Posts Tagged srb

What is RRC connection?

RRC connection


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.


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What is RB?

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.

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Various radio and data connections

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)


PDP context (UE-Node B-RNC-SGSN-GGSN)

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In Cell_FACH state, SRBs are cleared ?

Definitely No!

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What types of SRBs exist?

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).

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RB and SRB

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.).

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Radio interface protocol structure

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.

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