Question: In the context of Universal Subscriber Identity Module (USIM) Application Toolkit (USAT), what is the correct procedure for a Mobile Equipment (ME) to inform the UICC about the outcome of executing a proactive command, specifically when encountering a temporary issue due to being busy on another operation?
Option 1: The ME uses an SMS RP-ERROR message with a custom cause value.
Option 2: The ME employs a USSD Return Error message without specifying the cause.
Option 3: The ME initiates a new proactive command to resolve the temporary issue.
Option 4: The ME sends a TERMINAL RESPONSE, specifying the temporary problem (e.g., "ME currently busy on SS transaction" or "ME currently busy on USSD operation").
Explanation: According to USAT specifications, when an ME encounters a temporary problem while executing a proactive command from the UICC, it must inform the UICC using a TERMINAL RESPONSE. This response should include specific cause values for the temporary problem, such as being busy on an SS transaction or USSD operation, as defined within the USAT context. This ensures clear communication between the ME and UICC about command execution outcomes, facilitating appropriate further actions.