Question: What happens when a UE in substate 5GMM-DEREGISTERED.eCALL-INACTIVE receives a request from upper layers to establish an eCall over IMS?
Option 1: The UE ignores the request and remains in substate 5GMM-DEREGISTERED.eCALL-INACTIVE.
Option 2: The UE enters state 5GMM-NULL and powers off.
Option 3: The UE initiates 5GMM signalling with the network to establish a non-emergency call.
Option 4: The UE enters state 5GMM-DEREGISTERED.ATTEMPTING-REGISTRATION and uses relevant procedures to establish the eCall over IMS at the earliest opportunity.
Explanation: According to the specified behavior, when a UE in substate 5GMM-DEREGISTERED.eCALL-INACTIVE receives a request from upper layers to establish an eCall over IMS, it enters state 5GMM-DEREGISTERED.ATTEMPTING-REGISTRATION and then uses relevant 5GMM and 5GSM procedures to establish the eCall over IMS at the earliest opportunity.