The present disclosure provides a method for establishing a default radio data bearer on a secondary base station, and a corresponding master base station, secondary base station, and computer readable media. The method includes: notifying the secondary base station to establish the default radio data bearer; receiving, from the secondary base station, a notification of information about establishment of the default radio data bearer; and receiving, from the secondary base station, a notification of information about release of the default radio data bearer. The present disclosure also provides a method for data replication and data transmission performed by an entity where PDCP is located, a method for data replication performed by an entity where RLC is located, a data counting method performed by an entity where RLC is located, an entity where PDCP is located, an entity where RLC is located, and a computer readable medium.