One disclosure of the present specification provides a method by which a network node performs communication related to an MA PDU session. The method may comprise the steps of: receiving, from a UE, a SIP registration message including MA PDU session information; receiving, from another network node, a SIP message related to an IMS service for the MA PDU session; and transmitting, to a PCF node, information on whether the SIP message is related to a PS Data Off exempt service, on the basis of the reception of the MA PDU session information.