FIG. 28 is a schematic structural diagram 3 of an embodiment of a network system according to the present invention. As shown in FIG. 28, the network system includes a terminal 21A, a secondary base station 23A, and a primary base station 22A. The terminal 21A receives a notification message sent by the primary base station 22A, where the notification message is a reconfiguration message or a random access resource allocation message, then sends a random access request message to the secondary base station 23A according to the received notification message, and then adjusts, according to a received random access response message, time advance TA of the terminal 21A on a corresponding cell. The secondary base station 23A receives a secondary serving cell addition request message sent by the primary base station 22A or sends a secondary serving cell addition response message to the primary base station 22A, and the secondary base station 23A sends the random access response message to the terminal 21A according to the random access request message sent by the terminal 21A. The primary base station 22A sends the secondary serving cell addition request message to the secondary base station 23A or receives the secondary serving cell addition response message sent by the secondary base station 23A, and the secondary base station 23A sends, to the terminal 21A, the reconfiguration message, or the reconfiguration message and the random access resource allocation message.
