Core network node, access network node, wireless terminal, and communication method

Abstract

The purpose of the present invention is to provide a core network node which is capable of smoothly executing a wireless terminal registration process, even if congestion occurs in a mobile network. A core access network node (10) according to the present disclosure comprises: a detection unit (11) that detects congestion occurring at the core network node (10); and a communication unit (12) that, if congestion has occurred in the core network node (10), transmits to a wireless terminal (30) a message which indicates that congestion has occurred and which includes identification information of another core network node. The message gives an instruction to select the other core network node.

Description

Core network node, access network node, wireless terminal, communication method, and computer-readable medium

[0001] The present disclosure relates to a core network node, an access network node, a wireless terminal, a communication method, and a program.

[0002] When a wireless terminal uses a mobile network, it executes a registration process for the wireless terminal with the mobile network. The mobile network registers the wireless terminal after authenticating the wireless terminal. Once the wireless terminal is registered with the mobile network, it becomes able to use the mobile network.

[0003] Patent Literature 1 discloses a process to be performed when congestion occurs in a mobile network. For example, when an Access and Mobility Management Function (AMF) constituting a mobile network determines that congestion has occurred, it transmits a wait time to a User Equipment (UE) via an (Radio) Access Network (R)AN. The UE does not transmit a registration request message during the wait time.

[0004] Japanese Patent Application Laid-Open No. 2021-180523

[0005] When the congestion control disclosed in Patent Document 1 is performed, the UE cannot send a registration request message during the wait time period, which causes a problem in that the UE cannot receive services using the mobile network during that time.

[0006] In view of the above-mentioned problems, one of the objectives of the present disclosure is to provide a core network node, an access network node, a wireless terminal, a communication method, and a computer-readable medium that can smoothly execute registration processing for a wireless terminal even when congestion occurs in a mobile network.

[0007] A first core network node according to a first aspect of the present disclosure is a first core network node comprising: a detection unit that detects congestion occurring in the first core network node; and a communication unit that, when congestion occurs in the first core network node, transmits a message to a wireless terminal indicating that congestion has occurred, the message including identification information of a second core network node, and instructs the selection of the second core network node.

[0008] An access network node according to a second aspect of the present disclosure comprises: a communication unit that receives from a wireless terminal a message indicating that congestion has occurred in a first core network node and instructing the selection of a second core network node different from the first core network node; and a selection unit that selects, based on the identification information, the second core network node identified by the identification information as the destination of a registration request message included in the message, wherein the message includes identification information of the second core network node, and that transmits the registration request message to the second core network node.

[0009] A wireless terminal according to a third aspect of the present disclosure comprises: a receiving unit that receives a first message from a first core network node in which congestion has occurred, the first message indicating that congestion has occurred in the first core network node and instructing the selection of a second core network node different from the first core network node; and a transmitting unit that transmits a second message to the access network node, the first message including identification information of the second core network node, notifying the access network node that congestion has occurred in the first core network node and instructing the selection of the second core network node, the second message including identification information of the second core network node.

[0010] A communication method performed in a first core network node according to a fourth aspect of the present disclosure detects congestion occurring in the first core network node, and when congestion occurs in the first core network node, transmits a message indicating that congestion has occurred to a wireless terminal, the message including identification information of a second core network node, and instructs the selection of the second core network node.

[0011] A communication method performed in an access network node according to a fifth aspect of the present disclosure includes receiving from a wireless terminal a message indicating that congestion has occurred in a first core network node and instructing the selection of a second core network node different from the first core network node, the message including identification information of the second core network node, and based on the identification information, selecting the second core network node identified by the identification information as the destination of a registration request message included in the message, and transmitting the registration request message to the second core network node.

[0012] A communication method executed in a wireless terminal according to a sixth aspect of the present disclosure includes receiving a first message from a first core network node in which congestion has occurred, the first message indicating that congestion has occurred in the first core network node and instructing the selection of a second core network node different from the first core network node, the first message including identification information of the second core network node, and transmitting a second message to the access network node notifying the access network node that congestion has occurred in the first core network node and instructing the selection of the second core network node, the second message including identification information of the second core network node.

[0013] A program according to a seventh aspect of the present disclosure causes a computer that is a core network node to detect congestion that has occurred in the first core network node, and, when congestion has occurred in the first core network node, to send to a wireless terminal a message instructing the selection of a second core network node, the message including identification information of the second core network node, and indicating that congestion has occurred.

[0014] The present disclosure makes it possible to provide a core network node, an access network node, a wireless terminal, a communication method, and a program that can smoothly execute registration processing for a wireless terminal even when congestion occurs in a mobile network.

[0015] FIG. 1 is a configuration diagram of a communication system according to a first embodiment. FIG. 2 is a diagram showing a flow of communication processing in a core network node according to the first embodiment. FIG. 3 is a diagram showing a flow of communication processing in an access network node according to the first embodiment. FIG. 4 is a diagram showing a flow of communication processing in a radio terminal according to the first embodiment. FIG. 5 is a configuration diagram of a communication system according to a second embodiment. FIG. 6 is a diagram showing a flow of registration processing according to the second embodiment. FIG. 7 is a diagram showing a flow of registration processing according to the second embodiment. FIG. 8 is a diagram showing a flow of registration processing according to a third embodiment. FIG. 9 is a diagram showing a flow of registration processing according to the third embodiment. FIG. 10 is a diagram showing a configuration diagram of a core network node and an AMF node according to each embodiment. FIG. 11 is a diagram showing a configuration diagram of an access network node and a gNB according to each embodiment. FIG. 12 is a diagram showing a configuration diagram of a radio terminal and a UE according to each embodiment.

[0016] (First Embodiment) Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. An example configuration of a communication system according to the first embodiment will be described with reference to Fig. 1. The communication system in Fig. 1 includes a core network node 10, an access network node 20, and a wireless terminal 30.

[0017] First, a configuration example of the core network node 10 will be described. The core network node 10 may be a computer device operated by a processor executing a program stored in a memory. The core network node 10 may be, for example, a node device defined in the 3GPP (3rd Generation Partnership Project). Specifically, the core network node 10 may be an MME (Mobility Management Entity) or an AMF (Access and Mobility Function) node. The AMF node may be referred to as an AMF entity.

[0018] The core network node 10 includes a detection unit 11 and a communication unit 12. The detection unit 11 and the communication unit 12 may be software or a module that executes processing by a processor executing a program stored in a memory, or may be hardware such as a circuit or a chip.

[0019] The detection unit 11 detects congestion occurring in the core network node 10. For example, the detection unit 11 may detect the occurrence of congestion when the amount of data received by the core network node 10, the number of messages, or the like exceeds a threshold. Alternatively, the detection unit 11 may detect the occurrence of congestion when it detects that the number of messages, or the like, is smaller than normal. Alternatively, the detection unit 11 may detect the occurrence of congestion when the number of wireless terminals managed by the core network node 10 exceeds a threshold. Alternatively, the detection unit 11 may detect the occurrence of congestion when the usage rate of a processor or memory exceeds a threshold. The thresholds used for comparing with the number of messages, etc., the number of wireless terminals, and the processor, etc. are all different. The number of wireless terminals managed by the core network node 10 may be rephrased as the number of wireless terminals registered in the core network node 10.

[0020] When the detection unit 11 is notified by a management system or the like that manages the communication system that congestion has occurred in the core network node 10, the detection unit 11 may detect that congestion has occurred in the core network node 10. The detection unit 11 may periodically or at any timing transmit information regarding the amount of data to be transmitted and received, the number of messages to be transmitted and received, the number of wireless terminals to be managed, the processor or memory usage rate, etc. to the management system.

[0021] When congestion occurs in the core network node 10, the communication unit 12 transmits a message to the radio terminal 30 indicating that congestion has occurred, the message including identification information of at least one other core network node. The message instructs the radio terminal to select at least one other core network node corresponding to the identification information. The occurrence of congestion may be indicated, for example, by including in the message information for notifying the radio terminal 30 that congestion has occurred. Instructing the radio terminal to select another core network node may be indicated, for example, by including in the message information instructing the radio terminal to select another core network node. Also, for example, the message may include information indicating that congestion has occurred and information instructing the radio terminal to select another core network node. The communication unit 12 transmits the message to the radio terminal 30 via the access network node 20.

[0022] The information for notifying the radio terminal 30 that congestion has occurred may include, for example, identification information of the core network node 10 in which congestion has occurred. Furthermore, the information for notifying the radio terminal 30 that congestion has occurred may include information indicating a congestion level indicating the extent of congestion. The congestion level may be determined, for example, based on the difference between the number of messages or a threshold. The congestion level may also be, for example, an estimated value of the time since the congestion began or the congestion duration, or may be calculated based on these. The identification information of the core network node may be information assigned to each core network node to uniquely identify the core network node. Alternatively, the identification information of the core network node may be address information such as an IP address or a MAC address.

[0023] Next, a configuration example of the access network node 20 will be described. The access network node 20 may be a computer device operated by a processor executing a program stored in a memory. The access network node 20 may be a node device accessed by a wireless terminal 30 when using a mobile network. The access network node 20 may be, for example, a base station that wirelessly communicates with the wireless terminal 30. The base station may be, for example, a device defined in 3GPP, and specifically, may be an eNB (evolved Node B) or a gNB (gNode B). Alternatively, the access network node 20 may be an AP (Access Point) that performs wireless LAN (Local Area Network) communication.

[0024] The access network node 20 includes a communication unit 21 and a selection unit 22. The communication unit 21 and the selection unit 22 may be software or modules whose processes are performed by a processor executing a program stored in a memory, or the communication unit 21 and the selection unit 22 may be hardware such as a circuit or a chip.

[0025] The communication unit 21 receives from the radio terminal 30 a message indicating that congestion has occurred in the core network node 10 and instructing the selection of a core network node other than the core network node 10. The message includes an identifier of a core network node other than the core network node 10. The occurrence of congestion in the core network node 10 may be indicated by including in the message information for notifying the access network node 20 that congestion has occurred in the core network node 10. The instruction to select a core network node other than the core network node 10 may be instructed, for example, by including in the message information instructing the access network node to select a core network node other than the core network node 10. Also, for example, the message may indicate that congestion has occurred and may further include information instructing the selection of a core network node other than the core network node 10. The message received from the radio terminal 30 includes a registration request message.

[0026] The information for notifying the access network node 20 that congestion has occurred in the core network node 10 may be the same information as the information for notifying the radio terminal 30 that congestion has occurred, which information has been sent by the core network node 10 to the radio terminal 30. Alternatively, the information for notifying the access network node 20 that congestion has occurred in the core network node 10 may be different information from the information for notifying the radio terminal 30 that congestion has occurred. Specifically, the different information may be information in a different format.

[0027] The registration request message is a message used by the wireless terminal 30 to request registration of the wireless terminal 30 from a core network node when the wireless terminal 30 uses a mobile network.

[0028] The selection unit 22 selects another core network node identified by the received identification information as a destination of the registration request message. Selecting another core network node may be rephrased as determining another core network node as a destination of the registration request message. Alternatively, selecting another core network node may be rephrased as specifying another core network node identified by the received identification information from among multiple core network nodes.

[0029] The selection unit 22 may select, as the destination of the registration request message, a core network different from the other core network nodes identified by the received identification information, when the selection unit 22 has not received information indicating that congestion has occurred in the core network node 10. In other words, when the selection unit 22 has received information indicating that congestion has occurred in the core network node 10, the selection unit 22 does not select, as the destination of the registration request message, a core network different from the other core network nodes identified by the received identification information.

[0030] The communication unit 21 transmits the registration request message received from the wireless terminal 30 to the other core network node identified by the selection unit 22 .

[0031] Next, a configuration example of the wireless terminal 30 will be described. The wireless terminal 30 may be a computer device operated by a processor executing a program stored in a memory. The wireless terminal 30 is a terminal capable of wireless communication with the access network node 20 in accordance with a predetermined communication standard. The wireless terminal 30 may be, for example, a mobile phone terminal, a smartphone terminal, an IoT (Internet of Things) terminal, or the like. The communication standard may be, for example, a wireless communication standard such as so-called 4G (4th Generation) or 5G (5th Generation) defined by 3GPP, or a communication standard for wireless LAN communication.

[0032] The wireless terminal 30 has a receiving unit 31 and a transmitting unit 32. The receiving unit 31 and the transmitting unit 32 may be software or modules that are executed by a processor executing a program stored in a memory, or may be hardware such as a circuit or a chip.

[0033] The receiving unit 31 receives a first message from the core network node 10 in which congestion has occurred, indicating that congestion has occurred in the core network node 10 and instructing the selection of another core network node different from the core network node 10. The first message further includes identification information of the other core network node different from the core network node 10. The receiving unit 31 receives the message transmitted from the core network node 10 via the access network node 20.

[0034] The transmitter 32 notifies the access network node 20 that congestion has occurred in the core network node 10 and transmits a second message to the access network node 20 instructing the access network node 20 to select another core network node. The second message includes identification information of the other core network node. The second message further includes a registration request message.

[0035] The wireless terminal 30 becomes able to use the mobile network by receiving the response message to the registration request message.

[0036] Next, the flow of communication processing in the core network node 10 according to the first embodiment will be described with reference to Fig. 2. First, the detection unit 11 detects congestion that has occurred in the core network node 10 (S11). Next, when congestion has occurred in the core network node 10, the communication unit 12 transmits a message indicating the occurrence of congestion to the radio terminal 20, which includes identification information of another core network node different from the core network node 10 (S12). The message instructs the radio terminal 20 to select another core network node.

[0037] Next, the flow of communication processing in the access network node 20 according to the first embodiment will be described with reference to Fig. 3. First, the communication unit 21 receives from the radio terminal 30 a message indicating that congestion has occurred in the core network node 10 and instructing the radio terminal 30 to select another core network node other than the core network node 10 (S21). The message further includes identification information of the other core network node other than the core network node 10 and a registration request message. Next, the selection unit 22 selects, based on the identification information, the other core network node identified by the identification information as a destination of the registration request message (S22). Next, the communication unit 21 transmits the registration request message to the other core network node selected by the selection unit 22 (S23).

[0038] Next, the flow of communication processing in the radio terminal 30 according to the first embodiment will be described with reference to Fig. 4. First, the receiving unit 31 receives a first message from the core network node 10 in which congestion has occurred, indicating that congestion has occurred in the core network node 10 and instructing the radio terminal 30 to select another core network node different from the core network node 10 (S31). The message further includes identification information of the other core network node different from the core network node 10. Next, the transmitting unit 32 notifies the access network node 20 that congestion has occurred in the core network node 10 and transmits a second message to the access network node 20 instructing the radio terminal 30 to select another core network node (S32). The second message further includes identification information of the other core network node and a registration request message.

[0039] As described above, when congestion occurs in the core network node 10, the core network node 10 transmits identification information of another core network node to the radio terminal 30. Furthermore, the radio terminal 30 transmits to the access network node 20 information that congestion has occurred in the core network node 10 and identification information of another core network node that will take the place of the core network node 10. This allows the access network node 20 to transmit the registration request message received from the radio terminal 30 to the other core network node instead of the core network node 10. As a result, the other core network node can manage the radio terminal 30 instead of the core network node 10, and the radio terminal 30 can receive services using the mobile network.

[0040] (Embodiment 2) Next, an example configuration of a communication system according to embodiment 2 will be described with reference to Figure 5. The communication system in Figure 5 illustrates a 5G System (5GS) defined by 3GPP. The 5GS in Figure 5 includes a 5G Core (5GC) 40, a Radio Access Network (RAN) 50, and a User Equipment (UE) 60. Furthermore, the 5GC 40 includes an Access and Mobility Management Function (AMF) node 41 (hereinafter referred to as AMF 41), an AMF node 42 (hereinafter referred to as AMF 42), and a Network Repository Function (NRF) node 43 (hereinafter referred to as NRF 43). The RAN 50 includes a gNB 51. The AMF 41 and the AMF 42 correspond to the core network node 10 and include the same components as the core network node 10 in Figure 1. The gNB 51 corresponds to the access network node 20 and includes the same components as the access network node 20 in Figure 1. The UE 60 corresponds to the wireless terminal 30 and includes the same components as the wireless terminal 30 in Fig. 1. The node may be referred to as an entity or a device.

[0041] 5 shows that RAN 50 includes a gNB 51 that performs wireless communication with UE 60, but RAN 50 may also include a node device that performs communication other than wireless communication, for example, fixed communication, with UE 60. In this case, RAN 50 may be referred to as an AN (Access Network) or (R)AN.

[0042] Next, the flow of the registration process according to the second embodiment will be described with reference to Fig. 6. The registration process in Fig. 6 is described by referring to the sequence related to the registration procedure described in 3GPP TS23.502 V17.4.0, and extracting and explaining the processes necessary for the explanation according to the second embodiment. Registration is a process performed by UE 60 to use services provided in 5GS. In other words, when the registration process is completed and UE 60 is registered with AMF 41 or AMF 42 and the node equipment included in 5GC 40, UE 60 can use the services provided in 5GS.

[0043] First, assume that congestion occurs in the AMF 41 (S41). For example, the detection unit 11 constituting the AMF 41 may detect the congestion that has occurred in the AMF 41. Alternatively, a monitoring device or the like that monitors the 5GC 40 may notify the AMF 41 that congestion has occurred in the AMF 41, so that the detection unit 11 detects the congestion that has occurred in the AMF 41.

[0044] Next, UE 60 transmits an AN (Access Network) message including a Registration Request message to gNB 51 (S42). For example, UE 60 may transmit the Registration Request message to gNB 51 after activating UE 60. Furthermore, UE 60 may periodically or periodically transmit the Registration Request message to gNB 51. Alternatively, UE 60 may transmit the Registration Request message to gNB 51 when UE 60 enters a new TA (Tracking Area). Entering a new TA may be rephrased as moving to a new TA. The Registration Request message includes a Subscription Concealed Identifier (SUCI) or a 5G Globally Unique Temporary Identifier (5G-GUTI) as identification information for identifying UE 60.

[0045] The AN message further includes AN parameters. The AN parameters may include, for example, a 5G-S-TMSI (5G S Temporary Mobile Subscription Identifier) ​​or a GUAMI (Globally Unique AMF Identifier). The 5G-S-TMSI is identification information for identifying UE 60. The 5G-S-TMSI includes an AMF Set ID, an AMF Pointer, and a 5G-TMSI. The AMF Set ID is identification information for identifying an AMF set including one or more AMFs, and the AMF Pointer is identification information for identifying each AMF included in the AMF set. The 5G-TMSI is identification information of UE 60 managed in the AMF.

[0046] GUAMI is identification information for identifying an AMF. GUAMI includes MCC (Mobile Country Number), MNC (Mobile Network Code), AMF Region ID, AMF Set ID, and AMF Pointer. MCC represents a country or region, and MNC represents a carrier. AMF Region ID represents the region where the AMF is installed.

[0047] Next, gNB51 selects an AMF to which the Registration Request message is to be sent (S43). If the AN parameters include 5G-S-TMSI or GUAMI, gNB51 may select an AMF identified by 5G-S-TMSI or GUAMI. Alternatively, even if the AN parameters include 5G-S-TMSI or GUAMI, gNB51 may select an AMF different from the AMF identified by 5G-S-TMSI or GUAMI.

[0048] For example, gNB51 may select an AMF different from the AMF identified by 5G-S-TMSI or GUAMI when the AMF identified by 5G-S-TMSI or GUAMI included in the AN parameters is unavailable. Specifically, when gNB51 detects that a failure has occurred in the AMF identified by 5G-S-TMSI or GUAMI, it may select an AMF different from the AMF identified by 5G-S-TMSI or GUAMI. Alternatively, when gNB51 is notified in advance that the AMF identified by 5G-S-TMSI or GUAMI is unavailable, it may select an AMF different from the AMF identified by 5G-S-TMSI or GUAMI. Alternatively, when the load of the AMF identified by 5G-S-TMSI or GUAMI is greater than a predetermined value, gNB51 may not select the AMF identified by 5G-S-TMSI or GUAMI.

[0049] The gNB51 may select an AMF based on the AMF Region ID and the AMF Set ID. For example, the gNB51 may select an AMF to which the Registration Request message is to be sent from among multiple AMFs included in the AMF Set ID. Alternatively, the gNB51 may select an AMF in accordance with the policy of the operator managing 5GS, or may select an AMF taking into account the load status of the AMF. In step S43, it is assumed that the gNB51 selects the AMF41.

[0050] Next, the gNB 51 transmits the Registration Request message received from the UE 60 in step S42 to the AMF 41 (S44). Next, the AMF 41 transmits a Registration Reject message to the UE 60 via the gNB 51 to reject the Registration of the UE 60 because congestion has occurred in the AMF 41 (S45). The Registration Reject message includes information for notifying the UE 60 that congestion has occurred in the AMF 41, GUAMI representing, for example, the AMF 42 as an AMF different from the AMF 41, and information instructing the selection of the AMF 42. The information for notifying the UE 60 that congestion has occurred in the AMF 41 may be, for example, a cause value set to "congestion". The cause value is a parameter indicating the cause of rejecting the Registration of the UE 60. The information instructing the selection of AMF 42 may be, for example, an information element instructing the selection of an AMF identified by GUAMI included in the Registration Reject message. Also, the Registration Reject message may have a cause value indicating, for example, "congestion" and instructing the selection of an AMF identified by GUAMI included in the Registration Reject message.

[0051] The AMF 41 may include a GUAMI representing the AMF 42 that is not experiencing congestion in the Registration Reject message. Furthermore, if there are multiple AMFs that are not experiencing congestion, the AMF 41 may select any AMF from among the AMFs that are not experiencing congestion, or may select an AMF according to a predetermined policy. For example, the AMF 41 may select an AMF that is included in the same AMF Region ID or AMF Set ID as the AMF 41 from among the AMFs in operation that are not experiencing congestion. Alternatively, the AMF 41 may include the GUAMI of each of multiple AMFs that are not experiencing congestion in the Registration Reject message.

[0052] The AMF 41 may change the AMF to be selected depending on, for example, the degree of congestion. For example, when the degree of congestion that has occurred is greater than a predetermined standard and the impact of the congestion is significant, the AMF 41 may select an AMF managed by another telecommunications carrier, that is, an AMF that is not included in the 5GC 40. When the degree of congestion that has occurred is below a predetermined standard and the impact of the congestion is limited, the AMF 41 may select an AMF within the 5GC 40. The criterion for determining the degree of congestion may be determined using, for example, the downtime of the AMF, the number of affected UEs, or the like. Furthermore, for example, the criterion for determining the degree of congestion may be the number of packet losses, for example.

[0053] Furthermore, when the received Registration Request message indicates that it is Emergency Registration, the AMF 41 may transmit the Registration Reject message in step S45. That is, when the Registration Request message does not indicate that it is Emergency Registration, the AMF 41 does not need to include GUAMI, which indicates an AMF different from the AMF 41, in the Registration Reject message. In other words, the AMF 41 may register only the UE that transmits the emergency call with another AMF in which congestion is not occurring. This allows the UE that transmits the emergency call to complete the registration process with the other AMF in which congestion is not occurring. The Emergency Registration may be, for example, a message including information indicating a request for emergency service.

[0054] The AMF 42 not experiencing congestion selected by the AMF 41 may be a new AMF that is virtually constructed when congestion occurs in the AMF. For example, when a Management and Orchestration (MANO) constituting a Network Functions Virtualization (NFV) architecture detects that congestion has occurred in the AMF 41, the MANO may execute virtualization of the AMF by activating a Virtual Network Function (VNF) operating as an AMF.

[0055] Next, upon receiving the Registration Reject message, UE 60 transmits an AN message including a Registration Request message to gNB 51 in order to perform the Registration process again (S46). UE 60 sets, as an AN parameter, GUAMI included in the Registration Reject message received in step S45. Furthermore, UE 60 sets, in the AN parameter, information for notifying gNB 51 that congestion has occurred in AMF 41. For example, UE 60 may include, in gNB 51, flag information indicating that congestion has occurred in AMF 41. Alternatively, UE 60 may not set, in the AN parameter, identification information for identifying AMF 41, but may set, in the AN parameter, information indicating that congestion has occurred in any AMF. Alternatively, UE 60 may set, in the AN parameter, information indicating that the Registration Request message is to be transmitted again after receiving the Registration Reject message. Furthermore, UE 60 sets, in the AN parameter, information instructing selection of AMF 42. The information instructing the selection of AMF 42 may be, for example, an information element instructing the selection of an AMF identified by GUAMI set as an AN parameter. In addition, UE 60 may set, as an AN parameter, information instructing the selection of AMF 42 by notifying gNB 51 that congestion has occurred in AMF 41.

[0056] Next, the gNB51 selects an AMF to which the Registration Request message is to be sent (S47). The AN parameters may be set to GUAMI, information instructing the selection of an AMF linked to GUAMI, and information for notifying the gNB51 that congestion has occurred in the AMF41. In this case, the gNB51 identifies the AMF identified in GUAMI as the AMF to which the Registration Request message is to be sent. In other words, if the AN parameters are set to GUAMI, information instructing the selection of an AMF linked to GUAMI, and information for notifying the gNB51 that congestion has occurred in the AMF41, the gNB51 identifies the AMF identified in GUAMI without selecting another AMF. In other words, if the AN parameters are not set to information for notifying the gNB51 that congestion has occurred in the AMF41, the gNB51 may not identify the AMF identified in GUAMI. Further, for example, if information instructing the selection of an AMF linked to GUAMI is not set in the AN parameters, gNB51 may not identify an AMF identified in GUAMI. On the other hand, if information instructing the selection of an AMF linked to GUAMI and information for notifying gNB51 that congestion has occurred in AMF41 are set in the AN parameters, gNB51 forcibly identifies the AMF identified in GUAMI as the destination of the Registration Request message. Forcibly identifying an AMF means that gNB51 identifies an AMF identified in GUAMI without determining whether to select an AMF different from the AMF identified in GUAMI.

[0057] Next, gNB51 sends a Registration Request message to AMF42 represented by GUAMI set in the AN parameters (S48).

[0058] Next, AMF 42 executes authentication processing etc. for UE 60, and when the Registration processing for UE 60 is executed normally, AMF 42 transmits a Registration Accept message to UE 60 (S49). Furthermore, when UE 60 receives the Registration Accept message, it transmits a Registration Complete message to AMF 42 (S50). This completes the Registration processing for UE 60.

[0059] As described above, in the 5GS according to the second embodiment, if the Registration process is not performed normally due to congestion occurring in the AMF 41, the UE 60 transmits a Registration Request message again. At this time, the UE 60 transmits to the gNB 51 a message including information for notifying the gNB 51 that congestion has occurred in the AMF 41, the GUAMI notified from the AMF 41, and information instructing the selection of an AMF linked to the GUAMI. This allows the gNB 51 to transmit the Registration Request message received from the UE 60 to the AMF 42 in which congestion is not occurring. As a result, the Registration process for the UE 60 can be completed normally.

[0060] 6 has described the process in which the AMF 41 selects the AMF 42. However, as shown in FIG. 7, when congestion occurs in the AMF 41, the NRF 43 may select the AMF 42. Specifically, when the AMF 41 detects the occurrence of congestion in step S41, the AMF 41 transmits a message to the NRF 43 notifying that congestion has occurred (S51). Next, the NRF 43 transmits a message to the AMF 41 notifying the AMF 42 of GUAMI, which indicates the AMF 42 as an AMF in which congestion has not occurred (S52). Steps S42 to S50 in FIG. 7 are the same as those in FIG. 6, and therefore detailed description thereof will be omitted. When the AMF 41 receives the Registration Request message in step S44, the AMF 41 transmits a Registration Reject message including the GUAMI notified from the NRF 43 to the UE 60.

[0061] 7, the AMF 41 may notify the NRF 43 that congestion has occurred before receiving the Registration Request message, or may notify the NRF 43 that congestion has occurred after receiving the Registration Request message. That is, the AMF 41 may execute the processes of steps S51 and S52 between steps S44 and S45.

[0062] (Third embodiment) Next, a flow of a registration process according to a third embodiment will be described with reference to Fig. 8. The registration process in Fig. 8 is described by referring to the sequence related to the registration procedure and network-initiated deregistration described in 3GPP TS23.502 V17.4.0, and extracting and describing processes necessary for the description of the third embodiment. In Fig. 8, it is assumed that UE 60 is in a state in which the registration process between UE 60 and AMF 41 has been completed (registered state).

[0063] First, assume that congestion occurs in the AMF 41 (S61). For example, the detection unit 11 included in the AMF 41 may detect the congestion that has occurred in the AMF 41. Alternatively, the detection unit 11 may detect the congestion that has occurred in the AMF 41 by notifying the AMF 41 that congestion has occurred from a monitoring device or the like that monitors the 5GC 40.

[0064] Next, the AMF 41 transmits a Deregistration Request message to the UE 60 via the gNB 51 (S62). The Deregistration Request message is used as a message requesting deregistration of the UE 60 in the AMF 41. The Deregistration Request message includes information for notifying the UE 60 that congestion has occurred in the AMF 41, a GUAMI representing, for example, the AMF 42 as an AMF different from the AMF 41, and information instructing selection of the AMF 42. Alternatively, the AMF 41 may include the GUAMI of each of a plurality of AMFs in which congestion has not occurred in the Deregistration Request message.

[0065] Furthermore, when UE 60 is in a CM (Connection Management)-IDLE state, AMF 41 may perform paging for UE 60 and then transmit a Deregistration Request message to UE 60. The CM-IDLE state is a state in which a NAS (Non Access Stratum) signaling connection is not established between UE 60 and AMF 41.

[0066] The AMF 41 may send a Deregistration Request message to all UEs registered in the AMF 41 or all UEs managed by the AMF 41. Alternatively, the AMF 41 may send a Deregistration Request message to some UEs included in all UEs registered in the AMF 41.

[0067] For example, the AMF 41 may transmit a Deregistration Request message only to a UE that is indicated to be a priority terminal or a UE that is indicated to use a priority service. As a result, the UE that is indicated to be a priority terminal or a UE that is indicated to use a priority service can receive the priority service by performing a registration procedure with an AMF where congestion is not occurring.

[0068] Alternatively, the AMF 41 may send a Deregistration Request message only to UEs that are not priority terminals or that are not indicated to use a priority service. The AMF 41 may resolve the congestion occurring in the AMF 41 by deregistering UEs other than UEs that are not priority terminals. As a result, UEs that are indicated to be priority terminals registered in the AMF 41 or that are indicated to use a priority service can receive the priority service.

[0069] Next, when UE60 receives the Deregistration Request message, it sends a Deregistration Accept message to AMF41 via gNB51 (S63).

[0070] The processes from step S64 to step S68 are the same as steps S46 to S50 in Fig. 6, and therefore detailed description thereof will be omitted. In step S46, UE 60 sets the GUAMI included in the Registration Reject message as the AN parameter, but in step S64, UE 60 sets the GUAMI included in the Deregistration Request message as the AN parameter.

[0071] As described above, in the 5GS according to the third embodiment, if congestion occurs in the AMF 41 after the registration process between the UE 60 and the AMF 41 is completed, the registration of the UE 60 is released. After that, the UE 60 transmits a Registration Request message to perform the registration process again. At this time, the UE 60 transmits to the gNB 51 a message including information for notifying the gNB 51 that congestion has occurred in the AMF 41, the GUAMI notified from the AMF 41, and information instructing the selection of an AMF identified by the GUAMI. This allows the gNB 51 to transmit the Registration Request message received from the UE 60 to the AMF 42 in which congestion is not occurring. As a result, the UE 60 can successfully complete the registration process between the UE 60 and the AMF 42 in which congestion is not occurring.

[0072] 8 has described the process in which the AMF 41 selects the AMF 42. However, as shown in FIG. 9, when congestion occurs in the AMF 41, the NRF 43 may select the AMF 42. Specifically, when the AMF 41 detects the occurrence of congestion in step S61, the AMF 41 transmits a message notifying the NRF 43 of the occurrence of congestion (S71). Next, the NRF 43 transmits a message notifying the AMF 41 of GUAMI representing the AMF 42 as an AMF in which congestion does not occur (S72). Steps S62 to S68 in FIG. 9 are the same as those in FIG. 8, and therefore detailed description thereof will be omitted. When the AMF 41 receives a message from the NRF 43 in step S72, the AMF 41 transmits a Deregistration Request message including the GUAMI notified from the NRF 43 to the UE 60.

[0073] FIG. 10 is a block diagram showing an example configuration of an access network node 20 and a gNB 51 (hereinafter referred to as the access network node 20, etc.). Referring to FIG. 10, the access network node 20, etc. includes an RF transceiver 1001, a network interface 1003, a processor 1004, and a memory 1005. The RF transceiver 1001 performs analog RF signal processing to communicate with UEs. The RF transceiver 1001 may include multiple transceivers. The RF transceiver 1001 is coupled to an antenna 1002 and a processor 1004. The RF transceiver 1001 receives modulation symbol data (or OFDM symbol data) from the processor 1004, generates a transmit RF signal, and provides the transmit RF signal to the antenna 1002. The RF transceiver 1001 also generates a baseband receive signal based on the receive RF signal received by the antenna 1002 and provides it to the processor 1004.

[0074] The network interface 1003 is used to communicate with network nodes (e.g., other core network nodes) and may include, for example, a network interface card (NIC) compliant with the IEEE 802.3 series.

[0075] The processor 1004 performs data plane processing and control plane processing, including digital baseband signal processing for wireless communication.

[0076] The processor 1004 may include multiple processors. For example, the processor 1004 may include a modem processor (e.g., DSP) that performs digital baseband signal processing and a protocol stack processor (e.g., CPU or MPU) that performs control plane processing.

[0077] The memory 1005 is configured by a combination of volatile memory and non-volatile memory. The memory 1005 may include multiple physically independent memory devices. The volatile memory may be, for example, static random access memory (SRAM), dynamic RAM (DRAM), or a combination thereof. The non-volatile memory may be mask read only memory (MROM), electrically erasable programmable ROM (EEPROM), flash memory, a hard disk drive, or any combination thereof. The memory 1005 may include storage located remotely from the processor 1004. In this case, the processor 1004 may access the memory 1005 via the network interface 1003 or an I / O interface (not shown).

[0078] The memory 1005 may store software modules (computer programs) including instructions and data for performing processing by the access network node 20, etc., described in the above-described embodiments. In some implementations, the processor 1004 may be configured to read and execute the software modules from the memory 1005, thereby performing processing by the access network node 20, etc., described in the above-described embodiments.

[0079] FIG. 11 is a block diagram showing an example configuration of a radio terminal 30 and a UE 60 (hereinafter referred to as the radio terminal 30, etc.). A radio frequency (RF) transceiver 1101 performs analog RF signal processing to communicate with an access network node 20 or a gNB 51. The analog RF signal processing performed by the RF transceiver 1101 includes frequency up-conversion, frequency down-conversion, and amplification. The RF transceiver 1101 is coupled to an antenna 1102 and a baseband processor 1103. That is, the RF transceiver 1101 receives modulation symbol data (or OFDM symbol data) from the baseband processor 1103, generates a transmit RF signal, and supplies the transmit RF signal to the antenna 1102. The RF transceiver 1101 also generates a baseband receive signal based on the receive RF signal received by the antenna 1102 and supplies the baseband processor 1103.

[0080] The baseband processor 1103 performs digital baseband signal processing (data plane processing) and control plane processing for wireless communication. Digital baseband signal processing includes (a) data compression / decompression, (b) data segmentation / concatenation, (c) transmission format (transmission frame) generation / decomposition, (d) transmission path coding / decoding, (e) modulation (symbol mapping) / demodulation, and (f) generation of OFDM symbol data (baseband OFDM signal) using Inverse Fast Fourier Transform (IFFT). Meanwhile, control plane processing includes communication management for Layer 1, Layer 2, and Layer 3.

[0081] The baseband processor 1103 may include a modem processor (e.g., a Digital Signal Processor (DSP)) that performs digital baseband signal processing and a protocol stack processor (e.g., a Central Processing Unit (CPU) or a Micro Processing Unit (MPU)) that performs control plane processing. In this case, the protocol stack processor that performs control plane processing may be shared with the application processor 1104, which will be described later.

[0082] The application processor 1104 is also referred to as a CPU, MPU, microprocessor, or processor core. The application processor 1104 may include multiple processors (multiple processor cores). The application processor 1104 executes a system software program (operating system (OS)) and various application programs (e.g., a call application, a web browser, a mailer, a camera operation application, and a music playback application) read from the memory 1106 or a memory not shown, thereby realizing various functions of the wireless terminal 30, etc.

[0083] In some implementations, the baseband processor 1103 and the application processor 1104 may be integrated on a single chip, as indicated by the dashed line (1105) in Figure 11. In other words, the baseband processor 1103 and the application processor 1104 may be implemented as a single System on Chip (SoC) device 1105. An SoC device may also be called a system Large Scale Integration (LSI) or chipset.

[0084] The memory 1106 is volatile memory, nonvolatile memory, or a combination thereof. The memory 1106 may include multiple physically independent memory devices. Volatile memory is, for example, static random access memory (SRAM), dynamic RAM (DRAM), or a combination thereof. Nonvolatile memory is, for example, mask read only memory (MROM), electrically erasable programmable ROM (EEPROM), flash memory, or a hard disk drive, or any combination thereof. For example, the memory 1106 may include an external memory device accessible from the baseband processor 1103, the application processor 1104, and the SoC 1105. The memory 1106 may also include an internal memory device integrated within the baseband processor 1103, the application processor 1104, or the SoC 1105. Furthermore, the memory 1106 may include memory within a Universal Integrated Circuit Card (UICC).

[0085] The memory 1106 may store software modules (computer programs) including instructions and data for performing processing by the wireless terminal 30, etc., described in the above-described embodiments. In some implementations, the baseband processor 1103 or the application processor 1104 may be configured to read and execute the software modules from the memory 1106, thereby performing processing by the wireless terminal 30, etc., described in the above-described embodiments.

[0086] Fig. 12 is a block diagram showing an example configuration of the core network node 10, AMF 41, and AMF 42 (hereinafter referred to as core network node 10, etc.) described in the above embodiment. Referring to Fig. 12, the core network node 10, etc. includes a network interface 1201, a processor 1202, and a memory 1203. The network interface 1201 may be used to communicate with a network node. The network interface 1201 may include, for example, a network interface card (NIC) conforming to the IEEE 802.3 series. IEEE stands for Institute of Electrical and Electronics Engineers.

[0087] The processor 1202 reads and executes software (computer programs) from the memory 1203 to perform the processing of the core network node 10 and the like described using flowcharts in the above-described embodiments. The processor 1202 may be, for example, a microprocessor, an MPU, or a CPU. The processor 1202 may include multiple processors.

[0088] The memory 1203 is configured by a combination of volatile memory and non-volatile memory. The memory 1203 may include storage located remotely from the processor 1202. In this case, the processor 1202 may access the memory 1203 via an I / O (Input / Output) interface (not shown).

[0089] 12, the memory 1203 is used to store software modules. The processor 1202 reads and executes these software modules from the memory 1203, thereby performing the processing of the core network node 10 and the like described in the above-described embodiment.

[0090] As explained using Figure 12, each of the processors possessed by the core network node 10 etc. in the above-mentioned embodiments executes one or more programs including a group of instructions for causing a computer to perform the algorithm explained using the drawings.

[0091] In the above examples, the program includes instructions (or software code) that, when loaded into a computer, cause the computer to perform one or more functions described in the embodiments. The program may be stored on a non-transitory computer-readable medium or a tangible storage medium. By way of example and not limitation, computer-readable medium or tangible storage medium includes random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drive (SSD) or other memory technology, CD-ROM, digital versatile disc (DVD), Blu-ray disc or other optical disk storage, magnetic cassette, magnetic tape, magnetic disk storage or other magnetic storage device. The program may also be transmitted on a transitory computer-readable medium or communication medium. By way of example and not limitation, transitory computer-readable medium or communication medium includes electrical, optical, acoustic, or other forms of propagated signals.

[0092] The technical ideas of the present disclosure are not limited to the above-described embodiments, and can be modified as appropriate within the scope of the gist of the present disclosure.

[0093] Some or all of the above embodiments can be described as, but are not limited to, the following supplementary notes. (Supplementary Note 1) A first core network node comprising: a detection unit that detects congestion that has occurred in the first core network node; and a communication unit that, when congestion has occurred in the first core network node, transmits a message to a radio terminal, the message including identification information of a second core network node and indicating the occurrence of congestion, the message instructing the selection of the second core network node. (Supplementary Note 2) The first core network node according to Supplementary Note 1, wherein the message includes information elements that indicate the occurrence of congestion and instruct the selection of the second core network node. (Supplementary Note 3) The first core network node according to Supplementary Note 1, wherein the message includes a first information element that indicates the occurrence of congestion and a second information element that instructs the selection of the second core network node. (Supplementary Note 4) The first core network node according to any one of Supplementary Notes 1 to 3, wherein, when receiving from the radio terminal a registration request message requesting registration with the first core network node after congestion has occurred in the first core network node, the communication unit transmits to the radio terminal a response message indicating that congestion has occurred, the response message including the identification information of the second core network node, the response message instructing selection of the second core network node. (Supplementary Note 5) The first core network node according to Supplementary Note 4, wherein the communication unit transmits to the radio terminal, as the response message, a rejection message rejecting registration of the radio terminal. (Supplementary Note 6) The first core network node according to any one of Supplementary Notes 1 to 5, wherein the communication unit, when congestion occurs in the first core network node after the radio terminal is registered in the first core network node, transmits a release request message to the radio terminal, the release request message including the identification information of the second core network node and indicating that congestion has occurred, to request deregistration of the radio terminal, the release request message instructing selection of the second core network node.(Supplementary Note 7) The first core network node according to any one of Supplements 1 to 6, wherein the communication unit transmits the message including the identification information of the second core network node in which congestion is not occurring to the radio terminal. (Supplementary Note 8) The first core network node according to any one of Supplements 1 to 7, wherein the communication unit includes the identification information of the second core network node notified from a management node that manages the core network node in the message. (Supplementary Note 9) The first core network node according to Supplementary Note 8, wherein the communication unit transmits a notification message to the management node including information indicating that congestion has occurred in the first core network node, and receives the identification information of the second core network node included in a response message to the notification message. (Supplementary Note 10) The core network node according to any one of Supplements 1 to 9, wherein the communication unit transmits a message to the radio terminal that transmits a call of which processing is prioritized, the message including the identification information of the second core network node, indicating that congestion has occurred, and instructing the radio terminal to select the second core network node. (Supplementary Note 11) The first core network node according to any one of Supplementary Notes 1 to 9, wherein the communication unit transmits a message to the radio terminal other than a radio terminal transmitting a call whose processing is prioritized, the message including the identification information of the second core network node, indicating that congestion has occurred, and instructing to select the second core network node. (Supplementary Note 12) An access network node comprising: a communication unit that receives, from a radio terminal, a message indicating that congestion has occurred in the first core network node and instructing to select a second core network node different from the first core network node, the message including identification information of the second core network node, and a selection unit that selects, based on the identification information, the second core network node identified by the identification information, as a transmission destination of a registration request message included in the message, wherein the communication unit transmits the registration request message to the second core network node.(Supplementary Note 13) The access network node according to Supplementary Note 12, wherein the selection unit selects a destination of the registration request message from the second core network node or a core network node different from the second core network node if the message does not indicate that congestion has occurred in the first core network node, and selects the second core network node as a destination of the registration request message if the message indicates that congestion has occurred in the first core network node. (Supplementary Note 14) A radio terminal comprising: a receiving unit that receives, from a first core network node in which congestion has occurred, a first message indicating that congestion has occurred in the first core network node and instructing selection of a second core network node different from the first core network node; the first message including identification information of the second core network node; and a transmitting unit that notifies an access network node that congestion has occurred in the first core network node and instructs the access network node to select the second core network node, the second message including identification information of the second core network node. (Supplementary Note 15) The wireless terminal according to Supplementary Note 14, wherein the receiving unit receives, as the first message, a rejection message rejecting a registration request message, the rejection message notifying an access network node that congestion has occurred in the first core network node, the rejection message instructing selection of the second core network node, the rejection message including the identification information of the second core network node, and the transmitting unit, after receiving the rejection message, transmits to the access network node the second message further including a registration request message requesting registration with the second core network node.16. The radio terminal according to Supplementary Note 14 or 15, wherein the receiving unit receives, as the second message, a release request message for requesting deregistration of the radio terminal, the release request message notifying an access network node that congestion has occurred in the first core network node, the release request message instructing selection of the second core network node, the release request message including the identification information of the second core network node, and the transmitting unit, after receiving the release request message, transmits to the access network node the second message, further including a registration request message requesting registration with the second core network node. (Supplementary Note 17) A communication method executed in a first core network node, comprising: detecting congestion that has occurred in the first core network node; and, when congestion has occurred in the first core network node, transmitting a message indicating the occurrence of congestion, including identification information of a second core network node, to the radio terminal, the message instructing selection of the second core network node. (Supplementary note 18) The communication method according to Supplementary note 17, wherein the message includes an information element indicating that congestion has occurred and instructing selection of the second core network node. (Supplementary note 19) The communication method according to Supplementary note 17, wherein the message includes a first information element indicating that congestion has occurred and a second information element instructing selection of the second core network node. (Supplementary note 20) The communication method according to Supplementary note 17, wherein, when a registration request message requesting registration with the first core network node is received from the radio terminal after congestion has occurred in the first core network node, a response message indicating that congestion has occurred is transmitted to the radio terminal, the response message including the identification information of the second core network node, and instructs selection of the second core network node. (Supplementary note 21) The communication method according to Supplementary note 20, wherein a rejection message rejecting registration of the radio terminal is transmitted to the radio terminal as the response message.(Supplementary note 22) The communication method according to any one of Supplements 17 to 21, wherein, when congestion occurs in the first core network node after the radio terminal is registered in the first core network node, a release request message indicating that congestion has occurred is transmitted to the radio terminal, including the identification information of the second core network node, to request deregistration of the radio terminal, the release request message instructing selection of the second core network node. (Supplementary note 23) The communication method according to any one of Supplements 17 to 22, wherein the message including the identification information of the second core network node in which congestion is not occurring is transmitted to the radio terminal. (Supplementary note 24) The communication method according to any one of Supplements 17 to 23, wherein the identification information of the second core network node notified by a management node that manages the core network node is included in the message. (Supplementary note 25) The communication method according to Supplementary note 24, comprising transmitting a notification message including information indicating that congestion has occurred in the first core network node to the management node, and receiving the identification information of the second core network node included in a response message to the notification message. (Supplementary note 26) The communication method according to any one of Supplements 17 to 25, comprising transmitting, to the radio terminal transmitting a call of prioritized processing, a message including the identification information of the second core network node, indicating that congestion has occurred, and instructing selection of the second core network node. (Supplementary note 27) The communication method according to any one of Supplements 17 to 25, comprising transmitting, to the radio terminal other than the radio terminal transmitting a call of prioritized processing, a message including the identification information of the second core network node, indicating that congestion has occurred, and instructing selection of the second core network node.(Supplementary Note 28) A communication method executed in an access network node, comprising: receiving from a radio terminal a message indicating that congestion has occurred in a first core network node and instructing selection of a second core network node different from the first core network node, the message including identification information of the second core network node; selecting, based on the identification information, the second core network node identified by the identification information as a destination of a registration request message included in the message; and transmitting the registration request message to the second core network node. (Supplementary Note 29) The communication method according to Supplementary Note 28, wherein, when selecting a destination of the registration request message, if the message does not indicate that congestion has occurred in the first core network node, selecting a destination of the registration request message from the second core network node or a core network node different from the second core network node; and if the message indicates that congestion has occurred in the first core network node, selecting the second core network node as a destination of the registration request message. (Supplementary Note 30) A communication method executed in a radio terminal, comprising: receiving, from a first core network node in which congestion has occurred, a first message indicating that congestion has occurred in the first core network node and instructing selection of a second core network node different from the first core network node, the first message including identification information of the second core network node; and transmitting, to an access network node, a second message notifying the access network node that congestion has occurred in the first core network node and instructing selection of the second core network node, the second message including identification information of the second core network node.(Supplementary Note 31) The communication method according to Supplementary Note 30, comprising receiving, as the first message, a rejection message rejecting a registration request message, the rejection message notifying an access network node that congestion has occurred in the first core network node, the rejection message instructing selection of the second core network node, the rejection message including the identification information of the second core network node, and after receiving the rejection message, transmitting to the access network node the second message further including a registration request message requesting registration with the second core network node. (Supplementary Note 32) The communication method according to Supplementary Note 30 or 31, comprising receiving, as the second message, a release request message for requesting deregistration of the radio terminal, the release request message notifying an access network node that congestion has occurred in the first core network node, the release request message instructing selection of the second core network node, the release request message including the identification information of the second core network node, and, after receiving the release request message, transmitting to the access network node the second message, further including a registration request message requesting registration with the second core network node. (Supplementary Note 33) A program executed by a computer that is a first core network node, the program causing the computer that is a core network node to detect congestion that has occurred in the first core network node, and, when congestion has occurred in the first core network node, transmitting to the radio terminal a message instructing selection of a second core network node, the message including identification information of the second core network node, and indicating that congestion has occurred.(Supplementary Note 34) A program executed by a computer that is an access network node, the program receiving from a wireless terminal a message indicating that congestion has occurred in a first core network node and instructing the selection of a second core network node different from the first core network node, the message including identification information of the second core network node, and selecting, based on the identification information, the second core network node identified by the identification information as a destination of a registration request message included in the message, and transmitting the registration request message to the second core network node. (Supplementary Note 35) A program to be executed by a computer that is a wireless terminal, the program comprising: receiving, from a first core network node in which congestion has occurred, a first message indicating that congestion has occurred in the first core network node and instructing the selection of a second core network node different from the first core network node, the first message including identification information of the second core network node; and transmitting, to the access network node, a second message notifying an access network node that congestion has occurred in the first core network node and instructing the selection of the second core network node, the second message including identification information of the second core network node.

[0094] The technical ideas described in this disclosure are not limited to the above-described embodiments, and can be modified as appropriate within the scope of the invention.

[0095] Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the invention.

[0096] This application claims priority based on Japanese Patent Application No. 2022-093490, filed on June 9, 2022, the disclosure of which is incorporated herein in its entirety.

[0097] 10 Core network node 11 Detection unit 12 Communication unit 20 Access network node 21 Communication unit 22 Identification unit 30 Radio terminal 31 Reception unit 32 Transmission unit 40 5GC 41 AMF 42 AMF 43 NRF 50 RAN 51 gNB 60 UE

Claims

1. A first core network node, A detection means for detecting congestion occurring in the first core network node; and a communication means for transmitting, when congestion occurs in the first core network node, a message indicating that congestion has occurred, including identification information of a second core network node different from the first core network node, to a radio terminal via an access core network node. A first core network node.

2. The message further includes an information element indicating selection of the second core network node. A first core network node according to claim 1 .

3. The communication means includes:

3. The core network node according to claim 1, further comprising: a first core network node that is connected to the first core network node and that is connected to the second core network node; a second core network node that is connected to the first core network node and that is connected to the second core network node;

4. The communication means includes:

3. The first core network node according to claim 1 or 2, which transmits a message including the identification information of the second core network node, indicating that congestion has occurred, and instructing the selection of the second core network node to a wireless terminal other than a wireless terminal transmitting a call for which processing is prioritized.

5. An access network node, a receiving means for receiving, from a wireless terminal, a message indicating that congestion has occurred in a first core network node, the message including identification information of a second core network node different from the first core network node; a selection means for selecting the second core network node identified by the identification information as a destination of the registration request message when the message includes a registration request message; sending means for sending the registration request message to the second core network node.

6. A wireless terminal, receiving means for receiving a first message from a first core network node via an access network node, the first message indicating that congestion has occurred in the first core network node and including identification information of a second core network node different from the first core network node; sending means for sending a second message to the access network node indicating that congestion has occurred at the first core network node and including an identity of the second core network node; the second message includes a registration request message of the wireless terminal; Wireless terminal.

7. A communication method performed in a first core network node, comprising: Detecting congestion occurring in the first core network node; A communication method executed in a first core network node, when congestion occurs in the first core network node, transmitting a message indicating that congestion has occurred, including identification information of a second core network node different from the first core network node, to a wireless terminal via an access core network node.

8. The method of claim 7 , wherein the message further includes an information element indicating selection of the second core network node.

9. 9. The communication method according to claim 7 or 8, further comprising transmitting a message to the wireless terminal that transmits a call for which processing is prioritized, the message including the identification information of the second core network node, indicating that congestion has occurred, and instructing the selection of the second core network node.

10. 9. The communication method according to claim 7 or 8, further comprising transmitting a message including the identification information of the second core network node, indicating that congestion has occurred, and instructing the selection of the second core network node to a wireless terminal other than the wireless terminal transmitting a call for which processing is prioritized.

11. 1. A communication method performed in an access network node, comprising: receiving a message from a wireless terminal indicating that congestion has occurred in a first core network node and including identification information of a second core network node different from the first core network node; If the message includes a registration request message, selecting the second core network node identified by the identification information as a destination of the registration request message; A communications method performed in an access network node, the method comprising: transmitting the registration request message to the second core network node.

12. The message further includes an information element indicating selection of the second core network node, The method of claim 11, further comprising: transmitting the registration request message to the second core network node according to an information element indicating the selection.

13. 1. A communication method implemented in a wireless terminal, comprising: receiving a first message from a first core network node via an access network node, the first message indicating that congestion has occurred at the first core network node and including identification information of a second core network node different from the first core network node; sending a second message to the access network node indicating that congestion has occurred at the first core network node and including an identity of the second core network node; A method of communications performed in a wireless terminal, wherein the second message comprises a registration request message of the wireless terminal.

14. The communication method described in Claim 13, wherein the second message further includes an information element indicating selection of the second core network node.