EP4691054A1 - Roaming support for network slice admission control for on-demand network slices - Google Patents

Abstract

Systems and methods are disclosed for network control of on-demand network slice in a Visited Network of a UE. One method performed by a network node in a VPLMN of a UE comprises initiating NSAC with an NSACF upon UE registration to one or more network slices or PDU session over a network slice. The method comprises obtaining from the NSACF information indicating that the network slice(s) is on-demand and a deregistration time value from the on-demand network slice and/or a PDU session inactivity time value to release the PDU session from the on-demand network slice. Further, a method for fetching quota between two NSACFs is further provided, where, one NSACF obtains information from the other NSACF indicating slice(s) that are on- demand, a corresponding deregistration and/or the PDU sessions inactivity time values. Furthermore, method and systems for HPLMN enforcement of the use of the on- demand network slices are provided.

Description

Roaming support for Network Slice Admission Control for on-demand network slices RELATED APPLICATIONS This application claims the benefit of provisional patent application serial number 63/492887, filed on 2023-03-29 and 63/500697 filed on 2023-05-08, the disclosure of which are hereby incorporated herein by reference in its entirety. Technical Field [0001] The present disclosure relates to a cellular communications system and, more particularly, Network Slice Admission Control (NSAC) in a cellular communications system. Background [0002] Third Generation Partnership Project (3GPP) Technical Specification TS 23.501 V18.0.0 and TS 23.502 V18.0.0 define, among other things, aspects related to Network Slice Admission Control (NSAC). In particular, for a network slice, the NSAC procedures track the number of User Equipments (UEs) or Protocol Data Unit (PDU) sessions on each network slice and deny access to further UEs once a maximum number of UEs or a maximum number of PDU sessions has been reached for that network slice. Furthermore, they describe NSAC handling in roaming scenarios, mainly that NSAC of roaming UEs is performed by the VPLMN or HPLMN based on roaming agreement or Service level agreement (SLA) between them. More specifically, the following different NSAC roaming modes are described in the 3GPP standard (text reproduced for convenience): Mode 1: VPLMN NSAC Admission Mode: For NSAC of roaming UEs for maximum number of UEs per network slice and/or maximum number of PDU Sessions per network slice managed by the visited public land mobile network (VPLMN), the following principles shall be used: - For NSAC of the maximum number of UEs for a network slice identified as a single Network Slice Selection Assistance Information (S-NSSAI) of the Home PLMN (HPLMN), a NSAC function (NSACF) in the VPLMN can be configured with the maximum number of allowed roaming UEs per mapped S-NSSAI of the HPLMN for a S- NSSAI of the HPLMN that is subject to NSAC. In such a case, the Access and Mobility Management Functions (AMFs) trigger a request to a NSACF of the VPLMN. - For NSAC of the maximum number of PDU Sessions for S-NSSAI of the HPLMN, a NSACF in the VPLMN can be configured with the maximum number of allowed PDU Sessions in local breakout (LBO) mode per mapped S-NSSAI of the HPLMN for a S-NSSAI of the HPLMN that is subject to NSAC. In such a case, the anchor Session Management Function (SMF) in the VPLMN triggers a request to a NSACF of the VPLMN. - For NSAC of the maximum number of UEs for S-NSSAI of the VPLMN, AMFs trigger a request to an NSACF of the VPLMN to perform NSAC based on the S-NSSAI of the VPLMN subject to NSAC. The NSACF of the HPLMN is not involved. - For NSAC of the maximum number of PDU Sessions for S-NSSAI of the VPLMN in the Local BreakOut (LBO) roaming case, the SMF triggers a request to a NSACF of the VPLMN to perform NSAC based on the S-NSSAI of the VPLMN subject to NSAC. The NSACF of the HPLMN is not involved. ‐ The AMF or SMF (in LBO roaming case) in the VPLMN provides both the S- NSSAI in the VPLMN and the corresponding mapped S-NSSAI in the HPLMN to the NSACF in the VPLMN. The NSACF in the VPLMN performs NSAC for both S-NSSAI of the VPLMN and the corresponding mapped S-NSSAI of the HPLMN based on the SLA between the VPLMN and the HPLMN. In addition to configuring the VPLMN NFs with the maximum number of allowed roaming UEs per mapped S-NSSAI of the HPLMN subject to NSAC, and the maximum number of allowed PDU Sessions in LBO mode per mapped S-NSSAI of the HPLMN subject to NSAC, the VPLMN can optionally fetch this information from the HPLMN primary NSACF in a hierarchal architecture or from a centralized NSACF in a centralized architecture. If the NSACF in VPLMN does not have quota configured but can receive quota from the HPLMN, the NSACF in VPLMN may interact with the HPLMN for retrieving the quota before processing any incoming request. The VPLMN is either configured or discovers the NSACF in the HPLMN for quota retrieval. However, in this case, the VPLMN rejects any additional requests exceeding the received information. Mode 2: VPLMN with HPLMN assistance NSAC Admission In this admission mode HPLMN delegates NSAC for S-NSSAIs subject to NSAC to the VPLMN, both for number of registered UEs and the number of LBO PDU sessions. Every NSACF performing admission in the VPLMN for each S-NSSAI of the HPLMN that is subject to NSAC and mapped to a corresponding S-NSSAI of the VPLMN, fetches from the VPLMN primary NSACF in a hierarchal architecture the maximum number of registered UEs to be admitted and/or the maximum number of LBO PDU sessions to be allowed. The VPLMN primary or central NSACF, in turn, acquires the information from the HPLMN central or primary NSACF depending on the deployed architecture. The VPLMN is either configured or discovers the NSACF in the HPLMN for quota retrieval. If re-distribution of quota is required in the VPLMN in a hierarchal architecture, amongst multiple NSACFs than this is handled by the primary NSACF in VPLMN with no involvement from the HPLMN. The VPLMN NSACF discovers the HPLMN primary or central NSACF or be configured with the needed information. For any request(s) received in any NSACF in the VPLMN exceeding the received maximum number information, the NSACF interacts with the VPLMN primary NSACF which in turn interacts with the HPLMN primary or central NSACF to receive an updated roaming quota for the corresponding mapped S-NSSAI, which is then used to determine whether admission request is accepted or rejected, unless it is forbidden by the SLA. If an admission request is accepted, the UE entry is stored in the NSACF performing admission in the VPLMN. This applies to the number of registered UEs as well as the number of LBO PDU sessions. The primary NSACF in VPLMN may re-distribute the received updated roaming quota to the other peer NSACFs in VPLMN to perform NSAC for Roaming UEs Mode 3: HPLMN NSAC Admission Mode In this admission mode, the AMF or SMF in VPLMN interacts with HPLMN for admission, both for number of registered UEs or the number of LBO PDU sessions respectively. For each S-NSSAI of the HPLMN that is subject to NSAC and mapped to a corresponding S-NSSAI of the VPLMN, AMF performs NSAC admission for the number of registered UEs with the HPLMN central or primary NSACF for all inbound roamers from that HPLMN when they register in this VPLMN. The AMF discovers the HPLMN primary or central NSACF or be configured with the needed information. For each S-NSSAI of the HPLMN that is subject to NSAC and mapped to a corresponding S-NSSAI of the VPLMN, every SMF in this VPLMN performs NSAC admission for the number of LBO PDU sessions with the HPLMN central or primary NSACF for all inbound roamers from that HPLMN when they initiate an LBO PDU session. The SMFs discover the HPLMN primary or central NSACF or be configured with the needed information. For each S-NSSAI of the HPLMN that is subject to NSAC, the SMF performs NSAC according to the principles described in Clause 5.15.11.2 for home routed PDU sessions. In the HPLMN NSAC admission mode, the primary NSACF or central NSACF in HPLMN determines whether the NSAC admission request for a roaming UE is accepted or rejected. [0003] In 3GPP Release 17, a 5G system does not offer the ability for an operator to enforce when the UE can register with network slices based on e.g., only on actual need of connectivity in a network slice, or by configuration independent of detected need of connectivity, etc. A User Equipment (UE) in the 5G system typically choose to register and requests the network slices to register to (e.g., using the Configured network slices in the UE) and then use configured or provisioned policies to decide which network slice and optionally data network name (DNN) to connect to and establish a packet data unit (PDU) session. [0004] In 3GPP Release 18, a Technical Report (TR) 23.700-41 v.18.0.0 is released where the concept of on-demand network slices in the 5G system was introduced. An on-demand network slice is a network slice used by the UE on a need basis and enforced by the network on the UE (e.g., when required by an application in the network). More specifically, an operator can force/instruct a UE to register with that network slice when UE connectivity over the network slice is needed. So a UE does not request the (on-demand) network slice based on configuration as per the existing behavior. [0005] Network control for UE use of slices is currently supported for on-demand slices. However, there is currently no support for these control policies while roaming. The reason being that the primary goal for such control is to allow an operator to control its own resources. Applying this to roaming would indeed be equivalent to letting the HPLMN control resources of a VPLMN which it does not own. This specifically applies to Registrations and LBO PDU sessions. In either case, there are no resources in the HPLMN being used. Summary [0006] Certain aspects of the present disclosure and their embodiments may provide solutions to the aforementioned or other challenges. [0007] According to some embodiments, a method performed by an Access and Mobility management Function (AMF) is provided and comprises the steps of initiating a network slice admission control for one or more network slice of a telecommunication system during a registration procedure by a wireless device and the step of receiving information indicating at least one or more of the network slice is an on-demand network slice and a deregistration time value (which may be for example a deregistration timer value) for the on-demand network slice. The information further comprises for example a PDU session inactivity time value for the one or more network slice indicated as on- demand. The method in the AMF may comprise storing the received information. [0008] According to another example, the method comprises the AMF providing the information to the wireless device and /or providing the PDU session inactivity timer for the network slice to a Session management Function upon performing PDU session establishment for the network slice. [0009] According to other embodiments, a method performed by a Session Management Function (SMF) is provided and comprises the step of initiating a network slice admission control for a network slice during a PDU session establishment procedure of a PDU session over a network slice by a wireless device; and the step of receiving information indicating the network slice is an on-demand network slice and a PDU session inactivity time value for the on-demand network slice. [0010] For example, the information can further comprise a deregistration time value for the network slice indicated as on-demand network slice and the method may include the step of storing by the SMF the received information and the method may comprise providing the information to the wireless device and/or providing the deregistration time value for the network slice to an Access Management Function as part of the PDU session establishment procedure. In one example, the PDU session inactivity time value is a PDU session inactivity timer value. [0011] According to one or more embodiments, a method performed by a first network slice admission control function (NSACF) for fetching/updating a quota for a number of wireless devices allowed in one or more network slices and/or number of PDU sessions allowed in one or more network slices is provided. The method comprises the step of sending to a second NSACF a request which may comprise one or more S- network slice identifier (S-NSSAI) for fetching/updating the quota for one or more network slices and receiving from the second NSACF a response to the request comprising information indicating that at least one of the network slices is an on-demand network slice and also includes at least a registration time value, which may be a timer value, for the at least one of the on-demand network slice and/or a PDU session inactivity time value, which may be a timer value, for the at least one of the on-demand network slice. [0012] In one example the method includes the first NSACF storing the received information or performing NSAC based on the received information when requested by at least one of an Access and Mobility management function (AMF) or Session management Function (SMF). [0013] In one example, the first NSACF is a local NSACF in a Visited network and the second NSACF is a primary NSACF in a visited network or the first NSACF is a central NSACF in a visited network and the second NSACF is a central or primary NSACF in a home network wherein the visited network is for example a visited public land mobile network (VPLMN) and the home network is a home PLMN (HPLMN). [0014] According to one or more embodiments, a method performed by a network slice admission control function (NSACF) in a home Public Land Mobile Network (home NSCAF) for enforcing use of an on-demand network slice is provided, the method comprises the step of receiving from a first network function for a User Equipment (UE) a request for updating a number of UEs registered with the on-demand network slice; and the step of sending a response to the request comprising information indicating a deregistration timer for the on-demand network slice and starting the deregistration timer for the on-demand network slice. [0015] In one aspect, the method further comprises the step of sending an instruction to the network function to deregister the UE if the deregistration timer expires and no active Packet data Unit (PDU) session exists for the on-demand network slice. [0016] In another aspect, the method further comprises the step of receiving from a second network function for a User Equipment (UE) a second request for updating a number of PDU sessions established with the on-demand network slice, stopping the corresponding deregistration timer, and sending a response to the second request comprising information indicating a PDU session inactivity timer for the PDU session using the on-demand network slice. [0017] For example, the method comprises the step of receiving a notification that a PDU session using the on-demand network slice is either released or idle and in response to determining that the PDU session is the last active PDU session using the on-demand network slice, the home NSACF restarting the deregistration timer for the on-demand network slice. [0018] For example, the method further comprises notifying the first network function that the deregistration timer has restarted, and the first network node is for example an AMF in 5G and the second network function is for example the SMF in 5G system. [0019] According to an embodiment, a network node is provided that is configured to perform any of the embodiments described herein. [0020] According to an embodiment, a network node is provided that comprises one or more processors and memory comprising instructions which when executed by the one or more processors enable the network node to perform any of the embodiments described herein. [0021] According to an embodiment, a computer readable memory is provided and comprises instructions which when executed by one or more processors of one or more servers configures the one or more server to perform any of the embodiments described herein. Brief Description of the Drawings [0022] The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description serve to explain the principles of the disclosure. [0023] Figure 1 illustrates one example of a cellular communications system 100 in which embodiments of the present disclosure may be implemented; [0024] Figures 2 and 3 illustrate example embodiments of the cellular communication system of Figure 1; [0025] Figure 4 illustrates an example roaming architecture for the cellular communications system of Figure 1; [0026] Figures 5, 6 illustrate embodiments of the present disclosure for NSAC; [0027] Figure 7-0 illustrates embodiment of the present disclosure for quota fetching/updating; [0028] Figure 7-1 illustrates flow diagram of enforcement of on-demand network slice use at HPLMN in accordance with some embodiments; [0029] Figure 7-2 illustrates flow diagram of enforcement of on-demand network slice use at HPLMN in accordance with other embodiments; [0030] Figure 7-3 illustrates flow diagram of on-demand network slice deregistration by the HPLMN in accordance with some embodiments; [0031] Figure 8 illustrate a flow chart for NSAC implemented in an AMF in accordance with some embodiments; [0032] Figure 9 illustrate a flow chart for NSAC implemented in a SMF in accordance with other embodiments; [0033] Figure 10 illustrate a flow chart for quota fetching/updating implemented in a NSACF in accordance with some embodiments; [0034] Figure 10-1 illustrate a flow chart for enforcement of on-demand network slice implemented in a NSACF at a HPLMN in accordance with some embodiments; [0035] Figures 11, 12, and 13 are schematic block diagrams of example embodiments of a network node. Detailed description [0036] The embodiments set forth below represent information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure. [0037] Some of the embodiments contemplated herein will now be described more fully with reference to the accompanying drawings. Other embodiments, however, are contained within the scope of the subject matter disclosed herein, the disclosed subject matter should not be construed as limited to only the embodiments set forth herein; rather, these embodiments are provided by way of example to convey the scope of the subject matter to those skilled in the art. [0038] Generally, all terms used herein are to be interpreted according to their ordinary meaning in the relevant technical field, unless a different meaning is clearly given and/or is implied from the context in which it is used. All references to a/an/the element, apparatus, component, means, step, etc. are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any methods disclosed herein do not have to be performed in the exact order disclosed, unless a step is explicitly described as following or preceding another step and/or where it is implicit that a step must follow or precede another step. Any feature of any of the embodiments disclosed herein may be applied to any other embodiment, wherever appropriate. Likewise, any advantage of any of the embodiments may apply to any other embodiments, and vice versa. Other objectives, features, and advantages of the enclosed embodiments will be apparent from the following description. [0039] Radio Node: As used herein, a “radio node” is either a radio access node or a wireless communication device. [0040] Radio Access Node: As used herein, a “radio access node” or “radio network node” or “radio access network node” is any node in a Radio Access Network (RAN) of a cellular communications network that operates to wirelessly transmit and/or receive signals. Some examples of a radio access node include, but are not limited to, a base station (e.g., a New Radio (NR) base station (gNB) in a Third Generation Partnership Project (3GPP) Fifth Generation (5G) NR network or an enhanced or evolved Node B (eNB) in a 3GPP Long Term Evolution (LTE) network), a high-power or macro base station, a low-power base station (e.g., a micro base station, a pico base station, a home eNB, or the like), a relay node, a network node that implements part of the functionality of a base station (e.g., a network node that implements a gNB Central Unit (gNB-CU) or a network node that implements a gNB Distributed Unit (gNB-DU)) or a network node that implements part of the functionality of some other type of radio access node. [0041] Core Network Node: As used herein, a “core network node” is any type of node in a core network or any node that implements a core network function, the node can be a server or system of distributed servers. Some examples of a core network node include, e.g., an Access and Mobility Management Function (AMF), a User Plane Function (UPF), a Session Management Function (SMF), an Authentication Server Function (AUSF), a Network Slice Selection Function (NSSF), a Network Exposure Function (NEF), a Network Function (NF) Repository Function (NRF), a Policy Control Function (PCF), a Unified Data Management (UDM), a Network slice Admission Control function (NSACF) or the like. [0042] Communication Device: As used herein, a “communication device” is any type of device that has access to an access network. Some examples of a communication device include, but are not limited to: mobile phone, smart phone, sensor device, meter, vehicle, household appliance, medical appliance, media player, camera, or any type of consumer electronic, for instance, but not limited to, a television, radio, lighting arrangement, tablet computer, laptop, or Personal Computer (PC). The communication device may be a portable, hand-held, computer-comprised, or vehicle- mounted mobile device, enabled to communicate voice and/or data via a wireless or wireline connection. [0043] Wireless Communication Device: One type of communication device is a wireless communication device, which may be any type of wireless device that has access to (i.e., is served by) a wireless network (e.g., a cellular network). Some examples of a wireless communication device include, but are not limited to: a User Equipment device (UE) in a 3GPP network, a Machine Type Communication (MTC) device, and an Internet of Things (IoT) device. Such wireless communication devices may be, or may be integrated into, a mobile phone, smart phone, sensor device, meter, vehicle, household appliance, medical appliance, media player, camera, or any type of consumer electronic, for instance, but not limited to, a television, radio, lighting arrangement, tablet computer, laptop, or PC. The wireless communication device may be a portable, hand-held, computer-comprised, or vehicle-mounted mobile device, enabled to communicate voice and/or data via a wireless connection. [0044] Network Node: As used herein, a “network node” is any node that is either part of the RAN or the core network of a cellular communications network/system. [0045] Note that the description given herein focuses on a 3GPP cellular communications system and, as such, 3GPP terminology or terminology similar to 3GPP terminology is oftentimes used. However, the concepts disclosed herein are not limited to a 3GPP system. [0046] Note that, in the description herein, reference may be made to the term “cell”; however, particularly with respect to 5G NR concepts, beams may be used instead of cells and, as such, it is important to note that the concepts described herein are equally applicable to both cells and beams. [0047] Figure 1 illustrates one example of a cellular communications system 100 in which embodiments of the present disclosure may be implemented. In the embodiments described herein, the cellular communications system 100 is a 5G system (5GS) including a Next Generation RAN (NG-RAN) and a 5G Core (5GC); however, the present disclosure is not limited thereto. In this example, the RAN includes base stations 102-1 and 102-2, which in the 5GS include NR base stations (gNBs) and optionally next generation eNBs (ng-eNBs) (e.g., LTE RAN nodes connected to the 5GC), controlling corresponding (macro) cells 104-1 and 104-2. The base stations 102- 1 and 102-2 are generally referred to herein collectively as base stations 102 and individually as base station 102. Likewise, the (macro) cells 104-1 and 104-2 are generally referred to herein collectively as (macro) cells 104 and individually as (macro) cell 104. The RAN may also include a number of low power nodes 106-1 through 106-4 controlling corresponding small cells 108-1 through 108-4. The low power nodes 106-1 through 106-4 can be small base stations (such as pico or femto base stations) or RRHs, or the like. Notably, while not illustrated, one or more of the small cells 108-1 through 108-4 may alternatively be provided by the base stations 102. The low power nodes 106-1 through 106-4 are generally referred to herein collectively as low power nodes 106 and individually as low power node 106. Likewise, the small cells 108-1 through 108-4 are generally referred to herein collectively as small cells 108 and individually as small cell 108. The cellular communications system 100 also includes a core network 110, which in the 5G System (5GS) is referred to as the 5GC. The base stations 102 (and optionally the low power nodes 106) are connected to the core network 110. [0048] The base stations 102 and the low power nodes 106 provide service to wireless communication devices 112-1 through 112-5 in the corresponding cells 104 and 108. The wireless communication devices 112-1 through 112-5 are generally referred to herein collectively as wireless communication devices 112 and individually as wireless communication device 112. In the following description, the wireless communication devices 112 are oftentimes UEs and as such sometimes referred to herein as UEs 112, but the present disclosure is not limited thereto. [0049] Figure 2 illustrates a wireless communication system represented as a 5G network architecture composed of core Network Functions (NFs), where interaction between any two NFs is represented by a point-to-point reference point/interface. Figure 2 can be viewed as one particular implementation of the system 100 of Figure 1. The embodiments in the reminder of these document are described within the context of 5G network architecture using the 5G terminology, but the embodiments are also applicable to other systems/networks using network slicing, admission control of network slicing and on-demand network slicing can. Example of those systems/networks may be 6G systems/networks and beyond. [0050] Seen from the access side the 5G network architecture shown in Figure 2 comprises a plurality of UEs 112 connected to either a RAN 102 or an Access Network (AN) as well as an AMF 200. Typically, the R(AN) 102 comprises base stations, e.g. such as eNBs or gNBs or similar. Seen from the core network side, the 5GC NFs shown in Figure 2 include a NSSF 202, an AUSF 204, a UDM 206, the AMF 200, a SMF 208, a PCF 210, and an Application Function (AF) 212. [0051] Reference point representations of the 5G network architecture are used to develop detailed call flows in the normative standardization. The N1 reference point is defined to carry signaling between the UE 112 and AMF 200. The reference points for connecting between the AN 102 and AMF 200 and between the AN 102 and UPF 214 are defined as N2 and N3, respectively. There is a reference point, N11, between the AMF 200 and SMF 208, which implies that the SMF 208 is at least partly controlled by the AMF 200. N4 is used by the SMF 208 and UPF 214 so that the UPF 214 can be set using the control signal generated by the SMF 208, and the UPF 214 can report its state to the SMF 208. N9 is the reference point for the connection between different UPFs 214, and N14 is the reference point connecting between different AMFs 200, respectively. N15 and N7 are defined since the PCF 210 applies policy to the AMF 200 and SMF 208, respectively. N12 is required for the AMF 200 to perform authentication of the UE 112. N8 and N10 are defined because the subscription data of the UE 112 is required for the AMF 200 and SMF 208. N80 is the reference point between AMF 200 and NSACF 207 and N81 reference point is between SMF 208 and NSACF 207. [0052] The 5GC network aims at separating UP and CP. The UP carries user traffic while the CP carries signaling in the network. In Figure 2, the UPF 214 is in the UP and all other NFs, i.e., the AMF 200, SMF 208, PCF 210, AF 212, NSSF 202, AUSF 204, and UDM 206, are in the CP. Separating the UP and CP guarantees each plane resource to be scaled independently. It also allows UPFs to be deployed separately from CP functions in a distributed fashion. In this architecture, UPFs may be deployed very close to UEs to shorten the Round Trip Time (RTT) between UEs and data network for some applications requiring low latency. [0053] The 5G core network architecture is composed of modularized functions. For example, the AMF 200 and SMF 208 are independent functions in the CP. Separated AMF 200 and SMF 208 allow independent evolution and scaling. Other CP functions like the PCF 210 and AUSF 204 can be separated as shown in Figure 2. Modularized function design enables the 5GC network to support various services flexibly. [0054] Each NF interacts with another NF directly. It is possible to use intermediate functions to route messages from one NF to another NF. In the CP, a set of interactions between two NFs is defined as service so that its reuse is possible. This service enables support for modularity. The UP supports interactions such as forwarding operations between different UPFs. [0055] Figure 3 illustrates a 5G network architecture using service-based interfaces between the NFs in the CP, instead of the point-to-point reference points/interfaces used in the 5G network architecture of Figure 2. However, the NFs described above with reference to Figure 2 correspond to the NFs shown in Figure 3. The service(s) etc. that a NF provides to other authorized NFs can be exposed to the authorized NFs through the service-based interface. In Figure 3 the service based interfaces are indicated by the letter “N” followed by the name of the NF, e.g. Namf for the service based interface of the AMF 200 and Nsmf for the service based interface of the SMF 208, etc. The NEF 216 and the NRF 218 in Figure 3 are not shown in Figure 2 discussed above. However, it should be clarified that all NFs depicted in Figure 2 can interact with the NEF 216 and the NRF 218 of Figure 3 as necessary, though not explicitly indicated in Figure 2. [0056] Some properties of the NFs shown in Figures 2 and 3 may be described in the following manner. The AMF 200 provides UE-based authentication, authorization, mobility management, etc. A UE 112 even using multiple access technologies is basically connected to a single AMF 200 because the AMF 200 is independent of the access technologies. The SMF 208 is responsible for session management and allocates Internet Protocol (IP) addresses to UEs. It also selects and controls the UPF 214 for data transfer. If a UE 112 has multiple sessions, different SMFs 208 may be allocated to each session to manage them individually and possibly provide different functionalities per session. The AF 212 provides information on the packet flow to the PCF 210 responsible for policy control in order to support QoS. Based on the information, the PCF 210 determines policies about mobility and session management to make the AMF 200 and SMF 208 operate properly. The AUSF 204 supports authentication function for UEs or similar and thus stores data for authentication of UEs or similar while the UDM 206 stores subscription data of the UE 112. The NSACF 207 supports monitoring and controlling the number of registered UEs per network slice and/or the number of established PDU Sessions per network slice and supports event-based Network Slice status notification and reports to a consumer NF. The Data Network (DN), not part of the 5GC network, provides Internet access or operator services and similar. [0057] An NF may be implemented either as a network element on a dedicated hardware, as a software instance running on a dedicated hardware, or as a virtualized function instantiated on an appropriate platform, e.g., a cloud infrastructure. [0058] Figure 4 illustrates a wireless communication system represented as an example 5G network roaming architecture composed of core Network Functions (NFs), where interaction between any two NFs is represented by a point-to-point reference point/interface. Figure 4 can be viewed as one particular implementation of the system 100 of Figure 1. While the details of the various nodes illustrated in Figure 4 are known to those of skill in the art, while not essential for understanding the present disclosure, the interested reader is directed to 3GPP 23.501 (see, e.g., V18.0.0). [0059] As stated in the introduction, there currently exist certain challenges for support of roaming for on-demand network slice(s) (S-NSSAI). [0060] Certain aspects of the present disclosure and their embodiments may provide solutions to the aforementioned or other challenges. Embodiments of the solutions described herein may allow for a more dynamic support for VPLMN admission control of on-demand network slices in roaming scenarios and to restrict network control of the UE behavior for an on-demand network slice while roaming. The details of the embodiments are described for the three different roaming NSAC modes described above. [0061] However, there is an exception that allows some support, by an HPLMN for network control for the use of an S-NSSAI while roaming. As described in the embodiments herein, the proposed solution piggyback on current roaming support for NSAC and the S-NSSAI subject to NSAC as described in current 5G standard or beyond. [0062] An HPLMN currently, can require a VPLMN for a subscribed S-NSSAI subject to NSAC to validate with the HPLMN prior to admitting a UE or prior to establishing an LBO PDU session. [0063] According to the embodiments described herein, an S-NSSAI subject to NSAC can also be an on-demand network slice (S-NSSAI) if the HPLMN (e.g., HPLMN NSACF) desires so. In this case, supporting VPLMNs can support handling the inactivity deregistration time value as well as the PDU session inactivity time value for each of the on-demand network slice as provided by the HPLMN (NSACF). As will be used hereinafter, the time value for the deregistration or the PDU session inactivity may be a timer, an absolute time value, a time period or a time window. HPLMN enforcement of on-demand network slice: Even if the VPLMN supported on demand slices there was no way for the HPLMN to do any enforcement as is the case for non-roaming UEs. Hence the HPLMN has to rely on the VPLMN and/or the UE for any enforcement. This however would not be OK for HPLMNs who needed an enforcement mechanism under their full control. Therefore embodiments described herein enable an HPLMN to declare an S-NSSAI as being an on demand S-NSSAI, and to enforce related policies for its outbound roamers for the use of the S-NSSAI in an VPLMN, by declaring the S-NSSAI as subject to NSAC, and applying the HPLMN admission mode for NSAC of the S-NSSAI. This means that the S-NSSAI to be declared as an on-demand S-NSSAI by a HPLMN, must be subject to NSAC and the admission mode deployed with the VPLMN must be HPLMN admission. The NSACF of HPLMN can then enforce related policies for the use of such an S-NSSAI while roaming by its outbound roamers. This requires as well additional extensions to enable the NSACF in HPLMN to enforce on-demand policies for the S- NSSAI. Example Embodiment Related to mode 1 VPLMN NSAC Admission Mode: [0064] As described earlier, For VPLMN NSAC Admission Mode, network slice admission control of roaming UEs for maximum number of UEs per network slice and/or maximum number of PDU Sessions per network slice is managed by the VPLMN. [0065] For the VPLMN NSAC Admission mode, for supporting VPLMNs, VPLMN NSACF receives on-demand slice information comprising an indication that an S-NSSAI is on- demand S-NSSAI, a network slice deregistration inactivity time value (for the on- demand slice), as well as PDU Session(s) inactivity time value(s). If more than one S- NSSAI is indicated as on-demand, a network slice deregistration time value is provided for each S-NSSAI and an inactivity time value for all PDU sessions associated with each of the S-NSSAI are provided. [0066] The NSACF in the VPLMN can retrieve the on-demand slice information while for example fetching the quota from the HPLMN NSACF as illustrated in Figure 7. The NSACF in the VPLMN stores the received information. [0067] The AMF receives the Network Slice deregistration inactivity timer value while performing an update with the VPLMN NSACF as illustrated in Figure 5, in which case the NSACF in Figure 5 is the VPLMN NSACF. The SMF in VPLMN receives the PDU Sessions inactivity timer values from the VPLMN NSACF while performing an update with the VPLMN NSACF as illustrated in Figure 6, in which case the NSACF in Figure 6 is the VPLMN NSACF. [0068] For a centralized NSAC architecture in the VPLMN, the VPLMN NSACF being a centralized NSACF fetches from the HPLMN centralized NSACF or primary NSACF the on- demand slice information and may obtain that information when it also fetches the maximum number of registered UEs, and the maximum number of LBO PDU sessions to be enforced. The VPLMN NSACF provides that information to the AMF or SMF as described just above. [0069] For a hierarchal NSAC architecture in the VPLMN, the NSACF fetches from the VPLMN primary NSACF the on-demand slice information when for example fetching the maximum number of registered UEs, and the maximum number of LBO PDU sessions to be enforced. The VPLMN primary NSACF in turn, fetches from the HPLMN centralized NSACF or primary NSACF the information, which in turn is sent to the VPLMN NSACF. The VPLMN NSACF provides that information to the AMF or SMF as described just above. Example Embodiment Related to mode 2 VPLMN w ith HPLMN assistance NSAC Admission: [0070] As described earlier, for VPLMN with HPLMN assistance NSAC Admission Mode, a maximum number of allowed UEs per mapped S-NSSAI in HPLMN and/or a maximum number of allowed PDU Sessions in LBO mode per mapped S-NSSAI in HPLMN is allocated and delegated to the VPLMN for each S-NSSAI in HPLMN subject to NSAC. The information is stored in one NSCAF in the VPLMN responsible for NSAC for the S-NSSAI in the HPLMN, subject to NSAC. [0071] For the VPLMN with HPLMN assistance NSAC Admission mode, and for supporting VPLMNs, The VPLMN NSACF also receives (as part of the delegating) the on- demand network slice (S-NSSAI) information that comprise the on-demand S-NSSAI indication, Network Slice deregistration inactivity time value, as well as PDU Sessions inactivity time values while fetching the quota from the NSACF in HPLMN. The AMF receives the Network Slice deregistration inactivity time value while performing an update with the NSACF in VPLMN (as per Figure 5, in which case the NSACF in Figure 5 is a VPLMN NSACF). The SMF in VPLMN receives the PDU Sessions inactivity time values from the NSACF in VPLMN while performing an update with the NSACF in VPLMN (as per Figure 6, in which case the NSACF in Figure 6 is a VPLMN NSACF). [0072] For a centralized NSAC architecture in the VPLMN, the NSACF being a centralized NSACF fetches from the HPLMN centralized NSACF or primary NSACF the maximum number of registered UEs, and the maximum number of LBO PDU sessions to be enforced. For a hierarchal NSAC architecture in the VPLMN, the NSACF fetches from the VPLMN primary NSACF the maximum number of registered UEs, and the maximum number of LBO PDU sessions to be enforced. The VPLMN primary NSACF in turn, fetches from the HPLMN centralized NSACF or primary NSACF the maximum number of registered UEs, and the maximum number of LBO PDU sessions to be enforced; this information in turn is sent to the VPLMN NSACF. In both cases, and for supporting VPLMNs and if the S-NSSAI is an on-demand S-NSSAI, the NSACF receives the on- demand S-NSSAI information, i.e., on demand S-NSSAI indication, Network Slice deregistration inactivity time value and the PDU Sessions inactivity time value. The NSACF stores the received information. Example Embodiment Related to mode 3 HPLMN NSAC Admission: [0073] In this admission mode the AMF or SMF in VPLMN interacts with HPLMN for admission, both for number of registered UEs or the number of LBO PDU sessions respectively. [0074] For each S-NSSAI of the HPLMN that is subject to NSAC and mapped to a corresponding S-NSSAI of the VPLMN, AMF performs NSAC admission for the number of registered UEs with the HPLMN central or primary NSACF for all inbound roamers from that HPLMN when they register in this VPLMN. The AMF discovers the HPLMN primary or central NSACF or be configured with the needed information. [0075] If the S-NSSAI is an on-demand S-NSSAI, the AMF receives the Network Slice deregistration inactivity time value from the NSACF. The AMF stores, sets and handles the deregistration timer(s) based on the time value(s), e.g., deregisters the UE from the network slice when the deregistration timer expires. See Figure 5, in which case the NSACF in Figure 5 is the HPLMN NSACF. [0076] Furthermore, for each S-NSSAI of the HPLMN that is subject to NSAC and mapped to a corresponding S-NSSAI of the VPLMN, every SMF in this VPLMN performs NSAC admission for the number of LBO PDU sessions with the HPLMN central or primary NSACF for all inbound roamers from that HPLMN when they initiate an LBO PDU session. The SMFs discover the HPLMN primary or central NSACF or be configured with the needed information. For each S-NSSAI of the HPLMN that is subject to NSAC, the SMF performs NSAC according to the principles described in Clause 5.15.11.2 for home routed PDU sessions. [0077] If the S-NSSAI is an on-demand S-NSSAI, the SMF receives the PDU Sessions inactivity time value from the NSACF in the HPLMN. The SMF stores, sets and handles the PDU session inactivity timer based on the received time value, e.g., releases the PDU session when the timer expires. See Figure 6, in which case the NSACF in Figure 6 is the HPLMN NSACF. [0078] Figure 5 illustrates the number of UEs per network slice availability check and update procedure according with some embodiments. The procedure is based on the procedure described in TS 23.502 V.18.0.0 clause 4.2.11.2 which describes interaction between an access and mobility management function (AMF 200) and an NSACF (207). Figure 5 is applicable for any of the modes described above for updating (i.e. increase or decrease) the number of UEs registered with an S-NSSAI which is subject to NSAC. Embodiments herein modify the procedure to support on-demand network slice control for roaming scenarios. [0079] In step 1, the AMF triggers the Number of UEs per network slice availability check and update procedure to update the number of UEs registered with a network slice when a network slice subject to NSAC is included in the Allowed NSSAI (i.e. the AMF requests to register the UE with the S-NSSAI) or removed from the Allowed NSSAI (i.e. the AMF requests to de-register the UE from the S-NSSAI) for a UE. The trigger event at the AMF also includes the change of Allowed NSSAI in case of inter-AMF mobility. The procedure is triggered by a UE Registration procedure, at UE Deregistration procedure, at UE Configuration Update procedure. [0080] The AMF 200 obtains and stores the applicable NSAC admission mode (i.e., mode 1, mode 2 or mode 3). It may obtain the applicable NSAC mode from the subscription data manager. The NSACF (207) may be a local NSACF (when hierarchical NSAC architecture is used), a VPLMN NSACF or an HPLMN NSACF. [0081] At step 2, the AMF200 uses the Nnscaf_NSAC services, e.g., Nnsacf_NSAC_NumOfUEsUpdate service to update the number of UEs registered with a network slice in the NSACF. The AMF 200 provides the network slices S-NSSAI(s) registered for the UE, the UE Identifier (e.g., SUPI), the NF ID (e.g., AMF ID), Access Type and an update flag indicating increasing or decreasing the number of UEs registered for the network slice(s). [0082] In a centralized NSAC architecture: the NSACF 207 in Figure 5, if mode 1 or mode 2, is the VPLMN central NSACF or if mode 3, it is HPLMN central NSACF. In hierarchical NSAC architecture, the NSACF 207 in Figure 5 is a local NSACF communicating with a primary NSACF, both in VPLMN for mode 1 and mode 2 or in HPLMN in mode 3. Additional details described in TS 23.502 are also applicable for this step. [0083] At step 3, the NSACF 207 determines (as per the current standard) whether the Access Type provided by the AMF is configured for the NSAC based on its configuration. If the Access Type is not configured for the NSAC, the NSACF always accepts the request from the AMF without increasing or decreasing the number of UEs. If the Access Type is configured for the NSAC, the NSACF updates the current number of UEs registered for the S-NSSAI, i.e. increases or decrease the number of UEs registered per network slice based on the information provided by the AMF in the update flag parameter. If the update flag parameter from the AMF indicates increase, the NSACF 207 determines if the UE ID is already in the list of UEs registered with the network slice, the current number of UEs is not increased as the UE has already been counted as registered with the network slice. The NSACF creates a new entry associated with this new update and shall also maintain the old entry associated with previous update. The multiple entries for the same UE ID in the NSACF are differentiated based on the NF ID of the NF sending the update request. The NSACF removes the entry associated with the NF ID upon reception of a request having update flag indicating decrease. [0084] According to embodiments of the present disclosure, the NSACF 207 determines network slice(s) (S-NSSAIs) that is also an on-demand network slice (S- NSSAI) based on the network slices (S-NSSAI(s)) provided by the AMF in step 2. For each S-NSSAI that is also an on-demand S-NSSAI, the NSACF returns at step 4 the on- demand S-NSSAI indication and the S-NSSAI deregistration inactivity time value for the on-demand S-NSSAI. [0085] Optionally, the NSACF 207 provides to the AMF a PDU session inactivity time value for a PDU session that will potentially be established each of the S-NSSAI indicated as on-demand, and which the AMF 200 may later provide to the SMF 208 when the PDU session is established over the corresponding network slice. The AMF may at the same time provide to the SMF the indication that the network slice is also on-demand. [0086] The AMF stores the received information from the NSACF for the on-demand S-NSSAI(s) and perform for example one or more of the following: a. Signal to the UE information indicating one or more of the network slices is on-demand S-NSSAI. An indication for each of the on- demand network slice indicating that the network slice is on- demand is provided to the UE at registration accept message or configuration update message or any appropriate NAS message. b. Signal to the UE the deregistration timer for each of the on-demand network slice(s). The AMF 200 may signal the information to the UE in a registration accept message or configuration update message or any appropriate NAS message. The UE deregisters with the AMF when the timer expires. c. For each of the on-demand network slice (one or more) start the deregistration timer when the UE has no PDU sessions with any of the on-demand network slice and deregister the UE from the on- demand network slice(s) once the timer has expired. [0087] Figure 6 illustrates the number of PDU Sessions per network slice availability check and update procedure according with some embodiments. The procedure is based on the procedure described in TS 23.502 V.18.0.0 clause 4.2.11.4 which describes interaction between a session management function (SMF 208) and an NSACF 207. Figure 6 is applicable for any of the modes described above for updating (i.e. increase or decrease) the number of UEs registered with an S-NSSAI which is subject to NSAC. Embodiments herein modify the procedure to support on-demand network slice control for roaming scenarios. [0088] In step 1, the SMF triggers the Number of PDU sessions per network slice availability check and update procedure to update the number of PDU sessions established (or released) with a network slice when a network slice is subject to NSAC. The SMF anchoring the PDU session (LBO PDU session in VPLMN) triggers the Number of PDU Sessions per network slice availability check and update procedure for the network slices that are subject to NSAC at the beginning of a PDU Session Establishment procedure and as a last step of successful PDU Session Release procedure. The SMF 208 obtains and stores the applicable NSAC admission mode (i.e., mode 1, mode 2 or mode 3). It may obtain the applicable NSAC mode from the subscription data manager. The NSACF (207) may be a local NSACF (when hierarchical NSAC architecture is used), a VPLMN NSACF or an HPLMN NSACF. [0089] At step 2, the SMF208 uses the Nnscaf_NSAC services, e.g., Nnsacf_NSAC_NumOfPDUsUpdate service to update the number of PDU sessions with a network slice in the NSACF 207. The SMF 208 includes in the message the UE identifier, the PDU session ID(s), S-NSSAI(s) for which the number of PDU Sessions per network slice update is required, Access Type and the update flag. The update flag may include one of the following values: - 'increase' which indicates that the number of PDUs established on the S-NSSAI is to be increased when the procedure is triggered at the beginning of PDU Session Establishment procedure or when a new user plane leg is to be established for an MA PDU Session; - 'decrease' which indicates that the number of PDU Sessions on the S-NSSAI is to be decreased when the procedure is triggered at the end of PDU Sessions Release procedure or when an existing user plane leg is to be released for an MA PDU Session; or - 'update' which indicates that for existing PDU Session the Access Type is to be replaced with a new Access Type during inter access mobility. [0090] In a centralized NSAC architecture: the NSACF 207 in Figure 6, if mode 1 or mode 2, is the VPLMN central NSACF or if mode 3, it is HPLMN central NSACF. In hierarchical NSAC architecture, the NSACF 207 in Figure 6 is a local NSACF communicating with a primary NSACF, both in VPLMN for mode 1 and mode 2 or in HPLMN for mode 3. Additional details described in TS 23.502 are also applicable for this step. [0091] At step 3, the NSACF 207 (as per the current standard) The NSACF updates the current number of PDU Sessions established on the S-NSSAI, i.e. increase or decrease the number of PDU Sessions per network slice based on the information provided by the anchor SMF in the update flag parameter. [0092] According to embodiments of the present disclosure, the NSACF 207 determines whether the network slice(s) (S-NSSAI) provided by the SMF in step 2 is also an on-demand network slice (S-NSSAI). If at least one of the S-NSSAI(s) is an on- demand S-NSSAI, the NSACF returns at step 4 the on-demand S-NSSAI indication and the PDU session inactivity time value for the PDU session associated to the on-demand S-NSSAI. [0093] Optionally, the NSACF 207 provides to the SMF a deregistration inactivity time value for the network slice(s) indicated as on-demand. If received by the SMF 208, the SMF 208 may provide the deregistration time value for the network slice(s) to the AMF 200 as part of the PDU session establishment procedure and signaling from the SMF 208 to the AMF 200. [0094] The SMF 208 stores the received information from the NSACF 207 for the on- demand S-NSSAI and perform for example one or more of the following for a PDU session: a. Signal to the UE using NAS signalling (via the AMF 200) information indicating the network slice, S-NSSAI is on-demand. The NAS signalling message may be a PDU session establishment accept message or any appropriate NAS message. b. Signal to the UE the received PDU session inactivity timer for the on-demand network slice. The timer may also be included in the PDU session establishment accept message or any appropriate NAS message. The UE releases the PDU session once the timer expires and may send a PDU session release to the SMF. c. start the PDU session inactivity timer for the PDU session over the on-demand network slice and release the PDU session once the timer has expired. The SMF 208 may send a PDU session release to the UE. [0095] In an alternative embodiment, if the SMF received from the AMF 200 the indication of on-demand S-NSSAI and/or the PDU session inactivity time for the PDU session being established over an on-demand network slice (S-NSSAI) (which the AMF 200 may have obtained when doing the quota check at registration to the network slices), the SMF 208 stores the information and use it as described above. [0096] Figure 7-0 illustrates a quota update procedure according with some embodiments. The quota update procedure in Figure 7 is performed between two or more NSACF instances and is applicable for any of the modes described above, more specifically. The NSACF instances involved in the quota update procedure may be a VPLMN central NSACF (207-1) interacting with the HPLMN central/primary (207-2), or local NSACF (207-1) interacting with primary NSACF (207-2) in VPLMN which in turn interacts with HPLMN central or primary NSACF (207-3) depending on the mode of operation. More specifically: - In mode 1 centralized NSAC architecture in the VPLMN, the VPLMN (central) NSACF initiates a Quota update procedure to fetch the quota from the HPLMN (central or primary) NSACF. - In mode 1 hierarchical NSAC architecture in the VPLMN, the local NSACF in the VPLMN fetches the quota from the VPLMN primary NSACF and the VPLMN primary NSACF fetches the quota from either a central or a primary NSACF in the HPLMN. - In mode 2, same as mode 1 above. - In mode 3, there is no quota update between two NSACF instance as the AMF/SMF in VPLMN interacts with NSACF central or primary in the HPLMN, hence similar to embodiments covered in Figure 5 and 6). [0097] In step 1 of Figure 7, the first NSACF in the VPLMN triggering the quota update sends a quota update request to a second NSCAF (step 1). Details for mode 1 and mode 2 are provided below. [0098] For mode 1: The first NSACF in VPLMN fetches (fetch request, step 1) the maximum number of registered UEs to be enforced, and in the same fetch request or a subsequent request can fetch the maximum number of LBO PDU sessions to be enforced. In this mode (mode 1), NSAC can be performed in centralized or hierarchical architecture: For a centralized NSAC architecture in the VPLMN, the first NSACF being a centralized NSACF fetches from the HPLMN centralized NSACF or primary NSACF (second NSACF) the maximum number of registered UEs, and in the same procedure or different but similar procedure fetches the maximum number of LBO PDU sessions to be enforced. For a hierarchal NSAC architecture in the VPLMN, the (local) NSACF (first NSACF) fetches from the VPLMN primary NSACF (second NSACF) the maximum number of registered UEs, and in the same procedure or different but similar procedure fetches the maximum number of LBO PDU sessions to be enforced. The VPLMN primary NSACF in turn, fetches the same from the HPLMN centralized NSACF or primary NSACF (third NSACF) (step 1a, 2a); this information in turn is sent to the VPLMN NSACF (first NSACF). [0099] In accordance with some embodiments, for supporting VPLMNs and if the S- NSSAI(s) is (are) on demand S-NSSAI(s), the NSACF in the VPLMN (first NSACF) receives in step 2 from the second NSACF information indicating one or more of: a. On-demand S-NSSAI indication for one or more S-NSSAI. Depending on the trigger for quota update, the on-demand S- NSSAI indication may be for each S-NSSAI provided by the AMF as part of the Number of UE check and update procedure (Figure 5). Alternatively, the on-demand S-NSSAI indication may be for the S- NSSAI indicated by an SMF in the PDU session check and update procedure in Figure 6, b. a Network Slice deregistration inactivity time value for each of the one or more on-demand S-NSSAI(s), and c. PDU Sessions inactivity time for each of the one or more on- demand S-NSSAIs (all the S-NSSAIs indicated as being on-demand and registered for the UE) or PDU sessions inactivity time for the S- NSSAI used by the UE in a PDU session. The NSACF stores the received information. [0100] For mode 2: For a centralized NSAC architecture in the VPLMN, the first NSACF being a centralized NSACF fetches from the HPLMN centralized NSACF or primary NSACF (second NSACF) the maximum number of registered UEs for one or more S- NSSAI, and the maximum number of LBO PDU sessions to be enforced for one or more S-NSSAI. For a hierarchal NSAC architecture in the VPLMN, the first NSACF fetches from the VPLMN primary NSACF (Second NSACF) the maximum number of registered UEs, and the maximum number of LBO PDU sessions to be enforced. The VPLMN primary NSACF in turn, fetches from the HPLMN centralized NSACF or primary NSACF (third NSACF) the maximum number of registered UEs, and the maximum number of LBO PDU sessions to be enforced; this information in turn is sent to the VPLMN NSACF (first NSACF). [0101] In both of the above cases, and for supporting VPLMNs and if at least one S- NSSAI (provided by AMF or SMF) is an on-demand S-NSSAI, the first NSACF receives in step 2 from the second NSACF (as obtained from the thirst NSACF) information indicating one or more of: - On-demand S-NSSAI indication for one or more S-NSSAI. Depending on the trigger for quota update, the on-demand S-NSSAI indication may be for each S- NSSAI provided by the AMF as part of the Number of UE check and update procedure (Figure 5). Alternatively, the on-demand S-NSSAI indication may be for the S-NSSAI indicated by an SMF in the PDU session check and update procedure in Figure 6, - a Network Slice deregistration inactivity time value for each of the one or more on-demand S-NSSAI(s), and - PDU Sessions inactivity time value for each of the one or more on-demand S- NSSAIs (all the S-NSSAIs indicated as being on-demand and registered for the UE) or PDU sessions inactivity timer for the S-NSSAI used by the UE in a PDU session. [0102] The NSACF stores the received information. Furthermore, the first NSACF may receive quota update from the second NSACF if any information (deregistration time value, PDU session inactivity time value) related to the one or more on-demand S-NSSAI has changed in the second (or thirst NSACF). The first NSACF may receive the update in response to a subscription to receiving notification to the changes or the first NSACF may receive the updates without any solicitation from the first NSACF. Example embodiments for enforcements of the on-demand network slices: [0103] While roaming, two modes enable an HPLMN to control UE use of an S-NSSAI that is an on demand S-NSSAI; HPLMN delegated slice use mode and HPLMN enforced slice use mode. For both modes, the AMF in the VPLMN is informed at UE registration if any requested S-NSSAI is an on demand S-NSSAI, and which enforcement mode applies. Additionally, the SMF in the VPLMN is informed at PDU Session Establishment Request if the S-NSSAI is an on demand S-NSSAI, and which enforcement mode applies. HPLMN Delegated Slice Use mode: [0104] In this mode, the VPLMN applies its own timers, which may be based on timers received from the HPLMN NSACF. [0105] For supporting VPLMNs, the VPLMN identifies the configured S-NSSAI which maps to the on demand HPLMN S-NSSAI. The VPLMN handles the on-demand aspects for the S-NSSAI similar to the non-roaming scenario applying its own timers for the VPLMN S-NSSAI that maps to the HPLMN S-NSSAI. It may also use timer from the HPLMN. HPLMN Enforced slice Use mode: [0106] In this mode, the HPLMN controls and enforces the UE use of an on-demand S-NSSAI. To enable that, an on-demand S-NSSAI needs be subject to NSAC in this case. In addition, the HPLMN NSAC admission mode for the HPLMN inbound roamers shall be deployed in the VPLMN. NSACF in the HPLMN is the enforcing NF in this mode using timers configured in the NSACF NF. Additionally, the same NSACF must be used, both, for the number of registered UEs and number of PDU sessions. Note that an HPLMN can have unlimited quota for the number of registered UEs and number of PDU sessions for the S-NSSAI if the HPLMN desire to only enforce the on demand aspects for the S- NSSAI. For supporting VPLMNs, the AMF in the VPLMN receives the S-NSSAI deregistration inactivity timer while performing admission with the HPLMN NSACF at UE registration for a S-NSSAI that is also on demand. The AMF includes the S-NSSAI deregistration timer in the Registration Accept message sent to supporting UEs. For supporting VPLMNs, the SMF in the VPLMN receives the PDU Session inactivity timer while performing admission with the HPLMN NSACF at PDU Session Establishment request for a S-NSSAI that it also on demand. The SMF includes the S-NSSAI PDU session inactivity timer in the PDU Session Establishment Accept message sent to supporting UEs. [0107] HPLMN NSACF enforces the UE use of an on demand S-NSSAI as follows: - The NSACF starts the S-NSSAI deregistration timer at UE registration, and stops the S-NSSAI deregistration timer when the UE establishes a PDU Session i.e. when the NSACF receives the Nnsacf_NSAC_NumOfPDUsUpdate_Request message from the SMF. - If the S-NSSAI deregistration timer expires for a UE, NSACF requests the AMF to deregister the UE using the existing EAC notification mechanism extended to send the needed information to the AMF. - If the S-NSSAI PDU Session inactivity timer expires, the SMF deregisters the UE. If this is the last PDU Session, NSACF starts the S-NSSAI deregistration timer. Detailed Enforcement of deregistration timer by the HPLMN: [0108] According to some embodiments, at UE Registration, the AMF in VPLMN performs admission with the HPLMN NSACF node. The NSACF is configured with on demand slice(s). When the NSACF realizes that the slice for which an update request is received is an on-demand S-NSSAI, it returns to the AMF the slice deregistration timer which would be provided to the UE (either the same or another timer derived by the AMF based on the deregistration timer provided by the NSACF). The NSACF also enforces the current behavior in 23.501 of AMF for non-roaming UEs. This means that the NSACF starts a deregistration inactivity timer at UE registration which is stopped when the NSACF is informed that the UE started a PDU session (LBO or home routed) for that slice. When the deregistration timer for the on-demand network slice expires then the NSACF deregisters the UE from the network slice as illustrated in Figure 7-3. [0109] The AMF in the VPLMN also receives an indication that the on-demand S- NSSAI is subject to HPLMN enforcement or VPLMN enforcement. For HPLMN enforcement, this means that the on-demand S-NSSAI is subject to NSAC and HPLMN admission mode applies in this case, as described above. [0110] If the AMF in the VPLMN received an indication that VPLMN enforcement applies, then the VPLMN can choose to enforce the UE use of the on-demand S-NSSAI if it so chooses, and if it supports the feature. The deregistration timer provided to supporting UEs is provided by the AMF (same as provided by NSACF or timer derived from the NSACF deregistration). Such an enforcement is based on existing procedures in 23.501. [0111] Figure 7-1 illustrates details enforcement for the deregistration timer for an on-demand S-NSSAI by the HPLMN. [0112] In step 1 the UE performs 5G registration based on 3GPP TS 23.502, clause 4.2.2 [0113] In step 2 the AMF fetches the subscriber data. For outbound roamers, if the subscription data includes information that a subscribed S-NSSAI is an on-demand S- NSSAI, the applicable slice use enforcement mode, either HPLMN delegated and/or HPLMN enforced, is also included for the on-demand S-NSSAI. For HPLMN enforced mode, the on-demand S-NSSAI is also subject to NSAC. In this case, the AMF assumes that HPLMN NSAC admission mode applies for the S-NSSAI for the HPLMN outbound roamers. For HPLMN slice use delegated mode, the AMF behaviour for supporting VPLMNs is identical to the non-roaming case. [0114] As part of the subscription data fetched by the AMF, one or more S-NSSAI is included. The following show an embodiment of the data provided with the S-NSSAI as part of the Access and Mobility subscription data: Subscribed S-NSSAIs The Network Slices that the UE subscribes to. In the roaming case, it indicates the subscribed Network Slices applicable to the Serving PLMN (NOTE 11). If a subscribed S-NSSAI is subject to NSAC and equally is an on demand S-NSSAI, an indication to that effect is included, including the applicable slice use enforcement mode i.e. HPLMN delegated or HPLMN enforced. For such an S-NSSAI the HPLMN NSAC admission mode is assumed for the HPLMN outbound roamers. [0115] According to an embodiment, the AMF in the VPLMN discovers that a configured S-NSSAI is an on-demand S-NSSAI and discovers that the configured slice is subject to NSAC and that HPLMN admission is the applicable admission mode for inbound roamers, also determines the applicable enforcement mode. It is possible to include an indication with the on-demand indication that HPLMN enforcement applies in this case. This indicates to the AMF that the configured S-NSSAI is subject to NSAC and that HPLMN admission mode applies. [0116] In step 3a, the AMF sends to the NSACF in HPLMN an Ncnsacf_NumofUEsUpdate Request (UE, S-NSSAI (s), etc.) [0117] In step 3b the NSACF in the HPLMN determines that the slice is an on- demand S-NSSAI and include in its response to the AMF the deregistration timer for the on-demand S-NSSAI(S). The NSACF in the HPLMN is configured with this information. The NSACF returns the Ncnsacf_NumofUEsUpdate Response and includes the S-NSSAI deregistration timer for the on-demand network slice(s). [0118] In step 4, the NSACF starts the deregistration inactivity timer for the on- demand S-NSSAI(s). [0119] In step 5, the AMF in the VPLMN stores the deregistration inactivity timer and starts the timer for VPLMN enforcement if the VPLMN supports the feature. [0120] In step 6, the AMF returns the deregistration timer for supporting UEs. The AMF may provide the same deregistration timer provided by the NSACF or it may determine a deregistration timer taking into account the timer provided by the NSACF. The AMF may also provide to the UE an outbound roamers List of on demand S-NSSAIs which includes a list of S-NSSAIs that are on demand, and subject to NSAC with HPLMN NSAC admission. For each S-NSSAI the applicable S-NSSAI deregistration timer configured in the NSACF for the S-NSSAI. [0121] If the deregistration timer expires for an on-demand S-NSSAI, the NSACF deregisters the UE from the network slice based on procedure described in Figure 7-3. The deregistration occurs if no PDU session is established and active over the S-NSSAI. Detailed NSACF Enforcement for the PDU session inactivity timer in the HPLMN: [0122] According to some embodiments, at UE establishment of an LBO or home routed PDU session, when the SMF interacts with the NSACF at HPLMN for admission, the NSACF stops the S-NSSAI deregistration timer if the S-NSSAI is an on-demand S- NSSAI, and the timer is running. As stated above, the NSACF is configured with the on demand slice(s). [0123] When the NSACF in the HPLMN realizes that the slice for which an update request from the VPLMN is received is an on demand S-NSSAI, it returns to the SMF in the VPLMN, the PDU Session inactivity timer to be returned to the UE (optionally the SMF may derive an inactivity timer based on the received timer, in which case the derived timer is returned to the UE). [0124] In addition to the on-demand indication for a S-NSSAI, the SMF in VPLMN can also receive an indication that the on-demand S-NSSAI is subject to HPLMN enforcement or VPLMN enforcement. For HPLMN enforcement, this means that the on- demand S-NSSAI is subject to NSAC and HPLMN admission mode for inbound roamers applies in this case. HPLMN enforcement is performed by the NSACF. If the SMF in the VPLMN received an indication that VPLMN enforcement applies then the VPLMN can choose to enforce the UE use of the on-demand S-NSSAI if it so chooses. The PDU inactivity timer provided to supporting UEs in this case is provided by the SMF in VPLMN. [0125] According to some embodiments, the SMF may, instead of releasing the PDU session after the provided PDU session inactivity timer expires, it could perform the following: - When the PDU session timer expires for LBO sessions (UPF may inform the SMF), the SMF instead informs the NSACF with a new service request called Nnsacf_PDU SessionState Request. This is a new service to be supported by NSACF to enable the SMF to report session state to the NSACF, enabling the NSACF to determine whether to release the PDU session. This reporting is done by the SMF in VPLMN for LBO session and by SMF in HPLMN for home routed PDU sessions. - The NSACF may then restart the deregistration inactivity timer if this is the last PDU session for the UE. [0126] Figure 7-2 illustrates details enforcement for the PDU session inactivity timer for an on-demand S-NSSAI by the HPLMN. [0127] In step 1 the UE initiates an LBO PDU session establishment request based on based on existing procedures in 3GPP TS 23.502. [0128] In step 2 after fetching the SMF subscriber data from the UDM. For outbound roamers, if the subscription data includes information that a subscribed S-NSSAI is an on-demand S-NSSAI, the applicable slice use enforcement mode, either HPLMN delegated or HPLMN enforced, is also included for the on-demand S-NSSAI. For HPLMN enforced mode, the on-demand S-NSSAI is also subject to NSAC. In this case, the SMF assumes that HPLMN NSAC admission mode applies for the S-NSSAI for the HPLMN outbound roamers. For HPLMN slice use delegated mode, the SMF behaviour for supporting VPLMNs is identical to the non-roaming case. [0129] As part of the subscription data fetched by the SMF, one or more S-NSSAI is included. The following show an embodiment of the data provided with the S-NSSAI as part of the SM subscription data: Session Management Subscription data contains one or more S-NSSAI level subscription data: S-NSSAI Indicates the value of the S-NSSAI. If a subscribed S-NSSAI is subject to NSAC and is equally an on demand S-NSSAI, an indication to that effect is included, including the applicable slice use enforcement mode i.e. HPLMN delegated or HPLMN enforced. For such an S-NSSAI the HPLMN NSAC admission mode is assumed for the HPLMN outbound roamers. [0130] In step 3a, the SMF sends to the NSACF in HPLMN an Nnsacf_NumofPDUsUpdate Request (UE, S-NSSAI (s), PDU Session ID, etc.) [0131] In step 3b NSACF realizes that the slice is an on-demand S-NSSAI and includes in its response to the SMF the PDU session inactivity timer. The NSACF in the HPLMN returns the Nnsacf_NumofUEsUpdate Response including the PDU session inactivity timer configured in the NSACF. [0132] In step 4, the NSACF starts the S-NSSAI PDU Session inactivity timer and stops the S-NSSAI deregistration timer if it is running. The timer could be running if it is the first PDU session established for the on-demand S-NSSAI. It is desirable that the deregistration timer is synchronized as much as possible at the AMF and the NSACF in the HPLMN. Hence, the AMF should also stop the deregistration inactivity timer for the on-demand S-NSSAI on its own when it is aware that a PDU session is established using the on-demand S-NSSAI. [0133] In step 5a, the SMF in the VPLMN stores the PDU session inactivity timer, may derive another inactivity timer for the UE based on the received timer. [0134] In step 5b, the SMF in VPLMN return to the UE a PDU session establishment accept (via the AMF) and may include the PDU session inactivity timer configured in the NSACF or derived from the SMF for supporting UEs. If received, the UE uses the timer by releasing the PDU session context when the timer expires, if for example no data is transmitted over the PDU session. The SMF can also provide the timer to the UPF for monitoring. [0135] In step 6, if PDU session inactivity timer expires, the UPF informs SMF which in turn inform the NSAC if the SMF determines not to release the PDU session. If the PDU session is released by the UE before the timer expires, the SMF may inform the NSACF in the HPLMN or waits for the timer to expire before informing the NSACF. [0136] In steps 7a and step 7b, If the SMF has not released the PDU session after the timer expires, the SMF sends to the NSACF the new service Request Nnsacf_PDU SessionState Request (UE, PDU Session ID, Session state = idle) with a session state being declared as idle. If the SMF released the PDU session, it may still inform the NSACF with session state released instead. [0137] In step 8, the NSCAF release the PDU session if the SMF reported an idle session state indicating the timer has expired. If this is the last PDU session using the on-demand network slice, the NSACF (re)starts the deregistration inactivity timer. The NSACF may inform/notify the AMF to restart the deregistration timer or the AMF restarts the timer when it is aware from its interaction with the SMF that the PDU session is released or idle. [0138] According to other embodiment, in the case of home routed PDU session (i.e., when not LBO PDU session), the H-SMF does not provides the Inactivity Timer to the H- UPF unless the S-NSSAI is subject to NSAC with HPLMN NSAC admission and is an on- demand S-NSSAI. The H-SMF initiates session release when the H-SMF receives notification from H-UPF that the PDU Session inactivity session timer expired. Example embodiments of NSACF (in HPLMN) initiated UE deregistration: [0139] Figure 7-3 illustrates a flow diagram for home NSACF initiated UE deregistration in accordance with some embodiments. [0140] If the NSACF at step 1 decides to deregister a UE because of the expiration of the S-NSSAI deregistration timer or other reasons that could trigger deregistration prior to expiration of the timer at the AMF and/or UE, it notifies the AMF, at step 2, about the UE ID(s) to be deregistered. The NSACF triggers Nnsacf_NSAC_EACNotify operation including the S-NSSAI(s), and UE IDs for which the AMF initiates deregistration of the UE(s) (Step 3). Session Management Subscription data contains one or more S-NSSAI level subscription data: S-NSSAI Indicates the value of the S-NSSAI. If a subscribed S-NSSAI is subject to NSAC and is equally an on demand S-NSSAI, an indication to that effect is included, including the applicable slice use enforcement mode i.e. HPLMN delegated or HPLMN enforced. For such an S-NSSAI the HPLMN NSAC admission mode is assumed for the HPLMN outbound roamers. [0141] Figures 8, 9 and 10 illustrate embodiments of methods implemented in AMF, SMF and NSACF respectively in accordance with embodiments described for Figure 5, 6 and 7. [0142] Mainly, Figure 8 is a flow chart of a method performed by the Access and Management Function (AMF) during a registration or configuration update procedure in accordance with embodiments described herein, more specifically embodiments of the method are in accordance with Figure 5 (above). The method comprises the step 810 of initiating NSAC with an NSACF where it requests the NSACF to check and update the number of UE for the one or more S-NSSAI requested or allowed for the UEs (i.e., check if the number of UE for the one or more S-NSSAI has reached a quota). The method further comprises the step 820 of receiving from the NSACF (VPLMN NSACF or HPLMN NSACF) the result of the NSAC request which includes an indication that the one or more S-NSSAI is an on-demand S-NSSAI and obtain a deregistration time value for the one ore more S-NSSAI. [0143] Optionally, the AMF obtains a PDU session inactivity time value for a PDU session that will potentially be established over each of the one or more network slices, and which the AMF may later provide to the SMF when the PDU session is established over the corresponding network slice. At the same time, the AMF may also provide to the SMF the indication that the network slice is also on-demand. [0144] The AMF stores the received information from the NSACF for the on-demand S-NSSAI(s) and perform for example one or more of the following: a. Signal to the UE information indicating one or more of the network slices is on-demand S-NSSAI. An indication for each of the on- demand network slice indicating that the network slice is on- demand is provided to the UE at registration accept message or configuration update message or any appropriate NAS message. b. Signal to the UE the received deregistration timer for each of the on-demand network slice(s). The AMF 200 may signal the information to the UE in a registration accept message or configuration update message or any appropriate NAS message. The UE deregisters with the AMF when the timer expires. c. For each of the on-demand network slice (one or more) start the deregistration timer when the UE has no PDU sessions with any of the on-demand network slice and deregister the UE from the on- demand network slice(s) once the timer has expired. [0145] Figure 9 is a flow chart of a method performed by the Session Management Function (SMF) for a PDU session in accordance with embodiments described herein, more specifically embodiments of the method are in accordance with Figure 6 (above). The method comprises the step 910 of initiating NSAC with an NSACF where it requests the NSACF to check and update the number PDU sessions for the S-NSSAI(s). The method further comprises the step of receiving from the NSACF (VPLMN NSACF or HPLMN NSACF) the result of the NSAC request which includes an indication that at least one of the S-NSSAI(s) is an on-demand S-NSSAI and a PDU session inactivity time value for the S-NSSAI that is on-demand. [0146] Optionally, the SMF obtains a deregistration time value for controlling de- registration from a network slice (S-NSSAI) indicated as on-demand. If received, the SMF provides the deregistration time value to the AMF that controls the registration to the network slice. At the same time, the SMF may also indicate to the AMF that the network slice is also on-demand. [0147] The SMF 208 stores the received information from the NSACF 207 for the on- demand S-NSSAI(s) and perform for example one or more of the following for a PDU session: a. Signal to the UE using NAS signalling (via the AMF 200) information indicating the network slice, S-NSSAI is on-demand. The NAS signalling message may be a PDU session establishment accept message or any appropriate NAS message. b. Signal to the UE the received PDU session inactivity timer for the on-demand network slice. The timer may also be included in the PDU session establishment accept message or any appropriate NAS message. The UE releases the PDU session once the timer expires and may send a PDU session release to the SMF. c. start the PDU session inactivity timer for the PDU session over the on-demand network slice and release the PDU session once the timer has expired. The SMF 208 may send a PDU session release to the UE. [0148] Figure 10 is a flow chart of a method performed by a first NSACF for quota fetching/update from a second NSCAF in accordance with embodiments described herein and in accordance with Figure 7. [0149] The method comprises the step 1010 of sending a request to a second NSCAF (e.g., centralized NSACF) to fetch a quota for one or more network slice is required. The step may be triggered by a request from AMF or SMF as described in Figure 5, and 8 or by SMF as described in Figure 6 and 9. [0150] The method includes the step 1020 of obtaining from the second NSACF for the one or more network slices (S-NSSAIs) an indication that the network slice is on- demand and includes a deregistration time value for each of the network slice indicated as on-demand and may include the PDU session inactivity time value for the one or more network slice indicated as on-demand. The second NSACF may obtain the information from a third NSACF and provides it to the first NSACF. [0151] The first NSACF stores the information to perform NSAC for the NF consumers, i.e., AMF or SMF. [0152] Figure 10-1 is a flow chart of a method performed by a NSACF in the HPLMN (H-NSACF) for enforcing the registration timer. [0153] The method comprises the step 10-1-1 of receiving a request to update the number of UEs registered with an on-demand network slice(s). At step 10-1-2, the H- NSACF determines that the slice(s) is(are) an on-demand S-NSSAI(s) and include in its response to the AMF the deregistration timer(s) for the on-demand S-NSSAI(S). The H- NSACF is configured with this information or provided via an AF directly or indirectly. The H-NSACF returns the Ncnsacf_NumofUEsUpdate Response and includes the S- NSSAI deregistration timer(s) for the on-demand network slice(s) and start the de- registration timer(s). In some examples, If the deregistration timer for an on-demand S- NSSAI expires (i.e., no PDU session is active), the H-NSACF sends a notification to the corresponding AMF to initiate deregistration of the UE(s). If the H-NSACF receives from an SMF in VPLMN or HPLMN a request to update the number PDU session for an on- demand network slice, it stops the corresponding de-registration timer and provides a PDU session inactivity timer for the PDU session. If the H-NSACF receives a notification of a release or idle state of the PDU session using the on-demand S-NSSAI in the VPLMN (or HPLMN), and if the H-NSACF determines that the PDU session that has been released or in idle state is the last active PDU session using the on-demand S-NSSAI, starting the deregistration timer for the on-demand network slice. The H-NSACF may then inform the AMF that the deregistration timer should be restarted if the AMF is not aware that the last PDU session using the on-demand network slice is now released. If the notification from the SMF indicates idle state (i.e. the timer has expires at the SMF/UPF but the SMF determined not to release), then the H-NSACF determines whether to release the PDU session by instructing the SMF to release the idle PDU session or it may determine to extend the PDU session inactivity timer and informs the SMF. [0154] Example implementations of some aspects of some of the embodiments described herein is described below as revised versions of various sections from 3GPP TS 23.501 V18.0.0 and 3GPP TS 23.502 V18.0.0 (changes are underlined): ***** START FIRST REVISED SECTION OF 3GPP TS 23.501 V18.0.0 ***** 5.15.15.X Network Control for Slice Use while roaming While roaming, support by the HPLMN for network slice use of an S-NSSAI is restricted to a S-NSSAI subject to NSAC. For a VPLMN NSAC admission mode, for supporting VPLMNs, NSACF in VPLMN receives the on demand S- NSSAI indication, Network Slice deregistration inactivity timer value, as well as PDU Sessions inactivity timer value while fetching the quota from the NSACF in HPLMN. The AMF receives the Network Slice deregistration inactivity timer value while performing an update with the NSACF in VPLMN. The SMF in VPLMN receives the PDU Sessions inactivity timer value while performing an update with the NSACF in VPLMN. For a VPLMN with HPLMN assistance NSAC admission mode, and for supporting VPLMNs, NSACF in VPLMN receives the on demand S-NSSAI indication, Network Slice deregistration inactivity timer value, as well as PDU Sessions inactivity timer value while fetching the quota from the NSACF in HPLMN. The AMF receives the Network Slice deregistration inactivity timer value while performing an update with the NSACF in VPLMN. The SMF in VPLMN receives the PDU Sessions inactivity timer value while performing an update with the NSACF in VPLMN. For the HPLMN NSAC admission mode, and for supporting VPLMNs, the AMF, while performing admission with the NSACF in HPLMN, receives the on demand S-NSSAI indication and the Network Slice deregistration inactivity timer value. The SMF receieves the PDU Sessions inactivity timer values while performing admission with the NSACF in HPLMN. Received timer values by AMF, and SMF in all of the above cases are handled as per clauses 5.15.15.2, and 5.15.15.3. In all of the above cases, the NSACF in HPLMN/VPLMNdoes not need to send the information every time it receives an update, unless there is a change. Any received update overwrites existing information. ***** START SECOND REVISED SECTION OF 3GPP TS 23.501 V18.0.0 ***** 5.15.11.1 Network Slice Admission Control for maximum number of UEs For all three NSAC architectures defined below, for an S-NSSAI subject to NSAC, that is an on demand S-NSSAI, the NSACF returns additionally to the AMF, the on demand indication, and the applicable Network Slice deregistration inactivity timer when the AMF performs an update with the NSACF. The AMF applies the timer as defined in clauses 5.15.15.2, and 5.15.15.3. […] ***** START THIRD REVISED SECTION OF 3GPP TS 23.501 V18.0.0 ***** 5.15.11.2 Network Slice Admission Control for maximum number of PDU sessions For all three NSAC architectures defined below, for an S-NSSAI subject to NSAC, that is an on demand S-NSSAI, the NSACF returns to the SMF, additionally the on demand indication, and the PDU Session inactivity timer in addition when the SMF performs an update with the NSACF. The SMF applies the timer as defined in clauses 5.15.15.2, and 5.15.15.3. […] ***** START FIRST REVISED SECTION OF 3GPP TS 23.502 V18.3.0 ***** 4.2.11.5.1 Network Slice Admission Control Support for Roaming by VPLMN 4.2.11.5.1.0 VPLMN NSAC Admission For NSAC for roaming UEs, a maximum number of allowed UEs per mapped S-NSSAI in HPLMN and/or a maximum number of allowed PDU Sessions in LBO mode per mapped S-NSSAI in HPLMN is allocated to the VPLMN for each S-NSSAI in HPLMN and stored in one NSCAF in the VPLMN responsible for NSAC for the S- NSSAI in the HPLMN, subject to NSAC. The maximum number of UEs registered with a network slice monitoring and enforcement is done in the VPLMN by the NSACF in the VPLMN as per the description in Figure 4.2.11.2-1 with the following differences: - Step 2, in the Nnsacf_NSAC_NumOfUEsUpdate_Request service operation the AMF provides both the S- NSSAI in VPLMN and the corresponding mapped S-NSSAI in HPLMN to the NSACF in the VPLMN. - Step 3, the NSACF in the VPLMN performs NSAC for both the S-NSSAI in VPLMN and the corresponding mapped S-NSSAI in HPLMN based on the SLA between VPLMN and HPLMN. For LBO, enforcement of the maximum number of PDU Sessions established for an S-NSSAI is performed in the VPLMN by the NSACF in the VPLMN as per the description in Figure 4.2.11.4-1 with the following differences: - Step 2, in the Nnsacf_NSAC_NumOfPDUsUpdate_Request service operation the V-SMF provides both the S-NSSAI in VPLMN and the corresponding mapped S-NSSAI in HPLMN to the NSACF in the VPLMN. - Step 3, the NSACF in the VPLMN performs NSAC for both the S-NSSAI in VPLMN and the corresponding mapped S-NSSAI in HPLMN based on the SLA between VPLMN and HPLMN. An NSACF can optionally fetch the maximum number of registered UEs to be enforced, and the maximum number of LBO PDU sessions to be enforced rather than have them pre-configured. In this case, the following is performed: - For a centralized NSAC architecture in the VPLMN, the NSACF being a centralized NSACF fetches from the HPLMN centralized NSACF or primary NSACF the maximum number of registered UEs, and the maximum number of LBO PDU sessions to be enforced. - For a hierarchal NSAC architecture in the VPLMN, the NSACF fetches from the VPLMN primary NSACF the maximum number of registered UEs, and the maximum number of LBO PDU sessions to be enforced. The VPLMN primary NSACF in turn, fetches from the HPLMN centralized NSACF or primary NSACF the maximum number of registered UEs, and the maximum number of LBO PDU sessions to be enforced; this information in turn is sent to the VPLMN NSACF. For supporting VPLMNs and if the S-NSSAI is an on demand S-NSSAI, the NSACF in the VPLMN receives the on demand S-NSSAI indication, the Network Slice deregistration inactivity timer value, as well as PDU Sessions inactivity timer. The NSACF stores the received information. The VPLMN NSACF discovers the HPLMN primary or central NSACF or optionally be configured with the needed information as defined in clause 6.3.22 of TS 23.501[2]. For PDU Sessions in the home-routed roaming case, the SMF in HPLMN performs NSAC procedures for the S- NSSAI(s) subject to NSAC. 4.2.11.5.2 Network Slice Admission Control Support for Roaming by HPLMN 4.2.11.5.2.1 VPLMN with HPLMN assistance NSAC admission For NSAC for roaming UEs, a maximum number of allowed UEs per mapped S-NSSAI in HPLMN and/or a maximum number of allowed PDU Sessions in LBO mode per mapped S-NSSAI in HPLMN is allocated and delegated to the VPLMN for each S-NSSAI in HPLMN subject to NSAC. The information is stored in one NSCAF in the VPLMN responsible for NSAC for the S-NSSAI in the HPLMN, subject to NSAC. Monitoring and enforcement for the maximum number of UEs registered with a network slice monitoring is done by the NSACF in the VPLMN as per the description in Figure 4.2.11.2-1 with the following differences: - Step 2, in the Nnsacf_NSAC_NumOfUEsUpdate_Request service operation the V-AMF provides both the S- NSSAI in VPLMN and the corresponding mapped S-NSSAI in HPLMN to the NSACF in the VPLMN. - Step 3, the NSACF in the VPLMN performs NSAC for both the S-NSSAI in VPLMN and the corresponding mapped S-NSSAI in HPLMN. If the maximum number of registered UEs to be enforced is not available in the NSACF in the VPLMN, the following is performed: - For a centralized NSAC architecture in the VPLMN, the NSACF being a centralized NSACF fetches from the HPLMN centralized NSACF or primary NSACF the maximum number of registered UEs, and the maximum number of LBO PDU sessions to be enforced. - For a hierarchal NSAC architecture in the VPLMN, the NSACF fetches from the VPLMN primary NSACF the maximum number of registered UEs, and the maximum number of LBO PDU sessions to be enforced. The VPLMN primary NSACF in turn, fetches from the HPLMN centralized NSACF or primary NSACF the maximum number of registered UEs, and the maximum number of LBO PDU sessions to be enforced; this information in turn is sent to the VPLMN NSACF. In both of the above cases, and for supporting VPLMNs and if the S-NSSAI is an on demand S-NSSAI, the NSACF receives the on demand S-NSSAI indication, Network Slice deregistration inactivity timer value and the PDU Sessions inactivity timer value. The NSACF stores the received information. If the maximum number of Registered UEs have been reached, the NSACF in VPLMN forwards the request to the HPLMN for a decision. The NSACF contacts the same node as described above for acquiring the quota information. The appropriate NSCAF in HPLMN provides the final decision, which is conveyed back to the NSACF in the VPLMN. If admission is allowed or not granted normal processing is followed as described in the step. For LBO PDU sessions, enforcement of the maximum number of PDU Sessions established for an S-NSSAI is performed by the NSACF in the VPLMN as per the description in Figure 4.2.11.4-1 with the following differences: - Step 2, in the Nnsacf_NSAC_NumOfPDUsUpdate_Request service operation the V-SMF provides both the S-NSSAI in VPLMN and the corresponding mapped S-NSSAI in HPLMN to the NSACF in the VPLMN. - Step 3, the NSACF in the HPLMN performs NSAC for both the S-NSSAI in VPLMN and the corresponding mapped S-NSSAI in HPLMN based on the SLA between VPLMN and HPLMN. If the maximum number of LBO PDU sessions is not available in the NSACF in the VPLMN, the following is performed: - For a centralized NSAC architecture in the VPLMN, the NSACF being a centralized NSACF fetches from the HPLMN centralized NSACF or primary NSACF the maximum number of registered UEs, and the maximum number of LBO PDU sessions to be enforced. - For a hierarchal NSAC architecture in the VPLMN, the NSACF fetches from the VPLMN primary NSACF the maximum number of registered UEs, and the maximum number of LBO PDU sessions to be enforced. The VPLMN primary NSACF in turn, fetches from the HPLMN centralized NSACF or primary NSACF the maximum number of registered UEs, and the maximum number of LBO PDU sessions to be enforced; this information in turn is sent to the VPLMN NSACF. In both of the above cases, and for supporting VPLMNs and if the S-NSSAI is an on demand S-NSSAI, the NSACF receives the on demand S-NSSAI indication, Network Slice deregistration inactivity timer value and the PDU Sessions inactivity timer value. The NSACF stores the received information. If the maximum number of LBO PDU sessions have been reached, the NSACF in VPLMN forwards the request to the HPLMN for a decision. The NSACF contacts the same node as described above for acquiring the quota information. The appropriate NSCAF in HPLMN provides the final decision, which is conveyed back to the NSACF in the VPLMN. If admission is allowed or not granted normal processing is followed as described in the step. NSACF nodes to be contacted in all the above are either configured or discovered as defined in clause 6.3.22 of TS 23.501 [2]. For PDU sessions in the home-routed roaming case, the SMF in HPLMN performs NSAC for the S-NSSAI(s) subject to NSAC. 4.2.11.5.2.2 HPLMN NSAC Admission Monitoring and enforcement for the maximum number of UEs registered with a network slice monitoring is done by the NSACF in the HPLMN as per the description in Figure 4.2.11.2-1 with the following differences: - Step 2, in the Nnsacf_NSAC_NumOfUEsUpdate_Request service operation the V-AMF provides both the S- NSSAI in VPLMN and the corresponding mapped S-NSSAI in HPLMN to the NSACF in the HPLMN. - Step 3, the NSCAF in the HPLMN performs NSAC for both the S-NSSAI in VPLMN and the corresponding mapped S-NSSAI in HPLMN. For LBO enforcement of the maximum number of LBO PDU Sessions established for an S-NSSAI is performed by the NSACF in the HPLMN as per the description in Figure 4.2.11.4-1 with the following differences: - Step 2, in the Nnsacf_NSAC_NumOfPDUsUpdate_Request service operation the V-SMF provides both the S-NSSAI in VPLMN and the corresponding mapped S-NSSAI in HPLMN to the NSACF in the VPLMN. - Step 3, the NSACF in the HPLMN performs NSAC for both the S-NSSAI in VPLMN and the corresponding mapped S-NSSAI in HPLMN based on the SLA between VPLMN and HPLMN. NSACF nodes to be contacted in all the above are either configured or discovered ***** START SECOND REVISED SECTION OF 3GPP TS 23.502 V18.0.0 ***** 5.2.21.1 General The following table illustrates the NSACF services.

Table 5.2.21.1-1: List of NSACF services Service Name Service Operations Operation Example Semantics Consumer(s) Nnsacf_NSAC NumOfUEsUpdate Request/Response AMF, SMF (NOTE 1) NumOfPDUsUpdate SMF EACNotify AMF QuotaUpdate NSACF, AMF, SMF Nnsacf_SliceEventExposure Subscribe Subscribe/Notify NEF, NWDAF, AF (NOTE 2) Unsubscribe NEF, NWDAF, AF Notify NEF, NWDAF, AF NOTE 1: If EPS counting is required for the S-NSSAI, the SMF+PGW-C uses the Nnsacf_NumberOfUEs Update services operation and Nnsacf_NumberOfPDUsUpdate at PDN connection establishment procedure. NOTE 2: The AF can access NSACF services either via NEF to NSACF in case of untrusted AF or directly in case of trusted AF. 5.2.21.2.1 General Service Description: The Nnsacf_NSAC services control the number of UEs registered with a network slice and the number of PDU Sessions associated with a network slice for the network slices subject to NSAC. The consumer NF (e.g. AMF) can request the NSACF to check whether the number of UEs registered with a network slice has reached the maximum number of UEs per network slice and the consumer NF can also request the NSACF to update the number of UEs registered with a network slice. The SMF can request the NSACF to check whether the number of PDU Sessions established on a network slice has reached the maximum number of PDU Sessions per network slice and the SMF can also request the NSACF to update the number of PDU Sessions established on a network slice. Additionally, for a centralized NSAC architecture and/or a Hierarchical NSAC architecture, a centralized NSACF and/or Primary NSACF can provide the number of Registered UEs to be admitted by an AMF, and/or number of PDU sessions to be admitted by an SMF, and/or while roaming, and dependant on the applicable NSAC Admission mode the number of LBO PDU sessions to be admitted. Additionally, if the S-NSSAI is an on demand S-NSSAI, the on demand S-NSSAI indication, the Network Slice deregistration inactivity timer value, as well as PDU Sessions inactivity timer values are returned. ***** START THIRD REVISED SECTION OF 3GPP TS 23.502 V18.0.0 ***** Service Operation name: Nnsacf_NSAC_QuotaUpdate Description: Updates the NSACF with the number of Registered UEs to be enforced, the number of PDU sessions to be admitted, and in case of roaming, and dependant on the admission mode, the number of LBO PDU sessions to be admitted. Inputs, Required: S-NSSAI(s). The S-NSSAI parameter is the network slice subject to NSAC. Inputs, Optional: None Outputs, Required: Result indication. The Result indication parameter includes the outcome of the operation. Number of Registered UEs per S-NSSAI subject to NSAC to be admitted , or Number of PDU sessions per S-NSSAI subject to NSAC to be admitted, or in case of roaming and dependent on admission mode, number of LBO PDU sessions per S-NSSAI subject to NSAC to be admitted. Outputs, Optional: Additionally, if the S-NSSAI is an on demand S-NSSAI, the on demand S-NSSAI indication, S- NSSAI deregistration inactivity timer value, and PDU Session inactivity timer value are returned. This information can be returned only the first time the NSACF is contacted, unless there is a change in the information, in which case the most recent returned information overwrites older information. ***** START FOURTH REVISED SECTION OF 3GPP TS 23.502 V18.0.0 ***** 5.2.21.2.2 Nnsacf_NSAC_NumOfUEsUpdate service operation Service Operation name: Nnsacf_NSAC_NumOfUEsUpdate Description: Updates the number of UEs registered with a network slice (e.g. increase or decrease) when the UE registration status for a network slice subject to NSAC has changed. Also, if the number of the UEs registered with the network slice is to be increased and the Early Admission Control (EAC) mode in the NSACF is activated for that network slice (see Nnsacf_NSAC_EACNotify service operation), the NSACF first checks whether the number of UEs registered with the network slice has reached the maximum number of UEs per network slice threshold. If the maximum number of UEs registered with the network slice has already been reached, the UE registration for that network slice via the same Access Type configured in the NSACF is rejected. If the EAC is not activated, the NSACF increases or decreases the number of UEs per network slice as per the input parameters below. Inputs, Required: S-NSSAI(s), UE ID (SUPI), NF ID, Access Type, update flag. Inputs, Conditional: Notification endpoint for EAC Notification for the S-NSSAI. The S-NSSAI(s) parameter is a list of one or more network slices for which the number of UEs registered with a network slice is to be updated and checked if the maximum number of UEs per network slice threshold has already been reached. The UE ID parameter is used by the NSACF to maintain a list of UE IDs registered with the network slice. The NSACF also takes Access Type into account for increasing and decreasing the number of UEs per network slice as described in clause 5.15.11.1 of TS 23.501 [2]. The NF ID parameter is the NF instance ID of the NF (e.g. AMF or SMF + PGW-C) sending the request to the NSACF. The update flag input parameter indicates whether the number of UEs registered with a network slice is to be: - increased when the UE registers to a new network slice subject to NSAC. If the UE ID is already in the list of UEs registered with the network slice, the number of UEs registered with the network slice is not increased as the UE has already been counted as registered with the network slice. If the UE ID is not in the list of UE IDs registered with the network slice and the maximum number of UEs registered with the network slice has not been reached yet, the NSACF adds the UE ID in the list of UEs registered with the network slice and increases the number of the UEs registered with the network slice. If the UE_ID is not in the list of UEs registered with that S-NSSAI and the maximum number of UEs per network slice for that S-NSSAI has already been reached, then the NSACF returns maximum number of UEs per network slice reached result; - decreased when the UE deregisters for a network slice that is subject to NSAC. The NSACF decreases the number of the UEs registered with the network slice and removes the UE ID from the list of UEs registered with the network slice. The NSACF may optionally return the current status of the network slice availability (e.g. a percentage out of the maximum number of UEs registered with a network slice) in the availability status parameter. This information may be used for NSACF signalling and load balancing in case multiple NSACFs are serving the same network slice. Outputs, Required: Result indication. The Result indication parameter contains the outcome of the update and check operation in the NSACF and may indicate one of the values 'maximum number of UEs for the S-NSSAI not reached' or 'maximum number of UEs for the S-NSSAI reached'. Outputs, Optional: On demand S-NSSAI indication, Network Slice deregistration inactivity timer value, PDU Sessions inactivity timer value. For an on demand S-NSSAI subject to NSAC the following additional information is returned: - On demand S-NSSAI indication: indicates that the S-NSSAI is on demand. - S-NSSAI deregistration inactivity timer value. - PDU Sessions inactivity timer value. The AMF processes this information as per clauses X.X.X and Y.Y.Y ***** START FIFTH REVISED SECTION OF 3GPP TS 23.502 V18.0.0 ***** 5.2.21.2.4 Nnsacf_NSAC_NumOfPDUsUpdate service operation Service Operation name: Nnsacf_NSAC_NumOfPDUsUpdate Description: Updates the number of PDU Sessions established on a network slice (e.g. increase or decrease). Also, if the number of PDU Sessions on the network slice is to be increased, the NSACF first checks whether the number of the PDU Sessions on that network slice has reached the maximum number of PDU Sessions per network slice. If the maximum number of PDU Sessions on the network slice has already been reached, the PDU Session Establishment procedure is rejected. Inputs, Required: S-NSSAI, UE ID, PDU Session ID, Access Type, update flag. The S-NSSAI parameter is the network slice for which the number of PDU Sessions established on a network slice is to be updated. The UE ID parameter is used by the NSACF to maintain a list of UE IDs that has established PDU sessions with the network slice. PDU Session ID parameter is used by the NSACF to maintain for each UE ID, the PDU Session ID(s) for established PDU Sessions. The Access Type parameter indicates over which access network type the PDU Session is established. In the case of MA PDU Session, one or multiple Access Types may be included for a PDU Session ID. The update flag input parameter indicates 'increase', 'decrease' or 'update' as specified in clause 4.2.11.4. Inputs, Optional: None. Outputs, Required: Result indication, Access Type. The Result indication parameter contains the outcome of the update and check operation in the NSACF and may indicate one of the values 'maximum number of PDU Sessions for the S-NSSAI not reached' or 'maximum number of PDU Sessions for the S-NSSAI reached'. The Access Type parameter is associated with the Result indication parameter. Outputs, Optional: On demand S-NSSAI indication, Network Slice deregistration inactivity timer value, PDU Sessions inactivity timer value. For an on demand S-NSSAI subject to NSAC the following additional information is returned: - On demand S-NSSAI indication: indicates that the S-NSSAI is on demand. - S-NSSAI deregistration inactivity timer value. - PDU Sessions inactivity timer value. The SMF processes this information as per clauses X.X.X and Y.Y.Y . ***** END CHANGES ***** Further Description [0155] Figure 11 is a schematic block diagram of a network node 1100 according to some embodiments of the present disclosure. Optional features are represented by dashed boxes. The network node 1100 may be, for example, a core network node that implements a NF (e.g., AMF 200, SMF 206, NSACF 400, NSACF 207, UDM/HSS 402, or the like). As illustrated, the network node 1100 includes a one or more processors 1104 (e.g., Central Processing Units (CPUs), Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), and/or the like), memory 1106, and a network interface 1108. The one or more processors 1104 are also referred to herein as processing circuitry. The one or more processors 1104 operate to provide one or more functions of the network node 1100 as described herein (e.g., one or more functions of the AMF 200, SMF 206, NSACF 400, NSACF 207, UDM/HSS 402, or the like, as described herein. In some embodiments, the function(s) are implemented in software that is stored, e.g., in the memory 1106 and executed by the one or more processors 1104. [0156] Figure 12 is a schematic block diagram that illustrates a virtualized embodiment of the network node 1100 according to some embodiments of the present disclosure. Again, optional features are represented by dashed boxes. As used herein, a “virtualized” network node is an implementation of the network node 1100 in which at least a portion of the functionality of the network node 1100 is implemented as a virtual component(s) (e.g., via a virtual machine(s) executing on a physical processing node(s) in a network(s)). As illustrated, in this example, the network node 1100 includes one or more processing nodes 1200 coupled to or included as part of a network(s) 1202. Each processing node 1200 includes one or more processors 1204 (e.g., CPUs, ASICs, FPGAs, and/or the like), memory 1206, and a network interface 1208. In this example, functions 1210 of the network node 1100 described herein (e.g., one or more functions of the AMF 200, SMF 206, NSACF 400, NSACF 207, UDM/HSS 402, or the like, as described herein)are implemented at the one or more processing nodes 1200 or distributed across the two or more processing nodes 1200 in any desired manner. In some particular embodiments, some or all of the functions 1210 of the network node 1100 described herein are implemented as virtual components executed by one or more virtual machines implemented in a virtual environment(s) hosted by the processing node(s) 1200. [0157] In some embodiments, a computer program including instructions which, when executed by at least one processor, causes the at least one processor to carry out the functionality of the network node 1100 or a node (e.g., a processing node 1200) implementing one or more of the functions 1210 of the network node 1100 in a virtual environment according to any of the embodiments described herein is provided. In some embodiments, a carrier comprising the aforementioned computer program product is provided. The carrier is one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium (e.g., a non-transitory computer readable medium such as memory). [0158] Figure 13 is a schematic block diagram of the network node 1100 according to some other embodiments of the present disclosure. The network node 1100 includes one or more modules 1300, each of which is implemented in software. The module(s) 1300 provide the functionality of the network node 1100 described herein. This discussion is equally applicable to the processing node 1200 of Figure 12 where the modules 1300 may be implemented at one of the processing nodes 1200 or distributed across multiple processing nodes 1200. [0159] Any appropriate steps, methods, features, functions, or benefits disclosed herein may be performed through one or more functional units or modules of one or more virtual apparatuses. Each virtual apparatus may comprise a number of these functional units. These functional units may be implemented via processing circuitry, which may include one or more microprocessor or microcontrollers, as well as other digital hardware, which may include Digital Signal Processors (DSPs), special-purpose digital logic, and the like. The processing circuitry may be configured to execute program code stored in memory, which may include one or several types of memory such as Read Only Memory (ROM), Random Access Memory (RAM), cache memory, flash memory devices, optical storage devices, etc. Program code stored in memory includes program instructions for executing one or more telecommunications and/or data communications protocols as well as instructions for carrying out one or more of the techniques described herein. In some implementations, the processing circuitry may be used to cause the respective functional unit to perform corresponding functions according one or more embodiments of the present disclosure. [0160] While processes in the figures may show a particular order of operations performed by certain embodiments of the present disclosure, it should be understood that such order is exemplary (e.g., alternative embodiments may perform the operations in a different order, combine certain operations, overlap certain operations, etc.). [0161] Those skilled in the art will recognize improvements and modifications to the embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein. [0162] Some example embodiments of the present disclosure, but not limited thereto, are as follows: Embodiment 1. A method performed by an Access and Mobility management Function (AMF) comprising: initiating a network slice admission control for one or more network slice during a registration procedure by a wireless device; and receiving information indicating at least one or more of the network slice is an on-demand network slice and a deregistration time value for the on-demand network slice. Embodiment 2. The method of embodiment 1 wherein the information further comprises a PDU session inactivity time value for the one or more network slice indicated as on-demand. Embodiment 3. The method of embodiment 1 or 2 further comprising storing the received information. Embodiment 4. The method of embodiment 1 further comprising providing the information to the wireless device. Embodiment 5. The method of embodiment 2 further comprising providing the PDU session inactivity timer for the network slice to a Session management Function upon PDU session establishment for the network slice is performed. Embodiment 6. The method of any one of embodiment 1 to 5 wherein the deregistration time value is a deregistration timer value. Embodiment 7. A method performed by a Session Management Function (SMF) comprising: - initiating a network slice admission control for a network slice during a PDU session establishment procedure of a PDU session over a network slice by a wireless device; and - receiving information indicating the network slice is an on-demand network slice and a PDU session inactivity time value for the on-demand network slice. Embodiment 8. The method of embodiment 7 wherein the information further comprises a deregistration time value for the network slice indicated as on- demand. Embodiment 9. The method of embodiment 7 or 8 further comprising storing the received information. Embodiment 10. The method of embodiment 7 further comprising providing the information to the wireless device. Embodiment 11. The method of embodiment 8 further comprising providing the deregistration time value for the network slice to an Access Management Function as part of the PDU session establishment procedure. Embodiment 12. The method of any one of embodiment 7 to 11 wherein the PDU session inactivity time value is a PDU session inactivity timer value. Embodiment 13. A method performed by a first network slice admission control function (NSACF) for fetching/updating a quota for a number of wireless devices allowed in one or more network slice and/or number of PDU sessions allowed in one or more network slice, the method comprising: - sending to a second NSACF a request for fetching/updating the quota for one or more network slices; - receiving from the second NSACF a response to the request comprising information indicating that at least one of the network slices is an on-demand network slice and at least one of: - a registration time value for the at least one of the on-demand network slice, and - a PDU session inactivity time value for the at least one of the on-demand network slice. Embodiment 14. The method of embodiment 13 wherein the request comprises one or more S-network slice identifier (S-NSSAI). Embodiment 15. The method of embodiment 13 further comprising storing the received information. Embodiment 16. The method of embodiment 13 further comprising performing NSAC based on received information when requested by at least one of an Access and Mobility management function (AMF) or Session management Function (SMF). Embodiment 17. The method of embodiment 13 wherein the first NSACF is a local NSACF in a Visited network and the second NSACF is a primary NSACF in a visited network. Embodiment 18. The method of embodiment 13 wherein the first NSACF is central NSACF in a visited network and the second NSACF is a central or primary NSACF in a home network. Embodiment 19. The method of embodiment 18 wherein the visited network is a visited public land mobile network (VPLMN) and the home network is a home PLMN (HPLMN). Embodiment 20. The method of any one of embodiments 13 to 19 wherein the deregistration time value is a deregistration timer value and/or the PDU session inactivity time value is a PDU session inactivity timer value. Embodiment 21. A method performed by a network slice admission control function (NSACF) in a home Public Land Mobile Network for enforcing use of an on- demand network slice, the method comprising: - receiving from a first network function for a User Equipment (UE) a request for updating a number of UEs registered with the on-demand network slice; and - sending a response to the request comprising information indicating a deregistration timer for the on-demand network slice and starting the deregistration timer for the on-demand network slice. Embodiment 22. The method of embodiment 21 further comprising sending an instruction to the network function to deregister the UE if the deregistration timer expires and no active Packet data Unit (PDU) session exists for the on-demand network slice. Embodiment 23. The method of embodiment 21 further comprising receiving from a second network function for a User Equipment (UE) a second request for updating a number of PDU sessions established with the on-demand network slice; stopping the corresponding deregistration timer, and sending a response to the second request comprising information indicating a PDU session inactivity timer for the PDU session using the on-demand network slice. Embodiment 24. The method of any one of embodiment 21 to 23 further comprising: - receiving a notification that a PDU session using the on-demand network slice is either released or idle, - in response to determining that the PDU session is the last active PDU session using the on-demand network slice, restarting the deregistration timer for the on- demand network slice. Embodiment 25. The method of claim 24 further comprising notifying the first network function that the deregistration timer has restarted. Embodiment 26. A network node configured to perform the method of any of embodiments 1 to 25. Embodiment 27. A network node comprising one or more processors and memory comprising instructions which when executed by the one or more processors enable the network node to perform the method of any of embodiments 1 to 25. Embodiment 28. A computer readable memory comprising instructions which when executed by one or more processors of one or more servers configures the one or more server to perform any of the embodiments 1 to 25. [0163] Those skilled in the art will recognize improvements and modifications to the embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein.

Claims

Claims: 1. A method performed by an Access and Mobility management Function (AMF) comprising: initiating a network slice admission control for one or more network slice of a telecommunication system during a registration procedure by a wireless device; and receiving information indicating at least one or more of the network slice is an on-demand network slice and a deregistration time value for the on-demand network slice.

2. The method of claim 1 wherein the information further comprises a PDU session inactivity time value for the one or more network slice indicated as on-demand.

3. The method of claim 1 or 2 further comprising storing the received information.

4. The method of claim 1 further comprising providing the information to the wireless device.

5. The method of claim 2 further comprising providing the PDU session inactivity timer for the network slice to a Session management Function upon performing PDU session establishment for the network slice.

6. The method of any one of claims 1 to 5 wherein the deregistration time value is a deregistration timer value.

7. A method performed by a Session Management Function (SMF) comprising: - initiating a network slice admission control for a network slice during a PDU session establishment procedure of a PDU session over a network slice by a wireless device; and - receiving information indicating the network slice is an on-demand network slice and a PDU session inactivity time value for the on-demand network slice.

8. The method of claim 7 wherein the information further comprises a deregistration time value for the network slice indicated as on-demand.

9. The method of claim 7 or 8 further comprising storing the received information.

10. The method of claim 7 further comprising providing the information to the wireless device.

11. The method of claim 8 further comprising providing the deregistration time value for the network slice to an Access Management Function as part of the PDU session establishment procedure.

12. The method of any one of claims 7 to 11 wherein the PDU session inactivity time value is a PDU session inactivity timer value.

13. A method performed by a first network slice admission control function (NSACF) for fetching/updating a quota for a number of wireless devices allowed in one or more network slices and/or number of PDU sessions allowed in one or more network slices, the method comprising: - sending to a second NSACF a request for fetching/updating the quota for one or more network slices; - receiving from the second NSACF a response to the request comprising information indicating that at least one of the network slices is an on-demand network slice and at least one of: - a registration time value for the at least one of the on-demand network slice, and - a PDU session inactivity time value for the at least one of the on-demand network slice.

14. The method of claim 13 wherein the request comprises one or more S-network slice identifier (S-NSSAI).

15. The method of claim 13 further comprising storing the received information.

16. The method of claim 13 further comprising performing NSAC based on the received information when requested by at least one of an Access and Mobility management function (AMF) or Session management Function (SMF).

17. The method of claim 13 wherein the first NSACF is a local NSACF in a Visited network and the second NSACF is a primary NSACF in a visited network.

18. The method of claim 13 wherein the first NSACF is a central NSACF in a visited network and the second NSACF is a central or primary NSACF in a home network.

19. The method of claim 18 wherein the visited network is a visited public land mobile network (VPLMN) and the home network is a home PLMN (HPLMN).

20. The method of any one of claims 13 to 19 wherein the deregistration time value is a deregistration timer value and/or the PDU session inactivity time value is a PDU session inactivity timer value.

21. A method performed by a network slice admission control function (NSACF) in a home Public Land Mobile Network for enforcing use of an on-demand network slice, the method comprising: - receiving from a first network function for a User Equipment (UE) a request for updating a number of UEs registered with the on-demand network slice; and - sending a response to the request comprising information indicating a deregistration timer for the on-demand network slice and starting the deregistration timer for the on-demand network slice.

22. The method of claim 21 further comprising sending an instruction to the network function to deregister the UE if the deregistration timer expires and no active Packet data Unit (PDU) session exists for the on-demand network slice.

23. The method of claim 21 further comprising receiving from a second network function for a User Equipment (UE) a second request for updating a number of PDU sessions established with the on-demand network slice; stopping the corresponding deregistration timer, and sending a response to the second request comprising information indicating a PDU session inactivity timer for the PDU session using the on-demand network slice.

24. The method of any one of claims 21 to 23 further comprising: - receiving a notification that a PDU session using the on-demand network slice is either released or idle, - in response to determining that the PDU session is the last active PDU session using the on-demand network slice, restarting the deregistration timer for the on- demand network slice.

25. The method of claim 24 further comprising notifying the first network function that the deregistration timer has restarted.

26. A network node configured to perform the method of any one of claims 1 to 25.

27. A network node comprising one or more processors and memory comprising instructions which when executed by the one or more processors enable the network node to perform the method of any one of claims 1 to 25.

28. A computer readable memory comprising instructions which when executed by one or more processors of one or more servers configures the one or more server to perform the method of any one of claims 1 to 25.