Stun protocol used by FaceTime?

My mobile service provider Optus in Australia provides data breakdown in its app to let us monitor data usage. Recently at around iOS 14 update, it started to show up STUN usage while FaceTime data usage dropped. I asked Optus if STUN usage relates to FaceTime usage and they told me to ask Apple if STUN is a protocol used by Apple. Do any of you know if FaceTime uses the STUN protocol? Thanks!