General Questions 1

Q What are the functions of RRC Layer?

A Functions of RRC:

• Broadcast of System Information
• Transport for NAS layer messages
• Paging
• RRC Connection establishment and release procedure
• Signaling Connection Establishment and release procedure
• Security Mode Control
• Counter Mode Control

Q What are the functions of RLC Layer?

A Functios of RLC:

• In sequence delivery of PDUs to higher layer
• request retransmission of lost RLC PDUs
• Segmentation and re assembly of RLC PDUs

Q What are the functions of MAC Layer?

A  Functions of MAC:

• Mapping logical channels to transport channels
• TBS Selection
• TFRI selection
• Allocate resources for E-DCH UL transmission

Q What is the difference between a SDU and PDU?

A The SDU(Service Data Unit) is the input unit to a Layer. The layer does processing using this unit and can attach a header or remove a header depending upon the direction of flow. The output unit coming out of the layer is the Protocol Data Unit(PDU).

Q How is RRC layer involved in the RRC Connection Setup Procedure?

A RRC layer is responsible for configuring the lower layers in RNC, i.e. RLC, MAC, PHY. Upon receiving RRC Connection Setup Request, the RRC performs these steps:

• Configure PHY layer
• Make RLC entities for the Radio Bearers
• Configure UE contest at MAC
• Configure FP
• Send Radio Link Setup Request to NodeB via NBAP
• After the Radio Link Setup with NodeB, send the RRC Connection Setup to UE and wait for COMPLETE
• UE sends RRC CONNECTION SETUP COMPLETE on RB ID = 2, indicating the successful setup of RRC Connection.

Q What specification would you refer for RLC/MAC?

A 25.321 for MAC; 25.322 for RLC

Q What are RB ID=0 to RB ID=4 used for?

A RB ID 0 = RACH
RB ID = 1 RRC Messages
RB ID = 2 RRC Messages
RB ID = 3 NAS Messages
RB ID = 4 NAS Messages

Q What is loop back test mode?

A Test mode provided by 3GPP for testing. The UL data coming from the UE is looped back from RNC to the UE.