Wireless Oom » rab

No more confusion re. RB, SRB and RAB

wirelessoom — Wed, 26 May 2010 19:30:00 +0000

I drew some figure to clarify the definition of RB, SRB and RAB.

What is PDP contexts?

wirelessoom — Mon, 27 Jul 2009 05:58:50 +0000

PDP context

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.

What is RAB?

wirelessoom — Mon, 27 Jul 2009 05:56:08 +0000

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).

Various radio and data connections

wirelessoom — Mon, 27 Jul 2009 05:41:54 +0000

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)

What does RRC protocol do?

wirelessoom — Sun, 26 Jul 2009 13:59:23 +0000

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.

RAB vs. RB vs. SRB

wirelessoom — Fri, 19 Jun 2009 03:59:01 +0000

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).