In this embodiment of the present invention, the communications system 100 may be systems using various radio access technologies (radio access technology, RAT), for example, a Code Division Multiple Access (code division multiple access, CDMA) system, a Time Division Multiple Access (time division multiple access, TDMA) system, a Frequency Division Multiple Access (frequency division multiple access, FDMA) system, an orthogonal frequency division multiple access (orthogonal frequencydivision multiple access, OFDMA) system, a single carrier frequency division multiple access (single carrier FDMA, SC-FDMA) system, and another system. The terms “system” and “network” can be interchanged with each other. A radio technology such as Universal Terrestrial Radio Access (universal terrestrial radio access, UTRA) or CDMA2000 may be implemented in the CDMA system. UTRA may include a Wideband CDMA (wideband CDMA, WCDMA) technology and another technology obtained by transforming CDMA. CDMA2000 may cover interim standard (interim standard, IS) 2000 (IS-2000), IS-95, and IS-856. A radio technology such as Global System for Mobile Communications (global system for mobile communication, GSM) may be implemented in the TDMA system. A radio technology such as evolved universal terrestrial radio access (evolved UTRA, E-UTRA), Ultra Mobile Broadband (ultra mobile broadband, UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, or Flash OFDMA may be implemented in the OFDMA system. UTRA is corresponding to UMTS, and E-UTRA is corresponding to an evolved version of UMTS. A new version of UMTS, namely, E-UTRA, is used for 3GPP Long Term Evolution (long term evolution, LTE) and various versions evolved based on LTE.