dear Jack!
CLASSMARK ENQUIRY message (gsm 04.008) is used in Classmark interrogation procedure (if the information initially sent by the mobile station is not sufficient for network decision (e.g. when A5/1 ciphering not active in network): network want to know A5/2 is supported in MS or not)
On receipt of the CLASSMARK ENQUIRY message the mobile station sends a CLASSMARK CHANGE message to the network on the main DCCH. This message contains the mobile station classmark 2 information element.