Patent Description:
To meet the demand for wireless data traffic having increased since deployment of <NUM>th Generation (<NUM>) communication systems, efforts have been made to develop a <NUM>th Generation (<NUM>) or pre-<NUM> communication system. For this reason, <NUM> or pre-<NUM> communication system is also called 'Beyond <NUM> Network' or 'Post Long-Term Evolution (LTE) System'.

The <NUM> communication system defined by 3rd Generation Partnership Project (3GPP) is called an New Radio (NR) system. The <NUM> communication system is considered to be implemented in ultra-high frequency (millimeter (mm)Wave) bands, (e.g., <NUM> gigahertz (GHz) bands), so as to accomplish higher data rates, and in order to mitigate path loss of radio waves and increase a propagation distance of radio waves in an ultra-high frequency band, beamforming, massive multiple-input and multiple-output (MIMO), full-dimensional MIMO (FD-MIMO), array antenna, analog beamforming, and large-scale antenna technologies are applied to radio wave transmission and reception.

Also, in order to improve a network of a <NUM> communication system, technologies such as evolved small cells, advanced small cells, cloud radio access networks (cloud RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving networks, cooperative communication, Coordinated Multi-Points (CoMP), and received-interference cancelation, have been developed. In addition, for <NUM> communication systems, hybrid frequency shift keying (FSK) and quadrature amplitude modulation (QAM) (FQAM) and sliding window superposition coding (SWSC), which are advanced coding modulation (ACM) schemes, and filter bank multi-carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA), which are advanced access technologies, have been developed.

<CIT> pertains to a UE transmitting a non-access stratum (NAS) transport message to the core network to initiate a NAS transport procedure with the core network, receiving an indication message from the core network when a network function of the core network is unable to process the NAS transport message, the indication message including at least one of a payload type, a cause value, and timer information, and performing, by the processing circuitry of the UE, at least one of: re-initiating a NAS transport procedure based on timer information; aborting the NAS transport procedure; and releasing a protocol data unit (PDU) session.

"<NPL> is concerned with NAS protocol for 5GS.

<CIT> pertains to a core network adapted to detect a network slice congestion in a wireless communication system, upon receiving a service request from the UE through a first NAS signaling message that comprises a specific network slide identity, and indicate the network slice congestion using a second NAS signaling message to the UE, wherein the second NAS signaling message comprising a reject cause value and a back off timer for the specific network slice identity.

As described above, various technologies are now providable with the development of wireless communication systems, there is a need for a method of efficiently managing a wireless communication system by using such various technologies. The present disclosure relates to methods and apparatuses for managing a session when a network entity for managing mobility and a network entity for managing a session are separated from each other in a wireless communication system.

The present disclosure provides methods and apparatuse for managing a session in a wireless communication system in which a network entity for managing mobility and a network entity for managing a session are separated from each other, when a message for session management fails to be forwarded.

In the following description the subject-matter of <FIG> and <FIG> and their description is according to the invention as defined in the claims. The rest of the following description and figures (even if named embodiment(s)) does not or does not fully correspond to the invention as defined in the claims and is therefore not according to the invention as defined in the claims but is considered as useful for understanding the invention.

According to one embodiment of the present disclosure, in the case in which a network entity for managing mobility and a network entity for managing a session are separated from each other in a wireless communication system, various services may be efficiently supported when performing session management, by forwarding a session-related message.

Hereinafter, embodiments of the present disclosure are described in detail with reference to the accompanying drawings. In the description of embodiments, technical features that are well known to the technical field to which the present disclosure belongs but are not directly associated with the present disclosure are not described. This is not to obscure but to clearly deliver the gist of the present disclosure by omitting an unnecessary description.

For the same reason, in the accompanying drawings, some elements are exaggerated, omitted, or schematically shown. In addition, sizes of elements do not fully reflect actual sizes thereof. Like reference numbers are used to refer to like elements through at the drawings.

Advantages and features of the present disclosure and a method for achieving them will be apparent with reference to embodiments of the present disclosure described below together with the attached drawings. The present disclosure may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein, rather, these embodiments are provided such that the present disclosure will be thorough and complete, and will fully convey the concept of the present disclosure to those of ordinary skill in the art, and the present disclosure will be defined only by the concept of the claims. Like reference numerals denote like elements throughout the specification.

Here, it could be understood that each block in processing flowchart drawings and combinations of flowchart drawings may be performed by computer program instructions.

In addition, each block may indicate a portion of a module, a segment, or a code including one or more executable instructions for executing particular logical function(s). Also, in several substitutional embodiments, functions described in blocks may also be out of a sequence. For example, two consecutively shown blocks may be substantially performed at the same time in fact, or the blocks may be sometimes performed in a reverse order according to a corresponding function.

The term '. unit' used in the embodiments indicates a component including software or hardware, such as a field-programmable gate array (FPGA) or an application-specific integrated circuit (ASIC), and the '. unit' performs certain roles. However, the '. unit' does not always have a meaning limited to software or hardware. unit' may be configured either to be stored in an addressable storage medium or to execute one or more processors. Therefore, for example, the '. unit' includes components, such as software components, object-oriented software components, class components, and task components, processes, functions, attributes, procedures, subroutines, segments of program code, drivers, firmware, microcode, circuits, data, a database, data structures, tables, arrays, and variables. A function provided inside components and '. units' may be combined into a smaller number of components and '. units' or be further divided into additional components and '. In addition, components and '. units' may be implemented to reproduce one or more central processing units (CPUs) inside a device or a security multimedia card. Also, in an embodiment, the '. unit' may include one or more processors.

Terms referring to access nodes, terms referring to network entities or network functions, terms referring to messages, terms referring to interfaces between network entities, terms referring to a variety of identification information, and the like are exemplified for convenience of description. Accordingly, the present disclosure is not limited to the terms used herein, and may use other terms having technically identical meaning.

In the following description, the present disclosure will be described with terms and names defined in the <NUM>rd Generation Partnership Project (3GPP)Long-Term Evolution (LTE) standards, or terms and names modified therefrom, for the convenience of description. However, the present disclosure is not limited by these terms and names, and may be applied in the same way to systems that conform other standards. In the present disclosure, for convenience of descriptions, the terms 'eNB' and 'gNB' may be interchangeably used. That is, a base station mentioned as an eNB may refer to a gNB. In the present disclosure, the term 'terminal' may represent various wireless communication devices, as well as cellular phones, narrowband internet-of-Things (NB-IoT) devices, and sensors.

That is, in describing the embodiments of the present disclosure in detail, the main focus is placed on the communication standards defined by the 3GPP, but it will be understood by those skilled in the art that the gist of the present disclosure is applicable to other communication systems having similar technical backgrounds without significant modifications departing from the scope of the present disclosure.

In a <NUM>th Generation (<NUM>) or New Radio (NR) system, an access and mobility management function (AMF), which is a management entity for managing mobility of a terminal, and a session management function (SMF), which is an entity for managing a session, are separated from each other. Unlike in a <NUM>th Generation (<NUM>) LTE communication system in which a mobility management entity (MME) performs both mobility management and session management, an entity that performs mobility management and an entity that performs session management are separated from each other in a <NUM> or NR system, and thus a method of performing communication between a terminal and a network entity and a method of managing such communication may be changed.

In a <NUM> or NR system, when a terminal accesses a network through non-3GPP access, mobility management may be performed by an AMF through a non-3GPP inter-working function (N3IWF), and session management may be performed by an SMF. In addition, the AMF may process security-related information, which is an important element in mobility management.

As described above, in a <NUM> LTE system, an MME performs both mobility management and session management. In a <NUM> or NR system, a non-standalone architecture that performs communication by using network entities of such a <NUM> LTE system together may be supported.

An embodiment of the present disclosure is to solve an issue that may occur when a session-related message is not forwarded in transmission of a packet data unit (PDU) session establishment message from a user equipment (UE) to an SMF, and a session management message is not transmitted to the UE and a network in transmission of a downlink (DL) non-access stratum (NAS) transport message from an AMF to the UE.

According to an embodiment of the present disclosure, provided are a method and apparatus for seamlessly performing session management by defining a session management message transmission-related operation and a mobility-related operation to be performed by a UE and a network when the UE has attempted to transmit a PDU session establishment message to an SMF but the PDU session establishment message has failed to be forwarded, and a DL NAS transport message is transmitted from the AMF to the UE.

According to an embodiment of the present disclosure, operations may be defined to be performed by a UE and a network when authentication of a PDU session has failed and thus the network rejects or releases the PDU session, such that the operations of the UE and the network are synchronized according to whether authentication of a PDU session succeeds or fails, and thus communication is efficiently performed.

<FIG> is a diagram for describing a structure of a wireless communication system according to an embodiment of the present disclosure.

Referring to <FIG>, a core network of the wireless communication system according to an embodiment may include network functions (NFs), such as a user plane function (UPF) <NUM>, an SMF <NUM>, an AMF <NUM>, a <NUM> radio access network (RAN) <NUM>, user data management (UDM) <NUM>, and a policy control function (PCF) <NUM>.

In addition, for authentication of entities corresponding to the respective NFs, entities such as an authentication server function (AUSF) <NUM>, authentication, authorization and accounting (AAA) <NUM>, and the like may be included in the wireless communication system.

Hereinafter, a session management method will be described on the assumption that the wireless communication system is a <NUM> communication system, but this is merely an example, and the session management method according to the present disclosure is also applicable to other communication systems.

A UE (or a terminal) <NUM>-<NUM> may access a <NUM> core network through a base station (e.g., a <NUM> RAN, a radio access network) <NUM>, when performing communication through 3GPP access. Meanwhile, when the UE <NUM>-<NUM> performs communication through non-3GPP access, an N3IWF may exist, session management may be controlled through the UE, the non-3GPP access, the N3IWF, and an SMF, and mobility management may be controlled through the UE, the non-3GPP access, the N3IWF, and the AMF.

In a <NUM> or NR system, an entity that performs mobility management and session management is divided into the AMF <NUM> and the SMF <NUM>. Meanwhile, a <NUM> or NR system may support a stand-alone deployment structure for performing communication only with <NUM> or NR entities, and a non-stand-alone deployment structure using both <NUM> entities and <NUM> or NR entities.

<FIG> is a flowchart for describing a method of performing session management by using a NAS message in a <NUM> network environment, according to an embodiment of the present disclosure.

In operation <NUM>-<NUM>, a UE <NUM> may transmit a PDU SESSION ESTABLISHMENT REQUEST message to an SMF <NUM>. The PDU SESSION ESTABLISHMENT REQUEST message of operation <NUM>-<NUM> passing through a section between the UE <NUM> and an AMF <NUM> is carried in an uplink (UL) NAS TRANSPORT message as in operation <NUM>-<NUM>. (may be included therein and transmitted).

At this time, the PDU SESSION ESTABLISHMENT REQUEST message may be carried (included) in the UL NAS TRANSPORT message and transmitted from the UE <NUM> to the AMF <NUM> as in operation <NUM>-<NUM>, but may then fail to be forwarded to the SMF <NUM> for various reasons, for example, because the AMF <NUM> is unable to find an appropriate SMF.

In this case, as in operation <NUM>, the AMF <NUM> according to an embodiment transmits a DL NAS TRANSPORT message to the UE <NUM> to notify that the corresponding message has failed to be forwarded.

In operation <NUM>-<NUM>, the UE <NUM> may transmit the UL NAS TRANSPORT message to the AMF <NUM>.

In operation <NUM>, the AMF <NUM> may transmit the DL NAS TRANSPORT message to the UE <NUM>. According to an embodiment, the AMF <NUM> may set a timer in the DL NAS TRANSPORT message to be transmitted to the UE <NUM>. The set timer may be a back-off timer that expires at a time point at which the PDU SESSION ESTABLISHMENT REQUEST message is retransmitted.

The UE <NUM> having received the DL NAS TRANSPORT message may back off until the back-off timer expires.

Thereafter, when the back-off timer expires, the UE <NUM> may retransmit the PDU SESSION ESTABLISHMENT REQUEST message to the SMF <NUM> in operation <NUM>. The UE <NUM> may transmit the PDU SESSION ESTABLISHMENT REQUEST message to retry to establish the PDU session.

<FIG> is a flowchart for describing in more detail a method of performing session management by using a NAS message in a <NUM> network environment, according to an embodiment of the present disclosure.

In operation <NUM>-<NUM>, the UE <NUM> may transmit a UL NAS TRANSPORT message including a PDU SESSION ESTABLISHMENT REQUEST message to the AMF <NUM>.

In operation <NUM>-<NUM>, the AMF <NUM> needs to forward the PDU SESSION ESTABLISHMENT REQUEST message to the SMF <NUM>, but the PDU SESSION ESTABLISHMENT REQUEST message may fail to be forwarded to the SMF <NUM> for various reasons, for example, because the AMF <NUM> is unable to find an appropriate SMF. In such a case in which the forwarding fails, operation <NUM>-<NUM> is not performed.

In operation <NUM>, the AMF <NUM> may transmit a DL NAS TRANSPORT message to the UE <NUM> as the forwarding of the PDU SESSION ESTABLISHMENT REQUEST message has failed. The AMF <NUM> may transmit the DL NAS TRANSPORT message to inform the UE <NUM> that the PDU SESSION ESTABLISHMENT REQUEST message has not been forwarded.

In addition, the AMF <NUM> according to an embodiment may set a timer in the DL NAS TRANSPORT message to be transmitted to the UE <NUM>. The set timer may be a back-off timer that expires at a time point at which the PDU SESSION ESTABLISHMENT REQUEST message is transmitted again (retransmitted).

In operation <NUM>, as the back-off timer expires, the UE <NUM> may retry to establish the PDU session by retransmitting the PDU SESSION ESTABLISHMENT REQUEST message to the SMF <NUM> through the AMF <NUM>.

<FIG> is a flowchart for describing a method of performing session management based on a back-off timer value included in a NAS message in a <NUM> network environment, according to an embodiment of the present disclosure.

In operation <NUM>-<NUM>, the UE <NUM> transmits a PDU SESSION ESTABLISHMENT REQUEST message to the SMF <NUM>. The PDU SESSION ESTABLISHMENT REQUEST message of operation <NUM>-<NUM> passing through a section between the UE <NUM> and the AMF <NUM> is carried in a UL NAS TRANSPORT message as in operation <NUM>-<NUM> (is included therein and transmitted).

At this time, the PDU SESSION ESTABLISHMENT REQUEST message is carried (included) in the UL NAS TRANSPORT message and transmitted from the UE <NUM> to the AMF <NUM> as in operation <NUM>-<NUM>, but then fails to be forwarded to the SMF <NUM> for various reasons, for example, because the AMF <NUM> is unable to find an appropriate SMF.

In operation <NUM>, the AMF <NUM> may transmit the DL NAS TRANSPORT message to the UE <NUM>. According to an embodiment, the AMF <NUM> sets a timer in the DL NAS TRANSPORT message to be transmitted to the UE <NUM>. The set timer is a back-off timer that expires at a time point at which the PDU SESSION ESTABLISHMENT REQUEST message is transmitted again (retransmitted).

As shown in Table <NUM> or <NUM> below, the DL NAS TRANSPORT message includes a back-off timer for setting a time point at which the PDU SESSION ESTABLISHMENT REQUEST message is to be retransmitted.

In addition, when a multiple-session management message is not transmitted or some of session management messages are not transmitted, the DL NAS TRANSPORT message includes cause information in order to inform of a cause of the untransmitted message(s), which is information about a cause of a failure in forwarding of the PDU SESSION ESTABLISHMENT REQUEST that has not been forwarded, among a plurality of PDU SESSION ESTABLISHMENT REQUESTs for which forwarding from the AMF to a session management function, SMF, has been attempted. Such cause information may be coded with a single information element 'Multiple SM cause' as illustrated in <FIG>. According to another embodiment, the cause information may be coded together with a back-off timer as illustrated in <FIG> and coded into multiple SM cause with back-off timer value as shown in Table <NUM>.

The UE having received the DL NAS TRANSPORT message backs off until the back-off timer included in the DL NAS TRANSPORT message expires.

Thereafter, as the back-off timer expires, in operation <NUM>, the UE <NUM> retransmits the SESSION ESTABLISHMENT REQUEST message to the SMF <NUM> to retry to establish the PDU session. Meanwhile, the UE <NUM> may identify a forwardable session and an non-forwardable session by checking a multiple SM cause included in the DL NAS TRANSPORT message.

In operation <NUM>, the UE <NUM> retransmits the PDU SESSION ESTABLISHMENT REQUEST message to the SMF <NUM>. The UE <NUM> according to an embodiment may retransmit the PDU SESSION ESTABLISHMENT REQUEST message to the SMF <NUM> through the AMF <NUM> with respect to a session that is determined, by checking the multiple SM cause included in the DL NAS TRANSPORT message, to have failed to be forwarded.

Not according to the invention as claimed, alternatively, according to an embodiment, the UE <NUM> may transmit the PDU SESSION ESTABLISHMENT REQUEST message to the SMF <NUM> through the AMF <NUM> with respect to only a session that may be successfully forwarded, other than the session that is determined, by checking the multiple SM cause included in the DL NAS TRANSPORT message, to have failed to be forwarded.

<FIG> is a flowchart for describing in more detail a method of performing session management based on a back-off timer value included in a NAS message in a <NUM> network environment, according to an embodiment of the present disclosure.

In operation <NUM>-<NUM>, the UE <NUM> transmits a UL NAS TRANSPORT message including a PDU SESSION ESTABLISHMENT REQUEST message to the AMF <NUM>.

In operation <NUM>-<NUM>, the AMF <NUM> needs to forward the PDU SESSION ESTABLISHMENT REQUEST message to the SMF <NUM>, but the PDU SESSION ESTABLISHMENT REQUEST message fails to be forwarded to the SMF <NUM> for various reasons, for example, because the AMF <NUM> is unable to find an appropriate SMF. In such a case in which the forwarding has failed, operation <NUM>-<NUM> is not performed.

In operation <NUM>, the AMF <NUM> may transmits DL NAS TRANSPORT message to the UE <NUM> as the forwarding of the PDU SESSION ESTABLISHMENT REQUEST message has failed. The AMF <NUM> transmits the DL NAS TRANSPORT message to inform the UE <NUM> that the PDU SESSION ESTABLISHMENT REQUEST message has not been forwarded.

In addition, the AMF <NUM> according to an embodiment sets a timer in the DL NAS TRANSPORT message to be transmitted to the UE <NUM>. The set timer is a back-off timer that expires at a time point at which the PDU SESSION ESTABLISHMENT REQUEST message is retransmitted.

The UE <NUM> having received the DL NAS TRANSPORT message backs off until the back-off timer included in the DL NAS TRANSPORT message expires.

Thereafter, as the back-off timer expires, in operation <NUM>, the UE <NUM> retransmits the SESSION ESTABLISHMENT REQUEST message to the SMF <NUM> to retry to establish the PDU session. Meanwhile, the UE <NUM> may identify a session that has not failed to be forwarded and a session that has failed to be forwarded, by checking the multiple SM cause included in the DL NAS TRANSPORT message.

In operation <NUM>, the UE <NUM> transmits the PDU SESSION ESTABLISHMENT REQUEST message to the SMF <NUM>. The UE <NUM> according to an embodiment retransmits the PDU SESSION ESTABLISHMENT REQUEST message to the SMF <NUM> through the AMF <NUM> with respect to a session that is determined, by checking the multiple SM cause included in the DL NAS TRANSPORT message, to have failed to be forwarded.

<FIG> is a diagram for describing cause information included in a DL NAS TRANSPORT message, according to an embodiment of the present disclosure. Referring to <FIG>, reasons for failures in forwarding of a plurality of sessions may be coded into a single information element 'Multiple SM cause'.

<FIG> is a diagram for describing cause information included in a DL NAS TRANSPORT message, according to another embodiment of the present disclosure. Referring to <FIG>, reasons for failures in forwarding of a plurality of sessions may be coded together with values of a back-off timer.

Meanwhile, <FIG> and <FIG> are merely examples, and the structure of a cause IE included in a DL NAS TRANSPORT message is not limited thereto.

<FIG> is a flowchart for describing a method of performing session management based on a back-off timer value included in a NAS message in a <NUM> network environment, according to another embodiment of the present disclosure.

In operation <NUM>-<NUM>, the UE <NUM> may transmit a PDU SESSION ESTABLISHMENT REQUEST message to the SMF <NUM>. The PDU SESSION ESTABLISHMENT REQUEST message of operation <NUM>-<NUM> passing through a section between the UE <NUM> and the AMF <NUM> is carried in a UL NAS TRANSPORT message as in operation <NUM>-<NUM> (may be included therein and transmitted).

At this time, the PDU SESSION ESTABLISHMENT REQUEST message may be carried (included) in the UL NAS TRANSPORT message and transmitted to the AMF <NUM> as in operation <NUM>-<NUM>, but may then fail to be forwarded to the SMF <NUM> for various reasons, for example, because the AMF <NUM> is unable to find an appropriate SMF.

In operation <NUM>, the AMF <NUM> may transmit the DL NAS TRANSPORT message to the UE <NUM>. According to an embodiment, the AMF <NUM> may not set a timer in the DL NAS TRANSPORT message to be transmitted to the UE <NUM>. In addition, according to another example, the AMF <NUM> may set the value of a timer to <NUM> in the DL NAS TRANSPORT message to be transmitted to the UE <NUM>.

The UE <NUM> according to an embodiment does not retry to establish the PDU session when the timer value included in the DL NAS TRANSPORT message is <NUM> or no timer value is included in the DL NAS TRANSPORT message.

<FIG> is a flowchart for describing in more detail a method of performing session management based on a back-off timer value included in a NAS message in a <NUM> network environment, according to another embodiment of the present disclosure.

In operation <NUM>-<NUM>, the AMF <NUM> needs to forward the PDU SESSION ESTABLISHMENT REQUEST message to the SMF <NUM>, but the PDU SESSION ESTABLISHMENT REQUEST message may fail to be forwarded to the SMF <NUM> for various reasons, for example, because the AMF <NUM> is unable to find an appropriate SMF.

<FIG> is a flowchart for describing an operation according to a back-off timer value included in a PDU session establishment reject message in authentication of a session in a <NUM> network environment, according to an embodiment of the present disclosure.

In operation <NUM>, the UE <NUM> may transmit a PDU SESSION ESTABLISHMENT REQUEST message to the SMF <NUM>. The PDU SESSION ESTABLISHMENT REQUEST message may be transmitted from the UE <NUM> to the SMF <NUM> to request establishment of a PDU session.

In operation <NUM>, the SMF <NUM> may transmit a PDU SESSION AUTHENTICATION COMMAND message to the UE <NUM>. The SMF <NUM> may include a PDU session authentication process as a partial process of PDU session establishment according to a request by the UE <NUM>. Accordingly, the SMF may transmit a PDU SESSION AUTHENTICATION COMMAND message to the UE <NUM> to authenticate the PDU session.

In operation <NUM>, the UE <NUM> may transmit a PDU SESSION AUTHENTICATION COMPLETE message to the SMF <NUM>.

In operation <NUM>, the SMF <NUM> may transmit a PDU SESSION ESTABLISHMENT REJECT message to the UE. When it is determined that PDU session authentication is invalid (when the PDU session authentication fails), the SMF <NUM> may transmit the PDU SESSION ESTABLISHMENT REJECT message to the UE <NUM>. The PDU SESSION ESTABLISHMENT REJECT message according to an embodiment may include IEs listed in Table <NUM> below, and may include, for example, a back-off timer value.

In operation <NUM>, the UE <NUM> may transmit the PDU SESSION ESTABLISHMENT REQUEST message to the SMF <NUM>. When a back-off timer value is included in the received PDU SESSION ESTABLISHMENT REJECT message, the UE <NUM> may transmit the PDU SESSION ESTABLISHMENT REQUEST message to the SMF <NUM> after backing off for the back-off timer value. Meanwhile, in this case, the UE <NUM> may also transmit the PDU SESSION ESTABLISHMENT REQUEST message to an equivalent public land mobile network (EPLMN). The EPLMN corresponds to a PLMN recognized to be the same as or equivalent to the PLMN in which the UE <NUM> is currently located, and the UE <NUM> may transmit the PDU SESSION ESTABLISHMENT REQUEST message to the EPLMN selected based on a stored EPLMN list.

<FIG> is a flowchart for describing an operation according to a back-off timer value included in a PDU session establishment reject message in authentication of a session in a <NUM> network environment, according to another embodiment of the present disclosure.

In operation <NUM>, the SMF <NUM> may transmit a PDU SESSION AUTHENTICATION COMMAND message to the UE <NUM>. The SMF <NUM> may transmit the PDU SESSION AUTHENTICATION COMMAND message to the UE <NUM> to authenticate the PDU session.

In operation <NUM>, the SMF <NUM> may transmit a PDU SESSION ESTABLISHMENT REJECT message to the UE <NUM>. When it is determined that PDU session authentication is invalid (when the PDU session authentication fails), the SMF <NUM> may transmit the PDU SESSION ESTABLISHMENT REJECT message to the UE. The PDU SESSION ESTABLISHMENT REJECT message according to an embodiment may include IEs listed in Table <NUM> below. In addition, according to an embodiment, a back-off timer value included in the PDU SESSION ESTABLISHMENT REJECT message may be set to <NUM>.

In operation <NUM>, the UE <NUM> may determine that authentication of the PDU session has failed, and thus may not retry to transmit the PDU SESSION ESTABLISHMENT REQUEST message. That is, the UE <NUM> may determine that the authentication of the PDU session has failed upon receiving the PDU SESSION ESTABLISHMENT REJECT message from the SMF <NUM>. In this case, the UE <NUM> may determine whether to retry to request establishment of the PDU session based on the back-off value included in the PDU SESSION ESTABLISHMENT REJECT message. For example, the UE <NUM> may not retry to request establishment of the PDU session when the back-off value included in the SESSION ESTABLISHMENT REJECT message is <NUM>. However, this is merely an example, and the back-off value upon which the UE <NUM> does not retry request establishment of the PDU session is not limited to the above-described example.

<FIG> is a flowchart for describing an operation according to a back-off timer value included in a PDU session establishment release message in authentication of a session in a <NUM> network environment, according to an embodiment of the present disclosure.

In operation <NUM>, the SMF <NUM> may transmit a PDU SESSION RELEASE COMMAND message to the UE <NUM>. The SMF <NUM> may perform an authentication process on the PDU session through a PDU session authentication command even after establishment of the PDU session with the UE <NUM> is completed. In this case, when it is determined that the PDU session authentication is invalid (when the PDU session authentication process has failed), the SMF <NUM> may transmit the PDU SESSION RELEASE COMMAND message to the UE <NUM>.

In this case, the PDU SESSION RELEASE COMMAND message may include IEs listed in Table <NUM> below. For example, the PDU SESSION RELEASE COMMAND message may include a back-off timer value.

In operation <NUM>, the UE <NUM> may transmit a PDU SESSION ESTABLISHMENT REQUEST message to the SMF <NUM>. When a back-off timer value is included in the received PDU SESSION RELEASE COMMAND message, the UE <NUM> may transmit the PDU SESSION ESTABLISHMENT REQUEST message to the SMF <NUM> after backing off for the back-off timer value. In this case, the UE <NUM> may back off for the set back-off timer value and then transmit the PDU SESSION ESTABLISHMENT REQUEST message to the SMF <NUM>.

Meanwhile, in this case, the UE <NUM> may also transmit the PDU SESSION ESTABLISHMENT REQUEST message to an EPLMN. The EPLMN corresponds to a PLMN recognized to be the same as or equivalent to the PLMN in which the UE <NUM> is currently located, and the UE <NUM> may transmit the PDU SESSION ESTABLISHMENT REQUEST message to the EPLMN selected based on a stored EPLMN list.

<FIG> is a flowchart for describing an operation according to a back-off timer value included in a PDU session establishment release message in authentication of a session in a <NUM> network environment, according to another embodiment of the present disclosure.

In operation <NUM>, the SMF <NUM> may transmit a PDU SESSION RELEASE COMMAND message to the UE <NUM>. Even after the PDU session establishment with the UE <NUM> is completed, the SMF <NUM> may transmit a PDU session authentication command to the UE to perform PDU session authentication. In this case, when it is determined that the PDU session authentication is invalid (when the PDU session authentication process has failed), the SMF <NUM> may transmit the PDU SESSION RELEASE COMMAND message to the UE <NUM>.

In this case, the PDU SESSION RELEASE COMMAND message may include the IEs listed in Table <NUM> described above. For example, the PDU SESSION RELEASE COMMAND message may include a back-off timer value set to <NUM>.

In operation <NUM>, the UE <NUM> may determine that authentication of the PDU session has failed, and thus may not retry to transmit the PDU SESSION ESTABLISHMENT REQUEST message. The UE <NUM> may determine that the authentication of the PDU session has failed upon receiving a PDU SESSION ESTABLISHMENT RELEASE message from the SMF <NUM>. In this case, the UE <NUM> may determine whether to retry to request establishment of the PDU session based on the back-off value included in the PDU SESSION ESTABLISHMENT RELEASE message. For example, the UE <NUM> may not retry to request establishment of the PDU session when the back-off value included in the SESSION ESTABLISHMENT RELEASE message is <NUM>. However, this is merely an example, and the back-off value upon which the UE <NUM> does not retry to request establishment of the PDU session is not limited to the above-described example.

In operation <NUM>, the SMF <NUM> may transmit a PDU SESSION RELEASE COMMAND message to the UE <NUM>. Even after the PDU session establishment with the UE <NUM> is completed, the SMF <NUM> may transmit the PDU SESSION RELEASE COMMAND message to the UE to perform a PUD session authentication process. In this case, when it is determined that the PDU session authentication is invalid (when the PDU session authentication process has failed), the SMF <NUM> may transmit the PDU SESSION RELEASE COMMAND message to the UE <NUM>.

In operation <NUM>, the UE <NUM> may transmit a PDU SESSION MOFIFICATION REQUEST message to the SMF <NUM>. When a back-off timer value is included in the received PDU SESSION RELEASE COMMAND message, the UE <NUM> may transmit the PDU SESSION MODIFICATION REQUEST message to the SMF <NUM> after backing off for the back-off timer value. In this case, the UE <NUM> may back off for the set back-off timer value and then transmit the PDU SESSION MODIFICATION REQUEST message to the SMF <NUM>.

Meanwhile, in this case, the UE <NUM> may also transmit the PDU SESSION MODIFICATION REQUEST message to an EPLMN. The EPLMN corresponds to a PLMN recognized to be the same as or equivalent to the PLMN in which the UE <NUM> is currently located, and the UE <NUM> may transmit the PDU SESSION MODIFICATION REQUEST message to the EPLMN selected based on a stored EPLMN list.

In operation <NUM>, the SMF <NUM> may transmit a PDU SESSION RELEASE COMMAND message to the UE <NUM>. Even after the PDU session establishment with the UE <NUM> is completed, the SMF <NUM> may transmit the PDU SESSION RELEASE COMMAND message to the UE to perform a PUD session authentication process. In this case, when it is determined that the PDU session authentication is invalid (when the authentication process on the PDU session has failed), the SMF <NUM> may transmit the PDU SESSION RELEASE COMMAND message to the UE <NUM>.

In operation <NUM>, the UE <NUM> may determine that authentication of the PDU session has failed, and thus may not retry to transmit the PDU SESSION MODIFICATION REQUEST message. The UE <NUM> may determine that the authentication of the PDU session has failed upon receiving a PDU SESSION RELEASE message from the SMF <NUM>. In this case, the UE <NUM> may determine whether to retry to request PDU session modification based on the back-off value included in the PDU SESSION RELEASE message. For example, the UE <NUM> may not retry to request PDU session modification when the back-off value included in the PDU SESSION RELEASE message is <NUM>. However, this is merely an example, and the back-off value upon which the UE <NUM> does not retry to request modification of the PDU session is not limited to the above-described example.

<FIG> is a flowchart for describing operations of a UE and an SMF in authentication of a PDU session, according to an embodiment.

In operation <NUM>, the UE may transmit a PDU session establishment request message to the SMF. The PDU session establishment request message may be transmitted from the UE to the SMF to request establishment of the PDU session.

In operation <NUM>, the UE may receive a PDU session authentication command message from the SMF. The SMF may include a PDU session authentication process as a partial process of a PDU session establishment process according to the request of the UE, and may transmit the PDU session authentication command message to the UE to authenticate the PDU session.

In operation <NUM>, the UE may transmit a PDU session authentication complete message to the SMF.

In operation <NUM>, the SMF may determine whether the PDU session authentication is valid (whether the authentication succeeded or failed).

In operation <NUM>, when it is determined that the PDU session authentication is valid (when the PDU session authentication succeeded), a PDU session establishment process may be performed between the UE and the SMF, or a previously established PDU session may be maintained.

In operation <NUM>, the UE may receive, from the SMF, a PDU session establishment reject message in which a back-off timer is set. The UE may receive, from the SMF, the PDU session establishment reject message in which the back-off timer is set.

In operation <NUM>, the UE may check a value of the back-off timer included in the PDU session establishment reject message.

In operation <NUM>, when the value of the back-off timer is not <NUM>, the UE may retransmit the PDU session establishment request message after the back-off timer expires.

When the value of the back-off timer is <NUM>, in operation <NUM>, the UE may not perform an operation of retrying to establish the PDU session.

For example, when the UE receives the PDU session establishment reject message, the UE may start a timer based on a back-off timer included in the PDU session establishment reject message. In this case, as described above, when the value of the back-off timer is not <NUM>, the UE may cause the timer to expire after the value of the back-off timer, and then transmit the PDU session establishment request message to attempt PDU session establishment. On the other hand, when the value of the back-off timer included in the PDU session reject message is <NUM>, the UE may not try to establish the PDU session. For example, when PDU session establishment fails and is impossible, an operation, performed by the UE, of transmitting a PDU session request message after receiving a PDU session reject message may be unnecessary. In consideration of the above, the SMF may instruct the UE not to perform a PDU session establishment operation. In this case, for example, the SMF may transmit, to the UE, a PDU session reject message in which the value of a back-off timer is set to <NUM>. In this case, the UE may not try to establish the PDU session when the value of the back-off timer is <NUM>. That is, the value of the back-off timer set to <NUM> may be used as an indicator that disables a PDU session establishment attempt operation from being performed. Through this, the UE may be controlled not to perform an unnecessary operation.

Meanwhile, although <FIG> illustrates that the UE receives the PDU session establishment reject message, this is merely an example, and the UE may receive a PDU session establishment release message as described above with reference to <FIG>, <FIG>, <FIG>, and <FIG>.

That is, the value of a back-off timer in a PUD session establishment release message may also be set to <NUM> or a value other than <NUM>. In this case, for example, when the value of a back-off timer of a PDU session establishment release message is <NUM>, the UE may not transmit a PDU session establishment request message and may not perform a PUD session establishment operation. In addition, for example, when the value of a back-off timer in a PDU establishment release message is <NUM>, the UE may not transmit a PDU session modification request message and may not perform a PUD modification operation.

Furthermore, for example, when the value of a back-off timer in a PDU session establishment release message is not <NUM>, the UE may operate based on an operation of the back-off timer as described above.

<FIG> is a diagram illustrating a configuration of a UE according to an embodiment of the present disclosure.

As illustrated in <FIG>, the UE of the present disclosure may include a transceiver <NUM>, a memory <NUM>, and a processor <NUM>. The processor <NUM>, the transceiver <NUM>, and the memory <NUM> of the UE may operate according to the above-described communication method of a UE. However, the components of the UE are not limited to the above-described examples. For example, the UE may include more or fewer components than the above-described components. Furthermore, the processor <NUM>, the transceiver <NUM>, and the memory <NUM> may be implemented as a single chip.

The transceiver <NUM> collectively refers to a receiver and a transmitter of the UE, and may transmit and receive a signal to and from a base station or a network entity. The signal transmitted and received to and from the base station may include control information and data. To this end, the transceiver <NUM> may include a radio frequency (RF) transmitter for up-converting and amplifying a frequency of a signal being transmitted, and an RF receiver for low-noise-amplifying a received signal and down-converting a frequency of the received signal. However, this is merely an example of the transceiver <NUM>, the components of which are not limited to the RF transmitter and the RF receiver.

In addition, the transceiver <NUM> may include a wired/wireless transceiver, and may include various components for transmitting and receiving signals.

Also, the transceiver <NUM> may receive a signal through a radio channel, output the signal to the processor <NUM>, and transmit a signal output from the processor <NUM> through a radio channel.

Also, the transceiver <NUM> may receive a communication signal, output the communication signal to the processor, and transmit a signal output from the processor to a network entity through a wired/wireless network.

The memory <NUM> may store a program and data necessary for the operation of the UE. In addition, the memory <NUM> may store control information or data included in a signal obtained by the UE. The memory <NUM> may be implemented as a storage medium such as read-only memory (ROM), random-access memory (RAM), a hard disk, a compact disc-ROM (CD-ROM), or a digital versatile disc (DVD), or a combination thereof.

The processor <NUM> may control a series of operations to allow the UE to operate according to the above-described embodiments of the present disclosure. The processor <NUM> may include one or more processors. For example, the processor <NUM> may include a communication processor (CP) for performing control for communication and an application processor (AP) for controlling a higher layer such as an application program.

<FIG> is a diagram illustrating a configuration of a network entity according to an embodiment of the present disclosure.

As illustrated in <FIG>, the network entity of the present disclosure may include a transceiver <NUM>, a memory <NUM>, and a processor <NUM>. The processor <NUM>, the transceiver <NUM>, and the memory <NUM> of the network entity may operate according to the communication method of a network entity described above. However, the components of the network entity are not limited to the above-described examples. For example, the network entity may include more or fewer components than the above-described components. Furthermore, the processor <NUM>, the transceiver <NUM>, and the memory <NUM> may be implemented as a single chip. The network entity may include NFs such as an AMF and an SMF described above.

The transceiver <NUM> collectively refers to a receiver and a transmitter of the network entity, and may transmit and receive a signal to and from a UE or another network entity. Here, the transmitted or received signal may include control information and data. To this end, the transceiver <NUM> may include an RF transmitter for up-converting and amplifying a frequency of a signal being transmitted, and an RF receiver for low-noise-amplifying a received signal and down-converting a frequency of the received signal. However, this is merely an example of the transceiver <NUM>, the components of which are not limited to the RF transmitter and the RF receiver. The transceiver <NUM> may include a wired/wireless transceiver, and may include various components for transmitting and receiving signals.

Also, the transceiver <NUM> may receive a signal through a communication channel (e.g., a radio channel), output the signal to the processor <NUM>, and transmit a signal output from the processor <NUM> through a communication channel.

Also, the transceiver <NUM> may receive a communication signal, output the communication signal to the processor, and transmit a signal output from the processor to a UE or a network entity through a wired/wireless network.

The memory <NUM> may store a program and data necessary for the operation of the network entity. In addition, the memory <NUM> may store control information or data included in a signal obtained by the network entity. The memory <NUM> may be implemented as a storage medium such as ROM, RAM, a hard disk, a CD-ROM, or a DVD, or a combination thereof.

The processor <NUM> may control a series of operations to allow the network entity to operate according to the above-described embodiments of the present disclosure. The processor <NUM> may include one or more processors. Methods according to claims or embodiments described in the specification of the present disclosure may be implemented in hardware, software, or a combination of hardware and software.

When implemented in software, a computer-readable storage medium storing one or more programs (software modules) may be provided. The one or more programs stored in the computer-readable storage medium are configured for execution by one or more processors in an electronic device. The one or more programs include instructions that cause the electronic device to execute the methods according to the embodiments described in claims or the specification of the present disclosure.

The programs (e.g., software modules or software) may be stored in non-volatile memory including RAM or flash memory, ROM, electrically erasable programmable ROM (EEPROM), a magnetic disc storage device, a CD-ROM, a DVD or other optical storage device, or a magnetic cassette. Alternatively, the programs may be stored in memory including a combination of some or all of the above-mentioned storage media. In addition, a plurality of such memory units may be included.

Also, the programs may be stored in an attachable storage device accessible through any or a combination of communication networks such as the Internet, an intranet, a local area network (LAN), a wide LAN (WLAN), or a storage area network (SAN). The storage device may access, via an external port, a device for performing an embodiment of the present disclosure. In addition, a separate storage device on a communication network may access the device for performing an embodiment of the present disclosure.

Claim 1:
A method, performed by a user equipment, UE, of managing a session in a wireless communication system, the method comprising:
transmitting, to an access and mobility management function, AMF, a first uplink, UL, non-access stratum, NAS, transport message including a packet data unit, PDU, session establishment request;
receiving a downlink, DL, NAS transport message from the AMF; and
transmitting, based on a value of a back-off timer included in the DL NAS transport message, a second UL NAS transport message including the PDU session establishment request,
characterized in that the DL NAS transport message includes information about a cause of a failure in forwarding of the PDU session establishment request that has not been forwarded, among a plurality of PDU session establishment requests for which forwarding from the AMF to a session management function, SMF, has been attempted.