Umts signal flow

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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 ................................................................................................................. 21
3.1 Handover Overview ........................................................................................................................ 21
3.2 Soft Handover ................................................................................................................................. 22
3.2.1 Between Cells in NodeB ...................................................................................................... 24
3.2.2 Between NodeBs in the Same RNC..................................................................................... 24
3.2.3 Between RNCs..................................................................................................................... 25
3.3 Hard Handover................................................................................................................................ 26

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3.3.1 Inter-Frequency Hard Handover under the Same RNC ........................................................28
3.3.2 Inter-RNC Hard Handover under the same MSC .................................................................28
3.4 Inter-Systems Handover ..................................................................................................................29
3.4.1 Handover Between CS Domain Systems..............................................................................31
3.4.2 Handover Between PS Domain Systems ..............................................................................32
3.5 Forward Handover...........................................................................................................................34
4 Call Service Flow ......................................................................................................................................37
4.1 Overview .........................................................................................................................................37
4.2 Paging Flow.....................................................................................................................................37
4.2.1 Paging the UE in Idle Mode or PCH State............................................................................38
4.2.2 Paging the UE in CELL_DCH or CELL_FACH State .........................................................39
4.2.3 Examples of Paging Flow.....................................................................................................40
4.3 RRC Connection Establishment Flow.............................................................................................40
4.3.1 RRC Connection Establishment on Special Channles..........................................................41
4.3.2 Setting up RRC Connection on a Public Channel.................................................................42
4.3.3 RRC Connection Rejection...................................................................................................43
4.4 Direct Transfer Message Flow.........................................................................................................44
4.4.1 Initial Direct Transfer ...........................................................................................................44
4.4.2 Uplink Direct Transfer..........................................................................................................46
4.4.3 Downlink Direct Transfer.....................................................................................................47
4.5 UE Capability Information Flow.....................................................................................................47
4.5.1 UE Capability Information Query ........................................................................................48
4.5.2 UE Capability Information Update.......................................................................................49
4.6 RAB Establishment Flow ................................................................................................................49
4.6.1 DCH-DCH............................................................................................................................50
4.6.2 CCH-DCH ............................................................................................................................54

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4.6.3 CCH-CCH............................................................................................................................ 55
5 Service Release Flow................................................................................................................................ 57
5.1 Overview......................................................................................................................................... 57
5.2 Iu Signaling Connection Release Flow........................................................................................... 58
5.2.1 Signaling Connection Release Request................................................................................ 58
5.2.2 Signaling Connection Release.............................................................................................. 58
5.3 RAB Release Flow.......................................................................................................................... 59
5.4 Joint Release Flow of CS-Domain lu Signaling Connection and RAB .......................................... 61
5.5 RRC Connection Release Flow....................................................................................................... 63
5.5.1 Overview.............................................................................................................................. 63
5.5.2 Releasing an RRC Connection Established on a Special Channel....................................... 63
5.5.3 Releasing an RRC Connection Established on a Common Channel.................................... 64

1
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.

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

UMTS Signaling Flow
4
connection on the Iu interface and the RRC connection, are released.
The previously described two flows mainly describe in general how to make services in
the 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.

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
6
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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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 to
initiate 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

UMTS Signaling Flow
8
channel of the cell where the UE is located.
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

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and downlink traffic). In TDD mode, however, DCH and DSCH or USCH may be
mapped to different CCTrCHs, with their respective TFCIs completely independent.
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

UMTS Signaling Flow
10
reconfiguration)
2. Transition from the CELL_FACH state to the CELL_PCH state
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.

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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
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 FACH
without 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,

UMTS Signaling Flow
12
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
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. To
transport 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

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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)
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. 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

UMTS Signaling Flow
14
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.
4. UE measurement (URA_PCH)
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.

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.
PLMNSelection
andReselection
Location
Registration
PLMNs
available
PLMN
selected
Location
Registration
response
Registration
Area
changes
Indication
touser
User selection
of PLMN
Automatic/
Manual selection
CMrequests
NASControl
Radio measurements
Cell Selection
andReselection
Figure 3 Idle Mode Process
15

UMTS Signaling Flow
16
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

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

UMTS Signaling Flow
18
2. Reading the broadcast channel
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 performs
calculations 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

19
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
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.

21
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.
2. Monitor set: Cells not in the active set but monitored according to the adjacent

UMTS Signaling Flow
22
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

23
handover means the merging of uplinks is performed at NodeB.
During a softer handover, a mobile station is located where the coverage of two
adjacent 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.

UMTS Signaling Flow
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
24

Soft Handover Flow Between NodeBs in the Same RNC
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
25

UMTS Signaling Flow
Soft Handover Between RNCs in the Same MSC uses the Iur interface:
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.
26

27
Hard handovers correspond to Iub interface operations and Uu interface operations. Iub
interface operations correspond to radio link reconfiguration. Uu interface operations
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.

UMTS Signaling Flow
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
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.
28

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 the
systems 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
29

UMTS Signaling Flow
30
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 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
31
SRNCNODE 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
Figure 12 UTRAN⇒ GSM/BSS Handover

UMTS Signaling Flow
SRNCNODE BUE
HANDOVER TO UTRAN COMPLETE
CN
RELOCATION REQUEST
BSC
HANDOVER COMMAND
CLEAR COMMAND
HANDOVER REQUIRD
RELOCATION REQUEST ACK
RADIO LINK SETUP REQUEST
RADIO LINK SETUP RESPONSE
HANDOVER TO UTRAN COMMAND
RADIO LINK RESTORE INDICATION
RELOCATION DETECT
RELOCATION COMPLETE
CLEAR COMPLETE
Figure 13 GSM/BSS to the UTRAN Handover
3.4.2 Handover Between PS Domain Systems
32

SRNSBSSU E
2G
SG SN
new MS /
VLR
3 G
SGSN
Intersystem change decision
Routeing Area Update
SRNS Context Request
SRNS Context Response
SRNS Data Forward Com mand
Forward Packets
Iu Release Command
Iu Release Com plete
Location Update Accept
Location Update Request
Routeing Area Update
Routeing Area Update Complete
TMSI Reallocation
SGSN Context Request
SGSN Context Acknowledge
SGSN Context Response
Forward Packets
Figure 14 UMTS to GPRS Cell Reselection, the UE Initiated
33

UMTS Signaling Flow
SRNCNODE BUE
HANDOVER TO UTRAN COMPLETE
CN
RELOCATION REQUEST
BSC
HANDOVER COMMAND
CLEAR COMMAND
HANDOVER REQUIRD
RELOCATION REQUEST ACK
HANDOVER TO UTRAN COMMAND
RADIO LINK RESTORE INDICATION
RELOCATION DETECT
RELOCATION COMPLETE
CLEAR COMPLETE
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 the
common 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
34

(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).
Figure 16 Cell Update with SRNS Relocation
35

UMTS Signaling Flow
Figure 17 Cell Update via Iur without SRNS Relocation
Figure 18 Cell Update (core network)
36

37
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

UMTS Signaling Flow
38
DCCH channel of the existing connection on the radio interface. If the UE has any
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, when
the 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.

UE UTRAN
PAGING TYPE 1
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
39

UMTS Signaling Flow
40
non-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
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
6. CCCH
NodeB
NBAP
RRCRRC
RRCRRC
1.CCCH：: RRC CONNECTION REQUEST
RRCRRC
NBAP NBAP
7.DCCH: RRC CONNECTION SETUP COMPLETE
3. RADIO LINK SETUP REQUEST
4. RADIO LINK SETUP RESPONSE
2.Allocate parameters
such asRNTI、L1、
L2
5.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
41

UMTS Signaling Flow
42
resources and other resources (L1 and L2 resources).
3. The RNC sends the NodeB the RADIO LINK SETUP REQUEST to request the
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
4.CCCH
NodeB
RRCRRC
RRCRRC
1.CCCH: RRC CONNECTION REQUEST
RRCRRC
5.DCCH: RRC CONNECTION SETUP COMPLETE
2.Allocate parameters
such as RNTI、L1、
L2
: :RRC CONNECTION SETUP
3.Map the logical channels
used by UE to the common
channels
Figure 22 RRC Connection Setup (Public Channel)
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
43

UMTS Signaling Flow
44
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
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 TRANSFER
RRCRRC
RANAP
2.INITIAL UEMESSAGE
RANAP
SCCP SCCP
3.CONNECITONCONFIRM（SUCCESS）
4.CONNECTIONREFUSE（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
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 to
fail, 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.
45

UMTS Signaling Flow
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. UPLINKDIRECT TRANSFER
RRCRRC
RANAP
2.DIRECT TRANSFER
RANAP
Figure 25 Uplink Direct Transfer
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.
46

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.
UE CNSRNC
2. DOWNLINK DIRECT TRANSFER
RRCRRC
RANAP
1.DIRECT TRANSFER
RANAP
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.
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
47

UMTS Signaling Flow
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 is
transferred 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.
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.
48

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.
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
49

UMTS Signaling Flow
50
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).
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 the
synchronization 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
6.
NodeB
NBAP
RRCRRC
RRCRRC
NBAP NBAP
8.RADIO BEARER SETUP COMPLETE
3. RADIO LINK RECONFIGURATION
PREPARE (Synchronised)
READY (Synchronised)
RADIO BEARER SETUP
CN
RANAPRANAP
1. RAB ASSIGNMENT REQUEST
2.ALCAP setup
RANAPRANAP
9. RAB ASSIGNMENT RESPONSE
NBAP NBAP
COMMIT (Synchronised)
Figure 29 RAB Setup Flow (DCH-DCH, synchronously)
The signaling flow is described as follows:
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
51

UMTS Signaling Flow
52
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
described as follows.

UE SRNC
NBAP
6.
NodeB
NBAP
RRCRRC
RRCRRC
NBAP NBAP
7. RADIOBEARERSETUPCOMPLETE
3. RADIOLINKRECONFIGURATION
REQUEST
4. RADIOLINKRECONFIGURATION
RESPONSE
5.ALCAPSetup and synchronization
RADIOBEARERSETUP
CN
RANAPRANAP
1. RABASSIGNMENTREQUEST
2.ALCAPsetup
RANAPRANAP
8. RABASSIGNMENTRESPONSE
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
belongs, notifying the SRNC that the radio link reconfiguration is complete.
53

UMTS Signaling Flow
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
6.
NodeB
NBAP
RRCRRC
RRCRRC
NBAP NBAP
7. RADIO BEARER SETUP COMPLETE
3.
4.
RADIO BEARER SETUP
CN
RANAPRANAP
1. RABASSIGNMENT REQUEST
2. ALCAP setup
RANAPRANAP
8. RAB ASSIGNMENT RESPONSE
Figure 31 RAB Setup Flow (CCH-DCH)
54

55
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.

UMTS Signaling Flow
UE SRNC
3.
NodeB
RRCRRC
RRCRRC
4.RADIO BEARER SETUP COMPLETE
RADIO BEARER SETUP
CN
RANAPRANAP
1. RAB ASSIGNMENT REQUEST
2.ALCAPsetup
RANAPRANAP
5.RAB ASSIGNMENT RESPONSE
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.
56

57
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.
If multiple RABs are established in PS domain, the CN initiates the RAB release

UMTS Signaling Flow
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.
58

RNC CN
1.IU RELEASE COMMAND
2.IU 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:
59

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
UE
NodeB
ServingRNS
Serving
RNC
CN
RRCRRC
6.DCCH: RADIO BEARERRELEASE COMPLETE
NBAPNBAP
3.RADIO LINK RECONFIGURATION
READY
NBAPNBAP
COMMIT
RRCRRC
DCCH
4:RADIO BEARERRELEASE
Apply new transport format set
7.ALCAPIubData Transport Bearer Release
RANAP RANAP
1 RAB ASSIGNMENT REQUEST
[Release]
NBAPNBAP
2RADIOLINK RECONFIGURATION
PRPARE
[DCHDeletion]
RANAP RANAP
8. ALCAP IuData TransportBearer Release
not required towards PSdomain
UE
NodeB
ServingRNS
Serving
RNC
CN
RRCRRC
6.DCCH: RADIO BEARERRELEASE COMPLETE
NBAPNBAP
READY
NBAPNBAP
COMMIT
RRCRRC
DCCH
4:RADIO BEARERRELEASE
7.ALCAPIubData Transport Bearer Release
RANAP RANAP
1 RAB ASSIGNMENT REQUEST
[Release]
NBAPNBAP
2RADIOLINK RECONFIGURATION
PRPARE
[DCHDeletion]
RANAP RANAP
8. ALCAP IuData TransportBearer Release
not required towards PSdomain
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.
4. The SRNC sends a RADIO BEARER RELEASE message to the UE to start the
60

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 and
RAB
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
following figure.
61

UMTS Signaling Flow
UE
NodeB
Serving RNS
Serving
RNC
CN
RRCRRC
6.DCCH : RADIO BEARER RELEASE COMPLETE
NBAPNBAP
READY
NBAPNBAP
COMMIT
RRCRRC
DCCH
4:RADIO BEARER RELEASE
7.ALCAP Iub Data Transport Bearer Release
RANAP RANAP
1
NBAPNBAP
2 RADIO LINK RECONFIGURATION
PRPARE
[DCH Deletion]
RANAP RANAP
9. IU RELEASE COMPLETE
8. ALCAP Iu Data TransportBearer Release
UE
NodeB
Serving RNS
Serving
RNC
CN
RRCRRC
6.DCCH : RADIO BEARER RELEASE COMPLETE
NBAPNBAP
READY
NBAPNBAP
COMMIT
RRCRRC
DCCH
4:RADIO BEARER RELEASE
7.ALCAP Iub Data Transport Bearer Release
RANAP RANAP
1 IU RELEASE COMMAND
NBAPNBAP
2
PRPARE
[DCH Deletion]
RANAP RANAP
9.
8. ALCAP Iu 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.
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
62

63
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.

UMTS Signaling Flow
UE SRNCNodeB
NBAPNBAP
NBAPNBAP
1.RRC CONNECTION RELEASE
3. RADIO LINK DELETION REQUEST
RRCRRC
2.RRC CONNECTION RELEASE COMPLETE
RRCRRC
4. RADIO LINK DELETION RESPONSE
5.ALCAP Release
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.
64

UE SRNCNodeB
RRC CONNECTION RELEASE
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 these
messages are the same. The number of message retransfers and transfer interval are
controlled by the network.
65

Umts signal flow

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Umts signal flow