The following embodiments may correspond to both a case of EUTRA NR dual connectivity (ENDC) in which a core network is an evolved packet core (EPC) and a case of new radio dual connectivity (NRDC) in which a core network is a 5G core (5GC). Each of an MN and SNs may operate according to an RAT matching a DC type thereof, and accordingly, a terminal may also operate according to an RAT matching a DC type thereof. For example, in the following drawings, an MN RAT is represented by LTE, and an RRC message thereby is used for signaling. However, RRC messages corresponding to MN and SN RATs matching each DC type may be used. In addition, in a description given with an LTE or NR RAT in each embodiment, the LTE or NR RAT may be replaced with an MN or SN RAT for the DC type thereof.