A communication system is disclosed in which a base station receives, from at least one further base station, information identifying at least one respective tracking area associated with at least one cell of each further base station. The base station also receives, from a core network, information identifying a registration area for a user equipment (UE). The base station defines, based on the received information identifying at least one respective tracking area and the received information identifying a registration area, a radio access network (RAN) based notification area for the UE.