Default LTE APN bearer

Hello everyone as I use LTE I noticed something in the APN settings (settings> mobile data> access point names> *your APN*> last option (bearer)

There are two options :
- unspecified
- LTE

Does anyone know what those do?
FiReFlaMe
Previous:HTC HD2 (Leo) {R.I.P}, HTC Butterfly S(Sold)
Current:SE Xperia X1 (HTC Kovsky), HTC One X (Tegra 3), HTC One M8

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