This Recommendation specifies the interfaces for the Transport MPLS (T-MPLS) hierarchy, in particular the: encapsulation of T-MPLS client signals into the T-MPLS characteristic information that will be present on T-MPLS NNI links in the transport network; encapsulation of T-MPLS characteristic information into the T-MPLS link frames that will be present on T-MPLS NNI links in the transport network; T-MPLS link frame format interworking when T-MPLS subnetworks with different link frame formats are interconnected; T-MPLS hierarchy within the transport network and associated T-MPLS multiplexing; T-MPLS nested connection monitoring per hierarchy level within the transport network; T-MPLS OAM associated with nested connection monitoring in the transport network; encapsulation of in-band T-MPLS control plane information into the T-MPLS link frames that will be present on T-MPLS NNI links in the transport network. The T-MPLS network uses various server layer networks like OTH, SDH, PDH, ETH and RPR. The detailed requirements are specified in a number of ITU-T Recommendations, ANSI Standards, IEEE Standards and IETF RFC, which are referred to. This Recommendation specifies unicast LSPs; multicast LSPs are for further study. This Recommendation does not cover inter-operator control plane aspects of the T-MPLS NNI.