Patent Description:
Therefore, the <NUM> or pre-<NUM> communication system is also called a "Beyond <NUM> Network" or a "Post LTE System". In the <NUM> system, hybrid FSK and QAM modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access(NOMA), and sparse code multiple access (SCMA) as an advanced access technology have also been developed.

The Internet of everything (IoE), which is a combination of the loT technology and the big data processing technology through connection with a cloud server, has emerged. As technology elements, such as "sensing technology", "wired/wireless communication and network infrastructure", "service interface technology", and "security technology" have been demanded for loT implementation, a sensor network, a machine-to-machine (M2M) communication, machine type communication (MTC), and so forth have been recently researched. Such an loT environment may provide intelligent Internet technology services that create a new value to human life by collecting and analyzing data generated among connected things.

In line with this, various attempts have been made to apply <NUM> communication systems to loT networks. Application of a cloud radio access network (RAN) as the above-described big data processing technology may also be considered an example of convergence of the <NUM> technology with the loT technology.

In a <NUM> communication system, the connection with various access networks such as New Radio (NR), wireless LAN, wired LAN, and the like is supported. At this time, an access traffic steering (ATSSS) technology is a technology that enables traffic transmission using different access networks and is currently being developed.

<CIT> discloses a session processing method and a related device. <CIT> discloses a session management function (SMF) receives, from a user plane function (UPF), a data notification message for a multi access packet data unit (MA PDU) session.

In order to use ATSSS in a communication system complying with the current 3GPP standard, a User Equipment (UE), an Access and Mobility Management Function (AMF), a Session Management Function (SMF), and a User Plane Function (UPF) should support the function. When the UE is registered in a newAMF due to movement of the UE in the state in which the UE establishes one or more Multi Access Packet Data Unit (MA PDU) sessions through an old AMF, if the new AMF does not support ATSSS, the MA PDU sessions for the corresponding access should be necessarily released. A technology for releasing the MA PDU session does not exist at present, and the disclosure proposes a method and an apparatus for solving the problem.

In a wireless communication system according to an embodiment, when a User Equipment (UE) is registered in an Access and Mobility Management Function (AMF) which does not support ATSSS (registration procedure), a conventionally registered AMF may identify the registration and release the old MA PDU session or the UE may identify the registration and release the old MA PDU session.

The disclosure supports various schemes for releasing MA PDU sessions which cannot be supported by a 3GPP <NUM> system. When the UE is registered in an AMF which does not support ATSSS on the basis of embodiments of the disclosure, the old MA PDU sessions may be efficiently released.

As used herein, the "unit" refers to a software element or a hardware element, such as a Field Programmable Gate Array (FPGA) or an Application Specific Integrated Circuit (ASIC), which performs a predetermined function. However, the "unit" does not always have a meaning limited to software or hardware. The "unit" may be constructed either to be stored in an addressable storage medium or to execute one or more processors. Therefore, the "unit" includes, for example, software elements, object-oriented software elements, class elements or task elements, processes, functions, properties, procedures, sub-routines, segments of a program code, drivers, firmware, micro-codes, circuits, data, database, data structures, tables, arrays, and parameters. The elements and functions provided by the "unit" may be either combined into a smaller number of elements, or a "unit", or divided into a larger number of elements, or a "unit". Moreover, the elements and "units" or may be implemented to reproduce one or more CPUs within a device or a security multimedia card.

The disclosure relates to a method and an apparatus for supporting various services in a wireless communication system. Specifically, the disclosure describes a technology for providing an access traffic steering (Access Traffic Steering, Switching, Splitting (ATSSS)) function in a wireless communication system.

As used in the following description, terms for identifying access nodes, terms referring to network entities or network functions (NFs), terms referring to messages, terms referring to interfaces between network entities, terms referring to various identification information, and the like are illustratively used for the sake of convenience. Therefore, the disclosure is not limited by the terms as used below, and other terms referring to subjects having equivalent technical meanings may be used.

<FIG> illustrates the system architecture for supporting Access Traffic Steering, Switching, Splitting (ATSSS) in a 3GPP <NUM> system. Through the ATSSS function, traffic transmission can be performed through multiple paths (for example, 3GPP access <NUM> and non-3GPP access <NUM>) between a Protocol Data Unit (PDU) (or a packet data unit) session anchor User Plane Function (UPF) <NUM> and a User Equipment (UE) <NUM> as illustrated in <FIG>. Meanwhile, in order to use ATSSS, the User Equipment (UE) <NUM>, an Access and Mobility Management Function (AMF) <NUM>, a Session Management Function (SMF) <NUM>, and a User Plane Function (UPF) <NUM> should support the ATSSS.

<FIG> illustrates a problem to be solved by the disclosure. <FIG> illustrates a situation in which a UE <NUM> registers to a new AMF <NUM> due to UE movement <NUM> in the state in which the UE <NUM> already established one or more MA PDU sessions with an old AMF <NUM>. When the new AMF <NUM> does not support ATSSS (that is, ATSSS-incapable AMF), the old AMF <NUM> transmits context for the old MA PDU session to the new AMF through UE context transfer as indicated by reference numeral <NUM>. At this time, although the new AMF does not support ATSSS, if the MA PDU session is not released, an unexpected operation may occur due to the existence of MA PDU sessions that are not released. Accordingly, for the efficient operation of the MA PDU session, MA PDU sessions for the corresponding access should be necessarily released. A technology for releasing the MA PDU session does not exist at present, and the disclosure proposes a method and an apparatus for solving the problem.

<FIG> illustrates a method by which an old AMF releases an MA PDU session through UpdateSMContext according to an embodiment when a UE is registered in a new AMF which does not supports ATSSS.

Referring to <FIG>, in step <NUM>, the UE may transmit a registration request message to the new AMF in order to perform a registration process for the new AMF (steps <NUM> to <NUM>). Specifically, the UE may transmit an Access Node (AN) message including the registration request message to an AN in step <NUM>, and the AN receiving the AN message may determine an AMF in step <NUM> and transmit an N2 message including the registration request message to the determined AMF (that is, a new AMP) in step <NUM>.

In step <NUM>, the new AMF may transmit a Namf_Communication_UEContextTransfer request message to the old AMF. At this time, the corresponding message may include an access type and supported features of the UE. When the new AMF does not support ATSSS, the supported features do not include an MA PDU session support indicator.

When it is determined that the new AMF does not support ATSSS, the old AMF identifies whether there is an MA PDU session for the access type received in step <NUM> in UE context in step <NUM>. When there is an MA PDU session for the received access type, the old AMF may perform an operation for releasing the MA PDU session for the access type for the SMF. Specifically, the old AMF may transmit a Nsmf PDUSession_UpdateSMContext request message to the SMF. The Nsmf PDUSession_UpdateSMContext request message may include information on an SM context ID, a release indication, and access for MA PDU session release. At this time, the SM context ID is a context identifier for an MA PDU session ID which should be locally released, and should be shared between the AMF and the SMF. The release indication is an indicator indicating a release request, and the access for MA PDU session release is an access type which should be released.

At this time, the old AMF may determine whether the new AMF supports ATSSS as follows: <NUM>) an MA PDU session support indicator in a supported features field or parameter included in the request message of step <NUM>, <NUM>} an MA PDU session support indicator in a supported feature of an NF profile for the new AMF stored in a Network Repository Function (NRF), and <NUM>) local configuration of the AMF.

Upon receiving the message of step <NUM> from the AMF, the SMF determines whether to release only the access type for receiving the MA PDU session mapped to the SM context ID or release all accesses through a local policy in step <NUM>. The SMF may indicate to the UPF whether to release the MA PDU session only for one access or release MA PDU sessions for all accesses according to the determination result.

The SMF transmits a Nsmf PDUSession_UpdateSMContext response message including the result of the request of step <NUM> to the old AMF in step <NUM>.

Even though the response message from the SMF includes a message for making a request for transmission to the UE or the AN, the old AMF does not perform an operation such as transmission in step <NUM>. The old AMF transmits UE context to the new AMF in response to the request message of step <NUM>.

At this time, the old AMF does not insert context for MA PDU sessions successfully released from the message from the SMF into UE context to be transmitted to the new AMF.

In step <NUM>, the remaining registration procedures of the UE are performed. When MA PDU session context missed in the UE context received in step <NUM> exists in the UE, the UE may locally release the MA PDU session existing only in the UE through a synchronization process with the new AMF.

<FIG> illustrates a method by which an old AMF releases an old MA PDU session through ReleaseSMContext according to an embodiment when a UE is registered in a new AMF which does not supports ATSSS.

When it is determined that the new AMF does not support ATSSS, the old AMF identifies whether there is an MA PDU session for the access type received in step <NUM> in UE context in step <NUM>. When there is an MA PDU session for the received access type, the old AMF may perform an operation for releasing the MA PDU session for the access type for the SMF.

Specifically, the old AMF may transmit a Nsmf PDUSession_Release request message to the SMF. The Nsmf_PDUSession_Release request message may include information on an SM context ID and access for MA PDU session release. At this time, the SM context ID is a context identifier for an MA PDU session ID which should be locally released, and should be shared between the AMF and the SMF. The access for MA PDU session release is an access type which should be released.

At this time, the old AMF may determine whether the new AMF supports ATSSS as follows: <NUM>) an MA PDU session support indicator in a supported features included in the request message of step <NUM>, <NUM>) an MA PDU session support indicator in a supported feature of an NF profile for the new AMF stored in a Network Repository Function (NRF), and <NUM>) local configuration of the AMF.

Upon receiving the message of step <NUM> from the AMF, the SMF determines whether to release only the access type for receiving the MA PDU session mapped to the SM context ID or release all accesses through a local policy in step <NUM>. The SMF may indicate to the UPF whether to release only the access for the MA PDU session or release all accesses according to the determination result.

In step <NUM>, the SMF transmits a Nsmf PDUSession_ReleaseSMContext response including the result of the request of step <NUM>.

In step <NUM>, the old AMF transmits UE context to the new AMF in response to the request message of step <NUM>.

<FIG> illustrates an MA PDU session release method through an MA PDU session release request including a specific request type of the UE according to an embodiment when the UE is registered in a new AMF which does not support ATSSS.

In step <NUM>, the UE may perform a registration procedure of the new AMF. The registration procedure of the new AMF may be performed to be the same as the registration procedure of the new AMF according to the embodiments of <FIG> and <FIG>.

In step <NUM>, when an MA PDU session support indicator is not included in a registration accept message and there is a PDU session ID of the MA PDU session for an access type for which the registration accept message is received in a PDU session status of the registration accept message (<NUM>-<NUM>), the UE may insert the PDU session ID and a request type into a PDU session release request message with respect to all of the corresponding PDU session IDs and transmit the PDU session release request message to the new AMF (<NUM>-<NUM>).

At this time, the release type is used to indicate an access type which the UE desires to release. When the UE desires to release the MA PDU session only for the access type for which the registration accept message is received, the release type may indicate the corresponding access type. When the UE desires to release MA PDU sessions for all accesses, the release type may be configured as an indicator making a request for releasing all accesses.

In step <NUM>, the new AMF may transmit an N1 SM container received from the UE to the SMF through a Nsmf PDUSession_UpdateSMContext request message. At this time, the new AMF also transmits an SM context ID mapped to the PDU session ID.

When the release type indicates to release all accesses, the SMF completely releases the corresponding MA PDU session in step <NUM>. Meanwhile, when the release type indicates only one access type, the SMF may determine whether to release only the access type for which the MA PDU session mapped to the SM context ID or release all accesses through a local policy.

When it is determined to release only one access type on the basis of the determination of step <NUM>, the SMF indicates to release the MA PDU session for the corresponding access type to the UE, the Access Network (AN), and the UPF in step <NUM>.

Meanwhile, when it is determined to release all access types on the basis of the determination of step <NUM>, the SMF indicates to release the MA PDU session for all access types to the UE, the Access Network (AN), and the UPF.

<FIG> illustrates an MA PDU session release method through an MA PDU session release request of the UE according to an embodiment when the UE is registered in a new AMF which does not support ATSSS.

In step <NUM>, when an MA PDU session support indicator is not included in a registration accept message and a PDU session ID of an MA PDU session exists in a PDU session status of the registration accept message for an access type for which the registration accept message is received (<NUM>-<NUM>), all of the corresponding PDU session IDs into the UE inserts a PDU session release request message and transmits the PDU session release request message to the AMF (<NUM>-<NUM>).

In step <NUM>, the new AMF may transfer an N1 SM container received from the UE to the SMF through a Nsmf PDUSession_UpdateSMContext request message. At this time, the new AMF also transmits an SM context ID mapped to the PDU session ID.

In step <NUM>, the SMF indicates to releases the MA PDU session for all access types.

<FIG> illustrates a sequence diagram for a procedure in which the UE releases an old MA PDU session through local release according to an embodiment.

In step <NUM>, the UE performs a registration procedure of the new AMF. When an MA PDU session support indicator is not included in a registration accept message and a PDU session ID of an MA PDU session exists for the access type for which the registration accept message is received, the UE may locally release all of the corresponding PDU session IDs.

When the MA PDU sessions are locally released in step <NUM>, the UE may perform a service request procedure in step <NUM>. At this time, the PDU session IDs of the MA PDU sessions released in step <NUM> are not included in the PDU session status.

In step <NUM>, the new AMF may transfer an N1 SM container received from the UE to the SMF through a Nsmf PDUSession_ReleaseSMContext request message. At this time, the new AMF also transmits an SM context ID mapped to the PDU session ID.

In step <NUM>, the SMF may perform MA PDU session release for all access types.

<FIG> illustrates a method by which, when an AMF of the UE is changed into an AMF which does not support ATSSS during N2-based handover, an old AMF releases an old MA PDU session through UpdateSMContext according to an embodiment.

Referring to <FIG>, in step <NUM>, an N2 handover procedure may be performed. An old RAN (that is, a source RAN or an S-RAN) may transmit a handover-required message along with a target ID to an old AMF (that is, a source AMF or an S-AMF).

When it is determined that the old AMF cannot support the UE anymore, the old AMF may perform AMF discovery/selection to select a new AMF (that is, a targetAMF or a T-AMF) in step <NUM>. At this time, the old AMF can perform AMF discovery/selection through a Network Repository Function (NRF) or AMF discovery/selection through AMF local configuration.

When AMF discovery/selection can be performed through the NRF, the old AMF may transmit a Nnrf_NFDiscovery Request message to the NRF in step 803a. The corresponding message may include various query parameters for discovering a new AMF, and an NF type parameter may be configured as an AMF and transmitted.

In step 803b, the NRF may select a new AMF and transmit an NF profile of the corresponding AMF to the old AMF. At this time, the NF profile includes supported features for NF services which the AMF provides (for example, Namf_Communication). The supported features include information on whether ATSSS is supported (that is, MA PDU).

When the MA PDU parameter does not exist in the supported features of the message received in step 803b, the old AMF may determine that new AMF does not support ATSSS in step <NUM> and perform step <NUM>.

When the old AMF determines that the new AMF does not support ATSSS in step <NUM>, the old AMF identifies whether there is MA PDU session context in UE context of the old AMF. When there is MA PDU session context in UE context, the old AMF may perform an operation for releasing the MA PDU session for the SMF. Specifically, the old AMF may transmit a Nsmf PDUSession_UpdateSMContext request message to the SMF. The Nsmf PDUSession_UpdateSMContext request message may include information on an SM context ID, a release indication, and access for MA PDU session release. At this time, the SM context ID is a context identifier for an MA PDU session ID which should be locally released, and is shared between the AMF and the SMF. The release indication is an indicator indicating a release request, and the access for MA PDU session release is an access type which should be released.

At this time, the old AMF may determine that the new AMF does not support ATSSS through the following methods: <NUM>) the case in which there is no MA PDU support indicator in a supported feature of a response message from the NRF of step 803b when AMF discovery/selection through the NRF is supported, <NUM>) the case in which the old AMF had exchanged supported features in the past through communication with the new AMF and the case in which there is no MA PDU support indicator in supported features at that time and information indicating that the new AMF does not support ATSSS is stored on the basis thereof, and <NUM>) the case in which information indicating that the new AMF does not support ATSSS is stored through local configuration of the old AMF.

Upon receiving the message in step <NUM> from the AMF, the SMF determines whether to release only the access type for receiving the MA PDU session mapped to the SM context ID or release all accesses through a local policy in step <NUM>. The SMF may indicate to the UPF whether to release only the access for the MA PDU session or release all accesses according to the determination result.

The SMF may transmit a Nsmf PDUSession_UpdateSMContext response message including the result of the request of step <NUM> to the old AMF in step <NUM>.

Even though the message from the SMF includes a message for making a request for transmission to the UE or the AN, the old AMF does not perform an operation such as transmission in step <NUM>. The old AMF transmits a Namf_Communication_CreateUEContext request message in order to transfer UE context to the new AMF.

At this time, the old AMF does not insert context for successfully released MA PDU sessions into UE context to be transmitted to the new AMF.

In step <NUM>, the remaining procedures for N2-based handover of the UE may be performed. When MA PDU session context missed in the UE context received in step <NUM> exists in the UE, the UE may locally release the MA PDU session existing only in the UE through a synchronization process with the new AMF.

<FIG> illustrates a method of releasing an MA PDU session after the old AMF identifies that the UE is successfully registered in the new AMF according to an embodiment when the UE makes a request for registration in the AMF that does not support ATSSS.

Referring to <FIG>, in step <NUM>, the UE may transmit a registration request message to the new AMF in order to perform a registration process for the new AMF (steps <NUM> to <NUM>). Specifically, the UE may transmit an Access Node (AN) message including the registration request message to an AN in step <NUM>, and the AN may determine an AMF in step <NUM> and transmit an N2 message including the registration request message to the determined AMF (that is, a new AMF) in step <NUM>.

In step <NUM>, the new AMF may transmit a Namf_Communication_UEContextTransfer request message to the old AMF. At this time, the request message may include an access type and supported features of the UE. The supported features include information on whether the new AMF supports ATSSS, and the old AMF may recognize whether the new AMF supports ATSSS on the basis thereof.

In case that it is determined that the new AMF does not support ATSSS in step <NUM>, the old AMF may transmit UE context except for context for the MA PDU session to the new AMF in step <NUM>.

Since the AMF was changed, the new AMF may be registered in Unified Data Management (UDM) through a Nudm_UECM_Registration message (including a Subscription permanent Identifier (SUPI) and an access type) in step <NUM>.

In step <NUM>, the UDM may inform the old AMF which provides the service for the access type of the corresponding UE that the new AMF has been registered through a Nudm_UECM_DeregistrationNotification message (including an SUPI and an access type).

After receiving the message of step <NUM>, the old AMF may make a request for releasing the MA PDU session through a Nsmf PDUSession_UpdateSMContext request message or a Nsmf PDUSession_ReleaseSMContext request message to the SMF in step <NUM>. At this time, the messages may include a PDU session ID of the MA PDU session and an access type.

When the access type is specified in the message to the SMF, the SMF may perform release for the corresponding access of the MA PDU in step <NUM>. When the access type is not specified, release for both accesses may be performed.

In step <NUM>, the remaining registration procedures may be performed. The UE receives a registration accept message from the new AMF. At this time, when there is an MA PDU session which is not included in a PDU session status Information Element (IE) of the corresponding message, the UE may locally release the MA PDU session only for the access for which the registration accept message is received or locally release MA PDU sessions for both access types.

<FIG> illustrates a method by which, when an AMF of the UE is changed into a new AMF which does not supportATSSS during N2-based handover, the old AMF (S-AMF) receives a message indicating that the handover for the UE is successfully performed from the new AMF and then releases the MA PDU session according to an embodiment.

Referring to <FIG>, in step <NUM>, the S-RAN may transmit a handover-required message to the S-AMF.

When it is determined that the S-AMF (or old AMF) cannot support the UE anymore, the S-AMF performs AMF discovery/selection and selects a new AMF (that is, T-AMF) in step <NUM>. At this time, the S-AMF can perform AMF discovery/selection through a Network Repository Function (NRF) orAMF discovery/selection through AMF local configuration.

When AMF discovery/selection can be performed through the NRF, the S-AMF may transmit a Nnrf_NFDiscovery request message to the NRF in step 1003a. The corresponding message may include various query parameters for discovering a new AMF, and an NF type parameter may be configured as the AMF and transmitted.

In step 1003b, the NRF may select the new AMF and transmit an NF profile of the corresponding AMF to the S-AMF. At this time, the NF profile includes supported features for NF services (for example, Namf_Communication) which the AMF provides. The supported features include information indicating whether ATSSS is supported (that is, MA PDU).

In step <NUM>, the S-AMF may determine whether the T-AMF supports ATSSS. The S-AMF determines that the T-AMF does not support ATSSS in the following cases: <NUM>) the case in which the supported features of the message received in step 1003b do not have an MA PDU, <NUM>) the case in which the T-AMF knows that there is no MA PDU in the supported features of the previous message, and <NUM>) the case in which the T-AMF knows that ATSSS is not supported on the basis of local configuration.

When it is determined that the T-AMF does not supportATSSS, the S-AMF may transmit UE context except for MA PDU session context to the T-AMF in step <NUM>.

In step <NUM>, the UE may transmit a Handover Confirm message to the T-RAN and the T-RAN may transmit a Handover Notify message to the T-AMF as the N2 handover procedure.

In step <NUM>, the T-AMF may transmit a message indicating that the N2 handover for the UE has been successfully performed to the S-AMF.

After receiving the message of step <NUM>, the S-AMF may make a request for releasing the MA PDU session through a Nsmf PDUSession_UpdateSMContext request message or a Nsmf PDUSession_ReleaseSMContext request message to the SMF in step <NUM>. At this time, the messages may include a PDU session ID of the MA PDU session and an access type.

In step <NUM>, when the access type is specified in the message to the SMF, the SMF may perform release for the corresponding access of the MA PDU. When the access type is not specified, release for both accesses is performed.

In step <NUM>, the remaining handover procedures may be performed. The UE receives a registration accept message from the new AMF. At this time, when there is an MA PDU session which is not included in a PDU session status IE of the corresponding message, the UE may locally release the MA PDU session only for the access for which the registration accept message is received or locally release MA PDU sessions for both access types.

<FIG> illustrates a block diagram for the structure of a UE according to an embodiment.

Referring to <FIG>, the UE may include a transceiver <NUM>, a UE controller <NUM>, and a storage unit <NUM>. In the disclosure, the UE controller <NUM> may be defined as a circuit, an application-specific integrated circuit, or at least one processor.

The transceiver <NUM> may transmit and receive a signal to and from another network entity. The transceiver <NUM> may receive, for example, system information from a base station and receive a synchronization signal or a reference signal.

The UE controller <NUM> may control the overall operation of the UE according to an embodiment proposed in the disclosure. For example, the UE controller <NUM> may control the signal flow between blocks to perform the operation of the UE according to the aforementioned flowchart.

The storage unit <NUM> may store at least one piece of information transmitted and received through the transceiver <NUM> and information generated through the UE controller <NUM>.

<FIG> illustrates a block diagram for the structure of a higher node according to an embodiment.

The block diagram illustrated in <FIG> may be a block diagram of the aforementioned higher nodes, for example, the AMF, the SMF, and the UPF.

In the disclosure, core network entities or network functions such as the AMF, the SMP, and the UPF are all referred to as higher nodes.

Referring to <FIG>, the higher node may include a transceiver <NUM>, a higher node controller <NUM>, and a storage unit <NUM>. In the disclosure, the higher node controller <NUM> may be defined as a circuit, an application-specific integrated circuit, or at least one processor.

The transceiver <NUM> may transmit and receive a signal to and from another network entity. The transceiver <NUM> may transmit and receive a signal according to an embodiment to and from, for example, adjacent higher nodes.

The higher node controller <NUM> may control the overall operation of the higher node according to an embodiment proposed in the disclosure. For example, the higher node controller <NUM> may control the signal flow between blocks to perform the operation of the higher node according to the aforementioned flowchart.

The storage unit <NUM> may store at least one piece of information transmitted and received through the transceiver <NUM> and information generated through the higher node controller <NUM>.

According to the embodiments, when a UE registered in an AMF which supports ATSSS is registered in an AMF which does not support ATSSS, it is possible to efficiently release old MA PDU sessions to perform smooth communication.

Such a storage device may access, via an external port, a device which performs embodiments of the disclosure. Further, a separate storage device on the communication network may access a device which performs embodiments of the disclosure.

Claim 1:
A method performed by a first access and mobility management function, AMF, entity (<NUM>) in a wireless communication system, the method comprising:
receiving a first message including information on supported features of a second AMF entity (<NUM>);
identifying whether the second AMF entity (<NUM>) supports an access traffic steering, switching, splitting, ATSSS, function based on the information;
transmitting, to the second AMF entity (<NUM>), a second message including a user equipment, UE, context, wherein, in case that the second AMF entity does not support the ATSSS function, the UE context does not include a context for a multi-access packet data unit, MA PDU, session; and
transmitting, to a session management function, SMF, entity, a third message requesting to release the MA PDU session,
wherein the MA PDU session is released based on the third message.