The Application Layer （AL） defines the Look and Feel of the MMI， and implements actual Handling of User Inputs and Protocol Stack Events.

　　AL is a Task consisting of Windows （Instantiations of Window Classes）。

　　AL Communicates via Messages with the UI Task. UI is the Interface to the Protocol Stack.

　　The AL Windows are organised in a Tree Structure of Parents and Children.

　　AL must be customised to fit the individual Customer Requirements as well as Hardware Environment.

　　The Application Layer can be in One of the following General States：

　　ALNull： The Telephone is switched off.

　　ALStarting： The Software is being initialised.

　　ALAwaitSim： No SIM Card is inserted.

　　ALAwaitAuth： SIM PIN1 must be entered.

　　ALAwaitUnlock： SIM PIN1 is blocked.

　　ALReady： Ready to make and receive calls.

　　ALCallActive： One or more Calls are active.

　　ALAwaitShutDown： The Power Off Key has been pressed.