Ciena Corporation

Omnia Communications, Inc.

Ming-Teh Ma

Jeffrey N Weiss

Bappa Sinha

Ed Klein

James Regan

Christopher James White

Walter Dray

William J Regan

Dan Cedrone

A unidirectional ring operates in accordance with a call setup procedure in which a single node on the ring, referred to herein as the &ldquo;hub node,&rdquo; simultaneously (i) processes call setup information from and provides call setup information to an ATM network, and (ii) controls the call setup operations of the nodes on the ring. When a source node that is part of the ring initiates a call, the node directs a call setup message to the hub node. The hub node determines if there is sufficient bandwidth available on the ring for the call. If so, the hub node passes the call setup message to the ATM network, and simultaneously multicasts call setup information to the nodes on the ring. While the call setup message is progressing over the ATM network in a conventional manner, the nodes on the ring simultaneously set up the associated virtual path and/or virtual circuit and send back connection information to the hub node. The hub node monitors the connection information to ensure that the connection over the ring is established. If the call is ultimately rejected by the destination node, the hub node multicasts to the nodes on the ring an instruction directing them to tear down the associated virtual circuit and/or virtual path. When the hub node receives a call setup message which is directed to a destination node that is a ring node, the hub node determines if there is sufficient bandwidth available on the ring to handle the call. If so, the hub node sends an appropriate acknowledgment message back to the node that sent the message to the ring. The hub node also multicasts call setup information to the nodes on the ring, instructing them simultaneously to set up a virtual circuit and/or virtual path for the call. If the destination node rejects the call, the hub node sends an appropriate call rejection message over the network to the source node and instructs the ring nodes to tear down the associated virtual circuit and/or virtual path.

Rapid call establishment in ATM rings

A system with predefined primary and secondary routes sets up corresponding virtual circuits over both routes. A destination node maintains primary and secondary sets of routing tables that contain, respectively, routing information over each of the rings for every virtual circuit. A destination node disables the appropriate entries in the routing tables for the non-selected route, such that the node ultimately discards the traffic received over that route. To switch a virtual path, and thus all of the virtual circuits included therein, from the selected route to the nonselected route, the destination node disables and enables the appropriate entries in the primary and the secondary routing tables, to switch from using the set-up virtual circuits on the selected route to using the set-up virtual circuits on the non-selected route. To detect an event that triggers protection switching, such as path failure, the system uses &ldquo;Continuity OAM cells&rdquo; to provide path status information to the nodes. A source node periodically originates Continuity OAM cells over the primary and the secondary routes. A node that receives a Continuity OAM cell multicasts the cell to (a) the processor on the node and (b) without alteration to successive nodes on the same ring. If the node processor determines that the node has not received a predetermined number of Continuity OAM cells from the source node over the selected route within a selected number of time windows, the node determines that there is a path failure on the selected route. The affected destination node then triggers protection switching if, in the same windows, the node receives an appropriate number of Continuity OAM cells from the source node over the non-selected route. To facilitate detection of path degradation, the source nodes include error counts for the associated ring interface in the Continuity OAM cells. A destination node detects path degradation when the accumulated error rate over a selected route from a source node exceeds a predetermined maximum. The destination node then triggers protection switching if the accumulated error rate over the non-selected route is better than that over the selected route by a predetermined margin.

Rapid ring protection switching system

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Newton, MA, United States of America

Ming-Teh Ma