The RRC protocol supports the transfer of common NAS information (i.e. NAS informationwhich is applicable to all UEs) as well as dedicated NAS information (which is applicableonly to a specific UE). In addition, for UEs in RRC_IDLE, RRC supports notification of incoming calls.
The RRC protocol covers a number of functional areas.
• System information handles the broadcasting of system information, which includesNAS common information. Some of the system information is applicable only forUEs in RRC_IDLE while other system information is also applicable for UEs inRRC_CONNECTED.
• RRC connection control covers all procedures related to the establishment, modificationand release of an RRC connection, including paging, initial security activation,establishment of Signalling Radio Bearers (SRBs) and of radio bearers carrying userdata (Data Radio Bearers, DRBs), handoverwithin LTE (including transfer of UE RRCcontext information4), configuration of the lower protocol layers,5 access class barring
and radio link failure.
• Network controlled inter-RAT mobility includes (besides the mobility procedures)security activation and transfer of UE RRC context information.
• Measurement configuration and reporting for intra-frequency, inter-frequency andinter-RAT mobility, includes configuration and activation of measurement gaps.
•Miscellaneous functions including, for example, transfer of dedicated NAS informationand transfer of UE radio access capability information
And RRC plays very important role in control protocol stack as it handles connection of a UE to eNodeB.