LTE: Why does MME need "UE Radio Capability information" for an UE ?

Question

why does MME need the "UE Radio Capability" information for an UE during attach procedure ?

Answer 1

As part of Initial attach procedure UE will update UE Capabilities to eNB, eNB will update to MME and to MME this is an transparent container nothing will do with this at MME. This is an optional procedure basically. As part of Second time attach MME will provide that updated UE capabilities to eNB in Initial Context Setup request message. so that eNB is avoiding the redundant messaging of "UE capability request" to UE.

Answer 2

When an UE registers to the network first time, Network gets "Ue Radio Capability" information from UE as part of attach procedure and store it.
UE Radio Capability IE has a lots of information, some of the information is used by eNodeB.
I know that eNodeB uses the information received as form of UE Radio capability for the measurement and handover related stuff.

Feature group indicator carries some important information which may be required by MME. for example: How many AM and UM mode DRBs, UE supports.