ter working is never suspended. In the second case, possible only for routers and Ethernet switches, the load is shared between the two switch fabrics and each line card is connected with both of them. When a failure occurs no change in configuration has to be operated in the detection side of the line cards, simply no data will arrive from the failed switch fabric and all the data will be detected from the working one. This will be obtained by switching all the traffic on the working fabric in the transmitting line card side. This switch is either driven by the receiv- ing side that detected no signal (or a deteriorated signal) from one of the line cards or by the router central controller that detects a switch failure via alarms. Load balancing is a bit slower in recovering from a failure with respect to hot standby, but allows both statistical fluctuations of the received traffic to be better managed and in some cases the possibility to add best effort traffic that can be lost when a failure occurs. In large OXCs and in Tera routers, generally the two switch fabrics are also located in different racks, SO to add a further protection against some types of platform failures. The central processor is also duplicated and, generally, all the running software works in a mirroring configuration. This means that the state of the back-up processor is continu- ously updated to be the same to that of the main processor, comprising the fact that both processors have independent memories with replicated software and data. In this way, a processor failure can be recovered in a very short time by activating the other processor. Finally, line cards can be either locally protected by 1:N mechanisms, or protected in the framework of the global network protection. In this second case, especially if restoration mechanisms are used, the recovery time is longer, but there is a more efficient resources' exploitation. Other duplicated elements are generally the power feed and the fun units, SO to guaran- tee the equipment working in 