Wireless Oom

RRC messages are transferred by the lower layers through SRBs, which specify the characteristics of the logical, transport and physical channels.

SRB#0 : when establishing a RRC connection

1. uses CCCH logical channel

2. uses the RACH transport channel in the uplink

3. uses the FACH transport channel in the downlink

SRB#1 and SRB#2:

dedicated message generated at RRC layer through DCCH.

SRB#1 uses unacknowledged mode and SRB#2 acknowledged mode

SRB#3 and SRB#4:

dedicated messages from NAS layer through DCCH with acknowledged mode

SRB#3 with high priority, SRB#4 with low priority

Additional SRBs up to 32 can be used for messages with transparent mode (e.g., through DCCH, PCCH or BCCH).