Bearing compartment pressurization and shaft ventilation system

An assembly and method for providing buffer air and/or ventilation air within a gas turbine engine (10), the assembly includes an accessory gearbox (32) and a centrifugal compressor (34). The accessory gearbox is connected to a driven shaft (36) of the gas turbine engine. The centrifugal compressor is driven by the accessory gearbox during operation of the gas turbine engine to receive and compress a bleed air to produce the buffer air and/or the ventilation air. The buffer air and/or the ventilation air is communicated within the gas turbine engine.