This page on LTE protocol stack describes user plane and control plane protocol stack layers in LTE. LTE User plane layer consists of upper layers, NAS, PDCP, RLC, MAC, PHY and RF. LTE Control plane layer covers upper layers, NAS, RRC, PHY and RF.
Following figure depicts LTE protocol stack with main functions of each layer. NAS is not shown in the figure,it sits above RRC in the control plane(on left side) and above PDCP in the user plane(on right side). Above NAS upper layers exist.
The user plane LTE protocol stack consists of upper layers, NAS, PDCP, RLC, MAC, PHY and RF. The functions of each are outlined below: The modules are depicted in the figure on right side.
NAS: In the uplink it does packet filtering.
PDCP: In the uplink it performs sequence number addition, handover data handling,integrity protection, ciphering and header compression. In the downlink it does in sequence delivery,duplicate packet detection,integrity validation, deciphering,header decompression.
RLC: In the uplink it provides buffer status report,segmentation and concatenation,ARQ(for AM mode). In the downlink it does re-ordering,assembly and ARQ(for AM mode).
MAC: In the uplink it does channel mapping,multiplexing,handling control elements, random access procedure, logical channel priority,HARQ and sending BSRs. In the downlink it does channel mapping, de-multiplexing,DRX,Handling control elements,HARQ.
PHY:
• CRC attachment
• Coding block
• scrambling/descrambling
• modulation/de-modulation
• measurement
• Resource element mapping/demapping
• HARQ
• MIMO
RF:
• Radio Transmission and Reception
The control plane protocol stack layers in LTE consists of upper layers, NAS, RRC, PHY and RF. The functions of each are outlined below: The same is depicted in the figure on left hand side.
Upper layer: provide interfacing between upper layer information with lower layers(NAS).
NAS:
• Mobility Management
• Session Management
• Bearer Management
• Paging Control
• Security Management
RRC:
• Configuration Management
• Connection Management
• Paging control
• Security Management
• Broadcast
• Measurement configuration
• Measurement Reporting
• Cell selection and reselection
• Mobility Management
PHY and RF: functions are same as mentioned above.
There are two radio resource control (RRC) states are defined viz. RRC IDLE and RRC CONNECTED.
• RRC IDLE state, UE is known in EPC and has IP address but not known in E-UTRAN/eNB
• UE can receive broadcast/multicast data, monitors a paging channel to detect incoming calls, performs neighbor cell measurements and cell selection/reselection and acquires system information
• In the RRC IDLE state, a UE specific DRX (discontinuous reception) cycle may be configured by upper layers to enable UE power savings
• In the RRC CONNECTED state, UE known in EPC and E-UTRAN/eNB
• UE location is known at the cell level
• Mobility is UE-assisted, network-controlled
• UE also monitors control channels associated with the shared data channel to determine if data is scheduled for it, provides channel quality feedback information, performs neighbor cell measurements and measurement reporting and acquires system information
