Abstract: Logical hybrid ring arrangements are disclosed which can withstand a cut communication path or a failed node. A logical ring is formed by a cascade of (i) physical hybrid ring segments, each composed of a pair of unidirectional communication paths propagating multiplexed subchannels and interposed add-drop multiplexer nodes, and (ii) cross-connect nodes terminating the segments. Each cross-connect node routes an incoming subchannel from one segment to an outgoing subchannel on another segment. Each segment may operate at a different multiplexed signal rate, so a logical ring can be composed of segments operating at different rates. Moreover, subchannels on an incoming segment may be allocated to a plurality of outgoing segments, thereby configuring multiple logical rings which may serve to balance communication traffic over the logical rings.

Abstract: A bidirectional logical-ring network employs crossconnect nodes, which partition the network into segments and interconnect segments at the subchannel level to form logical ring structures. All segments are independent, and each segment includes a subset of Add-Drop Multiplex nodes (ADMs) and two pairs of links, one working and one protection. The formation of logical rings from the interconnection of independent segment subchannels preserves the self-healing advantages of conventional bidirectional ring networks and allows greater flexibility to effeciently accommodate bandwidth upgrade requests.