Provided are a transmission method and device, the method being applied to a terminal device, the terminal device being respectively connected with a primary
base station and a first secondary
base station, the method comprising: receiving a primary and secondary
cell update instruction sent by the primary
base station, the primary and secondary
cell update instruction comprising an identifier ofa second secondary base
station; according to the identifier of the second auxiliary base
station, establishing a first
protocol entity associated with the
data radio bearer DRB and the second auxiliary base
station; receiving first downlink data sent by a second auxiliary base station according to a first
protocol entity, and receiving second downlink data sent by the first auxiliary base stationaccording to a second
protocol entity, the second protocol entity being a protocol entity in which the DRB is associated with the first auxiliary base station; and combining the first downlink data and the second downlink data to obtain a packet data convergence protocol
PDCP data packet corresponding to the DRB. According to the embodiment of the invention, DAPS switching in a dual-connection scene can be realized, and the performance of
data transmission is improved.