I drew some figure to clarify the definition of RB, SRB and RAB.
PDP context
is
for PS service.
It consists of
1. RAB
2. CN bearer (bearer between SGSN and GGSN)
The PDP context is created with a defined QoS that is requested by the UE and granted by the network.
RAB (Radio Access Bearer)
is
created to provide user plane data transfer.
RAB comprises
1. RB and
2. connection from the SRNC to the SGSN (Iu bearer).
The RAB is created on reequest from the SGSN with a specific QoS request.
For a given UE, there can be multiple RABs per NAS service (speech or PS data service).
various types of connections that the UE will have with the network:
1. RL
2. RB
3. RAB
4. SRB
5. PDP
6. RRC connection
RL (UE-Node B)
RB (UE-Node B-RNC)
RAB (UE-Node B-RNC-SGSN)
PDP context (UE-Node B-RNC-SGSN-GGSN)
RRC is the main AS control protocol.
RRC performs
1. establishment, modification and release of RRC conncetions
RRC connections are used to transfer RRC signal messages and be used to transport higher layer NAS protocol messages.
2. establishment, modification and release of RAB (radio access bearer ), user plane data connection.
3. radio mobility functions, etc.
The AS provides the NAS with a service of information transfer between UE and the CN in what is named a Radio Access Bearer (RAB).
RAB consists of two:
1. Radio bearer (RB) between the UE and RNC
2. Iu Bearer between RNC and CN
RB is only for user data either in CS or PS mode.
RB is [...]
