Roaming guidance techniques in communication systems

Abstract

A node in a core network (CN) of a public land mobile network (PLMN) supports roaming boot (SOR). The node receives (220) an indication of a registration attempt to a roaming UE for which the PLMN operates as a home PLMN (HPLMN), the registration attempt occurring at a guest PLMN (VPLMN). The node obtains (242, 232) SOR information related to the registration attempt from an entity configured to provide SOR information of the CN; determining (250) whether to accept or deny a registration attempt based at least on the received response and an operator policy related to the UE and the VPLMN; and providing (260) a result of the determination to the VPLMN.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of the filing date of provisional U.S. patent application No. 63 / 393,969, entitled “Steering of Roaming Techniques in a Communication System,” filed on July 31, 2022. The entire contents of the provisional application are hereby expressly incorporated herein by reference. Technical Field

[0003] The present disclosure relates generally to wireless communications and, more particularly, to supporting roaming-related services. Background Art

[0004] The background description provided herein is for the purpose of generally presenting the context of the present disclosure. The work of the presently named inventors (to the extent that it is described in this background section) and aspects of this description that may not be identified as prior art at the time of filing are neither explicitly nor implicitly admitted to be prior art of the present disclosure.

[0005] In telecommunication systems, the profile of a user equipment (UE) resides in a Home Public Land Mobile Network (HPLMN). A PLMN typically includes a core network (CN) where multiple nodes support services such as voice calls, Short Message Service (SMS), IP Multimedia Service (IMS), etc., and a radio access network (RAN) where base stations support radio interfacing with the UE. Each PLMN is typically associated with a different mobile network operator.

[0006] The UE typically selects a PLMN when it is powered on or when returning from an area without cellular coverage. Because the HPLMN typically does not cover the entire geographic area in which the UE can operate, the UE temporarily registers with or "roams" to another PLMN in some cases. The PLMN to which the UE is currently registered is called a visitor PLMN (VPLMN).

[0007] The Global System for Mobile Communications Association (GSMA) has proposed that PLMNs support the following: Roaming Value Added Services (RVAS) such as Welcome SMS, which are used to provide the UE with information about the network the UE has registered, pricing information for certain services, country information, etc.; International Mobile Subscriber Identity (IMSI)-based routing to a specific core network; and Steering of Roaming (SOR), which generally refers to the ability of the HPLMN to exercise a certain amount of control over the selection of VPLMNs for roaming UEs. The PLMN may provide RVAS directly or outsource RVAS to a fully trusted entity, which may operate as an RVAS provider, an Internet Packet Exchange (IPX) provider, or a roaming hub provider (i.e., a provider of a central point or hub for exchanging roaming agreements).

[0008] Second, third, and fourth generation telecommunication networks may use proprietary techniques to support RVAS. These techniques may involve intercepting location update and registration signaling on the roaming interface between the HPLMN and the VPLMN, and sending an appropriate rejection cause to the UE in order to direct the UE to attempt to select a different VPLMN. However, changes in network topology and protocols in fifth generation (5G) networks effectively prevent third-party providers from providing RVAS in the same manner in 5G networks. For example, the Home Security Edge Protection Proxy (H-SEPP) of the HPLMN and the Visitor Security Edge Protection Proxy (V-SEPP) of the VPLM now encrypt the signaling in a manner that prevents IPX from spoofing location update / registration signaling (e.g., IPX spoofing). Figure 1 In addition, some of the RVAS use cases are not covered by existing 3rd Generation Partnership Project (3GPP) service requirements.

[0009] To this end, 3GPP has proposed that RVAS and in particular SOR functionality comply with standardized mechanisms. The standardized 5GS SOR mechanism allows the HPLMN to request the UE to automatically find and register on a VPLMN different from the VPLMN that the UE has found when another VPLMN is available and not in the prohibited list. The PLMN operator or third-party RVAS provider may operate a SOR application function (SOR-AF), which may provide SOR information for guiding the UE during registration, after registration, or in connected mode. The SOR information may include a list of preferred PLMN / access technology combinations, SOR connection mode control information (SOR-CMCI) together with corresponding indicators, SOR independent non-public network (SNPN) selection information (SOR-SNPN-SI) and / or security packets. The unified data management node (UDM) then sends the SOR information to the UE via N1 non-access stratum (NAS) signaling to facilitate PLMN selection. In addition, 3GPP has proposed that the SOR-AF subscribe to notifications from the HPLM UDM related to changes in the roaming status of the UE.

[0010] However, various procedures related to the SOR-AF, message delivery between the PLMN and the SOR-AF, and application programming interfaces (APIs) related to the SOR are still unclear. Summary of the invention

[0011] The disclosed techniques generally relate to SOR during or after a registration process. More specifically, these techniques allow a PLMN to determine whether to accept or reject a UE's registration attempt and whether to direct the UE to search for another network. These techniques further allow a roaming UE to access services when a suitable VPLMN exists. Still further, these techniques allow a PLMN to select and apply relevant SOR information consistent with certain validity criteria.

[0012] According to an example technique, the UDM (or another suitable node in the HPLMN) obtains SOR information that the UE is attempting to register at the VPLMN. The UDM may obtain this information from the SOR-AF via a network opening function (NEF). The UDM then determines whether to allow the UE to register with the VPLMN or reject the registration attempt, and sends a rejection reason (or, in some cases, an acceptance reason) to the UE.

[0013] In some cases, the UDM provides further guidance to the UE regarding future registration attempts to the VPLMN, for example, to temporarily but not permanently block the UE from attempting to register with the VPLMN. In this way, the UDM and NEF can enable the UE to receive an appropriate rejection cause that enables the UE to select another VPLMN and avoid a no-service scenario when other VPLMNs are available. In addition, the redirection mechanism is compatible with mechanisms that rely on a proprietary interface with the SOR-AF.

[0014] In some implementations, the techniques of this disclosure are compatible with use of the redirection mechanism in 4G networks and allow the redirection mechanism to operate correctly with the traditional SOR mechanism without creating a no-service scenario for UEs where the rejected VPLMN is the only available VPLMN.

[0015] An example implementation of these techniques is a method implemented in a node of a core network CN of a PLMN for supporting SOR steering. The method includes receiving an indication of a registration attempt for a roaming UE, for which the PLMN operates as an HPLMN, the registration attempt occurring at a VPLMN. The method further includes: obtaining SOR information related to the registration attempt from an entity configured to provide SOR information of the CN; determining whether to accept or reject the registration attempt based at least on a received response; and providing a result of the determination to the VPLMN.

[0016] Another example implementation of the techniques is a network node comprising processing hardware and configured to implement the above methods.

[0017] Another example implementation of these techniques is a method in a UE associated with an HPLMN for registering with a VPLMN. The method includes: transmitting a registration request to the VPLMN; receiving a message via the PLMN indicating whether the registration request is rejected or accepted, the message including SOR information and at least one of: (i) a retention indication, (ii) a retention timer value, or (iii) a rejection reason; and registering with the VPLMN or selecting a new VPLMN according to the received indication.

[0018] Another embodiment of the techniques is a UE that includes processing hardware and is configured to implement the above method. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a block diagram of an example computing environment in which the SOR techniques of the present disclosure may be implemented.

[0020] Figure 2A shows an example scenario in which the UDM determines whether to accept or reject a registration attempt of a roaming UE at a VPLMN by obtaining SOR information from the SOR-AF via another service;

[0021] Figure 2B Overall Figure 2A Similar, except that the SOR-AF subscribes to event notifications from the HPLMN and the UDM requests SOR information based on the registration;

[0022] Figure 3 is a flow chart of an example method for processing SOR information at a node of a PLMN operating as a home PLMN for a roaming UE and generating a notification related to a registration attempt for the UE;

[0023] Figure 4 is a flow chart of an example method for processing a registration accept message including SOR information, which method may be implemented in a UE of the present disclosure;

[0024] Figure 5A is a flow chart of an example method for processing a registration rejection message including a rejection reason and SOR information, which method may be implemented in a UE of the present disclosure;

[0025] Figure 5B is a flow chart of an example method for processing a registration reject message including a reject reason and a retain indication, which method may be implemented in a UE of the present disclosure;

[0026] Figure 5Cis a flowchart of an example method for processing a registration reject message including a dedicated reject cause and a retention timer, which method may be implemented in a UE of the present disclosure; and

[0027] Figure 6 An example scenario is shown in which the SOR-AF configures RVAS parameters for the HPLMN. DETAILED DESCRIPTION

[0028] Figure 1 An example computing environment 100 is shown that includes a UE 102 that communicates with a VPLMN 120A via a VPLMN RAN 110A that includes one or more base stations, and with a HPLMN 120B. The SOR techniques of the present disclosure may be implemented in computing environment 100, as briefly described below.

[0029] The VPLMN 120A includes a core network having an access and mobility management function (AMF) 121A, which is configured to manage authentication, registration, paging, and other related functions; a network exposure function (NEF) 122A, which allows the services of 3GPP network functions in the VLMN 120A to be securely exposed (e.g., via encryption and authentication mechanisms); a session management function (SMF) 123A, which is configured to manage PDU sessions; a user plane function (UPF) 124A, which is used to deliver user plane packets related to audio calls, video calls, and Internet traffic; a unified data management function (UDM) 125A, which is configured to store and manage security credentials, subscription information, etc.; and a unified data repository 126A, which the UDM 125 can use to store and retrieve subscription data. The VPLMN 120A may also include other components (which are omitted to reduce confusion) that support various functions and services. HPLMN 120B includes similar components in this example and Figure 1 In the drawings, these components are labeled with the same reference numerals and the letter 'B'.

[0030] VPLMN 120A and HPLMN 120B may communicate via link 134. Specifically, Visitor Security Edge Protection Proxy (V-SEPP) 130 of VPLMN 120A may securely communicate with Home Security Edge Protection Proxy (H-SEPP) 132 of HPLMN 120B via link 134 using N32 protocol.

[0031] In addition, the HPLMN NEF 122B may communicate with the SOR-AF 150, which may operate independently of the HPLMN 120B as, for example, a third-party service, and the HLPMN NEF 122B may access the SOR-AF via a network link. In another embodiment, the SOR-AF 150 operates as a node in the core network of the HPLMN 120B.

[0032] In some implementations, the HPLMN 120B may support one or more northbound APIs (i.e., providing lower-level network component access to higher-level network components) to provide a redirection mechanism such that, similar to the redirection mechanism of 4G networks where entities can simply intercept and spoof inter-PLMN messaging, the UE 102 may receive a rejection cause that directs the UE to consider other VPLMNs without causing the UE 102 to reject the only available VPLMN (at least for related services) and encounter a no-service condition. Thus, the HPLMN UDM 125B (or another suitable node of the HPLMN 120B) may selectively direct roaming UEs based on information from the SOR-AF 150.

[0033] For example, UE 102 may receive a registration reject message with a cause value set to "not allowed PLMN", "requested service option not authorized in this PLMN", or "serving network not authorized". If UE 102 simply adds the rejected VPLMN to a forbidden PLMN list typically implemented in a Universal Subscriber Identity Module (USIM), UE 102 will not subsequently access the VPLMN in automatic selection mode. However, when SOR-AF 150 steers UE 102 from VPLMN1 to VPLMN2 during registration, if VPLMN1 is the only available network, HPLMN 120B allows UE 102 to still roam to VPLMN1 instead of placing the UE in a no-service situation.

[0034] Reference now Figure 2A In example scenario 200A, the HPLMN UDM 125B and / or UDR 125B determines whether to accept or reject the attempt by the UE 102 to register with the PLMN 120A based on the SOR information received from the SOR-AF 150A.

[0035] More specifically, the UE 102 transmits 210 a registration request 210 to the VPLMN AMF 121A. The VPLMN AMF 121A and the HPLMN UDM / UDR 125B / 126B (“UDM 126B” for simplicity) exchange 220 initial messages related to the registration request and response, and the VPLMN AMF 121A performs 222 a Nudm_SDM_Get_request operation to request access and mobility subscription data of the UE 102 from the HPLMN UDM 125B.

[0036] In response, the HPLMN UDM 125B performs 230 a Nnef_SOR_get_request operation to obtain SOR information of the UE 102 related to the VPLMN 120A from the SOR-AF 150 via the NEF 122B. The NEF 122B sends 240 a Naf_SOR_get_request to the SOR-AF 150 and receives 242 a Naf_SOR_get_response from the SOR-AF 150. The NEF 122B then provides 232 a Nnef_SOR_get_response to the UDM 125B.

[0037] The UDM 125B uses the SOR information included in the Nnef_SOR_get_response to determine 250 whether to accept or reject the registration attempt previously received 210. In some cases, the UDM 125B may also use the policies of the HPLMN 125B. Figures 3 to 5C Discussing in more detail, the UDM 125B may specify a rejection reason corresponding to a registration procedure or, in another embodiment, specifically defined as a rejection of a registration attempt due to SOR. In some cases, the HPLMN UDM / UDR 125B / 126B also specifies a retention value and / or a retention timer to prevent the UE from missing an opportunity to roam to the VPLMN 120A when no other network is available. The UDM 125B may then specify 260 the registration result in a Nudm_SDM_Get_response operation. As part of the Nudm_SDM_Get_response operation, the UDM 125B may also provide 260 SOR information to the VPLMN AMF 121A.

[0038] The VPLMN AMF 121A then accepts or rejects 262 the registration request previously received 210 and provides the rejection reason, reservation value, reservation timer, etc. to the UE 102. In response, the UE 102 may perform PLMN selection based on the SOR information. The UE 102 may also maintain a list of preferred PLMN / access technology combinations, which the UE 102 may update based on the SOR information and the result (acceptance, rejection) of the transmitted 210 registration attempt.

[0039] Figure 2B Scenario 200B is shown that is generally similar to scenario 200A, except that the SOR-AF subscribes 202 to event notifications from the HPLMN 120B and the UDM 125B requests SOR information upon registration. The differences between scenario 200A and scenario 200B are discussed below.

[0040] The subscription 202 process may involve the SOR-AF 150 invoking a northbound API exposed via the NEF 122B. The SOR-AF 150 may request 202 the VPLMN 120A to notify the SOR-AF 150 of the roaming status of the UE attempting to roam to the VPLMN 120A, provide a location report of the UE, etc. After the UE 102 initiates 210 a registration request message and the VPLMN AMF 121A notifies the HPLMN UDM 125B accordingly, the UDM 125B exchanges 220, 230 messages and determines 250 whether to accept or reject the UE, as described with reference to FIG. Figure 2A described.

[0041] In response to the notification subscription 202, the UDM 125B notifies 231, 241 the SOR-AF 150 via the NEF 122B. The SOR-AF 150 applies 243, 233 the new SOR information to the UE 102 attempting to register with the VPLMN 120A, for example, using a dedicated procedure or a ParameterProvisioning procedure. In some cases, the procedure may trigger a PLMN selection at the UE 102. In this case, the SOR-AF 150 may designate the VPLMN / RAT tuple as the preferred PLMN / RAT tuple and assign the highest priority to the VPLMN / RAT. The UDM 125B may then provide 235, 245 a response to the parameter provisioning or updating procedure via the NEF 122B.

[0042] Figure 3 FIG. 5 provides a method for enabling the HPLMN 120B, the VPLMN 120A and the UE 102 to implement Figure 2A and Figure 2BEach of these methods can be implemented as a set of instructions stored on a non-transitory computer-readable medium and executable by one or more processors.

[0043] Figure 3 is a flow chart of an example method for processing SOR information at a node of a PLMN operating as a home PLMN for a roaming UE and generating a notification related to a registration attempt for the UE;

[0044] First reference Figure 3 , the UDM (e.g., UDM 125B) or another suitable node may perform the example method 300 to process the SOR information and generate a notification related to the registration attempt for the UE. In general, the UDM of the present disclosure may determine whether to accept or reject the registration attempt of the UE based on: (i) operator policies for roaming UEs and for the registered PLMN (VPLMN), and (ii) a message from the SOR-AF in response to a request from the UDM.

[0045] Specifically, at block 302, the UDM 125B may receive SOR information from the SOR-AF. The SOR is associated with a UE attempting to register at a VPLMN for which the UDM's PLMN operates as an HPLMN. Next, at block 304, the UDM may obtain an operator policy associated with the UE and / or the VPLMN. At block 306, the UDM uses the information obtained at blocks 302 and 305 to determine whether to accept or reject the registration attempt.

[0046] If the UDM determines to accept the request, flow proceeds to block 320 where the UDM generates an acceptance indication or notification for the VPLMN and includes the SOR information and the retention timer value in the notification. However, in other implementations, the UDM omits the retention timer value, the SOR information, or both from the notification.

[0047] Including a retention timer at block 320 allows the HPLMN to temporarily suspend access to the VPLMN. After a period of time corresponding to the retention timer value expires, the UE may retry registration with the VPLMN if necessary. In some cases, the UDM may set the retention timer value to zero. When the SOR information included by the UDM in the acceptance notification belongs to the VPLMN, the UE may consider the VPLM as a low priority access candidate (see Figure 4 ). According to TS 38.304, the UE may select a VPLMN again, depending on the cell selection process. Figure 4 As discussed, when the retention timer is greater than zero, the UE may include the VPLMN in a steered-away PLMN list.

[0048] Continue to refer Figure 3 , the UDM may provide an acceptance indication to the UE via the VPLMN at block 322 (see events 260 , 261 ).

[0049] If the UDM determines to reject the request, the flow proceeds from block 306 to block 308, where the UDM notifies the SOR-AF of the rejection. The flow may then proceed to block 310 or 312, depending on the implementation. At block 310, the UDM selects a rejection cause associated with the registration procedure for the UE from the rejection causes. Thus, the UDM uses the causes defined by the previous 3GPP standards in this implementation, independent of the development of the SOR technology. Alternatively, at block 312, the UDM selects a rejection cause specifically defined for temporarily restricting roaming to VPLM.

[0050] Regardless, flow proceeds to block 314 where the UDM includes the SOR information in the rejection indication or notification. At optional block 316, the UDM may include a retain indication or a retain timer in the rejection indication. At block 318, the UE provides the rejection indication to the UE via the PLMN.

[0051] The handling of SOR information, rejection reasons, retention indications, and / or retention timers is further discussed with reference to UE methods 400 and 500A-C.

[0052] Figure 4 The method 400 of the present invention begins at block 402, where the UE receives a registration accept message including SOR information and a retention timer value. If the UE determines that the retention timer is greater than zero, the process proceeds to block 406, where the UE includes the VPLMN in the list of steering PLMNs. For the UE, these VPLMNs are lower priority networks for roaming access purposes. The UE can maintain the list in a memory or in the USIM, and in some cases can also store the corresponding timer retention value.

[0053] At block 404, if the UE determines that the reservation value is zero, the block proceeds to block 408. At block 408, the UE may perform PLMN selection based on the SOR information and ignore the PLMNs included in the steering PLMN list for which the corresponding reservation timers are still running. When the SOR information received at block 402 belongs to a VPLMN, the UE may consider the VPLM as a low priority access candidate. At block 450, the UE may register with the VPLMN with the highest priority.

[0054] Therefore, the UE may use the retention timer to temporarily avoid attempting to register with the PLMN corresponding to the retention timer. When the retention timer expires, the UE removes the PLMN from the steering PLMN list.

[0055] When the UE is a legacy UE that does not recognize the retention timer, the UE will ignore the information element including the retention timer and operate as expected according to the acceptance indication. The legacy UE may continue to apply the legacy SOR mechanism according to the acceptance indication received at block 402.

[0056] Reference now Figure 5A , an example method 500 for processing a registration reject message including a reject cause and SOR information may be implemented in UE 102 or another suitable UE. At block 502, the UE receives a registration reject indication or notification for a certain PLMN, the registration reject indication or notification including a reject cause and, in some cases, SOR information.

[0057] At block 510, the UE adds the PLMN to a prohibited PLMN list, which the UE may store in a memory or USIM similar to the diversion PLMN list. If the rejection indication includes, for example, a cause value of "5GMM cause #11 (PLMN not allowed)" or "5GMM cause #73 (Service network not authorized)" or if the message includes a cause value of "5GMM cause #7 (5GS service not allowed)" in another implementation of the PLMN, then in automatic mode, the UE will not access the PLMNs on the prohibited list, except for disaster roaming services.

[0058] If the UE determines at block 520 that the rejection indication does not include SOR information related to the PLMN, flow proceeds to block 530 where the UE performs PLMN selection and ignores the PLMNs included in the forbidden PLMN list.

[0059] If the UE determines at block 510 that the rejection indication includes SOR information related to the PLMN, the flow proceeds to block 540 where the UE performs PLMN selection based on the SOR information and removes the PLMN from the forbidden PLMN list. At block 550, the UE may register with the VPLMN with the highest priority.

[0060] Overall reference Figure 5A, in order to avoid a no-service scenario at a roaming UE, the UDM may update the UE with new SOR information during or after the registration reject process. If the SOR information includes VPLMN information, the UE may remove the VPLMN from the prohibited PLMN list for 5GS service, or from the prohibited PLMN list (depending on the network implementation). Therefore, the SOR-AF and / or UDM may generate the SOR information for the registration reject message in the absence of a rejected VPLMN or with a VPLMN listed with a lower priority. If the registration reject message does not include SOR information, the UDM may update the SOR information when the UE performs a registration request for mobility update or periodic update or after the UE successfully registers with another VPLMN.

[0061] In addition, after receiving the Registration Reject message, the UE performs PLMN selection based on the EPLMN list or the latest SOR information (if available), while considering the VPLMN as a lower priority option, but not prohibited from access. Legacy UEs will not have backward compatibility issues because the UDM can use the same rejection cause. When the legacy UE does not recognize the SOR information in the Registration Reject message, the legacy UE can ignore the SOR information.

[0062] Figure 5B An example method 500B for processing a registration rejection message including a rejection reason and a retention indication is shown, which can be implemented in UE 102 or another suitable UE. At block 503, the UE receives a registration rejection indication with a rejection reason and a retention indication. At block 511, the UE adds the PLMN to the steering PLMN list and includes a corresponding retention timer in some cases. If the UE 102 determines that the steering PLMN list is empty (block 521), the UE performs PLMN selection based on the previous SOR information or the EPLMN list (block 531). Otherwise, the UE performs PLMN selection at block 531 and ignores the PLMN included in the steering list. At block 550, the UE may register with the VPLMN with the highest priority.

[0063] Therefore, the registration rejection message in the present implementation may include a rejection reason, a retention indication, and SOR information. The rejection reason may be, for example, "5GMM Reason #11 (PLMN not allowed)", "5GMM Reason #73 (Service network not authorized)" or "5GMM Reason #7 (5GS service not allowed)".

[0064] Here, with the rejection cause and the retention indication, the UE includes the VPLMN in the list of redirected PLMNs based on the EPLMN list or the latest SOR information (when available), which are redirected during the PLMN selection process and are considered to have lower priority. When the UE performs PLMN selection, the UE ignores the PLMNs in the list of redirected PLMNs.

[0065] Alternatively, the retention indication may be a retention timer value of the rejected VPLMN. The retention timer corresponds to a specific VPLMN and prevents the UE from selecting the VPLMN for a period of time. The UE maintains a retention timer for each PLMN in the redirection PLMN list. When the retention timer of a PLMN expires, the UE removes the PLMN from the redirection PLMN list. However, the UE ignores PLMNs for which an active retention timer is running.

[0066] Figure 5C 1 is a flow chart of an example method 500C for processing a registration rejection message including a dedicated rejection cause and a retention timer. At block 504, the UE receives a registration rejection indication having a rejection cause specifically defined for restricting access to a VPLMN and a retention timer value. At block 512, the UE adds the PLMN to a steering PLMN list and includes a corresponding retention timer. If the UE 102 determines that the steering PLMN list is empty (block 521), the UE performs PLMN selection based on a previous SOR information or an EPLMN list (block 531). Otherwise, the UE performs PLMN selection at block 531 and ignores the PLMNs included in the steering list. At block 550, the UE may register with the VPLMN with the highest priority.

[0067] Figure 6 An example scenario 600 is shown in which a SOR-AF configures RVAS parameters for the HPLMN.

[0068] The VPLMN AMF 121A first subscribes 640 to the notification service for RVAS updates from the UDM, which can be part of the registration request process when the registration request at the VPLMN is successful. Then, the SOR-AF determines to configure the RVAS parameters including the SOR information to the UDM / UDR of the target UE identifier using a dedicated procedure for RVAS or using an existing external parameter configuration procedure (643, 633, 680, 681).

[0069] When the UDM / UDR receives 633 the new parameter set to the RVAS, the UDM selects 682 the SOR information that meets the validity criteria and provides 661 the selected SOR information to the VPLMN AMF in a Nudm_SDM_Notification request message.

[0070] If any condition set by the SOR-AF is not satisfied, the UDM may skip 661, 691, 692 and 663, and indicate 635, 645 the provisioning failure reason in the return message of the Nnef_ParameterProvision_Create / Update / Delete response message and the Naf_ParameterProvision_Create / Update / Delete response message to the SOR-AF.

[0071] like Figure 6 As further shown, the UDM sends a notification message including the selected SOR information to the VPLMN AMF; the VPLMN AMF sends the selected SOR information to the UE via a DL NAS transport message; the UE may need to send an ack message to the AMF / UDM via a UL NAS transport message; the UDM further includes the ack message and the selected SOR information in the return message of the Nnef_ParameterProvision_Create / Update / Delete response message in step 10 and the Naf_ParameterProvision_Create / Update / Delete response message to the SOR-AF in step 11; and the UE maintains a preferred PLMN / access technology combination list accordingly based on the SOR information and the registration acceptance or registration rejection message. Then, the UE performs PLMN selection based on the EPLMN list or the SOR information (if available).

[0072] The following list of examples reflects various implementations expressly contemplated by the present disclosure:

[0073] Example 1. A method for supporting directed roaming (SOR) implemented in a node of a core network (CN) of a public land mobile network (PLMN), the method comprising: receiving an indication of a registration attempt for a UE, for which the PLMN operates as a home PLMN (HPLMN), and the registration attempt occurs at a visitor PLMN (VPLMN); obtaining SOR information related to the registration attempt from an entity configured to provide SOR information of the CN; determining whether to accept or reject the registration attempt based at least on a received response; and providing a result of the determination to the VPLMN.

[0074] Example 2. The method of example 1, wherein obtaining the SOR information comprises obtaining the SOR information from a SOR application function (SOR-AF).

[0075] Example 3. The method of Example 2, further comprising transmitting a request including an identifier of the VPLMN and an identifier of the UE to a network opening function (NEF) operating in the HPLMN.

[0076] Example 4. The method of Example 3, wherein obtaining the SOR information comprises receiving a response to the request from the NEF, the response comprising the SOR information.

[0077] Example 5. The method of Example 2, further comprising: determining that the entity is subscribed to notifications from the HPLMN related to a roaming status of the UE; and in response to a registration attempt, notifying the entity of the roaming status of the UE.

[0078] Example 6. The method of Example 5, wherein notifying the entity of the roaming status of the UE comprises transmitting a notification via a NEF.

[0079] Example 7. The method of Example 6, wherein obtaining the SOR information from the entity comprises receiving the SOR information from the entity via the NEF in response to transmitting the notification.

[0080] Example 8. The method of any one of Examples 5 to 7, wherein obtaining the SOR information comprises performing a parameter configuration process with the entity.

[0081] Example 9. A method according to any of the preceding examples, wherein determining whether to accept or reject the registration attempt comprises: determining an operator policy related to the UE and the VPLMN; and determining whether to accept or reject the registration attempt based on the operator policy and the received response from the entity.

[0082] Example 10. The method of any preceding example, further comprising: in response to determining to accept the registration attempt, providing the SOR information to the UE via the VPLMN.

[0083] Example 11. The method of Example 10, further comprising providing a retention timer value to the UE via the VPLMN, the retention timer value specifying a time period for the UE to avoid registering with the VPLMN.

[0084] Example 12. The method of Example 11, comprising setting the retention timer to zero in response to determining that the operator policy does not prevent the UE from immediately registering with the VPLMN.

[0085] Example 13. The method of any one of Examples 1 to 9, further comprising: in response to determining to reject the registration attempt, providing to the VPLMN (i) a rejection reason specified for the registration process selected from a plurality of cause values, and (ii) the SOR information received from the entity.

[0086] Example 14. The method according to any one of Examples 1 to 9 further includes: in response to determining that the registration attempt is rejected, providing to the VPLMN (i) a rejection reason specified for the registration process selected from multiple cause values, (ii) the SOR information received from the entity, and (iii) a retention indication for directing the UE to retain the VPLMN in the list of VPLMNs to be redirected from lower priority.

[0087] Example 15. The method of any one of Examples 1 to 9, further comprising: in response to determining that the registration attempt is rejected, providing to the VPLMN (i) a rejection reason specified for the registration process selected from a plurality of cause values, (ii) the SOR information received from the entity, and (iii) a retention timer value for directing the UE to keep the VPLMN in the list of VPLMNs to be diverted from lower priority for a specified period of time.

[0088] Example 16. The method of any one of Examples 1 to 9 or 12, further comprising: in response to determining to reject the registration attempt, providing to the VPLMN (i) a rejection reason specifically defined for temporarily restricting roaming to the VPLMN, (ii) the SOR information received from the entity, and (iii) a retention timer value for directing the UE to keep the VPLMN in the list of diverted lower priority VPLMNs for a specified period of time.

[0089] Example 17. The method of any one of Examples 13 to 16, further comprising: in response to determining to reject the registration attempt, notifying the entity that the registration attempt of the UE at the VPLMN is rejected.

[0090] Example 18. The method of any preceding example, wherein the SOR-AF operates independently of the HPMN as a third party service.

[0091] Example 19. A method according to any of the preceding examples, wherein the SOR-AF operates as a service within the HPMN.

[0092] Example 20. The method of any of the preceding examples, wherein the node is a unified data management node (UDM).

[0093] Example 21. A network node comprising processing hardware and configured to implement a method according to any of the preceding examples.

[0094] Example 22. A method for registering with a VPLMN in a UE associated with a HPLMN, the method comprising: transmitting a registration request to the VPLMN; receiving, via the PLMN, a message indicating whether the registration request is rejected or accepted, the message comprising SOR information and at least one of: (i) a retention indication, (ii) a retention timer value, or (iii) a rejection reason; and registering with the VPLMN or selecting a new VPLMN according to the received indication.

[0095] Example 23. The method of Example 22, wherein: the message indicates that the registration request is accepted; and the message includes the retention timer value.

[0096] Example 24. The method of Example 23, further comprising: in response to determining that the retention timer value is non-zero, adding the VPLMN to a list of steering PLMNs, wherein registering with the VPLMN or selecting the new VPLMN includes avoiding attempting to register with any PLMN included in the list of steering PLMNs.

[0097] Example 25. The method of Example 23, further comprising: in response to determining that the retention timer value is zero, removing the VPLMN from a steering PLMN list, wherein registering with the VPLMN or selecting the new VPLMN includes avoiding attempting to register with any PLMN included in the steering PLMN list.

[0098] Example 26. The method of Example 22, wherein: the message indicates that the registration request is rejected; and the message includes selecting the rejection reason specified for the registration process from among a plurality of cause values.

[0099] Example 27. The method of Example 22, wherein: the message indicates that the registration request is rejected; and the message includes the rejection reason defined for temporarily restricting roaming to the VPLMN.

[0100] Example 28. The method according to Example 26 or 27 further includes: adding the VPLMN to a prohibited PLMN list; and in response to determining that the SOR information belongs to the VPLMN, removing the VPLN from the prohibited PLMN list, wherein the UE avoids attempting to register with any PLMN included in the prohibited PLMN list.

[0101] Example 29. The method according to Example 26 or 27 further includes: adding the VPLMN to a prohibited PLMN list; and maintaining the VPLN in the prohibited PLMN list in response to determining that the SOR information does not belong to the VPLMN, wherein the UE avoids attempting to register with any PLMN included in the prohibited PLMN list.

[0102] Example 30. The method of Example 22, wherein: the message indicates that the registration request is denied; and the message includes the retention indication.

[0103] Example 31. The method of Example 30, further comprising: adding the VPLMN to a steering-away PLMN list.

[0104] Example 32. A UE comprising processing hardware and configured to implement a method according to any one of Examples 22 to 31.

[0105] Additional considerations

[0106] The following additional considerations apply to the foregoing discussion.

[0107] The client device (e.g., client device 102) in which the techniques of the present disclosure may be implemented may be any suitable device capable of wireless communication, such as a smartphone, a tablet computer, a laptop computer, a desktop computer, a mobile game console, a point of sale (POS) terminal, a health monitoring device, a drone, a camera, a media streaming dongle or another personal media device, a wearable device such as a smart watch, a wireless hotspot, a femtocell, or a broadband router. In addition, in some cases, the client device may be embedded in an electronic system such as a head unit of a vehicle or an advanced driver assistance system (ADAS). Further, the client device may operate as an Internet of Things (IoT) device or a mobile Internet device (MID). Depending on the type, the client device may include one or more general purpose processors, a computer readable memory, a user interface, one or more network interfaces, one or more sensors, and the like.

[0108] Certain embodiments are described in the present disclosure as including logic or multiple components or modules. A module can be a software module (e.g., a code stored on a non-temporary machine-readable medium) or a hardware module. A hardware module is a tangible unit that can perform certain operations and can be configured or arranged in a particular manner. A hardware module can include a dedicated circuit system or logic that is permanently configured (e.g., as a dedicated processor, such as a field programmable gate array (FPGA) or an application-specific integrated circuit (ASIC)) to perform certain operations. A hardware module can also include a programmable logic or circuit system (e.g., as contained in a general-purpose processor or other programmable processor) that is temporarily configured by software to perform certain operations. The decision to implement a hardware module in a dedicated and permanently configured circuit or in a temporarily configured circuit (e.g., configured by software) can be driven by cost and time considerations.

[0109] When implemented in software, the techniques may be provided as part of an operating system, a library used by multiple applications, a specific software application, etc. The software may be executed by one or more general-purpose processors or one or more special-purpose processors.

Claims

1. A method for supporting directed roaming (SOR) implemented in a node of a core network (CN) of a public land mobile network (PLMN), the method comprising: receiving an indication of a registration attempt for a UE, the PLMN operating as a home PLMN (HPLMN) for the UE, the registration attempt occurring at a visitor PLMN (VPLMN); obtaining SOR information associated with the registration attempt from an entity configured to provide SOR information for the CN; determining whether to accept or reject the registration attempt based at least on the received SOR information and an operator policy associated with the UE and the VPLMN; as well as A result of the determination is provided to the VPLMN.

2. The method according to claim 1, further comprising: A request including an identifier of the VPLMN and an identifier of the UE is transmitted to a network opening function (NEF) operating in the HPLMN.

3. The method according to claim 1 or 2, further comprising: determining that the entity subscribes to notifications from the HPLMN related to the roaming status of the UE; as well as In response to the registration attempt, the entity is notified of the roaming status of the UE.

4. The method of claim 3, wherein obtaining the SOR information from the entity comprises: The SOR information is received from the entity via the NEF in response to notifying the entity of the roaming status of the UE via the NEF.

5. The method according to any one of claims 1 to 4, further comprising: A retention timer value is provided to the UE via the VPLMN, the retention timer value specifying a time period for the UE to refrain from registering with the VPLMN.

6. The method of claim 5, comprising setting the retention timer to zero in response to determining that the operator policy does not prevent the UE from immediately registering with the VPLMN.

7. The method according to any one of claims 1 to 4, further comprising: In response to determining to reject the registration attempt, providing to the VPLMN one or more of: (i) select a rejection reason from among a plurality of reason values ​​to be specified for the registration process, (ii) said SOR information received from said entity, or (iii) a retention indication for directing the UE to retain the VPLMN in the list of VPLMNs that are directed away from lower priority levels.

8. A method in a UE associated with an HPLMN for registering with a VPLMN, the method comprising: Transmitting a registration request to the VPLMN; receiving, via the VPLMN, a message indicating whether the registration request is rejected or accepted, the message including SOR information and at least one of: (i) a retention indication, (ii) a retention timer value, or (iii) a rejection reason; as well as Register with the VPLMN or select a new VPLMN according to the received indication.

9. The method according to claim 8, wherein: The message indicates that the registration request is accepted; and The message includes the reserve timer value; and In response to determining that the retain timer value is non-zero, adding the VPLMN to a steering-away PLMN list, Wherein registering with the VPLMN or selecting the new VPLMN includes avoiding attempting to register with any PLMN included in the steering PLMN list.

10. The method according to claim 8, wherein: The message indicates that the registration request is accepted; and The message includes the retention timer value; the method further comprising: In response to determining that the retain timer value is zero, excluding the VPLMN from the steering-away PLMN list, Wherein registering with the VPLMN or selecting the new VPLMN includes avoiding attempting to register with any PLMN included in the steering PLMN list.

11. The method according to claim 8, wherein: The message indicates that the registration request is denied; and The message includes selecting the rejection reason specified for the registration process from among a plurality of cause values.

12. The method according to claim 8, wherein: The message indicates that the registration request is denied; and The message includes the rejection cause specifically defined for temporarily restricting roaming to the VPLMN.

13. The method according to claim 11 or 12, further comprising: Adding the VPLMN to a prohibited PLMN list; as well as In response to determining that the SOR information belongs to the VPLMN, removing the VPLMN from the forbidden PLMN list, The UE avoids attempting to register with any PLMN included in the forbidden PLMN list.

14. The method according to claim 11 or 12, further comprising: Adding the VPLMN to a prohibited PLMN list; as well as In response to determining that the SOR information does not belong to the VPLMN, maintaining the VPLMN in the prohibited PLMN list, The UE avoids attempting to register with any PLMN included in the forbidden PLMN list.

15. An apparatus comprising processing hardware and configured to implement a method according to any preceding claim.

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