ONOS-CU-CP is an implementation of the gNB-CU-CP as desribed in 3GPP TS 38.401.
ONOS-CU-CP hosts the RRC and the control plane part of the PDCP protocol of the gNB-CU for an en-gNB or a gNB. It terminates the E1 interface connected with the gNB-CU-UP, the F1-C interface connected with the gNB-DU, and the E2 interface connected with a SD-RAN controller (e.g. ONOS RIC).