Patent ID: 7821972

Claim:
In an intermediate network device for use in a network having a plurality of formations organized into levels, each formation including two or more interconnected intermediate network devices, a method for preventing the formation of loops in the network, the method comprising: defining at least one Provider Service Instance (PSI) at the intermediate network device; designating at least one port of the device for connection to a higher level formation, relative to the formation of the device, as a lower network-network interface (NNI); assigning a priority to the lower NNI; determining whether the assigned priority is a best priority for the at least one PSI as compared to one or more other lower NNIs by generating one or more registration messages, the one or more registration messages indicating the at least one PSI and the assigned priority, receiving one or more registration messages associated with the other lower NNIs, each of the one or more received registration messages carrying an other assigned priority for the at least one PSI, and comparing the other assigned priority for the at least one PSI; blocking the lower NNI from sending messages tagged with the at least one PSI where the other assigned priority is determined to be better than the priority assigned by the device to the lower NNI; and enabling messages tagged with the at least one PSI to pass through the lower NNI, where the assigned priority is determined to be the best priority.