RRC Layer Interview Question and Answers 1-5

Q1. What is the full form of RRC Layer? In Telecom Protocol Layer where it exist?

Ans RRC full form is Radio Resource Control. In telecom it exit in L3 Layer.
The Radio Resource Control (RRC) protocol is used in UMTS and LTE on the Air interface. It is a layer that exists between UE and eNB and exists at the IP level. This protocol is specified by 3GPP in TS 36.331 for LTE. RRC messages are transported via the PDCP-Protocol.

Q2. What are the functionality of RRC layer?

Ans The RRC protocol includes the following main functions:

• Broadcast of system information:
• Including NAS common information;
• 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.
• Including ETWS notification, CMAS notification;
• RRC connection control:
• Paging;
• 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;
• Initial security activation, i.e. initial configuration of AS integrity protection (SRBs) and AS ciphering (SRBs, DRBs);
• RRC connection mobility including e.g. intra-frequency and inter-frequency handover, associated security handling, i.e. key/ algorithm change, specification of RRC context information transferred between network nodes;
• Establishment/ modification/ release of RBs carrying user data (DRBs);
• Radio configuration control including e.g. assignment/ modification of ARQ configuration, HARQ configuration, DRX configuration;
• 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 prioritised bit rate (PBR) for each RB;- Recovery from radio link failure;
• Inter-RAT mobility including e.g. security activation, transfer of RRC context information;
• Measurement configuration and reporting:
• Establishment/ modification/ release of measurements (e.g. intra-frequency, inter-frequency and inter- RAT measurements);
• Setup and release of measurement gaps;
• 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-optimisation; . Rel 10 onwards SON.

Q3. How many states UE have in LTE?

Ans In LTE a UE have only 2 States (I) IDLE State (II) CONNECTED State.
RRC_IDLE:

• A UE specific DRX may be configured by upper layers.
• UE controlled mobility;
• The UE:
• Monitors a Paging channel to detect incoming calls, system information change, for ETWS capable UEs, ETWS notification, and for CMAS capable UEs, CMAS notification;
• Performs neighbouring cell measurements and cell (re-)selection;
• Acquires system information.

RRC_CONNECTED

• Transfer of unicast data to/from UE.
• At lower layers, the UE may be configured with a UE specific DRX.
• Network controlled mobility, i.e. cell change order with optional network assistance (NACC) to GERAN
• Monitors a Paging channel and/ or System Information Block Type 1 contents to detect system information change, for ETWS capable UEs, ETWS notification, and for CMAS capable UEs, CMAS notification;
• Monitors control channels associated with the shared data channel to determine if data is scheduled for it;
• Provides channel quality(CQI) and feedback(HARQ) information;
• Performs neighboring cell measurements and measurement reporting;
• Acquires system information.

Q4. What is the 1st message of RRC Layer, UE sent to network while it move from idle to connected state?

Ans When a UE send RRC connection request towards to enb at this time UE in idle state, after that enb send RRC connection setup when UE receive this message UE move idle to Connected state. And transmit the RRC connection setup complete message to enb.
Note: RRC re-configuration also responsible to move UE idle to dedicated state its depend upon on ue condition while ue perform attach procedure or update modify existing bearer.

Q5. What is the purpose of RRC connection request?

Ans The pupose of RRC connection request in LTE a ue want to attach to network or required radio resources so ue send RRC connection request message to enb.