Access Network Nodes and Control Nodes

Abstract

An access network node (12) receives a non-access stratum (NAS) message transmitted from user equipment (UE) (31) in association with a first public land mobile network (PLMN) (10). When none of the control nodes belonging to a core network (15) of the first PLMN (10) are selectable or available, the access network node (12) forwards the NAS message to a donor control node belonging to a core network (25) of a second PLMN (20). This allows, for example, a core network node belonging to a PLMN different from a PLMN selected by UE to process a NAS message on behalf thereof.

Description

[Technical Field]

[0001] The present disclosure relates to wireless communication networks. [Background technology]

[0002] Non-Patent Document 1 (NPL 1) provides key issues and solutions for supporting Minimization of Service Interruption (MINT) in 5G systems. Some solutions relate to Radio Access Network (RAN) sharing. For example, in Solution #10 shown in Chapter 6.10 of Non-Patent Document 2, when a disaster condition applies, a RAN node of a Public Land Mobile Network (PLMN) without a disaster condition becomes a RAN node shared between the PLMN without a disaster condition and the PLMN with a disaster condition. In this case, User Equipment (UEs) that were previously served by the PLMN with a disaster condition can register with the same PLMN (i.e., the PLMN with a disaster condition) through the shared RAN.

[0003] Some other solutions disclosed in Non-Patent Document 1 relate to registration procedures to PLMNs without disaster conditions for disaster roaming. Non-Patent Document 2 (e.g., Chapter 5.40), Non-Patent Document 3 (e.g., Chapter 4.2.2.2), and Non-Patent Document 4 (e.g., Chapters 3.1 and 3.10) also include the following disclosures related to disaster roaming registration:

[0004] A UE that supports MINT can be configured with the activation of disaster roaming and a list of PLMNs to be used in disaster conditions. Activation of disaster roaming is also referred to as an indication of whether disaster roaming is enabled in the UE.

[0005] Activation of disaster roaming is provided or performed by the UE's Home PLMN, and may be pre-configured in the Universal Subscriber Identity Module (USIM).

[0006] The list of PLMN(s) to be used in the disaster condition may be preconfigured in the USIM, or may be provided to the UE by the HPLMN or registered PLMN (RPLMN) during or after a successful registration procedure.

[0007] A Next Generation RAN (NG-RAN) of a PLMN that offers or provides disaster roaming service broadcasts an indication of accessibility for Disaster Roaming service. Additionally, the NG-RAN that offers disaster roaming service may broadcast a list of one or more PLMN(s) with disaster condition for which disaster roaming is offered by the available PLMN.

[0008] The UE determines a PLMN with disaster condition as follows: If the UE's RPLMN is included in the list of one or more PLMN(s) with disaster condition for which disaster roaming is offered by the available PLMNs broadcast by any NG-RAN cell, the UE determines that the RPLMN is a PLMN with disaster condition. Otherwise, if the HPLMN, the highest priority Equivalent HPLMN (EHPLMN), each PLMN included in the "User Controlled PLMN Selector with Access Technology" data file in the USIM, each PLMN included in the "Operator Controlled PLMN Selector with Access Technology" data file in the USIM, or other PLMNs are included in the list of one or more PLMN(s) with disaster condition for which disaster roaming is offered by the available PLMNs broadcast by any NG-RAN cell, the UE determines that PLMN is a PLMN with disaster condition.

[0009] A UE can only attempt disaster roaming (or select a PLMN for disaster roaming) if: - There is no authorized PLMN available; - Activation of disaster roaming is set in the UE; - The UE is not registered via a non-3GPP access connected to a 5G Core network (CN); - The PLMNs included in the list of PLMN(s) to be used in disaster condition associated with the determined PLMN with disaster condition are capable of accepting disaster inbound roamers from the determined PLMN with Disaster Condition.

[0010] If an NG-RAN cell in a PLMN without Disaster Condition broadcasts disaster-related information, the UE may select the PLMN without Disaster Condition for a disaster roaming attempt. Alternatively, if an NG-RAN cell in a PLMN without Disaster Condition broadcasts a list of one or more PLMN(s) with disaster condition for which disaster roaming is offered by the available PLMN, and the list includes the determined PLMN with disaster condition, the UE may select the PLMN without Disaster Condition for a disaster roaming attempt. [Prior art documents] [Non-patent literature]

[0011] [Non-Patent Document 1] 3GPP TR 24.811 V17.1.0 (2021-09) "3rd Generation Partnership Project; Technical Specification Group Core Network and Terminals; Study on the support for minimization of service interruption; (Release 17)", September 2021 [Non-patent document 2] 3GPP TS 23.501 V17.3.0 (2021-12) "3rd Generation Partnership Project; Technical Specification Group Services and System Aspects; System architecture for the 5G System (5GS); Stage 2 (Release 17)", December 2021 [Non-patent document 3] 3GPP TS 23.502 V17.3.0 (2021-12) "3rd Generation Partnership Project; Technical Specification Group Services and System Aspects; Procedures for the 5G System (5GS); Stage 2 (Release 17)", December 2021 [Non-patent document 4] 3GPP TS 23.122 V17.5.0 (2021-12) "3rd Generation Partnership Project; Technical Specification Group Core Network and Terminals; Non-Access-Stratum (NAS) functions related to Mobile Station (MS) in idle mode (Release 17)", December 2021 Summary of the Invention [Problem to be solved by the invention]

[0012] The inventors have studied MINT, disaster roaming, and similar technologies and found various problems. One problem relates to the selection of a core network node (e.g., Access and Mobility Management Function (AMF)) by a RAN node. When a RAN node receives an initial Non-Access Stratum (NAS) message (e.g., Registration Request, Service Request) from a UE, it selects a core network node (e.g., AMF) belonging to a PLMN selected by the UE according to a predetermined rule and forwards the NAS message to the selected AMF. However, due to a natural or man-made disaster, for example, the RAN node may be unable to select or use any core network node belonging to the PLMN selected by the UE. In this case, if a core network node belonging to a PLMN different from the PLMN selected by the UE can process the NAS message instead, this could contribute to improving service continuity for the UE. Another advantage of this is that it does not necessarily require the UE to support new technologies such as MINT and disaster roaming. However, current selection methods cannot achieve this.

[0013] Another challenge relates to the use of network slices in disaster roaming. Specifically, it is unclear how disaster roamer UEs in a PLMN without a disaster condition (or a PLMN offering disaster roaming) know which network slices are available to them in order to attempt disaster roaming.

[0014] Yet another problem relates to improving disaster roaming procedures. For example, when a core network node (e.g., AMF) of a PLMN that provides disaster roaming receives a disaster roaming registration request from a UE, the core network node may need to access a subscriber server or database (e.g., Unified Data Management (UDM)) of the UE's HPLMN to obtain the UE's subscription data. However, there may be a case where there is no roaming agreement between the PLMN that provides disaster roaming and the HPLMN. In such a case, the HPLMN's UDM may reject the request from the core network node of the PLMN that provides disaster roaming. It is preferable to be able to avoid such a situation.

[0015] One of the objectives that the embodiments disclosed herein aim to achieve is to provide an apparatus, a method, and a program that contribute to solving at least one of the problems described above. It should be noted that this objective is only one of the objectives that the embodiments disclosed in this specification aim to achieve. Other objectives or objectives and novel features will become apparent from the description of this specification or the accompanying drawings. [Means for solving the problem]

[0016] In a first aspect, an access network node includes a first communication interface, a second communication interface, and at least one processor. The first communication interface is configured to communicate with a plurality of UEs via a cell. The second communication interface is configured to connect to a first core network of a first PLMN and to connect to a second core network of a second PLMN different from the first PLMN. The at least one processor is configured to receive a Non-Access Stratum message associated with the first PLMN from a UE, and forward the Non-Access Stratum message to a donor control node in the second core network of the second PLMN if no control node in the first core network of the first PLMN is selectable or unavailable.

[0017] In a second aspect, a method performed by an access network node comprises the following steps: (a) connecting to a first core network of a first PLMN and connecting to a second core network of a second PLMN different from the first PLMN; (b) receiving a Non-Access Stratum message associated with the first PLMN and transmitted from the UE; and (c) if no control node belonging to the first core network of the first PLMN can be selected or is unavailable, forwarding the Non-Access Stratum message to a donor control node belonging to the second core network of the second PLMN.

[0018] In a third aspect, a control node used in a core network of a first PLMN includes a communications interface and at least one processor. The communications interface is configured to be coupled to an access network node. The at least one processor is configured to send a control message to the access network node specifying a donor control node belonging to a core network of a second PLMN different from a first PLMN to which the control node belongs. The control message causes the access network node to forward a Non-Access Stratum message associated with the first PLMN sent from a UE to the donor control node of the second PLMN if no control node belonging to the core network of the first PLMN is selectable or unavailable.

[0019] In a fourth aspect, a method performed by a control node used in a core network of a first PLMN includes sending a control message to an access network node specifying a donor control node belonging to a core network of a second PLMN different from the first PLMN to which the control node belongs, the control message causing the access network node to forward a Non-Access Stratum message associated with the first PLMN sent from a UE to the donor control node of the second PLMN if no control node belonging to the core network of the first PLMN is selectable or unavailable.

[0020] In a fifth aspect, a UE includes at least one memory and at least one processor coupled to the at least one memory. The at least one processor is configured to store in the at least one memory a list of one or more PLMNs to be used during a disaster condition. The at least one processor is configured to store in the at least one memory a list of one or more disaster roaming network slice identifiers associated with each PLMN included in the list of one or more PLMNs. The at least one processor is configured to select a disaster roaming PLMN from the list of one or more PLMNs. The at least one processor is configured to select at least one disaster roaming network slice identifier from the list of one or more disaster roaming network slice identifiers associated with the selected disaster roaming PLMN. The at least one processor is configured to transmit a registration request message toward a core network of the selected disaster roaming PLMN, indicating the selected disaster roaming PLMN and the selected disaster roaming network slice identifier.

[0021] In a sixth aspect, a method performed by a UE includes the following steps: (a) storing a list of one or more PLMNs to be used in disaster conditions; (b) storing a list of one or more disaster roaming network slice identifiers associated with each PLMN included in the list of one or more PLMNs; (c) selecting a disaster roaming PLMN from said list of one or more PLMNs; (d) selecting at least one disaster roaming network slice identifier from the list of one or more disaster roaming network slice identifiers associated with the selected disaster roaming PLMN; and (e) Sending a registration request message indicating the selected disaster roaming PLMN and the selected disaster roaming network slice identifier toward the core network of the selected disaster roaming PLMN.

[0022] In a seventh aspect, a core network node of a HPLMN of a UE or an RPLMN to which the UE is registered includes at least one memory and at least one processor coupled to the at least one memory, wherein the at least one processor is configured to provide the UE with a first list of one or more PLMNs to be used during a disaster condition, and further configured to provide the UE with a second list of one or more disaster roaming network slice identifiers associated with each PLMN included in the list of one or more PLMNs.

[0023] In an eighth aspect, a method performed by a core network node of a HPLMN of a UE or a RPLMN to which the UE is registered comprises the following steps: (a) providing the UE with a first list of one or more PLMNs to be used during a disaster condition; and (b) providing the UE with a second list of one or more disaster roaming network slice identifiers associated with each PLMN included in the list of one or more PLMNs;

[0024] In a ninth aspect, an access network node of a PLMN that provides disaster roaming includes at least one memory and at least one processor coupled to the at least one memory, wherein the at least one processor is configured to broadcast disaster-related information in a cell indicating that disaster roaming is offered, the disaster-related information including a list of one or more network slice identifiers for disaster roaming.

[0025] In a tenth aspect, a method performed by an access network node of a PLMN providing disaster roaming includes broadcasting disaster-related information in a cell indicating that disaster roaming is offered, the disaster-related information including a list of one or more disaster roaming network slice identifiers.

[0026] In an eleventh aspect, a core network node of a PLMN that provides disaster roaming includes at least one memory and at least one processor coupled to the at least one memory, wherein the at least one processor is configured to receive a registration request from a UE and, if the registration request indicates disaster roaming, include an indication of the disaster roaming in a message sent to a control node located in a Home PLMN of the UE and that manages subscriber information of the UE.

[0027] In a twelfth aspect, a method performed by a core network node of a PLMN that provides disaster roaming includes receiving a registration request from a UE, and if the registration request indicates disaster roaming, including an indication of disaster roaming in a message sent to a control node located in a Home PLMN of the UE and managing subscriber information of the UE.

[0028] In a thirteenth aspect, a program comprises a set of instructions (software code) that, when loaded into a computer, causes the computer to perform the method according to the second, fourth, sixth, eighth, tenth or twelfth aspect above. [Effects of the Invention]

[0029] According to the above-described aspects, it is possible to provide an apparatus, a method, and a program that contribute to solving at least one of the above-described problems. [Brief explanation of the drawings]

[0030] [Figure 1] 1 is a diagram illustrating an example of the configuration of a network system according to an embodiment; [Figure 2]10 is a flowchart illustrating an example of an operation of a RAN node according to an embodiment. [Figure 3] FIG. 10 is a sequence diagram illustrating an example of the operation of a RAN node and a core network node according to the embodiment. [Figure 4] FIG. 10 is a sequence diagram illustrating an example of the operation of a RAN node and a core network node according to the embodiment. [Figure 5] 1 is a diagram illustrating an example of the configuration of a network system according to an embodiment; [Figure 6] 10 is a flowchart illustrating an example of an operation of a UE according to the embodiment. [Figure 7] 10 is a flowchart illustrating an example of an operation of a UE according to the embodiment. [Figure 8] FIG. 10 is a diagram illustrating an example of signaling related to disaster roaming according to an embodiment. [Figure 9] FIG. 10 is a diagram illustrating an example of signaling related to disaster roaming according to an embodiment. [Figure 10] FIG. 10 is a diagram illustrating an example of signaling related to disaster roaming according to an embodiment. [Figure 11] FIG. 1 is a diagram illustrating a configuration example of a RAN node according to an embodiment. [Figure 12] FIG. 1 is a diagram illustrating a configuration example of a core network node according to an embodiment. [Figure 13] FIG. 2 is a diagram illustrating an example of the configuration of a UE according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0031] Hereinafter, specific embodiments will be described in detail with reference to the drawings. In each drawing, the same or corresponding elements are designated by the same reference numerals, and for clarity of explanation, duplicate explanations will be omitted as necessary.

[0032] The multiple embodiments described below can be implemented independently or in appropriate combination. These multiple embodiments have different novel features. Therefore, these multiple embodiments contribute to solving different purposes or problems and to achieving different effects.

[0033] The following embodiments will be described primarily with respect to 3GPP (registered trademark) LTE and 5G systems. However, these embodiments may be applied to other network systems. For example, these embodiments may be applied to other network systems that support technologies similar to 3GPP MINT and disaster roaming. Note that, unless otherwise specified, the term LTE used in this specification includes improvements and developments of LTE and LTE-Advanced to enable interworking with 5G systems.

[0034] As used herein, depending on the context, "if" may be construed to mean "when," "at or around the time," "after," "upon," "in response to determining," "in accordance with a determination," or "in response to detecting." These expressions may be construed to have the same meaning, depending on the context.

[0035] First Embodiment Fig. 1 shows an example of the configuration of a network system according to this embodiment. Each of the elements shown in Fig. 1 is a network function, and provides an interface defined by, for example, 3GPP. Each element (network function) shown in Fig. 1 can be implemented, for example, as a network element on dedicated hardware, as a software instance running on dedicated hardware, or as a virtualized function instantiated on an application platform.

[0036] 1 includes a RAN 11 and a core network 15. The RAN 11 may be a Next Generation Radio Access Network (NG-RAN), an Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (E-UTRAN), or a radio access network in another network system, or any combination thereof. The core network 15 may be a 5G Core (5GC), an Evolved Packet Core (EPC), or a core network in another network system, or any combination thereof.

[0037] The RAN 11 includes one or more RAN nodes 12. The one or more RAN nodes 12 may be one or both of gNBs and eNBs. The core network 15 includes one or more core network nodes. These core network nodes include one or more control plane nodes and one or more user plane (or data plane) nodes. In a 5G system, the control plane nodes include an Access and Mobility Management Function (AMF), a Session Management Function (SMF), and other nodes (e.g., Unified Data Management (UDM) and Policy Control Function (PCF)), and the user plane nodes include a User Plane Function (UPF). In an LTE system, the control plane nodes include a Mobility Management Entity (MME) and other nodes (e.g., a Home Subscriber Server (HSS) and Policy and Charging Rules Function (PCRF)), and the user plane nodes include a Serving Gateway (S-GW) and a Packet Data Network Gateway (P-GW).

[0038] As shown in FIG. 1 , the core network 15 is provided by a first PLMN 10. By way of example and not limitation, the RAN 11 may also be provided by the first PLMN 10. However, the RAN 11 may be provided by a different operator (e.g., a RAN operator) than either the first PLMN 10 or the second PLMN 20 (described below). For example, the core network 15 of the first PLMN 10 may be provided by a (full) Mobile Virtual Network Operator (MVNO) and utilize a RAN 11 operated by another operator. In the example of FIG. 1 , the PLMN identity (ID) of the first PLMN 10 is “A.” One or more RAN nodes 12 of the RAN 11 broadcast system information in a cell, including a set or list of one or more PLMNs. The PLMN list indicates the PLMNs available in the cell. In the example of FIG. 1 , the PLMN list broadcast by the RAN node 12 includes at least PLMN ID “A.” The list does not need to include PLMN ID "B" of the second PLMN 20 described below.

[0039] The UE 31 is capable of using the first PLMN 10. The Home PLMN (HPLMN) or Equivalent HPLMN (EHPLMN) of the UE 31 may be the first PLMN 10. Alternatively, the HPLMN of the UE 31 may be another PLMN that has a roaming agreement with the first PLMN 10. The UE 31 may be a UE that is permitted to register as an inbound roamer with the first PLMN 10. The UE 31 does not need to have an explicit roaming agreement with the second PLMN 20, which will be described later. There may be multiple UEs 31.

[0040] FIG. 2 illustrates an example of the operation of a RAN node 12.

[0041] In step 201, the RAN node 12 receives an NAS message associated with the first PLMN 10 transmitted from the UE 31. The NAS message may be, for example, a Registration Request message. The NAS message may be associated with the first PLMN 10 or PLMN ID "A" by being included in a Radio Resource Control (RRC) message together with PLMN ID "A". Specifically, the RAN node 12 receives an RRC message, for example, an RRC Setup Complete message, from the UE 31, that includes the NAS message. The RRC Setup Complete message may include the PLMN ID "A" or another identifier, for example, a Globally Unique AMF ID (GUAMI), that includes the PLMN ID "A".

[0042] If a control node (e.g., AMF) belonging to the core network 15 of the first PLMN 10 is selected according to a predetermined rule, the RAN node 12 forwards the NAS message to the selected control node. On the other hand, if no control node belonging to the core network 15 of the first PLMN 10 can be selected or is unavailable, as shown in step 202, the RAN node 12 forwards the NAS message to a donor control node (e.g., donor AMF) belonging to the core network 25 of the second PLMN 20. The term "donor control node" is an example, and other names may be used.

[0043] For example, the donor control node may recognize that the received NAS message requests registration with a first PLMN 10 different from the second PLMN 20, but may not reject the NAS message and may treat the UE 31 as if it were an inbound roamer to the second PLMN 20. The core network 25 of the second PLMN 20, including the donor control node, may provide home routed roaming for the UE 31. In other words, the donor control node of the core network 25 may exchange signaling with the RAN 11 and the core network 15 directly or via other network functions to establish a user plane connection via the RAN 11, a user plane node in the core network 25 of the second PLMN 20, and an (anchor) user plane node in the core network 15 of the first PLMN 10. The user plane connection may be a Protocol Data Unit (PDU) Session or an Evolved Packet System (EPS) bearer. Alternatively, the core network 25 may provide local breakout roaming to the UE 31. In other words, the donor control node of the core network 25 may exchange signaling with the RAN 11 and the core network 15 directly or via other network functions to establish a user plane connection via the RAN 11 and an (anchor) user plane node of the core network 25 of the second PLMN 20. The donor control node may do so based on an agreement between the operator of the second PLMN 20 and the operator of the first PLMN 10.

[0044] The following describes a procedure for configuring a donor control node in a RAN node 12. In some implementations, the RAN node 12 may receive a control message from a control node (e.g., AMF) belonging to the core network 15 of the first PLMN 10, specifying a donor control node belonging to the core network 25 of the second PLMN 20. The RAN node 12 may receive the above control message in a procedure for setting up or updating configuration data necessary for the RAN node 12 to interoperate with a control node belonging to the core network 15. In the case of a 5G system, this procedure may be an NG Setup procedure, a RAN Configuration Update procedure, or an AMF Configuration Update procedure.

[0045] In the example of FIG. 3 , the RAN node 12 sends an NG SETUP message or a RAN CONFIGURATION UPDATE message to the AMF 16, which is the control node of the first PLMN 10 (step 301). The AMF 16 responds to the RAN node 12 with an NG SETUP RESPONSE message or a RAN CONFIGURATION UPDATE ACKNOWLEDGE message (step 302). The NG SETUP RESPONSE message or the RAN CONFIGURATION UPDATE ACKNOWLEDGE message includes donor AMF information. The donor AMF information specifies a donor control node (i.e., donor AMF) belonging to the core network 25 of the second PLMN 20. The donor AMF information may include a name of the donor AMF (e.g., AMF Name). The AMF Name uniquely identifies the AMF. The AMF Name may be used as a human readable name. Additionally or alternatively, the donor AMF information may include an identifier of the donor AMF (e.g., GUAMI). If multiple donor AMFs exist, the AMF 16 may provide a list of the multiple donor AMFs to the RAN node 12. In other words, if multiple donor AMFs exist, the donor AMF information may include a list of the multiple donor AMFs.

[0046] In the example of Figure 4, the RAN node 12 receives an AMF CONFIGURATION UPDATE message from the AMF 16 of the first PLMN 10 (step 401). The AMF CONFIGURATION UPDATE message of step 401 includes donor AMF information. The donor AMF information specifies a donor control node (i.e., donor AMF) belonging to the core network 25 of the second PLMN 20. The donor AMF information may include one or both of a name (e.g., AMF Name) and an identifier (e.g., GUAMI) of the donor AMF. If multiple donor AMFs exist, the donor AMF information may include a list of the multiple donor AMFs. The RAN node 12 responds to the AMF 16 with an AMF CONFIGURATION UPDATE ACKNOWLEDGE message (step 402).

[0047] In other implementations, the RAN node 12 may receive a control message from a control node (e.g., the donor control node itself) belonging to the core network 25 of the second PLMN 20 indicating that a particular control node belonging to the core network 25 of the second PLMN 20 will act as a donor control node for the first PLMN 10. The RAN node 12 may receive the above control message in a procedure for setting up or updating configuration data necessary for the RAN node 12 to interoperate with a control node belonging to the core network 25. In the case of a 5G system, this procedure may be an NG Setup procedure, a RAN Configuration Update procedure, or an AMF Configuration Update procedure.

[0048] A control node (e.g., a donor control node) belonging to the core network 25 may notify the RAN node 12 of a Donor indicator indicating that the control node itself can operate as a donor AMF, and information about a corresponding PLMN that can operate as a Donor or a list of corresponding PLMNs that can operate as Donors. In the case of a 5G system, the notification may be set in an NG SETUP RESPONSE message, a RAN CONFIGURATION UPDATE ACKNOWLEDGE message, or an AMF CONFIGURATION UPDATE message.

[0049] The NG interface between the RAN node 12 and a control node (e.g., donor control node) belonging to the core network 25 of the second PLMN 20 may be established (Setup) in response to the occurrence of a disaster. As an example, the NG interface may be established (Setup) in response to the RAN node 12 broadcasting system information including disaster-related information. This procedure corresponds to step 901 in the procedure of FIG. 9 described later. As an example, the NG interface may be established (Setup) in response to the RAN node 12 receiving an RRC Setup Request message in which "Disaster Roaming" is set. This procedure corresponds to step 903 in the procedure of FIG. 9 described later.

[0050] For example, due to a natural or man-made disaster, the RAN node 12 may be unable to select or use any control node (e.g., AMF) belonging to the core network of the first PLMN 10 selected by the UE 31. According to the operations and procedures of the RAN node 12 and the core network node (e.g., AMF 16) described in this embodiment, the RAN node 12 can request a donor control node belonging to a second PLMN 20 different from the PLMN 10 selected by the UE 31 to process the NAS message of the UE 31 instead. This may contribute to improving service continuity for the UE 31. Another advantage is that this does not necessarily require the UE 31 to support new technologies such as MINT and disaster roaming.

[0051] By way of example and not limitation, the first PLMN 10 may be a PLMN (e.g., a commercial PLMN) operated by a commercial operator. In contrast, the second PLMN 20 providing the donor control node may be a PLMN (e.g., a governmental PLMN) operated by a government agency. The government agency may be a national, federal, state, or local government agency. Alternatively, the second PLMN 20 may be provided by another public agency, such as a public safety, public protection, or disaster relief organization. The donor control node may be equipped with a battery of sufficient capacity to continue service in the event of a power loss due to a natural or man-made disaster (e.g., flood, earthquake, tsunami, volcanic eruption, fire, or gas explosion). With such a network configuration, the PLMN 20 provided by the government or public agency may improve the continuity or robustness of communication services to the commercial operator's user UEs 31.

[0052] <Second embodiment> Figure 5 shows an example of the configuration of a network system according to this embodiment. Each of the elements shown in Figure 5 is a network function, and provides an interface defined by, for example, 3GPP. Each element (network function) shown in Figure 5 can be implemented, for example, as a network element on dedicated hardware, as a software instance running on dedicated hardware, or as a virtualized function instantiated on an application platform.

[0053] The network system shown in Figure 5 includes a first PLMN 60 including a RAN 61 and a core network 65. The network system shown in Figure 5 further includes a second PLMN 70 including a RAN 71 and a core network 75. The RAN 71 may be a radio access network in an NG-RAN, an E-UTRAN, or another network system, or any combination thereof. The RAN 61 may be a radio access network in an NG-RAN, an E-UTRAN, or another network system, or any combination thereof. The core network 65 may be a core network in a 5GC, an EPC, or another network system, or any combination thereof. Similarly, the core network 75 may be a core network in a 5GC, an EPC, or another network system, or any combination thereof. The RAN 61 includes one or more RAN nodes 62. The RAN 71 includes one or more RAN nodes 72.

[0054] The UE 81 is capable of using the first PLMN 60. The HPLMN or EHPLMN of the UE 81 may be the first PLMN 60. Alternatively, the HPLMN of the UE 81 may be another PLMN that has a roaming agreement with the first PLMN 60. The UE 81 may be a UE that is allowed to register as an inbound roamer with the first PLMN 60. The UE 81 does not need to have an explicit roaming agreement with the second PLMN 70. There may be multiple UEs 81.

[0055] In this embodiment, the second PLMN 70 provides disaster roaming in the cell of the RAN node 72 of the RAN 71. For example, if a failure condition applies to an area to which the cell of the RAN node 62 of the first PLMN 60 and the cell of the RAN node 72 of the second PLMN 70 belong, and the RAN node 62 of the first PLMN 60 is unavailable, the RAN node 72 of the second PLMN 70 may offer disaster roaming to users registered or available in the first PLMN 60.

[0056] The RAN node 72 providing disaster roaming broadcasts disaster-related information, including an indication of accessibility for Disaster Roaming service. The disaster-related information may also include a list of one or more PLMN(s) with disaster condition for which disaster roaming is offered by the available PLMN. The list indicates at least the first PLMN 60.

[0057] Furthermore, in this embodiment, the disaster-related information includes a list of one or more network slice identifiers for disaster roaming. The network slice identifier may be Single Network Slice Selection Assistance Information (S-NSSAI). The list may be, for example, a list of S-NSSAI(s) for Disaster Roaming. The S-NSSAI(s) for disaster roaming are identifiers of network slices that provide disaster roaming. The S-NSSAI(s) for disaster roaming are identifiers of network slices that are provided by a disaster roaming PLMN and that can be used by a disaster inbound roamer for disaster roaming. Additionally or alternatively, the disaster-related information may include a list of S-NSSAI(s) for which disaster roaming is offered. The S-NSSAI(s) for which disaster roaming is provided are the identifiers of the network slices of the PLMN(s) to which the disaster condition applies (or the PLMN(s) that are / have a disaster condition).

[0058] FIG. 6 shows an example of the operation of the UE 81.

[0059] In step 601, UE81 stores a list of PLMN(s) to be used in disaster condition in a memory (e.g., USIM). In step 602, UE81 stores a list of one or more S-NSSAIs associated with each PLMN included in the list of PLMN(s) to be used in disaster condition in memory. That is, the stored list of one or more S-NSSAIs includes S-NSSAI(s) valid for the associated PLMN.

[0060] The order of step 601 and step 602 is not limited. Steps 601 and 602 may be performed substantially simultaneously. For example, the UE 81 may receive a list of PLMN(s) to be used in a disaster condition and a list of S-NSSAI(s) from the AMF of the HPLMN or RPLMN in one NAS message (e.g., Registration Accept or UE Configuration Update Command). The HPLMN or RPLMN of the UE 81 may be the first PLMN 60.

[0061] The specific structures of the PLMN list in step 601 and the S-NSSAI list in step 602 are not particularly limited. For example, the PLMN list in step 601 and the S-NSSAI list in step 602 may be one integrated list. In other words, the UE 81 may store one or more combination lists, each of which is a combination of a PLMN to be used in a disaster condition and one or more S-NSSAIs for disaster roaming. The UE 81 may receive such one or more combination lists from the HPLMN or RPLMN.

[0062] Steps 603 to 605 may be performed when the UE 81 determines that a PLMN is in a disaster condition. For example, if the RPLMN (e.g., the first PLMN 60) of the UE 81 is included in the "list of one or more PLMN(s) with disaster condition for which disaster roaming is offered by the available PLMN" broadcast by any cell, the UE 81 may determine that the RPLMN is in a disaster condition. Otherwise, if the HPLMN, the highest priority EHPLMN, each PLMN included in the "User Controlled PLMN Selector with Access Technology" data file in the USIM, each PLMN included in the "Operator Controlled PLMN Selector with Access Technology" data file in the USIM, or other PLMNs are included in the list of one or more PLMN(s) with disaster condition for which disaster roaming is offered by the available PLMN broadcast by any cell, the UE 81 may determine that the PLMN is in a disaster condition.

[0063] In step 603, the UE 81 selects a PLMN for disaster roaming (e.g., the second PLMN 70) from a list of PLMN(s) to be used in disaster condition associated with a determined PLMN with disaster condition (e.g., the first PLMN 60). The UE 81 may select a PLMN (e.g., the second PLMN 70) included in the list of PLMN(s) to be used in disaster condition if the PLMN can accept disaster inbound roamers from the determined PLMN with Disaster Condition. Specifically, if a cell of the PLMN without Disaster Condition (e.g., the second PLMN 70) is broadcasting disaster-related information (e.g., an indication of accessibility for Disaster Roaming service), the UE 81 may select the PLMN without Disaster Condition for a disaster roaming attempt. Alternatively, if the cell of the PLMN without Disaster Condition (e.g., the second PLMN 70) broadcasts a list of one or more PLMN(s) with disaster condition for which disaster roaming is offered by the available PLMNs, and the list includes the determined PLMN with disaster condition (e.g., the first PLMN 60), the UE may select the PLMN without Disaster Condition (e.g., the second PLMN 70) for the disaster roaming attempt.

[0064] In step 604, the UE 81 selects at least one disaster roaming S-NSSAI from the list of S-NSSAI(s) associated with the selected disaster roaming PLMN.

[0065] The order of step 603 and step 604 is not limited. Steps 603 and 604 may be performed substantially simultaneously. For example, the UE 81 may consider disaster roaming S-NSSAI(s) provided by disaster roaming PLMN candidates in selecting a disaster roaming PLMN in step 603. Specifically, the UE 81 may operate as shown in Fig. 7. In step 701, the UE 81 determines that a disaster condition applies to the Registered PLMN, the Home PLMN, or other predetermined PLMN(s). In step 702, if the RAN of one PLMN included in a stored list of one or more PLMNs (i.e., list of PLMN(s) to be used in disaster condition) broadcasts disaster-related information indicating that disaster roaming is offered, and if the disaster-related information indicates at least one S-NSSAI included in the stored list of one or more S-NSSAIs associated with the one PLMN, the UE81 selects the one PLMN for a disaster roaming attempt.

[0066] 6, in step 605, the UE 81 transmits a registration request message indicating the selected disaster roaming PLMN and S-NSSAI to the core network (e.g., core network 75) of the selected disaster roaming PLMN (e.g., second PLMN 70). This allows the UE 81 to inform the core network node (e.g., AMF) of the disaster roaming PLMN of the disaster roaming S-NSSAI desired by the UE 81.

[0067] Specifically, the UE 81 may send an RRC message including the registration request message and the selected disaster roaming network slice identifier to the RAN (e.g., RAN 71) of the selected disaster roaming PLMN (e.g., second PLMN 70). The RRC message may be an RRC setup complete message. This allows the UE 81 to inform the RAN node (e.g., RAN node 72) of the disaster roaming PLMN of the desired disaster roaming S-NSSAI.

[0068] FIG. 8 shows the registration procedure under normal circumstances when disaster conditions are not applied to the HPLMN, RPLMN, etc. of the UE 81.

[0069] In step 801 , the UE 81 sends a Registration Request message to the AMF 66 , which is the control node of the first PLMN 60 .

[0070] In step 802, the AMF 66 registers with the UDM 97 of the HPLMN of the UE 81. Specifically, the AMF 66 sends Nudm_UECM_Registration to the UDM 97.

[0071] In step 803, the AMF 66 sends Nudm_SDM_Get to the UDM 97 to request the subscriber data of the UE 81 from the UDM 97.

[0072] In step 804, the UDM 97 provides the requested subscriber data of the UE 81 to the AMF 66. The subscriber information includes a List of PLMN(s) to be used in Disaster Condition associated with the first PLMN 60. The subscriber information further includes a List of S-NSSAI(s) for Disaster Roaming.

[0073] In step 805, the AMF 66 sends a Registration Accept message to the UE 81. The Registration Accept message includes a List of PLMN(s) to be used in Disaster Condition and a List of S-NSSAI(s) for Disaster Roaming.

[0074] The procedure in Fig. 8 is an example and may be modified as appropriate. As already described, the List of PLMN(s) to be used in Disaster Condition and the List of S-NSSAI(s) for Disaster Roaming included in the Registration Accept message may be one integrated list. For example, the AMF 66 of the first PLMN 60 may create the List of PLMN(s) to be used in Disaster Condition associated with the first PLMN 60 in accordance with the local configuration. For example, the AMF 66 of the first PLMN 60 may create the List of PLMN(s) to be used in Disaster Condition associated with the first PLMN 60 by referring to the subscriber information received in step 804 and the local configuration. Similarly, the AMF 66 of the first PLMN 60 may create the List of S-NSSAI(s) for Disaster Roaming associated with each PLMN included in the List of PLMN(s) to be used in Disaster Condition in accordance with the local configuration. The AMF 66 of the first PLMN 60 may create a mapping between the S-NSSAI(s) of each PLMN that provides disaster roaming and the S-NSSAI(s) of the HPLMN and provide this to the UE 81.

[0075] FIG. 9 illustrates a PLMN selection by a UE 81 for disaster roaming and a disaster roaming attempt to the selected PLMN.

[0076] In step 901, the RAN node 72 of the second PLMN 70 that provides disaster roaming broadcasts system information containing disaster-related information. The disaster-related information may include a list of S-NSSAI(s) for disaster roaming. Additionally or alternatively, the disaster-related information may include a list of S-NSSAI(s) for which disaster roaming is offered. The RAN node 72 of the second PLMN 70 may broadcast control information similar to that of the MINT (e.g., commonPLMNsWithDisasterCondition, applicableDisasterInfoList) in the system information.

[0077] The commonPLMNsWithDisasterCondition field included in a System Information Block (SIB) (e.g., SIB Type X) broadcast in a cell may indicate a list of PLMN(s) with disaster conditions which can be commonly applicable to PLMNs sharing the cell.

[0078] applicableDisasterInfoList is a list indicating the disaster conditions that apply to the networks indicated by the plmn-IdentityList in SIB Type 1 (SIB1). The first entry in this list indicates the disaster information that applies to the network(s) indicated by the first entry in plmn-IdentityList, the second entry in this list indicates the disaster information that applies to the network(s) indicated by the second entry in plmn-IdentityList, and so on. Each entry in this list may have one of the following values: noDisasterRoaming, oneBitApproach, commonPLMNs, or dedicatedPLMNs. If an entry in this list has the value noDisasterRoaming, disaster roaming is not allowed for this network. If an entry in this list has the value commonPLMNs, the PLMN(s) with disaster condition indicated in the field complamnsWithDisasterCondition apply to this entry. If an entry in this list contains the value dedicatedPLMNs, the listed PLMN(s) are disaster-conditional PLMN(s) that apply to the network(s) corresponding to this entry.

[0079] In step 902, the UE 81 performs PLMN selection. The UE 81 determines that there are no permitted available PLMNs. Furthermore, the UE 81 detects that a disaster condition applies to the RPLMN, HPLMN, or other predetermined PLMN(s). If a disaster condition applies and no PLMNs other than the PLMN(s) in the forbidden PLMN list are available, the UE 81 searches for PLMN(s) that offer disaster roaming from the forbidden PLMN list. The UE 81 may select a PLMN for disaster roaming according to the example described with reference to FIGS. 6 and 7. Here, the UE 81 selects the second PLMN 70 for the disaster roaming attempt.

[0080] In step 903, the UE 81 sends an RRC Setup Request message to the RAN node 72 of the second PLMN 70. The message includes an Establishment Cause indicating "Disaster Roaming".

[0081] In step 904, the RAN node 72 responds to the UE 81 with an RRC Setup message.

[0082] In step 905, the UE 81 sets up an RRC connection and sends an RRC Setup Complete message to the RAN node 72. The RRC Setup Complete message includes a Registration Request message indicating disaster roaming. In addition, the RRC Setup Complete message includes a PLMN ID selected by the UE 81 (i.e., PLMN ID "B" of the second PLMN 70). Furthermore, the RRC Setup Complete message includes an S-NSSAI for disaster roaming selected by the UE 81.

[0083] In step 906, the RAN node 72 selects an AMF 76, which is a control node of the second PLMN 70, and sends an INITIAL UE MESSAGE message containing the Registration Request message to the selected AMF 76. The RAN node 72 may select an AMF to which the Registration Request message is forwarded, taking into account that the establishment cause of the RRC connection is Disaster Roaming. For example, the RAN node 72 may select an AMF defined for disaster roaming. Additionally or alternatively, the RAN node 72 may select an AMF to which the Registration Request message is forwarded, taking into account the S-NSSAI for disaster roaming received from the UE 81. For example, the RAN node 72 may select an AMF associated with the S-NSSAI for disaster roaming. The Establishment Cause may be referred to as Disaster Emergency or Emergency Roaming instead of Disaster Roaming.

[0084] According to the process described in this embodiment, the UE 81 can know in advance via the RPLMN or the HPLMN the network slices available to disaster roamer UEs in the PLMN without disaster condition (or the PLMN offering disaster roaming). The RAN node of the PLMN offering disaster roaming can notify the available network slice identifiers for disaster roaming (e.g., S-NSSAI) by broadcasting. In addition, the UE 81 can notify the PLMN offering disaster roaming of the network slice identifiers for disaster roaming (e.g., S-NSSAI) desired by the UE 81 in the registration procedure.

[0085] <Third embodiment> An example of the configuration of the network system according to this embodiment is similar to the example shown in Fig. 5. Fig. 10 shows the operation of the AMF 76, which is the control node of the second PLMN 70, that receives a registration request for disaster roaming of the UE 81. The procedure in Fig. 10 (steps 1002 to 1006) may be performed after the procedure in Fig. 9 (step 906) described in the second embodiment.

[0086] In step 1001, the AMF 76 receives a Registration Request message for disaster roaming sent from the UE 81. In the case of a Registration Request for disaster roaming, the AMF 76 may skip the UE context transfer procedure for acquiring the UE context from the old AMF (e.g., the AMF of the first PLMN 60) because the old AMF is likely to be unavailable in the case of disaster roaming. In this case, the AMF 76 may request an unencrypted subscriber identifier (e.g., a Subscription Permanent Identifier (SUPI)) from the UE 81.

[0087] In step 1002, the AMF 76 requests registration from the UDM 97 of the HPLMN of the UE 81. Specifically, the AMF 76 sends Nudm_UECM_Registration to the UDM 97. At this time, the AMF 76 includes an indication of disaster roaming in the Nudm_UECM_Registration. There may be a case where there is no roaming agreement between the second PLMN 70 that provides disaster roaming and the HPLMN of the UE 81. In such a case, the UDM 97 of the HPLMN may reject the request from the AMF 76 of the PLMN 70 that provides disaster roaming. By including the indication of disaster roaming in the Nudm_UECM_Registration, the UDM 97 can recognize that the request is for disaster roaming. This prevents the request from being rejected by the UDM 97.

[0088] In step 1003, UDM 97 responds to AMF 76 with a Nudm_UECM_Registration response.

[0089] In step 1004, the AMF 76 sends Nudm_SDM_Get to the UDM 97 to request the subscriber data of the UE 81 from the UDM 97. As in step 1002, the AMF 76 may include an indication of disaster roaming in the Nudm_SDM_Get, thereby preventing the request from being rejected by the UDM 97.

[0090] In step 1005, the UDM 97 provides the requested subscriber data of the UE 81 to the AMF 76.

[0091] In step 1006, the AMF 76 sends a Registration Accept message to the UE 81.

[0092] Next, exemplary configurations of the RAN nodes 12, 62, and 72, the AMFs 16, 66, and 76, the UDM 97, and the UEs 31 and 81 according to the above-described embodiments will be described below.

[0093] Fig. 11 is a block diagram showing an example configuration of the RAN node 12 according to the above embodiment. The RAN nodes 62 and 72 may also have a configuration similar to that of the RAN node 12 shown in Fig. 11. Referring to Fig. 11, the RAN node 12 includes a radio frequency transceiver 1101, a network interface 1103, a processor 1104, and a memory 1105.

[0094] The RF transceiver 1101 performs analog RF signal processing for communication with UEs, including UEs 31. The RF transceiver 1101 may include multiple transceivers. The RF transceiver 1101 is coupled to the antenna array 1102 and the processor 1104. The RF transceiver 1101 receives modulation symbol data from the processor 1104, generates a transmit RF signal, and provides the transmit RF signal to the antenna array 1102. The RF transceiver 1101 also generates a baseband receive signal based on the receive RF signal received by the antenna array 1102 and provides the baseband receive signal to the processor 1104. The RF transceiver 1101 may include an analog beamformer circuit for beamforming. The analog beamformer circuit may include, for example, multiple phase shifters and multiple power amplifiers.

[0095] The network interface 1103 is used to communicate with network nodes (e.g., other RAN nodes, and control plane nodes and user plane nodes of the core network), and may include, for example, a network interface card (NIC) compliant with the IEEE 802.3 series.

[0096] The processor 1104 performs digital baseband signal processing (data plane processing) and control plane processing for wireless communication. The processor 1104 may include multiple processors. For example, the processor 1104 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.

[0097] For example, digital baseband signal processing by the processor 1104 may include signal processing of a Service Data Adaptation Protocol (SDAP) layer, a Packet Data Convergence Protocol (PDCP) layer, a Radio Link Control (RLC) layer, a Medium Access Control (MAC) layer, and a Physical (PHY) layer. Also, control plane processing by the processor 1104 may include processing of Non-Access Stratum (NAS) messages, RRC messages, MAC Control Elements (CE), and Downlink Control Information (DCI).

[0098] The processor 1104 may include a digital beamformer module for beamforming, which may include a multiple input multiple output (MIMO) encoder and precoder.

[0099] The memory 1105 is configured by a combination of volatile memory and non-volatile memory. The volatile memory is, for example, Static Random Access Memory (SRAM), Dynamic RAM (DRAM), or a combination thereof. The non-volatile 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. The memory 1105 may include storage located remotely from the processor 1104. In this case, the processor 1104 may access the memory 1105 via the network interface 1103 or an I / O interface.

[0100] The memory 1105 may store one or more software modules (computer programs) 1106 including instructions and data for performing the processing by the RAN node 12 described in the above embodiments. In some implementations, the processor 1104 may be configured to read and execute the software modules 1106 from the memory 1105 to perform the processing by the RAN node 12 described in the above embodiments.

[0101] It should be noted that if the RAN node 12 is a Central Unit (CU) (e.g., eNB-CU or gNB-CU) or a CU Control Plane (CP) Unit, the RAN node 12 may not include the RF transceiver 1101 (and the antenna array 1102).

[0102] Fig. 12 shows an example of the configuration of the AMF 16. The AMFs 66 and 76 may also have a configuration similar to that of the AMF 16 shown in Fig. 12. The UDM 97 may also have a configuration similar to that of the AMF 16 shown in Fig. 12. Referring to Fig. 12, the AMF 16 includes a network interface 1201, a processor 1202, and a memory 1203.

[0103] The network interface 1201 is used, for example, to communicate with other network functions (NFs) or nodes, and may include, for example, a network interface card (NIC) compliant with the IEEE 802.3 series.

[0104] The processor 1202 may be, for example, a microprocessor, a microprocessing unit (MPU), or a central processing unit (CPU). The processor 1202 may include multiple processors.

[0105] The memory 1203 is composed of volatile memory and nonvolatile memory. The memory 1203 may include multiple physically independent memory devices. The volatile memory is, for example, Static Random Access Memory (SRAM), Dynamic RAM (DRAM), or a combination thereof. The 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. The memory 1203 may include storage located remotely from the processor 1202. In this case, the processor 1202 may access the memory 1203 via the network interface 1201 or an I / O interface.

[0106] The memory 1203 may store one or more software modules (computer programs) 1204 including instructions and data for performing processing by the AMF 16 described in the above-described embodiments. In some implementations, the processor 1202 may be configured to read and execute the software modules 1204 from the memory 1203, thereby performing processing by the AMF 16 described in the above-described embodiments.

[0107] 13 is a block diagram showing an example of the configuration of UE 31. UE 81 may also have a configuration similar to that of UE 31 shown in FIG.

[0108] The Radio Frequency (RF) transceiver 1301 performs analog RF signal processing for communication with a RAN node (e.g., RAN node 12). The RF transceiver 1301 may include multiple transceivers. The analog RF signal processing performed by the RF transceiver 1301 includes frequency up-conversion, frequency down-conversion, and amplification. The RF transceiver 1301 is coupled to the antenna array 1302 and the baseband processor 1303. The RF transceiver 1301 receives modulation symbol data (or OFDM symbol data) from the baseband processor 1303, generates a transmit RF signal, and provides the transmit RF signal to the antenna array 1302. The RF transceiver 1301 also generates a baseband receive signal based on the receive RF signal received by the antenna array 1302 and provides the baseband receive signal to the baseband processor 1303. The RF transceiver 1301 may include an analog beamformer circuit for beamforming. The analog beamformer circuit includes, for example, multiple phase shifters and multiple power amplifiers.

[0109] The baseband processor 1303 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 of Layer 1 (e.g., transmit power control), Layer 2 (e.g., radio resource management and hybrid automatic repeat request (HARQ) processing), and Layer 3 (e.g., signaling related to attachment, mobility, and call management).

[0110] For example, the digital baseband signal processing by the baseband processor 1303 may include signal processing of an SDAP layer, a PDCP layer, an RLC layer, a MAC layer, and a PHY layer. Also, the control plane processing by the baseband processor 1303 may include processing of a Non-Access Stratum (NAS) protocol, an RRC protocol, MAC CEs, and DCIs.

[0111] The baseband processor 1303 may perform MIMO encoding and precoding for beamforming.

[0112] The baseband processor 1303 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. In this case, the protocol stack processor that performs control plane processing may be shared with the application processor 1304, which will be described later.

[0113] The application processor 1304 is also referred to as a CPU, an MPU, a microprocessor, or a processor core. The application processor 1304 may include multiple processors (multiple processor cores). The application processor 1304 executes the memory 1306 or a system software program (operating system (OS)) read from the memory and various application programs (e.g., a call application, a web browser, a mailer, a camera operation application, and a music playback application) to realize various functions of the UE 31.

[0114] In some implementations, the baseband processor 1303 and the application processor 1304 may be integrated on a single chip, as indicated by the dashed line (1305) in Figure 13. In other words, the baseband processor 1303 and the application processor 1304 may be implemented as a single System on Chip (SoC) device 1305. An SoC device may also be called a system Large Scale Integration (LSI) or a chipset.

[0115] The memory 1306 is volatile memory, nonvolatile memory, or a combination thereof. The memory 1306 may include multiple physically independent memory devices. The volatile memory is, for example, SRAM, DRAM, or a combination thereof. The nonvolatile memory is, for example, MROM, EEPROM, flash memory, or a hard disk drive, or any combination thereof. For example, the memory 1306 may include an external memory device accessible from the baseband processor 1303, the application processor 1304, and the SoC 1305. The memory 1306 may also include an internal memory device integrated within the baseband processor 1303, the application processor 1304, or the SoC 1305. Furthermore, the memory 1306 may include memory within a Universal Integrated Circuit Card (UICC).

[0116] The memory 1306 may store one or more software modules (computer programs) 1307 including instructions and data for performing the processes described in the above-described embodiments by the UE 31. In some implementations, the baseband processor 1303 or the application processor 1304 may be configured to read and execute the software modules 1307 from the memory 1306, thereby performing the processes of the UE 31 described in the above-described embodiments using the drawings.

[0117] It should be noted that the control plane processing and operations performed by UE31 described in the above embodiment can be realized by elements other than the RF transceiver 1301 and the antenna array 1302, namely, at least one of the baseband processor 1303 and the application processor 1304, and the memory 1306 storing the software module 1307.

[0118] As described with reference to Figures 11, 12, and 13, each of the processors included in the RAN node, AMF, UDM, and UE according to the above-described embodiments can execute one or more programs including instructions for causing a computer to perform the algorithms described with reference to the figures. The programs include instructions (or software code) that, when loaded into a computer, cause the computer to perform one or more functions described in the embodiments. The programs may be stored on a non-transitory computer-readable medium or a tangible storage medium. By way of example and not limitation, computer-readable media or tangible storage media include random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drive (SSD) or other memory technology, CD-ROM, digital versatile disk (DVD), Blu-ray disc or other optical disk storage, magnetic cassette, magnetic tape, magnetic disk storage, or other magnetic storage device. The programs may also be transmitted on a transitory computer-readable medium or communication medium. By way of example and not limitation, transitory computer-readable media or communication media include electrical, optical, acoustic, or other forms of propagated signals.

[0119] <Other embodiments> In the above-described embodiment, the RAN node 62 may broadcast control information regarding access to a network of another PLMN (e.g., a cell of the RAN node 72) in a disaster state. The control information may, for example, indicate that the UE 81 is permitted to roam to a network of a pre-specified (or configured) PLMN, that the UE 81 is to start detecting a network of a pre-specified (or configured) PLMN, or that the UE 81 is permitted to access a network of a specific PLMN. In response to receiving the control information, the UE 81 may initiate disaster roaming in the above-described embodiment.

[0120] Furthermore, the above-described embodiments are merely examples of application of the technical ideas obtained by the inventors of the present invention. In other words, the technical ideas are not limited to the above-described embodiments, and various modifications are possible.

[0121] For example, some or all of the above embodiments can be described as, but are not limited to, the following supplementary notes.

[0122] (Appendix 1) a first communication interface configured to communicate with a plurality of User Equipments (UEs) via a cell; a second communication interface configured to be coupled to a first core network of a first Public Land Mobile Network (PLMN) and to be coupled to a second core network of a second PLMN different from the first PLMN; at least one processor configured to receive a Non-Access Stratum message associated with the first PLMN and transmitted from a UE, and configured to forward the Non-Access Stratum message to a donor control node belonging to the second core network of the second PLMN if no control node belonging to the first core network of the first PLMN is selectable or unavailable; Equipped with Access network node. (Appendix 2) the at least one processor is configured, if a control node belonging to the first core network of the first PLMN is selected, to forward the Non-Access Stratum message to the selected control node. 1. An access network node as defined in Supplementary Note 1. (Appendix 3) the at least one processor is configured to receive the Non-Access Stratum message via a Radio Resource Control message containing an identifier of the first PLMN and the Non-Access Stratum message. 3. An access network node according to claim 1 or 2. (Appendix 4) The UE's Home PLMN transmitting the Non-Access Stratum message is the first PLMN; An access network node according to any one of Supplementary Note 1 to 3. (Appendix 5) the at least one processor is configured to receive, from a control node belonging to the first core network, a control message that specifies the donor control node belonging to the second core network; An access network node according to any one of Supplementary Note 1 to 4. (Appendix 6) the at least one processor is configured to receive the control message in a procedure for setting up or updating configuration data required for interoperation between a control node belonging to the first core network and the access network node. 5. An access network node as defined in Supplementary Note 5. (Appendix 7) The procedure is an NG Setup procedure, a RAN Configuration Update procedure, or an AMF Configuration Update procedure. 6. An access network node as defined in Supplementary Note 6. (Appendix 8) the at least one processor is configured to broadcast information in the cell indicating a list of one or more available PLMNs; the list includes an identifier of the first PLMN but does not include an identifier of the second PLMN; An access network node according to any one of Supplementary Note 1 to 7. (Appendix 9) connecting to a first core network of a first Public Land Mobile Network (PLMN) and connecting to a second core network of a second PLMN different from the first PLMN; receiving a Non-Access Stratum message associated with the first PLMN and transmitted from a User Equipment (UE); and if no control node belonging to the first core network of the first PLMN is selectable or unavailable, forwarding the Non-Access Stratum message to a donor control node belonging to the second core network of the second PLMN; Equipped with A method performed by an access network node. (Appendix 10) 1. A program for causing a computer to perform a method for an access network node, the method comprising: connecting to a first core network of a first Public Land Mobile Network (PLMN) and connecting to a second core network of a second PLMN different from the first PLMN; receiving a Non-Access Stratum message associated with the first PLMN and transmitted from a User Equipment (UE); and if no control node belonging to the first core network of the first PLMN is selectable or unavailable, forwarding the Non-Access Stratum message to a donor control node belonging to the second core network of the second PLMN; Equipped with program. (Appendix 11) A control node used in a core network of a first Public Land Mobile Network (PLMN), comprising: a communication interface configured to be connected to an access network node; at least one processor configured to send a control message to the access network node specifying a donor control node belonging to a core network of a second PLMN different from a first PLMN to which the control node belongs; Equipped with the control message causes the access network node to forward a Non-Access Stratum message associated with the first PLMN sent from a User Equipment (UE) to the donor control node of the second PLMN if no control node belonging to the core network of the first PLMN is selectable or unavailable; Control node. (Appendix 12) the at least one processor is configured to send the control message in a procedure for setting up or updating configuration data necessary for the control node and the access network node to interoperate. 12. The control node of claim 11. (Appendix 13) The procedure is an NG Setup procedure, a RAN Configuration Update procedure, or an AMF Configuration Update procedure. 13. The control node of claim 12. (Appendix 14) 1. A method performed by a control node used in a core network of a first Public Land Mobile Network (PLMN), comprising: sending a control message to an access network node specifying a donor control node belonging to a core network of a second PLMN different from a first PLMN to which said control node belongs; the control message causes the access network node to forward a Non-Access Stratum message associated with the first PLMN sent from a User Equipment (UE) to the donor control node of the second PLMN if no control node belonging to the core network of the first PLMN is selectable or unavailable; method. (Appendix 15) A program for causing a computer to perform a method for a control node used in a core network of a first Public Land Mobile Network (PLMN), comprising: the method comprising sending a control message to an access network node specifying a donor control node belonging to a core network of a second PLMN different from a first PLMN to which the control node belongs; the control message causes the access network node to forward a Non-Access Stratum message associated with the first PLMN sent from a User Equipment (UE) to the donor control node of the second PLMN if no control node belonging to the core network of the first PLMN is selectable or unavailable; program. (Appendix 16) At least one memory; at least one processor coupled to the at least one memory; Equipped with The at least one processor: storing in said at least one memory a list of one or more Public Land Mobile Networks (PLMNs) for use during disaster conditions; storing a list of one or more disaster roaming network slice identifiers associated with each PLMN included in the list of one or more PLMNs in the at least one memory; selecting a disaster roaming PLMN from the list of one or more PLMNs; selecting at least one disaster roaming network slice identifier from the list of one or more disaster roaming network slice identifiers associated with the selected disaster roaming PLMN; sending a registration request message indicating the selected disaster roaming PLMN and the selected disaster roaming network slice identifier toward a core network of the selected disaster roaming PLMN; It is configured as follows: User Equipment (UE). (Appendix 17) The at least one processor is configured to send a Radio Resource Control message including the registration request message and including the selected disaster roaming network slice identifier to a radio access network of the selected disaster roaming PLMN. UE as described in Appendix 16. (Appendix 18) The Radio Resource Control message is an RRC setup complete message; UE as described in Appendix 17. (Appendix 19) the at least one processor is configured to select the one PLMN as the disaster roaming PLMN if a radio access network of the one PLMN included in the stored list of the one or more PLMNs broadcasts disaster-related information indicating that disaster roaming is offered, and the disaster-related information indicates at least one network slice identifier included in the stored list of the one or more disaster roaming network slice identifiers associated with the one PLMN. 19. The UE according to any one of appendices 16 to 18. (Appendix 20) The disaster-related information indicates that disaster roaming is provided for a Registered PLMN to which the UE is registered or a Home PLMN of the UE. UE as described in Appendix 19. (Appendix 21) The at least one processor is configured to receive, from a Home PLMN of the UE or a Registered PLMN to which the UE is registered, a list of one or more PLMNs to be used during the disaster condition and a list of the one or more disaster roaming network slice identifiers associated with each PLMN included in the list of the one or more PLMNs. The UE according to any one of Supplementary Notes 16 to 20. (Appendix 22) The at least one processor is configured to receive, from a Home PLMN of the UE or a Registered PLMN to which the UE is registered, a list of one or more combinations, each of which is a combination of a PLMN to be used during a disaster condition and one or more disaster roaming network slice identifiers. The UE according to any one of Supplementary Notes 16 to 20. (Appendix 23) storing a list of one or more Public Land Mobile Networks (PLMNs) to be used during disaster conditions; storing a list of one or more disaster roaming network slice identifiers associated with each PLMN included in the list of one or more PLMNs; selecting a disaster roaming PLMN from the list of one or more PLMNs; selecting at least one disaster roaming network slice identifier from the list of one or more disaster roaming network slice identifiers associated with the selected disaster roaming PLMN; sending a registration request message indicating the selected disaster roaming PLMN and the selected disaster roaming network slice identifier toward a core network of the selected disaster roaming PLMN; The method is performed by a user equipment (UE). (Appendix 24) A program causing a computer to perform a method for User Equipment (UE), the method comprising: storing a list of one or more Public Land Mobile Networks (PLMNs) to be used during disaster conditions; storing a list of one or more disaster roaming network slice identifiers associated with each PLMN included in the list of one or more PLMNs; selecting a disaster roaming PLMN from the list of one or more PLMNs; selecting at least one disaster roaming network slice identifier from the list of one or more disaster roaming network slice identifiers associated with the selected disaster roaming PLMN; sending a registration request message indicating the selected disaster roaming PLMN and the selected disaster roaming network slice identifier toward a core network of the selected disaster roaming PLMN; A program that provides: (Appendix 25) A core network node of a Home Public Land Mobile Network (HPLMN) of a User Equipment (UE) or a registered PLMN to which the UE is registered, At least one memory; at least one processor coupled to the at least one memory; Equipped with The at least one processor: providing the UE with a first list of one or more PLMNs to be used during a disaster condition; providing the UE with a second list of one or more disaster roaming network slice identifiers associated with each PLMN included in the list of one or more PLMNs; It is configured as follows: Core network node. (Appendix 26) the first list and the second list are a single unified list; The integrated list is a list of one or more combinations, each of which is a combination of a PLMN to be used during a disaster condition and one or more disaster roaming network slice identifiers. 26. The core network node according to claim 25. (Appendix 27) 1. A method performed by a core network node of a Home Public Land Mobile Network (HPLMN) of a User Equipment (UE) or a registered PLMN in which the UE is registered, comprising: providing the UE with a first list of one or more PLMNs to be used during a disaster condition; providing the UE with a second list of one or more disaster roaming network slice identifiers associated with each PLMN included in the list of one or more PLMNs; How to prepare for this. (Appendix 28) A program that causes a computer to perform a method for a Home Public Land Mobile Network (HPLMN) of User Equipment (UE) or a core network node of a registered PLMN to which the UE is registered, the method comprising: providing the UE with a first list of one or more PLMNs to be used during a disaster condition; providing the UE with a second list of one or more disaster roaming network slice identifiers associated with each PLMN included in the list of one or more PLMNs; A program that provides: (Appendix 29) An access network node of a Public Land Mobile Network (PLMN) that provides disaster roaming, At least one memory; at least one processor coupled to the at least one memory; Equipped with the at least one processor is configured to broadcast disaster-related information in a cell indicating that disaster roaming is offered; The disaster-related information includes a list of one or more disaster roaming network slice identifiers. Access network node. (Appendix 30) The at least one processor: Receive a Radio Resource Control message from User Equipment (UE) that includes a registration request message to the PLMN that provides disaster roaming and that includes at least one network slice identifier for disaster roaming included in the list; Selecting a core network node to which the registration request message is forwarded based on the at least one disaster roaming network slice identifier included in the Radio Resource Control message; It is configured as follows: 29. An access network node according to claim 29. (Appendix 31) The at least one processor: Receive a Non-Access Stratum message from a User Equipment (UE) associated with disaster roaming and associated with at least one network slice identifier for disaster roaming included in the list; Selecting a core network node to which a Non-Access Stratum message is to be forwarded based on the association with the disaster roaming and the association with the network slice identifier for disaster roaming; It is configured as follows: 29. An access network node according to claim 29. (Appendix 32) the disaster-related information further includes a list of one or more Public Land Mobile Networks (PLMNs) having a disaster condition for which disaster roaming is provided; An access network node according to any one of Supplementary Notes 29 to 31. (Appendix 33) 1. A method performed by an access network node of a Public Land Mobile Network (PLMN) that provides disaster roaming, comprising: broadcasting disaster-related information in a cell indicating that disaster roaming is offered; The disaster-related information includes a list of one or more disaster roaming network slice identifiers. method. (Appendix 34) A method for an access network node of a Public Land Mobile Network (PLMN) that provides disaster roaming, the method comprising: The method comprises broadcasting disaster-related information in a cell indicating that disaster roaming is offered; The disaster-related information includes a list of one or more disaster roaming network slice identifiers. program. (Appendix 35) A core network node of a Public Land Mobile Network (PLMN) that provides disaster roaming, At least one memory; at least one processor coupled to the at least one memory; Equipped with The at least one processor: receiving a registration request from a User Equipment (UE); If the registration request indicates disaster roaming, include an indication of disaster roaming in a message sent to a control node located in the UE's Home PLMN and managing the UE's subscriber information. It is configured as follows: Core network node. (Appendix 36) the disaster roaming indication prompts the control node not to reject the request indicated in the message because there is no roaming agreement between the PLMN to which the core network node belongs and the Home PLMN. 36. The core network node of claim 35. (Appendix 37) The message indicates a registration request of the core network node to the control node or a request to send subscriber information of the UE. 37. A core network node according to claim 35 or 36. (Appendix 38) the core network node is an Access and Mobility Management Function (AMF); The control node is a Unified Data Management (UDM). A core network node according to any one of Supplementary Notes 35 to 37. (Appendix 39) the at least one processor is configured to skip a procedure of requesting a core network node of a PLMN to which the UE was previously registered to transfer a UE context of the UE if the registration request indicates disaster roaming. A core network node according to any one of Supplementary Notes 35 to 38. (Appendix 40) 1. A method performed by a core network node of a Public Land Mobile Network (PLMN) that provides disaster roaming, comprising: receiving a registration request from a User Equipment (UE); If the registration request indicates disaster roaming, include an indication of disaster roaming in a message sent to a control node located in the UE's Home PLMN and managing the UE's subscriber information. A method comprising: (Appendix 41) A program for causing a computer to perform a method for a core network node of a Public Land Mobile Network (PLMN) that provides disaster roaming, the method comprising: receiving a registration request from a User Equipment (UE); If the registration request indicates disaster roaming, include an indication of disaster roaming in a message sent to a control node located in the UE's Home PLMN and managing the UE's subscriber information. A program that provides:

[0123] This application claims priority based on Japanese Patent Application No. 2022-019381, filed on February 10, 2022, the disclosure of which is incorporated herein in its entirety. [Explanation of symbols]

[0124] 10 PLMN 11 RAN 12 RAN nodes 15 Core Network 16 AMF 25 Core Network 31UE 60 PLMN 61 RAN 62 RAN nodes 66 AMF 70 PLMN 71 RAN 72 RAN nodes 76 AMF 81UE 97 UDM 1104 processor 1105 Memory 1106 Modules 1202 processor 1203 memory 1204 modules 1303 Baseband Processor 1304 Application Processor 1306 memory 1307 Modules

Claims

1. means for connecting to a first core network of a first Public Land Mobile Network (PLMN) and connecting to a second core network of a second PLMN different from the first PLMN; means for receiving a Non-Access Stratum message associated with the first PLMN and transmitted from a User Equipment (UE); means for forwarding the Non-Access Stratum message to a donor control node belonging to the second core network of the second PLMN if no control node belonging to the first core network of the first PLMN is selectable or unavailable; Equipped with Access network node.

2. and means for forwarding the Non-Access Stratum message to a control node belonging to the first core network of the first PLMN if the control node is selected.

10. An access network node according to claim 1.

3. the receiving means is configured to receive the Non-Access Stratum message via a Radio Resource Control message containing an identifier of the first PLMN and the Non-Access Stratum message. An access network node according to claim 1 or 2.

4. The UE's Home PLMN transmitting the Non-Access Stratum message is the first PLMN. An access network node according to claim 1 or 2.

5. and means for receiving a control message from a control node belonging to the first core network, the control message specifying the donor control node belonging to the second core network. An access network node according to claim 1 or 2.

6. the means for receiving the control message is configured to receive the control message in a procedure for setting up or updating configuration data necessary for a control node belonging to the first core network and the access network node to interoperate. An access network node according to claim 5.

7. The procedure is an NG Setup procedure, a RAN Configuration Update procedure, or an AMF Configuration Update procedure. An access network node according to claim 6.

8. means for broadcasting information in the cell indicating a list of one or more available PLMNs; the list includes an identifier of the first PLMN but does not include an identifier of the second PLMN; An access network node according to claim 1 or 2.

9. A control node used in a core network of a first Public Land Mobile Network (PLMN), comprising: means for sending a control message to an access network node, the control message specifying a donor control node belonging to a core network of a second PLMN different from a first PLMN to which the control node belongs; Equipped with the control message causes the access network node to forward a Non-Access Stratum message associated with the first PLMN sent from a User Equipment (UE) to the donor control node of the second PLMN if no control node belonging to the core network of the first PLMN is selectable or unavailable; Control node.

10. the sending means is configured to send the control message in a procedure for setting up or updating configuration data necessary for the control node and the access network node to interoperate.

10. The control node of claim 9.

11. The procedure is an NG Setup procedure, a RAN Configuration Update procedure, or an AMF Configuration Update procedure. The control node of claim 10.

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