Method and apparatus for establishing a PDU session - Patent application

Abstract

A method and apparatus for establishing a protocol data unit (PDU) session are disclosed. According to an embodiment, a first network function determines whether a first session management function (SMF) for a PDU session to be established for a terminal device supports insertion / modification of a second SMF. When the first SMF for the PDU session determines that the first SMF does not support insertion / modification of the second SMF, the first network function sends a query request to a second network function to discover at least one second SMF that can serve the entire public land mobile network (PLMN) to which the first network function belongs. The first network function receives a query response from the second network function.

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE Embodiments of the present disclosure relate generally to communications, and more particularly, to a method and apparatus for protocol data unit (PDU) session establishment. [Background technology]

[0002] This section introduces aspects that may facilitate a better understanding of the present disclosure. Accordingly, the statements in this section should be read in this light and not understood as admissions about what is prior art or not prior art.

[0003] In Release 16 (Rel-16), the 3rd Generation Partnership Project (3GPP) specified a new feature in the 5th Generation Core (5GC) called "Deployment Topology with Specific Session Management Function (SMF) Service Area (DTSSA)". This feature allows an Access and Mobility Management Function (AMF) to insert / change an intermediate or Interworking SMF (I-SMF) when a User Equipment (UE) moves out of the serving area of ​​the current serving SMF in order to continue a PDU session served by the old SMF.

[0004] For home-routed PDU sessions, the same mechanism allows the AMF to select a new Visited SMF (V-SMF) when the UE moves out of the serving area of ​​the old V-SMF, as specified below in 3GPP Technical Specification (TS) 23.502 V16.3.0. 4.23 Support for deployment topologies with specific SMF service areas 4.23.1 General This section captures the changes to the 5GC procedures in other sections of this specification, as well as new procedures, to support deployment topologies with specific SMF service areas, as specified in TS 23.501 [2] subclause 5.34. For a home routed PDU session, if the UE moves out of the V-SMF serving area in the serving PLMN, the serving AMF may change the V-SMF, in which case the following procedures are applied for the V-SMF change (in other words, by replacing the I-SMF with the V-SMF). Summary of the Invention

[0005] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. It is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

[0006] One of the objectives of the present disclosure is to provide an improved solution for establishing a PDU session. In particular, one of the problems solved by the present disclosure is to prevent a PDU session from being interrupted.

[0007] According to a first aspect of the present disclosure, a method is provided that is implemented by a first network function. The method may comprise determining whether a first session management function (SMF) for a protocol data unit (PDU) session to be established for a terminal device supports insertion / modification of a second SMF. The method may further comprise, when the first SMF for the PDU session determines that it does not support insertion / modification of the second SMF, sending a query request to a second network function to discover at least one second SMF that can serve an entire public land mobile network (PLMN) to which the first network function belongs. The method may further comprise receiving a query response from the second network function.

[0008] In this way, the serving PLMN of the terminal device may be enabled to continue serving the PDU session during mobility of the terminal device when the first SMF does not support the insertion / change of the second SMF.

[0009] In an embodiment of the present disclosure, the insertion / change of the second SMF may be due to a change in location of a terminal device in a deployment topology (DTSSA) with a specific SMF service area.

[0010] In an embodiment of the present disclosure, the query request may indicate to preferentially discover at least one second SMF.

[0011] In an embodiment of the present disclosure, the query response may comprise information regarding at least one second SMF.

[0012] In an embodiment of the present disclosure, the query response may comprise information regarding at least one third SMF that cannot serve the entire PLMN if at least one second SMF that can serve the entire PLMN to which the first network function belongs is not available.

[0013] In an embodiment of the present disclosure, the first SMF may be a home SMF (H-SMF), and the second or third SMF may be a visited SMF (V-SMF).

[0014] In an embodiment of the present disclosure, the first SMF may be an anchor SMF, and the second or third SMF may be an intermediate SMF (I-SMF).

[0015] In an embodiment of the present disclosure, the first network function may be an access and mobility management function (AMF).

[0016] In an embodiment of the present disclosure, the second network function may be a network repository function (NRF).

[0017] In an embodiment of the present disclosure, the query request may comprise a first indicator indicating to discover only SMFs that can serve the entire PLMN.

[0018] In an embodiment of the present disclosure, the first indicator may be a Boolean query parameter with a value "TRUE" indicating to discover only SMFs that can serve the entire PLMN.

[0019] In an embodiment of the present disclosure, the query request may comprise a second indicator indicating to preferentially discover an SMF that can serve the entire PLMN.

[0020] In an embodiment of the present disclosure, the second indicator may be a Boolean query parameter with a value “TRUE” indicating to preferentially discover an SMF that can serve the entire PLMN.

[0021] In an embodiment of the present disclosure, the query request may comprise a predefined tracking area identity (TAI) representing the entire PLMN as a query parameter for the SMF to be discovered.

[0022] According to a second aspect of the present disclosure, a method is provided that is implemented by a second network function. The method may comprise receiving a query request from the first network function to discover at least one second SMF that can serve an entire PLMN to which the first network function belongs. The method may further comprise sending a query response to the first network function.

[0023] In an embodiment of the present disclosure, the query request may indicate to preferentially discover at least one second SMF.

[0024] In an embodiment of the present disclosure, the query response may comprise information regarding at least one second SMF.

[0025] In an embodiment of the present disclosure, the query response may comprise information regarding at least one third SMF that cannot serve the entire PLMN if at least one second SMF that can serve the entire PLMN to which the first network function belongs is not available.

[0026] In an embodiment of the present disclosure, the second network function may be an NRF.

[0027] In an embodiment of the present disclosure, the first network function may be an AMF.

[0028] In an embodiment of the present disclosure, the query request may comprise a first indicator indicating to discover only SMFs that can serve the entire PLMN.

[0029] In an embodiment of the present disclosure, the first indicator may be a Boolean query parameter with a value "TRUE" indicating to discover only SMFs that can serve the entire PLMN.

[0030] In an embodiment of the present disclosure, the query request may comprise a second indicator indicating to preferentially discover an SMF that can serve the entire PLMN.

[0031] In an embodiment of the present disclosure, the second indicator may be a Boolean query parameter with a value “TRUE” indicating to preferentially discover an SMF that can serve the entire PLMN.

[0032] In an embodiment of the present disclosure, the query request may comprise a predefined TAI representing the entire PLMN as a query parameter for the SMF to be discovered.

[0033] According to a third aspect of the present disclosure, a method is provided that is implemented by a first network function. The method may comprise determining whether a first SMF for a PDU session to be established for a terminal device supports insertion / modification of a second SMF. The method may further comprise determining a target second SMF for the PDU session when determining that the first SMF for the PDU session does not support insertion / modification of the second SMF. The determined target second SMF may be selected from one or more second SMFs that are preconfigured in the first network function and can serve the entire PLMN to which the first network function belongs.

[0034] In an embodiment of the present disclosure, the insertion / modification of the second SMF may be due to a change in location of the terminal device in the DTSSA.

[0035] In an embodiment of the present disclosure, the first SMF may be an H-SMF and the second SMF is a V-SMF.

[0036] In an embodiment of the present disclosure, the first SMF may be an anchor SMF and the second SMF may be an I-SMF.

[0037] In an embodiment of the present disclosure, the first network function may be an AMF.

[0038] According to a fourth aspect of the present disclosure, a first network node is provided. The first network node may comprise at least one processor and at least one memory. The at least one memory may include instructions executable by the at least one processor, whereby the first network node may be operable to determine whether a first SMF for a PDU session to be established for a terminal device supports insertion / modification of a second SMF. When the first network node determines that the first SMF for the PDU session does not support insertion / modification of a second SMF, the first network node may be further operable to send a query request to a second network function to discover at least one second SMF that can serve the entire PLMN to which the first network node belongs. The first network node may be further operable to receive a query response from the second network function.

[0039] In an embodiment of the present disclosure, the first network node may be operable to perform the method according to the first aspect above.

[0040] According to a fifth aspect of the present disclosure, a second network node is provided. The second network node may comprise at least one processor and at least one memory. The at least one memory may include instructions executable by the at least one processor, whereby the second network node may be operable to receive a query request from the first network function to discover at least one SMF that can serve an entire PLMN to which the first network function belongs. The second network node may further be operable to send a query response to the first network function.

[0041] In an embodiment of the present disclosure, the second network node may be operable to perform the method according to the second aspect above.

[0042] According to a sixth aspect of the present disclosure, a first network node is provided. The first network node may comprise at least one processor and at least one memory. The at least one memory may include instructions executable by the at least one processor, whereby the first network node may be operable to determine whether a first SMF for a PDU session to be established for a terminal device supports insertion / modification of a second SMF. The first network node may be further operable to determine a target second SMF for the PDU session when determining that the first SMF for the PDU session does not support insertion / modification of the second SMF. The determined target second SMF may be selected from one or more second SMFs preconfigured in the first network node and capable of serving the entire PLMN to which the first network node belongs.

[0043] In an embodiment of the present disclosure, the first network node may be operable to perform the method according to the third aspect above.

[0044] According to a seventh aspect of the present disclosure, there is provided a computer program product, which may comprise instructions that, when executed by at least one processor, cause the at least one processor to perform a method according to any one of the first to third aspects above.

[0045] According to an eighth aspect of the present disclosure, there is provided a computer-readable storage medium, which may comprise instructions that, when executed by at least one processor, cause the at least one processor to perform a method according to any one of the first to third aspects above.

[0046] According to a ninth aspect of the present disclosure, a first network node is provided. The first network node may comprise a determination module for determining whether a first SMF for a PDU session to be established for a terminal device supports insertion / modification of a second SMF. When the first network node determines that the first SMF for the PDU session does not support insertion / modification of a second SMF, the first network node may further comprise a transmission module for transmitting a query request to a second network function to discover at least one second SMF that can serve the entire PLMN to which the first network node belongs. The first network node may further comprise a receiving module for receiving a query response from the second network function.

[0047] According to a tenth aspect of the present disclosure, a second network node is provided. The second network node may comprise a receiving module for receiving a query request from the first network function to discover at least one SMF that can serve an entire PLMN to which the first network function belongs. The second network node may further comprise a transmitting module for transmitting a query response to the first network function.

[0048] According to an eleventh aspect of the present disclosure, a first network node is provided. The first network node may comprise a first determination module for determining whether a first SMF for a PDU session to be established for a terminal device supports insertion / modification of a second SMF. The first network node may further comprise a second determination module for determining a target second SMF for the PDU session when determining that the first SMF for the PDU session does not support insertion / modification of the second SMF. The determined target second SMF may be selected from one or more second SMFs preconfigured in the first network node and capable of serving the entire PLMN to which the first network node belongs.

[0049] According to a twelfth aspect of the present disclosure, a method implemented in a communication system is provided. The method may comprise determining, in a first network function, whether a first SMF for a PDU session to be established for a terminal device supports insertion / modification of a second SMF. The method may further comprise, when the first network function determines that the first SMF for the PDU session does not support insertion / modification of a second SMF, sending a query request to a second network function to discover at least one second SMF that can serve the entire PLMN to which the first network function belongs. The method may further comprise receiving, in the second network function, the query request from the first network function. The method may further comprise sending, in the second network function, a query response to the first network function. The method may further comprise receiving, in the first network function, a query response from the second network function.

[0050] According to a thirteenth aspect of the present disclosure, a communication system is provided. The communication system may include a first network node and a second network node. The first network node may be configured to determine whether a first SMF for a PDU session to be established for a terminal device supports insertion / modification of a second SMF, and when the first network node determines that the first SMF for the PDU session does not support insertion / modification of the second SMF, to send a query request to the second network node to discover at least one second SMF that can serve the entire PLMN to which the first network node belongs, and to receive a query response from the second network node. The second network node may be configured to receive the query request from the first network node and to send the query response to the first network node.

[0051] These and other objects, features and advantages of the present disclosure will become apparent from the following detailed description of illustrative embodiments thereof, which should be read in connection with the accompanying drawings. [Brief description of the drawings]

[0052] [Figure 1] FIG. 1 illustrates an exemplary communication system to which embodiments of the present disclosure are applicable. [Diagram 2] 1 is a flowchart illustrating a method performed by a first network function according to an embodiment of the present disclosure. [Diagram 3] 11 is a flowchart illustrating a method performed by a second network function according to an embodiment of the present disclosure. [Figure 4] 1 is a flowchart illustrating a method performed by a first network function according to an embodiment of the present disclosure. [Diagram 5] 1 is a flowchart illustrating an example process according to an embodiment of the present disclosure. [Figure 6] 1 is a flowchart illustrating an example process according to an embodiment of the present disclosure. [Figure 7] FIG. 1 is a block diagram illustrating an apparatus suitable for use in practicing some embodiments of the present disclosure. [Figure 8] FIG. 2 is a block diagram illustrating a first network node according to an embodiment of the present disclosure. [Figure 9] FIG. 2 is a block diagram illustrating a second network node according to an embodiment of the present disclosure. [Figure 10] FIG. 2 is a block diagram illustrating a first network node according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0053] For purposes of explanation, details are set forth in the following description in order to provide a thorough understanding of the disclosed embodiments. However, it will be apparent to one skilled in the art that the embodiments may be implemented without these specific details or with equivalent arrangements.

[0054] For the DTSSA feature mentioned above, if the V-SMF changes, the new V-SMF fetches the Session Management (SM) context of the PDU session from the old V-SMF, and then subsequently invokes a PDU Session Update Service operation on the H-SMF to pass the information of the new V-SMF, e.g., the new SM context identifier (PDU Session Ref Uniform Resource Identifier (URI)) on the new V-SMF, the Network Function (NF) Instance Identifier (ID) of the new V-SMF, in order to set up a new N16 interface. The H-SMF stores the received information and targets the N16 interface towards the new V-SMF for subsequent communication for the PDU session, e.g., during a UE Triggered Service Request procedure with I-SMF / V-SMF change, as described below in 3GPP TS 23.502 V16.3.0 with reference to Figure 4.23.4.3-1. ... In case of I-SMF change, the new I-SMF invokes a Nsmf_PDUSession_Update request towards the SMF (SUPI, PDU Session ID, new I-UPF DL tunnel info, SM context ID in I-SMF, access type, RAT type, DNAI list supported by new I-SMF). The new I-SMF uses the SM context ID in SMF received from the old I-SMF for this service operation. In case of I-SMF insertion, the new I-SMF invokes a Nsmf_PDUSession_Create request (new I-UPF DL tunnel information, new I-UPF tunnel endpoint for buffered DL data, SM context ID in the I-SMF, access type, RAT type, DNAI list supported by the new I-SMF) towards the SMF. The SM context ID in the I-SMF should be used by the SMF for further PDU session operations, e.g. to inform the new I-SMF of the PDU session release. If the SM context ID in the I-SMF exists (in other words in case of I-SMF change), the SMF replaces the SM context ID in the I-SMF. The new I-UPF tunnel endpoint for buffered DL data is used to establish a forwarding tunnel (from the old I-UPF controlled by the SMF to the new I-UPF controlled by the new I-SMF). Similar mechanisms are implemented during all UE mobility procedures, including mobility registration, N2 / Xn based handover, etc.

[0055] 3GPP specifies that in 5GC, an NF service consumer (e.g., AMF) may discover a target NF service producer (e.g., SMF) that supports a particular service (e.g., a PDU session service for establishing a PDU session request for a UE) via an NRF service.

[0056] An NF service producer (e.g., SMF) instance registers the NF profile of the NF service producer instance to the NRF when the NF service producer instance is up and running. Alternatively, the NF profile is registered to the NRF by an operation and maintenance (O&M) function. The NF profile includes necessary information about which services are supported and how the services can be accessed. The NF profile also includes information to enable the NRF to match / filter NF instances that fulfill discovery requests from NF service consumers. For example, the SMF may indicate a service area with a list of TAIs that the SMF can serve when the SMF registers the SMF's NF profile to the NRF, and the AMF may include the TAI (where the UE is located) in a discovery request toward the NRF to find an SMF instance that can serve the UE at its current location. The NF also indicates optional features that the NF supports in the NF profile. For example, the SMF indicates support for DTSSA if the SMF supports it.

[0057] To successfully serve home-routed PDU sessions with UE mobility, current 3GPP specifications require that the DTSSA feature be supported in both the Visited PLMN (VPLMN) (e.g., AMF / V-SMF) and the Home PLMN (HPLMN) (e.g., H-SMF) in case the V-SMF does not cover the entire PLMN area, i.e., when the UE moves out of the service area of ​​the current V-SMF, the AMF selects a new V-SMF, and the V-SMF updates the H-SMF to set up a new N16 interface for subsequent communication. The information of the new V-SMF is passed along with new information elements (IEs) that are only understood by SMFs with DTSSA support. The H-SMF thus also needs DTSSA support to handle these IEs and to be able to handle the V-SMF change. The Rel-15 H-SMF can support home-routed roaming but cannot support the V-SMF change.

[0058] If the VPLMN supports the DTSSA feature but the H-SMF does not, when a new V-SMF is selected, the new V-SMF cannot update the H-SMF with the new IE. This causes the H-SMF to still have an N16 interface towards the old V-SMF which cannot continue to serve the UE when the UE moves out of the V-SMF service area. As a result, the PDU session must be released.

[0059] The present disclosure proposes an improved solution for establishing a PDU session, which will be described in detail below with reference to Figures 1 to 10.

[0060] FIG. 1 is a diagram illustrating an exemplary communication system to which the embodiments of the present disclosure are applicable. As shown, the communication system includes a user equipment (UE), a (radio) access network ((R)AN), a user plane function (UPF), a data network (DN), an authentication server function (AUSF), an access and mobility management function (AMF), a session management function (SMF), a service communication proxy (SCP), a network slice selection function (NSSF), a network publishing function (NEF), a network repository function (NRF), a policy control function (PCF), a unified data management (UDM), and an application function (AF). The functional description of the above entities is specified in clause 6 of 3GPP TS23.501 V16.3.0, which is incorporated herein by reference in its entirety.

[0061] It should be noted that within the context of this disclosure, the term terminal device (or UE) as used herein may also be referred to as, for example, an access terminal, a mobile station, a mobile unit, a subscriber station, etc. The term terminal device (or UE) may refer to any end device (fixed or mobile) capable of accessing and receiving services from a wireless communication network. By way of example and not limitation, UEs may include portable computers, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback equipment, mobile phones, cellular phones, smartphones, tablets, wearable devices, personal digital assistants (PDAs), integrated or embedded wireless cards, externally plugged-in wireless cards, etc.

[0062] In an Internet of Things (IoT) scenario, a terminal device (or UE) may represent a machine or other device that performs monitoring and / or measurements and sends results of such monitoring and / or measurements to another terminal device (or UE) and / or network equipment. In this case, the terminal device (or UE) may be a machine-to-machine (M2M) device, which in the 3GPP context may be called a machine-type communication (MTC) device. Particular examples of such machines or devices may include sensors, metering devices such as power meters, industrial machinery, two-wheelers, vehicles, or home or personal appliances, e.g., refrigerators, televisions, personal wearables such as watches, etc.

[0063] The term "communication system" as used herein refers to a system conforming to any suitable communication standard, such as first generation (1G), 2G, 2.5G, 2.75G, 3G, 4G, 4.5G, 5G communication protocols, and / or any other protocols either now known or developed in the future. Moreover, communications between terminal devices and network nodes in a communication system may be performed according to any suitable generation of communication protocols, including, but not limited to, 1G, 2G, 2.5G, 2.75G, 3G, 4G, 4.5G, 5G communication protocols, and / or any other protocols either now known or developed in the future. In addition, a particular term used herein does not limit the disclosure to only the communication system associated with the particular term, but rather the disclosure may be more generally applicable to other communication systems.

[0064] FIG. 2 is a flow chart illustrating a method performed by a first network function according to an embodiment of the present disclosure. The first network function may be an AMF or any other entity having similar functionality. It should be noted that the network functions referred to herein may be implemented either as network elements on dedicated hardware, as software instances running on dedicated hardware, or as virtualized functions instantiated on a suitable platform, e.g., on a cloud infrastructure. In block 202, the first network function determines whether a first SMF for a PDU session to be established for the terminal device supports insertion / modification of a second SMF. The first SMF may also be referred to as a first type SMF, and the second SMF may also be referred to as a second type SMF. For example, the insertion / modification of the second SMF may be due to a location change of the terminal device in the DTSSA. As an example, the first SMF may be an H-SMF, and the second SMF may be a V-SMF. In this case, the terminal device is in home-routed roaming. As another example, the first SMF may be an anchor SMF and the second SMF may be an I-SMF. In this case, the terminal device is in a non-roaming state. For any one of the above examples, the first network function may inquire of the NRF (or any other entity having similar functionality) about features supported by the first SMF. The determination in block 202 may be performed according to whether the supported features include a feature (e.g., DTSSA) that supports the insertion / modification of the second SMF.

[0065] When the first SMF for the PDU session determines that the insertion / modification of the second SMF is not supported, the first network function sends a query request to the second network function in block 204 to discover at least one second SMF that can serve the entire PLMN to which the first network function belongs. The second network function may be an NRF or any other entity with similar functionality. In the above example where the first SMF is an H-SMF and the second SMF is a V-SMF, the PLMN to which the first network function belongs is a VPLMN.

[0066] As a first option, the query request may comprise a first indicator indicating to discover only SMFs that can serve the entire PLMN. As an illustrative example, the first indicator may be a Boolean query parameter with a value "TRUE" indicating to discover only SMFs that can serve the entire PLMN. As a second option, the query request may comprise a predefined TAI representing the entire PLMN as a query parameter for the SMF to be discovered. It should be noted that various other options may be used instead, as long as the second network function may be requested by the query request to discover only SMFs that can serve the entire PLMN.

[0067] In block 206, the first network function receives a query response from the second network function. For example, if at least one second SMF is located in the PLMN, the query response may comprise information about the at least one second SMF. Using the method shown in FIG. 2, the serving PLMN of the terminal device may be enabled to continue serving the PDU session during the mobility of the terminal device when the first SMF does not support the insertion / change of the second SMF.

[0068] The query request may also indicate to preferentially discover at least one second SMF. As a first option, the query request may comprise a second indicator indicating to preferentially discover an SMF capable of serving the entire PLMN. As an illustrative example, the second indicator may be a Boolean query parameter with a value "TRUE" indicating to preferentially discover an SMF capable of serving the entire PLMN. As a second option, the query request may comprise a predefined TAI representing the entire PLMN as a query parameter for the SMF to be discovered. It should be noted that various other options may be used instead, as long as the second network function may be requested by the query request to preferentially discover an SMF capable of serving the entire PLMN.

[0069] Correspondingly, if the at least one second SMF is located in the PLMN, the query response may comprise information on the at least one second SMF. If the at least one second SMF is not located in the PLMN, the query response may comprise information on the at least one third SMF that cannot serve the entire PLMN because the at least one second SMF that can serve the entire PLMN to which the first network function belongs is not available. In this case, the at least one third SMF may match one or more other query parameters included in the query request.

[0070] FIG. 3 is a flow chart illustrating a method implemented by a second network function according to an embodiment of the present disclosure. The second network function may be an NRF or any other entity with similar functionality. In block 302, the second network function receives a query request from the first network function to discover at least one second SMF that can serve the entire PLMN to which the first network function belongs. The first network function may be an AMF or any other entity with similar functionality. Block 302 corresponds to block 204. As described above with respect to block 204, as a first option, the query request may comprise a first indicator indicating to discover only SMFs that can serve the entire PLMN. For this option, in response to a query request containing such an indicator, the second network function may search for SMFs whose registered information does not include a specific served TAI, meaning that the entire PLMN can be served. As a second option, the query request may comprise a predefined TAI representing the entire PLMN as a query parameter for the SMF to be discovered. For this option, in response to a query request including a predefined TAI, the second network function may search for an SMF whose registered information includes the predefined TAI.

[0071] At block 304, the second network function sends a query response to the first network function. For example, if information regarding the at least one second SMF (e.g., its NF profile) is registered with the second network function, the query response may comprise such information.

[0072] As explained above, the query request may also indicate to preferentially discover at least one second SMF. As a first option, the query request may comprise a second indicator indicating to preferentially discover an SMF capable of serving the entire PLMN. As an illustrative example, the second indicator may be a Boolean query parameter with a value "TRUE" indicating to preferentially discover an SMF capable of serving the entire PLMN. In response to a query request containing such an indicator, the second network function may preferentially search for an SMF whose registered information does not include a specific served TAI, meaning that the entire PLMN can be served. In a second option, the query request may comprise a predefined TAI representing the entire PLMN as a query parameter for the SMF to be discovered. In response to a query request containing a predefined TAI, the second network function may preferentially search for an SMF whose registered information includes the predefined TAI.

[0073] For both options, if the at least one second SMF is located in the PLMN, the query response may comprise information about the at least one second SMF. If the at least one second SMF is not located in the PLMN, the query response may comprise information about the at least one third SMF that cannot serve the entire PLMN because the at least one second SMF that can serve the entire PLMN to which the first network function belongs is not available. In this case, the at least one third SMF may match one or more other query parameters included in the query request.

[0074] FIG. 4 is a flow chart illustrating a method implemented by a first network function according to an embodiment of the present disclosure. The first network function may be an AMF or any other entity having similar functionality. In block 402, the first network function determines whether a first SMF for a PDU session to be established for a terminal device supports insertion / modification of a second SMF. Block 402 is the same as block 202, and details of block 402 are omitted here. When determining that the first SMF for the PDU session does not support insertion / modification of a second SMF, the first network function determines a target second SMF for the PDU session in block 404. The determined target second SMF is selected from one or more second SMFs that are preconfigured in the first network function and can serve the entire PLMN to which the first network function belongs. In this way, the serving PLMN of the terminal device may be enabled to continue serving the PDU session during mobility of the terminal device when the first SMF does not support the insertion / change of the second SMF.

[0075] FIG. 5 is a flow chart illustrating an example process according to an embodiment of the present disclosure. As shown, the process involves nine entities for a home-routed roaming scenario: UE, (R)AN, AMF, Visited UPF (V-UPF), V-SMF, Home UPF (H-UPF), H-SMF, Home PCF (H-PCF), and UDM. In step 1, the UE sends a PDU session establishment request to the AMF via the (R)AN. In step 2, the AMF performs SMF selection. If the AMF detects that the H-SMF does not support DTSSA, the AMF selects a V-SMF that can serve the entire PLMN area. This allows the visited PLMN to continue serving the home-routed PDU session during UE mobility when the H-SMF does not support the DTSSA feature.

[0076] Specifically, the visited PLMN may deploy one or more V-SMFs capable of serving the full PLMN area or the entire PLMN area, and the V-SMF may register with the NRF to indicate that the V-SMF can serve the full PLMN area. In response to a home routed PDU session establishment request from a roaming UE, the AMF may select an H-SMF for the PDU session via the NRF in the home PLMN. During H-SMF discovery, the AMF may learn optional features (e.g., DTSSA) supported by the H-SMF. When the H-SMF does not support DTSSA, the AMF selects a V-SMF capable of serving the full PLMN area by any one of the following options: As a first option, as shown in FIG. 6, the AMF may include a new flag ("full-plmn-area" set to "TRUE") in the NRF discovery request indicating that only SMFs capable of serving the full PLMN area are returned. The NRF may process the new flag, browse all registered SMF instances, and pick up only those that can serve all PLMN areas. As a second option, a special TAI (e.g., PLMN_FULL_AREA_TAI with a special value) may be defined that represents all areas of a PLMN. The SMF may register this PLMN_FULL_AREA_TAI as a serving area, and the AMF may use this PLMN_FULL_AREA_TAI as a query parameter to find the SMF instance. As a third option, all V-SMFs serving all PLMN areas may be pre-configured in all AMFs.

[0077] In step 3a, the AMF sends a Nsmf_PDUSession_CreateSMContext request to the V-SMF. In step 3b, the V-SMF sends a Nsmf_PDUSession_CreateSMContext response to the AMF. In step 4, the V-SMF performs UPF selection. In step 5a, the V-SMF sends an N4 session establishment request to the V-UPF. In step 5b, the V-UPF sends an N4 session establishment response to the V-SMF. In step 6, the V-SMF sends a Nsmf_PDUSession_Create request to the H-SMF. In step 7, the H-SMF performs subscription data retrieval from the UDM. It should be noted that FIG. 6 illustrates only a part of the UE request PDU session establishment procedure for a home routed roaming scenario, and steps 1 and 3 to 7 may be the same as the corresponding steps in FIG. 4.3.2.2.2-1 of 3GPP TS23.502 V16.3.0.

[0078] Based on the process described above, the following changes are proposed to be made to 3GPP TS23.501 V16.4.0. Please note that the updates compared to this technical specification are underlined for easy recognition. 5.34 Support for deployment topologies with specific SMF service areas 6.3.2 SMF Discovery and Selection The SMF selection functionality is used to allocate the SMF supported by the AMF and SCP to manage the PDU session. The SMF selection procedure is described in clause 4.3.2.2.3 of TS 23.502 [3]. The SMF discovery and selection functionality follows the principles described in section 6.3.1. When the AMF performs discovery, it utilizes the NRF to discover the SMF instance unless the SMF information is available by other means, e.g., locally configured on the AMF. When the AMF attempts to discover an SMF instance, it provides the NRF with UE location information. The NRF provides the AMF with the NF profile of the SMF instance. In addition, the NRF also provides the AMF with the SMF service area of ​​the SMF instance. The SMF selection functionality in the AMF selects the SMF instance and SMF service instance based on the available SMF instances obtained from the NRF or based on the configured SMF information in the AMF. NOTE 1: The protocol aspects of access to the NRF are specified in TS 29.510

[58] . The SMF selection functionality is applicable to both 3GPP and non-3GPP accesses. The SMF selection for emergency services is explained in clause 5.16.4.5. The following factors may be considered during SMF selection: a) The selected Data Network Name (DNN). In case of home routed roaming, the DNN is not applied for V-SMF selection. b) The S-NSSAI of the HPLMN (for non-roaming and home-routed roaming scenarios), and the S-NSSAI of the VPLMN (for roaming with local breakout and home-routed roaming scenarios). c) NSI-ID. Note 2: The use of the NSI-ID in the network is optional and depends on the operator's deployment choice. If used, the NSI ID is associated with the S-NSSAI. d) The access technology being used by the UE. e) Support for control plane CIoT 5GS optimizations. f) Subscription information from the UDM, for example: -Per DNN: Whether LBO roaming is enabled. -Per S-NSSAI: Subscribed DNN. -(Per S-NSSAI, Subscribed DNN): Whether LBO roaming is enabled. -(S-NSSAI, Per Subscribed DNN): Whether EPC interaction is supported. - (Per S-NSSAI, subscribed DNN): Whether it is required to select the same SMF for all PDU sessions for the same S-NSSAI and DNN. g) Blank. h) Local operator policy. NOTE 3: These policies may take into account whether the SMF to be selected is an I-SMF, a V-SMF or an SMF. i) Load status of the candidate SMF. j) If an NWDAF is deployed, analysis (i.e. statistics or predictions) of the load of candidate SMFs received from the NWDAF (see TS 23.288

[86] ). k) UE location (in other words, TA). l) The service area of ​​the candidate SMF. m) Capability of the SMF to support MA PDU sessions. n) Whether interaction with the EPS is required. To support the allocation of static IPv4 addresses and / or static IPv6 prefixes as specified in clause 5.8.2.2.1, a dedicated SMF may be deployed for the indicated combination of DNN and S-NSSAI and registered with the NRF or provided by the UDM as part of the subscription data. In the case of delegated discovery, the AMF sends all available factors a) through d), k) and n) to the SCP. In addition, the AMF may indicate to the SCP which NRF to use (in the case of an NRF dedicated to the target slice). If there is an existing PDU session and a UE request to establish another PDU session for the same DNN and S-NSSAI of the HPLMN, and the UE subscription data indicates support for interacting with the EPS for this DNN and S-NSSAI of the HPLMN or the UE subscription data indicates that the same SMF is selected for all PDU sessions for the same S-NSSAI, DNN, the same SMF is selected in the non-roaming and LBO cases, or the same H-SMF in the home-routed roaming case. In addition, if the UE context in the AMF provides an SMF ID for an existing PDU session for the same DNN, S-NSSAI, the AMF uses the stored SMF ID for the additional PDU session. In any such case where the AMF can determine which SMF should be selected, if delegated discovery is used, the AMF indicates the desired NF instance ID so that the SCP can route the message to the relevant SMF. Otherwise, if the UE subscription data does not indicate support for interacting with the EPS for this DNN and S-NSSAI, a different SMF may be selected in the non-roaming and LBO cases, or a different H-SMF in the home-routed roaming case, for example, to support SMF load balancing or to support graceful SMF shutdown (e.g., the SMF starts not to accept any more new PDU sessions). In the case of home routed roaming, the SMF selection functionality selects an SMF in the VPLMN based on the S-NSSAI of the VPLMN, and selects an SMF in the HPLMN based on the S-NSSAI of the HPLMN, as specified in clause 4.3.2.2.3.3 of TS 23.502 [3]. When the UE requests to establish a PDU session for the DNN and S-NSSAI of the HPLMN, if the UE MM core network capability indicates that the UE supports the EPC NAS, and optionally, if the UE subscription indicates support for interacting with the EPS for this DNN and S-NSSAI of the HPLMN, the selection functionality (in the AMF or SCP) selects the combined SMF+PGW-C. Otherwise, a standalone SMF may be selected. If the UDM provides a subscription context that enables handling of PDU sessions in the VPLMN for this DNN and S-NSSAI of the HPLMN (in other words, using LBO), and optionally the AMF is configured to know that the VPLMN has a suitable roaming agreement with the UE's HPLMN, the following applies. -When the AMF performs discovery, the SMF selection functionality in the AMF selects an SMF from the VPLMN. If delegated discovery is used, the SCP selects the SMF from the VPLMN. If an SMF in the VPLMN cannot be derived for the DNN and S-NSSAI of the VPLMN, or if the subscription does not allow handling of PDU sessions in the VPLMN using LBO, the following applies. -When the AMF performs discovery, both the SMF in the VPLMN and the SMF in the HPLMN are selected, and the DNN and S-NSSAI of the HPLMN are used to derive the SMF identifier from the HPLMN. - If delegated discovery is used: The AMF performs discovery and selection of H-SMFs from the NRF. The AMF may indicate the maximum number of H-SMF instances to be returned from the NRF, in other words, the SMF selection in the NRF. The AMF sends a Nsmf_PDUSession_CreateSMContext request to the SCP, where the Nsmf_PDUSession_CreateSMContext request includes the endpoint (e.g., URI) of the selected H-SMF and the discovery and selection parameters specified in this clause, in other words the parameters for V-SMF selection. The SCP performs V-SMF discovery and selection and forwards the request to the selected V-SMF. The V-SMF sends a Nsmf_PDUSession_Create request towards the H-SMF via the SCP, and the V-SMF uses the received endpoint (e.g., URI) of the selected H-SMF to configure the target destination to be addressed. The SCP forwards the request to the H-SMF. Upon receiving a response from the V-SMF, the AMF obtains the service area of ​​the V-SMF from the NRF based on the received V-SMF ID. The AMF uses the service area of ​​the V-SMF to determine the need for V-SMF relocation upon subsequent UE mobility. If the initially selected SMF in the VPLMN (for roaming with LBO) detects that the SMF does not understand the information in the UE request, the SMF may reject the N11 message (related to the PDU session establishment request message) with an appropriate N11 cause that triggers the AMF to select both a new SMF in the VPLMN (for home routed roaming) and an SMF in the HPLMN. The AMF selects the SMF taking into account its support for CIoT 5GS optimization (e.g., control plane CIoT 5GS optimization). Further details of AMF selection for the I-SMF are described in section 5.34. In the case of a home routed scenario, if the AMF determines that the current V-SMF cannot serve the UE location, the AMF selects a new V-SMF. The selection / relocation is the same as the I-SMF selection / relocation described in clause 5.34. If the AMF detects that the selected H-SMF does not support a deployment with a specific SMF service area as described in clause 5.34, e.g. does not support V-SMF modification, the AMF should discover and select a V-SMF that can serve the entire PLMN.

[0079] Additionally, the following changes are proposed to be made to 3GPP TS23.502 V16.4.0: 4.23.5.1 PDU Session Establishment Procedure For non-roaming or LBO roaming, the PDU session establishment procedure includes the following cases: - If the service area of ​​the selected SMF includes the location where the UE is camped, the UE request PDU session establishment procedure is the same as described in clause 4.3.2.2.1. - If the service area of ​​the selected SMF does not include the location where the UE is camped, the AMF selects an I-SMF serving the area where the UE is camped. The UE requested PDU session establishment procedure for home routed roaming specified in subclause 4.3.2.2.2 is used to establish the PDU session. Compared with the procedure specified in subclause 4.3.2.2.2, the V-SMF and V-UPF are replaced by the I-SMF and I-UPF, and the H-SMF and H-UPF are replaced by the SMF and UPF (PSA), respectively. Also, only the S-NSSAI with the value specified by the serving PLMN is sent to the SMF. Figure 4.23.9.1-1 As specified in step 1, the I-SMF provides the SMF with the DNAI list supported by the I-SMF, and the SMF provides the I-SMF with the corresponding DNAI for this PDU session based on the DNAI list information received from the I-SMF. When Delegated Discovery is used, the SCP selects the SMF as described in Appendix E. For the home routed roaming case, the UE request PDU session establishment procedure for home routed roaming in clause 4.3.2.2.2 may be reused without modification. If the AMF detects that the H-SMF does not support DTSSA, the AMF selects a V-SMF that can serve the entire PLMN area.

[0080] In addition, the following changes are proposed to be made to 3GPP TS29.510 V16.3.0: 6.2.3.2.3.1 GET This operation retrieves a list of NF instances that are currently registered with the NRF and that meet some filter criteria, as well as their offered services, e.g., NF instances offering a certain service name, or NF instances of a given NF type (e.g., AMF). JPEG0007635255000001.jpg118170

[0081] In consideration of an embodiment in which the query request may indicate preferentially discovering at least one second SMF, as described above, it is proposed that the following changes be made to 3GPP TS 29.510 V16.3.0: 6.2.3.2.3.1 GET This operation retrieves a list of NF instances that are currently registered with the NRF and that meet some filter criteria, as well as their offered services, e.g., NF instances offering a certain service name, or NF instances of a given NF type (e.g., AMF). JPEG0007635255000002.jpg255170A.3 Nnrf_NFDiscovery API TIFF0007635255000003.tif255170TIFF0007635255000004.tif255170TIFF0007635255000005.tif92170

[0082] Based on the above description, at least one aspect of the present disclosure provides a method implemented in a communication system. The method may comprise determining, in a first network function, whether a first SMF for a PDU session to be established for a terminal device supports insertion / modification of a second SMF. The method may further comprise, when the first network function determines that the first SMF for the PDU session does not support insertion / modification of a second SMF, sending a query request to a second network function to discover at least one second SMF that can serve the entire PLMN to which the first network function belongs. The method may further comprise receiving, in the second network function, the query request from the first network function. The method may further comprise sending, in the second network function, a query response to the first network function. The method may further comprise receiving, in the first network function, a query response from the second network function.

[0083] 7 is a block diagram illustrating an apparatus suitable for use in practicing some embodiments of the present disclosure. For example, any one of the first network node and the second network node described above may be implemented through an apparatus 700. As shown, the apparatus 700 may include a processor 710, a memory 720 for storing a program, and optionally a communication interface 730 for communicating data with other external devices through wired and / or wireless communication.

[0084] The program includes program instructions that, when executed by the processor 710, enable the apparatus 700 to operate according to embodiments of the present disclosure as discussed above. That is, embodiments of the present disclosure may be implemented at least in part by computer software executable by the processor 710, or by hardware, or by a combination of software and hardware.

[0085] Memory 720 may be of any type suitable for the local technology environment and may be implemented using any suitable data storage technology, such as semiconductor-based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory, and removable memory. Processor 710 may be of any type suitable for the local technology environment and may include, by way of non-limiting examples, one or more of a general purpose computer, a special purpose computer, a microprocessor, a digital signal processor (DSP), and a processor based on a multi-core processor architecture.

[0086] 8 is a block diagram illustrating a first network node according to an embodiment of the present disclosure. As shown, the first network node 800 comprises a determining module 802, a transmitting module 804, and a receiving module 806. The determining module 802 may be configured to determine whether a first SMF for a PDU session to be established for a terminal device supports insertion / modification of a second SMF, as described above with respect to block 202. The transmitting module 804 may be configured to send a query request to a second network function to discover at least one second SMF that can serve the entire PLMN to which the first network node belongs, when the first network node determines that the first SMF for the PDU session does not support insertion / modification of a second SMF, as described above with respect to block 204. The receiving module 206 may be configured to receive a query response from the second network function, as described above with respect to block 206.

[0087] 9 is a block diagram illustrating a second network node according to an embodiment of the present disclosure. As shown, the second network node 900 comprises a receiving module 902 and a transmitting module 904. The receiving module 902 may be configured to receive a query request from the first network function to discover at least one SMF that can serve an entire PLMN to which the first network function belongs, as described above with respect to block 302. The transmitting module 904 may be configured to transmit a query response to the first network function, as described above with respect to block 304.

[0088] FIG. 10 is a block diagram illustrating a first network node according to an embodiment of the present disclosure. As shown, the first network node 1000 includes a first determining module 1002 and a second determining module 1004. The first determining module 1002 may be configured to determine whether a first SMF for a PDU session to be established for a terminal device supports insertion / modification of a second SMF, as described above with respect to block 402. The second determining module 1004 may be configured to determine a target second SMF for a PDU session when the first SMF for the PDU session determines that the first SMF does not support insertion / modification of a second SMF, as described above with respect to block 404. The determined target second SMF may be selected from one or more second SMFs preconfigured in the first network node and capable of serving the entire PLMN to which the first network node belongs. The above-described modules may be implemented by hardware, or software, or a combination of both.

[0089] Based on the above description, at least one aspect of the present disclosure provides a communication system. The communication system may include a first network node and a second network node. The first network node may be configured to determine whether a first SMF for a PDU session to be established for a terminal device supports insertion / modification of a second SMF, and when the first network node determines that the first SMF for the PDU session does not support insertion / modification of the second SMF, send a query request to the second network node to discover at least one second SMF that can serve the entire PLMN to which the first network node belongs, and receive a query response from the second network node. The second network node may be configured to receive the query request from the first network node and send the query response to the first network node.

[0090] In general, various exemplary embodiments may be implemented in hardware or dedicated circuits, software, logic, or any combination thereof. For example, although the disclosure is not limited thereto, some aspects may be implemented in hardware and other aspects may be implemented in firmware or software that may be executed by a controller, microprocessor, or other computing device. Although various aspects of the exemplary embodiments of the present disclosure may be illustrated and described as block diagrams, flow charts, or using some other graphical representation, it is well understood that these blocks, apparatus, systems, techniques, or methods described herein may be implemented, as non-limiting examples, in hardware, software, firmware, dedicated circuits or logic, general-purpose hardware or controller or other computing device, or some combination thereof.

[0091] Thus, it should be appreciated that at least some aspects of the exemplary embodiments of the present disclosure may be practiced in a variety of components, such as integrated circuit chips and modules, etc. Thus, it should be appreciated that the exemplary embodiments of the present disclosure may be realized in an apparatus embodied as an integrated circuit, where the integrated circuit may comprise circuitry (and possibly firmware) for embodying at least one or more of a data processor, a digital signal processor, a baseband circuit, and a radio frequency circuit that are configurable to operate in accordance with the exemplary embodiments of the present disclosure.

[0092] It should be appreciated that at least some aspects of the exemplary embodiments of the present disclosure may be embodied in computer-executable instructions, such as in one or more program modules executed by one or more computers or other devices. Generally, a program module includes routines, programs, objects, components, data structures, etc., that perform particular tasks or implement particular abstract data types when executed by a processor in a computer or other device. The computer-executable instructions may be stored in a computer-readable medium, such as a hard disk, an optical disk, a removable storage medium, a solid-state memory, a RAM, etc. As will be appreciated by those skilled in the art, the functionality of the program modules may be combined or distributed as desired in various embodiments. In addition, the functionality may be embodied in whole or in part in firmware or in hardware equivalents, such as integrated circuits, field programmable gate arrays (FPGAs), etc.

[0093] References in this disclosure to "one embodiment," "an embodiment," and the like indicate that the embodiment being described may include a particular feature, structure, or characteristic, but do not require that every embodiment include the particular feature, structure, or characteristic. Moreover, such phrases do not necessarily refer to the same embodiment. Furthermore, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one of ordinary skill in the art to implement such feature, structure, or characteristic in connection with other embodiments, whether or not explicitly described.

[0094] Terms such as "first", "second", etc. may be used herein to describe various elements, but it should be understood that these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element, without departing from the scope of the present disclosure. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed terms.

[0095] The terminology used herein is only for the purpose of describing particular embodiments and is not intended to limit the disclosure. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms unless the context clearly indicates otherwise. It will be further understood that the terms "comprises", "comprising", "has", "having", "includes" and / or "including" as used herein specify the presence of stated features, elements, and / or components, but do not preclude the presence or addition of one or more other features, elements, components and / or combinations thereof. As used herein, the terms "connect", "connects", "connecting" and / or "connected" encompass direct and / or indirect connections between two elements.

[0096] The present disclosure includes any novel feature or combination of features explicitly disclosed herein, or any generalization thereof. Various modifications and adaptations to the above exemplary embodiments of the present disclosure may become apparent to those skilled in the relevant art in view of the above description, when read in conjunction with the accompanying drawings. However, any and all modifications will still fall within the scope of the non-limiting exemplary embodiments of the present disclosure.

Claims

1. 1. A method implemented by a first network function, comprising: Determining (202) whether a first session management function (SMF) for a protocol data unit (PDU) session to be established for a terminal device supports insertion / modification of a second SMF; When the first SMF for the PDU session determines that the insertion / modification of the second SMF is not supported, sending a query request to a second network function to discover at least one second SMF that can serve an entire Public Land Mobile Network (PLMN) to which the first network function belongs (204); receiving (206) a query response from the second network function; Equipped with The method, wherein the insertion / change of the second SMF is due to a change in location of the terminal device in a deployment topology with a specific SMF service area (DTSSA).

2. 2. The method of claim 1, wherein the query request indicates to preferentially discover the at least one second SMF, and the query response comprises information about the at least one second SMF, and the query response comprises information about at least one third SMF that is not capable of serving the entire PLMN if the at least one second SMF that is capable of serving the entire PLMN to which the first network function belongs is not available.

3. 3. The method of claim 1 or 2, wherein the first SMF is a Home SMF (H-SMF), the second or third SMF is a Visited SMF (V-SMF), and / or the first SMF is an Anchor SMF, the second or third SMF is an Intermediate SMF (I-SMF), and / or the first network function is an Access and Mobility Management Function (AMF), and / or the second network function is a Network Repository Function (NRF).

4. 4. The method of claim 1, wherein the query request comprises a first indicator indicating to discover only SMFs that can serve the entire PLMN, the first indicator being a Boolean query parameter having a value "TRUE" indicating to discover only SMFs that can serve the entire PLMN.

5. 4. The method according to claim 1, wherein the query request comprises a second indicator indicating to preferentially discover an SMF capable of serving the entire PLMN, the second indicator being a Boolean query parameter having a value "TRUE" indicating to preferentially discover an SMF capable of serving the entire PLMN.

6. 6. The method of claim 1, wherein the query request comprises a predefined Tracking Area Identity (TAI) representing the entire PLMN as a query parameter for the SMF to be discovered.

7. A method implemented by a second network function, comprising: receiving (302) a query request from a first network function to discover at least one second Session Management Function (SMF) capable of serving an entire Public Land Mobile Network (PLMN) to which the first network function belongs; Sending a query response to the first network function (304); A method comprising:

8. 8. The method of claim 7, wherein the query request indicates to preferentially discover the at least one second SMF, and the query response comprises information about the at least one second SMF.

9. 9. The method of claim 8, wherein the query response comprises information about at least one third SMF that cannot serve the entire PLMN if the at least one second SMF that can serve the entire PLMN to which the first network function belongs is not available.

10. 10. The method of claim 7, wherein the second network function is a Network Repository Function (NRF) and the first network function is an Access and Mobility Management Function (AMF).

11. 11. The method of claim 7, wherein the query request comprises a first indicator indicating to discover only SMFs that can serve the entire PLMN, the first indicator being a Boolean query parameter having a value "TRUE" indicating to discover only SMFs that can serve the entire PLMN.

12. 11. The method according to claim 7, wherein the query request comprises a second indicator indicating to preferentially discover an SMF capable of serving the entire PLMN, the second indicator being a Boolean query parameter having a value "TRUE" indicating to preferentially discover an SMF capable of serving the entire PLMN.

13. 11. The method of claim 7, wherein the query request comprises a predefined Tracking Area Identity (TAI) representing the entire PLMN as a query parameter for the SMF to be discovered.

14. A first network node (700), At least one processor (710); At least one memory (720), said at least one memory (720) containing instructions executable by said at least one processor (710), whereby said first network node (700) Determining whether a first session management function (SMF) for a protocol data unit (PDU) session to be established for a terminal device supports insertion / modification of a second SMF; When determining that the first SMF for the PDU session does not support the insertion / modification of the second SMF, sending a query request to a second network function to discover at least one second SMF that can serve an entire Public Land Mobile Network (PLMN) to which the first network node belongs; receiving a query response from the second network function; At least one memory (720) operable to Equipped with A first network node (700), wherein the insertion / change of the second SMF is due to a change in location of the terminal device in a deployment topology with a specific SMF service area (DTSSA).

15. The first network node (700) of claim 14, wherein said first network node (700) is operable to perform the method according to any one of claims 2 to 6.

16. In a first network function, determining (202) whether a first session management function (SMF) for a protocol data unit (PDU) session to be established for a terminal device supports insertion / modification of a second SMF; When the first network function determines that the first SMF for the PDU session does not support the insertion / change of the second SMF, sending a query request to a second network function to discover at least one second SMF that can serve an entire Public Land Mobile Network (PLMN) to which the first network function belongs (204); receiving (302) the query request from the first network function at the second network function; sending (304) a query response at the second network function to the first network function; receiving (206) the query response from the second network function at the first network function; Equipped with A method implemented in a communication system, wherein the insertion / change of the second SMF is due to a change in location of the terminal device in a deployment topology with a specific SMF service area (DTSSA).

17. a first network node configured to: determine whether a first Session Management Function (SMF) for a Protocol Data Unit (PDU) session to be established for a terminal device supports insertion / modification of a second SMF; and, when determining that the first SMF for the PDU session does not support insertion / modification of the second SMF, send a query request to a second network node to discover at least one second SMF that can serve an entire Public Land Mobile Network (PLMN) to which the first network node belongs; and receive a query response from the second network node; the second network node configured to receive the query request from the first network node and to send the query response to the first network node; Equipped with The insertion / change of the second SMF is due to a change in location of the terminal device in a deployment topology with a specific SMF service area (DTSSA).

Images