In the C-plane, the NAS functional block is used for network attachment, authentication, setting up bearers,and mobility management. All NAS messages are ciphered and integrity protected by the MMEand UE.
The radio resource control (RRC) layer in the eNB makes handover decisions based on neighbor cell measurements reported by the UE, performs paging of the users over the air interface, broadcasts system information, controls UE measurement and reporting functions such as the periodicity of channel quality indicator (CQI) reports and further allocates cell-level temporary identifiers to active users.
It also executes transfer of UE context from the serving eNB to the target eNB during handover and performs integrity protection of RRC messages.
The RRC layer is responsible for setting up and maintenance of radio bearers.
In the U-plane, the Packet Data Convergence Protocol (PDCP) layer is responsible for compressing or decompressing the headers of user-plane IP packets using robust header compression (RoHC) to enable efficient use of air interface resources .
The radio link control (RLC) layer is used to format and transport traffic between the UE and the eNB