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UMTS Signaling Flow

ZTE University

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Content

UE State transition

Signaling flow

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Classification of Flows

In terms of protocol stack, signaling flows can beaccess layer signaling flows or non-access layer

signaling flows.

In terms of network composition, signaling flows

can be categorized as circuit-switched or packet-switched.

Access layer and non-access layer signaling flows

are actually so named from the perspective ofprotocol stack.

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Classification of Flows

The flows at the access layer include PLMNselection, cell selection, and radio resource

management flows.

The radio resource management flows are the

flows at the RRC layer, including the RRCconnection setup flow, flow of the signaling setup

between UEs and CNs, RAB setup flow, call

release flow, handover flow, and SRNS redirection

flow.

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UE Working Modes

There are two basic working modes: Idle

UE stands by without any service. Theres no connection

between UE and UTRAN.

Connected UE transferred to the connected mode after accomplishing RRC

Connection Setup.

UE has 4 states under the connected mode:Cell-DCH, Cell-

FACH, Cell-PCH, URA-PCH

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UE State

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UE States Under the Connected Mode

Cell-DCH UE is activated, and in service using its dedicated

channels.

There are dedicated channels in both uplink and

downlink. UTRAN knows exactly which cell the UE is in.

Cell-FACH

UE is activated, but without too much data to transmit,

so theres no need to assign dedicated channels to it.

Downlink data transmitted in FACH, while uplink in

RACH.

UTRAN knows exactly which cell the UE is in.

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UE States Under the Connected Mode

Cell-PCH

There is no data transmitted in both uplink and downlink.

UE needs to listen to PICH for paging information.

UE works in discrete receiving, which saves the power effectively.

UTRAN knows exactly which cell the UE is in.

UE needs to do cell update procedure when it passes cells.

URA-PCH

There is no data transmitted in both uplink and downlink.

UE needs to listen to PICH for paging information and receive

discretely. UTRAN only knows which URA (UTRAN Registration Area) UE

exists.

UE updates its location information only when its URA changes,

which further reduces the signaling saves resource.

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RRC State Transition (I)

After RRC Connection Setup, UE will

transit to CELL_FACH or CELL_DCH.

CN indicates UE using dedicated

channel (CELL_DCH) or common

channel (CELL_FACH) according to

the service request.

If there is no service right now, UE

will be indicated into PCH mode orrelease RRC connection back to

IDLE mode.

URA_PCH

CELL_DCHCELL_FACH

CELL_PCH

IDLE

DEAD

IDLE

DEAD

CELL_DCHCELL_FACH

IDLE

Sketch of RRC State Transition

Transit from IDLE Mode

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URA_PCH

CELL_DCH

CELL_PCH

IDLE

DEAD

IDLE

DEAD

CELL_FACH

IDLE

RRC State Transition (II)

UE do not occupy dedicated

channels In the mode of

CELL_FACH.

UE receives downlink data through

FACH(S-CCPCH).

UE transmits uplink data through

RACH(PRACH).

Transit from CELL_FACH Mode

Sketch of RRC State Transition

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URA_PCH

CELL_DCH CELL_FACH

CELL_PCH

IDLE

DEAD

IDLE

DEAD

CELL_DCH

IDLE

URA_PCH CELL_PCH

CELL_DCH

RRC State Transition (III)

UE transceives uplink and downlink

data through dedicated channels

(DPDCHs and DPCCHs).

During the time when there is no data

transmitted, CN may indicate UEs

transiting to URA_PCH or CELL_PCH.

Transit from CELL_DCH Mode

Sketch of RRC State Transition

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URA_PCH

CELL_DCH CELL_FACH

CELL_PCH

IDLE

DEAD

IDLE

DEAD

CELL_DCH

IDLE

CELL_DCH

URA_PCH CELL_PCH

CELL_FACH

CELL_PCHURA_PCH

RRC State Transition (IV)

UE has no activated uplink.

Paging Information makes UE back to

CELL_FACH or CELL_DCH mode.

In CELL_PCH, UE should transit to

CELL_FACH first to finish cell updating,

and go back if no service request.

In URA_PCH, if URA changes, UE also

transits to CELL_FACH to finish cell

updating first before it goes back toURA_PCH.

System resource can be saved in these

two modes.Sketch of RRC State Transition

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Content

UE State transition

Signaling flow

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Basic Conception (1)

RRC (Radio Resource Control) provides information transfer service to the NAS (Non

Access Stratum).

responsible for controlling the configuration of UMTS

radio interface Layers 1 and 2. RRC Connection

A point to point bi directional connection between the

RRC (Radio Resource Control) entities on the UE (User

Equipment) and UTRAN (UMTS Terrestrial RadioAccess Network).

The UE requires an RRC connection to access the

services of the UMTS network.

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Basic Conception (2)

RAB -Radio Access Bearer Identify the service the AS (Access Stratum) provides to

the NAS (Non Access Stratum) for transfer of user data

between the UE (User Equipment) and the CN (Core

Network). RB -Radio Bearer

The service provided by the Layer 2 for the transfer of

user data between UE (User Equipment) and UTRAN

(UMTS Terrestrial Radio Access Network).

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Basic Conception (3)

RL (Radio Link) RL is a logical association between single UE (User

Equipment) and a single UTRAN (UMTS Terrestrial

Radio Access Network) access point.

Its physical realization comprises one or more radiobearer transmissions.

It is possible for a UMTS mobile to have many radio

links established, when this occurs the mobile is said to

be in a soft handover.

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Sketch of the basic conceptions

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UE Calling Flow

Power on

Cell selection

Location

Update

Idle Mode

RRC

Establish

NAS

Establish

Hand Over

Cell/

URA update

Channel

reconfiguration

RB/RAB

Modification

RAB

Establish

RRC

Release

Call

Initiate

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UE in Idle Mode

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What Information needed for UE?

1

Strongest cell2Slot boundary

3Frameboundary

4

Primary SC5 Information in broadcasts

channel

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1st Step: Cell Selection and Slot

Synchronization

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DL Scrambling Code Rule

218

-1 DL Scrambling Codes in total (0..262142)

The

left

8192

Scramblingcodes

are

used

for

compression

mode

The

left

8192

Scramblingcodes

are

used

for

compression

mode

#511 Scrambling Code

Group

8176

8177

8191

8176P-SC

8177S-SC

8191S-SC

#510 Scrambling Code

Group

8160

8161

8175

8160

8161

8175

#504 Scrambling Code

Group

8064

8065

8079

8064

8065

8079

#7 Scrambling Code

Group112

113

127

8176P-SC

8177S-SC

8191S-SC

#1 Scrambling Code

Group

1

6

17

3

1

16P-SC

17S-SC

31S-SC

#0 Scrambling Code

Group

0

1

1

5

0P-SC

1S-SC

15S-SC

#0 Scrambling Code Cluster

#63 Scrambling Code Cluster

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2rd Step: Frame synchronization and

Scrambling code-group

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Scrambling-code identification

CPICH is predefine

sequence

Spreading Factor is 256

(Cch,256,0

)

Scrambling by P-

scrambling code

UE identified through

symbol-