A communication method performed by a user equipment (UE) in a mobile communication system, according to an embodiment, includes: transmitting, to an access and mobility management function (AMF) or a session management function (SMF), UE capability information including first information about whether or not extended session management is supported; receiving from the AMF or the SMF network capability information including second information about whether or not the extended session management is supported; and receiving, from the AMF or the SMF, a result of mapping a protocol data unit (PDU) session to an evolved packet system (EPS) bearer, performed based on the first information and the second information.