A mechanism for 1:1, 11, and UPSR path-switched protection switching, particularly for optical interface units in synchronous optical network (SONET) multiplexer equipment. A working unit and a standby unit pair protect each other in the event of a failure of the working unit or the failure of the span...http://www.google.es/patents/US6690644?utm_source=gb-gplus-sharePatente US6690644 - Mechanism for 1:1, 1
