LTE Signalling Radio Bearers (SRBs)
SRBs are used by the signalling layers (RRC and NAS):
- SRB0 -- RRC messages in Common Control Channel (CCCH)
- SRB1 -- RRC messages and NAS messages prior to SRB2 establishment. Both RRC/NAS will use Dedicated Control Channel (DCCH)
- SRB2 -- NAS messages using DCCH with lower priority than SRB1. It is always configured by EUTRAN after security activation.