FIG. 20 is a schematic signaling diagram of a fourth embodiment of a network system according to the present invention. As shown in FIG. 20, transmission of the signaling is divided into five steps. Step 1: A secondary base station sends a secondary serving cell addition response message to a primary base station, where the secondary serving cell addition response message includes a serial number of a random access preamble code and a serial number of a PRACH mask code. Optionally, the secondary serving cell addition response message further includes a response window size. Steps 2, 3, 4, and 5 are the same as the steps in the schematic signaling diagram of the second embodiment, and details are not described herein again. By comparing the schematic signaling diagram of the fourth embodiment with the schematic signaling diagram of the second embodiment, it is found that the serial number of the random access preamble code, the serial number of the PRACH mask code, and the response window size (optional) in the schematic signaling diagram of the fourth embodiment are determined by the secondary base station, and the serial number of the random access preamble code, the serial number of the PRACH mask code, and the response window size (optional) in the schematic signaling diagram of the second embodiment, however, are determined by the primary base station. In addition, step 2 is optional. When step 2 is skipped, the terminal uses a default time window to receive a random access response message. Before the terminal receives the random access resource allocation message sent by the primary base station, the terminal further receives a cell radio network temporary identifier of the terminal sent by a host, so that the primary base station uses the cell radio network temporary identifier to scramble the random access resource allocation message and then sends a scrambled random access resource allocation message to the terminal, so that the terminal uses the cell radio network temporary identifier to descramble a subsequently received random access resource allocation message. That is, the cell radio network temporary identifier is allocated by the primary base station to the terminal in advance.
