LTE: UE Capability Enquiry

Direction: E-UTRAN => UE
Signalling Radio Bearer: SRB1
RLC Mode: AM
Logical Channel: DCCH
Transport Channel: DL-SCH

The UE CAPABILITY ENQUIRY message is used to request the transfer of UE radio access capabilities for E-UTRA as well as for other RATs (UTRA, GERAN-CS, GERAN-PS, and CDMA2000)

As the UE’s AS capability may contain several RATs capabilities, the information can be rather very large. To reduce the overhead in the air interface during transition from RRC_IDLE mode to RRC_CONNECTED mode, MME stores UE's AS capability and provides it to eNodeB during initial UE context setup over S1 interface. In case if the MME doesn’t have the valid UE's AS capability, the MME does not provide UE's AS capability to the eNodeB. The eNobeB has to acquire UE's AS capability from UE using UE CAPABILITY ENQUIRY.

NOTE: Change of the UE's GERAN UE radio capabilities in RRC_IDLE is supported by use of TRACKING AREA UPDATE

This message contains only one IE as shown below;

ue-CapabilityRequest: List of the RATs for which the UE is requested to transfer the UE radio access capabilities i.e. E-UTRA, UTRA, GERAN-CS, GERAN-PS, CDMA2000

Example: UE CAPABILITY ENQUIRY for E-UTRA

Reference: 3GPP TS 36.331