Method and apparatus for handling SMF set mismatch

Abstract

The embodiment of the invention provides a method and device for processing SMF set mismatch. A method performed by an access and mobility function (AMF) may include obtaining third information about whether a resource is uniquely bound to a particular service instance in a first session management function (SMF). The method may also include obtaining fourth information about whether the second SMF supports reselection of an alternative first SMF instance within the SMF set of the first SMF. The method may also include detecting a first SMF failure. The method may also include reselecting an alternative service instance within the SMF set of the first SMF based on the third information and the fourth information.

Description

Technical Field

[0001] Non-limiting and exemplary embodiments of the present disclosure generally relate to the field of communication technology, and in particular to methods and apparatus for handling SMF (Session Management Function) set mismatches. Background Art

[0002] This section introduces aspects that may help to better understand the present disclosure. Therefore, the statements in this section should be read in this context and should not be understood as admissions about what is or is not in the prior art.

[0003] In communication networks, such as NR (New Radio) defined by the 3rd Generation Partnership Project (3GPP), NF set-based session resilience has been introduced, i.e., equivalent control plane network functions (NFs) can be grouped into NF sets. For example, several SMF instances are grouped into SMF sets. NFs within a NF set are interchangeable because they share the same context data. In the case of scenarios such as failure, load balancing, load rebalancing, etc., a NF can be replaced by an alternative NF within the same NF set.

[0004] The SMF can act as SMF, V-SMF (visiting SMF) or H-SMF (home SMF) roles for different PDU session contexts. The SMF set concept does not distinguish between different SMF roles. When the SMF registers the SMF set Id (identifier) ​​in the NRF (network repository function), it means that if the SMF is used for non-roaming (SMF role), roaming in (V-SMF role) or roaming out (H-SMF role) at the same time, the SMF can support SMF set-based recovery for all session contexts established using the SMF, V-SMF or H-SMF roles. Summary of the invention

[0005] This Summary is intended to introduce some concepts in a simplified form that are further described in the Detailed Description below. This Summary 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] In order to support SMF set restoration for roaming interworking between VPLMN and HPLMN, both VPLMN (visited PLMN (Public Land Mobile Network)) and HPLMN (home PLMN) are required to deploy SMF sets and support restoration functions for V-SMF and H-SMF roles.

[0007] In actual network deployment, it is unlikely that all PLMNs deploy SMF sets. It is also possible that a PLMN deploys an SMF set for non-roaming users, but the SMF set does not support recovery for roaming users, or the SMF set recovery does not comply with the roaming agreement.

[0008] It is not obvious to derive whether the peer SMF supports SMF Sets and if the peer SMF does not provide binding indication in request and response messages. NRF based service discovery may help but it will at least incur additional signalling delay and it cannot cover the case where SMF Sets are deployed for PDU Sessions of non-roaming UEs but not for home routed PDU Sessions. When such information on supporting SMF Sets is not available, it can lead to PDU Sessions served by a failed SMF being deleted unnecessarily or abandoned as pending resources.

[0009] In case the VPLMN or HPLMN has different SMF set recovery capabilities or configurations, the network behavior is not specified in the current 3GPP release and a possible mismatch between the VPLMN and the HPLMN may occur during an SMF failure scenario. The result is that time is required to reactivate all related PDU sessions and there is an impact on service availability.

[0010] For example, V-SMF supports SMF sets, but H-SMF does not. When a V-SMF failure is detected, H-SMF will delete the PDU session locally, while V-SMF may maintain the PDU session. Mobile termination services are affected.

[0011] V-SMF does not support SMF sets, while H-SMF supports SMF sets. When an H-SMF failure is detected, V-SMF will release the affected PDU sessions, which may cause the PDU sessions to be suspended in the alternative H-SMF, which will further suspend the sessions in its upstream nodes (such as PCF).

[0012] In 3GPP, the support for SMF(NF)(service) set is not very clearly defined, however, in the applicant's view, it contains at least two aspects for supporting SMF(NF). 1) All resource contexts of SMF services can be shared by at least one or more SMFs in the same SMF (service) set or their alternative SMFs, so that in the event of an SMF failure, the peer entity can select an alternative SMF when it detects that the SMF has failed. 2) When SMF detects that a peer entity fails, SMF may reselect an alternative peer entity based on the binding indication provided by the peer entity or the NF profile of the peer entity registered in the NRF.

[0013] In an embodiment, as long as an SMF supports item 2, it can claim that it supports the SMF set feature.

[0014] However, it seems reasonable to consider the case when SMF only supports entry 2, so it may be allowed to claim that it supports the SMF set, because obviously it is much easier from an implementation point of view to support entry 2 than to support entry 1, which requires larger changes in software and hardware.

[0015] However, imagine the following scenario: if the H-SMF does not support any recovery, i.e. its resources are only bound to a specific NF service instance, but since it can reselect another V-SMF if the V-SMF has failed, it will indicate its support for SETFRI.

[0016] Therefore, when the H-SMF fails, the peer SMF (V-SMF) may not trigger restoration immediately after detecting the failure of the H-SMF, and will do so only when there is a signaling message for the PDU session of the failed H-SMF to be sent. But when the peer V-SMF looks for a replacement H-SMF, it finds that there is no replacement H-SMF.

[0017] In fact, the PDU sessions in the H-SMF are deleted, all PDU sessions served by the H-SMF are suffering from the inability to receive any mobile terminated services, and a large number of suspended resources in the V-SMF and AMF.

[0018] To overcome or alleviate at least one of the above problems or other problems, a new solution for handling SMF set mismatch is needed.

[0019] In a first aspect of the present disclosure, a method performed by an access and mobility function (AMF) is provided. The method may include obtaining third information about whether a resource is uniquely bound to a specific service instance in a first session management function (SMF). The method may also include obtaining fourth information about whether a second SMF supports reselecting an alternative first SMF instance within a SMF set of the first SMF. The method may also include detecting a failure of the first SMF. The method may also include reselecting an alternative service instance within the SMF set of the first SMF based on the third information and the fourth information.

[0020] In an embodiment, the third information may be a Boolean value and / or the fourth information may be a Boolean value.

[0021] In an embodiment, obtaining the third information may include sending a network function (NF) discovery request to a network repository function (NRF) and receiving a NF discovery response including the third information from the NRF.

[0022] In an embodiment, obtaining the third information may include receiving a service response message or a service request message including the third information from the first SMF.

[0023] In an embodiment, obtaining the fourth information may include sending a NF discovery request to the NRF, and receiving a NF discovery response including the fourth information from the NRF.

[0024] In an embodiment, obtaining the fourth information may include receiving an update session management (SM) context response message including the fourth information from the first SMF.

[0025] In an embodiment, reselecting an alternative service instance within the SMF set of the first SMF based on the third information and the fourth information may include: when the third information indicates that the resource is not uniquely bound to a specific service instance in the first SMF, and the fourth information indicates that the second SMF supports reselection of an alternative first SMF instance within the SMF set of the first SMF, reselecting an alternative V-SMF service instance within the SMF set of the first SMF.

[0026] In an embodiment, reselecting an alternative service instance within the SMF set of the first SMF based on the third information and the fourth information may also include: when the third information indicates that the resource is not uniquely bound to a specific service instance in the first SMF, and the fourth information indicates that the second SMF does not support reselection of an alternative first SMF instance within the SMF set of the first SMF, reselecting an alternative first SMF service instance within the SMF set of the first SMF, and sending a request to the alternative first SMF to delete at least one affected protocol data unit PDU session toward a user equipment UE.

[0027] In an embodiment, reselecting an alternative service instance within the SMF set of the first SMF based on the third information and the fourth information may also include: when the third information indicates that the resource is uniquely bound to a specific service instance in the first SMF, releasing at least one affected PDU session without reselecting an alternative first SMF service instance.

[0028] In an embodiment, the first SMF may be a visited SMF and the second SMF may be a home SMF, or the first SMF may be an intermediate SMF and the second SMF may be an anchor SMF.

[0029] In an embodiment, the method may further include obtaining fifth information about whether the resource is uniquely bound to a specific service instance in the second SMF. The method may further include sending the fifth information to the first SMF.

[0030] In a second aspect of the present disclosure, a method performed by a first session management function (SMF) is provided. The method includes sending third information to the AMF about whether a resource is uniquely bound to a specific service instance in the first SMF. The method may also include sending fourth information to the AMF about whether the second SMF supports reselecting an alternative first SMF instance within the SMF set of the first SMF. The AMF may use the third information and the fourth information to reselect an alternative service instance within the SMF set of the first SMF when the first SMF fails.

[0031] In an embodiment, the fifth information is obtained from the access and mobility function AMF or the second SMF.

[0032] In an embodiment, the method may further include obtaining fifth information about whether the resource is uniquely bound to a specific service instance in the second SMF. The method may further include obtaining sixth information about whether the first SMF supports reselecting an alternative second SMF instance within the SMF set of the second SMF.

[0033] In an embodiment, the method may further include obtaining fourth information.

[0034] In an embodiment, obtaining the fourth information may include receiving the fourth information from the second SMF.

[0035] In an embodiment, the third information may be included in a service request or response message.

[0036] In an embodiment, the fourth information may be included in the update SM context response message.

[0037] In an embodiment, the method may further include sending third information to the second SMF.

[0038] In an embodiment, the first SMF may be a visited SMF and the second SMF may be a home SMF, or the first SMF may be an intermediate SMF and the second SMF may be an anchor SMF.

[0039] In a third aspect of the present disclosure, a method performed by a second session management function (SMF) is provided. The method may include receiving third information from a first SMF about whether a resource is uniquely bound to a specific service instance in the first SMF. The method may also include obtaining fourth information about whether the second SMF supports reselection of an alternative first SMF instance within the SMF set of the first SMF.

[0040] In an embodiment, the method may further include sending fifth information to the first SMF regarding whether the resource is uniquely bound to a specific service instance in the second SMF.

[0041] In an embodiment, the first SMF may be a visited SMF and the second SMF may be a home SMF, or the first SMF may be an intermediate SMF and the second SMF may be an anchor SMF.

[0042] In a fourth aspect of the present disclosure, an access and mobility function (AMF) is provided. The AMF includes a processor and a memory coupled to the processor. The memory stores instructions executable by the processor. The AMF is operable to obtain third information about whether a resource is uniquely bound to a specific service instance in a first session management function (SMF). The AMF is further operable to obtain fourth information about whether a second SMF supports reselecting an alternative first SMF instance within a SMF set of the first SMF. The AMF is further operable to detect a first SMF failure. The AMF is further operable to reselect an alternative service instance within the SMF set of the first SMF based on the third information and the fourth information.

[0043] In a fifth aspect of the present disclosure, a first session management function (SMF) is provided. The first SMF includes a processor and a memory coupled to the processor. The memory stores instructions executable by the processor. The first SMF is further operable to send third information to the AMF about whether a resource is uniquely bound to a specific service instance in the first SMF. The first SMF is further operable to send fourth information to the AMF about whether the second SMF supports reselecting an alternative first SMF instance within the SMF set of the first SMF. The AMF can use the third information and the fourth information to reselect an alternative service instance within the SMF set of the first SMF when the first SMF fails.

[0044] In a sixth aspect of the present disclosure, a second session management function (SMF) is provided. The second SMF includes a processor and a memory coupled to the processor. The memory stores instructions executable by the processor. The second SMF is operable to receive third information about whether a resource is uniquely bound to a specific service instance in the first SMF from the first SMF. The second SMF is further operable to obtain fourth information about whether the second SMF supports reselection of an alternative first SMF instance within the SMF set of the first SMF.

[0045] In a seventh aspect of the present disclosure, an AMF is provided. The AMF includes a first acquisition module configured to obtain third information about whether a resource is uniquely bound to a specific service instance in a first session management function (SMF). In an embodiment, the AMF further includes a second acquisition module configured to obtain fourth information about whether the second SMF supports reselecting an alternative first SMF instance within the SMF set of the first SMF. The AMF further includes a detection module configured to detect a failure of the first SMF. The AMF further includes a reselection module configured to reselect an alternative service instance within the SMF set of the first SMF based on the third information and the fourth information.

[0046] In an embodiment, the AMF may further include a third obtaining module configured to obtain fifth information about whether the resource is uniquely bound to a specific service instance in the second SMF.

[0047] In an embodiment, the AMF may further include a sending module configured to send the fifth information to the first SMF.

[0048] In an eighth aspect of the present application, a first SMF is provided. The first SMF may include a first sending module configured to send third information about whether a resource is uniquely bound to a specific service instance in the first SMF to the AMF. The first SMF may also include a second sending module configured to send fourth information about whether the second SMF supports reselection of an alternative first SMF instance within the SMF set of the first SMF to the AMF.

[0049] In an embodiment, the AMF may use the third information and the fourth information to reselect an alternative service instance within the SMF set of the first SMF when the first SMF fails.

[0050] In an embodiment, the first SMF may further include a first obtaining module configured to obtain fifth information about whether the resource is uniquely bound to a specific service instance in the second SMF. The first SMF may further include a second obtaining module configured to obtain sixth information about whether the first SMF supports reselection of an alternative second SMF instance within the SMF set of the second SMF.

[0051] In an embodiment, the first SMF may further include a third obtaining module configured to obtain fourth information.

[0052] In an embodiment, the first SMF may further include a third sending module configured to send third information to the second SMF.

[0053] In a ninth aspect of the present disclosure, a second SMF is provided. The second SMF may include a receiving module configured to receive third information from the first SMF about whether a resource is uniquely bound to a specific service instance in the first SMF. The second SMF may also include an obtaining module configured to obtain fourth information about whether the second SMF supports reselection of an alternative first SMF instance within the SMF set of the first SMF.

[0054] In an embodiment, the second SMF may further include a sending module configured to send fifth information on whether the resource is uniquely bound to a specific service instance in the second SMF to the first SMF.

[0055] In another aspect of the present disclosure, there is provided a computer program product comprising instructions, which, when executed by at least one processor, cause the at least one processor to perform the method according to any one of the first, second or third aspects.

[0056] In another aspect of the present disclosure, a computer-readable storage medium storing instructions is provided. When the instructions are executed by at least one processor, the instructions cause the at least one processor to perform the method according to any one of the first, second or third aspects.

[0057] Embodiments herein may provide many advantages, and the following is a non-exhaustive list of examples of advantages. In some embodiments herein, a reconstruction process is proposed to rebuild PDU sessions affected by SMF failures. In some embodiments herein, the time to recover PDU sessions affected by SMF failures can be reduced. In some embodiments herein, ghost session problems can be solved. In some embodiments herein, service availability can be improved. The embodiments herein are not limited to the above-mentioned features and advantages. Those skilled in the art will recognize other features and advantages after reading the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The above and other aspects, features and advantages of various embodiments of the present disclosure will become more apparent through the following detailed description with reference to the accompanying drawings, in which the same reference numerals or letters are used to represent the same or equivalent elements. In order to facilitate a better understanding of the embodiments of the present disclosure, the accompanying drawings are shown and are not necessarily drawn to scale, in which:

[0059] Figure 1 A first failure scenario according to an embodiment of the present disclosure is shown;

[0060] Figure 2 A second failure scenario according to an embodiment of the present disclosure is shown;

[0061] Figure 3A third failure scenario according to an embodiment of the present disclosure is shown;

[0062] Figure 4 A fourth failure scenario according to an embodiment of the present disclosure is shown;

[0063] Figure 5 A fifth failure scenario according to an embodiment of the present disclosure is shown;

[0064] Figure 6 A sixth fault scenario according to an embodiment of the present disclosure is shown;

[0065] Figure 7 The roaming 5G system architecture according to an embodiment of the present disclosure is schematically shown;

[0066] Figure 8 A method flow chart according to an embodiment of the present disclosure is shown;

[0067] Fig. 9 A flowchart of obtaining first information about whether a first SMF supports a first capability according to an embodiment of the present disclosure is shown;

[0068] Fig.10 A flowchart of obtaining second information about whether a second SMF supports a first capability according to an embodiment of the present disclosure is shown;

[0069] Fig.11 A method flow chart according to another embodiment of the present disclosure is shown;

[0070] Fig.12 A method flow chart according to another embodiment of the present disclosure is shown;

[0071] Fig.13 A flowchart of obtaining third information about whether a first SMF supports a local NF set for the first SMF and a peer NF set for a second SMF according to an embodiment of the present disclosure is shown;

[0072] Fig.14 A flowchart of obtaining fourth information about whether the second SMF supports a local NF set for the second SMF and a peer NF set for the first SMF according to an embodiment of the present disclosure is shown;

[0073] Fig.15 A flowchart of a method according to another embodiment of the present disclosure is shown;

[0074] Fig.16 A flowchart of a method according to another embodiment of the present disclosure is shown;

[0075] Fig.17 A flowchart of a method according to another embodiment of the present disclosure is shown;

[0076] Fig.18 A flowchart of a method according to another embodiment of the present disclosure is shown;

[0077] Fig.19 A flowchart of a method according to another embodiment of the present disclosure is shown;

[0078] Fig.20a A flowchart of a method according to another embodiment of the present disclosure is shown;

[0079] Fig.20b A flowchart of a method according to another embodiment of the present disclosure is shown;

[0080] Fig.21a A flowchart showing a method according to another embodiment of the present disclosure is shown;

[0081] Figure 21b A flowchart showing a method according to another embodiment of the present disclosure is shown;

[0082] Fig. 22 A flowchart showing a method according to another embodiment of the present disclosure is shown;

[0083] Fig.23 A flowchart showing a method according to another embodiment of the present disclosure is shown;

[0084] Fig.24 A flowchart showing a method according to another embodiment of the present disclosure is shown;

[0085] Fig.25 A flowchart showing a method according to another embodiment of the present disclosure is shown;

[0086] Fig.26 A flowchart showing a method according to another embodiment of the present disclosure is shown;

[0087] Fig.27a A flowchart showing a method according to another embodiment of the present disclosure is shown;

[0088] Figure 27b A flowchart showing a method according to another embodiment of the present disclosure is shown;

[0089] Fig.28 A flowchart showing a method according to another embodiment of the present disclosure is shown;

[0090] Fig.29 A flowchart showing a method according to another embodiment of the present disclosure is shown;

[0091] Fig.30 A flowchart showing a method according to another embodiment of the present disclosure is shown;

[0092] Fig.31A flowchart showing a method according to another embodiment of the present disclosure is shown;

[0093] Fig.32 A flowchart showing a method according to another embodiment of the present disclosure is shown;

[0094] Fig.33 A flowchart showing a method according to another embodiment of the present disclosure is shown;

[0095] Fig.34 A flowchart showing a method according to another embodiment of the present disclosure is shown;

[0096] Fig.35 A flowchart showing a method according to another embodiment of the present disclosure is shown;

[0097] Fig.36 A flowchart showing a method according to another embodiment of the present disclosure is shown;

[0098] Fig.37 A flowchart showing an example solution for a V-SMF failure according to an embodiment of the present disclosure is shown;

[0099] Fig.38 A flowchart showing an example solution to a V-SMF failure according to another embodiment of the present disclosure is shown;

[0100] Fig.39 A flowchart showing an example solution to a V-SMF failure according to another embodiment of the present disclosure is shown;

[0101] Fig.40 A flowchart showing an example solution for H-SMF failure according to an embodiment of the present disclosure is shown;

[0102] Fig.41 A flowchart showing an example solution to H-SMF failure according to another embodiment of the present disclosure is shown;

[0103] Fig.42a A flowchart showing an example solution to H-SMF failure according to another embodiment of the present disclosure is shown;

[0104] Figure 42b A flowchart showing a method according to another embodiment of the present disclosure is shown;

[0105] Fig.42c A flowchart showing a method according to another embodiment of the present disclosure is shown;

[0106] Fig.42d A flowchart showing a method according to another embodiment of the present disclosure is shown;

[0107] Figure 42eA flowchart showing a method according to another embodiment of the present disclosure is shown;

[0108] Figure 42f A flowchart showing a method according to another embodiment of the present disclosure is shown;

[0109] Figure 42g A flowchart showing a method according to another embodiment of the present disclosure is shown;

[0110] Figure 42h A flowchart showing a method according to another embodiment of the present disclosure is shown;

[0111] Fig.43 is a block diagram illustrating an apparatus suitable for practicing some embodiments of the present disclosure;

[0112] Fig.44 is a block diagram illustrating an AMF according to an embodiment of the present disclosure;

[0113] Fig.45 is a block diagram illustrating a first SMF according to an embodiment of the present disclosure;

[0114] Fig.46 is a block diagram illustrating a second SMF according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0115] Embodiments of the present disclosure are described in detail with reference to the accompanying drawings. It should be understood that these embodiments are discussed only for the purpose of enabling those skilled in the art to better understand and thus realize the present disclosure, rather than suggesting any limitation on the scope of the present disclosure. References to features, advantages or similar language throughout the specification do not mean that all features and advantages that can be implemented with the present disclosure should be in or in any single embodiment of the present disclosure. On the contrary, the language referring to features and advantages should be understood to mean that specific features, advantages or characteristics described in conjunction with the embodiments are included in at least one embodiment of the present disclosure. In addition, in one or more embodiments, the features, advantages and characteristics described in the present disclosure may be combined in any suitable manner. Those skilled in the relevant art will recognize that the present disclosure may be practiced without one or more of the specific features or advantages of a particular embodiment. In other cases, additional features and advantages may be recognized in certain embodiments, and the additional features and advantages may not exist in all embodiments of the present disclosure.

[0116] As used herein, the term "network" refers to a network that complies with any suitable communication standard, such as New Radio (NR), Long Term Evolution (LTE), Advanced LTE (LTE-A), Wideband Code Division Multiple Access (WCDMA), High Speed ​​Packet Access (HSPA), Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Single Carrier Frequency Division Multiple Access (SC-FDMA), and other wireless networks. A CDMA network can implement radio technologies such as Universal Terrestrial Radio Access (UTRA). UTRA includes WCDMA and other variants of CDMA. A TDMA network can implement radio technologies such as Global System for Mobile Communications (GSM). An OFDMA network can implement radio technologies such as Evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDMA, Ad-hoc networks, wireless sensor networks, etc. In the following description, the terms "network" and "system" may be used interchangeably. In addition, communication between two devices in a network may be performed according to any suitable communication protocol, including but not limited to communication protocols defined by standard organizations such as 3GPP. For example, the communication protocol may include first generation (1G), 2G, 3G, 4G, 4.5G, 5G communication protocols and / or any other protocol currently known or developed in the future.

[0117] The term "network device" or "network node" or "network function" refers to any suitable network function (NF) that can be implemented in a (physical or virtual) network element of a communication network. For example, a network function can be implemented as a network element on dedicated hardware, as a software instance running on dedicated hardware, or as a virtualized function instantiated on an appropriate platform (e.g., on a cloud infrastructure). For example, a 5G system (5GS) may include multiple NFs, such as AMF (Access and Mobility Function), SMF (Session Management Function), AUSF (Authentication Service Function), UDM (Unified Data Management), PCF (Policy Control Function), AF (Application Function), NEF (Network Exposure Function), UPF (User Plane Function) and NRF (Network Repository Function), RAN (Radio Access Network), SCP (Service Communication Agent), NWDAF (Network Data Analysis Function), NSSF (Network Slice Selection Function), NSSAAF (Network Slice Specific Authentication and Authorization Function), etc.

[0118] The term "terminal device" refers to any terminal device that can access a communication network and receive services therefrom. As an example and not limitation, a terminal device refers to a mobile terminal, a user equipment (UE) or other suitable device. A UE may be, for example, a subscriber station (SS), a portable subscriber station, a mobile station (MS) or an access terminal (AT). Terminal devices may include, but are not limited to, portable computers, image capture terminal devices such as digital cameras, game terminal devices, music storage and playback devices, mobile phones, cellular phones, smart phones, voice over IP (VoIP) phones, wireless local loop phones, tablet computers, wearable devices, personal digital assistants (PDAs), portable computers, desktop computers, wearable terminal devices, vehicle-mounted wireless terminal devices, wireless endpoints, mobile stations, laptop embedded devices (LEEs), laptop mounted devices (LMEs), USB dongles, smart devices, wireless customer premises equipment (CPEs), etc. In the following description, the terms "terminal device", "terminal", "user equipment" and "UE" may be used interchangeably. As an example, a terminal device may represent a UE configured to communicate in accordance with one or more communication standards (e.g., 3GPP's LTE standard or NR standard) issued by 3GPP (3rd Generation Partnership Project). As used herein, a "user equipment" or "UE" may not necessarily have a "user" in terms of a human user who owns and / or operates the associated device. In some embodiments, a terminal device may be configured to send and / or receive information without direct human interaction. For example, when triggered by an internal or external event, or in response to a request from a communication network, a terminal device may be designed to send information to the network according to a predetermined schedule. Alternatively, a UE may represent a device that is intended to be sold to a human user or operated by a human user but may not initially be associated with a specific human user.

[0119] As another example, in an Internet of Things (IoT) scenario, a terminal device may represent a machine or other device that performs monitoring and / or measurement, and sends the results of such monitoring and / or measurement to another terminal device and / or network device. In this case, the terminal device may be a machine-to-machine (M2M) device, which may be referred to as a machine type communication (MTC) device in the 3GPP context. As a specific example, the terminal device may be a UE that implements the 3GPP Narrowband Internet of Things (NB-IoT) standard. Specific examples of such machines or devices are sensors, metering devices (e.g., electricity meters, industrial machinery) or household or personal appliances (e.g., refrigerators, televisions), personal wearable devices (e.g., watches), etc. In other scenarios, a terminal device may represent a vehicle or other device that is capable of monitoring and / or reporting its operating status or other functions related to its operation.

[0120] References in the specification to "one embodiment," "an embodiment," "an exemplary embodiment," etc. indicate that the described embodiment may include a particular feature, structure, or characteristic, but not necessarily every embodiment includes the particular feature, structure, or characteristic. Furthermore, these phrases do not necessarily refer to the same embodiment. Furthermore, when a particular feature, structure, or characteristic is described in conjunction with an embodiment, whether or not explicitly described, it is considered to be within the knowledge of those skilled in the art to affect such feature, structure, or characteristic in relation to other embodiments.

[0121] It should be understood that although the terms "first" and "second" etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. For example, without departing from the scope of the exemplary embodiments, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed terms.

[0122] As used herein, the phrase "at least one of A and B" or "at least one of A or B" should be understood to mean "only A, only B, or both A and B". The phrase "A and / or B" should be understood to mean "only A, only B, or both A and B".

[0123] The terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the example embodiments. Unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" as used herein are also intended to include the plural forms. It will be further understood that when used herein, the terms "include", "comprise", "have", "have", "contain" and / or "cover" specify the presence of the features, elements and / or components, etc., but do not exclude the presence or addition of one or more other features, elements, components and / or combinations thereof.

[0124] Note that these terms used in this article are only used to facilitate description and to distinguish between nodes, devices or networks, etc. As technology develops, other terms with similar / same meanings may also be used.

[0125] In the following description and claims, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

[0126] Although the subject matter described in this article focuses on the mismatch problem for V-SMF and H-SMF roaming interworking, there are similar mismatch problems for scenarios where the I-SMF (intermediate SMF) and anchor SMF have different recovery capabilities or configurations.

[0127] The following mismatch problems can be considered.

[0128] V-SMF failure: - VPLMN does not deploy SMF set, no problem. -VPLMN deploys SMF set, and V-SMF supports SMF set functions o H-SMF supports SMF sets, and normal set processing is possible without any issues. o H-SMF does not support SMF Sets (the HPLMN may or may not deploy SMF Sets for non-roaming users), Mismatch between V-SMF and H-SMF - VPLMN deploys SMF set, but V-SMF does not support SMF set function o H-SMF supports SMF set, there is no match between V-SMF and H-SMF o H-SMF does not support SMF Sets (the HPLMN may or may not deploy SMF Sets for non-roaming users), Mismatch between AMF and V-SMF

[0129] H-SMF failure: - HPLMN does not deploy SMF set, no problem. -HPLMN deploys SMF set and H-SMF supports SMF set functions o V-SMF supports SMF sets, and normal set processing is available without any issues. o V-SMF does not support SMF Sets (VPLMN may or may not deploy SMF Sets for non-roaming users), There is a mismatch between the V-SMF and the H-SMF. -HPLMN deploys SMF set, but H-SMF does not support SMF set function o V-SMF supports SMF set, there is no match between V-SMF and H-SMF o The V-SMF does not support the SMF set (the VPLMN may or may not deploy the SMF set for non-roaming users), and there is a mismatch between the H-SMF and other NFs in the HPLMN such as UDM (Unified Data Management) or PCF (Policy Control Function).

[0130] Consider the following failure scenario. V-SMF failure: 1. V-SMF supports the SMF set for roaming interfaces (proposes to introduce new features for Nsmf_PDUSession service) aH-SMF supports SMF sets and applies normal SMF set logic with no changes. bH-SMF does not support SMF sets. H-SMF can reselect another V-SMF in the same set by AMF. The UE may keep the context waiting for the potential re-establishment triggered by the UE, or delete the affected PDU Session (legacy behavior for H-SMF and AMF). If the PDU Session is to be deleted, the AMF may request the UE to reactivate the PDU Session according to the local configuration; 2. V-SMF does not support SMF sets: a. Regardless of whether H-SMF supports SMF Sets, H-SMF shall delete the affected PDU Sessions. To cover 1b and 2a, it would be better to define another new feature so that AMF and H-SMF will know that it is supported. H-SMF failure: 1.H-SMF does not support SMF set, V-SMF releases PDU session 2. H-SMF supports SMF set (it is recommended to introduce new features for Nsmf_PDUSession service) aV-SMF supports SMF sets and applies the reselection of another SMF in the same SMF set; bV-SMF does not support SMF Set, V-SMF releases the affected PDU Session.

[0131] Figure 1 A first failure scenario according to an embodiment of the present disclosure is shown.

[0132] In the first failure scenario, the VPLMN deploys an SMF set, the V-SMF supports the SMF set, and the H-SMF does not support the SMF set.

[0133] like Figure 1As shown in , after detecting a V-SMF failure (i.e., vSMF1 failure), if the H-SMF does not support the SMF set, the H-SMF (i.e., hSMF1) will initiate the release of the associated PDU session. However, since the V-SMF (i.e., vSMF1 failure) supports the SMF set, the AMF in the VPLMN will reselect another SMF in the same SMF set A (taking vSMF2 as an example), and then the reselected vSMF2 will rebuild the SM (session management) context and initiate an update request to the H-SMF (i.e., hSMF1). However, the update request will not succeed because the H-SMF (i.e., hSMF1) has already triggered the release of the corresponding PDU session after detecting the vSMF1 failure. Since vSMF2 has no clues about the PDU session status on the original H-SMF side, V-SMF2 can only release its local SM context on a session basis after receiving an error response from the H-SMF (i.e., hSMF1). Therefore, reactivating all related PDU sessions takes time and affects service availability.

[0134] Figure 1 The messages shown may be the same as or similar to corresponding messages described in 3GPP TS 23.502 V17.2.1, the disclosure of which is incorporated herein by reference in its entirety.

[0135] Figure 2 A second failure scenario according to an embodiment of the present disclosure is shown.

[0136] In the second failure scenario, the VPLMN deploys the SMF set, but the V-SMF does not support the SMF set, while the H-SMF supports the SMF set.

[0137] Note that this situation may occur during the development phase when the SMF provider in the VPLMN has implemented the SMF set functionality for the SMF role but has not yet implemented the SMF set functionality for the V-SMF role.

[0138] like Figure 2As shown in , after detecting the failure of vSMF1, the AMF in the VPLMN reselects another SMF in the same SMF set A (taking vSMF2 as an example) for the established PDU session. The AMF sends a Nsmf_PDUSession_UpdateSMContext request to the reselected vSMF2. However, the reselected vSMF2 has no logic to restore the session context and trigger a PDU session update request to hSMF1 using the updated callbackUri of vSMF2, because the V-SMF does not support roaming recovery based on SMF sets. Instead, the reselected V-SMF rejects the Nsmf_PDUSession_UpdateSMContext request with an error response. Therefore, the AMF in the VPLMN can only trigger PDU session reactivation on a session basis after receiving an error response from v-SMF2. Reactivating all related PDU sessions takes time and affects service availability. If the reactivation selects an H-SMF in a different SMF set, ghost sessions may also exist on the original H-SMF.

[0139] Figure 2 The messages shown in may be the same as or similar to the corresponding messages described in 3GPP TS 23.502 V17.2.1, the disclosure of which is incorporated herein by reference in its entirety.

[0140] Figure 3 A third failure scenario according to an embodiment of the present disclosure is shown.

[0141] In the third failure scenario, the VPLMN deploys the SMF set, but the V-SMF does not support the SMF set, and the H-SMF does not support the SMF set.

[0142] like Figure 3As shown in , if the H-SMF does not support roaming recovery based on the SMF set, the H-SMF initiates the release of the associated PDU session. Because the VPLMN deploys the SMF set, the AMF in the VPLMN reselects another SMF (taking vSMF2 as an example) in the same SMF set A. The AMF sends a Nsmf_PDUSession_UpdateSMContext request to the reselected vSMF2. Similar to the second failure scenario, the reselected vSMF2 has no logic to restore the session context and trigger a PDU session update request to hSMF1 using the updated callbackUri of vSMF2, because the V-SMF does not support roaming recovery based on the SMF set. Instead, the reselected V-SMF will reject the Nsmf_PDUSession_UpdateSMContext request with an error response. Therefore, the AMF in the VPLMN can only trigger PDU session reactivation on a session basis after receiving an error response from the V-SMF. Reactivating all related PDU sessions takes time and affects service availability.

[0143] Figure 3 The messages shown may be the same as or similar to corresponding messages described in 3GPP TS 23.502 V17.2.1, the disclosure of which is incorporated herein by reference in its entirety.

[0144] Figure 4 A fourth failure scenario according to an embodiment of the present disclosure is shown.

[0145] In the fourth failure scenario, the HPLMN deploys the SMF set, the H-SMF supports the SMF set, and the V-SMF does not support the SMF set.

[0146] like Figure 4 As shown in , when the V-SMF in the VPLMN detects that hSMF1 in the SMF set B of the HPLMN fails, the V-SMF for the existing PDU session does not reselect other SMFs in SMF set B because the V-SMF does not support the SMF set function. Instead, the V-SMF triggers the SM context release to the AMF, and then the AMF triggers the PDU session reactivation. However, if the PDU reactivation selects an SMF in a different SMF set, a ghost session may exist in SMF set B.

[0147] like Figure 4 The messages shown may be the same as or similar to corresponding messages described in 3GPP TS 23.502 V17.2.1, the disclosure of which is incorporated herein by reference in its entirety.

[0148] Figure 5 A fifth failure scenario according to an embodiment of the present disclosure is shown.

[0149] In the fifth failure scenario, the HPLMN deploys the SMF set, but the H-SMF does not support the SMF set, while the V-SMF supports the SMF set.

[0150] The fifth failure scenario may occur during the development phase, when the SMF supplier in the HPLMN has implemented the SMF set functionality for the SMF role, but has not yet implemented the SMF set functionality for the H-SMF role.

[0151] like Figure 5 As shown in , there are problems with requests initiated by both VPLMN and HPLMN.

[0152] In VPLMN, after detecting the failure of hSMF1, V-SMF reselects another SMF in the same SMF set B (taking hSMF2 as an example) for the established PDU session, and sends a PDU session update request to the reselected hSMF2. However, hSMF2 has no logic to restore the session context, so hSMF2 rejects the PDU session update request with "CONTEXT_NOT_FOUND". Therefore, the AMF in VPLMN can only trigger PDU session reactivation on a session basis after receiving an error response from V-SMF. Reactivating all related PDU sessions takes time and affects service availability. If an H-SMF in a different SMF set is selected for reactivation, a ghost session may also exist on the original H-SMF.

[0153] In the HPLMN, the surrounding 5GC (5G core network) NFs consider the H-SMF to support the SMF set. For example, the PCF reselects another H-SMF in the same SMF set after detecting the failure of hSMF1, but the reselected H-SMF does not apply logic to rebuild the session context and process the notification request from the PCF. Depending on the specific implementation, if the H-UPF (home UPF) does not release the context associated with the failed hSMF1 (i.e., the H-UPF considers hSMF1 to be in the SMF set), the downlink data can reach the V-UPF and the network-triggered service request process can succeed. However, since the H-SMF does not process the UpdateNotify request from the PCF (containing PCC rules for MT calls), the call cannot be established.

[0154] Figure 5 The messages shown in may be the same as or similar to the corresponding messages described in 3GPP TS 23.502 V17.2.1, the disclosure of which is incorporated herein by reference in its entirety.

[0155] Figure 6 A sixth failure scenario according to an embodiment of the present disclosure is shown.

[0156] In the sixth failure scenario, the HPLMN deploys the SMF set, but the H-SMF does not support the SMF set, and the V-SMF does not support the SMF set.

[0157] like Figure 6 As shown in , when the vSMF in the VPLMN detects that hSMF1 in the SMF set B of the HPLMN fails, the vSMF triggers the SM context release to the AMF, and then the AMF triggers the PDU session reactivation. However, if the PDU reactivation selects an SMF in a different SMF set, a ghost session may appear in SMF set B.

[0158] Depending on the implementation, if the H-UPF does not release the context associated with the failed hSMF1 (i.e., the H-UPF believes that hSMF1 is in the SMF set), the downlink data will be sent to the V-UPF (visited V-UPF), but if the vSMF has released the associated context, a GTP-U (GPRS (General Packet Radio Service) User Plane Tunneling Protocol) error indication will be returned. The H-UPF may send an error indication report to other available hSMFs in SMF Set B. The hSMF behavior depends on the implementation. The hSMF may or may not be able to trigger context cleanup with the PCF and other 5GC NFs in the HPLMN.

[0159] Figure 6 The messages shown in may be the same as or similar to the corresponding messages described in 3GPP TS 23.502 V17.2.1, the disclosure of which is incorporated herein by reference in its entirety.

[0160] In order to overcome or alleviate at least one of the above problems or other problems, it is recommended to introduce a roaming resumption indication and a re-establishment indication to negotiate the capabilities between the VPLMN and the HPLMN so that the V-SMF and the H-SMF can make decisions based on the capabilities of the other end when a V-SMF or H-SMF failure occurs.

[0161] In an embodiment, a "vSMF roaming resumption indication" is introduced, which means that the V-SMF supports roaming resumption based on an SMF set (including a local set for the V-SMF and a peer set for the H-SMF).

[0162] In an embodiment, "hSMF roaming resumption indication" is introduced, which means that H-SMF supports roaming resumption based on SMF sets (including local set for H-SMF and peer set for V-SMF).

[0163] In an embodiment, a "vSMF reconstruction indication" is introduced, which means the ability to support PDU session reconstruction in the event of a V-SMF failure. It requires AMF, V-SMF and H-SMF to support such a capability so that PDU session reconstruction can work in the event of a V-SMF failure.

[0164] In an embodiment, if the above indication is not included in the request / response message and the SMF profile, it should be processed as the corresponding function for roaming interworking is not supported.

[0165] In an embodiment, if the resource context of V-SMF and H-SMF is uniquely bound to a specific NF service instance (i.e., there is no recovery), V-SMF and H-SMF are enabled to exchange this information, which can be achieved through an alternative scheme as described below.

[0166] In an embodiment, through the NF service discovery process for SMF selection, the AMF can determine whether the resources served by the candidate V-SMF or H-SMF are uniquely bound to a specific NF service instance, that is, there is no recovery if a failure occurs. It is then recommended that the AMF fill this information to the V-SMF and H-SMF in a new attribute in the Create SmContext request towards the V-SMF, for example, the new attribute can be preferably called vSmfNoResilence and hsmfNoResilence, which can be defined as a Boolean value with a default value of 0, and the V-SMF should forward these new attributes in the Create PDU Session request to the H-SMF.

[0167] In an embodiment, the V-SMF includes a new vSmfNoResilence in the Create PDU Session Request message, and the H-SMF includes a new hsmfNoResilence in the corresponding response message.

[0168] Using the proposed solution, it gives the peer SMF explicit information whether the SMF set is supported (at least for reselection in case of peer failure) and whether the resources it serves can be shared by at least one or more alternative SMFs.

[0169] Although the subject matter described herein can be implemented in any suitable type of system using any suitable components, the embodiments disclosed herein are directed to systems that conform to Figure 7 For simplicity, the communication system of the exemplary system architecture shown is described. Figure 7The system architecture of FIG. 1 depicts only some exemplary elements. In practice, the communication system may also include any additional elements suitable for supporting communication between terminal devices or between a wireless device and another communication device (e.g., a landline phone, a service provider, or any other network node or terminal device). The communication system may provide communication and various types of services to one or more terminal devices to facilitate the terminal devices to access and / or use services provided by or via the communication system.

[0170] Figure 7 The roaming 5G system architecture according to an embodiment of the present disclosure is schematically shown. For example, Figure 7 The architecture is similar to that described in 3GPP TS23.501V17.2.0 Figure 4 .2.4-1, the disclosure of which is incorporated herein by reference in its entirety. Figure 7 The system architecture may include some exemplary elements, such as AUSF, AMF, DN (data network), NEF, NRF, NSSF, PCF, SMF, UDM, UPF, AF, UE, (R)AN, SCP (service communication agent), NSACF (network slice admission control function), vSEPP (visit security edge protection agent), hSEPP (home security edge protection agent), etc.

[0171] According to an exemplary embodiment, Figure 7 As shown, the UE can establish a signaling connection with the AMF through reference point N1. The signaling connection can realize the NAS (non-access layer) signaling exchange between the UE and the core network, including the signaling connection between the UE and the (R)AN and the N2 connection between the (R)AN and the AMF for the UE. The (R)AN can communicate with the UPF through reference point N3. The UE establishes a protocol data unit (PDU) session to the DN (data network, such as an operator network or the Internet) through the UPF through reference point N6.

[0172] like Figure 7 As further shown in FIG. 1 , the exemplary system architecture also includes service-based interfaces (e.g., Nnrf, Nnef, Nausf, Nudm, Npcf, Namf, Nnsacf, and Nsmf) such as those exposed by NFs (e.g., NRF, NEF, AUSF, UDM, PCF, AMF, NSACF, and SMF). In addition, Figure 7 Some reference points such as N1, N2, N3, N4, N6, N32 and N9 are also shown, which can support the interaction between NF services in NF. For example, these reference points can be implemented through corresponding NF service-based interfaces and by specifying some NF service consumers and providers and their interactions to perform specific system processes.

[0173] Figure 7 The various NFs shown in the figure may be responsible for functions such as session management, mobility management, authentication, security, etc. AUSF, AMF, DN, NEF, NRF, NSSF, PCF, SMF, UDM, UPF, AF, UE, (R)AN, SCP, NSACF may include, for example, the functions defined in clause 6.2 of 3GPP TS23.501 V17.2.0.

[0174] Figure 8 A flow chart of a method according to an embodiment of the present disclosure is shown, which may be performed by a device implemented in an access and mobility function (AMF), or by a device at an AMF, or by a device implemented as an AMF, or by a device communicatively coupled to an AMF. Therefore, the device may provide components or modules for completing various parts of method 800 and components or modules for completing other processes together with other components.

[0175] At block 802, the AMF may obtain first information regarding whether a first session management function (SMF) supports a first capability for protocol data unit (PDU) session reconstruction in the event of a failure of the first SMF.

[0176] For example, the first capability may mean the capability of supporting PDU session reconstruction in case of V-SMF failure.

[0177] The AMF may obtain the first information in various ways. For example, the first SMF may register the first information in the NRF. In this case, the AMF may obtain the first information through NRF discovery. As another example, when the first SMF may send a message containing the first information to the AMF, the AMF may obtain the first information from the first SMF. As another example, the first information may be pre-configured in the network.

[0178] At block 804, the AMF may obtain second information regarding whether the second SMF supports the first capability.

[0179] The AMF may obtain the second information in various ways. For example, the second SMF may register the second information in the NRF. In this case, the AMF may obtain the second information through NRF discovery. As another example, when the second SMF may send a message containing the second information to the AMF, the AMF may obtain the second information from the second SMF. As another example, the second information may be pre-configured in the network.

[0180] At block 806, the AMF may send a PDU session creation session management (SM) context request to the first SMF. When the AMF, the first SMF, and the second SMF all support the first capability, the PDU session creation SM context request includes a first indication of supporting the first capability.

[0181] The PDU Session Create SM Context Request may create an AMF-SMF association to support the PDU Session. In an embodiment, the PDU Session Create SM Context Request may be the same or similar to the Nsmf_PDUSession_CreateSMContext request described in 3GPP TS23.502 V17.2.1.

[0182] In an embodiment, when any one of the AMF, the first SMF or the second SMF does not support the first capability, the first indication is not included in the PDU session create SM context request.

[0183] Fig. 9 A flowchart of obtaining first information about whether a first SMF supports a first capability according to an embodiment of the present disclosure is shown.

[0184] In an embodiment, the first SMF may register the first information in the NRF.

[0185] At block 902, the AMF may send a network function (NF) discovery request to a network repository function (NRF).

[0186] At block 904, the AMF may receive a NF discovery response including first information from the NRF.

[0187] In an embodiment, the NF Discovery Request / Response may be the same as the Nnrf_NFDiscovery_Request and Nnrf_NFDiscovery_Request Response described in 3GPP TS 23.502 V17.2.1.

[0188] Fig.10 A flowchart of obtaining second information about whether the second SMF supports the first capability according to an embodiment of the present disclosure is shown.

[0189] In an embodiment, the second SMF may register the second information in the NRF.

[0190] At block 1002, the AMF may send a network function (NF) discovery request to a network repository function (NRF).

[0191] At block 1004, the AMF may receive a NF discovery response including second information from the NRF.

[0192] In an embodiment, the NF Discovery Request / Response may be the same as the Nnrf_NFDiscovery_Request and Nnrf_NFDiscovery_Request Response described in 3GPP TS 23.502 V17.2.1.

[0193] Fig.11 A flowchart of a method according to another embodiment of the present disclosure is shown, which can be performed by a device implemented in AMF, or performed by a device at AMF, or performed by a device implemented as AMF, or performed by a device communicatively coupled to AMF. Therefore, the device can provide components or modules for completing various parts of method 1100 and components or modules for completing other processes together with other components. For the parts that have been described in the above embodiments, their description is omitted here for brevity.

[0194] At box 1102, the AMF can obtain first information about whether the first SMF supports a first capability of PDU session reconstruction in the event of a failure of the first SMF.

[0195] At block 1104, the AMF may obtain second information regarding whether the second SMF supports the first capability.

[0196] At block 1106, the AMF may send a PDU session creation SM context request to the first SMF. When the AMF, the first SMF, and the second SMF all support the first capability, the PDU session creation SM context request includes a first indication of supporting the first capability.

[0197] At block 1108, the AMF may receive a PDU Session Create SM Context Response from the first SMF. When the first SMF supports the first capability, the PDU Session Create SM Context Response includes a first indication. When the first SMF supports a local NF set for the first SMF and a peer NF set for the second SMF, the PDU Session Create SM Context Response includes an indication that the first SMF supports a local NF set for the first SMF and a peer NF set for the second SMF.

[0198] It should be noted that since the AMF can obtain the first indication and the indication that the first SMF supports the local NF set for the first SMF and the peer NF set for the second SMF in other ways (for example, through NRF discovery), in other embodiments, the PDU session creation SM context response may not include the first indication and the indication that the first SMF supports the local NF set for the first SMF and the peer NF set for the second SMF.

[0199] In an embodiment, when the first SMF supports a local NF set for the first SMF, it may mean that the first SMF supports non-roaming PDU session resumption based on the SMF set. For example, when the first SMF is a V-SMF and the first SMF supports a local SMF set for a user or UE in a VPLMN, it means that the first SMF supports non-roaming PDU session resumption based on the SMF set.

[0200] In an embodiment, when the first SMF supports a peer NF set for a second SMF, it may mean that the first SMF supports roaming PDU session resumption based on an SMF set. For example, when the first SMF is a V-SMF and the first SMF supports a peer SMF set for a user or UE in the HPLMN, it may mean that the first SMF supports roaming PDU session resumption based on an SMF set.

[0201] In an embodiment, when the first SMF supports a local NF set for the first SMF, it may mean that the first SMF supports SMF set based PDU session recovery, where the PDU session is established with the first SMF instead of with other SMFs in other networks or network slices.

[0202] In an embodiment, when a first SMF supports a peer NF set for a second SMF, it may mean that the first SMF supports SMF set-based PDU session recovery, where the PDU session is established with the first SMF and the second SMF.

[0203] Fig.12 A flowchart of a method according to another embodiment of the present disclosure is shown, which can be performed by a device implemented in AMF, or performed by a device at AMF, or performed by a device implemented as AMF, or performed by a device communicatively coupled to AMF. Therefore, the device can provide components or modules for completing various parts of method 1200 and components or modules for completing other processes together with other components. For the parts that have been described in the above embodiments, their description is omitted here for brevity.

[0204] At block 1202, the AMF may obtain third information regarding whether the first SMF supports a peer NF set for the second SMF.

[0205] In an embodiment, the AMF may obtain third information about whether the first SMF supports a local NF set for the first SMF and a peer NF set for the second SMF.

[0206] The AMF may obtain the third information in various ways. For example, the first SMF may register the third information in the NRF. In this case, the AMF may obtain the third information through NRF discovery. As another example, when the first SMF may send a message containing the third information to the AMF, the AMF may obtain the third information from the first SMF. As another example, the third information may be pre-configured in the network.

[0207] At block 1204, the AMF may obtain fourth information regarding whether the second SMF supports the peer NF set for the first SMF.

[0208] In an embodiment, the AMF may obtain fourth information about whether the second SMF supports a local network function (NF) set for the second SMF and a peer NF set for the first SMF.

[0209] In an embodiment, when the second SMF supports a local NF set for the second SMF, it may mean that the second SMF supports non-roaming PDU session resumption based on the SMF set. For example, when the second SMF is an H-SMF and the second SMF supports a local SMF set for a user or UE in the HPLMN, it means that the second SMF supports non-roaming PDU session resumption based on the SMF set.

[0210] In an embodiment, when the second SMF supports a peer NF set for the first SMF, it may mean that the second SMF supports roaming PDU session resumption based on the SMF set. For example, when the second SMF is an H-SMF and the second SMF supports a peer SMF set for a user or UE in a VPLMN. This means that the second SMF supports roaming PDU session resumption based on the SMF set.

[0211] In an embodiment, when the second SMF supports a local NF set for the second SMF, it may mean that the second SMF supports SMF set based PDU session recovery, where the PDU session is established with the second SMF instead of with other SMFs in other networks or network slices.

[0212] In an embodiment, when the second SMF supports a peer NF set for the first SMF, it may mean that the second SMF supports SMF set-based PDU session recovery, where the PDU session is established with the first SMF and the second SMF.

[0213] The AMF may obtain the fourth information in various ways. For example, the second SMF may register the fourth information in the NRF. In this case, the AMF may obtain the fourth information through NRF discovery. As another example, when the second SMF may send a message containing the fourth information to the AMF, the AMF may obtain the fourth information from the second SMF. As another example, the fourth information may be pre-configured in the network.

[0214] At block 1206, the AMF may send a PDU session creation session management (SM) context request including the third information and / or the fourth information to the first SMF.

[0215] In an embodiment, the third information is a Boolean value and / or the fourth information is a Boolean value.

[0216] For example, the third information may preferably be called vSmfNoResilence. The fourth information may preferably be called SMFNoResilence. The third information may be defined as a Boolean value. The default value may be 0. The fourth information may be defined as a Boolean value. The default value may be 0.

[0217] Fig.13 A flowchart of obtaining third information about whether a first SMF supports a local NF set for the first SMF and a peer NF set for a second SMF according to an embodiment of the present disclosure is shown.

[0218] In an embodiment, the first SMF may register the third information in the NRF.

[0219] At block 1302, the AMF may send a network function (NF) discovery request to a network repository function (NRF).

[0220] At block 1304, the AMF may receive a NF discovery response including third information from the NRF.

[0221] In an embodiment, the NF Discovery Request / Response may be the same as the Nnrf_NFDiscovery_Request and Nnrf_NFDiscovery_Request Response described in 3GPP TS 23.502 V17.2.1.

[0222] Fig.14 A flowchart of obtaining fourth information about whether the second SMF supports a local NF set for the second SMF and a peer NF set for the first SMF according to an embodiment of the present disclosure is shown.

[0223] In an embodiment, the second SMF may register the fourth information in the NRF.

[0224] At block 1402, the AMF may send a network function (NF) discovery request to a network repository function (NRF).

[0225] At block 1404, the AMF may receive a NF discovery response including fourth information from the NRF.

[0226] In an embodiment, the NF Discovery Request / Response may be the same as the Nnrf_NFDiscovery_Request and Nnrf_NFDiscovery_Request Response described in 3GPP TS 23.502 V17.2.1.

[0227] Fig.15 A flowchart of a method according to another embodiment of the present disclosure is shown, which can be performed by a device implemented in AMF, or performed by a device at AMF, or performed by a device implemented as AMF, or performed by a device communicatively coupled to AMF. Therefore, the device can provide components or modules for completing various parts of method 1500 and components or modules for completing other processes together with other components. For the parts that have been described in the above embodiments, their description is omitted here for brevity.

[0228] In an embodiment, the AMF, the first SMF, and the second SMF support the first capability. The first SMF supports a local NF set for the first SMF and supports a peer NF set for the second SMF. The second SMF does not support a local NF set for the second SMF and a peer NF set for the first SMF.

[0229] At block 1502, the AMF may detect a first SMF failure when receiving a notification from the NRF or using a PING frame. The AMF may receive a NF status notification request from the NRF, the request including information indicating the first SMF failure. For example, the NF status notification request may be a Nnrf_NFManagement_NFStatusNotify request as described in 3GPP TS23.502 V17.2.1.

[0230] At block 1504, the AMF may reselect an SMF within the peer NF set to replace the first SMF.

[0231] At block 1506, the AMF may send a PDU session update SM context request to the SMF used to replace the first SMF. The PDU session update SM context request may be a Nsmf_PDUSession_UpdateSMContext request as described in 3GPP TS23.502 V17.2.1.

[0232] In an embodiment, the AMF includes a vSMF recovery indication in a CreateSMContext request towards the selected V-SMF, and the V-SMF includes a vSMF roaming recovery indication and a vSMF re-establishment indication in a PDUSessionCreateRequest towards the H-SMF.

[0233] In an embodiment, when a first SMF failure occurs, the second SMF shall maintain the associated PDU session and wait for recovery. The AMF triggers reselection of the first SMF for the established SM context in an update request to trigger recovery, and the reselected first SMF includes updated vSMFId and vSMFPduSessionUri in an update request toward the second SMF.

[0234] Fig.16 A flowchart of a method according to another embodiment of the present disclosure is shown, which can be performed by a device implemented in AMF, or performed by a device at AMF, or performed by a device implemented as AMF, or performed by a device communicatively coupled to AMF. Therefore, the device can provide components or modules for completing various parts of method 1600 and components or modules for completing other processes together with other components. For the parts that have been described in the above embodiments, their description is omitted here for brevity.

[0235] In an embodiment, the AMF, the first SMF and the second SMF support the first capability. The first SMF supports the local NF set for the first SMF, but does not support the peer NF set for the second SMF. The second SMF supports the local NF set for the second SMF and the peer NF set for the first SMF.

[0236] At block 1602, the AMF may detect a first SMF failure upon receiving a notification from the NRF or using a PING frame.

[0237] At block 1604, the AMF may reselect an SMF to replace the first SMF.

[0238] At block 1606, the AMF may send a create SM context request to the SMF for reestablishing the PDU session.

[0239] In an embodiment, when the SMF used to replace the first SMF supports the first capability, the PDU session create SM context request includes a first indication.

[0240] In an embodiment, the Create SM Context Request includes information on whether the reselected SMF supports the Peer NF Set for the second SMF and / or information on whether the second SMF supports the Peer NF Set for the reselected SMF.

[0241] In an embodiment, the AMF includes a vSMF reestablishment indication in the CreateSMContext request towards the selected vSMF. The V-SMF relays the received vSMF reestablishment indication to the H-SMF in a PDUSessionCreateRequest, but the V-SMF does not include a vSMF roaming resumption indication because the vSMF does not support SMF sets.

[0242] In an embodiment, when the selected V-SMF fails, the H-SMF shall maintain the associated PDU session and wait for vSMF to rebuild. The AMF triggers PDU session reactivation to rebuild the affected PDU session, and the reselected V-SMF sends a PDUSessionCreateRequest to the original H-SMF. The H-SMF performs a Create onCreate to accept a new PDU session request.

[0243] Fig.17 A flowchart of a method according to another embodiment of the present disclosure is shown, which can be performed by a device implemented in AMF, or performed by a device at AMF, or performed by a device implemented as AMF, or performed by a device communicatively coupled to AMF. Therefore, the device can provide components or modules for completing various parts of method 1700 and components or modules for completing other processes together with other components. For the parts that have been described in the above embodiments, their description is omitted here for brevity.

[0244] In an embodiment, the AMF, the first SMF and the second SMF support the first capability. The first SMF supports the local NF set for the first SMF, but does not support the peer NF set for the second SMF. The second SMF does not support the local NF set for the second SMF and the peer NF set for the first SMF.

[0245] At block 1702, the AMF may detect a first SMF failure upon receiving a notification from the NRF or using a PING frame.

[0246] At block 1704, the AMF may reselect an SMF to replace the first SMF.

[0247] At block 1706, the AMF may send a create SM context request to the SMF for reestablishing the PDU session.

[0248] In an embodiment, the Create SM Context Request includes information on whether the reselected SMF supports the Peer NF Set for the second SMF and / or information on whether the second SMF supports the Peer NF Set for the reselected SMF.

[0249] In an embodiment, when the SMF used to replace the first SMF supports the first capability, the PDU session create SM context request includes a first indication.

[0250] Fig.18 A flowchart of a method according to another embodiment of the present disclosure is shown, which can be performed by a device implemented in AMF, or by a device at AMF, or by a device implemented as AMF, or by a device communicatively coupled to AMF. Therefore, the device can provide components or modules for completing various parts of method 1800 and components or modules for completing other processes together with other components. For the parts that have been described in the above embodiments, their description is omitted here for brevity.

[0251] In an embodiment, the first SMF does not support the first capability. The first SMF does not support a local NF set for the first SMF and a peer NF set for the second SMF. The second SMF supports a local NF set for the second SMF and a peer NF set for the first SMF.

[0252] At block 1802, the AMF may receive a PDU session SM context status notification from the first SMF, the notification including a resource status set to released and a release reason due to reactivation.

[0253] At block 1804, the AMF may send a create SM context request to the first SMF for reestablishing the PDU session.

[0254] In an embodiment, the Create SM Context Request includes information about whether the first SMF supports a Peer NF Set for the reselected second SMF and / or information about whether the reselected second SMF supports a Peer NF Set for the first SMF.

[0255] Fig.19 A flowchart of a method according to another embodiment of the present disclosure is shown, which can be performed by a device implemented in AMF, or performed by a device at AMF, or performed by a device implemented as AMF, or performed by a device communicatively coupled to AMF. Therefore, the device can provide components or modules for completing various parts of method 1900 and components or modules for completing other processes together with other components. For the parts that have been described in the above embodiments, their description is omitted here for brevity.

[0256] In an embodiment, the AMF, the first SMF and the second SMF support the first capability. The first SMF supports a local NF set for the first SMF and a peer NF set for the second SMF. The second SMF supports a local NF set for the second SMF, but does not support a peer NF set for the first SMF.

[0257] At block 1902, the AMF may receive a PDU session SM context status notification from the first SMF, the notification including a resource status set to released and a release reason due to reactivation.

[0258] At block 1904, the AMF may send a create SM context request to the first SMF for reestablishing the PDU session.

[0259] In an embodiment, the Create SM Context Request includes information about whether the first SMF supports a Peer NF Set for the reselected second SMF and / or information about whether the reselected second SMF supports a Peer NF Set for the first SMF.

[0260] In an embodiment, when the AMF, the first SMF and the reselected SMF used to replace the second SMF support the first capability, the PDU session create SM context request includes a first indication.

[0261] Fig.20a A flowchart of a method according to another embodiment of the present disclosure is shown, which can be performed by a device implemented in AMF, or by a device at AMF, or by a device implemented as AMF, or by a device communicatively coupled to AMF. Therefore, the device can provide components or modules for completing various parts of method 2000 and components or modules for completing other processes together with other components. For the parts that have been described in the above embodiments, their description is omitted here for brevity.

[0262] In an embodiment, the first SMF does not support the first capability. The first SMF does not support the local NF set for the first SMF and the peer NF set for the second SMF. The second SMF supports the local NF set for the second SMF, but does not support the peer NF set for the first SMF.

[0263] At block 2002, the AMF may receive a PDU session SM context status notification from the first SMF, the notification including a resource status set to released and a release reason due to reactivation.

[0264] At box 2004, the AMF may send a create SM context request to the first SMF for re-establishing the PDU session with the first SMF.

[0265] In an embodiment, the Create SM Context Request includes information on whether the first SMF supports a peer NF for the reselected second SMF set and / or information on whether the reselected second SMF supports a peer NF for the first SMF set.

[0266] In an embodiment, the first SMF is a visited SMF and the second SMF is a home SMF.

[0267] In an embodiment, the first SMF is an intermediate SMF and the second SMF is an anchor SMF.

[0268] Fig.20b A flow chart of a method according to another embodiment of the present disclosure is shown, which can be performed by a device implemented in AMF, or by a device at AMF, or by a device implemented as AMF, or by a device communicatively coupled to AMF. Therefore, the device can provide components or modules for completing various parts of method 2010 and components or modules for completing other processes together with other components. For the parts that have been described in the above embodiments, their description is omitted here for brevity.

[0269] At box 2012, the AMF can obtain fifth information about whether there are two or more SMFs in the peer NF set for the first SMF.

[0270] At box 2014, the AMF can obtain sixth information about whether there are two or more SMFs in the peer NF set for the second SMF.

[0271] At box 2016, the AMF may send a PDU SM context request including the fifth information and / or the sixth information to the first SMF.

[0272] In an embodiment, the third information and the sixth information are represented by a single parameter, and the fourth information and the fifth information are represented by a single parameter.

[0273] For example, the roaming recovery indication should actually mean supporting local sets and peer sets. The new content to be added is to indicate that there are multiple vSMFs in the same vSMF set and multiple hSMFs in the same hSMF set. The AMF discovers that there are multiple vSMFs in the same vSMF set and / or multiple hSMFs in the hSMF set, and this information is sent by the AMF to the vSMF. This information can be called "vSMF set indication" and "hSMF set indication". The vSMF forwards the vSMF set indication to the hSMF.

[0274] Fig.21a A flowchart of a method according to another embodiment of the present disclosure is shown, which can be performed by a device implemented in a first SMF, or by a device at the first SMF, or by a device implemented as a first SMF, or by a device communicatively coupled to the first SMF. Therefore, the device can provide components or modules for completing various parts of the method 2100 and components or modules for completing other processes together with other components. For the parts that have been described in the above embodiments, their description is omitted here for brevity.

[0275] At box 2102, the first SMF can receive a PDU session creation SM context request from an access and mobility function (AMF).

[0276] At block 2104, the first SMF may send a PDU session creation request to the second SMF.

[0277] At block 2106, the first SMF may receive a PDU session creation response from the second SMF.

[0278] In an embodiment, when the AMF, the first SMF and the second SMF support a first capability for PDU session reconstruction in the event of a failure of the first SMF, the PDU session create SM context request includes a first indication of support for the first capability.

[0279] In an embodiment, when the AMF, the first SMF and the second SMF support the first capability, the PDU session creation request includes a first indication.

[0280] In an embodiment, when the first SMF supports a local NF set for the first SMF and a peer NF set for the second SMF, the PDU session creation request further includes an indication that the first SMF supports the local NF set for the first SMF and the peer NF set for the second SMF.

[0281] In an embodiment, when the AMF, the first SMF and the second SMF support the first capability, the PDU session creation response includes a first indication.

[0282] In an embodiment, the first SMF supports a local NF set for the first SMF and a peer NF set for the second SMF, and the second SMF supports a local NF set for the second SMF and a peer NF set for the first SMF, and the PDU session creation response includes an indication that the second SMF supports a local NF set for the second SMF and a peer NF set for the first SMF.

[0283] In an embodiment, when any one of the AMF, the first SMF or the second SMF does not support the first capability, the first indication is not included in the PDU session create SM context request.

[0284] In an embodiment, when the second SMF supports the peer NF set for the first SMF, the PDU session creation response includes an indication that the second SMF supports the peer NF set for the first SMF.

[0285] In an embodiment, the PDU session creation SM context request includes third information about whether the first session management function (SMF) supports a peer network function (NF) set for the second SMF and / or fourth information about whether the second SMF supports a peer NF set for the first SMF, and the PDU session creation request includes the third information and / or the fourth information.

[0286] In an embodiment, the PDU session creation request includes information about whether the first SMF supports peer SMF reselection within the peer SMF set when a failure of the original peer SMF instance occurs.

[0287] In an embodiment, the PDU session creation response includes information about whether the second SMF supports peer SMF reselection within the peer SMF set when a failure of the original peer SMF instance occurs.

[0288] In some embodiments, to ensure that roaming recovery works end-to-end, it requires that both the vSMF and hSMF support both its own set of SMFs and the peer SMF set.

[0289] In some implementations, one's own SMF set may be referred to as a "roaming recovery indication" and the peer SMF set may be referred to as a "peer v / hSMF set support indication".

[0290] The meaning of its own SMF set ("roaming recovery indication") is two-fold: (1) supporting its own session context replication / backup in other SMF instances in the same set; (2) itself being deployed in the SMF set (multiple SMF instances are available in the SMF pool so that context replication / switching may be feasible after an SMF failure). Note that AMF can discover whether there are multiple instances in the same SMF set / pool when discovering vSMF and hSMF.

[0291] The meaning of "Peer SMF Set Support Indication" is a bit simple. It just means that the SMF supports peer SMF reselection within the peer SMF Set when the original SMF instance failure occurs.

[0292] Based on this principle, in the Create SM Context Request, AMF sends the "vSMF Roaming Recovery Indication" (its own vSMF set) and the "hSMF Roaming Recovery Indication" (its own hSMF set) to vSMF, and vSMF relays this information to hSMF. Through this exchange, vSMF knows whether the peer hSMF is deployed in the SMF set, and hSMF also knows whether vSMF is deployed in the SMF set. Please note that the "hSMF Roaming Recovery Indication" is a bit redundant between the vSMF and hSMF interfaces, because vSMF has already learned this from AMF in the Create SM Context Request. But there is no harm in conveying this information in the PDU Create Request / Response.

[0293] In an embodiment, the third information is a Boolean value and / or the fourth information is a Boolean value.

[0294] In an embodiment, the PDU session creation SM context request includes fifth information about whether there are two or more SMFs in the peer NF set for the first SMF and / or sixth information about whether there are two or more SMFs in the peer NF set for the second SMF, and the PDU session creation request includes the fifth information and / or the sixth information.

[0295] In an embodiment, the third information and the sixth information are represented by a single parameter, and the fourth information and the fifth information are represented by a single parameter.

[0296] For example, the roaming resumption indication should actually mean supporting the local set and the peer set. What is to be added is the indication of multiple vSMFs in the same vSMF set and multiple hSMFs in the same hSMF set. The vSMF and hSMF themselves can also detect this information. The vSMF and hSMF discover other members of the same set based on a proprietary implementation mechanism, and then the vSMF and hSMF can exchange this information.

[0297] Yet another possibility is to extend the concept of "vSMF Set Indication" and "hSMF Set Indication" to also cover the meaning of "vSMF Roaming Recovery Indication" and "hSMF Roaming Recovery Indication". Then just swap "vSMF Set Indication" and "hSMF Set Indication". This actually makes sense and is easy to implement, since vSMF Set Indication is always based on vSMF Recovery Indication, which also applies to hSMF. This solution actually replaces the parameter name Recovery Indication with Set Indication, and extends the concept that "Set Indication" means supporting local sets, peer sets, and also multiple members in the same set.

[0298] Figure 21bA flowchart of a method according to another embodiment of the present disclosure is shown, which can be performed by a device implemented in a first SMF, or by a device at the first SMF, or by a device implemented as a first SMF, or by a device communicatively coupled to the first SMF. Therefore, the device can provide components or modules for completing various parts of the method 2100 and components or modules for completing other processes together with other components. For the parts that have been described in the above embodiments, their description is omitted here for brevity.

[0299] At block 2112, the first SMF may determine sixth information regarding whether there are two or more SMFs in the peer NF set for the second SMF. The PDU session creation request includes the sixth information.

[0300] In an embodiment, the PDU session creation response includes fifth information about whether there are two or more SMFs in the peer NF set for the first SMF.

[0301] Fig. 22 A flowchart of a method according to another embodiment of the present disclosure is shown, and the method can be performed by a device implemented in a first SMF, or by a device at the first SMF, or by a device implemented as a first SMF, or by a device communicatively coupled to the first SMF. Therefore, the device can provide components or modules for completing various parts of the method 2200 and components or modules for completing other processes together with other components. For the parts that have been described in the above embodiments, their description is omitted here for brevity.

[0302] At box 2202, the first SMF may send a network function (NF) registration request including the NF profile of the first SMF to the NRF.

[0303] In an embodiment, the NF profile of the first SMF includes an indication of whether the first SMF supports the capability of PDU session reconstruction in the event of a failure of the first SMF.

[0304] In an embodiment, the NF profile of the first SMF includes an indication of whether the first SMF supports a local NF set for the first SMF and a peer NF set for the second SMF.

[0305] In an embodiment, the NF profile of the first SMF includes an indication of whether the first SMF supports a peer NF set for the second SMF (e.g., a vSMF roaming recovery indication).

[0306] Fig.23A flowchart of a method according to another embodiment of the present disclosure is shown, which can be performed by a device implemented in a first SMF, or by a device at the first SMF, or by a device implemented as a first SMF, or by a device communicatively coupled to the first SMF. Therefore, the device can provide components or modules for completing various parts of method 2300 and components or modules for completing other processes together with other components. For the parts that have been described in the above embodiments, their description is omitted here for brevity.

[0307] At block 2302, the first SMF may receive a PDU session create SM context request from an access and mobility function (AMF). Block 2302 is the same as block 2102.

[0308] At box 2304, the first SMF can send a PDU session creation SM context response to the AMF.

[0309] In an embodiment, when the first SMF supports the first capability, the PDU session create SM context response includes a first indication.

[0310] In an embodiment, when the first SMF supports a NF set for the first SMF and a peer NF set for the second SMF, the PDU Session Create SM Context Response includes an indication that the first SMF supports a local NF set for the first SMF and a peer NF set for the second SMF.

[0311] At block 2306 , the first SMF may send a PDU session creation request to the second SMF. Block 2306 is the same as block 2104 .

[0312] At block 2308, the first SMF may receive a PDU session creation response from the second SMF. Block 2308 is the same as block 2106.

[0313] Fig.24 A flowchart of a method according to another embodiment of the present disclosure is shown, which can be performed by a device implemented in a first SMF, or by a device at the first SMF, or by a device implemented as a first SMF, or by a device communicatively coupled to the first SMF. Therefore, the device can provide components or modules for completing various parts of method 2400 and components or modules for completing other processes together with other components. For the parts that have been described in the above embodiments, their description is omitted here for brevity.

[0314] In an embodiment, the first SMF does not support the first capability. The first SMF does not support a local NF set for the first SMF and a peer NF set for the second SMF. The second SMF supports a local NF set for the second SMF and a peer NF set for the first SMF.

[0315] At block 2402, the first SMF may receive a NF status notification request from the NRF, the NF status notification request including information indicating a second SMF failure. Alternatively, the first SMF may detect the second SMF failure via a PING frame or any other suitable means.

[0316] At box 2404, the first SMF may send a PDU session SM context status notification to the AMF, which includes a resource status set to released and a release reason due to reactivation.

[0317] At block 2406, the first SMF may receive a PDU session create SM context request from the AMF.

[0318] At block 2408, the first SMF may send a PDU session creation request to the reselected SMF for replacing the second SMF.

[0319] Fig.25 A flowchart of a method according to another embodiment of the present disclosure is shown, which can be performed by a device implemented in a first SMF, or by a device at the first SMF, or by a device implemented as a first SMF, or by a device communicatively coupled to the first SMF. Therefore, the device can provide components or modules for completing various parts of method 2500 and components or modules for completing other processes together with other components. For the parts that have been described in the above embodiments, their description is omitted here for brevity.

[0320] In an embodiment, the AMF, the first SMF and the second SMF support the first capability. The first SMF supports a local NF set for the first SMF and a peer NF set for the second SMF. The second SMF supports a local NF set for the second SMF, but does not support a peer NF set for the first SMF.

[0321] At block 2502, the first SMF may receive a NF status notification request from an NRF, the NF status notification request including information indicating a failure of the second SMF.

[0322] At box 2504, the first SMF can send a PDU session SM context status notification to the AMF, which includes a resource status set to released and a release reason due to reactivation.

[0323] At block 2506, the first SMF may receive a PDU session creation SM context request from the AMF. When the AMF, the first SMF, and the reselected SMF for replacing the second SMF support the first capability, the PDU session creation SM context request includes a first indication.

[0324] At block 2508, the first SMF may send a PDU session creation request to the reselected SMF. The PDU session creation request includes an indication that the first SMF supports a local NF set for the first SMF and a peer NF set for the second SMF. When the AMF, the first SMF, and the reselected SMF for replacing the second SMF support the first capability, the PDU session creation request includes the first indication.

[0325] At block 2510, the first SMF may receive a PDU session creation response from the reselected SMF. When the AMF, the first SMF, and the reselected SMF support the first capability, the PDU session creation response may include a first indication.

[0326] Fig.26 A flowchart of a method according to another embodiment of the present disclosure is shown, which can be performed by a device implemented in a first SMF, or by a device at the first SMF, or by a device implemented as a first SMF, or by a device communicatively coupled to the first SMF. Therefore, the device can provide components or modules for completing various parts of method 2600 and components or modules for completing other processes together with other components. For the parts that have been described in the above embodiments, their description is omitted here for brevity.

[0327] In an embodiment, the first SMF does not support the first capability. The first SMF does not support the local NF set for the first SMF and the peer NF set for the second SMF. The second SMF supports the local NF set for the second SMF, but does not support the peer NF set for the first SMF.

[0328] At block 2602, the first SMF may receive a NF status notification request from the NRF, the request including information indicating a failure of the second SMF.

[0329] At box 2604, the first SMF may send a PDU session SM context status notification to the AMF, which includes the resource status set to released and the release reason due to reactivation.

[0330] At block 2606, the first SMF may receive a PDU session create SM context request from the AMF.

[0331] At block 2608, the first SMF may send a PDU session creation request to the reselected SMF for replacing the second SMF.

[0332] In an embodiment, the first SMF is a visited SMF and the second SMF is a home SMF, or the first SMF is an intermediate SMF and the second SMF is an anchor SMF.

[0333] Fig.27a A flowchart of a method according to another embodiment of the present disclosure is shown, which can be performed by a device implemented in a second SMF, or by a device at the second SMF, or by a device implemented as a second SMF, or by a device communicatively coupled to the second SMF. Therefore, the device can provide components or modules for completing various parts of method 2700 and components or modules for completing other processes together with other components. For the parts that have been described in the above embodiments, their description is omitted here for brevity.

[0334] At block 2702, the second SMF may receive a PDU session creation request from the first SMF.

[0335] At block 2704, the second SMF may send a PDU session creation response to the first SMF.

[0336] In an embodiment, when the AMF, the first SMF and the second SMF support a first capability for PDU session reconstruction in the event of a failure of the first SMF, the PDU session creation request includes a first indication of support for the first capability.

[0337] In an embodiment, when the first SMF supports a local NF set for the first SMF and a peer NF set for the second SMF, the PDU session creation request further includes an indication that the first SMF supports the local NF set for the first SMF and the peer NF set for the second SMF.

[0338] In an embodiment, when the AMF, the first SMF and the second SMF support the first capability, the PDU session creation response includes a first indication.

[0339] In an embodiment, when the first SMF supports a local NF set for the first SMF and a peer NF set for the second SMF and the second SMF supports the local NF set for the second SMF and the peer NF set for the first SMF, the PDU session creation response includes an indication that the second SMF supports the local NF set for the second SMF and the peer NF set for the first SMF.

[0340] In an embodiment, when the second SMF supports the peer NF set for the first SMF, the PDU session creation response includes an indication that the second SMF supports the peer NF set for the first SMF.

[0341] In an embodiment, the PDU session creation request includes third information about whether the first SMF supports the peer NF set for the second SMF and / or fourth information about whether the second SMF supports the peer NF set for the first SMF.

[0342] In an embodiment, the PDU session creation request includes fifth information about whether there are two or more SMFs in the peer NF set for the first SMF and / or sixth information about whether there are two or more SMFs in the peer NF set for the second SMF.

[0343] In an embodiment, the third information and the sixth information are represented by a single parameter, and the fourth information and the fifth information are represented by a single parameter.

[0344] Figure 27b A flowchart of a method according to another embodiment of the present disclosure is shown, which can be performed by a device implemented in a second SMF, or by a device at the second SMF, or by a device implemented as a second SMF, or by a device communicatively coupled to the second SMF. Therefore, the device can provide components or modules for completing various parts of method 2710 and components or modules for completing other processes with other components. For the parts that have been described in the above embodiments, their description is omitted here for brevity.

[0345] At block 2712, the second SMF may determine fifth information regarding whether there are two or more SMFs in the peer NF set for the first SMF. The PDU Session Create Response includes the fifth information.

[0346] In an embodiment, the PDU session creation request includes sixth information about whether there are two or more SMFs in the peer NF set for the second SMF.

[0347] Fig.28 A flowchart of a method according to another embodiment of the present disclosure is shown, which can be performed by a device implemented in a second SMF, or by a device at the second SMF, or by a device implemented as a second SMF, or by a device communicatively coupled to the second SMF. Therefore, the device can provide components or modules for completing various parts of method 2800 and components or modules for completing other processes together with other components. For the parts that have been described in the above embodiments, their description is omitted here for brevity.

[0348] At block 2802, the second SMF may send an NF registration request including the NF profile of the second SMF to the NRF.

[0349] In an embodiment, the NF profile of the second SMF includes an indication of whether the second SMF supports the capability of PDU session reconstruction in the event of failure of the first SMF.

[0350] In an embodiment, the NF profile of the second SMF includes an indication of whether the second SMF supports a local NF set for the second SMF and a peer NF set for the first SMF.

[0351] In an embodiment, the NF profile of the second SMF includes an indication of whether the second SMF supports a peer NF set for the first SMF (e.g., hSMF roaming resumption indication).

[0352] Fig.29 A flowchart of a method according to another embodiment of the present disclosure is shown, which can be performed by a device implemented in a second SMF, or by a device at the second SMF, or by a device implemented as a second SMF, or by a device communicatively coupled to the second SMF. Therefore, the device can provide components or modules for completing various parts of method 2900 and components or modules for completing other processes together with other components. For the parts that have been described in the above embodiments, their description is omitted here for brevity.

[0353] In an embodiment, the AMF, the first SMF, and the second SMF support a first capability, the first SMF supports a local NF set for the first SMF and supports a peer NF set for the second SMF, and the second SMF does not support a local NF set for the second SMF and a peer NF set for the first SMF, and the method further comprises:

[0354] At block 2902, the second SMF may receive a NF status notification request from the NRF including information indicating a failure of the first SMF.

[0355] At block 2904, the second SMF may maintain at least one PDU session related to the first SMF.

[0356] At block 2906, the second SMF may receive a PDU session update request including an updated SMF identifier and an updated SMF PDU session uniform resource identifier from the reselected SMF used to replace the first SMF.

[0357] Fig.30 A flowchart of a method according to another embodiment of the present disclosure is shown, which can be performed by a device implemented in a second SMF, or by a device at the second SMF, or by a device implemented as a second SMF, or by a device communicatively coupled to the second SMF. Therefore, the device can provide components or modules for completing various parts of method 3000 and components or modules for completing other processes together with other components. For the parts that have been described in the above embodiments, their description is omitted here for brevity.

[0358] In an embodiment, the AMF, the first SMF and the second SMF support a first capability, the first SMF supports a local NF set for the first SMF but does not support a peer NF set for the second SMF, and the second SMF supports a local NF set for the second SMF and a peer NF set for the first SMF.

[0359] At block 3002, the second SMF may receive a NF status notification request from the NRF, the NF status notification request including information indicating a failure of the first SMF.

[0360] At block 3004, the second SMF may maintain at least one PDU session associated with the first SMF.

[0361] At block 3006, the second SMF may receive a PDU session creation request from the reselected SMF for replacing the first SMF.

[0362] In an embodiment, when the AMF, the reselected SMF for replacing the first SMF, and the second SMF support the first capability, the PDU session create SM context request includes a first indication.

[0363] At block 3008, the second SMF may perform creation on create to accept the PDU session creation request; and

[0364] At block 3010, the second SMF may send a PDU session creation response to the reselected SMF used to replace the first SMF.

[0365] In an embodiment, when the AMF, the SMF used to replace the first SMF and the second SMF support the first capability, the PDU session creation response includes a first indication.

[0366] Fig.31 A flowchart of a method according to another embodiment of the present disclosure is shown, which can be performed by a device implemented in a second SMF, or by a device at the second SMF, or by a device implemented as a second SMF, or by a device communicatively coupled to the second SMF. Therefore, the device can provide components or modules for completing various parts of the method 3100 and components or modules for completing other processes together with other components. For the parts that have been described in the above embodiments, their description is omitted here for brevity.

[0367] In an embodiment, the AMF, the first SMF and the second SMF support a first capability, the first SMF supports a local NF set for the first SMF but does not support a peer NF set for the second SMF, and the second SMF does not support a local NF set for the second SMF and a peer NF set for the first SMF.

[0368] At box 3102, the second SMF may receive a NF status notification request from the NRF including information indicating a failure of the first SMF.

[0369] At block 3104, the second SMF may maintain at least one PDU session associated with the first SMF.

[0370] At block 3106, the second SMF may receive a PDU session creation request from the reselected SMF for replacing the first SMF.

[0371] In an embodiment, when the AMF, the reselected SMF for replacing the first SMF, and the second SMF support the first capability, the PDU session create SM context request includes a first indication;

[0372] At box 3108, the second SMF can perform a create on a create to accept the PDU session creation request.

[0373] At block 3110, the second SMF may send a PDU session creation response to the reselected SMF used to replace the first SMF.

[0374] In an embodiment, when the AMF, the SMF used to replace the first SMF and the second SMF support the first capability, the PDU session creation response includes a first indication.

[0375] Fig.32 A flowchart of a method according to another embodiment of the present disclosure is shown, which can be performed by a device implemented in a second SMF, or by a device at the second SMF, or by a device implemented as a second SMF, or by a device communicatively coupled to the second SMF. Therefore, the device can provide components or modules for completing various parts of method 3200 and components or modules for completing other processes together with other components. For the parts that have been described in the above embodiments, their description is omitted here for brevity.

[0376] In an embodiment, the first SMF does not support the first capability, the first SMF does not support a local NF set for the first SMF and a peer NF set for the second SMF, and the second SMF supports a local NF set for the second SMF and a peer NF set for the first SMF.

[0377] At block 3202, the second SMF may send a service request to the third network function. The service request does not include an indication that the second SMF supports a local NF set for the second SMF and a peer NF set for the first SMF.

[0378] In an embodiment, the third network function includes at least one of a policy control function (PCF), a user plane function (UPF), and a unified data management (UDM).

[0379] In an embodiment, the first SMF is a visited SMF, and the second SMF is a home SMF. In an embodiment, the first SMF is an intermediate SMF, and the second SMF is an anchor SMF.

[0380] Fig.33 A flowchart of a method according to another embodiment of the present disclosure is shown, which can be performed by a device implemented in a third network function, or by a device at a third network function, or by a device implemented as a third network function, or by a device communicatively coupled to a third network function. Therefore, the device can provide components or modules for completing various parts of method 3300 and components or modules for completing other processes with other components. For the parts that have been described in the above embodiments, their description is omitted here for brevity.

[0381] At block 3302, the third network function may determine that the second SMF does not support a local NF set for the second SMF and a peer NF set for the first SMF.

[0382] At box 3304, when the second SMF fails, the third network function can perform a cleanup operation on the resource context related to the second SMF.

[0383] In an embodiment, the third network function may determine that the second SMF does not support the local NF set for the second SMF and the peer NF set for the first SMF by sending an NF discovery request to the NRF and receiving an NF discovery response from the NRF. The NF discovery response includes information indicating that the second SMF does not support the local NF set for the second SMF and the peer NF set for the first SMF.

[0384] In an embodiment, the third network function may determine that the second SMF does not support the local NF set for the second SMF and the peer NF set for the first SMF by receiving a service request from the second SMF. The service request does not include an indication that the second SMF supports the local NF set for the second SMF and the peer NF set for the first SMF.

[0385] In an embodiment, the third network function includes at least one of a policy control function (PCF), a user plane function (UPF), and a unified data management (UDM).

[0386] In an embodiment, the first SMF is a visited SMF and the second SMF is a home SMF, or the first SMF is an intermediate SMF and the second SMF is an anchor SMF.

[0387] Fig.34 A flowchart of a method according to another embodiment of the present disclosure is shown, which can be performed by a device implemented in an NRF, or by a device at an NRF, or by a device implemented as an NRF, or by a device communicatively coupled to an NRF. Therefore, the device can provide components or modules for completing various parts of method 3400 and components or modules for completing other processes with other components. For the parts that have been described in the above embodiments, their description is omitted here for brevity.

[0388] At box 3402, the NRF may receive a NF registration request including the NF profile of the SMF from the SMF.

[0389] At box 3404, the NRF may store the NF profile of the SMF.

[0390] In an embodiment, when the SMF is a first SMF and supports a first capability of PDU session reconstruction in case of failure of the first SMF, the NF profile of the first SMF includes a first indication of supporting the first capability.

[0391] In an embodiment, when the SMF is a first SMF and supports a local NF set for the first SMF and a peer NF set for a second SMF, the NF profile of the first SMF includes an indication that the first SMF supports a local NF set for the first SMF and a peer NF set for the second SMF.

[0392] In an embodiment, when the SMF is a second SMF and supports the first capability, the NF profile of the second SMF includes a first indication.

[0393] In an embodiment, when the SMF is a second SMF and supports a local NF set for the second SMF and a peer NF set for the first SMF, the NF profile of the second SMF includes an indication that the second SMF supports the local NF set for the second SMF and the peer NF set for the first SMF.

[0394] Fig.35 A flowchart of a method according to another embodiment of the present disclosure is shown, which can be performed by a device implemented in an NRF, or by a device at an NRF, or by a device implemented as an NRF, or by a device communicatively coupled to an NRF. Therefore, the device can provide components or modules for completing various parts of method 3500 and components or modules for completing other processes with other components. For the parts that have been described in the above embodiments, their description is omitted here for brevity.

[0395] At block 3502, the NRF may receive a network function discovery request from an access and mobility function (AMF).

[0396] At box 3504, the NRF may send a network function discovery response to the AMF including at least one indication of the NF profile of the SMF.

[0397] In an embodiment, the first SMF is a visited SMF and the second SMF is a home SMF, or the first SMF is an intermediate SMF and the second SMF is an anchor SMF.

[0398] The following description focuses on the solution for roaming interworking between V-SMF and H-SMF. However, the same solution principles also apply to scenarios where the I-SMF and anchor SMF have different recovery capabilities or configurations.

[0399] Fig.36 A flow chart of a method according to another embodiment of the present disclosure is shown. For some parts that have been described in the above embodiments, their description is omitted here for the sake of brevity.

[0400] In step 3601, vSMF sends a Nnrf_NFRegister request {vSMF roaming recovery indication, vSMF reconstruction indication} to vNRF.

[0401] In step 3602, hSMF sends a Nnrf_NFRegister request {hSMF roaming recovery indication, vSMF reconstruction indication} to hNRF.

[0402] In step 3603, AMF sends an hSMF discovery request to hNRF.

[0403] In step 3604, AMF receives the hSMF roaming recovery indication and vSMF re-establishment indication from the hNRF.

[0404] In step 3605, AMF sends a vSMF discovery request to vNRF.

[0405] In step 3606, AMF receives the vSMF roaming recovery indication and vSMF re-establishment indication from the vNRF.

[0406] At step 3607, AMF sends a Nsmf_PDUSession_CreateSMContext request to vSMF1. In an embodiment, the Nsmf_PDUSession_CreateSMContext request includes a vSMF reestablishment indication. In another embodiment, the Nsmf_PDUSession_CreateSMContext request includes a vSMF roaming resumption indication (which may be a Boolean value) and / or an hSMF roaming resumption indication (which may be a Boolean value).

[0407] In step 3608, AMF receives the Nsmf_PDUSession_CreateSMContext response {vSMF roaming recovery indication, vSMF reconstruction indication} from vSMF1.

[0408] In step 3609, vSMF1 sends a Nsmf_PDUSession_Create request to hSMF1. In an embodiment, the Nsmf_PDUSession_Create request includes a vSMF roaming recovery indication and a vSMF reestablishment indication. In another embodiment, the Nsmf_PDUSession_Create request includes a vSMF roaming recovery indication and / or an hSMF roaming recovery indication.

[0409] At step 3610, vSMF1 receives a Nsmf_PDUSession_Create response from hSMF1. In an embodiment, the Nsmf_PDUSession_Create response includes an hSMF roaming resumption indication.

[0410] In an embodiment, the new content to be added is the indication that there are multiple vSMFs in the same vSMF set and multiple hSMFs in the same hSMF set. Solution I: AMF discovers that there are multiple vSMFs in the same vSMF set and / or multiple hSMFs in the hSMF set, and AMF sends such information to vSMF, such as "vSMF set indication" and "hSMF set indication". vSMF forwards the vSMF set indication to hSMF. Solution II: vSMF and hSMF themselves can also detect such information. vSMF and hSMF discover other members in the same set based on a private implementation mechanism, and then vSMF and hSMF can exchange such information. Solution III: There is another possibility, which is to expand the concept of "vSMF set indication" and "hSMF set indication" to also cover the meaning of "vSMF roaming recovery indication" and "hSMF roaming recovery indication", then only "vSMF set indication" and "hSMF set indication" need to be exchanged. This actually makes sense and is simple to implement, because vSMF set indications are always based on vSMF recovery indications, which also applies to hSMF. This solution is actually to replace the parameter name recovery indication with set indications, and extend the following concepts: "set indication" means supporting local sets, peer sets, and also supporting multiple members in the same set.

[0411] In an embodiment, V-SMF and H-SMF register their capabilities to support roaming recovery and vSMF re-establishment in the NRF.

[0412] In an embodiment, AMF obtains the ability of V-SMF and H-SMF to support roaming recovery and vSMF reconstruction through NRF discovery.

[0413] In an embodiment, if AMF detects that both V-SMF and H-SMF support vSMF reconstruction, and AMF also supports vSMF reconstruction, AMF shall include vSMF reconstruction indication in the creation request towards V-SMF. Otherwise, AMF shall not include vSMF reconstruction.

[0414] In an embodiment, if V-SMF supports vSMF reconstruction, V-SMF shall include vSMF reconstruction indication (if received from AMF) in the creation request towards H-SMF. Please note that V-SMF supports vSMF reconstruction, which means that V-SMF can relay vSMF reconstruction indication (received from AMF) to H-SMF.

[0415] In an embodiment, if the V-SMF supports SMF sets, the V-SMF includes its roaming resumption indication in the creation request towards the H-SMF. Otherwise, the V-SMF should not send a roaming resumption indication to the H-SMF.

[0416] In an embodiment, if the AMF detects that the V-SMF and / or H-SMF supports SMF set-based recovery (i.e., roaming recovery indication) and the AMF also supports SMF set-based vSMF failure reselection, the AMF shall include the vSMF recovery indication and / or the hSMF recovery indication in the creation request towards the V-SMF. Otherwise, the AMF shall not include the vSMF recovery indication and / or the hSMF recovery indication.

[0417] In an embodiment, if the AMF detects that the V-SMF and / or H-SMF supports SMF set based recovery (i.e. roaming recovery indication), the AMF shall include a vSMF recovery indication and / or an hSMF recovery indication in the creation request towards the V-SMF.

[0418] In an embodiment, if the H-SMF supports the SMF set and the V-SMF also includes a roaming resumption indication in the creation request, the H-SMF includes the roaming resumption indication in the creation response toward the V-SMF. Otherwise, the H-SMF should not send a roaming resumption indication to the V-SMF.

[0419] Solutions for V-SMF faults: -V-SMF supports SMF set functions o H-SMF supports SMF set: oFollow normal set processing. o H-SMF does not support SMF sets: o If AMF, V-SMF and H-SMF support vSMF re-establishment, H-SMF shall maintain the affected PDU Session and wait for re-establishment triggered by AMF reselecting another vSMF in the same V-SMF set and performing the PDU Session Update procedure. Applicable to V-SMF failure scenario 1. o Otherwise, the H-SMF deletes the affected PDU Session and the AMF requests the UE to reactivate the affected PDU Session. -V-SMF does not support SMF set functions oWhether H-SMF supports SMF collection o If AMF, V-SMF and H-SMF support vSMF reconstruction, H-SMF shall maintain the affected PDU Session and wait for reconstruction triggered by AMF reselecting another vSMF and performing the Create on Create procedure for PDU Session. Applicable to V-SMF failure scenarios 2 and 3. o Otherwise, the H-SMF deletes the affected PDU Session and the AMF requests the UE to reactivate the affected PDU Session.

[0420] Solutions for H-SMF failures: -H-SMF supports SMF set functions o V-SMF supports SMF set: oFollow normal set processing o V-SMF does not support SMF sets o V-SMF releases the affected PDU Session and AMF requests the UE to reactivate the affected PDU Session. Applicable to H-SMF fault scenario 4. -H-SMF does not support SMF set functionality o Regardless of whether V-SMF supports the SMF Set, V-SMF releases the affected PDU Session and AMF requests UE to reactivate the affected PDU Session. Applicable to H-SMF failure scenarios 5 and 6

[0421] Fig.37 A flowchart of an example solution for V-SMF failure according to an embodiment of the present disclosure is shown. For the sake of brevity, descriptions of some parts that have been described in the above embodiments are omitted here.

[0422] Scenario 1: VPLMN deploys SMF sets, and V-SMF supports SMF sets, but H-SMF does not support SMF sets.

[0423] The AMF includes a vSMF reconstruction indication in the CreateSMContext request toward the selected V-SMF, and the V-SMF includes a vSMF roaming recovery indication and a vSMF reconstruction indication in the PDUSessionCreateRequest toward the H-SMF.

[0424] When the selected V-SMF fails, the H-SMF shall maintain the associated PDU session and wait for reestablishment. The AMF triggers vSMF reselection for the established SM context and triggers reestablishment in the update request. The reselected V-SMF includes the updated vSMFId and vSmfPduSessionUri in the update request towards the original H-SMF.

[0425] In step 3701, AMF sends a Nsmf_PDUSession_CreateSMContext request to vSMF1 and receives a response from vSMF1.

[0426] In an embodiment, the Nsmf_PDUSession_CreateSMContext request includes a vSMF reestablishment indication (i.e., the vSMF supports DU session reestablishment in the event of a vSMF failure). In another embodiment, the Nsmf_PDUSession_CreateSMContext request includes a vSMF roaming recovery indication (i.e., the vSMF supports roaming recovery) and / or an hSMF roaming recovery indication (i.e., the hSMF does not support roaming recovery).

[0427] In step 3702, vSMF1 sends a Nsmf_PDUSession_Create request to hSMF1.

[0428] In an embodiment, the Nsmf_PDUSession_Create request includes a vSMF roaming recovery indication and a vSMF reestablishment indication. In another embodiment, the Nsmf_PDUSession_Create request includes a vSMF roaming recovery indication and / or an hSMF roaming recovery indication received from the AMF.

[0429] At step 3703, vSMF1 receives a Nsmf_PDUSession_Create response from hSMF1. In an embodiment, the Nsmf_PDUSession_Create response includes a vSMF reestablishment indication (ie, hSMF supports PDU session reestablishment in case of vSMF failure).

[0430] In step 3704, vNRF (visiting NRF) sends a Nnrf_NFManagement_NFStatusNotify request to hSMF1 ("vSMF1 is paused").

[0431] In step 3705, hSMF1 maintains the PDU session associated with the failed vSMF and waits for reestablishment.

[0432] In step 3706, vNRF sends a Nnrf_NFManagement_NFStatusNotify request to AMF ("vSMF1 is suspended").

[0433] At step 3708, AMF triggers vSMF reselection for the established SM session.

[0434] In step 3709, AMF sends a Nsmf_PDUSession_UpdateSMContext request {SmConextUpdateData} to vSMF2.

[0435] In step 3710, vSMF2 sends a Nsmf_PDUSession_Update request {vsmfId=vSMF2Id, vsmfPduSessionUri=vSMF2} to hSMF1.

[0436] In step 3711. hSMF1 sends a Nsmf_PDUSession_Update response to vSMF2.

[0437] In step 3712, vSMF2 sends a Nsmf_PDUSession_UpdateSMContext response {SmConextUpdatedData} to AMF.

[0438] Fig.37 Some of the messages shown in may be the same as the corresponding messages described in 3GPP TS 23.502 V17.2.1. Fig.37 Some of the messages shown in may be enhanced according to embodiments of the present disclosure.

[0439] Fig.38 A flowchart of an example solution for V-SMF failure according to another embodiment of the present disclosure is shown. For the sake of brevity, descriptions of some parts already described in the above embodiments are omitted here.

[0440] Scenario 2 – VPLMN deploys SMF sets, but V-SMF does not support SMF sets, H-SMF supports SMF sets

[0441] AMF includes a vSMF re-establishment indication in the CreateSMContext request towards the selected vSMF. V-SMF relays the received vSMF re-establishment indication to H-SMF in PDUSessionCreateRequest, but V-SMF does not include a vSMF roaming recovery indication because vSMF does not support SMF sets.

[0442] When the selected V-SMF fails, the H-SMF shall maintain the associated PDU session and wait for vSMF to reestablish. The AMF triggers PDU session reactivation to reestablish the affected PDU session, and the reselected V-SMF sends a PDUSessionCreateRequest to the original H-SMF. The H-SMF performs a Create on Create to accept a new PDU session request.

[0443] In step 3801, AMF sends a Nsmf_PDUSession_CreateSMContext request to vSMF1 and receives a response from vSMF1.

[0444] In an embodiment, the Nsmf_PDUSession_CreateSMContext request includes a vSMF reestablishment indication (i.e., the vSMF supports PDU session reestablishment in the event of a vSMF failure). In another embodiment, the Nsmf_PDUSession_CreateSMContext request includes a vSMF roaming recovery indication (i.e., the vSMF does not support roaming recovery) and / or an hSMF roaming recovery indication (i.e., the hSMF supports roaming recovery).

[0445] In step 3802, vSMF1 sends a Nsmf_PDUSession_Create request to hSMF1.

[0446] In an embodiment, the Nsmf_PDUSession_Create request includes a vSMF reestablishment indication. In another embodiment, the Nsmf_PDUSession_Create request includes a vSMF roaming resumption indication and / or a hSMF roaming resumption indication received from the AMF.

[0447] At step 3803, hSMF1 sends a Nsmf_PDUSession_Create response to vSMF1. In an embodiment, the Nsmf_PDUSession_Create response includes a vSMF reestablishment indication (ie, hSMF supports PDU session reestablishment in case of vSMF failure).

[0448] At step 3804, vNRF sends a Nnrf_NFManagement_NFStatusNotify request ("vSMF1 paused") to hSMF1 and receives a response from hSMF1.

[0449] In step 3805, hSMF1 maintains the PDU session associated with the failed vSMF.

[0450] In step 3806, vNRF sends a Nnrf_NFManagement_NFStatusNotify request ("vSMF1 is paused") to AMF and receives a response from AMF.

[0451] In step 3807, AMF triggers PDU session reactivation.

[0452] In step 3808, AMF sends a Nsmf_PDUSession_CreateSMContext request to vSMF2 and receives a response from vSMF2.

[0453] In an embodiment, the Nsmf_PDUSession_CreateSMContext request includes a vSMF reestablishment indication (i.e., vSMF2 supports PDU session reestablishment in the event of a vSMF2 failure). In another embodiment, the Nsmf_PDUSession_CreateSMContext request includes a vSMF roaming recovery indication (i.e., vSMF does not support roaming recovery) and / or an hSMF roaming recovery indication (i.e., hSMF supports roaming recovery).

[0454] In step 3809, vSMF2 sends a Nsmf_PDUSession_Create request {vSMF reconstruction indication} to hSMF1.

[0455] In an embodiment, the Nsmf_PDUSession_Create request includes a vSMF reestablishment indication. In another embodiment, the Nsmf_PDUSession_Create request includes a vSMF roaming resumption indication and / or a hSMF roaming resumption indication received from the AMF.

[0456] In step 3810.hSMF1 performs creation on create.

[0457] In step 3811. hSMF1 sends a Nsmf_PDUSession_Create response to vSMF2.

[0458] In an embodiment, the Nsmf_PDUSession_Create response includes a vSMF re-establishment indication (ie, the hSMF supports PDU session re-establishment in case of vSMF failure).

[0459] Fig.38 Some of the messages shown may be identical to corresponding messages described in 3GPP TS 23.502 V17.2.1. Fig.38 Some of the messages shown may be enhanced according to embodiments of the present disclosure.

[0460] Fig.39 A flowchart of an example solution for V-SMF failure according to another embodiment of the present disclosure is shown. For the sake of brevity, descriptions of some parts already described in the above embodiments are omitted here.

[0461] Scenario 3 - VPLMN deploys SMF set but V-SMF does not support SMF set and H-SMF does not support SMF set.

[0462] As shown below, the same reconstruction solution as Scenario 2 is applied. That is, after the selected V-SMF failure occurs, the H-SMF should maintain the associated PDU session and wait for reconstruction. The AMF triggers PDU session reactivation to reconstruct the affected PDU session, and the reselected V-SMF sends a PDU session creation request to the original H-SMF. The H-SMF performs Create on Create to accept the new PDU session request.

[0463] In step 3901, AMF sends a Nsmf_PDUSession_CreateSMContext request to vSMF1 and receives a response from vSMF1.

[0464] In an embodiment, the Nsmf_PDUSession_CreateSMContext request includes a vSMF reestablishment indication (i.e., the vSMF supports PDU session reestablishment in the event of a vSMF failure). In another embodiment, the Nsmf_PDUSession_CreateSMContext request includes a vSMF roaming recovery indication (i.e., the vSMF does not support roaming recovery) and / or an hSMF roaming recovery indication (i.e., the hSMF does not support roaming recovery).

[0465] In step 3902, vSMF1 sends a Nsmf_PDUSession_Create request to hSMF1.

[0466] In an embodiment, the Nsmf_PDUSession_Create request includes a vSMF reestablishment indication. In another embodiment, the Nsmf_PDUSession_Create request includes a vSMF roaming resumption indication and / or a hSMF roaming resumption indication received from the AMF.

[0467] At step 3903, hSMF1 sends a Nsmf_PDUSession_Create response to vSMF1. In an embodiment, the Nsmf_PDUSession_Create response includes a vSMF reestablishment indication (ie, hSMF supports PDU session reestablishment in case of vSMF failure).

[0468] At step 3904, the vNRF (visiting NRF) sends a Nnrf_NFManagement_NFStatusNotify request ("vSMF1 is paused") to hSMF1 and receives a response from hSMF1.

[0469] In step 3905, hSMF1 maintains the PDU session associated with the failed vSMF1.

[0470] In step 3906, vNRF sends a Nnrf_NFManagement_NFStatusNotify request to AMF ("vSMF1 is suspended").

[0471] In step 3907, AMF triggers PDU session reactivation.

[0472] In step 3908, AMF sends a Nsmf_PDUSession_CreateSMContext request to vSMF2 and receives a response from vSMF2.

[0473] In an embodiment, the Nsmf_PDUSession_CreateSMContext request includes a vSMF reestablishment indication (i.e., the vSMF supports PDU session reestablishment in the event of a vSMF failure). In another embodiment, the Nsmf_PDUSession_CreateSMContext request includes a vSMF roaming recovery indication (i.e., the vSMF does not support roaming recovery) and / or an hSMF roaming recovery indication (i.e., the hSMF does not support roaming recovery).

[0474] In step 3909, vSMF2 sends a Nsmf_PDUSession_Create request to hMSF1.

[0475] In an embodiment, the Nsmf_PDUSession_Create request includes a vSMF reestablishment indication. In another embodiment, the Nsmf_PDUSession_Create request includes a vSMF roaming resumption indication and / or a hSMF roaming resumption indication received from the AMF.

[0476] In step 3910.hSMF1 performs a create on a create.

[0477] At step 3911, hSMF1 sends a Nsmf_PDUSession_Create response to vSMF2. In an embodiment, the Nsmf_PDUSession_Create response includes a vSMF reestablishment indication (ie, hSMF2 supports PDU session reestablishment in case of vSMF failure).

[0478] like Fig.39 Some of the messages shown may be the same as the corresponding messages described in 3GPP TS 23.502 V17.2.1. Fig.39 Some of the messages shown may be enhanced according to embodiments of the present disclosure.

[0479] Fig.40 A flowchart of an example solution for H-SMF failure according to an embodiment of the present disclosure is shown. For the sake of brevity, descriptions of some parts that have been described in the above embodiments are omitted here.

[0480] Scenario 4 - HPLMN deploys SMF set and H-SMF supports SMF set, but V-SMF does not support SMF set

[0481] If the selected V-SMF does not support vSMF re-establishment, the AMF does not include a vSMF re-establishment indication to the V-SMF. The V-SMF does not include a vSMF roaming recovery indication and a vSMF re-establishment indication in the PDUSessionCreateRequest toward the selected H-SMF. Since the H-SMF detects that the V-SMF does not support roaming recovery, the H-SMF does not return a roaming recovery indication in the response to the V-SMF. The H-SMF should also suppress the roaming recovery indication in the service request toward the surrounding 5GC NF in the HPLMN.

[0482] When the original H-SMF failure occurs, because the H-SMF does not include the hSMF roaming recovery indication in the service request (or discovered by NRF), the surrounding 5GC NFs in the HPLMN shall clear the context associated with the failed H-SMF. The associated V-SMF shall initiate an SM context release towards the AMF, and the AMF triggers PDU session reactivation for the affected PDU sessions.

[0483] The vSMF reconstruction indication is not used in the H-SMF failure scenario.

[0484] In step 4001. If the V-SMF does not support hSMF roaming resumption, the H-SMF shall suppress the roaming resumption indication in the request to other 5GC NFs in the HPLMN.

[0485] In step 4002, AMF sends a Nsmf_PDUSession_CreateSMContext request to vSMF1 and receives a Nsmf_PDUSession_CreateSMContext response from vSMF1.

[0486] In an embodiment, the Nsmf_PDUSession_CreateSMContext request includes a vSMF roaming resumption indication (ie, the vSMF does not support roaming resumption) and / or a hSMF roaming resumption indication (ie, the hSMF supports roaming resumption).

[0487] In step 4003, vSMF1 sends a Nsmf_PDUSession_Create request to hSMF1.

[0488] In another embodiment, the Nsmf_PDUSession_Create request includes a vSMF roaming resumption indication and / or a hSMF roaming resumption indication received from the AMF.

[0489] In step 4004, hSMF1 sends a Npcf_SMPolicyControl_Create request to PCF1 and receives a Npcf_SMPolicyControl_Create response from PCF1.

[0490] In step 4005, hSMF1 sends a Nsmf_PDUSession_Create response to vSMF1.

[0491] At step 4006, hNRF sends a Nnrf_NFManagement_NFStatusNotify request to vSMF1 ("hSMF1 pauses") and receives a Nnrf_NFManagement_NFStatusNotify response from vSMF1.

[0492] In step 4007, the PCF cleans up the context associated with the failed hSMF based on the capability indication in the initial service request.

[0493] In step 4008, vSMF1 sends Nsmf_PDUSession_SMContextStatusNotify{resourceStatus=release, reason=“REL_DUE_TO_REACTIVATION”} to AMF and receives a response from AMF.

[0494] In step 4009, AMF sends Nsmf_PDUSession_CreateSMContext to vSMF1 and receives a response from vSMF1.

[0495] In an embodiment, the Nsmf_PDUSession_CreateSMContext request includes a vSMF roaming resumption indication (ie, the vSMF does not support roaming resumption) and / or a hSMF roaming resumption indication (ie, the hSMF supports roaming resumption).

[0496] In step 4010, vSMF1 sends a Nsmf_PDUSession_Create request to hSMF2.

[0497] In another embodiment, the Nsmf_PDUSession_Create request includes a vSMF roaming resumption indication and / or a hSMF roaming resumption indication received from the AMF.

[0498] In step 4011.hSMF2 sends a Npcf_SMPolicyControl_Create request to PCF1 and receives a response from PCF1.

[0499] In step 4012, hSMF2 sends a Nsmf_PDUSession_Create response to vSMF1.

[0500] Fig.41 Some of the messages shown may be the same as the corresponding messages described in 3GPP TS23.502 V17.2.1.Some of the messages shown in FIG42 may be enhanced according to embodiments of the present disclosure.

[0501] Fig.41 A flowchart of an example solution for H-SMF failure according to another embodiment of the present disclosure is shown. For the sake of brevity, descriptions of some parts that have been described in the above embodiments are omitted here.

[0502] Scenario 5 – HPLMN deploys SMF sets but H-SMF does not support SMF sets, V-SMF supports SMF sets

[0503] AMF includes a vSMF re-establishment indication in the CreateSMContext request to vSMF, and V-SMF includes a vSMF roaming recovery indication and a vSMF re-establishment indication in the PDUSessionCreateRequest to the selected H-SMF. Since H-SMF does not support SMF sets, H-SMF does not include a roaming recovery indication in the response to V-SMF.

[0504] When the original H-SMF failure occurs, the surrounding 5GC NFs in the HPLMN shall clean up the contexts associated with the failed H-SMF, since the H-SMF did not include the hSMF roaming resumption indication in the service request (or discovered through NRF). The associated V-SMF shall initiate SM context release to the AMF, and the AMF triggers PDU session reactivation for the affected PDU sessions.

[0505] The vSMF reconstruction indication is not useful in hSMF failure scenarios.

[0506] In step 4101, AMF sends a Nsmf_PDUSession_CreateSMContext request to vSMF1 and receives a response from vSMF1.

[0507] In an embodiment, the Nsmf_PDUSession_CreateSMContext request includes a vSMF reestablishment indication (i.e., the vSMF supports PDU session reestablishment in the event of a vSMF failure). In another embodiment, the Nsmf_PDUSession_CreateSMContext request includes a vSMF roaming recovery indication (i.e., the vSMF supports roaming recovery) and / or an hSMF roaming recovery indication (i.e., the hSMF does not support roaming recovery).

[0508] In step 4102, vSMF1 sends a Nsmf_PDUSession_Create request to hSMF1.

[0509] In an embodiment, the Nsmf_PDUSession_Create request includes a vSMF reestablishment indication and a vSMF roaming recovery indication. In another embodiment, the Nsmf_PDUSession_Create request includes a vSMF roaming recovery indication and / or an hSMF roaming recovery indication received from the AMF.

[0510] In step 4103, hSMF1 sends a Npcf_SMPolicyControl_Create request to PCF1 and receives a Npcf_SMPolicyControl_Create response from PCF1.

[0511] At step 4104, hSMF1 sends a Nsmf_PDUSession_Create response to vSMF1. In an embodiment, the Nsmf_PDUSession_Create response includes a vSMF reestablishment indication (ie, hSMF supports PDU session reestablishment in case of vSMF failure).

[0512] In step 4105, hNRF sends a Nnrf_NFManagement_NFStatusNotify request to vSMF1 ("hSMF1 pauses") and receives a Nnrf_NFManagement_NFStatusNotify response from vSMF1.

[0513] In step 4106, the PCF cleans up the context associated with the failed hSMF according to the capability indication in the hSMF profile.

[0514] In step 4107, vSMF1 sends a Nsmf_PDUSession_SMContextStatusNotify request {resourceStatus=release, reason=“REL_DUE_TO_REACTIVATION”} to AMF and receives a Nsmf_PDUSession_SMContextStatusNotify response from AMF.

[0515] In step 4108, AMF sends a Nsmf_PDUSession_CreateSMContext request to vSMF1 and receives a response from vSMF1.

[0516] In an embodiment, the Nsmf_PDUSession_CreateSMContext request includes a vSMF reestablishment indication (i.e., the vSMF supports PDU session reestablishment in the event of a vSMF failure). In another embodiment, the Nsmf_PDUSession_CreateSMContext request includes a vSMF roaming recovery indication (i.e., the vSMF supports roaming recovery) and / or an hSMF roaming recovery indication (i.e., the hSMF2 does not support roaming recovery).

[0517] In step 4109, vSMF1 sends a Nsmf_PDUSession_Create request to hSMF2.

[0518] In an embodiment, the Nsmf_PDUSession_Create request includes a vSMF reestablishment indication and a vSMF roaming recovery indication. In another embodiment, the Nsmf_PDUSession_Create request includes a vSMF roaming recovery indication and / or an hSMF roaming recovery indication received from the AMF.

[0519] In step 4110, hSMF2 sends a Npcf_SMPolicyControl_Create request to PCF1 and receives a Npcf_SMPolicyControl_Create response from PCF1.

[0520] At step 4111. hSMF2 sends a Nsmf_PDUSession_Create response to vSMF1. In an embodiment, the Nsmf_PDUSession_Create response includes a vSMF reestablishment indication (ie, hSMF supports PDU session reestablishment in case of vSMF failure).

[0521] Fig.41 Some of the messages shown may be identical to corresponding messages described in 3GPP TS 23.502 V17.2.1. Fig.41 Some of the messages shown may be enhanced according to embodiments of the present disclosure.

[0522] Fig.42a A flowchart of an example solution for H-SMF failure according to another embodiment of the present disclosure is shown. For the sake of brevity, descriptions of some parts already described in the above embodiments are omitted here.

[0523] Scenario 6 - HPLMN deploys SMF set, but H-SMF does not support SMF set, and V-SMF does not support SMF set

[0524] As shown below, the same reestablishment solution as in scenario 5 applies. That is, after the original H-SMF failure occurs, the surrounding 5GC NFs in the HPLMN shall clean up the contexts associated with the failed H-SMF, since the H-SMF did not include the hSMF roaming resumption indication in the service request (or discovered through NRF). The associated V-SMF shall initiate an SM context release to the AMF, and the AMF triggers a PDU session reactivation for the affected PDU sessions.

[0525] In step 4201.AMF sends a Nsmf_PDUSession_CreateSMContext request to vSMF1 and receives a response from vSMF1.

[0526] In an embodiment, the Nsmf_PDUSession_CreateSMContext request includes a vSMF roaming resumption indication (ie, the vSMF does not support roaming resumption) and / or a hSMF roaming resumption indication (ie, the hSMF does not support roaming resumption).

[0527] In step 4202, vSMF1 sends a Nsmf_PDUSession_Create request to hSMF1.

[0528] In an embodiment, the Nsmf_PDUSession_Create request includes the vSMF roaming resumption indication and / or the hSMF roaming resumption indication received from the AMF.

[0529] In step 4203, hSMF1 sends a Npcf_SMPolicyControl_Create request to PCF1 and receives a Npcf_SMPolicyControl_Create response from PCF1.

[0530] In step 4204, hSMF1 sends a Nsmf_PDUSession_Create response to vSMF1.

[0531] At step 4205, hNRF (home NRF) sends a Nnrf_NFManagement_NFStatusNotify request to vSMF1 ("hSMF1 pauses") and receives a Nnrf_NFManagement_NFStatusNotify response from vSMF1.

[0532] In step 4206, the PCF cleans up the context associated with the failed hSMF according to the capability indication in the hSMF profile.

[0533] In step 4207, vSMF1 sends a Nsmf_PDUSession_SMContextStatusNotify request {resourceStatus=release, reason=“REL_DUE_TO_REACTIVATION”} to AMF and receives a Nsmf_PDUSession_SMContextStatusNotify response from AMF.

[0534] In step 4208, AMF sends a Nsmf_PDUSession_CreateSMContext request to vSMF1 and receives a response from vSMF1.

[0535] In an embodiment, the Nsmf_PDUSession_CreateSMContext request includes a vSMF roaming resumption indication (ie, the vSMF does not support roaming resumption) and / or a hSMF roaming resumption indication (ie, the hSMF does not support roaming resumption).

[0536] In step 4209, vSMF1 sends a Nsmf_PDUSession_Create request to hSMF2.

[0537] In an embodiment, the Nsmf_PDUSession_Create request includes the vSMF roaming resumption indication and / or the hSMF roaming resumption indication received from the AMF.

[0538] In step 4210. hSMF2 sends a Npcf_SMPolicyControl_Create request to PCF1 and receives a Npcf_SMPolicyControl_Create response from PCF1.

[0539] In step 4211. hSMF2 sends a Nsmf_PDUSession_Create response to vSMF1.

[0540] Fig.42a Some of the messages shown in may be the same as the corresponding messages described in 3GPP TS 23.502 V17.2.1. Fig.42a Some of the messages shown in may be enhanced according to embodiments of the present disclosure.

[0541] 3GPP TS23.527V17.3.1 may include the following contents. 6.X is used for the reestablishment process of the home routing PDU session 6.X.1 Overview This clause specifies the requirements in the AMF, V-SMF and H-SMF for the re-establishment procedure when the SMF set feature is not supported in the VPLMN or HPLMN. When both the V-SMF and the H-SMF support the SMF Set feature for roaming interface, the procedure specified in clause 6.5 shall be used to reestablish the home routing PDU session by reselecting an alternative V-SMF or H-SMF. The V-SMF and H-SMF may include a binding indication (i.e., the "3gpp-sbi-binding" HTTP header, see clause 5.2.3.2.6 of 3GPP TS 29.500

[10] ) in the service request and response messages, respectively (if supported) or set the "NF Set for Roaming Interface (SETFRI)" feature bit in the SupportFeature attribute to indicate that they support the SMF Set feature, as further described below. When establishing a Home Routing PDU Session or during the Inter-AMF Mobility Procedure for a Home Routing PDU Session, if the (target) AMF supports the "Recovery by Reselection of V-SMF on V-SMF Failure" (RVSMFR) feature, the corresponding feature bit shall be set in the supportFeatures attribute in the service request message towards the V-SMF. If both the AMF and the V-SMF support the "Recovery by Reselection of V-SMF on V-SMF Failure" (RVSMFR) feature, the V-SMF shall set the corresponding feature bit in the supportFeatures attribute in the service request message towards the H-SMF. If the V-SMF supports the SETFRI feature, the V-SMF shall set the corresponding feature bit in the supportFeatures attribute in the service request message towards the H-SMF and in the service response message towards the AMF. If the H-SMF supports RVSMFR or SETFRI, it shall set the corresponding feature bits in the supportedFeatures in the service response message towards the V-SMF, respectively. 6.X.2 V-SMF Failure When the H-SMF detects a V-SMF failure, it shall retrieve all PDU Sessions associated with the failed V-SMF and perform the following procedures on these PDU Sessions: - If V-SMF supports the SETFRI feature - If the H-SMF supports the SETFRI feature, the H-SMF shall maintain the PDU session and may reselect an alternative V-SMF, for example, when it needs to send any request message to the V-SMF; - If H-SMF does not support the SETFRI feature but H-SMF supports the RVSMFR feature, H-SMF shall maintain the PDU session and wait for PDU session reestablishment triggered by AMF reselecting another V-SMF in the same set (if both V-SMF and AMF support the RVSMFR feature); otherwise, H-SMF may delete the affected PDU If the PDU session is to be deleted, the AMF can request the UE to reactivate the PDU session according to the local configuration; - If V-SMF does not support the SETFRI feature: - Regardless of whether the H-SMF supports the SETFRI feature, the H-SMF may delete the affected PDU Sessions. When the AMF detects a V-SMF failure, it shall retrieve all PDU Sessions associated with the failed V-SMF and perform the following procedures on these PDU Sessions: - If the H-SMF and AMF support the RVSMFR feature, then if the V-SMF supports the SETFRI feature, the AMF shall reselect a replacement V-SMF that belongs to the same NF (service) set as the failed V-SMF. NOTE: It is assumed that if the SMF supports the SETFRI feature, it will support the SMF Set feature for non-roaming reference points. - Otherwise, the AMF shall release the affected PDU Session and may request the UE to reactivate the PDU Session according to local configuration. 6.X.2 H-SMF Failure When the V-SMF detects an H-SMF failure, it shall retrieve all PDU Sessions related to the failed H-SMF and perform the following procedures on these PDU Sessions: - If the H-SMF does not support the SETFRI feature, the V-SMF shall release the affected PDU Session; - If the H-SMF supports the SETFRI feature, the V-SMF may select another H-SMF (if the V-SMF also supports the SETFRI feature), otherwise the V-SMF shall release the PDU session. NOTE: Even if the H-SMF supports SMF Sets, there is no need to maintain resources associated with the affected PDU Sessions in the HPLMN.

[0542] Figure 42b A flowchart of a method according to another embodiment of the present disclosure is shown, which can be performed by a device implemented in AMF, or by a device at AMF, or by a device implemented as AMF, or by a device communicatively coupled to AMF. Therefore, the device can provide components or modules for completing various parts of method 4214 and components or modules for completing other processes together with other components. For the parts that have been described in the above embodiments, their description is omitted here for brevity.

[0543] At box 4215, the AMF may obtain third information about whether the resource is uniquely bound to a specific service instance in the first session management function (SMF).

[0544] At box 4216, the AMF may obtain fourth information about whether the second SMF supports reselection of an alternative first SMF instance within the SMF set of the first SMF.

[0545] At box 4217, the AMF can detect the first SMF failure.

[0546] At box 4218, the AMF may reselect an alternative service instance within the SMF set of the first SMF based on the third information and the fourth information.

[0547] For example, when the AMF detects a V-SMF failure, it shall retrieve all PDU Sessions associated with the failed V-SMF and perform the following procedures on these PDU Sessions:

[0548] - If the H-SMF supports the "Peer NF Set based Reselection" (PSETR) feature (e.g., the fourth information), and if the V-SMF supports the "Deployed Local SMF Set" (DLSET) feature (e.g., the third information), the AMF shall maintain the PDU session and shall reselect an alternative V-SMF service instance, for example when it needs to send any request message to the V-SMF.

[0549] - If the H-SMF does not support the PSETR feature and the V-SMF supports the DLSET feature, the AMF shall maintain the PDU Session and may reselect an alternative V-SMF service instance to request the selected alternative V-SMF to delete the PDU Session towards the UE and UPF. The V-SMF may request the UE to reactivate the PDU Session.

[0550] - For any other case, the AMF may locally release the affected PDU Session and / or notify the UE about the release of the PDU Session.

[0551] In an embodiment, the third information may be a Boolean value and / or the fourth information may be a Boolean value.

[0552] In an embodiment, obtaining the third information may include sending a network function (NF) discovery request to a network repository function (NRF) and receiving a NF discovery response including the third information from the NRF.

[0553] In an embodiment, obtaining the third information may include receiving a service response message or a service request message including the third information from the first SMF.

[0554] In an embodiment, obtaining the fourth information may include sending a NF discovery request to the NRF and receiving a NF discovery response including the fourth information from the NRF.

[0555] In an embodiment, obtaining the fourth information may include receiving an update session management (SM) context response message including the fourth information from the first SMF.

[0556] In an embodiment, reselecting an alternative service instance within the SMF set of the first SMF based on the third information and the fourth information may include: when the third information indicates that the resource is not uniquely bound to a specific service instance in the first SMF, and the fourth information indicates that the second SMF supports reselection of an alternative first SMF instance within the SMF set of the first SMF, reselecting an alternative V-SMF service instance within the SMF set of the first SMF.

[0557] In an embodiment, based on the third information and the fourth information, reselecting an alternative service instance within the SMF set of the first SMF may also include: when the third information indicates that the resources are not uniquely bound to a specific service instance in the first SMF, and the fourth information indicates that the second SMF does not support reselection of an alternative first SMF instance within the SMF set of the first SMF, reselecting an alternative first SMF service instance within the SMF set of the first SMF, and sending a request to the alternative first SMF to delete at least one affected protocol data unit (PDU) session toward a user equipment (UE).

[0558] In an embodiment, reselecting an alternative service instance within the SMF set of the first SMF based on the third information and the fourth information may include: when the third information indicates that the resources are uniquely bound to a specific service instance in the first SMF, releasing at least one affected PDU session without reselecting an alternative first SMF service instance.

[0559] In an embodiment, the first SMF may be a visited SMF and the second SMF may be a home SMF, or the first SMF may be an intermediate SMF and the second SMF may be an anchor SMF.

[0560] Fig.42c A flowchart of a method according to another embodiment of the present disclosure is shown, which can be performed by a device implemented in AMF, or performed by a device at AMF, or performed by a device implemented as AMF, or performed by a device communicatively coupled to AMF. Therefore, the device can provide components or modules for completing various parts of method 4220 and components or modules for completing other processes together with other components. For the parts that have been described in the above embodiments, their description is omitted here for brevity.

[0561] At box 4222, the AMF may obtain fifth information about whether the resource is uniquely bound to a specific service instance in the second SMF.

[0562] At box 4224, the AMF may send fifth information to the first SMF.

[0563] Fig.42d A flowchart of a method according to another embodiment of the present disclosure is shown, which can be performed by a device implemented in a first SMF, or by a device at the first SMF, or by a device implemented as a first SMF, or by a device communicatively coupled to the first SMF. Therefore, the device can provide components or modules for completing various parts of method 4230 and components or modules for completing other processes together with other components. For the parts that have been described in the above embodiments, their description is omitted here for brevity.

[0564] At block 4232, the first SMF may obtain fifth information regarding whether the resource is uniquely bound to a specific service instance in the second SMF.

[0565] At block 4234, the first SMF may obtain sixth information regarding whether the first SMF supports reselection of an alternative second SMF instance within the set of SMFs of the second SMF.

[0566] For example, when the V-SMF detects an H-SMF failure, it shall retrieve all PDU Sessions associated with the failed H-SMF and perform the following process on these PDU Sessions:

[0567] - If the V-SMF does not support the PSETR feature (e.g., the sixth information), the V-SMF may release the affected PDU session to the AMF and the UE, and may request the UE to reactivate the PDU session;

[0568] - If V-SMF supports PSETR feature: - If the H-SMF supports the DLSET feature (e.g. the fifth information), the V-SMF shall keep the PDU session and may reselect an alternative H-SMF service instance, e.g. when it needs to send any request message to the H-SMF; -If the H-SMF does not support the DLSET feature, the V-SMF may release the PDU session to the AMF and the UE, and the V-SMF may request the UE to reactivate the PDU session.

[0569] In an embodiment, the fifth information may be obtained from an Access and Mobility Function (AMF) or a second SMF.

[0570] Figure 42e A flowchart of a method according to another embodiment of the present disclosure is shown, which can be performed by a device implemented in a first SMF, or by a device at the first SMF, or by a device implemented as a first SMF, or by a device communicatively coupled to the first SMF. Therefore, the device can provide components or modules for completing various parts of method 4240 and components or modules for completing other processes together with other components. For the parts that have been described in the above embodiments, their description is omitted here for brevity.

[0571] At box 4242, the first SMF may send third information to the AMF regarding whether the resource is uniquely bound to a specific service instance in the first SMF.

[0572] At block 4244, the first SMF may send fourth information to the AMF regarding whether the second SMF supports reselecting an alternative first SMF instance within the SMF set of the first SMF. When the first SMF fails, the AMF may use the third information and the fourth information to reselect an alternative service instance within the SMF set of the first SMF.

[0573] Figure 42f A flowchart of a method according to another embodiment of the present disclosure is shown, which can be performed by a device implemented in a first SMF, or by a device at the first SMF, or by a device implemented as a first SMF, or by a device communicatively coupled to the first SMF. Therefore, the device can provide components or modules for completing various parts of method 4250 and components or modules for completing other processes together with other components. For the parts that have been described in the above embodiments, their description is omitted here for brevity.

[0574] At box 4252, the first SMF can obtain fourth information.

[0575] In an embodiment, the first SMF may obtain the fourth information by receiving the fourth information from the second SMF.

[0576] In an embodiment, the third information may be included in a service request or response message.

[0577] In an embodiment, the fourth information may be included in the update SM context response message.

[0578] Figure 42g A flowchart of a method according to another embodiment of the present disclosure is shown, which can be performed by a device implemented in a first SMF, or by a device at the first SMF, or by a device implemented as a first SMF, or by a device communicatively coupled to the first SMF. Therefore, the device can provide components or modules for completing various parts of method 4260 and components or modules for completing other processes together with other components. For the parts that have been described in the above embodiments, their description is omitted here for brevity.

[0579] At box 4262, the first SMF can send third information to the second SMF.

[0580] In an embodiment, the first SMF may be a visited SMF and the second SMF may be a home SMF, or the first SMF may be an intermediate SMF and the second SMF may be an anchor SMF.

[0581] Figure 42hA flowchart of a method according to another embodiment of the present disclosure is shown, which can be performed by a device implemented in a second SMF, or by a device at the second SMF, or by a device implemented as a second SMF, or by a device communicatively coupled to the second SMF. Therefore, the device can provide components or modules for completing various parts of method 4270 and components or modules for completing other processes with other components. For the parts that have been described in the above embodiments, their description is omitted here for brevity.

[0582] At block 4272, the second SMF may receive third information from the first SMF regarding whether the resource is uniquely bound to a specific service instance in the first SMF.

[0583] At block 4274, the second SMF may obtain fourth information regarding whether the second SMF supports reselection of an alternative first SMF instance within the set of SMFs of the first SMF.

[0584] For example, when the H-SMF detects a V-SMF failure, it shall retrieve all PDU Sessions associated with the failed V-SMF and perform the following process for these PDU Sessions:

[0585] - If the H-SMF supports the PSETR feature (e.g., the fourth message): - If the V-SMF supports the DLSET feature (e.g. the third information), the H-SMF shall maintain the PDU session and shall reselect an alternative V-SMF service instance, e.g. when it needs to send any request message to the V-SMF; - If the V-SMF does not support the DLSET feature, the H-SMF shall locally delete the affected PDU Sessions.

[0586] - If H-SMF does not support the PSETR feature: - The H-SMF shall delete the affected PDU Session.

[0587] At box 4276, optionally, the second SMF can send fifth information to the first SMF regarding whether the resource is uniquely bound to a specific service instance in the second SMF.

[0588] In an embodiment, the first SMF may be a visited SMF and the second SMF may be a home SMF, or the first SMF may be an intermediate SMF and the second SMF may be an anchor SMF.

[0589] Fig.434300 is a block diagram showing a device suitable for practicing some embodiments of the present disclosure. For example, any of the above-mentioned AMF, first SMF, second SMF, third NF or NRF can be implemented as device 4300 or implemented by device 4300.

[0590] The device 4300 includes at least one processor 4321, such as a digital processor (DP), and at least one memory (MEM) 4322 coupled to the processor 4321. The device 4300 may also include a transmitter TX and a receiver RX 4323 coupled to the processor 4321. The MEM 4322 stores a program (PROG) 4324. The PROG 4324 may include instructions that, when executed on the associated processor 4321, enable the device 4300 to operate according to embodiments of the present disclosure. The combination of at least one processor 4321 and at least one MEM 4322 may form a processing device 4325 suitable for implementing various embodiments of the present disclosure.

[0591] Various embodiments of the present disclosure may be implemented by a computer program executable by one or more of the processor 4321 , software, firmware, hardware, or a combination thereof.

[0592] MEM 4322 may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology such as, by way of non-limiting example, semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory, and removable memory.

[0593] Processor 4321 may be of any type suitable for the local technical environment, and may include one or more of the following: as non-limiting examples, 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.

[0594] In an embodiment where the apparatus is implemented as or at an AMF, the memory 4322 stores instructions executable by the processor 4321, whereby the AMF operates according to any method related to the AMF as described above.

[0595] In embodiments where the apparatus is implemented as or at a first SMF, the memory 4322 stores instructions executable by the processor 4321 whereby the first SMF operates according to any method associated with the first SMF as described above.

[0596] In embodiments where the apparatus is implemented as or at a second SMF, the memory 4322 stores instructions executable by the processor 4321 whereby the second SMF operates according to any of the methods described above in relation to the second SMF.

[0597] In an embodiment where the apparatus is implemented as or at a third NF, the memory 4322 stores instructions executable by the processor 4321, whereby the third NF operates according to any method related to the third NF as described above.

[0598] In embodiments where the apparatus is implemented as or at an NRF, the memory 4322 stores instructions executable by the processor 4321 whereby the NRF operates according to any of the methods described above in relation to the NRF.

[0599] Fig.44 A block diagram of an AMF provided for an embodiment of the present disclosure. As shown in the figure, AMF 4400 includes a first acquisition module 4401, which is configured to obtain third information about whether a resource is uniquely bound to a specific service instance in a first session management function (SMF). In an embodiment, AMF 4400 may also include a second acquisition module 4402, which is configured to obtain fourth information about whether the second SMF supports reselecting a replacement first SMF instance within the SMF set of the first SMF. AMF 4400 may also include a detection module 4403, which is configured to detect a failure of the first SMF. AMF 4400 further includes a reselection module 4404, which is configured to reselect an alternative service instance within the SMF set of the first SMF based on the third information and the fourth information.

[0600] In an embodiment, the AMF 4400 may further include a third obtaining module 4405 configured to obtain fifth information about whether the resource is uniquely bound to a specific service instance in the second SMF.

[0601] In an embodiment, the AMF 4400 may further include a sending module 4406 configured to send fifth information to the first SMF.

[0602] Fig.45 4500 is a block diagram showing a first SMF according to an embodiment of the present disclosure. As shown in the figure, the first SMF 4500 may include a first sending module 4501, which is configured to send third information about whether the resource is uniquely bound to a specific service instance in the first SMF to the AMF. The first SMF 4500 may also include a second sending module 4502, which is configured to send fourth information about whether the second SMF supports reselection of an alternative first SMF instance within the SMF set of the first SMF to the AMF.

[0603] In an embodiment, the AMF may use the third information and the fourth information to reselect an alternative service instance within the SMF set of the first SMF when the first SMF fails.

[0604] In an embodiment, the first SMF 4500 may further include a first obtaining module 4503, which is configured to obtain fifth information about whether the resource is uniquely bound to a specific service instance in the second SMF. The first SMF 4500 may also include a second obtaining module 4504, which is configured to obtain sixth information about whether the first SMF supports reselection of an alternative second SMF instance within the SMF set of the second SMF.

[0605] In an embodiment, the first SMF 4500 may further include a third obtaining module 4505 configured to obtain fourth information.

[0606] In an embodiment, the first SMF 4500 may further include a third sending module 4506 configured to send third information to the second SMF.

[0607] Fig.46 4600 is a block diagram showing a second SMF according to an embodiment of the present invention. As shown in the figure, the second SMF 4600 includes a receiving module 4601, which is configured to receive third information about whether the resource is uniquely bound to a specific service instance in the first SMF from the first SMF. The second SMF 4600 may also include an obtaining module 4602, which is configured to obtain fourth information about whether the second SMF supports reselection of an alternative first SMF instance within the SMF set of the first SMF.

[0608] In an embodiment, the second SMF 4600 may further include a sending module 4603 configured to send fifth information to the first SMF regarding whether the resource is uniquely bound to a specific service instance in the second SMF.

[0609] Embodiments herein may provide many advantages, and the following is a non-exhaustive list of examples of advantages. In some embodiments herein, a reconstruction process is proposed to rebuild PDU sessions affected by SMF failures. In some embodiments herein, the time to recover PDU sessions affected by SMF failures can be reduced. In some embodiments herein, ghost session problems can be solved. In some embodiments herein, service availability can be improved. The embodiments herein are not limited to the above-mentioned features and advantages. Those skilled in the art will recognize other features and advantages after reading the following detailed description.

[0610] The term unit or module may have the conventional meaning in the field of electronics, electrical devices and / or electronic devices, and may include, for example, electrical and / or electronic circuits, devices, modules, processors, memories, logical solid-state and / or discrete devices, computer programs or instructions for performing corresponding tasks, processes, calculations, output and / or display functions, etc., such as those described herein.

[0611] By using the functional unit, the AMF, the first SMF or the second SMF may not need a fixed processor or memory, and any computing resources and storage resources can be arranged from the AMF, the first SMF or the second SMF in the communication system. The introduction of virtualization technology and network computing technology can improve the efficiency of network resource utilization and the flexibility of the network.

[0612] According to one aspect of the present disclosure, a computer program product is provided, which is tangibly stored on a computer-readable storage medium and includes instructions. When the instructions are executed on at least one processor, the instructions cause the at least one processor to perform any of the methods described above.

[0613] According to one aspect of the present disclosure, a computer-readable storage medium is provided, which stores instructions. When the instructions are executed on at least one processor, the instructions cause the at least one processor to perform any of the methods described above.

[0614] In addition, the present disclosure may also provide a carrier containing the above-mentioned computer program, wherein the carrier is one of an electronic signal, an optical signal, a radio signal or a computer-readable storage medium. The computer-readable storage medium may be, for example, an optical disc or an electronic storage device, such as a RAM (random access memory), a ROM (read-only memory), a flash memory, a magnetic tape, a CD-ROM, a DVD, a Blu-ray disc, etc.

[0615] The techniques described herein can be implemented in various ways so that the device that implements one or more functions of the corresponding device described with the embodiments includes not only prior art components, but also components for implementing one or more functions of the corresponding device described with the embodiments, and it can include separate components for each separate function or components that can be configured to perform two or more functions. For example, these techniques can be implemented in hardware (one or more devices), firmware (one or more devices), software (one or more modules), or a combination thereof. For firmware or software, the implementation can be accomplished by modules (e.g., processes, functions, etc.) that perform the functions described herein.

[0616] Exemplary embodiments of the present invention have been described above with reference to the block diagrams and flowchart illustrations of the methods and apparatus. It will be understood that each block of the block diagrams and flowchart illustrations and combinations of blocks in the block diagrams and flowchart illustrations, respectively, can be implemented by various components including computer program instructions. These computer program instructions can be loaded onto a general-purpose computer, a special-purpose computer, or other programmable data processing device to produce a machine, whereby the instructions executed on the computer or other programmable data processing device create components for implementing the functions specified in the flowchart block or blocks.

[0617] In addition, although the operations are depicted in a particular order, this should not be understood as requiring that the operations be performed in the particular order shown or in sequence, or that all illustrated operations be performed to achieve the desired results. In some cases, multitasking and parallel processing may be advantageous. Similarly, although the above discussion contains several specific implementation details, these should not be interpreted as limitations on the scope of the subject matter described herein, but should be interpreted as descriptions of features that may be specific to a particular embodiment. Certain features described in the context of a separate embodiment may also be implemented in combination in a single embodiment. On the contrary, the various features described in the context of a single embodiment may also be implemented in multiple embodiments individually or in any suitable sub-combination.

[0618] Although this specification contains many specific implementation details, these should not be interpreted as limitations on the scope of any implementation or the scope of what may be claimed, but rather should be interpreted as descriptions of features that may be specific to a particular embodiment of a particular implementation. Certain features described in this specification in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, the various features described in the context of a single embodiment may also be implemented in multiple embodiments individually or in any suitable sub-combination. In addition, although the above-mentioned features may be described as working in certain combinations, or even initially claimed to be so protected, in some cases one or more features from the claimed combination may be deleted from the combination, and the claimed combination may be directed to a sub-combination or a variation of the sub-combination.

[0619] It is obvious to those skilled in the art that, as technology advances, the inventive concept can be implemented in various ways. The above embodiments are given for the purpose of describing rather than limiting the present disclosure, and it should be understood that, as those skilled in the art will readily appreciate, modifications and variations can be made without departing from the spirit and scope of the present disclosure. Such modifications and variations are considered to be within the scope of the present disclosure and the appended claims. The scope of protection of the present disclosure is defined by the appended claims.

Claims

1. A method (4214) performed by an access and mobility function (AMF), comprising: obtaining (4215) third information about whether the resource is uniquely bound to a specific service instance in the first session management function SMF; obtaining (4216) fourth information regarding whether the second SMF supports reselection of an alternative first SMF instance within the set of SMFs of the first SMF; Detecting (4217) a failure of the first SMF; as well as Based on the third information and the fourth information, reselect (4218) an alternative service instance within the set of SMFs of the first SMF.

2. The method according to claim 1, wherein: The third information is a Boolean value and / or the fourth information is a Boolean value.

3. The method according to claim 1 or 2, wherein: Obtaining the third information includes: Sending a network function NF discovery request to the network repository function NRF; and An NF discovery response including the third information is received from the NRF.

4. The method according to any one of claims 1 to 3, wherein: Obtaining the third information includes: A service response message or a service request message including the third information is received from the first SMF.

5. The method according to any one of claims 1 to 4, wherein: Obtaining the fourth information includes: Sending a NF discovery request to the NRF; and An NF discovery response including the fourth information is received from the NRF.

6. The method according to any one of claims 1 to 5, wherein: Obtaining the fourth information includes: An update session management SM context response message including the fourth information is received from the first SMF.

7. The method according to any one of claims 1 to 6, wherein: Based on the third information and the fourth information, reselecting an alternative service instance in the SMF set of the first SMF comprises: When the third information indicates that the resource is not uniquely bound to the specific service instance in the first SMF, and the fourth information indicates that the second SMF supports reselecting the alternative first SMF instance within the SMF set of the first SMF, the alternative V-SMF service instance is reselected within the SMF set of the first SMF.

8. The method according to any one of claims 1 to 7, wherein: Based on the third information and the fourth information, reselecting an alternative service instance in the SMF set of the first SMF comprises: When the third information indicates that the resource is not uniquely bound to the specific service instance in the first SMF, and the fourth information indicates that the second SMF does not support reselection of the alternative first SMF instance within the SMF set of the first SMF, reselecting the replacement first SMF service instance within the SMF set of the first SMF; and A request for deleting at least one affected protocol data unit (PDU) session towards a user equipment (UE) is sent to the replacement first SMF.

9. The method according to any one of claims 1 to 8, wherein: Based on the third information and the fourth information, reselecting an alternative service instance in the SMF set of the first SMF comprises: When the third information indicates that the resource is uniquely bound to the specific service instance in the first SMF, at least one affected PDU session is released without reselecting the alternative first SMF service instance.

10. The method according to any one of claims 1 to 9, wherein: The first SMF is a visited SMF and the second SMF is a home SMF, or the first SMF is an intermediate SMF and the second SMF is an anchor SMF.

11. The method according to any one of claims 1 to 10, further comprising: obtaining (4222) fifth information regarding whether the resource is uniquely bound to a specific service instance in the second SMF; as well as The fifth information is sent (4224) to the first SMF.

12. A method (4240) performed by a first session management function (SMF), comprising: sending (4242) third information to the AMF regarding whether the resource is uniquely bound to a specific service instance in the first SMF; sending (4244) fourth information to the AMF regarding whether the second SMF supports reselection of an alternative first SMF instance within the SMF set of the first SMF; The third information and the fourth information are used by the AMF to reselect an alternative service instance within the SMF set of the first SMF when the first SMF fails.

13. The method according to claim 12, further comprising: Obtain (4252) the fourth information.

14. The method according to claim 13, wherein: Obtaining the fourth information includes: The fourth information is received from the second SMF.

15. The method according to any one of claims 12 to 14, further comprising: The third information is sent (4262) to the second SMF.

16. The method according to any one of claims 12 to 15, wherein: The third information is included in a service request or response message.

17. The method according to any one of claims 12 to 16, wherein: The fourth information is included in the update SM context response message.

18. The method according to any one of claims 12 to 17, wherein: The first SMF is a visited SMF and the second SMF is a home SMF, or the first SMF is an intermediate SMF and the second SMF is an anchor SMF.

19. The method according to any one of claims 12 to 18, further comprising: obtaining (4232) fifth information regarding whether the resource is uniquely bound to a specific service instance in the second SMF; as well as Sixth information is obtained (4234) regarding whether the first SMF supports reselection of an alternative second SMF instance within the SMF set of the second SMF.

20. The method according to claim 19, wherein: The fifth information is obtained from the access and mobility function AMF or the second SMF.

21. A method (4270) performed by a second session management function SMF, comprising: receiving (4272) third information from the first SMF regarding whether a resource is uniquely bound to a specific service instance in the first SMF; as well as Fourth information is obtained (4274) regarding whether the second SMF supports reselection of an alternative first SMF instance within the set of SMFs of the first SMF.

22. The method according to claim 21, further comprising: Fifth information is sent (4276) to the first SMF regarding whether the resource is uniquely bound to a specific service instance in the second SMF.

23. The method according to claim 21 or 22, wherein: The first SMF is a visited SMF and the second SMF is a home SMF, or the first SMF is an intermediate SMF and the second SMF is an anchor SMF.

24. An access and mobility function AMF (4300), comprising: Processor(4321); as well as A memory (4322) coupled to the processor (4321), the memory (4322) storing instructions executable by the processor (4321), whereby the AMF (4300) is operable to: Obtaining third information about whether the resource is uniquely bound to a specific service instance in the first session management function SMF; Obtaining fourth information about whether the second SMF supports reselecting an alternative first SMF instance within the SMF set of the first SMF; Detecting a failure of the first SMF; as well as Based on the third information and the fourth information, a replacement service instance is reselected within the SMF set of the first SMF.

25. The AMF according to claim 24, wherein: The AMF is further operable to perform the method of any one of claims 2 to 11.

26. A first session management function SMF (4300), comprising: Processor(4321); as well as A memory (4322) coupled to the processor (4321), the memory (4322) storing instructions executable by the processor (4321), whereby the first SMF (4300) is operable to: Sending third information to the AMF about whether the resource is uniquely bound to a specific service instance in the first SMF; Sending fourth information to the AMF about whether the second SMF supports reselecting an alternative first SMF instance within the SMF set of the first SMF; The third information and the fourth information are used by the AMF to reselect an alternative service instance within the SMF set of the first SMF when the first SMF fails.

27. The first SMF of claim 26, wherein: The first SMF is further operable to perform the method of any one of claims 13 to 20.

28. A second session management function SMF (4300), comprising: Processor(4321); as well as A memory (4322) coupled to the processor (4321), the memory (4322) storing instructions executable by the processor (4321), whereby the second SMF (4300) is operable to: receiving third information from the first SMF regarding whether a resource is uniquely bound to a specific service instance in the first SMF; as well as Obtain fourth information about whether the second SMF supports reselection of an alternative first SMF instance within the SMF set of the first SMF.

29. The second SMF according to claim 28, wherein: The second SMF is further operable to perform the method of any one of claims 22 to 23.

30. A computer-readable storage medium storing instructions which, when executed by at least one processor, cause the at least one processor to perform the method according to any one of claims 1 to 23.

31. A computer program product comprising instructions which, when executed by at least one processor, cause the at least one processor to perform the method according to any one of claims 1 to 23.

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