Add/drop multiplexer and method, and Bi-directional line switcher ring featuring such multiplexers

摘要

An improved add/drop multiplexer in which groups of working channel tributaries have associated groups of protection channel tributaries is provided. Traffic is added by receiving it from an external service, and transmitting it on a configured group of working channel tributaries unless a protection event has occurred requiring it to be transmitted on the associated group of protection channel tributaries. Traffic received from protection or working channel tributaries is either dropped at the multiplexer if addressed to it, or transmitted on tributaries of the same type, be it working or protection. If working channel tributaries for use in the transmission relate to a physical link which is down, then the traffic is transmitted on the associated group of protection channel tributaries. In this way, all the working channel tributaries can be shared among users, rather than having a dedicated working channel tributary for each user.