LAC planning

1. Location, Routing, Service and
UTRAN Area Planning Aspects in
WCDMA
Version: Draft

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Revision History
Version Date Change Notes
0.1 10/08/2010 Draft version
Authors
The following persons have collaborated on this document:
Name Department
Pavel Romanenko NWS LTE RA E2E SA NE

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Contents
1. Introduction............................................................................4
2. Concept of LA, RA and URA areas in UMTS .........................5
2.1. General Induction ..........................................................................................5
2.2. Location area definition.................................................................................6
2.3. Routing area definition ..................................................................................7
2.4. UTRAN registration area definition ..............................................................9
2.5. LAC, RAC and SAC definition ....................................................................15
2.6. Relationship between the different areas..................................................17
2.7. Paging...........................................................................................................19
2.8.1. RANAP paging.............................................................................................20
2.8.2. Paging type 1 ...............................................................................................21
2.8.3. Paging type 2 ...............................................................................................23
2.8. Location area update and routing area update.........................................24
2.9.1. Location and routing areas update ............................................................25
2.9.2. Routing area update....................................................................................30
2.9.3. Combined updates.......................................................................................31
2.10. Summary of mobility management ............................................................31
3. Practical guide for UMTS LA, RA and URA areas Planning
and Optimization..................................................................33
3.1. Location and Routing Areas Planning and Optimization .........................33
3.2. Service Area Planning and Optimization...................................................42
3.3. UTRAN radio Area Planning and Optimization.........................................43

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1. Introduction
The main task of this document is to provide description in detail of
Location Area (LA), Routing Area (RA) and UTRAN registration area (URA)
planning.
The document audience is NSN internal employers, interested in Network
Planning, Initial Tuning and Optimisation.
The document operates and by theoretical foundations, dimensioning
simulations results and by practical cases and examples. The document
presents related parameters policy, collected from different projects shared
experience.
The concept of planned LA size is dependant on many factors, including
with NW size and load. But, the approached understanding of areas zones
planning is coming from general zones definitions that provided in chapter 2.
Chapter 2 summarizes the purpose of Mobility Management (MM) and
defines the Location and Routing Area.
The chapter 2 explains theory aspects of three WCDMA areas, their
interdependencies between each other and paging, and will give general
concepts of their planning.
The practical approach of three area concept planning depends on
current NW case, and sampled in chapter 3 of current document.
In many cased UMTS zones area parameterization is part of not initial tuning
and planning, but optimization phase, required after NW implementation and
loading.
The document is actual for most of cases in RU (Releases from RAS06 to
RU20,) and in I-HSPA Rel.2, just some RU20 and I-HSPA features potentials
are not included to practical chapter in the reason of lack of practical output’s
availability from them.

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2. Concept of LA, RA and URA areas in
UMTS
2.1. General Induction
3GPP definition
A UMTS network consists of three interacting domains:
• Core Network (CN)
• UMTS Terrestrial Radio Access Network (UTRAN)
• User Equipment (UE)
The main function of the core network is to provide switching, routing and
transit for user traffic. Core network also contains the databases and
network management functions.
The basic Core Network architecture for UMTS is based on GSM network
with GPRS. All equipment has to be modified for UMTS operation and
services. The UTRAN provides the air interface access method for User
Equipment. Base Station is referred as Node-B and control equipment for
Node-B's is called Radio Network Controller (RNC). UMTS system page
has an example, how UMTS network could be build.
It is necessary for a network to know the approximate location in order to
be able to page user equipment. Here is the list of system areas from
largest to smallest.
• UMTS systems (including satellite)
• Public Land Mobile Network (PLMN)
• MSC/VLR or SGSN
• Location Area
• Routing Area (PS domain)
• UTRAN Registration Area (PS domain)
• Cell
• Sub cell
Definitions of LA, RA and URA areas are tightly connected with basic UMTS
network structure, and intended both in Core and Radio Network Planning.
UMTS network domains interconnection visually effects on UE states and is
necessary for keeping in mind before making planning in any NW element.
The Core Network (CN) logical structure consists of two services domains:
Circuit-switched (CS) service domain
Packet-switched (PS) service domain.
For the first approach of possible UE states within different domains, the
figure below gives an overview of the UE registration and connection principles
within the UMTS, when the CN consists of separate PS and CS service nodes
or one combined CS and PS service node.

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Important note is that 3G-MSC and 3G-SGSN sub domains may be physically
co-located at one territory site.
Figure 2.1.UE registration and connection set-up for 3G-MSC and 3G-SGSN
2.2. Location area definition
3GPP definition
Location Areas (LA) is used to inform the core network of a UE’s location for CS
services.
A "Location Area" is a set of base stations that are grouped together to optimize
signaling. Typically, tens or even hundreds of base stations share a single Radio
Network Controller (RNC) in UMTS, the intelligence behind the base stations.
RNC handles allocation of radio channels, receives measurements from the
mobile phones, and controls handovers from base station to base station,
included to LA.
To each Location Area, a unique number called a "Location Area Code" is

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assigned. The location area code is broadcast by each base station, known as
Node B in UMTS, at regular intervals.
In UMTS NW structure, a location area is defined as a cluster of cells. The
cells are typically adjacent between each others.
For CS services, the whole network is divided into location areas. For
example, location area is used at CN initiated paging related to CS services. A
CS service related temporary identity might be assigned to the UE. This
temporary identity is then unique within a LA. A location area consists at
minimum of one cell and at maximum of the entire VLR area.
In UMTS, some operators define location areas equal to RNC or even MSC
areas, but this is not mandatory, the total LA planning is more complex.
The optimal size of a location area in terms of cells is limited by the LA
update load on one side and on the paging load on the other side. A small
location area will require less signaling load for paging on RNC and MSC, but
high load for LA updates in RNC and MSC. A large location area will result in a
high paging load for the RNC and MSC, but low load for LA updates will appear
in the BSC/RNC and the MSC. This leads to a typical optimization problem.
2.3. Routing area definition
3GPP definition
Routing Area (RA) is used to inform the core network of a UE’s location for PS
services.
The Routing Area is the PS domain equivalent of the location area. A "routing
area" is normally a subdivision of a "location area". Routing areas are used by
mobiles which are GPRS-attached. GPRS ("General Packet Radio Services")
new data transmission technology is optimized for "bursty" data communication
services, such as wireless internet/intranet, and multimedia services. It is also
known as IP ("Internet Protocol") because it will connect users directly to
Internet Service Providers (ISP).
The bursty nature of packet traffic means that more paging messages are
expected per mobile, and so it is worth knowing the location of the mobile more
accurately than it would be with traditional circuit-switched traffic. A change from
routing area to routing area (called a "Routing Area Update") is done in an
almost identical way to a change from location area to location area. The main
differences are that the "Serving GPRS Support Node" (SGSN) is the element
involved.
CN uses routing areas (RA) for PS services. The routing area is used at CN
initiated paging related to PS services. A PS service related temporary identity
might be allocated to the UE. This temporary identity is then unique within a RA.

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The same as LA, routing area is defined as a cluster of cells. The cells are
typically adjacent because the target is to maximize the dwelling time within one
routing area (which implicitly prevents a large number of routing area updates).
Routing areas are used for the packet switched part of the network to localize
the subscriber. Routing area consists of at minimum one cell and at maximum of
the entire location area. More than one routing area can be defined per location
area.
Minimum and maximum values in terms of number of cells are limited by
paging results in signaling load on RNC and SGSN on the one side. On the
other side the routing area update load of the SGSN limits the number of cells,
i.e. the size of a routing area.
In the packet oriented (PO) domain the change of a UE from one cell to
another can initiate two different types of ‘handover’ (either one of it or both) in
the CN (Core Network): a RAU (Routing Area Update) or SRNS relocation.
Routing Area Update
For inter-system changes, routing area changes inside GPRS, routing area
changes inside UMTS in UMTS PMM idle state and after SRNS relocation with
routing area change in UMTS PMM connected state. In the last case only a
subset of the routing area update procedure will be executed to update the HLR.
SRNS Relocation
In UMTS PMM connected state. Execution decided by UTRAN. After SRNS
relocation, a RAU in PMM connected state is triggered in order to update the
location towards HLR if the routing area has been changed.
In principle, the handover handling of the 3G SGSN has the same function as
in the 2G SGSN to provide a smooth service in case of roaming. There are
some differences, which results from the Iu interface and from the used
handover strategy in UMTS.
In GPRS the MS decides by itself to perform a cell change without interaction
to the BSS. This is valid especially for a change between cells of two BSS. The
SGSN takes care of undelivered or duplicated user packets. Different to that, in
UMTS the UTRAN will be responsible for the decision of a cell respectively RNC
change if the UE will be in the PMM connected state. The UTRAN may decide to
change the point of attach to the core network (SGSN) at any time which leads
to an RNC relocation.
The above-mentioned RNC relocation takes place only if an established radio
access bearer exists (UMTS PMM connected state). Otherwise (UMTS PMM
idle state) a normal routing area update will be done which may lead to an
SGSN change similar to that in the 2G SGSN.
Routing area update in UMTS PMM connected will follow the relocation
procedure if the RA was changed.

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2.4. UTRAN registration area definition
3GPP definition
“UTRAN registration area" is defined as an area, covered by a number of cells,
known internally only in UTRAN to provide a layer of abstraction between cells
and the routing area.
URA contains one or more cells and a routing area contains one or more URA.
The URA is used to track the location of an UE within UTRAN. URA is uniquely
identified using the URA Identity parameter.
Upon reception of RRC message UTRAN Cell Update or UTRAN Registration
Area Update from a UE the drift RNS inserts necessary information received in
the RRC message to the CELL/URA UPDATE INDICATION message and
sends the message to the serving RNS.
The location of the UE is known by UTRAN Registration Area level according
to last RA update. Some examples with URA state are provided below
First figure shows the RRC states in UTRAN RC Connected Mode, including
transitions between UTRAN RRC connected mode and GSM connected mode
for CS domain services, and between UTRA RRC connected mode and
GSM/GPRS packet modes for PS domain services. It also shows the transitions
between Idle Mode and UTRAN RRC Connected Mode and furthermore the
transitions within UTRAN RRC connected mode.
Figure 2.2 RRC States and State Transitions including GSM

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CELL_DCH state is characterized by:
a dedicated physical channel is allocated to the UE in uplink and downlink
the UE is known on cell level according to its current active set
dedicated transport channels, downlink and uplink (TDD) shared transport
channels, and a combination of these transport channels can be used by the UE
CELL_FACH state is characterized by:
No dedicated physical channel is allocated to the UE.
The UE continuously monitors a FACH in the downlink.
the UE is assigned a default common or shared transport channel in the
uplink (e.g. FACH) that it can use anytime according to the access procedure
for that transport channel
the position of the UE is known by UTRAN on cell level according to the cell
where the UE last made a cell update
in TDD mode, one or several USCH or DSCH transport channels may have
been established
CELL_PCH state is characterized by:
no dedicated physical channel is allocated to the UE
the UE selects a PCH with the algorithm, and uses DRX for monitoring the
selected PCH via an associated PICH
no uplink activity is possible
the position of the UE is known by UTRAN on cell level according to the cell
where the UE last made a cell update in CELL_FACH state
URA_PCH State is characterized by:
no dedicated channel is allocated to the UE
the UE selects a PCH with the algorithm, and uses DRX for monitoring the
selected PCH via an associated PICH
no uplink activity is possible
the location of the UE is known on UTRAN Registration area level according
to the URA assigned to the UE during the last URA update in CELL_FACH
state
The next example is Cell reselection procedure:

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Figure 2.3 States and procedures in the cell reselection process in connected
mode
When a cell reselection is triggered, the UE evaluates the cell reselection
criteria based on radio measurements, and if a better cell is found that cell is
selected, procedure Cell reselection. If the change of cell implies a change of
radio access technology, the RRC connection is released, and the UE enters
idle mode of the other RAT. If no suitable cell is found in the cell reselection
procedure, the UE eventually enters idle mode.
When an Initial cell reselection is triggered, the UE shall use the Initial cell
reselection procedure to find a suitable cell. One example where this procedure
is triggered is at radio link failure, where the UE may trigger an initial cell
reselection in order to request re-establishment of the RRC connection. If the
UE is unable to find a suitable cell, the UE eventually enters idle mode.
The URAs can be overlapping or even hierarchical. The same cell may
belong to several different URAs, and the UEs in that cell may have been
registered to different URAs. SIB 2 contains a list of URA identities indicating
which URAs this cell belongs to. This arrangement is done to further reduce the
amount of location update signaling because now the UEs moving back and
forth in the boundary area of two URAs do not have to update their URA location
information if the boundary cells do belong to both URAs.

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Figure 2.4 Overlapping UTRAN Registration Areas
The figure above illustrates a definition of three overlapping URAs with the
primary and the secondary URA IDs given for each cell:
• URA1 includes the cells A, B, D, E, F, G, H and I
• URA2 includes the cells B, C, F, G, I and J
• Cells F, G and I are URA2 cells, which overlap on URA1 (ID of the
secondary URA defined as URA1)
• Cell B is the URA1-cell overlapping on URA2, etc.
When the UE performs an URA Update through the cell D, the URA identity
of URA1 is assigned to this UE (the UE is registered on URA1). If the UE is
paged, the paging procedure must be executed, not only through the cells with
the Primary URA-ID defined as URA1, but also through the overlapping
(Secondary URA-ID) URA2-cells (F, G and I).
If the UE moves from URA1 to URA2 via the cells F and G (route:
D=>E=>F=>G), the RRC:URA Update procedure is not initiated since the URA
identity of URA1 is broadcast in these URA2-cells and the UE stays registered
on URA1.
When the UE registered on URA2 moves to the opposite direction (route:
G=>F=>E=>D), the URA Update is initiated when the UE selects the Cell E and
the RNC registers the UE on URA1.

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With Radio Network Planning of the URAs the following issues are possible:
URA can cover geographical areas e.g. highways planned to be in same
URA.
URA is typically including several Cells, but smaller than Location /
Routing Area.
One cell can belong to several URAs.
URA may overlap (geographically) and for that purpose up to 8 URA
identities can be broadcasted in one cell.
UE in URA_PCH state has always only one valid URA, which is the
primary URA of the cell (which UE has entered URA_PCH state, or in
which the UE has initiated the last URA Update procedure).
UE does not initiate URA Update procedure in the cells where the
assigned
URA is included in the URA-list.
When defining overlapping URAs it should be noted the UEs will be
paged via all cells on these URAs, and this may notably increase the
paging load in
UTRAN (reduction of Cell Update signaling and the impact caused to the
paging-load must be kept in balance).
Activating URA_PCH RRC state feature, gives following benefits to operator:
high Mobility UE’s (which are moving fast)
URA_PCH state is used instead of the Cell_PCH for the “high mobility”
UE
amount of cell updates decreased
three times longer UE stand-by time with NSN WCDMA RAN
better UE battery performance with always-on applications
with Cell_PCH/URA_PCH implemented, a short activation timer can be
used in Cell_FACH state while maintaining good browsing experience
keep-alive sent over Cell_FACH, state transition to Cell_DCH avoided
small signaling messages could be transferred via RACH/FACH
without dedicated radio / Iub resource allocation
URA_PCH RRC Connected Mode was innovated by URA_PCH (RAN833)
feature (introduced in NSN from RU 10). That feature makes Reduction of
RACH signaling load and UE power consumption.
Thanks to feature signaling load caused by the cell updates can be reduced
when the fast moving UEs are transferred to the URA_PCH state.
Starting from RU 10 NSN implementation supports all states within RRC
connected mode. URA_PCH helps to reduce the signaling load by reducing the
requirement for cell update procedures resulting from UE mobility. UE are
moved from CELL_PCH to URA_PCH if they complete more than a specific
number of cell re-selections within a specific time interval. Benefiting from
URA_PCH requires the radio network planner to define UTRAN Registration

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Areas (URA) in addition to Location Areas and Routing Areas. The drawback of
using URA_PCH is a slightly increased paging load, i.e. paging messages are
broadcast across URA rather than across individual cells. URA can be defined
to overlap with one another to avoid ping-pong scenarios for UE. A single cell
can belong to a maximum of 8 URA. The first URA listed within SIB2 represents
the primary URA while the remaining URA represent secondary URA. The
primary URA is selected when a UE first enters URA_PCH and also subsequent
to a cell update procedure. The UE only needs to complete a cell update
procedure if the selected URA does not appear within the list of URA within
SIB2.
In URA_PCH state the location of the UE is known by the URA level. There is
no dedicated channel allocated for the UE in URA_PCH state. The mobility in
this state is handled by RRC in URA Update procedure. In this state the UE
uses discontinuous reception (DRX) and monitors paging messages from RNC.
If the network wants to initiate any downlink activity, it needs to make a paging
request in all cells on the PCCH logical channel within the URA where the
location of the UE is known. Any Activity causes the UE to be transferred to the
Cell_FACH state, where the uplink access is performed on RACH.
In URA_PCH state, the UE:
listens to the PCH transport channel for the decoding of paging and
notification messages sent by the RAN,
listens to the BCH transport channel of the serving cell for the decoding
of system information messages,
initiates a URA updating procedure on URA change,
initiates a periodic URA update after timer T305 has expired in UE (if
configured),
initiates a Cell Update in case of paging response (via FACH state)
initiates a Cell Update in case of UL data transmission (If the UE needs to
transmit anything to the RNC, it moves to the Cell_FACH state and
executes a RRC: Cell Update procedure)
Summarized, comparing between CELL_PCH and URA_PCH is:
CELL_PCH alone minimizes paging load but causes more cell updates
than URA_PCH
URA_PCH alone causes very high paging load if URA = RNC area and
provide paging channel capacity approx 400/s
if URA is smaller than RCN area, then separate planning is needed for
URA
the optimal solution combines CELL_PCH + URA_PCH to minimize
paging and cell update load; URA_PCH alone is not a good solution
without Cell_PCH

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NSN solution:
both Cell PCH and URA PCH are supported
NSN RNC can detect if UE is moving and keep that UE in URA PCH
2.5. LAC, RAC and SAC definition
The routing area code (RAC) combines an integer value between 0 and 255
defined inside a LA.
The routing area identity (RAI), defined by an operator, identifies one or
several cells.
RAI is broadcast as system information and is used by the UE to determine,
when changing cell, if an RA border was crossed. If that is the case, the UE
initiates the RA update procedure.
A routing area is a subset of one, and only one, location area (LA), meaning
that a RA cannot span more than one LA. A RA is served by only one SGSN.
The following rules apply for the Routing Area Identity (RAI):
RAC is only unique when presented together with LAC
RAI is only unique when presented together with LAI
LAI = MCC + MNC + LAC
RAI = MCC + MNC + LAC + RAC
Where, “MCC + MNC” is the PLMN identity.
In order to respect the functional separation of core network and radio
network and to confine the radio (and thus cell coverage) aspects within
UTRAN, 3GPP WG RAN3 has not introduced the concept of UMTS Cell or
UMTS Cell Global Identity over Iu.
Instead of this, the concept of Service Area (SA) has been introduced. Such a
Service Area can be mapped onto one or more “cells” within a location area.
This mapping onto cells, however, is invisible to core network and will be
handled within UTRAN. A cell is allowed to belong to more than one service
area.
A Service Area Identifier (SAI) is described by following main rules:
SAI = MCC + MNC + LAC + SAC
The Service Area Code (SAC) has a length of two octets and is unique
within the location area
The other codes denote the Mobile Country Code (MCC), the Mobile
Network Code (MNC), and the Location Area Code (LAC)
The service area can be configured in the way that it matches the cell for
service information broadcast.
Release 99 requires that for the broadcast (BC) domain the service area
matches one cell. For the CS and PS domain, the service area can consist of

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more than one cell, e.g. cover the cells of one base station or more base
stations.
Practically, Service Areas are used for emergency calls location based
services and the Service Area Broadcast (SAB) feature which makes use of a
third S-CCPCH and Service Area Codes for SAB (SACB).
This system feature specification defines upper layer coordination for the
Service Area Broadcast. WCDMA Service Area Broadcast (SAB) service
corresponds to the SMS Cell Broadcast service defined for the GSM. Since cells
are not known by the CN, service area definition is used instead. The new
terminology has not changed the functionality of the service. As in 2G based
documents the term "Cell Broadcast" is still widely used, the terms "Service
Area Broadcast" and "Cell Broadcast" can be understood as synonyms so far.
The Cell Broadcast Service (CBS) is a service, which enables a provider of
information to submit short messages for broadcasting to a specified area within
the PLMN. These messages could be used for informing of, for example, PLMN
news, emergencies, traffic reports, road accidents, delayed trains, weather
reports, theatre programs, telephone numbers or tariffs.
CBS permits a number of unacknowledged general CBS messages to be
broadcast to all receivers within a particular region. CBS messages are
broadcast to defined geographical areas known as Service Area. Service Area
will consist of one cell. CBS messages originate from the Cell Broadcast Center
and Radio Network Controller can interface to one or more Cell Broadcast
Center.
The cell broadcast architecture in UMTS:
The basic network structure in the RAN is containing the RNC and
BTS.
The Cell Broadcast Center (CBC) is part of the core network and
connected via lu.
Service Area Broadcast Protocol (SABP) is used between the CBC
and RNC for CBS message transferring.
Broadcast/Multicast Control protocol is used between the RNC and MS
for the message broadcasting on the radio interface.
Architecture for the Cell Broadcast Service is given in Figure 2.5.
Uu
Cell
Broadcast
Center
(CBC)
RAN
RNC
BTS
BTSMS
MS
Iub
IuBC
Figure 2.5 Architecture for the Cell Broadcast Service in UMTS

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Broadcast messages which are transmitted by the RNC to the MS include two
types of messages: BMC CBS Message which contains user information and
BMC Schedule Message which contains scheduling of the BMC CBS messages.
BMC Schedule messages will be used to implement DRX function for the Cell
Broadcast Service and will be generated by the RNC.
The distribution of broadcast information relates on the mapping between
service area and cell will be controlled by the RNC. The provision of this
mapping information is an O&M function.
2.6. Relationship between the different areas
3GPP definition
• A RA consists of a number of cells belonging to RNC that are
connected to the same CN node
• A LA consists of a number of cells belonging to RNC that are
connected to the same CN node
• A RA is handled by only one CN serving node, i.e. by one 3G-SGSN;
• A LA is handled by only one CN serving node, i.e. by one 3G-
MSC/VLR
• A service area is a subset of a location area
• A URA is a subset of a routing area
The mapping between LA and RNC is handled within the MSC/VLR to which
the LA is assigned. The mapping between RA and RNC is handled within the
SGSN/SLR owning this RA. The mapping between LA and cells and
respectively between RA and cells is handled within RNC.
Three areas definitions picture is shown below in hierarchical area concept
figure.

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Figure 2.6 Hierarchical area concepts.
The size of LA/RA areas depends on specific NW case, those areas
can be different based on NW circumstances, and current picture shows just
that they are responsible for different services, signaling messages.
Figure 2.7 LA/RA areas interdependence

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2.7. Paging
3GPP definition
In computer operating systems there are various ways in which the operating
system can store and retrieve data from secondary storage for use in main
memory. One such memory management scheme is referred to as paging.
In Mobile Telecommunication, the thermion paging means indication to the
user about the need for transaction. Paging procedure is always initiated by the
network and is made in order to find out the actual location of the user. The
network request is carried out in the logical channel Paging Control Channel
(PCH).
This procedure is used to transmit paging information to selected UE in idle
mode using the paging control channel (PCCH).
A normal paging message to the RNC contains information on the area in
which the paging message shall be broadcast. This is indicated with the Paging
Area ID parameter. Value of LA of CS services (or RA for PS services) is taken
from the “Cell Identifier List”. If WCDMA cell is paged, the Cell Identifier List
contains just one dummy cell to derive the LA. Contrary to GSM, the RNC itself
builds up the list of cells to be paged.
Important is that paging is processing completely independently for CS and
PS services.
Paging is necessary for the CN to reach the UE from the specific location or
routing area. In idle mode, paging is always initiated by the CN. In CS paging,
the CN and further the RNC broadcast paging messages through base stations
of the location area in which the UE is situated. In PS paging, the CN and further
the RNC broadcast paging messages through base stations of the routing area
in which the UE is situated.
To save on power consumption, the UE can use discontinuous reception
(DRX). This means that the network pages the UE according to a preset
sequence of frames during specific intervals. This preset frame sequence
interval is called a DRX cycle. DRX cycles can vary in length, and in case the
UE is connected to two different CN domains with different DRX cycle lengths,
the UE uses the shortest DRX cycle. The UE can store each domain-specific
DRX cycle of each CN it is currently attached to.
If the CN sends a specific DRX cycle length coefficient, the RAN uses it in
the paging message. If there is no CN-specific coefficient, the RAN uses the
default value for CN-specific DRX cycle length coefficient in the radio network
database.
The RNC sends paging requests to all WCDMA BTSs which belong to the
paging area where the UE is currently registered. The cells in a single BTS can
belong to different paging areas.

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Each paging message on the Iu interface involves only the UE and
therefore, the RNC has to pack the pages into the relevant radio interface
paging message.
The paging procedure is divided into two parts:
the part from Core Network (CN) to RNC on the Iu interface (RANAP)
the UTRAN internal part on the Iub interface (NBAP) part
2.8.1. RANAP paging
3GPP definition
The CN initiates the procedure via sending a message PAGING. This
message shall contain information necessary for RNC to be able to page the
UE, like following:
1) CN Domain Indicator
2) International Mobile Subscriber Identity (Permanent NAS UE Identity)
3) Temporary Mobile Subscriber Identity (Temporary UE Identity)
4) Paging Area
5) Paging Cause
6) Non-Searching Indicator
More detail description is:
1) The CN Domain Indicator IE is used by the RNC to identify from which CN
the PAGING message originates.
2) The Permanent NAS UE Identity (IMSI) shall be used by the UTRAN paging
coordination function to check if a signaling connection towards the other
CN domain already exists for this UE. In that case, the radio interface
paging message can be sent via that connection instead of using the paging
broadcast channel.
3) The Temporary UE Identity IE (TMSI) is the identity of the user that shall be
used over the paging channel. If the Temporary UE Identity IE is not
included in the PAGING message, the RNC shall use the Permanent UE
Identity instead.
4) The Paging Area IE shall be used by the RNC to identify the area in which
the radio interface paging message shall be broadcast in case no signaling
connection, as described above, already exists for the UE. If the Paging
Area IE is not included in the PAGING message, the whole RNC area shall
be used as Paging Area.
5) The Paging Cause IE shall indicate to the RNC the reason for sending the
PAGING message. The paging cause is transferred transparently to the UE.
6) The Non Searching Indication IE shall be used by the RNC to decide
whether the UTRAN paging co-ordination function needs to be activated or

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not. In the absence of this IE, UTRAN paging co-ordination shall be
performed.
It should be noted that each PAGING message on the Iu interface relates to
only one UE and therefore the RNC has to pack the pages into the relevant
radio interface paging messages.
The core network is responsible for the paging repetition over the Iu
interface in case of non-successful paging.
For each of UTRAN state, sub-cases can be individuated (with essential
counters). From the picture above we have evidence that some overlapping
zones are possible (e.g. latency in RRC setup or mismatch from repetition
cycles in CN and UTRAN or LA/RA with more than 1 RNC.
Figure 2.8.Paging types 1 and 2 UTRAN state sub-cases with essential counters
Different paging procedures are available for idle and connected cases. UEs
in Idle Mode (or Cell-PCH or URA-PCH) listen to PICH once per DRX-cycle
UEs in Connected Mode can receive the paging directly on DPCH and it is not
necessary listen PCH.
Moreover when a UE in idle mode state is paged, the message is broadcasted
to all UEs in the LA or RA because the position of UE is known at this level from
the network; while if the UE is in Connected mode the position in note by the
UTRAN Registration Area that is typically a subset of the LA and RA.
2.8.2. Paging type 1
This procedure is used to transmit paging information to selected UE in idle
mode, CELL_PCH or URA_PCH state using the paging control channel (PCCH).
Upper layers in the network may request paging, to e.g. establish a signaling
connection. UTRAN may initiate paging in CELL_PCH or URA_PCH state, to
trigger UE state.
In addition, UTRAN may initiate paging in idle mode, CELL_PCH and
URA_PCH state to trigger reading of updated system information.

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The UE shall in idle mode, CELL_PCH state and URA_PCH state receives
the paging information for all monitored paging occasions. For an UE in idle
mode, the paging occasions are specified in TS 25.304 and depend on the IE
"CN domain specific DRX cycle length coefficient". For an UE in CELL_PCH
state and URA_PCH state the paging occasions depend also on the IE "UTRAN
DRX Cycle length coefficient" and the IE "DRX indicator.
Figure 2.9 RRC Idle Paging Type1 – Signaling
Excluding the RRC connection failures, the paging procedure can fail for
the following reasons:
1. UE out of coverage
2. signaling in the transmission network failure (negligible);
3. overload in RNC units (ICSU and RRMU, negligible);
4. PCH blocking
When the UE receives a PAGING TYPE 1 message, it checks each
occurrence of the IE "Paging record".
For each included paging record the UE shall compare the included identity with
the identity of the UE according to different scenarios in different cases, which
are listed:
1) An idle mode UE scenario is used:
•if the IE "paging originator" is CN, compare the included identities of
type CN UE identity
•with all of its allocated CN UE identities
•for each match, forward the identity and paging cause to the upper layer
entity indicated
•by the IE "CN domain identity"
•if the IE "paging originator" is UTRAN, ignore that paging record

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2) A connected mode UE scenario is used:
•if the IE "paging originator" is UTRAN, compare the included identities of
type "UTRAN
•originator" with its allocated U-RNTI
•for each match, the UE shall enter CELL_FACH state and perform a cell
update procedure
3) "Paging response" case scenario is used If the IE "paging originator" is CN,
ignore that paging record
2.8.3. Paging type 2
This procedure, also called UE dedicated paging, is used to transmit
dedicated paging information to one UE in connected mode in states
CELL_DCH and CELL_FACH. Upper layers in the network may request
initiation of paging, e.g. to establish a signaling connection.
Since paging type 2 is only required for UE in CELL_DCH and CELL_FACH
state in which the location of the UE is known on cell level, paging type 2 is not
in the scope of mobility management for location and routing area planning.
Generally, signaling messages scenarios for CELL_DCH and CELL_FACH
states are quite similar, but have some specified difference, which comes from
existing if CELL_FACH scenario RB Reconfiguration step.
In CELL_DCH case, the potential reasons of paging procedure failure are:
1. signaling in the transmission network failure (negligible)
2. overload in RNC units (ICSU and RRMU, negligible)
Figure 2.10 Cell-DCH Paging Type2 - Signaling

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Figure 2.11Cell-FACH Paging Type2 – Signaling
In Cell-FACH case, the additional messaging is adding, so the following
reasons can initiate failure of paging procedure:
1 signaling in the transmission network failure (negligible)
2 overload in RNC units (ICSU and RRMU, negligible)
3 RB reconfiguration failure
2.8. Location area update and routing area update
3GPP definition
In Cellular networks each base station covers a small geographical area
which is part of a uniquely identified location area. By integrating the coverage
of each of these base stations, a cellular network provides radio coverage over
a much wider area. A group of base stations is named a location area, or a
routing area.
The location update procedure allows a mobile device to inform the cellular
network, whenever it moves from one location area to the next. Mobiles are
responsible for detecting location area codes. When a mobile finds that the
location area code is different from its last update, it performs another update by
sending to the network, a location update request, together with its previous

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location, and it’s Temporary Mobile Subscriber Identity (TMSI).
There are several reasons why a mobile may provide updated location
information to the network. Whenever a mobile is switched on or off, the network
may require it to perform an IMSI attach or IMSI detach location update
procedure. Also, each mobile is required to regularly report its location at a set
time interval using a periodic location update procedure. Whenever a mobile
moves from one location area to the next while not on a call, a random location
update is required. This is also required of a stationary mobile that reselects
coverage from a cell in a different location area, because of signal fade. Thus a
subscriber has reliable access to the network and may be reached with a call,
while enjoying the freedom of mobility within the whole coverage area.
When a subscriber is paged in an attempt to deliver a call or SMS and the
subscriber does not reply to that page then the subscriber is marked as absent
in both the MSC/VLR and the HLR (Mobile not reachable flag MNRF is set). The
next time the mobile performs a location update the HLR is updated and the
mobile not reachable flag is cleared.
LA update procedure is processing by the WCDMA mobile subscriber
(MS) via the 3G-MSC if the WCDMA UE changes the location area or if a timer
has expired. The procedure determines the location of the UE (VLR address) for
the
HLR and the authentication parameters of the UE for VLR concerned.
Therefore, a LA update is performed when:
• The location area of the UE has changed
• A periodical update is required due to expiration of a time trigger
The routing area update procedure is initiated by the WCDMA UE via the
3GSGSN/SLR if the WCDMA UE changes the routing area. The procedure
determines the routing area of the WCDMA UE for the HLR and the
authentication parameters of the WCDMA UE for the 3G-SGSN/SLR concerned.
Hence, a routing area update is performed when the routing area of the UE
changed.
2.9.1. Location and routing areas update
The location updating procedure is always initiated by the mobile station.
In the case that the mobile station is initiating an emergency call but, due to
cell re-selection or redirection by the network, it moves to a different LAI then the
mobile station may delay the location updating procedure in the new LA until
after the emergency call is completed.
LAU (Location area update) is initiated by the UE to inform the CS service
domain of the CN that the UE has entered a new location area. In case the new
LA is in an area served by another CN node, the location area update also
triggers the registration of the subscriber in the new CN node and a LA update
for CS services towards the HLR.

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LAU is only initiated by the UE when the UE is in state CS-IDLE, and this
independently of the PS state. If the UE is CS-IDLE but RRC connected, which
means that the UE is in PS-CONNECTED state, location area update is initiated
by the UE when it receives information indicating a new location area.
The location updating procedure is a general procedure which is used for the
following purposes:
- Normal location updating
- Periodic updating
- IMSI attach
The normal location updating procedure is used to update the registration of
the actual Location Area of a mobile station in the network. The location
updating type information element in the LOCATION UPDATING REQUEST
message shall indicate normal location updating. Only applicable for mobile
stations supporting VGCS listening or VBS listening: A mobile station in RR
group receive mode is in the MM IDLE state, sub state RECEIVING GROUP
CALL (NORMAL SERVICE) or RECEIVING GROUP CALL (LIMITED
SERVICE). To perform a location updating, the MS in RR group receive mode
shall leave the group receive mode, establish an independent dedicated RR
connection to perform the location updating as described above and return to
the RR group receive mode afterwards.
The normal location updating procedure shall also be started if the network
indicates that the mobile station is unknown in the VLR as a response to MM
connection establishment request.
To limit the number of location updating attempts made, where location
updating is unsuccessful, an attempt counter is used. The attempt counter is
reset when a mobile station is switched on or a SIM/USIM card is inserted.
Upon successful location updating the mobile station sets the update status
to UPDATED in the SIM/USIM, and stores the Location Area Identification
received in the LOCATION UPDATING ACCEPT message in the SIM/USIM.
The attempt counter shall be reset.
The Mobile Equipment shall contain a list of "forbidden location areas for
roaming", as well as a list of "forbidden location areas for regional provision of
service". These lists shall be erased when the MS is switched off or when the
SIM/USIM is removed, and periodically (with period in the range 12 to 24 hours).
The location area identification received on the BCCH that triggered the location
updating request shall be added to the suitable list whenever a location update
reject message is received with the cause "Roaming not allowed in this location
area" or with the cause "Location Area not allowed". The lists shall
accommodate each 10, or more location area identifications. When the list is full
and a new entry has to be inserted, the oldest entry shall be deleted.
In a shared network, the MS shall choose one of the PLMN identities as
specified in 3GPP TS 23.122 [14]. The MS shall construct the Location Area
Identification of the cell from this chosen PLMN identity and the LAC received on
the BCCH. If the constructed LAI is different from the stored LAI, the MS shall
initiate the location updating procedure. Whenever a LOCATION UPDATING
REJECT message with the cause "PLMN not allowed" is received by the MS,
the PLMN identity used to construct the LAI which triggered the location

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updating procedure shall be stored in the "forbidden PLMN list". Whenever a
LOCATION UPDATING REJECT message is received by the MS with the cause
"Roaming not allowed in this location area", "Location Area not allowed", or "No
suitable cells in Location Area", the constructed LAI which triggered the location
updating procedure shall be stored in the suitable list.
The Mobile Equipment shall store a list of "equivalent PLMNs". This list is
replaced or deleted at the end of each location update procedure, routing area
update procedure and GPRS attach procedure. The stored list consists of a list
of equivalent PLMNs as downloaded by the network plus the PLMN code of the
registered PLMN that downloaded the list. The stored list shall not be deleted
when the MS is switched off. The stored list shall be deleted if the SIM/USIM is
removed. The maximum number of possible entries in the stored list is 16.
Periodic updating may be used to notify periodically the availability of the
mobile station to the network. Periodic updating is performed by using the
location updating procedure. The location updating type information element in
the LOCATION UPDATING REQUEST message shall indicate periodic
updating.
The procedure is controlled by the timer T3212 in the mobile station. If the
timer is not already started, the timer is started each time the mobile station
enters the MM IDLE sub state NORMAL SERVICE or Attempting TO UPDATE.
When the MS leaves the MM Idle State the timer T3212 shall continue running
until explicitly stopped.
The timer is stopped (shall be set to its initial value for the next start) when:
- LOCATION UPDATING ACCEPT or LOCATION UPDATING
REJECT message is received;
- AUTHENTICATION REJECT message is received;
- the first MM message is received, or security mode setting is
completed in the case of MM connection establishment, except when the most
recent service state is LIMITED SERVICE;
- Mobile station has responded to paging and thereafter has received
the first correct layer 3 messages except RR message;
- Mobile station is deactivated (i.e. equipment powered down or
SIM/USIM removed).
When the timer T3212 expires, the location updating procedure is started and
the timer shall be set to its initial value for the next start. If the mobile station is in
other state than MM Idle when the timer expires, the location updating
procedure is delayed until the MM Idle State is entered.
If the mobile station is in service state NO CELL AVAILABLE, LIMITED
SERVICE, PLMN SEARCH or PLMN SEARCH-NORMAL SERVICE when the
timer expires, the location updating procedure is delayed until this service state
is left.
In A/Gb mode and GERAN Iu mode, the (periodic) location updating
procedure is not started if the BCCH information at the time the procedure is
triggered indicates that periodic location shall not be used. The timeout value is
broadcasted in the L3-RR SYSTEM INFORMATION TYPE 3 message on the
BCCH, in the Control channel description IE.

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In UTRAN Iu mode, the (periodic) location updating procedure is not started if
the information on BCCH or in the last received dedicated system information at
the time the procedure is triggered indicates that periodic location shall not be
used. The timeout value is included in the CS domain specific system
information element.
The T3212 timeout value shall not be changed in the NO CELL AVAILABLE,
LIMITED SERVICE, and PLMN SEARCH and PLMN SEARCH-NORMAL
SERVICE states.
When a change of the T3212 timeout value has to be taken into account and
the timer is running (at change of the serving cell or, change of the broadcast
value of T3212), the MS shall behave as follows:
Let t1 be the new T3212 timeout value and let t be the current timer
value at the moment of the change to the new T3212 timeout value; then the
timer shall be restarted with the value t modulo t1.
When the mobile station is activated, or when a change of the T3212 timeout
value has to be taken into account and the timer is not running, the mobile
station shall behave as follows:
Let t1 be the new T3212 timeout value, the new timer shall be started
at a value randomly, uniformly drawn between 0 and t1.
The IMSI attach procedure is the complement of the IMSI detach procedure.
It is used to indicate the IMSI as active in the network.
In A/Gb mode and GERAN Iu mode, a flag (ATT) is broadcast in the L3-RR
SYSTEM INFORMATION TYPE 3 message. It indicates whether attach and
detach procedures are required to be used or not.
In UTRAN mode, a flag (ATT) is included in the CS domain specific system
information element. It indicates, whether attach and detach procedures are
required to be used or not.
The IMSI attach procedure is invoked if the detach/attach procedures are
required by the network and an IMSI is activated in a mobile station (i.e.
activation of a mobile station with plug-in SIM/USIM, insertion of a card in a
card-operated mobile station etc.) within coverage area from the network or a
mobile station with an IMSI activated outside the coverage area enters the
coverage area. The IMSI attach procedure is used only if the update status is
UPDATED and if the stored Location Area Identification is the same as the one
which is actually broadcasted on the BCCH of the current serving cell. In a
shared network, the MS shall choose one of the PLMN identities as specified in
3GPP TS 23.122 [14]. The MS shall use the IMSI attach procedure only if the
update status is UPDATED and the stored Location Area Identification is equal
to the combination of the chosen PLMN identity and the LAC received on the
BCCH. Otherwise a normal location updating procedure is invoked
independently of the ATT flag indication.
IMSI attach is performed by using the location updating procedure. The
location updating type information element in the LOCATION UPDATING
REQUEST message shall in this case indicate IMSI attach.
Example of LAU is shown on picture below.
There thermions “Old” and “New” mean network elements from/to which LA
update is coming.

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Figure 2.12 Location area update example

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2.9.2. Routing area update
Routing area update is initiated by the UE to inform the PS service domain of
the core network that the UE has entered a new routing area. In case the new
routing area is in an area served by another CN node, the routing area update
also triggers the registration of the subscriber in the new CN node and a location
update for PS services towards the HLR.
Routing area update is initiated by the UE when the UE is in state PS-IDLE,
independently of the CS state. If the UE is PS-IDLE but RRC connected, which
means that the UE is in CS-CONNECTED state, routing area update is initiated
by the UE when it receives information indicating a new routing area.
When the UE is in PS-CONNECTED state the UE initiates RA update when
RAI
in Mobility Management (MM) system information changes.
Figure 2.13 Routing area update example

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The load resulting from a location/routing area update in relation to a paging
message can in a first step be estimated based for instance on the number of
messages between the network elements which is about 7 to 1.
The paging load per area within the UTRAN corresponds to the number of
paging requests in this area. The larger the area, the more paging messages
are necessary. Although the number of paged MS is constant in the whole
network, the MS has to be page within the complete paging region resulting in a
paging load in each cell of the region.
2.9.3. Combined updates
WCDMA paging for CS and PS is completely separated. A combined
updated can be initiated by the SGSN. Information is exchanged with the 3G-
MSC/VLR via the Gs interface.
Combined mobility management between CS and PS domain enables a more
efficient usage of network resources. The Gs interface interfaces the MSC / VLR
to the SGSN is used to convey some CS related procedures via the SGSN. The
aim is a more efficient coordination of PS and CS services and functionality.
Combined mobility management procedure means that a combined attach,
combined RA / LA update and CS paging via SGSN only need to be performed
in the PS domain. If the circuit-switched MSC triggers paging over the Gs
interface, knowing that a subscriber is also attached to an SGSN, only a routing
area or even one cell has to be paged via the SGSN.
During a procedure, the SGSN informs the MSC/VLR of the action.
Special mobile stations such as class A and class B mobile stations can
initiate combined mobility management. Class A mobile stations (MS) support
the usage of data connections at the same time as speech connections,
whereas class B mobile stations (MS) only support one of the two connection
types at a time. The Gs interface allows a mobile subscriber having a class B
mobile station with an ongoing data connection to disconnect the data
connection and to accept an incoming speech call.
If the Gs interface is not available, the SGSN informs the mobile station that
the combined mobility management has failed. The mobile station will then
again perform the same procedure in the circuit-switched network. This would
cause an additional signaling load on the radio interface.
2.10. Summary of mobility management
Mobility management is divided into the following functions:
•Location management: update the UE location in CS domain (location
area) or in PS domain (routing area)
•Attach/detach: establish or delete an MM context for an UE in the network
node (MSC/VLR or SGSN)
•Paging and searching
•Subscriber database
•Security

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Here, subscriber database has two options:
1) VLR in CS domain and SLR in PS domain. For temporary storage of
subscriber data is delivered from HLR and mobility data delivered by MM
functions.
2) HLR contains data on subscription restrictions, services assigned to the
mobile subscribers and the current subscriber status including information
on the current location
In security realized guard against unauthorized service usage –
authentication and service request validation, ciphering
Figure 2.14.Mobility Management Summary structure

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3. Practical guide for UMTS LA, RA and URA
areas Planning and Optimization
3.1. Location and Routing Areas Planning and
Optimization
LA and RA planning principles are normally very similar and close to each
other, because of their definitions:
Location Areas (LA) are used with task to inform the core network of a
UE’s location in CS services
Routing Areas (LA) are used with task to inform the core network of a
UE’s location in PS services
The Routing Area is the PS domain equivalent of the location area
A "routing area" is normally a subdivision of a "location area"
Based on those 3GPP definitions, most of concepts for LA and RA planning
are the same. Normally, planning of Routing Area can be done based on
Location Area planning results. So, logically, LA planning is the main, the first
planned “player”, which usually determines RA planning.
Specific planning of UMTS areas size is based on specific NW circumstances
and conditions, but the initial idea that is coming from their basic fundamentals,
which details are presented in chapter 2, and shortly summarized for LA and
RA in table below:
Short Location Area Concepts
LA and RA are used by core network to follow subscriber’s track for CS and
PS domains accordingly
One RA is to be configured inside a single LA
One RA is handled by only one CN node, i.e. one SGSN
LA and RA updates (LAU and RAU) can happen normally, like mobility result
or periodically, based on timers, configured in RNC for LA, and in SGSN for
RA
The smallest possible size of a LA/RA is a single cell
The biggest possible size of a LA/RA is a set of cells, connected to single
VLR

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Changing of LA/RA size makes effect to level of signaling load
Planning the same LAC/RAC for 2G and 3G NWs is possible, but not
recommended
LA/RA areas’ borders should not be located in zones with high number of
updates
Some of issues, introduced above are more particularly described below, and
general practical projects experience based summary recommendation is
presented in the following subchapters.
1. One RA is to be configured inside a single LA
The reason of this rule is coming from 3GPP [WG RAN3]:
A routing area is a subset of one, and only one, location area (LA), meaning that
a RA cannot span more than one LA. Also, important, that a RA is served by
only one SGSN.
The following rules apply for the Routing Area Identity (RAI):
- RAC is only unique when presented together with LAI.
- LAI = MCC + MNC + LAC
- RAI = MCC + MNC + LAC + RAC, where “MCC + MNC” means the PLMN
identity.
Theoretically, that be explained by MM and GMM messages establishments
processing’s (3GPP TS 24.008 V8.2.0). Practically, RAC has to be assigned
only to singe RAC, but can be several RACs inside one LAC.
Previously, some mobile operators configured more than one Routing Area
inside one Location Area. That was explained by SGSN limits:
In the previously used releases, one Packet Processing Unit (PAPU) was
required to handle one area. Only with the Large Routing Area Support (LRAS)
feature more than one PAPU unit can serve the same area. This feature makes
it possible to define PAPU groups where multiple PAPUs can serve the same
routing areas or share the same Gb/Iu connections. But, from the SG6.0 release
onwards the LRAS feature is used in both 2G and 3G environments, so, starting
from mentioned Core Release, the best RA size planning method is to define
that the same as LA.
Because of that assumption, current document considers location and routing
areas practical planning together, and designates those by combined
abbreviation LA/RA.
It is only necessary to decrease the size of a RA area relative to a LA if there
is a large quantity of paging from the PS service domain; such case is really
unusual and can happen in much PS-oriented NWs.

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2. Normal and periodical LA and RA updates
LA and RA updates (LAU and RAU) can happen normally, like mobility result
or periodically, based on timers, configured in RNC for LA, and in SGSN for
RA.
Normal updates are processing as result from UE mobility, i.e. when a UE
moves across a LA or RA boundary.
Periodic location updating is used to inform the network that the mobile station
is available; the network requires from the mobile station to 'report in' at certain
time intervals. If there are no messages from the mobile station, the NW
assumes that the MS is out of the coverage area, or that it has not been turned
on, and incoming calls to the MS are not paged. This saves radio resources.
The time interval for periodic location updating is defined in the RNC set base
station parameters. The time-out value is continuously broadcast, so when a
mobile station enters the VLR area, it will automatically define how often it has
to report to the network. When the timer of the MS reaches the configured
timeout value, the MS initiates a periodic location update. Every time location
updating occurs, the MS and the VLR reset their timers.
In a periodic location update, the VLR area does not change, and location
updating in the HLR is not needed.
Periodic LA updates are completed with a frequency defined by the timer
T3212. This timer is broadcasted within System Information Block 1 (SIB1).
Periodic RA updates are completed with a frequency defined by the timer
T3312. This timer is sent to the UE within the Attach Accept and Routing Area
Update Accept messages. A UE will only initiate a LA update in the case it is in
CS-IDLE state. The LA update can be either normal or periodic and the UE can
be in either RRC Connected mode or RRC Idle mode. A UE can initiate a RA
update if it is in PS-IDLE state.
Optimization of timer for periodic LA is in deep dependency with normal
Location Update procedure success. Therefore, if Location Area is bigger
(rather big), so Periodic Location Updates happen more often, and vice verse,
as smaller LA size, so smaller need to make Periodic Update often.
The mentioned timer is configured on RNC by parameter CS_ T3212:

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Parameter name T3212
Abbreviated name CS_T3212
3GPP name T3212
Managed object IUCS
Parameter group SystemInfo
Category Telecom
Multiplicity 1
The timeout value, in decihours (6 min), for periodic
location updating. Given only for the CS domain. (Part of
the CS domain specific NAS System information in
SIB1).
The value 0 is used for an infinite timeout value, that is,
periodic location updating is not used.
Description
This parameter is part of System Information Block 1.
Range 0..255
Default value 0 decihours
RNC <-> UE
RAC <-> RNC
EM <-> RNC
Interfaces
RACApp <-> RAC
References
3GPP Reference: TS 24.008, Mobile radio interface
layer 3 specification; Core Network Protocols, TS
25.331, RRC Protocol Specification
In the case of really small and un-loaded NW, for example in recently
implemented or Trial NWs, is recommended to switch off Periodic
Location Update at all, so to configure parameter CS_T3212 as 0, so keep
the default parameter value.
In SGSN databuild parameters relevant to location area, routing area and cell
identity planning are presented in Error! Reference source not found..
Parameter name Periodic RA update timer (PRAU)
periodicRaUpdateTimerMin
Q3 Name:
periodicRaUpdateTimerSec
Description
The parameter indicates the interval of the MS's
periodic RA update
Enter the value in minutes and seconds (min sec).
The values range:
2.62 seconds with a 2 second step
1.31 minutes with a 1 minute step
36.180 minutes with a 6 minute step
Range
Value 0 means that this parameter is not in use

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MML Default 54 minutes
Interfaces
The value set for this parameter has to be smaller than
the value set for the MS reachable timer (MSRT)
parameter.
If enter value 0 for this parameter, the value of the
MSRT parameter has to be 0.
Optionally, with MS reachable timer (MSRT) parameter
and periodic RA update timer (PRAU) parameter values
means that the parameters, which are configured with
ZEJF command are not used at all if 250k PAPU mode
configuration is installed. Even if it is possible to
configure those values with ZEJF command, the fixed
MS reachable timer and fixed periodic RA update timer
parameter values are always used (marked with an
asterisk *) in 250k mode.
References
3GPP Reference: 3GPP TS 24.008, Mobile radio
interface Layer 3 Specification; Core network protocols;
Stage 3.
Similar to LA case, in really small and un-loaded NW can recommended to
switch off Periodic Routing Update at all, so to change default parameter value
to 0, just important also to change MSRT parameter.
3. The biggest possible size of a LA/RA is a set of cells,
connected to single VLR
That is mandatory rule, coming from general Core Areas basics,
Location/Routing areas have to be inside single VLR, and, normally, they are
smaller that VLR area size.
In planning stage, important to remember to configure LA/RA inside single
VLR, and never involve cells from other VLRs. Actually, VLR is not reference
point for LA/RA planning, the usual orienteer is RNC, many operators normally
plan LA/RA the same as RNC size.
4. Changing of LA/RA size makes effect to level of signaling
load
The mentioned effect is the main in LA/RA planning/optimization approach.
For better understanding of the dependency mechanism, let’s come to paging
messages theory. That mechanism is specified by following basics:
NSN RAN provides an 8 kbps PCH transport channel on the S-CCPCH
8 kbps is sufficient to include a single paging record per 10 ms
A single cell can thus page 100 UE per second

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S-CCPCH can be shared with the FACH-c and FACH-u but PCH always
has priority
High paging load has an impact upon FACH capacity when single S-
CCPCH is configured
Paging completed over either a Location Area, Routing Area, RNC or Cell
Utilisation of paging capacity is maximised when paging is completed
over a Cell (UE in CELL_PCH)
Allowing location areas to include multiple RNC reduces the effectiveness
of CELL_PCH reducing the paging load
Paging is common for every BTS within the LA, but LUP (Location area
update) is local to the border cells. Moreover, there are many project specific
conditions for the actual amount of LUP in the network, such as geographical LA
border design, dual band strategy, etc., which can’t be easily standardized.
A location area can be figured out as the minimum unit for delivering single
paging message. LUP will be switched on if LA border is crossed, so Uu
interface channel resources will be used for the LUP. Considering paging effects
of big LA and a small LA sizes, the main is how much paging’s load this LA is
going to carry and how much LUP will be generated by this LA design.
LA size practically differs:
1) The case of “too small LA size” can have the effect of too much LA borders
are configured and too much of location area updates can exist in NW. That
can generate continues unnecessary high load in Core and RAN both.
Therefore really small size of LA can unreasonably load Signaling and HW
resorse. Location border areas can suffer of too frequent location updates
procedures, LUP “ping-pong effect”. In too small LA area size, paging might be
lost if the subscriber changes the LA faster than the LUP procedure is able to
update the VLR/HLR with the correct LAI.
2) The case of “too big LA size” can have the effect, that paging messages
numbers, sent from WBTS in single LA are too high. The worst possible effect
can be that some paging messages might be lost due to paging queues
congestion in the WBTS, as far as INITIAL DIRECT TRANSFER COMMAND
(or REJECT) messages might be discarded.
Although both too small LA and too large LA size can cause problems,
relatively large LA size is more preferable than relatively small, but
recommended also to calculate the maximum paging load for a Location Area
before designing the number of LACs needed in the network.
In really rough, but useful in practical planning approach:
• In the case of planned LA/RA relatively larger, they may serve larger
numbers of UE and increase paging traffic level
• In the case of planned LA/RA smaller, quantity of normal LA updates
increases, and increases number of signaling messages
For practical usage, some assumptions can be admitted:

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1) NSN assumed, that single cell can page absolute maximum of 100 UE per
second. Paging messages procedure collapse close reaching the limit of 100
UE per second. However, practically observed the tangible collision will be
experienced even in much smaller paging load. Paging channel has effective
capacity configuration in approximately 35 of paging messages in second. So,
for practical planning 35 UE per second in paging is recommended to be
regarded.
2) 35 UE per second means 126000 UE per hour maximum. That is not
absolute maximum, getting much is possible, but not suggested because of
increasing risk of paging message lost.
3) Paging update command is included in normal mobile terminated call
signaling flow. Some assumption of percent of mobile terminated calls inside
total number of call attempts has to be agreed. That percent depends on NW
specific and can be provided by as customer requirement, or forecasted, based
on other customers’ wishes. In the lack of information, NSN initial planning
figure can be 30 %. There is no planning and approximate even assumption
method to calculate connected mode and SMS paging numbers. Those figures
depend mostly on LA size (how often UE cross LA border) and can be really
different for different NWs. In some obtained NWs monitoring (and big and
small LA sizes were presented) were exceedingly smaller than mobile
terminated calls. The extremely highest number of such paging is close to 10
of mobile terminated calls paging. So, assumption of paging events is 33 % of
total call attempts. That sample approach does not provide exact number, but
can be useful for approximate initial calculation.
4) Based on previous points info, the following formulas can be used for LAC
calculation:
Maximum number of Wcells in single LA = Maximum number of RNCs in
single LAC *Maximum numbers of carriers
Maximum number of RNCs in single LA = Maximum Number of pagings in
cell per hour / / [(Relation of Paging Messages to total number of call
attempts)*
Busy hour call attempts] = 126000 / (0.33* Busy hour call attempts)
Capacity of different RNC types is easily founded in Customer
Documentation Libraries, and summarized in the tables below.

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RNC196
48M 85M 122M 159M 196M 300M 450M 1000M
Number of
subscribers
59 000 122 000 181 000 240 000 300 000 300 000 360 000 1 000 000
BH call
attempts
52 000 108 000 160 000 216 000 272 000 272 000 320 000 1 000 000
Number of
carriers
384 576 768 960 1 152 1 152 1 152 1 800
Number of
BTS
170 256 340 420 512 512 512 600
Table 3.1 RNC 196 capacity steps
RNC450 RNC450/150 default RNC450/300 RNC450/450
Number of subscribers 181 000 284 000 360 000
Busy hour call attempts 240 000 375 000 576 000
Number of carriers 600 900 1 152
Number of BTSs 200 300 512
Table 3.2 RNC 450 capacity steps
High capacity RNC2600 Step 1 Step 2 Step 3
Number of subscribers 363 000 636 000 909 000
CS Busy hour call attempts 575 000 1 000 000 1 440 000
Number of carriers 1 440 2 100 2 800
Number of BTSs 1 440 2 100 2 800
Table 3.3 RNC 2600 capacity steps
Assumption of paging events as 33 % of total call attempts can be used in most
cases, but recommended to be analyzed based on NW circumstances.
Let’s sample RNC450/300, the figures are:
Maximum number of RNCs in single LA = 360000 / (0.33* 375000) ~1
So, started from RNC2600 capacity step 2 is strongly not recommended to plan
more than one RA inside LA zone.
Maximum number of Wcells in single LA = 1*900=900
In that RNC capacity number of cells and WBTSs is the same in RNC.
Introduced LA size calculation method is useful to avoid grow of signaling.
Important note: Introduced calculation assumption does not include 24
kbps Paging Channel (RAN1202) feature’s benefits, from which offering

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increased paging capacity is planned for RU20 and Paging Optimization
feature in I-HSPA Rel. 3.
5. Planning the same LAC/RAC for 2G and 3G NWs is
possible
That is possible to plan 2G and 3G networks using shared LAC/RAC (further
in document is used LAC only thermion, as RAC, fixed with LAC assumed).
Below will be summarized effects of such planning.
Positive effect Negative effect
-reducing the risk of missed paging
messages
-reduces number of area updates for
UE, moving between systems, that
possibly may reduce the signaling load
-increasing the network paging load as a
result of all paging messages being
broadcast on both system
-making LA planning and optimization
more complicated, as far as no
differentiation between 2G and 3G paging
and make the requirement to re coordinate
cell identities
The biggest problem in planning 2G and 3G shared LA is that 2G paging load
becomes 3G loading also, and vice verse. That effect will require reducing LA
size also.
In the case if shared approach is adopted then the 2G and 3G cells must be
planned with different Cell Identities.
Shared strategy may be not possible also to realize in practice because they
may not have the same coverage areas and not all sites being co-sited.
Summarized, shared strategy can be acceptable in small multiband NWs
trials, in which LAL planning and paging load issues are not really considerable.
All other cases, assigning of 3G location areas and routing areas different
identities to 2G location areas and routing areas is recommended.
Problems with connections establishing while completing inter-system cell re-
selection are not the mandatory reason to plan the same 2G/3G LA, just reason
to analyze problems source deeply.
6. LA/RA areas’ borders should not be located in zones with
high number of updates
That statement is starting point for the definition of 3G boundaries.
In the planning stage, the following territories should be avoided in LA/RA
boundaries:
major roads
railways
any transportation links

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potential high traffic areas (markets, business-areas)
First three rules are coming from high number of normal updates UE mobility,
last rule, - from high number of periodic updates in one small area.
In NW monitoring/tuning/optimization faze high number of LA/RA updates can
be the reason to change LA/RA zones’ boundaries.
In NW acceptance procedures, NW clusters’ for borders should be defined for
drive-tests not in LA/RA boundaries. That will help to verify the success of
update procedures and their impact for End-User Experience.
3.2. Service Area Planning and Optimization
Service Area can be configured for number of “cells” within a single location
area. That mapping is invisible for core network and handled within RAN. A cell
is allowed to belong to more than one service area.
Service Areas are used for emergency calls, location based services and the
Service Area Broadcast (SAB) feature performing.
In parameterization, two different are defined, SAC, used for emergency calls,
and SACB, assigned for SAB services.
Obviously, that SACB is actual one only when SAB services are really in use.
SAC can be assigned with the same values for different cells, but SACB has
to be identifiable for each cell.
Practically, impact from SAC planning is visible only in emergency calls
performing. The main rule is to plan uncial SAC for every cell; the smartest way
to simplify system design is to assign SAC and SACB the same as CI (Cell
Identify).
MO Class
Parameter
Name
Abbreviation Multiplicity
Range and
Step
WCEL
Service Area
Code
SAC 1 0..65535, step 1
WCEL
Service Area
Code for SAB
SACB 1 0..65535, step 1
The possible reason to change SAC can be two or more cells with very close
coverage, here can be the idea to configure emergency calls in one cell only. In
such case, Service Area can be defined different from cell area. Assigning to the
cell SAC equal to other cell’s CI means that emergency calls are switched off on
that cell. However, the practical case of such modification is normally not
exigible, because of small amount of emergency calls and load, generated by
them.

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3.3. UTRAN radio Area Planning and Optimization
Each cell has to be identified by URA identifier parameter. Correct URAId
leads reducing of signaling load in RNC and UE power consumption, by URA
state usage.
URAId planning include also URA group definition, those parameters are
shown below in fragment of typical WCDMA Radio Network Configuration
Parameter file.
MO
Class
Parameter
Name
Abbreviated
Name
Multiplicity
Range and
Step
WCEL
List of URA
identities
URAIdList 1
WCEL URA identity URAId 8
1..65535, step
1
Here List of URA Identifies is not one parameter, but set of parameters, -
Secondary URA Identifies. URAId itself is Primary Identifier, which is assigned to
the UE in this cell when the UE is registered on this URA.
Secondary URA IDs in the URA list are URA IDs of the
neighboring/overlapping URAs to which the cell belongs to, and they are
broadcast on BCH of this cell.
URA planning is always limited by RNC area planning, and, same as LA/RA
planning, balancing between paging and signaling load:
1) Too small URA area leads to the case, when UE has to complete cell updates
more frequently and the signaling load and also UE power consumption
increases. Also, can increase the risk of ping-pong effect on URA borders.
2) Too big URA area leads the case when, paging messages have to be
broadcast across an increased number of cells and the paging load
increases.
In initial planning step, URAId is recommended to define equal to RNC area.
In the further optimization, based on NW analysis, URA area can be updated,
based on network statistics for mobility and signaling activity.
If operator does not have risks of URA overlapping, Secondary URA
Identifiers are not even used, so in RNC damp file that parameter value is
shown as “-1”.

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Some other parameters are also related to URA planning topic:
MO
Class
Parameter Name Abbreviation
Range and
Step
Default
Value
RNC
Cell Reselection
Observing Time
CellReselectionObservi
ngTime
1..60 min, step
1 min
16 min
RNC Max cell reselections MaxCellReselections
0..100 times,
step 1 times
3 times
WCEL
Maximum number of
cell reselections
NCr 1..16, step 1 8
WCEL
Maximum number of
cell reselections in
non-HCS case
NonHCSNcr 1..16, step 1 8
WCEL
Evaluating period for
amount of
reselections in non-
HCS
NonHCSTcrMax
Not used (0),
30 s (1), 60 s
(2), 120 s (3),
180 s (4), 240 s
(5)
Not used
(0)
WCEL
Cell reselection
hysteresis 1
Qhyst1
0..40 dB, step 2
dB
0 dB
WCEL
Cell reselection
hysteresis 1 for
FACH
Qhyst1FACH
0..40 dB, step 1
dB
0 dB
WCEL
Cell reselection
hysteresis 1 for PCH
Qhyst1PCH
0..40 dB, step 1
dB
0 dB
WCEL
Cell reselection
hysteresis 2
Qhyst2
0..40 dB, step 2
dB
2 dB
WCEL
Cell reselection
hysteresis 2 for
FACH
Qhyst2FACH
0..40 dB, step 1
dB
2 dB
WCEL
Cell reselection
hysteresis 2 for PCH
Qhyst2PCH
0..40 dB, step 1
dB
2 dB
WCEL
Evaluating period for
amount of cell
reselections
TCrmax
Not used (0),
30 s (1), 60 s
(2), 120 s (3),
180 s (4), 240 s
(5)
60 s (2)

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WCEL
Cell reselection
triggering time
Treselection 0..31 s, step 1 s 2 s
WCEL
Cell reselection
triggering time for
FACH
TreselectionFACH
0..6.2 s, step
0.2 s
2 s
WCEL
Cell reselection
triggering time for
PCH
TreselectionPCH 0..31 s, step 1 s 2 s
Normally, in planning those parameters are not needed to have values,
different from defaults. For optimization some be tuned, let’s detail treat to of
them:
1) “Max cell reselections” This parameter specifies the maximum allowed
number of Cell Reselections in the CELL_FACH or CELL_PCH state before
transition to the URA_PCH state. The amount of cell reselection is counted in
both the CELL_FACH and CELL_PCH states. When the UE is in the
CELL_FACH state, the value of the counter MaxCellReselections cannot be
used as a trigger for the CELL_FACH to URA_PCH transition, but it is used
when deciding a target state after the MAC-c entity has sent an inactivity
indication to Layer 3.
2) “Cell Reselection Observing Time”. The timer is set when the first cell state
Update message due to 'cell reselection' is received while the UE is in
CELL_FACH or CELL_PCH state. In the expiry of the timer, the counter “Max
cell reselections” is reset. If there are too many reselections coming from
the UE within the observation time, the UE is switched to the URA_PCH
state. Otherwise the Cell_PCH state is chosen. Below is an example of the
target RRC state selection when value 3 is used for “Max cell reselections”:
Velocity, km/h Cell radius, km
Cell Update,
frequency
Target RRC, minutes
state
50 10 12 CELL_PCH
50 20 24 CELL_PCH
75 10 8 URA_PCH
75 20 16 CELL_PCH
100 10 6 URA_PCH
3) “Evaluating period for amount of cell reselections”. This parameter
defines the duration for evaluating the allowed amount of cell reselections. If
the number of cell reselections during the time period defined by that
parameter exceeds “Maximum number of cell reselections”, high mobility
has been detected. The parameter is needed only if HCS is used. The
parameter is used for cell selection and re-selection in both idle and connected
mode.
4) “Cell reselection triggering time”. This parameter defines the way UE
triggering the reselection of a new cell if the cell reselection criteria are fulfilled

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during the time interval, assigned by parameter. The use of 2s reselection time
may avoid too many cell reselections between cells and hence LA/RA updates
when crossing LA/RA border. Thus, there are less signaling and less call
failures at LA/RA border due to LA/RA update. The reselection time of 0s can
be used in areas of high mobility, for example highways.
5) “Cell reselection triggering time for FACH”. This parameter is used for cell
selection and re-selection in FACH. The UE triggers the reselection of a new
cell if the cell reselection criteria are fulfilled during the parameter defined time
interval. The reselection time of 2s may avoid too many cell reselections
between cells and hence LA/RA updates when crossing the LA/RA border.
Thus, there are less signaling and less call failures at the LA/RA border due to
the LA/RA update. The reselection time of 0s can be used in areas of high
mobility, such as highways.
6) “Cell reselection triggering time for PCH”. The parameter is used for cell
selection and re-selection in PCH. The UE triggers the reselection of a new cell
if the cell reselection criteria are fulfilled during the time interval. The
reselection time of 2s may avoid too many cell reselections between cells and
hence LA/RA updates when crossing the LA/RA border. Thus, there are less
signaling and less call failures at the LA/RA border due to the LA/RA update.
The reselection time of 0s can be used in areas of high mobility, such as
highways.