ms neighboring cell measurements and cell selection/reselection, and acquires System Information. RRC_CONNECTED is a state where transfer of unicast data to/from UE is performed and the UE may be configured with a UE specific DRX or Discontinuous Transmission (DTX). The UE monitors control channels associated with the shared data channel to determine if data is scheduled for it, provides channel quality and feedback information, performs neighboring cell measurements and measurement reporting, and acquires System Information. In the U-plane, the PDCP layer is responsible for compressing or decompressing the headers of IP packets using robust header compression to enable efficient use of air interface resources. This layer also performs ciphering of both user-plane and control-plane traffic. Because the NAS messages are carried in RRC, they are effectively double ciphered and integrity protected, once at the MME and again at the eNB. Therefore, the services and functions provided by the PDCP layer in the U-plane include header compression and decompression, transfer of user data between NAS and RLC layer, sequential delivery of upper layer PDUs and duplicate detection of lower layer SDUs at handover for radio link layer acknowledged mode, re-transmission of PDCP SDUs at handover for radio link layer acknowledged mode, and ciphering. The services and functions provided by the PDCP for the C-plane include ciphering and integrity protection, and transfer of control-plane data where PDCP receives PDCP SDUs from RRC and forwards them to the radio link control layer [29,31]. The RLC layer is used to format and transport traffic between the UE and the eNB. The RLC provides three different reliability modes for data transport, i.e., acknowledged mode (AM), unac- knowledged mode (UM), and transparent mode (TM). The unacknowledged mode is suitable for transport of real-time services since such services are delay-sensitive and cannot tolerate delay due to re-transmissions. The acknowledged mode is appropriate for non-real-ti