A communication system, comprising a first master base station, a second master base station, a first slave base station and a second slave base station, wherein the first master base station is configured to, after receiving a handover request message sent by the second master base station, in a case that the first slave base station is newly added, configure a service data adaptation protocol, SDAP, layer of a part of flows of a preset protocol data unit, PDU, session at the first master base station, and configure an SDAP layer of the rest part of flows of the preset PDU session at the newly added first slave base station, send a handover request response message carrying first preset information to the second master base station; wherein the first preset information comprises: first identity identifications of all flows of the preset PDU session configured for the first master base station and data forwarding addresses corresponding to the first identity identifications, and second identity identifications of all flows of the preset PDU session configured for the newly added first slave base station and data forwarding addresses corresponding to the second identity identifications; each of the data forwarding addresses corresponding to the first identity identifications is a first tunnel address, and the first tunnel address is configured to forward data to the first master base station; and each of the data forwarding addresses corresponding to the second identity identifications is a second tunnel address, and the second tunnel address is configured to enable the second master base station or the second slave base station to forward data to the first slave base station; the second master base station is configured to: receive a handover request response message carrying first preset information sent by the first master base station; and perform a data forwarding, according to the first identity identifications, the data forwarding addresses corresponding to the first identity identifications to the first master base station, and perform a data forwarding according to second identity identifications and the data forwarding addresses corresponding to the second identity identifications to the newly added first slave station. the first master base station is configured to, after receiving a handover request message sent by the second master base station, in a case that the first slave base station is newly added, configure a service data adaptation protocol, SDAP, layer of a part of flows of a preset protocol data unit, PDU, session at the first master base station, and configure an SDAP layer of the rest part of flows of the preset PDU session at the newly added first slave base station, send a handover request response message carrying first preset information to the second master base station; wherein the first preset information comprises: first identity identifications of all flows of the preset PDU session configured for the first master base station and data forwarding addresses corresponding to the first identity identifications, and second identity identifications of all flows of the preset PDU session configured for the newly added first slave base station and data forwarding addresses corresponding to the second identity identifications; each of the data forwarding addresses corresponding to the first identity identifications is a first tunnel address, and the first tunnel address is configured to forward data to the first master base station; and each of the data forwarding addresses corresponding to the second identity identifications is a second tunnel address, and the second tunnel address is configured to enable the second master base station or the second slave base station to forward data to the first slave base station; the second master base station is configured to: receive a handover request response message carrying first preset information sent by the first master base station; and perform a data forwarding, according to the first identity identifications, the data forwarding addresses corresponding to the first identity identifications to the first master base station, and perform a data forwarding according to second identity identifications and the data forwarding addresses corresponding to the second identity identifications to the newly added first slave station. receive a handover request response message carrying first preset information sent by the first master base station; and perform a data forwarding, according to the first identity identifications, the data forwarding addresses corresponding to the first identity identifications to the first master base station, and perform a data forwarding according to second identity identifications and the data forwarding addresses corresponding to the second identity identifications to the newly added first slave station.