Question: What does a Mobile Station (MS) do when it cannot encode the requested identity in an IDENTITY RESPONSE message due to the absence of a valid SIM?
Option 1: It sends an error message to the network.
Option 2: It uses a default identity.
Option 3: It ignores the request and continues with normal operations.
Option 4: It encodes the identity type as "No identity" in the IDENTITY RESPONSE message.
Explanation: When a Mobile Station (MS) is unable to encode the requested identity, typically due to not having a valid SIM available, it follows a specific procedure. In this case, the MS will indicate its inability to provide the requested identity by setting the identity type to "No identity" in the IDENTITY RESPONSE message sent back to the network. This action informs the network of the situation and is a standardized way for the MS to communicate its status under these conditions.