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UMTS (RRC connection establishment) - 17

RRC connection establishment [Under UMTS]
» RRC - 25.331 «
» Phy layer services - 25.302 «
» Phy procedures (FDD) - 25.214 «

Next step after PLMN and cell selection is network registration or attach. Registration procedure is NAS/MM responsibility, for which NAS requests RRC connection. RRC connection establishment require following signaling exchanges:

UE NB

UE is in idle mode. NAS has requested signaling connection from AS/RRC.

CCCH/RACH
RRC CONNECTION REQUEST
Message contain (initial) UE identity (TMSI, P-TMSI, IMSI or IMEI), Establishment cause (Originating Conversation call, Registration etc.) etc. UE/PHY will perform Random access procedure (over PRACH) to send the message.

CCCH/FACH/S-CCPCH
RRC CONNECTION SETUP
This message contain information about identity (U-RNTI, C-RNTI), RRC state indicator, Signaling radio bearers (i.e. radio bearers with identities 1 thru 4) and their mapping on transport channels. It may also contain physical frequency info, transport channel info (transport format set etc.), DCH/DPCH allocation (new state CELL_DCH) etc.

DCCH/RACH or DCCH/DCH
RRC CONNECTION SETUP COMPLETE
UE configures its MAC and acknowledges successful establishment with this message. UE may indicate its radio access capability with this message.

UE/RRC is in connected mode now.


If you remember, CCCH use transparent RLC mode. So message "RRC Connection Request" is passed transparently to MAC. To send this message, MAC/PHY invokes "random access" procedure over PRACH. Before we look at this procedure, let us look at interface between MAC and PHY.

For every transport channel, PHY need to know the characteristics of transport. This brings us to a important concept of "Transport Format (TF)" [3GPP TS 25.302]. Let us explore this in next article.

References: UMTS by Sanchez and Thioune, and WCDMA for UMTS by Holma and Toskala.

Copyright © Samir Amberkar 2010§ §

RRC states « UMTS Index » Transport Format