The control plane includes the application protocol. It also includes the signaling bearers for transporting the application protocol messages. The application protocol is used for setting up bearers in the radio network layer. For example, radio access bearers or radio links.

Figure shows “Control plane protocol stack” comprises Radio Resource Control (RRC), Packet Data Convergence Protocol (PDCP), Radio Link Control (RLC), Medium Access Control (MAC), Physical (PHY) and Non Access Stratum (NAS) sub layers. Apart from the non access stratum (NAS) protocols, all radio interface protocols terminate in the eNodeB on the network side.

Control plane protocol stacks in LTE

The LTE control plane protocol functions are:

LTE Physical (PHY) Sublayer:

The physical layer is between the UE and the eNodeB. The physical layer in LTE supports the Hybrid ARQ with soft combining, uplink power control, and multi-stream transmission and reception (MIMO).

LTE Media Access Control (MAC) Sublayer:

The MAC sublayer is between the UE and the eNodeB. Along with scheduling, it performs error correction through HARQ, priority handling across UEs as well as across different logical channels of a UE, traffic volume measurement reporting, and multiplexing or demultiplexing of different RLC radio bearers from the physical layer on transport channels.

LTE Radio Link Control (RLC) Sublayer:

The RLC sublayer is between the UE and the eNodeB. Along with transferring upper layer PDUs, the RLC does error correction through ARQ, in-sequence delivery of upper layer PDUs, duplicate detection, flow control and concatenation or re-assembly of packets.

LTE Packet Data Convergence Protocol (PDCP) Sublayer:

The PDCP sublayer is included in the control plane and is used for ciphering and integrity protection. In addition, PDCP sublayer is used for control plane data transmission. The PDCP receives PDCP SDUs from the RRC and forwards them to the RLC layer.

LTE Radio Resource Control (RRC) Sublayer:

The RRC sublayer is between the UE and the eNodeB. The RRC sublayer in essence performs broadcasting, paging, connection management, radio bearer control, mobility functions, UE measurement reporting and control.

LTE Non Access Stratum (NAS) Sublayer:

The NAS sublayer is between the UE and the MME. It performs authentication, security control, idle mode mobility handling, and idle mode paging origination.