Full coverage of a second generation (2G) or third generation (3G) network such as Global System for Mobile Communications (GSM) or Wideband Code Division Multiple Access (WCDMA) has been basically implemented.
With development of Long Term Evolution (Long Term Evolution, LTE) network technologies, LTE networks have covered some urban areas and traffic hotspot areas. In this way, in current communications networks, the LTE network coexists with the 2G or 3G network.
In a call process, user equipment (UE) may enter a 2G or 3G network from an LTE network. Because the LTE network has a different bearer mechanism from the 2G or 3G network, and the UE needs to be handed over from a packet switched (PS) domain to a circuit switched (CS) domain, interruption may occur in a voice call, which affects continuity of the voice call of a user.
Circuit switched fallback (CSFB) means fallback of UE covered by LTE to a network that has a CS domain when the UE processes a voice service. The US is triggered to be handed over from an LTE network to a CS domain of a 2G or 3G network, falls back, in a handover manner, to the network that has a CS domain, and processes the voice service in the network that has a CS domain.
However, in the prior art, after the UE falls back from the LTE network to the 2G or 3G network by means of handover, a registered public land mobile network PLMN of the UE changes from a first PLMN of the LTE network to a second PLMN of the 2G or 3G network.
When the UE returns to the LTE network from the 2G or 3G network, the UE may preferably camp on the second PLMN because the current registered PLMN of the UE is the second PLMN. As a result, the UE cannot return to the first PLMN in the LTE network, an LTE network operator of the first PLMN encounters a user turnover in a CSFB process, and operators cannot cooperate with each other.