| CPC H04L 65/1104 (2022.05) [H04L 65/1016 (2013.01); H04W 60/04 (2013.01); H04W 84/042 (2013.01)] | 17 Claims |
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1. A method of operating a terminal, the method comprising:
establishing a first radio access technology (RAT)-based network connection to a first base station;
transmitting a first message to the first base station based on a session initiation protocol;
starting an evolved packet system fallback (EPSFB) timer in response to the first message to the first base station;
determining whether to perform an EPSFB procedure or a transition procedure based on whether a message is received prior to an expiration of the EPSFB timer;
performing the EPSFB procedure or the transition procedure to connect a second RAT-based network to a second base station based on the determination; and
performing a voice communication session through the second RAT-based network based at least in part on the EPSFB procedure or the transition procedure,
wherein the transition procedure comprises:
identifying the second RAT-based network using a system information message;
performing a public land mobile network (PLMN) search for the identified second RAT; and
transmitting, to the first base station, a search result including state information on the second base station.
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