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UMTS Signaling Flow



Contents

1 Overview ........................................................................................................................................................1

1.1 Basic Signaling Flow ...............................................................................................................................1

1.1.1 Flow Classification ...................................................................................................................1

1.1.2 Description to Basic Signaling Flow ........................................................................................2

1.2 Basic Concept ...........................................................................................................................................4

1.2.1 UE Protocol State .....................................................................................................................4

1.2.2 UTRAN State Transition in Connection Mode ........................................................................8

2 Network Selection Flow ..............................................................................................................................15

2.1 UE Under Idle Mode ..............................................................................................................................15

2.1.1 Overview .................................................................................................................................15

2.1.2 PMMN Selection and Reselection .........................................................................................16

2.2 Cell Selection and Reselection ...............................................................................................................17

2.2.1 Cell Selection ..........................................................................................................................17

2.2.2 Cell Reselection ......................................................................................................................18

2.2.3 Cell Selection Away form Connection Mode .........................................................................18

2.2.4 Position Registraton ................................................................................................................19

3 Handover Flow in the System ....................................................................................................................20

3.1 Handover Overview ...............................................................................................................................20

3.2 Soft Handover ........................................................................................................................................21

3.2.1 Between Cells in NodeB ........................................................................................................23

3.2.2 Between NodeBs in the Same RNC .......................................................................................23

3.2.3 Between RNCs .......................................................................................................................24

3.3 Hard Handover .......................................................................................................................................25

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3.3.1 Inter-Frequency Hard Handover under the Same RNC ........................................................27

3.3.2 Inter-RNC Hard Handover under the same MSC ..................................................................27

3.4 Inter-Systems Handover .........................................................................................................................28

3.4.1 Handover Between CS Domain Systems ...............................................................................29

3.4.2 Handover Between PS Domain Systems ...............................................................................31

3.5 Forward Handover .................................................................................................................................33

4 Call Service Flow .........................................................................................................................................36

4.1 Overview ................................................................................................................................................36

4.2 Paging Flow ...........................................................................................................................................36

4.2.1 Paging the UE in Idle Mode or PCH State .............................................................................37

4.2.2 Paging the UE in CELL_DCH or CELL_FACH State ..........................................................38

4.2.3 Examples of Paging Flow .......................................................................................................39

4.3 RRC Connection Establishment Flow ...................................................................................................39

4.3.1 RRC Connection Establishment on Special Channles ...........................................................40

4.3.2 Setting up RRC Connection on a Public Channel .................................................................41

4.3.3 RRC Connection Rejection ....................................................................................................42

4.4 Direct Transfer Message Flow ...............................................................................................................42

4.4.1 Initial Direct Transfer .............................................................................................................43

4.4.2 Uplink Direct Transfer ............................................................................................................44

4.4.3 Downlink Direct Transfer .......................................................................................................45

4.5 UE Capability Information Flow ...........................................................................................................46

4.5.1 UE Capability Information Query ..........................................................................................46

4.5.2 UE Capability Information Update ........................................................................................47

4.6 RAB Establishment Flow .......................................................................................................................48

4.6.1 DCH-DCH ..............................................................................................................................48

4.6.2 CCH-DCH ..............................................................................................................................52

4.6.3 CCH-CCH ...............................................................................................................................53

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5 Service Release Flow ...................................................................................................................................55

5.1 Overview ................................................................................................................................................55

5.2 Iu Signaling Connection Release Flow ..................................................................................................56

5.2.1 Signaling Connection Release Request ..................................................................................56

5.2.2 Signaling Connection Release ................................................................................................56

5.3 RAB Release Flow .................................................................................................................................57

5.4 Joint Release Flow of CS-Domain lu Signaling Connection and RAB ................................................59

5.5 RRC Connection Release Flow ............................................................................................................61

5.5.1 Overview .................................................................................................................................61

5.5.2 Releasing an RRC Connection Established on a Special Channel .......................................61

5.5.3 Releasing an RRC Connection Established on a Common Channel ....................................62

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1 Overview

1.1 Basic Signaling Flow

1.1.1 Flow Classification

A variety of signaling flows exist in a UMTS system. In terms of protocol stack,

signaling flows can be access 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 of protocol stack. In the protocol stack, the RRC layer, RANAP layer, and

the protocol layers below them are access layers, while the MM, SM, CC, and SMS

layers above them are known as non-access layers. Simply put, the flow at the access

layer is the flow where the RNCs and NodeBs at the radio access layer need to take

part in the processing. The flow at a non-access layer refers to a signaling flow where

only UEs and CNs, but not RNCs or NodeBs, need to take part in the processing. The

signaling at the access layer paves the way for the signaling interaction at a non-access

layer. Through the signaling interaction at the access layer, a signaling path is

established between the UE and CN so that the signaling flow at a non-access layer can

be started.

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

resource management flows. The radio resource management flows are the flows at the

RRC layer, including the RRC connection setup flow, flow of the signaling setup

between UEs and CNs, RAB setup flow, call release flow, handover flow, and SRNS

redirection flow. For the handover and SRNS redirection flows, the cross-RNC and

cross-SGSN/MSC cases exist. In such cases, SGSN/MSC is also needed. Therefore,

from the perspective of protocol stack, the flows at the access layer are all bottom layer

flows, through which bottom layer bearer is established for the signaling flows at upper

layers.

The non-access flow layer flows mainly include the CS domain mobility management,

the CS domain call control, the PS domain mobility management, and the PS domain

session management.

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UMTS Signaling Flow

1.1.2 Description to Basic Signaling Flow

The following is the overview that briefly describes the basic signaling flow.

At first, the whole business flow from power on, to business, and then to power off can

be viewed in the case that the user is not mobile, which is described as follows.

Figure 1 Calling Service Flow

1. When a subscriber UE is powered on, the signaling interaction at the access layer

is performed first. PLMN selection is then performed to select the network of a carrier,

followed by cell selection to reside in an appropriate cell. After that, an RRC

connection is established and the signaling connection on the Iu interface is set up. At

this point, through the signaling flows at these access layers, a signaling channel is

established between the UE and the CN in preparations for the signaling flows at non-

access layers.

2. Then, the mobility management flows at non-access layers between UE and CN

are started. The subscriber then starts attached flows, including small flows such as

authentication, encryption, and location update.

3. After the flows such as authentication pass, the UE enters the service-related

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Chapter 1 Overview

flows at non-access layers. Such flows include the call connection flows of the circuit

domain and the session management flows of the packet domain. Through these flows,

the service bearer links are established for the service. After that, the subscriber can

start to make a call or access the Internet.

4. When the subscriber finishes using the service, the call connection flows of the

circuit domain and the session management flows of the packet domain are also

performed to tear down the service bearer links.

5. If the subscriber powers off his/her mobile phone, the mobility management flows

at non-access layers are performed between the UE and CN to separate the circuit

domain from the packet domain.

6. When the signaling interaction at non-access layers is complete, the system

performs the signaling flows at the access layer to tear down the Iu signaling

connection and RRC signaling connection previously established.

At this point, the whole flow in which a subscriber powers on his/her mobile phone,

uses the service, and powers off the mobile phone without moving is complete. This

shows that the completion of the service process requires the cooperation between the

signaling flows at the access layer and those at non-access layers. The flows at the

access layer establish the signal bearer for the flows at non-access layers.

The version below describes one service flow with which the user make the called

service.

1. The subscriber UE is in standby mode. The subscriber UE is paged from the

network side.

2. If no signaling connection exists between the UE and the CN, the signaling flows

at the access layer are performed between the UE, the RNC, and the CN to establish an

RRC connection and Iu interface signaling connection.

3. Then, the authentication and encryption flows of mobility management may be

performed.

4. After that, service bearer links are established through the call connection flows of

the circuit domain and session management flows of the packet domain so that the

service can be performed.

5. When the service is finished, the related service bearer links are torn down.

6. Then, the signaling connections at the access layer, including the signaling

3



UMTS Signaling Flow

connection on the Iu interface and the RRC connection, are released.

The previously described two flows mainly describe in general how to make services inthe case that the subscriber has no position change. This is only an overall and simple

description while various detailed flows are described in the subsequent chapters and

sections.

As mobile communication has the mobile feature, flows related to a variety of hanlding

mobilities are produced. For example, when the subscriber does not develop the

service, the position is changed, so as to produce such flows of mobility management

as position renewal; when the subscriber develops the service, the position changes so

as to produce such flows as handover and SRNS repositioning.

1.2 Basic Concept

1.2.1 UE Protocol State

A UE has two basic operation modes: idle mode and connection mode. Upon being

powered on, the UE stays in the idle mode while the mode is distinguished through

such access level flags as IMSI, TMSI or P-TMSI. Because UTRAN does not save the

UE information of the idle mode, the UTRAN can only page all UEs in one cell or all

UEs at the same time.

Only when a UE finishes the construction of the RRC connection can the UE changes

its idle mode to the connection mode: CELL_FACH or CELL_DCH state. The UE

connection mode, which is also called as the UE RRC state, reflects the UE connection

level and which kind of transfer channel the UE can use. When the RRC connection is

released, the UE changes its connection mode to the idle mode.

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Chapter 1 Overview

Figure 2 UE Operation Mode

When UE is in the connection mode, there are following four kinds of state:

1. CELL_DCH state

The CELL_DCH state has the following features:

A dedicated physical channel is assigned to the UE along the uplink and

downlink;

The cell to which the UE belongs can be obtained through the current active set of

the UE;

The UE can use the dedicated transport channel, uplink/downlink shard transport

channel, or a combination of these transport channels.

The UE enters the CELL_DCH state in the following two ways:

When the UE is in idle mode, the RRC connection is established on the dedicated

channel, and therefore the UE enters the CELL_DCH state from idle mode;

When in the CELL_FACH state, the UE uses the common transport channel and

uses the dedicated transport channel after a channel switchover. The UE enters the

5



UMTS Signaling Flow

CELL_DCH state from the CELL_FACH state.

2. CELL_FACH state

The CELL_FACH state has the following features:

No dedicated transfer channel is assigned to the UE

he UE continuously monitors one downlink FACH channel

A default uplink public channel or uplink shared transfer channel (such as RACH)

is assigned to the UE

The UE position in the cell level is known by UTRAN, which is the cell where the

UE initiated the latest cell renewal.

In the CELL_FACH sub state, the UE implements the following actions:

Monitor one FACH

Monitor the BCH transfer channels and the decoding system information

messages of the current service cell

When the current cell turns to be another UTRA cell, one renewal process of the

cell is initiated.

Unless one new cell is selected, the allocated C-RNTI in the current cell is used as

the UE flag of the public transfer channel.

Transmit the uplink signaling and small data packet in the RACH

In the CELL_RACH state, if the data service is not activated during a period of

time, the UE will enter the CELL_PCH state so as to reduce the power

comsumption. Furthermore, when the UE temporary gets rid of the CELL_PCH

state and implements the cell renewal, after the renewal is finished, it will return

the CELL_PCH if no requirements are necessary in the UE and the network side.

3. CELL_PCH state

The CELL_PCH state has the following features:

No dedicated channel is assigned for the UE.

The UE uses the non-continuous reception (DRX) technology to monitor the

information in the PCH transfer channel in some specified paging time.

No uplinking actve UE positions can be known by the UTRAN in the cell level,

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Chapter 1 Overview

which refers to the cell reported by the UE in the CELL_FACH state when the

latest cell renewal is initiated.

In the CELL_PCH state, the UE makes the following activities:

According to the DRX cycle monitor the paging time, and receive the paging

information on the PCH.

Monitor the BCH transfer channel of the current service cell to decode the system

information

When the cell changes, initiate the cell renewal process

In such case, the DCCH logic channel cannot be used. If the network tries toinitiate any activities, it needs to send one paging request on the PCCH logic

channel of the cell where the UE is located.

There are two ways for the UE to be converted to the CELL_FACH state: one way is to

make paging through the UTRAN while another way

4. URA_PCH state

The URA_PCH state has the following features:

No dedicated channel is allocated for the UE.

The UE uses the DRX technology to monitor the information on the PCH transfer

channel at some specific paging time.

No uplink activities are permitted.

The UE position is known by the UTRAN in the URA level, the specific one is the

URA reported in the CELL_FACH state when the latest URA renewal is initiated.

In the URA_PCH state, the UE make the following activities:

According to the DRX cycle monitor the paging time, and receive the paging

information on the PCH.

Monitor the BCH transfer channel of the current serive cell to decode the system

information

When the URA chages, the URA renewal process is initiated.

In such case, the DCCH logic channel cannot be used. If the network tries to

initiate any activities, it needs to send one paging request on the PCCH logic

channel of the cell where the UE is located.

7



UMTS Signaling Flow

In the URA_PCH state, no resources are allocated for the data transfer. Therefore,

if the UE has the data to transmit, firstly it is required to be coverted to the

CELL_FACH state.

1.2.2 UTRAN State Transition in Connection Mode

1.2.2.1 CELL_DCH state

1． Transition from the CELL_DCH state to the idle mode

The UE enters idle mode after releasing the RRC connection.

2. Transition from the CELL_DCH state to the CELL_FACH state

When all the dedicated physical channels are released, the state transitions to

CELL_FACH. The state transition is completed through clear signaling (for example,

physical channel reconfiguration, radio bearer reconfiguration, radio bearer release,

radio bearer establishment, and transport channel reconfiguration)

3. Transition from the CELL_DCH state to the CELL_PCH state

This state transition is completed through clear signaling (for example, physical

channel reconfiguration, radio bearer reconfiguration, radio bearer release, radio bearer

establishment, and transport channel reconfiguration).

4. Transition from the CELL_DCH state to the URA_PCH state

This state transition is completed through clear signaling (for example, physical

channel reconfiguration, radio bearer reconfiguration, radio bearer release, radio bearer

establishment, and transport channel reconfiguration)

5. Radio resource allocation task (CELL_DCH)

For DCH, multiple physical channel allocation policies should be provided. Such

allocation may be permanent (a DCH release message is needed) or based on time

segment or data volume.

For each burst packet, resource configuration can be completed through the fast

signaling on the DCH.

For each radio frame, the UE and network use the Transport Format Combination

Indicator (TFCI) to indicate the current data rates (respectively corresponding to uplink

and downlink traffic). In TDD mode, however, DCH and DSCH or USCH may be

mapped to different CCTrCHs, with their respective TFCIs completely independent.

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Chapter 1 Overview

DCH transport does not change because the DSCH/USCH exists at the same time. If

the configured combination set (the transport format set for a transport channel) is

found to be insufficient to maintain the QoS required by a transport channel, the

network starts a transport format set (TFS) for the transport channel for

reconfiguration. The reconfiguration can be completed during or between data

transport. In addition, on the network, physical channels can be configured and the

peak data rates can be increased or decreased.

For uplink data transport, the UE reports the service traffic observed to the network so

that the network can re-assess the current resource allocation. This report should

contain the volume of data to be transported, buffer statuses within the UE, and so on

6. RRC connection mobility task (CELL_DCH)

Whether to use macro diversity (soft handover) depends on the data quantity and

frequency.

RRC connection mobility is processed by measurement report, soft handover, and non-

synchronization/synchronization.

7. UE measurement (CELL_DCH)

The UE should perform the measurement according to the measurement control

information and send a measurement report.

The UE should use the connection mode measurement control information received in

other states until the UE is assigned new measurement control information

8. Capturing of system information (CELL_DCH)

In FDD mode, a UE with a specific capability (This UE supports the reception on one

SCCPCH and one DPCH simultaneously) can read the system information broadcast

on the FACH.

1.2.2.2 CELL_FACH State

1. Transition from the CELL_FACH state to the CELL_DCH state

This state transition is completed when a dedicated physical channel is established

through clear signaling (for example, physical channel reconfiguration, radio bearer

reconfiguration, radio bearer release, radio bearer establishment, and transport channel

reconfiguration)

2. Transition from the CELL_FACH state to the CELL_PCH state

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UMTS Signaling Flow

This state transition occurs when the UTRAN instructs the UE to enter the CELL_PCH

state through clear signaling, such as cell update confirmation and radio bearer

reconfiguration

3. Transition from the CELL_FACH state to idle mode

The UE enters the idle mode after releasing the RRC connection

4. Transition from the CELL_FACH state to the URA_PCH state

This state transition occurs when the UTRAN instructs the UE to enter the URA_PCH

state through clear signaling, such as URA update confirmation and radio bearer

reconfiguration.

5. Radio resource allocation task (CELL_FACH)

In the CELL_FACH state, the UE listens on a FACH. The UE should be able to send

uplink control signals and send small packets on the RACH.

The network can assign in advance transport channel parameters, such as the transport

format set, to the UE for use when the UE uses the DCH. When a physical channel is

assigned to the DCH, the UE should enter the CELL_DCH state and is used as the TFS

allocated in advance to the DCH

If no UE dedicated physical channel or transport channel configuration is specified, the

UE should use the common physical channel and transport channel configuration

according to the system information.

For uplink data transport, the UE reports the service traffic observed to the network so

that the network can re-assess the current resource allocation. This report should

contain the volume of data to be transported, buffer statuses within the UE, and so on.

When user data or control data is transmitted, a selection process is started to determine

whether to transport the data through a common transport channel or to transition to the

CELL_DCH state. This selection is dynamic and dependent on specific parameters,

such as service parameters (data size and packet burst frequency)

In FDD mode, the UTRAN can assign CPCH resources to the UE in the CELL_FACH

state. After being assigned CPCH resources, the UE continues to listen on the FACH.

The UE may use the RACH to send uplink control signals and small packets. The UE

can also choose to send large packets (larger than the packets carried on the RACH) on

the CPCH. The UE chooses either the RACH or one CPCH to maximally use the

available capacity on the channel

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Chapter 1 Overview

In FDD mode, for each CPCH used, the UE provides the UTRAN with CPCH

measurement data, including data, queue length (the size of the current data buffer),

average access time, and the service traffic of each CPCH used. Based on the

measurement information, the UTRAN can periodically reassign network resources.

The UTRAN assigns a CPCH set to each cell and assigns one to the UE. The UE can

dynamically access these CPCH resources without UTRAN control.

6. RRC connection mobility task (CELL_FACH)

In this state, the UE location on the cell level is known. When the UE selects a new cell

to observe the common downlink channel of the new cell, the UE uses the cell update

process to report to the UTRAN. Data transport can initiated on the downlink FACHwithout paging in advance.

The UE listens on the system information about the UE itself and neighboring cells on

the broadcast channel and BCCH, and determines whether to perform a cell location

update based on this information

The UE should perform cell re-selection and start the cell update process when

selecting a new UTRA cell. If another non-UTRA radio access system cell is selected,

the UE should enter the idle mode and complete access according to the system

specifications

7. UE measurement (CELL_FACH)



By default, the UE should use the measure control information broadcast in system

information. The network, however, can also provide measurement control information

in MEASUREMENT CONTROL messages. In this case, the messages have a higher

priority.

8. Sending and updating system information (CELL_FACH)

The UE should read the BCH to obtain valid system information. For each acquisition,

the UE may need the different combinations of the system information broadcast on the

BCH. The system information on the broadcast channel is arranged based on the time

the UE spends in obtaining the information needed.

After the system information is modified, the time arrangement information is updated

to reflect the change in the system information transported on the BCH. The new time

11



UMTS Signaling Flow

arrangement information is broadcast on the FACH to notify the UE of the change. If

the change is applicable to the UE, the modified system information is read on the

BCH.

1.2.2.3 CELL_PCH State

1. Transition from the CELL_PCH state to the CELL_FACH state

The UE transitions to the CELL_FACH state is realized through the paging (paging

type 1) from the UTRAN or any uplink access.

2. Radio resource allocation task (CELL_PCH)

In the CELL_PCH state, no resource is designated to be used for data transport. Totransport data, the UE must transition to another state.

The UE may use DRX to reduce power consumption. When the DRX is used, only one

paging occasion is needed for each DRX interval. The network may instruct the UE to

use a specific DRX interval length. The UE should determine its paging occasion in a

mode the same as the idle mode

3. RRC connection mobility task (CELL_PCH)

In the CELL_PCH state, the UE mobility is performed through the cell re-selection

process.

The UE should perform cell re-selection. When selecting a new UTRA cell, the UE

transites to the CELL_FACH state and starts a cell update process in the new cell. After

the cell update process is performed, if neither the UE nor the network transports data ,

the UE should return to the CELL_PCH state.

If another non-UTRA radio access system cell is selected, the UE should enter the idle

mode and complete access according to the system specifications.

When the UE activity is low, the UTRAN may order the UE to transition to the

URA_PCH state to reduce frequent cell updates. This transition is completed through

the CELL_FACH state. The UTRAN may provide a inactive timer and an optional

counter used to count the number of cell updates. When the number of cell updates

exceeds a certain limit (network parameter), the UTRAN orders the UE to transition to

the URA_PCH state.

4. UE measurement (CELL_PCH)


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Chapter 1 Overview


When no dedicated measurement control information is assigned to the UE, the UEshould uses the measurement control information according to the system information

5. Updating of transport and system information (CELL_PCH)

The UE should read the BCH to obtain valid system information. For each acquisition,

the UE may need the different combinations of the system information broadcast on the

BCH. The system information on the broadcast channel is arranged based on the time

the UE spends in obtaining the information needed.

1.2.2.4 URA_PCH State

1. Transition from the URA_PCH state to the CELL_FACH state (URA_PCH)

Any activity will cause the UE to transition to the CELL_FACH state. For example, the

RACH performs uplink access or the paging (paging type 1) from the UTRAN.

Note that an RRC connection cannot be released in the URA_PCH state. The UE must

first transition to the CELL_FACH state before releasing the signing.

2. Radio resource allocation task (URA_PCH)

In the URA_PCH state, no resource is designated to be used for data transport. To

transport data, the UE must transition to the CELL_FACH state.

The UE may use DRX to reduce power consumption. When the DRX is used, only one

paging occasion is needed for each DRX interval. The network may instruct the UE to

use a specific DRX interval length. The UE should determine its paging occasion in a

mode the same as the idle mode.

3. RRC connection mobility task (URA_PCH)

In the URA_PCH state, the location of the UE on the URA level is known.

In this state, mobility is completed through the URA re-selection process. The UE

should perform cell re-selection. When selecting a new UTRA cell (This URA cell is

not the one originally used by the UE), the UE should transition to the CELL_FACH

state and initiate a URA update to the network. After the URA update process is

performed, if neither the UE nor the network transports data , the UE should return to

the URA_PCH state.

If another non-UTRA radio access system cell is selected, the UE should enter the idle

mode and complete access according to the system specifications.

13



UMTS Signaling Flow

4. UE measurement (URA_PCH)

The UE should perform the measurement according to the measurement controlinformation and send a measurement report.

When no dedicated measurement control information is assigned to the UE, the UE

should uses the measurement control information according to the system information.

5. Sending and updating system information (URA_PCH)

In the URA_PCH state, the mechanism of sending and updating system information is

the same as that in CELL_PCH state.

14



2 Network Selection Flow

2.1 UE Under Idle Mode

2.1.1 Overview

When the UE powers on or is in the roaming mode, its primary task is to find out the

network and connect to it because the network service can be obtained only in this way.

Therefore, in the idle mode, the UE action is vital to the UE. How can the UE

implement the function? The following describes the flow.

In the idle mode, the UE action can be divided in details into PLMN selection and

reselection, cell choice and reselection and position registration. The relationships

between these three flows are described in the following figure.

PLMN Selectio

and Reselection

Location

Registration

PLMNs

available

PL M

selecte

Locatio

Registratio

respons

RegistratioAr e

change

Indic at ion

to user

User selectioof PLM

utomatic/ Ma nu al sel ec tion

CM reques

NA S C on tro l

Ra dio me as ur em en

Cell Selection

and Reselection

Figure 3 Idle Mode Process

15



UMTS Signaling Flow

After being powered on, the UE first selects a PLMN. After selecting a PLMN, the UE

begins to select a cell belonging to this PLMN. When such a cell is found, the

information about the neighboring cell can be obtained from the system information

(broadcast). Thus, the UE can select a cell with the best signals among these cells and

reside in the cell. Then, the UE initiates the location registration process (attach or

location update). If the operation succeeds, the UE resides in the cell. The UE resides

in the cell for four purposes:

1. To receive the system information broadcast by the PLMN.

2. To initiate the random access process in the cell.

3. To receive paging from the network.

4. To receive the broadcast services of the cell.

When the UE resides in the cell and the registration succeeds, as the UE moves, the

signal strengths of the current cell and the neighboring cell keep changing. In this case,

the UE needs to select a most suitable cell. This is known as the cell re-selection

process. This most suitable cell is not necessarily the cell that currently has the best

signals. The reason is this: suppose the UE is at the edge of a cell and moves to and fro

between the two cells, which happen to belong to different LAs or RAs. Thus, the UE

needs to keep initiating location updates. This wastes not only resources but also the

UE energy. Therefore, there are certain rules as to which cell to be reselected among all

the cells.

After the UE reselects a cell, if the cell is found to belong to another rLA or RA, the

UE initiates the location update process so that the network obtains the latest UE

location information. The UE discovers LA or RA changes through the SIB1 in the

system broadcast information

If the location registration or update fails, for example, when the network rejects the

UE, or when the current PLMN is out of the coverage area, the UE can perform PLMN

re-selection to select another usable PLMN.

2.1.2 PMMN Selection and Reselection

The purpose of PLMN selectionand reselection is to select one applicable (that can

provide the normal service), best PLMN. Through which can the UE realize the

purpose? The UE can maintain one PLMN list, which will list the PLMN according to

the priority, and then search from the higher priority to the lower priority so it is natural

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Chapter 1 Overview

to find out the PLMN with the highest priority. In addition, there are two kinds of

modes to select and reselect: automatic and manual. In brief, the automatic network

selection is to select one PLMN for the UE according to the PLMN priority sequence

while the manual network selection is to display all the currently applicable networks

to the subscriber, give him/her the righ to select one PLMN.

2.2 Cell Selection and Reselection

After selecting a PLMN, the UE begins to select a cell, aiming to select the cell

belonging to the PLMN and with the best signals.

If the UE stores information, such as frequency and scrambling code, related to the

PLMN, the UE performs a cell search (stored information cell selection) by using the

information. Thus, a network can be found quickly. This is because in most cases, the

UE is powered off and on in the same place. For example, the UE is powered off at

night and is powered on in the morning. Such information is stored in the SIM card or

the non-volatile memory of the mobile phone

2.2.1 Cell Selection

The procedure of cell selection is roughly as follows:

1. Cell search

The purpose of cell search is to find a cell, which, though, may not belong to the

selected PLMN. The steps of cell search are as follows (A frequency needs to be locked

first, of course):

The UE obtains timeslot synchronization through the primary SCH. After timeslot

synchronization, frame synchronization needs to be performed. Frame synchronization

is completed through the synchronization code of the secondary SCH. In this

procedure, the scrambling code group of the cell is also determined. Then, the UE

associates each scrambling code of the scrambling code group on the CPICH until it

finds the greatest one among the related results. Thus, the primary scrambling code is

determined.

Obviously, if the UE already knows some information about the cell, such as the

frequency used and even the primary scrambling code, the above-mentioned procedure

can be accelerated greatly.

2. Reading the broadcast channel

17



UMTS Signaling Flow

From the above-mentioned procedure, the UE obtains the scrambling code of the

PCCPCH, whose channel code is known and unique through the whole UTRAN. Thus,

the UE can read the information of the broadcast channel.

When reading the MIB, the UE can determine whether the found PLMN is the one

intended, because there is a PLMN domain in the MIB. If yes, the UE finds another

SIB and obtains its contents based on the scheduling information in other SIBs

contained in the MIB. If not, the UE has to look for the next frequency, starting the

procedure all over again (from cell search).

If the current PLMN is the one intended by the UE, the UE reads SIB3 and obtains

"Cell selection and re-selection". Through the information obtained, the UE performscalculations to determine whether the cell residence standards are met. If yes, the UE

considers the cell a suitable cell. The UE resides in the cell and reads the other system

information needed and initiates the location registration procedure.

If the above-mentioned conditions are not met, the UE reads SIB11 and obtains the

information on the neighboring cells. Thus, the UE can perform calculations and

determines whether the neighboring cell meets the cell selection residence standards.

If the UE finds that any neighboring meets the cell residence standards, the UE resides

in the cell, reads other system information needed, and initiates the location registration

procedure.

If the UE finds no cell that meets the cell residence standards, the UE considers that

there is coverage and continues the PLMN selection and re-selection.

2.2.2 Cell Reselection

In idle mode, the UE keeps monitoring the signal quality of the current cell and

neighboring cells to select the best cell for providing services. This is known as cell re-

selection. If the cell re-selection conditions are met within the re-selection time, the UE

selects the cell, resides in the cell, and reads the broadcast messages of the cell. Cell re-

selection is complete.

2.2.3 Cell Selection Away form Connection Mode

When the UE returns to the idle mode from the connection mode, it is required to make

the cell choice to find one situable cell. This choice process is the same as the ordinary

celll choice process. However, at this time, the choice of a cell is to select the cell used

in the connection mode. If no suitable cells are found in these cells, the stored

18



Chapter 1 Overview

information cell selection should be used.

2.2.4 Position Registraton

Refer to the related content of MM and GMM for these flows. Herein these flows are

omitted.

19



3 Handover Flow in the System

3.1 Handover Overview

Handover is one of the most remarkable features that distinguish mobile

communications from fixed communications. UTRA FD supports the following

handover modes:

1. Intra-mode handover: Softer handover, soft handover, and hard handover are intra-

mode handovers. A hard handover can be a intra-frequency handover or inter-

frequency handover

2. Transition Between Modes: It refers to the transition to the UTRA TDD mode.

3. Inter-system handover: For the R99, an inter-system handover refers a handover to

the GSM system, namely, a handover to the 900 MHz, 1800 MHz, 1900 MHz GSM

systems.

During a hard handover, before a new link is established, the old link of a mobile

station is released. That is, a channel can be established only after it is released. The old

channel is torn down before being synchronized with the new channel. The old and the

new channels do not take effect at the same time.

During a soft handover or softer handover, the mobile station and UTRAN maintain at

least one link between them. That is, a channel is removed before a new channel is

established. The original channel is removed only after the new channel takes effect.

Inter-frequency handovers and inter-system handovers are always hard handovers.

Intra-frequency handovers are not necessarily soft handovers. For example, if no Iur

interface exists, a cross-Iur interface intra-frequency handover is a hard handover, and

the new and old links cannot take effect at the same time. Here is another example. If

the transmitting diversity modes of intra-frequency cells are different, no soft handover

can be performed, either.

Basic Concepts:

1. Active set: Set of cells connected to a mobile station. Subscriber information is

sent from these cells.

20



Chapter 1 Overview

2. Monitor set: Cells not in the active set but monitored according to the adjacent

cell list assigned by the UTRAN belong to the monitor set. The UE measures the cells

in the monitor set. If the measurement results meet certain conditions, these cells may

be added to the active set. Therefore, the monitor set is sometimes known as the

candidate set.

3. Detected Set: Set of cells in neither the active set nor the monitor set.

Typical Handover Procedure: The typical handover procedure is measurement control

-> measurement report -> handover decision -> handover execution -> new

measurement control.

During the measurement control phase, the network sends measurement control

messages to notify the UE of the parameters of the measurement. During the

measurement report phase, the UE sends measurement report messages to the network.

During the handover decision phase, the network makes a handover decision based on

the measurement report. During the handover execution, phase, the UE and network

carry out the signaling flow and give responses according to the signaling.

3.2 Soft Handover

Mainly initiated by the network side, soft handovers are one of the indispensable core

technologies unique to the direct spread spectrum CDMA system. Soft handovers are

used to update UE active sets in the CELL-DCH state. During a soft handover, multiple

service channels are activated (for the diversity of service channels) between intra-

frequency channels to effectively lower the call drop rate in the handover. A soft

handover is performed at the same frequency in different base stations. A soft handover

performed between the sectors with the same frequency in the same base station is

known as a softer handover. When a softer handover is performed, diversity signals are

merged to the largest ratio at NodeB. This is different from a soft handover where

selective merging of diversity signals is performed at the RNC. The RNC soft handover

and softer handover flow consists of two steps: radio link operations on the Iub

interface and active set update operations on the Uu interface. Radio link operations on

the Iub interface are RADIO LINK SETUP, RADIO LINK ADDITION, and RADIO

LINK REMOVAL. Active set update operations on the Uu interface are soft addition,

software removal, and soft replacement.

Difference between a soft handover and a softer handover is as follows: Soft handover

means uplink link merging in macro-diversity status is performed at an RNC. Softer

21



UMTS Signaling Flow

handover means the merging of uplinks is performed at NodeB.

During a softer handover, a mobile station is located where the coverage of twoadjacent sectors of a base station overlaps. The mobile station and base station

communicate with each other through two air interface channels. There is one air

interface channel in each sector. Thus, two spread spectrum codes need to be used in

the downlink and the mobile station can distinguish these signals. The mobile station

receives and processes these two signals through Rake receiver. This process is very

similar to multi-path reception except that despread spectrum codes are need to be

generated for each sector to ensure correct despread spectrum operations. In the uplink,

a similar process is performed on the base station: The code division channel of the

mobile station is received in each sector, sent to the same baseband Rake receiver, and

merged to the maximum ratio through a normal method. During a softer handover, for

each connection, only one power control loop is active.

During a soft handover, a mobile station is located where the coverage of two sectors

of different base stations overlaps. Same as a softer handover, the mobile station and

two base stations perform communication through two different air interface channels

at the same time. Same as a softer handover, the mobile station receives two channels

(signals) through merging to the maximum ratio by using a Rake receiver. From the

perspective of the mobile station, there is very little difference between a soft handover

and a softer handover. In the uplink, however, the difference between a soft handover

and a softer handover is very great: Two base stations receive the code division

channels from the mobile station, but the received data is sent to the RNC for selective

merging. This is because the frame reliability indicator provided for external loop

power control needs to be used in the RNC to select the better frame from the two

candidate frames. Such selection occurs each time the interlacing interval is complete.

That is, the selection occurs ever 10 ms to 80 ms.

22



Chapter 1 Overview

3.2.1 Between Cells in NodeB

Figure 4 Soft Handover Inside NodeB

In this case, the radio uplink can be merged in NodeB or the SRNC. If the radio uplink

is merged in NodeB, it is known as a softer handover.

3.2.2 Between NodeBs in the Same RNC

Figure 5 Soft Handover Between NodeBs

Soft Handover Flow Between NodeBs in the Same RNC

23



UMTS Signaling Flow

Figure 6 Soft Handover Between NodeBs in the Same RNC

The softer handover flow is basically the same as the soft handover flow between

NodeBs. The only difference is that a softer handover is a handover in NodeB, with Iub

interface message as RADIO LINK ADDITION REQUEST, while the switching Iub

interface message between NodeBs is RADIO LINK SETUP REQUEST.

3.2.3 Between RNCs

Figure 7 Soft Handover Between RNCs in the Same MSC

Soft Handover Between RNCs in the Same MSC uses the Iur interface:

24



Chapter 1 Overview

Figure 8 Inter-Iur Interface Soft Handover

3.3 Hard Handover

Mainly initiated by the network side, a hard handover is used for the handovers

between the intra-frequency/inter-frequency channels of the UE in the CELL_DCH

state. During a hard handover, only one service is activated. An inter-frequency hard

handover changes the radio frequency of the connection between the UE and UTRAN.

the trigger decision between inter-frequency channels needs inter-frequency

measurement supported by the compression mode technologies The process of a hard

handover is to first tear down the communication with the original cell before gaining

access from the new cell. Therefore, the performance of a hard handover is not as good

as that of a soft handover. Thus, generally, an intra-frequency hard handover is

considered only when the system cannot perform a soft handover. If the two cells

involved in the handover belong to two different RNCs between which there is no Iur

interface, an intra-frequency hard handover occurs. Depending on the range involved, a

hard handover can be a hard handover between the FDD and TTD modes inside a cell,

a hard handover between cells under the same NodeB, a hard handover between cells

in the same RNC, or a hard handover between RNCs. Inter-RNC hard handovers fall

into two parts: hard cut-aways to the DRNC through the Iur interface and inter-RNC

hard cut-aways controlled by the core network. Inter-RNC hard cut-aways controlled

by the core network are the same as UE-related relocation.

Hard handovers correspond to Iub interface operations and Uu interface operations. Iub

interface operations correspond to radio link reconfiguration. Uu interface operations

25



UMTS Signaling Flow

are completed through the following five types of operations, of which physical

channel reconfiguration is the most commonly performed operation.

1. RADIO BEARER SETUP;

2. RADIO BEARER RELEASE;

3. RADIO BEARER RECONFIGURATION;

4. Transport channel reconfiguration;

5. Physical channel reconfiguration;

Compression Modes ： Also known as a slotted mode, a compression mode is used by

a non-all frequency receiver in a CDMA system to measure other frequencies. The

signal reception and transfer processing of a mobile phone stops for several

milliseconds so that physical layer resources are set aside for the measurement of other

frequencies. The reception and transfer are stopped not to lose data but to compress the

data transfer time. Frame compression in a compression mode can be completed in

three ways:

1. Upper-layer planning

The upper layer obtains the scheduling information of the compression mode, lowers

the data rate, and inserts DTX bits when a radio frame mapping is established to create

transfer slots.

2. Spreading spectrum factors reduced by half

Change spreading spectrum factors to improve data rates. For example, the physical

layer changes the timeslot sequence number assigned by the upper layer from the

timeslot format corresponding to the spreading spectrum factor 128 to the timeslot

format corresponding to the spreading spectrum factor 64. This effectively doubles the

number of symbols for valid physical timeslots and creates blank timeslots.

3. Puncturing methods

With the spread spectrum factor and channelized code sequence unchanged, the

puncturing of rate matching module in the code, multiplexing link at the physical layer

can be used to lower the data rates. The transfer gap lengths (TGL) generated in this

way, however, are relatively short.

A compression mode is generally used for the downlink. If the uplink enters the

compression mode, the downlink must enter the compression mode in cooperation at

26



Chapter 1 Overview

the same time.

Figure 9 Condensation Mode Principle

3.3.1 Inter-Frequency Hard Handover under the Same RNC

Figure 10 Inter-Frequency Hard Handover under the Same RNC

3.3.2 Inter-RNC Hard Handover under the same MSC

The hard handover between different RNCs under the same MSC does not use the Iur

interface process, which is the same as the hard handover process between different

MSCs. Both are the hard handover process accompanied by repositioning.

27



UMTS Signaling Flow

Figure 11 Re-position Caused by Inter-RNC Hard Handover

3.4 Inter-Systems Handover

The inter-systems handover is based on supporting the measurement between thesystems with the condensation mode, which is divided into two kinds: handover

between the CS domain systems and handover between the PS domain systems.

All the inter-system handovers in the CS domain are initiated by the network side and

completed through handover commands. There are three possibilities of CS system cut-

aways: 1) Based on a measurement report, the RNC determines that a handover to the

GSM system needs to be performed; 2) The CN specifies to perform a handover when

delivering RAB designation, namely, a inter-CS system switching; Direct retry (For

example, when no resource is available for distribution) In terms of flow, a CS-domain

28



Chapter 1 Overview

inter-system cut-away consists of two phases: Iu interface CS-domain inter-system cut-

away preparation and Uu interface inter-system cut-away request. Iu interface CS-

domain inter-system cut-away preparation phase corresponds to the relocation

preparation message. Uu interface inter-system cut-away request phase corresponds to

the cut-away message HANDOVER FROM UTRAN COMMAND. CS-domain inter-

system cut-aways involve the Iu interface relocation process and Uu interface system

CS-domain cut-away process. The Iu interface relocation process corresponds to the

resource allocation message. The Uu interface system CS-domain cut-away process

corresponds to the HANDOVER TO THE UTRAN COMPLETE message, with the Uu

interface system CS-domain cut-away process as an intermediate process.

A PS-domain handover can be initiated by the UE or by the network side. A PS-domain

cut-away is initiated by the network side for the UE in the CELL_DCH or

CELL_FACH state, involving the Uu interface PS-domain cut-away process and Iu

interface context information acquisition process. The Uu interface PS-domain cut-

away process corresponds to the CELL CHANGE ORDER FROM UTRAN message.

The Iu interface context information acquisition is an intermediate process,

corresponding to the Iu interface context information acquisition message. The PS-

domain cut-away initiated by the UE is for the UE in the CELL_FACH, CELL_PCH,

or URA_PCH state, triggered by the UE cell re-selection process and with no

corresponding message on Uu interface. Only the context information acquisition

process exists on the Iu interface. The context information acquisition process on the Iu

interface consists of two phases: Iu interface context information acquisition request

and context transfer, respectively corresponding to the messages SRNS CONTEXT

REQUEST/SRNC CONTEXT RESPONSE and SRNS DATA FORWARD

COMMAND/FORWARD SRNC CONTEX. Note that the failure of Iu interface

context information acquisition process does not affect subsequent flows. PS-domain

cut-in triggering corresponds to the RRC connection establishment request message.

The PS-domain cut-in initiated by the UE corresponds to the RRC connection

establishment request reason Inter-RAT cell re-selection. The PS-domain cut-in

initiated by the network side corresponds to the RRC connection establishment request

reason Inter-RAT cell change order. The subsequent RAB assignment message on Iu

interface contains the serial number information about the PDCP and GTP-U.

3.4.1 Handover Between CS Domain Systems

29

SRNC NODE BUE

HANDOVER FROM UTRAN COMMAND

HANDOVER COMPLETE

CN

RELOCATION REQUIRED

RELOCATION COMMAND

BSC

HANDOVER REQUEST

HANDOVER DETECT

HANDOVER COMPLETE

IU RELEASE COMMAND

IU RELEASE COMPLETE

HANDOVER RESPONSE

RADIO LINK DELETION REQUEST

RADIO LINK DELETION RESPONSE



UMTS Signaling Flow

Figure 12 UTRAN⇒GSM/BSS Handover

30

SRNC NODE BUE

HANDOVER TO UTRAN COMPLETE

CN

RELOCATION REQUEST

BSC

HANDOVER COMMAND

CLEAR COMMAND

HANDOVER REQUIRD

RELOCATION REQUEST ACK

RADIO LINK SETUP REQUEST

RA DIO LINK SETUP RESPON SE

HANDO VER TO UTRAN COMMAND

RADIO LINK RESTORE INDICATION

RELOCATION DETECT

RELOCATION C OMPLETE

CLEAR COMPLETE



Chapter 1 Overview

Figure 13 GSM/BSS to the UTRAN Handover

3.4.2 Handover Between PS Domain Systems

31

S R NSB S SU E2 G

S G S N

n e w M S/

V L R

3 G

S G S N

I n t e r s y s t e m c h a n g e d e c i s i o n

R o u t e i n g A r e a U p d a t e

S R N S C o n t e x t R e q u e s t

S R N S C o n t e x t R e s p o n s e

S R N S D a t a F o r w a r d C o m m a n d

F o r w a r d P a c k e t s

I u R e l e a s e C o m m a n d

I u R e l e a s e C o m p l e t e

L o c a t i o n U p d a t e A c c e p t

L o c a t i o n U p d a t e R e q u e s t

R o u t e i n g A r e a U p d a t e

R o u t e i n g A r e a U p d a t e C o m p l e t e

T M S I R e a l l o c a t i o n

S G S N C o n t e x t R e q u e s t

S G S N C o n t e x t A c k n o w l e d g e

S G S N C o n t e x t R e s p o n s e

F o r w a r d P a c k e t s



UMTS Signaling Flow

Figure 14 UMTS to GPRS Cell Reselection, the UE Initiated

32

SRNC NODE BUE

HANDOVER TO UTRAN COMPLETE

CN

RELOCATION REQUEST

BSC

HANDOVER COMMAND

CLEAR COMMAND

HANDOVER REQUIRD

RELOCATION REQUEST ACK


RA DIO LINK SETUP RESPON SE

HANDO VER TO UTRAN COMMAND

RADIO LINK RESTORE INDICATION

RELOCATION DETECT

RELOCATION C OMPLETE

CLEAR COMPLETE



Chapter 1 Overview

Figure 15 GPRS to UMTS Cell Reselection

3.5 Forward Handover

A forward handover means that the UE initiates a cell update/URA update for the

mobility management of the UE in the UTRAN connection mode but using only thecommon channel. A cell update generally refers to a notification of a location change of

the UE in the CELL_PCH/CELL_FACH state to the RNC for timely updating of the

information about the UE on the UTRAN side. A cell update is also used to monitor

RRC connections, switch RRC connection states, and perform the anomaly report

functions. The URA update flow is used for the UTRAN registration area URA update

by the UE in the URA_PCH state. Depending on ranges, forward handovers fall into

two types:

1. Cell update process among the cells in the RNC： Depending on parameter differences, this process can be divided into two flows: one requiring reconfiguration

(returning the RB/Trch/Phy reconfiguration complete message) and the other requiring

no reconfiguration (If a parameter such as a newly assigned C_RNTI, the UE needs to

return the Mobility Info Confirm message).

2. Cell update process among different RNC cells：This process is further divided

into two flows: one requiring relocation (updating SRNC) and the other requiring no

relocation (updating DRNC).

33



UMTS Signaling Flow

Figure 16 Cell Update with SRNS Relocation

Figure 17 Cell Update via Iur without SRNS Relocation

34



Chapter 1 Overview

Figure 18 Cell Update (core network)

35



4 Call Service Flow

4.1 Overview

When the UE finds a cell and reads the system messages of the cell, the UE can obtain

the parameter configuration information about the system and the conditions for

network access

There are two types of call establishment: UE as the caller and UE as the callee. The

difference between the two is that when the UE acts as the callee, the system needs to

page the UE in the specified area through the paging flow before the call is established.

Regardless of whether the UE acts as the caller or callee, call establishment and call

release contain the following procedure:

1. An RRC connection is established between the UE and UTRAN.

2. A connection is established between the UE and CN through a direct transfer

message.

3. UE capability information flow.

4. RAB establishment flow.

5. RAB release and Iu release flow.

6. RRC connection release flow.

4.2 Paging Flow

Paging can be initiated by the CN or UTRAN

The paging initiated by the CN is used to establish a signaling connection. The paging

initiated by the CN can be collaborated or non-collaborated. Through the RANAP

PAGING message, the CN indicates whether the RNC needs to perform UTRAN

collaborated paging.

In collaborated paging, the RNC checks whether the UE has any other CN-domain

signaling connection. If the UE has any other CN-domain signaling connection and is

in the CELL_DCH or CELL_FACH state, the paging message is delivered through the

DCCH channel of the existing connection on the radio interface. If the UE has any

36



Chapter 1 Overview

other CN-domain signaling connection and is in the CELL_PCH or URA_PCH state,

the paging message is delivered through the PCCH channel on the radio interface. If

the UE has no other CN-domain signaling connection, the paging message is delivered

through the PCCH channel.

In non-collaborated paging, the RNC directly delivers the paging message through the

PCCH channel in the paging area specified by the CN without checking whether UE

has any CN-domain signaling connection not in the paging domain.

In paging initiated by the UTRAN, the UE in the CELL_PCH or URA_PCH state can

be paged. The UE initiates a cell update process through a paging response to transit

the user state from CELL_PCH or URA_PCH to CELL_FACH. Alternatively, whenthe system information changes, the UTRAN triggers the UE (in idle mode,

CELL_PCH or URA_PCH state) to read the system information after the update again

goes through paging messages.

If the UE is in idle mode or in the CELL_PCH or URA_PCH state. The RNC pages the

UE by using the PAGING TYPE1 message through the PCCH channel.

The RNC pages the UE by using the PAGING TYPE2 message through the DCCH

channel.

4.2.1 Paging the UE in Idle Mode or PCH State

The UTRAN generally pages the UE in idle mode, CELL_PCH, or URA_PCH state by

using the PAGING TYPE1 message through the PCCH channel.

Such paging generally occurs in the following cases:

1. Paging is initiated by an upper level of the network side to establish a call or a

signaling connection;

2. The UTRAN initiates the paging that triggers UE state transition to transit the UE

state from CELL_PCH or URA_PCH to CELL_FACH;

3. When the system information changes, the UTRAN initiates the paging that

triggers the UE to read the updated system information. In this case, the value label of

the master information block (MIB) is contained in the "BCCH modification info" in

PAGING TYPE 1 message.

37



UMTS Signaling Flow

UE UTRAN

PAGING TYPE1

Figure 19 Paging Idle Type or PCH State

The UTRAN sends the PAGING TYPE1 message when an appropriate paging

opportunity is available to start the paging process. The UTRAN can select multiple

paging opportunities to repeatedly page a UE to increase the possibility of the UE

correctly receiving paging messages.

The UE in idle mode or PCH state monitors the appropriate paging opportunities and

receives the paging messages from the network layer.

4.2.2 Paging the UE in CELL_DCH or CELL_FACH State

The UTRAN generally pages the UE in CELL_DCH or CELL_FACH state by using

the PAGING TYPE2 message through the DCCH channel.

UE UTRAN

PAGING TYPE 2

Figure 20 Paging CELL_DCH or CELL_FACH State

The UTRAN sends the PAGING TYPE2 message through the DCCH channel to

initiate the paging process. Such paging is also known as dedicated paging. The UE

receives and reads the contents in the PAGING TYPE 2 message and reports the

paging reason, paging record category identifier, and other information to the non-

38



Chapter 1 Overview

access layer of the local side. The paging flow is complete.

This process does not affect any other RRC process running on the UE side.

If the UE finds any protocol error in the PAGING TYPE 2 message received, the UE

discards the paging message, uses the AM RLC mode through the uplink DCCH, and

sends the RRC STATUS message to the UTRAN.

4.2.3 Examples of Paging Flow

Description of the Signaling Flow:

1. The CN initiates paging and the UE in idle mode.

In this case, the UTRAN pages the UE by sending a PAGING TYPE1 message.

2. The CN initiates paging and the UE is in CELL_DCH or CELL_FACH state of

the connection mode.

In this case, the UTRAN pages the UE by sending a PAGING TYPEE2 message.

3. The CN initiates paging and the UE is in CELL_PCH or URA_PCH state of the

connection mode.

In this case, the UTRAN first transitions the state of the UE from CELL_PCH or

URA_PCH to CELL_FACH by sending a PAGING TYPE1 message. Then, the

UTRAN pages the UE by sending a PAGING TYPE2 message.

4. The UTRAN initiates paging and the UE is in CELL_PCH or URA_PCH state of

the connection mode.

In this case, the UTRAN pages the UE by 1. sending a PAGING TYPE1 message so

that the state of the UE transitions to CELL_FACH.

4.3 RRC Connection Establishment Flow

When the UE is in idle mode, if the NAS (non-access layer) of the UE requests the

establishment of a signaling connection, the UE initiates the RRC connection request

flow.

When the RNC receives an RRC connection request from the UE, the RNC determines

whether to accept or reject the request based on a specific algorithm. If the RNC

accepts the request, the RNC determines whether to establish the RRC connection on a

dedicated channel or common channel based a specific radio resource algorithm. The

39



UMTS Signaling Flow

RRC connection establishment flows vary with RRC connection establishment

channels. If the RRC connection cannot be established, the RNC rejects the

establishment of the RRC connection.

Description：RRC connection establishment requests are always initiated by the UE.

An RRC connection release request is initiated by the RNC. Each UE can have up to

one RRC connection.

4.3.1 RRC Connection Establishment on Special Channles

If the RRC connection is set up on the special channel, the RNC needs to allocate the

special radio resource for the UE, sets up the radio links, and sets up the ALCAP user

side carrier of the Iub interface for the radil links.

UE RNC

NBAP

.1CCCH

NodeB

NBAP

RRCRRC

RRCRRC

.1CCCH ：: RRC CONNECTION REQUEST

RRCRRC

NBAP NBAP

.1DCCH : RRC CONNECTION SETUP COMPLETE

.1 RADIO LINK SETUP REQUEST

.1 RADIO LINK SETUP RESPONSE

.1 Allocate parameters

such asRNTI、L1、

L1

.1 ALCAP Setup and synchronization

: RRC CONNECTION SETUP

Figure 21 RRC Connection Setup (Special Channel)


1. Through the uplink CCCH, the UE sends RRC CONNECTION REQUEST to

request for setting up an RRC connection.

2. According to the RRC connection request cause and the system resource state, the

RNC decides that the UE is set up on the special channel, and allocates RNTI, radio

resources and other resources (L1 and L2 resources).

3. The RNC sends the NodeB the RADIO LINK SETUP REQUEST to request the

40



Chapter 1 Overview

NodeB for allocating the specific radio link resources necessary for the RRC

connection.

4. After the NodeB resource is well-prepared, the RADIO LINK SETUP

RESPONSE is sent to the RNC.

5. The RNC uses the ALCAP protocols to set up the Iub interface user side transfer

bearer, and implements the synchronous process between the RNC and the NodeB.

6. Through the downlink CCCH channel, the RNC sends the UE the RRC

CONNECTION SETUP message, which includes the special channel information

included in the RNC.

7. After the UE verifies that the RRC connection setup succeeds, the newly setup

uplink DCCH channel sends the RNC the RRC CONNECTION SETUP COMPLETE

message. The RRC connection setup process is finished.

4.3.2 Setting up RRC Connection on a Public Channel

When the RRC connection is set up on the public channek, because the newly setup

cell public resources have been used, it is not required to set up the radio link or the

data transfer bearer on the user side. It is only necessary to map the logic channel used

by the UE on the cell public channel, and the rest process is similar to the situation that

the RRC is connected to set up on the special channel.

UE RNC

.1CCCH

NodeB

RR CRR C

RR CRR C

.1CCCH : RRC CONNECTION REQUEST

RR CRR C

.1DCCH : RRC CONNECTION SETUP CO MPLETE

.1 A llo ca te pa ra me ters

such as RNTI、L1、L1

: :RRC CONNECTION SETUP

.1Map the logical channel

used by UE to the comm

channels

Figure 22 RRC Connection Setup (Public Channel)

41



UMTS Signaling Flow

4.3.3 RRC Connection Rejection

If the RNC judges that this RRC connection request cannot be set up (such as the

resources are insufficient), the RNC directly sends the UE the RRC CONNECTION

REJECT message, in which the cuase of rejecting the RRC connection is indicated.

UE RNC

CCCH:RRC CONNECTION REQUEST

CCCH:RRC CONNECTION REJECT

Figure 23 RRC Connection Reject

4.4 Direct Transfer Message Flow

Direct transfer message refers to the signaling interaction NAS information between

the UE and the CN, such as authentication, service request, connection setup and so on.

As the information is transparently transmitted in the RNC, it is called Direct Transfer

Information.

What the RRC connection sets up is the signaling connection between the UE and the

RNC, so it is also required to go on setting up the signaling connection between the UE

and the CN so as to transmit the direct transfer information. When the RNC receives

the first piece of direct information (the INITIAL DIRECT TRANSFER information),

it sets up a signaling connection between the RNC and the CN, which is set up above

the SS7 SCCP.

After the signaling connections of the UE and CN are set up successfully, the

information the UE sends is sent to the RNC through the UPLINK DIRECT

TRANSFER information while the RNC coverts the information to the DIRECT

42



Chapter 1 Overview

TRANSFER information; the information that the CN sends to the UE is sent to the

RNC through the DIRECT TRANSFER message while the RNC converts the

information to the DOWNLINK DIRECT TRANSFER message to be sent to the UE.

4.4.1 Initial Direct Transfer

The initial direct transfer process is used to set up one signaling connection between

the RNC and the CN, and meanwhile bear one piece of initial NAS information. The

content of the NAS information is not explained in the RNC, but is forwarded to the

CN.

Description: When the UE stays at the CELL_PCH or the URA_PCH state, the UE will

at first make the cell renewal for making the initial direct transfer while the state is

transferred into the CELL_FACH state. The renewal reason is Uplink Data Transfer.

After the cell renewal successfully ends, the UE will go on with the initial direct

transfer.

UE CNSRNC

SCCP SCCP

.1 INITIAL DIRECT TRANSFERRR CRR C

RANAP

.1INITIAL UE MESSAGE

RANAP

SCCP SCCP

.1CONNECITON CONFIRM（SUCCESS）

.1CONNECTION REFUSE（FAILURE）

Figure 24 Initial Direct Transfer


1. After the RRC connection is set up, the UE sends the RNC the INITIAL DIRECT

TRANSFER information through the RRC connection while the information carries

such content as initial NAS information and NC flags sent to the CN by the UE.

2. The RNC receives the initial direct transfer information of the UE, and sends the

43



UMTS Signaling Flow

SCCP CONNECTION REQUEST information through the Iu interface while the

information data is the INITIAL UE MESSAGE sent to the CN by the RNC. The

information includes the information content sent to the CN by the UE.

3. If the CN prepares to accept the connection request, the CN returns the

CONNECTION CONFIRM information to the SCCP to indicate that the SCCP

connection setup succeeds. After the RNC receives the information, the signaling

connection setup is confirmed to be successful.

4. If the CN cannot accept the connection request, the CN returns the

CONNECTION REFUSE information to the SCCP while the SCCP connection setup

fails. If the RNC receives the information and verifies the signaling connection setup tofail, the RNC enables the RRC release process.

For the NAS content carried during the initial direct transfer process, the CN will send

the UE the acceptance or refusal information to the service through the downlink direct

transfer process.

4.4.2 Uplink Direct Transfer

When the UE needs to send a NAS message to the CN on an existing signaling

connection, the UE initiates the uplink direct transfer procedure.

Description: When the UE stays at the CELL_PCH or the URA_PCH state, it is

necessary to make the cell renewal before making the initial direct transfer while the

state is transferred into the CELL_FACH state. The renewal reason is Uplink Data

Transfer. After the cell renewal successfully ends, the UE will go on with the initial

direct transfer.

UE CNSRNC

.1 UPLINK DIRECT TRANSFERRRCRRC

RANAP

.1DIRECT TRANSFER

RANAP

Figure 25 Uplink Direct Transfer

44



Chapter 1 Overview

Uplink Direct Transfer:

1. The UE sends an UPLINK DIRECT TRANSFER message to the RNC to initiate

the uplink direct transfer process. The message contains such information as NAS

message and CN identification.

2. The RNC routes the message according to the CN identifier in the message and

sends the NAS information carried in the message to the CN through a DIRECT

TRANSFER message on Iu interface. The uplink direct transfer process is complete.

Description: If the UPLINK DIRECT TRANSFER message includes the Measured

Results on RACH information unit, it shows that the message carries the measurement

report while the UTRAN uses the related analyzed information content to control the

radio resource and the rest of the message is still transmitted to the CN.

4.4.3 Downlink Direct Transfer

When the CN needs to send the NAS message to the UE on the existing signaling

connection, it enables the downlink direct transfer process. The signaling flow of the

downlink direct transfer is shown in the following figure.

Figure 26 Downlink Direct Transfer

Signaling Flow Description:

1. The CN sends a DIRECT TRANSFER message to the RNC to initiate the

downlink direct transfer process. The message contains the NAS message.

45



UMTS Signaling Flow

2. The UTRAN sends a DOWNLINK DIRECT TRANSFER message through the

DCCH channel in AM RLC mode. The message carries the NAS information that the

CN sends to the UE and CN identifier.

The UE receives and reads the DOWNLINK DIRECT TRANSFER message carrying

the NAS information. If the received message contains a protocol error, the UE sends

an RRC STATUS message on the uplink DCCH in AM RLC mode.

4.5 UE Capability Information Flow

UE capability information includes security capability, location capability,

measurement capability, physical channel capability, and transport channel capability.

The vendors, specifications, and capabilities of UEs are different. Therefore, after an

RRC connection is established, the UE should send UE capability information to the

UTRAN so that the network side configures the UE according to the capability

parameters supported by the UE.

UE capability information can be transferred to the RNC in the following three

scenarios:

1. After an RRC connection is established, the UE capability information istransferred to the RNC through an RRC CONNECTION SETUP COMPLETE

message.

2. After an RRC connection is established, when the RNC finds that the

corresponding capability information does not exist, the RNC sends a UE

CAPABILITY ENQUIRY message to the UE. The UE sends the UE capability

information to the RNC through a UE CAPABILITY INFORMATION message;

3. After an RRC connection is established, when the UE capability information

changes, the UE sends the new UE capability information to the RNC through a UE

CAPABILITY INFORMATION message.

4.5.1 UE Capability Information Query

Through the UE capability information query, the UTRAN requests the UE for

enabling the UE capability query process, shown in the following figure.

46



Chapter 1 Overview

UE UTRAN

UE CAPABILITY ENQUIRY

Figure 27 UE Capability Query

Through the downlink DCCH logic channel, the UTRAN introduces the AMRLC

mode to send the UE CAPABILITY ENQUIRY message to implement the UE

capability information query process.

4.5.2 UE Capability Information Update

If the UTRAN initiates the UE capability information enquiry process or the UE

capability information changes during the RRC connection, the UE initiates the UE

capability information update process.

The UE capability information update process is used to transfer the radio network

related capabilities supported by the UE to the UTRAN.

Figure 28 UE Capability Information Update

1. The UE sends a UE CAPABILITY INFORMATION message in AM or UM RLC

mode on uplink DCCH. The message carries the UE capability information.

2. The UTRAN reads the UE capability information and sends a UE CAPABILITY

INFORMA CONFIRM message in AM or UM RLC mode on the downlink DCCH

channel. The UE capability information update process is complete.

47



UMTS Signaling Flow

4.6 RAB Establishment Flow

The RAB is used between the UE and CN to transfer voice, data, multimedia, and other

services. The RAB is established only after a signaling connection is established

between the UE and CN. RAB establishment is the function initiated by the CN for

execution by the UTRAN.

The basic procedure of RAB establishment is as follows: The CN initiates a RAB

ASSIGNMENT REQUEST message. The RNC configures the parameters related to

the radio network according tot he QoS parameters in the RAB ASSIGNMENT

REQUEST, and then returns a RAB ASSIGNMENT RESPONSE message to the CN to

indicate whether the RAB is established.

Description: A RAB ASSIGNMENT REQUEST is always initiated by the CN. Each

UE can have one or more RABs.

Depending on the RRC connection states before and after the RAB establishment, there

are three scenarios for the RAB establishment flow:

1. DCH-DCH: Before the RAB is established, an RRC connection uses the DCH.

After the RAB is established, an RRC connection uses the DCH;

2. CCH-DCH: Before the RAB is established, an RRC connection uses the CCH.After the RAB is established, an RRC connection uses the DCH;

3. CCH-CCH: Before the RAB is established, an RRC connection uses the CCH.

After the RAB is established, an RRC connection uses the CCH;

4.6.1 DCH-DCH

When the current RRC state of the UE is DCH, the RAB assigned can be established

on DCH only. Based on radio link reconfiguration, the RAB establishment flow can be

divided into two scenarios:

1. Synchronous reconfiguration of radio links

2. Asynchronous reconfiguration of radio links

The difference between the two is whether the new configuration parameter can be

used immediately when the NodeB and UE receive the configuration message

delivered by the Serving Radio Network Controller (SRNC).

48



Chapter 1 Overview

4.6.1.1 RAB Setup Flow of Synchronously Reconfiguring Radio Links

In this case, synchronization and reconfiguration of radio links need to be performed

among SRNC, NodeB, and UE. The synchronization process is as follows

1. When NodeB receives a reconfiguration radio link message delivered by the

SRNC, the NodeB cannot use the new configuration parameter immediately. Instead,

the NodeB prepares the corresponding radio resources, waits for the reconfiguration

execution message delivered by the SRNC, and obtains the synchronization time

specified by the SRNC;

2. Upon receiving the configuration message delivered by the SRNC, the UE also

cannot immediately use the new configuration parameter. Instead, the UE obtains thesynchronization time specified by the SRNC in the message;

3. At the synchronization time specified by the SRNC, NodeB and UE use the new

configuration parameter at the same time.

The figure of RAB Setup Flow of Synchronously Reconfiguring Radio Links is shown

in the following figure.

UE SRNC

NBAP

.1

NodeB

NBAP

RRCRRC

RRCRRC

NBAP NBAP

.1RADIO BEARER SETUP COMPLETE

.1RADIO LINK RECONFIGURATION

PREPARE (Synchronised)

.1RADIO LINK RECONFIGURATION

READY (Synchronised)

.1 ALCAPSetup and synchronization

RADIO BEARER SETUP

CN

RANAPRANAP

.1RAB ASSIGNMENT REQUEST

.1 ALCAPsetup

RANAPRANAP

.1RAB ASSIGNMENT RESPONSE

NBAP NBAP

.1RADIO LINK RECONFIGURATIONCOMMIT (Synchronised)

Figure 29 RAB Setup Flow (DCH-DCH, synchronously)

The signaling flow is described as follows:

49



UMTS Signaling Flow

1. The CN sends a RAB ASSIGNMENT REQUEST message to the UTRAN to

initiate the RAB establishment process.

2. Upon receiving the RAB establishment request, the SRNC maps the QoS

parameters of the RAB to AAL2 link feature parameters and radio resource feature

parameters. The ALCAP of Iu interface initiates the user plane transport bearer

establishment process according to the AAL2 link feature parameters (For the PS

domain, this step does not exist).

3. The SRNC sends a RADIO LINK RECONFIGURATION PREPARE message to

the controlled NodeB to request the controlled NodeB to prepare to add one or more

dedicated channels (DCHs) carrying RAB on the existing radio link.

4. NodeB allocates the resources accordingly and then sends a RADIO LINK

RECONFIGURATION READY message to the SRNC to which the NodeB belongs,

notifying the SRNC that the radio link reconfiguration preparation is complete.

5. The ALCAP of the Iub interface in the SRNC initiates the user plane transport

bearer establishment process on Iub interface. NodeB and SRNC exchange the

uplink/downlink synchronization frames of the DCH frame protocol for

synchronization.

6. The SRNC sends a RADIO BEARER SETUP message of the RRC protocol to the

UE.

7. The SRNC sends a RADIO LINK RECONFIGURATION COMMIT message to

the controlled NodeB.

8. After executing RB setup, the UE sends a RADIO BEARER SETUP COMPLETE

message to the SRNC.

9. Upon receiving the RADIO BEARER SETUP COMPLETE message, the SRNC

returns a RAB ASSIGNMENT RESPONSE message to the CN. The RAB

establishment flow is complete.

4.6.1.2 RAB Establishment Flow with Asynchronous Reconfiguration Radio Links

In this case, synchronization and reconfiguration of radio links does not need to be

performed among SRNC, NodeB, and UE. Upon receiving the configuration message

delivered by the SRNC, the NodeB and UE immediately use the new configuration

parameter.

RAB Establishment Flow with Asynchronous Reconfiguration Radio Links is

50



Chapter 1 Overview

described as follows.

UE SRNC

NBAP

.1

NodeB

NBAP

RR CRR C

RR CRR C

NBAP NBAP


.1 RADIO LINK RECONFIGURATION

REQUEST

.1 RADIO LINK RECONFIGURATIONRESPONSE

.1 AL CA PSetup andsynchronization

RADIO BEARER SETUP

CN

RANAPRANAP


.1 AL CA Psetup

RANAPRANAP


Figure 30 RAB Setup Flow (DCH-DCH, asynchronously)


1. The CN sends a RAB ASSIGNMENT REQUEST message of the RANAP

protocol to the SRNC to initiate the RAB establishment process.






3. In asynchronous mode, radio reconfiguration does not need to be performed

synchronously. The SRNC sends an NBAP RADIO LINK RECONFIGURATION

REQUEST message to the controlled NodeB to request the controlled NodeB to

establish a new DCH on the existing radio link.

4. Upon receiving the RADIO LINK RECONFIGURATION REQUEST message,

NodeB assigns the resources accordingly and then returns a RADIO LINK

RECONFIGURATION RESPONSE message to the SRNC to which the NodeB

51



UMTS Signaling Flow

belongs, notifying the SRNC that the radio link reconfiguration is complete.

5. The ALCAP of the Iub interface in the SRNC initiates the user plane transport bearer establishment process on Iub interface. NodeB and SRNC exchange the

uplink/downlink synchronization frames of the DCH frame protocol for

synchronization.


UE.

7. After executing radio bearer setup, the UE sends a RADIO BEARER SETUP

COMPLETE message to the SRNC




4.6.2 CCH-DCH

When a RRC connection is established on a CCH, the RNC can establish the assigned

RAB on a DCH according to the QoS parameters in the RAB assignment message. In

this case, the RRC connection state needs to be changed from CCH to DCH.

CCH-DCH RAB setup flow is shown in the following figure.

UE SRNC

NBAP

.1

NodeB

NBAP

RRCRRC

RRCRRC

NBAP NBAP


.1

.1

.1 ALCAP Setup and synchronization

RADIO BEARER SETUP

CN

RANAPRANAP

.1RABASSIGNMENT REQUEST

1. ALCAP setup

RANAPRANAP



RADIO LINK SETUP RESPONSE

Figure 31 RAB Setup Flow (CCH-DCH)

52



Chapter 1 Overview


1. The CN sends a RAB ASSIGNMENT REQUEST message of the RANAP protocol to the SRNC to initiate the RAB establishment process.






3. The SRNC starts the radio link establishment process on Iub interface and sends a

RADIO LINK SETUP REQUEST message to the controlled NodeB to request the

NodeB to assign the specific radio link resources required for the RRC connection.

4. Upon completing the resource preparations, NodeB sends a RADIO LINK

SETUP RESPONSE message to the RNC.

5. The RNC establishes the Iub interface user plane transport bearer through ALCAP

and completes the synchronization between the RNC and NodeB.


UE.

7. After executing radio bearer setup, the UE sends a RADIO BEARER SETUP

COMPLETE message to the SRNC.




4.6.3 CCH-CCH

When a RRC connection is established on a CCH, the RNC can continue to establish

the assigned RAB on a CCH according to the QoS parameters in the RAB assignment

message.

53



UMTS Signaling Flow

UE SRNC

.1

NodeB

RR CRR C

RR CRR C.1RADIO BEARER SETUP COMPLETE

RADIO BEARER SETUP

CN

RANAPRANAP


.1 AL CA Psetup

RANAPRANAP


Figure 32 RAB Setup Flow (CCH-CCH)

Description of signaling flow:

1. The CN sends the RAB ASSIGNMENT REQUEST information of the RANAP

protocol to enable the RAB setup request.

2. After the SRNC receives the RAB setup request, the SRNC maps the RAB QoS

parameter as the AAL2 link feature parameter and the radio resource feature parameter.

According to the AAL2 link feature parmameter, the Iu interface ALCAP enables the

transfer bearer setup process of the Iu interface user side.

3. The SRNC sends the UE the RADIO BEARER SETUP message of the RRC

protocol.

4. After the UE implements the radio bearer setup, the UE sends the SRNC the

RADIO BEARER SETUP COMPLETE message.

5. After the SRNC receives the information that the radio bearer has implemented

the setup, the SRNC sends the CN the RAB ASSIGNMENT RESPONSE message. The

RAB setup process is finished.

54



5 Service Release Flow

5.1 Overview

Service release flows fall into two types: high-layer release request initiated by the UE

and high-layer release request initiated by the CN. Regardless of release type, the

ultimate resource release process is initiated by the CN.

For a UE, such a scenario may exist: An RRC connection corresponds to multiple

RABs (For example, VP service and Web Browse service are performed at the same

time), and CS-domain and PS-domain correspond to a Iu signaling connection

respectively. Service release flow is roughly divided into several scenarios.

1. CS-domain service release

When the UE releases a CS-domain service:

If only one RAB is established in CS domain, the CN initiates an IU RELEASE

COMMAND message. Upon receiving this message, the RNC automatically

releases the Iu signaling connection and RAB. When the service release is

complete, the SRNC determines whether the RRC connection corresponds to any

Iu signaling connection (PS domain). If not, the RRC connection release process

is initiated.

If multiple RABs are established in CS domain, the CN initiates the RAB release

flow only for the RAB that needs to be released, without releasing the Iu signaling

connection.

2. PS-domain service release

When the UE releases a PS-domain service:

If only one RAB is established in PS domain, the CN first initiates the RAB

release flow for the RAB. When the release is complete, the CN sends an IU

RELEASE COMMAND message before releasing the Iu signaling connection on

Iu-PS interface. When the service release is complete, the SRNC determines

whether the RRC connection corresponds to any Iu signaling connection (CS

domain). If not, the RRC connection release process is initiated.

55



UMTS Signaling Flow

If multiple RABs are established in PS domain, the CN initiates the RAB release

flow only for the RAB that needs to be released, without releasing the Iu signaling

connection.

5.2 Iu Signaling Connection Release Flow

5.2.1 Signaling Connection Release Request

The Iu connection release flow is generally initiated directly the CN and can also be

initiated by the CN at the request of the UTRAN. The Iu connection release request

flow is used by the UTRAN to request the CN to initiate the Iu connection release

process.

RNC CN

IU RELEASE REQUEST

Figure 33 Signaling Connection Release Request

The SRNC sends an IU RELEASE REQUEST message to the CN domain to initiate

the Iu connection release request process. The message indicates the reason for

releasing the Iu connection. The CN determines how to react to the Iu connection

release request. For example, if the CN decides to release the Iu connection, the CN

initiates the Iu connection release process.

5.2.2 Signaling Connection Release

The Iu connection release process is used by the CN to release an Iu connection,

releasing all the UTRAN resources related to a specific Iu connection. The following

shows the signaling flow.

56



Chapter 1 Overview

RNC CN

.1IU RELEASE COMMAND

.1IU RELEASE COMPLETE

Figure 34 Signaling Connection Release

1. The CN sends an IU RELEASE COMMAND message to the UTRAN to initiate

the signaling connection release process. The message contains the reason for releasing

the signaling connection, for example, "Successful Relocation", "Normal Release",

"Release due to the UTRAN Generated Reason", "Relocation Cancelled", and "No

Remaining RAB". After sending the message, the CN no longer sends any connection-

oriented RNAP message on this connection.

2. Upon receiving the message, the RNC clears the related resources in the UTRAN.

The RNC sends an IU RELEASE COMPLETE message to the CN. The Iu connection

release process is complete.

5.3 RAB Release Flow

For the RAB release flow, like the RAB establishment flow, there are three scenarios:

1. DCH-DCH: Before the RAB is released, an RRC connection uses the DCH. After

the RAB is released, an RRC connection uses the DCH;

2. CCH-CCH: Before the RAB is released, an RRC connection uses the CCH. After

the RAB is released, an RRC connection uses the CCH

3. DCH-CCH: Before the RAB is released, an RRC connection uses the DCH. After

the RAB is released, an RRC connection uses the CCH;

Only the RAB release flow in the DCH-DCH scenario is described. The RAB release

flows in the other scenarios are similar.

Similar to the RAB establishment flow, on a radio interface, there are two scenarios for

the DCH-DCH RAB release:

57



UMTS Signaling Flow

1. Synchronous reconfiguration of radio links

2. Asynchronous reconfiguration of radio links

The RAB release flow of the DCH-DCH synchronous reconfiguration of radio links is

described

Figure 35 RAB Release (DCH-DCH, synchronomously)


1. The CN sends a RAB ASSIGNMENT REQUEST message (release) to start the

RAB release flow. The message indicates the ID of the RAB to be released.


the NodeB to request the NodeB to prepare for the releasing of the DCH carrying the

RAB.。

3. The NodeB sends a RADIO LINK RECONFIGURATION READY message to

the SRNC to notify the SRNC that the release preparations are complete.

58



Chapter 1 Overview

4. The SRNC sends a RADIO BEARER RELEASE message to the UE to start the

bearer release flow.


the NodeB.

6. The SRNC receives a RADIO BEARER RELEASE COMPLETE message from

the UE.

7. The RNC releases the data transport bearer on Iub interface.

8. The SRNC uses ALCAP. In case of AAL2 bearer, the SRNC sends an AAL2

release message to start releasing the Iu data transport bearer between the SRNC and

CN (This step is not needed for the PS domain).

9. The SRNC sends a RANAP RAB ASSIGNMENT RESPONSE to the CN. The

release flow is complete.

Note that, when the RNC user plane becomes abnormal, the RANAP sends a RAB

RELEASE REQUEST message to the CN to request the CN to release the affected

RAB.

RNC CN

RAB RELEASE REQUEST

Figure 36 RAB Release Request

5.4 Joint Release Flow of CS-Domain lu Signaling Connection andRAB

If only one service is created in the CS domain, when the service is released, the MSC

first sends an IU RELEASE COMMAND message to the RNC. Upon receiving the

message, the RNC releases the Iu signaling connection and RAB on Iu-CS interface at

the same time.

Joint Release Flow of CS-Domain lu Signaling Connection and RAB is shown in the

59



UMTS Signaling Flow

following figure.

UENodeB

ServingRNS

Serving

RNCCN

RRCRRC6.DCCH : RADIO BEARER RELEASE COMPLETE

NBAPNBAP

3.RADIO LINK RECONFIGURATIONREADY

NBAPNBAP

5.RADIO LINK RECONFIGURATIONCOMMIT

RRCRRC

DCCH

4:RADIO BEARER RELEASE

Apply new transport format set

7.ALCAPIubData Transport Bearer Release

RANAP RANAP1

NBAPNBAP

2 RADIO LINK RECONFIGURATIONPRPARE

[DCH Deletion]

RANAP RANAP9. IU RELEASE COMPLETE

8. ALCAPIu Data TransportBearer Release

UENodeB

ServingRNS

Serving

RNCCN

RRCRRC6.DCCH : RADIO BEARER RELEASE COMPLETE

NBAPNBAP

3.RADIO LINK RECONFIGURATIONREADY

NBAPNBAP

5.RADIO LINK RECONFIGURATIONCOMMIT

RRCRRC

DCCH

4:RADIO BEARER RELEASE

Apply new transport format set

7.ALCAPIubData Transport Bearer Release

RANAP RANAP1 IU RELEASE COMMAND

NBAPNBAP

2PRPARE

[DCH Deletion]

RANAP RANAP9.

8. ALCAPIu Data TransportBearer Release

Figure 37 Joint Release Flow of CS-Domain lu Signaling Connection and RAB

1. The CN sends an IU RELEASE COMMAND message the SRNC.


the NodeB to request the NodeB to prepare for the releasing of the DCH carrying the

RAB.

3. The NodeB sends a RADIO LINK RECONFIGURATION READY message to

the SRNC to notify the SRNC that the release preparations are complete.

4. The SRNC sends a RADIO BEARER RELEASE message to the UE to start the

bearer release flow.


the NodeB.

6. The SRNC receives a RADIO BEARER RELEASE COMPLETE message from

the UE.

60



Chapter 1 Overview

7. The RNC releases the data transport bearer on Iub interface.

8. The SRNC uses ALCAP. In case of AAL2 bearer, the SRNC sends an AAL2release message to start releasing the Iu data transport bearer between the SRNC and

CN.

9. The SRNC sends an IU RELEASE COMPLETE message the CN.

5.5 RRC Connection Release Flow

5.5.1 Overview

After the RAB is released, the SRNC determines whether any Iu signaling connection

borne by the same RRC exists in the system. If all the Iu signaling connections

corresponding to the UE are released, the RRC connection is released. To release an

RRC connection is to release the signaling links between the UE and UTRAN and all

the radio bearers. Through the RRC connection release flow, all the signaling

connections related to the UE are released on the radio interface.

Based on the resource consumption by the RRC connection, there are two types of

connection release: release of an RRC connection established on a dedicated channel

and release of an RRC connection established on a common channel.

An RRC connection can be released only when it is in the CELL_DCH or

CELL_FACH state. If the current RRC connection is in the CELL_PCH or URA_PCH

state, the UTRAN initiates paging to transition the UE state to CELL_FACH before

releasing the RRC connection.

Based on actual conditions, the RNC sends an RRC CONNECTION RELEASE

message in UM RLC mode on the downlink DCCH or CCCH.

If the DCCH is available during the RRC connection release, the UTRAN sends an

RRC CONNECTION RELEASE message through the downlink DCCH. Otherwise,

the UTRAN sends an RRC CONNECTION RELEASE message through the downlink

CCCH.

5.5.2 Releasing an RRC Connection Established on a Special Channel

The signaling flow of RRC Connection Release Set up on Special Channels is shown

in the following figure.

61



UMTS Signaling Flow

Figure 38 RRC Connection Release (Special Channel)

Description of signaling flow:

1. The SRNC sends an RRC CONNECTION RELEASE message to the UE through

the DCCH. The SRNC may sends the message for several times to ensure that the UE

receives the message.

2. The UE returns an RRC CONNECTION RELEASE COMPLETE message to the

SRNC.

3. The SRNC sends a RADIO LINK DELETION REQUEST message to NodeB to

delete the radio link resources in NodeB.

4. When the resources in the NodeB are deleted, NodeB returns a RADIO LINK

DELETION RESPONSE message to the SRNC.

5. The RNC uses ALCAP to initiate the releasing of the user plane transport bearer

on Iub interface.The RRC connection release flow is complete.

5.5.3 Releasing an RRC Connection Established on a Common Channel

The signaling flow of Releasing an RRC Connection Established on a Common

Channel is shown in the following figure.

62



Chapter 1 Overview

UE SRNCNodeB

RRCCONNECTIONRELEASE

RRCRRC

Figure 39 RRC Connection Release (Public Channel)

The SRNC sends an RRC CONNECTION RELEASE message through the CCCH to

the UE to initiate the RRC connection release flow, and the UE releases the resources.

When an RRC connection established on the common channel is released, no RRC

CONNECTION RELEASE COMPLETE message is sent. In addition, because cell

common resources are used, only the UE needs to be released directly and there is no

need to release NodeB resources and data transport bearer.

Description：

The UTRAN may send the RRC CONNECTION RELEASE message for several times

to ensure that the UE receives the message correctly. The RRC SN values of thesemessages are the same. The number of message retransfers and transfer interval are

controlled by the network.

3-UMTS Signaling Flow 71p.doc

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