Radio access type based restriction

Abstract

There is provided a method performed by a first network node configured to manage network sessions of user equipments (UEs). The method comprises receiving a request related to a network session associated with a first radio access type (RAT). The method further comprises obtaining first RAT information which indicates a list of one or more RATs allowed by a second network node. The second network node is configured to manage network nodes for managing network sessions of UEs. The method further comprises, after receiving the request and obtaining the first RAT information, determining whether to accept or reject the request, wherein whether to accept or reject the request is determined based on the list of one or more RATs allowed by the second network node. The method further comprises, after the determination, transmitting a response to the request, which indicates whether the request is accepted or rejected.

Description

RADIO ACCESS TYPE BASED RESTRICTIONTECHNICAL FIELD

[0001] This disclosure relates to radio access type (RAT) based restriction (hereinafter just “RAT restriction”).BACKGROUND

[0002] 5G Core (5GC) provides telecommunication services to users via different Radio Access Types (RATs) which provide different access capabilities. RAT identifies transmission technology used in the access network for both 3GPP (3rdGeneration Partnership Project) accesses and non-3GPP accesses.

[0003] In order to control user access to the network and apply differentiated charging, 3GPP TS (Technical Specification) 23.501 vl8.4.0 defines different types of mobility restrictions. One of the mobility restrictions is RAT restriction. In a restricted RAT, based on subscription, a user equipment (UE) may not be permitted to access the network.

[0004] For a given UE, the core network determines mobility restrictions based on UE subscription information. Unified data management (UDM) may allow or deny registration of users based on RAT restriction information and provide to access and mobility management function (AMF) information about the subscriber’s RAT restriction set by the operator for primary and / or secondary RAT.

[0005] Upon UE mobility within 5GC or between 5GC and Evolved Packet Core (EPC) using the same RAT or a different RAT, the RAT restrictions provided by UDM are passed to the new nodes involved in the connection procedures. For example, new AMF may retrieve RAT restriction information from old AMF as part of Namf communication UE context transfer, and new MME (Mobility Management Entity) / AMF may retrieve access restriction data from old AMF / MME using N26 GTPv2 interface.

[0006] The RAT restriction information may also be sent from MME to Radio Access Network (RAN) in the Handover Restriction List Information Element (IE) as described in 3GPP TS 36.413 V18.2.0. Similar handling also applies in 5GC where AMF sends the RAT restriction information to the RAN in the Mobility Restriction List IE as described in 3GPP TS 38.413V18.2.0.

[0007] RAN may trigger a handover taking the information in mobility restriction list or handover restriction list into consideration. Handover to a target cell for a restricted RAT will be blocked by RAN and will not be initiated by RAN. This is to prevent repeated handover attempts after the rejection of an initial handover attempt.

[0008] In idle mode mobility, it is the AMF / MME’s responsibility to restrict a UE based on RAT restriction, mainly based on subscription information. This applies to intra 5G mobility, inter RAT mobility, and intra 4G mobility.

[0009] There are multiple RATs defined in 5GC, and the RAT list keeps increasing as the technology evolves. RAT type is a concept used in Core Network (CN) such as, for example, in AMF, UDM, and to some intent in RAN. UE provides some indication to the network, which is converted to a RAT type. The UE indication could be provided via RAN and / or to AMF, and it can be propagated further in the core network.

[0010] The UE indication can be implicit (e.g., for New Radio (NR) RAT Type) or explicit(e.g., for Reduced Capability (RedCap) RAT type). In case the UE indication is explicit, the UE indication can be sent directly to AMF or via RAN to AMF. RAN enables indications “per RAT” to UE which may be a configuration, for example, per cell level. RAN can have a cell “supporting RATs” while other RAT(s) are not supported for that cell.

[0011] AMF may include a handover restriction list such that handover to cells with restricted RATs can be avoided. This means that RAN will not handover a UE to a cell indicated as “RAT restricted,” which is given by the handover restriction list.SUMMARY

[0012] Certain challenges presently exist. For example, because, in 3GPP TS 29.503 vl 8.4.0, RAT restrictions are defined using new enumerated values, it is not possible for UDM to indicate RAT restriction for a new RAT when the new RAT is not implemented and / or supported by UDM. In other words, it is not possible for UDM to indicate the RAT restriction for the new RAT because UDM does not know which new enumerated value to use to indicate the RAT restriction. This causes the new RAT to appear as not being restricted - i.e., being allowed from UDM perspective. This problem also applies to other interfaces, such asNamf communi cation UE context transfer service between AMFs, in the case old AMF does not support a new RAT that is supported by new AMF. Furthermore, this problem occurs in a mobility registration scenario where UE is moving from 4G to 5G and old MME is used. In this scenario, AMF in 5G does not know which RATs are supported or not supported by UDM.

[0013] Therefore, there is a need for a method and / or a system for explicitly indicating to entities (e.g., AMF) in a network as to which RATs are restricted and / or supported such that the entities do not assume that RATs are not restricted because of lack of explicit signaling of information about RAT restriction.

[0014] Accordingly, in one aspect of some embodiments of this disclosure, there is provided a method performed by a first network node which is configured to manage network sessions of user equipments, UEs. The method comprises receiving a request related to a network session, wherein the request related to a network session is associated with a first radio access type, RAT. The method further comprises obtaining first RAT information which indicates a list of one or more RATs allowed by a second network node, wherein the second network node is configured to manage network nodes for managing network sessions of UEs. The method further comprises, after receiving the request and obtaining the first RAT information, determining whether to accept or reject the request, wherein whether to accept or reject the request is determined based on the list of one or more RATs allowed by the second network node. The method further comprises, after the determination, transmitting a response to the request, which indicates whether the request is accepted or rejected.

[0015] In another aspect, there is provided a method performed by a first network node which is configured to manage network sessions of user equipments, UEs. The method comprises receiving, from a second network node a request related to a network session, wherein the second network node is configured to manage network sessions of UEs. The method further comprises obtaining first RAT information which indicates a list of one or more RATs allowed by a third network node, wherein the third network node is configured to manage network nodes for managing network sessions of UEs. The method further comprises, after receiving the request and obtaining the first RAT information, transmitting a response to the request, which indicates the list of one or more RATs allowed by the third network node.

[0016] In a different aspect, there is provided a method performed by a first network node which is configured to manage network nodes for managing network sessions of user equipments,UEs. The method comprises receiving, from a second network node, a request related to a network session, wherein the second network node is configured to manage network sessions of UEs. The method further comprises, after receiving the request, transmitting, to the second network node, a response to the request, which indicates a list of one or more RATs allowed by the first network node.

[0017] In a different aspect, there is provided a computer program comprising instructions which when executed by processing circuitry cause the processing circuitry to perform the method of any one of the above embodiments.

[0018] In a different aspect, there is provided a carrier containing the computer program of the above embodiment, wherein the carrier is one of an electronic signal, an optical signal, a radio signal, and a computer readable storage medium.

[0019] In a different aspect, there is provided a first network node for managing network sessions of user equipments, UEs. The first network node is configured to receive a request related to a network session, wherein the request related to a network session is associated with a first radio access type, RAT. The first network node is further configured to obtain first RAT information which indicates a list of one or more RATs allowed by a second network node, wherein the second network node is configured to manage network nodes for managing network sessions of UEs. The first network node is further configured to, after receiving the request and obtaining the first RAT information, determine whether to accept or reject the request, wherein whether to accept or reject the request is determined based on the list of one or more RATs allowed by the second network node. The first network node is further configured to, after the determination, transmit a response to the request, which indicates whether the request is accepted or rejected.

[0020] In a different aspect, there is provided a first network node for managing network sessions of user equipments, UEs. The first network node is configured to receive, from a second network node a request related to a network session, wherein the second network node is configured to manage network sessions of UEs. The first network node is further configured to obtain first RAT information which indicates a list of one or more RATs allowed by a third network node, wherein the third network node is configured to manage network nodes for managing network sessions of UEs. The first network node is further configured to, after receiving the request and obtaining the first RAT information, transmit a response to the request, whichindicates the list of one or more RATs allowed by the third network node.

[0021] In a different aspect, there is provided a first network node for managing network nodes that are configured to manage network sessions of user equipments, UEs. The first network node is configured to receive, from a second network node, a request related to a network session, wherein the second network node is configured to manage network sessions of UEs. The first network node is further configured to, after receiving the request, transmit, to the second network node, a response to the request, which indicates a list of one or more RATs allowed by the first network node.

[0022] In a different aspect, there is provided an apparatus comprising processing circuitry; and a memory, said memory containing instructions executable by said processing circuitry, whereby the apparatus is operative to perform the method of any one of the above embodiments.

[0023] Embodiments of this disclosure allow informing RAT restriction to entities in a network even when RATs are not allowed by UDM.BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate various embodiments.

[0025] FIG. 1 shows an exemplary scenario where some embodiments of this disclosure can be applied.

[0026] FIG. 2 shows an example of a registration process.

[0027] FIG. 3 shows an example of a registration process.

[0028] FIG. 4 shows a process according to some embodiments.

[0029] FIG. 5 shows a process according to some embodiments.

[0030] FIG. 6 shows a process according to some embodiments.

[0031] FIG. 7 shows a process according to some embodiments.

[0032] FIG. 8 shows a process according to some embodiments.

[0033] FIG. 9 shows a process according to some embodiments.

[0034] FIG. 10 shows a process according to some embodiments.

[0035] FIG. 11 shows a process according to some embodiments.

[0036] FIG. 12 shows an apparatus according to some embodiments.

[0037] FIG. 13 shows an apparatus according to some embodiments.DETAILED DESCRIPTION

[0038] FIG. 1 shows an exemplary scenario 100 where some embodiments of this disclosure can be applied. In scenario 100, there is provided a UE 102 which is capable of accessing data network (DN) 116 via 5GC network 114 using any of two RATs. In scenario 100, the two RATs are 1) “NR” which is used to provide a connection between UE 102 and a gNB Central Unit (CU) 112 via a gNB Distributed Unit (DU) 104 and 2) “NR_GEO” (Geostationary Earth Orbit) which is used to provide a connection between UE 102 and gNB CU 112 via a GEO satellite 106 and a gateway 108.

[0039] Note that the number and types of the RATs illustrated in FIG. 1 are provided for simple explanation purpose only and do not limit the embodiments of this disclosure in any way. More specifically, UE 102 may be capable of accessing DN 116 via 5GC network 114 using any one or more of the RATs that have been introduced since 3GPP Release 15 where 5GC was introduced. Table 1 provided below shows a list of different RATs that have been introduced since 3 GPP Release 15.Table 1 : Enumeration Values for Different RATs

[0040] Generally UEs cannot start using new RAT(s) until the new RAT(s) is supported in the 5GC. For example, in case a new RAT is not supported by UDM, by default, UDM does not allow the registration of a UE in the 5GC using the non-supported new RAT. As specified in 3GPP 29.503 vl 8.4.0 and illustrated in FIG. 2, this is enforced by UDM during Nudm UECM AMF registration procedure by UDM responding AMF with error 403 forbidden Cause “RAT NOT ALLOWED” when AMF attempts to register itself at UDM with an indication of the non-supported new RAT (“RAT=X” in the figure).

[0041] Those RATs that are supported in the 5GC can be included in a list of RATs that are restricted for use as a primary RAT (“primary RAT restrictions”) and / or a list of RATs thatare restricted for use a secondary RAT (“secondary RAT restrictions”). UDM may have these lists and share the lists with other network functions (NFs) in the 5GC, which are involved in mobility restrictions. For example, UDM may provide to AMF the primary and secondary RAT restrictions as part of AccessAndMobilitySubscription data such that AMF can forward the restrictions to AMF / MME and UEs.

[0042] The attributes shown in Table 2 provided below are defined in 3GPP TS 29.503 vl 8.4.0 to convey RAT restrictions to AMF in accessAndMobility Subscript! onData:Table 2

[0043] Certain challenges presently exist. As mentioned above, because, in 3GPP TS 29.503 vl 8.4.0, RAT restrictions are defined using new enumerated values, it is not possible for UDM to indicate RAT restriction for a new RAT when the new RAT is not implemented and / or supported by UDM. In other words, it is not possible for UDM to indicate the RAT restriction for the new RAT because UDM does not know which new enumerated value to use to indicate the RAT restriction. This causes the new RAT to appear as not being restricted - i.e., being allowed from UDM perspective.

[0044] As illustrated in FIG. 3, this problem also applies to other interfaces, such as Namf communi cation UE context transfer service between AMFs, in the case old AMF does not support a new RAT that is supported by new AMF. In FIG. 3, because the old AMF does not support a new RAT, when the old AMF sends a list of restricted RATs using the Namf communi cation UeContextTransfer response, the list does not include the new RAT even when the new RAT should be restricted. Then based on the absences of the new RAT in the list of restricted RATs, the new AMF may assume that the new RAT is allowed.

[0045] This problem also occurs in a mobility registration scenario where UE is moving from 4G to 5G and old MME is used. In this scenario, AMF in 5G does not know which RATs are supported or not supported by UDM.

[0046] In order to solve the above problem, in some embodiments of this disclosure, thereis provided a method and / or a system for explicitly indicating to entities (e.g., AMF) in a network as to which RATs are restricted and which RATs are supported (or supported and allowed) such that the entities do not assume that RATs are not restricted because of lack of explicit signaling of information about RAT restriction.

[0047] Note that, in this disclosure, a list of supported RATs may be a list of RATs that are supported by an UDM. If a RAT is not supported by the UDM, the UDM may not recognize the RAT. For example, the UDM may not understand the RAT identifier identifying the unsupported RAT.

[0048] On the contrary, a list of restricted RATs may be a list of RATs that is supported by the UDM but, for reason(s), the use of the RAT is restricted by the UDM. For example, in case a RAT is restricted by the UDM for a specific type of UE (e.g., RedCap UE) for a specific type of subscription, the UDM may not allow a UE to use the RAT if the UE is of the specific type and is associated with the specific type of subscription. In this disclosure, the term “an extended list of restricted RATs” is used. The extended list of restricted RATs may mean a combination of the list of restricted RATs and a list of RATs that are not included in the list of supported RATs.

[0049] A list of allowed RATs may be a list of RATs that is not only supported by the UDM but also is not restricted by the UDM. This means that the list of allowed RATs is a subset of the list of supported RATs. Like the list of restricted RATs, the list of allowed RATs may be associated with specific condition(s). For example, a RAT may be allowed to be used by UEs in case the UE is of a specific type and is associated with a specific type.

[0050] FIG. 4 shows a process 400 for indicating to entities in a network as to which RATs are restricted and which RATs are supported, according to some embodiments. Process 400 may begin with step s402. Step s402 comprises a first network node 402 receiving a request (e.g., registration request, Tracking Area (TA) update request, handover request, etc.) related to a network session from a third network node 406.

[0051] After first network node 402 receiving the request, process 400 may proceed to step s404. Step s404 comprises first network node 402 obtaining RAT information which includes a list of one or more RATs supported by a second network node (not shown). In some embodiments, the RAT information may also include a list of one or more RATs restricted by the second network node (not shown). Note that the second network node (not shown) and third network node 406may be the same or different. Even though FIG. 4 shows that step s404 is performed after step s402, in some embodiments, step s404 is performed before step s402.

[0052] After obtaining the RAT information, process 400 may proceed to step s406. Step s406 comprises determining whether to accept or reject the request based on the list of one or more RATs supported by the second network node and optionally the list of one or more RATs restricted by the second network node.

[0053] For example, in case the request s402 is associated with a specific RAT but the specific RAT is included in neither the list of supported RATs nor the list of restricted RATs, first network node 402 may reject the request. This exemplary scenario may arise when the network currently does not support the specific RAT and no value is defined for the specific RAT in the list of restricted RATs or in the list of supported RATs.

[0054] In another example, in case the request s402 is associated with a specific RAT and the specific RAT is included in both the list of supported RATs and the list of restricted RATs, first network node 402 may reject the request. This exemplary scenario may arise when the network currently supports the specific RAT but expressly restrict the use of the specific RAT.

[0055] After making the determination, process 400 may proceed to step s408. In step s408, first network node 402 transmits to third network node 406 a response to the request, which indicates whether the request is accepted or rejected.

[0056] FIGS. 5-8 show implementation examples of process 400 according to some embodiments.

[0057] FIG. 5 shows a process 500 for performing an initial registration of UE 502 according to some embodiments.

[0058] Process 500 is an example of process 400 shown in FIG. 4. More specifically, in process 500, new AMF 504 corresponds to first network node 402 in process 400, UE / gNB 502 corresponds to third network node 406 in process 400, and UDM 506 corresponds to the second network node which is mentioned with respect to process 400. As explained above, the second network node is not shown in FIG. 4. Process 500 may begin with step 1.

[0059] In step 1, UE 502 may transmit to new AMF 504 an initial registration request for registering UE 502 with RAT Y at new AMF 504. Because the registration request is for a specific RAT - i.e., RAT Y -, the registration request may include one or more parameters indicating RAT Y. Alternatively, the parameter(s) indicating RAT Y may be indicated on radiointerface or indicated by the RAN to new AMF 504. Examples of RAT are listed in Table 1 provided above.

[0060] After receiving the registration request, in step 1-1, new AMF 504 may determine whether an old AMF exists for UE 502. In case such old AMF exists for UE 502, process 500 proceeds to steps 2 and 3 in which new AMF 504 retrieves UE context information from old AMF 508. Otherwise, process 500 proceeds to step 4.

[0061] After determining that an old AMF exists for UE 502, in step 2, new AMF 504 may transmit to old AMF 508 a request for UE context information. One example of the request for UE context information is “Namf communication UeContextTransfer” message defined in 3GPP TS 29.518 vl8.6.0.

[0062] After receiving the request for UE context information, in step 3, old AMF 508 may transmit to new AMF 504 a response to the request for UE context information. One example of the response is “Namf communication UeContextTransfer” response message defined in 3GPP TS 29.518 vl8.6.0.

[0063] The response to the request may include or indicate a list of restricted RATs and / or a list of (subscribed) supported RATs (i.e., RATs restricted and / or supported by UDM 506). In one example, the response may include parameters each of which contains the list of restricted RATs or the list of supported RATs.

[0064] Upon obtaining the list of restricted RATs and the list of supported RATs, in step 3-1, new AMF 504 may determine whether the requested RAT (i.e., RAT Y) is included in the list of restricted RATs and / or the list of supported RATs and determine whether RAT Y is restricted or not based on whether the requested RAT (i.e., RAT Y) is included in the list of restricted RATs and / or the list of supported RATs.

[0065] For example, if RAT Y is included in both the list of supported RATs and the list of restricted RATs, new AMF 504 may determine that RAT Y is restricted. On the other hand, if RAT Y is included in the list of supported RATs but not in the list of restricted RATs, new AMF 504 may determine that RAT Y is not restricted.

[0066] In case RAT Y is included in neither the list of supported RATs (meaning that RAT Y is not supported by UDM 506) nor the list of restricted RATs, new AMF 504 may determine whether RAT Y is restricted or not based on its policy (“AMF policy”). For example, AMF policy may indicate that if RAT Y is included in neither the list of supported RATs nor the listof restricted RATs, or if RAT Y is included in the list of restricted RATs but not in the list of supported RATs, new AMF 504 should determine that RAT Y is restricted. Such AMF policy may be stored in UE context information at AMF.

[0067] Referring back to FIG. 5, if new AMF 504 determines that the requested RAT (i.e., RAT Y) is restricted, in step 3-2, new AMF 504 may transmit to UE 502 a registration response indicating that the registration request is not accepted. On the other hand, if new AMF 504 determines that the requested RAT is not restricted, in step 4, new AMF 504 may transmit to UDM 506 a request for registering new AMF 504 at UDM 506. One example of the request is Nudm UECM AMF Registration request message defined in 3GPP TS 29.518 vl8.6.0. The request may indicate the RAT requested by UE 502 - i.e., RAT Y. For example, the request may include a parameter called “RatType” of which value indicates RAT Y.

[0068] Upon receiving the request in step 4, in step 5, UDM 506 may check subscription information applicable for RAT Y and transmit a response indicating whether the request is accepted by UDM 506. One example of the response is “Nudm_UECM_AMF Registration” response defined in 3GPP TS 29.518 vl8.6.0. UDM 506 may accept the request as long as RAT Y is supported and not restricted for the UE.

[0069] Upon receiving the response in step 5, in step 6, new AMF 504 may transmit to UDM 506 a request for UE 502’ s access and mobility subscription data (e.g., Nudm_SDM Retrieve am-data defined in 3GPP TS 29.518 vl8.6.0). Then, in step 7, UDM 506 may transmit a response to the request (“200 OK” message defined in 3GPP TS 29.518 V18.6.0), which indicates whether the request is accepted or not. In some embodiments, the response may also include Access and Mobility subscription data which indicates a list of supported RATs and a list of restricted RATs. Note that these lists are the same lists that new AMF 504 received in step 3. However, because steps 2, 3, and 3-1 are optional (i.e., the steps are performed only when an old AMF exists for UE 502), sending the lists in step 7 is still necessary.

[0070] After receiving the response, in step 7-1, new AMF 504 may determine according whether to accept or reject the registration request received in step 1 based on whether the requested RAT (i.e., RAT Y) is included in the list of supported RATs and / or whether the list of restricted RATs. The way new AMF 504 makes this determination is same as the way new AMF 504 makes the determination in step 3-1.

[0071] After making the determination, in step 8, new AMF 504 transmits to UE 502 aregistration response indicating whether the registration request is accepted or not.

[0072] Note that after new AMF 504 receives the list of restricted RATs and / or the list of supported RATs, new AMF 504 may determine a handover restriction list which is a list of RATs for which a handover is restricted based on the list of restricted RATs and / or the list of supported RATs. Alternatively, new AMF 504 may determine a handover allowed list which is a list of RATs for which a hand over is allowed. New AMF 504 may send the handover restriction / allowed list to gNB 502 (RAN) such that RAN 502 can decide when to avoid triggering a handover. For example, if a currently serving UE’s requests a handover to RAT Y and if the handover restriction list includes RAT Y, RAN 502 may skip sending a handover request to its AMF. In another example, if a currently serving UE’s requests a handover to RAT Y and if the handover allowed list does not include RAT Y, RAN 502 may skip sending a handover request to its AMF.

[0073] FIG. 6 shows a process 600 for performing a mobility registration of UE 602 according to some embodiments. Even though FIG. 6 shows that process 600 comprises steps 1-6, not all steps needed for performing the mobility registration are shown in FIG. 6. Some steps are omitted for simple explanation purpose.

[0074] Process 600 is an example of process 400 shown in FIG. 4. More specifically, in process 600, new AMF 604 corresponds to first network node 402 in process 400, UE / gNB 602 corresponds to third network node 406 in process 400, and UDM 606 corresponds to the second network node which is mentioned with respect to process 400. As explained above, the second network node is not shown in FIG. 4. Process 600 may begin with step 1.

[0075] In step 1, UE 602 may transmit to new AMF 604 a mobility registration request for registering UE 602 with RAT Y at new AMF 604. Because the registration request is for a specific RAT - i.e., RAT Y -, the registration request may include one or more parameters indicating RAT Y. Alternatively, the parameter(s) indicating RAT Y may be indicated on radio interface or indicated by the RAN to new AMF 604. Examples of RAT are listed in Table 1 provided above.

[0076] After receiving the registration request, in step 1-1, new AMF 604 may determine that the registration request is for RAT Y. Then new AMF 604 may determine whether an old AMF exists for UE 602. In case an old AMF exists for UE 602, process 600 may proceed to steps 2 and 3 in which new AMF 604 retrieves UE context information from old AMF 608.Otherwise, process 600 proceeds to step 4. To explain the concept of the embodiments of this disclosure, let’s assume that an old AMF exists for UE 602. Then process 600 may proceed to step 2.

[0077] In step 2, new AMF 604 may transmit to old AMF 608 a request for UE context information. One example of the request for UE context information is “Namf communication UeContextTransfer” message defined in 3GPP TS 29.518 vl8.6.0.

[0078] After receiving the request for UE context information, in step 3, old AMF 608 may transmit to new AMF 604 a response to the request for UE context information. One example of the response is “Namf communication UeContextTransfer” response message defined in 3GPP TS 29.518 vl8.6.0.

[0079] The response to the request may include or indicate a list of restricted RATs and / or a list of (subscribed) supported RATs (i.e., RATs restricted and / or supported by UDM 606). In one example, the response may include parameters each of which contains the list of restricted RATs or the list of supported RATs.

[0080] Upon obtaining the list of restricted RATs and the list of supported RATs, in step 3-1, new AMF 604 may determine whether the requested RAT (i.e., RAT Y) is included in the list of restricted RATs and / or the list of supported RATs and determine whether RAT Y is restricted or not based on whether the requested RAT (i.e., RAT Y) is included in the list of restricted RATs and / or the list of supported RATs.

[0081] For example, if RAT Y is included in both the list of supported RATs and the list of restricted RATs, new AMF 604 may determine that RAT Y is restricted. On the other hand, if RAT Y is included in the list of supported RATs but not in the list of restricted RATs, new AMF 604 may determine that RAT Y is not restricted.

[0082] In case RAT Y is included in neither the list of supported RATs (meaning that RAT Y is not supported by UDM 606) nor the list of restricted RATs, new AMF 604 may determine whether RAT Y is restricted or not based on its policy (“AMF policy”). For example, AMF policy may indicate that if RAT Y is included in neither the list of supported RATs nor the list of restricted RATs, or if RAT Y is included in the list of restricted RATs but not in the list of supported RATs, new AMF 604 should determine that RAT Y is restricted. Such AMF policy may be stored in UE context information at AMF.

[0083] Referring back to FIG. 6, if new AMF 604 determines that the requested RAT (i.e.,RAT Y) is restricted, in step 4, new AMF 604 may transmit to UE 602 a registration response indicating that the registration request is not accepted (i.e., rejected).

[0084] On the other hand, if new AMF 604 determines that the requested RAT is not restricted, in step 4’, new AMF 604 may transmit to UDM 606 a request for registering new AMF 604 at UDM 606. One example of the request is Nudm UECM AMF Registration request message defined in 3GPP TS 29.518 vl8.6.0. The request may indicate the RAT requested by UE 602 - i.e., RAT Y. For example, the request may include a parameter called “RatType” of which value indicates RAT Y.

[0085] Upon receiving the request in step 4’, in step 5, UDM 606 may check subscription information applicable for RAT Y and transmit a response indicating whether the request is accepted by UDM 606. One example of the response is “Nudm UECM AMF Registration” response defined in 3GPP TS 29.518 vl8.6.0. UDM 606 may accept the request as long as RAT Y is supported and not restricted for the UE.

[0086] Upon receiving the response in step 5, new AMF 604 may determine whether to accept or reject the registration request. After making the determination, in step 6, new AMF 604 transmits to UE 602 a registration response indicating whether the registration request is accepted or not.

[0087] FIG. 7 shows a process 700 for performing a tracking area update (TAU) with a change of RAT (e.g., from NR to NR GEO), according to some embodiments. Even though FIG. 7 shows that process 700 comprises steps 1-4, not all steps needed for performing TAU are shown in FIG. 7. Some steps are omitted for simple explanation purpose.

[0088] Process 700 is a different example of process 400 shown in FIG. 4. More specifically, in process 700, old AMF 708 corresponds to first network node 402 in process 400, new MME 704 corresponds to third network node 406 in process 400, and UDM 706 corresponds to the second network node which is mentioned with respect to process 400. As explained above, the second network node is not shown in FIG. 4. Process 700 may begin with step 1.

[0089] In step 1, UE 702 may transmit a TAU request to new MME 704. The TAU request may include an indication indicating that the TAU request is for a specific RAT - i.e., RAT X. One example of the TAU request is defined in 3GPP TS 29.274 vl 8.7.0. The TAU request may include one or more parameters indicating RAT X. Alternatively, the parameter(s) indicating RAT X may be indicated on radio interface or indicated by the RAN to new MME 704.Examples of RAT are listed in Table 1 provided above.

[0090] After receiving the TAU request, in step 1-1, new MME 704 may determine that the registration request is for RAT X. Then new MME 704 may determine whether an old AMF exists for UE 702. In case an old AMF exists for UE 702, process 700 may proceed to steps 2 and 3 in which new MME 704 retrieves UE context information from old AMF 708.

[0091] In step 2, new MME 704 may transmit to old AMF 708 a request for UE context information. One example of the request for UE context information is “Context Request” defined in 3GPP TS 29.274 vl 8.7.0.

[0092] After receiving the context request, in step 3, old AMF 708 may transmit to new MME 704 a response to the context request. One example of the response is “context response” defined in 3GPP TS 29.274 vl 8.7.0.

[0093] The context response may include or indicate an extended restricted RATs which cannot be used by UEs for accessing RATs associated with UDM 706. In some embodiments, the extended restrict RATs may be created based on a combination of a list of restricted RATs and / or a list of (subscribed) supported RATs (i.e., RATs restricted and / or supported by UDM 706). In one example, the response may include extended access restriction data which contains the list of extended restricted RATs. Old AMF 708 may have obtained the list of supported RATs and the list of restricted RATs from another network function (NF) (e.g., UDM 706) before performing step 3.

[0094] In some embodiments, the context request that new MME 702 sends to old AMF 708 in step 2 indicates the requested RAT - i.e., RAT X. In such embodiments, upon receiving the context request, old AMF 708 may determine whether the requested RAT is restricted or not based on the extend list of restricted RATs. More specifically, old AMF 708 may determine whether RAT X is restricted or not based on whether RAT X is included in the extended list of restricted RATs.

[0095] In case old AMF 708 determines that RAT X is restricted, the context response may indicate that the target access is restricted for the subscriber. More specifically, in one example, the context response may include a Cause value indicating whether the target access is restricted for the subscriber.

[0096] After receiving the context response from old AMF 708, new MME 704 may determine whether to reject or accept the TAU request received in step 1 and transmit, in step 4,a TAU response indicating whether the TAU request is accepted or not.

[0097] FIG. 8 shows a process 800 for performing a handover (e.g., an N2 based handover) of UE 802 with a change of RAT (e.g., from NR to NR GEO), according to some embodiments. Even though FIG. 8 shows that process 800 comprises steps 1-4, not all steps needed for performing the handover are shown in FIG. 8. Some steps are omitted for simple explanation purpose.

[0098] Process 800 is a different example of process 400 shown in FIG. 4. In process 800, source AMF 804 corresponds to first network node 402 in process 400, UE / gNB 802 corresponds to third network node 406 in process 400, and UDM 806 corresponds to the second network node which is mentioned with respect to process 400. As explained above, the second network node is not shown in FIG. 4. Process 800 may begin with step 0.

[0099] In step 0, gNB 802 (a.k.a., RAN 802) determines whether to transmit to source AMF 804 a request for a handover of the UE with a RAT change, e.g., from RAT X to RAT Y. In determining whether to transmit the handover request, RAN 802 may consider a handover restriction list which is a list of RATs for which a handover is restricted. RAN 802 may have obtained the handover restriction list from another network function (NF) before performing step s802 (e.g., during process 500 shown in FIG. 5, as explained above).

[0100] Let’s assume that the handover request is for a UE handover with a RAT change to RAT Y. If RAT Y is not included in the handover restriction list, in step 1, RAN 802 may transmit the handover request to source AMF 804. On the other hand, if RAT Y is included in the handover restriction list, RAN 802 may not transmit the handover request to source AMF 804. This means that RAN 802 decides to trigger a handover to target RAT 808 only if RAT Y is not restricted. After transmitting the handover request, process 800 may proceed to step 1-1.

[0101] In step 1-1, source AMF 804 checks the handover request and determines whether the handover request can be accepted or not - i.e., whether the handover attempt by RAN 802 is allowed by source AMF 804. In determining whether the handover request (i.e., RAN request) can be accepted or not, source AMF 804 may consider UE context information which indicates a list of supported RATs and / or a list of restricted RATs. More specifically, source AMF 804 may determine whether the requested RAT (i.e., RAT Y) is restricted or not based on whether RAT Y is included in the list of restricted RATs and / or the list of supported RATs.

[0102] For example, if RAT Y is included in both the list of supported RATs and the listof restricted RATs, source AMF 804 may determine that RAT Y is supported but restricted. On the other hand, if RAT Y is included in the list of supported RATs but not in the list of restricted RATs, source AMF 804 may determine that RAT Y is supported and not restricted.

[0103] In case RAT Y is included in neither the list of supported RATs (meaning that RAT Y is not supported by UDM 806) nor the list of restricted RATs, source AMF 804 may determine whether RAT Y is restricted or not based on its policy (“AMF policy”). For example, the AMF policy may indicate that if RAT Y is included in neither the list of supported RATs nor the list of restricted RATs, or if RAT Y is included in the list of restricted RATs but not in the list of supported RATs, source AMF 804 should determine that RAT Y is restricted. Such AMF policy may be stored in UE context information at source AMF 804.

[0104] If source AMF 804 determines that RAT Y is restricted, source AMF 804 may reject the handover request and transmit, in step 2, to RAN 802 a handover preparation failure message indicating the rejection of the handover request.

[0105] On the other hand, if source AMF 804 determines that RAT Y is not restricted, source AMF 804 may determine that the handover process can continue. In this case, source AMF 804 may retrieve target AMF 806 and send, in step 2, a request to create UE context (e.g., Namf communication UeContextCreate request). In response to receiving the request, in step 3, target AMF 808 may transmit to source AMF 804 a response to the request (e.g., Namf communication UeContextCreate Response). Note that steps 2 and 3 in FIG. 8 are optional, and thus in some embodiments, the steps may not be performed.

[0106] In step 4, source AMF 804 may transmit a handover command to RAN 802. Then the remaining steps of the handover process, which include user plane data transfer are performed. Note that, during mobility registration, target AMF 808 may register itself in UDM 806 in the manner described above with respect to process 600 shown in FIG. 6.

[0107] There may be a scenario where the requested RAT (e.g., RAT Y) is not supported by source AMF 804. In such case, source AMF 804 may reject the handover request or may use an alternative RAT (a.k.a., “default RAT”) instead of the requested RAT. For example, if the initial requested RAT is RAT Y but source AMF 804 does not support RAT Y, source AMF 804 may determine to use RAT X instead. In this scenario, if target AMF 808 is okay with source AMF 804’ s decision to use the alternative RAT, then the handover may be performed. However, if target AMF 808 does not support or is not willing to replace the originally requested RATwith the alternative with RAT, the handover request may be rejected. In such scenario, registration procedure may be rejected by AMF and the UE may have to perform a registration again.

[0108] As explained above in detail, in processes 400-800 shown in FIGS. 4-8, in addition to the list of restricted RATs, the list of supported RATs is provided to network entities (e.g., new AMF 504 / 604, new MME 704, etc.) such that those receiving network entities know which RATs are supported by UDM to use by UEs for the UEs’ network accesses. However, in some embodiments, instead of the list of supported RATs, a list of allowed RATs may be provided to the network entities.

[0109] The list of allowed RATs may be a subset of the list of supported RATs. More specifically, the list of allowed RATs may be a list of RATs that are not only supported by UDM but also are permitted by UDM to use by the UEs for the UEs’ network accesses. The list of allowed RATs may be provided in a user level parameter.

[0110] In case the list of allowed RATs but not the list of restricted RATs is provided to the network entities, the network entities may determine that those RATs that are included in the list of allowed RATs are supported and permitted by UDM for UEs’ network accesses. On the other hand, the network entities may determine that those RATs that are not included in the list of allowed RATs are not supported and / or not permitted by UDM for UEs’ network accesses.[OHl] In case both the list of allowed RATs and the list of restricted RATs are provided to the network entities, the network entities may determine that those RATs that are included in the list of allowed RATs but that are not included in the list of restricted RATs are supported and permitted by UDM for UEs’ network accesses. On the other hand, the network entities may determine that those RATs that are not included in the list of allowed RATs but that are included in the list of restricted RATs are supported but not permitted by UDM for UEs’ network accesses. If RAT(s) are included in neither the list of allowed RATs nor the list of restricted RATs, the network entities may determine that those RATs are not supported by UDM for UE’s network accesses. If RAT(s) are included in both the list of allowed RATs and the list of restricted RATs, there is a conflict - i.e., the list of allowed RATs indicates that those RATs are supported and permitted while the list of restricted RATs indicates that those RATs are not permitted. In this scenario, the network entities may determine that the list of restricted RATs has a higher priority and thus determine that those RATs that are included in both lists are restricted - i.e., supportedbut not permitted by UDM for UEs’ network accesses.

[0112] FIG. 9 shows a process 900 performed by a first network node (e.g., 504, 604, or 708) which is configured to manage network sessions of user equipments, UEs. Process 900 may begin with step s902. Step s902 comprises receiving a request related to a network session, wherein the request related to a network session is associated with a first radio access type, RAT. Step s904 comprises obtaining first RAT information which indicates a list of one or more RATs supported by a second network node, wherein the second network node is configured to manage network nodes for managing network sessions of UEs. Step s906 comprises, after receiving the request and obtaining the first RAT information, determining whether to accept or reject the request, wherein whether to accept or reject the request is determined based on the list of one or more RATs supported by the second network node. Step s908 comprises, after the determination, transmitting a response to the request, which indicates whether the request is accepted or rejected.

[0113] In some embodiments, process 900 comprises obtaining second RAT information which indicates a list of one or more RATs that are restricted from being used by one or more UEs to access one or more radio access networks, RANs, associated with the second network node; and whether to accept or reject the request is determined further based on the list of one or more RATs that are restricted from being used by one or more UEs to access one or more RANs associated with the second network node.

[0114] In some embodiments, determining whether to accept or reject the request comprises determining whether the first RAT is included in: the list of one or more RATs supported by the second network node, and / or the list of one or more RATs that are restricted from being used by one or more UEs to access one or more RANs associated with the second network node.

[0115] In some embodiments, determining whether to accept or reject the request comprises determining to reject the request in case: the first RAT is included in the two lists, the first RAT is not included in any of the two lists, and / or the first RAT is included in the list of one or more RATs that are restricted from being used by one or more UEs to access a RAN associated with the second network node but is not included in the list of one or more RATs supported by the second network node.

[0116] In some embodiments, process 900 comprises obtaining policy information which indicates whether to accept or reject the request in case the first RAT is not included in any of the two lists, and whether to accept or reject the request is determined based on the policy informationin case the first RAT is not included in any of the two lists.

[0117] In some embodiments, obtaining the first RAT information and obtaining the second RAT information comprise: receiving a message including the first and second RAT information from: the second network node, or a third network node which is configured to manage network sessions of UEs.

[0118] In some embodiments, the request related to a network session is originated from a first UE, process 900 comprises transmitting, to the second network node, a request for the first UE’s access and mobility subscription data, and the first network node receives from the second network node the message including the first and second RAT information in response to transmitting the request for the first UE’s access and mobility subscription data.

[0119] In some embodiments, the request related to a network session is originated from a first UE, process 900 comprises transmitting, to the third network node, a request for the first UE’s context information, and the first network node receives from the third network node the message including the first and second RAT information in response to transmitting the request for the first UE’s context information.

[0120] In case that the first network node determines to reject the request related to a network session, the response to the request indicates that the request is rejected, and process 900 comprises, after determining to reject the request related to a network session, determining not to transmit, to the second network node, a request for registering the first network node at the second network node for the first UE’s network session.

[0121] In some embodiments, process 900 comprises: transmitting, to the second network node, a request data for the first UE’s access and mobility subscription data; and in response to transmitting the request for the first UE’s access and mobility subscription data, receiving, from the second network node, a response to the request for the first UE’s access and mobility subscription data, and the response to the request for the first UE’ s access and mobility subscription data comprises the first RAT information and the second RAT information.

[0122] In some embodiments, the request related to a network session is a registration request for registering a UE at the first network node, the first network node is an access and mobility management function, AMF, and the second network node is a unified data management, UDM.

[0123] In some embodiments, process 900 comprises: based on the list of one or moreRATs supported by the second network node and the list of one or more RATs that are restricted from being used by one or more UEs to access one or more RANs associated with the second network node, generating handover information which indicates: a list of RATs that are restricted from being used by one or more UEs to perform a handover to a particular RAN, and / or a list of RATs that are allowed to be used by one or more UEs to perform a handover to the particular RAN, and transmitting the handover information to the particular RAN.

[0124] In some embodiments, the request related to a network session is a request for a particular UE’s context information, the response to the request related to a network session indicates that the request is rejected, and the response to the request indicates that the rejection of the request is due to that the particular UE’s access to a network is restricted for the first RAT.

[0125] In some embodiments, process 900 comprises based on the list of one or more RATs supported by the second network node and the list of one or more RATs that are restricted from being used by one or more UEs to access one or more RANs associated with the second network node, generating RAT restriction information which indicates: a list of RATs that are restricted from being used by one or more UEs to access a particular RAN, and / or a list of RATs that are allowed to be used by one or more UEs to access the particular RAN, and transmitting the RAT restriction information to the first network node.

[0126] In some embodiments, the request related to a network session is received from a third network node, the third network node is a mobility management entity, MME, and the first network node is an AMF.

[0127] In some embodiments, the request related to a network session is a handover request to a different RAN, the first network node is a source AMF, and the second network node is an UDM.

[0128] In some embodiments, all RATs included in the list of one or more RATs supported by the second network node are allowed by the second network node to be used by one or more UEs for accessing one or more RATs associated with the second network node.

[0129] FIG. 10 shows a process 1000 performed by a first network node (e.g., 508 or 608) which is configured to manage network sessions of user equipments, UEs. Process 1000 may begin with step si 002. Step si 002 comprises receiving, from a second network node (e.g., 504 or 604) a request related to a network session, wherein the second network node is configured to manage network sessions of UEs. Step si 004 comprises obtaining first RAT information whichindicates a list of one or more RATs supported by a third network node (e.g., 506 or 606), wherein the third network node is configured to manage network nodes for managing network sessions of UEs; and after receiving the request and obtaining the first RAT information, transmitting (si 006) a response to the request, which indicates the list of one or more RATs supported by the third network node.

[0130] In some embodiments, process 1000 comprises obtaining second RAT information which indicates a list of one or more RATs that are restricted from being used by one or more UEs to access one or more radio access networks, RANs, associated with the third network node; and the response to the request further indicates the list of one or more RATs that are restricted from being used by one or more UEs to access one or more RANs associated with the third network node.

[0131] In some embodiments, obtaining the first RAT information and obtaining the second RAT information comprise: receiving a message including the first and second RAT information from the third network node.

[0132] In some embodiments, the request related to a network session is a request for a UE’s context information, and the response to the request contains the requested context information.

[0133] In some embodiments, the first network node is a first access and mobility management function, AMF, the second network node is a second AMF, and the third network node is an UDM.

[0134] In some embodiments, all RATs included in the list of one or more RATs supported by the third network node are allowed by the third network node to be used by one or more UEs for accessing one or more RATs associated with the third network node.

[0135] FIG. 11 shows a process 1100 performed by a first network node (e.g., 506 or 606) which is configured to manage network nodes for managing network sessions of user equipments, UEs. Process 1100 may begin with step si 102. Step si 102 comprises receiving, from a second network node (e.g., 504 or 604), a request related to a network session, wherein the second network node is configured to manage network sessions of UEs. Step si 104 comprises, after receiving the request, transmitting, to the second network node, a response to the request, which indicates a list of one or more RATs supported by the first network node.

[0136] In some embodiments, the response to the request further indicates a list of one ormore RATs that are restricted from being used by one or more UEs to access one or more radio access networks, RANs, associated with the first network node.

[0137] In some embodiments, the request related to a network session is a request for a UE’s access and mobility subscription data; and the response to the request contains the requested access and mobility subscription data.

[0138] In some embodiments, the first network node is an UDM, amd the second network node is an AMF.

[0139] In some embodiments, all RATs included in the list of one or more RATs supported by the first network node are allowed by the first network node to be used by one or more UEs for accessing one or more RATs associated with the first network node.

[0140] FIG. 12 is a block diagram of network node 1200 (e.g., 504, 506, 508, 604, 606, 608, 704, 706, 708, 804, 806, or 808), according to some embodiments. As shown in FIG. 12, network node 1200 may comprise: processing circuitry (PC) 1202, which comprises one or more processors (P) 1255 (e.g., one or more general purpose microprocessors and / or one or more other processors, such as an application specific integrated circuit (ASIC), field-programmable gate arrays (FPGAs), and the like), which processors may be co-located in a single housing or in a single data center or may be geographically distributed (e.g., network node 1200 may be a distributed computing apparatus comprising two or more computers or a monolithic computing apparatus consisting of a single computer); at least one network interface 1248 (e.g., a physical interface or air interface) comprising a transmitter (Tx) 1245 and a receiver (Rx) 1247 for enabling network node 1200 to transmit data to and receive data from other nodes connected to network 110 (e.g., an Internet Protocol (IP) network) to which network interface 1248 is connected (physically or wirelessly) (e.g., network interface 1248 may be coupled to an antenna arrangement comprising one or more antennas for enabling network node 1200 to wirelessly transmit / receive data); and a storage unit (a.k.a., “data storage system”) 1208, which may include one or more non-volatile storage devices and / or one or more volatile storage devices. In embodiments where PC 1202 includes a programmable processor, a computer readable storage medium (CRSM) 1242 may be provided. CRSM 1242 may store a computer program (CP) 1243 comprising computer readable instructions (CRI) 1244. CRSM 1242 may be a non-transitory computer readable medium, such as, magnetic media (e.g., a hard disk), optical media, memory devices (e.g., random access memory, flash memory), and the like. In some embodiments, theCRI 1244 of computer program 1243 is configured such that when executed by PC 1202, the CRI causes network node 1200 to perform steps described herein (e.g., steps described herein with reference to the flow charts). In other embodiments, network node 1200 may be configured to perform steps described herein without the need for code. That is, for example, PC 1202 may consist merely of one or more ASICs. Hence, the features of the embodiments described herein may be implemented in hardware and / or software.

[0141] FIG. 13 is a block diagram of base station 104 (e.g., 502, 602, 702, or 802), according to some embodiments for performing the base station methods disclosed herein. As shown in FIG. 13, base station 104 may comprise: processing circuitry (PC) 1302, which comprises one or more processors (P) 1355 (e.g., a general purpose microprocessor and / or one or more other processors, such as an application specific integrated circuit (ASIC), field- programmable gate arrays (FPGAs), and the like), which processors may be co-located in a single housing or in a single data center or may be geographically distributed (i.e., base station may be a distributed computing apparatus or a monolithic computing apparatus); a network interface 1368 comprising a transmitter (Tx) 1365 and a receiver (Rx) 1367 for enabling base station 104 to transmit data to and receive data from other nodes connected to a network 110 (e.g., an Internet Protocol (IP) network) to which network interface 1368 is connected; communication circuitry 1348 (e.g., radio transceiver circuitry comprising an Rx 1347 and a Tx 1345) coupled to an antenna system 1349 for wireless communication with UEs or other nodes; and a storage unit (a.k.a., “data storage system”) 1308, which may include one or more nonvolatile storage devices and / or one or more volatile storage devices. In embodiments where PC 1302 includes a programmable processor, a computer readable storage medium (CRSM) 1342 may be provided. CRSM 1342 may store a computer program (CP) 1343 comprising computer readable instructions (CRI) 1344. CRSM 1342 may be a non-transitory computer readable medium, such as, magnetic media (e.g., a hard disk), optical media, memory devices (e.g., random access memory, flash memory), and the like. In some embodiments, the CRI 1344 of computer program 1343 is configured such that when executed by PC 1302, the CRI causes base station 104 to perform steps described herein (e.g., steps described herein with reference to one or more flow charts). In other embodiments, base station 104 may be configured to perform steps described herein without the need for code. That is, for example, PC 1302 may consist merely of one or more ASICs. Hence, the features of the embodiments described herein may beimplemented in hardware and / or software.

[0142] The following table summarizes some embodiments of this disclosure..1.6.2.4 Type: AccessAndMobilitySubscriptionDataTable 6.1.6.2.4-1 : Definition of type AccessAndMobilitySubscriptionData

[0143] As used herein transmitting a message “to” or “toward” an intended recipient encompasses transmitting the message directly to the intended recipient or transmitting the message indirectly to the intended recipient (i.e., one or more other nodes are used to relay the message from the source node to the intended recipient). Likewise, as used herein receiving a message “from” a sender encompasses receiving the message directly from the sender or indirectly from the sender (i.e., one or more nodes are used to relay the message from the sender to the receiving node). Further, as used herein “a” means “at least one” or “one or more.”

[0144] Additionally, while the processes described above and illustrated in the drawings are shown as a sequence of steps, this was done solely for the sake of illustration. Accordingly, it is contemplated that some steps may be added, some steps may be omitted, the order of the steps may be re-arranged, and some steps may be performed in parallel.

Claims

CLAIMS1. A method (900) performed by a first network node (504, 604, or 708) which is configured to manage network sessions of user equipments, UEs, the method comprising: receiving (s902) a request related to a network session, wherein the request related to a network session is associated with a first radio access type, RAT; obtaining (s904) first RAT information which indicates a list of one or more RATs allowed by a second network node, wherein the second network node is configured to manage network nodes for managing network sessions of UEs; after receiving the request and obtaining the first RAT information, determining (s906) whether to accept or reject the request, wherein whether to accept or reject the request is determined based on the list of one or more RATs allowed by the second network node; and after the determination, transmitting (s908) a response to the request, which indicates whether the request is accepted or rejected.

2. The method of claim 1, wherein the method comprises obtaining second RAT information which indicates a list of one or more RATs that are restricted from being used by one or more UEs to access one or more radio access networks, RANs, associated with the second network node; and whether to accept or reject the request is determined further based on the list of one or more RATs that are restricted from being used by one or more UEs to access one or more RANs associated with the second network node.

3. The method of claim 2, wherein determining whether to accept or reject the request comprises determining whether the first RAT is included in: the list of one or more RATs allowed by the second network node, and / or the list of one or more RATs that are restricted from being used by one or more UEs to access one or more RANs associated with the second network node.

4. The method of claim 3, wherein determining whether to accept or reject the request comprises determining to reject the request in case:the first RAT is included in the two lists, the first RAT is not included in any of the two lists, and / or the first RAT is included in the list of one or more RATs that are restricted from being used by one or more UEs to access a RAN associated with the second network node but is not included in the list of one or more RATs allowed by the second network node.

5. The method of claim 3 or 4, wherein the method comprises obtaining policy information which indicates whether to accept or reject the request in case the first RAT is not included in any of the two lists, and whether to accept or reject the request is determined based on the policy information in case the first RAT is not included in any of the two lists.

6. The method of any one of claims 2-5, wherein obtaining the first RAT information and obtaining the second RAT information comprise: receiving a message including the first and second RAT information from: the second network node, or a third network node which is configured to manage network sessions of UEs.

7. The method of claim 6, wherein the request related to a network session is originated from a first UE, the method comprises transmitting, to the second network node, a request for the first UE’s access and mobility subscription data, and the first network node receives from the second network node the message including the first and second RAT information in response to transmitting the request for the first UE’s access and mobility subscription data.

8. The method of claim 6, wherein the request related to a network session is originated from a first UE, the method comprises transmitting, to the third network node, a request for the first UE’s context information, andthe first network node receives from the third network node the message including the first and second RAT information in response to transmitting the request for the first UE’s context information.

9. The method of claim 8, wherein in case that the first network node determines to reject the request related to a network session, the response to the request indicates that the request is rejected, and the method comprises, after determining to reject the request related to a network session, determining not to transmit, to the second network node, a request for registering the first network node at the second network node for the first UE’s network session.

10. The method of claim 8 or 9, wherein the method comprises: transmitting, to the second network node, a request data for the first UE’s access and mobility subscription data; and in response to transmitting the request for the first UE’s access and mobility subscription data, receiving, from the second network node, a response to the request for the first UE’s access and mobility subscription data, and the response to the request for the first UE’s access and mobility subscription data comprises the first RAT information and the second RAT information.

11. The method of any one of claims 1-10, wherein the request related to a network session is a registration request for registering a UE at the first network node, the first network node is an access and mobility management function, AMF, and the second network node is a unified data management, UDM.

12. The method of any one of claims 2-11, wherein the method comprises: based on the list of one or more RATs allowed by the second network node and the list of one or more RATs that are restricted from being used by one or more UEs to access one or moreRANs associated with the second network node, generating handover information which indicates: a list of RATs that are restricted from being used by one or more UEs to perform a handover to a particular RAN, and / or a list of RATs that are allowed to be used by one or more UEs to perform a handover to the particular RAN, and transmitting the handover information to the particular RAN.

13. The method of any one of claims 1-5, wherein the request related to a network session is a request for a particular UE’s context information, the response to the request related to a network session indicates that the request is rejected, and the response to the request indicates that the rejection of the request is due to that the particular UE’s access to a network is restricted for the first RAT.

14. The method of claim 13, wherein the method comprises: based on the list of one or more RATs allowed by the second network node and the list of one or more RATs that are restricted from being used by one or more UEs to access one or more RANs associated with the second network node, generating RAT restriction information which indicates: a list of RATs that are restricted from being used by one or more UEs to access a particular RAN, and / or a list of RATs that are allowed to be used by one or more UEs to access the particular RAN, and transmitting the RAT restriction information to the first network node.

15. The method of claim 13 or 14, wherein the request related to a network session is received from a third network node, the third network node is a mobility management entity, MME, and the first network node is an AMF.

16. The method of any one of claims 1-5, wherein the request related to a network session is a handover request to a different RAN, the first network node is a source AMF, and the second network node is an UDM.

17. The method of any one of claims 1-16, wherein all RATs included in the list of one or more RATs supported by the second network node are allowed by the second network node to be used by one or more UEs for accessing one or more RATs associated with the second network node.

18. A method (1000) performed by a first network node (508 or 608) which is configured to manage network sessions of user equipments, UEs, the method comprising: receiving (sl002), from a second network node (504 or 604) a request related to a network session, wherein the second network node is configured to manage network sessions of UEs; obtaining (sl004) first RAT information which indicates a list of one or more RATs allowed by a third network node (506 or 606), wherein the third network node is configured to manage network nodes for managing network sessions of UEs; and after receiving the request and obtaining the first RAT information, transmitting (si 006) a response to the request, which indicates the list of one or more RATs allowed by the third network node.

19. The method of claim 18, wherein the method comprises obtaining second RAT information which indicates a list of one or more RATs that are restricted from being used by one or more UEs to access one or more radio access networks, RANs, associated with the third network node; and the response to the request further indicates the list of one or more RATs that are restricted from being used by one or more UEs to access one or more RANs associated with the third network node.

20. The method of claim 19, wherein obtaining the first RAT information and obtaining the second RAT information comprise: receiving a message including the first and second RAT information from the third network node.

21. The method of any one of claims 18-20, wherein the request related to a network session is a request for a UE’s context information, and the response to the request contains the requested context information.

22. The method of any one of claims 18-21, wherein the first network node is a first access and mobility management function, AMF, the second network node is a second AMF, and the third network node is an UDM.

23. The method of any one of claims 18-22, wherein all RATs included in the list of one or more RATs supported by the third network node are allowed by the third network node to be used by one or more UEs for accessing one or more RATs associated with the third network node.

24. A method (1100) performed by a first network node (506 or 606) which is configured to manage network nodes for managing network sessions of user equipments, UEs, the method comprising: receiving (si 102), from a second network node (504 or 604), a request related to a network session, wherein the second network node is configured to manage network sessions of UEs; and after receiving the request, transmitting (si 104), to the second network node, a response to the request, which indicates a list of one or more RATs allowed by the first network node.

25. The method of claim 24, whereinthe response to the request further indicates a list of one or more RATs that are restricted from being used by one or more UEs to access one or more radio access networks, RANs, associated with the first network node.

26. The method of claim 24 or 25, wherein the request related to a network session is a request for a UE’s access and mobility subscription data; and the response to the request contains the requested access and mobility subscription data.

27. The method of claim 26, wherein the first network node is an UDM, and the second network node is an AMF.

28. The method of any one of claims 24-27, wherein all RATs included in the list of one or more RATs supported by the first network node are allowed by the first network node to be used by one or more UEs for accessing one or more RATs associated with the first network node.

29. A computer program (1243 or 1343) comprising instructions (1244 or 1344) which when executed by processing circuitry (1202 or 1302) cause the processing circuitry to perform the method of any one of claims 1-28.

30. A carrier containing the computer program of claim 29, wherein the carrier is one of an electronic signal, an optical signal, a radio signal, and a computer readable storage medium.

31. A first network node (504, 604, or 708) for managing network sessions of user equipments, UEs, the first network node being configured to: receive (s902) a request related to a network session, wherein the request related to a network session is associated with a first radio access type, RAT;obtain (s904) first RAT information which indicates a list of one or more RATs allowed by a second network node, wherein the second network node is configured to manage network nodes for managing network sessions of UEs; after receiving the request and obtaining the first RAT information, determine (s906) whether to accept or reject the request, wherein whether to accept or reject the request is determined based on the list of one or more RATs allowed by the second network node; and after the determination, transmit (s908) a response to the request, which indicates whether the request is accepted or rejected.

32. The first network node of claim 31, wherein the first network node is configured to perform the method of any one of claims 2-17.

33. A first network node (508 or 608) for managing network sessions of user equipments, UEs, the first network node being configured to: receive (sl002), from a second network node (504 or 604) a request related to a network session, wherein the second network node is configured to manage network sessions of UEs; obtain (si 004) first RAT information which indicates a list of one or more RATs allowed by a third network node (506 or 606), wherein the third network node is configured to manage network nodes for managing network sessions of UEs; and after receiving the request and obtaining the first RAT information, transmit (si 006) a response to the request, which indicates the list of one or more RATs allowed by the third network node.

34. The first network node of claim 33, wherein the first network node is configured to perform the method of any one of claims 19-23.

35. A first network node (506 or 606) for managing network nodes that are configured to manage network sessions of user equipments, UEs, the first network node being configured to: receive (si 102), from a second network node (504 or 604), a request related to a network session, wherein the second network node is configured to manage network sessions of UEs; andafter receiving the request, transmit (si 104), to the second network node, a response to the request, which indicates a list of one or more RATs allowed by the first network node.

36. The first network node of claim 35, wherein the first network node is configured to perform the method of any one of claims 25-28.

37. An apparatus (1200 or 1300) comprising: processing circuitry (1202 or 1302); and a memory (1242 or 1342), said memory containing instructions executable by said processing circuitry, whereby the apparatus is operative to perform the method of any one of claims 1-28.

Images