What does classmark change mean in GSM layer 3 signaling?

The content in this message is the capabilities of the mobile phone.

MS’s Classmark has three categories: Classmark1, Classmark2, and Classmark3. The network can learn about the various capabilities of the mobile station by asking the mobile station’s CLASSMARK, or it can also require the mobile station to report to the network immediately after establishing a link. Report its CLASSMARK3.

(1) Mobile phone passive response reporting: When ECSC is set to "No", the MS will report Classmark 2 in the CM SERV REQ of the Establishment Indication message, and then the MSC will after the A interface link CC is established, Before sending the CM Service Accepted message, determine whether to send the CLASSMARK ENQUIRY message based on whether the IE CM3 in the reported Classmark 2 is 1. When the MS reports the COMPLETE L3 INFO message in the Class Mark 2, the required Class Mark 3 flag is yes. The CLASSMARK ENQUIRE message is sent when the mobile phone receives it. After receiving it, the mobile phone returns the CLASSMARK CHANGE message to the network and reports the information of class label 3.

(2) The mobile phone actively reports: When ECSC is set to "Yes", the MS will report Classmark 2 in the CM SERV REQ of the Establishment Indication message, followed by a Classmark Change message and CLASSMARK3 information. This avoids the network query process.

At the same time, the mobile phone sends a "CLASSMARK CHANGE" message to the network - used to notify the network of a series of capabilities of the mobile phone. The network can choose whether to let the mobile phone report these messages. The ECSC parameter is used to control whether the mobile phone Report these messages (ECSC=ecsc Early classmark sending control).