The user plane includes the data streams and the data bearers for the data streams. The data streams are characterized by one or more frame protocols specified for that interface.
Figure shows “User-plane protocol stack” comprise Medium Access Control (MAC), Packet Data Convergence Protocol (PDCP), Radio Link Control (RLC) and Physical (PHY) sub layers. Apart from the serving gateway protocols, all radio interface protocols terminate in the eNodeB on the network side.
The LTE user plane protocol performs the following functions:
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).
Media Access Control (MAC) Sublayer :
The MAC sublayer is between the UE and the eNodeB. MAC sublayer 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/demultiplexing of different RLC sublayer.
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.
Packet Data Convergence Protocol (PDCP) Sublayer:
For the user plane, the PDCP sublayer performs header compression and ciphering.
Function of User Plane Protocol Stacks in LTE
The user plane protocol stack in LTE is responsible for the actual data transfer between the User Equipment (UE) and the core network. It handles the end-to-end transmission of user data, ensuring that packets are properly routed, delivered, and formatted according to the LTE specifications.
The stack is made up of several key layers:
- Physical Layer (PHY): This layer is responsible for transmitting and receiving the raw data over the air interface. It handles the modulation, coding, and physical signal processing.
- Medium Access Control (MAC): MAC handles the scheduling of data and its mapping onto available resources. It manages the data flows, ensures efficient use of the radio interface, and provides error correction through hybrid automatic repeat request (HARQ).
- Radio Link Control (RLC): RLC is responsible for segmenting and reassembling packets, ensuring reliable data transmission through error correction, retransmissions, and flow control. It also organizes the data for proper delivery in the right order.
- Packet Data Convergence Protocol (PDCP): PDCP compresses headers to reduce overhead, encrypts data to ensure confidentiality, and ensures data integrity by protecting against tampering.
- Service Data Adaptation Protocol (SDAP): SDAP manages Quality of Service (QoS) flows, mapping different types of data (e.g., voice, video, and internet traffic) to specific bearers to ensure they meet their QoS requirements.
These layers work together to ensure that data is efficiently transmitted from the UE to the eNodeB and across the LTE network to its destination. The user plane protocol stack focuses on data transport, quality of service, and error handling, making sure the user’s data experience is reliable and consistent.