Distributed preconfiguration of spare capacity in closed paths for network restoration

Abstract

A method for restoring traffic in a network. The network includes plural distinct nodes interconnected by plural distinct spans, each span having working links and spare links. Each node has a digital cross-connect switch for making and breaking connections between adjacent spans forming span pairs at a node. Cross-connections between spare links in adjacent spans are made such that sets of successive nodes through which the adjacent spans form span paths form closed paths. A method of finding and construction closed paths is described in which statelets are broadcast through the network. In a preferred method of implementation of the method, the statelet broadcast occurs not in response to a network failure, but across the entire network before any particular span failure and may be carried out during normal network operations as a continual re-configuration of the network.

1 - 53 . (canceled) 
     
     
         54 . A method of operating a telecommunications network in which the telecommunications network includes plural distinct nodes interconnected by plural distinct spans, each span of the plural distinct spans including working and spare parallel links between adjacent nodes, and each node having a switching machine for making and breaking connections between channels in adjacent spans, the method comprising:
 connecting spare capacity in closed paths, each closed path extending through a set of nodes, with at least one spare link between each pair of adjacent nodes in the closed path, in readiness for a span failure; and   configuring the telecommunications network to:
 (A) restore working traffic affected by a span failure on a span that is part of a closed path by routing signals along surviving nodes of the closed path; and 
 (B) restore working traffic affected by a span failure on a span between two nodes that are part of a closed path, and the span is not within the closed path, by routing signals along the closed path. 
   
     
     
         55 . A method of operating a telecommunications network in which the telecommunications network includes plural distinct nodes interconnected by plural distinct spans each node having a switching machine for making and breaking connections between channels in adjacent spans, the method comprising:
 connecting spare capacity in closed path self-healing rings, each closed path self-healing ring extending through a set of nodes, with at least one spare link between each pair of adjacent nodes in the closed path self-healing ring, in readiness for a span failure; and   configuring the telecommunications network to:
 (A) restore working traffic affected by a span failure on a span that is part of a closed path self-healing ring by routing signals along surviving nodes of the closed path self-healing ring; and 
 (B) restore working traffic affected by a span failure on a span between two nodes that are part of a closed path self-healing ring, and the span is not within the closed path self-healing ring, by routing signals along the closed path self-healing ring, thereby enabling the restoration path of a self-healing ring network while retaining the capacity efficiency of a span restorable mesh network. 
   
     
     
         56 . The method of  claim 55  wherein restoration protocol requires only the end nodes of a failed span to act to substitute traffic with no signaling requirement to or amongst other network nodes to restore traffic flow. 
     
     
         57 . The method of  claim 55  wherein two restoration paths per failure contribute to restoration of any network span failure including failures not on the closed path. 
     
     
         58 . A method of operating a telecommunications network in which the telecommunications network includes plural distinct nodes interconnected by plural distinct spans, each node having a cross-connect switch for making and breaking connections between links in adjacent spans forming span paths through the node, the method comprising:
 (a) providing a set of successive nodes capable of forming a path in the network, with at least one spare link between each pair of adjacent nodes in the path;   (b) transmitting between network nodes state messages that convey information related to network connectivity;   (c) receiving at least one of said incoming state messages at a network node, and transmitting at least one of said state messages from that node to one or more nodes adjacent to that node and connected to that node by at least one spare link;   (d) before any span failure, based on said connectivity information distributed via said state messages, determining one or more restoration routes between selected network nodes to be used to carry communications traffic; and   (e) upon detection of a span failure, routing affected communication traffic over said one or more predetermined restoration routes.   
     
     
         59 . The method of  claim 58  wherein each state message identifies the originating node. 
     
     
         60 . The method of  claim 58  wherein selection of restoration routes is based on connectivity information and one or more optimization criteria. 
     
     
         61 . The method of  claim 60  wherein the optimization attempts to minimize the number of unprotected spans in the network. 
     
     
         62 . The method of  claim 60  wherein the optimization attempts to minimize the total cost of network spans. 
     
     
         63 . The method of  claim 58  wherein one of the selected network nodes in one or more restoration routes chooses the restoration path to be used between the selected nodes. 
     
     
         64 . The method of  claim 63  wherein the node that chooses the restoration path to be used between the selected nodes notifies other nodes along the selected restoration path to alter connections to permit traffic flow along the selected restoration path. 
     
     
         65 . The method of  claim 58  wherein the restoration is carried out for a mesh type network.