Data transmission method, communication device and communication system

Abstract

Embodiments of the present application provide a data transmission method, a communication device and a communication system. The method comprises: receiving, by an access network device, a first downlink broadcast data packet from a user plane network element, the first downlink broadcast data packet carrying first data and a first sequence number; determining, by the access network device, a first PDCP sequence number corresponding to the first sequence number; and sending, by the access network device, a second downlink broadcast data packet to a terminal device, the second downlink broadcast data packet carrying the first data and the first PDCP sequence number. A sequence number is uniformly allocated to a downlink data broadcast data packet by a user plane network element, and then the source access network device and the target access network device map the sequence number allocated by the user plane network element to a PDCP sequence number. In this way, the source access network device and the target access network device can allocate the same PDCP sequence number to the same downlink data broadcast data packet, and when packet loss occurs, the terminal device can avoid discarding data packets that have not been repeatedly received, thereby improving the reliability of data transmission.

Description

Technical Field

[0001] This application relates to the field of communication technology, and in particular to data transmission methods, communication devices, and communication systems. Background Technology

[0002] Terminal devices may switch access network devices due to relocation or other reasons. To reduce air interface interruption latency during access network device handover, one handover method is as follows: During the handover process, the user plane network element simultaneously sends the same downlink data packet (also known as a downlink dual-cast data packet) to both the source and target access network devices. The source and target access network devices assign a Packet Data Convergence Protocol (PDCP) sequence number to the downlink data packet, and then each sends the downlink data packet carrying the PDCP sequence number to the same terminal device.

[0003] Under normal circumstances, the source access network device and the target access network device assign the same PDCP sequence number to the same downlink bicast data packet. Then, the terminal device performs deduplication on the received downlink bicast data packets from the source access network device and the target access network device based on the PDCP sequence number, that is, it discards one of the two identical downlink bicast data packets received.

[0004] However, when user plane network elements send downlink duocast data packets to source or target access network devices, packet loss may occur. This may cause the source and target access network devices to assign different PDCP sequence numbers to the same downlink duocast data packets, or to assign the same PDCP sequence number to different downlink duocast data packets. Consequently, when the terminal device deduplicates data packets, it may discard data packets that have not been received repeatedly, thus causing the terminal device to miss information from the access network device and reduce the reliability of data transmission. Summary of the Invention

[0005] This application provides a data transmission method, a communication device, and a communication system to prevent terminal devices from discarding data packets that have not been received repeatedly, ensuring that terminal devices do not miss information from access network devices, thereby improving the reliability of data transmission.

[0006] In a first aspect, embodiments of this application provide a data transmission method, comprising: an access network device receiving a first downlink dual-cast data packet from a user plane network element, the first downlink dual-cast data packet carrying first data and a first sequence number; the access network device determining a first Packet Data Convergence Protocol (PDCP) sequence number corresponding to the first sequence number; and the access network device sending a second downlink dual-cast data packet to a terminal device, the second downlink dual-cast data packet carrying the first data and the first PDCP sequence number.

[0007] Based on the above scheme, the user plane network element uniformly assigns sequence numbers to downlink data dualcast packets. Then, the source access network device and the target access network device map the sequence numbers assigned by the user plane network element to PDCP sequence numbers. This ensures that the source access network device and the target access network device assign the same PDCP sequence number to the same downlink data dualcast packets. In this way, when packet loss occurs, the terminal device is prevented from discarding data packets that have not been received repeatedly. As a result, the terminal device will not miss information from the access network device, avoids data loss or interruption during handover, and improves the reliability of data transmission.

[0008] In one possible implementation, the first sequence number is N3.

[0009] In one possible implementation, the access network device determines the first PDCP sequence number corresponding to the first sequence number, including: the access network device determines the first PDCP COUNT value corresponding to the first sequence number; the access network device determines the first PDCP sequence number corresponding to the first PDCP COUNT value.

[0010] In one possible implementation, the access network device is a source access network device; before receiving a first downlink dual-cast data packet from a user plane network element, the source access network device receives a third downlink dual-cast data packet from the user plane network element, the third downlink dual-cast data packet carrying second data and a second sequence number; the source access network device determines a mapping relationship based on the second sequence number and the second PDCP sequence number corresponding to the third downlink dual-cast data packet, the mapping relationship being used to determine the first PDCP sequence number corresponding to the first sequence number.

[0011] In one possible implementation, the source access network device sends indication information to the target access network device, the indication information being used to indicate the mapping relationship.

[0012] In one possible implementation, the indication information carries the second sequence number and the corresponding second PDCP sequence number; or, the indication information carries the difference between the second sequence number and the second PDCP sequence number; or, the indication information carries the second sequence number and the corresponding second PDCP COUNT value, the second PDCP COUNT value corresponding to the second PDCP sequence number; or, the indication information carries the difference between the second sequence number and the second PDCP COUNT value, the second PDCP COUNT value corresponding to the second PDCP sequence number.

[0013] Based on the above scheme, the source access network device can accurately determine the mapping relationship between the sequence number allocated by the UPF and the PDCP COUNT value (or PDCP sequence number) that the source access network device needs to allocate. Then, it indicates this mapping relationship to the target access network device through indication information. Thus, the target access network device can determine the mapping relationship between the sequence number allocated by the UPF and the PDCP COUNT value (or PDCP sequence number) that the target access network device needs to allocate. Consequently, both the source and target access network devices can accurately determine the PDCP sequence number corresponding to the sequence number in the downlink dualcast data packets received from the UPF based on this mapping relationship.

[0014] In one possible implementation, the source access network device makes a first request to the first device, the first request carrying information about the Quality of Service (QoS) flow group requested for bicast, the first device being the target access network device or a mobility management network element.

[0015] The source access network device receives a first response from the first device, the first response carrying information about a QoS stream group that accepts duocast, the QoS stream group that accepts duocast being part or all of the QoS stream group that requested duocast.

[0016] In one possible implementation, the access network device is a target access network device; the target access network device receives indication information from the source access network device, the indication information being used to indicate a mapping relationship, the mapping relationship being used to determine the first PDCP sequence number corresponding to the first sequence number.

[0017] In one possible implementation, the target access network device receives information about a QoS flow group requesting duocast; the target access network device determines information about a QoS flow group to accept duocast based on the information about the QoS flow group requesting duocast; and the target access network device sends the information about the QoS flow group to accept duocast to the session management network element.

[0018] In one possible implementation, the target access network device receives information about a QoS flow group requesting duocast, including: the target access network device receiving a handover request message from a source access network device, the handover request message carrying information about the QoS flow group requesting duocast; or, the target access network device receiving a handover request message from the mobility management network element, the handover request message carrying information about the QoS flow group requesting duocast.

[0019] Secondly, embodiments of this application provide a data transmission method, comprising: a user plane network element receiving configuration information, the configuration information carrying information of a QoS flow group accepting bicast, the QoS flow group accepting bicast including one or more QoS flow groups, the first QoS flow group being any one of the QoS flow groups accepting bicast; the user plane network element sequentially assigning an N3 sequence number to the downlink bicast data packets of the first QoS flow group.

[0020] Based on the above scheme, it is possible to configure the QoS flow group information for receiving biscast for user plane network elements, and then the user plane network elements can sequentially assign N3 sequence numbers to the downlink data packets of the QoS flow in the QoS flow group that receives biscast.

[0021] In one possible implementation, the user plane network element sends downlink bicast packets of the first QoS flow group to both the source access network device and the target access network device.

[0022] In one possible implementation, the QoS flows in each QoS flow group of the bicast-accepting QoS flow group are associated with the same data radio bearer, and the QoS flows in different QoS flow groups are associated with different data radio bearers.

[0023] In one possible implementation, the N3 sequence number is carried within the downlink protocol data unit (PDU) session information in the downlink bicast data packet of the first QoS flow group.

[0024] Thirdly, embodiments of this application provide a communication device, which may be an access network device or a chip for an access network device. The device has the function of implementing the first aspect or various possible implementation methods based on the first aspect. This function can be implemented in hardware or by hardware executing corresponding software. The hardware or software includes one or more modules corresponding to the above-described functions.

[0025] Fourthly, embodiments of this application provide a communication device, which can be a user plane network element or a chip for a user plane network element. The device has the function of implementing the second aspect described above or various possible implementation methods based on the second aspect. This function can be implemented in hardware or by hardware executing corresponding software. The hardware or software includes one or more modules corresponding to the above-described functions.

[0026] Fifthly, embodiments of this application provide a communication device including a processor coupled to a memory for storing programs or instructions. When the program or instructions are executed by the processor, the device implements the method of the first aspect, various possible implementations based on the first aspect, the method of the second aspect, or various possible implementations based on the second aspect. The memory may be located within or outside the device. The processor may include one or more processors.

[0027] In a sixth aspect, embodiments of this application provide a communication apparatus, including units or means for performing the methods of the first aspect, various possible implementations of the first aspect, the methods of the second aspect, or various steps of various possible implementations of the second aspect.

[0028] In a seventh aspect, embodiments of this application provide a communication device, including a processor and an interface circuit. The processor is used to control the interface circuit to communicate with other devices and to execute the method of the first aspect, various possible implementations of the first aspect, the method of the second aspect, or various possible implementations of the second aspect. The processor may include one or more.

[0029] Eighthly, embodiments of this application also provide a computer-readable storage medium including instructions that, when executed on a computer, cause the computer to perform the method of the first aspect, various possible implementations of the first aspect, the method of the second aspect, or various possible implementations of the second aspect.

[0030] In a ninth aspect, embodiments of this application also provide a computer program product that, when run on a computer, causes the computer to execute the method of the first aspect, various possible implementations of the first aspect, the method of the second aspect, or various possible implementations of the second aspect.

[0031] In a tenth aspect, embodiments of this application also provide a chip system including a processor coupled to a memory. The memory stores programs or instructions, which, when executed by the processor, cause the chip system to implement the method of the first aspect, various possible implementations based on the first aspect, the method of the second aspect, or various possible implementations based on the second aspect. The memory may be located within or outside the chip system. The processor may include one or more processors. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the 5G network architecture applicable to the embodiments of this application;

[0033] Figure 2 This is a diagram illustrating the packet loss process.

[0034] Figure 3(a) is a schematic diagram of a data transmission method provided in an embodiment of this application;

[0035] Figure 3(b) is a schematic diagram of another data transmission method provided in an embodiment of this application;

[0036] Figure 3(c) is a schematic diagram of another data transmission method provided in an embodiment of this application;

[0037] Figure 3(d) is a schematic diagram of another data transmission method provided in an embodiment of this application;

[0038] Figure 3(e) is a schematic diagram of another data transmission method provided in an embodiment of this application;

[0039] Figure 4 This is a schematic diagram of the data packet sending process;

[0040] Figure 5 This is a schematic diagram illustrating yet another data transmission method provided in an embodiment of this application;

[0041] Figure 6 This is a schematic diagram illustrating yet another data transmission method provided in an embodiment of this application;

[0042] Figure 7 This is a schematic diagram illustrating yet another data transmission method provided in an embodiment of this application;

[0043] Figure 8 A schematic diagram of a communication device provided in an embodiment of this application;

[0044] Figure 9 This is a schematic diagram of another communication device provided in an embodiment of this application. Detailed Implementation

[0045] refer to Figure 1 This is a schematic diagram of the fifth-generation (5G) network architecture applicable to the embodiments of this application. Figure 1 The 5G network architecture shown consists of three parts: terminal equipment, data network (DN), and operator network. The functions of some of these network elements are briefly described below.

[0046] The operator network may include one or more of the following network elements: Authentication Server Function (AUSF) network element, Network Exposure Function (NEF) network element, Policy Control Function (PCF) network element, Unified Data Management (UDM) network element, Unified Data Repository (UDR) network element, Network Repository Function (NRF) network element, Application Function (AF) network element, Access and Mobility Management Function (AMF) network element, Session Management Function (SMF) network element, and Radio Access Network (RAN) user plane function (UPF) network element. The portion of the operator network excluding the radio access network can be referred to as the core network.

[0047] In specific implementations, the terminal device in this application embodiment can be a device used to implement wireless communication functions. Specifically, the terminal device can be user equipment (UE), access terminal, terminal unit, terminal station, mobile station, mobile station, remote station, remote terminal, mobile device, wireless communication device, terminal agent, or terminal device in a 5G network or a future evolved public land mobile network (PLMN). The access terminal can be a cellular phone, cordless phone, session initiation protocol (SIP) phone, wireless local loop (WLL) station, personal digital assistant (PDA), handheld device with wireless communication functions, computing device or other processing device connected to a wireless modem, in-vehicle device or wearable device, virtual reality (VR) terminal device, augmented reality (AR) terminal device, wireless terminal in industrial control, wireless terminal in autonomous driving, wireless terminal in telemedicine, wireless terminal in smart grid, wireless terminal in transportation safety, wireless terminal in smart city, wireless terminal in smart home, etc. Terminal devices can be mobile or fixed.

[0048] The aforementioned terminal devices can establish connections with the operator's network through interfaces provided by the operator's network (such as N1), and use data and / or voice services provided by the operator's network. The terminal devices can also access the DN (Network Provider) through the operator's network, and use operator services deployed on the DN, and / or services provided by third parties. These third parties can be service providers outside of the operator's network and terminal devices, and can provide other data and / or voice services to the terminal devices. The specific form of these third parties can be determined based on the actual application scenario and is not limited here.

[0049] RAN, as an access network element, is a sub-network of the operator's network and serves as the implementation system between service nodes and terminal equipment within the operator's network. For a terminal device to access the operator's network, it first passes through the RAN, and then connects to the operator's network's service nodes via the RAN. The RAN equipment in this application is a device that provides wireless communication functions for terminal equipment; RAN equipment is also called access network equipment. The RAN equipment in this application includes, but is not limited to: next-generation base stations (gnodeB, gNB), evolved node B (eNB), radio network controllers (RNC), node Bs (NBs), base station controllers (BSCs), base transceiver stations (BTSs), home base stations (e.g., home evolved nodeB, or homenode B, HNB), baseband units (BBUs), transmitting and receiving points (TRPs), transmitting points (TPs), and mobile switching centers, etc.

[0050] The AMF (Automatic Mobility Management) network element primarily performs functions such as mobility management and access authentication / authorization. Additionally, it is responsible for transmitting user policies between the UE and the PCF (Programmable Component Filter).

[0051] The SMF network element mainly performs functions such as session management, execution of control policies issued by the PCF, selection of the UPF, and allocation of Internet Protocol (IP) addresses for the UE.

[0052] UPF network elements, as the interface between the network and the data network, perform functions such as user plane data forwarding, session / flow-based billing statistics, and bandwidth limiting.

[0053] UDM network elements are mainly responsible for managing contract data, user access authorization, and other functions.

[0054] UDR is primarily responsible for storing and retrieving data of various types, such as contract data, strategy data, and application data.

[0055] NEF network elements are primarily used to support the opening of capabilities and events.

[0056] AF (Application Provider) network elements primarily convey application-side requests to the network side, such as Quality of Service (QoS) requirements or user state event subscriptions. AF can be a third-party functional entity or an application service deployed by the operator, such as the IP Multimedia Subsystem (IMS) voice call service.

[0057] The PCF network element is mainly responsible for policy control functions such as billing at the session and service flow levels, QoS bandwidth guarantee and mobility management, and UE policy decision-making.

[0058] NRF network elements can be used to provide network element discovery functionality, providing network element information corresponding to the network element type based on requests from other network elements. NRF also provides network element management services, such as network element registration, updates, deregistration, and network element status subscription and push.

[0059] AUSF network element: mainly responsible for authenticating users to determine whether to allow users or devices to access the network.

[0060] A Domain Provider (DN) is a network located outside of the carrier's network. A carrier's network can connect to multiple DNs, and various services can be deployed on a DN, providing data and / or voice services to terminal devices. For example, a DN might be the private network of a smart factory. Sensors installed in the workshop can act as terminal devices, and a control server for these sensors is deployed within the DN. The control server provides services to the sensors. Sensors can communicate with the control server, receive instructions from it, and transmit the collected sensor data back to the control server accordingly. Another example is a DN serving as an internal office network for a company. Employees' mobile phones or computers can act as terminal devices, accessing information and data resources on the company's internal office network.

[0061] Figure 1 Nausf, Nnef, Npcf, Nudm, Naf, Namf, Nsmf, N1, N2, N3, N4, and N6 are interface sequence numbers. The meanings of these interface sequence numbers can be found in the definitions in the 3GPP standard protocols, and are not limited here.

[0062] It should be noted that, in the embodiments of this application, the mobility management network element can be... Figure 1 The AMF network element shown can also be other network elements in future communication systems that have the functions of the aforementioned AMF network element. The user plane network element can be... Figure 1 The UPF network element shown can also be other network elements in future communication systems that have the functions of the aforementioned UPF network element. The session management network element can be... Figure 1The SMF network element shown can also be other network elements in future communication systems that have the functions of the aforementioned SMF network element. The access network equipment can be... Figure 1 The RAN device shown can also be other network elements in future communication systems that have the functions of the aforementioned RAN device. For ease of explanation, in this embodiment, the mobility management network element is described as the AMF network element, the session management network element as the SMF network element, and the user plane network element as the UPF network element.

[0063] As described in the background section, when a UPF simultaneously sends the same downlink bicast data packet to both the source and destination access network devices, the terminal device may discard data packets that have not been received repeatedly during deduplication. This could lead to the terminal device missing information from the access network device, reducing the reliability of data transmission. A specific example will illustrate this below. Here, "deduplication" refers to discarding duplicate data packets that carry the same data. For instance, when a terminal device receives multiple data packets carrying the same PDCP sequence number, it will retain only one packet and discard the others.

[0064] For ease of explanation, in the embodiments of this application, the PDCP sequence number is also referred to as PDCP SN, where SN is the abbreviation for sequence.

[0065] For example, refer to Figure 2This diagram illustrates the packet loss process. The UPF simultaneously sends downlink dualcast data packets 1, 2, and 3 to both the source and destination access network devices. Normally, the source access network device assigns PDCP SNNX, PDCP SN X+1, and PDCP SN X+2 to the received downlink dualcast data packets 1, 2, and 3, respectively. The source access network device also assigns PDCP SN X, PDCP SN X+1, and PDCP SN X+2 to the received downlink dualcast data packets 1, 2, and 3, respectively. If the source access network device loses downlink dualcast data packet 3 and the destination access network device loses downlink dualcast data packet 2, then the source access network device actually assigns PDCP SN X and PDCP SN X+1 to downlink dualcast data packets 1 and 2, respectively, and the destination access network device actually assigns PDCP SN X and PDCP SN X+1 to downlink dualcast data packets 1 and 3, respectively. After receiving downlink dualcast data packets from both the source and destination access network devices, the terminal device considers downlink dualcast data packets carrying the same PDCP SN to be identical. Therefore, the terminal device assumes that downlink dualcast data packet 2 received from the source access network device and downlink dualcast data packet 3 received from the destination access network device are the same downlink dualcast data packets, and performs a deduplication operation, such as deleting downlink dualcast data packet 2 received from the source access network device or deleting downlink dualcast data packet 3 received from the destination access network device. However, in reality, downlink dualcast data packet 2 received from the source access network device and downlink dualcast data packet 3 received from the destination access network device only carry the same PDCP SN, but do not carry the same downlink data. Therefore, if downlink dual-cast data packet 2 received from the source access network device is deleted, the terminal device will lose the data within downlink dual-cast data packet 2, resulting in the accidental deletion of information that was not received repeatedly. Similarly, if downlink dual-cast data packet 3 received from the target access network device is deleted, the terminal device will also lose the data within downlink dual-cast data packet 3, again resulting in the accidental deletion of information that was not received repeatedly. Thus, the aforementioned packet loss process causes the terminal device to discard data packets that were not received repeatedly, leading to the terminal device missing information from the access network device and reducing the reliability of data transmission.

[0066] To address the aforementioned issues, this application provides a data transmission method. This method ensures that the same PDCP SN is assigned to identical downlink dual-cast data packets, and different PDCP SNs are assigned to different downlink dual-cast data packets. Therefore, in the event of packet loss at the source or target access network device, the terminal device will not discard data packets that have not been repeatedly received during deduplication. This prevents the terminal device from missing information from the access network device, avoids data loss or interruption during handover, and improves the reliability of data transmission.

[0067] Referring to Figure 3(a), a schematic diagram of a data transmission method provided in an embodiment of this application is shown. The method includes the following steps:

[0068] In step 301a, the UPF sends a first downlink dual-cast data packet to the access network device. The first downlink dual-cast data packet carries first data and a first sequence number. Accordingly, the access network device receives the first downlink dual-cast data packet.

[0069] Step 302a: The access network device determines the first PDCP sequence number corresponding to the first sequence number.

[0070] In step 303a, the access network device sends a second downlink dual-cast data packet to the terminal device. The second downlink dual-cast data packet carries the first data and the first PDCP sequence number. Accordingly, the terminal device receives the second downlink dual-cast data packet.

[0071] The aforementioned access network device can be either a source access network device or a target access network device, meaning that the UPF sends the same downlink bicast data packets to both the source and target access network devices.

[0072] Based on the above scheme, the UPF uniformly assigns sequence numbers to downlink data dual-cast packets. Then, the source access network device and the target access network device map the sequence numbers assigned by the UPF to PDCP sequence numbers. This ensures that the source access network device and the target access network device assign the same PDCP sequence number to the same downlink data dual-cast packets, thereby preventing the terminal device from discarding packets that have not been received repeatedly during deduplication. As a result, the terminal device will not miss information from the access network device, avoiding data loss or interruption during handover and improving the reliability of data transmission.

[0073] As one implementation method, UPF uniformly assigns the N3 sequence number to downlink bicast data packets. That is, the first sequence number carried by the aforementioned first downlink bicast data packet is the N3 sequence number.

[0074] As one implementation method, in step 302a above, the method by which the access network device determines the first PDCP sequence number corresponding to the first sequence number can be, for example, that the access network device determines the first PDCP sequence number corresponding to the first sequence number based on the mapping relationship between the sequence number allocated by the UPF and the PDCP sequence number that the access network device needs to allocate. Another example is that the access network device determines the first PDCP COUNT value corresponding to the first sequence number based on the mapping relationship between the sequence number allocated by the UPF and the PDCP count (COUNT) value that the access network device needs to allocate, and then determines the first PDCP sequence number corresponding to the first PDCP COUNT value. Here, one PDCP sequence number can be determined based on one PDCP COUNT value.

[0075] The PDCP COUNT value uniquely identifies a PDCP service data unit (SDU). The PDCP COUNT value consists of the Hyper Frame Number (HFN) and the PDCP SN. Optionally, the length of the HFN is equal to 32 minus the length of the PDCP SN.

[0076] Referring to Figure 3(b), which is a schematic diagram of a data transmission method provided in an embodiment of this application, the method is performed before step 301a above. The method involves the source access network device determining the mapping relationship between the sequence number allocated by the UPF and the PDCP sequence number (or PDCP COUNT value) that the source access network device needs to allocate, and then sending the indication information used to indicate the mapping relationship to the target access network device.

[0077] The method includes the following steps:

[0078] In step 301b, the UPF sends a third downlink bicast data packet to the source access network device. This third downlink bicast data packet carries the second data and the second sequence number. Correspondingly, the source access network device receives this third downlink bicast data packet.

[0079] In step 302b, the UPF sends the aforementioned third downlink bicast data packet to the target access network device. Correspondingly, the target access network device receives the third downlink bicast data packet.

[0080] The third downlink dualcast data packet is one of the first N downlink dualcast data packets sent by the UPF to the source and target access network devices, where N is a positive integer. For example, it could be the first or second downlink dualcast data packet sent by the UPF to the source and target access network devices.

[0081] Step 303b: The source access network device determines the mapping relationship based on the second sequence number and the second PDCP sequence number corresponding to the third downlink dualcast data packet. This mapping relationship can be used to determine the first PDCP sequence number corresponding to the first sequence number.

[0082] The source access network device can obtain the second sequence number from the third downlink dualcast data packet, and determine the second PDCP sequence number corresponding to the third downlink dualcast data packet based on the PDCP sequence number of the downlink data packet preceding the third downlink dualcast data packet. Then, the source access network device can determine the above mapping relationship based on the second sequence number and the second PDCP sequence number.

[0083] In this context, both the first and second serial numbers are assigned by the UPF. One possible method is that both the first and second serial numbers are N3 serial numbers. The following example, where both the first and second serial numbers are N3 serial numbers, illustrates the method for determining the mapping relationship.

[0084] It should be noted that the initial N3 sequence number can be pre-agreed or dynamically configured. For example, the SMF or UPF can indicate the initial value of the downlink N3 sequence number to the source access network equipment.

[0085] Example 1: The third downlink bicast data packet is the first downlink bicast data packet sent by the UPF to both the source and target access network devices. This third downlink bicast data packet carries an N3 sequence number of 1. The source access network device assigns a PDCP sequence number of 100 to the previous downlink data packet (which is a unicast data packet to the source access network device). Therefore, the source access network device determines that the PDCP sequence number assigned to this third downlink bicast data packet is 101. Thus, the mapping relationship between the N3 sequence number assigned by the UPF and the PDCP sequence number that the source access network device needs to assign is: N3 sequence number 1 corresponds to PDCP sequence number 101.

[0086] Example 2: The third downlink dualcast data packet is the second downlink dualcast data packet sent by the UPF to both the source and target access network devices. This third downlink dualcast data packet carries an N3 sequence number of 2. Since the first downlink dualcast data packet sent by the UPF to the source access network device was lost, the source access network device can determine that the first downlink dualcast data packet sent by the UPF was lost based on pre-configured rules, such as a pre-agreed N3 sequence number starting from 1. On the other hand, the source access network device assigned a PDCP sequence number of 100 to a downlink data packet preceding the third downlink dualcast data packet (this downlink data packet was unicast to the source access network device). Therefore, the source access network device determines that the PDCP sequence number assigned to the third downlink dualcast data packet is 102. Thus, the mapping relationship between the N3 sequence number assigned by the UPF and the PDCP sequence number that the source access network device needs to assign is: N3 sequence number 2 corresponds to PDCP sequence number 102. It should be noted that the PDCP sequence number is 102 instead of 101 because the source access network device recognizes that a downlink duocast data packet was lost before the third downlink duocast data packet, so it needs to skip one PDCP sequence number.

[0087] It should be noted that, as an alternative implementation method, step 303b can also be replaced by: the source access network device determining the mapping relationship based on the second sequence number and the second PDCP COUNT value corresponding to the third downlink dualcast data packet. This mapping relationship is used to indicate the mapping relationship between the sequence number allocated by the UPF and the PDCP COUNT value that the source access network device needs to allocate, wherein one PDCP COUNT value can determine one PDCP sequence number.

[0088] In step 304b, the source access network device sends indication information to the target access network device, which indicates the aforementioned mapping relationship. Correspondingly, the target access network device receives this indication information from the source access network device.

[0089] As one implementation method, the indication information carries a second sequence number and a second PDCP sequence number corresponding to the second sequence number. For example, in the first example above, the indication information carries 1:101. And in the second example above, the indication information carries 2:102.

[0090] As another implementation method, the indication information carries the difference between the second sequence number and the second PDCP sequence number. For example, in the example above, the indication information carries 100 (that is, the difference between 101 and 1, or the difference between 102 and 2).

[0091] As another implementation method, the indication information carries the second sequence number and the second PDCPCOUNT value corresponding to the second sequence number, and the second PDCP COUNT value corresponds to the second PDCP sequence number.

[0092] As another implementation method, the indication information carries the difference between the second sequence number and the second PDCP COUNT value, the second PDCP COUNT value corresponding to the second PDCP sequence number.

[0093] Based on this instruction information, the target access network device can learn the mapping relationship between the sequence number assigned by the UPF and the PDCP COUNT value (or PDCP sequence number) that the target access network device needs to be assigned.

[0094] In step 305b, the source access network device sends a fourth downlink dual-cast data packet to the terminal device. This fourth downlink dual-cast data packet carries the second data and the second PDCP sequence number. Accordingly, the terminal device receives the fourth downlink dual-cast data packet.

[0095] In step 306b, the target access network device sends the aforementioned fourth downlink dual-cast data packet to the terminal device. Correspondingly, the terminal device receives the fourth downlink dual-cast data packet.

[0096] The target access network device determines the second PDCP sequence number carried in the fourth downlink dual-cast data packet based on the above mapping relationship and the second sequence number in the third downlink dual-cast data packet.

[0097] It should be noted that there is no strict order requirement between steps 302b and 304b. Specifically, if the target access network device receives the third downlink dual-cast data packet from the UPF first, and then receives the above-mentioned indication information from the source access network device, the target access network device needs to buffer the third downlink dual-cast data packet. After receiving the indication information, it determines the second PDCP sequence number corresponding to the second sequence number in the third downlink dual-cast data packet according to the mapping relationship indicated by the indication information. Then, the target access network device sends the fourth downlink dual-cast data packet to the terminal device.

[0098] Based on the above scheme, the source access network device can accurately determine the mapping relationship between the sequence number allocated by the UPF and the PDCP COUNT value (or PDCP sequence number) that the source access network device needs to allocate. Then, it indicates this mapping relationship to the target access network device through indication information. Thus, the target access network device can determine the mapping relationship between the sequence number allocated by the UPF and the PDCP COUNT value (or PDCP sequence number) that the target access network device needs to allocate. Consequently, both the source and target access network devices can accurately determine the PDCP sequence number corresponding to the sequence number in the downlink dualcast data packets received from the UPF based on this mapping relationship.

[0099] Referring to Figure 3(c), which is a schematic diagram of a data transmission method provided in an embodiment of this application, the method is executed before step 301b above, and the method is used to configure QoS flow group information for UPF to request bicast.

[0100] The method includes the following steps:

[0101] In step 301c, the source access network device sends a first request to the target access network device, the first request carrying information about the QoS flow group requesting duocast. Accordingly, the target access network device receives the first request.

[0102] The first request could be a switch request message.

[0103] The QoS stream group requesting duocast comprises one or more QoS stream groups, each associated with a data radio bearer (DRB). That is, all QoS streams within a QoS stream group are mapped to the same DRB, and QoS streams from different QoS stream groups are mapped to different DRBs. One way to indicate the information of the QoS stream group requesting duocast is that the information for each QoS stream group requesting duocast may include a QoS stream group identifier, and one or more QoS stream identifiers associated with the QoS stream group identifier.

[0104] For example, a session might correspond to 3 DRBs, with each DRB containing a QoS flow group consisting of one or more QoS flows. Therefore, the first request could carry information for 3 QoS flow groups, with each QoS flow group corresponding to one DRB. Alternatively, the first request could carry information for 2 QoS flow groups, with each QoS flow group corresponding to one DRB. Or, the first request could carry information for one QoS flow group, with that QoS flow group corresponding to one DRB.

[0105] Step 302c: The target access network device determines the QoS flow group information to be accepted for duocast based on the QoS flow group information requested for duocast.

[0106] The QoS flow group accepting double broadcast is part or all of the QoS flow group requesting double broadcast. The target access network device can determine the information of the QoS flow group accepting double broadcast based on the following methods: for example, the target access network device determines the QoS flow group that contains high QoS priority (e.g., low latency and high reliability) QoS flows as the QoS flow group accepting double broadcast. As an example, when the air interface resources of the target cell (i.e., the cell accessed by the terminal device) in the target access network device are limited, the target access network device determines the QoS flow group that contains high QoS priority (e.g., low latency and high reliability) QoS flows as the QoS flow group accepting double broadcast.

[0107] As one implementation method, for a QoS flow group requesting double broadcast, the target access network device either accepts double broadcast for all QoS flows within that QoS flow group, or rejects double broadcast for all QoS flows within that QoS flow group. For example, if the QoS flow groups requesting double broadcast include QoS flow group 1, QoS flow group 2, and QoS flow group 3, then the QoS flow groups accepting double broadcast can be one or more of QoS flow groups 1, QoS flow group 2, and QoS flow group 3.

[0108] As another implementation method, for a QoS flow group requesting doublecast, the target access network device may accept doublecast for some QoS flows within the QoS flow group and reject doublecast for others. For example, if the QoS flow group requesting doublecast includes QoS flow group 1, QoS flow group 2, and QoS flow group 3, then the QoS flow group accepting doublecast may be some or all of the QoS flows in QoS flow group 1, QoS flow group 2, and QoS flow group 3. Exemplarily, the QoS flow group accepting doublecast may be all the QoS flows in QoS flow group 1 and some of the QoS flows in QoS flow group 2.

[0109] In step 303c, the target access network device sends a first response to the source access network device, the first response carrying information about accepting QoS flow groups for duocast. Correspondingly, the source access network device receives this first response.

[0110] The first response could be a switch confirmation message.

[0111] Optionally, the first response may indicate information about the QoS flow group that rejects the duocast, and may further indicate the reason for rejecting the duocast.

[0112] Optionally, if the source access network device receives information about a rejected QoS flow group from the target access network device in the first response, then when the source access network device receives data of the QoS flow within the rejected QoS flow group from the UPF, the source access network device discards the data and does not assign a PDCP SN to the data.

[0113] In step 304c, the target access network device sends information about accepting QoS flow groups via duocast to the SMF. Correspondingly, the SMF receives this information about accepting QoS flow groups via duocast.

[0114] For example, the target access network device can send information about accepting QoS flow groups for duocast to the AMF, and then the AMF sends information about accepting QoS flow groups for duocast to the SMF.

[0115] Optionally, the target access network device may also indicate to the SMF information on the QoS flow group that rejects duocast, and may further indicate the reason for rejecting duocast.

[0116] In step 305c, the SMF sends configuration information to the UPF, which carries information about the QoS flow groups that accept duocast. The UPF receives this configuration information accordingly.

[0117] Optionally, the SMF may also indicate to the UPF the information regarding the QoS stream group that refuses to receive duocast, and may further indicate the reason for refusing to receive duocast. Thus, the UPF stops sending QoS streams for the QoS stream group that refuses to receive duocast.

[0118] It should be noted that the above method for configuring the UPF to accept QoS flow group information for bicast is only one optional implementation method. In practical applications, there are other configuration methods, such as configuring the UPF to accept QoS flow group information for bicast through network management equipment.

[0119] Based on the above scheme, it is possible to configure the QoS flow group information for receiving bicast for the UPF, and then the UPF can sequentially assign N3 sequence numbers to the downlink data packets of the QoS flow in the receiving bicast QoS flow group.

[0120] As an alternative implementation, step 304c can also be performed by the source access network device. For example, after step 303c, the source access network device sends QoS flow group information for accepting duocast to the SMF via the AMF. In this case, the target access network device does not need to perform step 304c.

[0121] As one implementation method, after step 305c above, the UPF sends a configuration response to the SMF to indicate successful configuration. Then, the SMF sends a configuration response to the AMF to indicate successful configuration, and the AMF sends a configuration response to the target access network device to indicate successful configuration. The target access network device then executes step 303c above. That is, the target access network device sends a first response to the source access network device only after receiving the configuration response from the AMF. This first response carries information about accepting QoS flow groups for bicast.

[0122] Referring to Figure 3(d), which is a schematic diagram of a data transmission method provided in an embodiment of this application, the method is executed before step 301b above, and the method is used to configure QoS flow group information for UPF to request bicast.

[0123] The method includes the following steps:

[0124] In step 301d, the source access network device sends a first request to the AMF, which carries information about the QoS flow group requesting duocasting. Accordingly, the AMF receives the first request.

[0125] The first request could be a switch request message.

[0126] For a detailed description of the QoS flow group information requested for this duocast, please refer to the foregoing description, which will not be repeated here.

[0127] In step 302d, the AMF sends a handover request message to the target access network device. Correspondingly, the target access network device receives the handover request message.

[0128] The handover request message carries information about the QoS flow group requesting duocast.

[0129] Step 303d: The target access network device determines the QoS flow group information to be accepted for duocast based on the QoS flow group information requested for duocast.

[0130] The QoS flow group that accepts duocast is part or all of the QoS flow group that requests duocast. The method by which the target access network device determines the QoS flow group that accepts duocast can be referred to the foregoing description and will not be repeated here.

[0131] In step 304d, the target access network device sends information about accepting QoS flow groups via duocast to the AMF. Correspondingly, the AMF receives this information about accepting QoS flow groups via duocast.

[0132] In step 305d, the AMF sends a first response to the source access network device, which carries information about accepting QoS flow groups for duocast. Accordingly, the source access network device receives this first response.

[0133] The first response could be a switching command.

[0134] Optionally, the first response may indicate information about the QoS flow group that rejects the duocast, and may further indicate the reason for rejecting the duocast.

[0135] In step 306d, the AMF sends information about the QoS flow group that accepts duocast to the SMF. Correspondingly, the SMF receives this information about the QoS flow group that accepts duocast.

[0136] Optionally, the AMF may also indicate to the SMF information about the QoS flow groups that are denied duocast, and may further indicate the reason for denying duocast reception.

[0137] In step 307d, the SMF sends configuration information to the UPF, which carries information about the QoS flow groups that accept duocast. The UPF receives this configuration information accordingly.

[0138] Optionally, the SMF may also indicate to the UPF the information regarding the QoS stream group that refuses to receive duocast, and may further indicate the reason for refusing to receive duocast. Thus, the UPF stops sending QoS streams for the QoS stream group that refuses to receive duocast.

[0139] It should be noted that the above method for configuring the UPF to accept QoS flow group information for bicast is only one optional implementation method. In practical applications, there are other configuration methods, such as configuring the UPF to accept QoS flow group information for bicast through network management equipment.

[0140] Based on the above scheme, it is possible to configure the QoS flow group information for receiving bicast for the UPF, and then the UPF can sequentially assign N3 sequence numbers to the downlink data packets of the QoS flow in the receiving bicast QoS flow group.

[0141] As an alternative implementation, step 304d can also be performed by the source access network device. For example, after step 305d, the source access network device sends information about accepting QoS flow groups for duocast to the AMF, and then the AMF sends the same information to the SMF in step 306d. In this case, the target access network device does not need to perform step 304d.

[0142] As one implementation method, after step 307d above, the UPF sends a configuration response to the SMF to indicate successful configuration, and then the SMF sends a configuration response to the AMF to indicate successful configuration. The AMF then executes step 305d above. That is, the AMF sends the first response to the source access network device only after receiving the configuration response from the SMF. This first response carries information about the QoS flow group accepting duocast.

[0143] Referring to Figure 3(e), which is a schematic diagram of a data transmission method provided in an embodiment of this application, the method is the process of the UPF sending downlink bicast data packets after configuring the UPF with information on QoS flow groups that accept bicast.

[0144] The method includes the following steps:

[0145] Step 301e: UPF receives configuration information, which carries information about the QoS stream groups that accept duocast. The QoS stream groups that accept duocast include one or more QoS stream groups, and the first QoS stream group is any one of the QoS stream groups that accept duocast.

[0146] For example, the QoS flow group information for accepting bicast can be configured for the UPF through the embodiments corresponding to Figure 3(c) or Figure 3(d) above.

[0147] Optionally, the QoS flows in each QoS flow group that accepts bicast are associated with the same data radio bearer, and the QoS flows in different QoS flow groups are associated with different data radio bearers.

[0148] In step 302e, UPF assigns N3 sequence numbers to the downlink bicast data packets of the first QoS flow group.

[0149] Optionally, the N3 sequence number is carried in the downlink PDU session information in the downlink bicast data packet of the first QoS flow group.

[0150] For each QoS stream group within a QoS stream group that accepts bicast, the UPF will assign N3 sequence numbers sequentially to the data packets of the QoS streams within that QoS stream group and send them together. For example, if QoS stream group 1 contains QoS stream 1, QoS stream 2, and QoS stream 3, the UPF will assign N3 sequence numbers (e.g., 1, 2, ...) to the data packets of these three QoS streams sequentially. If QoS stream group 2 contains QoS stream 4 and QoS stream 5, the UPF will assign N3 sequence numbers (e.g., 1, 2, ...) to the data packets of these two QoS streams sequentially.

[0151] Subsequently, the UPF sends downlink bicast data packets of the first QoS flow group to both the source access network device and the target access network device.

[0152] It should be noted that the first downlink dual-cast data packet and the third downlink dual-cast data packet in the foregoing embodiments can be data packets of a QoS flow in a certain QoS flow group of the QoS flow group that receives the dual-cast.

[0153] Based on the above scheme, it is possible to configure the QoS flow group information for receiving bicast for the UPF, and then the UPF can sequentially assign N3 sequence numbers to the downlink data packets of the QoS flow in the receiving bicast QoS flow group.

[0154] The above solution will be illustrated with a specific example below. (Reference) Figure 4 This is a schematic diagram of the data packet sending process. Figure 4 The example shown is Figure 2 The solution shown is an example of this.

[0155] refer to Figure 4 After receiving QoS flow group information for accepting bicast, the UPF assigns a consecutive N3 sequence number to the downlink data of each QoS flow group and carries the N3 sequence number in the downlink PDU session information. The UPF sends downlink bicast data packets to the source access network device and the target access network device, referring to... Figure 4The UPF sends downlink dual-cast data packets 1, 2, and 3, carrying N3 sequence numbers 1, 2, and 3 respectively. Assuming the source access network device loses downlink dual-cast data packet 3 and the target access network device loses downlink dual-cast data packet 2, the source access network device first determines the mapping relationship between the N3 sequence number and the PDCP SN based on the received downlink dual-cast data packet 1: N3 sequence number 1 corresponds to PDCP sequence number 101. The source access network device then sends an indication (e.g., 1:101 or 100 (the difference between 101 and 1)) to the target access network device. Therefore, the source access network device can assign PDCP SN 101 and PDCP SN 102 to the received downlink dual-cast data packets 1 and 2 respectively, and the target access network device can assign PDCP SN 101 and PDCP SN 103 to the received downlink dual-cast data packets 1 and 3 respectively. After receiving downlink bicast data packets from both the source and target access network devices, the terminal device, based on the PDCP SN carried in the downlink bicast data packets, considers that downlink bicast data packet 1 received from the source access network device and downlink bicast data packet 1 received from the target access network device to be the same downlink bicast data packet. Therefore, it performs a deduplication operation to obtain downlink bicast data packet 1, downlink bicast data packet 2, and downlink bicast data packet 3, thus ensuring correct reception of downlink data packets. This avoids the terminal device discarding data packets that have not been received repeatedly during deduplication, ensuring that the terminal device does not miss information from the access network devices, preventing data loss or interruption during handover, and improving the reliability of data transmission.

[0156] The above scheme will be described below with reference to specific implementation methods.

[0157] The handover process involved in the embodiments of this application may include, but is not limited to, handover based on N2 and handover based on Xn. Here, the Xn interface is the interface between two access network devices, and the N2 interface is the interface between the access network device and the AMF. In addition to handover scenarios, the embodiments of this application are applicable to scenarios where an auxiliary access network device is added, thereby enabling dual-path transmission through two dual access network devices.

[0158] refer to Figure 5 This diagram illustrates a data transmission method provided in an embodiment of this application. The method is based on the transmission of downlink dual-cast data packets during N2 handover.

[0159] The method includes the following steps:

[0160] Step 501: The terminal device sends a measurement report to the source access network device. Correspondingly, the source access network device receives the measurement report.

[0161] When a terminal device determines that a measurement report is required to be submitted for a wireless signal, it sends a measurement report to the source access network device. For example, if the terminal device determines that the quality of the serving cell is below a set threshold, it sends a measurement report to the source access network device. Similarly, if the terminal device determines that the quality of a neighboring cell is above a set threshold, it sends a measurement report to the source access network device.

[0162] Step 502: The source access network device sends a handover request to the AMF. Accordingly, the AMF receives the handover request.

[0163] As one implementation method, in step 502, the source access network device sends an Initialize Context Setup Response message to the AMF, which carries the aforementioned handover requirements.

[0164] As another implementation method, in step 502, the source access network device sends a UE CONTEXT MODIFICATION RESPONSE message to the AMF, which carries the aforementioned handover requirement.

[0165] Step 503: The AMF sends a handover request message to the target access network device. Correspondingly, the target access network device receives the handover request message.

[0166] The handover request message carries information about the QoS flow group requesting duocast.

[0167] The specific description of the QoS flow group information requested for duocast can be found in the preceding description and will not be repeated here.

[0168] Step 504: The target access network device sends a handover confirmation message to the AMF. Correspondingly, the AMF receives the handover confirmation message.

[0169] The handover confirmation message carries information about the QoS stream group that accepts the duocast, and the QoS streams in the QoS stream group that accepts the duocast are some or all of the QoS streams in the QoS stream group that requested the duocast.

[0170] Optionally, the switch confirmation message can also indicate information about the QoS stream to be rejected for duocast, and further indicate the reason for rejecting duocast.

[0171] Step 505: The target access network device sends a dual-cast request message to the AMF. Correspondingly, the AMF receives the dual-cast request message.

[0172] The duocast request message carries information about the QoS flow group accepting the duocast and the downlink tunnel address information of the target access network device. This downlink tunnel address is the address on the target access network device used to receive downlink duocast data packets.

[0173] Optionally, the duocast request message also carries a session identifier, which is the session corresponding to the QoS flow group that accepts the duocast.

[0174] Step 506: The AMF configures the QoS flow group for accepting duocast to the UPF via the SMF.

[0175] For example, the AMF provides the source access network device information (such as the downlink tunnel address information of the target access network device) to the SMF, and the SMF issues forwarding rules to the UPF, instructing the UPF to start sending downlink bicast data packets.

[0176] Optionally, after accepting the configuration, the UPF sends a configuration response to the SMF, and the SMF sends a configuration response to the AMF.

[0177] Step 507: The AMF sends a handover command to the source access network device. Correspondingly, the source access network device receives the handover command.

[0178] The switching command carries information about the QoS flow group that accepts duocast.

[0179] Step 508: The source access network device sends a handover message to the terminal device. Accordingly, the terminal device receives the handover message.

[0180] Step 509: The source access network device sends an indication message to the target access network device. Accordingly, the target access network device receives the indication message.

[0181] This indication information is used to indicate the mapping relationship between the N3 serial number and the PDCP SN.

[0182] For example, after step 506 above, the UPF begins to send downlink bicast data packets to both the source access network device and the target access network device simultaneously. The downlink bicast data packets carry the N3 sequence number assigned by the UPF. For example, the UPF can start numbering the downlink data packets from 0 or 1.

[0183] One method for transmitting downlink dual-cast data packets is as follows: The UPF carries the data portion and the N3 sequence number together in different fields of a General Packet Radio Service (GPRS) Tunneling Protocol (GTP) (GTP-U) and sends them to the access network device. For example, the data portion is placed in the payload of GTP-U, and the N3 sequence number is placed in the subheader of GTP-U. Optionally, the N3 sequence number is carried in the data frame of the downlink PDU session information sent by the UPF to the access network device.

[0184] It should be noted that the N3 sequence number is different from the GTP sequence number in the GTP-U header of existing technologies. The N3 sequence number is also different from the GTP sequence number assigned sequentially by the UPF to all QoS flows in the PDU session, and it is also different from the N3 sequence number assigned sequentially only to a single QoS flow in the existing GTP-U header. Furthermore, the UPF can carry marking information in the first downlink unicast packet or an initial set number of downlink unicast packets. This marking information indicates that a unicast packet is being sent. Alternatively, before sending the first downlink unicast packet, the UPF can continuously send one or more indications to end unicast packet transmission, that is, send one or more indications to instruct the UPF to begin sending unicast packets, informing the source access network device that the UPF is about to start sending unicast packets.

[0185] When the source access network device receives a downlink dualcast data packet (which could be the first or second downlink dualcast data packet, etc., and can be identified by the aforementioned marking information carried in the downlink dualcast data packet), it obtains the N3 sequence number carried in the downlink dualcast data packet. Then, based on the PDCP SN corresponding to the downlink dualcast data packet and the N3 sequence number, it determines the mapping relationship between the N3 sequence number and the PDCP SN. For example, if the source access network device receives the first downlink dualcast data packet with an N3 sequence number of 1, and assuming the source access network device has already used or allocated a PDCP SN of 100, then the PDCP SN corresponding to this downlink dualcast data packet is 101. Therefore, the mapping relationship between the N3 sequence number and the PDCP SN is determined as follows: N3 sequence number 1 corresponds to PDCP sequence number 101. Subsequently, when the source access network device receives other downlink dualcast data packets, it can determine the corresponding PDCP SN based on the N3 sequence number carried in the downlink dualcast data packets. For example, if a downlink duocast data packet carrying N3 sequence number 100 is subsequently received, the source access network device will add PDCP SN 200 to the downlink duocast data packet.

[0186] After receiving the indication information, the target access network device can add a PDCP SN to the downlink dual-cast data packet received from the UPF according to the mapping relationship between the N3 sequence number and the PDCP SN indicated in the indication information. For example, if the target access network device receives a downlink dual-cast data packet carrying an N3 sequence number of 100, it will add PDCP SN 200 to the downlink dual-cast data packet according to the mapping relationship between the N3 sequence number and the PDCP SN indicated in the indication information. One possible implementation is as follows: The target access network device receives the downlink dual-cast data packet (e.g., a GTP-U data packet) from the UPF, extracts the IP packet from the GTP-U data packet as a PDCP SDU, adds the PDCP SN to generate a PDCP PDU, and then sends it to the terminal device through the protocol layer below PDCP.

[0187] It should be noted that if the target access network device receives downlink bicast data packets from the UPF before receiving the indication information, the target access network device can first cache these downlink bicast data packets, and then, upon receiving the indication information, determine the PDCP SN based on the cached downlink bicast data packets.

[0188] In one implementation, the indication information carries the mapping relationship between the N3 sequence number and the PDCP SN. In another implementation, the indication information carries either the difference between the N3 sequence number and the PDCP SN, or the difference between the PDCP SN and the N3 sequence number. This can be understood as the indication information being used to indicate the N3 sequence number and the corresponding PDCP SN.

[0189] Step 510: The terminal device sends a handover completion message to the target access network device. Correspondingly, the target access network device receives the handover completion message.

[0190] After the terminal device sends a handover completion message to the target access network device, it can send a PDCP status report to the target access network device, and the terminal device can also send uplink data packets to the target access network device.

[0191] Step 511: The target access network device sends a path handover request message to the AMF. Correspondingly, the AMF receives the path handover request message.

[0192] Optionally, the target access network device may carry an indication to stop downlink duocast in the path switching request message and notify the SMF via the AMF.

[0193] In step 512, the AMF notifies the UPF of the path switch via the SMF, and the UPF stops sending downlink bicast messages.

[0194] Optionally, the AMF notifies the UPF to stop downlink bicast via the SMF.

[0195] Step 513: The AMF sends a path handover response message to the target access network device. Accordingly, the target access network device receives the path handover response message.

[0196] Based on the above scheme, the UPF uniformly assigns N3 sequence numbers to downlink bicast packets receiving QoS flows, and sends the N3 sequence numbers in the downlink bicast packets to the source and destination access network devices. Subsequently, the source and destination access network devices can determine the PDCP SN corresponding to the downlink bicast packets based on the mapping relationship between the N3 sequence numbers and PDCP SNs, and add the N3 sequence number to the downlink bicast packets. Since the source and destination access network devices determine the PDCP SN corresponding to the received downlink bicast packets based on the same mapping relationship, the same PDCP SN will be determined for the same downlink bicast packet. This avoids the terminal device discarding packets that have not been received repeatedly when packets are lost, ensuring that the terminal device does not miss information from the access network devices, avoiding data loss or interruption during handover, and improving the reliability of data transmission.

[0197] In the above scheme, in step 509, the source access network device sends the aforementioned indication information to the target access network device through the Xn interface between the source access network device and the target access network device. As an alternative implementation of step 509, the source access network device can send the aforementioned indication information to the terminal device. For example, the source access network device can carry the aforementioned indication information in the handover message of step 508, and then the terminal device can send the aforementioned indication information to the target access network device. Alternatively, the terminal device can send the aforementioned indication information through the handover completion message of step 510.

[0198] In the above scheme, the information carried in step 505 can also be carried in step 504. In this case, step 505 does not need to be executed.

[0199] The above Figure 5 In a corresponding embodiment, the target access network device determines the QoS flow group information to be accepted for duocast based on the QoS flow group information requested for duocast. As an alternative implementation, the AMF can also request the QoS flow group information for duocast, determine the QoS flow group information to be accepted for duocast, and then carry the QoS flow group information to be accepted for duocast in step 503 above. In this way, step 504 does not need to carry the QoS flow group information to be accepted for duocast.

[0200] refer to Figure 6 This diagram illustrates a data transmission method provided in an embodiment of this application. The method is based on the transmission of downlink dual-cast data packets during the Xn handover process.

[0201] The method includes the following steps:

[0202] Step 601: The terminal device sends a measurement report to the source access network device. Correspondingly, the source access network device receives the measurement report.

[0203] When a terminal device determines that a measurement report is required to be submitted for a wireless signal, it sends a measurement report to the source access network device. For example, if the terminal device determines that the quality of the serving cell is below a set threshold, it sends a measurement report to the source access network device. Similarly, if the terminal device determines that the quality of a neighboring cell is above a set threshold, it sends a measurement report to the source access network device.

[0204] Step 602: The source access network device sends a handover request message to the target access network device. Correspondingly, the target access network device receives the handover request message.

[0205] The handover request message carries information about the QoS stream group for which duocast is requested. The QoS stream group for which duocast is requested includes one or more QoS stream groups, each of which is associated with a data radio bearer.

[0206] For a detailed description of the QoS flow group information requested for this duocast, please refer to the foregoing description, which will not be repeated here.

[0207] Step 603: The target access network device determines the QoS flow group that accepts duocast.

[0208] The target access network device determines which QoS flow group to accept for duocast based on the information of the QoS flow group requesting duocast.

[0209] For a detailed description of the QoS flow group that accepts duocast, please refer to the foregoing description, which will not be repeated here.

[0210] In step 604, the target access network device sends a dual-cast request message to the AMF. Correspondingly, the AMF receives the dual-cast request message.

[0211] The duocast request message carries information about the QoS flow group accepting the duocast and the downlink tunnel address information of the target access network device. This downlink tunnel address is the address on the target access network device used to receive downlink duocast data packets.

[0212] Optionally, the duocast request message also carries a session identifier, which is the session corresponding to the QoS flow group that accepts the duocast.

[0213] Step 605: The AMF configures the QoS flow group for accepting duocast to the UPF via the SMF.

[0214] For example, the AMF provides the source access network device information (such as the downlink tunnel address information of the target access network device) to the SMF, and the SMF issues forwarding rules to the UPF, instructing the UPF to start sending downlink bicast data packets.

[0215] Subsequently, the UPF uniformly assigns N3 sequence numbers to the QoS flows indicated by the information of the QoS flow group accepting duocast. For example, for each QoS flow group in the QoS flow group accepting duocast, when sending the data packets of the QoS flows within that QoS flow group, the UPF uniformly assigns N3 sequence numbers and carries them in the data packets of the QoS flows before sending them.

[0216] In step 606, the AMF sends a dual-cast acknowledgment message to the target access network device. Correspondingly, the target access network device receives the dual-cast acknowledgment message.

[0217] The duocast acknowledgment message carries information about the QoS flow group that accepts the duocast.

[0218] Step 607: The target access network device sends a handover confirmation message to the source access network device. Correspondingly, the source access network device receives the handover confirmation message.

[0219] The handover confirmation message carries information about the QoS flow group that accepts duocast.

[0220] Steps 608 to 613 are the same as steps 508 to 513 above, and will not be repeated here.

[0221] Based on the above scheme, the UPF uniformly assigns N3 sequence numbers to downlink bicast packets receiving QoS flows, and sends the N3 sequence numbers in the downlink bicast packets to the source and destination access network devices. Subsequently, the source and destination access network devices can determine the PDCP SN corresponding to the downlink bicast packets based on the mapping relationship between the N3 sequence numbers and PDCP SNs, and add the N3 sequence number to the downlink bicast packets. Since the source and destination access network devices determine the PDCP SN corresponding to the received downlink bicast packets based on the same mapping relationship, the same PDCP SN will be determined for the same downlink bicast packet. This avoids the terminal device discarding packets that have not been received repeatedly when packets are lost, ensuring that the terminal device does not miss information from the access network devices, avoiding data loss or interruption during handover, and improving the reliability of data transmission.

[0222] In the above scheme, in step 609, the source access network device sends the aforementioned indication information to the target access network device through the Xn interface between the source access network device and the target access network device. As an alternative implementation of step 609, the source access network device can send the aforementioned indication information to the terminal device. For example, the source access network device can carry the aforementioned indication information in the handover message of step 608, and then the terminal device can send the aforementioned indication information to the target access network device. Alternatively, the terminal device can send the aforementioned indication information through the handover completion message of step 610.

[0223] The above Figure 6 In a corresponding embodiment, the target access network device determines the QoS flow group information to be accepted for double-cast based on the QoS flow group information requested for double-cast. As an alternative implementation, the AMF can also determine the QoS flow group information to be accepted for double-cast based on the QoS flow group information requested for double-cast. For example, step 603 can be omitted, and the QoS flow group information requested for double-cast can be included in step 604. Then, the AMF determines the QoS flow group information to be accepted for double-cast based on the QoS flow group information requested for double-cast, and sends the QoS flow group information to be accepted for double-cast to the target access network device in step 606.

[0224] The above Figure 5 or Figure 6 In a corresponding embodiment, the QoS flow group information for accepting duocast is configured in the UPF during the handover process. Alternatively, the QoS flow group information for accepting duocast can be configured in the UPF before the handover. This allows the UPF to begin sending downlink duocast data packets to both the source and target access network devices before the handover, enabling the target access network device to receive downlink data packets from the UPF earlier. Therefore, if these downlink data packets cannot be correctly sent to the terminal device through the source access network device (e.g., due to an impending handover causing a link anomaly between the terminal device and the source access network device), they can still be sent to the terminal device through the target access network device, preventing the data packets sent by the UPF from failing to reach the terminal device.

[0225] As one implementation method, a first measurement report corresponds to a first event detected by the terminal device, and a second measurement report corresponds to a second event detected by the terminal device, wherein the trigger threshold of the first event is lower than the trigger threshold of the second event. For example, the channel quality trigger threshold of the first event is lower than the channel quality trigger threshold of the second event.

[0226] 1) Before the switchover:

[0227] When the source access network device receives the first measurement report from the terminal device, it notifies the SMF to configure the UPF for bicast transmission. After the SMF completes the bicast transmission configuration for the UPF, the UPF can begin sending downlink bicast data packets to both the source and target access network devices. Then, the source access network device can determine the mapping relationship between the N3 sequence number and the PDCP SN. This process is similar to... Figure 5 Steps 501 to 506 in the process, or similar to... Figure 6 Steps 601 to 605 in the process.

[0228] 2) Switching occurs:

[0229] When the source access network device receives the second measurement report from the terminal device, the source access network device triggers the existing handover process to complete the handover of the terminal device from the source access network device to the target access network device.

[0230] During handover, the source access network device can send indication information to the target access network device. This indication information indicates the mapping relationship between the N3 sequence number and the PDCP SN. For example, in an N2-based handover scenario, the source access network device includes this indication information in the handover request sent to the AMF, and then the AMF includes this indication information in the handover request message sent to the target access network device. As another example, in an Xn-based handover scenario, the source access network device includes this indication information in the handover request message sent to the target access network device.

[0231] Compared to Figure 5 and Figure 6 In a corresponding embodiment, this scheme can enable bicast configuration of the UPF in advance, and the source access network device can send the indication information used to indicate the mapping relationship to the target access network device in advance, so that the target access network device can determine the PDCP SN corresponding to the downlink bicast data packet received from the UPF earlier, thereby helping to reduce the latency of sending downlink bicast data packets to the terminal device.

[0232] It should be noted that the embodiments of this application are illustrated using downlink transmission as an example, but the embodiments of this application can also be applied to uplink transmission.

[0233] refer to Figure 7 This is a schematic diagram of a data transmission method provided in an embodiment of this application. The method includes the following steps:

[0234] Step 701: The terminal device sends a first uplink dual-cast data packet to the access network device, wherein the first downlink dual-cast data packet carries third data and a third PDCP sequence number. Correspondingly, the access network device receives the first uplink dual-cast data packet.

[0235] Step 702: The access network device determines the third sequence number corresponding to the third PDCP sequence number.

[0236] The third serial number can be N3 serial number or other pre-agreed serial number, etc.

[0237] It should be noted that the initial number of the N3 sequence number can be pre-agreed or dynamically configured. For example, the source access network device can indicate the initial value of the uplink N3 sequence number to the UPF.

[0238] In step 703, the access network device sends a second uplink bicast data packet to the UPF, the second uplink bicast data packet carrying third data and a third sequence number. Correspondingly, the UPF receives the second uplink bicast data packet.

[0239] The aforementioned access network device can be either a source access network device or a target access network device, meaning that the terminal device sends the same uplink bicast data packets to both the source and target access network devices.

[0240] Based on the above scheme, the terminal device uniformly assigns sequence numbers to uplink data dual-cast packets. Then, the source access network device and the target access network device map the PDCP sequence number assigned by the terminal device to the N3 sequence number. This ensures that the source access network device and the target access network device assign the same N3 sequence number to the same uplink data dual-cast packets, thereby preventing the UPF from discarding packets that have not been received repeatedly during deduplication. As a result, the UPF will not miss information from the access network device, avoiding data loss or interruption during handover and improving the reliability of data transmission.

[0241] Subsequently, UPF performs deduplication based on the N3 sequence number.

[0242] The method for determining the mapping relationship between PDCP sequence number and N3 sequence number in the uplink data transmission process is similar to the method for determining the mapping relationship between PDCP sequence number and N3 sequence number in the downlink data transmission process, and will not be repeated here.

[0243] refer to Figure 8 This is a schematic diagram of a communication device provided in an embodiment of this application. This communication device is used to implement the various steps of the corresponding access network equipment or user plane network element in the above embodiments, such as... Figure 8 As shown, the communication device 800 includes a transceiver unit 810 and a processing unit 820.

[0244] In the first embodiment, the communication device is used to implement the various steps of the corresponding access network devices in the above embodiments:

[0245] The transceiver unit 810 is configured to receive a first downlink dual-cast data packet from a user plane network element, the first downlink dual-cast data packet carrying first data and a first sequence number; and to send a second downlink dual-cast data packet to a terminal device, the second downlink dual-cast data packet carrying the first data and a first Packet Data Convergence Protocol (PDCP) sequence number; the processing unit 820 is configured to determine the first PDCP sequence number corresponding to the first sequence number.

[0246] Other operations performed by this communication device can be referred to the relevant descriptions in the foregoing method embodiments, and will not be repeated here.

[0247] In the second embodiment, the communication device is used to implement the steps of the corresponding user plane network elements in the above embodiments:

[0248] The transceiver unit 810 is used to receive configuration information, the configuration information carrying information about the QoS flow group accepting bicast, the QoS flow group accepting bicast includes one or more QoS flow groups, and the first QoS flow group is any one of the QoS flow groups accepting bicast; the processing unit 820 is used to sequentially assign N3 sequence numbers to the downlink bicast data packets of the first QoS flow group.

[0249] Other operations performed by this communication device can be referred to the relevant descriptions in the foregoing method embodiments, and will not be repeated here.

[0250] Optionally, the communication device may further include a storage unit for storing data or instructions (also referred to as code or program). Each of the aforementioned units can interact with or be coupled to the storage unit to implement the corresponding method or function. For example, the processing unit 820 can read data or instructions from the storage unit, enabling the communication device to implement the method described in the above embodiments.

[0251] It should be understood that the division of units in the above communication device is merely a logical functional division. In actual implementation, they can be fully or partially integrated into a single physical entity, or they can be physically separated. Furthermore, all units in the communication device can be implemented entirely through software calls from processing elements; all units can be implemented entirely in hardware; or some units can be implemented through software calls from processing elements, while others are implemented in hardware. For example, each unit can be a separate processing element, or it can be integrated into a chip within the communication device. Alternatively, it can be stored as a program in memory, called and executed by a processing element of the communication device. Moreover, these units can be fully or partially integrated together, or implemented independently. The processing element mentioned here can also be called a processor, which can be an integrated circuit with signal processing capabilities. In the implementation process, each step of the above method or each of the above units can be implemented through integrated logic circuits in the processor element or through software calls from processing elements.

[0252] In one example, a unit in any of the above communication devices can be one or more integrated circuits configured to implement the above methods, such as: one or more application-specific integrated circuits (ASICs), or one or more digital signal processors (DSPs), or one or more field-programmable gate arrays (FPGAs), or a combination of at least two of these integrated circuit forms. As another example, when a unit in the communication device can be implemented in the form of a processing element scheduler, the processing element can be a general-purpose processor, such as a central processing unit (CPU) or other processor capable of calling programs. Furthermore, these units can be integrated together and implemented as a system-on-a-chip (SOC).

[0253] refer to Figure 9 This is a schematic diagram of a communication device provided in an embodiment of this application, used to implement the operations of the access network device or user plane network element in the above embodiments. Figure 9 As shown, the communication device includes a processor 910 and an interface 930. Optionally, the communication device also includes a memory 920. The interface 930 is used to enable communication with other devices.

[0254] The methods executed by the access network device or user plane network element in the above embodiments can be implemented by the processor 910 calling a program stored in memory (which can be memory 920 in the access network device or user plane network element, or external memory). That is, the access network device or user plane network element may include a processor 910, which executes the methods executed by the access network device or user plane network element in the above method embodiments by calling a program in memory. The processor here can be an integrated circuit with signal processing capabilities, such as a CPU. The access network device or user plane network element can be implemented by one or more integrated circuits configured to implement the above methods. For example: one or more ASICs, or one or more microprocessors (DSPs), or one or more FPGAs, or a combination of at least two of these integrated circuit forms. Alternatively, the above implementation methods can be combined.

[0255] Specifically, Figure 8 The functions / implementation of the transceiver unit 810 and the processing unit 820 can be understood through... Figure 9 The processor 910 in the communication device 900 shown calls computer-executable instructions stored in the memory 920 to implement the function. Alternatively, Figure 8 The function / implementation process of the processing unit 820 in the middle can be achieved through Figure 9 The processor 910 in the communication device 900 shown calls computer execution instructions stored in the memory 920 to implement the communication. Figure 8 The function / implementation process of the transceiver unit 810 in the middle can be obtained through Figure 9 The interface 930 in the communication device 900 shown is used to implement this functionality. For example, the function / implementation process of the transceiver unit 810 can be implemented by the processor calling program instructions in memory to drive the interface 930.

[0256] Those skilled in the art will understand that the various numerical designations, such as "first," "second," etc., used in this application are merely for descriptive convenience and are not intended to limit the scope of the embodiments of this application, nor do they indicate a sequential order. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one" refers to one or more. "At least two" refers to two or more. "At least one," "any one," or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, at least one of a, b, or c can represent: a, b, c, ab, ac, bc, or abc, where a, b, and c can be single or multiple. "Multiple" refers to two or more, and other quantifiers are similar.

[0257] It should be understood that, in the various embodiments of this application, the sequence number of each process does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this invention.

[0258] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0259] In the above embodiments, implementation can be achieved entirely or partially through software, hardware, firmware, or any combination thereof. When implemented using software, it can be implemented entirely or partially in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of this application are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape), an optical medium (e.g., DVD), or a semiconductor medium (e.g., solid-state disk (SSD)).

[0260] The various illustrative logic units and circuits described in the embodiments of this application can be implemented or operate the described functions using a general-purpose processor, digital signal processor, application-specific integrated circuit (ASIC), field-programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof. The general-purpose processor can be a microprocessor; alternatively, it can also be any conventional processor, controller, microcontroller, or state machine. The processor can also be implemented using a combination of computing devices, such as a digital signal processor and a microprocessor, multiple microprocessors, one or more microprocessors combined with a digital signal processor core, or any other similar configuration.

[0261] The steps of the methods or algorithms described in the embodiments of this application can be directly embedded in hardware, software units executed by a processor, or a combination of both. The software units can be stored in random access memory (RAM), flash memory, read-only memory (ROM), EPROM, EEPROM, registers, hard disks, removable disks, CD-ROMs, or any other form of storage medium in the art. Exemplarily, the storage medium can be connected to the processor so that the processor can read information from and write information to the storage medium. Optionally, the storage medium can also be integrated into the processor. The processor and storage medium can be housed in an ASIC.

[0262] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0263] In one or more exemplary designs, the functions described herein can be implemented in hardware, software, firmware, or any combination of these three. If implemented in software, these functions can be stored on a computer-readable medium or transmitted on a computer-readable medium in the form of one or more instructions or code. Computer-readable media includes computer storage media and communication media that facilitate the transfer of computer programs from one location to another. Storage media can be any available media accessible to a general-purpose or special-purpose computer. For example, such computer-readable media can include, but is not limited to, RAM, ROM, EEPROM, CD-ROM or other optical disc storage, disk storage or other magnetic storage devices, or any other medium that can be used to carry or store program code in the form of instructions or data structures and other formats readable by a general-purpose or special-purpose computer or processor. Furthermore, any connection can be suitably defined as a computer-readable medium, for example, if the software is transmitted from a website, server, or other remote resource via a coaxial cable, fiber optic computer, twisted pair, digital subscriber line (DSL), or wirelessly, such as infrared, wireless, and microwave, it is also included in the definition of a computer-readable medium. The disks and discs mentioned include compressed disks, laser discs, optical discs, Digital Versatile Discs (DVDs), floppy disks, and Blu-ray discs. Disks typically copy data magnetically, while discs typically copy data optically using lasers. Combinations of these can also be contained in computer-readable media.

[0264] Those skilled in the art will recognize that, in one or more of the examples above, the functions described in this application can be implemented using hardware, software, firmware, or any combination thereof. When implemented in software, these functions can be stored in a computer-readable medium or transmitted as one or more instructions or code on a computer-readable medium. Computer-readable media include computer storage media and communication media, wherein communication media include any medium that facilitates the transfer of a computer program from one place to another. Storage media can be any available medium accessible to a general-purpose or special-purpose computer.

[0265] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this application. It should be understood that the above descriptions are merely specific embodiments of this application and are not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, or improvements made based on the technical solution of this application should be included within the scope of protection of this application. The above description in this application specification allows for the utilization or implementation of the content of this application by anyone skilled in the art. Any modifications based on the disclosed content should be considered obvious in the art. The basic principles described in this application can be applied to other variations without departing from the inventive nature and scope of this application. Therefore, the content disclosed in this application is not limited to the described embodiments and designs but can be extended to the maximum extent consistent with the principles and novel features disclosed in this application.

[0266] Although this application has been described in conjunction with specific features and embodiments, it is obvious that various modifications and combinations can be made thereto without departing from the spirit and scope of this application. Accordingly, this specification and drawings are merely illustrative descriptions of the application as defined by the appended claims, and are considered to cover any and all modifications, variations, combinations, or equivalents within the scope of this application. Clearly, those skilled in the art can make various alterations and modifications to this application without departing from its scope. Thus, if such modifications and modifications fall within the scope of the claims and their equivalents, this application is also intended to include such modifications and modifications.

Claims

1. A data transmission method, characterized in that, include: The source access network device receives a third downlink duocast data packet from a user plane network element, the third downlink duocast data packet carrying second data and a second sequence number; The source access network device determines the mapping relationship based on the second sequence number and the second PDCPCOUNT value corresponding to the third downlink dualcast data packet. The mapping relationship is used to indicate the mapping relationship between the sequence number allocated by the user plane network element and the PDCP COUNT value that needs to be allocated. The source access network device sends indication information to the target access network device. The indication information is used to indicate the mapping relationship. The indication information carries the second sequence number and the second PDCP COUNT value corresponding to the second sequence number, or the indication information carries the difference between the second sequence number and the second PDCP COUNT value. The source access network device receives a first downlink dualcast data packet from the user plane network element, the first downlink dualcast data packet carrying first data and a first sequence number; The source access network device determines the first PDCP COUNT value corresponding to the first sequence number according to the mapping relationship; The source access network device determines the first PDCP sequence number corresponding to the first PDCP COUNT value; The source access network device sends a second downlink dual-cast data packet to the terminal device. The second downlink dual-cast data packet carries the first data and the first PDCP sequence number.

2. The method as described in claim 1, characterized in that, The first sequence number is N3.

3. The method as described in claim 1 or 2, characterized in that, Also includes: The source access network device sends a first request to the first device, the first request carrying information about the Quality of Service (QoS) flow group requested for duocast, and the first device is the target access network device or a mobility management network element. The source access network device receives a first response from the first device, the first response carrying information about a QoS stream group that accepts duocast, wherein the QoS stream group that accepts duocast is part or all of the QoS stream group that requests duocast.

4. A data transmission method, characterized in that, include: The target access network device receives indication information from the source access network device. The indication information is used to indicate a mapping relationship, which is used to indicate the mapping relationship between the sequence number allocated by the user plane network element and the PDCP COUNT value to be allocated. The indication information carries a second sequence number and the second PDCP COUNT value corresponding to the second sequence number, or the indication information carries the difference between the second sequence number and the second PDCP COUNT value. The target access network device receives a first downlink dualcast data packet from the user plane network element, the first downlink dualcast data packet carrying first data and a first sequence number; The target access network device determines the first PDCP COUNT value corresponding to the first sequence number according to the mapping relationship; The target access network device determines the first PDCP sequence number corresponding to the first PDCP COUNT value; The target access network device sends a second downlink dual-cast data packet to the terminal device. The second downlink dual-cast data packet carries the first data and the first PDCP sequence number.

5. The method as described in claim 4, characterized in that, The first sequence number is N3.

6. The method as described in claim 4 or 5, characterized in that, Also includes: The target access network device receives information about the QoS flow group requesting duocast; The target access network device determines the QoS flow group information to accept the duocast based on the QoS flow group information requested for duocast. The target access network device sends the QoS flow group information for accepting biscast to the session management network element.

7. The method as described in claim 6, characterized in that, The target access network device receives information about the QoS flow group requesting duocast, including: The target access network device receives a handover request message from the source access network device, the handover request message carrying information about the QoS flow group for which duocast is requested; or... The target access network device receives a handover request message from a mobility management network element, the handover request message carrying information about the QoS flow group requesting duocast.

8. A communication device, characterized in that, include: The transceiver unit is used to receive a third downlink dual-cast data packet from a user plane network element, wherein the third downlink dual-cast data packet carries second data and a second sequence number; The processing unit is configured to determine a mapping relationship based on the second sequence number and the second PDCP COUNT value corresponding to the third downlink dualcast data packet. The mapping relationship is used to indicate the mapping relationship between the sequence number allocated by the user plane network element and the PDCPCOUNT value to be allocated. The transceiver unit is further configured to send indication information to the target access network device, the indication information being used to indicate the mapping relationship; the indication information carries the second sequence number and the second PDCP COUNT value corresponding to the second sequence number, or the indication information carries the difference between the second sequence number and the second PDCP COUNT value; The transceiver unit is further configured to receive a first downlink dual-cast data packet from the user plane network element, the first downlink dual-cast data packet carrying first data and a first sequence number; The processing unit is further configured to determine the first PDCP COUNT value corresponding to the first serial number according to the mapping relationship; and to determine the first PDCP serial number corresponding to the first PDCP COUNT value; The transceiver unit is further configured to send a second downlink dual-cast data packet to the terminal device, the second downlink dual-cast data packet carrying the first data and the first PDCP sequence number.

9. The apparatus as claimed in claim 8, characterized in that, The first sequence number is N3.

10. The apparatus as claimed in claim 8 or 9, characterized in that, The transceiver unit is further configured to: A first request is made to a first device, the first request carrying information about the Quality of Service (QoS) flow group requested for duocast, the first device being a target access network device or a mobility management network element; Receive a first response from the first device, the first response carrying information about a QoS stream group that accepts duocast, the QoS stream group that accepts duocast being part or all of the QoS stream group that requested duocast.

11. A communication device, characterized in that, include: The transceiver unit is configured to receive indication information from the source access network device, the indication information indicating a mapping relationship, the mapping relationship indicating the mapping relationship between the sequence number allocated by the user plane network element and the PDCP COUNT value to be allocated; the indication information carries a second sequence number and a second PDCP COUNT value corresponding to the second sequence number, or the indication information carries the difference between the second sequence number and the second PDCP COUNT value; and to receive a first downlink dualcast data packet from the user plane network element, the first downlink dualcast data packet carrying first data and a first sequence number; The processing unit is configured to determine the first PDCP COUNT value corresponding to the first serial number based on the mapping relationship; and to determine the first PDCP serial number corresponding to the first PDCP COUNT value. The transceiver unit is further configured to send a second downlink dual-cast data packet to the terminal device, the second downlink dual-cast data packet carrying the first data and the first PDCP sequence number.

12. The apparatus as claimed in claim 11, characterized in that, The first sequence number is N3.

13. The apparatus as claimed in claim 11 or 12, characterized in that, The transceiver unit is also used to receive information about a QoS flow group requesting duocast; and to send information about a QoS flow group accepting duocast to the session management network element. The processing unit is further configured to determine the QoS stream group accepting the duocast based on the information of the QoS stream group requesting the duocast.

14. The apparatus as claimed in claim 13, characterized in that, The transceiver unit is specifically used for: Receive a handover request message from the source access network device, the handover request message carrying information about the QoS flow group requesting duocast; or... The system receives a handover request message from a mobility management network element, the handover request message carrying information about the QoS flow group for which duocast is requested.

15. A computer-readable storage medium, characterized in that, Includes instructions that, when executed on a computer, cause the computer to perform the method as described in any one of claims 1 to 7.

16. A computer program product, characterized in that, The computer program product includes instructions that, when executed, implement the method as described in any one of claims 1 to 7.

17. A chip system, characterized in that, The system includes a processor coupled to a memory for storing programs or instructions that, when executed by the processor, implement the method as described in any one of claims 1 to 7.

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