Method and device for establishing call

Abstract

The invention provides a call establishment method and device, and the method comprises the steps: transmitting a first message to first network equipment through a first communication link, and enabling the first message to be used for requesting the establishment of a first call; if the confirmation message of the first message is not received, retransmitting the first message; when retransmission of the first message meets a first preset condition and a confirmation message of the first message is not received when the first preset condition is met, performing a reset operation to establish a second communication link between the terminal and the first network device; sending a second message to the first network device through the second communication link, wherein the second message is used for requesting to establish the first call; if the confirmation message of the second message is not received, retransmitting the second message; and if retransmission of the second message meets a second preset condition and the terminal does not receive a confirmation message of the second message when the second preset condition is met, performing domain switching operation to switch from the current first domain to the second domain, and establishing a first call in the second domain.

Description

Method and device for establishing a call

[0001] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office of China on November 22, 2022, with application number 202211468049.0 and invention name “Method and Device for Establishing a Call”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of communication technology, and in particular to a method and device for establishing a call. Background Art

[0003] During the call establishment process, the terminal may establish a communication link with the network device, and the terminal transmits data to the network device via a Transmission Control Protocol (TCP) message or a User Datagram Protocol (UDP) message on the communication link.

[0004] For example, after receiving a TCP message, the network device sends an ACK message corresponding to the TCP message to the terminal. Similarly, after receiving a UDP message, the network device sends an ACK message corresponding to the UDP message to the terminal. If the terminal does not receive the ACK message, it will repeatedly retransmit the TCP or UDP message to the network device, resulting in prolonged call establishment or call failure, and a poor user experience.

[0005] Summary of the Invention

[0006] The present application provides a method and apparatus for establishing a call to avoid the problem of a terminal continuously retransmitting TCP messages or UDP messages, which results in a long call establishment time or call failure, thereby reducing the user experience.

[0007] In a first aspect, the present application provides a method for establishing a call, which is applied to a terminal, a first wireless network belongs to a first domain, and a first communication link is established between the terminal and a first network device in the first wireless network. The method includes: sending a first message to the first network device through the first communication link, and the first message is used to request to establish a first call; if within a first preset time after sending the first message, a confirmation message of the first message sent by the first network device is not received on the first communication link, the first message is retransmitted to the first network device through the first communication link; when the retransmission of the first message meets the first preset condition, and when the terminal does not receive the confirmation message of the first message sent by the first network device on the first communication link when the retransmission of the first message meets the first preset condition, the terminal performs a reset operation, and the reset operation includes dismantling the first communication link and establishing a first call between the terminal and the first network device. Two communication links; sending a second message to the first network device via the second communication link, the second message being used to request the establishment of a first call; if no confirmation message of the second message sent by the first network device is received on the second communication link within a second preset time after sending the second message, retransmitting the second message to the first network device via the second communication link; if the retransmission of the second message meets a second preset condition, and when the retransmission of the second message meets the second preset condition, the terminal does not receive a confirmation message of the second message sent by the first network device on the second communication link, the terminal performs a domain switching operation to switch from the current first domain to the second domain, and sends a third message in the second domain to the second network device in the second wireless network for requesting the establishment of the first call to establish the first call in the second domain, the standard of the first wireless network being higher than the standard of the second wireless network, and the second wireless network belonging to the second domain. Thus, the terminal establishes a second communication link with the first network device through a reset operation, and attempts to establish the first call via the second message on the second communication link. When the retransmission of the second message meets the second preset condition and the terminal does not receive a confirmation message of the second message sent by the first network device on the second communication link when the retransmission of the second message meets the second preset condition, the terminal performs a domain switching operation and continues to establish the first call on the switched second domain, thereby improving the success rate of call establishment through different attempts, reducing the duration of call establishment, and improving user experience.

[0008] In one possible implementation, the type of the second communication link is the same as the type of the first communication link, and the type of the second message is the same as the type of the first message; or, the type of the second communication link is different from the type of the first communication link, and the type of the second message is different from the type of the first message. Regardless of whether the type of the second communication link is the same as the type of the first communication link, if the retransmission of the first message meets the first preset condition, and when the retransmission of the first message meets the first preset condition and the terminal does not receive an acknowledgment message of the first message sent by the first network device on the first communication link, the terminal can re-establish a new communication link through a reset operation. The new communication link has a higher probability of being normal, which can increase the possibility of successful message exchange, thereby increasing the success rate of call establishment and reducing the duration of call establishment.

[0009] In one possible implementation, the type of the second communication link is different from the type of the first communication link, and the type of the second message is different from the type of the first message, including: one of the first and second communication links is a Transmission Control Protocol (TCP) communication link, and the other of the first and second communication links is a User Datagram Protocol (UDP) communication link; one of the first and second messages is a TCP message, and the other of the first and second messages is a UDP message; the first communication link and the first message correspond to the same protocol, and the second communication link and the second message correspond to the same protocol. For example, a TCP message can be TCP[PSH,ACK], and the TCP message's acknowledgment message can be TCP[ACK]; a UDP message can be UDP[PSH,ACK], and the UDP message's acknowledgment message can be UDP[ACK]. In this way, when one type of communication link is abnormal, the terminal can establish another type of communication link to increase the likelihood of successful message exchange.

[0010] In one possible implementation, the type of the second communication link is the same as the type of the first communication link, and the type of the second message is the same as the type of the first message, including: the types of the first communication link and the second communication link are both TCP communication links or both are UDP communication links; the types in the first message and the second message are both TCP messages or both are UDP messages; the protocols corresponding to the first communication link and the first message are the same, and the protocols corresponding to the second communication link and the second message are the same.

[0011] In one possible implementation, the first preset condition includes a preset first retransmission time, which indicates the maximum duration of transmission of the first message on the first communication link; or the first preset condition includes a preset first retransmission count, which indicates the maximum number of times the first message is transmitted on the first communication link. The first retransmission time can be calculated from the first time the terminal sends the first message, such as T6 in FIG7 . In some examples, the first retransmission time can be calculated from the second time the terminal sends the first message, where the second transmission of the first message means the start of retransmission of the first message. In some examples, the first retransmission time can be calculated from the time the terminal generates a first call request (such as a SIP Request), which is encapsulated in the first message, such as T5 in FIG7 . This application does not limit the first retransmission time. The first retransmission count can be N, where N can be greater than 2, such as N=3. The starting point and specific value of the calculation of the first retransmission count are not limited, such as calculating the first retransmission count from the first time the first message is sent, or calculating the first retransmission count from the second time the first message is sent. It should be noted that starting the calculation means that the terminal starts timing, and ends timing after the timing reaches the first retransmission time, so that the terminal uses the first retransmission time to control the transmission of the first message.

[0012] In one possible implementation, the second preset condition includes a preset second retransmission time, which is used to indicate the maximum duration of transmission of the second message on the second communication link; or, the second preset condition includes a preset second number of retransmissions, which is used to indicate the maximum number of times the second message is transmitted on the second communication link.

[0013] In one possible implementation, the preset first retransmission time is less than the first duration, and / or the preset second retransmission time is less than the first duration, and the first duration is the duration specified in the standard protocol from the time the terminal starts sending the first message or the second message to the first network device to the time the terminal receives the reset message sent by the first network device, and the reset message is used to trigger the terminal to perform a reset operation. As a result, the terminal can attempt operations to improve call anomalies (such as reset and domain switching operations) in advance before waiting for the first network device to send the reset message, and can detect and improve anomalies early, so that the call can be established normally, thereby reducing the call establishment time while increasing the call establishment success rate and improving the user experience.

[0014] In a possible implementation, the preset first retransmission time is 6 seconds, and / or the preset second retransmission time is 6 seconds.

[0015] In one possible implementation, the method further includes at least one of the following: the first wireless network is a 4G wireless network or a 5G wireless network; the second wireless network is a 3G or 2G wireless network; the first domain is a packet switched (PS) domain; the second domain is a circuit switched (CS) domain; the first message is any TCP message or any UDP message during an IP multimedia system (IMS) call establishment process; the second message is any TCP message or any UDP message during an IMS call establishment process; or the third message is a request message during a CS call establishment process. For example, the IMS call establishment may be a VoNR call establishment or a VoLTE call establishment, and the CS call establishment refers to establishing a call in the CS domain.

[0016] In one possible implementation, the method further includes: the first wireless network is a 5G wireless network; the second wireless network is a 4G wireless network; the first domain is a domain corresponding to the 5G wireless network; and the second domain is a domain corresponding to the 4G wireless network. Thus, the terminal can fall back from the domain corresponding to the 5G wireless network to the domain corresponding to the 4G wireless network, establish the first call in the domain corresponding to the 4G wireless network, and thus establish the first call using the 4G wireless network. The 4G wireless network has superior network performance and can ensure the quality of the first call.

[0017] In one possible implementation, the method further includes: if the terminal fails to establish the first call in the second domain within a third preset time, the terminal again performing a domain change operation to switch from the current second domain to a third domain, and sending a fourth message in the third domain to a third network device in a third wireless network, wherein the fourth message is used to request establishment of the first call in the third domain, the second wireless network having a higher standard than the third wireless network, and the third wireless network belonging to the third domain. The failure of the terminal to establish the first call in the second domain within the third preset time means that the terminal fails to successfully establish the first call in the second domain within the third preset time (e.g., the terminal remains in a call state within the third preset time). The terminal may then perform another domain change operation, fall back to a lower third domain, and attempt to establish the first call in the third domain. By retrying to successfully establish the first call by retrying the domain change operation, the terminal can detect and correct the anomaly early, allowing the call to be established normally, thereby reducing the call establishment time and improving the call establishment success rate, thereby enhancing the user experience.

[0018] In one possible implementation, the method also includes at least one of the following: the third wireless network is a 3G or 2G wireless network; the third domain is a circuit switched CS domain; the first message and the second message are any TCP message or any UDP message during the process of establishing a call in a 5G wireless network; the third message is a request message during the process of establishing a call in a 4G wireless network; or, the fourth message is a request message during the process of establishing a CS call.

[0019] In the second aspect, the present application provides a method for establishing a call, which is applied to a terminal, a third wireless network belongs to a third domain, and a third communication link is established between the terminal and the network device in the third wireless network. The method includes: sending a fourth message to the network device in the third wireless network through the third communication link, and the fourth message is used to request to establish a second call; if a confirmation message of the fourth message sent by the network device in the third wireless network is not received, retransmitting the fourth message to the network device in the third wireless network through the third communication link; when the retransmission of the fourth message meets the preset conditions and the terminal does not receive the confirmation message of the fourth message sent by the network device in the third wireless network on the third communication link when the retransmission of the fourth message meets the preset conditions, performing a domain switching operation and establishing a second call on the switched domain.

[0020] In a possible implementation, performing the domain change operation includes: switching from the third domain to the fifth domain, and the standard of the third wireless network is higher than the standard of the fifth wireless network belonging to the fifth domain.

[0021] In a possible implementation, performing the domain change operation includes: switching from the third domain to the fourth domain, where the standard of the third wireless network is higher than the standard of a fourth wireless network belonging to the fourth domain;

[0022] If the second call fails to be established with the network device in the fourth wireless network in the fourth domain, the fourth domain is switched to the fifth domain, and the standard of the fourth wireless network is higher than that of the fifth wireless network.

[0023] In one possible implementation, the third wireless network is a 5G wireless network; the fourth wireless network is a 4G wireless network, and the fifth wireless network is a 3G or 2G wireless network; the third domain is a 5G domain; the fourth domain is a 4G domain, and the fifth domain is a circuit switched CS domain; and the fourth message is any TCP message or any UDP message in the IMS call establishment process.

[0024] In one possible implementation, the preset condition includes a preset retransmission time, which is used to indicate the maximum duration of transmission of the fourth message on the third communication link; or, the preset condition includes a preset number of retransmissions, which is used to indicate the maximum number of transmissions of the fourth message on the third communication link.

[0025] In one possible implementation, the preset retransmission time is less than the first duration, and the first duration is the duration specified in the standard protocol from the time the terminal starts sending the fourth message to the network device to the time the terminal receives the reset message sent by the network device. The reset message is used to trigger the terminal to perform a reset operation.

[0026] In a possible implementation, the preset retransmission time is 6 seconds.

[0027] In a third aspect, the present application provides a terminal comprising: one or more processors and a memory; the memory is used to store computer program code, the computer program code comprises computer instructions, and when the one or more processors execute the computer instructions, the terminal executes any of the above-described methods.

[0028] In a fourth aspect, the present application provides a computer-readable storage medium for storing a computer program, which, when executed, is specifically used to implement any of the methods described above.

[0029] In a fifth aspect, the present application provides a chip. When the chip is deployed inside a terminal, the chip is used to control the terminal to implement any of the methods described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG1 is a schematic diagram of establishing a call provided by the present application;

[0031] FIG2 is a signaling diagram of signaling interaction between a UE and a 4G network device provided by the present application;

[0032] FIG3 is another signaling diagram of signaling interaction between a UE and a 4G network device provided by the present application;

[0033] FIG4 is a schematic diagram of the message transmission at each layer provided by this application;

[0034] FIG5 is a signaling diagram of a method for establishing a call provided by the present application;

[0035] FIG6 is another signaling diagram of the method for establishing a call provided by the present application;

[0036] FIG7 is another signaling diagram of the method for establishing a call provided by the present application;

[0037] FIG8 is another signaling diagram of the method for establishing a call provided by the present application;

[0038] FIG9 is another signaling diagram of the method for establishing a call provided by the present application;

[0039] FIG10 is a hardware structure diagram of the terminal provided in this application. DETAILED DESCRIPTION

[0040] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. The terms used in the following embodiments are only for the purpose of describing specific embodiments and are not intended to be limiting of the present application. As used in the specification and appended claims of the present application, the singular expressions "one", "a kind of", "said", "above", "the" and "this" are intended to also include expressions such as "one or more", unless there is a clear contrary indication in the context. It should also be understood that in the embodiments of the present application, "one or more" refers to one, two or more; "and / or" describes the association relationship of associated objects, indicating that three relationships may exist; for example, A and / or B can represent: the existence of A alone, the existence of A and B at the same time, and the existence of B alone, where A and B can be singular or plural. The character " / " generally indicates that the related objects before and after are in an "or" relationship.

[0041] References to "one embodiment" or "some embodiments" in this specification mean that a particular feature, structure, or characteristic described in conjunction with that embodiment is included in one or more embodiments of the present application. Thus, phrases such as "in one embodiment," "in some embodiments," "in other embodiments," and "in yet other embodiments" appearing in various places in this specification do not necessarily refer to the same embodiment, but rather mean "one or more but not all embodiments," unless otherwise specifically emphasized. The terms "including," "comprising," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0042] The "multiple" involved in the embodiments of the present application means greater than or equal to two. It should be noted that in the description of the embodiments of the present application, the words "first" and "second" are only used for the purpose of distinguishing the description and cannot be understood as indicating or implying relative importance or order.

[0043] For the sake of convenience, the technical terms involved in the embodiments of this application are first explained:

[0044] A wireless communication system can be understood as including terminals and network equipment. Terminals can also be referred to as terminal equipment (Terminal Equipment), user equipment (UE), mobile stations, mobile terminals, etc. Terminals can be mobile phones, tablet computers, computers with wireless transceiver functions, virtual reality terminals, augmented reality terminals, wireless terminals in industrial control, wireless terminals in unmanned driving, wireless terminals in remote surgery, wireless terminals in smart grids, wireless terminals in transportation safety, wireless terminals in smart cities, wireless terminals in smart homes, etc. This application does not limit the specific technology and specific device form used by the terminal.

[0045] The network device is an access device that the terminal uses to access the mobile communication system wirelessly. It can be a base station, an evolved NodeB (eNodeB), a transmission reception point (TRP), a next-generation base station (next generation NodeB, gNB) in a 5G mobile communication system, a base station in a future mobile communication system, or an access node in a WiFi system, etc. It can also be a module or unit that completes part of the functions of a base station, for example, it can be a centralized unit (CU) or a distributed unit (DU). This application does not limit the specific technology and specific device form adopted by the network device.

[0046] Wireless communication systems include, but are not limited to, Global System of Mobile Communication (GSM) systems, Code Division Multiple Access (CDMA) systems, Wideband Code Division Multiple Access (WCDMA) systems, Long Term Evolution (LTE) systems, LTE Frequency Division Duplex (FDD) systems, LTE Time Division Duplex (TDD) systems, Universal Mobile Telecommunication System (UMTS), and Fifth Generation Mobile Communication Systems (5G).

[0047] The GSM system is also known as the second-generation communication system, or 2G. The CDMA and WCDMA systems are also known as the third-generation communication systems, or 3G. LTE systems, such as LTE TDD systems, are also known as the fourth-generation communication systems, or 4G.

[0048] High and low standards: Network standards are arranged in the order of development: 2G, 3G, 4G, and 5G. High and low standards refer to any two standards in the sequence. Standards earlier in the sequence are higher standards than those later, and standards later in the sequence are lower standards than those earlier. For example, 5G is the higher standard of 2G, 3G, and 4G, 3G is the higher standard of 2G, and 3G is the lower standard of 4G. Network standards refer to wireless network standards.

[0049] A high-definition voice call over a 4G wireless network can be a Voice over Long-Term Evolution (VoLTE) call, that is, a VoLTE call is a high-definition voice call conducted using a 4G wireless network. A high-definition voice call over a 5G wireless network can be a Voice over New Radio (VoNR) call, that is, a VoNR call is a high-definition voice call conducted using a 5G wireless network. During a terminal establishment call (such as a VoLTE call or a VoNR call), the terminal can transmit data to the network device over the established communication link using TCP or UDP messages, such as transmitting data to the network device using TCP [PSH, ACK] or UDP [PSH, ACK]. After receiving the TCP [PSH, ACK] or UDP [PSH, ACK] message, the network device sends an ACK message to the terminal, where PSH indicates that data (DATA) is being transmitted.

[0050] If the terminal does not receive the ACK message, it retransmits TCP[PSH,ACK] or UDP[PSH,ACK] to the network device. Retransmission means that the terminal continues to send TCP[PSH,ACK] or UDP[PSH,ACK] to the network device, which may cause the call establishment time to be too long or the call failure, thereby reducing the user experience.

[0051] Taking VoLTE calls as an example, Figure 1 shows an example of a terminal failing to establish a VoLTE call. The terminal has the VoLTE call function turned on, and the user clicks on the phone application on the terminal. The terminal turns on the phone application and displays the interface of the phone application shown in (1) in Figure 1. The user can make a call with the help of the interface shown in (1) in Figure 1 to start establishing a VoLTE call. For example, the user can select a phone from the contacts in the interface shown in (1) in Figure 1, or manually enter a phone. After the user clicks dial, the call interface shown in (2) in Figure 1 is displayed to start establishing a VoLTE call. If the terminal does not receive an ACK message sent by the network device during the establishment of the VoLTE call, the terminal continues to display the call interface to indicate that the call is still in the call state.

[0052] In the scenario where a terminal establishes a VoLTE call, the signaling interaction process between the terminal and the 4G network device is shown in Figure 2. In Figure 2, the UE is the terminal and the UE is the calling party. A TCP link is established between the UE and the 4G network device. The signaling interaction process may include the following steps:

[0053] S1. UE receives a user's dialing request (Dail).

[0054] S2. The UE sends a Session Initialization Protocol (SIP) request message to the 4G network device. The SIP request message is abbreviated as SIP Request, which instructs the UE to initiate a call as the caller through the SIP Request. The SIP Request may include at least one of the following messages: Invite, Update, or Prack (the Provisional Response ACKnowledgement). Invite invites the called party to a call; Update is used to change call parameters without changing the call status; Prack is a mechanism for ensuring the reliable transmission of temporary messages (101-199) in SIP messages, such as the reliability response of 200OK, which confirms the receipt of 183 call in progress / 180 ringing.

[0055] S3. The UE sends a TCP [PSH, ACK] to the 4G network device to request to establish a call via TCP [PSH, ACK].

[0056] The TCP messages exchanged between the UE and the 4G network device include a FLAGS (identifier) ​​field. The FLAGS field can use the following identifiers: SYN (SYNchronous, establishing an online connection), FIN (FINish, termination), ACK (ACKnowledgment, confirmation), PSH (PuSH, push), RST (ReSeT, reset), etc. SYN: indicates establishment of a connection, FIN: indicates closing a connection, ACK: indicates that the message requires a reply from the recipient, PSH: indicates data (DATA) transmission, RST: indicates connection reset, and connection reset means resetting the existing communication link and rebuilding a new one. In the embodiment of the present application, PSH and ACK can be targeted.

[0057] It should be noted that, those skilled in the art can understand that steps S2 and S3 can be understood as the UE first generating a SIP Request, then the UE encapsulating the SIP Request into a message (such as a TCP [PSH, ACK] message), and then the UE sending the message to the 4G network device (the message may be encapsulated into other messages and ultimately sent to the 4G network device), thereby sending the SIP Request to the 4G network device.

[0058] S4. The 4G network device sends TCP [ACK] to the UE.

[0059] S5. The 4G network device sends a SIP ACK message (abbreviated as SIP Request ACK) to the UE. The SIP Request ACK message is an acknowledgment message of the SIP Request sent by the 4G network device to the UE.

[0060] S6. The UE and the 4G network device exchange Call_Proceeding messages to indicate that the user's call has been received and to start processing the call to establish a call with the called party.

[0061] S7. The UE communicates with the called party through the 4G network device (Call…).

[0062] S8. The UE and the 4G network device exchange Bye (end session) messages to indicate the end of the call between the UE and the called party through the Bye message.

[0063] S9. UE informs the user that the call is ended (Disconnect).

[0064] Through Figure 2 above, the UE, as the calling party, and the called party complete the call establishment, call, and call termination. If a UDP link is established between the UE and the 4G network device, the UE sends a UDP [PSH, ACK] to the 4G network device in step S3, and the 4G network device sends a UDP [ACK] to the UE in step S4. Whether it is Invite, Update, Prack, etc., when the UE sends these messages, these messages can be encapsulated in a SIP Request and interact with the 4G network device in the manner shown in Figure 2 above. As shown in Figure 3, the following steps may be included:

[0065] S11. The UE receives a dialing request from a user.

[0066] S12. The UE sends SIP Request 1 to the 4G network device. SIP Request 1 is a SIP request message, and may include one of Invite, Update, and Prack messages. For example, SIP Request 1 may include Invite.

[0067] S13. The UE sends TCP [PSH, ACK] to the 4G network device.

[0068] It should be noted that, those skilled in the art can understand that step S12 and step S13 can be understood as the UE first generating a SIP Request1, then the UE encapsulating the SIP Request1 into a message (such as a TCP [PSH, ACK] message), and then the UE sending the message to the 4G network device (the message may be encapsulated into other messages and ultimately sent to the 4G network device), thereby sending the SIP Request1 to the 4G network device.

[0069] S14. The 4G network device sends a TCP [ACK] to the UE.

[0070] S15. The 4G network device sends a SIP Request1ACK to the UE. The SIP Request1ACK is an acknowledgment message of the 4G network device to the SIP Request1 sent by the UE.

[0071] S16. The UE sends SIP Request 2 to the 4G network device. SIP Request 2 is a SIP request message, and the message included in SIP Request 2 is different from the message included in SIP Request 1. For example, SIP Request 1 may include Invite, and SIP Request 2 may include Update or Prack.

[0072] S17. The UE sends TCP [PSH, ACK] to the 4G network device.

[0073] It should be noted that, those skilled in the art can understand that step S16 and step S17 can be understood as the UE first generating a SIP Request2, then the UE encapsulating the SIP Request2 into a message (such as a TCP [PSH, ACK] message), and then the UE sending the message to the 4G network device (the message may be encapsulated into other messages and ultimately sent to the 4G network device), thereby sending the SIP Request2 to the 4G network device.

[0074] S18. The 4G network device sends a TCP [ACK] to the UE.

[0075] S19. The 4G network device sends a SIP Request2ACK to the UE. The SIP Request2ACK is an acknowledgment message of the 4G network device to the SIP Request2 sent by the UE.

[0076] In this embodiment of the present application, the TCP[PSH,ACK] in step S13 is used to indicate the transmission of SIP Request1, and the TCP[ACK] in step S14 is an acknowledgment of the TCP[PSH,ACK] in step S13. The TCP[PSH,ACK] in step S17 is used to indicate the transmission of SIP Request2, and the TCP[ACK] in step S18 is an acknowledgment of the TCP[PSH,ACK] in step S17. Although both TCP[PSH,ACK] and TCP[ACK] are used, the two TCP[PSH,ACK] sent by the UE are different, such as in the case of different sequence numbers; and the two TCP[ACK] sent by the 4G network device are different, such as in the case of different sequence numbers.

[0077] S20: The UE and the 4G network device exchange Call_Proceeding messages to indicate that a call from the user has been received and to start processing the call to establish a call with the called party.

[0078] S21. The UE communicates with the called party through the 4G network device.

[0079] S22: The UE and the 4G network device exchange Bye messages to indicate that the call between the UE and the called party is ended through the Bye message.

[0080] S23. The UE informs the user that the call is ended.

[0081] In the VoNR call establishment scenario, the signaling interaction process between the UE and the 4G network device can be the same as the signaling interaction process between the UE and the 4G network device in the above-mentioned VoLTE call establishment scenario, and will not be elaborated here.

[0082] When a UE exchanges call-related SIP request messages with a 4G network device, the SIP request message can be encapsulated into a TCP message and sent. For example, the SIP request is encapsulated in a TCP [PSH, ACK] message and sent to the 4G network device via TCP [PSH, ACK]. The TCP [PSH, ACK] message can be encapsulated in other messages for transmission. Figure 4 shows how messages are transmitted at various layers when a UE exchanges messages with a 4G network device.

[0083] Call-related messages such as Invite, Update, and Prack sent by the UE are encapsulated into SIP Request at the SIP layer. The SIP Request is encapsulated into TCP[PSH,ACK] or UDP[PSH,ACK] at the TCP / UDP layer. TCP[PSH,ACK] or UDP[PSH,ACK] is transmitted to the Internet Protocol (IP) layer below the TCP / UDP layer. It then passes through the IP layer, the Packet Data Convergence Protocol (PDCP) layer, the Radio Link Control Protocol (RLC) layer, the Media Access Control Address (MAC) layer, and the Physical (PHY) layer encapsulation before being transmitted through the PHY layer to the communication link between the UE and the 4G network device. 4G network devices can receive messages sent by UE with the help of communication links. Because call-related messages such as Invite, Update, and Prack are encapsulated and transmitted layer by layer, the messages received by the 4G network devices carry call-related messages such as Invite, Update, and Prack. Therefore, the 4G network devices can receive call-related messages.

[0084] After receiving call-related messages, 4G network devices respond to them by sending ACK messages. These ACK messages are transmitted to the UE via the communication link, PHY layer, MAC layer, RLC layer, PDCP layer, IP layer, TCP / UDP layer, and SIP layer. The ACK message at the TCP / UDP layer is TCP[ACK] or UDP[ACK], and the ACK message at the SIP layer is SIP Request ACK. The ACK messages at other layers are not described here.

[0085] After the TCP / UDP layer of the UE sends TCP[PSH,ACK] or UDP[PSH,ACK], even if at least one of the PHY layer, MAC layer, RLC layer, PDCP layer, and IP layer receives the ACK message, if the TCP / UDP layer does not receive TCP[ACK] or UDP[ACK], the UE can retransmit TCP[PSH,ACK] or UDP[PSH,ACK] and distinguish each transmitted TCP[PSH,ACK] or UDP[PSH,ACK] by the sequence number.

[0086] The UE can retransmit TCP[PSH,ACK] or UDP[PSH,ACK] on the communication link established with the 4G network device, and the retransmission time is relatively long, such as the retransmission can last for more than 160 seconds (s). During the stage when the UE retransmits TCP[PSH,ACK] or UDP[PSH,ACK], the UE can be in a call state, as shown in (2) in Figure 1, and is always in the call interface, resulting in a long call establishment time or call failure, which reduces the user experience. The process of establishing a VoNR call between the UE and the 5G network device is similar to the process of establishing a VoLTE call mentioned above, and there is also the problem of a long call establishment time or call failure, which reduces the user experience.

[0087] After the UE retransmits TCP [PSH, ACK] or UDP [PSH, ACK] for a period of time, the 4G / 5G network device (referred to as the network device) detects that the UE has been retransmitting messages. The network device can send an RST message, such as TCP [RST], to the UE. The RST message indicates that the communication link between the UE and the network device is abnormal. The UE can determine that the communication link is abnormal based on the RST message, reestablish a new communication link, and continue to send messages to the network device through the new communication link. Because the UE reestablishes the new communication link after the message retransmission period and receives the RST message sent by the network device, it is difficult for the UE to detect the communication link abnormality in a timely manner, which can also cause the call establishment time to be too long, reducing the user experience.

[0088] To address the above issues, embodiments of the present application provide a method for establishing a call, wherein the UE controls message retransmission. When message retransmission meets preset conditions, the UE proactively performs at least one of a reset, a path change, and a domain change to improve the call anomaly. Specifically, the method for establishing a call provided in embodiments of the present application is primarily implemented in the following three ways:

[0089] 1) Controlling message retransmissions primarily involves controlling the retransmission time or number of retransmissions. These can be specified in preset conditions. The retransmission time indicates the maximum duration for message transmission over a communication link; the retransmission number indicates the maximum number of times a message can be transmitted over a communication link.

[0090] If the message retransmission interval is known, the number of message retransmissions within a period of time can be calculated based on the message retransmission interval and the current retransmission time. Therefore, specifying the retransmission time in the preset condition is equivalent to specifying the number of retransmissions. For example, in some examples, the UE n Seconds to control message retransmission, that is, in 2 0 , 2 1 , 2 2 ….The message is retransmitted once at a certain time interval. The time interval for message retransmission is known, so the UE can calculate the number of retransmissions within a period of time. For example, in some examples, the UE can retransmit once at the same interval, such as once every 1 second. Thus, the UE can also calculate the number of retransmissions within a period of time. In some examples, the retransmission time is less than the time from the UE starting to retransmit the message to the UE receiving the RST message sent by the network device. In some examples, the retransmission time is 6 seconds, then when the UE is retransmitted according to 2 n When the control message is retransmitted for 1 second, the number of retransmissions is equivalent to 3. In some examples, the retransmission time for the UE to retransmit TCP [PSH, ACK] or UDP [PSH, ACK] is 160 seconds or 120 seconds, and the retransmission time in the preset condition is less than 120 seconds.

[0091] 2) When the message retransmission meets the preset conditions and no RST message is received on the communication link when the preset conditions are met, the UE actively performs a reset operation. During the reset operation, the UE may or may not perform a path switching operation.

[0092] 3) When the message retransmission meets the preset conditions, the UE actively performs the domain change operation.

[0093] Taking a VoLTE call scenario or a VoNR call scenario as an example, the method for establishing a call provided in the embodiments of the present application is mainly implemented in the following three ways:

[0094] 1) Control TCP [PSH, ACK] or UDP [PSH, ACK] retransmissions. In some examples, the retransmission time of TCP [PSH, ACK] or UDP [PSH, ACK] is controlled. The retransmission time can also be called the message transmission no response timeout, such as a message transmission no response timeout of 6 seconds. The retransmission time is a preset duration. Specifically, the retransmission time is the maximum duration that the UE spends continuously transmitting TCP [PSH, ACK] or UDP [PSH, ACK].

[0095] During the call establishment process, the UE uses the retransmission time to time the UE's transmission of TCP[PSH,ACK] or UDP[PSH,ACK]. For example, in some examples, the UE starts timing from the Mth transmission of TCP[PSH,ACK] or UDP[PSH,ACK] and ends timing after the timing duration equals the retransmission time. During the timing process, the UE does not interrupt the transmission of TCP[PSH,ACK] or UDP[PSH,ACK], where M can be 1 or 2. If the UE's transmission of TCP[PSH,ACK] or UDP[PSH,ACK] is interrupted, the UE's timing is restored to 0. When the UE retransmits TCP[PSH,ACK] or UDP[PSH,ACK], the UE can restart timing from 0.

[0096] 2) After T1 seconds of no response in TCP[PSH,ACK] or UDP[PSH,ACK] transmission, the UE actively performs a reset operation and then performs UDP[PSH,ACK] transmission or TCP[PSH,ACK] transmission. In some examples, when the UE performs a reset operation, the TCP communication link is dismantled and the UDP communication link is re-established. The UE completes the switching operation while performing the reset operation and transmits UDP[PSH,ACK] on the UDP communication link. In some examples, when the UE performs a reset operation, the UDP communication link is dismantled and the TCP communication link is re-established. The UE completes the switching operation while performing the reset operation and transmits TCP[PSH,ACK] on the TCP communication link. In some examples, when the UE performs a reset operation, the TCP communication link is dismantled and the TCP communication link is re-established; in some examples, when the UE performs a reset operation, the UDP communication link is dismantled and the UDP communication link is re-established.

[0097] Wherein, T1 is the time it takes the UE to transmit TCP[PSH,ACK] or UDP[PSH,ACK] before performing a reset operation. This time can be counted starting from the Mth TCP[PSH,ACK] or UDP[PSH,ACK] transmitted after the UE receives the user's dial-up request, and ending when the timing duration equals the retransmission time, so that T1 is equal to the retransmission time. The value of M can be 1 or 2. For example, if the preset retransmission time is 6 seconds, then the timer starts from the first TCP[PSH,ACK] or UDP[PSH,ACK] transmitted after the UE receives the user's dial-up request. The time when the timing starts is used as the start time of T1, and ends after 6 seconds. The time when the timing ends can be used as the end time of T1, so that T1 = 6 seconds.

[0098] 3) After T2 seconds of no response during TCP [PSH, ACK] or UDP [PSH, ACK] transmission, the UE initiates a domain change. This domain change can be CSFB (Circuit Switched Fallback), which means falling back from the Packet Switching (PS) domain to the Circuit Switched (CS) domain. T1 and T2 can be the same or different.

[0099] Wherein, T2 is the time it takes for the UE to transmit TCP[PSH,ACK] or UDP[PSH,ACK] before performing the domain change operation. If the UE does not perform a reset operation before actively performing the domain change operation, then T2 can be counted from the Mth transmission of TCP[PSH,ACK] or UDP[PSH,ACK] after the UE receives the user's dial-up request, and ends when the timing duration is equal to the preset retransmission time. If the UE performs a reset operation before actively performing the domain change operation, then T2 starts from the Mth transmission of TCP[PSH,ACK] or UDP[PSH,ACK] after the UE performs the reset operation, and ends when the timing duration is equal to the value of the retransmission time. The value of M can be 1 or 2.

[0100] The UE can combine the above three methods, including: a combination of 1) and 2), a combination of 1) and 3), and a combination of 1), 2) and 3). However, when using the combination of 1), 2) and 3), please note that: because the CS domain is a circuit-switched domain, TCP / UDP is not applicable to the CS domain. Therefore, after the UE falls back to the CS domain, the UE cannot perform the reset operation and complete the switching operation during the reset operation. For the scenario where the UE falls back from the PS domain to the CS domain after changing domains, 2) is executed before 3). The above combination method enables the UE to try at least one operation for improving call abnormalities during the process of actively controlling message retransmission, so as to eliminate abnormalities in call establishment by trying different types of operations, so that the UE can establish a call normally, while reducing the call establishment time and improving the success rate of call establishment, thereby improving user experience.

[0101] In addition, the UE can actively control message retransmission. When it determines that the message retransmission meets the preset conditions and no RST message is received on the communication link when the preset conditions are met, the UE actively attempts to perform operations to improve the call abnormality. As a result, the UE can try to perform operations to improve the call abnormality in advance before the network device sends the RST message. The UE can detect and improve the abnormality early, so that the call can be established normally, thereby reducing the call establishment time and improving the call establishment success rate, thereby improving the user experience.

[0102] Still taking the VoLTE call scenario or the VoNR call scenario as an example, the method for establishing a call provided in an embodiment of the present application is described below with reference to the accompanying drawings. Please refer to Figure 5, which shows a process of the method for establishing a call, which may include the following steps:

[0103] S30. The UE receives a dialing request from the user.

[0104] S31. The UE sends a SIP Request to the 4G network device.

[0105] S32: The UE sends TCP [PSH, ACK] to the 4G network device. For understanding of steps S31 and S32, please refer to the description of steps S2 and S3, which will not be repeated here.

[0106] S33. After the UE sends TCP[PSH,ACK], the UE does not receive TCP[ACK] sent by the 4G network device. For example, the UE does not receive TCP[ACK] within a first preset time period after sending TCP[PSH,ACK]. The value of the first preset time period is not limited.

[0107] S34. The UE retransmits TCP [PSH, ACK] to the 4G network device. The sequence number of the retransmitted TCP [PSH, ACK] is different from the sequence number of the TCP [PSH, ACK] sent in step S32. In step S34, TCP Retransmission is used to indicate the retransmission of TCP [PSH, ACK].

[0108] In some examples, the retransmission time can be calculated from the time the UE sends a SIP Request to the 4G network device, as shown by T in Figure 5. The SIP Request is encapsulated in TCP[PSH,ACK] and sent. The first TCP[PSH,ACK] sent is after the SIP Request. Therefore, the TCP[PSH,ACK] retransmitted during the retransmission time includes the first TCP[PSH,ACK]. It should be noted that sending a SIP Request refers to the time from when the UE generates the SIP Request to when it is encapsulated in TCP[PSH,ACK] and when TCP[PSH,ACK] is sent. It can be understood that T in Figure 5 is the time it takes for the UE to continuously transmit TCP[PSH,ACK] after receiving the user's dial-up request. This time T starts from when the UE generates the SIP Request and ends when the timer duration is equal to the retransmission time value. Therefore, the value of T is equal to the preset retransmission time. After the time for the UE to transmit TCP [PSH, ACK] reaches the preset retransmission time, the UE may execute step S35 to perform a domain switching operation, the transmission of TCP [PSH, ACK] is interrupted, the UE falls back from the PS domain to the CS domain, and the timing of TCP [PSH, ACK] is restored to 0.

[0109] In some examples, the retransmission time can be calculated from the first time the UE sends TCP[PSH,ACK]. That is, in some examples, T in Figure 5 is the time it takes for the UE to continuously transmit TCP[PSH,ACK] after receiving the user's dial-up request. This time can be counted from the first TCP[PSH,ACK] transmitted after the UE receives the user's dial-up request, and ends when the timing is equal to the value of the retransmission time. Therefore, the value of T is equal to the preset retransmission time. After the time it takes for the UE to transmit TCP[PSH,ACK] reaches the preset retransmission time, the UE can execute step S35 to perform a domain switching operation, the transmission of TCP[PSH,ACK] is interrupted, the UE falls back from the PS domain to the CS domain, and the timing of TCP[PSH,ACK] is restored to 0. The purpose of restoring the timing of TCP[PSH,ACK] to 0 is to start timing from 0 the next time TCP[PSH,ACK] is transmitted.

[0110] The time from when the UE generates a SIP Request to when it is encapsulated into TCP[PSH,ACK] is in the millisecond level. Therefore, the retransmission time calculated from the first time the UE sends TCP[PSH,ACK] is close to the retransmission time calculated from the time the SIP Request is sent.

[0111] S35. The UE exchanges a Service Request_CSFB_Redial (Service Request for Falling Back to the CS Domain) message with the 4G network device. The Service Request_CSFB_Redial message indicates that the UE has performed a domain change operation, falling back from the PS domain to the CS domain (referred to as CS_Retry). The domain change operation is performed when TCP [PSH, ACK] meets certain conditions (such as the aforementioned retransmission time or retransmission count requirements) and when no TCP [ACK] is received on the communication link when the conditions are met.

[0112] S36: The UE and the 2G / 3G network device exchange a Call_Proceeding message.

[0113] S37. The UE communicates with the called party through the 2G / 3G network device.

[0114] S38. Bye messages are exchanged between the UE and the 2G / 3G network device.

[0115] S39. The UE informs the user that the call is ended.

[0116] The UE falls back from the PS domain to the CS domain via the Service Request_CSFB_Redial message, indicating that the UE has switched from a high-standard network to a low-standard network. After switching to the low-standard network, the UE can initiate call establishment in the low-standard network. The switch from a high-standard network to a low-standard network increases the UE's chance of successfully establishing a call. Therefore, falling back to the CS domain can reduce call establishment time and increase call establishment success rates, improving the user experience.

[0117] FIG6 shows another process of a method for establishing a call, which may include the following steps:

[0118] S40. The UE receives a dialing request from the user.

[0119] S41. The UE sends a SIP Request to the 4G network device.

[0120] S42: The UE sends TCP [PSH, ACK] to the 4G network device. For understanding of steps S41 and S42, please refer to the description of steps S2 and S3, which will not be repeated here.

[0121] S43. After the UE sends TCP [PSH, ACK], the UE does not receive TCP [ACK] sent by the 4G network device.

[0122] S44. The UE retransmits TCP [PSH, ACK] to the 4G network device. The sequence number of the retransmitted TCP [PSH, ACK] is different from the sequence number of the TCP [PSH, ACK] sent in step S42. In step S44, TCP Retransmission is used to indicate the retransmission of TCP [PSH, ACK].

[0123] S45. The UE continues to retransmit TCP [PSH, ACK] to the 4G network device. The sequence number of the retransmitted TCP [PSH, ACK] is different from the sequence number of the TCP [PSH, ACK] sent in step S42 and step S44. In step S45, TCP Retransmission is used to indicate the retransmission of TCP [PSH, ACK].

[0124] In some examples, the retransmission time can be calculated from the time the UE sends a SIP Request to the 4G network device, as shown by T3 in Figure 6. T3 can be the same as or different from T in Figure 5. The SIP Request is encapsulated and sent in TCP [PSH, ACK]. The first TCP [PSH, ACK] sent follows the SIP Request. Therefore, the retransmitted TCP [PSH, ACK] within the retransmission time includes the first TCP [PSH, ACK]. It should be noted that sending a SIP Request refers to the time from when the UE generates the SIP Request to when it is encapsulated in TCP [PSH, ACK] and then sends TCP [PSH, ACK]. It can be understood that T3 in Figure 6 is the time it takes the UE to continuously transmit TCP [PSH, ACK] after receiving the user's dial-up request. This time T3 can be counted from the time the UE generates the SIP Request and ends when the counted duration equals the retransmission time value. Therefore, the value of T3 is equal to the preset retransmission time. After the time for UE to transmit TCP[PSH, ACK] reaches the preset retransmission time, the UE may execute step S46 to perform a reset operation. At this time, the transmission of TCP[PSH, ACK] is interrupted and the timing of TCP[PSH, ACK] is restored to 0.

[0125] In some examples, the retransmission time can be calculated from the first time the UE sends TCP[PSH,ACK], and then after the UE sends a message and the retransmission time is reached, TCP[RST] is sent to the 4G network device. In this embodiment, it is no longer described in conjunction with the accompanying drawings. That is, T3 in Figure 6 is the time it takes for the UE to continuously transmit TCP[PSH,ACK] after receiving the user's dial-up request. This time T3 can be counted from the first TCP[PSH,ACK] transmitted after the UE receives the user's dial-up request, and the timing ends after the timing duration is equal to the value of the retransmission time. Therefore, the value of T3 is equal to the preset retransmission time. After the time the UE transmits TCP[PSH,ACK] reaches the preset retransmission time, the UE can execute step S46 to perform a reset operation. At this time, the transmission of TCP[PSH,ACK] is interrupted, and the timing of TCP[PSH,ACK] is restored to 0.

[0126] S46. The UE sends a TCP [RST] to the 4G network device.

[0127] TCP[RST] indicates that the UE has performed a reset operation. The reset operation dismantles the TCP communication link established between the UE and the 4G network device and re-establishes a new communication link. The new communication link can be a new TCP communication link, and SIP Request, TCP[PSH,ACK], etc. are sent on the new communication link. Then, if the new TCP communication link can transmit messages normally, the UE and the 4G network device can successfully exchange messages involved in call establishment, and the probability of the UE successfully establishing a call increases. The reset operation is performed when TCP[PSH,ACK] meets certain conditions (such as the above-mentioned retransmission time or retransmission number requirements), and when the conditions are met, no TCP[ACK] is received on the communication link.

[0128] S47. The UE sends a SIP Request to the 4G network device.

[0129] S48. The UE sends a TCP [PSH, ACK] packet to the 4G network device. After reestablishing the new communication link, the UE continues to send TCP [PSH, ACK] packets on that communication link to request call establishment. Step S48 and step S42 are used to request the establishment of the same call. For details about steps S47 and S48, please refer to the descriptions of steps S2 and S3 and are not repeated here.

[0130] S49. After the UE sends TCP[PSH,ACK], the UE does not receive TCP[ACK] sent by the 4G network device. If the UE does not receive TCP[ACK] within the second preset time of sending TCP[PSH,ACK], the value of the second preset time is not limited.

[0131] S50: The UE retransmits TCP [PSH, ACK] to the 4G network device. The sequence number of the retransmitted TCP [PSH, ACK] is different from the sequence number of the TCP [PSH, ACK] sent in the above step. In step S50, TCP Retransmission is used to indicate the retransmission of TCP [PSH, ACK].

[0132] From step S47 to step S50, the UE interacts with the 4G network device via the new TCP communication link, such as the UE resending the SIP Request, re-encapsulating the SIP Request in TCP [PSH, ACK], and so on. The retransmission time on the new TCP communication link can continue to be calculated from the time the SIP Request is sent in step S47, as shown by T4 in FIG6 . It should be noted that sending the SIP Request refers to the time from when the UE generates the SIP Request to when it is encapsulated in TCP [PSH, ACK] and TCP [PSH, ACK] is sent. T4 in FIG6 is the time it takes for the UE to continuously transmit TCP [PSH, ACK] after responding to TCP [RST]. The time T4 can be started from when the UE responds to TCP [RST] and generates the SIP Request, and ends when the timed duration is equal to the value of the retransmission time. Therefore, the value of T4 is equal to the preset retransmission time. After the time for the UE to transmit TCP [PSH, ACK] reaches the preset retransmission time, the UE may execute step S51 to perform a domain switching operation, the transmission of TCP [PSH, ACK] is interrupted, the UE falls back from the PS domain to the CS domain, and the timing of TCP [PSH, ACK] is restored to 0.

[0133] In some examples, T4 in FIG6 is the time it takes for the UE to continuously transmit TCP [PSH, ACK] after responding to TCP [RST]. This time can be counted starting from the first TCP [PSH, ACK] transmitted by the UE after responding to TCP [RST] and ending when the counted duration is equal to the value of the retransmission time. Thus, the value of T4 is equal to the preset retransmission time. After the time it takes for the UE to transmit TCP [PSH, ACK] reaches the preset retransmission time, the UE can execute step S51 to perform a domain switching operation. The transmission of TCP [PSH, ACK] is interrupted, the UE falls back from the PS domain to the CS domain, and the timing of TCP [PSH, ACK] is restored to 0.

[0134] In this embodiment, the TCP [PSH, ACK] timing is reset to 0 so that the next TCP [PSH, ACK] transmission starts from 0. T4 and T3 can be the same or different. If T4 and T3 are different, the UE may retransmit TCP [PSH, ACK] a different number of times on the old and new TCP communication links.

[0135] S51. The UE exchanges a Service Request_CSFB_Redial message with the 4G network device. The Service Request_CSFB_Redial message indicates that the UE has performed a domain change operation, falling back from the PS domain to the CS domain.

[0136] S52: The UE and the 2G / 3G network device exchange a Call_Proceeding message.

[0137] S53. The UE communicates with the called party through the 2G / 3G network device.

[0138] S54: Bye messages are exchanged between the UE and the 2G / 3G network device.

[0139] S55. The UE informs the user that the call is ended.

[0140] In Figure 6, after retransmitting TCP [PSH, ACK] for a certain period of time (e.g., T3), the UE proactively sends a TCP [RST] to reestablish a new TCP communication link. If the TCP communication link failure is recovered during the reestablishment process, the newly established TCP communication link is a normal communication link. Messages can be successfully exchanged between the UE and the 4G network device on this new TCP communication link, increasing the UE's chances of successfully establishing a call. If the new TCP communication link still fails, the UE can perform CSFB, falling back from the PS domain to the CS domain and establishing a call on the CS domain. This approach improves the call establishment success rate by implementing different types of attempts. Furthermore, the time from receiving the dial request to completing the domain switch operation is shortened, thereby reducing the call establishment time. For example, if the retransmission time is less than or equal to 6 seconds, the sum of the two retransmission times is less than or equal to 12 seconds. The reset and domain switch operations also take a shorter time, reducing the call establishment time compared to a 120-second retransmission.

[0141] FIG7 shows another process of establishing a call, which may include the following steps:

[0142] S60. The UE receives a dialing request from the user.

[0143] S61. The UE sends a SIP Request to the 4G network device.

[0144] S62: The UE sends TCP [PSH, ACK] to the 4G network device. For understanding of steps S61 and S62, please refer to the description of steps S2 and S3, which will not be repeated here.

[0145] S63. After the UE sends TCP [PSH, ACK], the UE does not receive TCP [ACK] sent by the 4G network device.

[0146] S64. The UE retransmits TCP [PSH, ACK] to the 4G network device. The sequence number of the retransmitted TCP [PSH, ACK] is different from the sequence number of the TCP [PSH, ACK] sent in step S42. In step S44, TCP Retransmission is used to indicate the retransmission of TCP [PSH, ACK].

[0147] S65. The UE continues to retransmit TCP [PSH, ACK] to the 4G network device.

[0148] In this embodiment, the retransmission time may be calculated from the time the UE sends a SIP Request to the 4G network device, as shown by T5 in FIG7 . T5 may be the same as or different from T3 in FIG6 . In some examples, the retransmission time may be calculated from the time the UE first sends a TCP [PSH, ACK] message. That is, T5 in FIG7 may be calculated (timed) from the time the UE first sends a TCP [PSH, ACK] message. Then, after the UE sends a message and the retransmission time has expired, it sends a TCP [RST] message to the 4G network device. This will not be described in conjunction with the accompanying drawings in this embodiment. For the explanation of T5, please refer to the explanation of T3 above and will not be repeated here.

[0149] S66. The UE sends a TCP [RST] to the 4G network device.

[0150] In this embodiment, TCP[RST] indicates that the UE has performed a reset operation. This reset operation dismantles the TCP communication link established between the UE and the 4G network device and reestablishes a new communication link. This new communication link can be a new UDP communication link. During the reset, routing is performed simultaneously to send UDP[PSH,ACK] messages and other messages over this UDP communication link. If the TCP communication link fails but the UDP communication link is able to transmit messages normally, the UE and the 4G network device can successfully exchange call establishment messages, increasing the UE's chances of successfully establishing a call.

[0151] S67. The UE sends a UDP [PSH, ACK] to the 4G network device to continue requesting to establish the above call through UDP [PSH, ACK].

[0152] It should be noted that, those skilled in the art can understand that step S67 can be understood as the UE encapsulating the generated SIP Request into a message (such as a UDP [PSH, ACK] message), and then the UE sending the message to the 4G network device (the message may be encapsulated into other messages and ultimately sent to the 4G network device), thereby sending the SIP Request to the 4G network device and continuing to request to establish the above-mentioned call through UDP [PSH, ACK].

[0153] S68. After the UE sends the UDP[PSH,ACK], the UE does not receive the UDP[ACK] sent by the 4G network device. If the UE does not receive the UDP[ACK] within the second preset time of sending the UDP[PSH,ACK], the value of the second preset time is not limited.

[0154] S69. The UE retransmits the UDP [PSH, ACK] to the 4G network device. The sequence number of the retransmitted UDP [PSH, ACK] is different from the sequence number of the UDP [PSH, ACK] sent in the above step. In step S69, UDP Retransmission is used to indicate the retransmission of UDP [PSH, ACK].

[0155] In some examples, after establishing a UDP communication link, the retransmission time can be calculated from the time the UE sends UDP [PSH, ACK], as shown by T6 in FIG7 . It should be noted that sending a SIP Request refers to the time from when the UE generates a SIP Request to when it is encapsulated into UDP [PSH, ACK] and the UDP [PSH, ACK] is sent. T6 in FIG7 is the time it takes for the UE to continuously transmit UDP [PSH, ACK] after responding to TCP [RST]. This time can be counted from the time the UE responds to TCP [RST] and generates a SIP Request, and the count ends after the counted duration equals the value of the retransmission time. Thus, the value of T6 is equal to the preset retransmission time. After the time the UE transmits UDP [PSH, ACK] reaches the preset retransmission time, the UE can execute step S70 to perform a domain change operation, the transmission of UDP [PSH, ACK] is interrupted, the UE falls back from the PS domain to the CS domain, and the timing of UDP [PSH, ACK] is restored to 0.

[0156] In some examples, after establishing the UDP communication link, the UE can continue to send SIP Requests, and the retransmission time is calculated from the time the SIP Request is sent. It should be noted that T6 in Figure 7 is the time it takes for the UE to continuously transmit UDP[PSH,ACK] after responding to TCP[RST]. This time can be counted from the first UDP[PSH,ACK] transmitted by the UE after responding to TCP[RST], and the timing ends after the timing duration is equal to the value of the retransmission time. Therefore, the value of T6 is equal to the preset retransmission time. After the time the UE transmits UDP[PSH,ACK] reaches the preset retransmission time, the UE can execute step S70 to perform a domain switching operation. The transmission of UDP[PSH,ACK] is interrupted, the UE falls back from the PS domain to the CS domain, and the timing of UDP[PSH,ACK] is restored to 0. The purpose of restoring the timing of UDP[PSH,ACK] to 0 is to start the timing from 0 when the next UDP[PSH,ACK] is transmitted.

[0157] The retransmission time of the UDP communication link can be the same as or different from the retransmission time of the TCP communication link.

[0158] S70. The UE and the 4G network device exchange a Service Request_CSFB_Redial message, where the Service Request_CSFB_Redial message indicates that the UE has performed a domain change operation, falling back from the PS domain to the CS domain.

[0159] S71. A Call_Proceeding message is exchanged between the UE and the 2G / 3G network device.

[0160] S72. The UE communicates with the called party through the 2G / 3G network device.

[0161] S73. Bye messages are exchanged between the UE and the 2G / 3G network device.

[0162] S74. The UE informs the user that the call is ended.

[0163] In Figure 7 above, after retransmitting TCP [PSH, ACK] for a certain period of time (e.g., T5), the UE proactively sends a TCP [RST]. This reestablishes a new UDP communication link via TCP [RST]. This allows the UE to successfully exchange messages with the 4G network device over a potentially functioning UDP communication link, even if the TCP communication link remains faulty. This increases the UE's chances of successfully establishing a call. If the UDP communication link still fails, the UE can perform CSFB, falling back from the PS domain to the CS domain and establishing a call in the CS domain. This combination of different attempts improves the success rate of call establishment. Furthermore, the time from receiving the dial request to completing the domain change operation is shorter, thereby reducing call establishment time.

[0164] In the above embodiment, the UE can directly fall back from the PS domain (such as 5G and 4G both belong to the PS domain) to the CS domain, and there is no distinction between 5G and 4G. In some examples of VoNR call establishment, when the UE performs a domain change operation, the UE can first fall back from the 5G domain to the 4G domain, and then fall back from the 4G domain to the CS domain. It can be understood that in an embodiment of the present application, if the domains corresponding to the 5G wireless network and the 4G wireless network are both PS domains, when the UE establishes a call through the 4G network device, the UE can interact with the 4G network device to send a Service Request_CSFB_Redial message and fall back from the PS domain to the CS domain; when the UE establishes a call through the 5G network device, the UE can interact with the 5G network device to send a Service Request_CSFB_Redial message and fall back from the PS domain to the CS domain.

[0165] If the domain corresponding to the 5G wireless network is different from the domain corresponding to the 4G wireless network, when the UE establishes a call through the 5G network device, the UE may first fall back from the domain corresponding to the 5G wireless network to the domain corresponding to the 4G wireless network, and try to establish the call through the 4G network device; if the call still cannot be established through the 4G network device, the UE falls back from the domain corresponding to the 4G wireless network to the CS domain. The process is shown in Figure 8 and may include the following steps:

[0166] S80. The UE receives a dialing request from the user.

[0167] S81. The UE sends a SIP Request to the 5G network device.

[0168] S82. The UE sends TCP [PSH, ACK] to the 5G network device.

[0169] S83. After the UE sends TCP[PSH,ACK], the UE does not receive TCP[ACK] sent by the 5G network device.

[0170] S84. The UE retransmits TCP [PSH, ACK] to the 5G network device.

[0171] S85. The UE continues to retransmit TCP [PSH, ACK] to the network device.

[0172] In some examples, the retransmission time is calculated from the time the UE sends a SIP Request to the 5G network device, as shown by T7 in Figure 8. T7 can be the same as or different from T3 in Figure 6 above. The SIP Request is encapsulated in TCP[PSH,ACK] and sent. The first TCP[PSH,ACK] sent is after the SIP Request. Therefore, the TCP[PSH,ACK] retransmitted within the retransmission time includes the TCP[PSH,ACK] sent for the first time. In some examples, the retransmission time can be calculated from the time the UE first sends TCP[PSH,ACK]. Then, after the UE sends a message and the retransmission time has expired, TCP[RST] is sent to the 5G network device. This will not be described in conjunction with the accompanying drawings in this embodiment. For the explanation of T7, please refer to the explanation of T3 above and will not be repeated here.

[0173] S86. The UE sends a TCP [RST] to the 5G network device. The TCP [RST] is used to dismantle the TCP communication link established between the UE and the 5G network device and re-establish a new TCP communication link. In some examples, the TCP [RST] is used to dismantle the TCP communication link established between the UE and the 5G network device and re-establish a new UDP communication link. The UE can send a UDP [PSH, ACK] on the UDP communication link. This will not be described in conjunction with the accompanying figures.

[0174] S87. The UE sends a SIP Request to the 5G network device.

[0175] S88. The UE sends TCP [PSH, ACK] to the 5G network device.

[0176] S89. After the UE sends TCP[PSH,ACK], the UE does not receive TCP[ACK] sent by the 5G network device.

[0177] S90: The UE retransmits the TCP [PSH, ACK] packet to the 5G network device. The UE interacts with the 5G network device via the new TCP communication link. For example, the UE retransmits the SIP Request and re-encapsulates the SIP Request within the TCP [PSH, ACK] packet. The retransmission time on the new TCP communication link can continue to be calculated from the time the SIP Request is sent in step S87, as shown by T8 in Figure 8. For an explanation of T8, please refer to the explanation of T4 above and will not be repeated here.

[0178] T8 and T7 can be the same or different. If T8 and T7 are different, the number of times the UE retransmits TCP [PSH, ACK] on the new and old TCP communication links may be different.

[0179] S91. The UE and the 5G network device exchange a Service Request_EPSFB_Redial (Service Request for Falling Back to the 4G Domain) message. The Service Request_EPSFB_Redial message indicates that the UE has performed a domain change operation, falling back from the 5G domain to the 4G domain. The 5G domain may be the domain corresponding to the 5G wireless network, and the 4G domain may be the domain corresponding to the 4G wireless network.

[0180] S92: The exchange of the Call_Proceeding message between the UE and the 4G network device fails. It can be understood that the failure to exchange the Call_Proceeding message means that the UE fails to complete the call establishment through the 4G network device within a certain time, and the certain time may be a third preset time.

[0181] S93. The UE and the 4G network device exchange a Service Request_CSFB_Redial message, where the Service Request_CSFB_Redial message indicates that the UE has performed a domain change operation again, falling back from the 4G domain to the CS domain.

[0182] S94. The UE and the 2G / 3G network device exchange a Call_Proceeding message.

[0183] S95. The UE communicates with the called party through the 2G / 3G network device.

[0184] S96. Bye messages are exchanged between the UE and the 2G / 3G network device.

[0185] S97. The UE informs the user that the call is ended.

[0186] By using the method shown in FIG8 , the UE can reduce the duration of call establishment while improving the success rate of call establishment.

[0187] In some examples, after the message retransmission meets the preset conditions, the UE may first perform a first reset operation. The first reset operation is used to re-establish a communication link of the same type as the previous communication link, and continue to initiate the establishment of a call on the communication link to continue interacting with the network device. If the message retransmission on the communication link meets the preset conditions after the first reset operation, the UE may perform a second reset operation and complete the switching operation at the same time after the second reset operation to re-establish a communication link of a different type from the previous communication link, and continue to initiate the establishment of a call on the communication link to continue interacting with the network device; if the message retransmission on the communication link meets the preset conditions after the second reset operation, the UE performs a domain switching operation. This method can also reduce the duration of the call establishment and increase the success rate of the call establishment. That is, the UE can perform multiple reset operations. If the call is still not established after multiple reset operations, the UE performs a domain switching operation. The domain switching operation can be shown in Figure 7 or Figure 8. The preset conditions corresponding to different reset operations can be the same or different.

[0188] FIG9 shows another process of establishing a call, which may include the following steps:

[0189] S100. UE receives a dialing request from a user.

[0190] S101. UE generates and sends a SIP Request, and encapsulates the SIP Request in UDP [PSH, ACK].

[0191] S102. The UE sends UDP [PSH, ACK] to the 5G network device.

[0192] S103. After the UE sends UDP [PSH, ACK], the UE does not receive the UDP [ACK] sent by the 5G network device.

[0193] S104. The UE retransmits UDP [PSH, ACK] to the 5G network device. The sequence number of the retransmitted UDP [PSH, ACK] is different from the sequence number of the UDP [PSH, ACK] sent in step S102. In step S104, UDP Retransmission is used to indicate the retransmission of UDP [PSH, ACK].

[0194] S105. The UE continues to retransmit UDP [PSH, ACK] to the 5G network device.

[0195] In this embodiment, the time it takes for the UE to transmit UDP [PSH, ACK] may be the time it takes for the UE to continuously transmit UDP [PSH, ACK] after receiving a user's dial-up request. This time may start from the first UDP [PSH, ACK] transmitted after the UE receives the user's dial-up request and end when the timed duration equals the value of the retransmission time. Thus, the time it takes for the UE to transmit UDP [PSH, ACK] is equal to the preset retransmission time, as shown by T9 in FIG9 . After the time it takes for the UE to transmit UDP [PSH, ACK] reaches the preset retransmission time, the UE may execute step S106 to perform a reset operation. At this time, the transmission of UDP [PSH, ACK] is interrupted, and the timing of UDP [PSH, ACK] is restored to 0, so that the timing starts from 0 when the next UDP [PSH, ACK] is transmitted.

[0196] S106. The UE sends a UDP [RST] to the 5G network device.

[0197] In this embodiment, UDP[RST] indicates that the UE has performed a reset operation. The reset operation dismantles the UDP communication link established between the UE and the 5G network device and re-establishes a new UDP communication link. If the re-established UDP communication link can transmit messages normally, the UE and the 5G network device can successfully exchange messages involved in establishing a call, and the probability of the UE successfully establishing a call increases.

[0198] S107. The UE sends a UDP [PSH, ACK] to the 5G network device to continue requesting to establish the above call through UDP [PSH, ACK].

[0199] It should be noted that, those skilled in the art can understand that step S107 can be understood as the UE encapsulating the generated SIP Request into a message (such as a UDP [PSH, ACK] message), and then the UE sends the message to the 5G network device (the message may be encapsulated into other messages and eventually sent to the 5G network device), thereby sending the SIP Request to the 5G network device and continuing to request to establish the above-mentioned call through UDP [PSH, ACK].

[0200] S108. After the UE sends the UDP[PSH,ACK], the UE does not receive the UDP[ACK] sent by the 5G network device. If the UE does not receive the UDP[ACK] within the second preset time of sending the UDP[PSH,ACK], the value of the second preset time is not limited.

[0201] S109. The UE retransmits the UDP [PSH, ACK] message to the 5G network device. The sequence number of the retransmitted UDP [PSH, ACK] message is different from the sequence number of the UDP [PSH, ACK] message sent in the above step. In step S109, UDP Retransmission is used to indicate the retransmission of the UDP [PSH, ACK] message.

[0202] In some examples, after establishing a UDP communication link, the retransmission time can be calculated from the time the UE sends UDP[PSH,ACK], as shown by T10 in FIG9 . It should be noted that T10 in FIG9 is the time it takes for the UE to continuously transmit UDP[PSH,ACK] after responding to UDP[RST]. This time can be counted from the first UDP[PSH,ACK] transmitted by the UE after responding to UDP[RST], and ends when the timing is equal to the value of the retransmission time. Thus, T10 can be used as the time the UE currently transmits UDP[PSH,ACK]. The value of T10 is equal to the preset retransmission time. After the time the UE transmits UDP[PSH,ACK] reaches the preset retransmission time, the UE can execute step S110 to perform a domain switching operation, the transmission of UDP[PSH,ACK] is interrupted, the UE falls back from the PS domain to the CS domain, and the timing of UDP[PSH,ACK] is restored to 0. The purpose of restoring the timing of UDP[PSH,ACK] to 0 is to start the timing from 0 when UDP[PSH,ACK] is transmitted next time.

[0203] In some examples, after establishing a UDP communication link, the UE may continue to generate SIP Requests, and the retransmission time may be calculated starting from the time the SIP Request is generated. That is, T10 in FIG9 may start timing after the UE responds to UDP[RST] and generates a SIP Request, and end timing after the timing duration is equal to the value of the retransmission time, so that the value of T10 is equal to the preset retransmission time. After the time for the UE to transmit UDP[PSH, ACK] reaches the preset retransmission time, the UE may execute step S110 to perform a domain switching operation, the transmission of UDP[PSH, ACK] is interrupted, the UE falls back from the PS domain to the CS domain, and the timing of UDP[PSH, ACK] is restored to 0.

[0204] S110. The UE and the 5G network device exchange a Service Request_CSFB_Redial message, where the Service Request_CSFB_Redial message indicates that the UE has performed a domain change operation, falling back from the PS domain to the CS domain.

[0205] S111: The UE and the 2G / 3G network device exchange Call_Proceeding messages.

[0206] S112. The UE communicates with the called party through the 2G / 3G network device.

[0207] S113: Bye messages are exchanged between the UE and the 2G / 3G network device.

[0208] S114. The UE notifies the user that the call is ended.

[0209] In Figure 9 above, after retransmitting UDP [PSH, ACK] for a certain period of time (such as T9), the UE actively sends UDP [RST] and re-establishes a new UDP communication link through UDP [RST]. In this way, the UE can successfully exchange messages with the 5G network equipment through a possibly normal UDP communication link, and the probability of the UE successfully establishing a call increases. If the UDP communication link still fails, the UE can perform CSFB, falling back from the PS domain to the CS domain, and establish a call in the CS domain. Through different types of attempts, the success rate of call establishment is improved. In addition, the time from the UE receiving the dial request to completing the domain change operation is short, which can reduce the duration of the call establishment.

[0210] In addition, in some examples, the UE can control whether to perform a reset operation or a domain change operation by controlling the number of transmissions of TCP[PSH,ACK] or UDP[PSH,ACK]. For example, in the signaling diagram of the method for establishing a call shown in Figure 5, the UE can start counting from the first transmission of TCP[PSH,ACK]. The count for the first transmission of TCP[PSH,ACK] is 1. If TCP[ACK] is not received, the UE retransmits TCP[PSH,ACK] (i.e., the second transmission of TCP[PSH,ACK]), and the count is 2 at this time. If TCP[ACK] is still not received, the UE continues to retransmit TCP[PSH,ACK] (i.e., the third transmission of TCP[PSH,ACK]), and the count is 3 at this time. And so on. When the count reaches the preset number of retransmissions, the UE performs a domain change operation. After the domain change operation is triggered, the UE's count is reset, that is, the UE's count is restored to 0, so that the count starts from 0 when TCP[PSH,ACK] is transmitted next time.

[0211] For example, in the signaling diagram of the method for establishing a call shown in FIG6 , after the UE receives a dial request, it starts transmitting TCP[PSH, ACK]. The UE can start counting from the first transmission of TCP[PSH, ACK]. The count for the first transmission of TCP[PSH, ACK] is 1. If no TCP[ACK] is received, the UE retransmits TCP[PSH, ACK] (i.e., the second transmission of TCP[PSH, ACK]), and the count is 2. If no TCP[ACK] is received, the UE continues to retransmit TCP[PSH, ACK] (i.e., the third transmission of TCP[PSH, ACK]), and the count is 3. And so on. When the count reaches the preset number of retransmissions, the UE performs a reset operation. After the reset operation is triggered, the UE's count is reset, i.e., the UE's count is restored to 0, so that the count starts from 0 when the next TCP[PSH, ACK] is transmitted. After the UE completes the reset operation, the UE starts transmitting TCP[PSH,ACK] again. Then, the UE starts counting from the first time it transmits TCP[PSH,ACK] after the reset operation, and the count is 1. If no TCP[ACK] is received, the UE retransmits TCP[PSH,ACK] (i.e., the second time it transmits TCP[PSH,ACK] after the reset operation), and the count is 2. If it still does not receive TCP[ACK], the UE continues to retransmit TCP[PSH,ACK] (i.e., the third time it transmits TCP[PSH,ACK] after the reset operation), and the count is 3. And so on. When the count reaches the preset number of retransmissions, the UE performs the reset operation. After the reset operation is triggered, the UE's count is reset, that is, the UE's count is restored to 0, so that the count starts from 0 when the next TCP[PSH,ACK] is transmitted.

[0212] The structure of a terminal implementing the above-mentioned call establishment method is shown in FIG10 , and may include: a processor, an external memory interface, an internal memory, a Universal Serial Bus (USB) interface, a charging management module, a power management module, a battery, antenna 1, antenna 2, a mobile communication module, a wireless communication module, a sensor module, buttons, a motor, an indicator, a camera, a display, and a Subscriber Identification Module (SIM) card interface. The audio module may include a speaker, a receiver, a microphone, an earphone interface, etc., and the sensor module may include a pressure sensor, a gyroscope sensor, an air pressure sensor, a magnetic sensor, an acceleration sensor, a distance sensor, a proximity light sensor, a fingerprint sensor, a temperature sensor, a touch sensor, an ambient light sensor, a bone conduction sensor, etc.

[0213] It is understood that the structures illustrated in the embodiments of the present application do not constitute specific limitations on the terminal. In other embodiments, the terminal may include more or fewer components than shown, or may combine or separate certain components, or arrange the components differently. The illustrated components may be implemented in hardware, software, or a combination of software and hardware.

[0214] The processor may include one or more processing units, for example, the processor may include an application processor (AP), a modem processor, a graphics processor (GPU), an image signal processor (ISP), a controller, a video codec, a digital signal processor (DSP), a baseband processor, and / or a neural network processor (NPU). Different processing units may be independent devices or integrated into one or more processors. The processor is the nerve center and command center of the terminal. The controller can generate operation control signals based on instruction opcodes and timing signals to complete the control of instruction fetching and execution.

[0215] The external memory interface can be used to connect an external memory card, such as a Micro SD card, to expand the storage capacity of the terminal. The external memory card communicates with the processor via the external memory interface to implement data storage. The internal memory can be used to store computer executable program code, which includes instructions. The processor executes various functional applications and data processing of the terminal by running the instructions stored in the internal memory. For example, in an embodiment of the present application, the processor causes the terminal to execute the method for establishing a call provided in an embodiment of the present application by running the instructions stored in the internal memory.

[0216] The wireless communication function of the terminal can be implemented by antenna 1, antenna 2, mobile communication module, wireless communication module, modem processor and baseband processor. In some embodiments, antenna 1 of the terminal is coupled with the mobile communication module, and antenna 2 is coupled with the wireless communication module, so that the terminal can communicate with the network and other devices through wireless communication technology. The wireless communication technology can include global system for mobile communications (GSM), general packet radio service (GPRS), code division multiple access (CDMA), wideband code division multiple access (WCDMA), time-division code division multiple access (TD-SCDMA), long term evolution (LTE), BT, GNSS, WLAN, NFC, FM, and / or IR technology. The GNSS may include a global positioning system (GPS), a global navigation satellite system (GLONASS), a Beidou navigation satellite system (BDS), a quasi-zenith satellite system (QZSS) and / or a satellite based augmentation system (SBAS).

[0217] The audio module is used to convert digital audio information into analog audio signal output, and is also used to convert analog audio input into digital audio signals. The audio module can also be used to encode and decode audio signals. In some embodiments, the audio module can be provided in the processor, or some functional modules of the audio module can be provided in the processor.

[0218] A speaker, also known as a horn, converts electrical audio signals into sound signals. The terminal can listen to music or make hands-free calls through the speaker.

[0219] The receiver, also known as the handset, converts electrical audio signals into sound signals. When a terminal receives a call or voice message, the user can hold the receiver close to their ear to hear the voice.

[0220] A microphone, also known as a "microphone" or "microphone," is used to convert sound signals into electrical signals. When making a call or sending a voice message, the user can put their mouth close to the microphone and speak, inputting the sound signal into the microphone. The terminal can be equipped with at least one microphone. In other embodiments, the terminal can be equipped with two microphones, which can not only collect sound signals but also implement noise reduction functions. In other embodiments, the terminal can also be equipped with three, four, or more microphones to collect sound signals, reduce noise, identify the sound source, implement directional recording functions, etc.

[0221] The headphone jack is used to connect wired headphones. It can be a USB port, a 3.5mm Open Mobile Terminal Platform (OMTP) standard port, or a cellular telecommunications industry association of the USA (CTIA) standard port.

[0222] The present application provides a terminal, including: one or more processors and a memory; the memory is used to store computer program code, the computer program code includes computer instructions, and when the one or more processors execute the computer instructions, the terminal executes the above-mentioned method for establishing a call.

[0223] The present application provides a computer-readable storage medium for storing a computer program. When the computer program is executed, it is specifically used to implement the above-mentioned method for establishing a call.

[0224] The present application provides a chip. When the chip is deployed inside a terminal, the chip is used to control the terminal to implement the above-mentioned method for establishing a call.

Claims

1. A method for establishing a call, characterized in that: Applied to a terminal, a first wireless network belongs to a first domain, a first communication link is established between the terminal and a first network device in the first wireless network, and the method includes: sending a first message to the first network device through the first communication link, where the first message is used to request to establish a first call; If, within a first preset time after sending the first message, the terminal does not receive a first confirmation message sent by the first network device on the first communication link, the terminal retransmits the first message to the first network device through the first communication link, wherein the first confirmation message is a confirmation message of the first message; When the retransmission of the first message satisfies a first preset condition, if the terminal still does not receive the first confirmation message on the first communication link, the terminal performs a reset operation, the reset operation including dismantling the first communication link and establishing a second communication link between the terminal and the first network device; sending a second message to the first network device through the second communication link, where the second message is used to request to establish the first call; If, within a second preset time after sending the second message, the terminal does not receive a second confirmation message sent by the first network device on the second communication link, the terminal retransmits the second message to the first network device through the second communication link, wherein the second confirmation message is a confirmation message of the second message; When the retransmission of the second message meets the second preset condition, if the terminal still does not receive the second confirmation message on the second communication link, the terminal performs a domain change operation to switch from the current first domain to the second domain, and sends a third message to the second network device in the second wireless network in the second domain, wherein the third message is used to request to establish the first call in the second domain, the standard of the first wireless network is higher than the standard of the second wireless network, and the second wireless network belongs to the second domain.

2. The method according to claim 1, characterized in that The first preset condition includes a preset first retransmission time, where the preset first retransmission time is used to indicate a maximum duration for transmitting the first message on the first communication link; The preset first retransmission time is less than a first duration, where the first duration is the duration specified in a standard protocol from the time the terminal starts sending the first message to the first network device to the time the terminal receives a reset message sent by the first network device, where the reset message is used to trigger the terminal to perform a reset operation; and / or, The second preset condition includes a preset second retransmission time, where the preset second retransmission time is used to indicate a maximum duration for transmitting the second message on the second communication link; The preset second retransmission time is less than the second duration, and the second duration is the duration specified in the standard protocol from the time the terminal starts sending the second message to the first network device to the time the terminal receives the reset message sent by the first network device. The reset message is used to trigger the terminal to perform a reset operation.

3. The method according to claim 1 or 2, characterized in that The method further comprises: The first wireless network is a 5G wireless network; The second wireless network is a 4G wireless network; The first domain is a domain corresponding to the 5G wireless network; and The second domain is a domain corresponding to the 4G wireless network.

4. The method according to claim 3, characterized in that The method also includes: if the terminal fails to establish the first call in the second domain within a third preset time, the terminal performs a domain change operation again to switch from the current second domain to a third domain, and sends a fourth message to a third network device in a third wireless network in the third domain, wherein the fourth message is used to request to establish the first call in the third domain, the standard of the second wireless network is higher than the standard of the third wireless network, and the third wireless network belongs to the third domain.

5. The method according to claim 4, characterized in that The method further comprises at least one of the following: The third wireless network is a 3G or 2G wireless network; The third domain is a circuit switched CS domain; The first message and the second message are any Transmission Control Protocol TCP message or any User Datagram Protocol UDP message during a call establishment process in a 5G wireless network; The third message is a request message during the process of establishing a call in a 4G wireless network; or The fourth message is a request message during the circuit switched CS call establishment process.

6. The method according to claim 1, characterized in that The type of the second communication link is the same as the type of the first communication link, and the type of the second message is the same as the type of the first message; or, The type of the second communication link is different from the type of the first communication link, and the type of the second message is different from the type of the first message.

7. The method according to claim 6, characterized in that The type of the second communication link is different from the type of the first communication link, and the type of the second message is different from the type of the first message, including: The type of one of the first communication link and the second communication link is a Transmission Control Protocol (TCP) communication link, and the type of the other of the first communication link and the second communication link is a User Datagram Protocol (UDP) communication link; A type of one of the first message and the second message is a TCP message, and a type of the other of the first message and the second message is a UDP message; The first communication link and the first message correspond to the same protocol, and the second communication link and the second message correspond to the same protocol.

8. The method according to claim 6, characterized in that The type of the second communication link is the same as that of the first communication link, and the type of the second message is the same as that of the first message, including: The types of the first communication link and the second communication link are both TCP communication links or both UDP communication links; The first message and the second message are both TCP messages or both UDP messages; The first communication link and the first message correspond to the same protocol, and the second communication link and the second message correspond to the same protocol.

9. The method according to any one of claims 1 to 8, characterized in that The first preset condition includes a preset first retransmission time, where the preset first retransmission time is used to indicate a maximum duration for transmitting the first message on the first communication link; and / or, The first preset condition includes a preset first retransmission number, and the preset first retransmission number is used to indicate the maximum number of times the first message is transmitted on the first communication link.

10. The method according to claim 9, characterized in that The second preset condition includes a preset second retransmission time, where the preset second retransmission time is used to indicate a maximum duration for transmitting the second message on the second communication link; and / or, The second preset condition includes a preset second retransmission number, and the preset second retransmission number is used to indicate the maximum number of times the second message is transmitted on the second communication link.

11. The method according to claim 10, characterized in that The preset first retransmission time is 6 seconds, and / or the preset second retransmission time is 6 seconds.

12. The method according to any one of claims 1, 2, 6 to 11, characterized in that The method further comprises at least one of the following: The first wireless network is a 4G wireless network or a 5G wireless network; The second wireless network is a 3G or 2G wireless network; The first domain is a packet switched PS domain; The second domain is a circuit switched CS domain; The first message is any TCP message or any UDP message in the IP Multimedia System IMS call establishment process; The second message is any TCP message or any UDP message in the IMS call establishment process; or, The third message is a request message during the CS call establishment process.

13. A terminal, characterized in that: include: one or more processors and memory; The memory is used to store computer program code, where the computer program code includes computer instructions. When the one or more processors execute the computer instructions, the terminal executes the method for establishing a call according to any one of claims 1 to 12.

14. A chip, characterized in that: When the chip is deployed inside a terminal, the chip is used to control the terminal to implement the method according to any one of claims 1 to 12.

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