chosen for configuration in step 702 service units used by protected services in receiving and transmitting directions of the node a are configured and working units and protecting units in the receiving and transmitting directions of the node a are configured specifically in the configuring process an oduk of a slot an interface and a path in the service units the working units and the protecting units in the receiving and transmitting directions of the node a is selected for example the oduk of slot 1 optical interface 3 and path 3 in the above mentioned units is selected in step 703 the path corresponding to the aps pcc available to all the nodes is queried since three kinds of service protection already exist in the ring network and the trails of the three service protection paths are x a b c y m f e n and n e d o respectively for the node a the signal entering the node a adopts the path corresponding to the aps pcc for which the sixth seventh and eighth bits of the mfas are 000 for the node b the signal entering the node b adopts the path corresponding to the aps pcc for which the sixth seventh and eighth bits of the mfas are 000 for the node c the signal entering the node c adopts the path corresponding to the aps pcc for which the sixth seventh and eighth bits of the mfas are 000 for the node d the signal entering the node d adopts the path corresponding to the aps pcc for which the sixth seventh and eighth bits of the mfas are 010 for the node e the signal entering the node e from.