Question: What should a receiver do when it encounters a reserved code in the TP-Failure-Cause (TP-FCS) field for a Short Message Service (SMS)?
Option 1: Ignore the error and attempt to retransmit the message
Option 2: Treat it as an unspecified error cause
Option 3: Automatically cancel the SMS service subscription
Option 4: Send a request for more detailed error information
Explanation: According to the specifications for handling TP-Failure-Cause in SMS, when a reserved code is received (indicating an unspecified or unrecognized error), the receiver should treat it as an unspecified error cause. This ensures consistent handling of unknown errors, preventing potential misinterpretation or inappropriate actions that could further disrupt service.