AMBR is the maximum possible bit rate configured by the LTE operator for a particular LTE user for all of their best effort services. The key word here is “possible”. This is the maximum possible if bandwidth is available and also dependent on what and how many services the user is using. It is a configured value by the LTE operator and does not change.
LTE data bearers that are classified as Non GBR are scheduled according to the AMBR for the subscriber. This means that of the total radio resources available to all the Non GBR bearers that a subscriber has active cannot exceed the AMBR.