Air sovereignty follows from state sovereignty and describes the fundamental right of a sovereign state to regulate the use of its airspace on its own (Aviation law = airlaw, in Germany i.e. by the (Luftverkehrsgesetz). Air Police measures (i.e. control flights) are secured for these tasks by stand-by Fighter aircraft.
Airspace above the total of land- and sea areas of a state forms part of the sovereign state area. The national Airspace as a rule follows the borderlines. Parts of the Airspace can also be let for use to other states. Intrusion into the airspace of one of the UN member states do not need any allowance when civil aviation is concerned (Convention on International Civil Aviation).
The upper limit of airspaces is not exactly defined by law. Established limits (e.g. the Kármán line) are not relevant with respect to international law for the demarcation of the airspaces under air sovereignty from non-sovereign universe.