The present disclosure relates to a method used in a User Equipment (UE) for transmitting data to a network side via at least a first and a second connection, and the associated UE. The method comprises: comparing a first number, M, of Packet Data Convergence Protocol (PDCP) Packet Data Units (PDUs) that have been successfully transmitted via the first connection with a second number, N, of PDCP PDUs that have been successfully transmitted via the second connection; and if M is larger than N by a predetermined threshold number, S, of PDCP PDUs, refraining from transmitting S PDCP PDUs to be transmitted following the N PDCP PDUs in the data via the second connection.