Question: When using the Universal Subscriber Identity Module (USIM) Application Toolkit (USAT) for IP Multimedia Subsystem (IMS) services, what action is required by the UICC regarding the Bearer Independent Protocol (BIP) channel at the conclusion of a Session Initiation Protocol (SIP) dialog initiated by an OPEN CHANNEL command?
Option 1: The UICC shall send a CLOSE CHANNEL command to close the BIP channel.
Option 2: The UICC shall automatically reopen the BIP channel for potential subsequent SIP dialogs.
Option 3: No action is required by the UICC; the BIP channel remains open indefinitely.
Option 4: The UICC shall send an OPEN CHANNEL command to ensure continuous connectivity.
Explanation: This is correct because, according to the specified behavior for IMS services, once a SIP dialog (initiated by an OPEN CHANNEL command) concludes, the UICC must take the specific action of sending a CLOSE CHANNEL command. This ensures efficient resource management by closing the BIP channel when it's no longer needed for active communication, aligning with the principles of temporary resource allocation in telecom networks.