Posts Tagged Iu bearer

What is RAB?

RAB (Radio Access Bearer)


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).


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RAB vs. RB vs. SRB

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 for both user data and signaling.

Especially for signaling purpose RB, we call it SRB: In the control plane, the signalling information is transfered through the Signaling Radio Bearer (SRB).

However, RAB consists of Iu bearer and user data RB (not SRB).


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