Patent EP-0285777-B1 (EP)
Title: Time division multiplex (tdm) switching system especially for pulse code modulated (pcm) telephony signals
IPC: H04Q11/04
Filed: 1988-03-10
Granted: 1993-10-06
Abstract: A TDM switching system for providing selected connections between large numbers of lines and trunks comprises in an integrated system, several TDM switching systems which are adapted to handle smaller numbers of lines and trunks so as to expand the capacity of such smaller TDM systems. The system has a distributed, modular architecture in which the lines and trunks (DCL) are arranged in a plurality of domains (10, 12, 14). The domains each have a link controller (16, 18, 20) which links the domains to interdomain PCM highways (IDH). The domains each include, as the members thereof, a plurality of devices (16, 22, 26, 28, 30). These member devices can be port interfaces (26) which connect telephone lines and trunks and convert the analog telephony signals into PCM signals and vice versa, circuits (28) which provide services, such as tones, conferencing, dual-tone multifrequency (DTMF) facilities, telephony processors (22) which contain the data base of the addresses (telephone numbers) of the various lines and trunks, ringing generators (30), and interface devices which provide a gateway for signals into the domains for the smaller TDM switching systems. Each domain has its own intradomain PCM highway (DPH) to which the devices are connected. Each domain may have a different complement of devices. The devices are modular and interchangeable. The architecture provides for communication of control signals which control the telephony signal process along separate links, unique to each device, which connect that device to the link controller (16). Signalling messages are communicated between domains along selected time slots in a series of cyclical time slots on the interdomain highway (IDH) and on the device control links which connect the devices to the link controllers (16, 18, 20). The devices contain digital signal generators for generating the signalling messages and communicating them over the device control links to the link controller (16), and via the link controller and the selected time slots on the interdomain highways (FDH) (either on a directed or broadcast basis as dictated by the signalling message) to the other domains via the link controllers (18, 20) thereof to selected devices therein so as to enable the establishment of connections and for the allocations of time slots for data and voice messages on the intradomain and interdomain highways. Since separate and unique control links are used, the system provides for independent continued operation of the remainder of the system in the event of failure in a particular device or even of an entire domain. Clock and sync signals are generated by selected devices or link controllers and provide master clock and sync signals whereby the interdomain connections may be synchronous throughout the system. Elastic stores may be used to enable each domain or particular device in the domain to operate asychronously while providing message data and voice signals in PCM format which can be communicated intelligently throughout the system.