Question: What happens to the Last-Used-TP-MR value in the (U)SIM after an SMS-SUBMIT has been successfully submitted to the network, and what is the range of values for TP-MR?
Option 1: The Last-Used-TP-MR value remains unchanged; TP-MR values range from 0 to 65535.
Option 2: The Last-Used-TP-MR value is updated with the TP-MR used in the SMS-SUBMIT operation; TP-MR values range from 0 to 255.
Option 3: The Last-Used-TP-MR value is reset to 0; TP-MR values range from 1 to 256.
Option 4: The Last-Used-TP-MR value is incremented by 2; TP-MR values range from -1 to 254.
Explanation: According to the SMS protocol, after each successful SMS-SUBMIT, the (U)SIM updates its Last-Used-TP-MR with the TP-MR used in that operation. This ensures sequential referencing of messages. The TP-MR field is defined to hold values between 0 and 255, allowing for up to 256 unique references before cycling back to 0. This mechanism aids in message tracking and handling, especially in cases of retries or errors.