UE and communication method thereof

A User Equipment (UE), comprising:

• a controller configured to register the UE with an evolved packet core (EPC) network and a fifth generation (5G) core (5GC) network via the same serving base station, wherein the EPC network is associated with a first access domain and the 5GC network is associated with a second access domain;
• and
• a transmission/reception unit configured to send a first emergency service request message to the EPC network for establishing an emergency call after the controller registers the UE with the EPC network and the 5GC network, and
• receive, in response to sending the first emergency service request message, a response message from the EPC network, wherein:
• the controller is further configured to determine whether the response message is accepting or rejecting the first emergency service request, and
• when the first emergency service request is determined to be rejected, select the second access domain and cause the transmission/reception unit to send a second emergency service request message to the 5GC network for establishing the emergency call based on the selected second access domain without considering a fallback instruction included in the response message.