Method and apparatus for improving cellular internet of things (CIOT) optimization in a telecommunications network

Abstract

The disclosure relates to a communication method and system for converging a 5th-Generation (5G) communication system, which is beyond a 4th-Generation (4G) system, with a technology for Internet of Things (IoT), and a communication method and system. The disclosure can be applied to intelligent services based on 5G communication technologies and IoT-related technologies, such as smart home, smart building, smart city, smart car, connected car, health care, digital education, smart retail, security and safety services. A method of redirecting a user equipment (UE) from a serving network to a target network whereby the serving network rejects a service request message is disclosed.

Description

Technical Field

[0001] This invention relates to cellular Internet of Things (CIoT) networks and improvements that can be made to one or more optimizations associated with them. Background Technology

[0002] To meet the increased demand for wireless data traffic since the deployment of 4G communication systems, efforts have been made to develop improved 5G or pre-5G communication systems. Therefore, 5G or pre-5G communication systems are also referred to as "super-4G networks" or "post-LTE systems." The implementation of 5G communication systems in higher frequency (mmWave) bands (e.g., the 60GHz band) is being considered to achieve higher data rates. To reduce radio wave propagation loss and increase transmission distance, beamforming, massive MIMO, full-dimensional MIMO (FD-MIMO), array antennas, analog beamforming, and massive MIMO technologies have been discussed in 5G communication systems. Furthermore, in 5G communication systems, development is underway to improve system networks based on advanced small cells, cloud radio access networks (RAN), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, mobile networks, cooperative communication, coordinated multipoint (CoMP), and receiver interference cancellation. In 5G systems, hybrid FSK and QAM modulation (FQAM) and sliding window superposition coding (SWSC) have been developed as advanced coding and modulation (ACM), as well as filter bank multicarrier (FBMC), non-orthogonal multiple access (NOMA) and sparse code multiple access (SCMA) as advanced access technologies.

[0003] The internet, a human-centric network in which humans generate and consume information, is now evolving into the Internet of Things (IoT), in which distributed entities, such as things, exchange and process information without human intervention. The Internet of Everything (IoE), a combination of IoT technologies connected to cloud servers and big data processing technologies, has emerged. Because IoT implementation requires technological elements such as sensing technology, wired / wireless communication and network infrastructure, service interface technology, and security technology, sensor networks, machine-to-machine (M2M) communication, machine-type communication (MTC), and more have recently been explored. Such an IoT environment can provide intelligent internet technology services that create new value for human life by collecting and analyzing data generated in connected things. IoT can be applied to various fields through the convergence and combination of existing information technology (IT) and various industrial applications, including smart homes, smart buildings, smart cities, smart cars or connected cars, smart grids, healthcare, smart appliances, and advanced medical services.

[0004] Consistent with this, various attempts have been made to apply 5G communication systems to IoT networks. For example, technologies such as sensor networks, machine-type communication (MTC), and machine-to-machine (M2M) communication can be implemented using beamforming, MIMO, and array antennas. Cloud radio access networks (RAN), as an application of the aforementioned big data processing technologies, can also be considered an example of the convergence between 5G and IoT technologies. Summary of the Invention

[0005] Technical issues

[0006] One aspect of the present invention provides a method and apparatus for improving cellular Internet of Things (CIoT) optimization in a telecommunications network, and a method and apparatus for supporting UE access control.

[0007] Solution to the problem

[0008] Embodiments of the present invention provide a method and apparatus for improving cellular Internet of Things (CIoT) optimization in a telecommunications network, and a method and apparatus for supporting UE access control.

[0009] To achieve the above objectives, the technical solution of the present invention is as follows.

[0010] In one embodiment, a method performed by a user equipment (UE) for redirecting the UE from a serving network to a target network includes: receiving a service denial with 5GMM reason #31 when the UE is in N1 mode; setting the 5GMM update state to 5U3 ROAMING NOT ALLOWED; resetting the service request attempt counter and entering the 5GMM-REGISTERED state. LIMITED-SERVICE; operates in single registration mode; processes Evolved Packet System (EPS) parameters, EPS Mobility Management (EMM) parameters, EMM status, and EPS update status; and discards a service denial message with reason #31 if received without integrity protection, wherein if Evolved Universal Terrestrial Radio Access (E-UTRA) capability is disabled, the UE enables the E-UTRA capability and disables the N1 mode capability for 3GPP access, wherein if a UE without indication of support for Cellular Internet of Things (CIoT) optimization receives 5GMM reason #31, or the UE receives 5GMM reason #31 through non-3GPP access, or from a cell belonging to a Standalone Non-Public Network (SNPN), this is considered an anomalous situation, wherein the serving network denies the service request message, and wherein the serving network is a 5GGC and the target network is an Evolved Packet Core (EPC), thereby the Access and Mobility Management (AMF) of the serving network transmits the service denial message and includes 5GMM reason #31 "redirection to EPC required".

[0011] In another embodiment, a method for managing a packet data network (PDN) connection, performed by a user equipment (UE), includes: verifying whether an associated PDU session is associated with a control plane-only indication when the PDN connection is established in S1 mode; operating in a single registration mode in a network supporting an N26 interface, wherein the PDN connection is established after a first inter-system change from S1 mode to N1 mode; and supporting more than 16 packet filters for PDUs, wherein the PDU session is one of the “IPv4”, “IPv6”, “IPv4v6”, or “Ethernet” PDU session types.

[0012] In another embodiment, a method for managing PDN connections in a UE, performed by a user equipment (UE), includes determining that a PDU session modification procedure should be performed for the purpose of instructing the UE to support Reflective Quality of Service (RQoS), wherein, after a system change from S1 mode to NB-N1 mode, if the UE determines that a PDU session modification procedure should be performed for the purpose of instructing the UE to support RQoS, the UE still does not transmit a PDU SESSION MODIFICATION REQUEST message.

[0013] In another embodiment, a method for operating a user equipment (UE) in NB-N1 mode, performed by the user equipment (UE), includes: informing the serving network of the number of data radio bearers (DRBs) that the UE is capable of supporting according to its capabilities.

[0014] In another embodiment, a method performed by a user equipment (UE) for requesting the establishment of user plane resources for multiple protocol data unit (PDU) sessions includes: requesting the establishment of user plane resources for multiple PDU sessions, wherein the number of PDU sessions is not greater than the maximum number of data radio bearers (DRBs) that the UE can support, and wherein when the UE requests user plane resources, the UE does not indicate the total number of user plane resources greater than the number of DRBs that the UE can support via an uplink data state information element (IE).

[0015] In another embodiment, a method performed by a network for establishing user plane resources in response to a request from a user equipment (UE), the method comprising: establishing user plane resources in response to a request from the UE, wherein the user plane resources are established if the total number of user plane resources does not exceed the maximum number of data radio bearers (DRBs) supported by the UE, wherein the access and mobility management (AMF) in the network requests the SMF in the network to establish user plane resources, and wherein the AMF verifies whether a new DRB can be established based on how many DRBs the UE can support.

[0016] In another embodiment, a method executed by a network for controlling the establishment of user plane resources for a user equipment (UE) includes: establishing user plane resources for the UE, wherein if a payload container type information element (IE) is set to "N1 SM information", a request type IE is set to "initial request", the access and mobility management (AMF) in the network verifies how many data radio bearers (DRBs) already exist for the UE, and if the AMF determines that there are user plane resources equal to the maximum number of DRBs supported by the UE, then the AMF (a) sends a message back to the UE; or (b) establishes a session as a control plane-only session.

[0017] Beneficial effects of the invention

[0018] Therefore, the present invention provides a method and apparatus for improving cellular Internet of Things (CIoT) optimization in a telecommunications network, and a method and apparatus for supporting UE access control. Attached Figure Description

[0019] To better understand the present invention and to illustrate how embodiments of the invention can be implemented, reference will now be made to the accompanying drawings by way of example only, wherein:

[0020] Figure 1 Signaling based on existing technology is shown.

[0021] Figure 2 The message format according to an embodiment of the present invention is shown.

[0022] Figures 3 to 5 This illustrates message formats that explain various problems in the prior art.

[0023] Figure 6 A block diagram of an entity according to an embodiment of the present disclosure is shown.

[0024] Figure 7 A user equipment (UE) according to an embodiment of the present disclosure is shown. Detailed Implementation

[0025] There are two main types of CIoT optimization, known as User Plane (UP) CIoT optimization and Control Plane (CP) CIoT optimization.

[0026] UP CIoT optimization refers to optimizations related to the use of user plane resources. CP CIoT optimization, on the other hand, refers to optimizations related to efficient data transmission on the control plane. Note that "data" can also refer to SMS and location service messages.

[0027] The Network Access Layer (NAS) specification TS 24.501 (for N1 mode) provides a description of these optimizations and includes specific sections specifying user equipment (UE) and network behavior when using CP CIoT optimizations. For example, sections 5.6.1.2.2 and 5.6.1.4.2 are specifically for the use of CP CIoT optimizations.

[0028] A key aspect of the CP CIoT optimization is that the UE can transmit data from idle mode using the Control Plane Service Request (CPSR) message, which is already defined in the aforementioned NAS specification.

[0029] Typically, a UE uses either UP or CP optimization at a time, although both may be used simultaneously, as explained later. When a UE uses CP CIoT optimization, its PDU session is used to transmit data via the control plane (i.e., via NAS signaling messages). However, a Protocol Data Unit (PDU) session for CP CIoT optimization can be a control plane-only session if the PDU session establishment accept message includes a control plane-only indication information element (IE), as described in the aforementioned NAS specification, or if the session is available for CP CIoT optimization and can be switched to a user plane session. Note that the latter is not a permanent switch to a user plane session, but rather that the UE can request the establishment of user plane resources and use those resources to transmit data on the user plane. The UE can request a switch to the user plane based on, for example, the amount of data to be transmitted or based on other unspecified conditions. However, it is important to note that a PDU session for CP CIoT optimization can be a session used only for control plane data, or it can allow the UE to request the establishment of user plane resources for transmitting data on the user plane while still considering the session as being for CP CIoT optimization.

[0030] When a PDU session is switched to the user plane (i.e., when user plane resources are established for such a PDU session), if the UE also supports uplink CIoT optimization, the UE can apply the uplink CIoT optimization to the session for which the user plane has already been established. Note that after releasing user plane resources, the UE continues to use the session as the session for CP CIoT optimization unless the UE requests the establishment of user plane resources again. Note that although user plane resources can be established for PDU sessions used for CP CIoT optimization, the UE continues to use CPSR messages when it needs to initiate a service request procedure for the corresponding PDU session.

[0031] For control plane CIoT 5G system (5GS) optimization, PDU sessions are established as control plane-only sessions, meaning these sessions are never switched to the user plane and are anchored in the Network Exposure Function (NEF). These PDU sessions are of the "unstructured" PDU session type. The entire process of establishing a PDU session anchored in the NEF is illustrated below according to Section 4.25.2 of TS 23.502. Figure 1 The process includes steps 1-3 as known in the prior art:

[0032] When a UE performs a PDU session establishment with the PDU session type being "unstructured", and the subscription information corresponding to the data network name (DNN) requested by the UE includes the "NEF ID of NIDD", the Session Management Function (SMF) initiates an SMF-NEF connection establishment process to the NEF corresponding to the "NEF ID" of the DNN / S-NSSAI combination.

[0033] Step 1:

[0034] For UE-requested PDU session establishment procedures in non-roaming scenarios, steps 1-7 and 9 of Clause 4.3.2.2.1, or steps 1-9 of Clause 4.3.2.2.2, for UE-requested PDU session establishment procedures in home-roaming scenarios. (H) The SMF receives the corresponding SUPI, DNN, and S-NSSAI session management subscription data, which is associated with the NIDD and the NIDD's NEF identity, such as GPSI and AF ID.

[0035] Step 2:

[0036] If the subscription information corresponding to the DNN and S-NSSAI includes the "NEF identity of NIDD" (NEF ID), then the SMF should create a PDU session for the NEF. The SMF invokes the Nnef_SMContext_Create request (user identity, PDU session ID, SMF ID, NIDD information, S-NSSAI, DNN) message to the NEF. UE capabilities supporting Reliable Data Service (RDS) are included in the PCO in the PDU session establishment request message.

[0037] If no AF and NEF have previously performed the NIDD configuration process for the user identity received in step 2, then NEF initiates the NIDD configuration process before step 3 (see Clause 4.25.3).

[0038] Step 3:

[0039] The NEF creates a NEF PDU session context and associates it with the user identity and PDU session ID. The NEF calls the Nnef_SMContext_Create response (user identity, PDU session ID, S-NSSAI, DNN) to the SMF to confirm the establishment of the UE's PDU session with the NEF. If the NEF supports and allows the use of RDS, it instructs the SMF and the SMF to include it in the PCO. If the NEF supports extended buffering, it includes an extended buffering support indication in the response and subscribes to mobility-related events with the Access and Mobility Management (AMF) to receive indications when the UE becomes reachable.

[0040] Other PDU sessions, although used for control plane CIoT 5GS optimization, can be anchored to the UPF (also known as N6 PDU sessions) by the AMF, as described in the aforementioned NAS specification, as follows:

[0041] If the UE and network support control plane CIoT 5GS optimization and N3 data transmission, then when the AMF receives a request from the UE to establish a PDU session, it determines whether the PDU session should be a NEF PDU session or an N6 PDU session as specified in 3GPP TS 23.501, and then:

[0042] a) If a NEF PDU session is to be established for an unstructured data type, the AMF includes a control plane instruction to the SMF for the requested PDU session;

[0043] b) If an N6 PDU session needs to be established, and the DNN or S-NSSAI of the newly requested N6 PDU session supports interaction with EPS as specified in TS23.502:

[0044] 1) If an existing N6 PDU session supporting EPS interaction with the UE exists, established using a control-only plane indication, the AMF includes a control-only plane indication to the SMF for the newly requested N6 PDU session; or

[0045] 2) If there are existing N6 PDU sessions that support EPS interaction with the UE, and these sessions were established without a control plane-only indication, the AMF will not include a control plane-only indication to the SMF for the newly requested N6 PDU session.

[0046] 3) If no existing N6 PDU session supports EPS interaction with the UE, the AMF determines, based on local policies, the UE's preferred CIoT network behavior, and supported CIoT network behavior, whether to include a control-only plane indication to the SMF for the newly requested N6 PDU session; and

[0047] c) If an N6 PDU session is to be established, and the DNN or S-NSSAI of the N6 PDU session does not support EPS interaction as specified in TS 23.502, the AMF determines whether to include a control plane-only indication for a new N6 PDU session requested by the SMF based on local policies, the UE's preferred CIoT network behavior, and supported CIoT network behavior.

[0048] Non-3GPP access does not support CIoT 5GS optimization (i.e., control plane CIoT 5GS optimization and user plane CIoT 5GS optimization).

[0049] NB-IoT devices are limited by the number of Data Radio Bearers (DRBs) they can support, with a maximum of two DRBs at a time. In 5G systems (5GS), unlike Evolved Packet Systems (EPS), UEs can selectively activate any PDU sessions they have already established. For example, if a UE has established three PDU sessions, this does not necessarily mean that the UE will have DRBs for all three PDU sessions. Based on the need to transmit data on a particular PDU session, the UE can request the establishment of UP resources only for one of its PDU sessions. Note that UP resources constitute DRBs and other resources, such as UPFs (User Plane Functions), between Radio Access Network (RAN) and Core Network (CN) nodes. Therefore, UP resources are not necessarily limited to DRBs but can be used to refer to DRBs.

[0050] To select which UP resource to establish for a specific PDU session, the UE uses an Uplink Data State Information Element (IE) to indicate which PDU session ID the resource is being requested for. The IE can be transmitted in a Control Plane Service Request (CPSR) message, Service Request (SR) message, or Registration Request message. Including the Uplink Data State IE in a Registration Request message is based on specific conditions defined in the aforementioned NAS specification. However, typically, CPSR or SR messages are used for the purpose of requesting the establishment of UP resources for at least one PDU session.

[0051] In NB-IoT, UP resources can be established for a maximum of 2 PDU sessions at a given time, because the UE is limited by the number of DRBs it can support in this mode.

[0052] Due to the aforementioned limitations, the NAS specification has defined certain restrictions on UEs optimized for user plane CIoT 5GS. For example, the following restrictions have been introduced for the service request process:

[0053] In NB-N1 mode, this procedure should not be used to request the establishment of user plane resources:

[0054] a) For more than two PDU sessions, if the following currently exist:

[0055] 1) No user plane resources were created for the UE;

[0056] 2) User plane resources established for a PDU session; or

[0057] b) For additional PDU sessions, if the UE already has user plane resources established for both PDU sessions.

[0058] The following restrictions are introduced to the PDU session establishment process (see bullet point c below):

[0059] The UE should not request the establishment of a PDU session:

[0060] a) Used for LADN when the UE is outside the LADN service area;

[0061] b) When the UE is in the "Active" state and the UE is not using a PDU session to transmit uplink IP packets for any 3GPP PS data shutdown exemption service, transfer the PDU session from non-3GPP access to 3GPP access (see sub-clause 6.2.10); or

[0062] c) When the UE is in NB-N1 mode, the UE has indicated a preference for user plane CIoT 5GS optimization, the network has accepted the use of user plane CIoT 5GS optimization for the UE, and the UE currently has user plane resources for establishing two other PDU sessions.

[0063] Despite these restrictions being set for the UE, the network still performs checks to ensure these restrictions are not ignored or incorrectly ignored. For example, during the PDU session establishment process, the AMF verifies whether the UE has already established UP resources for a maximum of two PDU sessions. If this is the case, any new request from the UE to establish a PDU session will either be established as a PDU session for control plane CIoT optimization or will be rejected by the AMF. This is described in the aforementioned NAS specification below:

[0064] Upon receiving a UL NAS TRANSPORT message, if the payload container type IE is set to "N1 SM Information", then the request type IE is set to "Initial Request", and

[0065] a) The UE is in NB-N1 mode;

[0066] b) The UE has indicated a preference for user plane CIoT 5GS optimization;

[0067] c) The network accepts user plane CIoT 5GS optimized usage; and

[0068] d) The AMF determines that there are user plane resources established for two other PDU sessions for this UE (see 3GPP TS23.501);

[0069] AMF should:

[0070] a) Return the unforwarded message specified in sub-clause 5.4.5.3.1, case h1), to the UE; or

[0071] b) Continue with PDU session establishment, including control plane CIoT 5GS optimized indication or control plane only indication to SMF.

[0072] It should be noted again that these restrictions apply only to NB-IoT devices, specifically UEs in NB-N1 mode under 5GC conditions.

[0073] Similar limitations exist for UEs in NB-IoT optimized for CIoT within Evolved Packet Systems (EPS), i.e., UEs in NB-S1 mode. However, a key difference between Evolved Packet Core (EPC) and 5GC is that EPC does not support selective user plane activation for UEs in connected mode (EPS Mobility Management (EMM) - connected mode). Thus, when in S1 mode, if the UE is in connected mode for data purposes, DRB and UP resources will be established for all packet data network (PDN) connections active in the UE.

[0074] Therefore, for example, if the UE has already established 3 PDN connections in EPS, when the UE transmits a service request message, the Mobility Management Entity (MME) will establish UP resources for all 3 PDN connections.

[0075] However, for NB-IoT devices, there is a limit to the maximum number of DRBs that can be supported in S1 mode. The UE can support 1 or 2 DRBs, where 2 is the maximum number of DRBs that can be supported, as described in 3GPP TS 24.301 V16.4.0:

[0076] For UEs in NB-S1 mode, when the UE sets the Multi-DRB Support bit to "Support Multi-DRB" during the Attach or Tracking Area Update procedure, the maximum number of UE-specific active user plane radio bearers is 2 (as defined in 3GPP TS 36.300), otherwise it is 1.

[0077] A UE in S1 mode indicates in its network capability IE whether it supports two DRBs by setting the "Multiple DRB Support" bit to "Support Multiple DRBs".

[0078] It should also be noted that for NB-S1 mode, DRB support is limited to the default EPS bearer, and dedicated EPS bearers are not supported in NB-S1 mode. This is similar to 5GS. 3GPP TS 24.301 V16.4.0 specifies the following regarding this:

[0079] In NB-S1 mode, a dedicated EPS bearer context activation procedure is not used. During inter-system mobility from WB-S1 mode to NB-S1 mode in EMM-IDLE mode, if the UE has at least one dedicated EPS bearer context in ESM state BEARER CONTEXTACTIVE, the UE should locally deactivate any such dedicated EPS bearer context and should include the EPS bearer context state IE in the TRACKING AREA UPDATE REQUEST message.

[0080] When the UE moves from WB-S1 mode to NB-S1 mode, the UE will deactivate any dedicated EPS bearers and include the EPS bearer context state (IE) in the TRACKING AREA UPDATE REQUEST message, as specified in 3GPP TS 24.301V16.4.0:

[0081] The UE should include the EPS bearer context state (IE) in the TRACKING AREA UPDATE REQUEST message:

[0082] -For case g;

[0083] -For case s;

[0084] -For case zb;

[0085] - If the UE has already established a PDN connection of type "non-IP" or Ethernet PDN; and

[0086] - If the UE is in EMM-IDLE mode and is moving between WB-S1 and NB-S1 modes for inter-system mobility, at least one dedicated EPS bearer context is locally deactivated.

[0087] It should be noted that the EPS bearer context state (IE) indicates which EPS bearer identifier is active in the UE, and the IE contains a bitmap, each bit of which corresponds to a well-known EPS bearer identifier (see Section 9.9.2.1 of 3GPP TS 24.301 V16.4.0).

[0088] A UE supporting both S1 and N1 modes can be redirected from its registered core network (CN) (e.g., 5GCN) to a target CN (e.g., EPC) and vice versa. The general concepts defined in the aforementioned NAS specification are described below:

[0089] Networks supporting CIoT optimization can redirect UEs between the EPC and the 5G core network (5GCN), as specified in sub-clause 5.31.3 of 3GPP TS23.501. The network may determine the redirection by considering the UE's N1 mode capability or S1 mode capability, the UE's supported and preferred CIoT network behavior, or the CIoT network behavior supported by the network.

[0090] Note: It is assumed that the network will avoid redirecting the UE back and forth between the EPC and 5GCN.

[0091] As specified in sub-clauses 5.5.1.2.5 and 5.5.1.3.5, the network redirects the UE to the EPC by rejecting a registration request with 5G Mobility Management (5GMM) reason #31 "Need to be redirected to EPC".

[0092] Upon receiving a rejection message, the UE disables the N1 mode capability for 3GPP access as specified in sub-clause 4.9.2, and enables the Evolved Universal Terrestrial Radio Access (E-UTRA) capability if it was disabled for moving to the EPC.

[0093] Networks that support CIoT optimization can also redirect the UE from the EPC to the 5GCN, as specified in sub-clause 5.3.19.2 of 3GPP TS 24.301.

[0094] Currently, in 5GS, AMF can redirect the UE to EPC by rejecting the registration request and including the 5GMM reason value #31.

[0095] Currently, in EPS, MME redirects the UE to 5GC by rejecting the Attach Request, Tracking Area Update (TAU) Request, or a combination of TAU Request messages, and includes the EMM reason value #31 "Need to redirect to 5GCN" (see 3GPP TS24.301V16.4.0).

[0096] Note that UE redirection is described in [4], which uses the term "direction" instead of redirection. The following is described in 3GPP TS23.501V16.4.0:

[0097] The UE selects the core network type (EPC or 5GC) based on the broadcast indications of EPC and 5GC, as well as the UE's preferred network behavior for EPC and 5GC. Networks supporting NB-IoT should broadcast an indication in the system information indicating whether N3 data transmission is supported.

[0098] When the UE performs the registration process, it includes its preferred network behavior (for 5G and EPC) in the registration request message, and the AMF responds with the 5G-supported network behavior in the registration acceptance message.

[0099] If the UE supports any CIoT 5GS optimizations included in the 5GC preferred network behavior, then when the UE performs an attach or TAU procedure and the UE includes its EPC preferred network behavior, the UE will also include its 5GC preferred network behavior.

[0100] In networks supporting CIoT features in EPC and 5GC, operators may switch UEs from specific CN types due to operator policies such as roaming agreements, preferred and supported network behaviors, load redistribution, etc. Operator policies in EPC and 5GC are assumed to avoid switching UEs back and forth between EPC and 5GC.

[0101] To redirect the UE from 5GC to EPC, when the UE transmits a registration request, the AMF transmits a registration rejection with an EMM reason value, indicating that the UE should not use 5GC. The UE disables N1 mode and re-enables S1 mode (if it was disabled). Then, as described in Clause 5.17.2, the UE performs an attach or TAU in EPC.

[0102] To redirect the UE from the EPC to the 5GC, when the UE requests an attach or TAU procedure, the MME transmits a rejection message with an EMM reason indicating that the UE should not use the EPC. The UE disables S1 mode and re-enables N1 mode (if it was disabled). Then, as described in Clause 5.17.2, the UE registers with the 5GC.

[0103] When determining whether to redirect a UE, the AMF / MME considers the UE's support for S1 / N1 modes, the UE's preferred network behavior, and the network behavior supported by the network to which the UE is redirected.

[0104] If the UE cannot find a cell that supports connectivity after redirection, the UE can re-enable the disabled N1 / S1 mode and then perform registration, attach, or TAU.

[0105] It can be seen that existing technical solutions for UE redirection or switching depend solely on rejecting specific NAS messages, namely by transmitting a registration rejection message in 5GS and an attach rejection or TAU rejection message in EPS.

[0106] There are some indications that a UE can transmit in 5GSM messages. For example, during the PDU session establishment process, if the UE supports more than 16 packet filters, the UE can transmit the maximum number of supported packet filters (IE) in the PDU SESSION ESTABLISHMENT REQUEST message.

[0107] Similarly, during PDU session establishment, the UE should indicate whether it supports Reflective Quality of Service (RQoS), as described below according to the aforementioned NAS specification:

[0108] If the UE supports reflective QoS and the following conditions apply, the UE should set the RQoS bit to "Support Reflective QoS" in the 5GSM Capability IE of the PDU SESSION ESTABLISHMENTREQUEST message:

[0109] a) The UE requests to establish a new PDU session of type "IPv4", "IPv6", "IPv4v6" or "Ethernet";

[0110] b) The UE requests that existing PDN connections in EPS of “IPv4”, “IPv6”, “IPv4v6”, or “Ethernet” PDN type or “non-IP” PDN type mapped to “Ethernet” PDU session type be transferred to 5GS; or

[0111] c) The UE requests to migrate existing PDN connections in untrusted non-3GPP access connected to an EPC of type “IPv4”, “IPv6”, or “IPv4v6” PDN to 5GS.

[0112] Similarly, when a UE transitions from EPS (i.e., from S1 mode) to 5GS (i.e., from N1 mode), if the UE has a PDN connection initially established in S1 mode, the UE will perform a PDU session modification procedure to report some of its capabilities, such as whether the UE supports more than 16 packet filters or whether the UE supports RQoS. The following from the aforementioned NAS specification describes this:

[0113] For a PDN connection established in S1 mode, after the first inter-system change from S1 mode to N1 mode, if the UE operates in single registration mode in a network that supports the N26 interface, the PDU session is of type "IPv4", "IPv6", "IPv4v6" or "Ethernet" PDU session.

[0114] a) If the UE is performing a PDU session modification procedure to indicate support for reflective QoS, the UE should set the RQoS bit to "Support Reflective QoS" in the 5GSM Capability IE of the PDU SESSIONMODIFICATION REQUEST message; or

[0115] b) If the UE is performing a PDU session modification procedure to indicate that reflective QoS is not supported, the UE should set the RQoS bit to "Reflective QoS is not supported" in the 5GSM capability IE of the PDU SESSIONMODIFICATION REQUEST message.

[0116] For a PDN connection established in S1 mode, after the first inter-system change from S1 mode to N1 mode, if the UE operates in single-registration mode in a network supporting the N26 interface, the PDU session is of type "IPv4", "IPv6", "IPv4v6", or "Ethernet" PDU session, and the UE supports more than 16 packet filters for the PDU session, then the UE should indicate the maximum number of packet filters supported by the PDU session in the Maximum Number of Supported Packet Filters IE of the PDU SESSION MODIFICATION REQUEST message.

[0117] The following are specified in the aforementioned NAS specification regarding interaction between N1 mode and S1 mode and the transfer of PDU sessions. During interaction, the UE must process specific parameters defined by the following rules in the aforementioned NAS specification:

[0118] If, after a system change from S1 mode to N1 mode, the PDU session includes mapped EPS bearer contexts or has an association between QoS flows and mapped EPS bearers, then the PDU session supports interactive operation with EPS. The SMF will not include any mapped EPS bearer contexts associated with PDU sessions used for LADN or as multihomed IPv6 PDU sessions. See Sub-clause 9.11.4.8 for the encoding of mapped EPS bearer contexts (IEs). In an MA PDU session, the UE will have a set of mapped EPS bearer contexts. The network can provide the set of mapped EPS bearer contexts for an MA PDU session by accessing the MA PDU session. In an MA PDU session, the UE should support modification or deletion of mapped EPS bearer contexts for MA PDU sessions created via the same or other accesses.

[0119] When switching between systems from N1 mode to S1 mode, the UE creates a default EPS bearer context and a dedicated EPS bearer context based on parameters of the mapped EPS bearer context or the association between QoS flows in the PDU session and the mapped EPS bearer (if available). The EPS bearer identifier assigned to the QoS flow of the default QoS rule becomes the EPS bearer identifier of the default bearer in the corresponding PDN connection. If no EPS bearer identifier is assigned to the QoS flow of the default QoS rule associated with the PDU session for 3GPP access, the UE performs a local release of the PDU session. If no EPS bearer identifier is assigned to the QoS flow of the PDU session associated with 3GPP access, and the QoS flow is not associated with the default QoS rule, the UE deletes the QoS rule and QoS flow description locally. The UE uses parameters from each PDU session that supports EPS interaction to create the corresponding default EPS bearer context and optional dedicated EPS bearer context, as follows:

[0120] a) The PDU session type of a PDU session should be mapped to the PDN type of the default EPS bearer context, as follows:

[0121] 1) If the PDU session type is "unstructured", then the PDN type should be set to "non-IP";

[0122] 2) If the PDU session type is "IPv4", then the PDN type should be set to "IPv4";

[0123] 3) If the PDU session type is "IPv6", then the PDN type should be set to "IPv6";

[0124] 4) If the PDU session type is "IPv4v6", then the PDN type should be set to "IPv4v6";

[0125] 5) If the PDU session type is "Ethernet", and the UE, network, or both do not support the Ethernet PDN type in S1 mode, then the PDN type should be set to "Non-IP"; and

[0126] 6) If the PDU session type is "Ethernet" and the UE and network support the Ethernet PDN type in S1 mode, then the PDN type should be set to "Ethernet".

[0127] b) The PDU address of the PDU session should be mapped to the PDN address of the default EPS bearer context, as shown below:

[0128] 1) If the PDU session type is "IPv4", "IPv6", or "IPv4v6", then set the PDN address of the default EPS bearer context to the PDU address of the PDU session; and

[0129] 2) If the PDU session type is "Ethernet" or "Unstructured", the PDN address of the default EPS bearer context is set to zero;

[0130] c) The DNN of the PDU session will be mapped to the APN of the default EPS bearer context;

[0131] d) The APN-AMBR and extended APN-AMBR received in the parameters of the default EPS bearer context of the mapped EPS bearer context will be mapped to the APN-AMBR and extended APN-AMBR of the default EPS bearer context.

[0132] e) For each PDU session in the PDU SESSION ACTIVE, PDU SESSION MODIFICATIONPENDING, or PDU SESSION INACTIVE PENDING state, the UE shall set the state of the mapped EPS bearer context to BEARER CONTEXT ACTIVE; and

[0133] f) For any other PDU session, the UE should set the state of the mapped EPS bearer context to bearer context inactive.

[0134] Furthermore, for each mapped EPS bearer context or PDU session, the association between the QoS flow and the mapped EPS bearer is as follows:

[0135] a) The EPS bearer identifier will be set to the EPS bearer identifier received in the mapped EPS bearer context, or the EPS bearer identifier associated with the QoS flow.

[0136] b) The EPS QoS parameters will be set to the mapped EPS QoS parameters of the EPS bearer received in the mapped EPS bearer context, or the EPS QoS parameters associated with the QoS flow.

[0137] c) The extended EPS QoS parameters will be set to the mapped extended EPS QoS parameters of the EPS bearer received in the mapped EPS bearer context, or the extended EPS QoS parameters associated with the QoS flow; and

[0138] d) The service flow template should be set to the service flow template mapped to the EPS bearer received in the mapped EPS bearer context, or the stored service flow template associated with the QoS flow, if available.

[0139] After the system-to-system change from N1 mode to S1 mode, the UE should associate the PDU session identifier, S-NSSAI, and session AMBR with the default EPS bearer context, and for each EPS bearer context mapped from one or more QoS flows, associate the QoS rules and QoS flow description of the QoS flow with the EPS bearer context.

[0140] After a system change from N1 mode to S1 mode, if the UE supports non-IP PDN type and the PDU session type is "Ethernet" or "Unstructured", the UE and SMF should maintain the PDU session type of the PDU session until the PDN connection corresponding to the PDU session is released.

[0141] Following the system transition from N1 mode to S1 mode, the UE and SMF will retain the following GSM attributes and capabilities associated with the PDU session until the PDN connection corresponding to the PDU session is released:

[0142] - Always enable PDU session indication;

[0143] - The maximum number of grouping filters supported;

[0144] - Reflects QoS support;

[0145] - The maximum data rate per UE for uplink user plane integrity protection supported by the UE, and the maximum data rate per UE for downlink user plane integrity protection supported by the UE; and

[0146] -Support for multihomed IPv6 PDU sessions.

[0147] After the system-to-system transition from N1 mode to S1 mode, the UE will assume that the network supports the following features on the PDN connection corresponding to the PDU session:

[0148] -PS data is off; and

[0149] -Local address in TFT.

[0150] If a QoS flow exists for IMS signaling, the EPS bearer associated with the QoS flow for IMS signaling becomes the EPS bearer for IMS signaling after the system changes from N1 mode to S1 mode.

[0151] The text above describes how, when a UE changes between N1 mode and S1 mode, it will create mapped EPS bearer contexts for the default bearer and the dedicated bearer. Specifically, "the UE will create the default EPS bearer context and the dedicated EPS bearer context based on the parameters of the mapped EPS bearer context or the association between the QoS flow in the PDU session and the mapped EPS bearer (if available)."

[0152] For example, when a UE moves from N1 mode to S1 mode, for each PDU session in the PDU SESSION ACTIVE, PDUSESSION MODIFICATION PENDING, or PDU SESSION INACTIVE PENDING state, the UE should set the state of the mapped EPS bearer context to BEARER CONTEXT ACTIVE. This means that the UE considers the EPS bearer context to be active and therefore can be transferred.

[0153] And "After the system change from N1 mode to S1 mode, the UE should associate the PDU session identifier, S-NSSAI and session AMBR with the default EPS bearer context, and for each EPS bearer context mapped from one or more QoS flows, associate the QoS rules and QoS flow descriptions of the QoS flows with the EPS bearer context", that is, the QoS rules and QoS flow descriptions are maintained and associated with the EPS bearer context.

[0154] Several problems exist in the prior art described above, and the purpose of the embodiments of the present invention is to solve these problems.

[0155] Specifically, as mentioned earlier, the AMF can only redirect the UE during the registration process. This means that if the UE is already in connected mode or has switched to connected mode via a service request procedure, the AMF will be unable to redirect the UE for a relatively long period. Similarly, if the UE continues to switch to connected mode via a service request procedure, the MME may be unable to redirect the UE that has been in connected mode for a relatively long time. This is specifically in... Figure 3 As shown in the figure, Figure 3 The steps involved in the registration process are shown, as well as the issue of the AMF remaining in a waiting state because the UE cannot be redirected since it does not transmit a registration request.

[0156] Furthermore, the UE indication in the EPS (Electronic Performance Frame) determines how many DRBs it can support, depending on the UE's NB-IoT capabilities. For 5G CIoT, the UE's RAT (Range Attribution) is the same, but it's connected to a 5G CN. Therefore, it's possible that an NB-IoT UE actually only supports one DRB, and if so, the AMF (Advanced Management Function) is unaware of this. In fact, existing AMFs assume that NB-IoT UEs always support two DRBs. This can lead to system-wide problems and unexpected UE and network behavior, such as when the network attempts to establish multiple DRBs for a UE that only supports one DRB. This is in... Figure 4 As shown in the figure, Figure 4 The signaling between the UE, RAN, and AMF is shown respectively.

[0157] Furthermore, a UE that first establishes a PDN connection in EPS can then transfer the session to 5GS. The UE can support the user plane, but the connection can be for control plane only. Therefore, such a connection does not use packet filtering. In the prior art, when a UE first moves from S1 mode to N1 mode, and the UE has a PDN connection established in S1 mode, if the UE supports more than 16 packet filters, the UE is required to report how many packet filters it supports. Alternatively, the UE should report whether it supports RQoS. However, because this is a control plane only connection, this information is useless to the network, as it will never be used for such a connection or session. Therefore, transmitting this information only unnecessarily consumes resources.

[0158] Figure 5 This section explains the issue and illustrates the signaling between the UE, MME, AMF, and SMF. It should be noted that if the UE does support more than 16 packet filters, the first inter-system change from S1 mode to N1 mode is always performed by the UE. Figure 4 Steps 5A / 5B in the instructions. No other conditions / exceptions will prevent the UE from taking this step.

[0159] When a UE uses Control Plane (CP) CIoT optimization, a PDN connection established in S1 mode can be a connection used to transmit data via the control plane. This PDN connection can be used exclusively for control plane data; that is, user plane resources will never be established for PDN connections. In this case, the UE will receive a "Control Plane Only Indication" in the session management message. Therefore, for any PDN connection associated with the Control Plane Only Indication, the UE can only transmit data via the control plane (i.e., via NAS), and the user plane will never be used. Consequently, packet filtering will never be used for such PDN connections. This will result in additional signaling and increased power consumption, especially for power-constrained NB-IoT devices.

[0160] The embodiments of the present invention are intended to address the shortcomings of the prior art, whether or not they are mentioned herein.

[0161] According to the present invention, an apparatus and method as set forth in the appended claims are provided. Other features of the invention will become apparent from the dependent claims and the following description.

[0162] According to a first aspect of the present invention, a method is provided for redirecting a user equipment (UE) from a serving network to a target network, thereby causing the serving network to reject a service request message.

[0163] In one embodiment, the serving network is 5GC and the target network is EPC, whereby the AMF of the serving network transmits a service rejection message, including 5GMM reason #31 "redirection to EPC required".

[0164] In one embodiment, when a UE in N1 mode receives a service rejection with 5GMM reason #31, the UE takes the following action:

[0165] a) The UE sets the 5GS update status to 5U3 ROAMING NOT ALLOWED (5U3 roaming is not allowed).

[0166] b) The UE resets the service request attempt counter and enters the state 5GMM-REGISTERED.LIMITED-SERVICE (5GMM registered, limited service).

[0167] c) If the E-UTRA capability is disabled, the UE enables the capability and disables the N1 mode capability for 3GPP access.

[0168] d) UE processing EPS parameters, EMM parameters, EMM status, and EPS update status when operating in single registration mode.

[0169] e) If 5GMM cause #31 is received by a UE that does not indicate support for CIoT optimization, or by a UE through a non-3GPP access, or from a cell belonging to a Standalone Non-Public Network (SNPN), this is considered an anomaly.

[0170] f) If a service denial message with reason #31 is received without integrity protection, the UE discards the message.

[0171] In one embodiment, the serving network is EPC and the target network is 5GC, whereby the MME of the serving network transmits a service rejection message, including EMM reason #31 "redirection to 5GCN required".

[0172] In one embodiment, when a UE in S1 mode receives a service rejection with EMM reason #31, the UE takes the following action:

[0173] a) The UE sets the EPS update status to EU3 ROAMING NOT ALLOWED (EU3 roaming is not allowed).

[0174] b) The UE resets the service request attempt counter and enters EMM-REGISTERED.LIMITED-SERVICE (EMM registration, limited service).

[0175] c) If the N1 mode capability for 3GPP access is disabled, the UE enables the capability and disables the E-UTRA capability.

[0176] d) UEs operating in single registration mode handle 5GMM parameters, 5GMM status, and 5GS update status.

[0177] e) If EMM cause #31 is received by a UE that does not indicate support for CIoT optimization, this is considered an abnormal situation.

[0178] According to a second aspect of the invention, a method for managing PDN connections is provided, wherein if the PDN connection is established in S1 mode, the UE verifies whether the associated PDU session is associated with a control plane-only indication.

[0179] In one embodiment, after the first inter-system change from S1 mode to N1 mode, a PDN connection is established, and the UE operates in single-registration mode in a network supporting the N26 interface, and the PDU session is one of the “IPv4”, “IPv6”, “IPv4v6” or “Ethernet” PDU session types, and the UE supports more than 16 packet filters for that PDU.

[0180] In one embodiment, if the UE determines that the PDU session is not associated with a control plane-only indication, the UE will include the maximum number of supported packet filters (IEs) in the PDUSESSION MODIFICATION REQUEST message.

[0181] In one embodiment, if the reason for transmitting the PDU SESSION MODIFICATION REQUEST message is to indicate the number of packet filters supported by the UE, then the message is not transmitted.

[0182] In one embodiment, if the reason for transmitting the PDU SESSION MODIFICATION REQUEST message is to indicate that the UE supports RQoS, then the message is not transmitted.

[0183] According to a third aspect of the invention, a method for managing PDN connections in a UE is provided, wherein after a system change from S1 mode to NB-N1 mode, if the UE determines that a PDU session modification procedure should be performed for the purpose of instructing the UE to support RQoS, the UE still does not transmit a PDU SESSION MODIFICATION REQUEST message.

[0184] In one embodiment, the third aspect method is performed regardless of the control plane indication.

[0185] According to a fourth aspect of the invention, a method for operating a UE in NB-N1 mode is provided, wherein the UE notifies the serving network of the number of data radio bearers (DRBs) that the UE can support, based on its capabilities.

[0186] In one embodiment, the UE notifies the network through bits in the message, where the first value of the bit means that the UE supports one DRB or multiple DRBs are not supported, and the second value of the bit means that the UE supports more than one DRB, which can be a maximum of M DRBs, where M is an integer.

[0187] In one embodiment, this bit is an octet of 5 bits (3 bits) of 5GMM capability IE.

[0188] According to a fifth aspect of the present invention, a method is provided for a UE to request the establishment of user plane resources for multiple PDU sessions, wherein the number of PDU sessions is not greater than the maximum number of DRBs that the UE can support.

[0189] In one embodiment, when a UE requests to use plane resources, the UE indicates the total number of user plane resources via the uplink data state IE that is greater than the number of DRBs that the UE can support.

[0190] According to a sixth aspect of the invention, a method is provided for establishing user plane resources in a network in response to a request from a UE, wherein user plane resources are established if the total number of user plane resources does not exceed the maximum number of DRBs supported by the UE.

[0191] In one embodiment, the AMF in the network requests the SMF in the network to establish user plane resources.

[0192] In one embodiment, the AMF verifies whether a new DRB can be established based on how many DRBs the UE can support.

[0193] According to a seventh aspect of the invention, a method is provided for controlling the establishment of user plane resources for a UE in a network, wherein if the payload container type IE is set to "N1 SM Information", the request type IE is set to "Initial Request", the AMF in the network verifies how many DRBs already exist for the UE, and if the AMF determines that there are user plane resources equal to the maximum number of DRBs supported by the UE, the AMF (a) returns a message to the UE; or (b) establishes a session as a control plane-only session.

[0194] According to an eighth aspect of the invention, an apparatus is provided that is arranged to perform any of the foregoing aspects.

[0195] Although several preferred embodiments of the invention have been shown and described, those skilled in the art will understand that various changes and modifications can be made without departing from the scope of the invention as defined by the appended claims.

[0196] According to the first embodiment, when the current serving (core) network (EPC or 5GC, and therefore MME or AMF respectively) determines to redirect the UE to the target system or (core) network (5GC or EPC), the current serving network may take the following actions:

[0197] *If the UE is in connected mode (i.e., EMM-CONNECTED mode for S1 mode, or 5GMM-CONNECTED mode for N1 mode)

[0198] If the UE is in N1 mode, the AMF sends a DEREGISTRATION REQUEST message to the UE, including the 5GMM reason #31 "Requires redirection to EPC".

[0199] *If the UE is in S1 mode, the MME sends a DETACH REQUEST message to the UE, including EMM reason #31 "Requires redirection to 5GCN".

[0200] If the UE is in idle mode (i.e., EMM-IDLE mode for S1 mode, or 5GMM idle mode for N1 mode), and the UE transitions to connected mode (i.e., EMM-CONNECTED mode for S1 mode, or 5GMM-CONNECTED mode for N1 mode) using a service request message, control plane service request message, or extended service request message (only applicable to S1 mode), and the core network (e.g., MME or AMF) determines to redirect the UE to the target core network (CN), then

[0201] *If the current CN node is an AMF (i.e., the UE is in N1 mode), the AMF should send a service denial message, including #31 "Redirection to EPC required".

[0202] *If the current CN node is an MME (i.e., the UE is in S1 mode), the MME should transmit a service rejection message, including #31 "Redirection to 5GCN required".

[0203] If the UE is in N1 mode and receives a DEREGISTRATION REQUEST message with reason #31 "Requires redirection to EPC":

[0204] If a UE receiving 5GMM reason #31 is not indicated to support CIoT optimization, or if a UE receiving 5GMM reason #31 via non-3GPP access is considered an abnormal situation, the UE's behavior is specified in sub-clause 5.5.1.2.7 of TS 24.501.

[0205] *If a 5GMM cause #31 value is received from a cell belonging to the SNPN, it is considered an abnormal situation, and the UE's behavior is specified in sub-clause 5.5.1.2.7.

[0206] The UE should set its 5GS update status to 5U3 ROAMING NOT ALLOWED (and store it according to sub-clause 5.1.3.2.2), and should delete any 5G-GUTIs, the last accessed registration TAI, the TAI list, and ngKSIs. Additionally, the UE will reset the registration attempt counter and enter the 5GMM-DEREGISTERED status.

[0207] *If the E-UTRA capability is disabled, the UE should enable the capability and disable the N1 mode capability for 3GPP access (see sub-clause 4.9.2 of TS 24.501).

[0208] *If the message is received via 3GPP access and the UE is operating in single registration mode, then for cases where the EPS attach procedure is rejected and the EMM reason has the same value, the UE should process the EMM parameters specified in 3GPP TS 24.301

[15] : EMM status, EPS update status, 4G-GUTI, TAI list, eKSI, and attach attempt counter.

[0209] If the UE is in N1 mode and receives a service denial message with 5GMM reason #31 "Requires redirection to EPC", the UE should take the same action as described above (for receiving a deregistration request in N1 mode). Optionally, in addition to some of the actions listed above, the UE should set the 5GS update state to 5U3 ROAMING NOT ALLOWED (and should store it according to sub-clause 5.1.3.2.2). The UE will reset the service request attempt counter and enter the state 5GMM-REGISTERED.LIMITED-SERVICE. The UE may enter this state instead of 5GMM-DEREGISTERED.

[0210] For a UE in N1 mode, if it receives a registration request message with reason #31 of 5GMM or a SERVICE REJECT message with reason #31 of 5GMM without integrity protection, the UE should discard the message.

[0211] If the UE is in S1 mode and receives a separation request message with EMM reason #31 "Need to redirect to 5GCN":

[0212] *If an EMM reason #31 is received by a UE that does not indicate support for CIoT optimization, it is considered an anomalous situation, and the UE's behavior is specified in sub-clause 5.5.1.2.6.

[0213] The UE should set the EPS update status to EU3 ROAMING NOT ALLOWED (and store it according to sub-clause 5.1.3.3), and should delete any GUTIs, recently accessed registered TAIs, TAI lists, and eKSIs. Additionally, the UE will reset the attach attempt counter and enter EMM-DEREGISTERED.

[0214] *If the N1 mode capability for 3GPP access is disabled, the UE should enable the capability and disable the E-UTRA capability (see sub-clause 4.5 of TS 24.301).

[0215] *If the UE operates in single registration mode, in the event that the initial registration process performed on the 3GPP access is rejected due to 5GMM with the same value, the UE will additionally process the 5GMM parameters specified in 3GPP TS 24.501: 5GMM status, 5G update status, 5G GUTI, last accessed registration TAI, TAI list, and ngKSI.

[0216] If the UE is in S1 mode and receives a service rejection message with EMM reason #31 "Requires redirection to 5GCN", the UE will take the same action as described above (for receiving a separation request in S1 mode). Optionally, in addition to some of the actions listed above, the UE should set the 5GS update state to EU3 ROAMING NOT ALLOWED (and should store it according to sub-clause 5.1.3.2.2). The UE will reset the service request attempt counter and enter EMM-REGISTERED.LIMITED-SERVICE. The UE may enter this state instead of EMM-DEREGISTERED.

[0217] For a UE in S1 mode, if it receives a DETACH REQUEST message or SERVICE REJECT message with EMM reason #31 without integrity protection, the UE should discard the message.

[0218] A UE in NB-N1 mode (i.e., in 5GS) should notify the network (e.g., the AMF) about the number of data radio bearers (DRBs) that the UE can support based on its capabilities. To this end, the UE can transmit a new instruction to the AMF in any 5GMM NAS message. This instruction can be implemented in new IEs or existing IEs known in the prior art.

[0219] Furthermore, the indication can be in digital form, i.e., indicating that the UE supports X DRBs, where X is an integer, and where the indication enables the UE to signal X.

[0220] Optionally, a new bit can be defined (in a new or existing IE), where the new bit can have one of the following two values:

[0221] If this bit is set to zero, it means that the UE supports one DRB, or that multiple DRBs are not supported. Alternatively, if this bit is set to one (i.e., 1), it means that the UE supports more than one DRB, and this can be a maximum of M, where M is an integer. For example, M can be an integer 2, so by setting this bit to "1", the UE indicates that it supports 2 DRBs. Or this value (i.e., 1) can be interpreted as meaning "support multiple DRBs".

[0222] For example, new bits can be used in the 5GMM capability IE bits. For example, bit 3 of the octet 5 of the prior art IE can be defined as a multiple DRB support bit (“multipleDRB” bit). This is in Figure 2 As shown in the table.

[0223] Note that IE with 5GMM capabilities is used as an example, but another IE can be used instead.

[0224] Thus, when transmitting a registration request, the UE should indicate its capability for the multipleDRB bit by setting an appropriate value in this bit. If the UE supports N3 data transmission (i.e., user plane data transmission) and multiple user plane (data) radio bearers, the UE should set the multipleDRB support bit to "Support Multiple DRB" in the 5GMM capability IE of the REGISTRATION REQUEST message.

[0225] In existing technology, the AMF verifies whether the UE has user plane resources to establish for a specific number of PDU sessions, currently 2. However, this is incorrect because the UE may actually support 1 DRB. Therefore, the UE cannot establish user plane resources for more DRBs than it can support, where the maximum number can be an integer M. For example, a UE in NB-N1 mode can support at most 1 or 2 DRBs.

[0226] The UE will not use the service request procedure to request the establishment of user plane resources for a number of PDU sessions exceeding the maximum number of DRBs that the UE can support. Therefore, if the UE transmits a Service Request (SR) message or a Control Plane Service Request (CPSR) message, the UE should ensure that:

[0227] *The uplink data state (IE) should not be set to request user plane resources for a number of PDU sessions that exceed or are greater than the maximum number of DRBs supported by the UE. Therefore, the total number of PDU sessions requesting user plane resources will not exceed the total number of DRBs supported by the UE.

[0228] * The allowed PDU session state IE should not be set so that the number of PDU sessions requesting user plane resources exceeds the maximum number of DRBs supported by the UE. Therefore, the total number of PDU sessions requesting user plane resources (which will be transferred to 3GPP access) will not exceed the total number of DRBs supported by the UE.

[0229] * Neither the Uplink Data State IE nor the Allow Data State IE should be used or set to request user plane resources (in both IEs) for a number of PDU sessions that exceed or exceed the maximum number of DRBs supported by the UE. Therefore, the total number of PDU sessions requesting user plane resources (in both IEs) should not exceed the total number of DRBs supported by the UE.

[0230] Thus, when the AMF receives an SR message or CPSR message containing the following:

[0231] *Uplink Data Status (IE): The AMF will verify whether the number of PDU sessions that will establish UP resources for the UE based on the IE (and possibly based on any PDU sessions that already have UPs established for the UE) is higher than the maximum number of DRBs supported by the UE based on the indication from the UE, as previously proposed.

[0232] If so, then AMF will:

[0233] * Do not request SMF to establish UP resources for UE; or

[0234] *The option to request the SMF to establish UP resources for the UE will be selected such that the total number of PDU sessions for which UP resources will be established does not exceed the maximum number of DRBs supported by the UE based on the indication from the UE, as previously stated.

[0235] *For the permitted data state IE, the AMF will verify whether the number of PDU sessions for which UP resources need to be established based on the IE (and possibly based on any PDU sessions that already have UPs established for the UE) exceeds the maximum number of DRBs supported by the UE based on the indication from the UE, as previously proposed. If so, then the AMF will:

[0236] * Do not request SMF to establish UP resources for UE; or

[0237] *The option to request the SMF to establish UP resources for the UE will be selected such that the total number of PDU sessions for which UP resources will be established does not exceed the maximum number of DRBs supported by the UE based on the indication from the UE, as previously stated.

[0238] For a UE in NB-N1 mode, if the uplink data state IE (or the allowed PDU session state IE) is included in the SR message or CPSR message, and there is no request to establish user plane resources for a number of PDU sessions that is higher than / greater than / more than the maximum number of DRBs that the UE can support (as previously described, i.e., based on the indication in the UE's 5GMM capability IE), then the AMF will instruct the SMF to re-establish user plane resources for the corresponding PDU sessions.

[0239] For UEs in NB-N1 mode, if the uplink data state IE (or allowed PDU session state IE) is included in the SR message or CPSR message, and indicates a request to establish user plane resources for a number of PDU sessions that is higher than / greater than / more than the maximum number of DRBs that the UE can support (as previously explained, i.e., based on the UE's indication in the 5GMM capability IE), then the AMF will not instruct the SMF to re-establish user plane resources for the corresponding PDU sessions.

[0240] For a UE in NB-N1 mode, if the uplink data state IE and the allowed PDU session state IE are included in the SR message or CPSR message, and indicate a request to establish user plane resources for a number of PDU sessions that is higher than / greater than / more than the maximum number of DRBs that the UE can support (as previously explained, i.e., based on the indication in the UE's 5GMM capability IE), then the AMF will not instruct the SMF to re-establish user plane resources for the corresponding PDU sessions.

[0241] When a UE requests to establish a PDU session and the UE is in NB-N1 mode and is using User Plane CIoT 5GS optimization, the AMF should take the following actions.

[0242] Upon receiving a UL NAS TRANSPORT message, if the payload container type IE is set to "N1 SM Information", then the request type IE is set to "Initial Request", and

[0243] a) The UE is in NB-N1 mode;

[0244] b) The UE has indicated a preference for user plane CIoT 5GS optimization;

[0245] c) Network acceptance uses user plane CIoT 5GS optimization; and

[0246] d) The AMF determines that there are user plane resources established for the total number of PDU sessions for the UE, and that the number is equal to the maximum number of DRBs supported by the UE (or have indicated that they support, as previously proposed);

[0247] AMF should:

[0248] a) Send a 5GSM message back to the UE in the DL NAS TRANSPORT message, including the 5GMM reason #92 "Insufficient user plane resources for PDU session". Note that another existing 5GMM reason can also be used; or

[0249] b) Continue with PDU session establishment, including control plane CIoT 5GS optimized indication or control plane only indication to SMF.

[0250] Note that the above procedure applies if the request type is set to "existing PDU session".

[0251] Based on the above, the AMF should not assume that the UE always supports two DRBs. Therefore, it cannot assume that if the UE has UP resources established for one PDU session, the network can establish UP resources for another new session. If the UE only supports one DRB, the AMF will either reject the new request for the PDU session (by transmitting a 5GSM message in the DL NAS TRANSPORT message, including the 5GMM reason #92 "Insufficient user plane resources for the PDU session") or continue the PDU session establishment, including a control plane CIoT 5GS optimization indication or a control plane-only indication to the SMF.

[0252] Therefore, determining whether to establish a new PDU session with user plane resources for a UE in NB-N1 mode should be based on what the UE supports in terms of the number of DRBs. Thus, the AMF should verify whether the UE has already established UP resources for the total number of PDU sessions, and whether that total number is the same as the maximum number of DRBs supported by the UE.

[0253] If the UE currently has UP resources for establishing multiple PDU sessions, and this number is less than the maximum number of DRBs the UE can support (as previously explained, based on the UE's indication in the 5GMM capability IE), then the AMF can accept the request from the UE to establish a PDU session and establish the corresponding UP resources.

[0254] If the UE currently has UP resources for establishing multiple PDU sessions, and this number is equal to the maximum number of DRBs that the UE can support (as previously explained, i.e., based on the UE's indication in the 5GMM capability IE), then the AMF will either reject the request (by transmitting a 5GSM message in the DL NAS TRANSPORT message, including the 5GMM reason #92 "Insufficient user plane resources for PDU session"), or continue establishing the PDU session, including a control plane CIoT 5GS optimization indication or a control plane-only indication to the SMF.

[0255] When a UE has a PDN connection initially established in S1 mode, and the UE performs its first inter-system change from S1 mode to N1 mode, if the PDN connection is established as a control plane-only connection (i.e., the UE receives a control plane-only indication IE in the ACTIVATE DEFAULT EPSBEARER CONTEXT REQUEST message), the UE will not transmit the maximum number of supported packet filters IE in the PDU SESSION MODIFICATION REQUEST message, even if the UE supports more than 16 packet filters for that PDU session. If a PDU session modification procedure (e.g., after the first inter-system change from S1 mode to N1 mode, and optionally, the UE operates in single-registration mode, and optionally, the network supports the N26 interface) is to be performed (optionally, separately) for the purpose of indicating the number of packet filters supported by the UE (optionally, when that number is greater than 16), the UE should not perform the PDU session modification procedure, optionally where not performing the PDU session modification procedure implies that the UE does not transmit a PDU session modification request message. However, if the UE determines that performing the PDU session modification procedure (e.g., the UE determines that transmitting a PDU session modification request message) is for reasons other than indicating the number of packet filters supported by the UE, then if the UE PDU session is determined to be associated with a control-only indication (even if the UE is indeed capable of supporting more than 16 packet filters), the UE should not include the maximum number of supported packet filters (IE) in the PDU SESSION MODIFICATION REQUEST message. Otherwise, if the PDU session is not associated with a control-only indication and the UE supports more than 16 packet filters, then if the UE determines to transmit a PDU SESSION MODIFICATION REQUEST message, the UE may include the maximum number of supported packet filters (IE) in that message.

[0256] Generally, the UE should determine whether the transferred session is a control plane-only session, and:

[0257] If the UE determines that the session is a control plane-only session, and if the UE supports more than 16 packet filters, the UE will not transmit the maximum number of supported packet filters (IE) in the PDU SESSION MODIFICATION REQUEST message. However, if the message is to be transmitted for (optionally only) the purpose of indicating the number of packet filters supported by the UE (optionally, when the number is greater than 16), the UE should not perform the PDU session modification procedure, optionally where not performing the PDU session modification procedure implies that the UE does not transmit the PDU session modification request message.

[0258] *If the UE determines that the session is not a control plane-only session, and if the UE supports more than 16 packet filters, the UE will not transmit the maximum number of supported packet filters (IE) in the PDU SESSION MODIFICATION REQUEST message.

[0259] For PDN connections established in S1 mode, after the first inter-system change from S1 mode to N1 mode, if the UE operates in single-registration mode in a network supporting the N26 interface, the PDU session is of type "IPv4", "IPv6", "IPv4v6", or "Ethernet" PDU session, and the UE supports more than 16 packet filters for that PDU session.

[0260] *If the PDU session is not a control plane-only session, the UE will indicate the maximum number of packet filters supported by the PDU session in the Maximum Number of Supported Packet Filters IE of the PDU SESSION MODIFICATIONREQUEST message;

[0261] Otherwise (i.e., if the PDU session is a control plane-only session), the UE will not indicate the maximum number of packet filters supported by the PDU session in the Maximum Number of Supported Packet Filters IE of the PDU SESSIONMODIFICATION REQUEST message.

[0262] When using user plane CIoT optimization, the above can also be applied to the general case of system-to-system changes from S1 mode to NB-N1 mode, because in NB-N1 mode, each PDU session only supports one default QoS rule. Thus, when the UE moves from NB-N1 mode to WB-N1 mode, the UE can then transmit a PDU session modification request message to indicate that it supports more than 16 packet filters (if this is the case) by including the maximum number of supported packet filters (IE) in the PDUSESSION MODIFICATION REQUEST message.

[0263] Another option is that the UE should not indicate that it supports RQoS after the system change from S1 mode to NB-N1 mode.

[0264] For example, for any combination of the following conditions (e.g., conditions that should be verified by the UE):

[0265] After the system-to-system change from S1 mode to NB-N1 mode, the UE operates in single registration mode, the network supports the N26 interface, and the UE supports RQoS.

[0266] Then, if the UE determines that it needs to perform a PDU session modification procedure for (optionally, only for) the purpose of instructing the UE to support RQoS, the UE should not perform the PDU session modification procedure, that is, the UE should not transmit a PDU session modification request message.

[0267] If the UE determines to perform a PDU session modification procedure (i.e., the UE determines to transmit a PDU session modification request message, for example, for other reasons), the UE may indicate that it does not support RQoS (or the UE may not indicate that it supports RQoS), even if the UE actually supports RQoS.

[0268] However, after the system change from NB-N1 mode to WB-N1 mode, the UE should send a PDU session modification request message to indicate whether it supports RQoS.

[0269] Note that for PDU sessions where the UE determines the session is associated with a control-plane-only session, the above also applies to any inter-system change from S1 mode to N1 mode. Similarly, for any such PDU session, the UE does not need to indicate that it supports RQoS, as this does not simply apply to control-plane-only PDU sessions. Thus, if the UE determines that a PDU session modification procedure is required for the purpose of indicating RQoS support (e.g., under the conditions listed above), then if the PDU session is associated with a control-plane-only indication, or for any other case where the UE performs an inter-system change from S1 mode to N1 mode (optionally, if the UE is operating in single-registration mode, and / or the network supports the N26 interface), the UE can further determine not to perform the PDU session modification procedure. The above can also apply to other new conditions, such as, but not limited to, the type of PDU session, such as an unstructured PDU session, or any other new PDU sessions that may be defined in the future, for which such capability (or any other capability) will not apply. Thus, for any capability that is not applicable under certain conditions, the UE can determine not to perform the necessary 5GSM procedure to indicate the capability in question. On the other hand, if the UE transmits a 5GSM message, it may not indicate the capability in question if that capability is not applicable to the UE's current operating mode. Thus, when the UE changes its operating mode (e.g., enters a new mode or performs an inter-system change to a new mode), the UE can transmit a 5GSM message in which the capability will be applied to the new mode.

[0270] Figure 6 A block diagram of an entity according to an embodiment of the present disclosure is shown.

[0271] refer to Figure 6Entity 600 may include processor 610, transceiver 620, and memory 630. However, not all of the components shown are necessary. Entity 600 may be composed of... Figure 6 The implementation can be achieved with more or fewer components. Furthermore, according to another embodiment, the processor 610, transceiver 620, and memory 630 can be implemented as a single chip.

[0272] The aforementioned components will now be described in detail.

[0273] Processor 610 may include one or more processors or other processing devices that control the proposed functions, processes, and / or methods. Operation of entity 600 may be performed by processor 610.

[0274] In one embodiment, processor 610 may map PRS to resource elements (REs) of a frame structure and transmit the frame structure such that the power used to transmit REs containing PRS is higher than the power used to transmit REs not containing PRS.

[0275] Transceiver 620 may include an RF transmitter for up-converting and amplifying the transmitted signal and an RF receiver for down-converting the received signal. However, according to another embodiment, transceiver 620 may be implemented with more or fewer components than shown in the components.

[0276] Transceiver 600 can be connected to processor 610 and transmit and / or receive signals. These signals may include control information and data. Furthermore, transceiver 620 can receive signals via a wireless channel and output signals to processor 610. Transceiver 620 can also transmit signals output from processor 610 via a wireless channel.

[0277] Memory 630 may store control information or data included in signals obtained by entity 600. Memory 630 may be connected to processor 610 and store at least one instruction or protocol or parameters for the proposed function, process, and / or method. Memory 630 may include read-only memory (ROM) and / or random access memory (RAM) and / or hard disk and / or CD-ROM and / or DVD and / or other storage devices.

[0278] Figure 7 A user equipment (UE) according to an embodiment of the present disclosure is shown.

[0279] refer to Figure 7 UE 700 may include a processor 710, a transceiver 720, and a memory 730. However, not all of the components shown are required. UE 700 may be composed of components such as processor 710, transceiver 720, and memory 730. Figure 7The implementation can be achieved with more or fewer components. Furthermore, according to another embodiment, the processor 710, transceiver 720, and memory 730 can be implemented as a single chip.

[0280] The aforementioned components will now be described in detail.

[0281] Processor 710 may include one or more processors or other processing devices that control the proposed functions, processes, and / or methods. Operation of UE 700 may be implemented by processor 710.

[0282] In one embodiment, processor 710 may measure signal strength from one or more base stations and transmit PRS with a power determined based on the measurement results.

[0283] In one embodiment, processor 710 can receive signaling from a base station and transmit PRS with a power determined based on the signaling.

[0284] Transceiver 720 may include an RF transmitter for up-converting and amplifying the transmitted signal and an RF receiver for down-converting the received signal. However, according to another embodiment, transceiver 720 may be implemented with more or fewer components than shown in the components.

[0285] Transceiver 720 can be connected to processor 710 and transmit and / or receive signals. These signals may include control information and data. Furthermore, transceiver 720 can receive signals via a wireless channel and output signals to processor 710. Transceiver 720 can also transmit signals output from processor 710 via a wireless channel.

[0286] The memory 730 may store control information or data included in signals obtained by the UE 700. The memory 730 may be connected to the processor 710 and store at least one instruction or protocol or parameters for the proposed function, process, and / or method. The memory 730 may include read-only memory (ROM) and / or random access memory (RAM) and / or hard disk and / or CD-ROM and / or DVD and / or other storage devices.

[0287] Some examples of this disclosure may be provided in the form of a base station (e.g., gNB) and / or its methods. Some examples of this disclosure may be provided in the form of a mobile device (e.g., UE) and / or its methods. Some examples of this disclosure may be provided in the form of a system and / or its methods including one or more base stations and one or more mobile devices.

[0288] The embodiments described herein can be implemented using any suitably configured apparatus and / or system. Such apparatus and / or system can be configured to perform the methods according to any aspect, embodiment, example, or claim disclosed herein. Such apparatus may include one or more elements, such as receivers, transmitters, transceivers, processors, controllers, modules, units, etc., each element configured to perform one or more corresponding process, operation, and / or method steps to implement the techniques described herein. For example, operation X can be performed by a module (or X module) configured to perform X. One or more elements can be implemented in hardware, software, or any combination of hardware and software.

[0289] Those skilled in the art will understand that the given process, operation, and / or method steps disclosed herein can be performed by a single entity (hardware and / or software), or the execution of such process, operation, and / or method steps can be distributed and performed by two or more cooperating entities. Those skilled in the art will also understand that a single entity (hardware and / or software) can be configured to perform one process, operation, and / or method step disclosed herein, or can be configured to perform two or more such process, operation, and / or method steps.

[0290] It should be understood that the examples of this disclosure can be implemented in the form of hardware, software, or any combination of hardware and software. Any such software can be stored in the form of volatile or non-volatile memory, such as a storage device like ROM, whether erasable or rewritable, or in the form of memory, such as RAM, memory chips, devices, or integrated circuits, or stored on optical or magnetically readable media, such as CDs, DVDs, disks, or magnetic tapes.

[0291] It should be understood that storage devices and storage media are embodiments of machine-readable storage media adapted to store one or more programs including instructions that, when executed, implement certain examples of this disclosure. Thus, certain examples provide programs comprising code for implementing methods, apparatus, or systems according to any example, embodiment, aspect, and / or claim disclosed herein, and / or machine-readable storage media for storing such programs. Furthermore, such programs can be transmitted electronically via any medium, such as communication signals transmitted via wired or wireless connections.

[0292] The flowcharts and diagrams described above illustrate examples of methods and processes that can be implemented according to the principles of this disclosure, and various changes can be made to the methods and processes shown in the flowcharts and diagrams. For example, although shown as a series of steps, the individual steps in each diagram can overlap, occur in parallel, occur in different orders, or occur multiple times. In another example, steps can be omitted or replaced by other steps.

[0293] Although this disclosure has been described with reference to exemplary embodiments, various changes and modifications will be apparent to those skilled in the art. This disclosure is intended to include such changes and modifications that fall within the scope of the appended claims. Nothing described herein should be construed as implying that any particular element, step, or function is an essential element that must be included within the scope of the claims. The scope of the patent subject matter is defined solely by the claims.

[0294] At least some of the example embodiments described herein can be constructed, in whole or in part, using dedicated hardware. Terms such as “component,” “module,” or “unit” as used herein may include, but are not limited to, hardware devices such as circuits in the form of discrete or integrated components, field-programmable gate arrays (FPGAs), or application-specific integrated circuits (ASICs) that perform a particular task or provide related functionality. In some embodiments, the described elements may be configured to reside on a tangible, persistent, addressable storage medium and may be configured to execute on one or more processors. In some embodiments, these functional elements may include, for example, components such as software components, object-oriented software components, class components and task components, processes, functions, attributes, procedures, subroutines, program code segments, drivers, firmware, microcode, circuits, data, databases, data structures, tables, arrays, and variables. Although example embodiments have been described with reference to the components, modules, and units discussed herein, these functional elements may be combined into fewer elements or separated into additional elements. Various combinations of optional features have been described herein, and it should be understood that the described features can be combined in any suitable combination. In particular, features of any example embodiment may be suitably combined with features of any other embodiment, unless such combination is mutually exclusive. Throughout this specification, the term "comprising" means that the specified ingredients are included, but the presence of other ingredients is not excluded.

[0295] Please note all papers and documents submitted concurrently with or prior to this specification in connection with this application, which are publicly available together with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[0296] All features disclosed in this specification (including any appended claims, abstract, and drawings), and / or all steps of any method or process so disclosed, may be combined in any combination except for combinations in which at least some of such features and / or steps are mutually exclusive.

[0297] Unless otherwise expressly stated, each feature disclosed in this specification (including any appended claims, abstract, and drawings) may be replaced by an alternative feature for the same, equivalent, or similar purpose. Therefore, unless otherwise expressly stated, each disclosed feature is merely one example of a series of equivalent or similar features.

[0298] This invention is not limited to the details of the foregoing embodiments. The invention extends to any novel one or any novel combination of features disclosed in this specification (including any appended claims, abstract, and drawings), or to any novel one or any novel combination of steps of any method or process so disclosed.

Claims

1. A method executed by a user equipment (UE) in a communication system, the method comprising: Send a service request message; In the case where the service request message is sent to the Access and Mobility Management Function (AMF): Receive a first service rejection message from the AMF, including the 5G5G Mobility Management 5GMM reason value #31; as well as Based on the 5GMM cause value, it was identified that redirection to the Evolved Packet Core (EPC) was required; and In the case where the service request message is sent to the Mobility Management Entity (MME): Receive a second service denial message from the MME, including the EPC Mobility Management (EMM) reason value #31; and Based on the EMM cause value, it is identified that redirection to the 5G core network 5GCN is required.

2. The method according to claim 1, further comprising: Based on the 5GMM cause value, the 5G system 5GS update status is set to 5U3 ROAMING NOT ALLOWED.

3. The method according to claim 2, further comprising: Based on the aforementioned 5GMM cause value: Reset the service request attempt counter; and Entering 5GMM-REGISTERED LIMITED-SERVICE status.

4. The method according to claim 1, further comprising: If a first service rejection message including the 5GMM cause value is received without integrity protection, the first service rejection message shall be discarded.

5. The method according to claim 1, wherein, The 5GMM cause value is considered an anomaly in the following situations: The 5GMM cause value is received by the UE, which has no indication of supporting cellular IoT (CIoT) optimization. The 5GMM cause value is received by the UE through a non-3GPP access route; or The 5GMM cause value is received from a cell belonging to an Independent Non-Public Network (SNPN).

6. The method according to claim 1, further comprising: Based on the aforementioned 5GMM cause value: Enable the E-UTRA capability when the Evolved Universal Terrestrial Radio Access (E-UTRA) capability is disabled; as well as Disable N1 mode capability for 3GPP access.

7. A method performed by a network node in a communication system, the method comprising: Receive service request messages from user equipment (UE); When the network node receiving the service request message corresponds to the Access and Mobility Management Function (AMF): The UE needs to be redirected to the Evolved Packet Core (EPC). as well as Send a first service rejection message to the UE including a 5G Mobility Management 5GMM reason value #31, wherein the 5GMM reason value indicates that the redirection to the EPC is required; and When the network node receiving the service request message corresponds to a Mobility Management Entity (MME): The UE needs to be redirected to the 5G core network 5GCN; and A second service denial message is sent to the UE, including the EPC Mobility Management (EMM) reason value #31, wherein the EMM reason value indicates that the redirection to the 5GCN is required.

8. The method according to claim 7, in, If the first service rejection message, including the 5GMM reason value, is sent to the UE without integrity protection, the first service rejection message is discarded.

9. The method of claim 7, wherein the 5GMM cause value is considered an anomaly in the following circumstances: Send the 5GMM reason value to the UE that does not indicate support for Cellular IoT (CIoT) optimization; The 5GMM cause value is sent to the UE via a non-3GPP access route; or The 5GMM cause value is sent by a cell belonging to an Independent Non-Public Network (SNPN).

10. A user equipment (UE) in a communication system, the UE comprising: transceiver; and A processor, coupled to the transceiver, is configured to: Send a service request message; In the case where the service request message is sent to the Access and Mobility Management Function (AMF): Receive a first service rejection message from the AMF, including the 5G5G Mobility Management 5GMM reason value #31; as well as Based on the 5GMM cause value, it was identified that redirection to the Evolved Packet Core (EPC) was required; and In the case where the service request message is sent to the Mobility Management Entity (MME): Receive a second service denial message from the MME, including the EPC Mobility Management (EMM) reason value #31; and Based on the EMM cause value, it is identified that redirection to the 5G core network 5GCN is required.

11. The UE according to claim 10, wherein, The processor is also configured to: Based on the aforementioned 5GMM cause value Set the 5GS update status of the 5G system to 5U3 ROAMING NOT ALLOWED; Reset the service request attempt counter; and Entering 5GMM-REGISTERED LIMITED-SERVICE status.

12. The UE according to claim 10, wherein, The processor is also configured to: If a first service rejection message including the 5GMM cause value is received without integrity protection, the first service rejection message shall be discarded.

13. The UE according to claim 10, wherein, The 5GMM cause value is considered an anomaly in the following situations: The 5GMM cause value is received by the UE, which has no indication of supporting cellular IoT (CIoT) optimization. The 5GMM cause value is received by the UE through a non-3GPP access route; or The 5GMM cause value is received from a cell belonging to an Independent Non-Public Network (SNPN).

14. A network node in a communication system, the network node comprising: transceiver; and A processor, coupled to the transceiver, is configured to: Receive service request messages from user equipment (UE); When the network node receiving the service request message corresponds to the Access and Mobility Management Function (AMF): The UE needs to be redirected to the Evolved Packet Core (EPC). as well as Send a first service rejection message to the UE including a 5G Mobility Management 5GMM reason value #31, wherein the 5GMM reason value indicates that the redirection to the EPC is required; and When the network node receiving the service request message corresponds to a Mobility Management Entity (MME): The UE needs to be redirected to the 5G core network 5GCN; and A second service denial message is sent to the UE, including the EPC Mobility Management (EMM) reason value #31, wherein the EMM reason value indicates that the redirection to the 5GCN is required.

15. The network node according to claim 14, in, If the first service rejection message including the 5GMM cause value is sent to the UE without integrity protection, the first service rejection message is discarded. The 5GMM cause value is considered an anomaly in the following situations: Send the 5GMM reason value to the UE that does not indicate support for Cellular IoT (CIoT) optimization; The 5GMM cause value is sent to the UE via a non-3GPP access route; or Cells belonging to the Independent Non-Public Network (SNPN) send the 5GMM reason value.

Images