Communication system, communication terminal, and network

Abstract

Provided is a technique capable of improving the robustness of a communication system. The communication system comprises a communication terminal. A first network configured so as to be capable of wireless communication with the communication terminal; and at least one second network configured to be able to communicate with the first network. In a state in which the communication terminal is connected to the first network and to the at least one second network via the first network, when the first network decides to release a connection between the first network and the communication terminal (ST1401), the communication terminal or the first network instructs the at least one second network to release a connection with the communication terminal (ST1405).

Description

This invention application is a divisional application of the invention patent application with international application number PCT / JP2020 / 029497, international application date July 31, 2020, application number 202080048206.5 entering the Chinese national phase, and name “Communication system, communication terminal and network”. Technical Field

[0001] The present disclosure relates to wireless communication technology. Background Art

[0002] In the 3rd Generation Partnership Project (3GPP), a standardization organization for mobile communication systems, a communication method called Long Term Evolution (LTE) in terms of the wireless section and System Architecture Evolution (SAE) in terms of the overall system structure including a core network and a radio access network (hereinafter collectively referred to as a network) is studied (for example, non-patent documents 1 to 5). This communication method is also called a 3.9G (3.9 Generation) system.

[0003] As the access method of LTE, OFDM (Orthogonal Frequency Division Multiplexing) is used in the downlink direction, and SC-FDMA (Single Carrier Frequency Division Multiple Access) is used in the uplink direction. In addition, unlike W-CDMA (Wideband Code Division Multiple Access), LTE does not include line switching and is only a packet communication method.

[0004] use Figure 1 The following describes the decisions regarding the frame structure of the LTE system in 3GPP described in Non-Patent Document 1 (Chapter 5). Figure 1 This is an explanatory diagram showing the structure of a radio frame used in a communication system of the LTE method. Figure 1In the radio frame, a radio frame is 10ms. The radio frame is divided into 10 subframes of equal size. The subframe is divided into 2 slots of equal size. The first subframe and the sixth subframe of each radio frame contain a downlink synchronization signal. The synchronization signal includes the first synchronization signal (Primary Synchronization Signal: P-SS) and the second synchronization signal (Secondary Synchronization Signal: S-SS).

[0005] Non-Patent Document 1 (Chapter 5) describes the decisions made by 3GPP regarding the channel structure in the LTE system. It is assumed that the same channel structure as that of the non-CSG cell is used in the CSG (Closed Subscriber Group) cell.

[0006] The Physical Broadcast Channel (PBCH) is a downlink transmission channel from a base station device (hereinafter sometimes referred to as "base station") to a communication terminal device (hereinafter sometimes referred to as "communication terminal") such as a mobile terminal device (hereinafter sometimes referred to as "mobile terminal"). The BCH transport block is mapped to four subframes in a 40ms interval. There is no clear signaling of 40ms timing.

[0007] The Physical Control Format Indicator Channel (PCFICH) is a downlink transmission channel from a base station to a communication terminal. The PCFICH notifies the communication terminal of the number of OFDM (Orthogonal Frequency Division Multiplexing) symbols used for PDCCHs from the base station. The PCFICH is transmitted in each subframe.

[0008] The Physical Downlink Control Channel (PDCCH) is a channel for downlink transmission from the base station to the communication terminal. PDCCH notifies the resource allocation information of the downlink shared channel (DL-SCH), which is one of the transmission channels described later, the resource allocation information of the paging channel (PCH), which is one of the transmission channels described later, and the HARQ (Hybrid Automatic Repeat reQuest) information related to the DL-SCH. PDCCH transmits the uplink scheduling grant. PDCCH transmits the response signal for the uplink transmission, namely Ack (Acknowledgement) / Nack (Negative Acknowledgement). PDCCH is also called L1 / L2 control signal.

[0009] The Physical Downlink Shared Channel (PDSCH) is a downlink transmission channel from a base station to a communication terminal. A downlink shared channel (DL-SCH) as a transport channel and a PCH as a transport channel are mapped to the PDSCH.

[0010] A physical multicast channel (PMCH) is a channel for downlink transmission from a base station to a communication terminal. A multicast channel (MCH) as a transport channel is mapped to the PMCH.

[0011] The Physical Uplink Control Channel (PUCCH) is a channel for uplink transmission from the communication terminal to the base station. PUCCH transmits the response signal (response signal) for downlink transmission, namely Ack / Nack. PUCCH transmits CSI (Channel State Information). CSI is composed of RI (Rank Indicator), PMI (Precoding Matrix Indicator), and CQI (Channel Quality Indicator) reports. RI refers to the rank information of the channel matrix of MIMO. PMI refers to the information of the precoding waiting matrix used in MIMO. CQI refers to quality information indicating the quality of the received data, or indicating the quality of the communication line. And PUCCH transmits a scheduling request (Scheduling Request: SR).

[0012] The physical uplink shared channel (PUSCH) is a channel for uplink transmission from a communication terminal to a base station. An uplink shared channel (UL-SCH), which is one of the transport channels, is mapped to the PUSCH.

[0013] The Physical Hybrid ARQ Indicator Channel (PHICH) is a channel for downlink transmission from a base station to a communication terminal. PHICH transmits Ack / Nack, a response signal for uplink transmission. The Physical Random Access Channel (PRACH) is a channel for uplink transmission from a communication terminal to a base station. PRACH transmits a random access preamble.

[0014] The downlink reference signal (Reference Signal: RS) is a codeword known as a communication system in the LTE mode. The following five types of downlink reference signals are defined. Cell-specific Reference Signal (CRS), MBSFN Reference Signal (MBSFN Reference Signal), UE-specific Reference Signal (UE-specific Reference Signal), i.e., Data Demodulation Reference Signal (DM-RS), Positioning Reference Signal (PRS), and Channel State Information Reference Signal (CSI-RS). As a measurement of the physical layer of the communication terminal, there is a measurement of the reference signal received power (Reference Signal Received Power: RSRP).

[0015] The uplink reference signal is also a symbol known as a communication system of the LTE scheme. The following two types of uplink reference signals are defined: a data demodulation reference signal (Demodulation Reference Signal: DM-RS) and a sounding reference signal (Sounding Reference Signal: SRS).

[0016] The transport channel described in Non-Patent Document 1 (Chapter 5) is described below. The broadcast channel (BCH) in the downlink transport channel is broadcast to the entire coverage area of ​​its base station (cell). The BCH is mapped to the physical broadcast channel (PBCH).

[0017] HARQ (HybridARQ: Hybrid ARQ) based retransmission control is applied to the downlink shared channel (DL-SCH). DL-SCH can broadcast to the entire coverage area of ​​the base station (cell). DL-SCH supports dynamic or semi-static resource allocation. Quasi-static resource allocation is also called persistent scheduling. DL-SCH supports discontinuous reception (DRX) of communication terminals in order to reduce power consumption of communication terminals. DL-SCH is mapped to the physical downlink shared channel (PDSCH).

[0018] The Paging Channel (PCH) supports DRX of the communication terminal in order to reduce the power consumption of the communication terminal. The PCH is required to be broadcast to the entire coverage area of ​​the base station (cell). The PCH is mapped to a physical resource such as the Physical Downlink Shared Channel (PDSCH) that can be dynamically used for traffic.

[0019] The multicast channel (MCH) is used to broadcast to the entire coverage area of ​​the base station (cell). MCH supports SFN synthesis of MBMS (Multimedia Broadcast Multicast Service) services (MTCH and MCCH) in multi-cell transmission. MCH supports quasi-static resource allocation. MCH is mapped to PMCH.

[0020] Retransmission control based on HARQ (Hybrid ARQ) is applied to the uplink shared channel (UL-SCH) in the uplink transmission channel. UL-SCH supports dynamic or semi-static resource allocation. UL-SCH is mapped to the physical uplink shared channel (PUSCH).

[0021] The Random Access Channel (RACH) is limited to control information. There is a risk of collision in the RACH. The RACH is mapped to the Physical Random Access Channel (PRACH).

[0022] HARQ is explained. HARQ is a technology that improves the communication quality of a transmission line by combining Automatic RepeatreQuest (ARQ) and Forward Error Correction (Forward Error Correction). HARQ has the following advantages: even for a transmission line with changed communication quality, error correction can be effectively used by retransmission. In particular, when retransmission is performed, the quality can be further improved by synthesizing the reception result of the initial transmission and the reception result of the retransmission.

[0023] An example of the retransmission method is described. When the receiving side cannot correctly decode the received data, in other words, when a CRC (Cyclic Redundancy Check) error occurs (CRC=NG), "Nack" is sent from the receiving side to the sending side. The sending side that receives "Nack" retransmits the data. When the receiving side can correctly decode the received data, in other words, when no CRC error occurs (CRC=OK), "Ack" is sent from the receiving side to the sending side. The sending side that receives "Ack" sends the next data.

[0024] The logical channel described in Non-Patent Document 1 (Chapter 6) is described below. The Broadcast Control Channel (BCCH) is a downlink channel for broadcasting system control information. The BCCH as a logical channel is mapped to the Broadcast Channel (BCH) as a transport channel or the Downlink Shared Channel (DL-SCH).

[0025] The Paging Control Channel (PCCH) is a downlink channel used to send paging information and changes to system information. PCCH is used when the network does not know the cell location of the communication terminal. The PCCH, which is a logical channel, is mapped to the Paging Channel (PCH), which is a transport channel.

[0026] The Common Control Channel (CCCH) is a channel used to send control information between a communication terminal and a base station. The CCCH is used when there is no RRC connection between the communication terminal and the network. In the downlink direction, the CCCH is mapped to the downlink shared channel (DL-SCH) as a transmission channel. In the uplink direction, the CCCH is mapped to the uplink shared channel (UL-SCH) as a transmission channel.

[0027] The Multicast Control Channel (MCCH) is a downlink channel used for point-to-multipoint transmission. The MCCH is used to send MBMS control information for one or more MTCHs from the network to the communication terminal. The MCCH is only used by the communication terminal during the MBMS reception process. The MCCH is mapped to the Multicast Channel (MCH) as a transport channel.

[0028] Dedicated Control Channel (DCCH) is a channel used to send dedicated control information between a communication terminal and the network in a point-to-point manner. DCCH is used when the communication terminal is in an RRC connection. DCCH is mapped to the uplink shared channel (UL-SCH) in the uplink and to the downlink shared channel (DL-SCH) in the downlink.

[0029] Dedicated Traffic Channel (DTCH) is a point-to-point communication channel used to send user information to dedicated communication terminals. DTCH exists in both uplink and downlink. DTCH is mapped to the uplink shared channel (UL-SCH) in the uplink and to the downlink shared channel (DL-SCH) in the downlink.

[0030] The multicast traffic channel (MTCH) is a downlink channel for transmitting traffic data from the network to the communication terminal. The MTCH is a channel used only for the communication terminal in the MBMS reception process. The MTCH is mapped to the multicast channel (MCH).

[0031] CGI refers to Cell Global Identifier. ECGI refers to E-UTRAN Cell Global Identifier. CSG (Closed Subscriber Group) cells are introduced in LTE, LTE-A (Long Term Evolution Advanced) and UMTS (Universal Mobile Telecommunication System).

[0032] The location tracking of the communication terminal is performed in units of an area consisting of one or more cells. The location tracking is performed to track the location of the communication terminal even in the standby state, so as to call the communication terminal, in other words, to be able to call the communication terminal. The area used for the location tracking of the communication terminal is called a tracking area.

[0033] In addition, 3GPP is advancing the standardization of Long Term Evolution Advanced (LTE-A) as Release 10 (see Non-Patent Documents 3 and 4). LTE-A is based on the wireless communication method of LTE and is constructed by adding some new technologies thereto.

[0034] In the LTE-A system, in order to support a wider frequency bandwidth (transmission bandwidths) up to 100 MHz, carrier aggregation (CA) of aggregating (also called aggregation) two or more component carriers (CC) is studied. CA is described in Non-Patent Document 1.

[0035] When CA is configured, the UE has a unique RRC connection (RRCconnection) with the network (Network: NW). In the RRC connection, one serving cell provides NAS mobility information and security input. This cell is called the primary cell (Primary Cell: PCell). In the downlink, the carrier corresponding to the PCell is the downlink primary component carrier (Downlink Primary Component Carrier: DLPCC). In the uplink, the carrier corresponding to the PCell is the uplink primary component carrier (Uplink Primary Component Carrier: ULPCC).

[0036] According to the capability of the UE (capability), a secondary cell (SCell) is formed to form a group of serving cells together with the PCell. In the downlink, the carrier corresponding to the SCell is the downlink secondary component carrier (DLSCC). In the uplink, the carrier corresponding to the SCell is the uplink secondary component carrier (ULSCC).

[0037] For one UE, a group of service cells consisting of one PCell and one or more SCells is formed.

[0038] In addition, new technologies of LTE-A include technologies supporting wider frequency bands (Widerbandwidth extension) and Coordinated Multiple Point transmission and reception (CoMP) technologies, etc. CoMP, which is being studied to implement LTE-A in 3GPP, is described in Non-Patent Document 1.

[0039] In addition, in order to cope with the large amount of traffic in the future, 3GPP is studying the use of small eNBs (hereinafter sometimes referred to as "small-scale base station devices") that constitute small cells. For example, the following technologies are being studied, namely, by setting up multiple small eNBs and constituting multiple small cells to improve frequency utilization efficiency and increase communication capacity. Specifically, there is dual connectivity (DC) in which a UE connects to two eNBs for communication. DC is described in Non-Patent Document 1.

[0040] Sometimes, one of the eNBs performing dual connectivity (DC) is called a "master eNB (abbreviated as MeNB)" and the other is called a "secondary eNB (abbreviated as SeNB)".

[0041] Mobile network traffic is increasing, and communication speeds are also increasing. If LTE and LTE-A are put into full-scale use, communication speeds will be further increased.

[0042] In addition, the fifth generation (hereinafter sometimes referred to as "5G") wireless access system is being studied with the goal of starting service for the upgraded mobile communication after 2020. For example, in Europe, the METIS organization is summarizing the requirements for 5G (see Non-Patent Document 5).

[0043] In the 5G wireless access system, with respect to the LTE system, assuming that the system capacity is 1000 times, the data transmission speed is 100 times, the data processing delay is 1 / 10, and the number of simultaneous connections of communication terminals is 100 times, further low power consumption and low cost of the device can be listed as necessary conditions.

[0044] In order to meet such requirements, 3GPP is advancing the discussion of 5G standards as Release 15 (see Non-Patent Documents 6 to 18). The technology of the wireless section of 5G is called "New Radio Access Technology" ("New Radio" is abbreviated as "NR").

[0045] Discussions on the NR system based on the LTE system and LTE-A system are continuously advancing, but changes and additions from the LTE system and LTE-A system are made in the following point.

[0046] As the access method of NR, OFDM is used in the downlink direction, and OFDM and DFT-s-OFDM (DFT-spread-OFDM) are used in the uplink direction.

[0047] In NR, higher frequencies can be used compared to LTE to increase transmission speeds and reduce processing delays.

[0048] In NR, an effort is made to ensure cell coverage by forming a narrow beam-shaped transmission and reception range (beamforming) while changing the direction of the beam (beam scanning).

[0049] The NR frame structure supports various subcarrier spacings, that is, various parameter sets (Numerology). In NR, one subframe is 1 millisecond, and one time slot consists of 14 symbols, regardless of the parameter set. In addition, the number of time slots contained in one subframe is one in the parameter set with a subcarrier spacing of 15kHz, and increases in proportion to the subcarrier spacing in other parameter sets (refer to non-patent document 13 (TS38.211 v15.2.0)).

[0050] The downlink synchronization signal in NR is sent from the base station as a synchronization signal burst (Synchronization Signal Burst; sometimes referred to as SS burst below) at a specified period for a specified duration. The SS burst consists of a synchronization signal module (Synchronization Signal Block; sometimes referred to as SS module below) for each beam of the base station. The base station changes the beam to send the SS module of each beam during the duration of the SS burst. The SS module consists of P-SS, S-SS and PBCH.

[0051] In NR, a phase tracking reference signal (PTRS) is added as a downlink reference signal of NR to reduce the influence of phase noise. PTRS is also added to the uplink reference signal in the same way as the downlink.

[0052] In NR, in order to flexibly switch DL / UL within a time slot, a time slot format indication (Slot Format Indication: SFI) is added to the information included in the PDCCH.

[0053] In addition, in NR, the base station pre-sets a part of the carrier frequency band for the UE (hereinafter sometimes referred to as Bandwidth Part (BWP)), and the UE transmits and receives between itself and the base station in the BWP, thereby striving to reduce power consumption in the UE.

[0054] In 3GPP, as DC modes, DC performed by LTE base stations and NR base stations connected to EPC, DC performed by NR base stations connected to 5G core systems, and DC performed by LTE base stations and NR base stations connected to 5G core systems are discussed (refer to non-patent documents 12, 16, and 19).

[0055] In addition, 3GPP is studying some new technologies, such as non-public network (NPN), connection to PLMN via NPN, connection to NPN via PLMN, etc. (see Non-Patent Documents 20 and 21). Prior art literature Non-patent literature

[0056] Non-patent document 1: 3GPP TS36.300 V15.4.0 Non-patent document 2: 3GPP S1-083461 Non-patent document 3: 3GPP TR 36.814 V9.2.0 Non-patent document 4: 3GPP TR 36.912 V15.0.0 Non-Patent Document 5: “Scenarios, requirements and KPIs for 5G mobile and wireless system”, ICT-317669-METIS / D1.1 Non-patent document 6: 3GPP TR 23.799 V14.0.0 Non-patent document 7: 3GPP TR 38.801 V14.0.0 Non-patent document 8: 3GPP TR 38.802 V14.2.0 Non-patent document 9: 3GPP TR 38.804 V14.0.0 Non-patent document 10: 3GPP TR 38.912 V14.1.0 Non-patent document 11: 3GPP RP-172115 Non-patent document 12: 3GPP TS37.340 V15.2.0 Non-patent document 13: 3GPP TS38.211 V15.2.0 Non-patent document 14: 3GPP TS38.213 V15.2.0 Non-patent document 15: 3GPP TS38.214 V15.2.0 Non-patent document 16: 3GPP TS38.300 V15.2.0 Non-patent document 17: 3GPP TS38.321 V15.2.0 Non-patent document 18: 3GPP TS38.212 V15.2.0 Non-Patent Document 19: 3GPP RP-161266 Non-patent document 20: 3GPP TR 23.734 V16.2.0 Non-patent document 21: 3GPP S2-1903275 Non-Patent Document 22: 3GPP TS23.501 V16.1.0 Non-patent document 23: IETF RFC7296, Internet<URL:https: / / tools.ietf.org / html / rfc7296> Non-patent document 24: 3GPP TS38.413 V15.3.0 Non-patent document 25: 3GPP TS23.502 V16.1.1 Non-Patent Document 26: 3GPP TS24.501 V16.1.0 Non-patent document 27: 3GPP TS38.331 V15.6.0 Non-patent document 28: IETF RFC3706, Internet<URL:https: / / tools.ietf.org / html / rfc3706> Summary of the invention Technical problem to be solved by the invention

[0057] The introduction of NPN using a 5G communication system (hereinafter sometimes referred to as a 5G system) in 3GPP is being discussed. For example, the introduction of NPN using 5G indoors in factories, etc. is being discussed (refer to non-patent document 20 (3GPPTR23.734 V16.2.0)). The connection from the UE to the public network via the NPN and the connection from the UE to the NPN via the public network are being discussed. However, as described above, the process in which two networks are cascaded is not defined. For example, the connection between the UE and the public network in the case of releasing the connection between the UE and the NPN in the connection to the public network via the NPN is not disclosed. As a result, the following problem may occur, namely: a malfunction may occur between the UE and the public network, and the operation in the communication system may become unstable.

[0058] In view of the above problems, one of the objectives of the present disclosure is to provide a technology that can improve the robustness of a communication system. Technical means for solving technical problems

[0059] According to the present disclosure, there is provided a communication system, comprising: a communication terminal; a first network configured to be able to communicate wirelessly with the communication terminal; and at least one second network configured to be able to communicate with the first network, the communication system being characterized in that, in a state where the communication terminal is connected to the first network and connected to the at least one second network via the first network, when the first network decides to release the connection between the first network and the communication terminal, the communication terminal or the first network instructs the at least one second network to release the connection with the communication terminal. According to the present disclosure, there is provided a communication terminal configured to be able to wirelessly communicate with a first network, characterized in that, in a state where the communication terminal is connected to the first network and connected to at least one second network via the first network, when the communication terminal is notified by the first network to release the connection between the first network and the communication terminal, the communication terminal instructs the at least one second network to release the connection with the communication terminal. According to the present disclosure, there is provided a network configured to be able to wirelessly communicate with a communication terminal and to be able to communicate with at least one other network, characterized in that, when the communication terminal is connected to the network and connected to the at least one other network via the network, the network instructs the at least one other network to release the connection with the communication terminal when deciding to release the connection between the network and the communication terminal. Effects of the Invention

[0060] According to the present disclosure, the robustness of the communication system can be improved.

[0061] The objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description and accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 This is an explanatory diagram showing the structure of a radio frame used in a communication system of the LTE method. Figure 2 This is a block diagram showing the overall configuration of a communication system 200 of the LTE scheme being discussed in 3GPP. Figure 3 This is a block diagram showing the overall structure of the NR-based communication system 210 discussed in 3GPP. Figure 4 This is a structural diagram of DC performed by eNB and gNB connected to EPC. Figure 5 This is a structural diagram of DC performed by gNB connected to the NG core. Figure 6 This is a structural diagram of DC performed by eNB and gNB connected to the NG core. Figure 7 This is a structural diagram of DC performed by eNB and gNB connected to the NG core. Figure 8 It is shown Figure 2 A block diagram of the structure of the mobile terminal 202 is shown. Fig. 9 It is shown Figure 2 A block diagram of the structure of the base station 203 is shown. Fig.10 is a block diagram showing the structure of an MME. Fig.11 It is a block diagram showing the structure of 5GC. Fig.12 This is a flowchart showing an overview of operations from cell search to standby performed by a communication terminal (UE) in a communication system using the LTE method. Fig.13 is a diagram showing an example of a cell structure of an NR system. Fig.14 This is a sequence diagram showing a first example of an operation of releasing a UE connected to an outer NW via an inner NW from connections with the inner NW and the outer NW in accordance with the first embodiment. Fig.15 This is a sequence diagram showing a first example of an operation of releasing a UE connected to an outer NW via an inner NW from connections with the inner NW and the outer NW in accordance with the first embodiment. Fig.16 This is a sequence diagram showing a second example of the operation of releasing a UE connected to an outer NW via an inner NW from connections with the inner NW and the outer NW in accordance with the first embodiment. Fig.17 This is a sequence diagram showing a second example of the operation of releasing a UE connected to an outer NW via an inner NW from connections with the inner NW and the outer NW in accordance with the first embodiment. Fig.18 This is a sequence diagram showing a third example of the operation of releasing a UE connected to an outer NW via an inner NW from connections with the inner NW and the outer NW, in accordance with the first embodiment. Fig.19 This is a sequence diagram showing a third example of the operation of releasing a UE connected to an outer NW via an inner NW from connections with the inner NW and the outer NW, in accordance with the first embodiment. Fig. 20 This is a sequence diagram showing a fourth example of the operation of releasing a UE connected to an outer NW via an inner NW from connections with the inner NW and the outer NW in accordance with the first embodiment. Fig.21 This is a sequence diagram showing a fourth example of the operation of releasing a UE connected to an outer NW via an inner NW from connections with the inner NW and the outer NW in accordance with the first embodiment. Fig. 22 This is a sequence diagram showing a first example of an operation of releasing registration of a UE connected to an outer NW via an inner NW, in accordance with Modification 1 of Embodiment 1. FIG. Fig.23 This is a sequence diagram showing a first example of an operation of releasing registration of a UE connected to an outer NW via an inner NW, in accordance with Modification 1 of Embodiment 1. FIG. Fig.24 This is a sequence diagram showing a first example of an operation of releasing registration of a UE connected to an outer NW via an inner NW, in accordance with Modification 1 of Embodiment 1. FIG. Fig.25 This is a sequence diagram showing a second example of the operation of releasing the registration of a UE connected to an outer NW via an inner NW, in accordance with Modification 1 of Embodiment 1. Fig.26 This is a sequence diagram showing a second example of the operation of releasing the registration of a UE connected to an outer NW via an inner NW, in accordance with Modification 1 of Embodiment 1. Fig. 27 This is a sequence diagram showing a second example of the operation of releasing the registration of a UE connected to an outer NW via an inner NW, in accordance with Modification 1 of Embodiment 1. Fig.28 This is a sequence diagram showing the operation of connecting the UE to the outer NW via the inner NW by initiating the connection start in the outer NW according to the second modification of the first embodiment. Fig.29 This is a sequence diagram showing the operation of connecting the UE to the outer NW via the inner NW by initiating the connection start in the outer NW according to the second modification of the first embodiment. Fig.30 This is a sequence diagram showing a first example of an operation of releasing an outer PDU session in conjunction with releasing an inner PDU session, regarding a UE connected to an outer NW via an inner NW, in accordance with a third variation of the first embodiment. Fig.31 This is a sequence diagram showing a first example of an operation of releasing an outer PDU session in conjunction with releasing an inner PDU session, regarding a UE connected to an outer NW via an inner NW, in accordance with a third variation of the first embodiment. Fig.32 This is a sequence diagram showing a first example of an operation of releasing an outer PDU session in conjunction with releasing an inner PDU session, regarding a UE connected to an outer NW via an inner NW, in accordance with a third variation of the first embodiment. Fig.33This is a sequence diagram showing a first example of an operation of releasing an outer PDU session in conjunction with releasing an inner PDU session, regarding a UE connected to an outer NW via an inner NW, in accordance with a third variation of the first embodiment. Fig.34 This is a sequence diagram showing a second example of the operation of releasing the outer PDU session along with the inner PDU session release for a UE connected to the outer NW via the inner NW in accordance with the modification 3 of the first embodiment. Fig.35 This is a sequence diagram showing a second example of the operation of releasing the outer PDU session along with the inner PDU session release for a UE connected to the outer NW via the inner NW in accordance with the modification 3 of the first embodiment. Fig.36 This is a sequence diagram showing variation 4 of implementation example 1, in which the outer U-plane operation is stopped along with the inner U-plane operation for a UE connected to the outer NW via the inner NW. Fig.37 This is a sequence diagram showing variation 4 of implementation example 1, in which the outer U-plane operation is stopped along with the inner U-plane operation for a UE connected to the outer NW via the inner NW. Fig.38 This is a sequence diagram showing a first example of the action of releasing the outer AN accompanying the transition to RRC_INACTIVE in relation to Modification 5 of Embodiment 1. Fig.39 This is a sequence diagram showing a second example of the action of releasing the outer AN accompanying the transition to RRC_INACTIVE in relation to Modification 5 of the first embodiment. Fig.40 This is a sequence diagram showing an operation of notifying the outer NW of UE setting update in the inner NW in accordance with Modification 6 of Embodiment 1. Fig.41 This is a sequence diagram showing an operation of notifying the inner NW of UE setting update in the outer NW in accordance with Modification 6 of Embodiment 1. Fig.42 This is a transition diagram of the CM state related to the inner NW that a UE connected to the outer NW via the inner NW has in Embodiment 2. Fig.43 This is a transition diagram of the CM state related to the outer NW that a UE connected to the outer NW via the inner NW has in Embodiment 2. Fig.44 This is a transition diagram of the CM state of a UE connected to an outer NW via an inner NW in accordance with Embodiment 2. DETAILED DESCRIPTION

[0063] Implementation Method 1 Figure 2 1 is a block diagram showing the overall structure of a communication system 200 of the LTE method discussed in 3GPP. Figure 2 The wireless access network is referred to as E-UTRAN (Evolved Universal Terrestrial Radio Access Network) 201. The communication terminal device, i.e., the mobile terminal device (hereinafter referred to as "mobile terminal (User Equipment: UE)") 202 can wirelessly communicate with the base station device (hereinafter referred to as "base station (E-UTRAN NodeB: eNB)") 203, and transmit and receive signals by wireless communication.

[0064] Here, the "communication terminal device" refers not only to mobile terminal devices such as mobile phone terminal devices, but also includes non-mobile devices such as sensors. In the following description, the "communication terminal device" may be simply referred to as a "communication terminal".

[0065] If the control protocols for the mobile terminal 202, such as RRC (Radio Resource Control), and the user plane (hereinafter sometimes also referred to as U-Plane), such as PDCP (Packet Data Convergence Protocol), RLC (Radio Link Control), MAC (Medium Access Control), and PHY (Physical layer) are terminated at the base station 203, then the E-UTRAN is composed of one or more base stations 203.

[0066] The control protocol RRC (Radio Resource Control) between the mobile terminal 202 and the base station 203 performs broadcast, paging, RRC connection management, etc. The states of the base station 203 and the mobile terminal 202 in RRC are RRC_IDLE and RRC_CONNECTED.

[0067] In RRC_IDLE, PLMN (Public Land Mobile Network) selection, system information (SI) broadcasting, paging, cell reselection, mobility, etc. are performed. In RRC_CONNECTED, the mobile terminal has an RRC connection and can send and receive data with the network. In addition, in RRC_CONNECTED, handover (HO), neighbor cell measurement, etc. are performed.

[0068] The base station 203 is composed of one or more eNBs 207. In addition, the system composed of EPC (Evolved Packet Core) as the core network and E-UTRAN 201 as the radio access network is called EPS (Evolved Packet System). Sometimes, EPC as the core network and E-UTRAN 201 as the radio access network are collectively referred to as "network".

[0069] The eNB 207 is connected to a mobility management entity (MME), an S-GW (Serving Gateway), or an MME / S-GW unit (hereinafter sometimes referred to as an "MME unit" 204) including the MME and the S-GW via an S1 interface, and control information is communicated between the eNB 207 and the MME unit 204. One eNB 207 can be connected to multiple MME units 204. The eNBs 207 are connected to each other via an X2 interface, and control information is communicated between the eNBs 207.

[0070] The MME unit 204 is an upper device, specifically, an upper node, and controls the connection between the eNB 207 as a base station and the mobile terminal (UE) 202. The MME unit 204 constitutes the EPC as a core network. The base station 203 constitutes the E-UTRAN 201.

[0071] The base station 203 may constitute one cell or multiple cells. Each cell has a predetermined range as a range in which communication with the mobile terminal 202 can be performed, i.e., a coverage range, and wireless communication is performed with the mobile terminal 202 within the coverage range. When one base station 203 constitutes multiple cells, each cell is configured to be able to communicate with the mobile terminal 202.

[0072] Figure 32 is a block diagram showing the overall structure of a 5G communication system 210 discussed in 3GPP. Figure 3 For explanation. The radio access network is called NG-RAN (Next Generation Radio Access Network) 211. UE 202 can wirelessly communicate with the NR base station device (hereinafter referred to as "NR base station (NG-RAN NodeB: gNB)") 213 to send and receive signals in the form of wireless communication. In addition, the core network is called 5G Core (5G Core: 5GC).

[0073] If the control protocols for UE202, such as RRC (Radio Resource Control), and the user plane (hereinafter sometimes also referred to as U-Plane), such as SDAP (Service Data Adaptation Protocol), PDCP (Packet Data Convergence Protocol), RLC (Radio Link Control), MAC (Medium Access Control), and PHY (Physical layer) are terminated at the NR base station 213, then the NG-RAN is composed of one or more NR base stations 213.

[0074] The function of the control protocol RRC (Radio Resource Control) between UE202 and NR base station 213 is the same as that of LTE. The states between NR base station 213 and UE202 in RRC include RRC_IDLE, RRC_CONNECTED, and RRC_INACTIVE.

[0075] RRC_IDLE and RRC_CONNECTED are the same as LTE. While RRC_INACTIVE maintains the connection between the 5G core and the NR base station 213, it broadcasts system information (SI), paging, cell reselection, and movement.

[0076] gNB217 is connected to the access / mobility management function (Access and Mobility Management Function: AMF), session management function (Session Management Functio: SMF), or UPF (User Plane Function), or the AMF / SMF / UPF unit (hereinafter sometimes referred to as "5GC unit") 214 including AMF, SMF and UPF through the NG interface. Communication of control information and / or user data is performed between gNB217 and the 5GC unit 214. The NG interface is a general term for the N2 interface between gNB217 and AMF, the N3 interface between gNB217 and UPF, the N11 interface between AMF and SMF, and the N4 interface between UPF and SMF. One gNB217 can be connected to multiple 5GC units 214. gNB217 are connected to each other through the Xn interface, and communication of control information and / or user data is performed between gNB217.

[0077] The NR base station 213 is also the same as the base station 203 and can constitute one or more cells. When one NR base station 213 constitutes multiple cells, each cell is configured to be able to communicate with the UE 202.

[0078] The gNB 217 can be divided into a central unit (hereinafter sometimes referred to as a CU) 218 ​​and a distributed unit (hereinafter sometimes referred to as a DU) 219. The CU 218 is configured as one in the gNB 217. The DU 219 is configured as one or more in the gNB 217. The CU 218 is connected to the DU 219 via the F1 interface, and control information and / or user data are communicated between the CU 218 and the DU 219.

[0079] The 5G communication system may also include the Unified Data Management (UDM) function and the Policy Control Function (PCF) described in the non-patent document 22 (3GPP TS23.501 V16.1.0). UDM and / or PCF may be included in Figure 3 In the 5GC department.

[0080] The 5G communication system may further include a non-3GPP interworking function (N3IWF) described in non-patent document 22 (3GPP TS23.501 V16.1.0). N3IWF can terminate the access network (AN) in the non-3GPP access between the UE and the UE.

[0081] Figure 4 This is a diagram showing the structure of DC based on eNB and gNB connected to EPC. Figure 4 In the figure, the solid line indicates the connection of U-Plane, and the dotted line indicates the connection of C-Plane. Figure 4 In the example, eNB 223-1 is the primary base station and gNB 224-2 is the secondary base station (this DC structure is sometimes referred to as EN-DC). Figure 4 In the figure, an example is shown in which the U-Plane connection between the MME unit 204 and the gNB 224-2 is performed via the eNB 223-1, but it can also be performed directly between the MME unit 204 and the gNB 224-2.

[0082] Figure 5 1 is a diagram showing the structure of a DC based on a gNB connected to an NG core. Figure 5 In the figure, the solid line indicates the connection of U-Plane, and the dotted line indicates the connection of C-Plane. Figure 5 In this example, gNB224-1 is the primary base station and gNB224-2 is the secondary base station (this DC structure is sometimes referred to as NR-DC). Figure 5 In the figure, an example is shown in which the U-Plane connection between the 5GC unit 214 and the gNB 224-2 is performed via the gNB 224-1, but it can also be performed directly between the 5GC unit 214 and the gNB 224-2.

[0083] Figure 6 : is a diagram showing the structure of DC based on eNB and gNB connected to NG core. Figure 6 In the figure, the solid line indicates the connection of U-Plane, and the dotted line indicates the connection of C-Plane. Figure 6 In the example, eNB 226-1 is the primary base station and gNB 224-2 is the secondary base station (this DC structure is sometimes referred to as NG-EN-DC). Figure 6 In the figure, an example is shown in which the U-Plane connection between the 5GC unit 214 and the gNB 224-2 is performed via the eNB 226-1, but it can also be performed directly between the 5GC unit 214 and the gNB 224-2.

[0084] Figure 72 is a diagram showing another structure of DC based on eNB and gNB connected to NG core. Figure 7 In the figure, the solid line indicates the connection of U-Plane, and the dotted line indicates the connection of C-Plane. Figure 7 In the example, gNB 224-1 is the primary base station and eNB 226-2 is the secondary base station (this DC structure is sometimes referred to as NE-DC). Figure 7 In the figure, an example is shown in which the U-Plane connection between the 5GC unit 214 and the eNB 226-2 is performed via the gNB 224-1, but it can also be performed directly between the 5GC unit 214 and the eNB 226-2.

[0085] Figure 8 It shows Figure 2 The structure of the mobile terminal 202 is shown in FIG. Figure 8 The transmission processing of the mobile terminal 202 shown in the figure is explained. First, the control data from the protocol processing unit 301 and the user data from the application unit 302 are saved in the transmission data buffer unit 303. The data saved in the transmission data buffer unit 303 is transmitted to the encoding unit 304 to implement encoding processing such as error correction. There may also be data that is directly output from the transmission data buffer unit 303 to the modulation unit 305 without implementing encoding processing. The data after the encoding processing by the encoding unit 304 is modulated in the modulation unit 305. Precoding in MIMO may also be performed in the modulation unit 305. The modulated data is converted into a baseband signal, and then output to the frequency conversion unit 306, and converted into a wireless transmission frequency. Thereafter, the transmission signal is sent from the antennas 307-1 to 307-4 to the base station 203. In Figure 8 , the example shows a case where the number of antennas is 4, but the number of antennas is not limited to 4.

[0086] In addition, the receiving process of the mobile terminal 202 is performed as follows. The wireless signal from the base station 203 is received through the antennas 307-1 to 307-4. The received signal is converted from the wireless receiving frequency to the baseband signal in the frequency conversion unit 306, and demodulated in the demodulation unit 308. In the demodulation unit 308, waiting calculation and multiplication processing can be performed. The demodulated data is transmitted to the decoding unit 309 for decoding processing such as error correction. Among the decoded data, the control data is transmitted to the protocol processing unit 301, and the user data is transmitted to the application unit 302. A series of processing of the mobile terminal 202 is controlled by the control unit 310. Therefore, although in Figure 8 Although omitted in FIG. 3 , the control unit 310 is connected to each of the units 301 to 309. Figure 8 In the present invention, the number of antennas used by the mobile terminal 202 for sending may be the same as or different from the number of antennas used for receiving.

[0087] Fig. 9 It is shown Figure 2 The structure of the base station 203 is shown in FIG. Fig. 9 The sending processing of the base station 203 shown is explained. The EPC communication unit 401 performs data transmission and reception between the base station 203 and the EPC (MME unit 204, etc.). The 5GC communication unit 412 performs data transmission and reception between the base station 203 and the 5GC (5GC unit 214, etc.). The other base station communication units 402 perform data transmission and reception with other base stations. The EPC communication unit 401, the 5GC communication unit 412 and the other base station communication units 402 exchange information with the protocol processing unit 403 respectively. The control data from the protocol processing unit 403, and the user data and control data from the EPC communication unit 401, the 5GC communication unit 412 and the other base station communication units 402 are saved in the sending data buffer unit 404.

[0088] The data stored in the transmission data buffer unit 404 is transmitted to the encoding unit 405 to implement encoding processing such as error correction. There may also be data that is directly output from the transmission data buffer unit 404 to the modulation unit 406 without implementing encoding processing. The encoded data is modulated in the modulation unit 406. Precoding in MIMO may also be performed in the modulation unit 406. The modulated data is converted into a baseband signal and then output to the frequency conversion unit 407 to be converted into a wireless transmission frequency. Thereafter, the transmission signal is sent to one or more mobile terminals 202 using antennas 408-1 to 408-4. Fig. 9 , the example shows a case where the number of antennas is 4, but the number of antennas is not limited to 4.

[0089] In addition, the receiving processing of the base station 203 is performed as follows. The wireless signal from one or more mobile terminals 202 is received by the antenna 408. The received signal is converted from the wireless receiving frequency to a baseband signal by the frequency conversion unit 407, and is demodulated in the demodulation unit 409. The demodulated data is transmitted to the decoding unit 410 for decoding processing such as error correction. Among the decoded data, the control data is transmitted to the protocol processing unit 403 or the 5GC communication unit 412 or the EPC communication unit 401, and other base station communication units 402, and the user data is transmitted to the 5GC communication unit 412, the EPC communication unit 401, and other base station communication units 402. A series of processing of the base station 203 is controlled by the control unit 411. Therefore, although in Fig. 9 Although omitted in FIG. 4 , the control unit 411 is connected to each unit 401 to 410. Fig. 9 In the example, the number of antennas used by the base station 203 for sending may be the same as or different from the number of antennas used for receiving.

[0090] Fig. 92 is a block diagram showing the structure of the base station 203, but the same structure can be used for the base station 213. Figure 8 and Fig. 9 , the number of antennas of the mobile terminal 202 and the number of antennas of the base station 203 may be the same or different.

[0091] Fig.10 is a block diagram showing the structure of an MME. Fig.10 In the above Figure 2 The structure of MME204a included in the MME unit 204 shown. The PDN GW communication unit 501 performs data transmission and reception between MME204a and PDN GW. The base station communication unit 502 performs data transmission and reception between MME204a and base station 203 via the S1 interface. In the case where the data received from the PDN GW is user data, the user data is transmitted from the PDN GW communication unit 501 to the base station communication unit 502 via the user plane communication unit 503, and is sent to one or more base stations 203. In the case where the data received from the base station 203 is user data, the user data is transmitted from the base station communication unit 502 to the PDN GW communication unit 501 via the user plane communication unit 503, and is sent to the PDN GW.

[0092] When the data received from the PDN GW is control data, the control data is transmitted from the PDN GW communication unit 501 to the control plane control unit 505. When the data received from the base station 203 is control data, the control data is transmitted from the base station communication unit 502 to the control plane control unit 505.

[0093] The control plane control unit 505 includes a NAS security unit 505-1, an SAE bearer control unit 505-2, an idle state mobility management unit 505-3, etc., and performs all processing for the control plane (hereinafter, sometimes also referred to as C-Plane). The NAS security unit 505-1 performs the security of NAS (Non-Access Stratum) messages, etc. The SAE bearer control unit 505-2 performs the management of SAE (System Architecture Evolution) bearers, etc. The idle state mobility management unit 505-3 performs mobility management in the idle state (idle state; LTE-IDLE state, or simply idle), generation and control of paging signals in the idle state, addition, deletion, update, retrieval, and tracking area list management of one or more mobile terminals 202 under coverage, etc.

[0094] MME204a distributes paging signals to one or more base stations 203. In addition, MME204a performs mobility control in the idle state. MME204a manages the tracking area list when the mobile terminal is in the idle state and in the active state. MME204a starts the paging protocol by sending a paging message to the cell belonging to the tracking area registered by the UE. The management of the CSG, the management of the CSG ID, and the whitelist management of the eNB207 connected to MME204a can be performed by the idle state mobility management unit 505-3.

[0095] Fig.11 It is a block diagram showing the structure of 5GC. Fig.11 The above Figure 3 The structure of the 5GC unit 214 is shown. Fig.11 Shown in Figure 5 The 5GC unit 214 shown includes the structure of AMF, the structure of SMF, and the structure of UPF. The data network communication unit 521 performs data transmission and reception between the 5GC unit 214 and the data network. The base station communication unit 522 performs data transmission and reception between the 5GC unit 214 and the base station 203 through the S1 interface, and / or performs data transmission and reception between the 5GC unit 214 and the base station 213 through the NG interface. In the case where the data received from the data network is user data, the user data is transmitted from the data network communication unit 521 to the base station communication unit 522 via the user plane communication unit 523, and is sent to one or more base stations 203 and / or base stations 213. In the case where the data received from the base station 203 and / or the base station 213 is user data, the user data is transmitted from the base station communication unit 522 to the data network communication unit 521 via the user plane communication unit 523, and is sent to the data network.

[0096] In the case where the data received from the data network is control data, the control data is transmitted from the data network communication unit 521 to the session management unit 527 via the user plane control unit 523. The session management unit 527 transmits the control data to the control plane control unit 525. In the case where the data received from the base station 203 and / or the base station 213 is control data, the control data is transmitted from the base station communication unit 522 to the control plane control unit 525. The control plane control unit 525 transmits the control data to the session management unit 527.

[0097] The control plane control unit 525 includes a NAS security unit 525-1, a PDU session control unit 525-2, an idle state (IdleState) mobility management unit 525-3, etc., and performs all processing for the control plane (hereinafter, sometimes also referred to as C-Plane). The NAS security unit 525-1 performs the security of NAS (Non-Access Stratum) messages, etc. The PDU session control unit 525-2 manages the PDU session between the mobile terminal 202 and the 5GC unit 214, etc. The idle state mobility management unit 525-3 performs mobility management in the standby state (idle state (IdleState); RRC_IDLE state, or simply called idle), generation and control of paging signals in the standby state, addition, deletion, update, retrieval, and tracking area list management of one or more mobile terminals 202 under coverage, etc.

[0098] The 5GC unit 214 allocates paging signals to one or more base stations 203 and / or base stations 213. In addition, the 5GC unit 214 performs mobility control in the idle state. The 5GC unit 214 manages the tracking area list when the mobile terminal is in the idle state, in the inactive state, and in the active state. The 5GC unit 214 starts the paging protocol by sending a paging message to the cell belonging to the tracking area registered by the UE.

[0099] Next, an example of a cell search method in a communication system is shown. Fig.12 This is a flowchart showing an overview of the cell search and standby operation performed by a communication terminal (UE) in an LTE communication system. If the communication terminal starts the cell search, in step ST601, the first synchronization signal (P-SS) and the second synchronization signal (S-SS) sent from the surrounding base stations are used to synchronize the slot timing and the frame timing.

[0100] P-SS and S-SS are collectively referred to as synchronization signals (SS). Synchronization codes corresponding to the PCIs assigned to each cell are allocated to the synchronization signal (SS). It is studied to set the number of PCIs to 504. Synchronization is achieved using these 504 PCIs, and the PCI of the synchronized cell is detected (determined).

[0101] Next, in step ST602, the reference signal (reference signal: RS) sent from the base station to each cell, i.e., the cell-specific reference signal (Cell-specific Reference Signal: CRS), is detected for the synchronized cell, and the RS received power (Reference Signal Received Power: RSRP) is measured. The reference signal (RS) uses a code that corresponds to the PCI one-to-one. This code can be used to obtain correlation and separate from other cells. By deriving the RS code for the cell based on the PCI determined in step ST601, the RS can be detected and the RS received power can be measured.

[0102] Next, in step ST603, a cell with the best RS reception quality is selected from the one or more cells detected up to step ST602, for example, a cell with the highest RS reception power, that is, the best cell is selected.

[0103] Then, in step ST604, the PBCH of the best cell is received to obtain the broadcast information, i.e., the BCCH. The MIB (Master Information Block) containing the cell structure information is mapped in the BCCH on the PBCH. Therefore, by receiving the PBCH and obtaining the BCCH, the MIB can be obtained. The MIB information includes, for example, the DL (downlink) system bandwidth (also called the transmission bandwidth configuration (transmission bandwidth configuration: dl-bandwidth)), the number of transmitting antennas, and the SFN (System Frame Number: system frame number).

[0104] Then in step ST605, the DL-SCH of the cell is received based on the cell structure information of the MIB, and the SIB (System Information Block) 1 in the broadcast information BCCH is obtained. SIB1 contains information related to accessing the cell, information related to cell selection, and scheduling information of other SIBs (SIBk; k≥2 integer). In addition, SIB1 also contains the Tracking Area Code (TAC).

[0105] Then in step ST606, the communication terminal compares the TAC of SIB1 received in step ST605 with the TAC part of the tracking area identity (TAI) in the tracking area list already held by the communication terminal. The tracking area list is also called the TAI list. TAI is identification information used to identify the tracking area, and is composed of MCC (Mobile Country Code), MNC (Mobile Network Code), and TAC (Tracking Area Code). MCC is the country code. MNC is the network code. TAC is the code number of the tracking area.

[0106] If the result of the comparison in step S606 is that the TAC received in step ST605 is the same as the TAC included in the tracking area list, the communication terminal enters the standby action in the cell. If the TAC received in step ST605 is not included in the tracking area list, the communication terminal passes through the cell and requests the core network (CoreNetwork, EPC) including MME, etc. to change the tracking area to perform TAU (Tracking Area Update).

[0107] exist Fig.12 In the example shown, an example of the action from cell search to standby in the LTE mode is shown, but in the NR mode, in addition to the best cell, the best beam can also be selected in step ST603. In addition, in the NR mode, in step ST604, beam information such as a beam identifier can be obtained. In addition, in the NR mode, in step ST604, scheduling information of the remaining minimum SI (Remaining MinimumSI: RMSI) can be obtained. In the NR mode, in step ST605, it can be set to receive RMSI.

[0108] The device constituting the core network (hereinafter sometimes referred to as the "core network side device") updates the tracking area list based on the TAU request signal and the identification number (UE-ID, etc.) of the communication terminal sent from the communication terminal. The core network side device sends the updated tracking area list to the communication terminal. The communication terminal rewrites (updates) the TAC list held by the communication terminal based on the received tracking area list. Thereafter, the communication terminal enters standby action in the cell.

[0109] Due to the popularity of smartphones and tablet terminals, the volume of cellular wireless communications has exploded, causing concerns about the shortage of wireless resources worldwide. In order to cope with this situation and improve the efficiency of frequency utilization, research has been conducted on miniaturization of cells and promotion of spatial separation.

[0110] In the existing cell structure, a cell formed by an eNB has a wide coverage area. Conventionally, cells are formed so that a certain area is covered by a wide coverage area of ​​a plurality of cells formed by a plurality of eNBs.

[0111] When the cell is miniaturized, the cell formed by the eNB has a narrower coverage area than the coverage area of ​​the cell formed by the existing eNB. Therefore, as in the prior art, a larger number of eNBs with miniaturized cells are required to cover a certain area than the existing eNBs.

[0112] In the following description, a cell with a relatively large coverage, such as a cell composed of existing eNBs, is referred to as a "macro cell", and an eNB constituting a macro cell is referred to as a "macro eNB". In addition, a cell with a relatively small coverage, such as a cell after cell miniaturization, is referred to as a "small cell", and an eNB constituting a small cell is referred to as a "small eNB".

[0113] The macro eNB may be, for example, the “Wide Area Base Station” described in Non-Patent Document 7.

[0114] Small eNBs may be, for example, low-power nodes, local nodes, and hotspots. In addition, small eNBs may be pico eNBs constituting pico cells, femto eNBs constituting femto cells, HeNBs, RRHs (Remote Radio Heads), RRUs (Remote Radio Units), RREs (Remote Radio Equipment), or RNs (Relay Nodes). In addition, small eNBs may also be "local area base stations" or "home base stations" as described in non-patent document 7.

[0115] Fig.13 An example of a cell structure in NR is shown. In a cell in NR, a narrow beam is formed and its direction is changed for transmission. Fig.13In the example shown, the base station 750 uses beam 751-1 at a certain time to transmit and receive with the mobile terminal. At other times, the base station 750 uses beam 751-2 to transmit and receive with the mobile terminal. Similarly, the base station 750 uses one or more of beams 751-3 to 751-8 to transmit and receive with the mobile terminal. Thus, the base station 750 forms a wide range of cells.

[0116] exist Fig.13 In FIG. 1 , an example is shown in which the number of beams used by the base station 750 is set to 8, but the number of beams may be different from 8. Fig.13 In the example shown, the number of beams used simultaneously by the base station 750 is set to one, but it can also be multiple.

[0117] The UE can be cascaded to multiple NWs. At least one of the multiple NWs can be an NPN. The UE can be connected to a base station (hereinafter, sometimes referred to as a RAN) under the control of a certain NW (hereinafter, may be referred to as an inner NW). The UE can be connected to other NWs (hereinafter referred to as outer NWs) via the RAN and the UPF in the inner NW (hereinafter sometimes referred to as the inner UPF). The UE can be connected to the outer NW via the N3IWF under the control of the outer NW. A connection can be established between the inner UPF and the N3IWF.

[0118] The inner NW can be an NPN or a PLMN. The outer NW can be a PLMN or an NPN. The above NPN can be a standalone NPN, that is, an NPN that does not support PLMN. Alternatively, the above NPN can also be an NPN integrated with a public network, that is, an NPN that is supported by a public network. The same applies to the following.

[0119] The UE may establish an N1 interface with the AMF in each of the multiple NWs. The UE may establish an N1 interface with the AMF in the inner NW (hereinafter sometimes referred to as the inner AMF) via the RAN. The UE may establish an N1 interface with the AMF in the outer NW (hereinafter sometimes referred to as the outer AMF) via the RAN, the inner UPF and the N3IWF. The N1 interface between the UE and the inner AMF and the N1 interface between the UE and the outer AMF may exist at the same time.

[0120] The UE can establish an AN (Access Network) connection in the inner NW with the RAN. The UE can establish an AN connection in the outer NW with the N3IWF. The outer AN connection of the UE can also be an IPsec connection using the Internet Key Exchange Protocol Version 2 (IKEv2) disclosed in non-patent document 23 (IETF RFC7296). The inner AN connection and the outer AN connection of the UE can exist at the same time.

[0121] In the connection between the UE and the inner NW, an N2 interface may be established between the RAN and the inner AMF. In the connection between the UE and the outer NW, an N2 interface may be established between the N3IWF and the outer AMF. The N2 interface between the RAN and the inner AMF and the N2 interface between the N3IWF and the outer AMF may exist at the same time.

[0122] In the connection between the UE and the inner NW, an N3 interface may be established between the RAN and the inner UPF. In the connection between the UE and the outer NW, an N3 interface may be established between the N3IWF and the UPF in the outer NW (hereinafter, sometimes referred to as the outer UPF). The N3 interface between the RAN and the inner UPF and the N3 interface between the N3IWF and the outer UPF may exist at the same time.

[0123] In the connection between the UE and the inner NW, an N4 interface may be established between the inner UPF and the SMF in the inner NW (hereinafter, sometimes referred to as the inner SMF). In the connection between the UE and the outer NW, an N4 interface may be established between the outer UPF and the SMF in the outer NW (hereinafter, sometimes referred to as the outer SMF). The N4 interface between the inner UPF and the inner SMF and the N4 interface between the outer UPF and the outer SMF may exist at the same time.

[0124] In the connection between the UE and the inner NW, an N11 interface may be established between the inner AMF and the inner SMF. In the connection between the UE and the outer NW, an N11 interface may be established between the outer AMF and the outer SMF. The N11 interface between the inner AMF and the inner SMF and the N11 interface between the outer AMF and the outer SMF may exist at the same time.

[0125] A UE cascaded to multiple NWs is connected to two AMFs via one RAN. Therefore, the connection between the inner AMF and the UE and the connection between the outer AMF and the UE have mutual dependence. On the other hand, the process when mutual dependence occurs between the two connections is not defined. As a result, it is impossible to directly apply the previous sequence. For example, there is a problem of unnecessary memory security in one AMF (for example, unnecessary data remains).

[0126] In the first embodiment, a method for solving the above-mentioned problem is disclosed.

[0127] The UE releases the outer NW before releasing the inner NW. The release of the inner NW may be initiated by the inner AMF. The UE may release the outer NW after an RRC release indication from a base station (hereinafter, sometimes referred to as RAN).

[0128] The RAN may issue an RRC release indication to the UE by an indication from the inner AMF to the RAN regarding the release of the N2 connection of the UE. The signaling for the indication from the inner AMF to the RAN may be, for example, an N2 UE Context Release Command as described in non-patent document 24 (TS38.413).

[0129] The UE may request the outer AMF to release the NAS connection between the UE and the outer NW. The UE may use, for example, NAS signaling to issue the request. A new NAS signaling indicating the request may be set. The NAS signaling may be, for example, a service release request. Thus, for example, in the communication system, it is possible to prevent the connection between the UE and the inner NW from being cut off while the connection between the UE and the outer NW remains unchanged. As a result, unnecessary memory usage in each device of the outer NW can be reduced.

[0130] The NAS signaling may include information related to the reason for the connection release request. The reason may be, for example, the disconnection of the inner NW. Thus, for example, each device of the outer NW may determine to perform processing other than disconnection of the outer NW, such as direct connection between the UE and the outer NW. As a result, the flexibility in the communication system can be improved.

[0131] The outer AMF may acknowledge the request from the UE. The outer AMF may send a positive response to the request to the UE. The outer AMF may send the response using NAS signaling. Thus, for example, the UE is able to recognize that the request is accepted. As a result, malfunctions in the communication system can be prevented.

[0132] As another example, the outer AMF may reject the request from the UE. The outer AMF may send a rejection response to the request to the UE. The outer AMF may send the response using NAS signaling. The response may include information related to the reason for the rejection. For example, the reason may include a reason related to maintaining the connection with the outer NW, and may also include a reason related to a direct connection to the outer NW. Thus, for example, each device of the outer NW can determine to perform processing other than disconnecting the outer NW, such as a direct connection between the UE and the outer NW. As a result, the flexibility in the communication system can be improved.

[0133] Even if the response from the outer AMF is a rejection response, the UE can perform RRC release with the RAN. As described above, the UE can perform cell selection or cell reselection to a base station under the control of the outer NW. The cell selection or cell reselection performed by the UE can also be performed in the following case: the reason included in the rejection response from the outer AMF is a reason related to the direct connection to the outer NW. Thereby, for example, the UE can quickly perform direct connection with the outer NW.

[0134] The UE can preferentially select or reselect the cell of the base station under the control of the outer NW in the above cell selection or cell reselection. Thus, for example, the UE can quickly perform direct connection with the outer NW.

[0135] The UE may have a timer related to the above-mentioned cell selection or cell reselection. The UE may initialize the timer when the connection with the inner NW starts, or when the RRC connection with the RAN starts, or when the connection with the outer NW is established. The UE may start the timer at the start of the above-mentioned cell selection or cell reselection. The UE may stop the timer when the RRC connection with the base station under the control of the outer NW is completed, or when the PRACH is sent to the base station under the control of the outer NW. The UE may use the expiration of the timer as an opportunity to perform normal cell selection or reselection, for example, perform cell selection or reselection without giving priority to the cell of the base station under the control of the outer NW. As a result, for example, in the UE, the management of the above-mentioned cell selection or reselection action becomes easy. The timer may be provided by the outer AMF or RAN. As a result, for example, in the outer AMF, the management of the above-mentioned cell selection or reselection action becomes easy.

[0136] The outer AMF can release the outer NW between the outer AMF and the UE. Thus, for example, in the case where multiple UEs are connected in the outer NW, the memory usage in each device of the outer NW can be reduced. The outer AMF can use the request from the UE to perform the release. The outer AMF can instruct the N3IWF to release the N2 connection related to the UE between the outer AMF and the N3IWF. The signaling used for the indication can be, for example, the N2 UE ContextRelease Command described in non-patent document 24 (TS38.413). The N3IWF can use the indication to release the N2 connection related to the UE. For example, the N3IWF can release the AN connection between the N3IWF and the UE. The release of the AN connection between the N3IWF and the UE can be the release of the IPsec setting. The UE notifies the N3IWF of the release of the IPsec setting. The signaling used for the notification can be, for example, the signaling of the IKEINFORMATIONAL exchange described in non-patent document 23 (IETF RFC7296). The signaling may also include a Delete payload described in non-patent document 23 (IETF RFC 7296). The Delete payload may include information (e.g., an identifier) ​​about the SA (Security Association) released in the IPsec setting. The N3IWF may release the IPsec setting between the N3IWF and the UE. The N3IWF may notify the UE to release the IPsec setting. For example, the release notification from the N3IWF to the UE may be performed using the same signaling as the above-mentioned release notification from the UE to the N3IWF.

[0137] The N3IWF may notify the outer AMF that the AN connection has been released. The notification may be a response to the release of the N2 connection of the UE. The signaling used for the notification may be, for example, N2 UE ContextRelease Complete as described in non-patent document 24 (TS38.413).

[0138] The outer AMF instructs the outer SMF to stop the U-layer connection in the PDU session with the UE. The instruction may also be Nsmf_PDUSession_UpdateSMContext (Nsmf_PDU session updates SM context) as shown in Section 5.2.8.2.6 of Non-Patent Document 25 (TS23.502).

[0139] The UE releases the RRC connection with the RAN. The UE may release the NAS connection between the UE and the outer NW after the UE requests the outer AMF to release the NAS connection between the UE and the outer NW. Thus, for example, the UE may request the outer AMF to release the connection with the outer NW before releasing the connection between the UE and the inner NW.

[0140] The RAN may notify the inner AMF that the RRC connection has been released. The notification may be a response to the N2 connection release of the UE. The signaling used for the notification may be, for example, N2 UE Context Release Complete as described in non-patent document 24 (TS38.413).

[0141] The inner AMF instructs the inner SMF to stop the U-layer connection in the PDU session with the UE. The indication may also be Nsmf_PDUSession_UpdateSMContext (Nsmf_PDU session updates SM context) as shown in Section 5.2.8.2.6 of Non-Patent Document 25 (TS23.502).

[0142] Fig.14 and Fig.15 This is a sequence diagram showing a first example of an operation of releasing a UE connected to an outer NW via an inner NW from connections with the inner NW and the outer NW. Fig.14 and Fig.15 Connect at the position of boundary line BL1415. Fig.14 and Fig.15 An example is shown where the connection release is initiated by the inner AMF.

[0143] exist Fig.14 In step ST1401 shown, the inner AMF decides to release the connection between the UE and the inner NW. In step ST1402, the inner AMF instructs the RAN to release the N2 connection between the inner AMF and the RAN regarding the UE. The signaling used for the indication may be, for example, the N2 UE Context Release Command described in non-patent document 24 (TS38.413).

[0144] exist Fig.14 In step ST1403, the RAN instructs the UE to release the RRC connection. The signaling used for this instruction may be the RRC Release described in non-patent document 27 (TS 38.331).

[0145] exist Fig.14In step ST1405 shown, the UE requests the outer AMF to release the NAS connection between the UE and the outer NW. For this request, NAS signaling can be used. The NAS signaling can be the existing signaling described in non-patent document 26 (TS24.501), or a new signaling (for example, Service termination request: service termination request) can be set. The NAS signaling may include information about the reason for the request. The information about the reason may be, for example, the release of the inner NW. The outer AMF can use the NAS signaling to initiate the action of releasing the outer NW.

[0146] exist Fig.14 In step ST1407, the outer AMF instructs the N3IWF to release the N2 connection between the outer AMF and the N3IWF regarding the UE. The signaling used for this indication may be, for example, the N2 UEContext Release Command described in non-patent document 24 (TS38.413).

[0147] exist Fig.14 In steps ST1408 and ST1409 shown in FIG. 1409 , the AN connection is released between the N3IWF and the UE. Fig.14 In the example shown, the IPsec settings are released between the N3IWF and the UE. In step ST1408, the N3IWF notifies the UE to release the IPsec settings. The signaling used for the notification may be, for example, the signaling of the IKEINFORMATIONAL exchange described in non-patent document 23 (IETF RFC7296). The signaling may also include the Delete payload described in non-patent document 23 (IETF RFC7296). The Delete payload may include information (e.g., an identifier) ​​about the SA (Security Association) released in the IPsec settings. The UE releases the IPsec settings with the N3IWF by receiving the notification of step ST1408. In step ST1409, the UE notifies the N3IWF of the release of the IPsec settings. For example, the same signaling as step ST1408 may be used for the notification from the UE to the N3IWF. By receiving the notification of step ST1409, the N3IWF recognizes that the IPsec settings at the UE have been released. In step ST1410, N3IWF notifies the outer AMF that the AN connection has been released.

[0148] exist Fig.15In step ST1415 shown, the outer AMF requests the outer SMF to stop the PDU session related to the UE. For the stop request of step ST1415, for example, the request of Nsmf_PDUSession_UpdateSMContext (Nsmf_PDU session updates SM context) disclosed in Section 5.2.8.2.6 of non-patent document 25 (TS23.502) can be used. The stop request of step ST1415 may include information about the PDU session of the stop object, such as information about the identifier of the PDU session. In step ST1416, the outer SMF requests the outer UPF to delete the tunnel information with the UE. The request of step ST1416 may include information about the PDU session of the tunnel information deletion object, such as information about the identifier of the PDU session. According to the request of step ST1416, the outer UPF deletes the tunnel information with the UE. In step ST1417, the outer UPF sends a response to the stop request for the PDU session to the outer SMF. In steps ST1416 and ST1417, for example, the N4 Session Modification procedure disclosed in Section 4.4.1.3 of non-patent document 25 (TS23.502) may be used. In step ST1418, the outer SMF sends a response to the stop request for the PDU session to the outer AMF. For the response to step ST1418, for example, the response of Nsmf_PDUSession_UpdateSMContext disclosed in Section 5.2.8.2.6 of non-patent document 25 (TS23.502) may be used. In step ST1419, the connection release with the UE is completed in the outer AMF, and the outer AMF transfers to CM-IDLE.

[0149] exist Fig.15 In step ST1425 shown, the UE releases the RRC connection with the RAN. In step ST1426, the connection between the UE and the inner AMF and the connection between the UE and the outer AMF are released, and the UE transfers to CM-IDLE.

[0150] exist Fig.15In step ST1430 shown, the RAN notifies the inner AMF that the N2 connection release related to the UE between the inner AMF and the RAN is completed. In step ST1435, the inner AMF requests the inner SMF to stop the PDU session related to the UE. For the stop request in step ST1435, the same signaling as step ST1415 can be used. In step ST1436, the inner SMF requests the inner UPF to delete the tunnel information between the UE. According to the request of step ST1436, the inner UPF deletes the tunnel information between the UE. In step ST1437, the inner UPF sends a response to the stop request for the PDU session to the inner SMF. For steps ST1436 and ST1437, the same signaling as steps ST1416 and ST1417 can be used. In step ST1438, the inner SMF sends a response to the stop request for the PDU session to the inner AMF. For the response in step ST1438, the same signaling as step ST1418 can be used. In step ST1439, the connection release between the inner AMF and the UE is completed, and the inner AMF transfers to CM-IDLE.

[0151] The UE may retain information indicating which AMF in the AMF of the connection destination is the inner AMF. The information may be, for example, an identifier of the inner AMF. For example, the information may be included in the information about the AMF of the connection destination retained by the UE, or may be included in the NAS context retained by the UE. Thus, for example, the UE can identify the inner AMF from the AMF of the connection destination, as a result of which malfunction in the communication system can be prevented.

[0152] As another example, the UE may retain information indicating whether each AMF at the connection destination is an inner AMF, or may retain information on which level each AMF at the connection destination is connected in the cascade connection of the NW. For example, this information may be included in the information about the AMF at the connection destination retained by the UE, or may be included in the NAS context retained by the UE. The UE may retain this information, for example, by combining the identifiers of each AMF. Thus, for example, the same effect as described above can be obtained.

[0153] The UE may maintain information about the number of levels in the NW cascade connection. For example, the information may be included in the information about the AMF of the connection destination maintained by the UE, or may be included in the NAS context maintained by the UE. For example, the UE may use the information to determine whether to make a cascade connection. As another example, the UE may use the information to determine whether to issue a connection release request to the outer AMF. Thus, for example, in the case where the UE is connected to only one NW, the UE may not send the request to the outer NW. As a result, the amount of signaling in the communication system can be reduced.

[0154] The UE may notify the upper layer (e.g., NAS layer) within the UE of information indicating that an RRC connection release indication has been received from the RAN. For example, the UE may issue the notification immediately after the UE receives signaling indicating the RRC connection release. The UE may issue the notification before a delay of 60 milliseconds as described, for example, in Section 5.3.8.3 of non-patent document 27 (TS 38.331). The UE may request the outer AMF to release the NAS connection between the UE and the outer NW within the delay. The UE may release the AN connection with the N3IWF within the delay (e.g., by sending an IKE INFORMATIONAL EXCHANGE including a Delete payload from the UE to the N3IWF). Therefore, for example, the UE may complete the release of the AN connection with the N3IWF before releasing the RRC connection.

[0155] The UE can use the information about whether there is a connection between the UE and the external NW to determine whether to make the notification. For example, when the UE is connected to the external NW, the UE can notify the upper layer (e.g., NAS layer) in the UE before the above-mentioned delay of 60 milliseconds. In addition, when the UE is not connected to the external NW, the UE can notify the upper layer (e.g., NAS layer) in the UE after the above-mentioned delay of 60 milliseconds. As a result, for example, the previous design can be used in the UE design, and as a result, the complexity in the UE design can be avoided.

[0156] The above delay time can be changed. For example, the delay time can be set to be greater than 60 milliseconds. Therefore, for example, the RRC connection can be prevented from being released before the AN connection between the UE and the N3IWF is released.

[0157] The inner AMF can change the delay time. The UE can notify the inner AMF of information about the outer NW in advance. The information may also be, for example, information indicating that the UE is connected to the outer NW via the inner NW. For the notification, NAS signaling can be used. The NAS signaling may be the signaling described in non-patent document 26 (TS24.501) or a new NAS signaling (e.g., outer NW connection notification). The inner AMF can use the information to change the delay time. The inner AMF may notify the RAN of information about the change in the standby time. The information may be, for example, the changed delay time or the amount of change in the delay time. For example, the information may be included in the indication of the release of the N2 connection. The RAN may notify the UE of the information. For example, the information may be included in the RRC Release signaling to notify the UE from the RAN.

[0158] As another example, the RAN may change the delay time. The UE may notify the RAN in advance of information about the outer NW. The information may also be, for example, information indicating that the UE is connected to the outer NW via the inner NW. The RAN may use the information to change the delay time. The RAN may notify the UE of information about the change in the standby time. The information may be, for example, the changed delay time or the amount of change in the delay time. For example, the information may be included in the RRC release (RRCRelease) signaling for notification. Therefore, for example, the change in the delay time may be performed with a smaller amount of signaling.

[0159] The UE may have a timer for managing the time until the RRC release. The timer may be, for example, a timer for managing the delay time. The UE may initialize the timer when the RRC connection between the RAN is established, may initialize the timer on the occasion of receiving a notification of the change in the delay time from the inner AMF and / or RAN, or may initialize the timer when the AN connection between the N3IWF and the N3IWF is established. The UE may start the timer on the occasion of receiving an RRC connection release indication from the RAN. The UE may stop the timer on the occasion of the release of the AN connection with the N3IWF. The UE may release the RRC connection with the RAN on the occasion of the expiration of the timer, and may perform the actions disclosed in Section 5.3.8.3 of Non-Patent Document 27 (TS38.331). Therefore, for example, in the UE, the management of the action of AN connection release becomes easy. The timer may be provided by the inner AMF or the RAN. Therefore, for example, in the AMF and / or the RAN, the management of the action of AN release becomes easy.

[0160] The UE and the RAN may maintain a timer used in the RRC (hereinafter sometimes referred to as the RRC timer) by type. That is, the timer may not be newly set for the outer NW. The UE may use the timer only in the connection with the inner NW, such as the RAN. The timer of each type may also be, for example, T302, T325, T380 described in non-patent document 27 (TS 38.331). The value of the timer may be changed in the same manner as the delay time. The value of the timer may be changed when the UE is connected to the outer NW via the inner NW. The value of the timer may be changed by the RAN or by the inner AMF. As a result, for example, the control of the UE in the communication system becomes easy. The method for changing the timer may be the same as the method for changing the delay time.

[0161] As another example, the UE may maintain multiple RRC timers for each category. For example, the UE may maintain an RRC timer for the inner NW and an RRC timer for the outer NW for each category. The RAN may maintain an RRC timer for the inner NW. The N3IWF may maintain an RRC timer for the outer NW. For example, the timer for each category may be the same as described above. The value of the RRC timer for the inner NW may be changed by the RAN or by the inner AMF. The value of the RRC timer for the outer NW may be changed by the N3IWF or by the outer AMF. Thus, for example, the flexibility of control of the UE in the communication system can be improved.

[0162] A dependency, such as a size relationship, may be set between the multiple timers. For example, the value of the RRC timer in the inner NW may be greater than or less than the value of the same RRC timer in the outer NW. The UE may notify the RAN of the value of the RRC timer in the outer NW. The UE may notify the N3IWF of the value of the RRC timer in the inner NW. The RAN and / or the N3IWF may use the notification to determine and / or change the value of the timer. Thus, for example, unexpected actions due to the expiration of a timer in one NW, such as a release action of the NW, may be prevented. As a result, the robustness in the communication system may be improved.

[0163] The RAN and / or N3IWF may notify the UE of the value of the timer determined and / or changed. The RAN and / or N3IWF may notify the reason for the decision and / or change in the notification. The reason may be, for example, information about the change of the RRC timer in the NW on the opposite side. Thus, for example, repeated changes of the RRC timers in the RAN and N3IWF may be prevented.

[0164] The UE can maintain multiple timers in the NAS layer. For example, the timers in the NAS layer can also be set for the inner NW and the outer NW respectively. The inner AMF and the outer AMF can maintain timers in the NAS layer. Thus, for example, the flexibility of UE control in the communication system can be improved. The timer in the NAS layer can be, for example, the service gap timer (Service Gap Timer) described in non-patent document 22 (TS23.501), or the barring timer (Barring Timer) described in non-patent document 26 (TS24.501), or T3540 described in non-patent document 26 (TS24.501).

[0165] The timer in the NAS layer can be common for the inner NW and the outer NW. Thus, for example, the memory usage in the UE can be reduced. The inner AMF and the outer AMF can share the timer, and either of the inner AMF and the outer AMF can maintain the timer. For each type of the timer, the subject that maintains the timer can be different or the same in the inner AMF and the outer AMF. The inner AMF and the outer AMF can notify each other about the information about the timer. The notification can be made via the UE. A new NAS signaling for the notification can be set. As another example, the notification can be made using signaling between the inner AMF and the outer AMF. The interface can be set between the inner AMF and the outer AMF. As another example, the notification can be made via the inner SMF. The inner AMF can notify the outer AMF via the inner SMF and the outer SMF, and the outer AMF can notify the inner AMF via the outer SMF and the inner SMF. The interface can be set between the inner SMF and the outer SMF. As other examples of the case where the notification is performed via SMF, the inner AMF may notify the outer AMF via the inner SMF, the inner UPF, and the N3IWF, may notify the outer AMF via the inner SMF, the inner UPF, the N3IWF, the outer UPF, and the outer SMF, or may notify the outer AMF via the RAN, the inner UPF, and the N3IWF. The outer AMF may notify the inner AMF via the N3IWF, the inner UPF, and the inner SMF, may notify the inner AMF via the outer SMF, the outer UPF, the N3IWF, the inner UPF, and the inner SMF, or may notify the inner AMF via the N3IWF, the inner UPF, and the RAN.

[0166] Other solutions are disclosed. The inner AMF notifies the UE of the connection release between the inner AMF and the present AMF. The inner AMF may use NAS signaling for the notification. A new NAS signaling for the notification may be set. The new NAS signaling may be, for example, a signaling of a service termination notification. The UE may request the release of the NAS connection between the present UE and the outer NW. The request may be made using the notification from the inner AMF to the present UE. The signaling used for the request may be the same as the above solution. The outer AMF may use the notification from the UE to release the outer NW connection with the UE. The release of the outer NW connection in the outer AMF may be the same as the above solution.

[0167] The UE can notify the inner AMF of information about the outer NW. This information may be, for example, information indicating that the UE is connected to the outer NW via the inner NW. For this notification, NAS signaling may be used. The NAS signaling may be the signaling described in non-patent document 26 (TS24.501) or a new NAS signaling (e.g., outer NW connection notification). The inner AMF may use this information to determine whether there is a notification of the release of the connection between the UE and this AMF. For example, the inner AMF may not use the notification indicating that the UE is not connected to the outer AMF to notify the release of the connection between the UE and this AMF. Therefore, for example, NAS signaling can be reduced.

[0168] The UE can notify the inner AMF to release the inner NW connection, and can also notify information indicating that it is not connected to the outer NW. The UE can send the notification after the connection between the outer NW is released. For example, the UE can send the notification after the AN connection between the UE and the N3IWF is released. The UE can use NAS signaling for this notification. The NAS signaling for this notification can be newly set. The new NAS signaling can be, for example, a signaling of Service termination ready. After the notification from the UE, the inner AMF can release the inner NW between the UE. That is, before the notification from the UE, the inner AMF may not perform the inner NW release action between the UE. Thereby, for example, the robustness in the communication system can be improved.

[0169] The UE can request the inner AMF to wait for the inner NW to release. NAS signaling can be used for this request from the UE to the inner AMF. A new NAS signaling representing the request can be set. The NAS signaling can also be, for example, a service termination wait request. The inner AMF can wait for the UE's connection release according to the request. Therefore, for example, even when the inner AMF initiates the UE's connection release, the outer NW can be notified.

[0170] The UE may include information about the standby time for connection release in the request. The UE may determine the information. The inner AMF may wait for the connection release of the inner NW during the standby time indicated by the information. The UE may perform connection release of the outer NW during the standby time. Therefore, for example, it is possible to prevent the connection release of the inner NW before the connection release of the outer NW is completed, as a result of which the robustness in the communication system can be improved.

[0171] As another example related to the standby time, the standby time can be determined according to the standard. The inner AMF can wait for the connection release of the inner AMF during the determined standby time according to the standby request from the UE. Therefore, for example, the robustness in the communication system can be improved in the same way as described above, and the signaling size in the communication system can be reduced.

[0172] The UE may have a timer for managing the standby time. The UE may initialize the timer when the RRC connection between the RAN is established, may initialize the timer upon receiving a notification of the delay time change from the inner AMF and / or the RAN, or may initialize the timer when the AN connection with the N3IWF is established. The UE may start the timer upon receiving an RRC connection release indication from the inner AMF. The UE may stop the timer upon the release of the AN connection with the N3IWF. The UE may release the RRC connection with the RAN upon the expiration of the timer, and may perform the actions disclosed in Section 5.3.8.3 of non-patent document 27 (TS38.331). Therefore, for example, in the UE, the management of the AN release action becomes easy. The timer may be provided by the RAN or the inner AMF. Therefore, for example, in the RAN and / or the inner AMF, the management of the AN release action becomes easy.

[0173] The UE initiates the connection release of the outer NW after sending the request to the inner AMF. As another example, the UE initiates the connection release of the outer NW before sending the request to the inner AMF. Thus, for example, the UE is able to quickly initiate the connection release of the outer NW. The above method can be used to perform the connection release with the outer NW.

[0174] The UE may notify the inner AMF that the inner NW connection may be released. The UE may send this notification after the connection with the outer NW is released. The notification may also be the same as above. The inner AMF uses the notification from the UE that the inner NW connection may be released to reopen the connection release of the UE in the inner NW.

[0175] As another example of notification of connection release reopening from UE to inner AMF, UE may not send the notification to inner AMF. The above action may be applied, for example, to the case where the standby time for connection release is notified from UE to inner AMF, or to the case where the standby time is predetermined. After the standby time has passed, inner AMF may reopen the connection release of UE in inner NW. Thus, for example, the amount of signaling in the communication system may be reduced.

[0176] Fig.16 and Fig.17This is a sequence diagram showing a second example of the operation of releasing a UE connected to an outer NW via an inner NW from the connections with the inner NW and the outer NW. Fig.16 and Fig.17 Connect at the boundary line BL1617. Fig.16 and Fig.17 An example is shown where the connection release is initiated by the inner AMF. Fig.16 and Fig.17 An example of the inner AMF notifying the UE to release the inner NW is also shown. Fig.16 and Fig.17 In, with Fig.14 and Fig.15 The same processes are denoted by the same step numbers, and the same descriptions are omitted.

[0177] Fig.16 Step ST1401 shown is the same as Fig.14 same.

[0178] exist Fig.16 In step ST1504 shown, the inner AMF notifies the UE to release the inner NW. The inner AMF may use NAS signaling to make the notification. The NAS signaling may be a signaling of a service termination notification (Servicetermination notification) or other signaling. The UE may recognize that the connection with the inner NW has been released by receiving the notification of step ST1504, and may perform the processing shown in the subsequent step ST1405. The inner AMF may retain the release of the inner NW until there is a response to step ST1504.

[0179] Fig.16 and Fig.17 Steps ST1405 to ST1419 shown are similar to Fig.14 and Fig.15 same.

[0180] exist Fig.17 In step ST1521 shown, the UE notifies the inner AMF that the inner NW connection can be released. The UE may use NAS signaling to issue the notification. A new NAS signaling for the notification may be set. The new NAS signaling may be, for example, a signaling indicating that service termination is ready.

[0181] exist Fig.17 In the process, according to the notification of step ST1521, the inner AMF performs the action of releasing the inner NW shown in steps ST1522 to ST1439. Fig.17 Step ST1522 shown is the same as Fig.14 The same as step ST1402 in. Fig.17 Step ST1523 shown is the same as Fig.14 The same as step ST1403 in.

[0182] Fig.17 Steps ST1425 and ST1426 shown are Fig.15 same.

[0183] Fig.17 Steps ST1430 to ST1439 shown are similar to Fig.15 same.

[0184] Other solutions are disclosed. The RAN may request the outer AMF to release the outer NW connection in the UE. The RAN may make the request when the inner AMF decides to release the inner NW connection in the UE. The inner AMF may instruct the RAN to release the inner NW connection. The RAN may use the indication to issue the request. Thus, for example, the amount of signaling in the communication system may be reduced.

[0185] The UE may notify the RAN of information indicating the connection to the outer NW via the inner NW. The information may also be information indicating the establishment of an AN connection between the UE and the N3IWF. The RAN may send the request to the outer AMF via the N3IWF. The N3IWF may release the AN connection with the UE. The N3IWF may use the request from the RAN to release the AN connection.

[0186] Other solutions are disclosed. The N3IWF can request the outer AMF to release the outer NW between it and the UE. The signaling used for the request can be, for example, the N2 UE context release request (ContextRelease Request) described in non-patent document 24 (TS 38.413). The N3IWF can issue the request when the AN connection between the UE and the N3IWF is released. The outer AMF can use the request to instruct the N3IWF to release the N2 connection. Thereby, for example, the amount of signaling in the communication system can be reduced.

[0187] The UE may release the AN connection with the N3IWF. The release may be performed using an indication of an RRC release from the RAN to the UE. The RRC release may be indicated using an indication of the release of the N2 connection of the UE from the inner AMF to the RAN. As an example of the UE releasing the AN connection, the UE may notify the N3IWF to release the IPsec settings. The N3IWF may use the notification to release the IPsec settings with the UE. The N3IWF may notify the UE to release the IPsec settings. The notification from the N3IWF to the UE may be performed after the IPsec settings in the N3IWF are released.

[0188] Fig.18 and Fig.19 1 is a sequence diagram showing a third example of the operation of releasing a UE connected to an outer NW via an inner NW from the connections with the inner NW and the outer NW. Fig.18 and Fig.19 Connect at the position of boundary line BL1819. Fig.18 and Fig.19 An example is shown where the connection release is initiated by the inner AMF. Fig.18 and Fig.19 An example of N3IWF releasing the outer NW is shown. Fig.18 and Fig.19 An example of releasing the AN connection in the UE by taking the RRC release indication as an opportunity is shown. Fig.18 and Fig.19 In, with Fig.14 and Fig.15 The same processes are denoted by the same step numbers, and the same descriptions are omitted.

[0189] Fig.18 Steps ST1401 to ST1403 shown are similar to Fig.14 same.

[0190] exist Fig.18 In step ST1604 shown, the UE releases the AN connection with the N3IWF. The AN connection release may be a release of the IPsec settings with the N3IWF. The UE notifies the N3IWF of the release of the IPsec settings. The signaling used for the notification may be, for example, the signaling of the IKE INFORMATIONAL exchange described in non-patent document 23 (IETF RFC7296). The signaling may also include the Delete payload described in non-patent document 23 (IETF RFC 7296). The Delete payload may include information (e.g., an identifier) ​​about the SA (Security Association) released in the IPsec settings. The N3IWF releases the IPsec settings with the UE by receiving the notification of step ST1604. In step ST1605, the N3IWF notifies the UE to release the IPsec settings. The notification from the N3IWF to the UE may be, for example, the same signaling as step ST1604.

[0191] exist Fig.19In step ST1606 shown, N3IWF requests the outer AMF to release the N2 connection between the outer AMF and N3IWF regarding the UE. The signaling used for the request may be, for example, the N2 UE context release request (Context Release Request) described in non-patent document 24 (TS38.413). The outer AMF performs the release action of the outer NW shown in steps ST1407 to ST1419 according to the request.

[0192] Fig.19 Steps ST1407 to ST1419 shown are similar to Fig.14 and Fig.15 same.

[0193] exist Fig.19 In step ST1425 shown, the UE releases the RRC connection with the RAN. The UE can release the connection when receiving the notification of the release of the IPsec setting in step ST1605. In step ST1426, the connection between the UE and the inner AMF and the connection between the UE and the outer AMF are released, and the UE transfers to CM-IDLE.

[0194] Fig.19 Steps ST1430 to ST1439 shown are similar to Fig.15 same.

[0195] The UE can release the AN connection with the N3IWF using the notification of the release of the connection between the UE and the present AMF from the inner AMF. The notification can be performed using NAS signaling in the same way as the above solution, or a new NAS signaling can be set for the notification. The new NAS signaling can be, for example, a signaling of a service termination notification. The UE can notify the inner AMF that the inner NW connection can be released. The UE can send the notification after the connection with the outer NW is released. For example, the UE can send the notification after the AN connection with the N3IWF is released. The UE can use NAS signaling to issue the notification. A new NAS signaling for the notification can be set. The new NAS signaling can be, for example, a signaling of service termination ready. After the notification from the UE, the inner AMF can release the inner NW between it and the UE. Therefore, for example, a situation in which the connection status of the UE is inconsistent between the UE and the outer AMF can be prevented.

[0196] Fig. 20 and Fig.214 is a sequence diagram showing a fourth example of the operation of releasing a UE connected to an outer NW via an inner NW from the connections with the inner NW and the outer NW. Fig. 20 and Fig.21 Connect at the boundary line BL 2021. Fig. 20 and Fig.21 An example is shown where the connection release is initiated by the inner AMF. Fig. 20 and Fig.21 An example of N3IWF releasing the outer NW is shown. Fig. 20 and Fig.21 An example of releasing the AN connection in the UE based on the inner NW release notification from the inner AMF is shown. Fig. 20 and Fig.21 In, with Figures 14 to 19 The same processes are denoted by the same step numbers, and the same descriptions are omitted.

[0197] Fig. 20 Step ST1401 shown is the same as Fig.14 Step ST1504 is the same as Fig.16 same.

[0198] exist Fig. 20 In step ST1604 shown in FIG. 16, the UE releases the AN connection with the N3IWF. The signaling for releasing the AN connection can be Fig.18 The UE may use step ST1504 to send the AN release signaling to the N3IWF. Fig. 20 Step ST1605 shown is the same as Fig.18 same.

[0199] Fig.21 Step ST1606 shown is the same as Fig.19 Steps ST1407 to ST1419 are the same as Fig.14 same.

[0200] exist Fig. 20 In step ST1521 shown, the UE notifies the inner AMF that the inner NW connection can be released. The signaling used for this notification can be the same as Fig.17 The UE can send the notification based on the reception of step ST1605.

[0201] Fig.21 Steps ST1522, ST1523 and Fig.17 Steps ST1425, ST1426, ST1430 to ST1439 are the same as Fig.15 same.

[0202] Other solutions are disclosed. The inner AMF can request the outer AMF to release the outer NW between it and the UE. Thus, for example, the processing load of the UE in the outer NW release action can be reduced. The UE can notify the inner AMF of information indicating that an N1 connection is established with the outer AMF. The notification from the UE to the inner AMF can be performed, for example, before the inner AMF decides to release the inner NW between it and the UE, or after the N1 connection is established between the UE and the outer AMF. The information can be, for example, information indicating that an AN connection is established between the UE and the N3IWF, or it can be the status of the UE (for example, CM status, RM status). The status can also be, for example, the status in the outer NW disclosed in Implementation 2.

[0203] The inner AMF can request the N3IWF to release the connection between the UE and the outer NW. The inner AMF can send the request via the inner SMF and the inner UPF. The interface can be set between the inner AMF and the N3IWF. The signaling on the interface can be used for the request sent by the inner AMF. The N3IWF can forward the request to the outer AMF.

[0204] As another example, the inner AMF may request the outer AMF to release the connection between the UE and the outer NW. The inner AMF may use signaling between the inner AMF and the outer AMF to issue the request. The interface may be set between the inner AMF and the outer AMF. As another example, the inner AMF may issue the request to the outer AMF via the inner SMF and the outer SMF. The interface may be set between the inner SMF and the outer SMF. As another example, the inner AMF may issue the request to the outer AMF via the inner SMF, the inner UPF, and the N3IWF, or may issue the request to the outer AMF via the RAN, the inner UPF, and the N3IWF. Therefore, for example, there is no need to add signaling in the interface between the above-mentioned devices, with the result that complexity in the communication system can be avoided.

[0205] The outer AMF can notify the inner AMF of the state of the outer AMF of the UE. The state can be the CM state or the RM state described in non-patent document 22 (TS23.501), or the 5GMM state described in non-patent document 26 (TS24.501). The outer AMF can use the signaling between the outer AMF and the inner AMF to issue the notification to the inner AMF. The interface can be set between the inner AMF and the outer AMF. As another example, the outer AMF can issue the notification to the inner AMF via the outer SMF and the inner SMF. The interface can be set between the inner SMF and the outer SMF. As another example, the outer AMF can issue the notification to the inner AMF via the N3IWF, the inner UPF, and the inner SMF, or it can issue the notification to the inner AMF via the N3IWF, the inner UPF, and the RAN. The inner AMF can use the notification to determine whether the outer NW needs to be released. Therefore, for example, there is no need to add signaling in the interface between the above-mentioned devices, with the result that complexity in the communication system can be avoided.

[0206] The inner AMF can notify the outer AMF of the status of the inner AMF of the UE. The status can be the CM status or RM status recorded in non-patent document 22 (TS23.501), or the 5GMM status recorded in non-patent document 26 (TS24.501). The inner AMF can use the signaling between the inner AMF and the outer AMF to issue the notification to the outer AMF. The interface can be set between the inner AMF and the outer AMF. As another example, the inner AMF can issue the notification to the outer AMF via the inner SMF and the outer SMF. The interface can be set between the inner SMF and the outer SMF. As another example, the inner AMF can issue the notification to the outer AMF via the inner SMF, the inner UPF, and the N3IWF, or it can issue the notification to the outer AMF via the RAN, the inner UPF, and the N3IWF. The outer AMF can use the notification to change the connection method with the UE. For example, when the state of the inner AMF is CM-IDLE, the outer AMF can instruct the UE to reside in a cell controlled by the outer NW. Thus, for example, the flexibility in the communication system can be improved.

[0207] The above-mentioned multiple solutions can be combined. For example, in the case where the N3IWF releases the outer NW, a change in the delay time in the RRC connection release can be used. The UE can notify the N3IWF of the release of the IPsec setting during the changed delay time. Therefore, for example, the UE can notify the release of the IPsec setting with a margin, as a result of which the robustness in the communication system can be improved.

[0208] The UE can be connected to multiple outer NWs via the inner NW. The multiple outer NWs can be connected in parallel. Any outer NW can be assigned to each communication service (e.g., audio, video, mission-critical communication). In a communication system in which the UE is connected in parallel to the multiple outer NWs, the method disclosed in Implementation 1 can be used, or the method disclosed in the following implementation or variation can be used. Thus, for example, the flexibility in the communication system can be improved.

[0209] As another example in which a UE is connected to multiple outer NWs via an inner NW, the multiple outer NWs may be connected in cascade. For example, in each outer NW and / or inner NW connected in cascade, the communication range and the communication object UE may be different. In a communication system in which a UE is connected in parallel to the multiple outer NWs, the method disclosed in Implementation 1 may be used, or the method disclosed in the following implementation or modification may be used. Thus, for example, the flexibility in the communication system may be improved.

[0210] According to the first embodiment, regarding the connection status of the UE, inconsistency between the UE and the external AMF can be prevented, resulting in improved robustness in the communication system.

[0211] Modification 1 of Implementation Example 1. In Embodiment 1, a method for releasing the AN of a UE cascaded to a plurality of NWs is disclosed. In this Modification 1, a method for releasing the registration of the UE is disclosed.

[0212] The UE deregisters the outer NW before deregistering the inner NW. This deregistration can be applied to the deregistration initiated by the UE. In the deregistration with each NW, the method disclosed in Section 4.2.2.3.2 of Non-Patent Document 25 (TS23.502) can also be used. Therefore, for example, the memory usage caused by the information related to the registration remaining in the outer NW can be reduced.

[0213] As another example, the UE may release the connection with the outer NW before the registration from the inner NW is released. For the release of the connection with the outer NW, the method disclosed in Implementation 1 may also be applied. For example, the UE may request the outer AMF to release the NAS connection between the UE and the outer NW. For this request, NAS signaling may be used. The NAS signaling may also be an existing signaling described in non-patent document 26 (TS24.501). Alternatively, new signaling (for example, a service termination request) may be set. As another example, the N3IWF may request the outer AMF to release the outer NW between the UE and the UE. The request may be made upon the release of the AN connection between the UE and the N3IWF.

[0214] As another example, the UE can maintain the connection with the outer NW even when the registration of the inner NW is released. For example, the UE can be connected to the RAN under the control of the outer NW. Therefore, for example, the continuity of the service of the outer NW to the UE can be ensured.

[0215] While maintaining the connection with the outer NW, the tracking area (Tracking Area) of the UE in the outer NW can be the same or different before and after the registration of the inner NW is released. For example, the AMF connected to the UE can be the same or different before and after the registration of the inner NW is released. When the AMF connected to the UE is the same, the process shown in Section 4.9.2.1 of non-patent document 25 (TS23.502) can also be used. When the AMF connected to the UE is different, the process shown in Section 4.12.8 of non-patent document 25 (TS23.502) can be used.

[0216] The outer AMF may notify the UE of relevant information about the base station whose tracking area and / or AMF become the same before and after the handover. The UE may preferentially connect to the base station included in the information in the handover. Therefore, for example, the UE is able to quickly perform the handover action and can reduce signaling in the communication system. As another example, the outer AMF may notify the UE of relevant information about the base station whose tracking area and / or AMF become different before and after the handover. The UE may preferentially connect to the base station not included in the information in the handover. Therefore, for example, when there are fewer base stations with different tracking areas and / or AMFs around the UE before and after the handover, the signaling size from the outer AMF to the UE can be reduced.

[0217] The UE may notify the outer AMF of information about the location of the UE, and may also notify the outer AMF of information about the base station to which the UE can connect. The information about the base station to which the UE can connect may include, for example, an identifier of the base station, and may also include information about the cell belonging to the base station (e.g., PCI). The UE may, for example, send the notification to the outer AMF before the above-mentioned switching. Therefore, for example, the outer AMF can quickly determine the base station whose tracking area and / or AMF become the same before and after the switching.

[0218] The UE can notify the outer AMF of the information about the deregistration of the inner NW. The UE can use NAS signaling to notify the information. The NAS signaling can also be the NAS signaling described in non-patent document 26 (TS24.501), or a new NAS signaling can be set. The outer AMF can use this information to determine the processing related to the connection between the UE. The processing can be, for example, the deregistration of the UE, the release of the connection between the UE and the outer NW, or the maintenance of the connection between the UE and the outer NW. In this way, for example, the flexibility in the communication system can be improved.

[0219] Other solutions are disclosed. The UE initiates deregistration of the outer NW before deregistration in the inner NW. For example, the above method can be applied when the inner NW initiates deregistration of the UE.

[0220] The UE can request the inner AMF to wait for the deregistration of the inner NW. NAS signaling can be used for this request from the UE to the inner AMF. A new NAS signaling representing the request can be set. The NAS signaling can also be, for example, a deregistration wait request. The inner AMF can wait for the deregistration of the UE according to the request. Thus, for example, even if the inner AMF initiates the deregistration of the UE, it can notify the outer NW.

[0221] The UE may include information about the standby time for deregistration in the request. The UE may determine the information. The inner AMF may wait for the deregistration of the inner NW during the standby time indicated by the information. The UE may perform the deregistration of the outer NW during the standby time. Therefore, for example, it is possible to prevent the deregistration of the inner NW from being performed before the deregistration of the outer NW is completed, with the result that the robustness in the communication system can be improved.

[0222] As another example related to the standby time, the standby time can be determined according to the standard. The inner AMF can wait for the registration release of the inner AMF during the determined standby time according to the standby request from the UE. Therefore, for example, the robustness in the communication system can be improved in the same way as described above, and the signaling size in the communication system can be reduced.

[0223] The UE may have a timer for managing the re-registration of deregistration. The timer may be, for example, a timer for managing the standby time. The UE may initialize the timer when the registration to the inner NW is completed. The UE may start the timer based on the fact that a deregistration indication is received from the inner AMF. The UE may stop the timer based on the deregistration from the outer NW. The UE may recognize the re-registration of deregistration from the inner NW based on the expiration of the timer. Therefore, for example, in the UE, the management of the deregistration action becomes easy.

[0224] The inner AMF may have a timer for managing the re-registration of deregistration. The timer may be, for example, a timer for managing the standby time. The inner AMF may initialize the timer when the registration with the inner NW of the UE is completed. The inner AMF may start the timer based on the fact that a deregistration indication has been sent to the UE. The inner AMF may stop the timer based on a re-registration deregistration notification from the UE. The inner AMF may re-register the deregistration from the inner NW of the UE based on the expiration of the timer. Therefore, for example, in the inner AMF, the management of the deregistration action becomes easy.

[0225] The UE initiates the deregistration of the outer NW after sending the request to the inner AMF. As another example, the UE initiates the deregistration of the outer NW before sending the request to the inner AMF. Therefore, for example, the UE is able to quickly initiate the deregistration of the outer NW. At the same time, for example, in a case where multiple UEs are registered in the outer NW, the memory usage in each device of the outer NW can be reduced. In the deregistration with the outer NW, the method disclosed in Section 4.2.2.3.2 of non-patent document 25 (TS23.502) can also be used.

[0226] The UE may request or notify the inner AMF to reopen the deregistration of the inner NW. The above request or notification may be made after the deregistration of the outer NW. For the request or notification, NAS signaling may be used. The NAS signaling may be a new signaling, such as De-registration ready. Alternatively, the NAS signaling may also be a signaling described in non-patent document 25 (TS23.502), such as a De-registration request or a De-registration accept. The UE may include information related to the reopening of the pending deregistration in the NAS signaling and notify the inner AMF thereof. The UE may include information about the NAS signaling of the deregistration of the inner NW sent from the inner AMF to the UE (e.g., an identifier of the NAS signaling) in the NAS signaling and notify the inner AMF. Therefore, for example, the inner AMF is able to quickly perform an association with the deregistration requested from the UE. As a result, the processing of the deregistration in the inner AMF may be quickly performed. The inner AMF uses the registration deregistration restart request or notification received from the UE to restart the UE's registration deregistration in the inner NW.

[0227] As another example of a request or notification for reopening the deregistration from the UE to the inner AMF, the UE may not make the request or notification to the inner AMF. For example, the above action may be applied when the standby time for deregistration is notified from the UE to the inner AMF. Alternatively, the above action may also be applied when the standby time is predetermined. After the standby time has passed, the inner AMF may reopen the deregistration of the UE in the inner NW. Thus, for example, the amount of signaling in the communication system may be reduced.

[0228] Figure 22 to Figure 24 This is a sequence diagram showing a first example of an operation of canceling the registration of a UE connected to an outer NW via the inner NW. Figure 22 to Figure 24 They are connected at the positions of boundary lines BL2223 and BL2324. Figure 22 to Figure 24 An example is shown where the deregistration is initiated by the inner AMF. Figure 22 to Figure 24 This shows an example in which the registration of the outer NW is deregistered along with the inner NW registration of the UE.

[0229] exist Fig. 22 In step ST1801 shown, the inner AMF decides to cancel the registration of the UE in the inner NW. In step ST1802, the inner AMF requests the UE to be deregistered from the inner NW. In this request, NAS signaling, such as the signaling of the deregistration request shown in non-patent document 25 (TS23.502), can also be used.

[0230] exist Fig. 22 In step ST1803 shown, the UE requests the inner AMF to wait for the deregistration. For this request, NAS signaling can be used. The NAS signaling can also be a new NAS signaling, such as a signaling of a deregistration standby request (De-registrationwait request). The NAS signaling can include information about the standby time for deregistration. The inner AMF can use this signaling to wait for the UE's deregistration. The inner AMF can wait for the UE's deregistration during the standby time period included in the signaling or during a predetermined standby time period. The inner AMF can wait for the UE's deregistration until receiving the notification of the re-registration of the deregistration from the UE described later. The starting point of the standby time in the inner AMF can also be the reception time point of the standby request in step ST1803.

[0231] exist Fig. 22 In step ST1805 shown in FIG. 18 , the UE requests the outer AMF to deregister from the outer NW. In this request, NAS signaling, such as the signaling of the deregistration request (De-registration request) shown in non-patent document 25 (TS23.502), may also be used. The outer AMF starts the action for deregistering the UE from the outer NW according to the request ( Fig.23 process ST1810).

[0232] exist Fig.23 In the process ST1810 shown, the processing shown in steps ST1811 to ST1826 is performed.

[0233] exist Fig.23In step ST1811 shown, the outer AMF requests the outer SMF to cancel the AMF-SMF collaboration accompanying the release of the PDU session of the UE. The request may also be the Nsmf_PDUSession_ReleaseSMContext service operation shown in Section 5.2.8.2.7 of non-patent document 25 (TS23.502). In step ST1812, the outer SMF requests the outer UPF to release resources such as the IP address allocated to the PDU session and associated U-layer resources. The outer UPF releases the resources for which there is a release request in step ST1812. In step ST1813, the outer UPF notifies the outer SMF that the above resources have been released. In steps ST1812 and ST1813, the N4 Session Modification Procedure shown in Section 4.4.1.3 of non-patent document 25 (TS23.502) may also be used. In step ST1814, the outer SMF responds to the outer AMF for the cancellation request of the AMF-SMF collaboration in step ST1811. The response may also be the Nsmf_PDUSession_ReleaseSMContext service operation shown in Section 5.2.8.2.7 of Non-Patent Document 25 (TS23.502).

[0234] exist Fig.23 In step ST1815 shown, the session management policy cooperation termination (SM Policy Association Termination) action shown in Section 4.16.6 of non-patent document 25 (TS23.502) is performed between the outer SMF and the outer PCF.

[0235] exist Fig.23In step ST1820 shown, the outer SMF performs an action of canceling the session management subscription data change notification (Session Management Subsctiption data changes notification) of the outer UDM with the outer UDM. This action may also be the Nudm_SDM_Unsubscribe service operation (Nsmf_SDM unsubscribe service action) shown in section 5.2.3.3.5 of non-patent document 25 (TS23.502). In step ST1822, the outer UDM performs an action of deleting the collaboration of the outer SMF, data network name (Data Network Name: DNN) and PDU session ID with the outer SMF. This action may also be the Nudm_UECM_Deregistration service operation (Nudm_UECM_registration cancellation service action) shown in section 5.2.3.2.3 of non-patent document 25 (TS23.502).

[0236] exist Fig.23 In step ST1825 shown, the outer AMF performs an action to release the Admission Management (AM) policy cooperation with the outer PCF. This action may also be the process of AMF-initiated AM Policy Association Termination shown in Section 4.16.3.2 of non-patent document 25 (TS23.502). In step ST1826, the outer AMF performs an action to release the UE policy cooperation with the outer PCF. This action may also be the process of AMF-initiated UE Policy Association Termination shown in Section 4.16.13.1 of non-patent document 25 (TS23.502).

[0237] exist Fig.24In step ST1830 shown, the outer AMF notifies the UE of the deregistration acceptance. The notification may also be the deregistration acceptance (De-registration accept) shown in non-patent document 25 (TS23.502). In step ST1831, the outer AMF instructs the N3IWF to release the N2 connection between the outer AMF and the N3IWF regarding the UE. The signaling used for the indication may be, for example, the N2 UEContext Release Command described in non-patent document 24 (TS38.413).

[0238] exist Fig.24 In steps ST1832 and ST1833 shown, the AN connection is released between the N3IWF and the UE. Fig.24 In the example shown, the IPsec settings are released between the N3IWF and the UE. The signaling in steps ST1832 and ST1833 and the actions between the N3IWF and the UE can be the same as Fig.14 The steps ST1408 and ST1409 shown in are the same. The UE can recognize that the deregistration from the outer NW is completed by completing the notification to the N3IWF in step ST1833.

[0239] exist Fig.24 In step ST1834 shown, N3IWF requests the outer AMF to release the N2 connection between the outer AMF and N3IWF regarding the UE. The signaling used for this notification may be, for example, N2UEContextReleaseComplete as described in non-patent document 24 (TS38.413).

[0240] exist Fig.24 In step ST1835 shown, the UE notifies the inner AMF of the reopening of the deregistration of the inner NW. The notification may also be, for example, the deregistration acceptance described in non-patent document 25 (TS23.502). The inner AMF starts the action for deregistering the UE from the inner NW according to the request ( Fig.24 process ST1840).

[0241] Fig.24 The process ST1840 shown in may be the same process as the process ST1810 showing the action of releasing the registration of the UE from the outer NW. In this case, the same process as the process ST1810 is applied to the inner NW.

[0242] exist Fig.24In step ST1851 shown, the inner AMF instructs the RAN to release the N2 connection between the inner AMF and the RAN regarding the UE. The signaling used for this indication may be, for example, the N2UEContextReleaseCommand described in non-patent document 24 (TS38.413).

[0243] exist Fig.24 In step ST1852 shown, the RAN instructs the UE to release the RRC connection. The signaling used for this instruction may be the RRC Release described in non-patent document 27 (TS 38.331). The UE releases the RRC connection with the RAN according to the release instruction of step ST1852. In addition, the UE recognizes the release of the registration from the inner NW through the release instruction in step ST1852.

[0244] exist Fig.24 In step ST1853 shown, the RAN notifies the inner AMF to complete the N2 connection release between the inner AMF and the RAN regarding the UE. The signaling used for the notification may be, for example, N2 UEContext Release Complete as described in non-patent document 24 (TS38.413).

[0245] exist Figure 22 to Figure 24 1835) shows that the UE notifies the inner AMF of the reopening of the deregistration of the inner NW, but this notification may not be made. For example, when the standby request for the deregistration of the inner NW shown in step ST1803 includes the standby time, this notification may not be made. Alternatively, when the standby time is predetermined, this notification may not be made. As a result, for example, the amount of signaling in the communication system can be reduced.

[0246] Other solutions are disclosed. The UE may notify the inner AMF in advance of information about the outer NW. The information contained in the notification may be, for example, the same as that in Implementation 1, and is information indicating that the UE is connected to the outer NW via the inner NW. The inner AMF may use the information to set the standby time until the registration of the UE is released. The inner AMF may notify the UE of information about the standby time. The notification may be included, for example, in a registration release request from the inner AMF to the UE. The UE may obtain the standby time until the registration of the inner NW is released based on the request. Therefore, for example, the above-mentioned standby request from the UE to the inner AMF is not required. As a result, the amount of signaling between the UE and the AMF can be reduced.

[0247] The UE may notify the outer AMF of the standby time, and may also notify the information related to the inner NW registration release. The UE may include the standby time in the registration release request to the outer AMF and notify it. The UE may include the information about the inner NW registration release in the registration release request to the outer AMF and notify it. For example, the information about the inner NW registration release may be notified as the reason for the registration release request to the outer AMF. The outer AMF may obtain the standby time until the inner NW registration release is reopened from the information of the standby time included in the registration release request from the UE and / or the relevant information of the inner NW registration release. The outer AMF may perform the registration release of the outer NW in the UE during the standby time. Therefore, it is possible to prevent the state where the registration release of the outer NW cannot catch up with the registration release of the inner NW. As a result, the robustness in the communication system can be improved.

[0248] The standby time until the inner NW registration is released may be predetermined. In the above, the inner AMF may not notify the UE of the standby time. The UE may notify the outer AMF of information related to the inner NW registration release. For example, information about the inner NW registration release may be notified as a reason for the registration release request to the outer AMF. The outer AMF may use the information to obtain the standby time. Therefore, for example, there is no need to notify the standby time from the inner AMF to the UE and from the UE to the outer AMF. As a result, the signaling size in the communication system can be reduced.

[0249] Figure 25 to Figure 27 1 is a sequence diagram showing a second example of the operation of canceling the registration of the UE connected to the outer NW via the inner NW. Figure 25 to Figure 27 Connect at the positions of boundary lines BL2526 and BL2627. Figure 25 to Figure 27 An example is shown where the deregistration is initiated by the inner AMF. Figure 25 to Figure 27 This shows an example of deregistration of the outer NW accompanied by deregistration of the inner NW of the UE. Figure 25 to Figure 27 An example is shown in which the inner AMF determines the standby time until the inner NW registration is released and notifies the UE of the determined standby time. Figure 25 to Figure 27 In, with Figure 22 to Figure 24 The same actions are marked with the same numbers, and the same descriptions are omitted.

[0250] exist Fig.25In step ST1900 shown, the UE notifies the inner AMF of information about the outer NW. The notification may include, for example, information indicating that the UE is connected to the outer NW via the inner NW. For the notification, NAS signaling can be used. The NAS signaling can be either the signaling described in non-patent document 26 (TS24.501) or a new NAS signaling, such as an outer NW notification (Outer Network notification). The inner AMF can use the information notified in step ST1900 to determine the standby time when deregistration occurs. This decision can be made simultaneously with step ST1801 described later.

[0251] Fig.25 Step ST1801 shown is the same as Fig. 22 same.

[0252] exist Fig.25 In step ST1902 shown in FIG. 19, the inner AMF requests the UE to deregister from the inner NW. The inner AMF may include information about the standby time in the request and notify the UE. The signaling used in step ST1902 may be the same as Fig. 22 The information about the standby time can be added as a parameter to the Fig. 22 The waiting time may also be based on the sending of step ST1902.

[0253] exist Fig.25 In step ST1905 shown in FIG. 19, the UE requests the outer AMF to deregister from the outer NW. The UE may include information about the standby time in the request and notify the outer AMF. The UE may include information about the inner NW deregistration in the request and notify the outer AMF. The signaling used in step ST1905 may be the same as Fig. 22 The information related to the standby time and / or the information related to the inner NW registration release may be added as a parameter to the Fig. 22 The same signaling as step ST1805.

[0254] Fig.26 The process shown in ST1810 and Fig. 27 Steps 1830 to 1834 shown in Fig.23 and 24 same.

[0255] exist Fig. 27 In step ST1935 shown, the waiting time expires, and the inner AMF starts process ST1840 after the waiting time expires. Fig. 27 The process ST1840 in Fig.24same.

[0256] Fig. 27 Steps 1851 to 1853 shown are similar to Fig.24 same.

[0257] In this modification 1, a case where the outer NW is deregistered along with the deregistration of the inner NW is disclosed, but instead of deregistering the outer NW, the connection release of the outer NW may be performed. When the connection release of the outer NW is performed, the method disclosed in the first embodiment may also be applied. Therefore, for example, the reregistration of the outer NW along with the reregistration of the inner NW is not required. As a result, the amount of signaling in the communication system can be reduced.

[0258] As another example, the connection of the outer NW can be maintained instead of the deregistration of the outer NW. The UE can notify the outer AMF of information related to the deregistration of the inner NW. The notification can use NAS signaling, for example. The NAS signaling can be either the signaling shown in non-patent document 26 (TS24.501) or a new NAS signaling, such as the inner NW deregistration notification. The outer NW can use this information to determine the cell under the control of the outer NW that becomes the connection destination of the UE. The outer NW can notify the UE of information about the cell. The UE can set the cell shown in the information as the cell (destination cell) of the connection switching destination. Therefore, for example, the continuity of the service provided by the outer NW to the UE can be ensured.

[0259] As another example, the action in the outer NW can be determined by the outer NW device (e.g., outer AMF, outer SMF, outer PCF). The UE can notify the outer AMF of information related to the inner NW registration release. The information can also be the same as described above. The outer AMF can transmit the information to the outer SMF or to the outer PCF. The outer NW device (e.g., outer AMF, outer SMF, outer PCF) can use the information to determine the action in the outer NW. The action can be, for example, outer NW registration release, outer NW connection release, or outer NW connection maintenance. As a result, for example, the flexibility in the communication system can be improved.

[0260] For a UE connected to an inner NW and an outer NW, the value of an implicit registration release timer in the inner NW may be set to be greater than the value of an implicit registration release timer in the outer NW. The inner AMF may notify the UE of information about the timer in the inner NW. The UE may notify the outer AMF of information about the timer in the outer NW. The outer AMF may use the information notified from the UE to change the value of the timer in the outer NW. Similarly, the outer AMF may notify the UE of information about the timer in the outer NW. The UE may notify the inner AMF of information about the timer in the outer NW. The inner AMF may use the information notified from the UE to change the value of the timer in the inner NW. Therefore, it is possible to prevent, for example, a situation in which the registration in the inner NW is implicitly released earlier than the outer NW. As a result, unnecessary memory usage in each device of the outer NW may be reduced.

[0261] According to the first modification, after the registration of the inner NW is released, the registration of the outer NW can be released or the connection can be released. As a result, it is possible to reduce unnecessary memory usage in each device of the outer NW.

[0262] Modification 2 of Implementation Example 1. In the first variation of the first embodiment, a method of deregistering a UE cascaded to a plurality of NWs is disclosed. In the second variation, a method of starting a connection of the UE is disclosed.

[0263] The UE starts the connection in the order of the inner NW and the outer NW. The above-mentioned action can be applied in the connection start initiated by the UE. In the connection start with each NW, the method disclosed in Section 4.2.2.3.2 of Non-Patent Document 25 (TS23.502) can also be used. Therefore, for example, in the connection start process with the outer NW, it is possible to prevent the connection with the outer NW from being interrupted.

[0264] The UE may send the generated uplink data to the inner UPF via the inner AMF and the inner SMF. The UE may determine whether to send the data to the inner AMF. The UE may use information about the uplink data, such as the size of the uplink data, to make the determination, or may use information about the QoS of the uplink data to make the determination. The determination may be made by the inner AMF or the inner SMF. Thus, for example, the UE can quickly send the uplink data.

[0265] The UE can send the generated uplink data to the outer UPF via the outer AMF and the outer SMF. The UE can determine whether to send the data to the outer AMF. The UE can use information about the uplink data, such as the size of the uplink data, to make the judgment, or use information about the QoS of the uplink data to make the judgment, or use the judgment result of whether it is via the above-mentioned inner AMF to make the judgment. The UE can include the judgment result of whether it is via the inner AMF in the uplink data and notify the outer AMF. The judgment can be made by the N3IWF, the outer AMF or the outer SMF. The N3IWF can use the judgment result to send the uplink data to the outer AMF. Thus, for example, the UE can quickly send uplink data.

[0266] Other solutions are disclosed. The outer AMF notifies the UE of the signaling indicating the start of the connection. For example, the notification can be used in the connection start initiated by the outer NW. The signaling can be, for example, NAS signaling, paging request signaling, or newly established NAS signaling. The newly established NAS signaling can include information about paging, and can also include information about other data, such as the IP address of the UE. The newly established NAS signaling may include pseudo data. The outer AMF can notify the UE of the signaling indicating the start of the connection via the N3IWF, the inner UPF, and the RAN.

[0267] An AN connection can be established between N3IWF and UE. For example, IPsec settings can be established between N3IWF and UE. For example, N3IWF and UE can send and receive IKE_SA_INIT signaling shown in non-patent document 23 (RFC7296) to each other. For example, N3IWF and UE can send and receive IKE_AUTH signaling shown in non-patent document 23 (RFC7296) to each other. The AN connection in N3IWF can be established, for example, by the signaling sent to the UE by the outer AMF reaching N3IWF. N3IWF can maintain the signaling indicating the start of the connection sent by the outer AMF until the AN connection with the UE is established.

[0268] The inner UPF may notify the inner SMF of the generation of downlink data for the UE. The inner SMF may notify the inner AMF of the generation of downlink data. The inner AMF may initiate paging for the UE. The inner UPF may make this notification to the inner SMF when the PDU session with the UE stops or when the PDU session is released. For example, the inner UPF may initiate this action by the fact that signaling for the AN connection (e.g., IKE_SA_INIT) arrives from the N3IWF to the inner UPF. The inner UPF may maintain the signaling for the AN connection until the paging of the UE is completed.

[0269] As another example, the inner UPF may notify the inner AMF of the generation of downlink data for the UE. The notification may be made directly from the inner UPF to the inner AMF. An interface may also be provided between the inner AMF and the inner AMF. The inner AMF may use the notification to initiate paging for the UE. Thus, for example, the connection of the UE in the inner NW may be started quickly.

[0270] The UE may start a service request procedure with the inner NW. The UE may start the procedure using paging received by the UE. The procedure may also be, for example, the procedure described in Section 4.2.3.2 of Non-Patent Document 25 (TS23.502).

[0271] The inner UPF may send this signaling for AN connection to the RAN. The RAN may send this signaling received from the inner UPF to the UE. The RAN may send this signaling to the UE after the UE transfers to RRC_CONNECTED.

[0272] As another example, the RAN may initiate paging. The RAN may, for example, initiate paging when the UE is RRC_INACTIVE. The RAN may, for example, initiate paging by signaling for the AN connection (e.g., IKE_SA_INIT) arriving at the RAN from the N3IWF. The RAN may maintain the signaling for the AN connection until the paging of the UE is completed.

[0273] The RAN may send the signaling to the UE. The RAN may send the signaling to the UE after the UE transitions to RRC_CONNECTED.

[0274] As another example, the UE may not be paged. For example, when the UE is RRC_CONNECTED or CM-CONNECTED, paging may not be performed. In this case, the N3IWF may send signaling (e.g., IKE_SA_INIT) for AN connection to the UE via the inner UPF and the RAN.

[0275] The UE can use the signaling from the N3IWF to establish an IPsec connection with the N3IWF. For example, the UE can send the signaling of IKE_SA_INIT shown in non-patent document 23 (RFC7296) to the N3IWF. The N3IWF can use the signaling from the UE to continue the action of establishing an IPsec connection with the UE. For example, the N3IWF and the UE can send and receive the signaling of IKE_AUTH shown in non-patent document 23 (RFC7296) to each other.

[0276] N3IWF may send signaling indicating the start of a connection sent from the outer AMF to the UE. The signaling may be signaling maintained in the N3IWF before an AN connection is established between the N3IWF and the UE.

[0277] The UE may start a service request process with the inner NW. The UE may start the process using signaling indicating the start of a connection sent from the outer AMF to the UE. The process may also be, for example, the process shown in Section 4.12.4.2 of Non-Patent Document 25 (TS23.502).

[0278] Fig.28 and Fig.29 1 is a sequence diagram showing an operation of connecting a UE to an outer NW via an inner NW by initiating a connection start by the outer NW. Fig.28 and Fig.29 Connect at the boundary line BL 2829. Fig.28 and 29 An example of actions by which the outer AMF initiates the start of a connection is shown. Fig.28 and 29 A case where the UE is RRC_IDLE before the connection starts, that is, an example where the UE is connected to neither the inner NW nor the outer NW before the connection starts is shown.

[0279] exist Fig.28 In step ST2001 shown, it is assumed that downlink data for UE is generated in the outer UPF. In step ST2002, the outer UPF notifies the outer SMF that the data has been generated. In step ST2003, the outer SMF sends a positive response of step ST2002 to the outer UPF. In step ST2004, the outer UPF transmits the downlink data of step ST2001 to the outer SMF. The outer UPF can retain the downlink data of step ST2001.

[0280] exist Fig.28 In step ST2005 shown, the outer SMF requests the outer AMF to transmit N1 and / or N2 messages. In step ST2006, the outer AMF sends a response to the request to the outer SMF. In steps ST2005 and ST2006, the Namf_Communication_N1N2MessageTransferservice operation shown in Section 5.2.2.2.7 of non-patent document 25 (TS23.502) may also be used.

[0281] exist Fig.28In step ST2007 shown, the outer AMF sends a signaling indicating the start of the connection to the N3IWF. The signaling may be, for example, NAS signaling for the UE, a paging request signaling, or a newly established NAS signaling. The newly established NAS signaling may include information about paging, and may also include information about other data, such as the IP address of the UE. The newly established NAS signaling may include dummy data. The N3IWF may maintain the signaling in step ST2007 until the AN connection with the UE is established.

[0282] exist Fig.28 In step ST2008 shown, the N3IWF sends a signaling to the inner UPF for establishing IPsec with the UE. The signaling may also be, for example, the signaling of IKE_SA_INIT shown in non-patent document 23 (RFC 7296). The N3IWF may send the signaling, for example, as downlink data for the UE.

[0283] exist Fig.28 In step ST2010 shown, the inner UPF notifies the inner SMF that data has been generated. In step ST2011, the inner SMF sends an affirmative response of step ST2010 to the inner UPF. The inner UPF may retain the downlink data of step ST2008.

[0284] In step ST2012, the inner UPF may transmit the downlink data of step ST2008 to the inner SMF. Step ST2012 may also be performed using an indication of the transmission of downlink data from the inner SMF to the inner UPF. The inner SMF may send this indication to the inner UPF in a positive response to step ST2010. The inner SMF may retain the downlink data of step ST2008. In this case, the inner UPF may not retain the downlink data of step ST2008. Thereby, for example, the memory usage in the inner UPF may be reduced.

[0285] exist Fig.29 In step ST2015 shown, the inner SMF requests the inner AMF to transmit N1 and / or N2 messages. In step ST2016, the inner AMF sends a response to the request to the inner SMF. In steps ST2015 and ST2016, the Namf_Communication_N1N2MessageTransferservice operation shown in Section 5.2.2.2.7 of non-patent document 25 (TS23.502) may also be used.

[0286] exist Fig.29In step ST2020, the inner AMF sends a UE paging to the RAN. In step ST2022, the RAN sends a paging to the UE.

[0287] exist Fig.29 In the process ST2030 shown, the UE initiates a service request process to the inner NW. As this process, the process shown in Section 4.2.3.2 of Non-Patent Document 25 (TS23.502) may also be used. Through this process, a connection between the UE and the inner NW is established.

[0288] exist Fig.29 In step ST2035 shown, the inner UPF sends the signaling for establishing IPsec sent by N3IWF to the UE. The inner UPF can use the downlink data of step ST2008 maintained by the inner UPF to send step ST2035. In step ST2036, the UE sends the signaling for establishing IPsec to the N3IWF. The signaling sent by the UE in step ST2036 may be, for example, the signaling of IKE_SA_INIT shown in non-patent document 23 (RFC7296). In step ST2037, an action of establishing IPsec is performed between the N3IWF and the UE. The action may also be, for example, the sending and receiving of the signaling of IKE_SA_AUTH shown in non-patent document 23 (RFC7296). In step ST2037, an AN connection is established between the N3IWF and the UE.

[0289] As Fig.29 In other examples related to step ST2035 shown in , the inner SMF can send the signaling for establishing IPsec sent by the N3IWF to the inner UPF. The inner UPF can send the signaling to the UE. In step ST2012, this action can be performed when the inner UPF transmits the downlink data of step ST2008 to the inner SMF. Thus, for example, the downlink data maintained by the inner SMF can be sent to the UE. As a result, the reliability of sending and receiving downlink data can be improved while reducing the memory usage in the inner UPF.

[0290] exist Fig.29 In step ST2040 shown, N3IWF sends the signaling indicating the start of the connection sent by the outer AMF to the UE. N3IWF can use the signaling in step ST2007 maintained by this N3IWF to send step ST2040. The signaling of step ST2040 can be encrypted and decrypted between N3IWF and UE through IPsec. By receiving the signaling in step ST2040, UE recognizes that there is downlink data from the outer NW.

[0291] exist Fig.29In the process ST2050 shown, the UE starts a service request process to the outer NW. As this process, the process shown in Section 4.2.3.2 of Non-Patent Document 25 (TS23.502) may also be used. In the process ST2050, the RRCConnection reconfiguration in the process shown in Section 4.2.3.2 of Non-Patent Document 25 (TS23.502) may not be performed. The connection between the UE and the outer NW is established through this process.

[0292] exist Fig.29 In step ST2060 shown, the outer UPF sends downlink data to the UE. The outer UPF can send the downlink data using the data of step ST2001 maintained by the outer UPF.

[0293] exist Fig.28 and 29 In the figure, although the case where the inner AMF and RAN send paging is shown, the inner AMF and RAN may not perform paging. For example, when the UE is RRC_CONNECTED in the inner NW, paging may not be performed. For example, when the UE is CM-CONNECTED, paging may not be performed. As a result, for example, downlink data transmission to the UE can be performed quickly.

[0294] exist Fig.28 and 29 In the figure, although the case where the inner AMF and RAN send paging is shown, it can be set that only RAN performs paging. For example, the above action can be performed when the UE is RRC_INACTIVE in the inner NW. For example, the above action can be performed when the UE is CM-CONNECTED. As a result, for example, the same effect as above can be obtained.

[0295] The downlink data in the outer NW can also be notified to the UE via the outer SMF and the outer AMF. The outer SMF can notify the UE of the downlink data via this SMF, the outer AMF, and the N3IWF. The outer SMF can determine whether to notify the UE of the downlink data via the outer SMF and the outer AMF. The outer SMF can use information related to the downlink data, such as the size of the downlink data, to make the determination, or can use information related to the QoS of the downlink data to make the determination. Thus, for example, the outer NW can quickly notify the UE of the downlink data.

[0296] The downlink data can also be notified to the UE via the inner SMF and the inner AMF. The downlink data can be either the downlink data in the inner NW or the downlink data sent from the outer NW. The inner SMF can notify the UE of the downlink data via this SMF, the inner AMF, and the RAN. The inner SMF can determine whether to notify the UE of the downlink data via this SMF and the inner AMF. The inner SMF can use information related to the downlink data, such as the size of the downlink data, to make the judgment, or use information related to the QoS of the downlink data to make the judgment, or use the judgment result of the above-mentioned outer SMF to make the judgment. The outer AMF can notify the inner SMF of the judgment result of the outer SMF. The outer AMF can include the judgment result of the outer SMF in the downlink data and notify the inner SMF of it. Thus, for example, the inner NW can quickly notify the UE of the downlink data.

[0297] According to the second modification, it is possible to establish a NW from the outer NW to the UE.

[0298] Modification 3 of Implementation Example 1. In the second variation of the first embodiment, a method for the outer NW to start connecting to a UE connected to a plurality of NWs in cascade connection is disclosed. In the third variation, a method for releasing the PDU session of the UE is disclosed.

[0299] The PDU session between the UE and the outer NW is released in the order of the inner NW. The above-mentioned action can be applied to the PDU session release initiated by the UE. For the PDU session release in each NW, the method disclosed in Section 4.3.4.2 of Non-Patent Document 25 (TS23.502) can be used. Therefore, for example, the connection interruption of the PDU session of the outer NW due to the release of the PDU session of the inner NW can be prevented.

[0300] Other solutions are disclosed. The inner AMF can notify the UE of the release of the PDU session of the inner NW (hereinafter sometimes referred to as the inner PDU session). For example, the notification can be made when the inner AMF decides to release the inner PDU session. The inner AMF can use NAS signaling to make the notification. As another example of the notification, the notification can also be made when the inner SMF decides to release the inner PDU session. The inner SMF can notify the inner AMF to release the inner PDU session. The inner AMF can transmit the notification from the inner SMF to the UE.

[0301] The UE requests the inner AMF to wait for the inner PDU session to be released. The UE can use NAS signaling to issue the request. The NAS signaling can be the signaling described in non-patent document 26 (TS24.501) or a new NAS signaling, such as PDU Session Release Notification. The inner AMF uses the request to delay the release of the inner PDU session. The inner AMF can transmit the request to the inner SMF. For example, the transmission can be performed when the inner SMF decides to release the inner PDU session. The inner SMF uses the notification transmitted from the inner AMF to delay the release of the inner PDU session.

[0302] The UE may include information about the standby time for deregistration in the request. The information and / or action related to the standby time may be the same as the standby time related to deregistration of the inner NW shown in Variation 1 of Implementation 1. Thus, for example, the inner PDU session can be prevented from being released before the outer PDU session is released. As a result, unnecessary memory usage in the outer NW can be reduced.

[0303] The UE may have a timer for managing the release of the inner PDU session. The timer may be, for example, a timer for managing the standby time. The UE may initialize the timer when the inner PDU session is established. The UE may start the timer based on the receipt of an inner PDU session release notification from the inner AMF. The UE may stop the timer based on the release of the outer PDU session. The UE may recognize the release of the inner PDU session based on the expiration of the timer. Therefore, for example, the management of the action of the inner PDU session release in the UE becomes easy.

[0304] The inner AMF may have a timer for managing the release of the inner PDU session. The timer may be, for example, a timer for managing the standby time. The inner AMF may initialize the timer when the inner PDU session is established. The inner AMF may start the timer based on the fact that an inner PDU session release notification is sent to the UE. The inner AMF may stop the timer based on an inner PDU session release reopening notification from the UE. The inner AMF may reopen the inner PDU session release from the UE based on the expiration of the timer. Therefore, for example, in the inner AMF, the management of the registration release action becomes easy.

[0305] The UE initiates the process of releasing the PDU session of the outer NW (hereinafter sometimes referred to as the outer PDU session). The UE may initiate the process of releasing the outer PDU session using, for example, an inner PDU session release notification sent from the inner AMF. The outer PDU session released by the UE may be, for example, an outer PDU session that shares a QoS flow with the inner PDU session released by the inner AMF. The UE requests the outer AMF to release the outer PDU session. The UE may, for example, use NAS signaling to make the request. The NAS signaling may also be NAS signaling shown in non-patent document 26 (TS24.501), such as a PDU session release request (PDU Session Release Request). New NAS signaling may be set. The request from the UE to the outer AMF may include information about the outer PDU session to be released, such as an identifier of the PDU session. The request from the UE to the outer AMF may include information about the release of the inner PDU session. Information about the release of the inner PDU session may be included in the request as a reason for the request, for example. The outer AMF may use the request to release the outer PDU session. As another example, the outer AMF may transmit the request to the outer SMF. The outer SMF may use the request to release the outer PDU session.

[0306] The outer AMF uses the request from the UE to request the N3IWF to release the AN resources accompanying the PDU session. The request from the outer AMF to the N3IWF can be made, for example, by using the UE to connect to the outer NW via the inner NW. The request from the outer AMF to the N3IWF can be made using information indicating that the UE releases the inner PDU session, for example, the reason included in the notification from the UE is information about the release of the inner PDU session. Thus, for example, in the design of the communication system, the previous design can be used, with the result that the complexity of the design in the communication system can be avoided.

[0307] The UE notifies the inner AMF that the outer PDU session has been released. The notification may be a notification of completion of the preparation for the release of the inner PDU session. The UE may use NAS signaling to send the notification to the inner AMF. The NAS signaling may be the signaling shown in non-patent document 26 (TS24.501) or a new NAS signaling, such as PDU session release ready. The inner AMF may use the notification to reopen the release of the inner PDU session. As another example, the inner AMF may transmit the request to the inner SMF. The inner SMF may use the request to release the inner PDU session.

[0308] Figure 30 to Figure 32This is a sequence diagram showing a first example of an operation of releasing an outer PDU session in conjunction with an inner PDU session release, with respect to a UE connected to an outer NW via an inner NW. Figure 30 to Figure 32 Connected at the positions of the boundaries BL3031 and BL3132. Figure 30 to Figure 32 An example of the inner AMF initiating an inner PDU session release is shown.

[0309] exist Fig.30 In step ST2101 shown, the inner AMF decides to release the PDU session. In step ST2102, the inner AMF notifies the UE to release the inner PDU session. For this notification, a newly established NAS signaling, such as PDU Session Release Notification, can be used. The signaling may include information about the inner PDU session to be released, such as information about the identifier of the PDU session. The signaling may include information related to the NW slice corresponding to the PDU session, such as NSSAI (Network Slice Selection Assistance Information) and / or S-NSSAI (Single Network Slice Selection Assistance Information) shown in non-patent document 22 (TS23.501). The UE recognizes the inner PDU session release by receiving the notification of step ST2102.

[0310] exist Fig.30 In step ST2103 shown, the UE requests the inner AMF to wait for the inner PDU session to be released. For this request, NAS signaling can be used. The NAS signaling can also be a new NAS signaling, such as a signaling of a PDU session release wait request. The signaling can include information about the standby time for the PDU session release. The inner AMF can use the signaling to wait for the PDU session to be released. The inner AMF can wait for the release of the PDU session during the standby time included in the signaling or during a predetermined standby time. The inner AMF can wait for the release of the PDU session before receiving the notification of registration cancellation and reopening from the UE as described later. The starting point of the standby time in the inner AMF can also be the reception time point of the standby request in step ST2103.

[0311] exist Fig.30In step ST2105 shown, the UE requests the outer NW to release the outer PDU session. For the AMF, NAS signaling can be used. The NAS signaling can also be an existing signaling recorded in non-patent document 26 (TS24.501), such as a PDU Session Release Request. New signaling can be set. The NAS signaling may include information about the reason for the request. The information about the reason may be, for example, the release of the inner PDU session. The outer AMF can use the NAS signaling to initiate the action of releasing the outer PDU session.

[0312] exist Fig.30 In step ST2106 shown, the outer AMF requests the outer SMF to release the outer PDU session. For this request, for example, the Nsmf_PDUSession_UpdateSMContext service operation described in Section 5.2.8.2.6 of non-patent document 25 (TS23.502) may also be used. In step ST2107, the outer SMF requests the outer UPF to release the N4 session. The outer UPF releases the resources of the outer PDU session by receiving the request of step ST2107. In step ST2108, the outer UPF notifies the outer SMF of the response to the N4 session release request. In steps ST2107 and ST2108, the N4 Session Release (N4 SessionRelease) process described in Section 4.4.1.4 of non-patent document 25 (TS23.502) may also be used. In step ST2109, the outer SMF notifies the outer AMF of the response to the outer PDU session release request. For this response, for example, the Nsmf_PDUSession_UpdateSMContext service operation described in Section 5.2.8.2.6 of Non-Patent Document 25 (TS23.502) may be used.

[0313] exist Fig.30 In step ST2110 shown, the outer AMF requests the N3IWF to release the AN resources accompanying the PDU session between the outer AMF and the N3IWF. For this request, for example, the signaling of the N2 Resource Release Request described in non-patent document 24 (TS 38.413) can be used. The N3IWF starts the release of the AN resources accompanying the PDU session with the UE by receiving the request in step ST2110.

[0314] exist Fig.30In steps ST2115 and ST2116 shown, the AN resources associated with the PDU session are released between the N3IWF and the UE. Fig.30 In the example shown, the IPsec SA (Security Association) is released between the N3IWF and the UE. In step ST2115, the N3IWF notifies the UE to release the IPsec SA. The signaling used for the notification may be, for example, the signaling of the IKE INFORMATIONAL exchange described in non-patent document 23 (IETF RFC7296). The signaling may also include a Delete payload described in non-patent document 23 (IETF RFC 7296). The Delete payload may include information about the IPsec SA (e.g., an identifier). The UE releases the IPsec SA by receiving the notification of step ST2115. In step ST2116, the UE notifies the N3IWF to release the IPsec SA. The notification from the UE to the N3IWF may be, for example, the same signaling as step ST2115. By receiving the notification of step ST2116, the N3IWF recognizes that the AN resources accompanying the PDU session in the UE have been released.

[0315] exist Fig.30 The IPsec SA released in steps ST2115 and ST2116 shown may be only the IPsec SA used for the outer PDU session. The UE and N3IWF may not release the IPsec SA used for C-layer communication between the UE and the outer NW. Therefore, for example, signaling between the UE and the outer AMF can be communicated quickly.

[0316] exist Fig.30 In step ST2120 shown, N3IWF sends a response to the release request of AN resources accompanying the PDU session to the outer AMF. For this response, for example, the signaling of N2Resource Release Ack (N2 Resource Release Response) described in non-patent document 24 (TS38.413) can also be used.

[0317] exist Fig.31In step ST2125 shown, the outer AMF sends information about the N2 connection between the N3IWF and the outer AMF to the outer SMF. In step ST2130, the outer SMF sends a response to the information to the outer AMF. In steps ST2125 and ST2130, for example, the Nsmf_PDUSession_UpdateSMContext serviceoperation described in Section 5.2.8.2.6 of Non-Patent Document 25 (TS23.502) can be used.

[0318] exist Fig.31 In step ST2135 shown, the N3IWF instructs the UE to release the PDU session. The N3IWF can use NAS signaling sent from the outer AMF to send the indication. The UE uses this indication to release the resources of the UE related to the outer PDU session. In step ST2136, the UE sends a response to the indication to the N3IWF. In step ST2140, the N3IWF sends the NAS signaling received in step ST2136 to the outer AMF.

[0319] exist Fig.31 In step ST2141 shown, the outer AMF sends information about the N1 connection between the UE and the outer AMF to the outer SMF. In step ST2142, the outer SMF sends a response to the information to the outer AMF. In steps ST2141 and ST2142, for example, the Nsmf_PDUSession_UpdateSMContext service operation described in non-patent document 25 (TS23.502) can be used.

[0320] exist Fig.31 In step ST2145 shown, the outer AMF and the outer SMF notify each other of the release of the session management context (SM context) of the outer PDU session. In step ST2145, for example, Nsmf_PDUSession_SMContextStatusNotify (Nsmf_PDU session_SM context status notification) described in Section 5.2.8.2.8 of non-patent document 25 (TS23.502) may also be used.

[0321] exist Fig.31In step ST2150 shown, the session management policy cooperation termination (SM Policy Association Termination) action shown in Section 4.16.6 of non-patent document 25 (TS23.502) is performed between the outer SMF and the outer PCF.

[0322] exist Fig.31 In step ST2160 shown, the UE notifies the inner AMF that the outer PDU session has been released. The notification may be a notification of completion of the preparation for the release of the inner PDU session. The UE may use NAS signaling to send the notification to the inner AMF. The NAS signaling may also be the signaling shown in non-patent document 26 (TS24.501), such as a PDU session release request. The NAS signaling may be a new NAS signaling, such as PDU session release ready. The inner AMF reopens the inner PDU session release by receiving the notification of step ST2160.

[0323] exist Fig.31 Steps ST2165, ST2166 and ST2167 shown and Fig.32 In step ST2170 shown in FIG. 1 , the same processing as that performed between the outer NW devices described above is performed between the inner NW devices ( Fig.30 The same processing as steps ST2106, ST2107, ST2108 and ST2109) is performed.

[0324] exist Fig.32 In step ST2175 shown in , the inner AMF requests the RAN to release the AN resources accompanying the inner PDU session between the inner AMF and the RAN. For this request, for example, the signaling of the N2 Resource Release Request described in non-patent document 24 (TS 38.413) can be used. The RAN starts releasing the AN resources accompanying the inner PDU session with the UE by receiving the notification of step ST2175.

[0325] exist Fig.32In step ST2176 shown, a release action of AN resources accompanying the inner PDU session is performed between the RAN and the UE. The RAN may request the UE to release the inner PDU session. For this request, RRC signaling may also be used, such as the RRC Reconfiguration disclosed in non-patent document 27 (TS 38.331). The RRC signaling may include an indication of the release of the inner PDU session. The UE may use the signaling to release the inner PDU session. The UE may send a response to the indication to the RAN. The response may also be, for example, the RRC Reconfiguration Complete disclosed in non-patent document 27 (TS 38.331).

[0326] exist Fig.32 In step ST2177 shown, the RAN sends a response to the release request of the AN resources accompanying the inner PDU session to the inner AMF. For this response, for example, the signaling of N2 Resource Release Ack (N2 Resource Release Response) described in non-patent document 24 (TS38.413) can also be used.

[0327] exist Fig.32 In steps ST2178 and ST2179 shown in the figure, the above-mentioned processing performed between the inner AMF and the inner SMF is performed in the same manner as that performed between the outer AMF and the outer SMF ( Fig.31 The same processing as steps ST2125 and ST2130).

[0328] exist Fig.32 In step ST2180 shown, the UE sends a positive response to the PDU session release request to the RAN. The response may be, for example, NAS signaling from the UE to the inner AMF. The response sent from the UE to the RAN may be, for example, RRC signaling including the NAS signaling. In step ST2181, the RAN sends the NAS signaling received in step ST2180 to the inner AMF.

[0329] exist Fig.32 In steps ST2182, ST2183, ST2184, and ST2185 shown in FIG. 1 , the above-mentioned processing ( Fig.31 The same processing as steps ST2141, ST2142, ST2145 and ST2150) is performed.

[0330] exist Figure 30 to Figure 32 Although it is shown that N3IWF uses different signaling to indicate the AN connection release and the outer PDU session release for the outer PDU session, the same signaling can also be used. For example, Fig.30 Steps ST2115 and Fig.31 The processing in step ST2135 can be performed using the same signaling. Fig.30 Steps ST2116 and Fig.31 The processing of step ST2136 can be performed with the same signaling. Therefore, for example, the amount of signaling between the UE and the N3IWF can be reduced.

[0331] exist Figure 30 to Figure 32 Although the N3IWF is shown to release the outer PDU session after the AN connection for the outer PDU session is released, the N3IWF may release the outer PDU session before the AN connection for the outer PDU session is released. For example, steps ST2135 and ST2136 may be performed between steps ST2110 and ST2115. Therefore, for example, the UE can quickly perform the process of step ST2160, and as a result, the process of releasing the PDU session in the communication system can be quickly performed.

[0332] It can be set that the notification of the release of the PDU session for the UE from the inner AMF can be made only when the inner AMF grasps that the UE is connected to the outer NW via the inner NW. The UE can notify the inner AMF of information about the outer NW in advance. The notification can also be, for example, the same notification as variant 1 of implementation example 1. The inner AMF can notify the inner SMF of the notification. The inner SMF can use the notification to wait for the PDU session release. Therefore, for example, the inner PDU session can be prevented from being released before the outer PDU session is released, thereby improving the robustness of the communication system.

[0333] Other solutions are disclosed. The inner AMF can perform NW-initiated PDU session release. The UE can notify the inner AMF of information about the outer NW in advance. The notification can also be the same as above. The inner AMF can use the notification to identify that this AMF is the inner AMF. Thereby, for example, the robustness in the communication system can be improved.

[0334] As another example, the outer AMF may not perform NW-initiated PDU session release, and the two AMFs included in the inner NW and outer NW connection structure may not perform NW-initiated PDU session. The UE may notify the outer AMF of information about the inner NW in advance. The UE may notify the inner AMF of information about the outer NW in advance. The inner AMF and / or the outer AMF may use the notification from the UE to determine whether NW-initiated PDU session release can be performed. Thus, for example, the robustness in the communication system can be improved.

[0335] Other solutions are disclosed. The inner SMF notifies the inner AMF to release the inner PDU session. For example, the notification can be made when the inner SMF decides to release the inner PDU session. The inner SMF can use signaling between AMF-SMF, such as the Namf_Communication_N1N2MessageTransferservice operation disclosed in Section 5.2.2.2.7 of non-patent document 25 (TS23.502) to make the notification. The inner SMF can make the notification before the N4 session release request with the inner UPF. Therefore, for example, the inner PDU session release can be performed after notifying the UE, as a result of which the inner PDU session can be prevented from being released before the outer PDU session is released. Thereby, the robustness in the communication system can be improved.

[0336] The inner AMF notifies the UE to release the inner PDU session. This notification may be the same as the above solution. The UE requests the inner AMF to wait for the inner PDU session to be released. This request may be the same as the above solution.

[0337] The inner AMF requests the inner SMF to wait for the inner PDU session to be released. The inner SMF may use signaling between AMF-SMF, such as the Namf_Communication_N1N2MessageTransfer service operation disclosed in Section 5.2.2.2.7 of Non-Patent Document 25 (TS23.502) to make this request. The request may include information about the standby time.

[0338] The UE initiates the process of releasing the outer PDU session. The release process may also be the same as the above solution.

[0339] The UE notifies the inner AMF that the outer PDU session has been released. The notification may be a notification of completion of preparation for the release of the inner PDU session. The notification may be the same as the above solution. The inner AMF transmits the notification to the inner SMF. The transmission may also be performed, for example, as the Nsmf_PDUSession_ReleaseSMContext service operation described in Section 5.2.8.2.7 of non-patent document 25 (TS23.502). The inner SMF may use this transmission to perform PDU session release processing with the inner UPF.

[0340] Figure 33 to Figure 35This is a sequence diagram showing a second example of the action of releasing the outer PDU session along with the inner PDU session release regarding a UE connected to the outer NW via the inner NW. Figure 33 to Figure 35 Connect at the positions of boundaries BL3334 and BL 3435. Figure 33 to Figure 35 An example of the inner SMF initiating the inner PDU session release is shown. Figure 33 to Figure 35 In, with Figure 30 to Figure 32 The same processes are denoted by the same step numbers, and the same descriptions are omitted.

[0341] exist Fig.33 In step ST2201 shown, the inner SMF decides to release the PDU session. In step ST2202, the inner SMF notifies the inner AMF to release the inner PDU session. This notification of step ST2202 can be performed using signaling between AMF-SMF, such as the Namf_Communication_N1N2MessageTransfer service operation disclosed in Section 5.2.2.2.7 of Non-Patent Document 25 (TS23.502).

[0342] Fig.33 Steps ST2102 and ST2103 shown are the same as Fig.30 same.

[0343] exist Fig.33 In step ST2204 shown, the inner AMF requests the inner SMF to wait for the inner PDU session release. The request of step ST2204 can be made using signaling between AMF and SMF, such as the Namf_Communication_N1N2MessageTransfer service operation disclosed in Section 5.2.2.2.7 of non-patent document 25 (TS23.502). The request of step ST2204 may include information about the standby time. The inner SMF reserves the inner PDU session release through the request.

[0344] Figure 33 to Figure 35 Steps ST2105 to ST2185 shown are similar to Figure 30 to Figure 32 same.

[0345] In the inner NW, there may be unreleased PDU sessions. For example, the inner PDU session used for sending and receiving C-layer data in the outer NW may not be released. The UE may notify the inner AMF of information about the PDU session. The inner AMF may notify the inner SMF of the information. Therefore, for example, C-layer communication in the outer NW may be performed stably.

[0346] The method disclosed in the first variant of the first embodiment can be applied to the PDU session release. Thus, the same effect as that of the first variant of the first embodiment can be obtained.

[0347] The method disclosed in this variant 3 can be applied to a PDU session release initiated by the RAN. For example, the RAN can notify the UE to release the inner PDU session. The UE can request the outer AMF to release the outer PDU session. As another example, the N3IWF can initiate the PDU session release. The N3IWF can notify the UE of the outer PDU session release. Therefore, for example, in the RAN and / or the N3IWF, unnecessary memory usage can be reduced.

[0348] The method disclosed in this variant 3 can be applied to the release of a PDU session initiated by a PCF. For example, the inner PCF can notify the inner AMF to release the inner PDU session. The notification can be made via the inner SMF. The inner AMF can transmit the notification to the UE. The UE can transmit the notification to the outer AMF. Thus, for example, in the PCF, unnecessary memory usage can be reduced.

[0349] According to this modification example 3, it is possible to release unnecessary external PDU sessions. As a result, it is possible to reduce the memory usage in the UE and the external NW device.

[0350] Modification 4 of Implementation Example 1. In variant 3 of implementation example 1, a method for releasing a PDU session from an inner NW for a UE connected in cascade to a plurality of NWs is disclosed. In this variant 4, a method for stopping a U-layer connection in a PDU session of the UE is disclosed.

[0351] In the communication system, before the U-layer connection stop in the inner PDU session (hereinafter sometimes referred to as the inner U-layer stop), the U-layer connection stop in the outer PDU session (hereinafter sometimes referred to as the outer U-layer stop) is performed. The above action can be performed when the inner SMF initiates the inner U-layer stop.

[0352] The inner SMF notifies the inner AMF of the inner U-plane stop. In this notification, the signaling shown in non-patent document 25 (TS23.502) can be used, or new signaling, such as Namf_UplaneDeactivation (Namf_Uplane deactivation), can be used. The signaling shown in non-patent document 25 (TS23.502) may include information about the U-plane stop, such as information indicating the U-plane stop and / or a PDU session identifier.

[0353] The inner AMF notifies the UE of the inner U-plane deactivation. In this notification, the NAS signaling shown in non-patent document 25 (TS23.502) may also be used. For this notification, new NAS signaling, such as U-plane deactivation notification, may also be used. The above signaling may include information about the U-plane deactivation, such as information indicating the U-plane deactivation and / or a PDU session identifier.

[0354] The UE can request the inner AMF to wait for the inner U-plane to stop. In this request, the NAS signaling shown in non-patent document 25 (TS23.502) can also be used. For this request, new NAS signaling, such as U-plane deactivation wait request, can also be used. The above signaling may include information about the U-plane deactivation wait request, such as information about the content of waiting to stop, information about the PDU session of the U-plane to be stopped, and / or the U-plane deactivation wait time.

[0355] In other examples, the U-layer standby stop time included in the request from the UE to the inner AMF can be predetermined. Thus, for example, the size of the signaling from the UE to the inner AMF can be reduced.

[0356] The inner AMF can request the inner SMF to wait for the inner U-layer to stop. For this request, the signaling shown in non-patent document 25 (TS23.502), such as Nsmf_PDUSession_UpdateSMContext (Nsmf_PDU session update SM context), can also be used. For this request, new signaling can be used, such as a response to the above-mentioned Namf_UplaneDeactivation (Namf_Uplane deactivation). For this request, Nsmf_UplaneDeactivationWait (Namf_Uplane deactivation wait) can be used. The above-mentioned signaling may include information about the standby for the U-layer to stop. This information may be the same as the information included in the inner U-layer stop standby request from the above-mentioned UE to the inner AMF.

[0357] In other examples, the U-layer stop standby time included in the request from the inner AMF to the inner SMF can be predetermined. Thus, for example, the size of the signaling from the inner AMF to the inner SMF can be reduced.

[0358] The UE may have a timer for managing the inner U-layer stop. The timer may be, for example, a timer for managing the standby time. The UE may initialize the timer when the inner PDU session is established. The UE may start the timer based on the fact that the inner U-layer stop notification is received from the inner AMF. The UE may stop the timer based on the completion of the outer U-layer stop. The UE may recognize the stop of the inner U-layer based on the expiration of the timer. Therefore, for example, the management of the action of the inner U-layer stop in the UE becomes easy.

[0359] The inner AMF may have a timer for managing the inner U-layer stop. The timer may be, for example, a timer for managing the standby time. The inner AMF may initialize the timer when the inner PDU session is established. The inner AMF may start the timer based on the fact that an inner U-layer stop notification is sent to the UE. The inner AMF may stop the timer based on the inner U-layer stop restart notification from the UE. The inner AMF may restart the inner U-layer stop of the UE based on the expiration of the timer. Therefore, for example, in the inner AMF, the management of the registration release action becomes easy. The SMF may have the timer. Therefore, for example, the management of the registration release action in the inner SMF becomes easy.

[0360] The UE may request the outer AMF to stop the outer U-plane. For this request, the NAS signaling shown in non-patent document 25 (TS23.502), such as a PDU session modification request, may also be used. For this request, new NAS signaling, such as a U-plane deactivation request, may also be used. The above signaling may include information about stopping the PDU session of the U-plane connection. For example, the UE may decide to stop the U-plane connection of the outer PDU session including the QoS flow associated with the stopped inner U-plane connection.

[0361] The outer AMF can request the outer SMF to stop the outer U-layer. For this request, the signaling shown in non-patent document 25 (TS23.502), such as Nsmf_PDUSession_UpdateSMContext (Nsmf_PDU session updates SM context), can also be used. For this request, new signaling, such as Nsmf_UplaneDeactivation (Namf_Uplane deactivation), can be used. The above signaling may include information about stopping the PDU session of the U-layer connection. The outer SMF can use this information to start the action of stopping the outer U-layer.

[0362] The outer SMF can send a response to the outer U-layer stop request to the outer AMF. The outer SMF can send the response after the N4 session change request, response and / or N4 session release request and response between the outer SMF and the outer UPF. The response from the outer SMF to the outer AMF can replace the Namf_Communication_N1N2MessageTransfer (Namf_Communication_N1N2 message transfer service action) shown in non-patent document 25 (TS23.502). The outer AMF can use the response to perform the release processing of N2 PDU session resources between the N3IWF. The N3IWF can release AN resources, such as sub-SA in IPsec, between the UE.

[0363] The UE can request the inner AMF to restart the inner U-plane that has been on standby, request the inner U-plane to stop, or notify the inner U-plane of the completion of preparation for stopping. In this request, the NAS signaling shown in non-patent document 25 (TS23.502) can also be used. For this request, new NAS signaling can be used, such as a notification of U-plane deactivation ready.

[0364] As another example, the UE may not request the inner AMF to reopen the inner U-layer stop, may not request the inner U-layer stop, and may not notify the completion of the preparation for the inner U-layer stop. For example, when the UE sends an inner U-layer stop including the above-mentioned standby time to the inner AMF, the above-mentioned request or notification may not be made. For example, the above-mentioned request or notification may not be made when the standby time is predetermined. Therefore, for example, the signaling between the UE and the inner AMF can be reduced.

[0365] The inner AMF can request the inner SMF to reopen the inner U layer that has been on standby, can request the inner U layer to stop, or can notify the inner U layer that the preparation for stopping is complete. For this request, the signaling shown in non-patent document 25 (TS23.502), such as Nsmf_PDUSession_UpdateSMContext (Nsmf_PDU session updates SM context), can also be used. For this request, new signaling can be used, such as Nsmf_UplaneDeactivationReady (Namf_Uplane deactivation preparation is complete).

[0366] As another example, the inner AMF may not request the inner SMF to reopen the inner U-layer stop, may not request the inner U-layer stop, and may not notify the inner U-layer stop of completion of preparation. For example, when the inner AMF requests the inner SMF to stop the inner U-layer including the above-mentioned standby time, the above-mentioned request or notification may not be made. For example, the above-mentioned request or notification may not be made when the standby time is predetermined. Therefore, for example, the signaling between the inner AMF and the inner SMF can be reduced.

[0367] The inner SMF can restart the process stopped by the inner U layer by receiving the above request and / or preparation completion notification. As another example, the inner SMF can restart the process stopped by the inner U layer when the above standby time expires.

[0368] Figure 36 to Figure 37 This is a sequence diagram showing the action of stopping the outer U-layer along with stopping the inner U-layer for a UE connected to the outer NW via the inner NW. Figure 36 to Figure 37 Connect at the position of boundary line BL3637. Figure 36 to Figure 37 An example of the inner SMF initiating a stop of the inner U layer is shown.

[0369] exist Fig.36 In step ST2301 shown, the inner SMF determines that the U-layer connection of the inner PDU session is stopped.

[0370] exist Fig.36 In step ST2305 shown, the inner SMF notifies the inner AMF that the inner U-plane is stopped. In this notification, the signaling shown in non-patent document 25 (TS23.502) can be used, or new signaling, such as Namf_UplaneDeactivation (Namf_Uplane deactivation), can be used. The notification of step ST2305 may include information about the U-plane stop, such as information indicating the U-plane stop and / or a PDU session identifier.

[0371] exist Fig.36 In step ST2306 shown, the inner AMF notifies the UE of the inner U-plane deactivation. In this notification, the NAS signaling shown in non-patent document 25 (TS23.502) can be used, or new NAS signaling, such as U-plane deactivation notification (U-plane deactivation notification), can be used. The notification of step ST2306 may include the same information as step ST2305.

[0372] exist Fig.36In step ST2307 shown, the UE requests the inner AMF to wait for the inner U-plane to stop. In this request, the NAS signaling shown in non-patent document 25 (TS23.502) can also be used. For this request, new NAS signaling, such as U-plane deactivation wait request (U-plane deactivation waitrequest), can also be used. The request of step ST2307 may include information about the U-plane stop waiting, for example, information about the content of waiting to stop, information about the PDU session of the U-plane to be stopped, and / or the U-plane stop standby time.

[0373] exist Fig.36 In step ST2308 shown, the inner AMF requests the inner SMF to wait for the inner U plane to stop. In this request, the signaling shown in non-patent document 25 (TS23.502) can also be used. For this request, new signaling can be used, such as Nsmf_PDUSession_UpdateSMContext (Nsmf_PDU session updates SM context). For this request, new signaling can be used, such as a response to the above-mentioned Namf_UplaneDeactivation (Namf_Uplane deactivation). For this request, Nsmf_UplaneDeactivationWait (Namf_Uplane deactivation wait) can be used. The request of step ST2308 may include the same information as step ST2307.

[0374] exist Fig.36 In step ST2310 shown, the UE requests the outer AMF to stop the outer U-plane. For this request, the NAS signaling shown in non-patent document 25 (TS23.502), such as the PDU session modification request, may also be used. For this request, new NAS signaling, such as the U-plane deactivation request, may also be used. The request of step ST2310 may include information about stopping the PDU session of the U-plane connection.

[0375] exist Fig.36In step ST2315 shown, the outer AMF requests the outer SMF to stop the outer U-layer. For this request, the signaling shown in non-patent document 25 (TS23.502), such as Nsmf_PDUSession_UpdateSMContext (Nsmf_PDU session updates SM context), can also be used. For this request, new signaling, such as Nsmf_UplaneDeactivation (Namf_Uplane deactivation), can be used. The above signaling may include information about stopping the PDU session of the U-layer connection. The outer SMF can use this information to start the action of stopping the outer U-layer.

[0376] exist Fig.36 In step ST2317 shown, the outer SMF requests the outer UPF to perform N4 session modification. For this request, for example, the N4 session modification request (N4 session modification request) shown in non-patent document 25 (TS23.502) can also be used. As another example, the outer SMF can request the outer UPF to release the N4 session.

[0377] exist Fig.36 In step ST2318 shown, the outer UPF sends a response to the N4 session modification request to the outer SMF. For this sending, for example, the N4 session modification response (N4 session modification response) shown in non-patent document 25 (TS23.502) can also be used. As another example, the outer UPF can send a response to the N4 session release request to the outer SMF.

[0378] exist Fig.36 In step ST2320 shown, the outer SMF sends a response to the outer U-layer stop request to the outer AMF. For sending this response, the signaling shown in non-patent document 25 (TS23.502), such as Nsmf_PDUSession_UpdateSMContext (Nsmf_PDU session updates SM context), can also be used. For sending this response, Namf_Communication_N1N2MessageTransfer (Nsmf_communication_N1N2 information transfer) can also be used. For sending this response, new signaling, such as Nsmf_UplaneDeactivationResponse (Namf_Uplane deactivation response), can be used.

[0379] exist Fig.36In step ST2322 shown in FIG. 1 , the outer AMF requests the N3IWF to release the AN resources accompanying the PDU session between the outer AMF and the N3IWF. Step ST2322 can be Fig.30 The same as step ST2110 in.

[0380] exist Fig.36 In steps ST2325 and ST2326 shown in FIG. 1 , the AN resources accompanying the PDU session are released between the N3IWF and the UE. Steps ST2325 and ST2326 can be used in conjunction with Fig.30 Steps ST2115 and ST2116 are the same.

[0381] exist Fig.36 In step ST2328 shown in FIG. 1 , N3IWF sends a response to the request of step ST2322 to the outer AMF. Step ST2328 can be Fig.30 The same as step ST2120 in.

[0382] exist Fig.37 In step ST2330 shown in FIG. 1 , the outer AMF sends information about the N2 connection between the N3IWF and the outer AMF to the outer SMF. In step ST2331, the outer SMF sends a response to the information to the outer AMF. Steps ST2330 and ST2331 may be similar to Fig.31 Steps ST2125 and ST2130 are the same.

[0383] exist Fig.37 In step ST2340 shown, the UE requests the inner AMF to reopen the inner U-plane. For sending this request, the NAS signaling shown in non-patent document 25 (TS23.502) can be used. For sending this request, new NAS signaling can be used, such as a notification of U-plane deactivation ready. The request may include information about reopening the PDU session of the U-plane connection.

[0384] exist Fig.37 In step ST2341 shown, the inner AMF requests the inner SMF to reopen the inner U-layer. For this request, the signaling shown in non-patent document 25 (TS23.502), such as Nsmf_PDUSession_UpdateSMContext (Nsmf_PDU session updates SM context), can also be used. For this request, new signaling, such as Nsmf_UplaneDeactivationReady (Nsmf_Uplane deactivation preparation completed), can be used. The request may include information about reopening the PDU session for the U-layer connection.

[0385] exist Fig.37 In steps ST2345 and ST2347 shown in FIG. 1 , the processing performed between the inner NW devices is the same as that performed between the outer NW devices ( Fig.36 The above processing is the same as steps ST2317 and ST2318).

[0386] exist Fig.37 In step ST2349 shown, the RAN resource release process accompanying the PDU session is performed between the inner SMF and the inner AMF. In step ST2349, the Namf_Communication_N1N2MessageTransferservice operation shown in Section 5.2.2.2.7 of Non-Patent Document 25 (TS23.502) can be used.

[0387] exist Fig.37 In steps ST2350 to ST2354 shown in FIG. Fig.32 The same processing is performed as in steps ST2175 to ST2179 shown.

[0388] exist Fig.37 In step ST2340 shown, the case where the UE requests the inner AMF for a standby time for stopping the U-layer connection is shown, but the UE may not make the request. For example, when the UE notifies the inner AMF of the standby time for stopping the U-layer connection, the above request may not be made. For example, when the standby time is predetermined, the above request may not be made. In step ST2341, the same processing may be performed on the standby request for stopping the U-layer connection from the inner AMF to the inner SMF. For example, when the inner AMF notifies the inner SMF of the standby time for stopping the U-layer connection, the inner AMF may not make the request. For example, when the standby time is predetermined, the inner AMF may not make the request. Thereby, for example, signaling in the communication system can be reduced.

[0389] It can be set to stop with the inner U layer without stopping the outer U layer. For example, in the outer NW, only the IPsec connection between the UE and the N3IWF can be released. The outer AMF can use the outer U layer stop request from the UE to instruct the N3IWF to release the AN resources accompanying the PDU session. It can be set that the outer AMF does not request the outer U layer stop to the outer SMF. Therefore, for example, the inner U layer stop can be performed quickly.

[0390] As described above, the outer AMF can perform implicit deregistration of the UE. Therefore, for example, restart after the inner U-layer is stopped can be performed quickly.

[0391] The outer UPF can send downlink data for the UE to the N3IWF, and the N3IWF can maintain the downlink data. For example, the above actions can be performed when the inner U layer is stopped and the outer U layer is not stopped. The N3IWF can use the reception of the downlink data to re-establish the IPsec connection with the UE. For the re-establishment of the IPsec connection between the N3IWF and the UE, for example, the method disclosed in variant example 5 of implementation example 1 can be applied. The reopening of the IPsec connection between the N3IWF and the UE can be performed after the inner U layer is reopened. Therefore, for example, the reopening after the inner U layer is stopped can be performed quickly.

[0392] As another example, the outer UPF may maintain downlink data for the UE. The outer UPF may notify the outer SMF of the generation of downlink data. The communication resumption between the outer UPF and the UE may be performed using the method disclosed in variant 2 of implementation example 1. Thus, for example, the memory usage in the N3IWF may be reduced.

[0393] There may be a PDU session that does not stop the U-layer connection. For example, regarding the inner PDU session used for sending and receiving C-layer data in the outer NW, it can be set to not stop the U-layer connection. The UE can notify the inner AMF of information about the PDU session. The inner AMF can notify the inner SMF of the information. Therefore, for example, C-layer communication in the outer NW can be performed stably.

[0394] The inner SMF can determine whether to notify the inner AMF of the inner U-layer stop. The inner SMF can use information about the outer NW connection to make this determination. The UE can notify the inner AMF of information about the outer NW. The inner AMF can notify the inner SMF of information about the outer NW. The notification from the UE to the inner AMF can be used to perform the notification from the inner AMF to the inner SMF. Thus, for example, signaling in the communication system can be reduced.

[0395] The outer PDU session can be released as the inner U layer is stopped. The outer U layer can be stopped as the inner PDU session is released. In the above case, this variant 4 can also be combined with variant 3 of implementation example 1. The UE can request the outer AMF to release the outer PDU session or stop the outer U layer. As a result, flexible applications in communication systems, for example, become possible.

[0396] According to this variation 4, the U-layer connection stop of the outer PDU session can be executed by stopping the U-layer connection of the inner PDU session. As a result, the efficiency in the communication system can be improved.

[0397] Modification 5 of Implementation Example 1. In variant 4 of implementation mode 1, a method for stopping a U-plane connection in a PDU session of a UE cascade-connected to multiple NWs is disclosed. In this variant 5, the related actions of the outer NW accompanying the RRC_INACTIVE transition of the UE are disclosed.

[0398] The outer NW may be released when the UE transitions to RRC_INACTIVE. The release of the outer NW may also be performed by the same method as in Embodiment 1. Therefore, for example, the memory usage in each device of the outer NW can be reduced.

[0399] Other solutions are disclosed. For the UE that has been transferred to RRC_INACTIVE, the outer NW may not be released.

[0400] In the above, the following problems occur. That is, for a UE connected to an outer NW via an inner NW, IPsec is used in an AN connection with the outer NW. Therefore, even after an RRC_INACTIVE transfer, a keepalive disclosed in non-patent document 28 (IETF RFC3706) is sent and received between the UE and the N3IWF. Therefore, due to the keepalive transmission from the N3IWF to the UE, paging from the RAN to the UE occurs, and the UE returns to RRC_CONNECTED. As a result, a problem occurs in which the amount of power consumption reduction of the UE is reduced.

[0401] The following discloses a solution to the above-mentioned problem.

[0402] The UE releases the AN connection with the outer NW with the RRC_INACTIVE transition. The UE can initiate the release of the IPsec connection with the N3IWF.

[0403] The UE requests the outer AMF to release the AN connection with the outer NW. For this request, the NAS signaling disclosed in non-patent document 26 (TS24.501) may also be used. New NAS signaling may be set, such as NAS signaling for service suspend request. The above NAS signaling may include information indicating that the UE will transfer to RRC_INACTIVE. This information may be included in the request, for example, as a parameter of the reason (Cause) in the request. The outer AMF recognizes that the UE transfers to RRC_INACTIVE by receiving the request. The outer AMF may maintain the NAS connection with the UE.

[0404] The outer AMF may send a response to the request to the UE. For sending the response, the NAS signaling disclosed in non-patent document 26 (TS24.501) may also be used. New NAS signaling may be set, such as NAS signaling of a service suspend request process response (Service suspend Ack).

[0405] The outer AMF may request the N3IWF to stop the N2 connection between the present AMF and the N3IWF regarding the UE. For this request, the N2 signaling described in non-patent document 24 (TS 38.413), such as the N2 UEContext ReleaseCommand, may be used. New N2 signaling, such as the N2 UE SuspendCommand, may be set and used. The above-mentioned N2 signaling may include information about the UE, such as an identifier of the UE. The above-mentioned N2 signaling may include information indicating that the N2 connection related to the UE will be stopped. Therefore, for example, unnecessary signaling between the outer NW and the UE may be prevented, thereby reducing the amount of signaling in the communication system. At the same time, useless recovery to RRC_CONNECTED in the UE due to the signaling may be prevented, thereby reducing the power consumption of the UE.

[0406] The request from the outer AMF to the N3IWF can be made, for example, by using the UE to connect to the outer NW via the inner NW. Thus, for example, in the design of the communication system, the previous design can be used, and as a result, the complexity of the design in the communication system can be avoided.

[0407] As another example, the outer AMF may not request the N3IWF to stop the N2 connection between the AMF and the N3IWF related to the UE. Thus, for example, the amount of signaling in the communication system can be reduced.

[0408] N3IWF releases the AN connection with the UE. This release of the AN connection may be, for example, the release of IPsec settings. N3IWF may notify the UE to release the IPsec settings. The UE may use this notification to release the IPsec settings with N3IWF. The UE may notify N3IWF to release the IPsec settings. The release of the IPsec settings between N3IWF and the UE may be performed in the same manner as disclosed in Implementation 1. After performing this notification to N3IWF, the UE transitions to RRC_INACTIVE.

[0409] The outer UPF, outer SMF, outer AMF and / or N3IWF may maintain an outer PDU session related to the UE that has been transferred to RRC_INACTIVE. For example, the N3IWF and / or outer UPF may maintain resources on the N2 interface used by the outer PDU session. As another example, the outer SMF may maintain settings related to the outer PDU session. Thus, for example, when the UE recovers from RRC_INACTIVE to RRC_CONNECTED, the recovery action can be performed quickly.

[0410] The N3IWF may notify the outer AMF of the restoration of the N2 connection between the present N3IWF and the outer AMF of the UE. For the notification, the N2 signaling described in non-patent document 24 (TS 38.413) may be used. New N2 signaling, such as N2 UE Resume Indication, may be set and used. The above N2 signaling may include information about the UE, such as an identifier of the UE. The above N2 signaling may include information indicating the restoration of the N2 connection related to the UE.

[0411] As another example, the outer AMF may not request the N3IWF to restore the N2 connection between the AMF and the N3IWF related to the UE. For example, the outer AMF may not request the restoration of the N2 connection without requesting the N3IWF to stop the N2 connection. Thus, for example, the amount of signaling in the communication system can be reduced.

[0412] The UE may notify an upper layer (e.g., a NAS layer) in the UE of information indicating that a transition indication to RRC_INACTIVE is received from the RAN. The notification may also be performed in the same manner as the method disclosed in Embodiment 1. For example, the UE may perform the notification immediately after the UE receives the transition indication from the RAN. For example, the UE may issue the notification before the 60 millisecond delay described in Section 5.3.8.3 of Non-Patent Document 27 (TS 38.331).

[0413] As another example, it can be set that the UE does not request the outer AMF to release the AN connection with the outer NW. The UE can initiate the release of the AN connection with the N3IWF. For example, the UE can release the IPsec connection with the N3IWF. The UE can notify the N3IWF to release IPsec. The N3IWF can use the notification to release the IPsec settings with the UE. The N3IWF can notify the UE to release IPsec. As a result, for example, the amount of signaling in the communication system can be reduced.

[0414] As in Embodiment 1, the delay time may also be changed. For example, the delay time may be set to be greater than 60 milliseconds. Thus, for example, the RRC connection may be prevented from being released before the AN connection between the UE and the N3IWF is released.

[0415] The inner AMF may change the delay time, and the RAN may change the delay time, as in Embodiment 1. The method by which the inner AMF and / or the RAN change the delay time may also be the same as in Embodiment 1.

[0416] The UE may have a timer for managing the time until the RRC is stopped. The timer may be, for example, a timer for managing the delay time. The action associated with the timer may be the same as the RRC release disclosed in Implementation 1. Thus, for example, in the UE, the management of the RRC stop action becomes easy. The timer may be provided by the inner AMF or RAN. Thus, for example, in the AMF and / or RAN, the management of the RRC stop action becomes easy.

[0417] Fig.38 This is a sequence diagram showing a first example of an operation of releasing the outer AN in conjunction with RRC_INACTIVE transition, for a UE connected to the outer NW via the inner NW. Fig.38 An example is shown in which the outer AN connection is an IPsec connection and the N3IWF initiates the IPsec setup release. Fig.38 In, with Figure 14 to Figure 15 and Figure 28 to Figure 29 The same processes are denoted by the same step numbers, and common descriptions are omitted.

[0418] exist Fig.38 In step ST2401 shown, the RAN instructs the UE to transfer to RRC_INACTIVE. For this instruction, the RRC release (RRCRelease) signaling shown in non-patent document 27 (TS 38.331) can be used. The signaling may include information to stop the UE. As in embodiment 1, the signaling may include information about the standby time until the transfer to RRC_INACTIVE.

[0419] exist Fig.38In step ST2405 shown, the UE requests the outer AMF to release the AN connection with the outer NW. For this request, the NAS signaling disclosed in non-patent document 26 (TS24.501) can also be used. New NAS signaling, such as NAS signaling for service suspend request (Service suspend), can be set. The request in step ST2405 may include information indicating that the UE has transferred to RRC_INACTIVE. This information can be included in the request, for example, as a parameter of the reason (Cause) in the request.

[0420] exist Fig.38 In step ST2406 shown, the outer AMF sends a response to the request of step ST2405 to the UE. For sending the response, the NAS signaling disclosed in non-patent document 26 (TS24.501) can also be used. New NAS signaling, such as NAS signaling of service stop request process response (Service suspend Ack), can be set.

[0421] exist Fig.38 In step ST2407 shown, the outer AMF requests the N3IWF to stop the N2 connection between the present AMF and the N3IWF related to the UE. For this request, the N2 signaling described in non-patent document 24 (TS 38.413), such as the N2UEContext Release Command, can be used. New N2 signaling, such as the N2 UE Suspend Command, can be set and used. The request of step ST2407 may include information related to the UE, such as an identifier of the UE, or include information indicating that the N2 connection related to the UE will be stopped.

[0422] Fig.38 Steps ST1408 and ST1409 shown in FIG. Fig.14 same.

[0423] exist Fig.38 In step ST2415 shown, the UE transitions to RRC_INACTIVE according to the instruction received in step ST2401. The UE may transition to RRC_INACTIVE after sending step ST1409.

[0424] Fig.38 The actions after step ST2001 shown represent the actions of UE recovering from RRC_INACTIVE.

[0425] Fig.38 Step ST2001 shown is the same as Fig.28In step ST2420, the outer UPF notifies the N3IWF of the downlink data generated in step ST2001. The N3IWF may also retain the downlink data received in step ST2420. The N3IWF reopens the IPsec connection with the UE by receiving the downlink data in step ST2420.

[0426] exist Fig.38 In step ST2421 shown in FIG. 1 , the N3IWF sends a signaling to the inner UPF for establishing IPsec with the UE. In step ST2422, the inner UPF sends the signaling of step ST2421 to the RAN. The signaling of steps ST2421 and ST2422 can be the same as Fig.28 The same as step ST2008 in.

[0427] exist Fig.38 In step ST2423 shown, the RAN sends a paging to the UE. The paging transmission of step ST2423 may be performed based on step ST2422. In step ST2425, a process for RRC recovery is performed between the UE and the RAN. The process may include, for example, an RRC recovery request from the UE to the RAN, an RRC recovery indication from the RAN to the UE, and an RRC recovery completion from the UE to the RAN. In step ST2426, the UE recovers to RRC_CONNECTED.

[0428] exist Fig.38 In step ST2430 shown, the RAN sends the signaling for IPsec establishment sent by the N3IWF to the UE. The RAN can use the signaling of step ST2422 maintained by the RAN to send step ST2430.

[0429] Fig.38 Steps ST2036 and ST2037 shown are Fig.29 same.

[0430] exist Fig.38 In step ST2438 shown, the N3IWF requests the outer AMF to reopen the N2 connection between the N3IWF and the outer AMF related to the UE. For this notification, the N2 signaling described in non-patent document 24 (TS38.413) can be used. New N2 signaling, such as N2 UE ResumeIndication, can be set and used. The request of step ST2438 may include information related to the UE, such as an identifier of the UE, or include information indicating that the N2 connection related to the UE has been restored.

[0431] exist Fig.38In step ST2440 shown, N3IWF sends downlink data to UE. N3IWF may also send the downlink data using the data of step ST2420 maintained by N3IWF.

[0432] exist Fig.38 In FIG. 24, the outer AMF sends a response to the request of step ST2401 to the UE, but the response may not be sent. The UE can determine that the request of step ST2401 has been accepted by releasing the IPsec settings in steps ST1408 and ST1409. Thus, for example, the amount of NAS signaling between the UE and the outer AMF can be reduced.

[0433] Other solutions are disclosed. The UE may initiate the release of the IPsec settings. The UE may release the IPsec settings between the UE and the N3IWF by receiving an indication of a transition to RRC_INACTIVE from the RAN. The UE may notify the N3IWF of the release. The N3IWF may release the IPsec settings between the UE and the N3IWF by receiving the notification. Therefore, for example, signaling of an N2 stop from the outer AMF to the N3IWF is not required. As a result, the amount of signaling in the N2 interface can be reduced.

[0434] Fig.39 This is a sequence diagram showing a second example of the operation of releasing the outer AN in association with the RRC_INACTIVE transition, regarding a UE connected to the outer NW via the inner NW. Fig.39 An example is shown in which the outer AN connection is an IPsec connection and the UE initiates the IPsec setup release. Fig.39 In, with Figure 14 to Figure 15 , Figure 18 to Figure 19 , Figure 28 to Figure 29 and Fig.38 The same processes are denoted by the same step numbers, and common descriptions are omitted.

[0435] Fig.39 Steps ST2401 to ST2406 shown are similar to Fig.38 same.

[0436] exist Fig.39 In steps ST1604 and ST1605 shown in FIG. Fig.18 Similarly, before notifying the UE of the IPsec setting release from the N3IWF, the IPsec setting release is notified from the UE to the N3IWF.

[0437] Fig.39 Steps ST2415 to ST2440 shown are similar to Fig.29 and Fig.38 same.

[0438] Other solutions are disclosed. The UE may not maintain the connection with the outer NW connected via the inner NW. The period of maintaining the connection may be set to infinity. As another example, the signaling of the Tracking Area Update (Tracking Area Update) and / or the RAN Notification Area Update (RAN Notification Area update, RNA update) in the UE may be used to maintain the connection. In the above, the UE may not issue a service stop request to the inner AMF. Thus, for example, the amount of signaling in the communication system can be reduced.

[0439] In the case where the network between the UE and the N3IWF is a 3GPP access, such as an inner NW, the above-mentioned non-implementation of maintaining the connection, setting the period of maintaining the connection to infinity, and / or using the signaling of the tracking area update and / or the RAN notification area update to maintain the connection can be performed. In the case where a cascade connection is performed between the UE and the inner NW and the outer NW, the above-mentioned non-implementation of maintaining the connection, setting the period of maintaining the connection to infinity, and / or using the signaling of the tracking area update and / or the RAN notification area update to maintain the connection can be performed. The UE can notify the N3IWF of information about the network between the UE and the N3IWF. The UE can notify the N3IWF of information about the above-mentioned cascade connection, such as information about whether there is a cascade connection. As another example, the UE can notify the outer AMF of the information. The outer AMF can transmit the information to the N3IWF. For example, the outer AMF can use the fact that the UE is connected to the outer NW via the inner NW to transmit the information to the N3IWF. The subject that determines whether to not implement the above-mentioned connection maintenance can be the UE, the N3IWF, or the outer AMF. Similarly, the subject that determines whether to set the connection maintenance period to infinity can be the UE, the N3IWF, or the outer AMF. The subject used to determine whether to use the signaling of the tracking area update and / or the RAN notification area update to perform the connection maintenance action can be the UE, the N3IWF, or the outer AMF. Therefore, for example, the signaling amount between the UE and the N3IWF can be reduced.

[0440] According to this modification example 5, it is possible to suppress the N3IWF from sending a keep-alive message to the UE in the RRC_INACTIVE state. Therefore, it is possible to suppress the UE from returning to RRC_CONNECTED to send and receive the keep-alive message. As a result, the power consumption of the UE can be reduced.

[0441] Modification 6 of Implementation Example 1. In the fifth variation of the first embodiment, the operation of the outer NW associated with the RRC_INACTIVE transition of the UE connected to a plurality of NWs in cascade connection is disclosed. In the sixth variation, a method of updating the configuration associated with the UE is disclosed.

[0442] The UE notifies the outer AMF of information related to the setting update in the inner NW. The notification by the UE can be set to be performed, for example, when the inner AMF decides to update the UE settings.

[0443] The UE may use NAS signaling to issue the notification. The NAS signaling may also be the NAS signaling shown in non-patent document 25 (TS23.502). New NAS signaling may be set and used, such as UE configuration update notification.

[0444] The UE may include in the notification information about the NW for which the setting has been updated, such as information indicating that it is an inner NW. The UE may include in the notification information about the updated setting. The updated setting may include, for example, parameters disclosed in Section 8.2.19 of Non-Patent Document 26 (TS24.501). For example, the updated setting may include information about the NW slices allowed in the NW.

[0445] The outer AMF can use this notification to update the UE settings in the outer NW. Therefore, for example, it is possible to prevent inconsistencies between the inner NW and the outer NW for the settings of the same UE. As a result, for example, the same QoS can be ensured between the inner NW and the outer NW.

[0446] The outer AMF may also use NAS signaling, such as the signaling of the UEConfiguration Update command described in non-patent document 25 (TS23.502) to perform the update. The signaling may include information about the reason for the update. The reason for the update may be, for example, an update of the UE configuration in another NW.

[0447] The UE may use the reason included in the notification to determine whether it is necessary to notify the AMF of another NW of the setting update in one NW. For example, in the case where the reason is the setting update in another NW, the UE may not notify the AMF of the other NW of the setting update of the UE. Therefore, for example, when the UE setting update in the outer NW is performed by the UE setting update in the inner NW, the UE setting update in the outer NW can be prevented from causing the UE setting update in the inner NW. That is, the loop of UE setting update can be prevented.

[0448] The outer AMF can notify the N3IWF of the updated UE settings. For this notification, for example, N2 signaling can be used. The N3IWF can use this notification to change the IPsec settings related to the setting update. For example, the N3IWF can reset the sub-SA of IPsec. Therefore, for example, according to the setting update of the inner NW, the updated QoS can be met even in the outer NW.

[0449] The notification from the outer AMF to the N3IWF can be performed, for example, by using the fact that the UE is connected to the outer NW via the inner NW. The notification from the outer AMF to the N3IWF can be performed using information about the setting update of the UE in the inner NW, for example, the reason included in the notification from the UE is the information about the setting update in the inner NW. Thus, for example, in the design of the communication system, the previous design can be used, and as a result, the complexity of the design of the communication system can be avoided.

[0450] As another example, the UE may change the IPsec settings related to the setting update. For example, the UE may reconfigure the sub-SA of IPsec. Thus, for example, N2 signaling from the outer AMF to the N3IWF may be reduced.

[0451] Fig.40 This is a sequence diagram showing an operation of notifying the outer NW of UE setting update in the inner NW, regarding a UE connected to the outer NW via the inner NW. Fig.40 An example is shown in which the UE notifies the outer AMF of setting updates in the inner NW.

[0452] exist Fig.40 In step ST2600 shown, the inner AMF determines the update of the UE settings.

[0453] exist Fig.40 In the process ST2601 shown, the inner NW settings in the UE are updated. The process ST2601 is composed of steps ST2602 to ST2606.

[0454] exist Fig.40In step ST2602 shown, the inner AMF sends a UE configuration update indication to the UE. The inner AMF may also use NAS signaling, such as the UEConfiguration Update command described in non-patent document 25 (TS23.502), to make the indication. The signaling may include information about the reason for the update. The UE may update the settings of the UE in the inner NW according to the indication in step ST2602. In step ST2603, the UE notifies the inner AMF that the configuration update of the UE is complete. The UE may also use NAS signaling, such as the UEConfiguration Update complete described in non-patent document 25 (TS23.502), to make the notification. In step ST2604, the UE notifies the lower layer, such as the RRC layer, of the configuration update.

[0455] exist Fig.40 In step ST2605 shown, the inner AMF notifies the inner UDM that the UE has completed the setting change. In this notification, for example, the Nudm_SDM_Info service operation described in Section 5.2.2.3.6 of Non-Patent Document 25 (TS23.502) may also be used. In step ST2606, the inner AMF notifies the RAN of the update of the UE setting. For this notification, N2 signaling may be used.

[0456] exist Fig.40 In step ST2610 shown, the UE notifies the outer AMF that the inner NW setting of the UE has been updated. In the notification of step ST2610, NAS signaling, such as the NAS signaling shown in non-patent document 25 (TS23.502), may also be used. New NAS signaling, such as UE configuration update notification, may be set. The notification of step ST2610 may include information about the NW whose settings are updated, such as information indicating that it is an inner NW. The notification of step ST2610 may include information about the updated settings. The updated settings may include, for example, parameters disclosed in Section 8.2.19 of non-patent document 22 (TS23.501). For example, the updated settings may include information about the NW slices allowed in the NW.

[0457] exist Fig.40In step ST2614 shown, the outer AMF may decide to update the UE settings. The UE settings that the outer AMF decides to update may be UE settings related to the outer NW. The outer AMF may use the notification of step ST2610 to perform step ST2614.

[0458] exist Fig.40 In the process ST2615 shown, the inner NW settings in the UE are updated. The process ST2615 is composed of steps ST2616 to ST2625.

[0459] exist Fig.40 In steps ST2616, ST2617, ST2618, and ST2619 shown, the same processing as steps ST2602, ST2603, ST2604, and ST2605 is performed between the outer AMF, the outer UDM, and the UE. In step ST2620, the outer AMF notifies the N3IWF of the update of the UE settings. For this notification, N2 signaling can be used. In step ST2625, the IPsec setting change is performed between the N3IWF and the UE.

[0460] Fig.40 The indication of step ST2616 shown may include information about the reason for the update. The reason for the update may be, for example, an update of the UE settings in the inner NW. The UE may decide not to notify the inner AMF of the update of the settings in the outer NW based on the reason included in the notification. Therefore, for example, when the UE settings in the outer NW are updated by the UE settings in the inner NW, the UE settings in the outer NW may be prevented from causing the UE settings in the inner NW to be updated. That is, a cycle of UE settings updates can be prevented.

[0461] The same method can also be applied to the case where the outer AMF updates the UE settings. The UE can notify the inner AMF of information about the setting update in the outer NW. This notification from the UE to the inner NW can be the same as the notification of information about the setting update in the inner NW from the UE to the outer NW described above. Therefore, for example, the settings of the inner NW can be updated by reflecting the setting update of the outer NW. As a result, for example, the same QoS can be ensured between the inner NW and the outer NW.

[0462] The UE configuration update from the inner AMF to the UE may include information about the reason for the update. The reason for the update may be, for example, an update of the UE configuration in another NW. Thus, for example, a loop of the above-mentioned UE configuration update can be prevented.

[0463] Fig.41 This is a sequence diagram showing an operation of notifying the inner NW of UE setting update in the outer NW, regarding a UE connected to the outer NW via the inner NW. Fig.41 An example is shown in which the UE notifies the inner AMF of the setting update in the outer NW. Fig.41 In, with Fig.40 The same processing is assigned the same number, and common description is omitted.

[0464] exist Fig.41 In step ST2701 shown, the outer AMF decides to update the UE settings.

[0465] Fig.41 The process ST2615 shown is the same as Fig.40 same.

[0466] exist Fig.41 In step ST2710 shown, the UE notifies the inner AMF that the outer NW setting of the UE has been updated. For the notification of step ST2710, the same signaling as step ST2610 can be used. The notification of step ST2710 can include the same information as in step ST2610.

[0467] exist Fig.41 In step ST2711 shown, the inner AMF may decide to update the UE settings. The UE settings updated by the inner AMF may be UE settings related to the inner NW. The inner AMF may perform step ST2711 using the notification of step ST2710.

[0468] Fig.41 The process ST2601 shown is the same as Fig.40 same.

[0469] The UE can notify the outer AMF of information about the QoS flow in the inner NW. The information can be an identifier of the QoS flow or a 5QI disclosed in non-patent document 22 (TS23.501). For example, the information can be included in a notification to the outer AMF regarding a UE setting update in the inner NW. The outer AMF can use the information for a UE setting update in the outer NW. The UE can also notify the inner AMF of the same information. Therefore, for example, a situation in which QoS inconsistency between an outer PDU session and an inner PDU session can be prevented. As a result, QoS in the communication system can be ensured.

[0470] This notification can be used for PDU session establishment or PDU session change (PDU session modification). The UE can notify the outer AMF of information about the QoS flow in the inner NW. The information can be an identifier of the QoS flow or a 5QI disclosed in non-patent document 22 (TS23.501). The outer AMF can transmit the information to the outer SMF. The outer SMF can use the information to establish an outer PDU session. The UE can also notify the inner AMF of the same information. Therefore, for example, a situation in which the QoS is inconsistent between the outer PDU session and the inner PDU session can be prevented. As a result, the QoS in the communication system can be ensured.

[0471] The outer NW and the inner NW can use the same or duplicate information about the NW slice. This information is, for example, NSSAI. Therefore, for example, the same QoS can be ensured in the inner NW and the outer NW, while at the same time improving the efficiency of the communication system.

[0472] Information indicating the correspondence between the inner PDU session and the outer PDU session may be set. For example, the information may be information about the inner PDU session used in (or included in) the outer PDU session. The UE may notify the inner AMF of the information, or may notify the outer AMF. The inner AMF may notify the inner SMF of the information. The outer AMF may notify the outer SMF of the information. The inner SMF may notify the inner UPF of the information. The outer SMF may notify the outer UPF of the information. Therefore, for example, it is possible to prevent resources from being repeatedly ensured in each of the inner PDU session and the outer PDU session that uses the inner PDU session. As a result, the memory usage in each device of the communication system may be reduced, and the efficiency in the communication system may be improved.

[0473] As another example, information indicating the correspondence between the NW slice of the inner NW and the NW slice of the outer NW may be set. Information indicating the correspondence between the QoS flow in the inner NW and the QoS flow in the outer NW may be set. The subject of notifying the information and / or the notification destination of the information may also be the same as above. Therefore, the same effect as above can be obtained.

[0474] The method disclosed in this variant 6 can be used in the NW registration process of the UE, and can also be used in the service request process. For example, the UE can include information about the UE settings in the inner NW in the registration request (RegistrationRequest) sent to the outer AMF via the N3IWF. As another example, the UE can include information about the UE settings in the inner NW in the service request (Service Request) sent to the outer AMF via the N3IWF. The outer AMF can use this information to determine the UE settings in the outer NW. Therefore, for example, the outer AMF can quickly establish NW settings without inconsistent settings between the inner NW and the outer NW.

[0475] According to the sixth modification, it is possible to prevent the setting inconsistency between the inner NW and the outer NW.

[0476] Implementation Method 2 In Embodiment 1 to Modification 6 of Embodiment 1, processes related to UE cascade-connected to a plurality of NWs are disclosed. In this Embodiment 2, a method for state management of the UE is disclosed.

[0477] The UE has a state for the inner NW and a state for the outer NW. The above state can be, for example, a CM (Connection Management) state, an RM (Registration Management) state, or a 5G MM (5G Mobility Management) state described in Non-Patent Document 26 (TS24.501).

[0478] The CM states may include CM-IDLE and CM-CONNECTED. A UE in CM-IDLE state may be a UE that has not established a NAS signaling connection with the AMF. A UE in CM-IDLE state may perform cell selection and / or cell reselection, and may also perform PLMN selection. A UE in CM-CONNECTED state may be a UE that has established a NAS signaling connection with the AMF. An AMF in CM-IDLE state may not establish NAS signaling with the UE. An AMF in CM-CONNECTED state may establish NAS signaling with the UE.

[0479] The RM state may include RM-DEREGISTERED and RM-REGISTERED. The UE in the RM-DEREGISTERED state may be a UE that has not registered with the network. The network may be a PLMN or an NPN. The same applies below. The UE may attempt to register with the network selected by the UE. The UE in the RM-REGISTERED state may be a UE registered with the network. The UE may also update the registration information periodically. The registration information may also be, for example, the location information of the UE. The AMF in the RM-DEREGISTERED state may accept or reject the initial registration request from the UE. The AMF in the RM-REGISTERED state may start a timer for implicit deregistration (Implicit Deregistration timer).

[0480] The state used by the inner NW may not be affected by the establishment / release of the connection of the outer NW, nor may it be affected by the establishment / release of the registration of the outer NW. For example, a UE that is CM-CONNECTED in the inner NW may remain CM-CONNECTED without relying on the establishment / release of the connection of the outer NW. A UE that is RM-REGISTERD in the inner NW may remain RM-REGISTERED without relying on the registration / release of the outer NW.

[0481] The state used for the inner NW can be transferred at least through the connection establishment / release of the inner NW, and can also be set to be transferred at least through the registration establishment / release of the inner NW. For example, a UE that is CM-CONNECTED in the inner NW can be transferred to CM-IDLE at least through the connection release of the inner NW. A UE that is CM-IDLE in the inner NW can be transferred to CM-CONNECTED at least through the connection establishment of the inner NW. The same is true for the RM state. For example, a UE that is RM-REGISTERD in the inner NW can be transferred to RM-DEREGISTERED at least through the registration release of the inner NW. A UE that is RM-DEREGISTERED in the inner NW can be transferred to RM-REGISTERD at least through the registration establishment of the inner NW.

[0482] The state used by the outer NW can be transferred with the release of the connection of the inner NW, or it can be set to transfer with the deregistration of the inner NW. For example, a UE that is CM-CONNECTED in the outer NW can be transferred to CM-IDLE by releasing the connection of the inner NW. A UE that is RM-REGISTERD in the outer NW can be transferred to RM-DEREGISTERED by deregistration of the inner NW.

[0483] Fig.42 and 43 The diagram shows the state transition of a UE connected to an outer NW via an inner NW. Fig.42 shows the CM state about the inner NW, Fig.43 The CM state with respect to the outer NW is shown.

[0484] exist Fig.42 In the case where a UE that is CM-IDLE in the inner NW is at least connected to the inner NW, for example, when at least an AN signaling connection in the inner NW is established, it is transferred to CM-CONNECTED.

[0485] exist Fig.42 In the CM-CONNECTED state, a UE in the inner NW maintains the CM state even when only the connection to the outer NW is established, for example, when the AN signaling in the outer NW is established / released. A UE in the CM-CONNECTED state in the inner NW transitions to CM-IDLE when at least the AN signaling connection in the inner NW is released.

[0486] exist Fig.43 In the case where a UE that is CM-IDLE in the outer NW is at least connected to the outer NW, for example, when at least an AN signaling connection in the outer NW is established, it is transferred to CM-CONNECTED.

[0487] exist Fig.43 In the embodiment, a UE that is CM-CONNECTED in the outer NW is transferred to CM-IDLE when the connection of the inner NW and / or the outer NW is released, for example, when the AN signaling connection in the inner NW and / or the outer NW is released.

[0488] exist Fig.42 and Fig.43 The CM state is shown in the figure, but the same is true for the RM state. Therefore, for example, even in the RM state, it is possible to prevent the states of the UE, the inner AMF, and the outer AMF from being inconsistent, and as a result, it is possible to prevent malfunctions in the communication system.

[0489] Other solutions are disclosed. The states for the inner NW and the outer NW are unified. For example, the CM state of the UE may be transferred to CM-CONNECTED by establishing a connection with the inner NW, and may be transferred to CM-IDLE by releasing the connection with the inner NW. As another example, the CM state of the UE may be CM-CONNECTED only when a connection is established between the inner NW and the outer NW, and may be CM-IDLE in other cases. The same is true for the RM state.

[0490] As another example of unifying the states for the inner NW and the outer NW, a state indicating that a cascade connection is being performed may be added. For example, the UE may be set to CM-IDLE when the connection with both the inner NW and the outer NW is released. The UE may be set to CM-CONNECTED when a connection is established with the inner NW. The UE may be set to an increased state, such as CM-CASCADE-CONNECTED, when connections with both the inner NW and the outer NW are established. Therefore, for example, the number of state machines in the UE may be reduced, and as a result, the memory usage in the UE may be reduced. The same is true for the RM state. Therefore, for example, the number of RM state machines in the UE may be reduced, and as a result, the same effect as described above is obtained.

[0491] Fig.44 FIG. 4 is a diagram showing another example of state transition of a UE connected to an outer NW via an inner NW. Fig.44 In the UE, there are three states: CM-IDLE, CM-CONNECTED and CM-CASCADE-CONNECTED.

[0492] exist Fig.44 In the case where a UE in CM-IDLE establishes a connection with the inner NW, for example, when an AN signaling connection is established in the inner NW, the UE is transferred to CM-CONNECTED.

[0493] exist Fig.44 In the case where a CM-CONNECTED UE establishes a connection with an outer NW, for example, when an AN signaling connection is established in the outer NW, the state is transferred to CM-CASCADE-CONNECTED. When a CM-CONNECTED UE has a connection with an inner NW released, for example, when an AN signaling connection is released in the inner NW, the state is transferred to CM-IDLE.

[0494] exist Fig.44In the case where the connection of the UE in CM-CASCADE-CONNECTED to the outer NW is released, for example, when the AN signaling connection in the outer NW is released, the UE is transferred to CM-CONNECTED. In the case where the connection of the UE in CM-CASCADE-CONNECTED to the inner NW is released, for example, when the AN signaling connection in the inner NW is released, the UE is transferred to CM-IDLE.

[0495] exist Fig.44 CM state is shown in FIG, but the same is true for RM state. Therefore, for example, for RM state, the number of state machines can be reduced, and as a result, the memory usage in the UE can be reduced.

[0496] AMF may have a unified state for inner NW and outer NW. For example, the unified state may be possessed by the inner AMF, by the outer AMF, or by both the inner AMF and the outer AMF. Thus, for example, the same state machine may be provided between the UE, the inner AMF, and the outer AMF, with the result that design complexity in the communication system may be avoided. Therefore, for example, a situation in which the states of the UE, the inner AMF, and the outer AMF are inconsistent may be prevented, with the result that malfunctions in the communication system may be prevented.

[0497] The UE can notify the inner AMF of information about the outer NW. This information can be, for example, the same as the information disclosed in Implementation 1, and can also include information related to the state of the outer NW of this UE. The UE can notify this information through NAS signaling, for example, in the same way as Implementation 1. The inner AMF can use this information to update the state of this AMF related to the UE. Therefore, for example, it is possible to prevent the state inconsistency between the UE, the inner AMF and the outer AMF, as a result, it is possible to prevent malfunctions in the communication system.

[0498] The UE may notify the outer AMF of information about the inner NW. The information may be the same as the above information, for example. Thus, for example, the same effect as above can be obtained.

[0499] As another example of unifying the states for the inner NW and the outer NW, a parameter regarding the number of network connection levels of the UE may be added. For example, in the case where the UE is connected only to the inner NW, the value of this parameter in the CM state of the UE is set to 1, and in the case where the UE is connected to the inner NW and the outer NW, the value of this parameter is set to 2. In the above, in the case of connecting to an NW further out than the outer NW, the value of this parameter may be set to 3. This parameter may be set in the RM state. This parameter may be set in the CM state of the AMF, or may be set in the RM state of the AMF. Therefore, for example, the complexity of state management in cascade connections with more than three networks may be avoided.

[0500] Other solutions are disclosed. The state of the outer NW may not be affected by the establishment / release of the connection of the inner NW, and may not be affected by the establishment / release of the registration of the inner NW. For example, the connection with the outer NW may be maintained when the inner NW connection is released, and the registration with the outer NW may be maintained when the inner NW registration is released. Thus, for example, the flexibility in the communication system may be improved.

[0501] The method disclosed in this embodiment 2 can also be applied to the 5GMM state in non-patent document 26 (TS24.501). Therefore, for example, even for the 5GMM state, the number of state machines can be reduced, and as a result, the memory usage in the UE can be reduced.

[0502] According to the second embodiment, the number of state machines in the UE can be reduced, and as a result, the memory usage in the UE can be reduced. In addition, the inconsistency between the states of the UE, the outer AMF, and the inner AMF can be prevented, and as a result, malfunctions in the communication system can be prevented. In addition, by preventing the malfunction, it is possible to prevent the start of processing in each device of the communication system from being delayed from the timing that should have been performed.

[0503] The above-mentioned embodiments and their modifications are merely examples, and the embodiments and their modifications can be freely combined. In addition, arbitrary components of the embodiments and their modifications can be appropriately changed or omitted.

[0504] For example, in each of the above embodiments and their variations, a subframe is an example of a time unit for communication in a fifth-generation base station communication system. It may also be a scheduling unit. In each of the above embodiments and their variations, processing recorded in subframe units may be performed in TTI units, time slot units, sub-time slot units, and mini-time slot units.

[0505] The present disclosure has been described in detail, but the above description is in all aspects illustrative and not restrictive, and numerous modifications not shown are conceivable. Description of symbols

[0506] 200, 210 are communication systems, 202 are communication terminal devices, and 203 are base station devices.

Claims

1. A communication terminal device connected to a plurality of networks, wherein: The plurality of networks include a first network including a user plane function (UPF) and a second network. The communication terminal device is connected to the first network and is connected to the second network via the user plane function of the first network, The communication terminal device transmits, to the second network, signaling for releasing a connection between the communication terminal device and the second network.

2. The communication terminal device according to claim 1, wherein: The communication terminal device releases the connection between the communication terminal device and the second network while maintaining the connection between the communication terminal device and the first network.

3. The communication terminal device according to claim 2, wherein: The communication terminal device releases the connection between the communication terminal device and the second network while maintaining a protocol data unit (PDU) session between the communication terminal device and the first network.

4. The communication terminal device according to claim 1, wherein: The second network includes a non-3GPP interworking function (N3IWF: None-GPP Interworking Function) and an access / mobility management function (AMF: Access and Mobility Management Function), The communication terminal device is connected to the access / mobility management function via the user plane function of the first network and the non-3GPP interworking function of the second network, The communication terminal device sends the signaling to the access / mobility management function.

5. The communication terminal device according to claim 4, characterized in that The communication terminal device establishes an access network (AN: Access Network) connection in the second network with the non-3GPP interworking function.

6. The communication terminal device according to claim 5, characterized in that The non-3GPP interworking function sends information related to the release of the access network connection to the access / mobility management function.

7. The communication terminal device according to claim 6, characterized in that The second network also includes a session management function (SMF: Session Management Function), The access / mobility management function transmits information on the termination of a user plane connection in a protocol data unit (PDU) session between the communication terminal device and the second network to the session management function.

8. The communication terminal device according to claim 1, wherein: The communication terminal device starts releasing the Internet Protocol Security (IPsec) setting.

9. The communication terminal device according to claim 1, wherein: The second network includes a non-3GPP interworking function (N3IWF: None-GPP Interworking Function) and an access / mobility management function (AMF: Access and Mobility Management Function), The communication terminal device is connected to the access / mobility management function via the user plane function of the first network and the non-3GPP interworking function of the second network, The non-3GPP interworking function sends a signaling for releasing the connection between the communication terminal device and the second network to the access / mobility management function.

10. The communication terminal device according to claim 1, wherein: The communication terminal device independently has a connection management (CM: Connection Management) state in the first network and a connection management state in the second network.

11. The communication terminal device according to claim 1, wherein: The communication terminal device independently has a registration management (RM: Registration Management) state in the first network and a registration management state in the second network.

12. The communication terminal device according to claim 1, wherein: The first network is a public land mobile network (PLMN: Public Land Mobile Network), The second network is an independent non-public network (NPN: Non Public Network).

13. The communication terminal device according to claim 1, wherein: The first network is an independent non-public network (NPN: Non Public Network), The second network is a public land mobile network (PLMN: Public Land Mobile Network).

14. A communication system comprising a communication terminal device connected to a plurality of networks, wherein: The plurality of networks include a first network including a user plane function (UPF) and a second network. The communication terminal device is connected to the first network and is connected to the second network via the user plane function of the first network, The communication terminal device transmits, to the second network, signaling for releasing a connection between the communication terminal device and the second network.

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