A User Equipment, UE , comprising: a controller ; a transmission and/or reception unit ; and a storage unit , wherein the transmission and/or reception unit is configured to: in a registration procedure, transmit a registration request message to a core network ; and receive a registration accept message from the core network , the registration request message includes first information indicating whether the UE supports control plane CIoT 5GS optimization or not, the registration accept message includes second information indicating whether the control plane CIoT 5GS optimization is supported by the network or not, and the transmission and/or reception unit is configured to: in a PDU session establishment procedure after the registration procedure, include a header compression configuration information element, IE, in a PDU session establishment request message in a case that the UE indicates that the control plane CIoT 5GS optimization is supported in the registration request message; and transmit, to the core network, a NAS message including the PDU session establishment request message including the header compression configuration IE after receiving the registration accept message. a controller ; a transmission and/or reception unit ; and a storage unit , wherein the transmission and/or reception unit is configured to: in a registration procedure, transmit a registration request message to a core network ; and receive a registration accept message from the core network , the registration request message includes first information indicating whether the UE supports control plane CIoT 5GS optimization or not, the registration accept message includes second information indicating whether the control plane CIoT 5GS optimization is supported by the network or not, and the transmission and/or reception unit is configured to: in a PDU session establishment procedure after the registration procedure, include a header compression configuration information element, IE, in a PDU session establishment request message in a case that the UE indicates that the control plane CIoT 5GS optimization is supported in the registration request message; and transmit, to the core network, a NAS message including the PDU session establishment request message including the header compression configuration IE after receiving the registration accept message. in a registration procedure, transmit a registration request message to a core network ; and receive a registration accept message from the core network , transmit a registration request message to a core network ; and receive a registration accept message from the core network , the registration request message includes first information indicating whether the UE supports control plane CIoT 5GS optimization or not, the registration accept message includes second information indicating whether the control plane CIoT 5GS optimization is supported by the network or not, and the transmission and/or reception unit is configured to: in a PDU session establishment procedure after the registration procedure, include a header compression configuration information element, IE, in a PDU session establishment request message in a case that the UE indicates that the control plane CIoT 5GS optimization is supported in the registration request message; and transmit, to the core network, a NAS message including the PDU session establishment request message including the header compression configuration IE after receiving the registration accept message. include a header compression configuration information element, IE, in a PDU session establishment request message in a case that the UE indicates that the control plane CIoT 5GS optimization is supported in the registration request message; and transmit, to the core network, a NAS message including the PDU session establishment request message including the header compression configuration IE after receiving the registration accept message. <EOS>