Some of the basic terms which we use in telecom domain are RB(Radio Bearer), SRB(Signalling Radio Bearer), RAB(Radio Access Bearer), AS (Access Stratum), NAS (Non Access Stratum) and RRC connection. Lets try to understand these terms:
RRC connection exists when a UE goes through the connection establishment procedure and has been allocated resources in the UTRAN and a U-RNTI. When RRC connection get established, UE will also have some SRBs. Now whats the difference between RRC connection and RB? RRC connection is like a railway track on which RB is like carriages on the track.Carriage defines what kind of good will be dleivered and in what quantity similarily RBs will define what kind of data goes on RRC. RB can carry signalling or data.So for example if QoS gets changed then RB associated with that RRC connection will need to reconfigured.
RAB is the combination of RB and the Iu bearer.
UE and CN (Core Network, MSC for circuit switched service, SGSN for packet switched service) need to communicate with each other for various procedures. NAS protocols support the talk between UE and CN. It does not care below access method (could be LTE, UTRAN, GSM/GPRS).
AS is a group of protocols that are specific to access network.
Now what is bearer: so its a logical connection between differnet nodes which make sure that packets going through same bearer go through the same QoS. Each bearer is associated with certain QoS parameters like Packet Delay, Packet loss etc so each packet going through same bearer will have same QoS parameters.
