FIG. 7 is a specification change example related to an operation example in an embodiment of the present invention. As illustrated in FIG. 7, AS-Config, which is a configuration of radio access layer, is transferred from a source gNB to a target gNB through “HandoverPreparationInformation”. The AS-Config has all fields necessary to describe AS context related to functions to be configured. Accordingly, “need” or “cond”, which is applied to the fields of an RRC message between the user apparatus 20 and the base station apparatus 10, is not necessarily applied to the fields of an RRC message between the base station apparatuses 10. In the field interpretation, “need” means identification, maintenance, no-action, release, or the like, and “cond” means a configuration condition or a message condition. Some fields of an RRC message between the base station apparatuses 10 are always included regardless of “need” or “cond”. For example, an information element “discardTimer” is a field that must be included.

That is, the information that is mandatory between the network nodes is transmitted as a mandatory field regardless of the configuration related to the corresponding field between the user apparatus 20 and the base station apparatus 10, thereby allowing the network to function appropriately.