Need to know how iphone is transferring the turn to turn info from google maps through carplay which mechanism or which protocal exactly used?

When I ask google why I am not able to get the turn to turn info from google maps present in apple maps via carplay through iAP(ipod accessory protocal) service

I got the below comment from google

hi ravi, i do not know if google maps works through any of the apple accessory protocol/s.

but it definitely works via carplay - which specific protocols are used, i would not know.

if that case who is supporting to trasfer the turn to turn info from iphone over carplay? ---> this is my question