How do mobile software's update work over the internet?

For example, how do our mobiles understand that a new software upgrade is available and what protocol/method do they follow to download the new software? Are our mobiles constantly polling the server that maintains the software repository, since the end-systems are over the internet and anything from the server can only arrive as a response to a request over the application layer. Is there any standard protocol/mechanism available in the literature?

Thank you.