This Recommendation describes the automatic protection switching (APS) protocol to support optical data unit k (ODUk) shared ring protection (SRP) in the optical transport network (OTN). Shared ring protection provides two types of switching: SRP-1 with 1 ODU per lambda, and SRP-p with p ODUs per lambda. SRP protects ODUs within a physical ring with ODU cross-connects. The interconnects are in general of type optical transport module-n (OTM-n), as specified in [ITU-T G.709]. The network objectives are given in Annex A.