In LTE, there are 3 signalling radio bearers are defined.
- SRB - 0 : which is nothing but common control channel. As soon as the cell setup procedure is finished, it becomes operational. It is not dedicated for an UE. Every UE uses this channel to send initial RRC messages.
- SRB - 1: It is associated with UE. Every UE has its own dedicated signalling radio bearer. As the time of RRC connection setup procedure , it is established.
-SRB-2: It is another dedicated signalling radio bearer which is mainly used to NAS messages. It is an optional signalling radio bearer. Even if this is not present SRB1 shall be used for both RRC and NAS signalling messages.