Question: In a Universal Subscriber Identity Module (USIM) Application Toolkit (USAT) context, when class "e" and "t" are supported for UICC access to IMS, what happens to all SIP requests and responses received by the Mobile Equipment (ME) within an established SIP dialog?
Option 1: They are sent directly to the network without involving the UICC.
Option 2: They are stored in the ME for later processing and not forwarded to the UICC.
Option 3: They are sent to the UICC only if they are SIP ACK requests.
Option 4: They are discarded by the ME to prevent overload.
Explanation: According to the USIM Application Toolkit specifications for UICC access to IMS, when classes "e" and "t" are supported, all SIP requests and responses (not just specific types like ACK) received by the Mobile Equipment within an established SIP dialog are indeed sent to the UICC. This ensures the UICC is fully informed and can manage the session appropriately, which is crucial for services relying on IMS. **Option 1** correctly reflects this behavior, while the other options misrepresent the handling of SIP requests and responses in this context.