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Tuesday, 24 January 2012

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



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 


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.


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).


  1. Thank you so much for sharing this info

  2. lucid explanations...thanks!!!!!

  3. Thanks for the great article! BTW, here’s a IMEI checker tool as a community service intended to validate whether GSM or CDMA phones have LTE feature or not.