Wireless Oom » srb

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 RRC connection?

wirelessoom — Mon, 27 Jul 2009 06:01:31 +0000

RRC connection

exists

when a UE went through the connection establishment procedure and has been allocated resources in the UTRAN and a U-RNTI.

With RRC connection, some SRBs are allocated.

What is RB?

wirelessoom — Mon, 27 Jul 2009 05:47:15 +0000

RB (Radio Bearer)

is a layer 2 connection between the UE and the RNC.

It is used for both control signaling and user data.

RB used for signaling is called an SRB.

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)

In Cell_FACH state, SRBs are cleared ?

wirelessoom — Sat, 20 Jun 2009 05:35:52 +0000

Definitely No!

What types of SRBs exist?

wirelessoom — Fri, 19 Jun 2009 07:42:46 +0000

RRC messages are transferred by the lower layers through SRBs, which specify the characteristics of the logical, transport and physical channels.

SRB#0 : when establishing a RRC connection

1. uses CCCH logical channel

2. uses the RACH transport channel in the uplink

3. uses the FACH transport channel in the downlink

SRB#1 and SRB#2:

dedicated message generated at RRC layer through DCCH.

SRB#1 uses unacknowledged mode and SRB#2 acknowledged mode

SRB#3 and SRB#4:

dedicated messages from NAS layer through DCCH with acknowledged mode

SRB#3 with high priority, SRB#4 with low priority

Additional SRBs up to 32 can be used for messages with transparent mode (e.g., through DCCH, PCCH or BCCH).

RB and SRB

wirelessoom — Fri, 19 Jun 2009 05:17:46 +0000

Layer 2 provides upper layers with information transmission between the UE and UTRAN by means of Radio Bearers (RBs) and Signaling Radio Bearers (SRBs).

RBs are for transmission of user data.

SRBs are for transmission of control information that can be originated either in the RRC or in upper layers.

RB specifies the configuration and the parameters of layer 2 and physical layer depending on the characteristics of the service (voice, interactive service, etc.).

Radio interface protocol structure

wirelessoom — Fri, 19 Jun 2009 04:09:55 +0000

Radio interface protocol structure:

Note that RB vs. SRB

At the UTRAN side, RLC and above protocols are located at RNC.

MAC protocols: some functionalities are at Node B, others are at RNC.

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).

I'm confused! RRC connection, RB, SRB, signaling connection ?!

wirelessoom — Thu, 18 Jun 2009 18:18:29 +0000

Now I got the idea!!!

RRC connection:

To transfer RRC messages (messages generated at RRC layer itself and NAS messages) between UE and UTRAN.

RRC messages are transferred by the lower layers through Signaling Radio Bearers (SRBs).

Thus, establishment of RRC connections mean establishments of different SRBs.

Only a single connection.

———-

Signal connection:

Establishment is needed in order to transfer NAS signal messages. That is, messages are exchanged between UE and CN.

However, note that this NAS signal messages still use SRBs between UE and UTRAN!!

————–

RB:

The upper layer signalling messages (exchanged by the UE and the CN) may request the initiation of a user service (beloning to certain service class and with different requirements) .Then, RB will be established. RB is a user data.