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