A second access network device, characterized by comprising: a receiving module , configured to receive a handover request message from a first access network device, wherein the handover request message carries an identifier of a terminal and an identifier of a target inter-RAT cell, and the first access network device is an access network device to which a serving cell in which the terminal is located belongs; a configuration module , configured to configure a resource for the terminal in the target inter-RAT cell based on the handover request message received by the receiving module; and a sending module , configured to send a handover response message to the first access network device, wherein the handover response message carries information about the resource configured by the configuration module, wherein a communication RAT used by the serving cell of a source core network is different from a communication RAT used by the target inter-RAT cell of a target core network; the receiving module is further configured to receive, after receiving a path switching response message from a core network device, a sequence number state transition message from the first access network device, wherein the sequence number state transition message carries at least one of a sequence number of a data packet not successfully sent to the terminal and a sequence number of a data packet lost in a transmission process; and the sending module is further configured to: when a sequence number state transition message received by the receiving module carries a sequence number of a data packet lost in the transmission process, send a retransmission request message, wherein the retransmission request message is used to request the terminal to resend a data packet corresponding to the sequence number of the data packet lost in the transmission process. a receiving module , configured to receive a handover request message from a first access network device, wherein the handover request message carries an identifier of a terminal and an identifier of a target inter-RAT cell, and the first access network device is an access network device to which a serving cell in which the terminal is located belongs; a configuration module , configured to configure a resource for the terminal in the target inter-RAT cell based on the handover request message received by the receiving module; and a sending module , configured to send a handover response message to the first access network device, wherein the handover response message carries information about the resource configured by the configuration module, wherein a communication RAT used by the serving cell of a source core network is different from a communication RAT used by the target inter-RAT cell of a target core network; the receiving module is further configured to receive, after receiving a path switching response message from a core network device, a sequence number state transition message from the first access network device, wherein the sequence number state transition message carries at least one of a sequence number of a data packet not successfully sent to the terminal and a sequence number of a data packet lost in a transmission process; and the sending module is further configured to: when a sequence number state transition message received by the receiving module carries a sequence number of a data packet lost in the transmission process, send a retransmission request message, wherein the retransmission request message is used to request the terminal to resend a data packet corresponding to the sequence number of the data packet lost in the transmission process. <EOS>