Rolling Lobes, Half, Belted, and Convoluted Air Bellows
Except for LRVs the air spring is the common solution for a secondary suspension between bogie and car body.
As an option steel and / or layer springs may take this function as well as hydraulic solutions.
The biggest advantage of the air spring is its unbeatable reliability, the height adjustment of the car body and the excellent comfort for the passengers. Unlike the primary springs air springs generally are a combination of different springs. For maintenance you may consider them independently but should also consider the complex combination of the parts involved.