its and no capacity is reserved to a specific virtual circuit. Thus, different circuits compete for the use of the capacity within the rules stated by the QoS management. This means that even if a virtual circuit is reserved for protection it is used also by other virtual circuits. This exploitation in any case is carried out SO that, when protection is acti- vated, there is always an available bandwidth for the recovery of the circuits under failure due to the resources reservation process carried out when the virtual circuits were set up. In the case of the transport network, when a capacity is reserved for protection, no other TDM channel can occupy it since TDM transmission is continuous in time and different channels cannot coexist in the same bandwidth. This is why, besides standard 1+1 protection, shared protection is also defined in the transport network to optimize the use of transmission resources. If share protection is used, the wavelength channels are divided into groups SO that all the channels traversing at least one common element are in the same group. The mean- ing of these groups is that they collect wavelength channels that could be hit by the same failure. When a wavelength channel is set up, a protection channel is also set up, but this opera- tion is done considering the available protection capacity already reserved for wavelength channels in different groups. This method is based on the hypothesis that a double failure is quite improbable and on the observation that, since wavelength channels in different groups do not traverse a com- mon element, only a double failure can disable both of them. Telecommunication Networks Another way to try to use the protection capacity is to use it to route it the so-called low- priority traffic, that is, channels that can be lost in case of failure. If a failure occurs, the low-priority traffic is stopped and the protection capacity is used to recover standard traffic disabled by the failure. Even from this simple and incomplete description it is clear 