programs are used to support maintenance and fault processing programs, mass storage (customer and system database) programs, file management system programs, and I/O programs supporting external devices, such as printers, modems, and alarms.