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.
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.)
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.
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.