A method for implementing Sub Net Connection Protection, SNCP, with Sub-layer monitoring, SNC/S, on an ODUk, comprising: configuring a first Tandem Connection Monitoring, TCM, level and a second TCM level to an ODUk service and characterized by: configuring a first SNC/S protection and a second SNC/S protection for the ODUk service, wherein a dual-transmitter node and a first selective-receiver node are obtained under the first SNC/S protection and the dual-transmitter node and a second selective-receiver node are obtained under the second SNC/S protection, wherein the first SNC/S protection includes a first working service trail and a first protection service trail that are between the dual-transmitter node and the first selective-receiver node and use the first TCM level, and wherein the second SNC/S protection includes a second working service trail and a second protection service trail that use the second TCM level; if a signal flow direction of the first TCM level is from the dual-transmitter node to the first selective-receiver node over the first working service trail and the first protection service trail and a signal flow direction of the second TCM level is from the dual-transmitter node to the second selective-receiver node over the second working service trail and the second protection service trail, handling the first TCM level through a tributary unit that is a function unit used by the first TCM level and the second TCM level through optical line units that are function units used by the second TCM level; wherein the optical line units are connected to the tributary unit via a cross-connect unit and comprise a first optical line unit, OLU, a second OLU and a third OLU, wherein the first OLU corresponds to the first protection service trail, the second OLU corresponds to the first working service trail and the second working service trail, and the third OLU corresponds to the second protection service trail. configuring a first Tandem Connection Monitoring, TCM, level and a second TCM level to an ODUk service and characterized by: configuring a first SNC/S protection and a second SNC/S protection for the ODUk service, wherein a dual-transmitter node and a first selective-receiver node are obtained under the first SNC/S protection and the dual-transmitter node and a second selective-receiver node are obtained under the second SNC/S protection, wherein the first SNC/S protection includes a first working service trail and a first protection service trail that are between the dual-transmitter node and the first selective-receiver node and use the first TCM level, and wherein the second SNC/S protection includes a second working service trail and a second protection service trail that use the second TCM level; if a signal flow direction of the first TCM level is from the dual-transmitter node to the first selective-receiver node over the first working service trail and the first protection service trail and a signal flow direction of the second TCM level is from the dual-transmitter node to the second selective-receiver node over the second working service trail and the second protection service trail, handling the first TCM level through a tributary unit that is a function unit used by the first TCM level and the second TCM level through optical line units that are function units used by the second TCM level; wherein the optical line units are connected to the tributary unit via a cross-connect unit and comprise a first optical line unit, OLU, a second OLU and a third OLU, wherein the first OLU corresponds to the first protection service trail, the second OLU corresponds to the first working service trail and the second working service trail, and the third OLU corresponds to the second protection service trail. configuring a first SNC/S protection and a second SNC/S protection for the ODUk service, wherein a dual-transmitter node and a first selective-receiver node are obtained under the first SNC/S protection and the dual-transmitter node and a second selective-receiver node are obtained under the second SNC/S protection, wherein the first SNC/S protection includes a first working service trail and a first protection service trail that are between the dual-transmitter node and the first selective-receiver node and use the first TCM level, and wherein the second SNC/S protection includes a second working service trail and a second protection service trail that use the second TCM level; if a signal flow direction of the first TCM level is from the dual-transmitter node to the first selective-receiver node over the first working service trail and the first protection service trail and a signal flow direction of the second TCM level is from the dual-transmitter node to the second selective-receiver node over the second working service trail and the second protection service trail, handling the first TCM level through a tributary unit that is a function unit used by the first TCM level and the second TCM level through optical line units that are function units used by the second TCM level; wherein the optical line units are connected to the tributary unit via a cross-connect unit and comprise a first optical line unit, OLU, a second OLU and a third OLU, wherein the first OLU corresponds to the first protection service trail, the second OLU corresponds to the first working service trail and the second working service trail, and the third OLU corresponds to the second protection service trail.