In the control plane, control-relevant information is exchanged between the network and the user equipment. The establishment and management of sessions occurs at the highest layer on the control plane called non-access stratum (NAS). The next layer, radio resource control (RRC), exchanges control information with the device to set important parameters for the session.
In the user plane, the network and the user equipment exchange user data. The highest layers are the application and IP layers and refer to the worldwide web and other applications running on it. Data then goes through the service data adaptation protocol (SDAP), a new protocol layer for quality of service (QoS) management.
The higher protocol layers are based on LTE. The IP header is replaced with a 5G equivalent at the packet data convergence protocol (PDCP) layer. The radio link control (RLC) layer organizes the data and retransmission, if necessary. Prioritization and hybrid automated retransmission requests take place at the media access control (MAC) layer.
The last layer in the protocol structure is the physical layer (PHY). This layer involves aspects relevant for the communication channel between the user equipment and the core network as well as other aspects like modulation and beamforming.
The greatest changes for the protocol structure in 5G are at the PHY layer. There are a few important changes on layer 2 as well including:
A new SDAP layer for QoS management in the user plane that provides mapping between QoS flow and data radio bearers and marking for QoS flow IDs in downlink and uplink packets all the way to the 5G core.
A new feature that enables PDCP duplication, mapping packet data units (PDUs) to more than one logical channel and sending them over different component carriers.
RLC/MAC layer support for beam management procedures and transmission modes that use different numerologies and transmission time intervals. Processing latency reduces as well. In LTE, the MAC layer had a huge header that pointed to the different PDUs. In 5G, the header is placed in front of the packet greatly reducing latency.
I hope you find it useful, feel free to ask any question.
