Cabinet/Carrier Shelf Local Controllers | Legacy PBX

Many, but not all, intermediate/large PBX systems have local control cards that support one or a group of port carrier shelves housed in a port equipment cabinet. The primary functions of the local control cards are passing control signals from the Main System Processor to the port circuit cards and providing a signaling link between the peripherals (via the port circuit card microcontrollers) and the main control complex. It effectively analyzes, controls, and supervises the port circuit cards and peripherals at the cabinet or carrier shelf level. Other common functions of the local controller are local TDM bus talk slot assignments and supervising and monitoring local switch network connections and voice signaling transport. Localizing the switch network access function can greatly reduce the call processing load on the Main System Processor. The reduced processing load can be especially significant for PBX systems with a distributed or dispersed switch network design. Local controllers can also perform a variety of diagnostics and circuit test operations such as passing status updates to the main control complex.

Local controllers, like the port circuit card microcontrollers, do not control call processing functions but merely execute operations under the supervision of the Main System Processor. The type of processing element used as a local controller differs from system to system. Based on the localized and limited role it has in the call processing operation, it is not necessary for the processing element to be a current microprocessor platform; many PBX systems have retained the same local control boards for more than 5 years. The local controllers perform their tasks based on firmware programs resident on the printed circuit board.

Some PBX system call processing designs offer fully duplicated local controller function as a standard or optional system attribute. In an intermediate/large line size system, local controller card problems sometimes can affect hundreds of system ports. Processor failure or error will result in loss of service to all ports supported by the local controller, unless a back-up controller is available.