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Abstract

A distributed, digital voice/data communications and switching system for connecting stations which may provide voice-only transmission, data only or voice and data. The system comprises one or more physical nodes, each serving (in an exemplary case) up to about 30 ports (i.e., station interfaces); nodes may be geographically distributed on the user's premises or one or more nodes may be collected together at a common location. The nodes are interconnected via a hierarchical network configuration formed of at least two, generally three, and perhaps even four interlocking networks. The first network is a slotted ring (the 'regional' ring) employing coaxial cable to connect the nodes; it carries all control messages transmitted among the nodes, as well as the users' data traffic, using a frame which circulates continuously at about 20 Mbps. The second network is a 'star' arrangement carrying PCM-encoded digitized voice traffic; at the hub of the star, in one of the nodes, is a digital voice switch. An optional third network provides a ring-type local area network (the 'nodal ring') which connects together a multiplicity of stations at a given node. Each station may include an analog key telephone; further, a personal computer or data terminal may be connected to the phone for transmission purposes. The nodal ring uses frequency division multiplexing to support both analog voice and data transmission over twisted-pair wiring; in the node, the analog voice is digitized and connected to the star network, while digital data is connected to the regional ring for transmission to other nodes. A fourth (so-called 'national') ring may be used to interconnect a plurality of regional rings, to allow the system to grow to greater size. Both the hardware and software are modular and may be distributed among the nodes. The software (firmware) comprises a number of processes (or modules) which operate independently of one another and communicate solely by means of messages transmitted over the system's rings and buses internal to the node(s).

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First Claim