LTE Protocol Architechture

Type 2 LTE Frame Structure

Type 2 LTE Frame Structure

LTE Protocol Architecture:

3GPP™ Long Term Evolution (LTE) also referred to as E-UTRAN, 

The protocol stack functions consist of the:

• Non Access Statum(NAS)
• Packet Data Convergence Protocol (PDCP)
• Radio Resource Control (RRC)
• Radio Link Control (RLC)
• Medium Access Control(MAC)
• Physical Layer(PHY) 

The difference between control plane and user plan shown in the figure below.

Radio Interface Protocol

CONTROL PLANE PROTOCOLS

RADIO RESOURCE CONTROL (RRC):

The RRC protocol includes the following main functions:

• Broadcast of system information:

1. Including NAS common information
2. Information applicable for UEs in RRC_IDLE, e.g.
• cell (re-)selection parameters, 
• neighbouring cell information and information (also) applicable for UEs in RRC_CONNECTED, e.g. 
• common channel configuration information.
3. Including ETWS notification;

• RRC connection control:

1. Paging;
2. Establishment/ modification/ release of RRC connection, including e.g. assignment/ modification of UE identity (C-RNTI), establishment/ modification/ release of SRB1 and SRB2, access class barring;
3. Initial security activation, i.e. initial configuration of AS integrity protection (SRBs) and AS ciphering (SRBs, DRBs);
4. RRC connection mobility including e.g. infra-frequency and inter-frequency handover, associated security handling, i.e. key/ algorithm change, specification of RRC context information transferred between network nodes;
5. Establishment/ modification/ release of RBs carrying user data (DRBs);
6. Radio configuration control including e.g. assignment/ modification of ARQ configuration, HARQ configuration, DRX configuration;
7. QoS control including assignment/ modification of semi-persistent scheduling (SPS) configuration information for DL and UL, assignment/ modification of parameters for UL rate control in the UE, i.e. allocation of a priority and a prioritized bit rate (PBR) for each RB;
8. Recovery from radio link failure;

• Inter-RAT mobility including e.g. security activation, transfer of RRC context information;

• Measurement configuration and reporting:

1. Establishment/ modification/ release of measurements (e.g. infra-frequency, inter-frequency and inter- RAT measurements);
2. Setup and release of measurement gaps;
3. Measurement reporting;

• Other functions including e.g. transfer of dedicated NAS information and non-3GPP dedicated information, transfer of UE radio access capability information, support for E-UTRAN sharing (multiple PLMN identities);

• Generic protocol error handling;
• Support of self-configuration and self-optimization 

MEDIA ACCESS CONTROL(MAC):

The following functions are supported by MAC sublayer:

• Mapping between logical channels and transport channels;
• Multiplexing of MAC SDUs from one or different logical channels onto transport blocks (TB) to be delivered to the physical layer on transport channels;
• De-multiplexing of MAC SDUs from one or different logical channels from transport blocks (TB) delivered from the physical layer on transport channels;
• Scheduling information reporting;
• Error correction through HARQ;
• Priority handling between UEs by means of dynamic scheduling;
• Priority handling between logical channels of one UE;
• Logical Channel prioritization;
• Transport format selection.

RADIO LINK CONTROL(RLC): 

The following functions are supported by the RLC sub layer:

• Transfer of upper layer PDUs;
• Error correction through ARQ (only for AM data transfer);
• Concatenation, segmentation and reassembly of RLC SDUs (only for UM and AM data transfer);
• Re-segmentation of RLC data PDUs (only for AM data transfer);
• Reordering of RLC data PDUs (only for UM and AM data transfer);
• Duplicate detection (only for UM and AM data transfer);
• RLC SDU discard (only for UM and AM data transfer);
• RLC re-establishment;
• Protocol error detection (only for AM data transfer).