Data transmission method and apparatus

Abstract

Provided in the present application are a data transmission method and apparatus, which can improve the user experience of a terminal apparatus during a handover process, and can be applied to an NTN, such as a satellite communication system. The method comprises: a first access network apparatus determining that it is necessary to hand over a terminal apparatus to a second access network apparatus; the first access network apparatus sending a buffered data packet to the second access network apparatus, wherein the buffered data packet comprises a data packet in a MAC layer buffer and / or an RLC layer buffer, and the buffered data packet comprises at least one of the following: a downlink MAC layer data packet, an uplink MAC layer data packet, a downlink RLC layer data packet, or a first uplink RLC layer data packet; the second access network apparatus sending first information to the terminal apparatus, wherein the first information comprises the downlink MAC layer data packet and / or the downlink RLC layer data packet; and the terminal apparatus sending second information to the second access network apparatus, wherein the second information comprises the uplink MAC layer data packet and / or a second uplink RLC layer data packet.

Description

Methods and apparatus for data transmission

[0001] This application claims priority to Chinese Patent Application No. 202411936537.9, filed on December 25, 2024, entitled "Method and Apparatus for Data Transmission", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of communications, and more specifically, to a method and apparatus for data transmission. Background Technology

[0003] In the New Radio (NR) air interface, data packets pass through the following layers from top to bottom: Service Data Adaptation Protocol (SDAP), Packet Data Convergence Protocol (PDCP), Radio Link Control (RLC), Medium Access Control (MAC), and Physical Layer (PHY). Above SDAP is the Transmission Control Protocol (TCP) / Internet Protocol (IP) layer, which belongs to the IP network protocol stack. For uplink data, after the base station's SDAP layer decrypts the data, the IP packet is exposed, and the base station performs IP routing and forwarding based on the destination IP address. For downlink data, after the terminal device's SDAP layer decrypts the data, it is handed over to the upper layer for processing.

[0004] In existing cross-site handover processes, to ensure service continuity, the source base station needs to transfer data to the target base station. This is because after a terminal device disconnects from the source base station, it takes time to access the target base station and establish an RRC connection. Only after the RRC connection between the terminal device and the target base station is established will the target base station notify the core network. Before this, the core network still considers the terminal device to be under the source base station and will send data to the source base station that needs to be transmitted to the terminal device. However, since the terminal device has already disconnected from the source base station, the source base station needs to transfer the downlink data from the core network to the target base station, which then sends it to the terminal device. In addition to data from the core network, the source base station also needs to send the SDU corresponding to any cached but incompletely transmitted PDCP protocol data units (PDUs) to the target base station. The target base station then regenerates the PDCP PDU and sends it to the terminal device. Both of these data packet transfers (data packets arriving from the core network to the source base station and data packets that have not been fully transmitted at the source base station) are at the PDCP layer. The source base station also transfers the PDCP service data unit (SDU) to the target base station, which then sends it to the terminal device.

[0005] How to improve performance and thus enhance user experience during the switching process is a question that needs to be considered. Summary of the Invention

[0006] This application provides a data transmission method and apparatus that can improve the user experience of a terminal device (terminal equipment) during the handover process.

[0007] Firstly, a data transmission method is provided, which can be applied to, for example, executed by, a first access network device. The first access network device can be an access network equipment, or a device within the access network equipment (e.g., a module, communication module, circuit or chip responsible for communication functions (such as a modem chip, or a SoC chip or SIP chip containing a modem core), chip system, or processor), or a logical node, logical module, or software capable of implementing all or part of the functions of the access network equipment. The method includes: determining that a terminal device needs to be switched to a second access network device, wherein the first access network device is the source access network device of the terminal device, and the second access network device is the target access network device of the terminal device; sending buffered data packets to the second access network device, the buffered data packets including data packets in a Media Access Control (MAC) layer buffer and / or a Radio Link Control (RLC) layer buffer, the buffered data packets including at least one of the following: downlink MAC layer data packets, uplink MAC layer data packets, downlink RLC layer data packets, or a first uplink RLC layer data packet. The first uplink RLC layer data packet can be understood as the first uplink RLC layer data packet successfully received by the first access network device; the first uplink RLC layer data packet and the second uplink RLC layer data packet belong to the same PDCP layer data packet, and the second uplink RLC layer data packet is the uplink RLC layer data packet that the first access network device failed to receive.

[0008] Based on the above technical solution, when a terminal device switches from a first access network device to a second access network device, the first access network device transfers the data packets cached in the MAC buffer and / or RLC layer buffer to the second access network device. The subsequent transmission is completed between the second access network device and the terminal device. The automatic repeat request (ARQ) buffer and hybrid automatic repeat request (HARQ) buffer on the terminal device side do not need to be cleared, which can realize seamless switching of the terminal device and thus improve the user experience of the terminal device during the switching process.

[0009] In conjunction with the first aspect, in some implementations of the first aspect, the cached data packet further includes first indication information. This first indication information indicates at least one of the following: the HARQ process number, redundancy version information, or code block group information corresponding to the downlink MAC layer data packet and the uplink MAC layer data packet, respectively. Based on this implementation, the second access network device can determine which HARQ process is used for transmission of the downlink MAC layer data packet and the uplink MAC layer data packet based on their respective HARQ process numbers. This enables the second access network device to correctly send downlink MAC layer data packets and correctly receive uplink MAC layer data packets, thereby improving data transmission reliability. Furthermore, based on the redundancy version information corresponding to the downlink MAC layer data packets and the uplink MAC layer data packets, the second access network device can determine which bits in the MAC PDU need to be transmitted during downlink MAC layer data packet transmission and which bits in the MAC PDU are transmitted by the terminal device during uplink MAC layer data packet transmission. This enables the second access network device to correctly send the bit information of the downlink MAC layer data packets and correctly receive the bit information of the uplink MAC layer data packets, thereby improving data transmission reliability. The second access network device can obtain the identifier of the downlink code block group that was not successfully transmitted based on the code block group information corresponding to the downlink MAC layer data packet, and can obtain the identifier of the uplink code block group that was not successfully received based on the code block group information corresponding to the uplink MAC layer data packet. This enables the second access network device to retransmit the downlink code block group that was not successfully transmitted and to receive the uplink code block group that was not successfully received, thereby improving the reliability of data transmission.

[0010] In conjunction with the first aspect, in some implementations of the first aspect, the cached data packet further includes second indication information. This second indication information indicates the key information used during data transmission between the first access network device and the terminal device. Based on this implementation, the second access network device can use this key information to decrypt the received uplink MAC layer data packet / second uplink RLC layer data packet from the terminal device after it is submitted to the PDCP layer. This avoids retransmissions due to decryption failures, thereby improving data transmission efficiency.

[0011] In conjunction with the first aspect, in some implementations of the first aspect, the cached data packets further include third indication information. This third indication information indicates that the downlink MAC layer data packets and the downlink RLC layer data packets are data packets requiring downlink transmission, and the uplink MAC layer data packets and the first uplink RLC layer data packets are data packets requiring uplink transmission. Based on this implementation, the second access network device, according to the third indication information, can determine which data packets in the cached data packets from the first access network device require downlink transmission and which require uplink transmission, thus ensuring correct data packet transmission and improving data transmission reliability.

[0012] In conjunction with the first aspect, in some implementations of the first aspect, the cached data packet further includes fourth indication information, which indicates at least one of the following: the sequence number of the downlink RLC layer data packet, the sequence number used by the second access network device to transmit downlink RLC layer data packets from the upper layer, the maximum value of the sequence number of successfully received uplink RLC layer data packets, or the sequence number of an unsuccessfully received uplink RLC layer data packet. Based on this implementation, the second access network device can determine the sequence number used by the unsuccessfully transmitted downlink RLC layer data packet based on the sequence number of the downlink RLC layer data packet or the sequence number used to transmit the downlink RLC layer data packet from the upper layer, and use this sequence number to transmit the downlink RLC layer data packet, thereby achieving correct transmission of the downlink RLC layer data packet and improving the reliability of data transmission. The second access network device can determine the sequence number used by the next uplink RLC layer data packet transmitted by the terminal device based on the maximum value of the sequence number of the uplink RLC layer data packet successfully received by the first access network device, thereby achieving correct reception of the uplink RLC layer data packet and improving the reliability of data transmission. The second access network device can also know the sequence number of the uplink RLC layer data packet that the first access network device failed to receive, and thus know the sequence number of the uplink RLC layer data packet to be transmitted (retransmitted) by the terminal device. This enables the correct reception of the uplink RLC layer data packet and improves the reliability of data transmission.

[0013] In conjunction with the first aspect, some implementations of the first aspect further include: sending a request message to the second access network device, the request message requesting the establishment of at least one tunnel for transmitting the buffered data packets, the request message including tunnel identification information of the first access network device; and receiving a response message from the second access network device, the response message including tunnel identification information of the second access network device. In this implementation, establishing a dedicated tunnel to send the buffered data packets (data packets in the MAC layer buffer and / or RLC layer buffer) to the second access network device, compared to reusing an existing Xn tunnel (data channel) for transferring PDCP SDUs to send the buffered data packets to the second access network device, allows for the simultaneous transfer of buffered data packets (data packets in the MAC layer buffer and / or RLC layer buffer) and PDCP SDUs to the second communication device, thereby improving data transmission efficiency.

[0014] Optionally, the first access network device reuses the existing Xn tunnel (data channel) used for transferring PDCP SDUs to send the buffered data packets to the second access network device. In this implementation, it is not necessary to establish an additional tunnel.

[0015] In conjunction with the first aspect, in some implementations of the first aspect, the request information further includes fifth indication information. This fifth indication information is used to instruct the first tunnel to be used for transmitting the downlink MAC layer data packets and / or the uplink MAC layer data packets, and the second tunnel to be used for transmitting the downlink RLC layer data packets and / or the first uplink RLC layer data packets. The at least one tunnel includes both the first tunnel and the second tunnel. In this optional implementation, establishing tunnels for transmitting MAC layer data packets and tunnels for transmitting RLC layer data packets, with the first tunnel used for transmitting MAC layer data packets and the second tunnel used for transmitting RLC layer data packets, allows for the simultaneous transmission (transfer) of MAC layer data packets and RLC layer data packets to the second communication device, thereby improving data transmission efficiency.

[0016] In conjunction with the first aspect, in some implementations of the first aspect, the request information further includes sixth indication information. This sixth indication information is used to instruct the first tunnel to transmit the downlink MAC layer data packets and / or the downlink RLC layer data packets, and the second tunnel to transmit the uplink MAC layer data packets and / or the first uplink RLC layer data packets. The at least one tunnel includes both the first tunnel and the second tunnel. In this optional implementation, different tunnels are established for uplink and downlink data packets. The first tunnel is used to transmit downlink data packets (downlink MAC layer data packets and / or downlink RLC layer data packets), and the second tunnel is used to transmit uplink data packets (uplink MAC layer data packets and / or the first uplink RLC layer data packets). This allows for the simultaneous transmission of downlink and uplink data packets to the second communication device, improving data transmission efficiency.

[0017] In conjunction with the first aspect, in some implementations of the first aspect, the request information further includes seventh indication information. This seventh indication information is used to instruct the first tunnel to transmit MAC layer data packets corresponding to the first HARQ process number, and the second tunnel to transmit MAC layer data packets corresponding to the second HARQ process number. The at least one tunnel includes both the first tunnel and the second tunnel. In this optional implementation, establishing a separate tunnel for each HARQ process number allows for the simultaneous transmission of MAC layer data packets corresponding to different HARQ process numbers to the second communication device, thereby improving data transmission efficiency.

[0018] In conjunction with the first aspect, in some implementations of the first aspect, the seventh indication information is further used to indicate the redundancy version information and / or code block group information of the MAC layer data packets corresponding to the first HARQ process number and the second HARQ process number, respectively. Based on this implementation, the second access network device can determine, according to the redundancy version information, which bits in the MAC PDU need to be transmitted during downlink MAC layer data packet transmission, and which bits in the MAC PDU are transmitted by the terminal device during uplink MAC layer data packet transmission. This enables the second access network device to correctly send the bit information of the downlink MAC layer data packets and correctly receive the bit information of the uplink MAC data packets, thereby improving the reliability of data transmission. According to the code block group information, the second access network device can determine the identifiers of downlink code block groups that were not successfully transmitted and uplink code block groups that were not successfully received. This enables the second access network device to retransmit the downlink code block groups that were not successfully transmitted and to receive the uplink code block groups that were not successfully received, thereby improving the reliability of data transmission.

[0019] In conjunction with the first aspect, in some implementations of the first aspect, the request information further includes second indication information. This second indication information is used to indicate key information used during data transmission between the first access network device and the terminal device. This key information is used by the second access network device to decrypt uplink MAC layer data packets / second uplink RLC layer data packets received from the terminal device and submitted to the PDCP layer. This avoids retransmissions due to decryption failures, thereby improving data transmission efficiency. This second indication information can be carried in the request information sent to the second access network device, or it can be carried in a cached data packet sent to the second access network device, or it can be sent to the second access network device in other ways; this application does not limit this.

[0020] In conjunction with the first aspect, in certain implementations of the first aspect, the downlink MAC layer data packet includes downlink code block groups that were not successfully transmitted, and the code block group information corresponding to the downlink MAC layer data packet includes any one of the following: the identifier of the downlink code block group that was not successfully transmitted and / or the identifier of the downlink code block group that was successfully transmitted, the number of code block groups included in the downlink MAC layer data packet and the identifier of the downlink code block group that was not successfully transmitted, or the number of code block groups included in the downlink MAC layer data packet and the identifier of the downlink code block group that was successfully transmitted; the uplink MAC layer data packet includes uplink code block groups that were successfully received, and the code block group information corresponding to the uplink MAC layer data packet includes any one of the following: the identifier of the uplink code block group that was successfully received and / or the identifier of the uplink code block group that was not successfully received, the number of code block groups included in the uplink MAC layer data packet and the identifier of the uplink code block group that was successfully received, or the number of code block groups included in the uplink MAC layer data packet and the identifier of the uplink code block group that was not successfully received. Based on this implementation, the second access network device can obtain the identifier of the downlink code block group that was not successfully transmitted according to the code block group information corresponding to the downlink MAC layer data packet, and the second access network device can obtain the identifier of the uplink code block group that was not successfully received according to the code block group information corresponding to the uplink MAC layer data packet. This enables the second access network device to retransmit the downlink code block group that was not successfully transmitted and to receive the uplink code block group that was not successfully received, thereby improving the reliability of data transmission.

[0021] Secondly, a data transmission method is provided, which can be applied to a second access network device, such as being executed by the second access network device, which can be an access network equipment, or a device within the access network equipment (e.g., a module, communication module, circuit or chip responsible for communication functions (such as a modem chip, or a SoC chip or SIP chip containing a modem core), chip system or processor), or a logical node, logical module or software that can implement all or part of the functions of the access network equipment. The method includes: receiving buffered data packets from a first access network device, the buffered data packets including data packets in a MAC layer buffer and / or an RLC layer buffer, the buffered data packets including at least one of the following: downlink MAC layer data packets, uplink MAC layer data packets, downlink RLC layer data packets, or a first uplink RLC layer data packet, the first access network device being a source access network device of a terminal device, and the second access network device being a target access network device of the terminal device; sending first information to the terminal device, the first information including the downlink MAC layer data packets and / or the downlink RLC layer data packets; receiving second information from the terminal device, the second information including the uplink MAC layer data packets and / or the second uplink RLC layer data packets, the first uplink RLC layer data packets and the second uplink RLC layer data packets belonging to the same Packet Data Convergence Protocol (PDCP) layer data packets.

[0022] The method provided in the second aspect is the method on the second access network device side corresponding to the first aspect, and its beneficial effects can be referred to the first aspect.

[0023] In conjunction with the second aspect, in some implementations of the second aspect, the cached data packet further includes first indication information, which is used to indicate at least one of the following: HARQ process number, redundancy version information, or code block group information corresponding to the downlink MAC layer data packet that was not successfully sent and the uplink MAC layer data packet that was not successfully decoded.

[0024] In conjunction with the second aspect, in some implementations of the second aspect, the cached data packet further includes second indication information, which is used to indicate key information used in the data transmission process between the first access network device and the terminal device.

[0025] In conjunction with the second aspect, in some implementations of the second aspect, the cached data packet further includes third indication information, which is used to indicate that the downlink MAC layer data packet and the downlink RLC layer data packet are data packets that need to be transmitted downlink, and the uplink MAC layer data packet and the first uplink RLC layer data packet are data packets that need to be transmitted uplink.

[0026] In conjunction with the second aspect, in some implementations of the second aspect, the cached data packet further includes fourth indication information, which is used to indicate at least one of the following: the sequence number of the downlink RLC layer data packet, the sequence number used by the second access network device to transmit downlink RLC layer data packets from the upper layer, the maximum value of the sequence number of the successfully received uplink RLC layer data packet, or the sequence number of the unsuccessfully received uplink RLC layer data packet.

[0027] In conjunction with the second aspect, some implementations of the second aspect further include: receiving request information from the first access network device, the request information requesting the establishment of at least one tunnel for transmitting the cached data packets, the request information including tunnel identification information of the first access network device; and sending response information to the first access network device, the response information including tunnel identification information of the second access network device.

[0028] In conjunction with the second aspect, in some implementations of the second aspect, the request information further includes fifth indication information, which is used to indicate that the first tunnel is used to transmit the downlink MAC layer data packet and / or the uplink MAC layer data packet, and the second tunnel is used to transmit the downlink RLC layer data packet and / or the first uplink RLC layer data packet, wherein the at least one tunnel includes the first tunnel and the second tunnel.

[0029] In conjunction with the second aspect, in some implementations of the second aspect, the request information further includes sixth indication information, which is used to indicate that the first tunnel is used to transmit the downlink MAC layer data packets and / or the downlink RLC layer data packets, and the second tunnel is used to transmit the uplink MAC layer data packets and / or the first uplink RLC layer data packets, wherein the at least one tunnel includes the first tunnel and the second tunnel.

[0030] In conjunction with the second aspect, in some implementations of the second aspect, the request information further includes seventh indication information, which is used to indicate that the first tunnel is used to transmit MAC layer data packets corresponding to the first HARQ process number, and the second tunnel is used to transmit MAC layer data packets corresponding to the second HARQ process number, wherein the at least one tunnel includes the first tunnel and the second tunnel.

[0031] In conjunction with the second aspect, in some implementations of the second aspect, the seventh indication information is further used to indicate the redundancy version information and / or code block group information of the MAC layer data packets corresponding to the first HARQ process number and the second HARQ process number, respectively.

[0032] In conjunction with the second aspect, in some implementations of the second aspect, the request information further includes second indication information, which is used to indicate key information used in the data transmission process between the first access network device and the terminal device.

[0033] In conjunction with the second aspect, in some implementations of the second aspect, the first information further includes eighth indication information, which indicates that the first information originates from the first access network device. Based on this implementation, the terminal device, according to the eighth indication information, can determine that after downlink MAC layer data packets and / or downlink RLC layer data packets from the first access network device are delivered to the PDCP layer, it uses the key (old key) used during data transmission with the first access network device for decryption. This avoids decryption failures caused by the terminal device using the key (new key) used during data transmission with the second access network device, improving the terminal device's decryption efficiency for data packets and thus improving data transmission efficiency.

[0034] In conjunction with the second aspect, in some implementations of the second aspect, the second information further includes ninth indication information. This ninth indication information is used to indicate that the second information, after being submitted to the upper layer, should be parsed using the key used during data transmission between the first access network device and the terminal device. Based on this implementation, the second access network device, according to the ninth indication information, can successfully parse the second information using the key used during data transmission between the first access network device and the terminal device after submitting it to the PDCP layer. This avoids retransmissions due to parsing failures, thereby improving data transmission efficiency.

[0035] In conjunction with the second aspect, some implementations of the second aspect further include: if the second information includes uplink RRC layer data packets originating from the Radio Resource Control (RRC) layer, then the uplink RRC layer data packets are discarded. It should be noted that the control plane messages (RRC messages) sent by the terminal device also need to pass through the MAC layer. The uplink RRC layer data packets originating from the RRC layer included in the second information are sent by the terminal device to the first access network device, and the second access network device cannot use them directly and must discard them.

[0036] In conjunction with the second aspect, in some implementations of the second aspect, the downlink MAC layer data packet includes downlink code block groups that were not successfully transmitted. The code block group information corresponding to the downlink MAC layer data packet includes any one of the following: the identifier of the downlink code block group that was not successfully transmitted and / or the identifier of the downlink code block group that was successfully transmitted; the number of code block groups included in the downlink MAC layer data packet and the identifier of the downlink code block group that was not successfully transmitted; or the number of code block groups included in the downlink MAC layer data packet and the identifier of the downlink code block group that was successfully transmitted. The uplink MAC layer data packet includes uplink code block groups that were successfully received. The code block group information corresponding to the uplink MAC layer data packet includes any one of the following: the identifier of the uplink code block group that was successfully received and / or the identifier of the uplink code block group that was not successfully received; the number of code block groups included in the uplink MAC layer data packet and the identifier of the uplink code block group that was successfully received; or the number of code block groups included in the uplink MAC layer data packet and the identifier of the uplink code block group that was not successfully received.

[0037] Thirdly, a data transmission method is provided, which can be applied to a terminal device, such as being executed by the terminal device. The terminal device can be a terminal equipment, or a device within the terminal device (e.g., a module, communication module, circuit or chip responsible for communication functions (such as a modem chip, also known as a baseband chip, or a system-on-chip (SoC) chip containing a modem core or a system-in-package (SIP) chip), a chip system, or a processor), or a logical node, logical module, or software capable of implementing all or part of the terminal equipment's functions. The method includes: receiving first information from a second access network device, the first information including downlink MAC layer data packets in the MAC layer buffer of a first access network device, and / or downlink RLC layer data packets in the RLC layer buffer, wherein the first access network device is the source access network device of the terminal device, and the second access network device is the target access network device of the terminal device; and sending second information to the second access network device, the second information including uplink MAC layer data packets, and / or second uplink RLC layer data packets.

[0038] The method provided in the third aspect is the terminal device-side method corresponding to the first and second aspects, and its beneficial effects can be referred to the first and second aspects.

[0039] In conjunction with the third aspect, in some implementations of the third aspect, the first information further includes eighth indication information, which is used to indicate that the first information comes from the first access network device.

[0040] In conjunction with the third aspect, in some implementations of the third aspect, the second information further includes a ninth indication information, which is used to indicate that the key used in the data transmission process between the first access network device and the terminal device is used for parsing after the second information is submitted to the upper layer.

[0041] In conjunction with the third aspect, some implementations of the third aspect further include: if the first information includes downlink RRC layer data packets originating from the RRC layer, then the downlink RRC layer data packets are discarded. It should be noted that control plane messages (RRC messages) sent by the first access network device also need to pass through the MAC layer. For the downlink MAC layer data packets corresponding to these control plane messages, when the terminal device decodes them and finds they are RRC layer data packets, they need to be discarded; because RRC messages are control signaling between the terminal device and the first access network device, when the terminal device switches to the second access network device, the control signaling of the first access network device cannot continue to be used and needs to be discarded.

[0042] Fourthly, a communication device is provided, which can be the first access network device described in the first aspect. The communication device includes: a processing module, configured to determine that a terminal device needs to be switched to a second access network device, wherein the first access network device is the source access network device of the terminal device, and the second access network device is the target access network device of the terminal device.

[0043] The transceiver module is used to send buffered data packets to the second access network device. The buffered data packets include data packets in the Media Access Control (MAC) layer buffer and / or the Radio Link Control (RLC) layer buffer. The buffered data packets include at least one of the following: downlink MAC layer data packets, uplink MAC layer data packets, downlink RLC layer data packets, or a first uplink RLC layer data packet.

[0044] In conjunction with the fourth aspect, in some implementations of the fourth aspect, the cached data packet further includes first indication information, which is used to indicate at least one of the following: the HARQ process number, redundancy version information, or code block group information corresponding to the downlink MAC layer data packet and the uplink MAC layer data packet, respectively.

[0045] In conjunction with the fourth aspect, in some implementations of the fourth aspect, the cached data packet further includes second indication information, which is used to indicate key information used in the data transmission process between the first access network device and the terminal device.

[0046] In conjunction with the fourth aspect, in some implementations of the fourth aspect, the cached data packet further includes third indication information, which is used to indicate that the downlink MAC layer data packet and the downlink RLC layer data packet are data packets that need to be transmitted downlink, and the uplink MAC layer data packet and the first uplink RLC layer data packet are data packets that need to be transmitted uplink.

[0047] In conjunction with the fourth aspect, in some implementations of the fourth aspect, the cached data packet further includes fourth indication information, which is used to indicate at least one of the following: the sequence number of the downlink RLC layer data packet, the sequence number used by the second access network device to transmit downlink RLC layer data packets from the upper layer, the maximum value of the sequence number of the successfully received uplink RLC layer data packet, or the sequence number of the unsuccessfully received uplink RLC layer data packet.

[0048] In conjunction with the fourth aspect, in some implementations of the fourth aspect, the transceiver module is further configured to send a request message to the second access network device, the request message requesting the establishment of at least one tunnel for transmitting the cached data packets, the request message including tunnel identification information of the first access network device;

[0049] The transceiver module is further configured to receive response information from the second access network device, the response information including tunnel identification information of the second access network device.

[0050] In conjunction with the fourth aspect, in some implementations of the fourth aspect, the request information further includes fifth indication information, which is used to indicate that the first tunnel is used to transmit the downlink MAC layer data packet and / or the uplink MAC layer data packet, and the second tunnel is used to transmit the downlink RLC layer data packet and / or the first uplink RLC layer data packet, wherein the at least one tunnel includes the first tunnel and the second tunnel.

[0051] In conjunction with the fourth aspect, in some implementations of the fourth aspect, the request information further includes sixth indication information, which is used to indicate that the first tunnel is used to transmit the downlink MAC layer data packet and / or the downlink RLC layer data packet, and the second tunnel is used to transmit the uplink MAC layer data packet and / or the first uplink RLC layer data packet, wherein the at least one tunnel includes the first tunnel and the second tunnel.

[0052] In conjunction with the fourth aspect, in some implementations of the fourth aspect, the request information further includes a seventh indication information, which is used to indicate that the first tunnel is used to transmit MAC layer data packets corresponding to the first HARQ process number, and the second tunnel is used to transmit MAC layer data packets corresponding to the second HARQ process number, wherein the at least one tunnel includes the first tunnel and the second tunnel.

[0053] In conjunction with the fourth aspect, in some implementations of the fourth aspect, the seventh indication information is further used to indicate the redundancy version information and / or code block group information of the MAC layer data packets corresponding to the first HARQ process number and the second HARQ process number, respectively.

[0054] In conjunction with the fourth aspect, in some implementations of the fourth aspect, the request information further includes second indication information, which is used to indicate key information used in the data transmission process between the first access network device and the terminal device.

[0055] In conjunction with the fourth aspect, in certain implementations of the fourth aspect, the downlink MAC layer data packet includes downlink code block groups that were not successfully transmitted. The code block group information corresponding to the downlink MAC layer data packet includes any one of the following: the identifier of the downlink code block group that was not successfully transmitted and / or the identifier of the downlink code block group that was successfully transmitted; the number of code block groups included in the downlink MAC layer data packet and the identifier of the downlink code block group that was not successfully transmitted; or the number of code block groups included in the downlink MAC layer data packet and the identifier of the downlink code block group that was successfully transmitted. The uplink MAC layer data packet includes uplink code block groups that were successfully received. The code block group information corresponding to the uplink MAC layer data packet includes any one of the following: the identifier of the uplink code block group that was successfully received and / or the identifier of the uplink code block group that was not successfully received; the number of code block groups included in the uplink MAC layer data packet and the identifier of the uplink code block group that was successfully received; or the number of code block groups included in the uplink MAC layer data packet and the identifier of the uplink code block group that was not successfully received.

[0056] Fifthly, a communication device is provided, which can be the second access network device described in the second aspect. The communication device includes: a transceiver module for receiving buffered data packets from a first access network device, wherein the buffered data packets include data packets in a MAC layer buffer and / or an RLC layer buffer, and the buffered data packets include at least one of the following: downlink MAC layer data packets, uplink MAC layer data packets, downlink RLC layer data packets, or a first uplink RLC layer data packet, wherein the first access network device is a source access network device of a terminal device, and the second access network device is a target access network device of the terminal device;

[0057] The transceiver module is further configured to send first information to the terminal device, the first information including the downlink MAC layer data packet and / or the downlink RLC layer data packet;

[0058] The transceiver module is further configured to receive second information from the terminal device, the second information including the uplink MAC layer data packet and / or the second uplink RLC layer data packet, wherein the first uplink RLC layer data packet and the second uplink RLC layer data packet belong to the same Packet Data Convergence Protocol (PDCP) layer data packet.

[0059] In conjunction with the fifth aspect, in some implementations of the fifth aspect, the cached data packet further includes first indication information, which is used to indicate at least one of the following: HARQ process number, redundancy version information, or code block group information corresponding to the downlink MAC layer data packet that was not successfully sent and the uplink MAC layer data packet that was not successfully decoded.

[0060] In conjunction with the fifth aspect, in some implementations of the fifth aspect, the cached data packet further includes second indication information, which is used to indicate key information used in the data transmission process between the first access network device and the terminal device.

[0061] In conjunction with the fifth aspect, in some implementations of the fifth aspect, the cached data packet further includes third indication information, which is used to indicate that the downlink MAC layer data packet and the downlink RLC layer data packet are data packets that need to be transmitted downlink, and the uplink MAC layer data packet and the first uplink RLC layer data packet are data packets that need to be transmitted uplink.

[0062] In conjunction with the fifth aspect, in some implementations of the fifth aspect, the cached data packet further includes fourth indication information, which is used to indicate at least one of the following: the sequence number of the downlink RLC layer data packet, the sequence number used by the second access network device to transmit downlink RLC layer data packets from the upper layer, the maximum value of the sequence number of a successfully received uplink RLC layer data packet, or the sequence number of an unsuccessfully received uplink RLC layer data packet.

[0063] In conjunction with the fifth aspect, in some implementations of the fifth aspect, the transceiver module is further configured to receive request information from the first access network device, the request information requesting the establishment of at least one tunnel for transmitting the cached data packets, the request information including tunnel identification information of the first access network device;

[0064] The transceiver module is further configured to send response information to the first access network device, the response information including tunnel identification information of the second access network device.

[0065] In conjunction with the fifth aspect, in some implementations of the fifth aspect, the request information further includes fifth indication information, which is used to indicate that the first tunnel is used to transmit the downlink MAC layer data packet and / or the uplink MAC layer data packet, and the second tunnel is used to transmit the downlink RLC layer data packet and / or the first uplink RLC layer data packet, wherein the at least one tunnel includes the first tunnel and the second tunnel.

[0066] In conjunction with the fifth aspect, in some implementations of the fifth aspect, the request information further includes sixth indication information, which is used to indicate that the first tunnel is used to transmit the downlink MAC layer data packet and / or the downlink RLC layer data packet, and the second tunnel is used to transmit the uplink MAC layer data packet and / or the first uplink RLC layer data packet, wherein the at least one tunnel includes the first tunnel and the second tunnel.

[0067] In conjunction with the fifth aspect, in some implementations of the fifth aspect, the request information further includes a seventh indication information, which is used to indicate that the first tunnel is used to transmit MAC layer data packets corresponding to the first HARQ process number, and the second tunnel is used to transmit MAC layer data packets corresponding to the second HARQ process number, wherein the at least one tunnel includes the first tunnel and the second tunnel.

[0068] In conjunction with the fifth aspect, in some implementations of the fifth aspect, the seventh indication information is further used to indicate the redundancy version information and / or code block group information of the MAC layer data packets corresponding to the first HARQ process number and the second HARQ process number, respectively.

[0069] In conjunction with the fifth aspect, in some implementations of the fifth aspect, the request information further includes second indication information, which is used to indicate key information used in the data transmission process between the first access network device and the terminal device.

[0070] In conjunction with the fifth aspect, in some implementations of the fifth aspect, the first information further includes eighth indication information, which is used to indicate that the first information comes from the first access network device.

[0071] In conjunction with the fifth aspect, in some implementations of the fifth aspect, the second information further includes a ninth indication information, which is used to indicate that the key used in the data transmission process between the first access network device and the terminal device is used for parsing after the second information is submitted to the upper layer.

[0072] In conjunction with the fifth aspect, in some implementations of the fifth aspect, the communication device further includes: a processing module, configured to discard the uplink RRC layer data packet if the second information includes an uplink RRC layer data packet originating from the RRC layer.

[0073] In conjunction with the fifth aspect, in certain implementations of the fifth aspect, the downlink MAC layer data packet includes downlink code block groups that were not successfully transmitted. The code block group information corresponding to the downlink MAC layer data packet includes any one of the following: the identifier of the downlink code block group that was not successfully transmitted and / or the identifier of the downlink code block group that was successfully transmitted; the number of code block groups included in the downlink MAC layer data packet and the identifier of the downlink code block group that was not successfully transmitted; or the number of code block groups included in the downlink MAC layer data packet and the identifier of the downlink code block group that was successfully transmitted. The uplink MAC layer data packet includes uplink code block groups that were successfully received. The code block group information corresponding to the uplink MAC layer data packet includes any one of the following: the identifier of the uplink code block group that was successfully received and / or the identifier of the uplink code block group that was not successfully received; the number of code block groups included in the uplink MAC layer data packet and the identifier of the uplink code block group that was successfully received; or the number of code block groups included in the uplink MAC layer data packet and the identifier of the uplink code block group that was not successfully received.

[0074] In a sixth aspect, a communication device is provided, which can be the terminal device described in the third aspect. The communication device includes: a transceiver module for receiving first information from a second access network device, the first information including downlink MAC layer data packets in the MAC layer buffer of the first access network device and / or downlink RLC layer data packets in the RLC layer buffer, the first access network device being the source access network device of the terminal device, and the second access network device being the target access network device of the terminal device.

[0075] The transceiver module is further configured to send second information to the second access network device, the second information including uplink MAC layer data packets and / or, second uplink RLC layer data packets.

[0076] In conjunction with the sixth aspect, in some implementations of the sixth aspect, the first information further includes eighth indication information, which is used to indicate that the first information comes from the first access network device.

[0077] In conjunction with the sixth aspect, in some implementations of the sixth aspect, the second information further includes a ninth indication information, which is used to indicate that the key used in the data transmission process between the first access network device and the terminal device is used for parsing after the second information is submitted to the upper layer.

[0078] In conjunction with the sixth aspect, in some implementations of the sixth aspect, the communication device further includes: a processing module, configured to discard the downlink RRC layer data packet if the first information includes a downlink RRC layer data packet originating from the RRC layer.

[0079] A seventh aspect provides a communication device comprising: a processor configured to implement the method as described in the first aspect or any possible implementation thereof. Optionally, the communication device further comprises an interface circuit configured to receive signals from other communication devices and transmit them to the processor, or to send signals from the processor to other communication devices.

[0080] Eighthly, a communication device is provided, comprising: a processor configured to implement the method as described in the second aspect or any possible implementation thereof. Optionally, the communication device further comprises an interface circuit configured to receive signals from other communication devices and transmit them to the processor, or to send signals from the processor to other communication devices.

[0081] A ninth aspect provides a communication device comprising: a processor configured to implement the method as described in the third aspect or any possible implementation thereof. Optionally, the communication device further comprises an interface circuit configured to receive signals from other communication devices and transmit them to the processor, or to send signals from the processor to other communication devices.

[0082] In a tenth aspect, a communication system is provided, comprising a first access network device for performing the method as described in the first aspect, a second access network device for performing the method as described in the second aspect, and a terminal device for performing the method as described in the third aspect.

[0083] Eleventhly, a computer-readable storage medium is provided, the computer-readable medium storing a computer program; when the computer program is executed by a processor, the methods in the first to third aspects or any possible implementation of the first to third aspects are performed.

[0084] In a twelfth aspect, a computer program product is provided, the computer program product comprising a computer program that, when executed, causes the methods of the first to third aspects or any possible implementation thereof to be performed.

[0085] The solutions provided in aspects four through twelfth above are used to implement or cooperate with the methods provided in aspect one, aspect two, or aspect three above, and therefore can achieve the same or corresponding beneficial effects as aspect one, aspect two, or aspect three, which will not be elaborated here. Attached Figure Description

[0086] Figure 1 is a schematic diagram of the architecture of the communication system applicable to the embodiments of this application;

[0087] Figure 2 is an example diagram of an open radio access network (open RAN, O-RAN, or ORAN) system;

[0088] Figure 3a is a schematic diagram of the architecture of an NTN communication system;

[0089] Figure 3b is a schematic diagram of the architecture of another NTN communication system;

[0090] Figure 3c is a schematic diagram of the architecture of another NTN communication system;

[0091] Figure 3d is a schematic diagram of the architecture of another NTN communication system;

[0092] Figure 4 is a schematic diagram of the processing of user plane data packets in NR through the higher-level protocol stack;

[0093] Figure 5 is a schematic diagram of HARQ redundant version transmission;

[0094] Figure 6 is a schematic flowchart of a data transmission method provided in an embodiment of this application;

[0095] Figure 7 is a schematic diagram of the control plane protocol stack;

[0096] Figure 8 is a schematic flowchart illustrating an example of a data transmission method provided in an embodiment of this application.

[0097] Figure 9 is a schematic flowchart illustrating another example of the data transmission method provided in the embodiments of this application;

[0098] Figure 10 is a schematic block diagram of a communication device according to an embodiment of this application;

[0099] Figures 11 to 13 are schematic block diagrams of another communication device according to an embodiment of this application. Detailed Implementation

[0100] The technical solution provided in this application will now be described with reference to the accompanying drawings.

[0101] The embodiments of this application can be applied to various communication systems, such as wireless local area network (WLAN) systems, narrowband internet of things (NB-IoT) systems, global system for mobile communications (GSM) systems, enhanced data rate for GSM evolution (EDGE) systems, wideband code division multiple access (WCDMA) systems, code division multiple access 2000 (CDMA2000) systems, time division-synchronization code division multiple access (TD-SCDMA) systems, long term evolution (LTE) systems, satellite communication systems, 5th generation (5G) systems, or future communication network systems. The method provided in the embodiments of this application can be applied to terrestrial network communication systems as well as non-terrestrial network (NTN) communication systems. The NTN system can be an NTN system integrated with 4G, 5G, and any future generation of communication systems, such as NR NTN, IoT NTN, etc. The NTN communication system can be, for example, a satellite communication system, or it can include drones, high altitude platform stations (HAPS), and other air access network equipment; this application does not limit this.

[0102] Figure 1 is a schematic diagram of the architecture of the communication system applicable to the embodiments of this application. The communication system includes a radio access network (RAN) 100 and a core network (CN) 200. RAN 100 includes at least one RAN node (110a and 110b in Figure 1, collectively referred to as 110) and at least one terminal device (120a-120j in Figure 1, collectively referred to as 120). RAN may also include other RAN nodes, such as wireless relay devices and / or wireless backhaul devices (not shown in Figure 1). Terminal device 120 is wirelessly connected to RAN node 110. RAN node 110 is wirelessly or wired connected to core network 200. The core network device in core network 200 and RAN node 110 in RAN 100 may be different physical devices, or they may be the same physical device integrating core network logical functions and radio access network logical functions.

[0103] RAN 100 can be a cellular system related to the 3rd Generation Partnership Project (3GPP), such as 4G, 5G mobile communication systems, non-terrestrial network (NTN) systems, or future communication network systems. RAN 100 can also be O-RAN, cloud radio access network (CRAN), or wireless fidelity (WiFi) systems, or a communication system that integrates two or more of the above systems.

[0104] The terminal device 120 involved in this application embodiment can also be referred to as a terminal, user equipment (UE), mobile station, mobile terminal, etc. Terminal devices can be widely used in various scenarios, such as NTN, device-to-device (D2D), vehicle-to-everything (V2X) communication, machine-type communication (MTC), Internet of Things (IoT), virtual reality, augmented reality, industrial control, autonomous driving, telemedicine, smart grids, smart furniture, smart offices, smart wearables, smart transportation, smart cities, etc. Terminal devices can be mobile phones, tablets, computers with wireless transceiver capabilities, wearable devices, vehicles, drones, helicopters, airplanes, ships, robots, robotic arms, smart home devices, etc. Terminal devices can also be communication modules with satellite communication capabilities, satellite phones or their components, or satellite communication terminals, such as very small aperture terminals (VSAT) (commonly referred to as VSAT terminals), portable stations, fixed stations, vehicle-mounted or airborne satellite communication terminals, etc. It should be understood that satellite communication terminals can act as micro base stations to further provide data interfaces to accessed user equipment.

[0105] The RAN node 110 involved in this embodiment can also be called an access network device, RAN entity, or access node, etc., and constitutes part of the communication system to help terminal devices achieve wireless access. Multiple RAN nodes 110 in the communication system 1000 can be nodes of the same type or different types. In some scenarios, the roles of RAN node 110 and terminal device 120 are relative. For example, network element 120i in Figure 1 can be a helicopter or drone, which can be configured as a mobile base station. For terminal devices 120j that access RAN 100 through network element 120i, network element 120i is a base station; but for base station 110a, network element 120i is a terminal. RAN node 110 and terminal device 120 are sometimes referred to as communication devices. For example, network elements 110a and 110b in Figure 1 can be understood as communication devices with base station functions, and network elements 120a-120j can be understood as communication devices with terminal functions.

[0106] In one possible scenario, a RAN node can be a base station, an evolved NodeB (eNodeB), an access point (AP), a transmission reception point (TRP), a next-generation NodeB (gNB), or a base station in a future communication network system. A RAN node can be a macro base station (as shown in Figure 1, 110a), a micro base station or indoor station (as shown in Figure 1, 110b), a relay node or donor node, or a radio controller in a CRAN scenario. A RAN node can also be a satellite (or satellite base station) or a high altitude platform station (HAPS), or base station equipment mounted on a satellite / HAPS. The satellite can include at least one of the following: a geostationary Earth orbit (GEO) satellite (or geosynchronous orbit satellite) or a non-geostationary Earth orbit (NGEO) satellite. A non-geostationary Earth orbit satellite can include at least one of the following: a medium Earth orbit (MEO) satellite or a low Earth orbit (LEO) satellite. No restrictions are imposed here. RAN nodes can also be gateway stations (also known as ground stations, earth stations, signaling stations, gateways, or gateway stations). Optionally, RAN nodes can also be servers, wearable devices, vehicles, or in-vehicle equipment. For example, the access network equipment in vehicle-to-everything (V2X) technology can be a roadside unit (RSU).

[0107] In another possible scenario, multiple RAN nodes collaborate to assist terminal devices in achieving wireless access, with different RAN nodes implementing some of the base station's functions. For example, RAN nodes can be CUs, DUs, CUs (control plane, CP), CUs (user plane, UP), or radio units (RUs). CUs and DUs can be set up separately or included in the same network element, such as the baseband unit (BBU). CU and DU nodes separate the gNB's protocol layers; some protocol layer functions are centrally controlled by the CU, while the remaining partial or complete protocol layer functions are distributed in the DU, which is centrally controlled by the CU. As one implementation, the CU deploys the RRC layer, Packet Data Convergence Protocol (PDCP) layer, and Service Data Adaptation Protocol (SDAP) layer from the protocol stack; the DU deploys the radio link control (RLC) layer, media access control (MAC) layer, and physical layer (PHY) from the protocol stack. Therefore, the CU has RRC, PDCP, and SDAP processing capabilities. The DU has RLC, MAC, and PHY processing capabilities. It is understood that the above functional division is merely an example and does not constitute a limitation on the CU and DU. The RU can be included in radio frequency equipment or radio frequency units, such as in a remote radio unit (RRU), an active antenna unit (AAU), or a remote radio head (RRH).

[0108] In different systems, CU (or CU-CP and CU-UP), DU, or RU may have different names, but those skilled in the art will understand their meaning. For example, in an O-RAN system, CU can also be called O-CU (Open CU), DU can also be called O-DU, CU-CP can also be called O-CU-CP, CU-UP can also be called O-CU-UP, and RU can also be called O-RU. For ease of description, this application uses CU, CU-CP, CU-UP, DU, and RU as examples. Any of the units among CU (or CU-CP, CU-UP), DU, and RU in this application can be implemented through software modules, hardware modules, or a combination of software and hardware modules.

[0109] The core network equipment involved in this application refers to equipment in the core network (CN) that provides service support for terminal equipment. Examples of some core network equipment include: access and mobility management function (AMF) entities, session management function (SMF) entities, user plane function (UPF) entities, etc., which will not be listed here.

[0110] The AMF entity is responsible for access management and mobility management of terminal devices, including mobility management, connection management, transparent proxy, and access authentication and authorization. The SMF entity is responsible for session management, UPF selection and control, configuring traffic control on the UPF, routing traffic to the correct destination, policy enforcement, and QoS-related control. The UPF entity is the user plane functional entity, responsible for handling the user plane path of PDU sessions. It should be noted that in this application, entities can also be referred to as network elements or functional entities. For example, the AMF entity can also be called an AMF network element or an AMF functional entity, and the SMF entity can also be called an SMF network element or an SMF functional entity, etc.

[0111] Figure 2 is an example diagram of an O-RAN system. An O-RAN system may include components other than those shown in Figure 2. As shown in Figure 2, access network devices (e.g., eNB, gNB, or next-generation access network devices) communicate with the core network (CN) via a backhaul link and with terminal devices via an air interface.

[0112] Specifically, the baseband unit (BBU) in the access network equipment communicates with the core network via a backhaul link, and the radio unit (RU) in the access network equipment communicates with at least one terminal device via an air interface. The BBU communicates with at least one RU via a fronthaul link. The BBU and RU may or may not be co-located.

[0113] A BBU comprises at least one CU and at least one DU, which can communicate via at least one midhaul link.

[0114] There is an interface between the DU and RU. Depending on the functions of the DU and RU, and / or the different switching methods, the interface between the DU and RU can be a common public radio interface (CPRI) or an enhanced common public radio interface (eCPRI).

[0115] To facilitate understanding of the embodiments of this application, the technical solutions related to the embodiments of this application will be briefly introduced below.

[0116] 1. Non-terrestrial communications

[0117] Non-terrestrial networks (NTNs) include satellite communication networks or unmanned aerial system (UAS) communication networks. NTNs offer advantages such as wide coverage, long communication distance, high reliability, high flexibility, and high throughput. Unaffected by geographical environment, weather conditions, or natural disasters, NTN communication has been widely applied in aviation, maritime, and military communications. Introducing satellites into 5G can provide communication services to areas difficult to cover with terrestrial networks, such as oceans and forests. It can enhance the reliability of 5G communication, providing more stable and higher-quality communication services for users on trains, airplanes, and other modes of transportation. It can also provide more data transmission resources and support a larger number of connections.

[0118] In non-terrestrial communication networks, some network devices are not deployed on the ground; for example, satellites operate in the air. These non-terrestrial network devices may move at relatively high speeds. For instance, satellites can move at speeds as high as 7.56 km / s.

[0119] Satellite communication research has been a hot topic in the field since the 1860s. Thanks to the current concept of "anytime, anywhere" communication, the importance of satellite communication networks will further increase in the future. Generally speaking, the higher the satellite's orbit, the larger its coverage area, but the longer the communication latency. Generally speaking, satellite orbits can be divided according to altitude as follows:

[0120] (1) Low Earth Orbit (LEO): Orbital altitude is 160-2000 km;

[0121] (2) Medium Earth Orbit (MEO): Orbital altitude is 2000-35786 km;

[0122] (3) Geostationary Earth orbit (GEO): The orbital altitude is 35,786 km. The relative position of satellites in this orbit to the Earth is not affected by the Earth's rotation.

[0123] Non-terrestrial network equipment includes satellites, high altitude platform stations (HAPS) equipment, and unmanned aerial vehicles (UAVs). This application uses satellites as an example of non-terrestrial network equipment for illustration.

[0124] The satellite can be a transparent satellite in an NTN-based RAN system. Figure 3a shows a schematic diagram of an NTN communication system architecture. In this transparent satellite scenario, the satellite's role is radio frequency filtering, frequency conversion, and amplification. That is, the satellite primarily acts as a Layer 1 relay node, regenerating physical layer signals, and does not involve any higher protocol layers. The satellite communicates with the ground-based NTN gateway via radio signals. The gateway is connected to the gNB via a wired connection. In this architecture, the satellite can be understood as the RRU of the ground-based gNB. The satellite simply provides basic physical signal coverage; however, the RRU's function requires the gateway and the link between the satellite and the gateway to reach the satellite. No protocol layer processing or logical interfaces are established during this process.

[0125] The satellite can also be a regenerative satellite without an inter-satellite link. This satellite possesses the processing capabilities of a base station and can function as one. Figure 3b illustrates another NTN communication system architecture, in which the satellite acts as a base station, possessing all the protocol layer processing functions of a base station. The satellite gNB transmits back to the ground gateway station via microwave, and the gateway station connects to the 5G core network via a wired connection. In the regenerative satellite scenario, the link between the gNB and the gateway station is generally referred to as the satellite radio interface (SRI) or feed link.

[0126] Satellites can also function as regenerative satellites with inter-satellite links, possessing base station processing capabilities and thus acting as base stations. Figure 3c shows a schematic diagram of another NTN communication system architecture. The difference between the communication system architecture shown in Figure 3c and that shown in Figure 3b is that the communication system architecture in Figure 3c includes inter-satellite communication links, enabling the establishment of Xn interfaces between satellites. Furthermore, when the satellite is not visible to the ground gateway, it can transmit data back to the ground via other satellites. In contrast, the communication system architecture in Figure 3b lacks inter-satellite communication links.

[0127] The satellite can also be a regenerable satellite with DU processing capabilities as a base station. Figure 3d is a schematic diagram of another NTN communication system architecture. In this scenario, the satellite can be a gNB-DU, which connects to the ground gNB-CU through a ground gateway station.

[0128] The satellite can also be a satellite with integrated access and backhaul (IAB) node functionality. In this scenario, the satellite acts as an IAB node, similar to the system architecture shown in 3d, but the difference is that in this architecture, in addition to deploying DU, the satellite also deploys MT modules. Backhaul is performed using the MT modules and the NR air interface of the ground base station, eliminating the need to establish a separate microwave backhaul link between the satellite and the gateway station.

[0129] II. Fixed cell and moving cell

[0130] 1. Stationary Cell: In NTN, if a satellite's coverage of the ground is fixed for a period of time, after that time, the satellite's coverage jumps to another area and continues to provide fixed coverage for a period of time. For non-GEO satellites, there is no such thing as permanently fixed ground coverage; therefore, the "fixed cell" mentioned here should strictly be called a quasi-fixed cell.

[0131] 2. Moving cell: In NTN, if the angle at which the satellite beam illuminates the ground is fixed, the coverage area of ​​the satellite on the ground is constantly changing. This scenario is called a moving cell.

[0132] 3. Resynchronization after satellite switch

[0133] In a transparent satellite architecture, satellites transparently forward cell signals from ground base stations. In Rel-17, the handover process for terminal devices within the NTN is the same as on the ground. Specifically, adjacent satellites forward signals from different cells, and the terminal device performs cell handover (including handover between different cells within the same site and inter-site handover). In Rel-18, standardization allows two adjacent satellites to forward signals from the same cell (PCI remains unchanged). When switching satellites, the terminal device does not need to switch cells. This eliminates the interaction during the handover process and avoids sending Layer 3 RRC reconfiguration messages (handover commands) to the terminal device. Due to satellite movement, a large number of terminal devices may need to handover simultaneously; this significantly reduces signaling overhead. Handover in the PCI-unchanged scenario is called "satellite switch with re-sync," meaning resynchronization after switching satellites. In other words, the terminal device only needs to resynchronize downlink and uplink with the new satellite. Since there is no cell change, the higher-layer network configurations (including MAC / RLC / PDCP) can continue to be used without reconfiguration. For the terminal device, these higher-layer configurations can also continue to be used, and the terminal device's HARQ buffer does not need to be cleared.

[0134] The workflow of satellite switch with re-sync is roughly as follows: The current satellite broadcasts its service termination time (t-service) and the start time of the new satellite (t-start) in System Information Block 19 (SIB19). Based on the information in SIB19, the terminal device performs downlink (DL) synchronization with the new satellite in advance after t-start. Then, after the t-service time arrives, it directly performs uplink (UL) synchronization and data transmission on the new satellite. In other words, satellite switch with re-sync does not require any handover command instructions; the terminal device directly performs satellite handover based on the information broadcast in the old satellite's SIB19. From the workflow, it can be seen that satellite switch with re-sync is only suitable for fixed cell scenarios because only in fixed cells are the times when the old satellite disappears and the new satellite appears determined. In moving cell scenarios, the satellite coverage area is constantly changing, and there is no uniform "disappearance" and "appearance" time for all terminal devices.

[0135] IV. NR User Plane Processing Flow

[0136] Figure 4 is a schematic diagram of the processing of user plane data packets in NR through the higher-level protocol stack. The diagram shows the processing flow for two IP packets. Please note that this is for two IP packets from the same terminal device, not for two separate terminal devices. All descriptions of data packet processing, retransmission, and HARQ processes in this application are for a single terminal device. From the perspective of higher layers, data packets from different terminal devices will not be analyzed in the same process.

[0137] In the NR air interface, data packets pass through the following layers from top to bottom: SDAP, PDCP, RLC, MAC, and PHY (PHY is not shown in Figure 4). Above SDAP is TCP / IP, belonging to the IP network protocol stack. For uplink data, after the base station decrypts the SDAP layer, the IP packet is exposed, and the base station performs IP routing forwarding based on the destination IP address. For downlink data, after the terminal device decrypts the SDAP layer, it is handed over to the upper layer for processing. The NR air interface focuses on the processing at and below the SDAP layer. The functions of each layer can be summarized as follows: the SDAP layer is responsible for mapping Quality of Service (QoS) flow to transmission resources; the PDCP layer is responsible for data encryption, integrity protection, and in-order delivery; RLC and MAC are responsible for data segmentation and reassembly and reliable transmission, ultimately mapping to the physical layer's transport block (TB). RLC and MAC introduce acknowledgement (ACK) / negative acknowledgement (NACK) feedback; when the sender receives a NACK, it retransmits the data packet. The feedback mechanisms of RLC and MAC differ slightly, which will be explained in the next section. For each layer, on the sending side, a data packet is called an SDU before being processed by that layer, and a PDU after processing. The so-called "processing" means adding a header to the SDU data packet to generate the corresponding PDU, and then submitting it to the next layer for further processing. On the receiving side, the opposite is true; the header is removed from the PDU to generate the SDU. As shown in Figure 4, after a PDCP PDU reaches the RLC layer, it may be split into multiple RLC SDU segments. Each RLC SDU segment generates an RLC PDU after adding a header. After the RLC PDU reaches the MAC layer, it will be reassembled into different MAC PDUs / TBs depending on the transmission resources. If a certain TB has a large capacity, it can accommodate multiple RLC PDUs. That is to say, a MAC PDU may contain multiple RLC PDUs, which may come from different PDCP PDUs. As shown in the bold black TB in Figure 4, this TB represents a MAC PDU that includes two RLC PDUs, which come from two different PDCP PDUs.

[0138] Both RLC and MAC have feedback mechanisms. The RLC layer has three modes: transparent mode (TM), unacknowledged mode (UM), and acknowledged mode (AM). In TM mode, the RLC layer does no processing; the PDCP PDU is directly delivered to the MAC layer. In UM mode, the RLC layer only splits the data packets, breaking the PDCP PDU into multiple RLC SDUs, adding RLC headers to each, and generating multiple RLC PDUs, but there is no feedback mechanism. In AM mode, in addition to data packet splitting, the RLC layer has a feedback mechanism called ARQ. After each RLC PDU is transmitted, the receiver needs to send an ACK. If the receiver does not receive an ACK, it sends a NACK. When the sender receives a NACK, or if no feedback is received after a period of time, the transmission is considered to have failed, and the RLC PDU needs to be retransmitted. The MAC layer's feedback mechanism is HARQ, which differs from the RLC layer's ARQ in that:

[0139] (1) The MAC layer has multiple HARQ processes (e.g., the protocol specifies a maximum of 8) transmitting in parallel. When the data transmission of a certain HARQ process is completed, subsequent data packets are added to that HARQ process, which improves the transmission efficiency. The RLC layer has only one ARQ process. The next data packet will only be transmitted after the transmission of a data packet is confirmed to be successful.

[0140] (2) In the RLC layer, all bits of an RLC PDU are transmitted at a time. In the MAC layer, only a portion of the bits in a MAC PDU are transmitted at a time. For retransmission, the RLC layer retransmits the complete RLC data packet; while the MAC layer retransmits only a portion of the bits in a MAC PDU. The MAC layer transmits only a portion of the bits in both new and retransmissions because a large number of redundant bits are added to the MAC data packet to combat the worst channel conditions. According to the principle of wireless communication, by adding redundant bits to the data before encoding, transmission errors can be resisted, and the data bits can be correctly recovered. The more redundant bits, the higher the tolerance for transmission errors. However, the actual channel may not be so bad, and MAC transmission does not need to transmit all the redundant bits every time, as this would be too resource-intensive. Therefore, MAC retransmission introduces the concept of "redundancy version (RV)". Figure 5 is a schematic diagram of HARQ redundant version transmission. As shown in Figure 5, only a portion of the bits are transmitted each time. In the initial transmission, all system bits (the actual data packet part) and a small number of parity bits (redundant bits) are transmitted, denoted by RV0. If channel conditions are good, the receiver can successfully decode the data by transmitting only the bits corresponding to RV0, because RV0 includes all the system bits. Under good channel conditions, a small number of redundant bits can compensate for channel instability. However, if the receiver fails to decode due to poor channel conditions and sends a NACK, the transmitter will transmit the subsequent check bits, denoted as RV2, in the next retransmission. If the receiver continues to fail to decode, the transmitter will transmit the bits corresponding to RV3 (including the end of the check bits and the beginning of the system bits). If this continues, the transmitter will transmit the portion corresponding to RV1 (including the end of the system bits and the beginning of the check bits); retransmissions will continue in the order of RV0-RV2-RV3-RV1, cycling through the data. For the receiver, after the initial decoding failure, these bits (the portion of RV0) are not discarded but buffered. After a retransmission, the retransmitted portion (the portion of RV2) is combined with the initially received bits and decoded again. If it still fails, continue to buffer, receive and retransmit (RV3), and then merge again, and so on. This is the soft merging of the MAC layer.

[0141] For MAC layer retransmissions, there is another technique to save retransmission overhead: HARQ retransmission at the code block group (CBG) granularity. For example, a MAC PDU includes 80 code blocks (CBs), which can be divided into 8 CBGs, each containing 10 CBs. During a MAC PDU transmission, if the receiver determines that only one CBG failed to decode, while the other 7 CBGs were successfully decoded, it can use HARQ feedback to instruct the sender to retransmit the CBG that failed to decode. In this way, retransmission overhead is saved.

[0142] The following describes the user plane process (data transfer) during handover: In the existing cross-site handover process, to ensure service continuity, the source base station needs to transfer data to the target base station. This is because it takes time for the terminal device to connect to the target base station and establish an RRC connection after disconnecting from the source base station. Only after the terminal device and the target base station have established an RRC connection will the target base station notify the core network that the terminal device has switched to the target base station. Before this, the core network still considers the terminal device to be under the source base station and will send data to the source base station that needs to be transmitted to the terminal device. However, since the terminal device has already disconnected from the source base station, the source base station needs to transfer the downlink data sent by the core network to the target base station, which then sends it to the terminal device. In addition to the data arriving from the core network, the source base station also needs to send the SDU corresponding to the incompletely transmitted PDCP PDU cached on the base station side to the target base station, which then regenerates the PDCP PDU and sends it to the terminal device. The transfer of both types of data packets (data packets arriving from the CN to the source base station, and data packets whose transmission at the source base station has not been completed) is done at the PDCP layer. The source base station transfers the PDCP SDU to the target base station, which then uses its new key to encrypt the data using PDCP, generating a PDCP PDU, which is then sent to the terminal device. The terminal device parses the PDU using the new key from the target base station. Information related to the new key from the target base station is sent to the terminal device in the handover command. During terminal device handover, all data buffers below the PDCP layer (RLC and MAC layers) are cleared. That is, if there are still RLC PDUs / MAC PDUs that have not been fully transmitted (e.g., the terminal device sends a MAC PDU to the source base station via uplink but has not yet received an ACK from the source base station; or the terminal device receives a MAC PDU via downlink but has not successfully decoded it, and the source base station is still retransmitting it, but the terminal device disconnects from the source base station), the current transmission will not continue. All PDUs below the PDCP layer are directly cleared (fully refreshed), and retransmission or reception begins at the PDCP layer.

[0143] Currently, terminal devices need to clear the HARQ buffer after switching cells or resynchronizing. However, in a transparent satellite architecture with satellite switch-with-sync, although the terminal device resynchronizes with the new satellite, since the terminal device has not switched cells and the time for the terminal device to access the new satellite is fixed, the HARQ buffer does not need to be cleared, thus reducing the impact on the terminal device. It should be noted that if the HARQ buffer (MAC layer buffer) is not cleared, the RLC layer buffer will also not be cleared.

[0144] Rel-19 discusses regenerative satellite architecture, and considering the benefits of satellite switch with re-sync introduced in Rel-18, the aim is to extend this feature to the regenerative satellite architecture. However, applying satellite switch with re-sync to the regenerative satellite architecture presents several challenges. In Rel-18, satellite switch with re-sync was possible because two transparent satellites could relay signals from the same cell. However, in regenerative satellites, the two satellites are essentially two independent base stations; switching satellites for a terminal device means switching base stations. Designing processes that allow terminal devices to retain the benefits of satellite switch with re-sync even when switching base stations—such as eliminating the need for handover commands and clearing HARQ / ARQ buffers—to improve the user experience, is a critical issue that needs to be addressed in the future evolution of NTN.

[0145] For satellite switchover with re-sync under regenerated satellites, switching satellites means switching base stations. Currently, in base station switching scenarios, the inter-site data transfer during the handover process is based on PDCP SDUs, without data transfer below the PDCP layer. The target base station cannot know the RLC / MAC packet transmission status of the source base station, and both the ARQ buffer and HARQ buffer on the terminal device side and the source base station side need to be cleared. Therefore, seamless handover for terminal devices is not possible, significantly impacting the user experience.

[0146] To this end, this application provides a data transmission method. When a terminal device switches from a source base station to a target base station, the source base station sends (transfers) the cached RLC layer data packets and MAC layer data packets to the target base station. The ARQ buffer and HARQ buffer on the terminal device side do not need to be cleared, which can realize seamless switching of the terminal device and thus improve the user experience of the terminal device during the switching process.

[0147] Figure 6 is a schematic flowchart illustrating a data transmission method 600 provided in an embodiment of this application. The first access network device in this embodiment can be an access network device, or a device within an access network device (e.g., a module, communication module, circuit or chip responsible for communication functions (such as a modem chip, or a SoC chip or SIP chip containing a modem core), chip system, or processor), or a logical node, logical module, or software capable of implementing all or part of the access network device's functions. The second access network device in this embodiment can be an access network device, or a device within an access network device (e.g., a module, communication module, circuit or chip responsible for communication functions (such as a modem chip, or a SoC chip or SIP chip containing a modem core), chip system, or processor), or a logical node, logical module, or software capable of implementing all or part of the access network device's functions. The terminal device in this application embodiment can be a terminal equipment, or a device within a terminal equipment (e.g., a module, communication module, circuit or chip responsible for communication functions (such as a modem chip, also known as a baseband chip, or a SoC chip or SIP chip containing a modem core), chip system, or processor), or a logical node, logical module, or software capable of implementing all or part of the terminal equipment's functions. Furthermore, the processing performed by a single execution entity can also be divided into multiple execution entities, which can be logically and / or physically separated. For example, the processing performed by an access network device can be divided into execution by at least one of CU, DU, RU, etc.

[0148] S610, the first access network device determines that the terminal device needs to be switched to the second access network device. The first access network device is the source access network device of the terminal device, and the second access network device is the target access network device of the terminal device. The first access network device can be understood as the source base station, and the second access network device can be understood as the target base station. For example, the first access network device and the second access network device are different satellite base stations or terrestrial base stations.

[0149] For example, the first access network device sends a handover request message to the second access network device based on the measurement report information reported by the terminal device; after receiving the handover request message, the second access network device sends a handover request confirmation message to the first access network device; after receiving the handover request confirmation message from the second access network device, the first access network device determines that it needs to hand over the terminal device to the second access network device.

[0150] For example, the first access network device determines whether the terminal device needs to be switched to the second access network device based on the service downtime of the first access network device and the service starttime of the second access network device. In this example, the first access network device and the second access network device can be satellite base stations suitable for fixed cell scenarios.

[0151] Optionally, the first access network device does not send MAC layer data packets or ACK / NACK for MAC layer data packets within one one-way propagation delay preceding the service interruption time of the first access network device. Similarly, the terminal device does not send MAC layer data packets or ACK / NACK for MAC layer data packets within one one-way propagation delay preceding the service interruption time of the first access network device. Taking the first access network device side as an example, the same applies to the terminal device side. For downlink, if the first access network device sends MAC layer data packets or ACK / NACK for MAC layer data packets within the aforementioned one-way propagation delay, the terminal device will not receive them because it will immediately disconnect from the first access network device. For uplink, if the first access network device receives MAC layer data packets within the aforementioned one-way propagation delay, although the first access network device can receive them, the terminal device will also not receive the ACK fed back by the first access network device. Both the HARQ buffer of the terminal device and the HARQ buffer of the first access network device may buffer data packets. Optionally, in the CU-DU separation architecture, since the ephemeris information is maintained by the CU in the first access network device, the CU in the first access network device can indicate the DU handover time or ephemeris in the first access network device.

[0152] S620, the first access network device sends buffered data packets to the second access network device. These buffered data packets include data packets in the MAC layer buffer and / or RLC layer buffer. The buffered data packets include at least one of the following: downlink MAC layer data packets, uplink MAC layer data packets, downlink RLC layer data packets, or a first uplink RLC layer data packet. Correspondingly, the second access network device receives the buffered data packets from the first access network device. The sending of buffered data packets from the first access network device to the second access network device can be understood as the first access network device transferring its buffered data packets to the second access network device. The data packets in the MAC layer buffer include downlink MAC layer data packets and / or uplink MAC layer data packets. The data packets in the RLC layer buffer include downlink RLC layer data packets and / or a first uplink RLC layer data packet.

[0153] Downlink MAC layer data packets in the MAC layer buffer can be understood as downlink MAC layer data packets that were not successfully sent, or downlink MAC layer data packets that were not acknowledged as correctly received. For example, if a first access network device has sent a downlink MAC layer data packet but has not received an ACK from the terminal device regarding that downlink MAC layer data packet, the first access network device needs to send the downlink MAC layer data packet to a second access network device so that the second access network device can retransmit it to the terminal device.

[0154] The uplink MAC layer data packets in the MAC layer buffer can be understood as uplink MAC layer data packets that have not been successfully decoded. The fact that the uplink MAC layer data packets buffered in the MAC layer buffer have not yet been delivered to the upper layer indicates that the uplink MAC layer data packets have not been successfully decoded. These buffered uplink MAC layer data packets need to be sent to the second access network device, and the terminal device will retransmit them to the second access network device. This allows the second access network device to perform soft merging based on this buffered data and the retransmitted data from the terminal device.

[0155] Downlink RLC layer packets in the RLC layer buffer can be understood as downlink RLC layer packets that were not successfully sent, or downlink RLC layer packets that were not acknowledged as correctly received. For example, if the RLC layer uses AM mode, the downlink RLC layer packets include downlink RLC layer packets that have not been delivered to the MAC layer, and downlink RLC layer packets that have been delivered to the MAC layer (already sent) but for which an ACK has not been received. In addition to buffering downlink RLC packets already delivered to the MAC layer (lower layer), the first access network device's RLC layer buffer also buffers downlink RLC packets that have been assembled but have not yet entered the MAC layer for processing (e.g., due to a lack of idle HARQ processes).

[0156] It should be noted that there is no soft merging mechanism for HARQ in the RLC layer, and there is no operation of "buffering the received part when the uplink is not successfully decoded". Therefore, there are no "uplink RLC layer data packets that are not successfully decoded" in the RLC layer buffer. In the RLC layer, if decoding fails, the data packets are directly discarded.

[0157] The first uplink RLC layer data packet in the RLC layer buffer can be understood as a successfully received first uplink RLC layer data packet. The first and second uplink RLC layer data packets belong to the same PDCP layer data packet; the second uplink RLC layer data packet is an uplink RLC layer data packet that the first access network device failed to receive. Because the first and second uplink RLC layer data packets belong to the same PDCP layer data packet, the first access network device, after receiving only the first uplink RLC layer data packet, cannot recover the PDCP PDU. It needs to send the successfully received first uplink RLC layer data packet to the second access network device. After receiving the second uplink RLC layer data packet, the second access network device recovers the PDCP PDU based on both the first and second uplink RLC layer data packets.

[0158] It should be noted that the downlink MAC layer data packets buffered in the HARQ buffer and the downlink RLC layer data packets buffered in the ARQ buffer that have been submitted to the MAC layer but have not yet received an ACK share many bits, but both need to be transferred to the second access network device. Considering that if the downlink MAC layer data packets buffered in the HARQ buffer consistently fail to transmit successfully, RLC layer retransmission is required (the downlink RLC layer data packets are submitted to the MAC layer for retransmission). Although the MAC layer has a HARQ mechanism, it is not completely reliable; when MAC layer transmission fails (e.g., reaching the maximum number of retransmissions), the entire RLC PDU needs to be retransmitted.

[0159] Optionally, in HARQ retransmission technology with CBG granularity, the downlink MAC layer data packets in the MAC layer buffer include downlink code block groups that were not successfully transmitted. In other words, the downlink MAC layer data packets include downlink code block groups that the first access network device has sent to the terminal device but has not received an ACK from. These downlink code block groups need to be sent to the second access network device for the second access network device to continue retransmitting to the terminal device. Optionally, the uplink MAC layer data packets in the MAC layer buffer include successfully received uplink code block groups. The first access network device sends the successfully received uplink code block groups to the second access network device, and the terminal device will continue to transmit the code block groups that were not successfully transmitted in the MAC PDU to the second access network device. The second access network device will then reassemble the uplink code block groups from the first access network device and the uplink code block groups received from the terminal device into a complete MAC PDU.

[0160] Optionally, the cached data packets may further include first indication information, which indicates at least one of the following: HARQ process number, redundancy version information, or code block group information corresponding to the downlink MAC layer data packets and the uplink MAC layer data packets, respectively. The redundancy version information includes redundancy version number (RV) indication information or retransmission count indication information.

[0161] Optionally, the code block group information corresponding to the downlink MAC layer data packet includes any one of the following: the identifier of the downlink code block group that was not successfully transmitted and / or the identifier of the downlink code block group that was successfully transmitted; the number of code block groups included in the downlink MAC layer data packet and the identifier of the downlink code block group that was not successfully transmitted; or the number of code block groups included in the downlink MAC layer data packet and the identifier of the downlink code block group that was successfully transmitted. Based on this implementation, the second access network device can obtain the identifier of the downlink code block group that was not successfully transmitted according to the code block group information corresponding to the downlink MAC layer data packet, and can realize the retransmission of the downlink code block group that was not successfully transmitted, thereby improving the reliability of data transmission. In this application, the identifier of the code block group can also be understood as the code block group number or index.

[0162] It should be noted that, when the code block group information corresponding to the downlink MAC layer data packet includes the identifiers of downlink code block groups that were not successfully transmitted and / or the identifiers of downlink code block groups that were successfully transmitted, the number of code block groups included in a downlink MAC PDU is fixed or known. The second access network device can determine the identifiers corresponding to the downlink code block groups that were not successfully transmitted based on the identifiers of the downlink code block groups that were not successfully transmitted and / or the identifiers of the downlink code block groups that were successfully transmitted, and then perform downlink transmission on the downlink code block groups that were not successfully transmitted by the first access network device.

[0163] Optionally, the code block group information corresponding to the uplink MAC layer data packet includes any one of the following: the identifier of the successfully received uplink code block group and / or the identifier of the unsuccessfully received uplink code block group; the number of code block groups included in the uplink MAC layer data packet and the identifier of the successfully received uplink code block group; or the number of code block groups included in the uplink MAC layer data packet and the identifier of the unsuccessfully received uplink code block group. Based on this implementation, the second access network device can obtain the identifier of the unsuccessfully received uplink code block group according to the code block group information corresponding to the uplink MAC layer data packet, thereby obtaining the identifier of the uplink code block group subsequently transmitted by the terminal device. This enables the second access network device to receive the unsuccessfully received uplink code block group, thereby improving the reliability of data transmission. It should be noted that when the code block group information corresponding to the uplink MAC layer data packet includes the identifier of the successfully received uplink code block group and / or the identifier of the unsuccessfully received uplink code block group, the number of code block groups included in an uplink MAC PDU is fixed or known.

[0164] For example, the first indication information is used to indicate the HARQ process number corresponding to the downlink MAC layer data packet and the uplink MAC layer data packet, respectively. This allows the second access network device to know which HARQ process is used to transmit the downlink MAC layer data packet and the uplink MAC layer data packet, respectively. This enables the second access network device to correctly send downlink MAC layer data packets and correctly receive uplink MAC layer data packets, thereby improving the reliability of data transmission.

[0165] For example, the first indication information is used to indicate the redundancy version information corresponding to the downlink MAC layer data packet and the uplink MAC layer data packet, respectively. This allows the second access network device to know which bits in the MAC PDU need to be transmitted when transmitting downlink MAC layer data packets, and which bits in the MAC PDU are transmitted by the terminal device during uplink MAC layer data packet transmission. This enables the second access network device to correctly send the bit information of the downlink MAC layer data packet and correctly receive the bit information of the uplink MAC data packet, thereby improving the reliability of data transmission.

[0166] For example, the first indication information is used to indicate the code block group information corresponding to the downlink MAC layer data packet and the uplink MAC layer data packet, respectively. The second access network device can obtain the identifier of the downlink code block group that was not successfully transmitted based on the code block group information corresponding to the downlink MAC layer data packet, and the second access network device can obtain the identifier of the uplink code block group that was not successfully received based on the code block group information corresponding to the uplink MAC layer data packet. This enables the second access network device to retransmit the downlink code block group that was not successfully transmitted and to receive the uplink code block group that was not successfully received, thereby improving the reliability of data transmission.

[0167] Optionally, the cached data packets also include second indication information, which indicates the key information used during data transmission between the first access network device and the terminal device. This key information is used by the second access network device to decrypt the uplink MAC layer data packets / second uplink RLC layer data packets received from the terminal device and submitted to the PDCP layer. It should be noted that the uplink MAC layer data packets / first uplink RLC layer data packets sent by the first access network device to the second access network device have already been processed at the PDCP layer. Subsequent retransmissions of uplink MAC layer data packets and second uplink RLC layer data packets from the terminal device to the second access network device have also been processed at the PDCP layer. In other words, the terminal device has already used this key information to encrypt the uplink MAC layer data packets and uplink RLC layer data packets. Therefore, the second access network device needs to know this key information for decryption to avoid retransmissions due to decryption failure, thereby improving data transmission efficiency.

[0168] Optionally, the cached data packets also include third indication information, which indicates that downlink MAC layer data packets and downlink RLC layer data packets are data packets that need to be transmitted downlink, and uplink MAC layer data packets and first uplink RLC layer data packets are data packets that need to be received uplink. Based on this third indication information, the second access network device can determine which data packets in the cached data packets from the first access network device need to be transmitted downlink and which data packets need to be transmitted uplink, thus ensuring correct data packet transmission and improving data transmission reliability.

[0169] Optionally, the cached data packets also include fourth indication information, which indicates at least one of the following: the sequence number of the downlink RLC layer data packet, the sequence number used by the second access network device to transmit downlink RLC layer data packets from the upper layer, the maximum value of the sequence number of the uplink RLC layer data packet successfully received by the first access network device, or the sequence number of the uplink RLC layer data packet that the first access network device failed to receive. Based on this optional implementation, the sequence numbers used by the RLC layer can be aligned between the second access network device and the terminal device to ensure the successful transmission of RLC layer data packets.

[0170] For example, the fourth indication information is used to indicate the sequence number of a downlink RLC layer data packet (a downlink RLC layer data packet that was not successfully transmitted), or the sequence number used by the second access network device to transmit downlink RLC layer data packets from the upper layer. In this example, the fourth indication information can be understood as DL RLC layer data packet transmission status information. The downlink RLC layer data packet from the upper layer can be understood as a newly transmitted downlink RLC layer data packet. Based on the sequence number of the downlink RLC layer data packet, or the sequence number used to transmit the downlink RLC layer data packet from the upper layer, the second access network device can determine the sequence number used by the downlink RLC layer data packet that was not successfully transmitted, and use this sequence number to transmit the downlink RLC layer data packet, thus achieving correct transmission of the downlink RLC layer data packet and improving the reliability of data transmission.

[0171] For example, the fourth indication information is used to indicate the maximum value of the sequence number of the uplink RLC layer data packet (first RLC layer data packet) successfully received by the first access network device, or the sequence number of the uplink RLC layer data packet that the first access network device failed to receive. In this example, the fourth indication information can be understood as UL RLC layer data packet reception status information. Based on the maximum value of the sequence number of the uplink RLC layer data packet successfully received by the first access network device, the second access network device can determine the sequence number used by the next uplink RLC layer data packet transmitted by the terminal device, thus achieving correct reception of the uplink RLC layer data packet and improving data transmission reliability. Similarly, based on the sequence number of the uplink RLC layer data packet that the first access network device failed to receive, the second access network device can also determine the sequence number used by the next uplink RLC layer data packet transmitted (retransmitted) by the terminal device, achieving correct reception of the uplink RLC layer data packet and improving data transmission reliability.

[0172] For example, the fourth indication information is used to indicate the maximum value of the sequence number of the uplink RLC layer data packet (first RLC layer data packet) successfully received by the first access network device and the sequence number of the uplink RLC layer data packet that the first access network device failed to receive. The sequence number of the uplink RLC layer data packet that the first access network device failed to receive is less than the maximum value of the sequence number of the uplink RLC layer data packet successfully received by the first access network device. For example, if the first access network device receives RLC layer data packets with sequence numbers 1, 3, and 5, but does not receive RLC layer data packets with sequence numbers 2 and 4, then the first access network device indicates the maximum value (5) received and the sequence numbers (2, 4) of the unreceived RLC layer data packets that are less than the maximum value through the fourth indication information. For RLC layer data packets with sequence numbers greater than the maximum value (5) received, there is no need to indicate this to the second access network device, because the second access network device can infer from the maximum value (5) that none of the RLC layer data packets with sequence numbers greater than the maximum value have been received.

[0173] For example, the first instruction information, the second instruction information, the third instruction information and the fourth instruction information are carried in the header of the data packet that the first access network device sends to the second access network device.

[0174] There are several ways to implement the first access network device sending cached data packets to the second access network device. In one implementation, the first access network device reuses an existing Xn tunnel (data channel) used for transferring PDCP SDUs to send the cached data packets to the second access network device. In this implementation, no additional tunnel needs to be established. In another implementation, a dedicated tunnel is established to send the cached data packets to the second access network device. In this implementation, an additional tunnel needs to be established, as shown in steps S621 and S622. It should be noted that the tunnel in this embodiment can be understood as a data channel.

[0175] Optionally, in step S621, before the first access network device sends the buffered data packets (including data packets in the MAC layer buffer and / or RLC layer buffer) to the second access network device, the first access network device sends a request message to the second access network device. This request message requests the establishment of at least one tunnel for transmitting the buffered data packets, and includes tunnel identification information of the first access network device. Correspondingly, the second access network device receives the request message from the first access network device.

[0176] Optionally, in step S622, the second access network device sends a response message to the first access network device, the response message including the tunnel identification information of the second access network device.

[0177] In this optional implementation, a dedicated tunnel is established to send buffered data packets (data packets in the MAC layer buffer and / or RLC layer buffer) to the second access network device. Compared with reusing the existing Xn tunnel (data channel) used for transferring PDCP SDUs to send buffered data packets to the second access network device, this implementation can simultaneously transfer buffered data packets (data packets in the MAC layer buffer and / or RLC layer buffer) and PDCP SDUs to the second communication device, thereby improving data transmission efficiency.

[0178] It should be noted that when requesting the establishment of multiple tunnels, the request information includes multiple tunnel identifiers from the first access network device, and the response information includes multiple tunnel identifiers from the second access network device. The multiple tunnel identifiers from the first access network device and the multiple tunnel identifiers from the second access network device correspond one-to-one. When requesting the establishment of a single tunnel, the request information includes one tunnel identifier from the first access network device, and the response information includes one tunnel identifier from the second access network device. In this case, data packets in the MAC layer buffer and data packets in the RLC layer buffer both use the same tunnel for transmission.

[0179] Optionally, the response information may also include tunnel identification information of the first access network device corresponding to the tunnel identification information of the second access network device, used to indicate which tunnel the tunnel identification information on the second access network device side specifically corresponds to. It should be noted that if only one tunnel is established between the first access network device and the second access network device, the response information does not need to include the tunnel identification information of the first access network device. If multiple tunnels are established between the first access network device and the second access network device, the response information may carry the tunnel identification information of the first access network device.

[0180] For example, tunnel identification information includes transport network layer (TNL) address and / or tunnel endpoint ID (TEID).

[0181] For example, the request information sent by the first access network device to the second access network device and the response information sent by the second access network device to the first access network device are respectively carried in different Xn interface application (AP) messages, which can be simply referred to as XnAP messages.

[0182] Optionally, the request information further includes fifth indication information, which indicates that the first tunnel is used to transmit downlink MAC layer data packets and / or uplink MAC layer data packets, and the second tunnel is used to transmit downlink RLC layer data packets and / or first uplink RLC layer data packets, wherein at least one tunnel includes the first tunnel and the second tunnel. In this optional implementation, establishing tunnels for transmitting MAC layer data packets and tunnels for transmitting RLC layer data packets, with the first tunnel used for transmitting MAC layer data packets and the second tunnel used for transmitting RLC layer data packets, allows for the simultaneous transmission of MAC layer data packets and RLC layer data packets to the second communication device, improving data transmission efficiency. In other words, the fifth indication information indicates the association between the tunnel identifier and the protocol layer corresponding to the data packets transmitted by that tunnel.

[0183] Optionally, the request information also includes sixth indication information, which indicates that the first tunnel is used to transmit downlink MAC layer data packets and / or downlink RLC layer data packets, and the second tunnel is used to transmit uplink MAC layer data packets and / or the first uplink RLC layer data packets, wherein at least one tunnel includes the first tunnel and the second tunnel. In this optional implementation, different tunnels are established for uplink data packets and downlink data packets respectively. The first tunnel is used to transmit downlink data packets (downlink MAC layer data packets and / or downlink RLC layer data packets), and the second tunnel is used to transmit uplink data packets (uplink MAC layer data packets and / or the first uplink RLC layer data packets), which can enable simultaneous transmission of downlink data packets and uplink data packets to the second communication device, thereby improving data transmission efficiency. In other words, the sixth indication information indicates the association between the tunnel identifier and the uplink or downlink transmission direction.

[0184] If the request information also includes the sixth indication information, the cached data packet sent by the first access network device to the second access network device may not carry (excluding) the aforementioned third indication information.

[0185] Optionally, if a tunnel is established for each of the uplink and downlink data packets, the response information may also include indication information indicating whether the tunnel is used to transmit uplink or downlink data packets, for identifying the tunnel.

[0186] Optionally, the request information also includes seventh indication information, which indicates that the first tunnel is used to transmit MAC layer data packets corresponding to the first HARQ process number, and the second tunnel is used to transmit MAC layer data packets corresponding to the second HARQ process number, wherein at least one tunnel includes the first tunnel and the second tunnel. In this optional implementation, establishing a separate tunnel for each HARQ process allows for the simultaneous transmission of MAC layer data packets corresponding to different HARQ process numbers to the second communication device, thereby improving data transmission efficiency. In other words, the seventh indication information indicates the association between the tunnel identifier and the HARQ process number.

[0187] For example, the seventh indication information is also used to indicate the redundancy version information and / or code block group information of the MAC layer data packets corresponding to the first HARQ process number and the second HARQ process number, respectively. Based on the redundancy version information, the second access network device can determine which bits in the MAC PDU need to be transmitted during downlink MAC layer data packet transmission, and which bits in the MAC PDU are transmitted by the terminal device during uplink MAC layer data packet transmission. This enables the second access network device to correctly send the bit information of the downlink MAC layer data packets and correctly receive the bit information of the uplink MAC data packets, thereby improving the reliability of data transmission. Based on the code block group information, the second access network device can determine the identifiers of downlink code block groups that were not successfully transmitted, and / or the identifiers of uplink code block groups that were not successfully received. This enables the second access network device to retransmit the downlink code block groups that were not successfully transmitted and to receive the uplink code block groups that were not successfully received, thereby improving the reliability of data transmission.

[0188] If the request information also includes the seventh indication information, the cached data packet sent by the first access network device to the second access network device may not carry (excluding) the aforementioned first indication information.

[0189] Optionally, if a separate tunnel is established for each HARQ process, the response information may also include the HARQ process number corresponding to each tunnel, which is used to identify the tunnel.

[0190] It should be noted that when establishing a separate tunnel for each HARQ process, the tunnel used to transmit RLC layer data packets is different from the tunnel used to transmit MAC layer data packets. Furthermore, during the request to establish a tunnel for transmitting RLC layer data packets, the request information does not include the HARQ process number corresponding to that tunnel (there is only one ARQ process for the RLC layer), redundancy version information, or code block group information.

[0191] Optionally, the request information also includes second indication information, which is used to indicate the key information used during data transmission between the first access network device and the terminal device. This key information is used by the second access network device to decrypt the uplink MAC layer data packet / second uplink RLC layer data packet received from the terminal device and submitted to the PDCP layer, thus avoiding retransmissions due to decryption failure and improving data transmission efficiency. This second indication information, used to indicate the key information, can be carried in the request information and sent to the second access network device, or it can be carried in a buffered data packet and sent to the second access network device, or it can be sent to the second access network device in other ways; this application does not limit this.

[0192] S630, the second access network device sends first information to the terminal device. The first information includes downlink MAC layer data packets (downlink MAC layer data packets that the first access network device failed to send) and / or downlink RLC layer data packets (downlink RLC layer data packets that the first access network device failed to send). Correspondingly, the terminal device receives the first information.

[0193] For example, the buffered data packets received by the second access network device from the first access network device include downlink MAC layer data packets and downlink RLC layer data packets. Since there are many identical bits between the downlink MAC layer data packets and the downlink RLC layer data packets, for a downlink RLC layer data packet that has been submitted to the MAC layer (already sent) but has not received an ACK, the second access network device will not directly send the downlink RLC layer data packet to the terminal device (submitted to the MAC layer). Only after a MAC layer transmission failure will it be submitted to the MAC layer again for retransmission to the terminal device. For downlink RLC layer data packets that have not been submitted to the MAC layer, after the RLC PDU that has already been submitted to the MAC layer confirms successful transmission, it is then submitted to the MAC layer and sent (initial transmission) to the terminal device.

[0194] Optionally, the first information further includes eighth indication information, which indicates that the first information originates from the first access network device. For example, the eighth indication information is carried in the header of a data packet sent from the second access network device to the terminal device. Based on the eighth indication information, the terminal device can determine that after the downlink MAC layer data packet and / or the downlink RLC layer data packet from the first access network device are delivered to the PDCP layer, it uses the key (old key) used during data transmission with the first access network device for decryption. This avoids decryption failure caused by the terminal device using the key (new key) used during data transmission with the second access network device, improving the terminal device's decryption efficiency and thus improving data transmission efficiency. The eighth indication information can be understood as indication information sent by the data packet from the first access network device (source base station).

[0195] It should be noted that the second access network device may also indicate to the terminal device that the first information comes from the first access network device through downlink control information (DCI) used to schedule the first information, without limitation.

[0196] Optionally, the second access network device does not send the eighth indication information to the terminal device. After the terminal device switches to the second access network device, it attempts to decrypt the data submitted to the PDCP layer using the key (new key) used during data transmission with the second access network device. If the decryption fails, the old key is used for decryption.

[0197] Optionally, if the first information includes a downlink RRC layer data packet originating from the RRC layer, the terminal device discards the downlink RRC layer data packet. Specifically, if the terminal device parses the data packet in the first information and finds that it is a downlink RRC layer data packet at the upper layer, then it discards the downlink RRC layer data packet.

[0198] It should be noted that the first access network device sends MAC layer data packets and / or RLC layer data packets to the second access network device without determining the upper layer of these data packets. The same MAC PDU may contain data from different PDCP PDUs; for example, one PDCP PDU within the same MAC PDU might contain RRC layer data, while another might contain normal user plane data. Control plane messages (RRC messages) sent by the first access network device also need to pass through the MAC layer. For the downlink MAC layer data packets corresponding to these control plane messages, once the terminal device decodes them and finds they are RRC layer data packets, they need to be discarded. This is because RRC messages are control signaling between the terminal device and the first access network device. When the terminal device switches to the second access network device, the control signaling of the first access network device cannot be used and must be discarded. Figure 7 is a schematic diagram of the control plane protocol stack. The highest layer of the control plane is the RRC layer, and below the RRC layer, the data passes through the PDCP layer, RLC layer, MAC layer, and PHY layer. The difference between the control plane and the user plane protocol stack in Figure 4 is that the control plane does not have a Quality of Service (QoS) flow, so it does not have an SDAP layer, but it still needs the PDCP layer and below for air interface transmission of control plane messages.

[0199] S640, the terminal device sends second information to the second access network device. This second information includes an uplink MAC layer data packet (an uplink MAC layer data packet that the terminal device failed to send), and / or a second uplink RLC layer data packet (an uplink RLC layer data packet that the terminal device failed to send). The second uplink RLC layer data packet belongs to the same PDCP layer data packet as the first uplink RLC layer data packet successfully received by the first access network device. In other words, the second information includes the uplink MAC layer data packet buffered in the terminal device's MAC layer buffer, and / or the uplink RLC layer data packet buffered in the terminal device's RLC layer buffer. Correspondingly, the second access network device receives the second information from the terminal device.

[0200] In this scenario, the uplink MAC layer data packets sent by the terminal device to the second access network device and the uplink MAC layer data packets sent by the first access network device to the second access network device belong to the same MAC PDU, but carry different or partially different bits. For example, the uplink MAC layer data packets sent by the first access network device to the second access network device carry bits corresponding to RV0 and RV2. The terminal device first sends the bits corresponding to RV3 to the second access network device. The second access network device combines and decodes (decodes) the bits corresponding to RV0, RV2, and RV3. If the second access network device fails to decode and sends a NACK to the terminal device, the terminal device continues to send the bits corresponding to RV1 to the second access network device, and the second access network device continues to combine and decode. For example, the uplink MAC layer data packet sent by the first access network device to the second access network device carries bits corresponding to RV0, RV2, and RV3. The terminal device first sends the bit corresponding to RV1 to the second access network device. The second access network device merges and decodes the bits corresponding to RV0, RV2, RV3, and RV1. If the second access network device fails to decode and sends a NACK to the terminal device, the terminal device continues to send the bit corresponding to RV0 to the second access network device, and the second access network device continues to merge and decode.

[0201] It should be noted that step S620 can be executed before step S630 or after step S630, and this application does not impose any restrictions on this.

[0202] Optionally, the second information also includes a ninth indication, which indicates that the second information should be parsed using the key used during data transmission between the first access network device and the terminal device after it is submitted to the upper layer. Based on this implementation, the second access network device, according to the ninth indication, can successfully parse the second information using the key used during data transmission between the first access network device and the terminal device after submitting it to the PDCP layer, avoiding retransmissions due to parsing failures and thus improving data transmission efficiency. It should be noted that the uplink MAC layer data packets (uplink MAC layer data packets that the terminal device failed to send) and / or the second uplink RLC layer data packets (uplink RLC layer data packets that the terminal device failed to send) sent by the terminal device to the second access network device have already been encrypted at the PDCP layer using the key used during data transmission between the terminal device and the first access network device, and the second access network device needs to use this key for decryption.

[0203] Optionally, if the second information includes uplink RRC layer data packets originating from the RRC layer, the second access network device discards the uplink RRC layer data packets. Specifically, if the second access network device parses the data packets in the second information and finds that they are uplink RRC layer data packets at the upper layer, it discards the uplink RRC layer data packets. It should be noted that the control plane messages (RRC messages) sent by the terminal device also need to pass through the MAC layer. The uplink RRC layer data packets originating from the RRC layer included in the second information are sent by the terminal device to the first access network device, and the second access network device cannot use them directly and must discard them.

[0204] Based on the technical solution provided in the embodiments of this application, when a terminal device switches from a first access network device to a second access network device, the first access network device transfers the data packets cached in the MAC buffer and / or RLC layer buffer to the second access network device, and the subsequent transmission is completed between the second access network device and the terminal device. The ARQ buffer and HARQ buffer on the terminal device side do not need to be cleared, which can realize seamless switching of the terminal device, thereby improving the user experience of the terminal device during the switching process.

[0205] The CU and DU in the access network device (first access network device and second access network device) may not be concentrated in the same network element, and the access network device may be a CU-DU separated architecture.

[0206] In the case of a CU-DU separated architecture in the access network device, the processing of the RLC layer and MAC layer is the function of the DU in the access network device, and the processing of the PDCP layer is the function of the CU in the access network device. Taking a first access network device including CU1 and DU1, and a second access network device including CU2 and DU2 as an example, if the existing tunnel is not reused, it is necessary to establish an F1 tunnel between DU1 and CU1, an Xn tunnel between CU1 and CU2, and an F1 tunnel between CU2 and DU2. In the case of a CU-DU separated architecture in the access network device, the process of establishing a tunnel between the first access network device and the second access network device is shown in steps S810 to S860 of Figure 8. Figure 8 is a schematic flowchart of an example of a data transmission method provided in the embodiments of this application.

[0207] S810, DU1 sends a first F1 interface application (AP) message (referred to as the first F1AP message) to CU1. This first F1AP message requests the establishment of at least one tunnel (F1 tunnel) for transmitting data packets in the MAC layer buffer. The first F1AP message carries the F1 tunnel identification information on the DU1 side. Correspondingly, CU1 receives the first F1AP message from DU1.

[0208] It should be noted that DU1 can use the existing F1 tunnel used for transmitting RLC layer data packets to send data packets in the RLC layer buffer to CU1, so it is not necessary to establish a tunnel for transmitting data packets in the RLC layer buffer.

[0209] Optionally, before DU1 sends the first F1AP message to CU1, the first access network device determines that the terminal device needs to be switched to the second access network device. The first access network device is the source access network device of the terminal device, and the second access network device is the target access network device of the terminal device.

[0210] Optionally, a tunnel is established for each HARQ process, and the HARQ process number corresponding to the tunnel is carried in the first F1AP message.

[0211] Optionally, if a separate tunnel is established for each HARQ process, the first F1AP message also carries redundant version information of the MAC layer data packets to be transmitted in the current HARQ process.

[0212] Optionally, different tunnels are established for uplink MAC layer data packets and downlink MAC layer data packets respectively, and the first F1AP message carries indication information of whether the tunnel is used to transmit uplink MAC layer data packets or downlink MAC layer data packets.

[0213] S820, CU1 sends a first XnAP message to CU2. This first XnAP message carries request information requesting the establishment of at least one tunnel for transmitting buffered data packets (including packets in the MAC layer buffer and / or the RLC layer buffer). This request information includes Xn tunnel identification information on the CU1 side. Correspondingly, CU2 receives the first XnAP message from CU1.

[0214] It should be noted that the request information may also carry at least one of the above-mentioned second instruction information, the above-mentioned fifth instruction information, the above-mentioned sixth instruction information, or the above-mentioned seventh instruction information. For a specific description, please refer to the description in the method embodiment of Figure 6, which will not be repeated here.

[0215] S830, CU2 sends a second F1AP message to DU2. This second F1AP message requests the establishment of at least one tunnel (F1 tunnel) for transmitting data packets in the MAC layer buffer. The second F1AP message carries the F1 tunnel identification information on the CU2 side. Correspondingly, DU2 receives the second F1AP message from CU2.

[0216] It should be noted that CU2 can use the existing F1 tunnel for transmitting RLC layer data packets to send data packets from the RLC layer buffer of the first access network device to DU2, so it is not necessary to establish a tunnel for transmitting data packets in the RLC layer buffer.

[0217] Optionally, a tunnel is established for each HARQ process, and the HARQ process number corresponding to the tunnel is carried in the second F1AP message.

[0218] Optionally, if a separate tunnel is established for each HARQ process, the second F1AP message also carries redundant version information of the MAC layer data packets to be transmitted in the current HARQ process.

[0219] Optionally, different tunnels are established for uplink MAC layer data packets and downlink MAC layer data packets respectively, and the second F1AP message carries indication information of whether the tunnel is used to transmit uplink MAC layer data packets or downlink MAC layer data packets.

[0220] In S840, in response to the second F1AP message in S830, DU2 sends a third F1AP message to CU2, which carries the F1 tunnel identification information on the DU2 side. Correspondingly, CU2 receives the third F1AP message from DU2.

[0221] Optionally, the third F1AP message also carries the F1 tunnel identification information on the CU2 side obtained from the second F1AP message, used to indicate which tunnel the F1 tunnel identification information on the DU2 side specifically corresponds to. It should be noted that if only one tunnel is established between CU2 and DU2 for transmitting data packets in the MAC layer buffer, the third F1AP message does not need to carry the F1 tunnel identification information on the CU2 side. If multiple tunnels are established between CU2 and DU2, the third F1AP message may carry the F1 tunnel identification information on the CU2 side.

[0222] Optionally, if a separate tunnel is established for each HARQ process, the third F1AP message also carries the HARQ process number corresponding to the tunnel, which is used to identify the tunnel (to indicate which tunnel the F1 tunnel identification information on the DU2 side specifically corresponds to).

[0223] Optionally, if a tunnel is established for each of the uplink MAC layer data packets and the downlink MAC layer data packets, the third F1AP message also carries indication information indicating whether the tunnel is used to transmit uplink MAC layer data packets or downlink MAC layer data packets, for identifying the tunnel.

[0224] S850, in response to the first XnAP message in step S820, CU2 sends a second XnAP message to CU1. This second XnAP message carries response information, including the Xn tunnel identification information on the CU2 side. Correspondingly, CU1 receives the second XnAP message from CU2.

[0225] Optionally, the response information also includes Xn tunnel identification information on the CU1 side obtained from the first XnAP message, used to indicate which tunnel the Xn tunnel identification information on the CU2 side specifically corresponds to. It should be noted that if only one tunnel is established between CU2 and CU1 for transmitting data packets in the MAC layer buffer and / or RLC layer buffer, the second XnAP message does not need to carry the Xn tunnel identification information on the CU1 side. If multiple tunnels are established between CU2 and CU1, the second XnAP message may carry the Xn tunnel identification information on the CU1 side. Further descriptions of the response information can be found in the description in the method embodiment of Figure 6, and will not be repeated here.

[0226] S860, in response to the first F1AP message in step S810, CU1 sends a fourth F1AP message to DU1, which carries the F1 tunnel identification information on the CU1 side. Correspondingly, DU1 receives the fourth F1AP message from CU1.

[0227] Optionally, the second XnAP message also carries the F1 tunnel identification information on the DU1 side obtained from the first F1AP message, used to indicate which tunnel the F1 tunnel identification information on the CU1 side specifically corresponds to. It should be noted that if only one tunnel is established between CU1 and DU1 for transmitting data packets in the MAC layer buffer, the fourth F1AP message does not need to carry the F1 tunnel identification information on the DU1 side. If multiple tunnels are established between CU1 and DU1, the fourth F1AP message may carry the F1 tunnel identification information on the DU1 side.

[0228] Optionally, if a separate tunnel is established for each HARQ process, the fourth F1AP message also carries the HARQ process number corresponding to the tunnel, which is used to identify the tunnel (to indicate which tunnel the F1 tunnel identification information on the CU1 side specifically corresponds to).

[0229] Optionally, if a tunnel is established for each of the uplink MAC layer data packets and the downlink MAC layer data packets, the fourth F1AP message also carries indication information indicating whether the tunnel is used to transmit uplink MAC layer data packets or downlink MAC layer data packets, for identifying the tunnel.

[0230] It should be noted that step S850 can also be executed immediately after step S820, and step S860 can also be executed immediately after step S810. This application does not limit this.

[0231] Furthermore, steps S810 and S860 are optional. DU1 may not send the first F1AP message, and correspondingly, CU1 may not send the fourth F1AP message. DU1 may reuse an existing F1 tunnel used for transmitting RLC layer data packets to send data packets from the MAC layer buffer and / or the RLC layer buffer (buffered data packets) of the first access network device to CU1. Steps S830 and S840 are also optional. CU2 may not send the second F1AP message, and correspondingly, DU2 may not send the third F1AP message. CU2 may reuse an existing F1 tunnel used for transmitting RLC layer data packets to send data packets from the MAC layer buffer and / or the RLC layer buffer (buffered data packets) of the first access network device to DU2.

[0232] S870, DU1 sends the aforementioned buffered data packets to DU2 via CU1 and CU2. The transmission path of the buffered data packets is: DU1-CU1-CU2-DU2.

[0233] S880, DU2 in the second access network device sends the aforementioned first information to the terminal device.

[0234] S890, the terminal device sends the aforementioned second information to DU2 in the second access network device.

[0235] When the CU and DU in the access network device are concentrated in the same network element, and the existing Xn tunnel used for transferring PDCP PDUs is not reused, only an Xn tunnel for transmitting data packets in the MAC layer buffer and / or RLC layer buffer needs to be established between the first access network device and the second access network device. The specific tunnel establishment process can be referred to in steps S820 and S850 in Figure 8. It is only necessary to replace the execution subject CU1 with the first access network device and the execution subject CU2 with the second access network device.

[0236] Optionally, the process of establishing a tunnel for transmitting MAC PDUs can be separate from the process of establishing a tunnel for transmitting RLC PDUs. For example, a tunnel for transmitting MAC PDUs can be established first between the first access network device and the second access network device, followed by a tunnel for transmitting RLC PDUs between the two devices. Alternatively, a tunnel for transmitting RLC PDUs can be established first between the first access network device and the second access network device, followed by a tunnel for transmitting MAC PDUs between the two devices. It should be noted that during the request to establish a tunnel for transmitting RLC PDUs, the request information does not carry the HARQ process number corresponding to the tunnel (the RLC layer has only one ARQ process), redundancy version information, or code block group information.

[0237] Figure 9 is a schematic flowchart illustrating another example of the data transmission method provided in this application. In the O-RAN architecture, the RAN intelligent controller (RIC) is primarily responsible for network management and control. In this example, when a terminal device switches from a first access network device to a second access network device, the RIC controls the establishment of the tunnel between the first and second access network devices. This is exemplified by a first access network device comprising CU1 and DU1, and a second access network device comprising CU2 and DU2.

[0238] S910, DU1 sends a first message to RIC via the E2 interface. This first message requests the establishment of at least one tunnel for transmitting data packets in the MAC layer buffer of DU1. The data packets in DU1's MAC layer buffer include downlink MAC layer data packets and / or uplink MAC layer data packets. Correspondingly, RIC receives the first message from DU1.

[0239] Optionally, the first message carries the aforementioned first instruction information, as detailed in the preceding description.

[0240] It should be noted that step S910 is optional. When the first access network device and the second access network device are satellite base stations, the RIC can also determine the service stop time of the first access network device and the service start time of the second access network device based on the ephemeris information, thereby determining the time when a tunnel for transmitting data packets in the MAC layer buffer needs to be established.

[0241] S920, RIC sends a second message to DU1, which includes F1 tunnel identification information on the DU1 side and F1 tunnel identification information on the CU1 side. Correspondingly, DU1 receives the second message from RIC. The F1 tunnel identification information on the DU1 side and the F1 tunnel identification information on the CU1 side are used for establishing the F1 tunnel between DU1 and CU1.

[0242] Optionally, the second message carries the aforementioned first instruction information, as detailed in the preceding description.

[0243] S930, RIC sends a third message to CU1, which includes F1 tunnel identification information on the DU1 side and F1 tunnel identification information on the CU1 side, as well as Xn tunnel identification information on the CU1 side and Xn tunnel identification information on the CU2 side. Correspondingly, CU1 receives the third message from RIC. Among them, the Xn tunnel identification information on the CU1 side and Xn tunnel identification information on the CU2 side are used for establishing the Xn tunnel between CU1 and CU2.

[0244] Optionally, the third message carries the aforementioned first instruction information, as detailed in the preceding description.

[0245] S940, RIC sends a fourth message to CU2, which includes Xn tunnel identification information on the CU1 side and the CU2 side, as well as F1 tunnel identification information on the CU2 side and the DU2 side. Correspondingly, CU2 receives the fourth message from RIC. The F1 tunnel identification information on the CU2 side and the DU2 side is used for establishing the F1 tunnel between CU2 and DU2.

[0246] Optionally, the fourth message carries the aforementioned first instruction information, as detailed in the preceding description.

[0247] S950, RIC sends a fifth message to DU2, which includes F1 tunnel identification information on both the CU2 and DU2 sides. Correspondingly, DU2 receives the fifth message from RIC.

[0248] Optionally, the fifth message carries the aforementioned first instruction information, as detailed in the preceding description.

[0249] S960, DU1 sends the data packets in the MAC layer buffer to DU2 through CU1 and CU2. The transmission path of the data packets in the MAC layer buffer is: DU1-CU1-CU2-DU2.

[0250] S970, DU2 in the second access network device sends downlink MAC layer data packets to the terminal device.

[0251] S980, the terminal device sends an uplink MAC layer data packet to DU2 in the second access network device.

[0252] The data transmission method provided in the embodiments of this application has been described above. The execution subject for performing the above data transmission method will be described below.

[0253] Figure 10 is a schematic block diagram of a communication device 1000 according to an embodiment of this application. This device can be applied to a first access network device using the method described in Figure 6 or Figure 8 in an embodiment of this application. The communication device 1000 includes:

[0254] Processing module 1010 is used to determine that the terminal device needs to be switched to a second access network device, wherein the first access network device is the source access network device of the terminal device, and the second access network device is the target access network device of the terminal device.

[0255] The transceiver module 1020 is used to send buffered data packets to the second access network device. The buffered data packets include data packets in the Media Access Control (MAC) layer buffer and / or the Radio Link Control (RLC) layer buffer. The buffered data packets include at least one of the following: downlink MAC layer data packets, uplink MAC layer data packets, downlink RLC layer data packets, or a first uplink RLC layer data packet.

[0256] Optionally, the cached data packet further includes first indication information, which is used to indicate at least one of the following: the Hybrid Automatic Repeat Request (HARQ) process number, redundancy version information, or code block group information corresponding to the downlink MAC layer data packet and the uplink MAC layer data packet, respectively.

[0257] Optionally, the cached data packet further includes second indication information, which is used to indicate the key information used during data transmission between the first access network device and the terminal device.

[0258] Optionally, the cached data packets further include third indication information, which indicates that the downlink MAC layer data packets and the downlink RLC layer data packets are data packets that need to be transmitted downlink, and the uplink MAC layer data packets and the first uplink RLC layer data packets are data packets that need to be transmitted uplink.

[0259] Optionally, the cached data packet further includes fourth indication information, which is used to indicate at least one of the following: the sequence number of the downlink RLC layer data packet, the sequence number used by the second access network device to transmit downlink RLC layer data packets from the upper layer, the maximum value of the sequence number of the successfully received uplink RLC layer data packet, or the sequence number of the unsuccessfully received uplink RLC layer data packet.

[0260] Optionally, the transceiver module 1020 is further configured to send a request message to the second access network device, the request message requesting the establishment of at least one tunnel for transmitting the cached data packets, the request message including tunnel identification information of the first access network device;

[0261] The transceiver module 1020 is further configured to receive response information from the second access network device, the response information including tunnel identification information of the second access network device.

[0262] Optionally, the request information further includes fifth indication information, which indicates that the first tunnel is used to transmit the downlink MAC layer data packets and / or the uplink MAC layer data packets, and the second tunnel is used to transmit the downlink RLC layer data packets and / or the first uplink RLC layer data packets, wherein the at least one tunnel includes the first tunnel and the second tunnel.

[0263] Optionally, the request information further includes a sixth indication information, which indicates that the first tunnel is used to transmit the downlink MAC layer data packets and / or the downlink RLC layer data packets, and the second tunnel is used to transmit the uplink MAC layer data packets and / or the first uplink RLC layer data packets, wherein the at least one tunnel includes the first tunnel and the second tunnel.

[0264] Optionally, the request information further includes a seventh indication information, which indicates that the first tunnel is used to transmit MAC layer data packets corresponding to the first HARQ process number, and the second tunnel is used to transmit MAC layer data packets corresponding to the second HARQ process number, wherein the at least one tunnel includes the first tunnel and the second tunnel.

[0265] Optionally, the seventh indication information is further used to indicate the redundancy version information and / or code block group information of the MAC layer data packets corresponding to the first HARQ process number and the second HARQ process number, respectively.

[0266] Optionally, the request information may further include second indication information, which is used to indicate the key information used during data transmission between the first access network device and the terminal device.

[0267] Optionally, the downlink MAC layer data packet includes downlink code block groups that were not successfully transmitted. The code block group information corresponding to the downlink MAC layer data packet includes any one of the following: the identifier of the downlink code block group that was not successfully transmitted and / or the identifier of the downlink code block group that was successfully transmitted, the number of code block groups included in the downlink MAC layer data packet and the identifier of the downlink code block group that was not successfully transmitted, or the number of code block groups included in the downlink MAC layer data packet and the identifier of the downlink code block group that was successfully transmitted.

[0268] The uplink MAC layer data packet includes successfully received uplink code block groups. The code block group information corresponding to the uplink MAC layer data packet includes any one of the following: the identifier of the successfully received uplink code block group and / or the identifier of the unsuccessfully received uplink code block group, the number of code block groups included in the uplink MAC layer data packet and the identifier of the successfully received uplink code block group, or the number of code block groups included in the uplink MAC layer data packet and the identifier of the unsuccessfully received uplink code block group.

[0269] Figure 11 is a schematic block diagram of another communication device 1100 according to an embodiment of this application. This device can be applied to the second access network device of the method described in Figure 6 or Figure 8 in the embodiments of this application. The communication device 1100 includes:

[0270] The transceiver module 1110 is configured to receive buffered data packets from a first access network device. The buffered data packets include data packets in a MAC layer buffer and / or an RLC layer buffer. The buffered data packets include at least one of the following: downlink MAC layer data packets, uplink MAC layer data packets, downlink RLC layer data packets, or a first uplink RLC layer data packet. The first access network device is the source access network device of the terminal device, and the second access network device is the target access network device of the terminal device.

[0271] The transceiver module 1110 is further configured to send first information to the terminal device, the first information including the downlink MAC layer data packet and / or the downlink RLC layer data packet;

[0272] The transceiver module 1110 is further configured to receive second information from the terminal device, the second information including the uplink MAC layer data packet and / or the second uplink RLC layer data packet, wherein the first uplink RLC layer data packet and the second uplink RLC layer data packet belong to the same Packet Data Convergence Protocol (PDCP) layer data packet.

[0273] Optionally, the cached data packet further includes first indication information, which is used to indicate at least one of the following: HARQ process number, redundancy version information, or code block group information corresponding to the downlink MAC layer data packet that was not successfully sent and the uplink MAC layer data packet that was not successfully decoded.

[0274] Optionally, the cached data packet further includes second indication information, which is used to indicate the key information used during data transmission between the first access network device and the terminal device.

[0275] Optionally, the cached data packets further include third indication information, which indicates that the downlink MAC layer data packets and the downlink RLC layer data packets are data packets that need to be transmitted downlink, and the uplink MAC layer data packets and the first uplink RLC layer data packets are data packets that need to be transmitted uplink.

[0276] Optionally, the cached data packet further includes fourth indication information, which is used to indicate at least one of the following: the sequence number of the downlink RLC layer data packet, the sequence number used by the second access network device to transmit downlink RLC layer data packets from the upper layer, the maximum value of the sequence number of the successfully received uplink RLC layer data packet, or the sequence number of the unsuccessfully received uplink RLC layer data packet.

[0277] Optionally, the transceiver module 1110 is further configured to receive request information from the first access network device, the request information requesting the establishment of at least one tunnel for transmitting the cached data packets, the request information including tunnel identification information of the first access network device;

[0278] The transceiver module 1110 is further configured to send response information to the first access network device, the response information including tunnel identification information of the second access network device.

[0279] Optionally, the request information further includes fifth indication information, which indicates that the first tunnel is used to transmit the downlink MAC layer data packets and / or the uplink MAC layer data packets, and the second tunnel is used to transmit the downlink RLC layer data packets and / or the first uplink RLC layer data packets, wherein the at least one tunnel includes the first tunnel and the second tunnel.

[0280] Optionally, the request information further includes a sixth indication information, which indicates that the first tunnel is used to transmit the downlink MAC layer data packets and / or the downlink RLC layer data packets, and the second tunnel is used to transmit the uplink MAC layer data packets and / or the first uplink RLC layer data packets, wherein the at least one tunnel includes the first tunnel and the second tunnel.

[0281] Optionally, the request information further includes a seventh indication information, which indicates that the first tunnel is used to transmit MAC layer data packets corresponding to the first HARQ process number, and the second tunnel is used to transmit MAC layer data packets corresponding to the second HARQ process number, wherein the at least one tunnel includes the first tunnel and the second tunnel.

[0282] Optionally, the seventh indication information is further used to indicate the redundancy version information and / or code block group information of the MAC layer data packets corresponding to the first HARQ process number and the second HARQ process number, respectively.

[0283] Optionally, the request information may further include second indication information, which is used to indicate the key information used during data transmission between the first access network device and the terminal device.

[0284] Optionally, the first information may further include eighth indication information, which indicates that the first information is from the first access network device.

[0285] Optionally, the second information further includes a ninth indication, which is used to indicate that the key used in the data transmission process between the first access network device and the terminal device is used for parsing after the second information is submitted to the upper layer.

[0286] Optionally, the communication device 1100 further includes a processing module 1120, configured to discard the uplink RRC layer data packet if the second information includes an uplink RRC layer data packet originating from the RRC layer.

[0287] Optionally, the downlink MAC layer data packet includes downlink code block groups that were not successfully transmitted. The code block group information corresponding to the downlink MAC layer data packet includes any one of the following: the identifier of the downlink code block group that was not successfully transmitted and / or the identifier of the downlink code block group that was successfully transmitted, the number of code block groups included in the downlink MAC layer data packet and the identifier of the downlink code block group that was not successfully transmitted, or the number of code block groups included in the downlink MAC layer data packet and the identifier of the downlink code block group that was successfully transmitted.

[0288] The uplink MAC layer data packet includes successfully received uplink code block groups. The code block group information corresponding to the uplink MAC layer data packet includes any one of the following: the identifier of the successfully received uplink code block group and / or the identifier of the unsuccessfully received uplink code block group, the number of code block groups included in the uplink MAC layer data packet and the identifier of the successfully received uplink code block group, or the number of code block groups included in the uplink MAC layer data packet and the identifier of the unsuccessfully received uplink code block group.

[0289] Figure 12 is a schematic block diagram of another communication device 1200 according to an embodiment of this application. This device can be applied to the terminal device of the method described in Figure 6 or Figure 8 in the embodiments of this application. The communication device 1200 includes:

[0290] Transceiver module 1210 is used to receive first information from a second access network device. The first information includes downlink MAC layer data packets in the MAC layer buffer of the first access network device and / or downlink RLC layer data packets in the RLC layer buffer. The first access network device is the source access network device of the terminal device, and the second access network device is the target access network device of the terminal device.

[0291] The transceiver module 1210 is further configured to send second information to the second access network device, the second information including uplink MAC layer data packets and / or, second uplink RLC layer data packets.

[0292] Optionally, the first information may further include eighth indication information, which indicates that the first information is from the first access network device.

[0293] Optionally, the second information further includes a ninth indication, which is used to indicate that the key used in the data transmission process between the first access network device and the terminal device is used for parsing after the second information is submitted to the upper layer.

[0294] Optionally, the communication device 1200 further includes a processing module 1220, configured to discard the downlink RRC layer data packet if the first information includes a downlink RRC layer data packet originating from the RRC layer.

[0295] Figure 13 is a schematic block diagram of another communication device 1300 provided in an embodiment of this application. This communication device 1300 can be applied to the aforementioned first access network device, second access network device, or terminal device. The communication device 1300 includes a processor 1310, which implements the data transmission method provided in the embodiment of this application through logic circuits or executing code instructions.

[0296] Optionally, the communication device 1300 may also include interface circuitry 1320. Processor 1310 and interface circuitry 1320 are coupled to each other. It is understood that interface circuitry 1320 may be a transceiver or an input / output interface.

[0297] Optionally, the communication device 1300 may also include a memory 1330 for storing instructions executed by the processor 1310, or storing input data required by the processor 1310 to execute instructions, or storing data generated after the processor 1310 executes instructions.

[0298] The aforementioned processor 1310 may be an integrated circuit chip with signal processing capabilities. In implementation, each step of the above method embodiments can be completed by integrated logic circuits in the processor's hardware or by software instructions. The aforementioned processor may be a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components. It can implement or execute the methods, steps, and logic block diagrams disclosed in the embodiments of this application. The general-purpose processor may be a microprocessor or any conventional processor. The steps of the methods disclosed in the embodiments of this application can be directly embodied in the execution of a hardware decoding processor, or executed by a combination of hardware and software modules in the decoding processor. The software modules may reside in random access memory, flash memory, read-only memory, programmable read-only memory, electrically erasable programmable memory, registers, or other mature storage media in the art. This storage medium is located in memory; the processor reads information from the memory and, in conjunction with its hardware, completes the steps of the above method.

[0299] This application also provides a communication system, including a first access network device, a second access network device, and a terminal device in the data transmission method provided in this application.

[0300] This application also provides a computer-readable storage medium storing a computer program for implementing the methods in the above-described method embodiments. When the computer program is run on a computer, the computer can implement the methods in the above-described method embodiments.

[0301] This application also provides a computer program product, which includes a computer program that, when run on a computer, causes the methods in the above method embodiments to be executed.

[0302] This application also provides a chip, including a processor connected to a memory for storing computer programs, and the processor for executing the computer programs stored in the memory, so that the chip performs the methods described in the above method embodiments.

[0303] It should be understood that, in the embodiments of this application, for a technical feature, the technical features in that technical feature are distinguished by "first", "second" and "third", and there is no order of precedence or size among the technical features described by "first", "second" and "third".

[0304] Furthermore, the term "and / or" in this application is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship. The term "at least one" in this application can represent "one" and "two or more." For example, A, B, and C can represent: A existing alone, B existing alone, C existing alone, A and B existing simultaneously, A and C existing simultaneously, C and B existing simultaneously, and A, B, and C existing simultaneously.

[0305] In the embodiments of this application, "send" and "receive" indicate the direction of signal transmission. For example, "send information to XX" can be understood as the destination of the information being XX, which may include direct transmission via the air interface or indirect transmission via the air interface by other units or modules. "Receive information from YY" can be understood as the source of the information being YY, which may include direct reception from YY via the air interface or indirect reception from YY via the air interface by other units or modules. "Send" can also be understood as the "output" of the chip interface, and "receive" can also be understood as the "input" of the chip interface.

[0306] In other words, sending and receiving can occur between devices, such as between access network devices and terminal devices, or within a device, such as between components, modules, chips, software modules, or hardware modules within the device via buses, wiring, or interfaces.

[0307] It is understandable that information may undergo necessary processing, such as encoding and modulation, between the source and destination, but the destination can understand the valid information from the source. Similar statements in this application can be interpreted in a similar way and will not be elaborated further.

[0308] In the embodiments of this application, "instruction" can include direct and indirect instructions, as well as explicit and implicit instructions. The information indicated by a certain piece of information (hereinafter referred to as instruction information) is called the information to be instructed. In specific implementation, there are many ways to indicate the information to be instructed, such as, but not limited to, directly indicating the information to be instructed, such as the information to be instructed itself or its index. It can also indirectly indicate the information to be instructed by indicating other information, where there is an association between the other information and the information to be instructed; or it can indicate only a part of the information to be instructed, while the other parts are known or pre-agreed upon. For example, the instruction can be implemented by using a pre-agreed (e.g., protocol predefined) arrangement of various information, thereby reducing the instruction overhead to a certain extent. This application does not limit the specific method of instruction. It is understood that for the sender of the instruction information, the instruction information can be used to indicate the information to be instructed; for the receiver of the instruction information, the instruction information can be used to determine the information to be instructed.

[0309] In this application, unless otherwise specified, the same or similar parts between the various embodiments can be referred to each other. In the various embodiments of this application, and in the various implementation methods / methods / implementations within each embodiment, unless otherwise specified or logically conflicting, the terminology and / or descriptions between different embodiments and between the various implementation methods / methods / implementations within each embodiment are consistent and can be mutually referenced. The technical features in different embodiments and the various implementation methods / methods / implementations within each embodiment can be combined according to their inherent logical relationships to form new embodiments, implementation methods, methods, or implementation approaches. The embodiments described below do not constitute a limitation on the scope of protection of this application.

[0310] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0311] 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.

[0312] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between apparatuses or units may be electrical, mechanical, or other forms.

[0313] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0314] In addition, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

[0315] If the aforementioned functions are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0316] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method of data transmission, characterized by, Applied to a first access network device, the method includes: It is determined that the terminal device needs to be switched to the second access network device, wherein the first access network device is the source access network device of the terminal device, and the second access network device is the target access network device of the terminal device; Send buffered data packets to the second access network device. The buffered data packets include data packets in the Media Access Control (MAC) layer buffer and / or the Radio Link Control (RLC) layer buffer. The buffered data packets include at least one of the following: downlink MAC layer data packets, uplink MAC layer data packets, downlink RLC layer data packets, or a first uplink RLC layer data packet.

2. The method of claim 1, wherein, Also includes: Send a request message to the second access network device, the request message requesting the establishment of at least one tunnel for transmitting the cached data packets, the request message including the tunnel identification information of the first access network device; Receive response information from the second access network device, the response information including tunnel identification information of the second access network device.

3. A method of data transmission, characterized by Applied to a second access network device, the method includes: The device receives a buffered data packet from a first access network device, the buffered data packet including data packets in a MAC layer buffer and / or an RLC layer buffer, the buffered data packet including at least one of the following: downlink MAC layer data packet, uplink MAC layer data packet, downlink RLC layer data packet, or a first uplink RLC layer data packet, the first access network device being the source access network device of the terminal device, and the second access network device being the target access network device of the terminal device; Send first information to the terminal device, the first information including the downlink MAC layer data packet and / or the downlink RLC layer data packet; The terminal device receives second information, which includes the uplink MAC layer data packet and / or the second uplink RLC layer data packet, wherein the first uplink RLC layer data packet and the second uplink RLC layer data packet belong to the same Packet Data Convergence Protocol (PDCP) layer data packet.

4. The method according to any one of claims 1 to 3, characterized in that, The cached data packet also includes first indication information, which is used to indicate at least one of the following: HARQ process number, redundancy version information, or code block group information corresponding to the downlink MAC layer data packet that was not successfully sent and the uplink MAC layer data packet that was not successfully decoded.

5. The method according to any one of claims 1 to 4, characterized in that, The cached data packet also includes second indication information, which is used to indicate the key information used during data transmission between the first access network device and the terminal device.

6. The method according to any one of claims 1 to 5, characterized in that, The cached data packets also include third indication information, which indicates that the downlink MAC layer data packets and the downlink RLC layer data packets are data packets that need to be transmitted downlink, and the uplink MAC layer data packets and the first uplink RLC layer data packets are data packets that need to be transmitted uplink.

7. The method according to any one of claims 1 to 6, characterized in that, The cached data packet further includes fourth indication information, which is used to indicate at least one of the following: the sequence number of the downlink RLC layer data packet, the sequence number used by the second access network device to transmit downlink RLC layer data packets from the upper layer, the maximum value of the sequence number of the successfully received uplink RLC layer data packet, or the sequence number of the unsuccessfully received uplink RLC layer data packet.

8. The method of claim 3, wherein, Also includes: The system receives a request from the first access network device, the request request requesting the establishment of at least one tunnel for transmitting the cached data packets, the request request including tunnel identification information of the first access network device; The response information is sent to the first access network device, the response information including the tunnel identification information of the second access network device.

9. The method according to claim 2 or 8, characterized in that, The request information also includes a fifth indication, which indicates that the first tunnel is used to transmit the downlink MAC layer data packet and / or the uplink MAC layer data packet, and the second tunnel is used to transmit the downlink RLC layer data packet and / or the first uplink RLC layer data packet, wherein the at least one tunnel includes the first tunnel and the second tunnel.

10. The method according to claim 2 or 8, characterized in that, The request information also includes a sixth indication, which indicates that the first tunnel is used to transmit the downlink MAC layer data packets and / or the downlink RLC layer data packets, and the second tunnel is used to transmit the uplink MAC layer data packets and / or the first uplink RLC layer data packets, wherein the at least one tunnel includes the first tunnel and the second tunnel.

11. The method according to claim 2 or 8, characterized in that, The request information also includes a seventh indication information, which indicates that the first tunnel is used to transmit MAC layer data packets corresponding to the first HARQ process number, and the second tunnel is used to transmit MAC layer data packets corresponding to the second HARQ process number, wherein the at least one tunnel includes the first tunnel and the second tunnel.

12. The method according to claim 11, characterized in that, The seventh indication information is also used to indicate the redundancy version information and / or code block group information of the MAC layer data packets corresponding to the first HARQ process number and the second HARQ process number, respectively.

13. The method according to claim 2, or any one of 8 to 12, characterized in that, The request information further comprises second indication information, which is used to indicate key information used in data transmission between the first access network device and the terminal device.

14. The method of claim 3, wherein, The first information further comprises eighth indication information, which is used to indicate that the first information is from the first access network device.

15. The method of claim 3 or 14, wherein, The second information further comprises ninth indication information, which is used to indicate that the first access network device and the terminal device use the key used in data transmission after the second information is submitted to the upper layer.

16. The method of any one of claims 3 or 14 or 15, wherein, Further comprising: If the second information comprises uplink RRC layer data packets from a radio resource control (RRC) layer, the uplink RRC layer data packets are discarded.

17. The method of claim 4 or 12, wherein, The downlink MAC layer data packet comprises unsuccessfully transmitted downlink code block groups, and code block group information corresponding to the downlink MAC layer data packet comprises any of the following: an identifier of the unsuccessfully transmitted downlink code block groups and / or an identifier of successfully transmitted downlink code block groups, a number of code block groups included in the downlink MAC layer data packet and an identifier of the unsuccessfully transmitted downlink code block groups, or a number of code block groups included in the downlink MAC layer data packet and an identifier of the successfully transmitted downlink code block groups; The uplink MAC layer data packet comprises successfully received uplink code block groups, and code block group information corresponding to the uplink MAC layer data packet comprises any of the following: an identifier of the successfully received uplink code block groups and / or an identifier of unsuccessfully received uplink code block groups, a number of code block groups included in the uplink MAC layer data packet and an identifier of the successfully received uplink code block groups, or a number of code block groups included in the uplink MAC layer data packet and an identifier of the unsuccessfully received uplink code block groups.

18. A method of data transmission, characterized by, The method is applied to a terminal device, and the method comprises: receiving first information from a second access network device, wherein the first information comprises downlink MAC layer data packets in a MAC layer buffer of a first access network device and / or downlink RLC layer data packets in a RLC layer buffer of the first access network device, the first access network device is a source access network device of the terminal device, and the second access network device is a target access network device of the terminal device; sending second information to the second access network device, wherein the second information comprises uplink MAC layer data packets and / or second uplink RLC layer data packets.

19. The method of claim 18, wherein, The first information further comprises eighth indication information, which is used to indicate that the second information is from the first access network device.

20. The method of claim 18 or 19, wherein, The second information further comprises ninth indication information, which is used to indicate that the key used in the data transmission process between the first access network device and the terminal device after the second information is submitted to the upper layer is used for analysis.

21. The method of any one of claims 18-20, wherein, Further comprising: If the first information comprises downlink RRC layer data packets from the RRC layer, discarding the downlink RRC layer data packets.

22. A communications device, characterized by Comprising: a processing module, configured to determine that the terminal device needs to be switched to a second access network device, the first access network device being a source access network device of the terminal device, and the second access network device being a target access network device of the terminal device; a transceiver module, configured to send buffered data packets to the second access network device, the buffered data packets comprising data packets in a medium access control (MAC) layer buffer and / or a radio link control (RLC) layer buffer, and the buffered data packets comprising at least one of the following: downlink MAC layer data packets, uplink MAC layer data packets, downlink RLC layer data packets, or first uplink RLC layer data packets.

23. The apparatus of claim 22, wherein the transceiver module is further configured to send request information to the second access network device, the request information requesting establishment of at least one tunnel for transmission of the buffered data packets, and the request information comprising tunnel identification information of the first access network device; the transceiver module is further configured to receive response information from the second access network device, the response information comprising tunnel identification information of the second access network device.

24. A communications device, characterized by Comprising: a transceiver module, configured to receive buffered data packets from a first access network device, the buffered data packets comprising data packets in a MAC layer buffer and / or an RLC layer buffer, and the buffered data packets comprising at least one of the following: downlink MAC layer data packets, uplink MAC layer data packets, downlink RLC layer data packets, or first uplink RLC layer data packets, the first access network device being a source access network device of a terminal device, and the second access network device being a target access network device of the terminal device; the transceiver module is further configured to send first information to the terminal device, the first information comprising the downlink MAC layer data packets and / or the downlink RLC layer data packets; the transceiver module is further configured to receive second information from the terminal device, the second information comprising the uplink MAC layer data packets and / or second uplink RLC layer data packets, the first uplink RLC layer data packets and the second uplink RLC layer data packets belonging to a same packet data convergence protocol (PDCP) layer data packet.

25. The apparatus of any of claims 22 to 24, wherein the buffered data packets further comprise first indication information, which is used to indicate at least one of the following: a HARQ process number, redundancy version information, or code block group information corresponding to the unsuccessfully transmitted downlink MAC layer data packets and the unsuccessfully decoded uplink MAC layer data packets, respectively.

26. The apparatus of any of claims 22 to 25, wherein The buffered data packet further comprises second indication information, which is used to indicate key information used in a data transmission process between the first access network device and the terminal device.

27. The apparatus of any one of claims 22-26, The buffered data packet further comprises third indication information, which is used to indicate that the downlink MAC layer data packet and the downlink RLC layer data packet are data packets that need to be transmitted in a downlink direction, and the uplink MAC layer data packet and the first uplink RLC layer data packet are data packets that need to be transmitted in an uplink direction.

28. The apparatus of any one of claims 22-27, The buffered data packet further comprises fourth indication information, which is used to indicate at least one of a sequence number of the downlink RLC layer data packet, a sequence number used by the second access network device to transmit a downlink RLC layer data packet from an upper layer, a maximum value of a sequence number of a successfully received uplink RLC layer data packet, or a sequence number of an unsuccessfully received uplink RLC layer data packet.

29. The apparatus of claim 24, The transceiver module is further configured to receive request information from the first access network device, the request information requesting establishment of at least one tunnel for transmitting the buffered data packet, and the request information comprising tunnel identification information of the first access network device. The transceiver module is further configured to send response information to the first access network device, the response information comprising tunnel identification information of the second access network device.

30. The apparatus of claim 23 or 29, The request information further comprises fifth indication information, which is used to indicate that a first tunnel is used to transmit the downlink MAC layer data packet and / or the uplink MAC layer data packet, and a second tunnel is used to transmit the downlink RLC layer data packet and / or the first uplink RLC layer data packet, and wherein the at least one tunnel comprises the first tunnel and the second tunnel.

31. The apparatus of claim 23 or 29, The request information further comprises sixth indication information, which is used to indicate that a first tunnel is used to transmit the downlink MAC layer data packet and / or the downlink RLC layer data packet, and a second tunnel is used to transmit the uplink MAC layer data packet and / or the first uplink RLC layer data packet, and wherein the at least one tunnel comprises the first tunnel and the second tunnel.

32. The apparatus of claim 23 or 29, The request information further comprises seventh indication information, which is used to indicate that a first tunnel is used to transmit a MAC layer data packet corresponding to a first HARQ process number, and a second tunnel is used to transmit a MAC layer data packet corresponding to a second HARQ process number, and wherein the at least one tunnel comprises the first tunnel and the second tunnel.

33. The apparatus of claim 32, The seventh indication information is further used for indicating redundancy version information and / or code block group information of the MAC layer data packets corresponding to the first HARQ process number and the second HARQ process number respectively.

34. The apparatus of any one of claims 23 or 29-33, wherein, The request information further comprises second indication information, which is used for indicating key information used in data transmission between the first access network device and the terminal device.

35. The apparatus of claim 24, wherein, The first information further comprises eighth indication information, which is used for indicating that the first information is from the first access network device.

36. The apparatus of claim 24 or 35, wherein, The second information further comprises ninth indication information, which is used for indicating that the second information is parsed using the key used in data transmission between the first access network device and the terminal device after the second information is submitted to an upper layer.

37. The apparatus of any one of claims 24 or 35 or 36, wherein, The communication apparatus further comprises: The processing module is configured to discard an uplink RRC layer data packet from a radio resource control (RRC) layer if the second information comprises the uplink RRC layer data packet.

38. The apparatus of claim 25 or 33, wherein, The downlink MAC layer data packet comprises unsuccessfully transmitted downlink code block groups, and the code block group information corresponding to the downlink MAC layer data packet comprises any one of the following: an identifier of the unsuccessfully transmitted downlink code block groups and / or an identifier of successfully transmitted downlink code block groups, a number of code block groups comprised by the downlink MAC layer data packet and an identifier of the unsuccessfully transmitted downlink code block groups, or a number of code block groups comprised by the downlink MAC layer data packet and an identifier of the successfully transmitted downlink code block groups; The uplink MAC layer data packet comprises successfully received uplink code block groups, and the code block group information corresponding to the uplink MAC layer data packet comprises any one of the following: an identifier of the successfully received uplink code block groups and / or an identifier of unsuccessfully received uplink code block groups, a number of code block groups comprised by the uplink MAC layer data packet and an identifier of the successfully received uplink code block groups, or a number of code block groups comprised by the uplink MAC layer data packet and an identifier of the unsuccessfully received uplink code block groups.

39. A communications device, characterized by comprises: The transceiver module is configured to receive first information from a second access network device, the first information comprising downlink MAC layer data packets in a MAC layer buffer and / or downlink RLC layer data packets in a RLC layer buffer of the first access network device, the first access network device being a source access network device of the terminal device, and the second access network device being a target access network device of the terminal device. The transceiver module is further configured to send second information to the second access network device, the second information comprising uplink MAC layer data packets and / or second uplink RLC layer data packets.

40. The apparatus of claim 39, wherein, The first information further comprises eighth indication information, which is used to indicate that the first information is from the first access network device.

41. The apparatus of claim 39 or 40, wherein, The second information further comprises ninth indication information, which is used to indicate that the second information is parsed using a key used in a data transmission process between the first access network device and the terminal device after the second information is submitted to an upper layer.

42. The apparatus of any one of claims 39-41, wherein, The communication apparatus further comprises: The processing module is configured to discard a downlink RRC layer data packet from the RRC layer if the first information comprises the downlink RRC layer data packet.

43. A communications device, characterized by The apparatus comprises a processor configured to implement a method according to any one of claims 1 to 21.

44. A communication system, characterized by The apparatus comprises: The first access network device, the second access network device, and the terminal device are configured to implement a method according to any one of claims 1 to 21.

45. A computer-readable storage medium, comprising: The apparatus comprises: The computer readable medium stores a computer program; The computer program, when executed by a processor, causes a method according to any one of claims 1 to 21 to be performed.

46. A computer program product, characterised in that, The computer program, when executed, causes a method according to any one of claims 1 to 21 to be performed.

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