MM
GSM 04.08 http://www.etsi.fr
The main function of the Mobility Management (MM) sub-layer is to support the mobility of user terminals, such as informing the network of its present location and providing user identity confidentiality. A further function of the MM sub-layer is to provide connection management services to the different entities of the upper Connection Management (CM) sub-layer
Read more about this topic: Cellular Data Communication Protocol