Constrained optical mesh protection for transmission systems

This invention relates to optical transmission networks, to nodes for use in such networks, to link selectors for use in such nodes, to controllers for link selectors, to protection path sharing arrangements for optical transmission links, to methods of transmitting data over such networks, to software for managing such networks, and to software for determining configuration of secondary paths in such networks. To provide improved protection bandwidth efficiency for a fast recovery from a fault in an optical network, a protection ring for sharing between some of the protection paths has a pre-configured route so as to overlap on a given one of the links, with other protection paths or other rings. A selector for the given link selects which of the overlapping secondary paths is allocated to the given link at any time. Thus, two types of sharing of protection paths are combined to achieve more efficient use of protection bandwidth. The link selector can be controlled locally and so can operate more rapidly. The local control, essentially independent of the switches used to set up the secondary path through the network, makes the combination easier to scale to larger, more complex networks than shared rings alone.