The LTE eNB 1 and the NR gNB 2 described in the above embodiments may be implemented based on a Cloud Radio Access Network (C-RAN) concept. The C-RAN is also referred to as a Centralized RAN. In this case, processes and operations performed by each of the LTE eNB 1 and the gNB 2 described in the above embodiments may be provided by a Digital Unit (DU) included in the C-RAN architecture, or by a combination of a DU and a Radio Unit (RU). The DU is also referred to as a Baseband Unit (BBU) or a Central Unit (CU). The RU is also referred to as a Remote Radio Head (RRH), a Remote Radio Equipment (RRE), a Distributed Unit (DU), or a Transmission and Reception Point (TRP). That is, processes and operations performed by each of the LTE eNB 1 and the gNB 2 described in the above embodiments may be provided by one or more radio stations (or RAN nodes).

Further, the above-described embodiments are merely examples of applications of the technical ideas obtained by the inventors. These technical ideas are not limited to the above-described embodiments and various modifications may be made thereto.

For example, the whole or part of the above embodiments can be described as, but not limited to, the following supplementary notes.

(Supplementary Note 1)

A second radio access network (RAN) node to be used in a radio communication system that supports a first RAT and a second RAT, the second RAN node being associated with the second RAT, the second RAN node comprising:

a memory; and

at least one processor coupled to the memory and configured to send a radio resource configuration of the second RAT to a radio terminal via a first RAN node associated with the first RAT, wherein