6 Services expected from lower layers

25.3313GPPProtocol specificationRadio Resource Control (RRC)Release 17TS

6.1 Services expected from Layer 2

The services provided by layer 2 are described in [2], [15] and [16].

6.2 Services expected from Layer 1

The services provided by layer 1 are described in [2].

6.3 Signalling Radio Bearers

The Radio Bearers (RB) available for transmission of RRC messages are defined as "signalling radio bearers" and are specified in the following. The UE and UTRAN shall select the signalling radio bearers for RRC messages using RLC-TM, RLC-UM or RLC-AM on the DCCH and CCCH, according to the following:

– Signalling radio bearer RB0 shall be used for all messages sent on the CCCH (UL: RLC-TM, DL: RLC-UM).

– Signalling radio bearer RB1 shall be used for all messages sent on the DCCH, when using RLC unacknowledged mode (RLC-UM).

– Signalling radio bearer RB2 shall be used for all messages sent on the DCCH, when using RLC acknowledged mode (RLC-AM), except for the RRC messages carrying higher layer (NAS) signalling and the MEASUREMENT REPORT message carrying the IE "Application layer measurement reporting".

– Signalling radio bearer RB3 and optionally Signalling radio bearer RB4 shall be used for the RRC messages carrying higher layer (NAS) signalling and sent on the DCCH in RLC acknowledged mode (RLC-AM), as specified in subclauses 8.1.8., 8.1.9 and 8.1.10.

– Signalling radio bearer RB4 shall be used for UE INFORMATION RESPONSE message and the MEASUREMENT REPORT message carrying the IE "Application layer measurement reporting".

– Additionally, RBs whose identities shall be set between 5 and 32 may be used as signalling radio bearer for the RRC messages on the DCCH sent in RLC transparent mode (RLC-TM).

– RRC messages on the SHCCH are mapped either on RACH or on the USCH in the uplink using TM and either on FACH or on the DSCH using RLC-UM. These messages are only specified for TDD mode.

– RRC messages on the MCCH are mapped on FACH using RLC-UM. The transport channel configuration for MCCH is indicated on BCCH. For this signalling radio bearer no identity is applied.

– RRC messages on the MSCH are mapped on FACH using RLC-UM. The transport channel configuration for MSCH is indicated on MCCH. For this signalling radio bearer no identity is applied.

The Radio Bearer configuration for signalling radio bearer RB0, SHCCH, BCCH on FACH, PCCH on PCH, BCCH mapped to BCH, RB0 mapped on HS-DSCH (FDD only) and RACH, BCCH mapped on HS-DSCH (FDD and 1.28 Mcps TDD only), PCCH mapped to HS-DSCH (FDD and 1.28 Mcps TDD only) and RB0 mapped on HS-DSCH and common E-DCH (FDD and 1.28 Mcps TDD only) are specified in subclauses 13.6, 13.6a, 13.6b, 13.6c, 13.6e, 13.6f, 13.6g and 13.6h.

Ciphering is never applied to signalling radio bearer RB0 or signalling radio bearers using RLC TM.