WO2019206248A1 - 一种电路交换回退方法及装置 - Google Patents

一种电路交换回退方法及装置 Download PDF

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Publication number
WO2019206248A1
WO2019206248A1 PCT/CN2019/084422 CN2019084422W WO2019206248A1 WO 2019206248 A1 WO2019206248 A1 WO 2019206248A1 CN 2019084422 W CN2019084422 W CN 2019084422W WO 2019206248 A1 WO2019206248 A1 WO 2019206248A1
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WIPO (PCT)
Prior art keywords
communication system
message
request
determining
csfb
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PCT/CN2019/084422
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English (en)
French (fr)
Inventor
金辉
窦凤辉
庄宏成
方平
Original Assignee
华为技术有限公司
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Priority claimed from CN201810850349.2A external-priority patent/CN110418384B/zh
Application filed by 华为技术有限公司 filed Critical 华为技术有限公司
Priority to US17/044,001 priority Critical patent/US11425611B2/en
Priority to EP19791820.4A priority patent/EP3761704A4/en
Publication of WO2019206248A1 publication Critical patent/WO2019206248A1/zh

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W36/00—Hand-off or reselection arrangements

Definitions

  • the present application relates to the field of mobile communications technologies, and in particular, to a circuit switched fallback method and apparatus.
  • circuit switched fallback is a circuit switched (CS) domain of a user equipment (UE) switching from a 4G communication network to a 3G communication network or a CS domain of a 2G communication network.
  • CSFB circuit switched fallback
  • a UE in a 5G communication system that is calling or called if the UE switches to the 4G communication system, the UE cannot establish a call in the 4G communication system due to the limitation of the condition of the switched 4G network, which may cause the UE to perform CSFB. Therefore, the circuit is returned to the circuit switched domain for calling or called, and in the above process, the UE that initiates the voice call in the 5G communication system needs to wait for the network side to transmit through the 4G communication system if the UE is transferred to the 4G communication system.
  • the message indicating that the voice call failed by the UE can be used for the CSFB; the UE that receives the voice call in the 5G communication system, if the UE is transferred to the 4G communication system, the UE needs to wait for the UE to send the indication for the UE to be CSFB can be performed by a circuit-switched fallback message called termination (or mobile terminated, MT).
  • termination or mobile terminated, MT.
  • the above UE waits for the message sent by the network side and initiates the CSFB process, which causes the voice call setup time to be too long and affects the user experience.
  • the present invention provides a circuit switched fallback method and apparatus for solving the problem that the call setup time is too long when a UE in a call or a called party experiences a communication system handover.
  • an embodiment of the present application provides a circuit switching fallback method, in which a UE that initiates a call in a 5G communication system receives a first request, and after receiving the first request, the UE receives the 4G communication system after being transferred to the 4G communication system.
  • the UE determines that the voice call bearer cannot be established in the 4G communication system, and the UE initiates the CSFB, wherein the first message is used by the UE to determine the call request failure, wherein the first request indicates that the UE is to be transferred to the 4G communication system.
  • the UE may initiate the CSFB process after determining that the voice call bearer cannot be established in the 4G communication system, thereby shortening the call setup duration.
  • the first request is a second message or a third message, wherein the second message is used by the UE to be handed over to the 4G communication system, and the third message is used for the UE to determine to be redirected to the 4G Communication Systems.
  • the UE may determine that the voice call bearer cannot be established in the 4G communication system:
  • the UE determines that the received response message corresponding to the joint location update request carries the first information, and the joint location update request is a joint location update request of the circuit switching and the packet switching sent by the UE in the 4G communication system, where the first information is used for determining by the UE.
  • the IP multimedia subsystem IMS voice service cannot be performed through the 4G communication system; or the UE determines that the response message corresponding to the received joint registration request carries the second information, and the joint registration request is the circuit switching and grouping sent by the UE in the 4G communication system.
  • the exchanged joint registration request, the second information is used by the UE to determine that the IP multimedia subsystem IMS voice service cannot be performed through the 4G communication system; or the UE determines that the signal strength between the base station and the base station of the 4G communication system is less than a threshold; or, the UE determines that there is no The measurement report that is greater than the threshold is reported to the base station of the 4G communication system; or the UE determines that the measurement report that is not less than the threshold is reported to the base station of the 4G communication system; or the UE determines that the duration of receiving the second message has reached the first pre- Set the duration, and the UE does not receive the RRC connection reconfiguration message, and the second message is used by the UE.
  • the UE is switched to the 4G communication system; or the UE determines that the duration of receiving the third message has reached the second preset duration, and the UE does not receive the RRC connection reconfiguration message, and the third message is used by the UE to be redirected to the 4G.
  • the communication system; or, the UE determines that the duration of receiving the response message corresponding to the joint registration request has reached a third preset duration, and the UE does not receive the RRC connection reconfiguration message, and the joint registration request is a circuit that the UE sends in the 4G communication system.
  • the UE may send an extended service request message initiated by the mobile terminal in the 4G communication system to initiate the CSFB process. Therefore, by setting the service type of the extended service request message, the UE can make the core network device receiving the extended service request message accurately process the extended service request message.
  • the embodiment of the present application provides a circuit switching fallback method, in which a UE that receives a call request in a 5G communication system receives a second request, and after receiving the 4G communication system, the UE receives the 4G communication system.
  • the UE determines that the voice call bearer cannot be established in the 4G communication system, and the UE initiates the CSFB, wherein the fourth message is used by the UE to initiate the mobile termination MT circuit switching fallback CSFB according to the fourth message.
  • the UE Since the UE does not need to wait for the fourth message sent by the 4G communication system during the above UE receiving the call, the UE can initiate the CSFB process after determining that the voice call bearer cannot be established in the 4G communication system, thereby shortening the call setup duration.
  • the second request is a second message or a third message, wherein the second message is used by the UE to determine to be handed over to the 4G communication system, and the third message is used for the UE to be redirected to the 4G communication system.
  • the UE may determine that the voice call bearer cannot be established in the 4G communication system: the UE determines that the response message corresponding to the received joint location update request carries the first The information, the joint location update request is a joint location update request of the circuit switching and the packet switching sent by the UE in the 4G communication system, where the first information is used by the UE to determine that the IP multimedia subsystem IMS voice service cannot be performed through the 4G communication system; or, the UE Determining that the response message corresponding to the received joint registration request carries the second information, the joint registration request is a joint registration request of the circuit switching and the packet switching sent by the UE in the 4G communication system, and the second information is used by the UE to determine that the 4G communication cannot be passed.
  • the joint location update request is a joint location update request of the circuit switching and the packet switching sent by the UE in the 4G communication system, where the first information is used by the UE to determine that the IP multimedia subsystem IMS voice service cannot be performed through the 4G communication system; or
  • the system performs an IP multimedia subsystem IMS voice service; or the UE determines that the signal strength between the base station and the base station of the 4G communication system is less than a threshold; or the UE determines that the measurement report that is greater than the threshold is not reported to the base station of the 4G communication system; or, the UE Determining that no measurement report of not less than the threshold is reported to the base station of the 4G communication system; or, the UE determines The duration of receiving the second message has reached the first preset duration, and the UE does not receive the RRC connection reconfiguration message, and the second message is used by the UE to determine that the handover is handed over to the 4G communication system; or the UE determines to receive The duration of the third message has reached the second preset duration, and the UE does not receive the RRC connection reconfiguration message, and the third message is used by the UE to be redirected to the 4G communication system; or the UE determines that the joint registration request is received.
  • the duration of the response message has reached a third preset duration, and the UE does not receive the RRC connection reconfiguration message, and the joint registration request is a joint registration request of the circuit switching and the packet switching sent by the UE in the 4G communication system; wherein, the RRC connection is heavy
  • the match message is used by the UE to determine to establish a voice call bearer within the 4G communication system.
  • the UE may send an extended service request message initiated by the mobile terminal in the 4G communication system to initiate the CSFB process. Therefore, by setting the service type of the extended service request message, the UE can make the core network device receiving the extended service request message accurately process the extended service request message.
  • the LAU may also be updated in the circuit switched origination location area to establish an MM connection through the LAU, and wait for a request to establish a call message after establishing the MM connection;
  • the UE may also not initiate the LAU but wait for a network paging message in the circuit switched domain to wait for the called party.
  • the UE may initiate a LAU in circuit switching by sending a LAU request, wherein the LAU request may carry a follow on indication, and/or the LAU request may carry a circuit switched fallback move.
  • the circuit switched fallback mobile terminated call (CSMT) indication may be used to indicate whether the LAU request may carry a follow on indication.
  • the embodiment of the present application provides a user equipment UE, which has the function of implementing the user equipment behavior in the method provided in any of the foregoing possible aspects of the first aspect or the foregoing first aspect.
  • the functions may be implemented by hardware, implemented by hardware, or by software and hardware.
  • the hardware or software includes one or more modules corresponding to the functions described above.
  • Another user equipment UE may include a request receiving module, a call bearer setup determining module, and a CSFB initiating module, where the request receiving module is configured to send a call request in the first communications system by the UE.
  • a call bearer setup determining module configured to be transferred to the UE After the second communication system, before the UE receives the first message from the second communication system, determining that a voice call bearer cannot be established in the second communication system, the first message is used for the UE Determining that the call request fails; the CSFB initiating module is configured to initiate a circuit switched fallback CSFB in the second communication system if the UE determines that the voice call bearer cannot be established in the second communication system;
  • the first communication system is a 5G communication system
  • the second communication system is a 4G communication system.
  • the first request may be a second message or a third message, wherein the second message is used by the UE to determine to be handed over to the 4G communication system, and the third message is used for the UE to determine to be redirected to the 4G communication system .
  • the call bearer setup determining module is configured to determine that the voice call bearer cannot be established in the second communication system after satisfying at least one of the following: determining a response corresponding to the joint location update request received by the UE
  • the message carries the first information
  • the joint location update request is a joint location update request of the circuit switching and the packet switching sent by the UE in the second communication system, where the first information is used by the UE to determine that the IP multimedia subsystem cannot be performed through the second communication system.
  • the response message corresponding to the joint registration request received by the UE carries the second information, where the joint registration request is a joint registration request of the circuit switching and the packet switching sent by the UE in the second communication system, and the second information
  • the joint registration request is a joint registration request of the circuit switching and the packet switching sent by the UE in the second communication system
  • the second information For determining that the IP multimedia subsystem IMS voice service cannot be performed by the second communication system; or determining that the signal strength between the UE and the base station of the second communication system is less than a threshold; or determining that the UE has no base station to the second communication system Reporting a measurement report larger than the threshold; or determining that the UE is not reporting to the second communication system
  • the base station reports a measurement report that is not less than the threshold; or determines that the duration of the second message received by the UE has reached the first preset duration, and the UE does not receive the RRC connection reconfiguration message, and the second message is used by the UE to determine Switching to the second
  • the communication system or determining that the duration of the response message corresponding to the UE receiving the joint registration request has reached a third preset duration, and the UE does not receive the RRC connection reconfiguration message, and the joint registration request is sent by the UE in the second communication system.
  • the CSFB initiating module is specifically configured to: send an extended service request message in the second communication system, and the service type of the extended service request message is a mobile terminal (mobile original, MO).
  • Another user equipment UE includes a transmitter, a processor, and a receiver.
  • the receiver may receive the first communication system after the UE sends a call request in the first communication system. a first request;
  • the processor may be configured to determine that the voice call bearer cannot be established in the second communication system after the UE receives the first message from the second communication system after being transferred to the second communication system, the first message Used to indicate that the UE is to be transferred to the second communication system;
  • the transmitter can be used to determine that the voice call bearer cannot be established in the second communication system, and initiate a circuit switched fallback CSFB in the second communication system;
  • One communication system is a 5G communication system
  • the second communication system is a 4G communication system.
  • the first request may be a second message or a third message, wherein the second message is used for the UE to determine to be handed over to the 4G communication system, and the third message is used for the UE to determine to be redirected to the 4G communication system .
  • the processor may be configured to determine that the voice call bearer cannot be established in the second communication system after the at least one of the following is determined: determining that the response message corresponding to the joint location update request received by the UE is carried in the response message
  • the first information, the joint location update request is a joint location update request of the circuit switching and the packet switching sent by the UE in the second communication system, where the first information is used by the UE to determine that the IP multimedia subsystem IMS voice service cannot be performed through the second communication system.
  • the joint registration request is a joint registration request of the circuit switching and the packet switching sent by the UE in the second communication system, and the second information is used for the UE.
  • the extended service request message may be sent in the second communication system, and the service type of the extended service request message is initiated by the mobile terminal.
  • the embodiment of the present application provides a user equipment UE, where the UE has a function of implementing user equipment behavior in the method provided in any of the foregoing possible aspects of the second aspect or the second aspect.
  • the functions can be implemented by hardware, or by software implementation of the corresponding software, or by software and hardware.
  • the hardware or software includes one or more modules corresponding to the functions described above.
  • a UE provided by the embodiment of the present application may include a request receiving module, a call bearer establishment determining module, and a CSFB initiating module.
  • the request receiving module is configured to receive, after receiving a call request in the first communications system, the UE receives the call request.
  • a second request sent by the first communication system the second request indicating that the UE is to be transferred to the second communication system
  • a call bearer setup determining module configured to receive the UE from the UE after being transferred to the second communication system Before the fourth message of the second communication system, it is determined that the voice call bearer cannot be established in the second communication system, and the fourth message is used by the UE to initiate the mobile termination MT circuit switching back-off CSFB according to the fourth message; the CSFB initiation module And in the case that the UE determines that the voice call bearer cannot be established in the second communication system, initiating a circuit switched fallback CSFB in the second communication system; wherein, the first communication system is a 5G communication system, and the second communication system is 4G communication system.
  • the second request is a second message or a third message, wherein the second message is used by the UE to determine to be handed over to the 4G communication system, and the third message is used for the UE to be redirected to the 4G communication system.
  • the call bearer setup determining module may be configured to determine that the voice call bearer cannot be established in the second communications system after determining that at least one of the following is determined: determining that the UE receives the joint location update request corresponding to the The response message carries the first information, and the joint location update request is a joint location update request of the circuit switching and the packet switching sent by the UE in the second communication system, where the first information is used by the UE to determine that the IP multimedia subclass cannot be performed by the second communication system.
  • the joint registration request is a joint registration request of the circuit switching and the packet switching sent by the UE in the second communication system
  • second The information is used by the UE to determine that the IP multimedia subsystem IMS voice service cannot be performed by the second communication system; or, determine that the signal strength between the UE and the base station of the second communication system is less than a threshold; or determine that the UE does not go to the second communication system.
  • the base station reports a measurement report that is greater than the threshold; or determines that the UE does not go to the second communication system
  • the base station reports a measurement report that is not less than the threshold; or determines that the duration of the second message received by the UE has reached the first preset duration, and the UE does not receive the RRC connection reconfiguration message, and the second message is used.
  • the UE determines that the handover is handed over to the second communication system; or determines that the duration of the third message received by the UE has reached the second preset duration, and the UE does not receive the RRC connection reconfiguration message, and the third message is used by the UE to determine that the UE is Or the UE is in the second communication system, and the UE has not received the RRC connection reconfiguration message, and the UE does not receive the RRC connection reconfiguration message, and the UE is not in the second communication system.
  • the CSFB initiating module may send an extended service request message in the second communication system when the CSFB is initiated, and the service type Service type of the extended service request message is the mobile terminal initiating the MO.
  • the UE may further include a LAU initiating module for initiating a location area update LAU in the circuit switched domain; or the UE may further include a network paging message receiving module for receiving the network paging in the circuit switched domain Message. Therefore, the UE may initiate a location area update LAU through the LAU initiating module to establish an MM connection through the LAU procedure, and wait for a request to establish a call message after establishing the MM connection, or the UE may receive the message in the circuit switched domain through the network paging message receiving module. The network pages the message to receive the called party.
  • the LAU initiating module may be used to send a LAU request when the circuit switched domain initiates a location area update LAU, the LAU request may carry a follow down indication and/or the LAU request may carry a circuit switched back to move the called party.
  • CSMT instructions may be used to send a LAU request when the circuit switched domain initiates a location area update LAU, the LAU request may carry a follow down indication and/or the LAU request may carry a circuit switched back to move the called party.
  • Another user equipment UE includes a transmitter, a processor, and a receiver.
  • the receiver is configured to receive, after the UE receives the call request in the first communication system, the first communication system sends a second request indicating that the UE is to be transferred to the second communication system;
  • the processor is operative to receive a fourth message from the second communication system at the UE after being transferred to the second communication system
  • the fourth message is used by the UE to initiate the mobile termination MT circuit switching back-off CSFB according to the fourth message; the transmitter can be used to determine that the UE cannot be in the second communication system.
  • a circuit switched fallback CSFB is initiated within the second communication system; wherein the first communication system is a 5G communication system and the second communication system is a 4G communication system.
  • the second request may be a second message or a third message, where the second message is used by the UE to determine that the handover is handed over to the second communication system, and the third message is used for The UE determination is redirected to the second communication system.
  • the processor is specifically configured to: after satisfying at least one of the following, determine that the voice call bearer cannot be established in the second communication system: determining a response message corresponding to the joint location update request received by the UE Carrying the first information, the joint location update request is a joint location update request of the circuit switching and packet switching sent by the UE in the second communication system, where the first information is used by the UE to determine that the IP multimedia subsystem IMS voice cannot be performed through the second communication system.
  • the service message; or, the response message corresponding to the joint registration request received by the UE carries the second information, where the joint registration request is a joint registration request of the circuit switching and the packet switching sent by the UE in the second communication system, and the second information is used for
  • the UE determines that the IP multimedia subsystem IMS voice service cannot be performed by the second communication system; or determines that the signal strength between the UE and the base station of the second communication system is less than a threshold; or determines that the UE has not reported to the base station of the second communication system a measurement report that is greater than the threshold; or, determining that the UE has not reported to the base station of the second communication system
  • the measurement report is less than the threshold; or, determining that the duration of the second message received by the UE has reached the first preset duration, and the UE does not receive the RRC connection reconfiguration message, and the second message is used by the UE to determine that the handover is handed over to the UE.
  • the extended service request message may be sent in the second communication system, and the service type of the extended service request message is initiated by the mobile terminal.
  • the transmitter can also be used to initiate a location area update LAU in the circuit switched domain, or the receiver can be used to receive network paging messages in the circuit switched domain.
  • the UE may initiate a location area update LAU through the transmitter to establish an MM connection through the LAU procedure, and wait for a request to establish a call message after establishing the MM connection, or the UE may receive a network paging message in the circuit switched domain through the receiver, Receive the called party.
  • the transmitter can be used to send a LAU request when the circuit switched domain initiates a location area update LAU, the LAU request can carry a follow last indication and/or the LAU request can carry a circuit switched fallback mobile called CSMT indication .
  • an embodiment of the present application provides a computer program product, including a computer program, when executed on a computer or a processor, the computer or processor is configured to implement the first aspect described above.
  • a computer program product including a computer program, when executed on a computer or a processor, the computer or processor is configured to implement the first aspect described above.
  • the embodiment of the present application provides a computer readable storage medium for storing programs and instructions.
  • the programs and instructions When the programs and instructions are executed in a computer, the computer may be configured to execute the method embodiment of the first aspect.
  • an embodiment of the present application provides a chip.
  • the chip may be coupled to a transceiver for performing the functions involved in any one of the possible embodiments of the method embodiment, the method embodiment, or the method for performing the method of the second aspect described above.
  • FIG. 1 is a schematic diagram of an exemplary calling scene CSFB process in the prior art
  • FIG. 2 is a schematic diagram of another exemplary calling scene CSFB process in the prior art
  • FIG. 3 is a schematic flow chart of an exemplary called scene CSFB in the prior art
  • FIG. 4 is a schematic diagram of another exemplary called scene CSFB process in the prior art
  • FIG. 5 is a schematic structural diagram of an exemplary communication system according to an embodiment of the present disclosure.
  • FIG. 6 is a schematic structural diagram of an exemplary user equipment UE according to an embodiment of the present disclosure.
  • FIG. 7 is a schematic flowchart diagram of an exemplary circuit switched fallback method according to an embodiment of the present disclosure.
  • FIG. 8 is a schematic flowchart diagram of another exemplary circuit switched fallback method according to an embodiment of the present disclosure.
  • FIG. 9 is a schematic flowchart of an exemplary method for circuit switching backoff of a calling scenario according to an embodiment of the present disclosure.
  • FIG. 10 is a schematic flowchart diagram of another exemplary calling circuit circuit switching backoff method according to an embodiment of the present disclosure.
  • FIG. 11 is a schematic flowchart diagram of an exemplary method for circuit switching backoff of a called scenario according to an embodiment of the present disclosure
  • FIG. 12 is a schematic flowchart diagram of another exemplary method for circuit switching backoff of a called scenario according to an embodiment of the present disclosure
  • FIG. 13 is a schematic structural diagram of another exemplary user equipment UE according to an embodiment of the present disclosure.
  • FIG. 14 is a schematic structural diagram of still another exemplary user equipment UE according to an embodiment of the present disclosure.
  • At least one refers to one, or more than one, including one, two, three, and more.
  • Carrying may mean that a message is used to carry certain information or data, or that a message is composed of certain information.
  • the process of the UE initiating the CSFB is as shown in FIG. 1 :
  • Step 101 The UE 600 in the 5G communication system initiates IP multimedia subsystem (IMS) caller signaling, and the IMS caller signaling is sent to the service call continuity application server.
  • IMS IP multimedia subsystem
  • SCC AS IP multimedia subsystem
  • the IMS calling signaling may carry information such as the voice coding mode information supported by the UE, the IP address information of the UE, the port number, and the like;
  • Step 102 The proxy-call session control function (P-CSCF) receives the 183 message sent by the calling peer device through the IMS server, where the IMS server may be an SCC AS, and the 183 message is received by the called device. a response message sent after the call request;
  • P-CSCF proxy-call session control function
  • Step 103 The P-CSCF sends a session management function to the network element of the 5G communication system through a policy control function (PCF)/policy and charging rules function (PCRF).
  • PCF policy control function
  • PCF policy control function
  • PCF policy control function
  • PCF policy and charging rules function
  • SMF sends a request to establish a voice transmission channel
  • Step 104 The SMF sends a request for establishing a voice transmission channel to the NG RAN through an access and mobility management function (AMF); the NG RAN refers to a 5G base station;
  • AMF access and mobility management function
  • Step 105 The NG RAN determines that the voice transmission channel cannot be established
  • Step 106 The NG RAN instructs the UE to perform 4G signal measurement, and sends a request message that the UE is handed over to the 4G communication system to the UE;
  • Step 107 The NG RAN notifies the SMF that the voice transmission channel cannot be established through the AMF; wherein the NG RAN may send an N2 message to the AMF to indicate that the quality of service (QoS) data flow is refused due to the IMS voice backoff.
  • the AMF may send an SM request with a PDU modification command ack to the SMF;
  • Step 108 After the UE switches to the 4G communication system, the UE performs a long term evolution (LTE) and a CS area tracking area update (TAU) process;
  • LTE long term evolution
  • TAU CS area tracking area update
  • Step 109 The PDN GateWay (PGW) sends a voice transmission channel setup request to the 4G base station eNB, so that the voice transmission channel establishment request is re-initiated within 4G.
  • PGW PDN GateWay
  • Step 110 If the eNB determines that the voice transmission channel cannot be established, the eNB returns a reject message to the PGW.
  • Step 111 The PGW sends a reject message to the P-CSCF through the PCRF.
  • Step 112 The P-CSCF sends a Cancel message to the SCC AS, to notify the SCC AS to cancel the call.
  • Step 113 The P-CSCF sends a message to the UE for the UE to determine that the voice call cannot be established in the 4G system, for example, sending a 500 reject message;
  • Step 114 After receiving the message for the UE to determine that the voice call cannot be established within the 4G system, the UE initiates the CSFB within the LTE.
  • FIG. 2 After the UE initiates a call in the 5G communication system, the UE switches to the 4G communication system and the UE cannot establish a voice call bearer in the 4G, another CSFB process is shown in FIG. 2:
  • Step 201 The UE 600 in the 5G communication system initiates IMS caller signaling, and the IMS caller signaling is sent to the SCC AS.
  • the IMS caller signaling may carry the voice coding mode information supported by the UE, the IP address information of the UE, Port number and other information;
  • Step 202 The P-CSCF receives the 183 message sent by the calling peer device through the IMS server, where the IMS server may be an SCC AS, and the 183 message is a response message sent by the called end device after receiving the call request.
  • the IMS server may be an SCC AS
  • the 183 message is a response message sent by the called end device after receiving the call request.
  • Step 203 The P-CSCF sends a request for establishing a voice transmission channel to the SMF of the 5G communication system through the PCF/PCRF.
  • Step 204 The SMF sends a request for establishing a voice transmission channel to the NG RAN through the AMF; the NG RAN refers to the 5G base station;
  • Step 205 The NG RAN determines that the voice transmission channel cannot be established.
  • Step 206 The NG RAN instructs the UE to perform 4G signal measurement, and sends a request message that the UE is switched to the 4G communication system to the UE;
  • Step 207 The NG RAN notifies the SMF that the voice transmission channel cannot be established through the AMF; wherein the NG RAN may send an N2 message to the AMF 201 to indicate that the QoS data flow is refused due to the IMS voice backoff, and the AMF 201 may send the carry PDU modification command to the SMF. Confirm the SM request for the character;
  • Step 208 The NG RAN sends an RRC connection release message to the UE, and redirects the UE from the 5G communication system to the 4G communication system.
  • Step 209 After receiving the RRC connection release message, the UE reselects to the 4G base station, and sends a CS/PS domain joint registration request and includes a handover indication in the joint registration message.
  • Step 210 The PGW sends a voice transmission channel establishment request to the 4G base station eNB, so that the voice transmission channel establishment request is re-initiated within 4G;
  • Step 211 If the eNB determines that the voice transmission channel cannot be established, the eNB returns a reject message to the PGW.
  • Step 212 The PGW sends a reject message to the P-CSCF through the PCRF.
  • Step 213 The P-CSCF sends a Cancel message to the SCC AS, to notify the SCC AS to cancel the call.
  • Step 214 The P-CSCF sends a message to the UE for the UE to determine that the voice call cannot be established in the 4G system, such as sending a 500 reject message.
  • Step 215 After receiving the message for the UE to determine that the voice call cannot be established in the 4G system, the UE initiates the CSFB in the LTE.
  • the UE can only initiate the CSFB and establish a call in the circuit domain only after receiving the message that the UE determines that the voice call cannot be established in the 4G system.
  • the process of waiting for the message will cause the UE to initiate CSFB for too long, resulting in a call setup time that is too long.
  • the process of the UE initiating the CSFB is as shown in FIG. 3:
  • Step 301 The UE 600 in the 5G communication system receives the IMS called signaling, and the IMS called signaling is sent by the SCC AS; the IMS called signaling can carry the voice coding mode information and the call supported by the calling peer device. Information such as the IP address information and port number of the peer device;
  • Step 302 The UE 600 sends a 183 message to the P-CSCF.
  • the 183 message may carry the coding mode information and the like selected by the UE 600.
  • Step 303 The P-CSCF sends a request for establishing a voice transmission channel to the SMF of the 5G communication system through the PCF/PCRF.
  • Step 304 The SMF sends a request for establishing a voice transmission channel to the NG RAN through the AMF.
  • Step 305 The NG RAN determines that the voice transmission channel cannot be established.
  • Step 306 The NG RAN instructs the UE to perform 4G signal measurement, and sends a request message that the UE is switched to the 4G communication system to the UE;
  • Step 307 The NG RAN notifies the SMF that the voice transmission channel cannot be established through the AMF; wherein the NG RAN may send an N2 message to the AMF 301 to indicate that the MF data flow is rejected due to the IMS voice backoff, and the AMF may send the carry PDU modification command to the SMF. Confirm the SM request for the character;
  • Step 308 After the UE switches to the 4G communication system, the UE performs a TAU process of the LTE and CS domains.
  • Step 309 The PGW sends a voice transmission channel establishment request to the eNB, so that the voice transmission channel establishment request is re-initiated within 4G;
  • Step 310 If the eNB determines that the voice transmission channel cannot be established, the eNB returns a reject message to the PGW.
  • Step 311 The PGW sends a reject message to the P-CSCF through the PCRF.
  • Step 312 The P-CSCF sends a reject message to the SCC AS.
  • Step 313 The SCC AS re-selects the called access domain, and selects the CS domain to perform the call again.
  • Step 314 The SCC AS initiates the call again through the P-CSCF, and the call is routed to the mobile switching center (MSC) currently registered by the UE;
  • MSC mobile switching center
  • Step 315 The MSC sends a call request to a mobile management entity (MME).
  • MME mobile management entity
  • Step 316 The MME sends a message to the UE for determining, by the UE, that the MT CSFB is performed, and the message may be a call request of the circuit domain.
  • Step 317 After receiving the message for the UE to determine the MT CSFB, the UE initiates the MT CSFB.
  • Step 402 The UE 600 sends a 183 message to the P-CSCF.
  • the 183 message may carry the coding mode information and the like selected by the UE 600.
  • Step 403 The P-CSCF sends a request for establishing a voice transmission channel to the SMF of the 5G communication system through the PCF/PCRF.
  • Step 404 The SMF sends a request for establishing a voice transmission channel to the NG RAN through the AMF.
  • Step 405 The NG RAN determines that the voice transmission channel cannot be established.
  • Step 406 The NG RAN instructs the UE to perform 4G signal measurement, and sends a request message that the UE is switched to the 4G communication system to the UE;
  • Step 407 The NG RAN notifies the SMF that the voice transmission channel cannot be established through the AMF; wherein the NG RAN may send an N2 message to the AMF 401 to indicate that the MF data flow is rejected due to the IMS voice backoff, and the AMF may send the carry PDU modification command to the SMF. Confirm the SM request for the character;
  • Step 408 The NG RAN sends an RRC connection release message to the UE, and redirects the UE from the 5G communication system to the 4G communication system.
  • Step 409 After receiving the RRC connection release message, the UE reselects to the 4G base station, and sends a CS/PS domain joint registration request and includes a handover indication in the joint registration message.
  • Step 410 The PGW sends a voice transmission channel establishment request to the eNB, so that the voice transmission channel establishment request is re-initiated within 4G.
  • Step 411 If the eNB determines that the voice transmission channel cannot be established, the eNB returns a reject message to the PGW.
  • Step 412 The PGW sends a reject message to the P-CSCF through the PCRF.
  • Step 413 The P-CSCF sends a reject message to the SCC AS.
  • Step 414 The SCC AS re-selects the called access domain, and selects the CS domain to perform the re-call;
  • Step 415 The SCC AS initiates a call again through the P-CSCF, and the call is routed to the MSC currently registered by the UE;
  • Step 416 The MSC initiates a call request to the MME.
  • Step 417 The MME sends a message to the UE for determining, by the UE, that the MT CSFB is performed, and the message may be a call request of the circuit domain.
  • Step 418 After receiving the message for the UE to determine the MT CSFB, the UE initiates the MT CSFB.
  • the UE can initiate the CSFB after receiving the message sent by the MME for the UE to determine the MT CSFB, and then establish a call in the circuit domain, and wait.
  • the process of this message will cause the UE to initiate CSFB for too long, resulting in a call setup time that is too long.
  • the embodiment of the present application provides a circuit switching fallback method and apparatus.
  • the communication system to which the circuit switching fallback method provided by the embodiment of the present application is applicable may be a 5G communication system.
  • the N26 interface can be used in the 5G core network.
  • the UE context is transmitted between the meta-AMF 501 and the 4G core network element MME 502 to implement seamless handover of the communication system where the UE is located, and the UE can maintain the pre-transition internet protocol (internet) in the transferred communication system.
  • internet internet protocol
  • the MME 502 may select the SMF+PGW-C 503 that the 5G and the 4G are set for the UE, so as to keep the PGW-C corresponding to the UE unchanged.
  • the first communication system involved in the embodiment of the present application may be a 5G communication system, and the second communication system is a 4G communication system; if the first communication system may be a 4G communication system, the second communication system is a 5G communication system. .
  • the UE 600 that is applicable to the circuit-switched fallback method provided by the embodiment of the present application may have a structure as shown in FIG. 6. It can be seen that the UE 600 may include a processor 601, which may be used to support The UE 600 implements the steps involved in the UE 600 in the circuit switched fallback method provided by the embodiment of the present application. For example, the UE 600 may determine that the voice call bearer cannot be established in the second communication system. For example, the UE 600 may also have the transceiver. The 603, wherein the transceiver 603 can be used by the UE 600 to receive and/or transmit a message (or data), for example, the UE 600 receives the first request or the second request, or is used by the UE 600 in the first communication.
  • the CSFB is initiated in the system, or is used by the UE 600 to receive the response message, the first message, the second message, the third message, or the fourth message involved in the circuit switched fallback method provided by the embodiment of the present application; for example,
  • the transceiver 602 in the UE 600 may be composed of a transmitter and a receiver, the transmitter may be used to implement the transmitting function of the transceiver 602, and the receiver may be used to implement the receiving function of the transceiver 602.
  • the UE 600 may further include a memory 603, where the computer program and instructions are stored, and the memory 603 may be coupled to the processor 601 for supporting the processor 601 to call the computer program and instructions in the memory 603 to implement the embodiment of the present application.
  • the steps involved in the UE 600 are provided in the circuit switched fallback method.
  • the memory 602 can also be used to store data.
  • the processor 601 in the above UE 600 may be a central processing unit, a general purpose processor, a digital signal processor, an application specific integrated circuit, a field programmable gate array or other programmable logic device, a transistor logic device, a hardware component or Any of the various logical blocks, modules and circuits described in connection with the disclosure of the embodiments of the present application can be implemented or executed in any combination.
  • the processor may also be a combination of computing functions, for example, including one or more microprocessor combinations, combinations of digital signal processors and microprocessors, and the like.
  • the UE 600 can use the voice service in the 5G communication system, and the UE 600 needs the UE 600 to be a terminal, a mobile station (MS, a mobile station), a mobile terminal, etc., and the UE 600 can
  • the core network entity of one or more communication systems communicates and accepts network services provided by the core network entity.
  • the UE 600 in the embodiment of the present application may be a mobile phone (or "cellular" phone), a computer with a mobile terminal, etc., and the UE 600 may also be portable, pocket-sized, handheld, built-in or Mobile device on the car.
  • the UE 600 may also be a communication chip having a communication module.
  • the first communication system is a 5G communication system
  • the second communication system is a 4G communication system.
  • FIG. 7 a circuit switching fallback method provided by the embodiment of the present application is described. The method includes the following steps:
  • Step S101 After transmitting the call request in the 5G communication system, the UE 600 receives the first request sent by the 5G communication system, and the first request indicates that the UE 600 is to be transferred to the 4G communication system;
  • Step S102 After being transferred to the 4G communication system, the UE 600 determines that the voice call bearer cannot be established in the 4G communication system before receiving the first message from the 4G communication system, where the first message is used by the UE 600 to determine the call.
  • the request fails; in the implementation, the first message here may be a 500 reject message sent by the P-CSCF to the UE;
  • Step S103 The UE 600 initiates the CSFB in the 4G communication system if it is determined that the voice call bearer cannot be established in the 4G communication system.
  • the UE 600 can pass the step S103 after determining that the voice call bearer cannot be established in the 4G communication system through step S102.
  • the UE may initiate the CSFB after waiting for the method of initiating the CSFB as shown in FIG. 1, and may wait for the 500 to reject the 500 reject message sent by the P-CSCF in step 113, thereby shortening the UE.
  • the call setup duration of 600 is compared; the UE may initiate the CSFB by waiting for the 500 reject message sent by the P-CSCF in step 214 after performing step 209, as compared with the method of initiating CSFB as shown in FIG. 2; Therefore, the call setup waiting time of the UE 600 is shortened.
  • the first communication system is a 5G communication system
  • the second communication system is a 4G communication system.
  • Another circuit-switched fallback method provided by the embodiment of the present application is described with reference to FIG. 8. The method includes the following steps:
  • Step S201 After receiving the call request in the 5G communication system, the UE 600 receives the second request sent by the 5G communication system, and the second request indicates that the UE 600 is to be transferred to the 4G communication system;
  • Step S202 After being transferred to the 4G communication system, the UE 600 determines that the voice call bearer cannot be established in the 4G communication system before receiving the fourth message from the 4G communication system, and the fourth message is used to indicate that the UE 600 is according to the fourth The message is used to initiate the MT CSFB; in the implementation, the fourth message here may be a circuit domain call request message sent by the MME to the UE 600, for the UE to perform the MT CSFB after the receipt for the CS domain call;
  • Step S203 The UE 600 initiates the CSFB in the 4G communication system if it is determined that the voice call bearer cannot be established in the 4G communication system.
  • the UE 600 can pass the step of step S202 to determine that the voice call bearer cannot be established in the 4G communication system.
  • the CSFB is initiated.
  • the UE may not wait for the message sent by the MME for the UE 600 to initiate the MT CSFB in step 316 after performing step 308.
  • CSFB thus shortening the call setup waiting time of the UE 600; compared to the method of initiating CSFB as shown in FIG. 4, the UE may not spend time waiting for the UE 600 to be sent by the MME in step 417 after performing step 409.
  • the CS CSFB message can initiate CSFB, shortening the call setup duration of the UE 600.
  • the first request sent by the 5G communication system received by the UE 600 may be a second message, where the second message may be used by the UE 600 to determine that it is handed over to the 4G communication system.
  • the message in particular, the second message may be a request message indicating that the UE 600 is switched to the 4G communication system; in another implementation, the first request sent by the 5G communication system received by the UE 600 may also be the third message.
  • the message, the third message herein may be a message for the UE 600 to determine to be redirected to the 4G communication system, in particular, the third message may be a request message indicating that the UE 600 is redirected to the 4G communication system, in implementation
  • the request message that the UE 600 is redirected to the 4G communication system may be a radio resource control (RRC) connection release message sent to the UE 600.
  • RRC radio resource control
  • the second request sent by the 5G communication system received by the UE 600 may also be a second message or a third message, where the second message may be indicating that the UE 600 is switched to the 4G communication system.
  • the request message, the third message here may be a message for the UE 600 to be redirected to the 4G communication system, and the specific implementation of the second request may refer to the implementation manner of the foregoing first request.
  • the UE 600 determines that there are multiple ways to establish a voice call bearer in the 4G communication system. Several possible implementation manners are respectively exemplified below, indicating that the UE 600 determines that the UE cannot be in the 4G communication system.
  • the method of establishing a voice call bearer is
  • the UE 600 determines that the voice call bearer cannot be established in the 4G communication system.
  • the UE 600 can determine whether the 4G communication system supports the IP Multimedia Subsystem IMS voice according to the following method:
  • the UE 600 may initiate a joint location update of circuit switching and packet switching in the 4G communication system, and determine 4G according to the response message corresponding to the received joint location update. Whether the communication system supports the IP Multimedia Subsystem IMS voice. Specifically, the UE 600 may send a joint location update request for circuit switching and packet switching to the 4G core network element MME, and after receiving the response message corresponding to the joint location update request, the UE 600 determines that the response message includes the first information.
  • the UE 600 determines that the 4G communication system supports the IP multimedia subsystem IMS voice.
  • the first information herein may be an indication that the 4G communication system does not support the indication of IMS voice or the inability to establish IMS voice within the 4G communication system.
  • the UE 600 may initiate joint registration of circuit switching and packet switching in the 4G communication system, and determine 4G communication according to the response message corresponding to the received joint registration. Whether the system supports the IP Multimedia Subsystem IMS voice.
  • the UE 600 may send a circuit-switched and packet-switched joint registration request to the 4G core network element MME, and after receiving the response message corresponding to the joint location update request, the UE 600 determines that the response message includes the second information, It is then determined that the 4G communication system does not support the IP Multimedia Subsystem IMS voice, thereby determining that the voice call bearer cannot be established within the 4G communication system; otherwise, the UE 600 determines that the 4G communication system supports the IP Multimedia Subsystem IMS voice.
  • the second information herein may be an indication that the 4G communication system does not support the IP Multimedia Subsystem IMS voice over the PS session or the IMS voice cannot be established within the 4G communication system.
  • the UE 600 determines that the 4G communication system supports the IP multimedia subsystem IMS voice, it does not mean that the UE 600 must be able to establish a voice call bearer in the 4G communication system.
  • the UE 600 can determine whether the voice call bearer can be established in the 4G communication system according to the signal strength between the base station and the base station in the 4G communication system.
  • the UE 600 determines whether the signal strength between the UE and the base station in the 4G communication system is less than a threshold.
  • the threshold here may be the lowest signal strength that the UE can establish a voice bearer in the 4G communication system.
  • the signal strength between the UE 600 and the base station of the 4G communication system after the transfer to the 4G communication system is not strong, and the signal strength requirement between the UE 600 and the base station in the process of establishing the voice call bearer in the 4G communication system is not satisfied, so that the UE 600 can It is determined that the voice call bearer cannot be established in the 4G communication system; otherwise, if the UE 600 determines that the signal strength between the UE and the base station in the 4G communication system is greater than or equal to the threshold, the UE 600 and the 4G are transferred after the UE 600 is transferred to the 4G communication system.
  • the signal strength between the base stations in the communication system satisfies the signal strength requirement for establishing a voice call bearer in the 4G communication system.
  • the UE 600 may not perform CSFB. It should be noted that the UE 600 may also determine here whether the signal strength between itself and the base station in the 4G communication system is less than or equal to the threshold, and if so, the UE 600 determines that the voice call bearer cannot be established within the 4G communication system.
  • the UE 600 can determine the signal strength in all the measurement reports that are reported to the base station in the 4G communication system, and whether there is a signal strength that is not less than the threshold.
  • the threshold here may be that the UE can be established in the 4G communication system.
  • the UE 600 determines that the voice call bearer cannot be established in the 4G communication system; if the UE 600 determines that the UE 600 has previously sent There is at least one signal strength greater than or equal to the threshold in the measurement report, indicating that the signal strength between the UE 600 and the base station at least once satisfies the requirement of the signal strength between the UE 600 and the base station in establishing the voice call bearer process in the 4G communication system. At this time, the UE 600 may not perform CSFB.
  • the UE 600 may also determine, by the UE 600, the signal strength in the measurement report sent by the base station in the 4G communication system, whether there is a signal strength greater than the threshold, if the UE 600 determines that the base station of the 4G communication system has not been reported before. If the measurement report is greater than the threshold, the UE 600 determines that the voice call bearer cannot be established within the 4G communication system.
  • the UE 600 can determine that the voice call bearer cannot be established in the 4G communication system according to the length of time that the RRC connection reconfiguration message is not received by the radio resource.
  • the UE 600 may determine to establish a voice bearer in the 4G communication system according to the received RRC connection reconfiguration message sent by the base station.
  • the UE 600 may perform CSFB to avoid the UE 600 for a long time. Waiting for the RRC connection reconfiguration message.
  • the UE 600 is no longer required to perform CSFB.
  • the UE 600 may determine that the voice call bearer cannot be established in the 4G communication system after determining that the duration of the second message received by the UE has reached the first preset duration and the RRC reconfiguration message has not been received yet.
  • the second message here may be a message indicating that the UE 600 is switched to the 4G communication system; if the UE 600 determines that the RRC reconfiguration message is received, the duration of the second message received by the UE has not reached the first preset duration, the UE 600 determines not to perform CSFB.
  • the UE 600 after determining that the duration of receiving the third message has reached the second preset duration, and the UE still does not receive the RRC reconfiguration message, it determines that the voice call cannot be established in the 4G communication system.
  • the third message in the bearer may be a message indicating that the UE 600 is redirected to the 4G communication system; if the UE 600 determines that the RRC reconfiguration message is received, the duration of the third message received by the UE 600 has not reached the second preset duration. The UE 600 determines not to perform CSFB.
  • the UE 600 may determine that the voice call bearer cannot be established in the 4G communication system after determining that the duration of the response message received by the UE has reached the third preset duration and the RRC reconfiguration message has not been received by itself.
  • the response message here may be a response message corresponding to the joint registration request of the circuit switching and the packet switching initiated by the UE 600 in the 4G communication system; if the UE 600 determines that the RRC reconfiguration message is received, the response message is received by itself.
  • the duration has not reached the third preset duration, and the UE 600 determines not to perform CSFB.
  • the first preset duration, the second preset duration, and the third preset duration may be determined according to statistics of a duration required for the UE to establish a voice bearer in the 4G communication system, for example, the first preset.
  • the duration, the second preset duration, and the third preset duration are statistical averages of the length of time required for the UE to establish a voice bearer in the 4G communication system.
  • the first preset duration, the second preset duration, and the third preset duration may be preset values in the UE 600.
  • the timings of the first preset duration, the second preset duration, and the third preset duration may be implemented by using a counter. For example, after receiving the second message, the UE 600 may start the first counter to perform the timing of the first preset duration, and if the UE 600 has not received the RRC reconfiguration message, the UE 600 has not received the RRC reconfiguration message. The UE 600 may determine that the reconfiguration message cannot establish a voice call bearer in the 4G communication system; the UE 600 may also start the second counter after receiving the third message, and perform timing of the second preset duration, and then count in the second counter.
  • the UE 600 may determine that the reconfiguration message cannot establish a voice call bearer in the 4G communication system; the UE 600 may also receive a joint registration request for circuit switching and packet switching. After the corresponding response message, the third counter is started to perform the timing of the third preset duration. When the third counter is counted, if the UE 600 has not received the RRC reconfiguration message, the UE 600 may determine that the reconfiguration message cannot be A voice call bearer is established in the 4G communication system.
  • the manner in which the UE 600 determines that the voice call bearer cannot be established in the 4G communication system is only an example.
  • the UE 600 may adopt one or more of the foregoing manners.
  • the combination of multiples in the determination determines whether a voice call bearer cannot be established within the 4G communication system. For example, after determining that the 4G communication system supports the IP multimedia subsystem IMS voice, the UE 600 determines that the voice call bearer cannot be established in the 4G communication system according to the mode 2; for example, the UE 600 receives the indication.
  • the UE 600 After the UE 600 is switched to the second message of the 4G communication system, if the UE 600 determines that the signal strength between the base station and the base station of the 4G communication system is less than the threshold, it may also determine, according to the foregoing manner 3, whether the second message cannot be received. Receiving an RRC connection reconfiguration message within a preset duration, if yes, the UE 600 determines that the voice call bearer cannot be established in the 4G communication system; otherwise, if the UE 600 receives the RRC connection reconfiguration message within the first preset duration, Then, even if the UE 600 determines that the signal strength between itself and the base station of the 4G communication system is less than the threshold, the UE 600 can no longer perform CSFB.
  • the manner in which the UE 600 performs CSFB in the 4G communication system may be that the UE 600 sends a connection state extended service request message to the MME in the 4G communication system, the extended service request.
  • the message may be an extended service request message whose service type is mobile originated (MO).
  • MO mobile originated
  • the UE 600 may also initiate a location area update (LAU) in the circuit switched domain.
  • LAU location area update
  • the called UE 600 may send a LAU request to the MSC, where the LAU request may carry circuit switching.
  • a circuit switched fallback mobile terminated call (CSMT) indication or a follow on indication is used to establish a mobility management (MM) connection.
  • CSMT circuit switched fallback mobile terminated call
  • MM mobility management
  • the UE 600 can wait for the network. Request to set up a message.
  • the UE 600 may also not actively initiate the LAU procedure, but wait for the network paging in the circuit switched domain to wait for the called party.
  • the 5G communication system shown in FIG. 5 is used as an example.
  • the UE 600 in the 5G communication system is transferred to the 4G after the call request is sent, the UE 600 in the embodiment of the present application performs the CSFB process.
  • the steps can be included:
  • Step 901 The UE 600 in the 5G communication system initiates IMS caller signaling, and the IMS caller signaling is sent to the SCC AS.
  • the IMS caller signaling may carry the voice coding mode information supported by the UE 600 and the IP address of the UE 600. Information, port number and other information;
  • Step 902 The P-CSCF receives the 183 message sent by the calling peer device through the IMS server; the IMS server here may be the SCC AS; the 183 message refers to the response message sent by the called end device after receiving the call request;
  • Step 903 The P-CSCF sends a request for establishing a voice transmission channel to the SMF of the 5G communication system through the PCF/PCRF.
  • Step 904 The SMF sends a request for establishing a voice transmission channel to the NG RAN through the AMF 501; the NG RAN refers to the 5G base station;
  • Step 905 The NG RAN determines that the voice transmission channel cannot be established.
  • Step 906 The NG RAN instructs the UE 600 to perform 4G signal measurement, and sends a request message that the UE 600 is switched to the 4G communication system to the UE 600;
  • Step 907 The NG RAN notifies the SMF through the AMF 501 that the voice transmission channel cannot be established; wherein the NG RAN may send an N2 message to the AMF 501 to indicate that the QoS data flow is refused due to the IMS voice backoff, and the AMF 501 may send the carried PDU modification to the SMF.
  • the SM request to confirm the character;
  • Step 908 After switching to the 4G communication system, the UE 600 sends a joint location update request of circuit switching and packet switching, and receives a response message corresponding to the joint location update request.
  • Step 909 The UE 600 determines whether the first message is not carried in the response message. If yes, step 910 is performed. Otherwise, step 911 is performed.
  • the first information is used by the UE 600 to determine that the IMS voice service cannot be performed through the 4G communication system.
  • the first information may be an indication that the 4G communication system does not support IMS voice;
  • Step 910 The UE 600 determines whether the signal strength between the eNB and the eNB is not less than a threshold. If yes, the process ends. Otherwise, step 911 is performed, where the eNB is a base station connected to the UE 600 in the 4G communication system; the UE 600 determines itself and the eNB. The signal strength between the UEs is not less than the threshold, and the UE 600 may continue to wait for the voice bearer to be established in the 4G communication system after ending the process;
  • Step 911 The UE 600 performs mobile initiation CSFB in the 4G communication system, and then ends the process.
  • the UE 600 may send an extended service request message with the service type MO to the MME 502 to initiate the MO CSFB.
  • the UE 600 can determine whether it is necessary to initiate the CSFB by using the steps 909 and 910 after the step 108, and if the result is that the CSFB needs to be initiated, the UE 600 is used.
  • the CSFB of the calling process can be initiated by step 911. Therefore, the UE 600 no longer needs to wait for the network side to perform step 109 to step 113, and no longer needs to receive the 500 reject message sent by the P-CSCF through step 113, thereby realizing the acceleration of CSFB. Initiate to save the call setup time.
  • the process of the CSFB performed by another UE 600 may include the following steps:
  • Step 1001 The UE 600 in the 5G communication system initiates IMS caller signaling, and the IMS caller signaling is sent to the SCC AS.
  • the IMS caller signaling may carry the voice coding mode information supported by the UE 600 and the IP address of the UE 600. Information, port number and other information;
  • Step 1002 The P-CSCF receives the 183 message sent by the calling peer device through the IMS server; the IMS server here may be an SCC AS;
  • Step 1003 The P-CSCF sends a request for establishing a voice transmission channel to the SMF of the 5G communication system through the PCF/PCRF.
  • Step 1004 The SMF sends a request for establishing a voice transmission channel to the NG RAN through the AMF 501; the NG RAN refers to the 5G base station;
  • Step 1005 The NG RAN determines that the voice transmission channel cannot be established
  • Step 1006 The NG RAN instructs the UE 600 to perform 4G signal measurement, and sends a request message that the UE 600 is switched to the 4G communication system to the UE 600;
  • Step 1007 The NG RAN notifies the SMF through the AMF 501 that the voice transmission channel cannot be established; wherein the NG RAN may send an N2 message to the AMF 501 to indicate that the QoS data flow is refused due to the IMS voice backoff, and the AMF 501 may send the carried PDU modification to the SMF.
  • the SM request to confirm the character;
  • Step 1008 The NG RAN sends an RRC connection release message to the UE 600, and redirects the UE 600 to the 4G communication system.
  • Step 1009 After the UE 600 redirects to the 4G communication system according to the RRC connection release message, sends a joint registration request of circuit switching and packet switching, and receives a response message corresponding to the joint registration request.
  • Step 1010 The UE 600 determines whether the second message is not carried in the response message. If yes, step 1011 is performed. Otherwise, step 1012 is performed.
  • the second information is used by the UE 600 to determine that the IMS voice service cannot be performed through the 4G communication system.
  • the second information may be an indication that the 4G communication system does not support IMS voice;
  • Step 1011 The UE 600 determines whether the signal strength between the eNB and the eNB is not less than a threshold. If yes, the process ends. Otherwise, in step 1012, the eNB is a base station connected to the UE 600 in the 4G communication system; the UE 600 determines itself and the eNB. The signal strength between the UEs is not less than the threshold, and the UE 600 may continue to wait for the voice bearer to be established in the 4G communication system after ending the process;
  • Step 1012 The UE 600 performs the calling CSFB in the 4G communication system, and then ends the process.
  • the UE 600 may send an extended service request message with the service type MO to the MME 1002 to initiate the CSFB.
  • the UE 600 can determine whether it is necessary to initiate the CSFB by using the steps 1010 and 1011 after the step 209, and the UE 600 needs to initiate the CSFB.
  • the CSFB of the calling process can be initiated by the step 1012. Therefore, the UE 600 no longer needs to wait for the network side to perform step 210 to step 214, and no longer needs to receive the 500 reject message sent by the P-CSCF through step 214, thereby realizing the acceleration of CSFB. Initiate to save the call setup time.
  • the process of the UE 600 performing the CSFB may include the following steps:
  • Step 1101 The UE 600 in the 5G communication system receives the IMS called signaling, and the IMS called signaling is sent by the SCC AS; the IMS called signaling can carry the voice coding mode information and the call supported by the calling peer device. Information such as the IP address information and port number of the peer device;
  • Step 1102 The UE 600 sends a 183 message to the P-CSCF.
  • the 183 message may carry the coding mode information and the like selected by the UE 600.
  • Step 1103 The P-CSCF sends a request for establishing a voice transmission channel to the SMF of the 5G communication system through the PCF/PCRF.
  • Step 1104 The SMF sends a request for establishing a voice transmission channel to the NG RAN through the AMF 501; the NG RAN refers to the 5G base station;
  • Step 1105 The NG RAN determines that the voice transmission channel cannot be established.
  • Step 1106 The NG RAN instructs the UE 600 to perform 4G signal measurement, and sends a request message that the UE 600 is switched to the 4G communication system to the UE 600;
  • Step 1107 The NG RAN notifies the SMF through the AMF 501 that the voice transmission channel cannot be established; wherein the NG RAN may send an N2 message to the AMF 501 to indicate that the QoS data flow is refused due to the IMS voice backoff, and the AMF 501 may send the PDU modification to the SMF.
  • the SM request to confirm the character;
  • Step 1108 After the UE 600 switches to the 4G communication system, send a joint location update request of circuit switching and packet switching, and receive a response message corresponding to the joint location update request.
  • Step 1109 The UE 600 determines whether the first message is not carried in the response message. If yes, step 1110 is performed. Otherwise, step 1111 is performed.
  • the first information is used by the UE 600 to determine that the IMS voice service cannot be performed through the 4G communication system.
  • the first information may be an indication that the 4G communication system does not support IMS voice;
  • Step 1110 The UE 600 determines whether the signal strength between the eNB and the eNB is not less than a threshold. If yes, the process ends. Otherwise, step 1111 is performed, where the eNB is a base station connected to the UE 600 in the 4G communication system; the UE 600 determines itself and the eNB. The signal strength between the UEs is not less than the threshold, and the UE 600 may continue to wait for the voice bearer to be established in the 4G communication system after ending the process;
  • Step 1111 The UE 600 performs mobile initiation CSFB in the 4G communication system.
  • the UE 600 may send an extended service request message with a service type of MO to the MME 502 to initiate CSFB and implement CSFB.
  • Step 1112 After returning to the CS domain, the UE 600 sends a LAU request in the CS domain to establish an MM connection.
  • the LAU request may carry a CSMT indication or carry a follow on indication.
  • Step 1113 After the MM connection is established, the UE 600 receives a request to establish a call setup message, thereby establishing a call according to the prior art.
  • the UE 600 can determine, by step 1109 and step 1110, whether it is necessary to initiate the CSFB after the step 308, and if the result is that the CSFB needs to be initiated, the UE 600 is used.
  • the CSFB of the calling process can be initiated by the step 1111. Therefore, the UE 600 no longer needs to wait for the network side to perform step 309 to step 316, and the message sent by the MME for the UE 600 to determine to initiate the MT CSFB is no longer needed to be received by step 316.
  • CSFB can be initiated to speed up the initiation of CSFB and save call setup time.
  • the process of the CSFB performed by another UE 600 may include the following steps:
  • Step 1201 The UE 600 in the 5G communication system receives the IMS called signaling, and the IMS called signaling is sent by the SCC AS; the IMS called signaling can carry the voice coding mode information and the call supported by the calling peer device. Information such as the IP address information and port number of the peer device;
  • Step 1202 The UE 600 sends a 183 message to the P-CSCF.
  • the 183 message may carry the coding mode information and the like selected by the UE 600.
  • Step 1203 The P-CSCF sends a request for establishing a voice transmission channel to the SMF of the 5G communication system through the PCF/PCRF.
  • Step 1204 The SMF sends a request for establishing a voice transmission channel to the NG RAN through the AMF 501; the NG RAN refers to the 5G base station;
  • Step 1205 The NG RAN determines that the voice transmission channel cannot be established
  • Step 1206 The NG RAN instructs the UE 600 to perform 4G signal measurement, and sends a request message that the UE 600 is switched to the 4G communication system to the UE 600;
  • Step 1207 The NG RAN notifies the SMF through the AMF 501 that the voice transmission channel cannot be established; wherein the NG RAN may send an N2 message to the AMF 501 to indicate that the QoS data flow is refused due to the IMS voice backoff, and the AMF 501 may send the PDU modification to the SMF.
  • the SM request to confirm the character;
  • Step 1208 The NG RAN sends an RRC connection release message to the UE 600, and redirects the UE 600 to the 4G communication system.
  • Step 1209 After the UE 600 redirects to the 4G communication system according to the RRC connection release message, sends a joint registration request of circuit switching and packet switching, and receives a response message corresponding to the joint registration request.
  • Step 1210 The UE 600 determines whether the second message is not carried in the response message. If yes, step 1211 is performed. Otherwise, step 1212 is performed.
  • the second information is used by the UE 600 to determine that the IMS voice service cannot be performed through the 4G communication system.
  • the second information may be an indication that the 4G communication system does not support IMS voice;
  • Step 1211 The UE 600 determines whether the signal strength between the eNB and the eNB is not less than a threshold. If yes, the process ends. Otherwise, step 1212 is performed, where the eNB is a base station connected to the UE 600 in the 4G communication system; the UE 600 determines itself and the eNB. The signal strength between the UEs is not less than the threshold, and the UE 600 may continue to wait for the voice bearer to be established in the 4G communication system after ending the process;
  • Step 1212 The UE 600 performs CSFB in the 4G communication system.
  • the UE 600 may send an extended service request message with the service type MO to the MME 502 to initiate the CSFB.
  • Step 1213 After returning to the CS domain, the UE 600 sends a LAU request in the CS domain to establish an MM connection.
  • the LAU request may carry a CSMT indication or carry a follow on indication.
  • Step 1214 After the MM connection is established, the UE 600 receives a request to establish a call setup up message, establishes a call, thereby establishing a call in accordance with the prior art.
  • the UE 600 can determine, by step 1210 and step 1211, whether it is necessary to initiate CSFB after step 409. If the result of the determination is that the CSFB needs to be initiated, the UE 600 is used.
  • the CSFB of the calling process can be initiated by the step 1212. Therefore, the UE 600 no longer needs to wait for the network side to perform step 410 to step 417, and the message sent by the MME for the UE 600 to determine to initiate the MT CSFB is no longer needed to be received through step 417.
  • CSFB can be initiated to speed up the initiation of CSFB and save call setup time.
  • the embodiment of the present application further provides a method for establishing a call, where the method includes:
  • the UE determines to be transferred to the second communication system during the initiation or reception of the call in the first communication system;
  • the UE determines that the voice call bearer cannot be established in the second communication system
  • the UE initiates a CSFB request within the second communication system and makes a voice call in the CS domain.
  • the UE can determine that the voice bearer cannot be established in the second communication system in advance, and the CSFB can be rolled back to the CS domain for voice call in advance to shorten the call setup delay.
  • the first communication system may be a 5G communication system and the second communication system may be a 4G communication system.
  • the UE determines to be transferred to the second communication system, including:
  • the UE receives the request message that is switched to the 4G communication system; or,
  • the UE receives a request message redirected to the 4G communication system.
  • the UE can determine that the UE is transferred to the second communication system.
  • the UE determines that the voice call bearer cannot be established in the second communication system, including:
  • the UE initiates a joint location update request for circuit switching and packet switching in the second communication system, and the UE receives a response message corresponding to the location update request, and determines that the response message carries that the second communication system does not support the IP multimedia subsystem IMS voice. Instructions; or,
  • the UE initiates a joint registration request for circuit switching and packet switching in the second communication system, and the UE receives a response message corresponding to the registration request, and determines that the response message carries an indication that the second communication system does not support the IMS voice of the IP multimedia subsystem. .
  • the UE can determine that the voice bearer cannot be established in the second communication system by receiving the response message corresponding to the joint location update request of the circuit switching and the packet switching, or receiving the response message corresponding to the joint registration request of the circuit switching and the packet switching.
  • the UE determines that the voice call bearer cannot be established in the second communication system, including:
  • the UE determines that the signal strength between the UE and the base station of the second communication system is less than a threshold; or, the UE determines that the UE does not report a measurement report that is greater than a threshold to the base station eNB of the second communication system.
  • the UE can determine that the voice bearer cannot be established in the second communication system.
  • the UE determines that the voice call bearer cannot be established in the second communication system, including:
  • the UE receives the request message that is handed over to the 4G communication system, and starts the timer. When the timer expires, the UE determines that the RRC connection reconfiguration message is not received by the RRC connection; or
  • the UE receives the request message redirected to the 4G communication system, and starts the timer. When the timer expires, the UE determines that the RRC connection reconfiguration message is not received.
  • the UE After the timer is started, the UE does not receive the RRC connection reconfiguration message before the timer expires, and then determines that the voice call bearer cannot be established in the second communication system, and then performs CSFB, which can prevent the UE from misjudged and ensure that the UE independently initiates CSFB. reliability.
  • the timer is pre-configured in the UE, or is dynamically configured by the UE according to statistics of the length of time required to establish a voice bearer.
  • the UE initiates a circuit switched CS fallback request in the second communication system, including:
  • the UE initiates an extended service request message of the service type Service type to the mobile originating MO in the second communication system.
  • the UE can ensure that the core network device correctly processes the UE's request.
  • the UE after the UE performs CSFB, it also includes:
  • the UE initiates a LAU in the CS domain; or, the UE waits for a network paging message in the CS domain.
  • the UE can shorten the setup delay of the call.
  • the UE initiates a LAU in the CS domain, including:
  • the UE sends a LAU request, the LAU request carries a follow on indication, and/or the LAU request carries a CSMT indication.
  • the UE can ensure that the core network device maintains a connection with the UE, thereby accelerating the call setup process.
  • the embodiment of the present application further provides a UE, which may have the structure shown in FIG. 6 and has the behavior function of the UE 600 in the foregoing method embodiment.
  • the processor 601 in the UE 600 as shown in FIG. 6 can be used to perform step S102; the transceiver 602 can be used to perform steps S101, S103.
  • the processor 601 in the UE 600 as shown in FIG. 6 can be used to perform step S202; the transceiver 602 can be used to perform steps S201, S203.
  • the first request may be a second message or a third message, where the second message is used by the UE to determine that the handover is handed over to the first In a second communication system, the third message is used by the UE to be redirected to the second communication system.
  • the second request may be a second message or a third message, where the second message is used by the UE to determine that the handover is handed over to the first In a second communication system, the third message is used by the UE to be redirected to the second communication system.
  • the processor 601 can be configured to determine that the voice call bearer cannot be established in the second communication system after determining that at least one of the following is satisfied:
  • the response message corresponding to the joint location update request received by the UE 600 carries the first information, and the joint location update request is a joint location update request of the circuit switching and packet switching sent by the UE 600 in the second communication system, where the first information is used.
  • the UE 600 determines that the IMS voice service cannot be performed through the second communication system; or
  • the response message corresponding to the joint registration request received by the UE 600 carries the second information, where the joint registration request is a joint registration request of the circuit switching and the packet switching sent by the UE 600 in the second communication system, and the second information is used by the UE 600 to determine Unable to perform IMS voice service through the second communication system; or
  • the signal strength between the UE 600 and the base station of the second communication system is less than a threshold
  • the UE 600 does not report a measurement report larger than the threshold to the base station of the second communication system.
  • the UE 600 does not report a measurement report not less than the threshold to the base station of the second communication system.
  • the UE 600 receives the second message for the first preset duration, and the UE 600 does not receive the RRC connection reconfiguration message, and the second message indicates that the UE 600 is handed over to the second communication system; or
  • the UE 600 receives the third message for a second preset duration, and the UE 600 does not receive the RRC connection reconfiguration message, and the third message indicates that the UE 600 is redirected to the second communication system; or
  • the UE 600 receives the response message corresponding to the joint registration request for a third preset duration, and the UE 600 does not receive the RRC connection reconfiguration message, and the joint registration request is the circuit switching and grouping sent by the UE 600 in the second communication system.
  • the RRC connection reconfiguration message is used by the UE 600 to determine to establish a voice call bearer in the second communication system.
  • the transceiver 602 is specifically configured to:
  • the service type Service type of the extended service request message is a mobile terminal initiating MO.
  • the transceiver 602 is also used to:
  • the transceiver 602 is specifically configured to:
  • the LAU request is sent, the LAU request may carry a follow on indication, and/or the LAU request may carry a CSMT indication.
  • the UE adopts a modular design.
  • the UE 1300 adopting a modular design may include a request receiving module 1301, a call bearer establishment determining module 1302, and a CSFB initiating module 1303;
  • the request receiving module 1301 is configured to determine, after the UE sends a call request in the first communications system, that the first request is received, where the first request is used to indicate that the UE 1300 is to be transferred to the second communications system;
  • the module 1302 is configured to determine that the voice call bearer cannot be established in the second communications system after the UE 1300 is transferred to the second communications system, before the UE 1300 receives the first message, where the first message is used by the UE 1300 to determine the UE determining.
  • the call request fails.
  • the CSFB initiation module 1303 is configured to determine that the voice call bearer cannot be established in the second communication system, and initiate CSFB in the second communication system.
  • the first communication system is a 5G communication system.
  • the second communication system is a 4G communication system.
  • the request receiving module 1301 is further configured to: after the UE receives the call request in the first communication system, receive a second request, where the first request is used to indicate that the UE 1300 is to be transferred to the second communication system;
  • the establishing determining module 1302 is further configured to determine that the voice call bearer cannot be established in the second communications system before the UE 1300 receives the fourth message, where the fourth message is used by the UE 1300 to initiate the MT CSFB according to the fourth message; the CSFB initiating module 1303 And in the case that it is determined that the voice call bearer cannot be established in the second communication system, the CSFB is initiated in the second communication system; wherein the first communication system is a 5G communication system, and the second communication system is a 4G communication system.
  • the first request may be a second message or a third message, where the second message is used by the UE to determine that the handover is handed over to the second communication system, and the third message is used for the Determining that the UE determination is redirected to the second communication system;
  • the second request may be a second message or a third message, wherein the second message is used by the UE to determine that the handover is handed over to the second communication system, The third message is used by the UE to be redirected to the second communication system.
  • the call bearer setup determining module 1302 may determine that the voice call bearer cannot be established in the second communication system after determining that at least one of the following is satisfied: determining that the UE 1300 receives the joint location update request corresponding to the The response message carries the first information, and the joint location update request is a circuit switched and packet switched joint location update request sent by the UE 1300 in the second communication system, where the first information is used by the UE 1300 to determine that the second communication system cannot perform IP.
  • Multimedia subsystem IMS voice service or,
  • the joint registration request is a joint registration request of the circuit switching and the packet switching sent by the UE in the second communication system
  • the second information is used by the UE to determine that the The second communication system performs an IP multimedia subsystem IMS voice service
  • the joint registration request is a circuit switching and packet switching sent by the UE in the second communication system.
  • the RRC connection reconfiguration message is used by the UE to determine to establish a voice call bearer in the second communication system.
  • the CSFB initiating module 1303 may be configured to send an extended service request message in the second communication system when the CSFB is initiated, and the service type Service type of the extended service request message is the mobile terminal initiating the MO.
  • the UE 1300 may further include a LAU initiating module 1304 for initiating a location area update LAU in the circuit switched domain; or
  • the UE 1300 may also include a network paging message receiving module 1305 for receiving network paging messages in the circuit switched domain.
  • the LAU initiation module 1304 can be used to send a LAU request when the LAU is initiated, and the LAU request can carry a follow on indication and/or a CSMT indication.
  • Fig. 14 shows a simplified schematic diagram of another possible design structure of the UE involved in the above embodiment.
  • the UE 1400 includes a transmitter 1401, a receiver 1402, a controller/processor 1403, a memory 1404, and a modem processor 1405.
  • the transmitter 1401 can adjust (e.g., analog convert, filter, amplify, upconvert, etc.) the output samples to generate a transmit signal when the UE 1400 transmits a message, the transmit signal being transmitted by the antenna via the uplink.
  • the antenna receives the downlink signal and the receiver 1402 conditions (eg, filters, amplifies, downconverts, digitizes, etc.) the downlink signal received from the antenna and provides input samples.
  • the encoder receives the service data and the signaling message to be sent on the uplink.
  • the service type in the embodiment of the present application is an extended service request message initiated by the mobile terminal, a LAU request, etc., and the service data and signaling are performed.
  • the modulator further processes (e.g., symbol maps and modulates) the encoded service data and signaling messages and provides output samples.
  • the demodulator processes (eg, demodulates) the input samples and provides symbol estimates.
  • the decoder processes (e.g., deinterleaves and decodes) the symbol estimate and provides decoded data and signaling messages that are sent to the UE 1400.
  • the encoder, modulator, demodulator and decoder can be implemented by a synthesized modem processor 1405. These units are processed according to the radio access technology employed by the radio access network (e.g., access technologies of LTE and other evolved systems).
  • the controller/processor 1403 performs control management on the actions of the UE 1400 for performing the processing performed by the UE in the above embodiment. For example, other processes for determining that the UE 1400 is transferred to the second communication system and/or the circuit switched fallback method described herein.
  • the controller/processor 1403 can be used to support the UE 1400 in implementing the functions that the processor 601 shown in FIG. 6 can implement.
  • Memory 1404 stores program code and data for controller/processor 1403 to implement the respective functions.
  • the transmitter 1401 can be used to support the UE 1400 in implementing the transmit function that the transceiver 602 shown in FIG. 6 can implement.
  • the receiver 1402 can be used to support the UE 1400 to implement the receiving function that the transceiver 602 shown in FIG. 6 can implement.
  • the embodiment of the present application further provides a computer readable storage medium, where some instructions are stored, and when the instructions are executed, the computer may be executed to perform the foregoing method embodiments and method embodiments.
  • the readable storage medium is not limited, and may be, for example, a RAM (random-access memory), a ROM (read-only memory), or the like.
  • the embodiment of the present application further provides a computer program product.
  • the computer program product When the computer program product is run by a computer, the computer may be caused to perform any one of the foregoing method embodiments and method embodiments.
  • the functionality involved in the UE design is not limited to:
  • the embodiment of the present application further provides a chip, which may be coupled to a transceiver, and is used to implement any possible design of the foregoing method embodiment and method embodiment.
  • the chip may be a chip located in the UE provided by the embodiment of the present application.
  • the embodiment of the present application further provides a device, which has a processing module and a communication interface, and the processing module is used to perform any possible design of the foregoing method embodiment and method embodiment.
  • the communication interface is used for communication by the device.
  • the communication interface may have the functions of the transceiver in any one of the possible embodiments of the method embodiment and the method embodiment.
  • the apparatus further includes a storage module for storing program instructions and data necessary for processing the module.
  • the device is a chip or chip system.
  • the computer program instructions can also be stored in a computer readable memory that can direct a computer or other programmable data processing device to operate in a particular manner, such that the instructions stored in the computer readable memory produce an article of manufacture comprising the instruction device.
  • the apparatus implements the functions specified in one or more blocks of a flow or a flow and/or block diagram of the flowchart.
  • These computer program instructions can also be loaded onto a computer or other programmable data processing device such that a series of operational steps are performed on a computer or other programmable device to produce computer-implemented processing for execution on a computer or other programmable device.
  • the instructions provide steps for implementing the functions specified in one or more of the flow or in a block or blocks of a flow diagram.
  • At least one means one or more, and "a plurality” means two or more.
  • At least one of the following or a similar expression thereof refers to any combination of these items, including any combination of a single item or a plurality of items.
  • at least one of "a, b, or c" may mean: a, b, c, ab ( That is, a and b), ac, bc, or abc, wherein a, b, and c may be single or plural.
  • the size of the serial numbers of the above processes does not mean the order of execution, and some or all of the steps may be performed in parallel or sequentially, and the execution order of each process shall be
  • the intrinsic logic is determined without any limitation on the implementation process of the embodiments of the present application.
  • each device embodiment may refer to related methods in the related method embodiments. Partial understanding.
  • the apparatus can include any number of transmitters, receivers, processors, memories, etc., to perform the functions or operations performed by the apparatus in the various apparatus embodiments of the present application.

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Abstract

本申请提供一种电路交换回退方法及装置，该方法由发起主叫过程后的UE，接收到所述第一通信系统发送的第一请求；UE在被转移到第二通信系统后，在确定接收到来自第二通信系统的第一消息之前，若UE确定无法在第二通信系统内建立语音呼叫承载，则UE在第二通信系统内发起CSFB，第一消息用于UE确定呼叫请求失败，从而UE无需等待第二通信系统网络侧发送的第一消息即可在第二通信系统内进行CSFB，缩短了呼叫等待时长。

Description

一种电路交换回退方法及装置
本申请要求于2018年4月26日提交中国国家知识产权局、申请号为201810385818.8、申请名称为“一种呼叫建立的方法、终端及装置”的中国专利申请的优先权，以及于2018年7月28日提交中国国家知识产权局、申请号为201810850349.2、申请名称为“一种电路交换回退方法及装置”的中国专利申请的优先权，它们的全部内容通过引用结合在本申请中。
技术领域
本申请涉及移动通信技术领域，尤其涉及一种电路交换回退方法及装置。
背景技术
现有技术中，电路交换回退(circuit switched fallback，CSFB)是用户设备(UE)从4G通信网络切换到3G通信网络的电路交换(circuit switched，CS)域或者2G通信网络的CS域进行语音呼叫的方案。
目前，5G通信系统中进行呼叫或被叫中的UE，若UE切换至4G通信系统，由于切换后的4G网络的条件所限制而导致UE无法在4G通信系统建立呼叫，则可能导致UE进行CSFB从而退回电路交换域进行呼叫或被叫，而在上述过程中，在5G通信系统发起语音呼叫的UE，若该UE被转移到4G通信系统，则该UE需要等待网络侧通过4G通信系统发送的用于指示UE所述语音呼叫失败的消息才能进行CSFB；在5G通信系统接收语音呼叫的UE，若该UE被转移到4G通信系统，则该UE需要等待网络侧发送的用于指示UE进行被叫终止(或称为移动终止，mobile terminated，MT)的电路交换回退的消息，才能进行CSFB。以上UE等待网络侧发送的消息并发起CSFB的过程，造成语音呼叫建立时间过长，影响用户体验。
发明内容
本申请提供一种电路交换回退方法及装置，用以解决呼叫或被叫中的UE发生通信系统切换时，呼叫建立时间过长的问题。
第一方面，本申请实施例提供一种电路交换回退方法，在5G通信系统内发起呼叫的UE，在接收第一请求，在UE被转移到4G通信系统后，在接收到4G通信系统的第一消息之前，UE确定无法在4G通信系统内建立语音呼叫承载，则UE发起CSFB，其中，第一消息用于UE确定呼叫请求失败，其中，第一请求指示UE将被转移到4G通信系统。
由于以上UE发起呼叫过程中，UE不需要等待4G通信系统的发送的第一消息即可由UE在确定无法在4G通信系统内建立语音呼叫承载后发起CSFB过程，从而可缩短呼叫建立时长。
一种可能的设计中，第一请求为第二消息或第三消息，其中，第二消息用于UE确定被切换(handover)到4G通信系统，第三消息用于UE确定被重定向到4G通信 系统。
一种可能的设计中，在UE确定满足下列中的至少一项后，UE可确定无法在4G通信系统内建立语音呼叫承载：
UE确定收到的联合位置更新请求对应的响应消息中携带第一信息，联合位置更新请求是UE在4G通信系统内发送的电路交换和分组交换的联合位置更新请求，第一信息用于UE确定无法通过4G通信系统进行IP多媒体子系统IMS语音业务；或者，UE确定收到的联合注册请求对应的响应消息中携带第二信息，联合注册请求是UE在4G通信系统内发送的电路交换和分组交换的联合注册请求，第二信息用于UE确定无法通过4G通信系统进行IP多媒体子系统IMS语音业务；或者，UE确定与4G通信系统的基站之间的信号强度小于阈值；或者，UE确定没有向4G通信系统的基站上报过大于阈值的测量报告；或者，UE确定没有向4G通信系统的基站上报过不小于阈值的测量报告；或者，UE确定接收到第二消息的时长已达到第一预设时长，且UE未收到无线资源控制RRC连接重配消息，第二消息用于UE确定被切换handover到4G通信系统；或者，UE确定接收到第三消息的时长已达到第二预设时长，且UE未收到RRC连接重配消息，第三消息用于UE确定被重定向到4G通信系统；或者，UE确定接收到联合注册请求对应的响应消息的时长已达到第三预设时长，且UE未收到RRC连接重配消息，联合注册请求为UE在4G通信系统内发送的电路交换和分组交换的联合注册请求；其中，RRC连接重配消息用于UE确定在4G通信系统内建立语音呼叫承载。
一种可能的设计中，UE可在4G通信系统内发送业务类型为移动终端发起的扩展业务请求消息，以发起CSFB过程。从而通过设置扩展业务请求消息的业务类型，UE可以令接收扩展业务请求消息的核心网设备准确处理该扩展业务请求消息。
第二方面，本申请实施例提供一种电路交换回退方法，在5G通信系统内接收到呼叫请求的UE，接收第二请求，在UE被转移到4G通信系统后，在接收到4G通信系统的第四消息之前，UE确定无法在4G通信系统内建立语音呼叫承载，则UE发起CSFB，其中，第四消息用于UE根据第四消息去发起移动终止MT电路交换回退CSFB。
由于以上UE接受呼叫过程中，UE不需要等待4G通信系统发送的第四消息即可由UE在确定无法在4G通信系统内建立语音呼叫承载后发起CSFB过程，从而可缩短呼叫建立时长。
一种可能的设计中，第二请求为第二消息或第三消息，其中，第二消息用于UE确定被切换到4G通信系统，第三消息用于UE确定被重定向到4G通信系统。
一种可能的设计中，在UE确定满足下列中的至少一项后，UE可确定无法在4G通信系统内建立语音呼叫承载：UE确定收到的联合位置更新请求对应的响应消息中携带第一信息，联合位置更新请求是UE在4G通信系统内发送的电路交换和分组交换的联合位置更新请求，第一信息用于UE确定无法通过4G通信系统进行IP多媒体子系统IMS语音业务；或者，UE确定收到的联合注册请求对应的响应消息中携带第二信息，联合注册请求是UE在4G通信系统内发送的电路交换和分组交换的联合注册请求，第二信息用于UE确定无法通过4G通信系统进行IP多媒体子系统IMS语音业务；或者，UE确定与4G通信系统的基站之间的信号强度小于阈值；或者，UE确定没有 向4G通信系统的基站上报过大于阈值的测量报告；或者，UE确定没有向4G通信系统的基站上报过不小于阈值的测量报告；或者，UE确定接收到第二消息的时长已达到第一预设时长，且UE未收到无线资源控制RRC连接重配消息，第二消息用于UE确定被切换handover到4G通信系统；或者，UE确定接收到第三消息的时长已达到第二预设时长，且UE未收到RRC连接重配消息，第三消息用于UE确定被重定向到4G通信系统；或者，UE确定接收到联合注册请求对应的响应消息的时长已达到第三预设时长，且UE未收到RRC连接重配消息，联合注册请求为UE在4G通信系统内发送的电路交换和分组交换的联合注册请求；其中，RRC连接重配消息用于UE确定在4G通信系统内建立语音呼叫承载。
一种可能的设计中，UE可在4G通信系统内发送业务类型为移动终端发起的扩展业务请求消息，以发起CSFB过程。从而通过设置扩展业务请求消息的业务类型，UE可以令接收扩展业务请求消息的核心网设备准确处理该扩展业务请求消息。
一种可能的设计中，UE在4G通信系统内发起电路交换回退之后，还可以在电路交换发起位置区更新LAU，以通过LAU建立MM连接，并在建立MM连接之后等待请求建立呼叫消息；或者，UE也可以不发起LAU，而在电路交换域等待网络寻呼消息，以等待被叫。
一种可能的设计中，UE可以通过发送LAU请求的方式在电路交换发起LAU，其中，LAU请求中可以携带继续(follow on)指示，和/或，LAU请求中可以携带电路交换回退移动被叫(circuit switched fallback mobile terminated call，CSMT)指示。
第三方面，本申请实施例提供了一种用户设备UE，该UE具有实现上述第一方面或上述第一方面的任何一种可能的设计中提供的方法中用户设备行为的功能。所述功能可以通过硬件实现，也可以通过硬件执行相应的软件实现，也可以通过软件和硬件结合实现。硬件或软件包括一个或多个与上述功能相对应的模块。
本申请实施例提供的另一种用户设备UE，可包括请求接收模块、呼叫承载建立确定模块以及CSFB发起模块；其中，请求接收模块，用于在所述UE在第一通信系统内发送呼叫请求后，接收到所述第一通信系统发送的第一请求，所述第一请求指示所述UE将被转移到第二通信系统；呼叫承载建立确定模块，用于在所述UE在被转移到第二通信系统之后，在所述UE接收到来自所述第二通信系统的第一消息之前，确定无法在所述第二通信系统内建立语音呼叫承载，所述第一消息用于所述UE确定所述呼叫请求失败；CSFB发起模块，用于在所述UE确定无法在所述第二通信系统内建立语音呼叫承载的情况下，在所述第二通信系统内发起电路交换回退CSFB；其中，第一通信系统为5G通信系统，第二通信系统为4G通信系统。
一种可能的设计中，第一请求可以是第二消息或第三消息，其中，第二消息用于UE确定被切换到4G通信系统，第三消息用于UE确定被重定向到4G通信系统。
一种可能的设计中，呼叫承载建立确定模块可用于，在满足下列中的至少一项后，确定无法在第二通信系统内建立语音呼叫承载：确定UE接收到的联合位置更新请求对应的响应消息中携带第一信息，联合位置更新请求是UE在第二通信系统内发送的电路交换和分组交换的联合位置更新请求，第一信息用于UE确定无法通过第二通信系统进行IP多媒体子系统IMS语音业务；或者，确定UE接收到的联合注册请求对应 的响应消息中携带第二信息，联合注册请求是UE在第二通信系统内发送的电路交换和分组交换的联合注册请求，第二信息用于UE确定无法通过第二通信系统进行IP多媒体子系统IMS语音业务；或者，确定UE与第二通信系统的基站之间的信号强度小于阈值；或者，确定UE没有向第二通信系统的基站上报过大于阈值的测量报告；或者，确定UE没有向第二通信系统的基站上报过不小于阈值的测量报告；或者，确定UE接收到第二消息的时长已达到第一预设时长，且UE未收到无线资源控制RRC连接重配消息，第二消息用于UE确定被切换到第二通信系统；或者，确定UE接收到第三消息的时长已达到第二预设时长，且UE未收到RRC连接重配消息，第三消息用于UE确定被重定向到4G通信系统；或者，确定UE接收到联合注册请求对应的响应消息的时长已达到第三预设时长，且UE未收到RRC连接重配消息，联合注册请求为UE在第二通信系统内发送的电路交换和分组交换的联合注册请求；其中，RRC连接重配消息用于UE确定在第二通信系统内建立语音呼叫承载。
一种可能的设计中，CSFB发起模块具体用于：在第二通信系统内发送扩展业务请求消息，扩展业务请求消息的业务类型(Service type)为移动终端发起(mobile original，MO)。
本申请实施例提供的另一种用户设备UE，包括发送器、处理器以及接收器；其中，接收器，可在UE在第一通信系统内发送呼叫请求后，接收到第一通信系统发送的第一请求；处理器可用于UE在被转移到第二通信系统之后，在UE接收到来自第二通信系统的第一消息之前，确定无法在第二通信系统内建立语音呼叫承载，第一消息用于指示UE将被转移到第二通信系统；发送器可用于UE确定无法在第二通信系统内建立语音呼叫承载的情况下，在第二通信系统内发起电路交换回退CSFB；其中，第一通信系统为5G通信系统，第二通信系统为4G通信系统。
一种可能的设计中，第一请求可以为第二消息或第三消息，其中，第二消息用于UE确定被切换到4G通信系统，第三消息用于UE确定被重定向到4G通信系统。
一种可能的设计中，处理器可用于，在满足下列中的至少一项后，确定无法在第二通信系统内建立语音呼叫承载：确定UE接收到的联合位置更新请求对应的响应消息中携带第一信息，联合位置更新请求是UE在第二通信系统内发送的电路交换和分组交换的联合位置更新请求，第一信息用于UE确定无法通过第二通信系统进行IP多媒体子系统IMS语音业务；或者，确定UE接收到的联合注册请求对应的响应消息中携带第二信息，联合注册请求是UE在第二通信系统内发送的电路交换和分组交换的联合注册请求，第二信息用于UE确定无法通过第二通信系统进行IP多媒体子系统IMS语音业务；或者，确定UE与第二通信系统的基站之间的信号强度小于阈值；或者，确定UE没有向第二通信系统的基站上报过大于阈值的测量报告；或者，确定UE没有向第二通信系统的基站上报过不小于阈值的测量报告；或者，确定UE接收到第二消息的时长已达到第一预设时长，且UE未收到无线资源控制RRC连接重配消息，第二消息用于UE确定被切换handover到第二通信系统；或者，确定UE接收到第三消息的时长已达到第二预设时长，且UE未收到RRC连接重配消息，第三消息用于UE确定被重定向到4G通信系统；或者，确定UE接收到联合注册请求对应的响应消息的时长已达到第三预设时长，且UE未收到RRC连接重配消息，联合注册请求为UE在 第二通信系统内发送的电路交换和分组交换的联合注册请求；其中，RRC连接重配消息用于UE确定在第二通信系统内建立语音呼叫承载。
一种可能的设计中，发送器发起CSFB时，可在第二通信系统内发送扩展业务请求消息，扩展业务请求消息的业务类型为移动终端发起。
第四方面，本申请实施例提供了一种用户设备UE，该UE具有实现上述第二方面或上述第二方面的任何一种可能的设计中提供的方法中用户设备行为的功能。功能可以通过硬件实现，也可以通过硬件执行相应的软件实现，也可以通过软件和硬件结合实现。硬件或软件包括一个或多个与上述功能相对应的模块。
本申请实施例提供的一种UE，可包括请求接收模块、呼叫承载建立确定模块以及CSFB发起模块；其中，请求接收模块，用于在UE在第一通信系统内接收到呼叫请求后，接收到第一通信系统发送的第二请求，第二请求指示UE将被转移到第二通信系统；呼叫承载建立确定模块，用于在UE在被转移到第二通信系统之后，在UE接收到来自第二通信系统的第四消息之前，确定无法在第二通信系统内建立语音呼叫承载，第四消息用于所述UE根据所述第四消息去发起移动终止MT电路交换回退CSFB；CSFB发起模块，用于在UE确定无法在第二通信系统内建立语音呼叫承载的情况下，在第二通信系统内发起电路交换回退CSFB；其中，第一通信系统为5G通信系统，第二通信系统为4G通信系统。
一种可能的设计中，第二请求为第二消息或第三消息，其中，第二消息用于UE确定被切换到4G通信系统，第三消息用于UE确定被重定向到4G通信系统。
一种可能的设计中，呼叫承载建立确定模块可用于，在确定满足下列中的至少一项后，确定无法在第二通信系统内建立语音呼叫承载：确定UE接收到的联合位置更新请求对应的响应消息中携带第一信息，联合位置更新请求是UE在第二通信系统内发送的电路交换和分组交换的联合位置更新请求，第一信息用于UE确定无法通过第二通信系统进行IP多媒体子系统IMS语音业务；或者，确定UE接收到的联合注册请求对应的响应消息中携带第二信息，联合注册请求是UE在第二通信系统内发送的电路交换和分组交换的联合注册请求，第二信息用于UE确定无法通过第二通信系统进行IP多媒体子系统IMS语音业务；或者，确定UE与第二通信系统的基站之间的信号强度小于阈值；或者，确定UE没有向第二通信系统的基站上报过大于阈值的测量报告；或者，确定UE没有向第二通信系统的基站上报过不小于阈值的测量报告；或者，确定UE接收到第二消息的时长已达到第一预设时长，且UE未收到无线资源控制RRC连接重配消息，第二消息用于UE确定被切换handover到第二通信系统；或者，确定UE接收到第三消息的时长已达到第二预设时长，且UE未收到RRC连接重配消息，第三消息用于UE确定被重定向到4G通信系统；或者，确定UE接收到联合注册请求对应的响应消息的时长已达到第三预设时长，且UE未收到RRC连接重配消息，联合注册请求为UE在第二通信系统内发送的电路交换和分组交换的联合注册请求；其中，RRC连接重配消息用于UE确定在第二通信系统内建立语音呼叫承载。
一种可能的设计中，CSFB发起模块在发起CSFB时，可以在第二通信系统内发送扩展业务请求消息，扩展业务请求消息的业务类型Service type为移动终端发起MO。
一种可能的设计中，UE还可包括LAU发起模块，用于在电路交换域发起位置区更新LAU；或者，UE还可包括网络寻呼消息接收模块，用于在电路交换域接收网络寻呼消息。从而UE可通过LAU发起模块，发起位置区更新LAU，以通过LAU过程建立MM连接，并在建立MM连接之后等待请求建立呼叫消息，或者，UE可通过网络寻呼消息接收模块在电路交换域接收网络寻呼消息，以接收被叫。
一种可能的设计中，LAU发起模块在电路交换域发起位置区更新LAU时，可用于发送LAU请求，LAU请求可携带继续follow on指示和/或，LAU请求可携带电路交换回退移动被叫CSMT指示。
本申请实施例提供的另一种用户设备UE，包括发送器、处理器以及接收器；其中，接收器可用于在UE在第一通信系统内接收到呼叫请求后，接收到第一通信系统发送的第二请求，第二请求指示所述UE将被转移到第二通信系统；处理器可用于在UE在被转移到第二通信系统之后，在UE接收到来自第二通信系统的第四消息之前，确定无法在第二通信系统内建立语音呼叫承载，第四消息用于UE根据第四消息去发起移动终止MT电路交换回退CSFB；发送器可用于在UE确定无法在第二通信系统内建立语音呼叫承载的情况下，在第二通信系统内发起电路交换回退CSFB；其中，第一通信系统为5G通信系统，第二通信系统为4G通信系统。
一种可能的设计中，第二请求可以是第二消息或第三消息，其中，第二消息用于所述UE确定被切换handover到所述第二通信系统，所述第三消息用于所述UE确定被重定向到所述第二通信系统。
一种可能的设计中，处理器具体用于，在满足下列中的至少一项后，确定无法在第二通信系统内建立语音呼叫承载：确定UE接收到的联合位置更新请求对应的响应消息中携带第一信息，联合位置更新请求是UE在第二通信系统内发送的电路交换和分组交换的联合位置更新请求，第一信息用于UE确定无法通过第二通信系统进行IP多媒体子系统IMS语音业务；或者，确定UE接收到的联合注册请求对应的响应消息中携带第二信息，联合注册请求是UE在第二通信系统内发送的电路交换和分组交换的联合注册请求，第二信息用于UE确定无法通过第二通信系统进行IP多媒体子系统IMS语音业务；或者，确定UE与第二通信系统的基站之间的信号强度小于阈值；或者，确定UE没有向第二通信系统的基站上报过大于阈值的测量报告；或者，确定UE没有向第二通信系统的基站上报过不小于阈值的测量报告；或者，确定UE接收到第二消息的时长已达到第一预设时长，且UE未收到无线资源控制RRC连接重配消息，第二消息用于UE确定被切换handover到第二通信系统；或者，确定UE接收到第三消息的时长已达到第二预设时长，且UE未收到RRC连接重配消息，第三消息用于UE确定被重定向到4G通信系统；或者，确定UE接收到联合注册请求对应的响应消息的时长已达到第三预设时长，且UE未收到RRC连接重配消息，联合注册请求为UE在第二通信系统内发送的电路交换和分组交换的联合注册请求；其中，RRC连接重配消息用于UE确定在第二通信系统内建立语音呼叫承载。
一种可能的设计中，发送器发起CSFB时，可在第二通信系统内发送扩展业务请求消息，扩展业务请求消息的业务类型为移动终端发起。
一种可能的设计中，发送器还可以用于在电路交换域发起位置区更新LAU，或 者，接收器还可用于在电路交换域接收网络寻呼消息。从而UE可通过发送器发起位置区更新LAU，以通过LAU过程建立MM连接，并在建立MM连接之后等待请求建立呼叫消息，或者，UE可通过接收器在电路交换域接收网络寻呼消息，以接收被叫。
一种可能的设计中，在电路交换域发起位置区更新LAU时发送器可用于发送LAU请求，LAU请求可携带继续follow on指示和/或，LAU请求可携带电路交换回退移动被叫CSMT指示。
第五方面，本申请实施例提供了一种计算机程序产品，包括计算机程序，该计算机程序在某一计算机或处理器上执行时，将会使所述计算机或处理器实现上述第一方面所述方法实施例、方法实施例的任意一种可能的设计中所涉及的功能。
第六方面，本申请实施例提供了一种计算机可读存储介质，用于存储程序、指令，这些程序、指令在计算机中被调用执行时，可以使得计算机执行上述第一方面所述方法实施例、方法实施例的任意一种可能的设计中所涉及的功能。
第七方面，本申请实施例提供了一种芯片。该芯片可以与收发器耦合，用于执行上述第一方面所述方法实施例、方法实施例的任意一种可能的设计中所涉及的功能，或者，用于执行上述第二方面所述方法实施例、方法实施例的任意一种可能的设计中所涉及的功能。
附图说明
图1为现有技术中一种示例性的主叫场景CSFB流程示意图；
图2为现有技术中另一种示例性的主叫场景CSFB流程示意图；
图3为现有技术中一种示例性的被叫场景CSFB流程示意图；
图4为现有技术中另一种示例性的被叫场景CSFB流程示意图；
图5为本申请实施例提供的一种示例性的通信系统架构示意图；
图6为本申请实施例提供的一种示例性的用户设备UE的结构示意图；
图7为本申请实施例提供的一种示例性的电路交换回退方法的流程示意图；
图8为本申请实施例提供的另一种示例性的电路交换回退方法的流程示意图；
图9为本申请实施例提供的一种示例性的主叫场景电路交换回退方法的流程示意图；
图10为本申请实施例提供的另一种示例性的主叫场景电路交换回退方法的流程示意图；
图11为本申请实施例提供的一种示例性的被叫场景电路交换回退方法的流程示意图；
图12为本申请实施例提供的另一种示例性的被叫场景电路交换回退方法的流程示意图；
图13为本申请实施例提供的另一种示例性的用户设备UE的结构示意图；
图14为本申请实施例提供的又一种示例性的用户设备UE的结构示意图。
具体实施方式
为了使本申请的目的、技术方案和优点更加清楚，下面将结合附图对本申请作进 一步地详细描述。
下面对本申请涉及或可能涉及的词语进行解释：
至少一个，是指一个，或一个以上，即包括一个、两个、三个及以上。
携带，可以是指某消息用于承载某信息或数据，也可以是指某消息由某信息构成。
另外，在本申请的描述中，除非另有说明，“多个”的含义是两个或两个以上。另外需要理解的是，在本申请实施例的描述中，“第一”、“第二”等词汇，仅用于区分描述的目的，而不能理解为指示或暗示相对重要性，也不能理解为指示或暗示顺序。
目前在5G通信系统中的UE主动发起呼叫后，UE切换到4G通信系统且UE无法在4G建立语音呼叫承载时，UE发起CSFB的过程如图1所示：
步骤101：5G通信系统中的UE 600发起IP多媒体子系统(IP multimedia subsystem，IMS)主叫信令，该IMS主叫信令被发送至服务集中化和连续性应用服务器(service call continuity application server，SCC AS)，IMS主叫信令可携带UE支持的语音编码方式信息、UE的IP地址信息、端口号等信息；
步骤102：代理呼叫会话控制功能(proxy-call session control funtion，P-CSCF)接收呼叫对端设备通过IMS服务器发送的183消息，这里的IMS服务器可以是SCC AS，183消息是被叫端设备收到呼叫请求后发送的响应消息；
步骤103：P-CSCF通过策略控制功能(policy control function,PCF)/策略与计费规则功能单元(policy and charging rules function，PCRF)向5G通信系统的网元会话管理功能实体(session management function，SMF)发送建立语音传输通道的请求；
步骤104：SMF通过接入与移动性管理功能(access and mobility management function，AMF)向NG RAN发送建立语音传输通道的请求；NG RAN是指5G基站；
步骤105：NG RAN确定无法建立语音传输通道；
步骤106：NG RAN指示UE进行4G信号测量，并向UE发送UE被切换(handover)到4G通信系统的请求消息；
步骤107：NG RAN通过AMF向SMF通知无法建立语音传输通道；其中，NG RAN可以向AMF发送N2消息(message)，以指示由于IMS语音回退拒绝建立服务质量(quality of service，QoS)数据流，AMF可以向SMF发送携带PDU修改命令确认字符的SM请求(SM request with PDU modification command ack)；
步骤108：UE在切换到4G通信系统后，UE执行长期演进(long term evolution，LTE)和CS域的联合跟踪区更新(tracking area update，TAU)的过程；
步骤109：PDN网关(PDN GateWay，PGW)向4G基站eNB发送语音传输通道建立请求，从而在4G内重新发起语音传输通道建立请求；
步骤110：若eNB确定无法建立语音传输通道，则eNB向PGW回复拒绝消息；
步骤111：PGW通过PCRF向P-CSCF发送拒绝消息；
步骤112：P-CSCF向SCC AS发送取消(Cancel)消息，用于通知SCC AS取消呼叫；
步骤113：P-CSCF向UE发送用于UE确定无法在4G系统内建立语音呼叫的消息，如发送500拒绝消息；
步骤114：在收到用于UE确定无法在4G系统内建立语音呼叫的消息后，UE在LTE内发起CSFB。
在5G通信系统中的UE主动发起呼叫后，UE切换到4G通信系统且UE无法在4G建立语音呼叫承载时，另一种CSFB过程如图2所示：
步骤201：5G通信系统中的UE 600发起IMS主叫信令，该IMS主叫信令被发送至SCC AS，IMS主叫信令可携带UE支持的语音编码方式信息、UE的IP地址信息、端口号等信息；
步骤202：P-CSCF接收呼叫对端设备通过IMS服务器发送的183消息，这里的IMS服务器可以是SCC AS，183消息是被叫端设备收到呼叫请求后发送的响应消息；
步骤203：P-CSCF通过PCF/PCRF向5G通信系统的SMF发送建立语音传输通道的请求；
步骤204：SMF通过AMF向NG RAN发送建立语音传输通道的请求；NG RAN是指5G基站；
步骤205：NG RAN确定无法建立语音传输通道；
步骤206：NG RAN指示UE进行4G信号测量，并向UE发送UE被切换到4G通信系统的请求消息；
步骤207：NG RAN通过AMF向SMF通知无法建立语音传输通道；其中，NG RAN可以向AMF 201发送N2消息，以指示由于IMS语音回退拒绝建立QoS数据流，AMF201可以向SMF发送携带PDU修改命令确认字符的SM请求；
步骤208：NG RAN向UE发送RRC连接释放消息，将UE从5G通信系统重定向到4G通信系统；
步骤209：UE在收到RRC连接释放消息后，重选到4G基站，并发送CS/PS域联合注册请求并在该联合注册消息中包含handover指示；
步骤210：PGW向4G基站eNB发送语音传输通道建立请求，从而在4G内重新发起语音传输通道建立请求；
步骤211：若eNB确定无法建立语音传输通道，则eNB向PGW回复拒绝消息；
步骤212：PGW通过PCRF向P-CSCF发送拒绝消息；
步骤213：P-CSCF向SCC AS发送Cancel消息，用于通知SCC AS取消呼叫；
步骤214：P-CSCF向UE发送用于UE确定无法在4G系统内建立语音呼叫的消息，如发送500拒绝消息；
步骤215：在收到用于UE确定无法在4G系统内建立语音呼叫的消息后，UE在LTE内发起CSFB。
可见，如图1、图2所示的主叫UE发起CSFB的流程中，UE只有接收到用于UE确定无法在4G系统内建立语音呼叫的消息，才能发起CSFB进而在电路域建立呼叫，而等待该消息的过程会导致UE发起CSFB的时间过长，造成呼叫建立时间过长。
另外，目前在5G通信系统中的UE接收到呼叫请求后，UE切换到4G通信系统且UE无法在4G建立语音呼叫承载时，UE发起CSFB的过程如图3所示：
步骤301：5G通信系统中的UE 600接收到IMS被叫信令，该IMS被叫信令被是SCC AS发送的；IMS被叫信令可携带呼叫对端设备支持的语音编码方式信息、呼叫 对端设备的IP地址信息、端口号等信息；
步骤302：UE 600向P-CSCF发送183消息；183消息可以携带UE 600选定的编码方式信息等；
步骤303：P-CSCF通过PCF/PCRF向5G通信系统的SMF发送建立语音传输通道的请求；
步骤304：SMF通过AMF向NG RAN发送建立语音传输通道的请求；
步骤305：NG RAN确定无法建立语音传输通道；
步骤306：NG RAN指示UE进行4G信号测量，并向UE发送UE被切换到4G通信系统的请求消息；
步骤307：NG RAN通过AMF向SMF通知无法建立语音传输通道；其中，NG RAN可以向AMF 301发送N2消息，以指示由于IMS语音回退拒绝建立QoS数据流，AMF可以向SMF发送携带PDU修改命令确认字符的SM请求；
步骤308：UE在切换到4G通信系统后，UE执行LTE和CS域的TAU过程；
步骤309：PGW向eNB发送语音传输通道建立请求，从而在4G内重新发起语音传输通道建立请求；
步骤310：若eNB确定无法建立语音传输通道，则eNB向PGW回复拒绝消息；
步骤311：PGW通过PCRF向P-CSCF发送拒绝消息；
步骤312：P-CSCF向SCC AS发送拒绝消息；
步骤313：SCC AS重新进行被叫接入域选择，选择CS域进行再次呼叫；
步骤314：SCC AS通过P-CSCF再次发起呼叫，该呼叫被路由到UE当前注册的移动交换中心(mobile switching center，MSC)；
步骤315：MSC向移动管理实体(mobile management entity，MME)发送呼叫请求；
步骤316：MME向UE发送用于UE确定进行MT CSFB的消息，该消息可以是电路域的呼叫请求；
步骤317：UE在收到用于UE确定进行MT CSFB的消息后，发起MT CSFB。
在5G通信系统中的UE接收到呼叫请求后，若切换到4G通信系统且UE无法在4G建立语音呼叫承载时，另一种CSFB过程如图4所示：
步骤402：UE 600向P-CSCF发送183消息；183消息可以携带UE 600选定的编码方式信息等；
步骤403：P-CSCF通过PCF/PCRF向5G通信系统的SMF发送建立语音传输通道的请求；
步骤404：SMF通过AMF向NG RAN发送建立语音传输通道的请求；
步骤405：NG RAN确定无法建立语音传输通道；
步骤406：NG RAN指示UE进行4G信号测量，并向UE发送UE被切换到4G通信系统的请求消息；
步骤407：NG RAN通过AMF向SMF通知无法建立语音传输通道；其中，NG RAN可以向AMF 401发送N2消息，以指示由于IMS语音回退拒绝建立QoS数据流，AMF可以向SMF发送携带PDU修改命令确认字符的SM请求；
步骤408：NG RAN向UE发送RRC连接释放消息，将UE从5G通信系统重定向到4G通信系统；
步骤409：UE在接收到RRC连接释放消息后，重选到4G基站，并发送CS/PS域联合注册请求并在该联合注册消息中包含handover指示；
步骤410：PGW向eNB发送语音传输通道建立请求，从而在4G内重新发起语音传输通道建立请求；
步骤411：若eNB确定无法建立语音传输通道，则eNB向PGW回复拒绝消息；
步骤412：PGW通过PCRF向P-CSCF发送拒绝消息；
步骤413：P-CSCF向SCC AS发送拒绝消息；
步骤414：SCC AS重新进行被叫接入域选择，选择CS域进行再次呼叫；
步骤415：SCC AS通过P-CSCF再次发起呼叫，该呼叫被路由到UE当前注册的MSC；
步骤416：MSC向MME发起呼叫请求；
步骤417：MME向UE发送用于UE确定进行MT CSFB的消息，该消息可以是电路域的呼叫请求；
步骤418：UE在收到用于UE确定进行MT CSFB的消息后，发起MT CSFB。
可见，如图3、图4所示的被叫UE发起CSFB的流程中，UE在接收到MME发送的用于UE确定进行MT CSFB的消息后才能发起CSFB，之后在电路域建立呼叫，而等待该消息的过程会导致UE发起CSFB的时间过长，造成呼叫建立时间过长。
为解决如图1、图2、图3以及图4所示的UE发起CSFB的过程造成呼叫建立时间过长的问题，本申请实施例提供一种电路交换回退方法及装置。
下面，结合附图对本申请实施例进行详细说明。首先，介绍本申请实施例提供的通信系统，然后介绍本申请实施例提供的UE，最后介绍本申请实施例提供的电路交换回退方法的具体实现方式。
本申请实施例提供的一种电路交换回退方法所适用的通信系统可以为5G通信系统，如图5所示，当UE在4G和5G之间移动时，可通过N26接口在5G核心网网元AMF 501和4G核心网网元MME 502之间进行UE上下文(context)的传递，以实现UE所在通信系统的无缝转移，UE可在转移后的通信系统中保持转移前的网际协议(internet protocol，IP)地址，且UE对应的PGW-C(PDN GateWay，PDN网关)不变；其中，当UE在4G内建立的公用数据网(public data network，PDN)连接(PDN connection)被无缝转移到5G过程中，MME 502可以为UE选择5G与4G合设的SMF+PGW-C 503，从而保持UE对应的PGW-C不变。
应注意，本申请实施例中涉及的第一通信系统可以是5G通信系统，则第二通信系统为4G通信系统；若第一通信系统可以是4G通信系统，则第二通信系统为5G通信系统。
本申请实施例提供的一种电路交换回退方法所适用的UE 600，该UE 600可以具有如图6所示的结构，可见，UE 600可以包括处理器601，该处理器601可以用于支持UE 600实现本申请实施例提供的电路交换回退方法中UE 600涉及的步骤，例如，可用于UE 600确定无法在第二通信系统内建立语音呼叫承载；示例性的，UE 600还 可以具有收发器603，其中，收发器603可以用于UE 600进行消息(或数据)的接收和/或发送，例如用于UE 600接收第一请求或第二请求，或者，用于UE 600在第一通信系统内发起CSFB，或者用于UE 600接收本申请实施例提供的电路交换回退方法所涉及的响应消息、第一消息、第二消息、第三消息或者第四消息等等；示例性的，UE600中的收发器602，可以由发送器和接收器构成，发送器可用于实现收发器602的发送功能，接收器可用于实现收发器602的接收功能；示例性的，UE 600还可以包括存储器603，其中存储有计算机程序、指令，存储器603可以与处理器601耦合，用于支持处理器601调用存储器603中的计算机程序、指令以实现本申请实施例提供的电路交换回退方法中UE 600涉及的步骤，另外，存储器602还可以用于存储数据。
应理解，上述UE 600中的处理器601可以是中央处理器，通用处理器，数字信号处理器，专用集成电路，现场可编程门阵列或者其他可编程逻辑器件、晶体管逻辑器件、硬件部件或者其任意组合，其可以实现或执行结合本申请实施例公开内容所描述的各种示例性的逻辑方框，模块和电路。所述处理器也可以是实现计算功能的组合，例如包含一个或多个微处理器组合，数字信号处理器和微处理器的组合等等。
在实施中，UE 600能够在5G通信系统使用语音业务，UE 600需要UE 600可以是终端(Terminal)、移动台(MS，Mobile Station)、移动终端(Mobile Terminal)等设备，该UE 600能够与一个或多个通信系统的核心网实体进行通信，并接受核心网实体提供的网络服务。举例来说，本申请实施例中的UE 600可以是移动电话(或称为“蜂窝”电话)、具有移动终端的计算机等，UE 600还可以是便携式、袖珍式、手持式、计算机内置的或者车载的移动装置。UE 600也可以是具有通信模块的通信芯片。
下面以第一通信系统为5G通信系统，第二通信系统为4G通信系统为例，结合图7说明本申请实施例提供的一种电路交换回退方法，该方法包括以下步骤：
步骤S101：UE 600在5G通信系统内发送呼叫请求后，接收到5G通信系统发送的第一请求，第一请求指示UE 600将被转移到4G通信系统；
步骤S102：UE 600在被转移到4G通信系统之后，在接收到来自4G通信系统的第一消息之前，确定无法在4G通信系统内建立语音呼叫承载，其中，第一消息用于UE 600确定呼叫请求失败；在实施中，这里的第一消息，可以是P-CSCF向UE发送的500拒绝消息；
步骤S103：UE 600在确定无法在4G通信系统内建立语音呼叫承载的情况下，在4G通信系统内发起CSFB。
采用以上方法，处于5G通信系统中的UE 600在发送呼叫请求后，若UE 600被转移到4G通信系统，UE 600能够在通过步骤S102确定无法在4G通信系统内建立语音呼叫承载后通过步骤S103发起CSFB，相比于如图1所示的发起CSFB的方法，UE在执行步骤108后可不再花费时间等待步骤113中P-CSCF所发送的500拒绝消息，即可发起CSFB，因此缩短了UE 600的呼叫建立等待时长；相比于如图2所示的发起CSFB的方法，UE在执行步骤209后可不再花费时间等待步骤214中P-CSCF所发送的500拒绝消息，即可发起CSFB，因此缩短了UE 600的呼叫建立等待时长。
仍以第一通信系统为5G通信系统，第二通信系统为4G通信系统为例，结合图8说明本申请实施例提供的另一种电路交换回退方法，该方法包括以下步骤：
步骤S201：UE 600在5G通信系统内接收呼叫请求后，接收到5G通信系统发送的第二请求，所述第二请求指示UE 600将被转移到4G通信系统；
步骤S202：UE 600在被转移到4G通信系统之后，在接收到来自4G通信系统的第四消息之前，确定无法在4G通信系统内建立语音呼叫承载，第四消息用于指示UE 600根据第四消息去发起MT CSFB；在实施中，这里的第四消息，可以是MME向UE 600发送的电路域呼叫请求消息，用于UE在收到后进行MT CSFB以进行CS域通话；
步骤S203：UE 600在确定无法在4G通信系统内建立语音呼叫承载的情况下，在4G通信系统内发起CSFB。
采用以上方法，处于5G通信系统中的UE 600在接收到呼叫请求后，若UE 600被转移到4G通信系统，UE 600能够在通过步骤S202确定无法在4G通信系统内建立语音呼叫承载后，通过步骤S203发起CSFB，相比于如图3所示的发起CSFB的方法，UE在执行步骤308后可不再花费时间等待步骤316中MME所发送的用于UE 600发起MT CSFB的消息，即可发起CSFB，因此缩短了UE 600的呼叫建立等待时长；相比于如图4所示的发起CSFB的方法，UE在执行步骤409后可不再花费时间等待步骤417中MME所发送的用于UE 600发起MT CSFB的消息，即可发起CSFB，缩短了UE 600的呼叫建立等待时长。
在步骤S101的具体实施中，UE 600所接收的5G通信系统发送的第一请求，可以是第二消息，这里的第二消息可以是用于UE 600确定被切换(handover)到4G通信系统的消息，具体来说，第二消息可以是指示UE 600被切换到4G通信系统的请求消息；在另一种实现方式中，UE 600所接收的5G通信系统发送的第一请求还可以是第三消息，这里的第三消息可以是用于UE 600确定被重定向到4G通信系统的消息，具体来说，第三消息可以是指示UE 600被重定向到4G通信系统的请求消息，在实施中，UE 600被重定向到4G通信系统的请求消息可以是发送到UE 600的无线资源控制(radio resource control，RRC)连接释放(release)消息。
在步骤S201的具体实施中，UE 600所接收的5G通信系统发送的第二请求，也可以是第二消息或第三消息，其中，第二消息可以是指示UE 600被切换到4G通信系统的请求消息，这里的第三消息可以是用于UE 600确定被重定向到4G通信系统的消息，所述第二请求的具体实现方式，可参照上述第一请求的实现方式。
在步骤S102以及步骤S202的具体实施中，UE 600确定无法在4G通信系统内建立语音呼叫承载的方式可以有多种，下面分别举例几种可能的实现方式，说明UE 600确定无法在4G通信系统内建立语音呼叫承载的方法：
方式一，UE 600可在确定4G通信系统不支持进行IMS语音后，确定无法在4G通信系统内建立语音呼叫承载
UE 600可根据以下方法确定4G通信系统是否支持进行IP多媒体子系统IMS语音：
一种实现方式中，UE 600在确定被转移到4G通信系统后，可以在4G通信系统内发起电路交换和分组交换的联合位置更新，并根据收到的联合位置更新所对应的响应消息确定4G通信系统是否支持进行IP多媒体子系统IMS语音。具体来说，UE 600可以向4G核心网网元MME发送电路交换和分组交换的联合位置更新请求，UE 600在收到联合位置更新请求对应的响应消息后，若确定响应消息中包括第一信息，则确定4G通信 系统不支持进行IP多媒体子系统IMS语音，从而确定无法在4G通信系统内建立语音呼叫承载；否则，UE 600确定4G通信系统支持进行IP多媒体子系统IMS语音。在实施中，这里的第一信息可以是4G通信系统不支持进行IMS语音的指示或者无法在4G通信系统内建立IMS语音的指示。
另一种实现方式中，UE 600在确定被转移到4G通信系统后，可以在4G通信系统内发起电路交换和分组交换的联合注册，并根据收到的联合注册所对应的响应消息确定4G通信系统是否支持进行IP多媒体子系统IMS语音。具体来说，UE 600可以向4G核心网网元MME发送电路交换和分组交换的联合注册请求，UE 600在收到联合位置更新请求对应的响应消息后，若确定响应消息中包括第二信息，则确定4G通信系统不支持进行IP多媒体子系统IMS语音，从而确定无法在4G通信系统内建立语音呼叫承载；否则，UE 600确定4G通信系统支持进行IP多媒体子系统IMS语音。在实施中，这里的第二信息可以是4G通信系统不支持通过PS会话进行IP多媒体子系统IMS语音的指示或者无法在4G通信系统内建立IMS语音的指示。
应注意，以上实现方式中，UE 600若判断4G通信系统支持进行IP多媒体子系统IMS语音，并不代表UE 600一定能够在4G通信系统内建立语音呼叫承载。
方式二，UE 600可根据自身与4G通信系统中基站之间的信号强度，判断是否能够在4G通信系统内建立语音呼叫承载
一种实现方式为，UE 600判断自身与4G通信系统中的基站之间的信号强度是否小于阈值，这里的阈值可以是UE在4G通信系统能够建立语音承载的最低信号强度，若小于，则说明UE 600在转移到4G通信系统后与4G通信系统基站之间的信号强度不强，不满足4G通信系统内建立语音呼叫承载过程对UE 600与基站之间的信号强度的要求，从而UE 600可确定无法在4G通信系统内建立语音呼叫承载；否则，若UE 600确定自身与4G通信系统中的基站之间的信号强度大于或等于阈值，说明UE 600转移到4G通信系统后，UE 600与4G通信系统中的基站之间的信号强度满足在4G通信系统内建立语音呼叫承载的信号强度要求，此时UE 600可以不进行CSFB。应注意，这里也可以由UE 600确定自身与4G通信系统中的基站之间的信号强度是否小于或等于阈值，若是，则UE600确定无法在4G通信系统内建立语音呼叫承载。
另一种实现方式为，UE 600可以判断此前向4G通信系统中的基站上报的全部测量报告中的信号强度，是否存在不小于阈值的信号强度，这里的阈值可以是UE在4G通信系统能够建立语音承载的最低信号强度，若UE 600确定此前没有向4G通信系统的基站上报过不小于阈值的测量报告，则说明UE 600在转移到4G通信系统后与4G通信系统基站之间的信号强度，从未达到过在4G通信系统内建立语音呼叫承载过程对UE 600与基站之间的信号强度的要求，此时，UE 600确定无法在4G通信系统内建立语音呼叫承载；若UE 600确定此前发送的测量报告中至少存在一个大于或等于阈值的信号强度，则说明UE 600与基站之间的信号强度至少曾经满足4G通信系统内建立语音呼叫承载过程对UE 600与基站之间的信号强度的要求，此时UE 600可以不进行CSFB。应注意，这里也可以由UE 600确定自身此前向4G通信系统中的基站发送的测量报告中的信号强度，是否存在大于阈值的信号强度，若UE 600确定此前没有向4G通信系统的基站上报过大于阈值的测量报告，则UE 600确定无法在4G通信系统内建立语音呼叫承载。
方式三，UE 600可根据自身未收到无线资源控制RRC连接重配消息的时长，确定无法在4G通信系统内建立语音呼叫承载
UE 600在转移到4G通信系统后，可以根据接收到的基站发送的RRC连接重配消息，确定在4G通信系统中建立语音承载。在本申请实施例中，可令UE 600在预设时长内未收到RRC连接重配消息后，确定无法在4G通信系统内建立语音呼叫承载，因此UE 600可以进行CSFB，避免UE 600长时间等待RRC连接重配消息。另外在实施中，还可以在UE 600确定预设时长内能够收到RRC连接重配消息后，令UE 600不再进行CSFB。
一种实现方式为，UE 600可在确定自身接收到第二消息的时长已达到第一预设时长，且自身仍未收到RRC重配置消息后，确定无法在4G通信系统内建立语音呼叫承载，这里的第二消息，可以是指示UE 600被切换到4G通信系统的消息；若UE 600确定接收到RRC重配置消息时，自身接收到第二消息的时长尚未达到第一预设时长，UE 600确定不进行CSFB。
另一种实现方式中，UE 600可在确定自身接收到第三消息的时长已达到第二预设时长，且自身仍未收到RRC重配置消息后，确定无法在4G通信系统内建立语音呼叫承载，这里的第三消息，可以是指示UE 600被重定向到4G通信系统的消息；若UE 600确定接收到RRC重配置消息时，自身接收到第三消息的时长尚未达到第二预设时长，UE600确定不进行CSFB。
另一种实现方式中，UE 600可在确定自身接收到响应消息的时长已达到第三预设时长，且自身仍未收到RRC重配置消息后，确定无法在4G通信系统内建立语音呼叫承载，这里的响应消息，可以是UE 600在4G通信系统内发起的电路交换和分组交换的联合注册请求所对应的响应消息；若UE 600确定接收到RRC重配置消息时，自身接收到响应消息的时长尚未达到第三预设时长，UE 600确定不进行CSFB。
应注意，这里的第一预设时长、第二预设时长以及第三预设时长，可以是根据UE在4G通信系统中建立语音承载所需时长的统计数据确定的，例如，第一预设时长、第二预设时长以及第三预设时长均为UE在4G通信系统中建立语音承载所需时长的统计平均值。在实施中，第一预设时长、第二预设时长以及第三预设时长，可以是预设在UE 600中的数值。
在实施中，可以通过计数器实现上述第一预设时长、第二预设时长以及第三预设时长的计时。举例来说，UE 600可以在收到第二消息后，启动第一计数器，执行第一预设时长的计时，则在第一计数器计数结束时，若UE 600尚未收到RRC重配置消息，则UE 600可以确定重配置消息无法在4G通信系统内建立语音呼叫承载；UE 600也可以在收到第三消息后，启动第二计数器，执行第二预设时长的计时，则在第二计数器计数结束时，若UE 600尚未收到RRC重配置消息，则UE 600可以确定重配置消息无法在4G通信系统内建立语音呼叫承载；UE 600还可以在收到电路交换和分组交换的联合注册请求所对应的响应消息后，启动第三计数器，执行第三预设时长的计时，则在第三计数器计数结束时，若UE 600尚未收到RRC重配置消息，则UE 600可以确定重配置消息无法在4G通信系统内建立语音呼叫承载。
应注意，以上UE 600确定无法在4G通信系统内建立语音呼叫承载的方式只是举例说明，本申请实施例提供的电路交换回退方法中，UE 600可通过以上方式中的某一项 或以上方式中的多项的组合判断是否无法在4G通信系统内建立语音呼叫承载。举例来说，UE 600可以根据所述方式一确定4G通信系统支持进行IP多媒体子系统IMS语音后，根据方式二确定无法在4G通信系统内建立语音呼叫承载；又如，UE 600在收到指示UE600被切换到4G通信系统的第二消息后，若UE 600确定与4G通信系统的基站之间的信号强度小于阈值，还可以根据上述方式三，判断是否无法在收到第二消息后的第一预设时长内收到RRC连接重配消息，若是，则UE 600确定无法在4G通信系统内建立语音呼叫承载；否则，若UE 600在第一预设时长内收到了RRC连接重配消息，则即便UE 600确定自身与4G通信系统的基站之间的信号强度小于阈值，UE 600仍可以不再进行CSFB。
在步骤S103以及步骤S203的实施中，UE 600在4G通信系统内进行CSFB的方式可以是UE 600向4G通信系统中的MME发送连接态的扩展业务请求(extend service request)消息，该扩展业务请求消息可以是业务类型(service type)为移动发起(mobile originated，MO)的扩展业务请求消息。从而，根据步骤S103发起的MO CSFB，使得主叫UE 600建立CS域呼叫。
在步骤S203之后，UE 600还可以在电路交换域发起位置区更新(location area update，LAU)，具体来说，作为被叫的UE 600可以向MSC发送LAU请求，该LAU请求中可以携带电路交换回退移动被叫(circuit switched fallback mobile terminated call，CSMT)指示或继续(follow on)指示，用于建立移动性管理(mobile management，MM)连接，在MM连接建立后，UE 600可以等待网络的请求建立呼叫(set up)消息。另外，UE 600在4G通信系统内进行Mo CSFB之后，UE 600也可以不主动发起LAU过程，而在电路交换域等待网络寻呼(paging)以等待被叫。
仍以图5所示的5G通信系统为例，如图9所示，若5G通信系统中的UE 600在发送呼叫请求后转移到4G，本申请实施例提供的一种UE 600进行CSFB的过程可以包括以下步骤：
步骤901：5G通信系统中的UE 600发起IMS主叫信令，该IMS主叫信令被发送至SCC AS；IMS主叫信令可携带UE 600支持的语音编码方式信息、UE 600的IP地址信息、端口号等信息；
步骤902：P-CSCF接收呼叫对端设备通过IMS服务器发送的183消息；这里的IMS服务器可以是SCC AS；183消息是指被叫端设备收到呼叫请求后发送的响应消息；
步骤903：P-CSCF通过PCF/PCRF向5G通信系统的SMF发送建立语音传输通道的请求；
步骤904：SMF通过AMF 501向NG RAN发送建立语音传输通道的请求；NG RAN是指5G基站；
步骤905：NG RAN确定无法建立语音传输通道；
步骤906：NG RAN指示UE 600进行4G信号测量，并向UE 600发送UE 600被切换到4G通信系统的请求消息；
步骤907：NG RAN通过AMF 501向SMF通知无法建立语音传输通道；其中，NG RAN可以向AMF 501发送N2消息，以指示由于IMS语音回退拒绝建立QoS数据流，AMF501可以向SMF发送携带PDU修改命令确认字符的SM请求；
步骤908：UE 600在切换到4G通信系统后，发送电路交换和分组交换的联合位置更新请求，并接收联合位置更新请求对应的响应消息；
步骤909：UE 600判断响应消息中是否未携带有第一信息，若是，则执行步骤910，否则执行步骤911，第一信息用于UE 600确定无法通过4G通信系统进行IMS语音业务；在实施中，第一信息可以是4G通信系统不支持进行IMS语音的指示；
步骤910：UE 600判断自身与eNB之间的信号强度是否不小于阈值，若是，则结束本流程，否则，执行步骤911，eNB为4G通信系统中UE 600连接的基站；UE 600判断自身与eNB之间的信号强度不小于阈值，则UE 600可在结束本流程后继续等待在4G通信系统中建立语音承载；
步骤911：UE 600在4G通信系统内进行移动发起CSFB，之后结束本流程；在实施中，UE 600可以向MME 502发送业务类型为MO的扩展业务请求消息，以发起MO CSFB。
采用以上方法，相比于图1所示发起CSFB的流程，UE 600在步骤108之后，只需要通过步骤909和步骤910即可自行判断是否需要发起CSFB，如果判断结果为需要发起CSFB，UE 600可以通过步骤911发起主叫流程的CSFB，因此，UE 600不再需要等待网络侧执行步骤109至步骤113，以及不再需要通过步骤113接收P-CSCF发送的500拒绝消息，从而实现CSFB的加快发起，节省呼叫建立时长。
如图10所示，若5G通信系统中的UE 600在发送呼叫请求后转移到4G，本申请实施例提供的另一种UE 600进行CSFB的过程可以包括以下步骤：
步骤1001：5G通信系统中的UE 600发起IMS主叫信令，该IMS主叫信令被发送至SCC AS；IMS主叫信令可携带UE 600支持的语音编码方式信息、UE 600的IP地址信息、端口号等信息；
步骤1002：P-CSCF接收呼叫对端设备通过IMS服务器发送的183消息；这里的IMS服务器可以是SCC AS；
步骤1003：P-CSCF通过PCF/PCRF向5G通信系统的SMF发送建立语音传输通道的请求；
步骤1004：SMF通过AMF 501向NG RAN发送建立语音传输通道的请求；NG RAN是指5G基站；
步骤1005：NG RAN确定无法建立语音传输通道；
步骤1006：NG RAN指示UE 600进行4G信号测量，并向UE 600发送UE 600被切换到4G通信系统的请求消息；
步骤1007：NG RAN通过AMF 501向SMF通知无法建立语音传输通道；其中，NG RAN可以向AMF 501发送N2消息，以指示由于IMS语音回退拒绝建立QoS数据流，AMF501可以向SMF发送携带PDU修改命令确认字符的SM请求；
步骤1008：NG RAN向UE 600发送RRC连接释放消息，将UE 600重定向到4G通信系统；
步骤1009：在UE 600根据RRC连接释放消息重定向到4G通信系统后，发送电路交换和分组交换的联合注册请求，并接收联合注册请求对应的响应消息；
步骤1010：UE 600判断响应消息中是否未携带有第二信息，若是，则执行步骤1011，否则执行步骤1012，第二信息用于UE 600确定无法通过4G通信系统进行IMS语音业务； 在实施中，第二信息可以是4G通信系统不支持进行IMS语音的指示；
步骤1011：UE 600判断自身与eNB之间的信号强度是否不小于阈值，若是，则结束本流程，否则，执行步骤1012，eNB为4G通信系统中UE 600连接的基站；UE 600判断自身与eNB之间的信号强度不小于阈值，则UE 600可在结束本流程后继续等待在4G通信系统中建立语音承载；
步骤1012：UE 600在4G通信系统内进行主叫CSFB，之后结束本流程；在实施中，UE 600可以向MME 1002发送业务类型为MO的扩展业务请求消息，以发起CSFB。
采用以上方法，相比于图2所示发起CSFB的流程，UE 600在步骤209之后，只需要通过步骤1010和步骤1011即可自行判断是否需要发起CSFB，如果判断结果为需要发起CSFB，UE 600可以通过步骤1012发起主叫流程的CSFB，因此，UE 600不再需要等待网络侧执行步骤210至步骤214，以及不再需要通过步骤214接收P-CSCF发送的500拒绝消息，从而实现CSFB的加快发起，节省呼叫建立时长。
如图11所示，若5G通信系统中的UE 600在收到呼叫请求后转移到4G，本申请实施例提供的一种UE 600进行CSFB的过程可以包括以下步骤：
步骤1101：5G通信系统中的UE 600接到IMS被叫信令，该IMS被叫信令被是SCC AS发送的；IMS被叫信令可携带呼叫对端设备支持的语音编码方式信息、呼叫对端设备的IP地址信息、端口号等信息；
步骤1102：UE 600向P-CSCF发送183消息；183消息可以携带UE 600选定的编码方式信息等；
步骤1103：P-CSCF通过PCF/PCRF向5G通信系统的SMF发送建立语音传输通道的请求；
步骤1104：SMF通过AMF 501向NG RAN发送建立语音传输通道的请求；NG RAN是指5G基站；
步骤1105：NG RAN确定无法建立语音传输通道；
步骤1106：NG RAN指示UE 600进行4G信号测量，并向UE 600发送UE 600被切换到4G通信系统的请求消息；
步骤1107：NG RAN通过AMF 501向SMF通知无法建立语音传输通道；其中，NG RAN可以向AMF 501发送N2消息，以指示由于IMS语音回退拒绝建立QoS数据流，AMF501可以向SMF发送携带PDU修改命令确认字符的SM请求；
步骤1108：在UE 600切换到4G通信系统后，发送电路交换和分组交换的联合位置更新请求，并接收联合位置更新请求对应的响应消息；
步骤1109：UE 600判断响应消息中是否未携带有第一信息，若是，则执行步骤1110，否则执行步骤1111，第一信息用于UE 600确定无法通过4G通信系统进行IMS语音业务；在实施中，第一信息可以是4G通信系统不支持进行IMS语音的指示；
步骤1110：UE 600判断自身与eNB之间的信号强度是否不小于阈值，若是，则结束本流程，否则，执行步骤1111，eNB为4G通信系统中UE 600连接的基站；UE 600判断自身与eNB之间的信号强度不小于阈值，则UE 600可在结束本流程后继续等待在4G通信系统中建立语音承载；
步骤1111：UE 600在4G通信系统内进行移动发起CSFB；在实施中，UE 600可以 向MME 502发送业务类型为MO的扩展业务请求消息，以发起CSFB，实现CSFB；
步骤1112：UE 600在退回CS域后，在CS域发送LAU请求，用于建立MM连接；该LAU请求中可以携带CSMT指示或携带follow on指示；
步骤1113：在MM连接建立之后，UE 600接收请求建立呼叫set up消息，从而按照现有技术建立呼叫。
采用以上方法，相比于图3所示发起CSFB的流程，UE 600在步骤308之后，只需要通过步骤1109和步骤1110即可自行判断是否需要发起CSFB，如果判断结果为需要发起CSFB，UE 600可以通过步骤1111发起主叫流程的CSFB，因此，UE 600不再需要等待网络侧执行步骤309至步骤316，以及不再需要通过步骤316接收MME发送的用于UE600确定去发起MT CSFB的消息即可发起CSFB，从而实现CSFB的加快发起，节省呼叫建立时长。
如图12所示，若5G通信系统中的UE 600在收到呼叫请求后转移到4G，本申请实施例提供的另一种UE 600进行CSFB的过程可以包括以下步骤：
步骤1201：5G通信系统中的UE 600接到IMS被叫信令，该IMS被叫信令被是SCC AS发送的；IMS被叫信令可携带呼叫对端设备支持的语音编码方式信息、呼叫对端设备的IP地址信息、端口号等信息；
步骤1202：UE 600向P-CSCF发送183消息；183消息可以携带UE 600选定的编码方式信息等；
步骤1203：P-CSCF通过PCF/PCRF向5G通信系统的SMF发送建立语音传输通道的请求；
步骤1204：SMF通过AMF 501向NG RAN发送建立语音传输通道的请求；NG RAN是指5G基站；
步骤1205：NG RAN确定无法建立语音传输通道；
步骤1206：NG RAN指示UE 600进行4G信号测量，并向UE 600发送UE 600被切换到4G通信系统的请求消息；
步骤1207：NG RAN通过AMF 501向SMF通知无法建立语音传输通道；其中，NG RAN可以向AMF 501发送N2消息，以指示由于IMS语音回退拒绝建立QoS数据流，AMF501可以向SMF发送携带PDU修改命令确认字符的SM请求；
步骤1208：NG RAN向UE 600发送RRC连接释放消息，将UE 600重定向到4G通信系统；
步骤1209：在UE 600根据RRC连接释放消息重定向到4G通信系统后，发送电路交换和分组交换的联合注册请求，并接收联合注册请求对应的响应消息；
步骤1210：UE 600判断响应消息中是否未携带有第二信息，若是，则执行步骤1211，否则执行步骤1212，第二信息用于UE 600确定无法通过4G通信系统进行IMS语音业务；在实施中，第二信息可以是4G通信系统不支持进行IMS语音的指示；
步骤1211：UE 600判断自身与eNB之间的信号强度是否不小于阈值，若是，则结束本流程，否则，执行步骤1212，eNB为4G通信系统中UE 600连接的基站；UE 600判断自身与eNB之间的信号强度不小于阈值，则UE 600可在结束本流程后继续等待在4G通信系统中建立语音承载；
步骤1212：UE 600在4G通信系统内进行CSFB；在实施中，UE 600可以向MME 502发送业务类型为MO的扩展业务请求消息，以发起CSFB；
步骤1213：UE 600在退回CS域后，在CS域发送LAU请求，用于建立MM连接；该LAU请求中可以携带CSMT指示或携带follow on指示；
步骤1214：在MM连接建立之后，UE 600接收请求建立呼叫set up消息，建立呼叫，从而按照现有技术建立呼叫。
采用以上方法，相比于图4所示发起CSFB的流程，UE 600在步骤409之后，只需要通过步骤1210和步骤1211即可自行判断是否需要发起CSFB，如果判断结果为需要发起CSFB，UE 600可以通过步骤1212发起主叫流程的CSFB，因此，UE 600不再需要等待网络侧执行步骤410至步骤417，以及不再需要通过步骤417接收MME发送的用于UE600确定去发起MT CSFB的消息即可发起CSFB，从而实现CSFB的加快发起，节省呼叫建立时长。
基于同一发明构思，本申请实施例还提供一种呼叫建立的方法，该方法包括：
UE在第一通信系统内发起或接收呼叫过程中，确定被转移到第二通信系统；
UE确定无法在所述第二通信系统内建立语音呼叫承载；
UE在第二通信系统内发起CSFB请求，在CS域进行语音呼叫。
从而UE通过本地判断，可以不需要等待网络侧的只是消息而提前确定无法在第二通信系统建立语音承载，进一步可提前进行CSFB回退到CS域进行语音呼叫，缩短呼叫建立时延。
一种可能的设计中，第一通信系统可以是5G通信系统，第二通信系统可以是4G通信系统。UE确定被转移到第二通信系统，包括：
UE接收到被切换到4G通信系统的请求消息；或者，
UE接收到被重定向到4G通信系统的请求消息。
从而UE通过接收handover消息或重定向消息，可以判断出UE被转移到了第二通信系。
一种可能的设计中，UE确定无法在所述第二通信系统内建立语音呼叫承载，包括：
UE在第二通信系统内发起电路交换和分组交换的联合位置更新请求，UE接收位置更新请求对应的响应消息，确定响应消息中携带了所述第二通信系统不支持进行IP多媒体子系统IMS语音的指示；或者，
UE在第二通信系统内发起电路交换和分组交换的联合注册请求，UE接收注册请求对应的响应消息，确定响应消息中携带了所述第二通信系统不支持进行IP多媒体子系统IMS语音的指示。
从而UE通过接收电路交换和分组交换的联合位置更新请求对应的响应消息，或者接收电路交换和分组交换的联合注册请求对应的响应消息，可以确定无法在第二通信系统建立语音承载。
一种可能的设计中，UE确定无法在所述第二通信系统内建立语音呼叫承载，包括：
UE确定所述UE与第二通信系统的基站间的信号强度小于阈值；或者，UE确定所述UE没有向第二通信系统的基站eNB上报过大于阈值的测量报告。
UE通过对信号强度与阈值的比较，可以确定无法在第二通信系统建立语音承载。
一种可能的设计中，UE确定无法在所述第二通信系统内建立语音呼叫承载，包括：
UE收到被切换handover到4G通信系统的请求消息，开启定时器，定时器过期时，UE确定未收到无线资源控制RRC连接重配消息；或者，
UE接收到被重定向到4G通信系统的请求消息，开启定时器，定时器过期时，UE确定未收到无线资源控制RRC连接重配消息。
UE通过开启定时器，在定时器过期前未收到RRC连接重配消息则确定无法在第二通信系统内建立语音呼叫承载，进而进行CSFB，可以防止UE误判，保证了UE自主发起CSFB的可靠性。
在实施中，定时器预先配置在UE内，或者，由UE根据建立语音承载所需时长的统计数据动态配置。
一种可能的设计中，UE在第二通信系统内发起电路交换CS回退请求，包括：
UE在第二通信系统内发起业务类型Service type为移动发起MO的扩展业务请求消息。
UE通过设置Service type，可以保证核心网设备正确的处理UE的请求。
一种可能的设计中，UE进行CSFB之后，还包括：
UE在CS域发起LAU；或者，UE在CS域等待网络寻呼消息。
UE通过提前进入CS域，可以缩短呼叫的建立时延。
一种可能的设计中，UE在CS域发起LAU，包括：
UE发送LAU请求，该LAU请求中携带follow on指示，和/或，LAU请求中携带CSMT指示。
UE通过在LAU请求中携带follow on指示和/或CSMT指示，可以保证核心网设备与UE保持连接，从而加速呼叫建立过程。
基于同一发明构思，本申请实施例还提供一种UE，该UE可以具有如图6所示的结构，且具有上述方法实施例中UE 600的行为功能。
基于如图7所示的电路交换回退方法，如图6所示的UE 600中的处理器601可用于执行步骤S102；收发器602可用于执行步骤S101、S103。
基于如图8所示的电路交换回退方法，如图6所示的UE 600中的处理器601可用于执行步骤S202；收发器602可用于执行步骤S201、S203。
一种可能的设计中，基于图7所示的电路交换回退方法，第一请求可以是第二消息或第三消息，其中，第二消息用于所述UE确定被切换handover到所述第二通信系统，所述第三消息用于所述UE确定被重定向到所述第二通信系统。
一种可能的设计中，基于图8所示的电路交换回退方法，第二请求可以是第二消息或第三消息，其中，第二消息用于所述UE确定被切换handover到所述第二通信系统，所述第三消息用于所述UE确定被重定向到所述第二通信系统。
一种可能的设计中，处理器601可用于，在确定满足下列中的至少一项后，确定无法在第二通信系统内建立语音呼叫承载：
UE 600收到的联合位置更新请求对应的响应消息中携带第一信息，联合位置更新请求是UE 600在第二通信系统内发送的电路交换和分组交换的联合位置更新请求，第一信息用于UE 600确定无法通过第二通信系统进行IMS语音业务；或者
UE 600收到的联合注册请求对应的响应消息中携带第二信息，联合注册请求是UE 600在第二通信系统内发送的电路交换和分组交换的联合注册请求，第二信息用于UE 600确定无法通过第二通信系统进行IMS语音业务；或者
UE 600与第二通信系统的基站之间的信号强度小于阈值；或者
UE 600没有向第二通信系统的基站上报过大于阈值的测量报告；或者
UE 600没有向第二通信系统的基站上报过不小于阈值的测量报告；或者
UE 600接收到第二消息的时长已达到第一预设时长，且UE 600未收到无线资源控制RRC连接重配消息，第二消息指示UE 600被切换handover到第二通信系统；或者
UE 600接收到第三消息的时长已达到第二预设时长，且UE 600未收到RRC连接重配消息，第三消息指示UE 600被重定向到第二通信系统；或者
UE 600接收到联合注册请求对应的响应消息的时长已达到第三预设时长，且UE600未收到RRC连接重配消息，联合注册请求为UE 600在第二通信系统内发送的电路交换和分组交换的联合注册请求；
其中，RRC连接重配消息用于UE 600确定在第二通信系统内建立语音呼叫承载。
一种可能的设计中，收发器602具体用于：
在第二通信系统内发送扩展业务请求消息，所述扩展业务请求消息的业务类型Service type为移动终端发起MO。
一种可能的设计中，收发器602还用于：
在电路交换域发起LAU；或者
在CS域接收网络寻呼消息。
一种可能的设计中，收发器602具体用于：
发送LAU请求，LAU请求可携带follow on指示，和/或，LAU请求可携带CSMT指示。
如图13所示，本申请实施例提供的UE的另一种可能的结构中，UE采用模块化设计。示例性的，采用模块化设计的UE 1300可包括请求接收模块1301、呼叫承载建立确定模块1302以及CSFB发起模块1303；
其中，请求接收模块1301，用于在UE在第一通信系统内发送呼叫请求后，确定接收到第一请求，第一请求用于指示UE 1300将被转移到第二通信系统；呼叫承载建立确定模块1302，用于在UE 1300被转移到第二通信系统之后，在UE 1300接收到第一消息之前，确定无法在第二通信系统内建立语音呼叫承载，第一消息用于UE 1300确定UE确定所述呼叫请求失败；CSFB发起模块1303，用于确定无法在所述第二通信系统内建立语音呼叫承载的情况下，在第二通信系统内发起CSFB；其中，第一通信系统为5G通信系统，第二通信系统为4G通信系统。
示例性的，请求接收模块1301还可用于在UE在第一通信系统内接收到呼叫请求后，接收到第二请求，第一请求用于指示UE 1300将被转移到第二通信系统；呼叫承载建立确定模块1302还可用于在UE 1300接收到第四消息之前，确定无法在第二通信系统内建立语音呼叫承载，第四消息用于UE 1300根据第四消息去发起MT CSFB；CSFB发起模块1303，用于在确定无法在所述第二通信系统内建立语音呼叫承载的情 况下，第二通信系统内发起CSFB；其中，第一通信系统为5G通信系统，第二通信系统为4G通信系统。
一种可能的设计中，第一请求可以是第二消息或第三消息，其中，第二消息用于所述UE确定被切换handover到所述第二通信系统，所述第三消息用于所述UE确定被重定向到所述第二通信系统；第二请求可以是第二消息或第三消息，其中，第二消息用于所述UE确定被切换handover到所述第二通信系统，所述第三消息用于所述UE确定被重定向到所述第二通信系统。
一种可能的设计中，呼叫承载建立确定模块1302可在确定满足下列中的至少一项后，确定无法在第二通信系统内建立语音呼叫承载：确定UE 1300接收到的联合位置更新请求对应的响应消息中携带第一信息，联合位置更新请求是UE 1300在第二通信系统内发送的电路交换和分组交换的联合位置更新请求，第一信息用于UE 1300确定无法通过第二通信系统进行IP多媒体子系统IMS语音业务；或者，
确定UE接收到的联合注册请求对应的响应消息中携带第二信息，联合注册请求是UE在第二通信系统内发送的电路交换和分组交换的联合注册请求，第二信息用于UE确定无法通过第二通信系统进行IP多媒体子系统IMS语音业务；或者，
确定UE与第二通信系统的基站之间的信号强度小于阈值；或者，确定UE没有向第二通信系统的基站上报过大于阈值的测量报告；或者，
确定UE没有向第二通信系统的基站上报过不小于阈值的测量报告；或者，
确定UE接收到第二消息的时长已达到第一预设时长，且UE未收到无线资源控制RRC连接重配消息，第二消息用于UE确定被切换handover到第二通信系统；或者，
确定UE接收到第三消息的时长已达到第二预设时长，且UE未收到RRC连接重配消息，第三消息用于UE确定被重定向到4G通信系统；或者，
确定UE接收到联合注册请求对应的响应消息的时长已达到第三预设时长，且UE未收到RRC连接重配消息，联合注册请求为UE在第二通信系统内发送的电路交换和分组交换的联合注册请求；
其中，RRC连接重配消息用于UE确定在第二通信系统内建立语音呼叫承载。
一种可能的设计中，CSFB发起模块1303在发起CSFB时，可用于在第二通信系统内发送扩展业务请求消息，扩展业务请求消息的业务类型Service type为移动终端发起MO。
一种可能的设计中，UE 1300还可包括LAU发起模块1304，用于在电路交换域发起位置区更新LAU；或者，
UE 1300还可包括网络寻呼消息接收模块1305，用于在电路交换域接收网络寻呼消息。
一种可能的设计中，LAU发起模块1304在发起LAU时，可用于发送LAU请求，LAU请求可携带follow on指示和/或CSMT指示。
图14示出了上述实施例中所涉及的UE的另一种可能的设计结构的简化示意图。其中，UE 1400包括发射器1401，接收器1402，控制器/处理器1403，存储器1404和调制解调处理器1405。
示例性的，所述发射器1401可在UE 1400发送消息时调节(例如，模拟转换、滤 波、放大和上变频等)输出采样生成发送信号，该发送信号经上行链路由天线进行发射。在下行链路上，天线接收下行链路信号，接收器1402调节(例如，滤波、放大、下变频以及数字化等)从天线接收的下行链路信号并提供输入采样。其中，编码器接收要在上行链路上发送的业务数据和信令消息，例如本申请实施例中的业务类型为移动终端发起的扩展业务请求消息、LAU请求等，并对业务数据和信令消息进行处理(例如，格式化、编码和交织)。调制器进一步处理(例如，符号映射和调制)编码后的业务数据和信令消息并提供输出采样。解调器处理(例如，解调)输入采样并提供符号估计。解码器处理(例如，解交织和解码)该符号估计并提供发送给UE 1400的已解码的数据和信令消息。编码器、调制器、解调器和解码器可以由合成的调制解调处理器1405来实现。这些单元根据无线接入网采用的无线接入技术(例如，LTE及其他演进系统的接入技术)来进行处理。
控制器/处理器1403对UE 1400的动作进行控制管理，用于执行上述实施例中由UE进行的处理。例如用于确定UE 1400被转移到第二通信系统和/或本发明所描述的电路交换回退方法的其他过程。
作为示例，控制器/处理器1403可用于支持UE 1400实现图6所示的处理器601能够实现的功能。存储器1404存储用于控制器/处理器1403实现相应功能涉及的程序代码和数据。发射器1401可用于支持UE 1400实现图6所示的收发器602能够实现的发送功能。接收器1402可用于支持UE 1400实现图6所示的收发器602能够实现的接收功能。
基于与上述方法实施例相同构思，本申请实施例还提供了一种计算机可读存储介质，其上存储有一些指令，这些指令被调用执行时，可以使得计算机执行上述方法实施例、方法实施例的任意一种可能的设计中UE所涉及的功能。本申请实施例中，对可读存储介质不做限定，例如，可以是RAM(random-access memory，随机存取存储器)、ROM(read-only memory，只读存储器)等。
基于与上述方法实施例相同构思，本申请实施例还提供了一种计算机程序产品，当所述计算机程序产品被计算机运行时，可以使得计算机执行上述方法实施例、方法实施例的任意一种可能的设计中UE所涉及的功能。
基于与上述方法实施例相同构思，本申请实施例还提供了一种芯片，该芯片可以与收发器耦合，用于实现上述方法实施例、方法实施例的任意一种可能的设计中UE所涉及的功能。该芯片可以是位于本申请实施例提供的UE中的芯片。
基于与上述方法实施例相同构思，本申请实施例还提供了一种装置，该装置具有处理模块与通信接口，该处理模块用于执行上述方法实施例、方法实施例的任意一种可能的设计中UE所执行的步骤。通信接口用于所述装置进行通信，示例性的，通信接口可具有上述方法实施例、方法实施例的任意一种可能的设计中收发器的功能。
一种可能的设计中，所述装置还包括存储模块，用于存储处理模块必要的程序指令和数据。
一种可能的设计中，所述装置为芯片或芯片系统。
本申请是参照根据本申请实施例的方法、设备(系统)、和计算机程序产品的流程图和/或方框图来描述的。应理解可由计算机程序指令实现流程图和/或方框图中 的每一流程和/或方框、以及流程图和/或方框图中的流程和/或方框的结合。可提供这些计算机程序指令到通用计算机、专用计算机、嵌入式处理机或其他可编程数据处理设备的处理器以产生一个机器，使得通过计算机或其他可编程数据处理设备的处理器执行的指令产生用于实现在流程图一个流程或多个流程和/或方框图一个方框或多个方框中指定的功能的装置。
这些计算机程序指令也可存储在能引导计算机或其他可编程数据处理设备以特定方式工作的计算机可读存储器中，使得存储在该计算机可读存储器中的指令产生包括指令装置的制造品，该指令装置实现在流程图一个流程或多个流程和/或方框图一个方框或多个方框中指定的功能。
这些计算机程序指令也可装载到计算机或其他可编程数据处理设备上，使得在计算机或其他可编程设备上执行一系列操作步骤以产生计算机实现的处理，从而在计算机或其他可编程设备上执行的指令提供用于实现在流程图一个流程或多个流程和/或方框图一个方框或多个方框中指定的功能的步骤。
本申请中，“至少一个”是指一个或者多个，“多个”是指两个或两个以上。“以下至少一项(个)”或其类似表达，是指的这些项中的任意组合，包括单项(个)或复数项(个)的任意组合。例如，“a,b,或c中的至少一项(个)”，或，“a,b,和c中的至少一项(个)”，均可以表示：a,b,c,a-b(即a和b),a-c,b-c,或a-b-c，其中a,b,c分别可以是单个，也可以是多个。
应理解，在本申请的各种实施例中，上述各过程的序号的大小并不意味着执行顺序的先后，部分或全部步骤可以并行执行或先后执行，各过程的执行顺序应以其功能和内在逻辑确定，而不应对本申请实施例的实施过程构成任何限定。
本申请各方法实施例之间相关部分可以相互参考；各装置实施例所提供的装置用于执行对应的方法实施例所提供的方法，故各装置实施例可以参考相关的方法实施例中的相关部分进行理解。
本申请各装置实施例中给出的装置结构图仅示出了对应的装置的简化设计。在实际应用中，该装置可以包含任意数量的发射器，接收器，处理器，存储器等，以实现本申请各装置实施例中该装置所执行的功能或操作。
尽管已描述了本申请中一些可能的实施例，但本领域内的技术人员一旦得知了基本创造性概念，则可对这些实施例作出另外的变更和修改。所以，所附权利要求意欲解释为包括本申请实施例以及落入本申请范围的所有变更和修改。
显然，本领域的技术人员可以对本申请进行各种改动和变型而不脱离本申请的精神和范围。这样，倘若本申请的这些修改和变型属于本申请权利要求及其等同技术的范围之内，则本申请也意图包含这些改动和变型在内。

Claims (32)

  1. 一种电路交换回退方法，其特征在于，包括：
    用户设备UE在第一通信系统内发送呼叫请求后，接收到所述第一通信系统发送的第一请求，所述第一请求指示所述UE将被转移到第二通信系统；
    所述UE在被转移到第二通信系统之后，在接收到来自所述第二通信系统的第一消息之前，所述UE确定无法在所述第二通信系统内建立语音呼叫承载，所述第一消息用于所述UE确定所述呼叫请求失败；
    所述UE在确定无法在所述第二通信系统内建立语音呼叫承载的情况下，所述UE在所述第二通信系统内发起电路交换回退CSFB；
    其中，所述第一通信系统为5G通信系统，所述第二通信系统为4G通信系统。
  2. 根据权利要求1所述的方法，其特征在于，所述第一请求为第二消息或第三消息；
    所述第二消息用于所述UE确定被切换handover到所述第二通信系统；
    所述第三消息用于所述UE确定被重定向到所述第二通信系统。
  3. 根据权利要求1或2所述的方法，其特征在于，所述UE确定无法在所述第二通信系统内建立语音呼叫承载，包括下列中的至少一项：
    所述UE在所述第二通信系统内发送电路交换和分组交换的联合位置更新请求，接收所述联合位置更新请求对应的响应消息，并确定所述位置更新请求对应的响应消息中携带第一信息，所述第一信息用于所述UE确定无法通过所述第二通信系统进行IP多媒体子系统IMS语音业务；或者，
    所述UE在所述第二通信系统内发送电路交换和分组交换的联合注册请求，接收所述联合注册请求对应的响应消息，并确定所述注册请求对应的响应消息中携带第二信息，所述第二信息用于所述UE确定无法通过所述第二通信系统进行IP多媒体子系统IMS语音业务；或者，
    所述UE确定所述UE与所述第二通信系统的基站之间的信号强度小于阈值；或者，
    所述UE确定所述UE没有向所述第二通信系统的基站上报过大于阈值的测量报告；或者，
    所述UE确定所述UE没有向所述第二通信系统的基站上报过不小于阈值的测量报告；或者，
    所述UE确定所述UE接收到第二消息的时长已达到第一预设时长，且所述UE确定未收到无线资源控制RRC连接重配消息，所述第二消息指示所述UE被切换handover到所述第二通信系统；或者，
    所述UE接收到第三消息的时长已达到第二预设时长，且所述UE确定未收到RRC连接重配消息，所述第三消息指示所述UE被重定向到所述第二通信系统；或者，
    所述UE接收到响应消息的时长已达到第三预设时长，且所述UE确定未收到RRC 连接重配消息，所述响应消息为所述UE在所述第二通信系统内发起的电路交换和分组交换的联合注册请求对应的响应消息；
    其中，所述RRC连接重配消息用于所述UE确定在所述第二通信系统内建立语音呼叫承载。
  4. 根据权利要求1至3任一项所述的方法，其特征在于，所述UE在第二通信系统内发起电路交换回退CSFB，包括：
    所述UE在所述第二通信系统内发送扩展业务请求消息，所述扩展业务请求消息的业务类型Service type为移动终端发起MO。
  5. 一种电路交换回退方法，其特征在于，包括：
    用户设备UE在第一通信系统内接收到呼叫请求后，接收到所述第一通信系统发送的第二请求，所述第二请求指示所述UE将被转移到第二通信系统；
    所述UE在被转移到第二通信系统之后，在接收到来自所述第二通信系统的第四消息之前，所述UE确定无法在所述第二通信系统内建立语音呼叫承载，所述第四消息用于所述UE根据所述第四消息去发起移动终止MT电路交换回退CSFB；
    所述UE在确定无法在所述第二通信系统内建立语音呼叫承载的情况下，所述UE在所述第二通信系统内发起电路交换回退CSFB；
    其中，所述第一通信系统为5G通信系统，所述第二通信系统为4G通信系统。
  6. 根据权利要求5所述的方法，其特征在于，所述第二请求为第二消息或第三消息；
    所述第二消息用于所述UE确定被切换handover到所述第二通信系统；
    所述第三消息用于所述UE确定被重定向到所述第二通信系统。
  7. 根据权利要求5或6所述的方法，其特征在于，所述UE确定无法在所述第二通信系统内建立语音呼叫承载，包括下列中的至少一项：
    所述UE在所述第二通信系统内发送电路交换和分组交换的联合位置更新请求，接收所述联合位置更新请求对应的响应消息，并确定所述位置更新请求对应的响应消息中携带第一信息，所述第一信息用于所述UE确定无法通过所述第二通信系统进行IP多媒体子系统IMS语音业务；或者，
    所述UE在所述第二通信系统内发送电路交换和分组交换的联合注册请求，接收所述联合注册请求对应的响应消息，并确定所述注册请求对应的响应消息中携带第二信息，所述第二信息用于所述UE确定无法通过所述第二通信系统进行IP多媒体子系统IMS语音业务；或者，
    所述UE确定所述UE与所述第二通信系统的基站之间的信号强度小于阈值；或者，
    所述UE确定所述UE没有向所述第二通信系统的基站上报过大于阈值的测量报 告；或者，
    所述UE确定所述UE没有向所述第二通信系统的基站上报过不小于阈值的测量报告；或者，
    所述UE确定所述UE接收到第二消息的时长已达到第一预设时长，且所述UE确定未收到无线资源控制RRC连接重配消息，所述第二消息指示所述UE被切换handover到所述第二通信系统；或者，
    所述UE接收到第三消息的时长已达到第二预设时长，且所述UE确定未收到RRC连接重配消息，所述第三消息指示所述UE被重定向到所述第二通信系统；或者，
    所述UE接收到响应消息的时长已达到第三预设时长，且所述UE确定未收到RRC连接重配消息，所述响应消息为所述UE在所述第二通信系统内发起的电路交换和分组交换的联合注册请求对应的响应消息；
    其中，所述RRC连接重配消息用于所述UE确定在所述第二通信系统内建立语音呼叫承载。
  8. 根据权利要求5至7任一项所述的方法，其特征在于，所述UE在第二通信系统内发起电路交换回退CSFB，包括：
    所述UE在所述第二通信系统内发送扩展业务请求消息，所述扩展业务请求消息的业务类型Service type为移动终端发起MO。
  9. 根据权利要求5至8任一项所述的方法，其特征在于，所述用户设备UE在第二通信系统内发起电路交换回退之后，还包括：
    所述UE在电路交换域发起位置区更新LAU；或者，
    所述UE在电路交换域接收网络寻呼消息。
  10. 根据权利要求9所述的方法，其特征在于，所述UE在电路交换域发起位置区更新LAU，包括：
    所述UE发送LAU请求，所述LAU请求携带继续follow on指示和/或电路交换回退移动被叫CSMT指示。
  11. 一种电路交换回退的用户设备UE，其特征在于，包括：
    请求接收模块，用于在所述UE在第一通信系统内发送呼叫请求后，接收到所述第一通信系统发送的第一请求，所述第一请求指示所述UE将被转移到第二通信系统；
    呼叫承载建立确定模块，用于在所述UE在被转移到第二通信系统之后，在所述UE接收到来自所述第二通信系统的第一消息之前，确定无法在所述第二通信系统内建立语音呼叫承载，所述第一消息用于所述UE确定所述呼叫请求失败；
    CSFB发起模块，用于在所述UE确定无法在所述第二通信系统内建立语音呼叫承载的情况下，在所述第二通信系统内发起电路交换回退CSFB；
    其中，所述第一通信系统为5G通信系统，所述第二通信系统为4G通信系统。
  12. 根据权利要求11所述的UE，其特征在于，所述第一请求为第二消息或第三消息；
    所述第二消息用于所述UE确定被切换handover到所述第二通信系统；
    所述第三消息用于所述UE确定被重定向到所述第二通信系统。
  13. 根据权利要求11或12所述的UE，其特征在于，所述呼叫承载建立确定模块用于确定无法在所述第二通信系统内建立语音呼叫承载，包括：
    所述呼叫承载建立确定模块用于在确定满足下列中的至少一项后，确定无法在所述第二通信系统内建立语音呼叫承载：
    确定所述UE接收到的联合位置更新请求对应的响应消息中携带第一信息，所述联合位置更新请求是所述UE在所述第二通信系统内发送的电路交换和分组交换的联合位置更新请求，所述第一信息用于所述UE确定无法通过所述第二通信系统进行IP多媒体子系统IMS语音业务；
    确定所述UE接收到的联合注册请求对应的响应消息中携带第二信息，所述联合注册请求是所述UE在所述第二通信系统内发送的电路交换和分组交换的联合注册请求，所述第二信息用于所述UE确定无法通过所述第二通信系统进行IP多媒体子系统IMS语音业务；
    确定所述UE与所述第二通信系统的基站之间的信号强度小于阈值；
    确定所述UE没有向所述第二通信系统的基站上报过大于阈值的测量报告；
    确定所述UE没有向所述第二通信系统的基站上报过不小于阈值的测量报告；
    确定所述UE接收到第二消息的时长已达到第一预设时长，且所述UE未收到无线资源控制RRC连接重配消息，所述第二消息用于所述UE确定被切换handover到所述第二通信系统；
    确定所述UE接收到第三消息的时长已达到第二预设时长，且所述UE未收到RRC连接重配消息，所述第三消息用于所述UE确定被重定向到4G通信系统；
    确定所述UE接收到联合注册请求对应的响应消息的时长已达到第三预设时长，且所述UE未收到RRC连接重配消息，所述联合注册请求为所述UE在所述第二通信系统内发送的电路交换和分组交换的联合注册请求；
    其中，所述RRC连接重配消息用于所述UE确定在所述第二通信系统内建立语音呼叫承载。
  14. 根据权利要求11至13任一项所述的UE，其特征在于，所述CSFB发起模块用于在所述第二通信系统内发起电路交换回退CSFB，包括：
    所述CSFB发起模块在所述第二通信系统内发送扩展业务请求消息，所述扩展业务请求消息的业务类型Service type为移动终端发起MO。
  15. 一种电路交换回退的用户设备UE，其特征在于，包括请求接收模块、呼叫承载建立确定模块、CSFB发起模块：
    所述请求接收模块，用于在所述UE在第一通信系统内接收到呼叫请求后，接收到所述第一通信系统发送的第二请求，所述第二请求指示所述UE将被转移到第二通信系统；
    所述呼叫承载建立确定模块，用于在所述UE在被转移到第二通信系统之后，在所述UE接收到来自所述第二通信系统的第四消息之前，确定无法在所述第二通信系统内建立语音呼叫承载所述第四消息用于所述UE根据所述第四消息去发起移动终止MT电路交换回退CSFB；
    所述CSFB发起模块，用于在所述UE确定无法在所述第二通信系统内建立语音呼叫承载的情况下，在所述第二通信系统内发起电路交换回退CSFB；
    其中，所述第一通信系统为5G通信系统，所述第二通信系统为4G通信系统。
  16. 根据权利要求15所述的用户设备UE，其特征在于，所述第二请求为第二消息或第三消息；
    所述第二消息用于所述UE确定被切换handover到所述第二通信系统；
    所述第三消息用于所述UE确定被重定向到所述第二通信系统。
  17. 根据权利要求15或16所述的用户设备UE，其特征在于，所述呼叫承载建立确定模块用于确定无法在所述第二通信系统内建立语音呼叫承载，包括：
    所述呼叫承载建立确定模块用于在确定满足下列中的至少一项后，确定无法在所述第二通信系统内建立语音呼叫承载：
    确定所述UE接收到的联合位置更新请求对应的响应消息中携带第一信息，所述联合位置更新请求是所述UE在所述第二通信系统内发送的电路交换和分组交换的联合位置更新请求，所述第一信息用于所述UE确定无法通过所述第二通信系统进行IP多媒体子系统IMS语音业务；
    确定所述UE接收到的联合注册请求对应的响应消息中携带第二信息，所述联合注册请求是所述UE在所述第二通信系统内发送的电路交换和分组交换的联合注册请求，所述第二信息用于所述UE确定无法通过所述第二通信系统进行IP多媒体子系统IMS语音业务；
    确定所述UE与所述第二通信系统的基站之间的信号强度小于阈值；
    确定所述UE没有向所述第二通信系统的基站上报过大于阈值的测量报告；
    确定所述UE没有向所述第二通信系统的基站上报过不小于阈值的测量报告；
    确定所述UE接收到第二消息的时长已达到第一预设时长，且所述UE未收到无线资源控制RRC连接重配消息，所述第二消息用于所述UE确定被切换handover到所述第二通信系统；
    确定所述UE接收到第三消息的时长已达到第二预设时长，且所述UE未收到RRC连接重配消息，所述第三消息用于所述UE确定被重定向到4G通信系统；
    确定所述UE接收到联合注册请求对应的响应消息的时长已达到第三预设时长， 且所述UE未收到RRC连接重配消息，所述联合注册请求为所述UE在所述第二通信系统内发送的电路交换和分组交换的联合注册请求；
    其中，所述RRC连接重配消息用于所述UE确定在所述第二通信系统内建立语音呼叫承载。
  18. 根据权利要求15至17任一项所述的用户设备UE，其特征在于，所述CSFB发起模块用于在所述第二通信系统内发起电路交换回退CSFB，包括：
    所述CSFB发起模块在所述第二通信系统内发送扩展业务请求消息，所述扩展业务请求消息的业务类型Service type为移动终端发起MO。
  19. 根据权利要求15至18任一项所述的用户设备UE，其特征在于，所述UE还包括：
    LAU发起模块，用于在电路交换域发起位置区更新LAU；
    或者，所述UE还包括：
    网络寻呼消息接收模块，用于在电路交换域接收网络寻呼消息。
  20. 根据权利要求19所述的用户设备UE，其特征在于，所述LAU发起模块用于在电路交换域发起位置区更新LAU，包括：
    所述LAU发起模块发送LAU请求，所述LAU请求携带继续follow on指示和/或电路交换回退移动被叫CSMT指示。
  21. 一种电路交换回退用户设备UE，其特征在于，包括发送器、处理器以及接收器：
    所述接收器，用于在所述UE在第一通信系统内发送呼叫请求后，接收到所述第一通信系统发送的第一请求，所述第一请求指示所述UE将被转移到第二通信系统；
    所述处理器，用于所述UE在被转移到第二通信系统之后，在所述UE接收到来自所述第二通信系统的第一消息之前，确定无法在所述第二通信系统内建立语音呼叫承载，所述第一消息用于所述UE确定无法在所述第二通信系统内建立语音呼叫；
    所述发送器，用于在所述UE确定无法在所述第二通信系统内建立语音呼叫承载的情况下，在所述第二通信系统内发起电路交换回退CSFB；
    其中，所述第一通信系统为5G通信系统，所述第二通信系统为4G通信系统。
  22. 根据权利要求21所述的用户设备UE，其特征在于，所述第一请求为第二消息或第三消息；
    所述第二消息用于所述UE确定被切换handover到所述第二通信系统；
    所述第三消息用于所述UE确定被重定向到所述第二通信系统。
  23. 根据权利要求21或22所述的用户设备UE，其特征在于，所述处理器用于确定无法在所述第二通信系统内建立语音呼叫承载，包括：
    所述处理器用于在确定满足下列中的至少一项后，确定无法在所述第二通信系统内建立语音呼叫承载：
    确定所述UE接收到的联合位置更新请求对应的响应消息中携带第一信息，所述联合位置更新请求是所述UE在所述第二通信系统内发送的电路交换和分组交换的联合位置更新请求，所述第一信息用于所述UE确定无法通过所述第二通信系统进行IP多媒体子系统IMS语音业务；
    确定所述UE接收到的联合注册请求对应的响应消息中携带第二信息，所述联合注册请求是所述UE在所述第二通信系统内发送的电路交换和分组交换的联合注册请求，所述第二信息用于所述UE确定无法通过所述第二通信系统进行IP多媒体子系统IMS语音业务；
    确定所述UE与所述第二通信系统的基站之间的信号强度小于阈值；
    确定所述UE没有向所述第二通信系统的基站上报过大于阈值的测量报告；
    确定所述UE没有向所述第二通信系统的基站上报过不小于阈值的测量报告；
    确定所述UE接收到第二消息的时长已达到第一预设时长，且所述UE未收到无线资源控制RRC连接重配消息，所述第二消息用于所述UE确定被切换handover到所述第二通信系统；
    确定所述UE接收到第三消息的时长已达到第二预设时长，且所述UE未收到RRC连接重配消息，所述第三消息用于所述UE确定被重定向到4G通信系统；
    确定所述UE接收到联合注册请求对应的响应消息的时长已达到第三预设时长，且所述UE未收到RRC连接重配消息，所述联合注册请求为所述UE在所述第二通信系统内发送的电路交换和分组交换的联合注册请求；
    其中，所述RRC连接重配消息用于所述UE确定在所述第二通信系统内建立语音呼叫承载。
  24. 根据权利要求21至23任一项所述的用户设备UE，其特征在于，所述发送器用于在所述第二通信系统内发起电路交换回退CSFB，包括：
    所述发送器在所述第二通信系统内发送扩展业务请求消息，所述扩展业务请求消息的业务类型Service type为移动终端发起MO。
  25. 一种电路交换回退的用户设备UE，其特征在于，包括发送器、处理器以及接收器：
    所述接收器，用于在所述UE在第一通信系统内接收到呼叫请求后，接收到所述第一通信系统发送的第二请求，所述第二请求指示所述UE将被转移到第二通信系统；
    所述处理器，用于在所述UE在被转移到第二通信系统之后，在所述UE接收到来自所述第二通信系统的第四消息之前，确定无法在所述第二通信系统内建立语音呼叫承载所述第四消息用于所述UE根据所述第四消息去发起移动终止MT电路交换回退CSFB；
    所述发送器，用于在所述UE确定无法在所述第二通信系统内建立语音呼叫承载的情况下，在所述第二通信系统内发起电路交换回退CSFB；
    其中，所述第一通信系统为5G通信系统，所述第二通信系统为4G通信系统。
  26. 根据权利要求25所述的用户设备UE，其特征在于，所述第二请求为第二消息或第三消息；
    所述第二消息用于所述UE确定被切换handover到所述第二通信系统；
    所述第三消息用于所述UE确定被重定向到所述第二通信系统。
  27. 根据权利要求25或26所述的用户设备UE，其特征在于，所述处理器用于确定无法在所述第二通信系统内建立语音呼叫承载，包括：
    所述处理器用于在确定满足下列中的至少一项后，确定无法在所述第二通信系统内建立语音呼叫承载：
    确定所述UE接收到的联合位置更新请求对应的响应消息中携带第一信息，所述联合位置更新请求是所述UE在所述第二通信系统内发送的电路交换和分组交换的联合位置更新请求，所述第一信息用于所述UE确定无法通过所述第二通信系统进行IP多媒体子系统IMS语音业务；
    确定所述UE接收到的联合注册请求对应的响应消息中携带第二信息，所述联合注册请求是所述UE在所述第二通信系统内发送的电路交换和分组交换的联合注册请求，所述第二信息用于所述UE确定无法通过所述第二通信系统进行IP多媒体子系统IMS语音业务；
    确定所述UE与所述第二通信系统的基站之间的信号强度小于阈值；
    确定所述UE没有向所述第二通信系统的基站上报过大于阈值的测量报告；
    确定所述UE没有向所述第二通信系统的基站上报过不小于阈值的测量报告；
    确定所述UE接收到第二消息的时长已达到第一预设时长，且所述UE未收到无线资源控制RRC连接重配消息，所述第二消息用于所述UE确定被切换handover到所述第二通信系统；
    确定所述UE接收到第三消息的时长已达到第二预设时长，且所述UE未收到RRC连接重配消息，所述第三消息用于所述UE确定被重定向到4G通信系统；
    确定所述UE接收到联合注册请求对应的响应消息的时长已达到第三预设时长，且所述UE未收到RRC连接重配消息，所述联合注册请求为所述UE在所述第二通信系统内发送的电路交换和分组交换的联合注册请求；
    其中，所述RRC连接重配消息用于所述UE确定在所述第二通信系统内建立语音呼叫承载。
  28. 根据权利要求25至27任一项所述的用户设备UE，其特征在于，所述发送器用于在所述第二通信系统内发起电路交换回退CSFB，包括：
    所述发送器在所述第二通信系统内发送扩展业务请求消息，所述扩展业务请求消息的业务类型Service type为移动终端发起MO。
  29. 根据权利要求25至28任一项所述的用户设备UE，其特征在于，所述发送器还用于：
    在电路交换域发起位置区更新LAU；或者，
    所述接收器还用于：
    在电路交换域接收网络寻呼消息。
  30. 根据权利要求29所述的用户设备UE，其特征在于，所述发送器用于在电路交换域发起位置区更新LAU，包括：
    所述发送器发送LAU请求，所述LAU请求携带继续follow on指示和/或电路交换回退移动被叫CSMT指示。
  31. 一种装置，其特征在于，所述装置被配置为能控制用户设备UE执行如权利要求1-4或5-10中任一所述的方法。
  32. 根据权利要求31所述的装置，其特征在于，所述装置为所述UE，或所述装置为所述UE的一部分。
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