Method and user equipment for fallback for voice call from 5G mobile communication to 4G

Abstract

An embodiment of the present description provides a method for performing a fallback operation for a voice call, if a UE performed only a single registration, in an environment in which an N26 interface is not provided between an access and mobility management function (AMF) and a mobility management entity (MME). The method can comprise the steps of: for transmission or reception of a voice call, the UE transmitting a service request message to the AMF; and receiving from the AMF a response message to the service request message. The response message can comprise an indicator which indicates a fallback operation without the N26 interface. The method can comprise a step for transmitting an attach request message, which comprises a PDN connection request message, to the MME on the basis of the indicator.

Claims

1. A method of performing a fallback operation of a voice call when only a single-registration is performed in an environment in which an N26 interface between an Access and Mobility Management Function (AMF) and a Mobility Management Entity (MME) is not provided, the method performed by a user equipment (UE) and comprising: performing, by the UE, a Next Generation (NG) core registration procedure and an IP Multimedia Subsystem (IMS) registration procedure; determining, by the UE, a mobile orienting (MO) of a voice call; transmitting, by the UE, a service request message to the AMF for originating or terminating the voice call; receiving a service request reject message in response to the service request message from the AMF, wherein the service request reject message comprises information indicating a fallback operation without the N26 interface; transmitting a Tracking Area Update (TAU) request message to the MME before transmitting an attach request message; receiving from the MME a TAU reject message comprising an indicator indicating a packet data network (PDN) connection establishment procedure for handover is required, wherein the indicator is for Handover PDN Connection Setup Support; and transmitting, by the UE, the attach request message comprising a PDN connection request message to the MME based on the indicator.

2. The method of claim 1, wherein the attach request message comprises an indicator indicating that the attach request message is for handover.

3. The method of claim 1, further comprising: receiving information about an operation mode from a base station of an NG Radio Access Network (NG RAN); and determining whether to perform a fallback operation based on the information about the operation mode.

4. The method of claim 3, wherein the operation mode comprises: a first mode in which a base station of the NG RAN supports only access to an NG core; a second mode in which the base station of the NG RAN supports only access to a 4G Evolved Packet Core (EPC); and a third mode in which the base station of the NG RAN supports both access to the NG core and access to the 4G EPC.

5. A user equipment (UE) for performing a fallback operation of a voice call when only a single-registration is performed in an environment in which an N26 interface between an Access and Mobility Management Function (AMF) and a Mobility Management Entity (MME) is not provided, the UE comprising: a transceiver; and a processor configured to control the transceiver, wherein the processor is further configured to: perform a Next Generation (NG) core registration procedure and an IP Multimedia Subsystem (IMS) registration procedure, determine a mobile orienting (MO) of a voice call, transmit a service request message to the AMF for originating or terminating the voice call, receive a service request reject message in response to the service request message from the AMF, wherein the service request reject message comprises information indicating a fallback operation without the N26 interface; transmit a Tracking Area Update (TAU) request message to the MME before transmitting an attach request message, receive from the MME a TAU reject message comprising an indicator indicating a PDN connection establishment procedure for handover is required, wherein the indicator is for Handover PDN Connection Setup Support, and transmit the attach request message comprising a PDN connection request message to the MME based on the indicator.

6. The UE of claim 5, wherein the attach request message comprises an indicator indicating that the attach request message is for handover.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a diagram illustrating a structure of an evolved mobile communication network.

(2) FIG. 2 is a diagram illustrating an expected structure of next-generation mobile communication from a node viewpoint.

(3) FIG. 3a is a diagram illustrating an example of an architecture for implementing the concept of network slicing.

(4) FIG. 3b is a diagram illustrating another example of an architecture for implementing the concept of network slicing.

(5) FIG. 4a illustrates an architecture for interworking when an UE does not roam, and FIG. 4b illustrates an architecture for interworking when an UE roams.

(6) FIG. 5a illustrates a fallback operation of a mobile orienting (MO) call, and FIG. 5b illustrates a fallback operation of a mobile terminating (MT) call.

(7) FIG. 6 is a diagram illustrating a method of selecting a fallback method during a registration procedure according to a first scheme of a first disclosure of the present specification.

(8) FIG. 7 is a diagram illustrating a method in which an AMF selects a fallback method at a time point in which an UE transmits a service request message for a MO/MT call according to a second scheme of a first disclosure of the present specification.

(9) FIG. 8 is a diagram illustrating a method in which an NG RAN selects a fallback scheme by a request of an AMF at a time point in which an UE transmits a service request message for a MO/MT call according to a second scheme of a first disclosure of the present specification.

(10) FIG. 9 is a flowchart illustrating a method in which a UE initiates a PDN connection request procedure for a fallback operation according to a first scheme of a second disclosure of the present specification.

(11) FIG. 10 is a flowchart illustrating a method in which an AMF requests a PDN connection request procedure to an NG RAN for a fallback operation according to a second scheme of a second disclosure of the present specification.

(12) FIG. 11 is a flowchart illustrating an optimization method of minimizing delay according to a third scheme of a second disclosure of the present specification.

(13) FIG. 12 is a flowchart illustrating a method of obtaining information necessary for fallback determination according to a third disclosure of the present specification.

(14) FIG. 13 illustrates a method of determining whether to fall back when an operation mode of a base station is broadcasted according to a fourth disclosure of the present specification.

(15) FIG. 14 is a block diagram illustrating a configuration of a UE 100 and a network node according to an embodiment of the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

(16) The present invention is described in light of UMTS (Universal Mobile Telecommunication System) and EPC (Evolved Packet Core), but not limited to such communication systems, and may be rather applicable to all communication systems and methods to which the technical spirit of the present invention may apply. The technical terms used herein are used to merely describe specific embodiments and should not be construed as limiting the present invention. Further, the technical terms used herein should be, unless defined otherwise, interpreted as having meanings generally understood by those skilled in the art but not too broadly or too narrowly. Further, the technical terms used herein, which are determined not to exactly represent the spirit of the invention, should be replaced by or understood by such technical terms as being able to be exactly understood by those skilled in the art. Further, the general terms used herein should be interpreted in the context as defined in the dictionary, but not in an excessively narrowed manner.

(17) The expression of the singular number in the specification includes the meaning of the plural number unless the meaning of the singular number is definitely different from that of the plural number in the context. In the following description, the term include or have may represent the existence of a feature, a number, a step, an operation, a component, a part or the combination thereof described in the specification, and may not exclude the existence or addition of another feature, another number, another step, another operation, another component, another part or the combination thereof.

(18) The terms first and second are used for the purpose of explanation about various components, and the components are not limited to the terms first and second. The terms first and second are only used to distinguish one component from another component. For example, a first component may be named as a second component without deviating from the scope of the present invention.

(19) It will be understood that when an element or layer is referred to as being connected to or coupled to another element or layer, it can be directly connected or coupled to the other element or layer or intervening elements or layers may be present. In contrast, when an element is referred to as being directly connected to or directly coupled to another element or layer, there are no intervening elements or layers present.

(20) Hereinafter, exemplary embodiments of the present invention will be described in greater detail with reference to the accompanying drawings. In describing the present invention, for ease of understanding, the same reference numerals are used to denote the same components throughout the drawings, and repetitive description on the same components will be omitted. Detailed description on well-known arts which are determined to make the gist of the invention unclear will be omitted. The accompanying drawings are provided to merely make the spirit of the invention readily understood, but not should be intended to be limiting of the invention. It should be understood that the spirit of the invention may be expanded to its modifications, replacements or equivalents in addition to what is shown in the drawings.

(21) In the drawings, user equipments (UEs) are shown for example. The UE may also be denoted a terminal or mobile equipment (ME). The UE may be a laptop computer, a mobile phone, a PDA, a smartphone, a multimedia device, or other portable device, or may be a stationary device such as a PC or a car mounted device.

Definition of Terms

(22) For a better understanding, the terms used herein are briefly defined before going to the detailed description of the invention with reference to the accompanying drawings.

(23) UE/MS is an abbreviation of User Equipment/Mobile Station, and it refers to a terminal device.

(24) An EPS is an abbreviation of an Evolved Packet System, and it refers to a core network supporting a Long Term Evolution (LTE) network and to a network evolved from an UMTS.

(25) A PDN is an abbreviation of a Public Data Network, and it refers to an independent network where a service for providing service is placed.

(26) A PDN-GW is an abbreviation of a Packet Data Network Gateway, and it refers to a network node of an EPS network which performs functions, such as the allocation of a UE IP address, packet screening & filtering, and the collection of charging data.

(27) A Serving gateway (Serving GW) is a network node of an EPS network which performs functions, such as mobility anchor, packet routing, idle mode packet buffering, and triggering an MME to page UE.

(28) An eNodeB is an eNodeB of an Evolved Packet System (EPS) and is installed outdoors. The cell coverage of the eNodeB corresponds to a macro cell.

(29) An MME is an abbreviation of a Mobility Management Entity, and it functions to control each entity within an EPS in order to provide a session and mobility for UE.

(30) A session is a passage for data transmission, and a unit thereof may be a PDN, a bearer, or an IP flow unit. The units may be classified into a unit of the entire target network (i.e., an APN or PDN unit) as defined in 3GPP, a unit (i.e., a bearer unit) classified based on QoS within the entire target network, and a destination IP address unit.

(31) An Access Point Name (APN) is the name of an access point that is managed in a network and provides to UE. That is, an APN is a character string that denotes or identifies a PDN. Requested service or a network (PDN) is accessed via P-GW. An APN is a name (a character string, e.g., internet.mnc012.mcc345.gprs) previously defined within a network so that the P-GW can be searched for.

(32) A PDN connection is a connection from UE to a PDN, that is, an association (or connection) between UE represented by an IP address and a PDN represented by an APN. It means a connection between entities (i.e., UE-PDN GW) within a core network so that a session can be formed.

(33) UE context is information about the situation of UE which is used to manage the UE in a network, that is, situation information including an UE ID, mobility (e.g., a current location), and the attributes of a session (e.g., QoS and priority)

(34) NAS (Non-Access-Stratum): A higher stratum of a control plane between a UE and an MME. The NAS supports mobility management, session management, IP address management, etc., between the UE and the network.

(35) PLMN: as an abbreviation of Public Land Mobile Network, means a network identification number of a mobile communication provider. In roaming case of the UE, the PLMN is classified into a home PLMN (HPLMN) and a visited PLMN (VPLMN).

(36) <Disclosure of the Present Specification>

(37) Hereinafter, methods according to the disclosure of the present specification will be described.

(38) Specifically, the disclosure of the present specification describes a method in which a UE falls back to a 4G RAT (i.e., E-UTRAN) or a 4G core (e.g., EPC) that may stably receive a voice call service while being connected to an NG RAT or an NG core (e.g., 5G core). In the NG RAT or NG core, the voice call service may not be physically provided or may be physically provided, but may not be provided by a policy of a provider due to low reliability.

(39) Hereinafter, a voice call service is mainly described, but a description of the present specification may be extended that a service falls back a PDN/PDU session that may be distinguished by an Access Point Name (APN)/Data Network Name (DNN) to a specific RAT or a specific core network.

(40) I. First Disclosure: Selection of Fallback Method

(41) FIG. 6 is a diagram illustrating a method of selecting a fallback method during a registration procedure according to a first scheme of a first disclosure of the present specification.

(42) 1) The UE transmits a registration request message (e.g., attach request message) to an AMF so as to register to an NG core (e.g., 5G core). UE usage setting is included in the registration request message. The UE usage setting includes setting or preference information on whether the UE is a voice call service centric terminal or a data service centric terminal.

(43) 2) The AMF receives the registration request message and then obtains and verifies subscriber information from UDM. Further, the AMF obtains and verifies policy information from a PCF. The AMF obtains and verifies wireless configuration information from an RAN. Further, the AMF may determine information set in advance therein. Further, the AMF may obtain and verify information through interaction with a third network.

(44) 3) The AMF determines whether a voice call is supported or not in an NG RAT or NG core to which the UE is accessed based on the obtained and verified information. If a voice call is not supported, the AMF selects one of the following several fallback methods for a voice call.

(45) i. Intra-system PS handover between an NR cell and an E-UTRA cell in which a change in a core network is not accompanied

(46) ii. Inter-system PS handover between a NG core (e.g., a 5G core) and a 4G core (e.g., an EPC) in which a change in a core network is accompanied

(47) iii. As described later in a chapter II, there may be several methods such as fallback (i.e., a method of changing the core network by a start operation by the UE when an N26 interface is not provided and a single-registration is performed) initiated by the UE suggested in the present specification.

(48) 4) The AMF transmits a registration accept message (e.g., attach accept message) to the UE. In this case, the registration accept message (e.g., attach accept message) may include indication indicating that fallback is required for a voice call service or indication indicating that a voice call service is provided by Voice over LTE (VoLTE). The fact that a voice call service is provided by the VoLTE means that a voice call service is fallen back. Further, the registration accept message (e.g., attach accept message) may include information on a selected fallback method, as described above.

(49) 5) When the registration is completed, the UE performs a procedure for IMS registration.

(50) FIG. 7 is a diagram illustrating a method in which an AMF selects a fallback method at a time point in which an UE transmits a service request message for a MO/MT call according to a second scheme of a first disclosure of the present specification.

(51) 1) The UE performs both a procedure of registering to the NG core (e.g., 5G core) and an IMS registration procedure.

(52) 2) The UE receives a paging signal due to MT of a voice call and then receives an SIP INVITE message or determines MO of the voice call.

(53) 3) Thereafter, the UE transmits a service request message to the AMF. In this case, as described with reference to FIG. 6, the service request message may include indication indicating that fallback is required for a voice call service. The indication may be received from the AMF during a registration process. As described with reference to FIG. 6, the service request message may include information on a fallback method determined and delivered by the AMF.

(54) 4) The AMF selects a fallback method based on the information received from the UE and obtained various information as described with reference to FIG. 6. In this case, the AMF may select a fallback method different from a fallback method instructed by the information included in the service request message. For example, when information referred in selecting a specific fallback method is changed during the registration process shown in FIG. 6, the AMF may select another fallback method instead of a previously selected specific fallback method based on the changed information.

(55) 5) In order to perform a fallback operation for a voice call of the UE, the AMF may transmit an N2-AP request message to an NG RAN. Information on the selected fallback method may be included in the request message.

(56) 6) The NG RAN performs a fallback operation. A fallback method that may not be technically initiated in the NG RAN is excluded. A handover procedure is performed according to the fallback operation.

(57) 7) The UE performs inter-PS handover from a NG core (e.g., 5G core) to a 4G core (e.g., EPC) according to the fallback operation and then performs an IMS call establishment procedure.

(58) FIG. 8 is a diagram illustrating a method in which an NG RAN selects a fallback scheme by a request of an AMF at a time point in which an UE transmits a service request message for a MO/MT call according to a second scheme of a first disclosure of the present specification.

(59) Most of steps of FIG. 8 are similar to those of FIG. 7. Hereinafter, only different steps will be described.

(60) 1-3) The steps are similar to steps 1-3 of FIG. 7, and therefore, the description of FIG. 7 is applied instead of redundant description.

(61) 4) In order to perform a fallback operation for a voice call of the UE, the AMF may transmit an N2-AP request message to an NG RAN. In this case, the AMF may transmit obtained various information to the NG RAN, as described above.

(62) 5) Therefore, the NG RAN selects a fallback method based on the obtained various information. In this case, various information referring for selecting the fallback method may be obtained by the AMF and delivered to the NG RAN or may be information obtained by the NG RAN.

(63) II. Second Disclosure

(64) In a situation in which an N26 interface is not provided and in which the UE may perform only a single-registration, the UE may not perform handover for a fallback operation, and the second disclosure of the present specification suggests a method of changing a core network according to an interworking procedure.

(65) FIG. 9 is a flowchart illustrating a method in which a UE initiates a PDN connection request procedure for a fallback operation according to a first scheme of a second disclosure of the present specification.

(66) Most of steps of FIG. 9 are similar to those of FIG. 7. Hereinafter, only different steps will be described.

(67) 1-3) The steps are similar to steps 1-3 of FIG. 7, and therefore, the description of FIG. 7 is applied instead of redundant description.

(68) 4) The AMF selects a fallback method based on information received from the UE and obtained various information as described with reference to FIG. 6. In this case, the AMF may select a fallback method different from a fallback method instructed by information included in the service request message. For example, in FIG. 9, a fallback scheme of a name fallback without N26 is selected. The fallback scheme is a scheme (i.e., the UE changes a core network thereof to a 4G EPS) in which the UE initiates a fallback operation in an environment in which PS handover is not provided (e.g., an environment in which PS handover is not physically provided or is not politically provided).

(69) 5) The AMF transmits a service request reject message in response to the service request message. The service request reject message may include information on the selected fallback method. Here, the selected fallback scheme may be a scheme in which the UE initiates a fallback operation. The service request reject message may include information (e.g., shown all/partial PDN) requesting or instructing to fall back all sessions set to the current NG core (e.g., 5G core) or a session for only an IMS to the EPC.

(70) 6) Therefore, the UE performs a procedure similar to an interworking procedure of the case of performing a single-registration mode in an environment in which an N26 interface is not provided instead of performing a handover procedure for fallback. That is, the UE performs an attach procedure and a PDN connection establishment procedure to the EPC according to a request/instruction received from a network.

(71) Specifically, the UE generates a GUTI for 4G from a GUTI for 5G and performs a TAU procedure using the generated GU for 4G. Therefore, an MME of the 4th generation EPC determines that a TAU is impossible because a previous serving node of the UE is an AMF of an NG core (e.g., 5th generation core) and transmits an indicator Handover PDN Connection Setup Support to the UE while transmitting a TAU reject message. The indicator means that it is required to perform the PDN connection setup procedure for handover.

(72) Therefore, the UE transmits an attach request message including a PDN connection request message based on the instructor. In this case, the attach request message includes a handover indicator indicating that the attach request message is for handover. In this case, the UE transmits together information (e.g., IMS APN) necessary for IMS PDN session connection. When the information received from the network contains information that requests/instructs all or specific PDN connection other than an IMS PDN, the corresponding PDN connection may also be requested.

(73) 7) The UE performs a procedure (e.g., INS registration, IMS call establishment procedure) necessary for an IMS-based voice call with the EPC.

(74) FIG. 10 is a flowchart illustrating a method in which an AMF requests a PDN connection request procedure to an NG RAN for a fallback operation according to a second scheme of a second disclosure of the present specification.

(75) Most of steps of FIG. 10 are similar to those of FIG. 9. Hereinafter, only different steps will be described.

(76) 1-4) The steps are similar to steps 1-4 of FIG. 9, and therefore, the description of FIG. 9 is applied instead of redundant description.

(77) 5) In order to perform a fallback operation for a voice call of the UE, the AMF may transmit an N2-AP request message to an NG RAN. Information on the selected fallback scheme may be included in the message. Here, the selected fallback scheme may be a scheme in which the UE initiates a fallback operation. The message may include information (e.g., shown all/partial PDN) requesting or instructing to fall back all sessions currently set in the NG core (e.g., 5G core) or a session for only an IMS to the EPC. Therefore, the NG RAN transmits an RRC connection release message to the UE. The RRC connection release message may include information on the selected fallback method.

(78) Unlike the step 4 of FIG. 10, the RAN instead of the AMF may select a fallback method. In this case, the AMF may obtain information necessary for selection of the fallback scheme and then transmit the information to the NG RAN. Alternatively, the NG RAN may obtain information necessary for selection of the fallback scheme.

(79) 6-7) The steps are similar to steps 6-7 of FIG. 9, and therefore, the description of FIG. 9 is applied instead of redundant description.

(80) FIG. 11 is a flowchart illustrating an optimization method of minimizing delay according to a third scheme of a second disclosure of the present specification.

(81) 1) The UE performs a procedure of registering to a NG core (e.g., 5G core). In this case, as described with reference to FIG. 6, information on a fallback scheme selected by the network may be included in the registration accept message (e.g., attach accept message). The selected fallback method may be a fallback method of a name fallback without N26, as described above.

(82) 2) The UE performs an IMS registration procedure for a voice call service.

(83) 3) The UE determines MO of a voice call.

(84) 4) Therefore, the UE performs a fallback operation based on information on the fallback method received in the step 1). That is, in order to change the core network to a 4G EPC, the UE performs a PDN connection request procedure. That is, the UE immediately performs a PDN connection request procedure instead of transmitting a service request message.

(85) 5) The UE performs a procedure (e.g., INS registration, IMS call establishment procedure) necessary for an IMS-based voice call with the EPC.

(86) III. Third Disclosure

(87) FIG. 12 is a flowchart illustrating a method of obtaining information necessary for fallback determination according to a third disclosure of the present specification.

(88) As can be seen with reference to FIG. 12, the AMF obtains information from the UE, the NG RAN (i.e., including the base station), and other network nodes in addition to its own information preset therein. In particular, the AMF may perform a procedure for determining an RAN operation mode to be described later in the section IV and whether an X2 interface exists between a gNB and an eNB in addition to AS setting information about VoLTE support from the base station.

(89) IV. Fourth Disclosure: Broadcast Information about an Operating Mode of the Base Station and Operation of the UE According to the Broadcasting

(90) According to the fourth disclosure of the present specification, a base station of the NG RAN (or referred to as Evolved E-UTRAN) may operate in one of the following modes and the operation mode may be broadcasted to the UE through a signal/message (e.g., SIB).

(91) i) S1 mode: This mode means that the base station of the NG RAN supports only access to a 4G EPC. Accordingly, the base station should perform an operation similar to that of an existing 4G RAN. In this manner, when the base station of the NG RAN operates in a mode S1, the base station may not broadcast information on an operation mode thereof.

(92) ii) NG mode: This mode means that the base station of the NG RAN supports only access to the NG core (i.e., 5G core).

(93) iii) S1 & NG mode: This mode means that the base station of the NG RAN provides both access to the 4G EPC and access to the NG core (i.e., 5G core).

(94) FIG. 13 illustrates a method of determining whether to fall back when an operation mode of a base station is broadcasted according to a fourth disclosure of the present specification.

(95) 1) The UE performs both a procedure of registering to an NG core (e.g., 5G core) and an IMS registration procedure.

(96) 2) The UE receives a paging signal due to MT of the voice call and then receives an SIP INVITE message or determines MO of the voice call.

(97) 3) The UE determines an operation mode of a currently accessed RAN based on information included in a signal/message (e.g., SIB) broadcasted by the base station.

(98) 4) The UE determines whether fallback to an EPC is available through the corresponding base station. For example, when the current base station is operating in an S1 & NG mode that may be connected to two core networks (i.e., NG core and 4G EPC), the UE may determine that the UE may be fallen back to the EPC without change of the base station. When the base station is currently operating in an NG mode, the UE may determine that fallback requiring inter-RAT handover (HO) is required.

(99) The determination may be performed based on other information preset to the UE in addition to information on the operation mode.

(100) 5) The UE may transmit a service request message or an attach request message including a PDN connection request message according to a determination result thereof.

(101) 6) The UE performs a fallback process.

(102) The foregoing description may be implemented in hardware. This will be described with reference to the drawings.

(103) FIG. 14 is a block diagram illustrating a configuration of a UE and a network node according to an embodiment of the present invention.

(104) As shown in FIG. 14, the UE (or UE) 100 includes a storage means 101, a controller 102, and a transceiver 103. The network node may be an access network (AN), a radio access network (RAN), an AMF, a CP function node, and an SMF. The network node includes a storage means 511, a controller 512, and a transceiver 513.

(105) The storage means stores the above-described method.

(106) The controllers control the storage means and the transceivers. Specifically, the controllers each execute the methods stored in the storage means. The controllers transmit the above-described signals through the transceivers.

(107) While the invention has been described with reference to exemplary embodiments, the scope of the invention is not limited to specific embodiments, but the invention may be modified, changed, or improved in various forms within the spirit of the present invention and the scope described in claims.