Communication method, terminal device, access network device, medium and chip

Abstract

A communication method, a terminal device, an access network device, a medium and a chip are provided. The method includes that the terminal device acquires a cell change cause indication. The cell change cause indication indicates that a first cell change of the terminal device from a source cell to a first target cell or a second cell change of the terminal device from the first target cell to a second target cell is associated with a communication service of the terminal device. The first target cell adopts a first radio access technology, and the source cell and the second target cell adopt a second radio access technology different from the first radio access technology. The method further includes that the terminal device sends the cell change cause indication to a second target access network device providing the second target cell. Therefore, the second target access network device can distinguish the communication service process from an inter-system ping-pong event, and avoid that an invalid and redundant optimization of an inter-system handover parameter is triggered by a normal communication service process of the terminal device.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of communications, and more particularly, to a communication method, a terminal device, an access network device, a computer readable storage medium, and a chip. BACKGROUND

[0002] Handover between cells employing different radio access technologies (RATs) can be referred to as inter-system handover. Too frequent inter-system handover can result in waste of communication resources and poor communication robustness. Therefore, by identifying that the inter-system handover involves an inter-system ping-pong event, the inter-system handover parameters can be optimized to avoid too frequent inter-system handover.

[0003] However, if the inter-system ping-pong event is identified inappropriately, the inter-system handover parameters can also be adjusted excessively, resulting in waste of system resources and reduced communication efficiency. SUMMARY

[0004] The present application provides a solution for communication.

[0005] In a first aspect of the present application, a communication method implemented at a terminal device is provided. The method comprises: obtaining, by the terminal device, a cell change cause indication, the cell change cause indication indicating that a first cell change of the terminal device from a source cell to a first target cell or a second cell change of the terminal device from the first target cell to a second target cell is associated with a communication service of the terminal device, the first target cell employing a first radio access technology (RAT), and the source cell and the second target cell employing a second RAT different from the first RAT; and sending, by the terminal device, the cell change cause indication to a second target access network device to which the second target cell belongs. In this way, the second target access network device can distinguish the communication service process from the inter-system ping-pong event, and avoid triggering optimization of invalid and redundant inter-system handover parameters for the normal communication service process of the terminal device.

[0006] In a possible implementation, the cell change cause indication comprises: a reason for the terminal device to change out of the source cell or to change out of the first target cell, and / or a reason for the terminal device to change to the first target cell or to change to the second target cell.

[0007] In a possible implementation, the cell change cause indication indicates at least one of the following: the first cell change is associated with a voice fallback procedure of the terminal device from the source cell to the first target cell; or the second cell change is associated with a fast return procedure of the terminal device from the first target cell to the second target cell. In this way, the voice service procedure of the terminal device is prevented from triggering an invalid and redundant inter-system handover parameter optimization.

[0008] In a possible implementation, the terminal device further acquires at least one of the following: an indication of a type of the voice fallback procedure and an indication of a cell change execution manner. The indication of the type of the voice fallback procedure indicates that the voice fallback procedure is an evolved packet system voice fallback procedure or an inter-radio access technology voice fallback procedure. The cell change execution manner includes handover or redirection.

[0009] In a possible implementation, the voice fallback procedure includes a normal call voice fallback procedure or an emergency call voice fallback procedure, and the fast return procedure includes a normal call voice fast return procedure or an emergency call voice fast return procedure.

[0010] In a possible implementation, the terminal device acquires the cell change cause indication includes that the terminal device acquires the cell change cause indication from a source access network device to which the source cell belongs.

[0011] In a possible implementation, the terminal device acquires the cell change cause indication from the source access network device includes that the terminal device receives, from the source access network device, a first cell change command associated with the first cell change, and the first cell change command includes the cell change cause indication. Sending the cell change cause indication to the terminal device through the first cell change command can avoid additional signaling overhead.

[0012] In a possible implementation, the terminal device acquires the cell change cause indication includes that the terminal device acquires the cell change cause indication from a first target access network device to which the first target cell belongs.

[0013] In a possible implementation, the terminal device acquires the cell change cause indication from the first target access network device includes that the terminal device receives, from the first target access network device, a second cell change command associated with the second cell change, and the second cell change command includes the cell change cause indication. Sending the cell change cause indication to the terminal device through the second cell change command can avoid additional signaling overhead.

[0014] In a possible implementation, the terminal device sending the cell change cause indication to the second target access network device includes: the terminal device sending, to the second target access network device, a radio resource control reconfiguration complete message including the cell change cause indication, in response to receiving, from a first target access network device to which a first target cell belongs, a second cell handover command associated with a second cell change.

[0015] In a possible implementation, the terminal device sending the cell change cause indication to the second target access network device includes: the terminal device receiving, from the second target access network device, a request for historical information of the terminal device; and the terminal device sending, to the second target access network device, the historical information including the cell change cause indication. Sending the cell change cause indication together with the historical information to the second target access network device can avoid additional signaling overhead.

[0016] In a possible implementation, the first RAT can be one of a second generation (2G) RAT, a third generation (3G) RAT, and a fourth generation (4G) RAT, and the second RAT can be a fifth generation (5G) RAT. rd Generation,3G)RAT and fourth generation (4th Generation,4G)RAT, and the second RAT can be a fifth generation (5G) RAT.

[0017] In a second aspect of the present application, a communication method implemented at a first target access network device is provided. The method includes: the first target access network device obtaining a cell change cause indication, the cell change cause indication indicating that a first cell change of a terminal device from a source cell to a first target cell of the first target access network device or a second cell change from the first target cell to a second target cell is associated with a communication service of the terminal device, the first target cell using a first RAT, and the source cell and the second target cell using a second RAT different from the first RAT; and the first target access network device providing the cell change cause indication to a second target access network device to which the second target cell belongs.

[0018] In a possible implementation, the first target access network device further obtains at least one of: an indication of a type of a voice fallback procedure and an indication of a cell change execution manner. The indication of the type of the voice fallback procedure indicates that the voice fallback procedure is an evolved packet system voice fallback procedure or an inter-radio access technology voice fallback procedure. The cell change execution manner includes handover or redirection.

[0019] In a possible implementation, the first target access network device obtaining the cell change cause indication includes: the first target access network device obtaining the cell change cause indication from a source access network device to which the source cell belongs.

[0020] In a possible implementation, the first target access network device obtaining the cell change cause indication from the source access network device includes: the first target access network device obtaining historical information of the terminal device from the source access network device, and the historical information including the cell change cause indication. Sending the cell change cause indication together with the historical information to the first target access network device can avoid additional signaling overhead.

[0021] In a possible implementation, the first target access network device providing the cell change cause indication to the second target access network device includes: the first target access network device providing second historical information of the terminal device to the second target access network device, the second historical information including the cell change cause indication, the second historical information including the first historical information, and / or third historical information of the terminal device recorded by the first target access network device. Sending the cell change cause indication together with the historical information to the second target access network device can avoid additional signaling overhead.

[0022] In a possible implementation, the first target access network device providing the cell change cause indication to the second target access network device includes: the first target access network device providing a handover request for the second cell change to the second target access network device, and the handover request including the cell change cause indication. Sending the cell change cause indication together with the handover request to the second target access network device can avoid additional signaling overhead.

[0023] In a third aspect of the present application, a communication method implemented at a second target access network device is provided. The method includes: the second target access network device obtaining a cell change cause indication, the cell change cause indication indicating that a first cell change of a terminal device from a source cell to a first target cell or a second cell change of the terminal device from the first target cell to a second target cell of the second target access network device is associated with a communication service of the terminal device, the first target cell adopting a first RAT, and the source cell and the second target cell adopting a second RAT different from the first RAT; and the second target access network device sending the cell change cause indication to a source access network device to which the source cell belongs. In this way, the source access network device can distinguish the communication service process from the inter-system ping-pong event, and avoid triggering optimization of invalid and redundant inter-system handover parameters for the normal communication service process of the terminal device.

[0024] In a possible implementation, the second target access network device further obtains at least one of the following: an indication of a type of a voice fallback process and an indication of a cell change execution manner. The indication of the type of the voice fallback process indicates that the voice fallback process is an evolved packet system voice fallback process or an inter-radio access technology voice fallback process. The cell change execution manner includes handover or redirection.

[0025] In a possible implementation, the second target access network device obtaining the cell change cause indication from the terminal device includes: receiving a radio resource control reconfiguration complete message from the terminal device, the radio resource control reconfiguration complete message including the cell change cause indication.

[0026] In a possible implementation, the second target access network device obtaining the cell change cause indication includes: obtaining the cell change cause indication from the terminal device.

[0027] In a possible implementation, the second target access network device obtaining the cell change cause indication from the terminal device includes: sending a request for historical information of the terminal device to the terminal device; and receiving the historical information from the terminal device, the historical information including the cell change cause indication. Sending the cell change cause indication together with the historical information to the second target access network device can avoid additional signaling overhead.

[0028] In a possible implementation, the obtaining the cell change cause indication includes: obtaining the cell change cause indication from a source access network device to which a source cell belongs.

[0029] In a possible implementation, the obtaining the cell change cause indication from the source access network device includes: obtaining historical information of the terminal device from the source access network device, the historical information including the cell change cause indication. Sending the cell change cause indication together with the historical information to the second target access network device can avoid additional signaling overhead.

[0030] In a possible implementation, the obtaining the cell change cause indication includes: obtaining the cell change cause indication from a first target access network device to which a first target cell belongs.

[0031] In a possible implementation, the obtaining the cell change cause indication from the first target access network device includes: obtaining second historical information of the terminal device from the first target access network device, the second historical information including the cell change cause indication, the second historical information including first historical information of the terminal device obtained by the first target access network device from a source access network device to which a source cell belongs, and / or third historical information of the terminal device recorded by the first target access network device. Sending the cell change cause indication together with the historical information to the second target access network device can avoid additional signaling overhead.

[0032] In a possible implementation, the obtaining the cell change cause indication from the first target access network device includes: receiving a handover request for a second cell change from the first target access network device, the handover request including the cell change cause indication.

[0033] In a fourth aspect of the present disclosure, a communication method implemented at a source access network device is provided. The method comprises: obtaining, by the source access network device, a cell change cause indication indicating that a first cell change or a second cell change is associated with a communication service of a terminal device. The first cell change comprises a change of the terminal device from a source cell provided by the source access network device to a first target cell, and the second cell change comprises a change of the terminal device from the first target cell to a second target cell. The first target cell adopts a first radio access technology, and the source cell and the second target cell adopt a second radio access technology. The first radio access technology is different from the second radio access technology. Further, the source access network device determines, based on the cell change cause indication, that the first cell change and the second cell change are not associated with an inter-system ping-pong event. Thus, the source access network device can distinguish the communication service procedure from the inter-system ping-pong event, and avoid triggering an invalid and redundant optimization of inter-system handover parameters for the normal communication service procedure of the terminal device.

[0034] In a possible implementation, the source access network device obtaining the cell change cause indication comprises: obtaining the cell change cause indication from a second target access network device to which the second target cell belongs.

[0035] In a possible implementation, the cell change cause indication indicates that at least one of the following: the first cell change is associated with a voice fallback procedure of the terminal device from the source cell to the first target cell; and the second cell change is associated with a fast return procedure of the terminal device from the first target cell to the second target cell.

[0036] In a possible implementation, the method further comprises: obtaining, by the source access network device, at least one of the following: an indication of a type of the voice fallback procedure, and an indication of a cell change execution manner. The indication of the type of the voice fallback procedure indicates that the voice fallback procedure is an evolved packet system voice fallback procedure or an inter-radio access technology voice fallback procedure. The cell change execution manner comprises handover or redirection.

[0037] In a possible implementation of the first aspect, the second aspect, the third aspect or the fourth aspect, the cell change cause indication comprises: a reason for the terminal device to change out of the source cell or to change out of the first target cell, and / or a reason for the terminal device to change to the first target cell or to change to the second target cell.

[0038] In a possible implementation of the first aspect, the second aspect, the third aspect or the fourth aspect, the cell change cause indication indicates that at least one of the following: the first cell change is associated with a voice fallback procedure of the terminal device from the source cell to the first target cell; or the second cell change is associated with a fast return procedure of the terminal device from the first target cell to the second target cell. Thus, an invalid and redundant optimization of inter-system handover parameters triggered by a voice service procedure of the terminal device is avoided.

[0039] In a possible implementation form of the first aspect, the second aspect, the third aspect or the fourth aspect, the voice fallback procedure comprises a normal call voice fallback procedure or an emergency call voice fallback procedure, and the fast return procedure comprises a normal call voice fast return procedure or an emergency call voice fast return procedure.

[0040] In a possible implementation form of the first aspect, the second aspect, the third aspect or the fourth aspect, the first RAT is one of a 2G RAT, a 3G RAT and a 4G RAT, and the second RAT is a 5G RAT.

[0041] In a fifth aspect, a communication apparatus is provided, which comprises units or modules or means for performing the steps described in the first aspect. The communication apparatus can be a terminal or a device for a terminal.

[0042] For example, the communication apparatus comprises an obtaining unit and a sending unit. The obtaining unit is configured to obtain a cell change cause indication, the cell change cause indication indicating that a first cell change of a terminal device from a source cell to a first target cell or a second cell change of the terminal device from the first target cell to a second target cell is associated with a communication service of the terminal device, the first target cell adopting a first RAT, and the source cell and the second target cell adopting a second RAT different from the first RAT. The sending unit is configured to send the cell change cause indication to a second target access network device to which the second target cell belongs.

[0043] In a sixth aspect, an access network device is provided, which comprises units or modules or means for performing the steps described in the second aspect.

[0044] For example, the access network device comprises an obtaining unit and a providing unit. The obtaining unit is configured to obtain a cell change cause indication, the cell change cause indication indicating that a first cell change of a terminal device from a source cell to a first target cell managed by the access network device or a second cell change of the terminal device from the first target cell to a second target cell is associated with a communication service of the terminal device, the first target cell adopting a first RAT, and the source cell and the second target cell adopting a second RAT different from the first RAT. The providing unit is configured to provide the cell change cause indication to a second target access network device to which the second target cell belongs.

[0045] In a seventh aspect, an access network device is provided, which comprises units or modules or means for performing the steps described in the third aspect.

[0046] The access network device comprises an obtaining unit and a determining unit. The obtaining unit is configured to obtain a cell change cause indication, the cell change cause indication indicating that a first cell change of the terminal device from a source cell to a first target cell or a second cell change of the terminal device from the first target cell to a second target cell managed by the access network device is associated with a communication service of the terminal device, the first target cell adopting a first RAT, and the source cell and the second target cell adopting a second RAT different from the first RAT. The determining unit is configured to determine, based on the cell change cause indication, that the first cell change and the second cell change are not associated with an inter-system ping-pong event.

[0047] In an eighth aspect of the present application, an access network device is provided, comprising units or modules or means for performing the steps described in the fourth aspect above.

[0048] The access network device comprises an obtaining unit and a determining unit. The obtaining unit is configured to obtain a cell change cause indication, the cell change cause indication indicating that a first cell change of the terminal device from a source cell to a first target cell or a second cell change of the terminal device from the first target cell to a second target cell managed by the access network device is associated with a communication service of the terminal device, the first target cell adopting a first RAT, and the source cell and the second target cell adopting a second RAT different from the first RAT. The determining unit is configured to determine, based on the cell change cause indication, that the first cell change and the second cell change are not associated with an inter-system ping-pong event.

[0049] In a ninth aspect of the present application, a communication apparatus is provided. The communication apparatus comprises at least one processor and at least one memory coupled to the at least one processor and storing instructions for execution by the at least one processor. The instructions, when executed by the at least one processor, cause the communication apparatus to implement the method according to any one of the first aspect, the second aspect, the third aspect and the fourth aspect.

[0050] In a tenth aspect of the present application, a computer-readable storage medium is provided. The computer-readable storage medium has stored thereon a computer program, which, when executed by a processor, implements the method according to any one of the first aspect, the second aspect, the third aspect and the fourth aspect.

[0051] In an eleventh aspect of the present application, a computer program product is provided. The computer program product is tangibly stored on a computer-readable medium and includes computer-executable instructions that, when executed, cause a device to implement the method according to any one of the first aspect, the second aspect, the third aspect and the fourth aspect.

[0052] In a twelfth aspect of the present application, a chip is provided. The chip is configured to perform the method according to any one of the first aspect, the second aspect, the third aspect and the fourth aspect.

[0053] In a thirteenth aspect of the present application, a communication system is provided. The communication system includes the communication device according to the fifth aspect, the access network device according to the sixth aspect, the access network device according to the seventh aspect and the access network device according to the eighth aspect. BRIEF DESCRIPTION OF DRAWINGS

[0054] The features, advantages, and other aspects of the present embodiments will become more apparent from the following detailed description in conjunction with the accompanying drawings. Several implementations of the present application are illustrated in the drawings, in which:

[0055] Figure 1 A schematic block diagram of a communication network in which possible implementations of the present application can be implemented is shown;

[0056] Figure 2A and 2B A schematic block diagram of a communication network in which possible implementations of the present application can be implemented is shown;

[0057] Figure 3 A signaling interaction diagram of an example communication procedure according to one possible implementation of the present application is shown;

[0058] Figure 4 and Figure 5 A signaling interaction diagram of an example communication procedure according to another possible implementation of the present application is shown;

[0059] Figure 6 A signaling interaction diagram of an example communication procedure according to yet another possible implementation of the present application is shown;

[0060] Figure 7 and Figure 8 A signaling interaction diagram of an example communication procedure according to still another possible implementation of the present application is shown;

[0061] Figure 9 A flowchart of a communication method according to one possible implementation of the present application is shown;

[0062] Figure 10 A flowchart of a communication method according to another possible implementation of the present application is shown;

[0063] Figure 11 A flowchart of a communication method according to yet another possible implementation of the present application is shown;

[0064] Figure 12 a schematic block diagram of a terminal device according to a possible implementation manner of the present application is shown;

[0065] Figure 13 a schematic block diagram of a first access network device according to another possible implementation manner of the present application is shown;

[0066] Figure 14 a schematic block diagram of a second access network device according to still another possible implementation manner of the present application is shown; and Figure 15 is a simplified block diagram of an example device suitable for implementing a possible implementation manner of the present application.

[0067] In the various drawings, same or similar reference numerals denote same or similar elements. DETAILED DESCRIPTION

[0068] Possible implementation manners of the present application will be described in more detail below with reference to the accompanying drawings.

[0069] In the description of possible implementation manners of the present application, the term "comprising" and its conjugations should be understood to encompass the elements presented in the description, but not exclude other elements. The term "based on" should be understood as "based at least on". The term "a possible implementation manner" or "the possible implementation manner" should be understood as "at least one possible implementation manner". The terms "first", "second" and the like can refer to different or similar objects. Other explicit or implicit definitions can also be included below. Expressions such as "at least one of A, B and C" or "at least one of A, B or C" should be understood as any of the following: at least one A; at least one B; at least one C; at least one A and at least one B; at least one A and at least one C; at least one B and at least one C; at least one A, at least one B and at least one C, which is exemplified by A, B and C with three elements, and the meaning thereof can be obtained according to the foregoing rules when there are more elements in the expression.

[0070] Figure 1 a schematic block diagram of a communication network 100 in which possible implementation manners of the present application can be implemented is shown. As shown in the figure, the communication network 100 includes access network devices 110, 120 and 130 and a terminal device 140.

[0071] The access network devices 110, 120, and 130 are Radio Access Network (RAN) devices that provide access for the terminal device 140 to a wireless network. Examples of the RAN device can include, but are not limited to, a Next generation NodeB (gNB), a Transmission Reception Point (TRP), an Evolved Node B (eNB), a Radio Network Controller (RNC), a Node B (NB), a Base Station Controller (BSC), a Base Transceiver Station (BTS), a Home Base Station (for example, a Home eNB, or a Home NB), a Base Band Unit (BBU), or a Wireless Fidelity (WiFi) Access Point (AP), an Integrated Access and Backhaul (IAB) node, and the like. In a possible implementation, at least one of the access network devices 110, 120, and 130 can include a Centralized Unit (CU), or a Distributed Unit (DU), or both the CU and the DU.

[0072] The terminal device 140 is a device with wireless transceiving function. The terminal device 140 can be deployed on land, including indoors or outdoors, handheld or vehicle-mounted; can also be deployed on water surface (such as ships, etc.); and can also be deployed in the air (such as airplanes, balloons and satellites, etc.). The terminal device 140 can be a mobile phone, a tablet computer, a computer with wireless transceiving function, a virtual reality (VR) terminal device, an augmented reality (AR) terminal device, a wireless terminal device in industrial control, a wireless terminal device in self-driving, a wireless terminal device in remote medical treatment, a wireless terminal device in smart grid, a wireless terminal in transportation safety, a wireless terminal device in smart city, a wireless terminal device in smart home, a user equipment (UE) or the like.

[0073] It can be understood that Figure 1 The number of access network devices and terminal devices shown in FIG. 1 is merely an example and is not intended to suggest any limitation. According to actual needs, the communication network 100 can include any appropriate number of access network devices and terminal devices.

[0074] The access network device 110 adopts a first RAT, and the access network devices 120 and 130 adopt a second RAT different from the first RAT, that is, the communication standard of the access network device 110 is different from the communication standard of the access network devices 120 and 130. In a possible implementation, the first RAT can be one of 2G, 3G and 4G RAT, and the second RAT can be 5G RAT. Although in the following, the possible implementation of the present application will be described by taking the first RAT as 4G RAT and the second RAT as 5G RAT as an example, in other possible implementations, the first RAT and the second RAT can also be other RATs as long as they are different from each other. For example, in another possible implementation, the first RAT can be 2G or 3G RAT, and the second RAT can be 4G RAT.

[0075] At least one of the access network devices 110, 120 and 130 provides services for the terminal device 140. The service areas of the access network devices 110, 120 and 130 are respectively referred to as cells 112, 122 and 132.

[0076] In a possible implementation, the communication service of the terminal device 140 can trigger the terminal device 140 to change from the cell 132 to the cell 112, and then change from the cell 112 to the cell 122. In such a possible implementation, the access network device 130 is also referred to as a source access network device 130, and the cell 132 is also referred to as a source cell 132; the access network device 110 is also referred to as a first target access network device 110, and the cell 112 is also referred to as a first target cell 112; the access network device 120 is also referred to as a second target access network device 120, and the cell 122 is also referred to as a second target cell 122. Hereinafter, the cell change of the terminal device 140 from the cell 132 to the cell 112 is also referred to as a first cell change, and the cell change of the terminal device 140 from the cell 112 to the cell 122 is also referred to as a second cell change.

[0077] The cell change can also be referred to as a cell changeover. In a possible implementation, the execution manner of the cell change or the cell changeover can include handover or redirection.

[0078] In a possible implementation, the communication network 100 can adopt a dual connectivity mode. In the dual connectivity mode, the terminal device 140 can be simultaneously connected to a master node and a secondary node, and the master node can be an access network device adopting a 5G RAT, and the secondary node can be an access network device adopting a 4G RAT, the master node can establish a control plane connection with the 5G core network, and the master node or the secondary node can respectively establish a user plane connection with the 5G core network. This will be described with reference to Figure 2A .

[0079] Figure 2A A schematic block diagram of a communication network 200A in which a possible implementation of the present application can be implemented is shown. The communication network 200A can be regarded as an example implementation of the communication network 100. As Figure 2A shown, the communication network 200A includes the access network devices 110, 120 and 130 and the terminal device 140. The communication network 200A adopts a dual connectivity mode. The access network devices 120 and 130 adopting the 5G RAT are connected to the 5GC 150, and the access network device 110 adopting the 4G RAT is also connected to the 5GC 150. In the communication network 200A, the access network devices 120 or 130 serve as a master node, and the access network device 110 serves as a secondary node. The terminal device 140 is simultaneously connected to one of the access network devices 120 and 130 and the access network device 110.

[0080] It can be understood that in the dual connectivity mode, the terminal device 140 changes from the cell of the master node to the cell of the secondary node for some types of communication services (e.g., voice services). In this case, other communication services of the terminal device 140 (e.g., communication services other than voice services) are still in the master node. After the completion of the communication service, the terminal device 140 can change from the cell of the secondary node to the cell of the master node and re-access the cell of the master node. In addition, the source cell in the dual connectivity scenario is the cell of the master node, and the first target cell is the cell of the secondary node. The re-accessed cell of the master node can be different from the source cell.

[0081] In another possible implementation, the communication network 100 can adopt a single connectivity mode. In the single connectivity mode, the access network devices adopting the 5G RAT can be connected to the 5G core network 5GC, and the access network devices adopting the 4G RAT can be connected to the Evolved Packet Core (EPC). The terminal device 140 is connected to only the access network devices adopting the 5G RAT or only the access network devices adopting the 4G RAT.

[0082] In the single connectivity mode, the terminal device 140 can change from a source cell adopting the 5G RAT to a target cell adopting the 4G RAT for some types of communication services (e.g., voice services). In this case, the terminal device 140 switches all communication services to the target cell. After the completion of the communication service, the terminal device 140 can change from the target cell back to the cell of the source system and re-access the cell of the source system. The cell of the source system can be the source cell or other cells adopting the same RAT as the source cell. This will be described with reference to Figure 2B .

[0083] Figure 2B A schematic block diagram of a communication network 200B in which possible implementations of the present application can be implemented is shown. The communication network 200B can be regarded as another example implementation of the communication network 100. In the communication network 200B, the access network devices 120 and 130 adopting the 5G RAT are connected to the 5GC 150 respectively, and the access network device 110 adopting the 4G RAT is connected to the EPC 160.

[0084] In a possible implementation, examples of the communication service triggering the terminal device 140 to perform the first cell change and the second cell change can include, but are not limited to, voice services, data services. In the following, possible implementations of the present application will be described taking voice services as an example. However, it should be understood that the solutions of the present application are also applicable to other communication services other than voice services.

[0085] In the implementation where the communication service is voice service, the 5G network can not support voice service (e.g., VoNR). The reason why the 5G network does not support voice service can be at least one of the following: the 5GC does not deploy IMS; although the 5GC deploys IMS, there is no 5G cell coverage or the 5G cell coverage is poor; the 5GC deploys IMS, but the capability of the terminal device does not support voice service based on the 5G network. In such an implementation, before establishing a voice call, the terminal device 140 can cause the voice service to fallback to the 4G network by switching or redirecting to a 4G cell (e.g., the cell 112 using the 4G RAT) to ensure the progress of the voice service. Alternatively, the terminal device 140 can use Single Radio Voice Call Continuity (SRVCC) to switch to a 3G or 2G cell (e.g., the cell 112 using the 3G or 2G RAT) to cause the voice service to fallback to the 3G or 2G network. After the terminal device 140 completes the voice service in the 4G, 3G, or 2G network and deletes the voice service bearer, if the terminal device 140 determines that there is no “non-switchable” service on the terminal device 140, the terminal device 140 triggers a fast return procedure to cause the terminal device 140 to re-access the 5G cell.

[0086] As can be seen, the voice service procedure involves a first inter-system handover from the 5G cell to the 4G, 3G, or 2G cell, and a second inter-system handover from the 4G, 3G, or 2G cell to the 5G cell.

[0087] Similarly, an Inter-system Ping-pong event also involves two inter-system handovers. Specifically, the Inter-system Ping-pong event is defined as follows: a terminal device is handed over from a cell in a source system (e.g., a 5G system) to a cell in a target system (e.g., an Evolved Packet System (EPS)) different from the source system, and then within a predefined limited time, the terminal device is handed back to a cell in the source system, and the coverage of the source system is sufficient to meet the service used by the terminal device. This event can occur more than once. After determining that the Inter-system Ping-pong event occurs, the access network device after the second inter-system handover will indicate the Inter-system Ping-pong event to the source access network device. Accordingly, the source access network device can optimize the inter-system handover parameters, such as increasing the threshold for inter-system handover, to avoid the Inter-system Ping-pong event from occurring again.

[0088] It can be understood from the above description that the inter-system ping-pong event is for a case that the source system cell coverage quality meets the service requirement, but inter-system handover is performed due to unreasonable inter-system handover parameters, and then the handover back to the source system is triggered due to the coverage quality. The two inter-system handovers in the voice service procedure are triggered by the ongoing communication service procedure, and are irrelevant to the coverage and inter-system handover parameters. Therefore, in order to avoid the optimization of the invalid and redundant inter-system handover parameters triggered by the normal communication service procedure of the terminal device, the communication service procedure needs to be distinguished from the inter-system ping-pong event.

[0089] At least in view of the above problems and potential other related problems, the present application proposes a communication method. By providing a cell change cause indication to an access network device after a second inter-system handover, to indicate that a first inter-system cell change or a second inter-system cell change is associated with a communication service of a terminal device, the access network device can determine that the two inter-system cell changes are irrelevant to an inter-system ping-pong event. The possible implementation manners of the present application will be described in detail below with reference to Figures 3 to 15 .

[0090] Figure 3 A signaling interaction diagram of an example communication procedure 300 according to a possible implementation manner of the present application is shown. For the purpose of discussion, the communication procedure 300 will be described with reference to the various elements shown in Figure 1 . However, it should be understood that the communication procedure 300 can also be performed between an access network device and a terminal device in any other communication scenario.

[0091] As shown in Figure 3 , the terminal device 140 acquires (310) a cell change cause indication, which indicates that a first cell change of the terminal device 140 from a source cell 132 to a first target cell 112 or a second cell change from the first target cell 112 to a second target cell 122 is associated with a communication service of the terminal device 140. The first target cell 112 adopts a first RAT, and the source cell 132 and the second target cell 122 adopt a second RAT different from the first RAT.

[0092] As mentioned before, the "cell change" can also be referred to as "cell changeover", and the execution manner of the cell change or cell changeover can include handover or redirection. Therefore, in one implementation manner, the cell change cause indication can be a handover cause indication.

[0093] The terminal device 140 sends (320) the cell change cause indication to the second target access network device 120 to which the second target cell 122 belongs. Accordingly, the second target access network device 120 receives (325) the cell change cause indication. Further, the second target access network device 120 determines (330), based on the cell change cause indication, that the first cell change and the second cell change are not associated with the inter-system ping-pong event. As a result, the second target access network device 120 can not indicate the inter-system ping-pong event to the source access network device 130, so as to avoid triggering the optimization of invalid and redundant inter-system handover parameters, save system resources, and improve communication efficiency.

[0094] In a possible implementation, the cell change cause indication can indicate that at least one of the following: the first cell change is associated with a voice fallback procedure of the terminal device 140 from the source cell 132 to the first target cell 112, and the second cell change is associated with a fast return procedure of the terminal device 140 from the first target cell 112 to the second target cell 122.

[0095] In a possible implementation, the terminal device 140 can further acquire at least one of the following: an indication of a type of the voice fallback procedure and an indication of a cell change execution manner. The indication of the type of the voice fallback procedure can indicate that the voice fallback procedure is an evolved packet system fallback (EPS fallback) procedure or an inter radio access technology fallback (Inter RAT fallback) procedure. The cell change execution manner can include handover or redirection.

[0096] In a possible implementation, the first RAT can be one of a 2G, 3G, and 4G RAT, and the second RAT can be a 5G RAT. In another possible implementation, the first RAT can be a 2G or 3G RAT, and the second RAT can be a 4G RAT.

[0097] In a possible implementation, the terminal device 140 can acquire the cell change cause indication from the source access network device 130 to which the source cell 132 belongs. In such an implementation, the terminal device 140 can receive, from the source access network device 130, a first cell change command associated with the first cell change, where the first cell change command can include the cell change cause indication. This will be described with reference to Figure 4 .

[0098] Figure 4 A signaling interaction diagram of an example communication procedure 400 according to possible implementations of the present application is shown. For the purpose of discussion, reference will be made to Figure 2BThe communication process 400 is described in relation to various elements shown in FIG. 4. The communication process 400 can be regarded as an example implementation of the communication process 300. In the communication process 400, the terminal device 140 performs initial VoNR voice service setup or is in a VoNR voice service.

[0099] In a possible implementation, to setup the VoNR voice service, the terminal device 140 can send a request message to the 5GC 150 to request setup of a voice session. The 5GC 150, upon receiving the request message, can forward it to the source access network device 130. The request message can instruct the source access network device 130 to setup a voice dedicated bearer with a 5G Quality of Service Indicator (5QI) of 1. If the source cell 132 does not support VoNR, at 410, the source access network device 130 can reply to the 5GC 150 with a reject message and indicate voice fallback, and can determine a target access network device (e.g., the first target access network device 110) for cell change according to the switch parameter configuration and the capability of the terminal device 140.

[0100] Upon determining the first target access network device 110, the source access network device 130 can send a handover request to the 5GC 150 via an NG interface, and the 5GC 150 can forward context information of the terminal device 140 to the EPC 160. The EPC 160 can send a handover request to the first target access network device 110 via an S1 interface. The EPC 160, upon receiving a response message to the handover request from the first target access network device 110, can forward the response message to the 5GC 150. Alternatively, the source access network device 130 can send a handover request to the first target access network device 110 via an X2 interface, and the first target access network device 110 can send a response message to the handover request to the source access network device 130 via the X2 interface.

[0101] Further, the 5GC 150 can send a handover command to the source access network device 130, and the source access network device 130 can send (420) the handover command (i.e., a first handover command) to the terminal device 140. The first handover command includes a cell change cause indication. Accordingly, the terminal device 140 receives (425) the first handover command. The cell change cause indication can indicate that the handover of the terminal device 140 to the first target cell 112 is associated with a voice fallback procedure from the source cell 132 to the first target cell 112.

[0102] In a possible implementation, the first handover command from the source access network device 130 can include, but is not limited to, a Mobility from NR Command.

[0103] In a possible implementation, to reduce the signaling overhead, the source access network device 130 can send the cell change cause indication in the first handover command in association with information of the first target cell 112. The information of the first target cell 112 can include, but is not limited to, an identification (ID) of the first target cell 112, for example.

[0104] Subsequently, the terminal device 140 changes (430) to the first target cell 112 to establish the VoLTE service. For example, a tracking area update (TAU) procedure can be initiated between the terminal device 140 and the EPC 160, so that the EPC 160 can trigger establishment of a voice dedicated bearer with a QoS class identifier (QCI) of 1.

[0105] In addition, the terminal device 140 can record the cell change cause indication in the history information of the terminal device 140. For example, the terminal device 140 can record the cell change cause indication in association with the related information of the first target cell 112. Alternatively, the terminal device 140 can record the cell change cause indication in association with the related information of the source cell 132.

[0106] In a possible implementation, the terminal device 140 can further record an indication of a type of the voice fallback procedure in the history information of the terminal device 140. The indication of the type of the voice fallback procedure can indicate that the voice fallback procedure is an EPS voice fallback procedure or an Inter RAT voice fallback procedure. For example, as shown in FIG. 4, in an implementation in which the access network devices 120 and 130 employing 5G RAT are connected to the 5GC 150, and the access network device 110 employing 4G RAT is connected to the EPC 160, the indication of the type of the voice fallback procedure can indicate that the voice fallback procedure is the EPS voice fallback procedure. Figure 2B Figure 2A For another example, as shown in FIG. 5, in an implementation in which the access network devices 120 and 130 employing 5G RAT and the access network device 110 employing 4G RAT are all connected to the 5GC 150, the indication of the type of the voice fallback procedure can indicate that the voice fallback procedure is the Inter RAT voice fallback procedure.

[0107] In another possible implementation, the terminal device 140 can further record an indication of a cell change execution manner in the history information of the terminal device 140. The indication of the cell change execution manner can indicate whether the terminal device 140 performs the cell change through handover or redirection.

[0108] ​In yet another possible implementation, the terminal device 140 can also record a joint indication of the type of voice fallback procedure and the cell change execution manner in the history information of the terminal device 140. For example, the joint indication can indicate one of the following: an EPS voice fallback procedure executed by the terminal device 140 through handover, an EPS voice fallback procedure executed by the terminal device 140 through redirection, an Inter RAT voice fallback procedure executed by the terminal device 140 through handover, and an Inter RAT voice fallback procedure executed by the terminal device 140 through redirection.

[0109] After the voice service ends, the first target access network device 110 determines (440) a target access network device of the cell change. For example, the first target access network device 110 can determine the second target access network device 120 as the target access network device of the cell change based on the coverage quality information of the primary serving cell and the inter-system neighboring cell reported by the terminal device 140. Subsequently, the terminal device 140 performs (450) handover from the first target cell 112 managed by the first target access network device 110 to the second target cell 122 managed by the second target access network device 120.

[0110] After the terminal device 140 accesses the second target cell 122, the second target access network device 120 sends (460) a request for the history information of the terminal device 140 to the terminal device 140. In response to receiving (465) the request, the terminal device 140 sends (470) the history information of the terminal device 140 to the second target access network device 120, the history information including the cell change cause indication. Accordingly, the second target access network device 120 receives (476) the history information of the terminal device 140.

[0111] In a possible implementation, the terminal device 140 can store information of a cell camped by the terminal device 140 as part of user history information (UE History Information, UHI). The information of the camped cell can include, for example, an identity of the camped cell and a camping time, and the like. In such an implementation, the terminal device 140 can include the cell change cause indication obtained from the source access network device 130 in the UHI. For example, the terminal device 140 can store the cell change cause indication in association with information of the first target cell 112 to indicate that the cell change to the first target cell 112 is associated with the voice fallback procedure of the terminal device 140 from the source cell 132 to the first target cell 112. In such an implementation, the terminal device 140 can send the UHI including the cell change cause indication to the second target access network device 120 to enable the second target access network device 120 to obtain the history information of the terminal device 140. Alternatively, the terminal device 140 can store the cell change cause indication in association with information of the source cell 132 to indicate that the change out of the source cell 132 is associated with the voice fallback procedure of the terminal device 140 from the source cell 132 to the first target cell 112.

[0112] Upon receiving the cell change cause indication, the second target access network device 120 determines (330) that the first cell change and the second cell change are not associated with the inter-system ping-pong event based on the cell change cause indication, or based on the cell change cause indication and the camping time in the first target cell. As such, the second target access network device 120 can not indicate the inter-system ping-pong event to the source access network device 130, thereby avoiding triggering the source access network device 130 to adjust the handover parameters based on the inter-system ping-pong event. Moreover, since the adjustment of the handover parameters in the case that the two inter-system handovers are not associated with the inter-system ping-pong event will occupy the processing time of the source access network device, the solution of the present application can improve the communication efficiency.

[0113] In another possible implementation, the second target access network device 120 can not perform the action 330, i.e., does not determine (330) that the first cell change and the second cell change are irrelevant to the inter-system ping-pong event based on the cell change cause indication. Instead, the second target access network device 120 can send the cell change cause indication to the source access network device 130 to which the source cell belongs. For example, the second target access network device 120 can generate an inter-system ping-pong report including the cell change cause indication. The second target access network device 120 can send the inter-system ping-pong report to the source access network device 130 through one of the following messages: a handover report message over Xn interface, or an uplink ran configuration transfer message or a downlink ran configuration transfer message over NG interface. Upon receiving the cell change cause indication, the source access network device 130 can determine that the first cell change and the second cell change are irrelevant to the inter-system ping-pong event based on the cell change cause indication, and thus does not perform the mobile parameter optimization.

[0114] In addition to obtaining the cell change cause indication from the source access network device 130, in one possible implementation, the terminal device 140 can also obtain the cell change cause indication from the first target access network device 110. In such an implementation, the terminal device 140 receives, from the first target access network device 110, a second handover command associated with the second cell change, the second handover command including the cell change cause indication. This will be described with reference to Figure 5

[0115] Figure 5 A signaling interaction diagram illustrating an example communication procedure 500 according to possible implementations of the present application is shown. For the purpose of discussion, the communication procedure 500 will be described with reference to various elements shown in Figure 2B The communication procedure 500 can be regarded as another example implementation of the communication procedure 300. In the communication procedure 500, the terminal device 140 performs initial VoNR voice service establishment or is in VoNR voice service. Actions such as 410, 430, 440, 430, 465, 470, 475 and 330 in the communication procedure 500 are similar to the corresponding actions in the communication procedure 400, and thus will not be described again. The communication procedure 500 differs from the communication procedure 400 in that the terminal device 140 does not include the cell change cause indication in the first handover command received (510) from the source access network device 130. Instead, the terminal device 140 includes the cell change cause indication in the second handover command received (560) from the first access network device 110.

[0116] ​Specifically, after the voice service of the terminal device 140 ends and the first target access network device 110 determines (440) the target access network device (e.g., the second target access network device 120) of cell change, the first target access network device 110 sends (520) a handover request to the EPC 160 to request the terminal device 140 to be quickly returned to the second target cell 122 of the second target access network device 120. After the EPC 160 receives (525) the handover request, the EPC 160 sends (530) the handover request to the 5GC 150. Optionally, the EPC 160 can send the context information of the terminal device 140 to the 5GC 150 together with the handover request. After the 5GC 150 receives (535) the handover request, the 5GC 150 sends (540) the handover request to the second target access network device 120 to notify the second target access network device 120 to make handover preparation. After the second target access network device 120 receives (545) the handover request, the second target access network device 120 sends a handover preparation complete message (not shown in the figure) to the 5GC 150, and then the 5GC 150 forwards the handover preparation complete message (not shown in the figure) to the EPC 160.

[0117] After receiving the handover preparation complete message, the EPC 160 sends (550) a handover command for switching from the first target cell 112 to the second target cell 122 to the first target access network device 110. After receiving (555) the handover command, the first target access network device 110 sends (560) a handover command (i.e., a second handover command) for switching from the first target cell 112 to the second target cell 122 to the terminal device 140. The second handover command includes a cell change reason indication to indicate that the switching to the second target cell 122 is associated with the fast return procedure.

[0118] In a possible implementation, the second handover command from the first target access network device 110 can include, but is not limited to, a Mobility from EUTRA Command.

[0119] In a possible implementation, in order to reduce signaling overhead, the first target access network device 110 can send the cell change reason indication in association with the related information of the second target cell 122 in the second handover command.

[0120] Upon receiving the second handover command (565), the terminal device 140 may record the cell change reason indication in its historical information. For example, the terminal device 140 may record the cell change reason indication in association with the information of the second target cell 122. For example, to record the cell change reason indication in association with the information of the second target cell 122, the cell change reason indication and the information of the second target cell 122 may be recorded in an entry of a list.

[0121] In one possible implementation, in response to receiving (565) a second handover command including a cell change reason indication, terminal device 140 may send a Radio Resource Control Reconfiguration Complete (RRCReconfigurationComplete) message to second target access network device 120. The RRCReconfigurationComplete message includes a cell change reason indication to indicate to second target access network device 120 that the change to second target cell 122 is associated with a voice fallback procedure or a fast return procedure.

[0122] In another possible implementation, similar to process 400, in process 500, the second target access network device 120 may not perform action 330, that is, it may not determine (330) that the first cell change and the second cell change are unrelated to the inter-system ping-pong event based on the cell change reason indication. Alternatively, the second target access network device 120 may send the cell change reason indication to the source access network device 130 to which the source cell belongs. Upon receiving the cell change reason indication, the source access network device 130 may determine, based on the cell change reason indication, that the first cell change and the second cell change are unrelated to the inter-system ping-pong event, and thus not perform mobility parameter optimization.

[0123] It should be understood that the above is for reference only. Figure 2B The various elements shown describe communication processes 400 and 500. However, at least one of communication processes 400 and 500 can also be executed between terminal devices, access network devices, and core network devices in any other communication scenario. For example, at least one of communication processes 400 and 500 can also be... Figure 2A This is performed between terminal devices, access network devices, and core network devices in the communication network 200A shown. In this implementation, messages exchanged between the first target access network device 110 and the second target access network device 120 can be forwarded solely through 5GC 150.

[0124] The above is for reference only. Figures 3 to 5An implementation manner that the terminal device 140 sends the cell change cause indication to the second target access network device 120 (i.e., the second target access network device 120 acquires the cell change cause indication from the terminal device 140) is described. In another possible implementation manner, the second target access network device 120 can also acquire the cell change cause indication from the first target access network device 110. In the following, the communication process 600 according to the possible implementation manner of the present application will be described with reference to various elements shown in Figures 6 to 8 This is described.

[0125] Figure 6 A signaling interaction diagram of an example communication process 600 according to a possible implementation manner of the present application is shown. For the purpose of discussion, the communication process 600 will be described with reference to various elements shown in Figure 1 However, it should be understood that the communication process 600 can also be performed between an access network device and a terminal device in any other communication scenario.

[0126] As Figure 6 shown, the first target access network device 110 acquires (610) the cell change cause indication indicating that the first cell change of the terminal device 140 from the source cell 132 to the first target cell 112 or the second cell change from the first target cell 112 to the second target cell 122 is associated with the communication service of the terminal device 140. The first target cell 112 adopts a first RAT, and the source cell 132 and the second target cell 122 adopt a second RAT different from the first RAT.

[0127] The first target access network device 110 sends (620) the cell change cause indication to the second target access network device 120. Accordingly, the second target access network device 120 receives (625) the cell change cause indication. Further, the second target access network device 120 determines (630), based on the cell change cause indication or based on the cell change cause indication and the camping time at the first target cell, that the first cell change and the second cell change are not associated with the inter-system ping-pong event. Thus, the second target access network device 120 can not indicate the inter-system ping-pong event to the source access network device 130, so as to avoid triggering the optimization of the invalid and redundant inter-system handover parameters.

[0128] In another possible implementation, the second target access network device 120 can not perform the action 630. Instead, the second target access network device 120 can send the cell change cause indication to the source access network device 130 to which the source cell belongs. For example, the second target access network device 120 can generate an inter-system ping-pong report including the cell change cause indication. The second target access network device 120 can send the inter-system ping-pong report to the source access network device 130 through one of the following messages: a handover report message over Xn interface, or an uplink ran configuration transfer message or a downlink ran configuration transfer message over NG interface. Upon receiving the cell change cause indication, the source access network device 130 can determine, based on the cell change cause indication, that the first cell change and the second cell change are not related to an inter-system ping-pong event, and thus not perform the mobile parameter optimization.

[0129] In a possible implementation, the cell change cause indication can indicate that at least one of the following: the first cell change is associated with a voice fallback procedure of the terminal device 140 from the source cell 132 to the first target cell 112, and the second cell change is associated with a fast return procedure of the terminal device 140 from the first target cell 112 to the second target cell 122.

[0130] In a possible implementation, the first RAT can be one of 2G, 3G and 4G RAT, and the second RAT can be 5G RAT. In another possible implementation, the first RAT can be 2G or 3G RAT, and the second RAT can be 4G RAT.

[0131] In a possible implementation, the first target access network device 110 can obtain the cell change cause indication from the source access network device 130 to which the source cell 132 belongs. In such an implementation, the first target access network device 110 can obtain, from the source access network device 130, historical information of the terminal device 140. The historical information can include information of cells in which the terminal device 140 camps, camping time, and cell change cause indication. This will be described with reference to Figure 7 .

[0132] Figure 7 A signaling interaction diagram illustrating an example communication procedure 700 according to possible implementations of the present application is shown. For the purpose of discussion, the communication procedure 700 will be described with reference to various elements shown in Figure 2B . The communication procedure 700 can be regarded as an example implementation of the communication procedure 600.

[0133] In the communication process 700, the source access network device 130 records the history information of the terminal device 140, which includes the cell change cause indication. For example, the source access network device 130 can store the history information of the terminal device 140 as a UHI, which contains the cell change cause indication. Further, the first target access network device 110 acquires the UHI containing the cell change cause indication from the source access network device 130 via a handover request from the source cell 132 to the first target cell 112. After the terminal device 140 completes the voice service in the first target cell 112, the first target access network device 110 further provides the UHI containing the cell change cause indication to the second target access network device 120 via a handover request from the first target cell 112 to the second target cell 122.

[0134] Specifically, similar to the communication process 400, in the communication process 700, the terminal device 140 performs initial VoNR voice service establishment or is in the VoNR voice service. The action 410 in the communication process 700 is similar to the action 410 in the communication process 400, and thus is not described in detail.

[0135] After determining (410) the target access network device of the cell change (e.g., the first target access network device 110), the source access network device 130 records (710) the history information of the terminal device 140. The history information includes the cell change cause indication. In one possible implementation, the source access network device 130 can store the cell change cause indication as part of the UHI. For example, the source access network device 130 can store the cell change cause indication in association with the information of the source cell 132 to indicate that the reason for the terminal device 140 changing from the source cell 132 of the source access network device 130 is associated with the voice fallback procedure from the source cell 132 to the first target cell 112 of the first target access network device 110. Alternatively, the source access network device 130 can store the cell change cause indication in association with the information of the first target cell 112 to indicate that the reason for the terminal device 140 changing to the first target cell 112 is associated with the voice fallback procedure from the source cell 132 to the first target cell 112.

[0136] Further, the source access network device 130 sends (720) a handover request from the source cell 132 to the first target cell 112 to the 5GC 150. The handover request comprises the UHI of the terminal device 140, which comprises the cell change cause indication. After the 5GC 150 receives (725) the handover request, the 5GC 150 sends (730) the handover request to the EPC 160. The handover request comprises the UHI of the terminal device 140, which comprises the cell change cause indication. After the EPC 160 receives (735) the handover request, the EPC 160 sends (740) the handover request to the first target access network device 110 to inform the first target access network device 110 to prepare for the handover. The handover request comprises the UHI of the terminal device 140, which comprises the cell change cause indication. After the first target access network device 110 receives (745) the handover request, the first target access network device 110 sends a handover preparation complete message (not shown in the figure) to the EPC 160, and further the EPC 160 forwards the handover preparation complete message (not shown in the figure) to the 5GC 150.

[0137] Alternatively, in another possible implementation, the source access network device 130 can not send the above-mentioned handover request to the first target access network device 110 through the 5GC 150 and the EPC 160, but send the above-mentioned handover request to the first target access network device 110 through an X2 interface.

[0138] Further, in another possible implementation, the UHI can further comprise an indication of a cell change execution manner. The indication of the cell change execution manner can indicate whether the cell change is performed by handover or redirection.

[0139] In addition, in another possible implementation, the UHI can further comprise an indication of a type of the voice fallback procedure to indicate whether the voice fallback procedure is an EPS voice fallback procedure or an Inter RAT voice fallback procedure.

[0140] In yet another possible implementation, the UHI can further comprise a joint indication of the type of the voice fallback procedure and the cell change execution manner. For example, the joint indication can indicate one of the following: an EPS voice fallback procedure performed by handover, an EPS voice fallback procedure performed by redirection, an Inter RAT voice fallback procedure performed by handover, and an Inter RAT voice fallback procedure performed by redirection.

[0141] Upon receiving the handover preparation complete message, the 5GC 150 sends a handover command (not shown in the figure) to the source access network device 130 for the handover from the source cell 132 to the first target cell 112. Upon receiving the handover command, the source access network device 130 sends a handover command (not shown in the figure) to the terminal device 140 for the handover from the source cell 132 to the first target cell 112. In response to receiving the handover command, the terminal device 140 hands over (430) from the source cell 132 to the first target cell 112 to establish the VoLTE service. The action 430 in the communication process 700 is similar to the action 430 in the communication process 400, and thus is not described in detail.

[0142] After the voice service ends, the first target access network device 110 determines (440) the target access network device (e.g., the second target access network device 120) for the cell change. The action 440 in the communication process 700 is similar to the action 440 in the communication process 400, and thus is not described in detail.

[0143] Further, the first target access network device 110 sends (750) a handover request to the EPC 160 for the handover from the first target cell 112 of the first target access network device 110 to the second target cell 122 of the second target access network device 120 to request the fast return of the terminal device 140 to the second target cell 122. The handover request includes the cell change cause indication. Upon receiving (755) the handover request, the EPC 160 sends (760) the handover request to the 5GC 150. The handover request includes the UHI of the terminal device 140, which includes the cell change cause indication. Optionally, the EPC 160 can send the context information of the terminal device 140 to the 5GC 150 together with the handover request. Upon receiving (765) the handover request, the 5GC 150 sends (770) the handover request to the second target access network device 120 to notify the second target access network device 120 to prepare for the handover. The handover request includes the UHI of the terminal device 140, which includes the cell change cause indication. Upon receiving (775) the handover request, the second target access network device 120 sends a handover preparation complete message (not shown in the figure) to the 5GC 150, and the 5GC 150 forwards the handover preparation complete message (not shown in the figure) to the EPC 160.

[0144] Upon receiving the handover preparation complete message, EPC 160 sends a handover command (not shown in the figure) to the first target access network device 110, requesting a handover from the first target cell 112 to the second target cell 122. Upon receiving this handover command, the first target access network device 110 sends a handover command (not shown in the figure) to the terminal device 140, requesting a handover from the first target cell 112 to the second target cell 122. In response to receiving this handover command, the terminal device 140 hands over from the first target cell 112 to the second target cell 122.

[0145] After terminal device 140 switches to the second target cell 122, the second target access network device 120 determines (780) that the first cell change and the second cell change are unrelated to the inter-system ping-pong event based on the cell change reason indication. Therefore, the second target access network device 120 can avoid indicating the inter-system ping-pong event to the source access network device 130, thereby avoiding triggering the source access network device 130 to adjust the inter-system handover parameters.

[0146] In another possible implementation, similar to process 400, in process 700, the second target access network device 120 may not perform action 780, i.e., it may not determine that the first cell change and the second cell change are unrelated to the inter-system ping-pong event based on the cell change reason indication. Alternatively, the second target access network device 120 may send the cell change reason indication to the source access network device 130 to which the source cell belongs. Upon receiving the cell change reason indication, the source access network device 130 may determine that the first cell change and the second cell change are unrelated to the inter-system ping-pong event based on the cell change reason indication, thereby not performing mobility parameter optimization.

[0147] The above is for reference only. Figure 7 The description details an implementation whereby the source access network device 130 records historical information of the terminal device 140, including an indication of the reason for a cell change. Alternatively, in another possible implementation, the first target access network device 110 may record historical information of the terminal device 140, including an indication of the reason for a cell change. This will be referred to... Figure 8 Describe it.

[0148] Figure 8 A signaling interaction diagram of an example communication process 800 according to a possible implementation of this application is shown. For purposes of discussion, reference will be made to... Figure 2B The various elements shown describe the communication process 800. The communication process 800 can be viewed as another example implementation of the communication process 600.

[0149] In the communication process 800, the first target access network device 110 records the history information of the terminal device 140, which includes the cell change cause indication. Further, after the terminal device 140 completes the voice service in the first target cell 112, the first target access network device 110 provides the cell change cause indication to the second target access network device 120 via the handover request from the first target cell 112 to the second target cell 122.

[0150] Specifically, similar to the communication process 400, in the communication process 800, the terminal device 140 performs initial VoNR voice service establishment or is in the VoNR voice service. The action 410 in the communication process 800 is similar to the action 410 in the communication process 400, and thus is not described in detail.

[0151] After determining (410) the target access network device for cell change (e.g., the first target access network device 110), the source access network device 130 sends (810) a handover request from the source cell 132 to the first target cell 112 to the 5GC 150. Unlike the communication process 700, the cell change cause indication is not included in the UHI in the handover request from the source access network device 130. Further, the 5GC 150 sends (820) the handover request to the EPC 160. Subsequently, the EPC 160 sends (830) the handover request to the first target access network device 110 to notify the first target access network device 110 to prepare for handover. The first target access network device 110 receives the handover request and sends a handover preparation complete message (not shown in the figure) to the EPC 160, and then the EPC 160 forwards the handover preparation complete message (not shown in the figure) to the 5GC 150.

[0152] After receiving the handover preparation complete message, the 5GC 150 sends a handover command (not shown in the figure) to the source access network device 130 for handover from the source cell 132 to the first target cell 112. After receiving the handover command, the source access network device 130 sends a handover command (not shown in the figure) to the terminal device 140 for handover from the source cell 132 to the first target cell 112. In response to receiving the handover command, the terminal device 140 hands over (430) from the source cell 132 to the first target cell 112 to establish the VoLTE service. The action 430 in the communication process 800 is similar to the action 430 in the communication process 400, and thus is not described in detail.

[0153] After the voice service ends, the first target access network device 110 determines (440) the target access network device for cell change (e.g., the second target access network device 120). The action 440 in the communication process 800 is similar to the action 440 in the communication process 400, and thus is not described in detail.

[0154] Further, the first target access network device 110 records (840) the history information of the terminal device 140. The history information includes the cell change cause indication. In a possible implementation, the first target access network device 110 can store the cell change cause indication in the UHI. For example, the first target access network device 110 can store the cell change cause indication in association with the information of the first target cell 112, to indicate that the reason for the terminal device 140 changing from the first target cell 112 is associated with the fast return procedure from the first target cell 112 to the second target cell 122.

[0155] Further, the first target access network device 110 sends (850) a handover request from the first target cell 112 of the first target access network device 110 to the second target cell 122 of the second target access network device 120 to the EPC 160, to request fast return of the terminal device 140 to the second target cell 122. The handover request includes the cell change cause indication. After receiving (855) the handover request, the EPC 160 sends (860) the handover request to the 5GC 150. The handover request includes the cell change cause indication. Optionally, the EPC 160 can send the context information of the terminal device 140 to the 5GC 150 together with the handover request. After receiving (865) the handover request, the 5GC 150 sends (880) the handover request to the second target access network device 120, to notify the second target access network device 120 to prepare for handover. The handover request includes the cell change cause indication.

[0156] In a possible implementation, the first target access network device 110 can include the cell change cause indication in the UHI of the terminal device 140, and further include the UHI in the handover request from the first target cell 112 to the second target cell 122, to send to the second target access network device 120.

[0157] In another possible implementation, the first target access network device 110 can include the cell change cause indication in a field or information element other than the UHI, and further include the field or information element in the handover request from the first target cell 112 to the second target cell 122, to send to the second target access network device 120. For example, the field or information element can be a field or information element specially used to carry the cell change cause indication, and the scope of the present application is not limited in this aspect.

[0158] After receiving (875) the handover request, the second target access network device 120 sends a handover preparation complete message (not shown in the figure) to the 5GC 150, and further the 5GC 150 forwards the handover preparation complete message (not shown in the figure) to the EPC 160.

[0159] Upon receiving the handover preparation complete message, the EPC 160 sends a handover command (not shown in the figure) to the first target access network device 110 for switching from the first target cell 112 to the second target cell 122. Upon receiving the handover command, the first target access network device 110 sends a handover command (not shown in the figure) to the terminal device 140 for switching from the first target cell 112 to the second target cell 122. In response to receiving the handover command, the terminal device 140 switches from the first target cell 112 to the second target cell 122.

[0160] After the terminal device 140 switches to the second target cell 122, the second target access network device 120 determines (880) that the first cell change and the second cell change are not related to the inter-system ping-pong event based on the cell change cause indication. As such, the second target access network device 120 can not indicate the inter-system ping-pong event to the source access network device 130, and thus can avoid triggering the source access network device 130 to adjust the inter-system handover parameters.

[0161] In another possible implementation, similar to the procedure 400, in the procedure 800, the second target access network device 120 can not perform the action 880, i.e., does not determine that the first cell change and the second cell change are not related to the inter-system ping-pong event based on the cell change cause indication. Instead, the second target access network device 120 can send the cell change cause indication to the source access network device 130 to which the source cell belongs. Upon receiving the cell change cause indication, the source access network device 130 can determine that the first cell change and the second cell change are not related to the inter-system ping-pong event based on the cell change cause indication, and thus does not perform the mobile parameter optimization.

[0162] It should be understood that the above description of various elements shown in Figure 2B illustrates the communication procedures 700 and 800. However, at least one of the communication procedures 700 and 800 can also be performed between a terminal device, an access network device, and a core network device in any other communication scenario. For example, at least one of the communication procedures 700 and 800 can also be performed between a terminal device, an access network device, and a core network device in the communication network 200A shown in Figure 2A illustrates the communication procedures 700 and 800. However, at least one of the communication procedures 700 and 800 can also be performed between a terminal device, an access network device, and a core network device in any other communication scenario. For example, at least one of the communication procedures 700 and 800 can also be performed between a terminal device, an access network device, and a core network device in the communication network 200A shown in

[0163] It should be understood that the various possible implementations of the present application described above can refer to each other, and the same terms have the same meanings if not specifically stated.

[0164] Figure 9A flowchart of a communication method 900 according to a possible implementation of the present application is shown. In a possible implementation, the method 900 can be implemented by a terminal device 140 in the example communication network 100, 200A or 200B, e.g., by a processor or processing unit of the terminal device 140 in cooperation with other components (e.g., a transceiver). In other possible implementations, the method 900 can also be implemented by other communication apparatuses independent of the example communication network 100, 200A or 200B.

[0165] At block 910, the terminal device 140 obtains a cell change cause indication. The cell change cause indication indicates that the first cell change of the terminal device 140 from the source cell to the first target cell or the second cell change of the terminal device 140 from the first target cell to the second target cell is associated with a communication service of the terminal device 140. The first target cell adopts a first RAT, and the source cell and the second target cell adopt a second RAT different from the first RAT.

[0166] At block 920, the terminal device 140 sends the cell change cause indication to a second target access network device to which the second target cell belongs. In this way, the second target access network device can distinguish the communication service procedure from the inter-system ping-pong event, and avoid triggering optimization of invalid and redundant inter-system handover parameters for the normal communication service procedure of the terminal device 140.

[0167] In a possible implementation, the terminal device 140 obtaining the cell change cause indication comprises the terminal device 140 obtaining the cell change cause indication from a source access network device to which the source cell belongs.

[0168] In a possible implementation, the terminal device 140 obtaining the cell change cause indication from the source access network device comprises: the terminal device 140 receiving a first cell change command associated with the first cell change from the source access network device, the first cell change command comprising the cell change cause indication. Sending the cell change cause indication to the terminal device 140 through the first cell change command can avoid additional signaling overhead.

[0169] In a possible implementation, the terminal device 140 obtaining the cell change cause indication comprises: the terminal device 140 obtaining the cell change cause indication from a first target access network device to which the first target cell belongs.

[0170] In a possible implementation, the terminal device 140 obtaining the cell change cause indication from the first target access network device comprises: the terminal device 140 receiving a second cell change command associated with the second cell change from the first target access network device, the second cell change command comprising the cell change cause indication. Sending the cell change cause indication to the terminal device 140 through the second cell change command can avoid additional signaling overhead.

[0171] In a possible implementation, the terminal device 140 sending the cell change cause indication to the second target access network device includes: the terminal device 140 receiving, from the second target access network device, a request for historical information of the terminal device 140; and the terminal device 140 sending the historical information to the second target access network device, the historical information including the cell change cause indication. Sending the cell change cause indication together with the historical information to the second target access network device can avoid additional signaling overhead.

[0172] Figure 10 A flowchart of a communication method 1000 according to a possible implementation of the present application is shown. In a possible implementation, the method 1000 can be implemented by the first access network device 110 in the example communication network 100, 200A or 200B, for example, can be implemented by the processor or processing unit of the first access network device 110 in cooperation with other components (for example, the transceiver). In other possible implementations, the method 1000 can also be implemented by other communication apparatuses independent of the example communication network 100, 200A or 200B.

[0173] At block 1010, the first target access network device 110 obtains a cell change cause indication. The cell change cause indication indicates that a first cell change of a terminal device from a source cell to a first target cell of the first target access network device 110 or a second cell change from the first target cell to a second target cell is associated with a communication service of the terminal device. The first target cell adopts a first RAT, and the source cell and the second target cell adopt a second RAT different from the first RAT.

[0174] At block 1020, the first target access network device 110 provides the cell change cause indication to a second target access network device to which the second target cell belongs.

[0175] In a possible implementation, the first target access network device 110 obtaining the cell change cause indication includes: the first target access network device 110 obtaining the cell change cause indication from a source access network device to which the source cell belongs.

[0176] In a possible implementation, the first target access network device 110 obtaining the cell change cause indication from the source access network device includes: the first target access network device 110 obtaining historical information of the terminal device from the source access network device, the historical information including the cell change cause indication. Sending the cell change cause indication together with the historical information to the first target access network device 110 can avoid additional signaling overhead.

[0177] In a possible implementation, the first target access network device 110 providing the cell change cause indication to the second target access network device 120 comprises: the first target access network device 110 providing second history information of the terminal device 140 to the second target access network device 120, the second history information comprising the cell change cause indication, the second history information comprising the first history information, and / or third history information of the terminal device recorded by the first target access network device. Sending the cell change cause indication together with the history information to the second target access network device can avoid additional signaling overhead.

[0178] In a possible implementation, the first target access network device 110 providing the cell change cause indication to the second target access network device comprises: the first target access network device 110 providing a handover request for the second cell change to the second target access network device, the handover request comprising the cell change cause indication. Sending the cell change cause indication together with the handover request to the second target access network device can avoid additional signaling overhead.

[0179] Figure 11 A flowchart of a communication method 1100 according to a possible implementation of the present application is shown. In a possible implementation, the method 1100 can be implemented by the second access network device 120 in the example communication network 100, 200A or 200B, for example, by a processor or processing unit of the second access network device 120 in cooperation with other components (for example, a transceiver). In other possible implementations, the method 1100 can also be implemented by other communication apparatuses independent of the example communication network 100, 200A or 200B.

[0180] At block 1110, the second target access network device 120 acquires the cell change cause indication. The cell change cause indication indicates that the first cell change of the terminal device from the source cell to the first target cell or the second cell change of the terminal device from the first target cell to the second target cell of the second target access network device 120 is associated with the communication service of the terminal device. The first target cell adopts the first RAT, and the source cell and the second target cell adopt the second RAT different from the first RAT.

[0181] At block 1120, the second target access network device 120 determines, based on the cell change cause indication, that the first cell change and the second cell change are not associated with the inter-system ping-pong event. In this way, the second target access network device 120 can treat the communication service process differently from the inter-system ping-pong event, avoiding the optimization of invalid and redundant inter-system handover parameters triggered by the normal communication service process of the terminal device.

[0182] In a possible implementation, the second target access network device 120 acquiring the cell change cause indication comprises: acquiring the cell change cause indication from the terminal device.

[0183] In a possible implementation, the second target access network device 120 acquires the cell change cause indication from the terminal device includes: sending a request for historical information of the terminal device to the terminal device; and receiving the historical information from the terminal device, the historical information including the cell change cause indication. Sending the cell change cause indication together with the historical information to the second target access network device 120 can avoid additional signaling overhead.

[0184] In a possible implementation, the acquiring the cell change cause indication includes: acquiring the cell change cause indication from a source access network device to which the source cell belongs.

[0185] In a possible implementation, the acquiring the cell change cause indication from the source access network device includes: acquiring historical information of the terminal device from the source access network device, the historical information including the cell change cause indication. Sending the cell change cause indication together with the historical information to the second target access network device 120 can avoid additional signaling overhead.

[0186] In a possible implementation, the acquiring the cell change cause indication includes: acquiring the cell change cause indication from a first target access network device to which the first target cell belongs.

[0187] In a possible implementation, the acquiring the cell change cause indication from the first target access network device includes: acquiring second historical information of the terminal device from the first target access network device, the second historical information including the cell change cause indication, the second historical information including first historical information of the terminal device acquired by the first target access network device from a source access network device to which a source cell belongs, and / or third historical information of the terminal device recorded by the first target access network device. Sending the cell change cause indication together with the historical information to the second target access network device 120 can avoid additional signaling overhead.

[0188] In a possible implementation of the method 900, 1000 or 1100, the cell change cause indication includes: a reason for which the terminal device changes out of the source cell or changes out of the first target cell, and / or a reason for which the terminal device changes to the first target cell or changes to the second target cell.

[0189] In a possible implementation of the method 900, 1000 or 1100, the cell change cause indication indicates that at least one of: the first cell change is associated with a voice fallback procedure of the terminal device from the source cell to the first target cell; and the second cell change is associated with a fast return procedure of the terminal device from the first target cell to the second target cell. In this way, optimization of a redundant inter-system handover parameter triggered by an invalid voice service procedure of the terminal device is avoided.

[0190] In a possible implementation of the method 900, 1000 or 1100, the voice fallback procedure comprises a normal call voice fallback procedure or an emergency call voice fallback procedure, and the fast return procedure comprises a normal call voice fast return procedure or an emergency call voice fast return procedure.

[0191] In a possible implementation of the method 900, 1000 or 1100, the first RAT is one of a 2G RAT, a 3G RAT and a 4G RAT, and the second RAT is a 5G RAT.

[0192] With the method 900, 1000 or 1100, triggering optimization of invalid and redundant inter-system handover parameters can be avoided, system resources are saved, and communication efficiency is improved.

[0193] The above description of possible implementations of the application applies equally to the method 900, 1000 and 1100, and thus is not repeated. Figures 1 to 8 The above description of possible implementations of the application applies equally to the method 900, 1000 and 1100, and thus is not repeated.

[0194] Figure 12 A schematic block diagram of a communication apparatus 1200 is shown, according to a possible implementation of the application. The communication apparatus 1200 can be implemented as a device or a chip in a device, and the scope of the application is not limited in this respect. The communication apparatus 1200 can comprise a plurality of modules for performing the corresponding steps of the method 900 as discussed in Figure 9 , for example. Figure 1 , 2A or 2B.

[0195] As shown in Figure 12 , the communication apparatus 1200 comprises an obtaining unit 1210 and a sending unit 1220. The obtaining unit 1210 is configured to obtain a cell change cause indication. The cell change cause indication indicates that a first cell change of a terminal device from a source cell to a first target cell or a second cell change of the terminal device from the first target cell to a second target cell is associated with a communication service of the terminal device, the first target cell adopts a first RAT, and the source cell and the second target cell adopt a second RAT different from the first RAT. The sending unit 1220 is configured to send the cell change cause indication to a second target access network device to which the second target cell belongs.

[0196] In a possible implementation, the obtaining unit 1210 is configured to obtain the cell change cause indication from a source access network device to which the source cell belongs.

[0197] In a possible implementation, the obtaining unit 1210 is configured to receive, from the source access network device, a first cell change command associated with the first cell change, the first cell change command comprising the cell change cause indication. Transmitting the cell change cause indication to the communication apparatus 1200 via the first cell change command can avoid extra signaling overhead.

[0198] In a possible implementation, the obtaining unit 1210 is configured to obtain the cell change cause indication from a first target access network device to which the first target cell belongs.

[0199] In a possible implementation, the obtaining unit 1210 is configured to receive, from the first target access network device, a second cell change command associated with the second cell change, the second cell change command comprising the cell change cause indication. Transmitting the cell change cause indication to the communication apparatus 1200 via the second cell change command can avoid extra signaling overhead.

[0200] In a possible implementation, the communication apparatus 1200 further includes a receiving unit. The receiving unit is configured to receive, from the second target access network device, a request for history information of the communication apparatus 1200. The transmitting unit 1220 is configured to transmit, to the second target access network device, the history information, the history information comprising the cell change cause indication. Transmitting the cell change cause indication to the second target access network device together with the history information can avoid extra signaling overhead.

[0201] Figure 13 A schematic block diagram of an access network device 1300 according to a possible implementation of the present application is shown. The access network device 1300 can be implemented as a device or a chip in a device, and the scope of the present application is not limited in this respect. The access network device 1300 can include a plurality of modules to perform corresponding steps in the method 1000 as discussed in Figure 10 , for example. Figure 1 , 2A or 2B.

[0202] As discussed in Figure 13As shown, the access network device 1300 includes an obtaining unit 1310 and a providing unit 1320. The obtaining unit 1310 is configured to obtain a cell change cause indication, the cell change cause indication indicating that a first cell change of a terminal device from a source cell to a first target cell of the access network device 1300 or a second cell change from the first target cell to a second target cell is associated with a communication service of the terminal device, the first target cell adopting a first RAT, the source cell and the second target cell adopting a second RAT different from the first RAT. The providing unit 1320 is configured to provide the cell change cause indication to a second target access network device to which the second target cell belongs.

[0203] In a possible implementation, the obtaining unit 1310 is configured to obtain the cell change cause indication from a source access network device to which the source cell belongs.

[0204] In a possible implementation, the obtaining unit 1310 is configured to obtain, from the source access network device, historical information of the terminal device, the historical information including the cell change cause indication. Sending the cell change cause indication together with the historical information to the access network device 1300 can avoid additional signaling overhead.

[0205] In a possible implementation, the providing unit 1320 is configured to provide, to the second target access network device, historical information of the terminal device, the historical information including the cell change cause indication. Sending the cell change cause indication together with the historical information to the second target access network device can avoid additional signaling overhead.

[0206] In a possible implementation, the providing unit 1320 is configured to provide, to the second target access network device, a handover request for the second cell change, the handover request including the cell change cause indication. Sending the cell change cause indication together with the handover request to the second target access network device can avoid additional signaling overhead.

[0207] Figure 14 A schematic block diagram of an access network device 1400 is shown, which is according to a possible implementation of the present application. The access network device 1400 can be implemented as a device or a chip in a device, and the scope of the present application is not limited in this respect. The access network device 1400 can include a plurality of modules to perform corresponding steps in the method 1100 as discussed in Figure 11 , for example. Figure 1 , 2A or a part of the second target access network device 120 as shown in 2B.

[0208] As Figure 14As shown, the access network device 1400 comprises an obtaining unit 1410 and a providing unit 1420. The obtaining unit 1410 is configured to obtain a cell change cause indication, the cell change cause indication indicating that a first cell change of a terminal device from a source cell to a first target cell or a second cell change of the terminal device from the first target cell to a second target cell of the access network device 1400 is associated with a communication service of the terminal device, the first target cell adopting a first RAT, the source cell and the second target cell adopting a second RAT different from the first RAT. The determining unit 1420 is configured to determine, based on the cell change cause indication, that the first cell change and the second cell change are irrelevant to an inter-system ping-pong event.

[0209] In a possible implementation, the cell change cause indication indicates that at least one of the following: the first cell change is associated with a voice fallback procedure of the terminal device from the source cell to the first target cell; and the second cell change is associated with a fast return procedure of the terminal device from the first target cell to the second target cell. In this way, an invalid and redundant optimization of inter-system handover parameters triggered by a voice service procedure of the terminal device is avoided.

[0210] In a possible implementation, the obtaining unit 1410 is configured to obtain the cell change cause indication from the terminal device.

[0211] In a possible implementation, the obtaining unit 1410 is configured to send, to the terminal device, a request for historical information of the terminal device; and receive the historical information from the terminal device, the historical information comprising the cell change cause indication. Sending the cell change cause indication together with the historical information to the access network device 1400 can avoid additional signaling overhead.

[0212] In a possible implementation, the obtaining unit 1410 is configured to obtain the cell change cause indication from a source access network device to which the source cell belongs.

[0213] In a possible implementation, the obtaining unit 1410 is configured to obtain, from the source access network device, historical information of the terminal device, the historical information comprising the cell change cause indication. Sending the cell change cause indication together with the historical information to the access network device 1400 can avoid additional signaling overhead.

[0214] In a possible implementation, the obtaining unit 1410 is configured to obtain the cell change cause indication from a first target access network device to which the first target cell belongs.

[0215] In a possible implementation, the obtaining unit 1410 is configured to obtain, from the first target access network device, historical information of the terminal device, the historical information comprising the cell change cause indication. Sending the cell change cause indication together with the historical information to the access network device 1400 can avoid additional signaling overhead.

[0216] In one possible implementation of the communication device 1200, access network device 1300, or access network device 1400, the cell change reason indication includes: the reason why the terminal device changes out of the source cell or changes out of the first target cell, and / or the reason why the terminal device changes to the first target cell or changes to the second target cell.

[0217] In one possible implementation of the communication device 1200, access network device 1300, or access network device 1400, the cell change reason indication specifies at least one of the following: a first cell change is associated with a voice fallback procedure from the source cell to the first target cell of the terminal device; and a second cell change is associated with a fast return procedure from the first target cell to the second target cell of the terminal device. This avoids the terminal device's voice service procedures triggering invalid and redundant optimization of inter-system handover parameters.

[0218] In one possible implementation of the communication device 1200, access network device 1300, or access network device 1400, the voice fallback process includes a normal call voice fallback process or an emergency call voice fallback process. For example, the communication device may initiate a voice service by switching or redirecting from a 5G cell to an LTE cell. The fast return process includes a normal call voice fast return process or an emergency call voice fast return process. For example, after the voice service of the communication device ends, it may return from an LTE cell to a 5G cell by switching or redirecting.

[0219] In one possible implementation of the communication device 1200, access network device 1300, or access network device 1400, the first RAT is one of 2G RAT, 3G RAT, and 4G RAT, and the second RAT is 5G RAT.

[0220] The above is for reference only. Figures 1 to 11 The details of the possible implementations of this application described also apply to the communication device 1200, the access network device 1300, and the access network device 1400, and therefore will not be repeated hereafter.

[0221] Figure 15 This is a simplified block diagram of an example device 1500 suitable for implementing possible implementations of this application. Device 1500 can be used to implement, for example... Figure 1 , 2A The device 1500 may be the terminal device 140, the first target access network device 110, or the second target access network device 120 shown in Figure 2B. As shown, the device 1500 includes one or more processors (or processing units) 1510, and may also include one or more memories 1520 coupled to the processor 1510, and may also include a communication interface 1540 coupled to the processor 1510.

[0222] The communication interface 1540 can be used to communicate with other devices or apparatuses, such as transmission or reception of data and / or signals. The communication interface 1540 can have at least one communication interface for communication. The communication interface can include any interface necessary to communicate with other devices. Illustratively, the communication interface can be a transceiver, circuit, bus, module, or other type of communication interface.

[0223] The processor 1510 can include, but is not limited to, at least one of the following: a general-purpose computer, a special-purpose computer, a microcontroller, a Digital Signal Processor (DSP), or one or more of a controller-based multi-core controller architecture. The device 1500 can have multiple processors, such as an application-specific integrated circuit chip, which is time-dependent on a clock synchronized with the main processor.

[0224] The memory 1520 can include one or more non-volatile memories and one or more volatile memories. Examples of non-volatile memories include, but are not limited to, at least one of the following: Read-Only-Memory (ROM) 1524, Electrically Programmable Read-Only-Memory (EPROM), flash memory, hard disk, Compact Disc (CD), Digital Video Disk (DVD), or other magnetic storage and / or optical storage. Examples of volatile memories include, but are not limited to, at least one of the following: Random Access Memory (RAM) 1522, or other volatile memories that do not last during power-off duration.

[0225] The computer program 1530 includes computer executable instructions executed by the associated processor 1510. The program 1530 can be stored in the ROM 1520. The processor 1510 can perform any suitable action and processing by loading the program 1530 into the RAM 1520.

[0226] Possible implementations of the present application can be implemented by means of the program 1530, such that the device 1500 can perform any of the processes discussed with reference to Figures 2 to Figure 11 Possible implementations of the present application can also be implemented by hardware or by a combination of software and hardware.

[0227] In some embodiments, the program 1530 can be tangibly embodied in a computer- readable medium, which can include a memory device in the device 1500 (such as the memory 1520) or another storage device accessible by the device 1500. The program 1530 can be loaded into the RAM 1522 from the computer-readable medium for execution by the computing device. The computer-readable medium can include any type of tangible non-transitory storage medium, for example, ROM, EPROM, flash memory, hard disk, CD-ROM, DVD, etc.

[0228] The present application also provides a communication system. The communication system includes the communication apparatus 1200, the access network device 1300 and the access network device 1400 as described above.

[0229] In general, the various possible implementations of the present application can be realized in hardware or special-purpose circuits, software, logic or any combination thereof. Some aspects can be realized in hardware, while other aspects can be realized in firmware or software which can be executed by a controller, microprocessor or other computing device. While various aspects of possible implementations of the present application are illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein can be implemented in, as non-limiting examples, hardware, software, firmware, special-purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

[0230] The present application also provides at least one computer program product which is tangibly stored on a non-transitory computer-readable storage medium. The computer program product includes computer-executable instructions, such as those included in program modules, executed by devices at a target real or virtual processor to perform the processes / methods as described above with reference to FIGS. 2 to Figure 11 Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, etc. that perform particular tasks or implement particular abstract data types. In various possible implementations, the functionality of program modules can be combined or split between program modules as desired. Machine-executable instructions for program modules can be executed within the local or distributed device. In a distributed device, program modules can be located in both local and remote memory storage devices.

[0231] Program code for carrying out the methods of the present application can be written in any combination of one or more programming languages. This program code can be provided to a processor or controller of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the program code, when executed by the processor or controller, produces the functions / operations specified in the flowcharts and / or block diagrams. The program code can be embodied in whole or in part within a machine-readable medium. The machine-readable medium can be a storage medium, a memory device, or a memory on a processor, or a combination thereof.

[0232] In the context of the present application, a machine-readable medium can be a tangible medium that can contain or store program for use by or in connection with an instruction execution system, apparatus, or device. The machine-readable medium can be a machine-readable signal medium or a machine-readable storage medium. The machine-readable medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of the machine-readable storage medium would include an electrical connection based on one or more wires, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0233] Moreover, while operations can be depicted in the drawings in a particular, chronological order, this should not be understood as requiring or implying that the operations be performed in that order - and certainly that all illustrated operations be performed, or that they be performed pursuant to a particular chronological arrangement. In certain circumstances, multitasking and parallel processing can be advantageous. Likewise, while several specific implementation details have been included in the above discussion, these should not be taken as indicative of certain features being required in all circumstances. Certain features described in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable sub-combination.

[0234] Although the subject matter has been described in language specific to structural features and / or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

1. A communication method, comprising: obtaining, by a terminal device, a handover cause indication, the handover cause indication indicating that a first handover of the terminal device from a source cell to a first target cell or a second handover of the terminal device from the first target cell to a second target cell is associated with a communication service of the terminal device, the first target cell using a first radio access technology, the source cell and the second target cell using a second radio access technology different from the first radio access technology; and sending, by the terminal device, the handover cause indication to a second target access network device to which the second target cell belongs, wherein the handover cause indication is used to determine, by the second target access network device, that the first handover or the second handover is not associated with an inter-system ping-pong event. 2.The method of claim 1, wherein the handover cause indication comprises: a cause of a handout of the terminal device from the source cell or a handout of the terminal device from the first target cell, and / or a cause of a handin of the terminal device to the first target cell or a cause of a handin of a cell to the second target cell. 3.The method of claim 1 or 2, wherein the handover cause indication indicates at least one of: the first handover is associated with a voice fallback procedure of the terminal device from the source cell to the first target cell; and the second handover is associated with a fast return procedure of the terminal device from the first target cell to the second target cell. 4.The method of claim 3, further comprising: obtaining, by the terminal device, at least one of: an indication of a type of the voice fallback procedure, the indication of the type of the voice fallback procedure indicating that the voice fallback procedure is an evolved packet system voice fallback procedure or an inter-radio access technology voice fallback procedure; and an indication of a cell handover execution mode, the cell handover execution mode comprising a handout. 5.The method of claim 3, wherein the voice fallback procedure comprises a normal call voice fallback procedure or an emergency call voice fallback procedure, and the fast return procedure comprises a normal call voice fast return procedure or an emergency call voice fast return procedure. 6.The method of claim 1, wherein the obtaining, by the terminal device, of the handover cause indication comprises: obtaining, by the terminal device, the handover cause indication from a source access network device to which the source cell belongs. 7.The method of claim 6, wherein the obtaining, by the terminal device, of the handover cause indication from the source access network device comprises: receiving, by the terminal device, a first handover command associated with the first handover from the source access network device, the first handover command comprising the handover cause indication. 8.The method of claim 1, wherein the obtaining, by the terminal device, of the handover cause indication comprises: obtaining, by the terminal device, the handover cause indication from a first target access network device to which the first target cell belongs. 9.The method of claim 8, wherein the obtaining, by the terminal device, of the handover cause indication from the first target access network device comprises: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The terminal device receives, from the first target access network device, a second handover command associated with the second handover, the second handover command comprising the handover cause indication.

10. The method of claim 1, wherein the terminal device sending the handover cause indication to the second target access network device comprises: The terminal device sends, to the second target access network device, a radio resource control reconfiguration complete message in response to receiving, from a first target access network device to which the first target cell belongs, a second handover command associated with the second handover, the radio resource control reconfiguration complete message comprising the handover cause indication.

11. The method of claim 1, wherein the terminal device sending the handover cause indication to the second target access network device comprises: The terminal device receives, from the second target access network device, a request for historical information of the terminal device; and The terminal device sends, to the second target access network device, the historical information, the historical information comprising the handover cause indication.

12. A communication method, comprising: A first target access network device obtaining a handover cause indication indicating that a first handover of a terminal device from a source cell to a first target cell of the first target access network device or a second handover from the first target cell to a second target cell is associated with a communication service of the terminal device, the first target cell employing a first radio access technology, the source cell and the second target cell employing a second radio access technology different from the first radio access technology; and The first target access network device providing the handover cause indication to a second target access network device to which the second target cell belongs, wherein the handover cause indication is used by the second target access network device to determine that the first handover or the second handover is not associated with an inter-system ping-pong event.

13. The method of claim 12, wherein the handover cause indication comprises: a reason for the terminal device to hand over out of the source cell or to hand over out of the first target cell, and / or a reason for the terminal device to hand over to the first target cell or to hand over to the second target cell.

14. The method of claim 12, wherein the handover cause indication indicates at least one of: the first handover is associated with a voice fallback procedure of the terminal device from the source cell to the first target cell; and the second handover is associated with a fast return procedure of the terminal device from the first target cell to the second target cell.

15. The method of claim 12, further comprising: The first target access network device obtaining at least one of: an indication of a type of voice fallback procedure, the indication of the type of voice fallback procedure indicating that the voice fallback procedure is an evolved packet system voice fallback procedure or an inter-radio access technology voice fallback procedure; and an indication of a cell handover execution mode, the cell handover execution mode comprising a handover. ​ ​ 16. The method according to claim 14, wherein the voice fallback process includes a normal call voice fallback process or an emergency call voice fallback process, and the fast return process includes a normal call voice fast return process or an emergency call voice fast return process.

17. The method of claim 12, wherein the first target access network device obtains the handover reason indication by: The first target access network device obtains the handover reason indication from the source access network device to which the source cell belongs.

18. The method of claim 17, wherein obtaining the handover reason indication from the source access network device by the first target access network device comprises: The first target access network device obtains the first historical information of the terminal device from the source access network device, and the first historical information includes the handover reason indication.

19. The method of claim 18, wherein the first target access network device provides the handover reason indication to the second target access network device comprising: The first target access network device provides the second target access network device with the second historical information of the terminal device, the second historical information including the handover reason indication, the second historical information including the first historical information, and / or, the third historical information of the terminal device recorded by the first target access network device.

20. The method according to any one of claims 12 to 19, wherein the first target access network device provides the handover reason indication to the second target access network device comprising: The first target access network device sends a handover request to the second target access network device for the second handover, the handover request including the handover reason indication.

21. A communication method, comprising: The second target access network device obtains a handover reason indication, which indicates that a first handover of the terminal device from the source cell to the first target cell or a second handover from the first cell to the second target cell of the second target access network device is associated with the communication service of the terminal device. The first target cell uses a first radio access technology, and the source cell and the second target cell use a second radio access technology different from the first radio access technology. Based on the handover reason indication, the second target access network device determines that the first handover and the second handover are unrelated to the inter-system ping-pong event.

22. The method of claim 21, wherein the switching reason indication includes: The reason why the terminal device switches out of the source cell or the first target cell, and / or, The reason for the terminal device switching to the first target cell or the reason for switching to the second target cell.

23. The method of claim 21 or 22, wherein the switching reason indication specifies at least one of the following: The first handover is associated with the voice fallback process of the terminal device from the source cell to the first target cell; or The second handover is associated with the fast return process of the terminal device from the first target cell to the second target cell.

24. The method of claim 23, further comprising: The second target access network device acquires at least one of the following: The indication of the type of the voice fallback procedure indicates that the voice fallback procedure is an evolved packet system voice fallback procedure or an inter-radio access technology voice fallback procedure. as well as Instructions for cell handover execution mode, wherein the cell handover execution mode includes handover.

25. The method according to claim 23, wherein the voice fallback process includes a normal call voice fallback process or an emergency call voice fallback process, and the fast return process includes a normal call voice fast return process or an emergency call voice fast return process.

26. The method of claim 21, wherein the second target access network device obtains the handover reason indication by: Obtain the switching reason indication from the terminal device.

27. The method of claim 26, wherein the second target access network device obtains the handover reason indication from the terminal device by: The terminal device receives a radio resource control reconfiguration complete message, which includes the handover reason indication.

28. The method of claim 26, wherein the second target access network device obtains the handover reason indication from the terminal device by: Send a request for historical information of the terminal device to the terminal device; as well as The historical information is received from the terminal device, and the historical information includes the switching reason indication.

29. The method of claim 21, wherein obtaining the switching reason indication comprises: The handover reason indication is obtained from the first target access network device to which the first target cell belongs.

30. The method of claim 29, wherein obtaining the handover reason indication from the first target access network device comprises: The second historical information of the terminal device is obtained from the first target access network device. The second historical information includes the handover reason indication, the first historical information of the terminal device obtained by the first target access network device from the source access network device to which the source cell belongs, and / or the third historical information of the terminal device recorded by the first target access network device.

31. The method of claim 29, wherein obtaining the handover reason indication from the first target access network device comprises: The first target access network device receives a cell handover request for the second handover, the cell handover request including the handover reason indication.

32. A communication method, comprising: The source access network device obtains a handover reason indication, wherein the handover reason indication is a first handover or a second handover associated with the communication service of the terminal device, wherein the first handover includes the terminal device switching from a source cell provided by the source access network device to a first target cell, and the second handover includes the terminal device switching from the first target cell to a second target cell, wherein the first target cell uses a first radio access technology, and the source cell and the second target cell use a second radio access technology; and Based on the handover reason indication, the source access network device determines that the first handover and the second handover are unrelated to the inter-system ping-pong event.

33. The method of claim 32, wherein the source access network device obtains the handover reason indication by: Receive an inter-system ping-pong event report from the second target access network device to which the second target cell belongs, the inter-system ping-pong event report including the handover reason indication.

34. The method of claim 32, wherein the switching reason indication specifies at least one of the following: The first handover is associated with the voice fallback process of the terminal device from the source cell to the first target cell; and The second handover is associated with the fast return process of the terminal device from the first target cell to the second target cell.

35. The method of claim 32, further comprising: The source access network device acquires at least one of the following: An indication of the type of voice fallback procedure, wherein the voice fallback procedure is an evolved packet system voice fallback procedure or an inter-radio access technology voice fallback procedure. as well as Instructions for cell handover execution mode, wherein the cell handover execution mode includes handover.

36. A terminal device comprising a unit for performing the method according to any one of claims 1 to 11.

37. An access network device comprising a unit for performing the method according to any one of claims 12 to 20.

38. An access network device comprising a unit for performing the method according to any one of claims 21 to 31.

39. An access network device comprising a unit for performing the method according to any one of claims 32 to 35.

40. A communication device, comprising: At least one processor; as well as At least one memory coupled to the at least one processor and storing instructions for execution by the at least one processor, the instructions, when executed by the at least one processor, causing the communication device to implement the method according to any one of claims 1 to 11, 12 to 20, 21 to 31 and 32 to 35.

41. A computer-readable storage medium storing a computer program that, when executed by a processor, implements the method according to any one of claims 1 to 11, 12 to 20, 21 to 31, and 32 to 35.

42. A chip configured to perform the method according to any one of claims 1 to 11, 12 to 20, 21 to 31 and 32 to 35.

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