TECHNICAL FIELD

The present invention relates to a network device and a radio communication method that support Dual registration in which the same user device is simultaneously registered in a plurality of radio communication networks.

BACKGROUND ART

3rd Generation Partnership Project (3GPP) specifies Long Term Evolution (LTE), and with an aim of further speeding, specifies LTE-Advanced (hereinafter, it is assumed that 4G includes the LTE-Advanced). Moreover, in the 3GPP, specifications of a successor system of the LTE (hereinafter, referred to as 5G) called 5G New Radio (NR) and the like are being studied.

In such 5G specifications, dually registering a user device (User Equipment, UE) simultaneously in the 4G (specifically, Evolved Packet Core (EPC)) and the 5G (specifically, 5G Core (5GC)) (Dual registration) has been agreed upon (for example, Non-Patent Document 1).

Because, a state in which the UE is simultaneously registered in the EPC and the 5GC is allowed in the Dual registration, UE context can be arbitrarily transferred between the EPC and the 5GC as per the necessity. Accordingly, in the Dual registration mode, it is considered that new services can be supported flexibly.

PRIOR ART DOCUMENT

Non-Patent Document

Non-Patent Document 1: 3GPP TS 23.501 V0.4.0 Section 5.17.2.3 Mobility in dual-registration mode, 3rd Generation Partnership Project; Technical Specification Group Services and System Aspects; System Architecture for the 5G System; Stage 2 (Release 15), 3GPP, April 2017

SUMMARY OF THE INVENTION

However, the Dual registration explained above has the following problems. For example, if the UE has been dually registered, when the UE performs the existing attach procedure to attach to the EPC, the 5GC is notified that the UE is attached to the EPC.

Moreover, in the existing attach procedure, when notified that the UE is attached to the EPC, a network device that constitutes 5GC (Access and Mobility Management Function (AMF)) deletes the UE context (specifically, Session Management (SM) context) in the 5GC, and cancels the registration of the UE in the 5GC. Similarly, another network device that constitutes the 5GC, too, cancels the registration of the UE in the 5GC, and the IP level connectivity of the UE in the 5GC gets canceled.

A similar problem occurs even when the UE performs the existing attach procedure to attach to the 5GC in a state in which the UE is dually registered.

The present invention has been made in view of the above circumstances. One object of the present invention is to provide a network device and a radio communication method capable of maintaining Dual registration more reliably while utilizing an attach procedure of an existing user device when the Dual registration in which the network device is simultaneously registered in the EPC and the 5GC is applied.

A network device according to one aspect of the present invention is a network device (MME100, AMF200) that constitutes a radio communication system (radio communication system10) that supports dual registration in which same user device (UE50) is simultaneously registered on a first communication network (e.g., EPC) and a second communication network (e.g., 5GC) having a different communication scheme than that of the first communication network. The network device includes a connection processing unit (attach processing unit101) that acquires via the first communication network a message (Attach Request, Registration Request) through which the user device requests to connect to the first communication network; and a registration processing unit (UE registration processing unit103) that notifies, after the massage has been acquired by the connection processing unit, another network device (HSS110, UDM500) or the user device a dual registration indication (Dual registration indication) that indicates that the user device has been dually registered.

A network device according to another aspect of the present invention is a network device that constitutes a radio communication system that supports dual registration in which same user device is simultaneously registered on a first communication network and a second communication network having a different communication scheme than that of the first communication network. The network device includes a connection processing unit that acquires via the first communication network a message through which the user device requests to connect to the first communication network; and a registration processing unit that stops notifying another network device of a connection indication (Initial Attach Indicator) that indicates that the user device is connected to the first communication network, when the user device has been dually registered and the connection processing unit has acquired the message.

A radio communication method according to still another aspect of the present invention is a radio communication method that supports dual registration in which same user device is simultaneously registered on a first communication network and a second communication network having a different communication scheme than that of the first communication network. The radio communication method includes requesting including the user device requesting connection to the first communication network and transmitting to the first communication network a message that includes a dual registration indication that indicates that the user device has been dually registered; and notifying including the first communication network notifying, after the massage has been acquired, another network device of the dual registration indication that indicates that the user device has been dually registered.

A radio communication method according to still another aspect of the present invention is a radio communication method that supports dual registration in which same user device is simultaneously registered on a first communication network and a second communication network having a different communication scheme than that of the first communication network. The radio communication method includes requesting including the user device requesting connection to the first communication network and transmitting to the first communication network a message that includes a dual registration indication that indicates that the user device has been dually registered; and stopping including the first communication network stopping, after the massage has been acquired, the notification to another network device of a connection indication that indicates that the user device is connected to the first communication network.

