US Patent 7478382 Synchronized ring software download

According to a disclosed embodiment of the invention, software download and installation in a ring network are synchronized in a two-stage operation in order to minimize service disruption time. In a first phase, the MPM's and UIM's in all the nodes are upgraded in parallel. Each node has two main processing modules, allowing one to be upgraded while the other continues to operate the node. In a second phase, the RIM's at the edges of a single ring segment are upgraded, one ring segment after the other, during which time each terminal node continues to operate with respect to the span connecting to its opposite side. While a span is non-operative, traffic is wrapped or diverted as necessary to maintain service of the ring. While one RIM of a node is being upgraded, the other RIM remains operational.