Recommendation M.2120 defines maintenance of transport network, Recommendation G.784 defines the management of SDH-based network element. This Recommendation defines the object model based on Recommendation Q.822 according to the requirements described in Recommendations G.784 and M.2120 with respect to unidirectional performance monitoring. This model uses generic mechanisms defined in Recommendation Q.822. The information model for bidirectional performance monitoring is covered by Recommendation G.774.1. This Recommendation reuses functionality of Recommendation G.774.1 wherever possible.