GBR
Guaranteed Bit Rate. A minimum bit rate requested by an application. In LTE, minimum GBR bearers and non-GBR bearers may be provided. Minimum GBR bearers are typically used for applications like Voice over Internet Pro- tocol (VoIP), with an associated GBR value; higher bit rates can be allowed if resources are available. Non-GBR bearers do not guarantee any particular bit rate, and are typically used for applications as web-browsing.
MBR
Maximum Bit Rate. This is to restrict the traffic flow in a particular bearer. If the traffic exceeds this then it will be dropped. ( MBR does not apply to non-GBR bearers, only GBR bearers.)
APN-AMBR
The APN-AMBR defines the total bit rate that is allowed for all non-GBR bearers associated with a specific APN. The APN-AMBR limits the total non-GBR traffic for an APN, independent of the number of PDN connections and non-GBR bearers that are opened for that APN. For example, if an operator provides an APN for Internet, the operator may then limit the total bandwidth for that APN.
UE-AMBR
The UE-AMBR is defined per subscriber and defines the total bit rate allowed to be consumed for all non-GBR bearers of a UE. The subscription profile contains the UE-AMBR. The eNodeB enforces the UE-AMBR.
There are different AMBR values for uplink and downlink directions - UL APN-AMBR, DL APN-AMBR, and UL UE-AMBR, DL UE-AMBR.