LTE Protocol stack is divided into Three Layers.
Layer 1 (Physical Layer)
Layer 2 (PDCP,MAC,RLC Layers)
Layer 3 (NAS and RRC Layers)
Functions of each Layer.
NAS: 3GPP TS 24.301
- EPS bearer management
- Paging origination
- EPC connection management-IDLE mobility handling
- Security mode control
- Tracking area update
- PDN connectivity and dysconnectivity procedure.
RRC: 3GPP TS 36.331
- RRC protocol layer exists in UE & eNodeb.
- It is part of LTE air interface control plane.
- Broadcast of System Information related to the non-access stratum (NAS) and access stratum (AS)
- Establishment, maintenance and release of an RRC connection between the UE and E-UTRAN
- Mobility functions
- QoS management functions.
- UE measurement reporting and control of the reporting.
- Recovery from radio link failure
PDCP: 3GPP TS 36.323
- PDCP protocol layer exists in UE & eNodeb
- Header compression and decompression of IP data packet.
- Transfer of user data.
- Maintenance the PDCP sequence number.
- Security of data.
- Ciphering and Integrity Protection.
- Transfer of control plane data.
RLC: 3GPP TS 36.322
- Concatenation, Segmentation and reassembly of RLC SDUs.
- Retransmission of RLC PDUs (Only for AM data transfer)
- Reordering of RLC data PDUs (Only for UM and AM data transfer.
- Protocol error detection and recovery.
MAC: 3GPP TS 36.323
- Prioritization among various data streams for a given UE.
- Error Correction trough HARQ.
- Mapping between logical channels and transport channels.
- Transport format selection.
- Encode raw data before modulation.
- Measure the air interface to know the channel quality.
- Link adaptation.
- Power control.