Mobility Management and Call Processing This section provides an introductory overview of mobility management (., allowing a subscriber to roam) and call processing (the setting up and clearing down of calls) in GSM networks. Mobility management entails keeping track of the MS while it is on the move. The mobility management procedures vary across three distinct scenarios, namely | Mobility Management and Call Processing This section provides an introductory overview of mobility management . allowing a subscriber to roam and call processing the setting up and clearing down of calls in GSM networks. Mobility management entails keeping track of the MS while it is on the move. The mobility management procedures vary across three distinct scenarios namely MS is turned off MS is turned on but is idle MS has an active call In the first scenario when it cannot be reached by the network because it does not respond to the paging message the MS is considered to be in the turned-off state. In this scenario the MS obviously fails to provide any updates in relation to changes in Location Area LA if any exist. In this state the MS is considered detached from the system IMSI detached . In the second scenario the MS is in the ready state to make or receive calls. The system considers it attached IMSI attached and it can be successfully paged. While on the move the MS must inform the system about any changes in LA this is known as location updating. In the third scenario the system has active radio channels that are allowed to the MS for conversation data flow. The MS is required to change to new radio channels if the quality of current channels drops below a certain level this is known as handover. The MSC sometimes BSC makes the decision to handover an analysis of information that is obtained real-time from the MS and BTS. All operations revolve around the three scenarios presented above. The rest of this chapter examines these operations in more detail beginning with simple operations paging IMSI detach attach. Following more complex operations are presented such as location update call handover mobile terminated call mobile originated call and mobile-to-mobile call. Location Update Location updating is the mechanism that is used to determine the location of an MS in the idle state. The MS initiates location updating which can occur when The MS is first
