A communication method

Abstract

The present disclosure provides a method for communication of a user equipment, a user equipment and a computer-readable storage medium. The method includes: determining whether the UE is provided with only an evolved packet system service by the current network; if it is determined that the UE is provided with only an evolved packet system service by the current network, searching for other networks different from the current network; and initiating a registration process in the searched other networks.

Description

Technical Field

[0001] The present disclosure relates to the field of mobile communications, and more particularly, to a terminal communication method. Background Art

[0002] The LTE network of traditional CDMA (Code Division Multiple Access) operators does not support the CSFB (Circuit Switched Fallback) function, or the new network operator only provides LTE (Long Term Evolution) network services, resulting in users who roam (for example, domestic network co-construction and sharing roaming or international roaming) to the target LTE network that does not support CDMA technology and has not activated VoLTE being unable to use voice services.

[0003] There is a need for a new method for communication of user equipment. Summary of the invention

[0004] According to one aspect of the present disclosure, a method for communication of a user equipment (UE) is provided, the method comprising: receiving a registration message from a current network and determining whether an evolved packet system-only service is provided; if it is determined that the UE is provided with an evolved packet system-only service, searching for other networks different from the current network; and initiating a registration process in the searched other networks.

[0005] According to one aspect of the present disclosure, initiating a registration process in the searched network includes: initiating a registration process of an IMSI attach type or a registration process of a combined attach type.

[0006] According to one aspect of the present disclosure, if the registration process of the IMSI attachment type is successful, the UE is provided with packet switching services by the current network and circuit switching services by other searched networks; and if the registration process of the joint attachment type is successful, the UE is provided with both packet switching services and circuit switching services by other searched networks.

[0007] According to an aspect of the present disclosure, the searched other network providing circuit switching services includes one of UMTS or GSM networks; and the searched other network providing both packet switching services and circuit switching services includes one of LTE, UMTS or GSM networks.

[0008] According to an aspect of the present disclosure, the current network is a network other than a home network of the UE.

[0009] According to one aspect of the present disclosure, before initiating a registration process in other searched networks: determine whether the other searched networks belong to one of the UE's home network, a jointly built and shared network, and a roaming network based on a public land mobile network (PLMN) list of system information 1 (SIB1) of a cell of the current network; and initiate a registration process for a network that belongs to one of the UE's home network, a jointly built and shared network, and a roaming network.

[0010] According to one aspect of the present disclosure, initiating a registration process in other searched networks includes: sorting the other searched networks according to the signal strength of the received broadcast channel or pilot channel; and initiating a registration process in the other searched networks in the sorted order.

[0011] According to one aspect of the present disclosure, the method further includes: before searching for other networks different from the current network, checking whether the UE's current USIM is a USIM that can only be subscribed to and provided with only evolved packet system services; and if the current USIM is not a USIM that can only be subscribed to and provided with only evolved packet system services, searching for other networks different from the current network.

[0012] According to one aspect of the present disclosure, the registration message includes one of: an attach accept message; and a tracking area update accept message, and when one of the following conditions is met, it is judged that only evolved packet system service is provided: the EPS attachment result information element value in the received attach accept message is 1; the EPS update result information element value in the received tracking area update accept message is 0 and the EPS attachment result information element value in the most recently received attach accept message is 2; and the EPS update result information element value in the received tracking area update accept message is 0 and the EPS update result information element value in the most recently received tracking area update accept message is 1.

[0013] According to another aspect of the present disclosure, a method for communication of a user equipment (UE) is provided, the method comprising: receiving a registration message from a current network and determining whether only an evolved packet system service is provided; if it is determined that the UE is provided only an evolved packet system service, determining whether the network supports packet-switched session IP multimedia subsystem voice; and if the current network supports packet-switched session IP multimedia subsystem voice, initiating an initial IMS registration process to the current network based on a VoLTE switch state of the UE or a VoLTE service state of the UE.

[0014] According to another aspect of the present disclosure, initiating a registration process to the network based on the VoLTE switch state of the UE or the VoLTE service state of the UE includes: if the VoLTE switch state of the UE is on, initiating an IMS initial registration process to the current network.

[0015] According to another aspect of the present disclosure, initiating a registration process to the network based on the VoLTE switch state of the UE or the VoLTE service state of the UE includes: if the VoLTE switch state of the UE is off, the UE determines whether the VoLTE service has been activated; and if the VoLTE service of the UE has been activated, prompting to turn on the VoLTE switch, and initiating an IMS initial registration process to the current network after detecting that the VoLTE switch is turned on.

[0016] According to yet another aspect of the present disclosure, if the IMS initial registration is successful, the UE performs voice service in a VoLTE manner.

[0017] According to another aspect of the present disclosure, the method also includes searching for other networks different from the current network when one of the following conditions is met; and initiating a registration process in the other searched networks: the current network or the searched network does not support packet switched session IP multimedia subsystem voice; the UE does not support the VoLTE function; the UE's VoLTE switch is not detected to be changed from the off state to the on state; the UE's VoLTE service activation fails; and the UE detects that the user chooses not to activate the VoLTE service.

[0018] According to another aspect of the present disclosure, initiating a registration process in the searched network includes: initiating a registration process of an IMSI attach type or a registration process of a combined attach type.

[0019] According to yet another aspect of the present disclosure, a method for communication of a user equipment (UE) is provided, the method comprising: receiving a system message from a current network and checking first PLMN ID information in a public land mobile network (PLMN) column carried in the system message, if the first PLMN ID is included in a stored list of networks providing only evolved packet system services, searching for other networks different from the current network; and initiating a registration process in the searched network.

[0020] According to yet another aspect of the present disclosure, the method further includes: if a registration message indicating provision of the E-PSS service is received, updating the PLMN ID of the current network into the stored list of networks providing the E-PSS service.

[0021] According to one aspect of the present disclosure, a method for communication of a user equipment (UE) is provided, the method comprising: determining whether the UE is provided with only an evolved packet system service by a current network; if it is determined that the UE is provided with only an evolved packet system service by the current network, searching for other networks different from the current network; and initiating a registration process in the searched other networks.

[0022] According to another aspect of the present disclosure, determining whether the UE is provided with only evolved packet system service by the current network includes: receiving a registration message or a system message from the current network; and determining whether the UE is provided with only evolved packet system service by the current network based on the registration message or the system message.

[0023] According to another aspect of the present disclosure, the registration message includes one of: an attach accept message; and a tracking area update accept message, and wherein, when one of the following conditions is met, it is judged that the UE is provided with only evolved packet system service by the current network: the (Evolved Packet System) EPS attachment result information element value in the received attach accept message is 1; the EPS update result information element value in the received tracking area update accept message is 0 and the EPS attachment result information element value in the most recently received attach accept message is 2; and the EPS update result information element value in the received tracking area update accept message is 0 and the EPS update result information element value in the most recently received tracking area update accept message is 1.

[0024] According to another aspect of the present disclosure, the method further includes: when it is determined according to the system message that the UE is not provided with an E-PSS service by the current network, initiating a registration process in the current network.

[0025] According to another aspect of the present disclosure, determining whether the UE is provided with only evolved packet system service by the current network according to a system message includes: determining whether the UE is provided with only evolved packet system service by the current network based on a public land mobile network (PLMN) list carried in the system message.

[0026] According to another aspect of the present disclosure, based on the PLMN list carried in the system message, determining whether the UE is provided with only evolved packet system services by the current network includes: when the first PLMN ID in the PLMN list carried in the system message is inconsistent with the home PLMN ID corresponding to the International Mobile Subscriber Identity (IMSI), determining whether the first PLMN ID in the PLMN list carried in the system message is included in the stored list of networks providing only evolved packet system services; if included in the stored list of networks providing only evolved packet system services, determining that the UE is provided with only evolved packet system services.

[0027] According to another aspect of the present disclosure, the method further includes: when the first PLMN ID in the PLMN list carried in the system message is consistent with the home PLMN ID corresponding to the IMSI, initiating a registration process in the current network.

[0028] According to yet another aspect of the present disclosure, the method further includes: if a registration message indicating provision of the E-PSS service is received, updating the PLMN ID of the current network into the stored list of networks providing the E-PSS service.

[0029] According to another aspect of the present disclosure, initiating a registration process in the other searched networks includes: initiating a registration process of an IMSI attach type or a registration process of a combined attach type.

[0030] According to another aspect of the present disclosure, if the registration process of the IMSI attachment type is successful, the UE is provided with packet switching services by the current network and circuit switching services by other searched networks; and if the registration process of the joint attachment type is successful, the UE is provided with both packet switching services and circuit switching services by other searched networks.

[0031] According to another aspect of the present disclosure, the other networks searched for providing circuit switching services include one of Universal Mobile Telecommunications System (UMTS) or Global System for Mobile Communications (GSM) networks; and the other networks searched for providing both packet switching services and circuit switching services include one of Long Term Evolution (LTE), UMTS or GSM networks.

[0032] According to yet another aspect of the present disclosure, the current network is a network other than a home network of the UE.

[0033] According to another aspect of the present disclosure, initiating a registration process in other searched networks includes: determining other networks for initiating registration among the other searched networks based on a public land mobile network (PLMN) corresponding to the other searched networks; and initiating a registration process for the determined other networks.

[0034] According to another aspect of the present disclosure, among the other networks searched, based on the PLMN corresponding to the other networks searched, determining the other networks to initiate registration includes: determining whether the PLMN ID in the PLMN list carried in the system message of the other networks searched is included in the stored list of networks providing only evolved packet system services; if not included in the stored list of networks providing only evolved packet system services, determining to initiate registration for the other networks searched.

[0035] According to another aspect of the present disclosure, initiating a registration process in other searched networks includes: sorting the other searched networks according to the signal strength of the received broadcast channel or pilot channel; and initiating a registration process in the other searched networks according to the sorted order.

[0036] According to another aspect of the present disclosure, the method further includes: before searching for other networks different from the current network, checking whether the current USIM of the UE is a USIM that can only be subscribed to and provided with only evolved packet system services; and if the current USIM is not a USIM that can only be subscribed to and provided with only evolved packet system services, searching for other networks different from the current network.

[0037] According to one aspect of the present disclosure, a method for communication of a user equipment (UE) is provided, the method comprising: receiving a registration message from a current network; if it is determined based on the received registration message that the UE is provided with only an evolved packet system service by the current network, and the current network supports packet-switched session IP multimedia subsystem voice, then initiating an initial IMS registration process to the current network based on a high-definition voice (VoLTE) switch state of the UE or a VoLTE service state of the UE.

[0038] According to another aspect of the present disclosure, initiating a registration process to the network based on the VoLTE switch state of the UE or the VoLTE service state of the UE includes: if the VoLTE switch state of the UE is on, initiating an IMS initial registration process to the current network.

[0039] According to another aspect of the present disclosure, initiating a registration process to the network based on the VoLTE switch state of the UE or the VoLTE service state of the UE includes: if the VoLTE switch state of the UE is off, the UE determines whether the VoLTE service has been activated; and if the VoLTE service of the UE has been activated, prompting to turn on the VoLTE switch, and initiating an IMS initial registration process to the current network after detecting that the VoLTE switch is turned on.

[0040] According to yet another aspect of the present disclosure, if the IMS initial registration is successful, the UE performs voice service in a VoLTE manner.

[0041] According to another aspect of the present disclosure, the method also includes searching for other networks different from the current network when one of the following conditions is met; and initiating a registration process in the other searched networks: the current network or the searched network does not support packet switched session IP multimedia subsystem voice; the UE does not support the VoLTE function; the UE's VoLTE switch is not detected to be changed from the off state to the on state; the UE's VoLTE service activation fails; and the UE detects that the user chooses not to activate the VoLTE service.

[0042] According to another aspect of the present disclosure, initiating a registration process in the searched network includes: initiating a registration process of an IMSI attach type or a registration process of a combined attach type.

[0043] According to one aspect of the present disclosure, a method for communication of a user equipment (UE) is provided, the method comprising: if a system message of a current network does not contain a system information block (SIB) 24 and / or scheduling information of SIB 24, constructing SIB24; and performing a reselection process to a new radio (NR) independent networking (SA) cell based on the constructed SIB24.

[0044] According to another aspect of the present disclosure, before executing the reselection process to the NR SA cell based on the constructed SIB24, it also includes: judging whether the radio resource control (RRC) connection release message contains a redirection message to the NR SA cell; if it contains a redirection message to the NR SA cell, executing the redirection process to the NR SA cell; if it does not contain a redirection message to the NR SA cell, executing the reselection process to the NR SA cell based on the constructed SIB24.

[0045] According to another aspect of the present disclosure, constructing SIB24 includes: obtaining NR SA cell information based on at least one of the following: the NR SA cell in which the UE has resided, or the NR SA system neighbor cell carried in the measurement control sent by the network when the UE is in a connected state, or the NR SA cell information provided by the server; and constructing SIB24 based on the acquired NRSA cell information.

[0046] According to one aspect of the present disclosure, a user equipment (UE) for communication is provided, including: a transceiver for receiving signals from a base station and sending signals to the base station; a memory for storing executable instructions; and a processor for executing the stored instructions to execute the above method.

[0047] According to one aspect of the present disclosure, a user equipment (UE) is provided, comprising: a judgment unit configured to judge whether the UE is provided with only evolved packet system service by the current network; a search unit configured to search for other networks different from the current network if it is judged that the UE is provided with only evolved packet system service by the current network; and a registration unit configured to initiate a registration process in the other searched networks.

[0048] According to another aspect of the present disclosure, the determination unit is further configured to: receive a registration message or a system message from the current network; and determine whether the UE is provided with only an evolved packet system service by the current network according to the registration message or the system message.

[0049] According to another aspect of the present disclosure, the registration message includes one of: an attach accept message; and a tracking area update accept message, and wherein, when one of the following conditions is met, it is judged that the UE is provided with only evolved packet system service by the current network: the (Evolved Packet System) EPS attachment result information element value in the received attach accept message is 1; the EPS update result information element value in the received tracking area update accept message is 0 and the EPS attachment result information element value in the most recently received attach accept message is 2; and the EPS update result information element value in the received tracking area update accept message is 0 and the EPS update result information element value in the most recently received tracking area update accept message is 1.

[0050] According to another aspect of the present disclosure, the registration unit is further configured to: when it is determined according to the system message that the UE is not provided with an evolved packet system service by the current network, initiate a registration process in the current network.

[0051] According to another aspect of the present disclosure, the determination unit is further configured to determine whether the UE is provided with only an evolved packet system service by the current network based on a public land mobile network (PLMN) list carried in the system message.

[0052] According to another aspect of the present disclosure, when judging whether the UE is provided with only evolved packet system service by the current network based on the PLMN list carried in the system message, the judging unit is further configured to: when the first PLMN ID in the PLMN list carried in the system message is inconsistent with the home PLMN ID corresponding to the international mobile subscriber identity (IMSI), judge whether the first PLMN ID in the PLMN list carried in the system message is included in the stored list of networks providing only evolved packet system service; if it is included in the stored list of networks providing only evolved packet system service, judge that the UE is provided with only evolved packet system service.

[0053] According to another aspect of the present disclosure, the registration unit is further configured to: when the first PLMN ID of the PLMN list carried in the system message is consistent with the home PLMN ID corresponding to the IMSI, initiate a registration process in the current network.

[0054] According to another aspect of the present disclosure, the user equipment further includes: an updating unit configured to update the PLMN ID of the current network to the stored list of networks providing only evolved packet system services if a registration message indicating provision of only evolved packet system services is received.

[0055] According to another aspect of the present disclosure, the registration unit is further configured to initiate a registration process of IMSI attachment type or a registration process of joint attachment type when initiating a registration process in other searched networks.

[0056] According to another aspect of the present disclosure, if the registration process of the IMSI attachment type is successful, the UE is provided with packet switching services by the current network and circuit switching services by other searched networks; and if the registration process of the joint attachment type is successful, the UE is provided with both packet switching services and circuit switching services by other searched networks.

[0057] According to another aspect of the present disclosure, the other networks searched for providing circuit switching services include one of Universal Mobile Telecommunications System (UMTS) or Global System for Mobile Communications (GSM) networks; and the other networks searched for providing both packet switching services and circuit switching services include one of Long Term Evolution (LTE), UMTS or GSM networks.

[0058] According to yet another aspect of the present disclosure, the current network is a network other than a home network of the UE.

[0059] According to another aspect of the present disclosure, the registration unit is further configured to: determine other networks for initiating registration among the other networks searched, based on a public land mobile network (PLMN) corresponding to the other networks searched; and initiate a registration process for the determined other networks.

[0060] According to another aspect of the present disclosure, when determining other networks for initiating registration among the other networks searched for based on the PLMN corresponding to the other networks searched for, the registration unit determines whether the PLMN ID in the PLMN list carried in the system message of the other networks searched for is included in the stored list of networks providing only evolved packet system services; if it is not included in the stored list of networks providing only evolved packet system services, it is determined to initiate registration for the other networks searched for.

[0061] According to another aspect of the present disclosure, when initiating a registration process in other searched networks, the registration unit is also configured to: sort the other searched networks according to the signal strength of the received broadcast channel or pilot channel; and initiate a registration process in the other searched networks in the sorted order.

[0062] According to another aspect of the present disclosure, the user equipment also includes a checking unit, which checks whether the UE's current USIM is a USIM that can only be subscribed to and provided with only evolved packet system services before searching for other networks different from the current network, and when the current USIM is not a USIM that can only be subscribed to and provided with only evolved packet system services, the searching unit searches for other networks different from the current network.

[0063] According to another aspect of the present disclosure, a user equipment (UE) is provided, comprising: a receiving unit configured to receive a registration message from a current network; a registering unit configured to initiate an initial IMS registration process to the current network based on a high-definition voice (VoLTE) switch state of the UE or a VoLTE service state of the UE, if it is determined based on the received registration message that the UE is provided with only an evolved packet system service by the current network, and the current network supports packet-switched session IP multimedia subsystem voice.

[0064] According to another aspect of the present disclosure, when initiating a registration process to the network based on the VoLTE switch state of the UE or the VoLTE service state of the UE, the registration unit is also configured to: if the VoLTE switch state of the UE is on, initiate an IMS initial registration process to the current network.

[0065] According to another aspect of the present disclosure, when a registration process is initiated to the network based on the VoLTE switch state of the UE or the VoLTE service state of the UE, the registration unit is also configured to: if the VoLTE switch state of the UE is off, the UE determines whether the VoLTE service has been activated; and if the VoLTE service of the UE has been activated, prompt to turn on the VoLTE switch, and initiate an IMS initial registration process to the current network after detecting that the VoLTE switch is turned on.

[0066] According to yet another aspect of the present disclosure, if the IMS initial registration is successful, the UE performs voice service in a VoLTE manner.

[0067] According to another aspect of the present disclosure, when one of the following conditions is met, the search unit is also configured to search for other networks different from the current network; and the registration unit initiates a registration process in the other searched networks: the current network or the searched network does not support packet switched session IP multimedia subsystem voice; the UE does not support the VoLTE function; the UE's VoLTE switch is not detected to be changed from the off state to the on state; the UE's VoLTE service activation fails; and the UE detects that the user chooses not to activate the VoLTE service.

[0068] According to another aspect of the present disclosure, when initiating a registration process in the searched network, the registration unit is further configured to: initiate a registration process of an IMSI attach type or a registration process of a joint attach type.

[0069] According to one aspect of the present disclosure, a user equipment (UE) is provided, comprising: a construction unit, configured to construct a system information block (SIB) 24 and / or scheduling information of SIB 24 if a system message of a current network does not contain SIB 24; and an execution unit, configured to perform a reselection process to a new radio (NR) independent networking (SA) cell based on the constructed SIB24.

[0070] According to another aspect of the present disclosure, the user equipment also includes a judgment unit, and before executing the reselection process to the NR SA cell based on the constructed SIB24, the judgment unit is also configured to judge whether the radio resource control (RRC) connection release message contains a redirection message to the NR SA cell, if the redirection message to the NR SA cell is contained, the execution unit is configured to execute the redirection process to the NR SA cell, and if the redirection message to the NR SA cell is not contained, the execution unit executes the reselection process to the NR SA cell based on the constructed SIB24.

[0071] According to another aspect of the present disclosure, the construction unit is also configured to obtain NR SA cell information based on at least one of the following: the NR SA cell in which the UE has resided, or the NRSA system neighbor cell carried in the measurement control sent by the network when the UE is in a connected state, or the NR SA cell information provided by the server; and construct SIB24 based on the acquired NRSA cell information. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] The above and other objects, features and advantages of the present disclosure will become more apparent through the following description of the embodiments of the present disclosure with reference to the accompanying drawings, in which:

[0073] Figure 1 A flowchart showing an example process according to a first embodiment of the present disclosure;

[0074] Figure 2 A flowchart showing an example process according to a second embodiment of the present disclosure;

[0075] Figure 3 A flowchart showing an example process according to a third embodiment of the present disclosure is shown;

[0076] Figure 4 A flowchart showing an example process according to a fourth embodiment of the present disclosure;

[0077] Figure 5A flowchart showing an example process according to a fifth embodiment of the present disclosure;

[0078] Figure 6 A flowchart showing an example process according to a sixth embodiment of the present disclosure;

[0079] Figure 7 A flowchart showing an example process according to a seventh embodiment of the present disclosure;

[0080] Figure 8 is a flowchart illustrating an example process according to an eighth embodiment of the present disclosure;

[0081] Fig. 9 is a flowchart illustrating an example process according to a ninth embodiment of the present disclosure;

[0082] Fig.10 is a flowchart illustrating an example process according to a tenth embodiment of the present disclosure;

[0083] Fig.11 is a flowchart illustrating an example process according to an eleventh embodiment of the present disclosure;

[0084] Fig.12 is a flowchart illustrating an example process according to a twelfth embodiment of the present disclosure;

[0085] Fig.13 is a flowchart illustrating an example process according to a thirteenth embodiment of the present disclosure;

[0086] Fig.14 is a flowchart illustrating an example process according to a fourteenth embodiment of the present disclosure;

[0087] Fig.15 is a flowchart illustrating an example process according to a fifteenth embodiment of the present disclosure; and

[0088] Fig.16 is a block diagram illustrating a UE according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0089] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present disclosure. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present disclosure.

[0090] It will be understood by those skilled in the art that, unless expressly stated, the singular forms "one", "said", and "the" used herein may also include plural forms. It should be further understood that the term "comprising" used in the specification of the present disclosure refers to the presence of the features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. It should be understood that when we refer to an element as being "connected" or "coupled" to another element, it may be directly connected or coupled to the other element, or there may also be an intermediate element. In addition, the "connection" or "coupling" used herein may include wireless connection or wireless coupling. The term "and / or" used herein includes all or any unit and all combinations of one or more associated listed items. In addition, the terms "first" and "second" used herein may describe various constituent elements, but they should not limit the corresponding constituent elements.

[0091] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as those generally understood by those skilled in the art in the field to which the present disclosure belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless specifically defined as here.

[0092] It will be understood by those skilled in the art that the "terminal" and "terminal device" used herein include both devices with wireless signal receivers, which are devices with only wireless signal receivers without transmission capabilities, and devices with receiving and transmitting hardware, which are devices with receiving and transmitting hardware capable of performing two-way communication on a two-way communication link. Such devices may include: cellular or other communication devices, which have a single-line display or a multi-line display or a cellular or other communication device without a multi-line display; PCS (Personal Communications Service), which may combine voice, data processing, fax and / or data communication capabilities; PDA (Personal Digital Assistant), which may include a radio frequency receiver, a pager, Internet / intranet access, a web browser, a notepad, a calendar and / or a GPS (Global Positioning System) receiver; conventional laptop and / or palmtop computers or other devices, which have and / or include a conventional laptop and / or palmtop computer or other device with a radio frequency receiver. The "terminal" or "terminal device" used herein may be portable, transportable, installed in a vehicle (air, sea and / or land), or adapted and / or configured to operate locally, and / or in a distributed form, at any other location on the earth and / or in space. The "terminal" or "terminal device" used herein may also be a communication terminal, an Internet terminal, a music / video playing terminal, such as a PDA, a MID (Mobile Internet Device) and / or a mobile phone with a music / video playing function, or a smart TV, a set-top box and other devices.

[0093] Various aspects of the present disclosure provide a terminal communication method, that is, when a terminal that does not support CDMA technology and the currently used USIM card has not activated the VoLTE service (or the terminal does not support the VoLTE function or the terminal supports the VoLTE function but the VoLTE switch on the terminal interface is in a turned-off state) selects / reselects / switches / roams to a 4G network that does not support the CSFB function, or the currently used USIM card has not activated the VoLTE service (or the terminal does not support the VoLTE function or the terminal supports the VoLTE function but the VoLTE switch on the terminal interface is in a turned-off state) The terminal selects / reselects / switches / roams to a network that only provides 4G / 5G network services, and the terminal will not be able to use voice services. The terminal intelligently searches for UMTS / GSM networks of other networks and tries to complete CS domain registration; or searches for LTE / UMTS / GSM networks of other networks to complete the joint attachment process, so that EPS / non-EPS services (or PS (Packet The VoLTE service is available in the following ways: either the user is guided to enable the VoLTE switch or the network is guided to complete the VoLTE service activation and IMS registration to make the VoLTE service available.

[0094] Because some early LTE terminals on the market have problems decoding the extended system message SIB24 in the LTE system, when the LTE network broadcasts SIB24 in the system message, the above-mentioned terminals will be restarted continuously and unable to provide services.

[0095] In response to the problem that some early-listed LTE terminals are restarted due to the broadcast of SIB24 by the LTE system, the present disclosure provides a solution to the above problem. In order to circumvent the above-mentioned terminal restart problem, the LTE base station may not broadcast SIB24 in the system message, so that some early-listed LTE terminals will not have SIB24 decoding errors. However, if SIB24 is not broadcast in the LTE system, the 5G SA terminal will not be able to complete the inter-system cell reselection from LTE to the 5G SA cell in the idle state. In order to solve this problem, the 5G SA terminal can construct a SIB24 based on the 5G SA cell where it once resided, or the 5G SA neighboring cell issued by the LTE system measurement control, or the 5G SA cell pushed to the terminal by the terminal big data background. When the LTE network is in an idle state, the 5G SA terminal can perform inter-system cell reselection according to the constructed SIB24. In this way, not only the restart problem of some early LTE terminals is solved, but also the problem that the 5G SA terminal cannot reselect to the 5GSA cell when it is idle in the LTE network can be solved.

[0096] Since CDMA (Code Division Multiple Access) technology can no longer undergo subsequent technological evolution, almost all CDMA network operators around the world are considering clearing and decommissioning their CDMA networks. In order to accelerate the process of clearing and decommissioning CDMA networks, some operators no longer require terminals to support CDMA technology. Currently, many 5G (5th Generation) terminals no longer support CDMA technology.

[0097] Currently, there are some new network operators that have just joined the telecommunications market. These new network operators may not deploy 3G / 2G networks anymore. Instead, their first commercial network is usually the 4G (4th Generation) network.

[0098] In addition, from the perspective of network operators, the cost pressure of network construction is increasing. Especially with the commercialization of 5G technology, the wavelength used is shorter, and operators need to deploy more base stations to achieve the ideal outdoor and indoor coverage level. Therefore, network co-construction and sharing among different operators has become a trend. The current mainstream co-construction and sharing method is mainly shared access network, that is, shared base stations. In the process of network co-construction and sharing, users will reselect / switch between the home operator and the shared operator network. When the terminal is turned on or enters a new tracking area (or location area, routing area), the terminal will search for the cell and read the system information of the cell. Taking the LTE (Long Term Evolution) network as an example, if the first PLMN ID in the PLMN (Public Land Mobile Network) list in the System Information Block Type 1 (SIB1) is consistent with the PLMN identifier in the IMSI (International Mobile Subscriber Identity) of the USIM (Universal Subscriber Identity Module) card currently used by the terminal, or the PLMN ID is included in the EHPLMN (Equivalent Home PLMN) list in the USIM card (or built-in in the terminal), the terminal considers that the network to which the cell belongs is the home network. When the first PLMN ID in the PLMN list in system information 1 (SIB1) is inconsistent with the PLMN identifier in the IMSI of the USIM card currently used by the terminal and the PLMN ID is not included in the EHPLMN list in the USIM card (or built-in to the terminal), if other PLMN IDs in the PLMN list in the system information 1 (SIB1) are consistent with the PLMN identifier in the IMSI of the USIM card currently used by the terminal, or the other PLMN IDs are included in the EHPLMN list in the USIM card (or built-in to the terminal), the terminal considers that the network to which the cell belongs is a shared network.In a network co-construction and sharing scenario or an international roaming scenario, the following scenario may occur due to various reasons: when a user who has not activated VoLTE (Voice Over LTE, high-definition voice, or voice transmission through an LTE network) or the terminal itself does not support the VoLTE function, or the terminal supports the VoLTE function but the switch of the VoLTE service on the terminal is turned off (the terminal does not support CDMA), selects / reselects / switches / roams from its home network (the home network supports LTE / UMTS (Universal Mobile Telecommunications System) / GSM (Global System for Mobile Communications)) to a shared network (i.e., the target network), and the operator to which the target network belongs may be a traditional CDMA network operator, that is, its 3G / 2G network uses CDMA technology and 4G uses LTE technology, or the operator to which the target network belongs is a brand-new network operator, and its network only has 4G / 5G networks. In this scenario, when the above-mentioned user performs the EPS (Evolved Packet System) ATTACH (attachment) (or TAU (Tracking Area Update)) process in the target network, for such users, the target network will only send an ATTACH ACCEPT message with an attachment result of EPS Only type or a TAU ACCEPT message with a TAU update result of TAupdated to the user. This will cause such users (the USIM card currently used has not activated the VoLTE service or the terminal itself does not support the VoLTE function or the terminal itself supports the VoLTE function but the switch of the VoLTE service on the terminal interface is turned off) to select / reselect / switch / roam to the target network, and can only use EPS services (i.e. data services) but not non-EPS services (i.e., cannot make or receive calls). Since the user cannot use voice services at this time, the user cannot make or receive calls, which brings many inconveniences to the user's daily exchanges and communication.

[0099] After the terminal completes registration in the LTE network, according to the current communication standards and technical implementation, the terminal either uses CSFB mode, VoLTE mode, or CDMA mode for voice calls. The current commercial CSFB mode is either to fall back from LTE to UMTS or from LTE to GSM. Since CDMA technology has evolved to CDMA2000 and no longer evolves backward, the original CDMA operators have abandoned this technology. In the environment of CDMA network frequency clearance and network withdrawal, some terminals no longer support CDMA technology. When a terminal user who does not support CDMA technology selects / reselects / switches to a shared CDMA operator (or a new operator) LTE network in China or roams to a foreign CDMA operator (or a new operator) LTE network, if the USIM card currently used by such user in the home network has not activated the VoLTE service or the terminal itself does not support the VoLTE function or the terminal supports the VoLTE function but the VoLTE switch on the terminal interface is turned off (i.e., using CSFB to make voice calls in the home network), since the target LTE network does not support the CSFB function (note: for CDMA operators, their 2G / 3G networks are carried by CDMA technology and generally do not have GSM / UMTS networks, so they do not have the CSFB function. For a new operator, the GSM / UMTS network is already an outdated network and is generally not used for deployment, so the first commercial network is usually LTE, so its network does not have the CSFB function), so only EPS services can be provided in the target network, and non-EPS services (cannot make or receive calls) cannot be provided.

[0100] In the scenario of co-construction and sharing, if the target operator wants to support CSFB in its LTE network, it must configure the UMTS / GSM related parameters of the shared network into its network. The workload of parameter configuration is huge, time-consuming and labor-intensive, and most operators will not choose to do so. In the scenario of international roaming, the LTE network of the target CDMA operator in the roaming area (or the target network in the roaming area is a brand new network) cannot support CSFB due to the lack of UMTS / GSM network.

[0101] For current network operators, it is unlikely to enable VoLTE for all their users due to the capacity of the IMS (IP Multimedia Subsystem) core network and other factors. Therefore, VoLTE users and non-VoLTE users will coexist for a long time on the same operator's network.

[0102] In this context, the above-mentioned problem of only being able to use PS domain services will always exist. That is, the LTE network of traditional CDMA operators does not support the CSFB function, resulting in the selection / reselection / switching / roaming to the LTE network. The terminal itself does not support CDMA technology and the USIM card used is not activated for VoLTE service, or the terminal itself does not support CDMA technology or VoLTE service, or the terminal itself does not support CDMA technology and the terminal itself supports VoLTE service but the VoLTE switch on the terminal interface is turned off. Users cannot use voice services. In addition, for a network that can only provide 4G / 5G services, its LTE network does not support the CSFB function, resulting in the selection / reselection / switching / roaming to the LTE network. The USIM card used is not activated for VoLTE service, or the terminal itself does not support VoLTE service, or the terminal itself supports VoLTE service but the VoLTE switch on the terminal interface is turned off. Users cannot use voice services.

[0103] In order to solve the problem that voice services cannot be used in an LTE network that can only provide EPS services, so that users can also use voice services when this happens, the following solution is proposed.

[0104] For domestic co-construction and sharing scenarios, when the above problems occur, the terminal can try to search for the UMTS / GSM network of the home network (or other shared networks), and initiate a registration process of type IMSI attachment under the searched UMTS / GSM network to obtain CS domain services (can make calls). In this way, EPS services can be provided by the LTE network of the shared network, and CS domain services are provided by the UMTS / GSM network of the home network (or other shared networks). When the above problems occur, the terminal can also try to search for the LTE / UMTS / GSM network of the home network (or other shared networks), and initiate a registration process of type joint attachment under the searched LTE / UMTS / GSM network to obtain EPS / non-EPS services (or PS / CS domain services) (can make calls). In this way, EPS / non-EPS services (or PS / CS domain services) can be provided by the shared network or by the LTE / UMTS / GSM network of other shared networks. Optionally, when the above problem occurs, the terminal searches for the LTE / UMTS / GSM network of the home network (or other available shared network) (the search can be performed according to the LTE–>UMTS–>GSM priority, or in a random order. Since the LTE network can provide a higher rate and can guarantee a better user experience, the UMTS network is second, and the GSM network is the worst.), and attempts to initiate registration in the searched home network or shared network (registration can be performed according to the above search priority (or random order). If the LTE network registration fails, try the UMTS network. If the UMTS network registration still fails, try the GSM network. It is also possible not to register in the above order and randomly select the searched network for registration) to obtain EPS / non-EPS services (or PS / CS domain services). After successful registration, EPS / non-EPS services (or PS and CS services) are available. If registration fails, it can return to the shared network that originally only provided EPS services, and maintain the state where only EPS services are available.

[0105] For international roaming scenarios, when the above problem occurs, the terminal can try to search for UMTS / GSM networks of other networks in the roaming area, and initiate a registration process of type IMSI attachment in the searched UMTS / GSM network to obtain CS domain services. In this way, EPS services and CS domain services are provided by the LTE network and UMTS / GSM network of two different visited networks in the roaming area, respectively. Optionally, when the above problem occurs, the terminal searches for LTE / UMTS / GSM networks of other networks in the roaming area (can be in accordance with the LTE–>UMTS–>GSM priority, or random order), and tries to initiate a registration process in other searched networks (can be registered according to the above search priority (or random order), if the LTE network registration fails, then try UMTS, if the UMTS network registration still fails, then try the GSM network, or can not be in accordance with the above order, randomly select the searched network for registration) process to obtain EPS / non-EPS services (or PS / CS domain services). After successful registration, EPS / non-EPS services (or PS and CS services) are available. If registration fails, the network can return to the roaming visited network that originally only provided EPS services, and maintain the state where only EPS services are available.

[0106] Optionally, for domestic co-construction and sharing scenarios or international roaming scenarios, when the above problem occurs, after the terminal is turned on or enters a new location area and receives an Attach Accept (or TAU Accept) message with a result of EPS Only, if the Attach Accept message (or TAU Accept message) indicates that the network supports IMS Voice Over PSSession, and the terminal itself supports the VoLTE function and the local VoLTE switch on the terminal side is on, the terminal initiates the IMS initial registration process to the network. If the terminal receives a network response message carrying a Retry-after field, the network will activate the VoLTE function for the user within the timer carried in the Retry-after field, and after the timer specified in the Retry-after field expires, the terminal will initiate the IMS initial registration process again. Since the user's VoLTE function has been activated on the network side, the IMS initial registration process will be successfully completed. In this way, the terminal can perform voice services through VoLTE in a shared network or a roaming visited network.

[0107] Optionally, for domestic co-construction and sharing scenarios or international roaming scenarios, after the terminal is turned on or enters a new location area and receives an Attach Accept message with an Attach result of EPS Only or a TAU Accept message with an EPS update result of TAupdated (both the EPS service and non-EPS service of the terminal were previously available), if the AttachAccept message indicates that the network supports IMS Voice Over PS Session, the terminal can first determine whether the USIM card currently used by the user has activated the VoLTE service (it can be determined by but not limited to sending a query for the supplementary service of the USIM card to determine whether the VoLTE service has been activated or based on the previously recorded VoLTE registration status or the previously recorded supplementary service query results). At this time, if the terminal itself supports the VoLTE function and the local VoLTE switch on the terminal side is in the off state, the interface can prompt or guide the user to turn on the VoLTE switch so that the terminal can perform voice services through VoLTE after the initial registration with IMS is successful.

[0108] Optionally, the terminal can have a built-in PLMN list that only provides EPS services (the list can indicate whether the corresponding PLMN is a PLMN belonging to a traditional CDMA operator or a PLMN that can only provide 4G / 5G network services). The PLMN information in this list can be registered and updated through user presets or based on previous registration history records. For domestic co-construction and sharing scenarios or international roaming scenarios, when the terminal is turned on or enters a new location area to read the system information of the cell, the first PLMN ID information in the PLMN list carried in the system information SIB1 is compared with the built-in PLMN list that only provides EPS services in the terminal. If the PLMN ID is included in this list and the PLMN is a PLMN that can only provide 4G / 5G network services, and it is determined that the current network does not support VoLTE or the currently used USIM card has not activated the VoLTE service or the terminal itself does not support VoLTE services or the terminal itself supports VoLTE but the VoLTE switch on the terminal interface is off, then the registration process is not initiated in the network where the cell is located; if the PLMN If the ID is included in this list and the PLMN is a PLMN of a traditional CDMA operator, and it is determined that the terminal itself does not support CDMA technology and the current network does not support VoLTE, or the terminal itself does not support CDMA technology and the current USIM card has not activated the VoLTE service, or the terminal itself does not support CDMA technology and VoLTE service, or the terminal itself does not support CDMA technology and the terminal itself supports VoLTE but the VoLTE switch on the terminal interface is off, then the registration process is not initiated in the network where the cell is located. Then search for the LTE / UMTS / GSM network of the home network or other shared networks or other visited networks in the roaming area (can be based on LTE–>UMTS–>GSM priority, or random order). And try to initiate the registration process under the searched network (can register according to the above search priority, if the LTE network registration fails, then try UMTS, if the UMTS network registration still fails, then try the GSM network, or initiate registration in random order) to obtain EPS / non-EPS services (or PS / CS domain services). If the registration is successful, EPS / non-EPS services (or PS / CS domain services) are available. If the registration fails, the network can return to the shared network that originally only provided EPS services or the roaming visited network, maintaining a state where only EPS services are available.

[0109] In the existing network, different operators generally release USIM cards that only sign up for EPS services, such as data cards or IoT cards, etc. Such cards can be distinguished by the PLMN identifier in the IMSI of the USIM card. For a terminal with such a card inserted, when it receives an Attach Accept message (for TAU Accept message, EPS update result is TAupdated) with the attach result of EPS only from the LTE network in a domestic co-construction and sharing scenario or an international roaming scenario, since the USIM card only signs up for EPS services, this is a normal process. Therefore, no operation is required, and the state in which only EPS services are available can be maintained.

[0110] In the existing network, different operators generally issue USIM cards that only sign up for EPS services, such as data cards or IoT cards, etc. Such cards can be distinguished by the PLMN identifier in the IMSI of the USIM card. For a terminal with such a card inserted, when it receives an Attach Accept message with an attach result of EPSonly from the LTE network in a domestic co-construction and sharing scenario or an international roaming scenario (for a TAU Accept message, the EPS update result is TAupdated), since the USIM card only signs up for EPS services, this is a normal process. Therefore, no operation is required, and the state where only EPS services are available can be maintained.

[0111] Since the release of the first commercial version R8, the functions of the LTE system have been continuously expanded and enhanced in subsequent versions. In particular, in the R12 version, the system message was expanded and the SIB24 system message was introduced. The purpose of introducing this system message is mainly to solve the problem of how to perform inter-system cell reselection between LTE and 5G SA cells when a terminal supporting 5G (fifth generation) SA (Standalone) resides on the LTE network and is idle in the LTE network. Due to the introduction of SIB24, the existing LTE network needs to be upgraded to support the sending of SIB24.

[0112] For early LTE terminals working in the LTE network, they will naturally be affected by the network upgrade, that is, when receiving system broadcast messages, they will also receive SIB24 system messages. Some LTE terminals, after receiving SIB24, ASN.1 (Abstract Syntax Notation One) decoding is normal, and the system message will be discarded according to the normal processing flow (because SIB24 solves the problem of cell reselection in idle state between LTE and 5G SA, for LTE terminals that do not support 5G SA, this message should be ignored). However, some LTE terminals have system compatibility problems. After receiving SIB24, they cannot complete normal ASN.1 decoding, and will discard the entire SIB1 carrying the scheduling information of SIB24 that cannot be decoded normally, causing the terminal to restart continuously and cannot be used normally.

[0113] The evolution of system standards is a long process. The problem of abnormal operation of some LTE terminals due to the introduction of SIB24 in the LTE system is unexpected. For this problem, it is caused by errors in the ASN.1 decoding process of some LTE terminals, so the most direct solution is to directly modify the above errors and then push the modified version to the terminals with problems. However, these LTE terminals are scattered in the hands of users, and it is difficult to control the upgrade process of users. There are many users who do not upgrade the version. In this case, network operators usually take temporary avoidance measures, that is, not broadcast SIB24 in system messages, so as to avoid the problem of abnormal operation of some LTE terminals. At present, the 5G SA network is still under construction, and some areas may not be covered by 5G SA signals. Therefore, for terminals that support 5G SA, in places without 5G SA coverage, they will inevitably reside in LTE networks with better coverage. If the LTE network does not broadcast SIB24 in the system information, when the 5G SA is in an idle state under the LTE network, it will not be able to reselect to the 5G SA cell. This goes against the original intention of the operator to give priority to 5G, and also affects the user experience (usually the user experience under the 5G SA system is better than that under the LTE system). When SIB24 is not broadcast in the system message under the LTE network, in order to enable the 5G SA terminal to complete the cell reselection function between the LTE and 5G SA systems in the LTE idle state, some terminal / chip manufacturers adopt various private processing solutions. The mainstream solution is to start the periodic background search function at a fixed time, that is, the terminal starts the 5G SA cell search process every 1 minute or longer in the LTE idle state. If a suitable 5G SA cell can be found during the search process, the cell reselection process between the LTE and 5G SA systems is executed; if no suitable 5G SA cell is found, the terminal maintains the original state under the LTE system until the next background search timer times out. When the area where the terminal is located is not covered by a 5G SA cell or the 5G SA cell does not meet the inter-system cell reselection conditions, the terminal will frequently search for 5G SA cells under the LTE network, which will undoubtedly increase the power consumption of the terminal.

[0114] As for the problem of SIB24 causing abnormal operation of the terminal, the current solutions have certain problems. Therefore, the following solutions are proposed:

[0115] Since the LTE terminal is already in the hands of the user, it is difficult to control its version upgrade. Therefore, the premise for solving this problem is still not to broadcast the SIB24 system message in the LTE network. At the same time, in order to solve the problem that the terminal supporting 5G SA cannot complete the LTE to 5G SA inter-system cell reselection in the LTE idle state, the existing 5G SA cell can be used to construct a SIB24 system message. The above-mentioned existing 5G SA cell information can come from the 5G SA cell where the terminal has resided, or from the 5G SA system neighboring cell carried by the terminal in the measurement control in the connected network, or the 5G SA cell information provided by the server, etc.

[0116] When a 5G SA terminal enters an idle state from a connected state in the LTE system, the terminal executes the LTE to 5G SA inter-system cell reselection process according to the SIB24 it constructed, just like receiving a real SIB24 system message.

[0117] This solution does not require version upgrades for LTE terminals, so it has certain advantages over the above-mentioned existing solutions in terms of time cost and operating cost.

[0118] The USIM card mentioned in this specification also includes an embedded SIM card (eSIM).

[0119] Various embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings.

[0120] First embodiment

[0121] Figure 1 A flowchart of an example process according to the first embodiment of the present disclosure is shown.

[0122] For domestic co-construction and sharing scenarios, when the above problem occurs, the terminal can try to search for the UMTS / GSM network of the home network (or other available shared networks), and initiate a registration process of type IMSI attachment under the searched UMTS / GSM network to obtain CS domain services (can make calls). After successful registration, EPS services are provided by the LTE network of the shared network, and CS domain services are provided by the UMTS / GSM network of the home network (or other available shared networks). If the registration fails, the terminal can return to the original shared network and maintain a state where only EPS services are available.

[0123] like Figure 1As shown, in step 101, the specific operations on the UE side are as follows: when the terminal is turned on or moves to a new tracking area, the terminal initiates an RRC establishment process under the searched LTE cell (if the RRC has not been established yet); after the RRC is successfully established, the terminal sends an EPS Attach (EPS attachment) type of combined EPS / IMSI Attach (joint EPS / IMSI attachment) Attach Request (Attach Request) message, or EPS update (EPS update) type of combined TA / LAupdating (joint TA / LA update) or combined TA / LAupdating with IMSI attach (joint TA / LA update and IMSI attachment) Tracking Area Update Request (Tracking Area Update Request, TAU Request) message to the network, and receives an Attach Accept (Attachment Accept) or Tracking Area Update Accept (TAU Accept, TAU Accept) message from the network.

[0124] In step 102, the specific operation on the UE side is as follows: determine whether the value of the EPS attachresult information element in the received Attach Accept message is 1 (i.e., EPS only), or the value of the EPS attach result information element in the most recently received Attach Accept message is 2 (Combined EPS / IMSI attach) and the value of the EPS Update result information element in the Tracking Area Update Accept message received this time is 0 (i.e., TA updated), or the value of the EPS Update result information element in the most recently received Tracking Area Update Accept message is 1 (Combined TA / LA updated) and the value of the EPSUpdate result information element in the Tracking Area Update Accept message received this time is 0 (i.e., TA updated). When the above judgment conditions are true, the terminal considers that the result of Attach (or TAU) is of EPS Only type.

[0125] In step 103, the specific operation of the UE side is as follows: the terminal side has a built-in PLMN list of USIMs that can only sign EPS only services, and compares the PLMN identifier in the IMSI of the currently used USIM card with the above list one by one. If the PLMN identifier is included in the above list, it is considered that the currently used USIM card belongs to a USIM card that can only sign EPS only services. Otherwise, it is considered that the currently used USIM card can sign both EPS services and non-EPS services.

[0126] In step 104, the specific operation on the UE side is as follows: the terminal checks whether the first PLMN ID in the PLMN list in the system information 1 (SIB1) of the current serving cell is consistent with the PLMN identifier in the IMSI of the USIM card currently used by the terminal or whether the first PLMN ID is included in the EHPLMN list in the USIM card (or the EHPLMN list built into the terminal). If the above judgment condition is true, the terminal considers that the network to which the cell belongs is the home network. The terminal checks whether the non-first PLMN ID in the PLMN list in the system information 1 (SIB1) of the current serving cell is consistent with the PLMN identifier in the IMSI of the USIM card currently used by the terminal or whether the non-first PLMN ID is included in the EHPLMN list in the USIM card (or the EHPLMN list built into the terminal). If the above judgment condition is true, the terminal considers that the network to which the cell belongs is a shared network.

[0127] There is no order requirement for executing the above steps 102 to 104, and the UE side can execute them in a random order.

[0128] In step 105, the specific operation on the UE side is as follows: the terminal starts the cell search process (i.e., turns on the radio frequency module, scans the corresponding frequency points and frequency bands supported by the terminal in sequence, and reads the system information of the cell), and determines whether the cell belongs to the home network or the shared network according to the method in step 104. If both cells belonging to the home network and cells belonging to the shared network are available, they can be sorted according to the signal strength of the broadcast channel or pilot channel received by the terminal (the signal strength here is P-CCPCH (Primary Common Control Physical Channel) or CPICH RSCP (Received Signal Code Power) for UMTS, and RSSI (Received Signal Strength Indication) for GSM).

[0129] In step 106, the terminal initiates the RRC (or RR) establishment process in the searched UMTS / GSM cell. After the RRC (or RR) is successfully established, a location area update request message (Location Update Request) with Location Updating Type (Location Update Type) as IMSI attach (IMSI attach) is sent to the network. If the current network registration fails (the registration failure here means that the Location Update Accept (Location Update Accept) message is not received or the authentication process is rejected by the network during the registration process or the network does not respond during the registration process, etc.), the above registration process is initiated on the cell with the second strongest signal according to the signal strength order described in step 105. Of course, the terminal can also preferably initiate registration with the home network, or randomly select an available network to initiate registration.

[0130] In step 107, the specific operation of the UE side is as follows: the terminal side determines whether the Location Update Accept message sent by the UMTS / GSM network is received during the registration process in step 106. In the above-mentioned registration process initiated by the terminal and the type is IMSI attachment, as long as the terminal receives the Location Update Accept message sent by any of the networks, it is determined that the registration process is successful. If the Location Update Accept message sent by the network is not received under all the available UMTS / GSM networks searched, it is determined that the registration process has failed.

[0131] If the registration process in step 107 is successful, both the EPS service and the CS domain service of the terminal are available, which effectively solves the problem that the terminal cannot use voice services in the shared network.

[0132] That is, through the above process, in the shared network construction scenario, in the EPS Only LTE network, not only can the PS domain services be used normally, but the CS domain of the home network or other shared networks can also be used to carry voice services.

[0133] Second embodiment

[0134] Figure 2 A flowchart of an example process according to the second embodiment of the present disclosure is shown.

[0135] Optionally, when the above problem occurs, the terminal searches for the LTE / UMTSUMTS / GSM network of the home network (or other available shared network) (can be in accordance with the priority of LTE–>UMTSUMTS–>GSM, or in random order. Since the LTE network can provide a higher rate and can guarantee a better user experience, the UMTS network user experience is second, and the GSM network user experience is the worst.), and attempts to initiate registration in the searched home network (or other available shared network) (can be registered according to the above search priority, if the LTE network registration fails, then try UMTSUMTS, if the UMTSUMTS network registration still fails, then try the GSM network, or randomly select the above network for registration) process to obtain EPS / non-EPS services (or PS / CS domain services). If the registration is successful, EPS / non-EPS services (or PS and CS services) are available; if the registration fails, the terminal can return to the shared network that can only provide EPS services initially, and maintain the state where only EPS services are available.

[0136] like Figure 2 As shown, steps 201 to 204 are Figure 1 Steps 101 to 104 shown in FIG. 1 are the same, so a detailed description thereof will be omitted. Figure 1 There is no order requirement for the execution of steps 202 to 204, and the UE side can execute them in a random order.

[0137] In step 205, the specific operation of the UE side is as follows: the terminal starts the cell search process (i.e., turns on the radio frequency module, sequentially scans the corresponding frequency points and frequency bands supported by the terminal, and reads the system information of the cell), and determines whether the cell belongs to the home network or the shared network according to the method of step 204. If both cells belonging to the home network and cells belonging to the shared network are available, they can be sorted according to the signal strength of the broadcast channel or pilot channel or reference signal received by the terminal (the signal strength here is the RSRP of the cell-specific reference signal for LTE, the P-CCPCH or CPICH RSCP for UMTS, and the RSSI for GSM).

[0138] In step 206, the specific operation on the UE side is as follows: the terminal initiates an RRC (or RR) establishment process in the searched LTE / UMTS / GSM cell. After the RRC (or RR) is successfully established, if the current cell is an LTE cell, the terminal sends an attachment request (Attach Request) message with EPSAttach type (EPS attachment type) being combined EPS / IMSI attach (combined EPS / IMSI attachment) to the network; if the current cell is a UMTS / GSM cell, when the network operation mode (NMO, Network Mode of Operation network operation mode) is NMO I, the terminal sends an attachment request message (AttachRequestI) with Attach type (attachment type) being combined GPRS / IMSI attach (combined GPRS / IMSI attachment) to the network; when the network operation mode is NMO II, the terminal sends a location area update request message (Location Update Request) with Location Updating Type (location update type) being IMSI attach (IMSI attachment) and an attachment request message (Attach request) with Attach type (attachment type) being GPRS attach (GPRS attachment) to the network. If the current network registration fails (registration failure here means that the Attach Accept message (for LTE) with EPS Attach result (EPS attachment result) being combined EPS / IMSI attach (combined EPS / IMSI attachment) is not received, or the Attach accept message (for UMTS / GSM NMO I) is not received, or the Location Update Accept and Attach accept messages (for UMTS / GSM NMO II) are not received, or an abnormal situation such as the authentication process being rejected by the network or the network not responding during the registration process occurs), the terminal can initiate the above registration process on the cell with the second strongest signal according to the signal strength order described in step 205. Of course, the terminal can also preferably initiate registration with the home network, or randomly select an available network to initiate registration.

[0139] In step 207, the specific operation on the UE side is as follows: the terminal side determines whether the Attach accept (for LTE network, the EPS attachresult field in the message should be combined EPS / IMSI attach) / Location Update Accept message sent by the LTE / UMTS / GSM network is received during the registration process in step 206. In the registration process initiated by the above terminal and the type is IMSI attachment, as long as the terminal receives the Attach accept (for LTE network, the EPSattach result field in the message should be combined EPS / IMSI attach) / Location Update Accept message sent by any of the networks, it is determined that the registration process is successful. If the Attach accept (for LTE network, the EPS attach result field in the message should be combined EPS / IMSI attach) / Location Update Accept message sent by the network is not received under all available LTE / UMTS / GSM networks searched, it is determined that the registration process has failed.

[0140] If the registration process in step 207 is successful, the terminal EPS / non-EPS service (for LTE) or PS / CS domain (for UMTS / GSM) service is available, which effectively solves the problem that the terminal cannot use voice service in the shared network.

[0141] That is, through the above process, in the shared network scenario, in the EPS Only LTE network, by selecting the home network or other shared networks, not only can the PS domain services be used normally, but the CS domain can also be used to carry voice services.

[0142] Third embodiment

[0143] Figure 3 A flowchart of an example process according to the third embodiment of the present disclosure is shown.

[0144] For international roaming scenarios, when the above problem occurs, the terminal can try to search for UMTS / GSM networks of other visited networks in the roaming area, and initiate a registration process of type IMSI attachment under the searched UMTS / GSM network to obtain CS domain services. If the registration is successful, both EPS services and CS services are available, so that EPS services and CS domain services are provided by the LTE network and UMTS / GSM network of two different visited networks in the roaming area respectively. If the registration fails, it can return to the roaming area visited network that can only provide EPS services initially, and maintain the state where only EPS services are available.

[0145] like Figure 3 As shown, steps 301 to 303 are Figure 1 Steps 101 to 103 are the same as shown in FIG. 1 and steps 306 and 307 are the same as those shown in FIG. Figure 1 Steps 106 and 107 shown in FIG. 1 are the same, so a detailed description thereof will be omitted.

[0146] In step 304, the specific operation on the UE side is as follows: the terminal checks whether the MCC value in the first PLMN ID in the PLMN list in the system information 1 (SIB1) of the current serving cell is consistent with the MCC value in the PLMN identifier in the IMSI of the USIM card currently used by the terminal. If they are consistent, the terminal considers that the network to which the cell belongs is a foreign operator network and the current scenario is international roaming.

[0147] Similar to Figure 1 There is no order requirement for the execution of steps 302 to 304, and the UE side can execute them in a random order.

[0148] In step 305, the specific operations on the UE side are as follows: the terminal starts the cell search process (i.e., turns on the RF module, scans the corresponding frequency points and frequency bands supported by the terminal in sequence, and reads the system information of the cell). When there are multiple cells belonging to different PLMNs available, they can be sorted according to the broadcast channel or pilot channel signal strength received by the terminal (the signal strength here is P-CCPCH or CPICH RSCP for UMTS and RSSI for GSM).

[0149] If the registration process in step 307 is successful, both EPS services and CS domain services of the terminal are available, which effectively solves the problem that the terminal cannot use voice services in the visited network in the international roaming scenario.

[0150] That is, through the above process, in the roaming scenario, in the EPS Only LTE network, not only can the PS domain services be used normally, but also the CS domain can be used to carry voice services by selecting other visited networks in the roaming area.

[0151] Fourth embodiment

[0152] Figure 4 A flowchart of an example process according to a fourth embodiment of the present disclosure is shown.

[0153] Optionally, when the above problem occurs, the terminal searches for LTE / UMTS / GSM networks of other operators' visited networks in the roaming area (can be in accordance with LTE–>UMTS–>GSM priority, or random order), and attempts to initiate registration in other visited networks found (can be registered according to the above search priority, if LTE network registration fails, then try UMTS, if UMTS network registration still fails, then try GSM network, the latter is registered in random order) process, so as to obtain EPS / non-EPS services (or PS / CS domain services). If the registration is successful, EPS / non-EPS services (or PS and CS services) are available; if the registration fails, it returns to the roaming operator network that can only provide EPS services initially, and maintains the state that only EPS services are available.

[0154] like Figure 4 As shown, steps 401 to 404 are Figure 3 Steps 301 to 304 are the same as shown in FIG. 1 and steps 405 to 407 are the same as those shown in FIG. Figure 2 Steps 205 to 207 shown in FIG. 1 are the same as those shown in FIG. 1 , and thus their detailed description will be omitted. Figure 1 There is no order requirement for the execution of steps 402 to 404, and the UE side can execute them in a random order.

[0155] If the registration process in step 407 is successful, the terminal EPS / non-EPS service (for LTE) or PS / CS domain (for UMTS / GSM) service is available, which effectively solves the problem that the terminal cannot use voice service in the visited network in the international roaming scenario.

[0156] That is, through the above process, in the roaming scenario, in the EPS Only LTE network, by selecting other visited networks in the roaming area, not only can the PS domain services be used normally, but also the CS domain can be used to carry voice services.

[0157] Fifth embodiment

[0158] Figure 5 is a flowchart illustrating an example process according to the fifth embodiment of the present disclosure.

[0159] Optionally, for domestic co-construction and sharing scenarios or international roaming scenarios, when the above problem occurs, after the terminal receives the EPS Only Attach Accept (or TAU Accept) message when it is turned on or enters a new location area, if the message indicates that the network supports IMS Voice Over PS Session, the terminal supports the VoLTE function and the local VoLTE switch on the terminal side is on, the terminal initiates the IMS initial registration process to the network. After the terminal receives a response message carrying the Retry-after field from the network side, the network will activate the VoLTE function for the user within the timer carried by the Retry-after field. After the timer specified in the Retry-after field expires, the terminal initiates the IMS initial registration process again. Since the user's VoLTE function has been activated on the network side at this time, the IMS initial registration process will be successfully completed. In this way, the terminal can perform voice services through VoLTE in a shared network.

[0160] like Figure 5 As shown, steps 501 to 503 are Figure 1 Steps 101 to 103 shown in FIG. 1 are the same, so a detailed description thereof will be omitted.

[0161] Specifically, in step 504, the specific operation on the UE side is as follows: the terminal checks whether the IMS voice over PS session indicator (indicator of IMS voice via PS session) is IMS Voice Over PS Session in S1 mode supported (supporting IMS voice via PS session in S1 mode) in the received Attach Accept (attachment acceptance) or TAU Accept (TAU acceptance) message. If the above judgment condition is true, it is considered that the network supports IMS Voice Over PS Session (IMS voice via PS session). For terminals that support VoLTE, there will be a switch for VoLTE service on its interface. When this switch is on, the terminal can use VoLTE for voice services (IMS registration is successful), otherwise the terminal needs to use CSFB for voice services.

[0162] Similar to Figure 1 There is no order requirement for the execution of steps 502 to 504, and the UE side can execute them in a random order.

[0163] In step 505, the specific operations on the UE side are as follows: the terminal sends a SIP REGISTER (Session Initiation Protocol REGISTER) message to the network.

[0164] In step 506, the specific operations on the UE side are as follows: after the terminal receives the SIP4XX response message carrying the Retry-after field sent by the network, it parses the Retry-after field and reads the timer (timer) value carried by the field, starts the corresponding timer, and after the timer times out, sends a SIP REGISTER message to the network.

[0165] In step 507, the specific operation on the UE side is as follows: the terminal receives a response message to the SIP REGISTER from the network. If a 200OK response message is received, it is determined that the IMS registration process is successful, otherwise it is a failure.

[0166] If the IMS registration process in step 507 is successful, the EPS service of the terminal is available, and VoLTE is used for voice services. In the scenario of domestic network co-construction and sharing or international roaming, the problem that the terminal cannot use voice services in the domestic shared network or the roaming visited network is effectively solved.

[0167] That is, through the above process, in a roaming scenario, the user can not only use the PS domain services normally in the EPS Only LTE network, but also use the VoLTE mode to carry voice services.

[0168] Sixth embodiment

[0169] Figure 6 is a flowchart illustrating an example process according to the sixth embodiment of the present disclosure.

[0170] For domestic co-construction and sharing scenarios or international roaming scenarios, after the terminal is turned on or enters a new location area and receives an Attach Accept message with an Attach result of EPS Only or a TAU Accept message with an EPS update result of TAupdated (both the EPS service and non-EPS service of the terminal were previously available), if the Attach Accept message indicates that the network supports IMS Voice Over PSSession, the terminal can first determine whether the USIM card currently used by the user has activated the VoLTE service (it can be determined by but not limited to sending a query for the supplementary service of the USIM card to determine whether the VoLTE service has been activated or based on the previously recorded VoLTE registration status or the previously recorded supplementary service query results). At this time, if the terminal itself supports the VoLTE function and the local VoLTE switch on the terminal side is in the off state, the terminal can prompt or guide the user to turn on the VoLTE switch on the interface so that the terminal can initiate the IMS initial registration process to the network. If the IMS initial registration process is successfully completed, the terminal can perform voice services in the shared network (or in the roaming visited network) through the VoLTE mode.

[0171] like Figure 6 As shown, steps 601 to 603 are Figure 5 Steps 501 to 503 shown in FIG. 5 are the same, so a detailed description thereof will be omitted.

[0172] In step 604, the specific operation on the UE side is as follows: the terminal checks in the received Attach Accept or TAU Accept message that the IMS voice over PS session indicator is IMS Voice Over PS Session inS1mode supported. If the above judgment condition is true, it is considered that the network supports IMS Voice Over PSSession.

[0173] In step 605, the specific operation on the UE side is as follows: the terminal sends an HTTP GET request to the network to query the supplementary service status of the currently used USIM card, and determines whether the USIM card has activated the VoLTE service based on the response message returned by the network. If an HTTP 403Forbidden message is received, it is determined that the USIM card has not activated the VoLTE service; if an HTTP 200OK message is received, it is determined that the USIM card has activated the VoLTE service. Alternatively, it is determined whether the currently used USIM card has activated the VoLTE service based on the previously recorded VoLTE registration status or the previously recorded supplementary service query result.

[0174] In step 606, the specific operation of the UE side is as follows: some terminals do not support the VoLTE function, and some terminals support the VoLTE function. For terminals that support VoLTE, there is usually a switch for the VoLTE service on its interface. When this switch is turned on, the terminal can use the VoLTE method for voice services (IMS registration is successful), otherwise the terminal needs to use the CSFB method for voice services.

[0175] Similar to Figure 1 There is no order requirement for the execution of steps 602 to 606, and the UE side can execute them in a random order.

[0176] In step 607, the specific operation on the UE side is as follows: when it is determined in step 606 that the VoLTE switch on the terminal side is in the off state, the user is prompted or guided to turn on the switch on the interface, and a friendly reminder may be given that voice services may not be possible if the switch is not turned on.

[0177] In step 608, the specific operation on the UE side is as follows: if the state of the VoLTE switch is ON, it means that the user has turned on the VoLTE switch according to the interface prompt or guidance, otherwise it is not turned on.

[0178] In step 609, the specific operations on the UE side are as follows: the terminal sends a SIP REGISTER message to the network.

[0179] In step 610, the UE side specifically operates as follows: the terminal receives a response message to the SIP REGISTER from the network. If a 200OK response message is received, it is determined that the IMS registration process is successful, otherwise it is a failure.

[0180] If the IMS registration process of step 610 is successful, the EPS service of the terminal is available, and VoLTE is used for voice services. In the scenario of domestic network co-construction and sharing or international roaming, the problem that the terminal cannot use voice services in the domestic shared network or the roaming visited network is effectively solved.

[0181] That is, through the above process, in a roaming scenario, the user can not only use the PS domain services normally in the EPS Only LTE network, but also use the VoLTE mode to carry voice services.

[0182] Seventh embodiment

[0183] Figure 7 is a flowchart illustrating an example process according to the seventh embodiment of the present disclosure.

[0184] The terminal can have a built-in PLMN list that only provides EPS services (the list can indicate whether the corresponding PLMN is a PLMN belonging to a traditional CDMA operator or a PLMN that can only provide 4G / 5G network services). The PLMN information in this list can be registered and updated through user presets or based on previous registration history records. For domestic co-construction and sharing scenarios or international roaming scenarios, when the terminal is turned on or enters a new location area to read the system information of the cell, the first PLMN ID information in the PLMN list carried in the system information SIB1 is compared with the built-in PLMN list that only provides EPS services in the terminal. If the PLMN ID is included in this list and the PLMN is a PLMN that can only provide 4G / 5G network services, and it is determined that the current network does not support VoLTE or the currently used USIM card has not activated the VoLTE service or the terminal itself does not support VoLTE services or the terminal itself supports VoLTE but the VoLTE switch on the terminal interface is off, then the registration process is not initiated in the network where the cell is located; if the PLMN If the ID is included in this list and the PLMN is a PLMN of a traditional CDMA operator, and it is determined that the terminal itself does not support CDMA technology and the current network does not support VoLTE, or the terminal itself does not support CDMA technology and the current USIM card has not activated the VoLTE service, or the terminal itself does not support CDMA technology and VoLTE service, or the terminal itself does not support CDMA technology and the terminal itself supports VoLTE but the VoLTE switch on the terminal interface is off, then the registration process is not initiated in the network where the cell is located. Then search for the LTE / UMTS / GSM network of the home network or other shared networks or other visited networks in the roaming area (can be based on LTE–>UMTS–>GSM priority, or random order). And try to initiate the registration process under the searched network (can register according to the above search priority, if the LTE network registration fails, then try UMTS, if the UMTS network registration still fails, then try the GSM network, or initiate registration in random order) to obtain EPS / non-EPS services (or PS / CS domain services). If the registration is successful, EPS / non-EPS services (or PS / CS domain services) are available. If the registration fails, the network can return to the shared network that originally only provided EPS services or the roaming visited network, maintaining a state where only EPS services are available.

[0185] like Figure 7 As shown, in step 701, the specific operations on the UE side are as follows: after the terminal is turned on or moved to a new tracking location, the terminal starts the cell search process (i.e., turns on the RF module and scans the corresponding frequency points and frequency bands supported by the terminal in sequence) and reads the system information of the cell.

[0186] In step 702, the specific operations on the UE side are as follows: the terminal checks whether the first PLMN ID in the PLMN list in the system information 1 (SIB1) of the current serving cell is in the PLMN list built into the terminal that only provides EPS Only services. According to the first PLMN ID information in the PLMN list carried in the system information SIB1, it is compared with the PLMN list built into the terminal that only provides EPS services. If the PLMN ID is included in this list and the PLMN is a PLMN that can only provide 4G / 5G network services, it is determined that the current network does not support VoLTE or the currently used USIM card has not activated the VoLTE service (which can be determined by but not limited to the previously recorded VoLTE registration status of the USIM card or the previously recorded supplementary service query results) or the terminal itself does not support the VoLTE service or the terminal itself supports VoLTE but the VoLTE switch on the terminal interface is off. When the above judgment condition is true, the registration process is not initiated in the network where the cell is located; if the PLMN The ID is included in this list and the PLMN is a PLMN belonging to a traditional CDMA operator. At the same time, it is determined that the terminal itself does not support CDMA technology and the current network does not support VoLTE, or the terminal itself does not support CDMA technology and the currently used USIM card has not activated the VoLTE service (which can be determined by but not limited to the previously recorded VoLTE registration status of the USIM card or the previously recorded supplementary service query results), or the terminal itself does not support CDMA technology and VoLTE service, or the terminal itself does not support CDMA technology and the terminal itself supports VoLTE but the VoLTE switch on the terminal interface is off. When the above judgment conditions are true, the registration process is not initiated in the network where the cell is located.

[0187] In step 703, the specific operations on the UE side are as follows: the terminal initiates the RRC connection establishment process in the current LTE cell terminal. After the RRC connection is successfully established, the terminal sends an attachment request (Attach Request) with EPS Attach type as combined EPS / IMSI attach or a tracking area update request message (TAU Request: Tracking AreaUpdate Request) with EPS update type as combined TA / LAupdating (or combinedTA / LAupdating with IMSI attach) to the network.

[0188] In step 704, the specific operation on the UE side is as follows: determine whether the EPS attachresult information element value in the received Attach Accept message is 1 (i.e. EPS only) or whether the EPS Update result information element value in the received Tracking Area Update Accept message is 0 (i.e. TA updated, it is necessary to ensure that the EPS attach result information element value in the most recently received AttachAccept message is 2 (Combined EPS / IMSI attach) or the EPS Update result information element value in the most recently received Tracking Area Update Accept message is 1 (Combined TA / LA updated)). When the above judgment conditions are true, the terminal considers that the result of Attach (or TAU) is of EPSOnly type.

[0189] If the judgment condition in step 704 is false, both EPS / non-EPS services are available to the terminal in the current network.

[0190] In step 705, the UE side specifically operates as follows: register or update the current PLMN identifier into the terminal's built-in PLMN list that only provides EPS services. Figure 1 Steps 104-107, or Figure 2 Steps 204-207, or Figure 3 Steps 304-307, or Figure 4 Steps 404-407; or Figure 5 Steps 503-507, or Figure 6 Steps 603 to 610.

[0191] That is, through the above process, in a roaming scenario, the user can not only use the PS domain services normally in the EPS Only LTE network, but also use the CS domain or the VoLTE mode to carry voice services.

[0192] Eighth embodiment

[0193] Figure 8 is a flowchart illustrating an example process according to the eighth embodiment of the present disclosure.

[0194] When a 5G SA terminal enters an idle state from a connected state in an LTE cell, if SIB24 has been received in the cell, the terminal performs a cell reselection process between the LTE and 5G SA systems according to the received SIB24; if SIB24 has not been received in the cell, a SIB24 system message is constructed according to the following existing 5G SA cell information. The above existing 5G SA cell information may come from a 5G SA cell where the terminal has resided (for example, the 5G SA cell is a cell adjacent to the LTE cell where the terminal currently resides) (including cell frequency and cell reselection priority information), or from a 5G SA system neighboring cell (including cell frequency information) carried by the terminal in the measurement control of the connected network, or 5G SA cell information (including cell frequency and cell reselection priority) provided by a server (for example, a big data platform). As an example, the server that provides 5G SA cell information may be the terminal manufacturer's own server, the operator's server, or other third-party servers, etc. When the terminal is in a network connection state, it can report the information of the cell in which it is currently residing, the current location information, and the neighboring cells of the current cell to the server. For the above information, the server can push it to other terminals for purposes such as cell switching or reselection. When the 5G SA cell in the constructed SIB24 system message comes from the 5G SA neighboring cell carried in the measurement control sent by the network when the terminal is in a connected state, since the measurement control only contains the frequency information of the neighboring cell, if the above cell information is used for the purpose of cell reselection, it is necessary to specify the cell reselection priority of the above 5G SA cell. According to the operator's 5G network priority strategy, the cell reselection priority of the above 5G SA cell is usually specified to be higher than the cell reselection priority of the LTE cell where the terminal is currently located. After the terminal successfully constructs SIB24 (including at least one 5G SA neighboring cell), the terminal executes the LTE to 5G SA system inter-cell reselection process according to the SIB24 it constructs, just like receiving a real SIB24 system message. If the constructed SIB24 does not contain any 5G SA neighboring cells, the terminal needs to maintain the current state under the LTE network.

[0195] like Figure 8 As shown, in step 801, the specific operations on the UE side are as follows: the 5G SA terminal receives the RRCConnection Release message in the LTE cell and enters the idle state from the connected state, and the message does not contain redirection information;

[0196] In step 802, the specific operations on the UE side are as follows: after the 5G SA terminal enters the idle state in the LTE cell, it determines whether the SIB24 system message has been received;

[0197] In step 803, the specific operations on the UE side are as follows: If the 5G SA terminal has received a SIB24 system message in the currently resident LTE cell, the terminal completes the LTE to 5G SA system cell reselection process.

[0198] In step 804, the specific operation on the UE side is as follows: if the 5G SA terminal has not received a SIB24 system message in the currently resident LTE cell, the terminal needs to construct a SIB24 system message based on the following existing 5G SA cell information. The above existing 5G SA cell information can come from the 5G SA cell (including cell frequency and cell reselection priority information) where the terminal has resided before, or from the 5G SA system neighboring cell (including cell frequency information) carried by the terminal in the measurement control of the network in the connected state, or the 5G SA cell information provided by the server (including cell frequency and cell reselection priority), etc. When the 5G SA cell in the constructed SIB24 system message comes from the 5G SA neighboring cell carried in the measurement control sent by the network when the terminal is in the connected state, since the measurement control only contains the frequency information of the 5G SA neighboring cell, if the above cell information is used for the purpose of cell reselection, the cell reselection priority of the above 5G SA cell needs to be specified. According to the operator's 5G network priority strategy, the cell reselection priority of the above-mentioned 5G SA cell can usually be specified to be higher than the cell reselection priority of the LTE cell where the terminal is currently located.

[0199] In step 805, the UE side specifically operates as follows: determining whether the SIB24 constructed by the 5G SA terminal contains at least one 5G SA neighbor cell information;

[0200] In step 806, the specific operations on the UE side are as follows: if the SIB24 constructed by the 5G SA terminal contains at least one 5G SA neighbor cell information, the terminal executes the LTE to 5G SA system cell reselection process according to the SIB24 constructed by it, just like receiving a real SIB24 system message.

[0201] In step 807, the specific operations on the UE side are as follows: If the SIB24 constructed by the 5G SA terminal does not contain any 5G SA neighbor cell information, the terminal needs to maintain the current state under the LTE network.

[0202] In another embodiment, in the above process, SIB24 constructed by the 5G SA terminal may also occur at other times, for example, when the terminal is in an LTE connected state. That is, through the above process, the 5G SA terminal is low-power, and can use the existing 5G SA cell information to quickly search for 5G SA cells, complete inter-system cell reselection between LTE and 5G SA cells, and early LTE terminals can also work normally.

[0203] Ninth embodiment

[0204] Fig. 9 is a flowchart illustrating an example process according to the ninth embodiment of the present disclosure.

[0205] In step 901, the specific operations on the UE side are as follows: after the terminal is turned on or moves (it may be cell selection, cell reselection or switching) to a new tracking area, the terminal starts a cell search process and reads the system information of the current serving cell.

[0206] In step 902, the UE side specifically operates as follows: the terminal checks whether the first PLMN ID in the PLMN list in the system information 1 (SIB1) of the current serving cell is in the PLMN list that only provides EPS Only service built into the terminal. If the result is true, execute step 914; otherwise, execute step 903.

[0207] In step 903, the specific operations on the UE side are as follows: the terminal initiates the RRC connection establishment process in the current LTE cell terminal. After the RRC connection is successfully established, the terminal sends an attachment request (Attach Request) with EPS Attach type as combined EPS / IMSI attach or a tracking area update request message (TAU Request: Tracking Area Update Request) with EPS update type as combined TA / LA updating (or combinedTA / LA updating with IMSI attach) to the network, and receives an Attach Accept message or a Tracking Area Update Accept message from the network side.

[0208] In step 904, the specific operation on the UE side is as follows: determine whether the value of the EPS attachresult information element in the received Attach Accept message is 1 (i.e. EPS only) or whether the value of the EPS Update result information element in the received Tracking Area Update Accept message is 0 (i.e. TA updated, it is necessary to ensure that the value of the EPS attach result information element in the most recently received AttachAccept message is 2 (Combined EPS / IMSI attach) or the value of the EPS Update result information element in the most recently received Tracking Area Update Accept message is 1 (Combined TA / LA updated)). When the above judgment condition is true, the terminal considers that the result of Attach (or TAU) is of EPSOnly type. At the same time, it is necessary to determine whether the carried EMM cause value is #16 or #17 or #18. If the above judgment result is true, execute step 906; otherwise, execute step 905.

[0209] In step 905, the specific operations on the UE side are as follows: the terminal performs subsequent actions according to the corresponding process.

[0210] In step 906, the specific operation of the UE side is as follows: the terminal determines whether the IMS voice service is available, that is, whether the current network supports VoLTE (judged by the VoPS field carried in the Attach Accept or Tracking Area Update Accept message sent by the network, if VoPS=1, it means that the network supports VoLTE, otherwise it does not support) and whether the currently used USIM card has activated the VoLTE service (which can be determined by but not limited to the previously recorded VoLTE registration status of the USIM card or the previously recorded supplementary service query result) and whether the terminal itself supports the VoLTE function. If the result is true, execute step 907, otherwise execute step 913.

[0211] In step 907, the specific operation on the UE side is as follows: determine whether the VoLTE switch (if any) on the terminal user interface is in the off state, if true, execute step 908; otherwise, execute step 910.

[0212] In step 908, the specific operations on the UE side are as follows: the terminal starts a guidance interface to guide the user to turn on the VoLTE switch.

[0213] In step 909 , the specific operation on the UE side is as follows: determine whether the user turns on the VoLTE switch according to the guidance process described in step 908 , if the result is true, execute step 910 , otherwise execute step 913 .

[0214] In step 910, the UE side specifically operates as follows: the terminal initiates an IMS registration process, specifically, the terminal sends a SIP REGISTER message to the network.

[0215] In step 911, the UE side specifically operates as follows: the terminal determines whether the IMS registration is successful, that is, whether a 200OK response message for the SIP REGISTER request message sent by the network is received. If the result is true, execute step 912; otherwise, execute step 913.

[0216] In step 912, the specific operations on the UE side are as follows: the terminal maintains a state where both data services and voice services are available in the 4G network of the current PLMN.

[0217] In step 913, the UE side specifically operates as follows: the terminal adds the current PLMN ID (ie, the PLMN ID carried in the AttachAccept or Tracking Area Update Accept message sent by the network) to the PLMN list providing EPS only service stored locally in the terminal.

[0218] In step 914, the specific operations on the UE side are as follows: the terminal searches for other available PLMN 4G, 3G or 2G networks.

[0219] In step 915, the specific operation on the UE side is as follows: if a 4G network is available among the available networks searched by the terminal, execute step 917; otherwise, execute step 916.

[0220] In step 916, the specific operation on the UE side is as follows: among the available networks searched by the terminal, if a 3G / 2G network is available (if 3G / 2G networks of multiple PLMNs are available, they can be prioritized according to signal strength), execute step 924; otherwise, execute step 927.

[0221] In step 917, the specific operations on the UE side are as follows: if there are multiple 4G networks of PLMN available in the network searched by the terminal, they can be prioritized according to signal strength, and the PLMN to which the cell with the best signal belongs is selected as the current PLMN, and a joint attachment process is initiated under the 4G network of the current PLMN.

[0222] In step 918, the UE side specifically operates as follows: the terminal side checks whether the AttachAccept message from the network side is received and whether the EPS attach result information element value is 2. If the result is true, execute step 923; otherwise, execute step 919.

[0223] In step 919, the specific operation on the UE side is as follows: determine whether the EPS attachresult information element value in the received Attach Accept message is 1 (i.e. EPS only) and whether the carried EMM cause value is #16 or #17 or #18. If the result is true, execute step 920; otherwise, execute step 921.

[0224] In step 920, the specific operations on the UE side are as follows: the operations on the terminal side are the same as step 913.

[0225] In step 921, the specific operations on the UE side are as follows: the terminal side determines whether other PLMNs are available. If true, the other PLMN (the PLMN with the second strongest signal can be selected) is set as the current PLMN and step 917 is executed; otherwise, step 922 is executed.

[0226] In step 922 , the specific operations on the UE side are as follows: the terminal may try to search for the 3G / 2G network of the current PLMN and execute step 916 .

[0227] In step 923, the specific operations on the UE side are as follows: the terminal keeps both EPS service and Non-EPS service available in the current PLMN.

[0228] In step 924, the specific operations on the UE side are as follows: the terminal initiates an IMSI attachment process in the 3G / 2G network of the current PLMN, that is, the terminal initiates an RRC (or RR) connection establishment process to the network and sends a Location Updating Request message to the network side.

[0229] In step 925, the specific operation of the UE side is as follows: whether the terminal side receives a Location Updating Accept message from the network side, if the result is true, execute step 928; otherwise, execute step 926.

[0230] In step 926, the specific operations on the UE side are as follows: the terminal side determines whether a 3G or 2G network of other PLMN is available. If true, the other PLMN (the PLMN with the second strongest signal can be selected) is set as the current PLMN and step 924 is executed; otherwise, step 927 is executed.

[0231] In step 927, the specific operations on the UE side are as follows: the terminal returns to the initial PLMN and keeps the EPS Only service available.

[0232] In step 928, the specific operations on the UE side are as follows: the terminal maintains the EPS data service under the initial PLMN and maintains the CS domain service under the current PLMN.

[0233] Tenth embodiment

[0234] Fig.10 is a flowchart illustrating an example process according to a tenth embodiment of the present disclosure.

[0235] In step 1001, the specific operations on the UE side are as follows: after the terminal is turned on or moves (it may be cell selection, cell reselection or switching) to a new tracking area, the terminal starts a cell search process and reads the system information of the current serving cell.

[0236] In step 1002, the UE side specifically operates as follows: the terminal checks whether the first PLMN ID in the PLMN list in the system information 1 (SIB1) of the current serving cell is in the PLMN list that only provides EPS Only service built into the terminal. If the result is true, execute step 1014; otherwise, execute step 1003.

[0237] In step 1003, the specific operations on the UE side are as follows: the terminal initiates the RRC connection establishment process in the current LTE cell terminal. After the RRC connection is successfully established, the terminal sends an attachment request (Attach Request) with EPS Attach type as combined EPS / IMSI attach or a tracking area update request message (TAU Request: Tracking AreaUpdate Request) with EPS update type as combined TA / LAupdating (or combinedTA / LAupdating with IMSI attach) to the network, and receives an Attach Accept message or a Tracking AreaUpdate Accept message from the network side.

[0238] In step 1004, the specific operation on the UE side is as follows: determine whether the value of the EPS attachresult information element in the received Attach Accept message is 1 (i.e. EPS only) or whether the value of the EPS Update result information element in the received Tracking Area Update Accept message is 0 (i.e. TAupdated, it is necessary to ensure that the value of the EPS attach result information element in the most recently received AttachAccept message is 2 (Combined EPS / IMSI attach) or the value of the EPS Update result information element in the most recently received Tracking Area Update Accept message is 1 (Combined TA / LA updated)). When the above judgment condition is true, the terminal considers that the result of Attach (or TAU) is of EPSOnly type. At the same time, it is necessary to determine whether the carried EMM cause value is #16 or #17 or #18. If the above judgment result is true, execute step 1006; otherwise, execute step 1005.

[0239] In step 1005, the specific operations on the UE side are as follows: the terminal performs subsequent actions according to the corresponding process.

[0240] In step 1006, the specific operation of the UE side is as follows: the terminal determines whether the IMS voice service is available, that is, whether the current network supports VoLTE (judged by the VoPS field carried in the Attach Accept or Tracking Area Update Accept message sent by the network, if VoPS=1, it means that the network supports VoLTE, otherwise it does not support it) and whether the currently used USIM card has activated the VoLTE service (which can be determined by but not limited to the previously recorded VoLTE registration status of the USIM card or the previously recorded supplementary service query result) and whether the terminal itself supports the VoLTE function. If the result is true, step 1007 is executed, otherwise step 1013 is executed.

[0241] In step 1007, the specific operation on the UE side is as follows: determine whether the VoLTE switch (if any) on the terminal user interface is in the off state, if true, execute step 1008; otherwise, execute step 1010.

[0242] In step 1008, the specific operations on the UE side are as follows: the terminal starts a guidance interface to guide the user to turn on the VoLTE switch.

[0243] In step 1009 , the specific operation on the UE side is as follows: determine whether the user turns on the VoLTE switch according to the guidance process described in step 1008 , if the result is true, execute step 1010 , otherwise execute step 1013 .

[0244] In step 1010, the UE side specifically operates as follows: the terminal initiates an IMS registration process, specifically, the terminal sends a SIP REGISTER message to the network.

[0245] In step 1011, the UE side specifically operates as follows: the terminal determines whether the IMS registration is successful, that is, whether a 200OK response message for the SIP REGISTER request message sent by the network is received. If the result is true, execute step 1012; otherwise, execute step 1013.

[0246] In step 1012, the specific operations on the UE side are as follows: the terminal maintains a state in which both data services and voice services are available in the 4G network of the current PLMN.

[0247] In step 1013, the UE side specifically operates as follows: the terminal adds the current PLMN ID (ie, the PLMN ID carried in the AttachAccept or Tracking Area Update Accept message sent by the network) to the PLMN list providing EPS only service stored locally in the terminal.

[0248] In step 1014, the specific operations on the UE side are as follows: the terminal searches for other available PLMN 4G networks.

[0249] In step 1015, the specific operation on the UE side is as follows: if a 4G network is available among the available networks searched by the terminal, execute step 1016; otherwise, execute step 1021.

[0250] In step 1016, the specific operations on the UE side are as follows: if there are multiple 4G networks of PLMN available in the network searched by the terminal, they can be prioritized according to signal strength, and the PLMN to which the cell with the best signal belongs is selected as the current PLMN, and a joint attachment process is initiated under the 4G network of the current PLMN.

[0251] In step 1017, the UE side specifically operates as follows: the terminal side checks whether the AttachAccept message from the network side is received and whether the EPS attach result information element value is 2. If the result is true, execute step 1022; otherwise, execute step 1018.

[0252] In step 1018, the specific operation on the UE side is as follows: determine whether the EPS attachresult information element value in the received Attach Accept message is 1 (i.e., EPS only) and whether the carried EMM cause value is #16 or #17 or #18. If the result is true, execute step 1019; otherwise, execute step 1020.

[0253] In step 1019, the specific operations on the UE side are as follows: the operations on the terminal side are basically the same as step 1013.

[0254] In step 1020, the specific operations on the UE side are as follows: the terminal side determines whether other PLMNs are available, and if so, executes step 1016; otherwise, executes step 1021.

[0255] In step 1021, the specific operations on the UE side are as follows: the terminal may try to search for the 3G / 2G network of the current PLMN.

[0256] In step 1022, the specific operations on the UE side are as follows: the terminal keeps both EPS service and Non-EPS service available in the current PLMN.

[0257] That is, through the above process, at least the following can be achieved:

[0258] Time saving: When IMS voice (and / or CDMA) is not available, the UE can avoid registering with a PLMN that only provides EPS services;

[0259] Providing 4G and VoLTE / CSFB: Users can use 4G for EPS services and VoLTE or CSFB for voice / SMS services.

[0260] Eleventh Embodiment

[0261] Fig.11 is a flowchart illustrating an example process according to the eleventh embodiment of the present disclosure.

[0262] In step 1101, the specific operations on the UE side are as follows: after the terminal is turned on or moves (it may be cell selection, cell reselection or switching) to a new tracking area, the terminal starts a cell search process and reads the system information of the current serving cell.

[0263] In step 1102, the UE side specifically operates as follows: the terminal checks whether the first PLMN ID in the PLMN list in the system information 1 (SIB1) of the current serving cell is in the PLMN list that only provides EPS Only service built into the terminal. If the result is true, execute step 1114; otherwise, execute step 1103.

[0264] In step 1103, the specific operations on the UE side are as follows: the terminal initiates the RRC connection establishment process in the current LTE cell terminal. After the RRC connection is successfully established, the terminal sends an attachment request (Attach Request) with EPS Attach type as combined EPS / IMSI attach or a tracking area update request message (TAU Request: Tracking AreaUpdate Request) with EPS update type as combined TA / LAupdating (or combinedTA / LAupdating with IMSI attach) to the network, and receives an Attach Accept message or Tracking AreaUpdate Accept message from the network side.

[0265] In step 1104, the specific operation on the UE side is as follows: determine whether the value of the EPS attachresult information element in the received Attach Accept message is 1 (i.e. EPS only) or whether the value of the EPS Update result information element in the received Tracking Area Update Accept message is 0 (i.e. TA updated, it is necessary to ensure that the value of the EPS attach result information element in the most recently received AttachAccept message is 2 (Combined EPS / IMSI attach) or the value of the EPS Update result information element in the most recently received Tracking Area Update Accept message is 1 (Combined TA / LA updated)). When the above judgment condition is true, the terminal considers that the result of Attach (or TAU) is of EPSOnly type. At the same time, it is necessary to determine whether the carried EMM cause value is #16 or #17 or #18. If the above judgment result is true, execute step 1106; otherwise, execute step 1105.

[0266] In step 1105, the specific operations on the UE side are as follows: the terminal performs subsequent actions according to the corresponding process.

[0267] In step 1106, the specific operation of the UE side is as follows: the terminal determines whether the IMS voice service is available, that is, whether the current network supports VoLTE (judged by the VoPS field carried in the Attach Accept or Tracking Area Update Accept message sent by the network, if VoPS=1, it means that the network supports VoLTE, otherwise it does not support) and whether the currently used USIM card has activated the VoLTE service (which can be determined by but not limited to the previously recorded VoLTE registration status of the USIM card or the previously recorded supplementary service query result) and whether the terminal itself supports the VoLTE function. If the result is true, execute step 1107, otherwise execute step 1113.

[0268] In step 1107, the specific operation on the UE side is as follows: determine whether the VoLTE switch (if any) on the terminal user interface is in the off state, if true, execute step 1108; otherwise, execute step 1110.

[0269] In step 1108, the specific operations on the UE side are as follows: the terminal starts a guidance interface to guide the user to turn on the VoLTE switch.

[0270] In step 1109 , the specific operation on the UE side is as follows: determine whether the user turns on the VoLTE switch according to the guidance process described in step 1108 , if the result is true, execute step 1110 , otherwise execute step 1113 .

[0271] In step 1110, the UE side specifically operates as follows: the terminal initiates an IMS registration process, specifically, the terminal sends a SIP REGISTER message to the network.

[0272] In step 1111, the UE side specifically operates as follows: the terminal determines whether the IMS registration is successful, that is, whether a 200OK response message for the SIP REGISTER request message sent by the network is received. If the result is true, execute step 1112; otherwise, execute step 1113.

[0273] In step 1112, the specific operations on the UE side are as follows: the terminal maintains a state in which both data services and voice services are available in the 4G network of the current PLMN.

[0274] In step 1113, the UE side specifically operates as follows: the terminal adds the current PLMN ID (ie, the PLMN ID carried in the AttachAccept or Tracking Area Update Accept message sent by the network) to the PLMN list providing EPS only service stored locally in the terminal.

[0275] In step 1114, the specific operations on the UE side are as follows: the terminal searches for other available 3G or 2G networks of PLMN.

[0276] In step 1115, the specific operations on the UE side are as follows: among the available networks searched by the terminal, if a 3G / 2G network is available (if 3G / 2G networks of multiple PLMNs are available, they can be prioritized according to signal strength), execute step 1116; otherwise, execute step 1119.

[0277] In step 1116, the specific operations on the UE side are as follows: the terminal initiates an IMSI attachment process in the 3G / 2G network of the current PLMN, that is, the terminal initiates an RRC (or RR) connection establishment process to the network and sends a Location Updating Request message to the network side.

[0278] In step 1117, the specific operation on the UE side is as follows: whether the terminal side receives the LocationUpdating Accept message from the network side, if the result is true, execute step 1120; otherwise, execute step 1118.

[0279] In step 1118, the specific operations on the UE side are as follows: the terminal side determines whether a 3G or 2G network of other PLMN is available, and if so, executes step 1116; otherwise, executes step 1119.

[0280] In step 1119, the specific operations on the UE side are as follows: the terminal returns to the initial PLMN and keeps the EPS Only service available.

[0281] In step 1120, the specific operations on the UE side are as follows: the terminal maintains the EPS data service under the initial PLMN, and maintains the CS domain service under the current PLMN.

[0282] That is, through the above process, at least the following can be achieved:

[0283] Time saving: When IMS voice (and / or CDMA) is not available, the UE can avoid registering with a PLMN that only provides EPS services;

[0284] Providing 4G and CS domains: Users can use 4G for EPS services and use the CS domain for voice / SMS services.

[0285] Twelfth Embodiment

[0286] Fig.12 is a flowchart illustrating an example process according to the twelfth embodiment of the present disclosure.

[0287] In step 1201, the specific operations on the UE side are as follows: after the terminal is turned on or moves (it may be cell selection, cell reselection or switching) to a new tracking area, the terminal starts a cell search process and reads the system information of the current serving cell.

[0288] In step 1202, the specific operations on the UE side are as follows: the terminal initiates the RRC connection establishment process in the current LTE cell terminal. After the RRC connection is successfully established, the terminal sends an attachment request (Attach Request) with EPS Attach type as combined EPS / IMSI attach or a tracking area update request message (TAU Request: Tracking Area Update Request) with EPS update type as combined TA / LA updating (or combinedTA / LA updating with IMSI attach) to the network, and receives an Attach Accept message or a Tracking Area Update Accept message from the network side.

[0289] In step 1203, the specific operation on the UE side is as follows: determine whether the value of the EPS attachresult information element in the received Attach Accept message is 1 (i.e. EPS only) or whether the value of the EPS Update result information element in the received Tracking Area Update Accept message is 0 (i.e. TA updated, it is necessary to ensure that the value of the EPS attach result information element in the most recently received AttachAccept message is 2 (Combined EPS / IMSI attach) or the value of the EPS Update result information element in the most recently received Tracking Area Update Accept message is 1 (Combined TA / LA updated)). When the above judgment condition is true, the terminal considers that the result of Attach (or TAU) is of EPSOnly type. At the same time, it is necessary to determine whether the carried EMM cause value is #16 or #17 or #18. If the above judgment result is true, execute step 1205; otherwise, execute step 1204.

[0290] In step 1204, the specific operations on the UE side are as follows: the terminal performs subsequent actions according to the corresponding process.

[0291] In step 1205, the specific operation of the UE side is as follows: the terminal determines whether the IMS voice service is available, that is, whether the current network supports VoLTE (judged by the VoPS field carried in the Attach Accept or Tracking Area Update Accept message sent by the network, if VoPS=1, it means that the network supports VoLTE, otherwise it does not support) and whether the currently used USIM card has activated the VoLTE service (which can be determined by but not limited to the previously recorded VoLTE registration status of the USIM card or the previously recorded supplementary service query result) and whether the terminal itself supports the VoLTE function. If the result is true, execute step 1206, otherwise execute step 1212.

[0292] In step 1206, the specific operation on the UE side is as follows: determine whether the VoLTE switch (if any) on the terminal user interface is in the off state, if true, execute step 1207; otherwise, execute step 1209.

[0293] In step 1207, the specific operations on the UE side are as follows: the terminal starts a guidance interface to guide the user to turn on the VoLTE switch.

[0294] In step 1208 , the specific operation on the UE side is as follows: determine whether the user turns on the VoLTE switch according to the guidance process described in step 1208 , if the result is true, execute step 1209 , otherwise execute step 1212 .

[0295] In step 1209, the UE side specifically operates as follows: the terminal initiates an IMS registration process, specifically, the terminal sends a SIP REGISTER message to the network.

[0296] In step 1210, the UE side specifically operates as follows: the terminal determines whether the IMS registration is successful, that is, whether a 200OK response message for the SIP REGISTER request message sent by the network is received. If the result is true, execute step 1211; otherwise, execute step 1212.

[0297] In step 1211, the specific operations on the UE side are as follows: the terminal maintains a state in which both data services and voice services are available in the 4G network of the current PLMN.

[0298] In step 1212, the specific operations on the UE side are as follows: the terminal searches for other available PLMN 4G networks.

[0299] In step 1213, the specific operation on the UE side is as follows: if a 4G network is available among the available networks searched by the terminal, execute step 1214; otherwise, execute step 1217.

[0300] In step 1214, the specific operations on the UE side are as follows: if there are multiple 4G networks of PLMN available in the network searched by the terminal, they can be prioritized according to signal strength, and the PLMN to which the cell with the best signal belongs is selected as the current PLMN, and a joint attachment process is initiated under the 4G network of the current PLMN.

[0301] In step 1215, the UE side specifically operates as follows: the terminal side checks whether the AttachAccept message from the network side is received and whether the EPS attach result information element value is 2. If the result is true, execute step 1218; otherwise, execute step 1216.

[0302] In step 1216, the specific operations on the UE side are as follows: the terminal side determines whether other PLMNs are available. If true, select other available PLMNs (the PLMN with the second strongest signal can be selected) as the current PLMN and execute step 1217; otherwise, execute step 1214.

[0303] In step 1217, the specific operations on the UE side are as follows: the terminal may try to search for the 3G / 2G network of the current PLMN.

[0304] In step 1218, the specific operations on the UE side are as follows: the terminal keeps both EPS service and Non-EPS service available in the current PLMN.

[0305] That is, through the above process, at least the following can be achieved:

[0306] Users can use 4G for EPS services and VoLTE or CSFB for voice / SMS services.

[0307] Thirteenth Embodiment

[0308] Fig.13 is a flowchart illustrating an example process according to the thirteenth embodiment of the present disclosure.

[0309] In step 1301, the specific operations on the UE side are as follows: after the terminal is turned on or moves (it may be cell selection, cell reselection or switching) to a new tracking area, the terminal starts a cell search process and reads the system information of the current serving cell.

[0310] In step 1302, the specific operations on the UE side are as follows: the terminal initiates the RRC connection establishment process in the current LTE cell terminal. After the RRC connection is successfully established, the terminal sends an attachment request (Attach Request) with EPS Attach type as combined EPS / IMSI attach or a tracking area update request message (TAU Request: Tracking Area Update Request) with EPS update type as combined TA / LA updating (or combinedTA / LA updating with IMSI attach) to the network, and receives an Attach Accept message or a Tracking Area Update Accept message from the network side.

[0311] In step 1303, the specific operation on the UE side is as follows: determine whether the value of the EPS attachresult information element in the received Attach Accept message is 1 (i.e. EPS only) or whether the value of the EPS Update result information element in the received Tracking Area Update Accept message is 0 (i.e. TA updated, it is necessary to ensure that the value of the EPS attach result information element in the most recently received AttachAccept message is 2 (Combined EPS / IMSI attach) or the value of the EPS Update result information element in the most recently received Tracking Area Update Accept message is 1 (Combined TA / LA updated)). When the above judgment condition is true, the terminal considers that the result of Attach (or TAU) is of EPSOnly type. At the same time, it is necessary to determine whether the carried EMM cause value is #16 or #17 or #18. If the above judgment result is true, execute step 1305; otherwise, execute step 1304.

[0312] In step 1304, the specific operations on the UE side are as follows: the terminal performs subsequent actions according to the corresponding process.

[0313] In step 1305, the specific operation of the UE side is as follows: the terminal determines whether the IMS voice service is available, that is, whether the current network supports VoLTE (judged by the VoPS field carried in the Attach Accept or Tracking Area Update Accept message sent by the network, if VoPS=1, it means that the network supports VoLTE, otherwise it does not support it) and whether the currently used USIM card has activated the VoLTE service (which can be determined by but not limited to the previously recorded VoLTE registration status of the USIM card or the previously recorded supplementary service query result) and whether the terminal itself supports the VoLTE function. If the result is true, execute step 1306, otherwise execute step 1312.

[0314] In step 1306, the specific operation on the UE side is as follows: determine whether the VoLTE switch (if any) on the terminal user interface is in the off state, if true, execute step 1307; otherwise, execute step 1309.

[0315] In step 1307, the specific operations on the UE side are as follows: the terminal starts a guidance interface to guide the user to turn on the VoLTE switch.

[0316] In step 1308 , the specific operation on the UE side is as follows: determine whether the user turns on the VoLTE switch according to the guidance process described in step 1308 , if the result is true, execute step 1309 , otherwise execute step 1312 .

[0317] In step 1309, the UE side specifically operates as follows: the terminal initiates an IMS registration process, specifically, the terminal sends a SIP REGISTER message to the network.

[0318] In step 1310, the UE side specifically operates as follows: the terminal determines whether the IMS registration is successful, that is, whether a 200OK response message for the SIP REGISTER request message sent by the network is received. If the result is true, execute step 1311; otherwise, execute step 1312.

[0319] In step 1311, the specific operations on the UE side are as follows: the terminal maintains a state in which both data services and voice services are available in the 4G network of the current PLMN.

[0320] In step 1312, the specific operations on the UE side are as follows: the terminal searches for other available PLMN 3G or 2G networks.

[0321] In step 1313, the specific operations on the UE side are as follows: among the available networks searched by the terminal, if a 3G / 2G network is available (if 3G / 2G networks of multiple PLMNs are available, they can be prioritized according to signal strength), execute step 1314; otherwise, execute step 1317.

[0322] In step 1314, the specific operations on the UE side are as follows: the terminal initiates an IMSI attachment process in the 3G / 2G network of the current PLMN, that is, the terminal initiates an RRC (or RR) connection establishment process to the network and sends a Location Updating Request message to the network side.

[0323] In step 1315, the specific operation on the UE side is as follows: whether the terminal side receives the LocationUpdating Accept message from the network side, if the result is true, execute step 1318; otherwise, execute step 1316.

[0324] In step 1316, the specific operations on the UE side are as follows: the terminal side determines whether a 3G or 2G network of other PLMN is available, and if so, executes step 1314; otherwise, executes step 1317.

[0325] In step 1317, the specific operations on the UE side are as follows: the terminal returns to the initial PLMN and keeps the EPS Only service available.

[0326] In step 1318, the specific operations on the UE side are as follows: the terminal maintains the EPS data service under the initial PLMN and maintains the CS domain service under the current PLMN.

[0327] That is, through the above process, at least the following can be achieved:

[0328] Users can use 4G for EPS services and use VoLTE or CS domain for voice / SMS services.

[0329] Fourteenth Embodiment

[0330] Fig.14 is a flowchart illustrating an example process according to the fourteenth embodiment of the present disclosure.

[0331] In step 1401, the specific operations on the UE side are as follows: after the terminal is turned on or moves (it may be cell selection, cell reselection or switching) to a new tracking area, the terminal starts a cell search process and reads the system information of the current serving cell.

[0332] In step 1402, the specific operations on the UE side are as follows: the terminal initiates the RRC connection establishment process in the current LTE cell terminal. After the RRC connection is successfully established, the terminal sends an attachment request (Attach Request) with EPS Attach type as combined EPS / IMSI attach or a tracking area update request message (TAU Request: Tracking Area Update Request) with EPS update type as combined TA / LA updating (or combinedTA / LA updating with IMSI attach) to the network, and receives an Attach Accept message or a Tracking Area Update Accept message from the network side.

[0333] In step 1403, the specific operation on the UE side is as follows: determine whether the value of the EPS attachresult information element in the received Attach Accept message is 1 (i.e. EPS only) or whether the value of the EPS Update result information element in the received Tracking Area Update Accept message is 0 (i.e. TA updated, it is necessary to ensure that the value of the EPS attach result information element in the most recently received AttachAccept message is 2 (Combined EPS / IMSI attach) or the value of the EPS Update result information element in the most recently received Tracking Area Update Accept message is 1 (Combined TA / LA updated)). When the above judgment condition is true, the terminal considers that the result of Attach (or TAU) is of EPSOnly type. At the same time, it is necessary to determine whether the carried EMM cause value is #16 or #17 or #18. If the above judgment result is true, execute step 1405; otherwise, execute step 1404.

[0334] In step 1404, the specific operations on the UE side are as follows: the terminal performs subsequent actions according to the corresponding process.

[0335] In step 1405, the specific operation of the UE side is as follows: the terminal determines whether the IMS voice service is available, that is, whether the current network supports VoLTE (judged by the VoPS field carried in the Attach Accept or Tracking Area Update Accept message sent by the network, if VoPS=1, it means that the network supports VoLTE, otherwise it does not support) and whether the currently used USIM card has activated the VoLTE service (which can be determined by but not limited to the previously recorded VoLTE registration status of the USIM card or the previously recorded supplementary service query result) and whether the terminal itself supports the VoLTE function. If the result is true, step 1406 is executed, otherwise step 1410 is executed.

[0336] In step 1406, the specific operation on the UE side is as follows: determine whether the VoLTE switch (if any) on the terminal user interface is on, if the result is true, execute step 1407; otherwise, execute step 1410.

[0337] In step 1407, the UE side specifically operates as follows: the terminal initiates an IMS registration process, specifically, the terminal sends a SIP REGISTER message to the network.

[0338] In step 1408, the UE side specifically operates as follows: the terminal determines whether the IMS registration is successful, that is, whether a 200OK response message for the SIP REGISTER request message sent by the network is received. If the result is true, execute step 1409; otherwise, execute step 1410.

[0339] In step 1409, the specific operations on the UE side are as follows: the terminal maintains a state in which both data services and voice services are available in the 4G network of the current PLMN.

[0340] In step 1410, the specific operations on the UE side are as follows: the terminal searches for other available PLMN 4G networks.

[0341] In step 1411, the specific operation on the UE side is as follows: among the available networks searched by the terminal, if a 4G network is available, execute step 1412; otherwise, execute step 1415.

[0342] In step 1412, the specific operations on the UE side are as follows: if there are multiple 4G networks of PLMN available in the network searched by the terminal, they can be prioritized according to signal strength, and the PLMN to which the cell with the best signal belongs is selected as the current PLMN, and a joint attachment process is initiated under the 4G network of the current PLMN.

[0343] In step 1413, the UE side specifically operates as follows: the terminal side checks whether the AttachAccept message from the network side is received and whether the EPS attach result information element value is 2. If the result is true, execute step 1416; otherwise, execute step 1414.

[0344] In step 1414, the specific operations on the UE side are as follows: the terminal side determines whether other PLMNs are available, and if so, executes step 1412; otherwise, executes step 1415.

[0345] In step 1415, the specific operations on the UE side are as follows: the terminal attempts to search for the 3G / 2G network of the current PLMN.

[0346] In step 1416, the specific operations on the UE side are as follows: the terminal keeps both EPS service and Non-EPS service available in the current PLMN.

[0347] That is, through the above process, at least the following can be achieved:

[0348] Users can use 4G for EPS services and CSFB for voice / SMS services (SMS for SGS).

[0349] Fifteenth Embodiment

[0350] Fig.15 is a flowchart illustrating an example process according to the fifteenth embodiment of the present disclosure.

[0351] In step 1501, the specific operations on the UE side are as follows: after the terminal is turned on or moves (it may be cell selection, cell reselection or switching) to a new tracking area, the terminal starts a cell search process and reads the system information of the current serving cell.

[0352] In step 1502, the specific operations on the UE side are as follows: the terminal initiates the RRC connection establishment process in the current LTE cell terminal. After the RRC connection is successfully established, the terminal sends an attachment request (Attach Request) with EPS Attach type as combined EPS / IMSI attach or a tracking area update request message (TAU Request: Tracking Area Update Request) with EPS update type as combined TA / LA updating (or combined TA / LA updating with IMSI attach) to the network, and receives an Attach Accept message or a Tracking Area Update Accept message from the network side.

[0353] In step 1503, the specific operation on the UE side is as follows: determine whether the value of the EPS attachresult information element in the received Attach Accept message is 1 (i.e. EPS only) or whether the value of the EPS Update result information element in the received Tracking Area Update Accept message is 0 (i.e. TA updated, it is necessary to ensure that the value of the EPS attach result information element in the most recently received AttachAccept message is 2 (Combined EPS / IMSI attach) or the value of the EPS Update result information element in the most recently received Tracking Area Update Accept message is 1 (Combined TA / LA updated)). When the above judgment condition is true, the terminal considers that the result of Attach (or TAU) is of EPSOnly type. At the same time, it is necessary to determine whether the carried EMM cause value is #16 or #17 or #18. If the above judgment result is true, execute step 1505; otherwise, execute step 1504.

[0354] In step 1504, the specific operations on the UE side are as follows: the terminal performs subsequent actions according to the corresponding process.

[0355] In step 1505, the specific operation of the UE side is as follows: the terminal determines whether the IMS voice service is available, that is, whether the current network supports VoLTE (judged by the VoPS field carried in the Attach Accept or Tracking Area Update Accept message sent by the network, if VoPS=1, it means that the network supports VoLTE, otherwise it does not support it) and whether the currently used USIM card has activated the VoLTE service (which can be determined by but not limited to the previously recorded VoLTE registration status of the USIM card or the previously recorded supplementary service query result) and whether the terminal itself supports the VoLTE function. If the result is true, step 1507 is executed, otherwise step 1510 is executed.

[0356] In step 1506, the specific operation on the UE side is as follows: determine whether the VoLTE switch (if any) on the terminal user interface is on, if the result is true, execute step 1507; otherwise, execute step 1510.

[0357] In step 1507, the UE side specifically operates as follows: the terminal initiates an IMS registration process, specifically, the terminal sends a SIP REGISTER message to the network.

[0358] In step 1508, the UE side specifically operates as follows: the terminal determines whether the IMS registration is successful, that is, whether a 200OK response message for the SIP REGISTER request message sent by the network is received. If the result is true, execute step 1509; otherwise, execute step 1510.

[0359] In step 1509, the specific operations on the UE side are as follows: the terminal maintains a state in which both data services and voice services are available in the 4G network of the current PLMN.

[0360] In step 1510, the specific operations on the UE side are as follows: the terminal searches for other available PLMN 3G or 2G networks.

[0361] In step 1511, the specific operations on the UE side are as follows: among the available networks searched by the terminal, if a 3G / 2G network is available (if 3G / 2G networks of multiple PLMNs are available, they can be prioritized according to signal strength), execute step 1512; otherwise, execute step 1515.

[0362] In step 1512, the specific operations on the UE side are as follows: the terminal initiates an IMSI attachment process in the 3G / 2G network of the current PLMN, that is, the terminal initiates an RRC (or RR) connection establishment process to the network and sends a Location Updating Request message to the network side.

[0363] In step 1513, the specific operation on the UE side is as follows: whether the terminal side receives the LocationUpdating Accept message from the network side, if the result is true, execute step 1514; otherwise, execute step 1516.

[0364] In step 1514, the specific operations on the UE side are as follows: the terminal side determines whether a 3G or 2G network of other PLMN is available, and if so, executes step 1512; otherwise, executes step 1515.

[0365] In step 1515, the specific operations on the UE side are as follows: the terminal returns to the initial PLMN and keeps the EPS Only service available.

[0366] In step 1516, the UE side specifically operates as follows: the terminal maintains the EPS data service under the initial PLMN and maintains the CS domain service under the current PLMN. That is, through the above process, at least the following can be achieved:

[0367] Users can use 4G for EPS services and use the CS domain for voice / SMS services.

[0368] Through the above ninth to fifteenth embodiments, at least the following beneficial effects can be achieved:

[0369] -Always online with VoLTE HD voice call / SMS (Short Message Service) priority: Call (VoLTE priority) and SMS services will always be available, and important calls or SMS will not be lost. Users can make / receive calls (or send / receive SMS) at any time.

[0370] - For the tenth to thirteenth embodiments, even if the VoLTE option switch is turned off, IMS supports calls and SMS. Users can always use HD Voice (VoLTE) calls.

[0371] - For the tenth, twelfth and fourteenth embodiments, CSFB supported calls and SMS. Users can always use CSFB supported calls and SMS services (SG's SMS).

[0372] - For the eleventh, thirteenth and fifteenth embodiments, calls and SMS supported by the CS domain. Users can always use the call and SMS services supported by the CS domain.

[0373] -4G EPS service priority: If a 4G cell is available, 4G will be used. Users can enjoy the high data rate of the 4G network. The user experience will be greatly improved.

[0374] - Fast Registration: If the EPS Only PLMN list is used, then in some cases, the UE can skip registering to a PLMN where call / SMS is not available and immediately search for other available PLMNs for registration. The user can quickly obtain call / SMS services.

[0375] Fig.16 is a block diagram illustrating a UE according to an embodiment of the present disclosure.

[0376] refer to Fig.16 UE (1600) includes a transceiver (1601), a processor (1602) and a memory (1603). The transceiver (1601), the processor (1602) and the memory (1603) are configured to perform the operations shown in the figure (for example, Figures 1 to 15 ) or the operations of the UE described above.

[0377] pass Fig.16 The operation of the UE shown in the EPS Only LTE network can not only use PS domain services normally, but also use CS domain or carry voice services through VoLTE.

[0378] "User Equipment" or "UE" herein may refer to any terminal with wireless communication capabilities, including but not limited to mobile phones, cellular phones, smart phones or personal digital assistants (PDAs), portable computers, image capture devices such as digital cameras, gaming devices, music storage and playback devices, and any portable unit or terminal with wireless communication capabilities, or Internet facilities that allow wireless Internet access and browsing, etc.

[0379] The term "base station" (BS) or "network equipment" used in this document may refer to eNB, eNodeB, NodeB or base transceiver station (BTS) or gNB, etc., depending on the technology and terminology used.

[0380] The "memory" here can be of any type suitable for the technical environment of this article and can be implemented using any suitable data storage technology, including but not limited to semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory.

[0381] The “processor” here may be of any type suitable for the technical environment of this article, including but not limited to one or more of the following: a general-purpose computer, a special-purpose computer, a microprocessor, a digital signal processor DSP, and a processor based on a multi-core processor architecture.

[0382] The above description is only a preferred embodiment of the present disclosure and is not intended to limit the present disclosure. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present disclosure shall be included in the scope of protection of the present disclosure.

[0383] It will be appreciated by those skilled in the art that the present disclosure includes devices for performing one or more of the operations described in the present disclosure. These devices may be specially designed and manufactured for the desired purpose, or may include known devices in general-purpose computers. These devices have computer programs stored therein, which are selectively activated or reconstructed. Such computer programs may be stored in a device (e.g., computer) readable medium or in any type of medium suitable for storing electronic instructions and coupled to a bus, respectively, the computer readable medium including but not limited to any type of disk (including floppy disk, hard disk, optical disk, CD-ROM, and magneto-optical disk), ROM (Read-Only Memory), RAM (Random Access Memory), EPROM (Erasable Programmable Read-Only Memory), EEPROM (Electrically Erasable Programmable Read-Only Memory), flash memory, magnetic card or optical card. That is, the readable medium includes any medium that stores or transmits information in a readable form by a device (e.g., computer).

[0384] Those skilled in the art will appreciate that each block in these structure diagrams and / or block diagrams and / or flow charts and combinations of blocks in these structure diagrams and / or block diagrams and / or flow charts can be implemented using computer program instructions. Those skilled in the art will appreciate that these computer program instructions can be provided to a general-purpose computer, a professional computer, or a processor of other programmable data processing methods to implement, thereby executing the scheme specified in the block or multiple blocks of the structure diagrams and / or block diagrams and / or flow charts disclosed in the present disclosure through the processor of the computer or other programmable data processing method.

[0385] Those skilled in the art will appreciate that the various operations, methods, steps, measures, and schemes discussed in the present disclosure may be alternated, altered, combined, or deleted. Furthermore, other steps, measures, and schemes in the various operations, methods, and processes discussed in the present disclosure may also be alternated, altered, rearranged, decomposed, combined, or deleted. Furthermore, the steps, measures, and schemes in the prior art that are similar to those disclosed in the present disclosure may also be alternated, altered, rearranged, decomposed, combined, or deleted.

[0386] The above description is only a partial implementation mode of the present disclosure. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present disclosure. These improvements and modifications should also be regarded as the protection scope of the present disclosure.

Claims

1. A method for communication of a user equipment (UE), the method comprising: Determine whether the UE is provided with only evolved packet system service by the current network; If it is determined that the UE is provided with only an evolved packet system service by the current network, searching for other networks different from the current network; as well as Determine whether the PLMN ID in the PLMN list carried in the system message of the searched other network is included in the stored list of networks providing only evolved packet system services; If the network is not included in the stored list of networks providing only evolved packet system services, it is determined to initiate registration for other searched networks.

2. The method according to claim 1, determining whether the UE is provided with only evolved packet system service by the current network, comprising: Receive registration messages or system messages from the current network; as well as Determine whether the UE is provided with only evolved packet system service by the current network according to the registration message or system message.

3. The method according to claim 2, in, The registration message includes one of the following: Attach Accept message; and Tracking area update accept message, And wherein, when one of the following conditions is met, it is determined that the UE is provided with only evolved packet system service by the current network: The value of the EPS Attach Result IE in the received Attach Accept message is 1; The EPS Update Result IE value in the received Tracking Area Update Accept message is 0 and the EPS Attach Result IE value in the most recently received Attach Accept message is 2; and The value of the EPS Update Result IE in the received Tracking Area Update Accept message is 0 and the value of the EPS Update Result IE in the most recently received Tracking Area Update Accept message is 1.

4. The method according to claim 2, further comprising: When it is determined according to the system message that the UE is not provided with the evolved packet system-only service, a registration process is initiated in the current network.

5. The method according to claim 2, determining whether the UE is provided with only evolved packet system service by the current network according to the system message, comprises: Based on the public land mobile network (PLMN) list carried in the system message, it is determined whether the UE is provided with only evolved packet system service by the current network.

6. The method according to claim 5, judging whether the UE is provided with only evolved packet system service by the current network based on the PLMN list carried in the system message, comprises: When the first PLMN ID of the PLMN list carried in the system message is inconsistent with the home PLMN ID corresponding to the International Mobile Subscriber Identity (IMSI), determining whether the first PLMN ID of the PLMN list carried in the system message is included in the stored list of networks providing only evolved packet system services; If the network is included in the stored list of networks providing only the evolved packet system service, it is determined that the UE is provided with only the evolved packet system service.

7. The method according to claim 6, further comprising: When the first PLMN ID in the PLMN list carried in the system message is consistent with the home PLMN ID corresponding to the IMSI, a registration process is initiated in the current network.

8. The method according to claim 4 or 7, further comprising: If a registration message indicating that the E-PSS service is provided is received, the PLMN ID of the current network is updated to the stored list of networks providing the E-PSS service.

9. The method according to claim 1, wherein: The registration process of initiating registration in other searched networks includes: Initiate a registration procedure of type IMSI attach or a registration procedure of type combined attach.

10. The method according to claim 9, wherein: If the registration procedure of type IMSI attach is successful, the UE is provided with a packet switching service by the current network and a circuit switching service by the searched other network; as well as If the registration procedure of the combined attach type is successful, the UE is provided with both packet switching services and circuit switching services by the searched other network.

11. The method according to claim 10, wherein: The searched other network providing circuit switched service comprises one of a Universal Mobile Telecommunications System (UMTS) or a Global System for Mobile Communications (GSM) network; and The searched other network providing both packet switched services and circuit switched services comprises one of a Long Term Evolution (LTE), UMTS or GSM network.

12. The method according to claim 1, wherein: The current network is a network other than the home network of the UE.

13. The method according to claim 1, wherein: The registration process of initiating registration in other searched networks includes: sorting the searched other networks according to the signal strength of the received broadcast channel or pilot channel; and Initiate a registration process in the searched other networks in the sorted order.

14. The method according to claim 1, further comprising: Before searching for other networks different from the current network, checking whether the current USIM of the UE is a USIM that can only be subscribed to and provided with only evolved packet system services; as well as If the current USIM is not a USIM that can only subscribe to be provided with only E-packet System services, other networks different from the current network are searched.

15. A method for communication of a user equipment (UE), the method comprising: Receive a registration message from the current network; If it is determined based on the received registration message that the UE is provided with only evolved packet system service by the current network, and the current network supports packet switched session IP multimedia subsystem voice, initiating an initial IMS registration process to the current network based on the high definition voice (VoLTE) switch state of the UE or the VoLTE service state of the UE; When a first preset condition is met, searching for other networks different from the current network; Determine whether the PLMN ID in the PLMN list carried in the system message of the searched other network is included in the stored list of networks providing only evolved packet system services; If the network is not included in the stored list of networks providing only evolved packet system services, it is determined to initiate registration for other searched networks.

16. The method according to claim 15, wherein: The process of initiating registration with the network based on the VoLTE switch state of the UE or the VoLTE service state of the UE includes: If the VoLTE switch state of the UE is on, an IMS initial registration process is initiated to the current network.

17. The method according to claim 15, wherein: The process of initiating registration with the network based on the VoLTE switch state of the UE or the VoLTE service state of the UE includes: If the VoLTE switch state of the UE is off, the UE determines whether the VoLTE service has been activated; and If the VoLTE service of the UE has been activated, a prompt is given to turn on the VoLTE switch, and after detecting that the VoLTE switch is turned on, an IMS initial registration process is initiated to the current network.

18. The method according to any one of claims 15 to 17, wherein: If the initial IMS registration is successful, the UE performs voice services in VoLTE mode.

19. The method according to any one of claims 15 to 17, wherein: The first preset condition includes: The current network or the searched network does not support packet-switched session IP multimedia subsystem voice; The UE does not support the VoLTE function; The VoLTE switch of the UE is not detected and is changed from the off state to the on state; The VoLTE service activation of the UE fails; and The UE detects that the user chooses not to activate the VoLTE service.

20. The method according to claim 15, wherein: The registration process initiating in the searched network includes: Initiate a registration procedure of type IMSI attach or a registration procedure of type combined attach.

21. A user equipment (UE), comprising: a transceiver, receiving signals from a base station and transmitting signals to the base station; A memory for storing executable instructions; as well as A processor runs the stored instructions to perform the method according to any one of claims 1 to 20.

22. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the method according to any one of claims 1 to 20 is implemented.

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