fault on one of the receiving optical fibers of the first and second optical fiber loops means for switching off a transmitting optical fiber of the optical fiber loop to which the fault detected receiving optical fiber belongs means for maintaining reception of signals for the node through the one of the receiving optical fibers of the first and second optical fiber loops if the fault detected receiving optical fiber is the other receiving optical fiber of the first and second optical fiber loops or switching reception of signals for the node through the other receiving optical fiber of the first and second optical fiber loops if the fault detected receiving optical fiber is the one receiving optical fiber of the first and second optical fiber loops and means for maintaining transmission of signals from the node through a transmitting optical fiber of an optical fiber loop to which the fault detected receiving optical fiber does not belong whereby the interface performs both protection and safety measures for the network node fig1 a illustrates a node 10 connected to another node not shown at the remote end of an exemplary two fiber link which forms a fiber loop between the two nodes the node 10 is represented by a multiplexer 12 which gathers signals.