LOCATION MANAGEMENT
IN
PCS NETWORKS
Dissertation submitted
IN PARTIAL FULFILLMENT OF THE REQUIREMENT
FOR THE AWARD OF THE DEGREE OF
MASTER OF TECHNOLOGY
IN
COMPUTER APPLICATIONS
By
Manikanta Velaga
Admission No. 612895
Under the Guidance of
Dr.Chiranjeev kumar
Senior Lecturer
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING
INDIAN SCHOOL OF MINES
DHANBAD-826004
MAY, 2006
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ABSTRACT
Mobility management is the essential technology that supports mobile terminals to give
service through wireless networks when they are moving into a new service area. Two
main aspects need to be considered in mobility management. “Location management”
(addressing, location registration and update, tracking and paging) and “Handoff
management” (Handoff trigger and initiation, connection routing, smoothing). Location
management is how to track the Mobile Terminals (MTs) those move from place to
place. Location management is a key issue in Personal Communication Service (PCS)
networks.
Location tracking operations in a personal communications service networks are
expensive. As the number of PCS subscribers increases, the system overheads involved
with the location management will increase beyond the capacity of the current network
design. Methods for reducing the overheads are critically important for the design and
implementation of PCS networks. The key issue is to minimize the cost of location
management in PCS networks. More research work has been going on this location
management. More number of peoples are proposing new methods for reducing the cost
of location registration and call delivery.
Here an idea proposed to reduce cost of Location management in the Home
Location Register (HLR)/Visitor Location Register (VLR) based scheme “Dynamic HLR
location management in PCS networks”. In this “Dynamic HLR location management”
when ever an MT moves from one SA to another SA, a dynamic copy of mobile terminal
location information in the nearest (current) HLR database will be provide. So that no
needs to access the master HLR for location registration and call delivery always.
“Dynamic HLR scheme” always interact with a dynamic copy of location information of
an MT is made in the nearest (current) HLR which can be accessed for the location
management. This “Dynamic HLR Location management” method is limitation for some
cases Such that a mobile terminal moving across service areas.
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Suppose a mobile terminal moving via some service areas. For example SA1,
SA2………SA10 are the service areas. Mobile terminal is moving from SA1 to SA10.
Then according to “Dynamic HLR Location management” for every movement in
between one SA to another SA it takes the whole process of signal translations. So that
avoiding this extra signaling cost in this “Dynamic HLR Location” method, here a new
idea is proposed. In this proposed idea, cache information is maintained at each HLR
database. When ever the MT moves from old service area to new service area, an entry
will entered in to the cache which is maintained by the old service area. This entry tells
about information of MT (that is it tells “to which SA it has gone”).
In the proposed “Pointer based HLR” method the length of the pointer chain is not
considered. The constraint on the length (i.e number of service areas) through which a
MT can be searched must be known.
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1. INTRODUCTION
Mobility management [4] has widely been recognized as one of the most
important and challenging problems for a seamless access to wireless networks and
mobile services. Mobility management is the essential technology that supports roaming
users with mobile terminals to enjoy their services through wireless networks when they
are moving into a new service area.
It is the fundamental technology used to automatically support mobile terminals
enjoying their services while simultaneously roaming freely without the disruption of
communications.
From the viewpoint of functionality, mobility management mainly enables
communication networks to “Locate roaming terminals in order to deliver data packets,
that is function for static scenario” and “Maintain connections with terminals moving into
new areas, that is function for dynamic scenario”. Mobility management contains two
distinct areas that are location management and handoff management. The former
concerns how to locate a mobile terminal, track its movement, and update the location
information while the latter focuses mostly on the control of the change of a mobile
terminal's access point during active data transmission.
1.1 Mobility Management Operations
Two main aspects need to be considered in mobility management, they are
“Location management” (addressing, location registration and update, tracking and
paging) and “Handoff management” (Handoff trigger and initiation, connection routing,
smoothing). Performance of the mobility management is also important.
1.1.1 Location management
Location management equals locate roaming terminals in order to deliver data
packets to them despite the fact that their locations may change from time to time. The
essence of location management is constituted by the mechanisms for mapping the name
of a mobile terminal to its address.
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1.1.2 Handoff management
Handoff management enables the PCS networks to maintain sessions with mobile
terminals while they change their attachment points with system’s infrastructure. Such
changes are called handoff or handover operations.
1.2 Operations of Location management
*Location registration, also known as location update or tracking, that is the
procedure that the mobile terminal informs the network and other terminals of its new
location
through special messages by updating the corresponding location information
entries stored in some databases in the networks.
*Location paging, also known as locating or searching. In most cases location
information stored in databases is only the approximate position of a mobile terminal.
Location paging is then the procedure that, when calls/ packets need to be delivered to the
target mobile terminal, the network tries to find the mobile terminal's exact locality.
1.3 Key research issues for location management
*Addressing, that is how to represent and assign address information to mobile
terminals. The problem is becoming more severe since the future mobile communication
systems will be based on the internetworking and interoperability of diverse and
heterogeneous networks of different operators and technologies. A global addressing
scheme is needed, e.g. IPv6 address, to locate the roaming terminals.
*Database structure that is how to organize the storage and distribution of the
location information of mobile terminals. Database structure can be either centralized or
distributed, or the hybrid of these two schemes. Tradeoff is needed between access speed,
storage overhead, and traffic overhead due to the access to the related databases. Caching
is also an important technique for the improvement of access performance.
* Location update time that is when a mobile terminal should update its location
information by renewing its entries in corresponding database. Schemes for location
update can be either static or dynamic. In a static scheme location update is triggered by
some fixed conditions like time period or network topology change.
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* Paging scheme, which is how to determine the exact location of a mobile
terminal within a limited time. Obviously an adequate tradeoff is needed between time
overhead and bandwidth overhead. There are also both static and dynamic schemes for
location paging. In static cases paging is simply done to the whole certain area where the
mobile terminal must be in. For a dynamic method, the main problem is to firstly
organize the paging areas into groups and then recognize the based on information like
distance probability, moving velocity, etc.
1.4 Brief description of PCS networks
The appearance of the Personal communication service networks[4] enable people and
devices to communicate independently of their location and while they move from place
to place .The ability to communicate to “anyone, anywhere and anytime “is not only a
technological progress and it has an enormous affect on our life. For providing
continuous communication to mobile terminals every PCS network employs a mobility
management mechanism for locating mobile terminals and for maintaining their sessions
while they are moving from place to place. PCS systems are based on the “cellular
architecture”. They use terrestrial infrastructure network for providing communication
services to mobile terminals through radio channels. The service coverage area of the
system is divided into cells. Each cell includes a base station that communicates with the
mobile terminals in its cell area via radio channels. A number of geographically adjacent
base stations are grouped together and connected to a Base Station Controller (BSC) that
manages their radio resources. The later is attached to a Mobile Switching Center (MSC)
that connects the base stations to the infrastructure network and provides them a
switching functionality for both communication and signaling. In these systems the radio
channels are considered as the most expensive resource since the number of radio
channels that is given to each system is limited. For efficient usage of these channels the
PCS systems employ the frequency reuse principle.
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.
An example of a typical structure of a PCS network is depicted in Figure1. For
providing continuous communication to mobile terminals every PCS network employs a
mobility management composed of two components, location management and handoff
management. In contrast to the telephone number in traditional telecommunication
systems that specifies the location of the end user, the PCS subscriber number does not
provide the location of the mobile terminal. Therefore, the system must maintain a
location management mechanism for locating its mobile terminals. This mechanism maps
subscriber numbers to the current location of the requested users for call delivery
operations.
Figure1: An example of typical PCS network
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A location management is used for finding the location of mobile terminals and it
is composed of three components. These are “location database” for mapping subscriber
addresses to locations in certain degree of accuracy, an “update operation” for informing
the location database regarding changes in mobile terminal locations, and a “search
operation” for locating the mobile terminals based on the information stored at the
location database. Location management schemes are differ in the way the location
database is organized as well as the update and search algorithms. The efficiency of such
scheme is measured by its ability to perform update and search operations with low
communication and processing overheads.
The current PCS systems, such as “Global System for Mobile Communications”
(GSM) and “Interim Standard” (IS) are use similar schemes for location management.
The coverage area is divided into location areas (LA), each consists of a group of cells
that forms a continuous geographic area. The system records for each mobile terminal its
current resident LA. This information is stored at two level data hierarchy that uses two
types of location servers, a home location register (HLR) and a visitor location register
(VLR). The HLR database contains the permanent data (e.g directory number, profile
information, current location, and validation period) of the MTs whose primary
subscription is within the area. For each MT, HLR contains a pointer to the VLR to assist
routing incoming calls. A VLR is associated with a Mobile Switching Center (MSC) in
the networks. It contains temporary record for all MTs currently active within the service
area of the MSC. The VLR retrieves information for handling calls to or from a visiting
MT.
A mobile terminal performs update operations periodically and when it crosses
LA boundaries. At these operations the system updates the proper VLR server about the
user location, and when it moves from one VLR region to another region the system also
update the user’s HLR server. When an incoming call arrives a “location request”
message is sent to the mobile terminal’s HLR. The HLR determines the serving VLR of
the called user and send a “route request” message to this VLR. The later simultaneously
pages the mobile terminal in all the cells of the LA where the user is register. After
locating the mobile terminal’s current cell, a connection is established between the call
initiator and this cell.
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1.5 Organization of the thesis
Chapter2 includes brief explanation of the schemes based on two tier HLR/VLR
architectures, cache pointer entries and IS-41 standard. Chapter3 includes brief
explanation of the proposed scheme. Chapter4 includes the implementation of the
concept under proposed scheme in UNIX platform. Chapter5 includes the comparison of
the proposed scheme with “Dynamic HLR location” scheme through mathematical
analysis. And finally Chapter6 includes conclusion.
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2. LITERATURE SURVEY
In [1], author has proposed a new location management strategy that is based on the
centralized database architecture with HLR/VLR concept. That is “New Caching-based
Location Management Scheme in Personal Communication Systems”. It’s basic idea is to
reduce the cost of call delivery using location information cached at MSC/VLR. Other
proposed caching –based scheme may have cached invalid location information as MT
moves into a new registration area. However, this scheme can’t cache invalid location
information as announcing the location of MT to Mobile Switching Center (MSC)/VLR
or invalidating the location information by MSC/VLR. That is, cached location
information, a miss can’t occur. Therefore, the call setup delay for this proposed scheme
is always shorter than or equal to that of the current method (IS-41, GSM MAP).
That “New Caching-based Location Management” scheme minimizes the total
signaling cost on location management by reducing cost of call delivery more than
increased the cost of the location update. The analysis of the “New Caching-based”
scheme using simulation shows that new scheme outperforms or equals the current
methods (IS-41, GSM MAP) in cost and has a much better performance at high “call to
mobility ratio” (CMR).
The current methods (IS-41, GSM MAP) for location management employ
HLR/VLR concepts, centralized database architecture. Currently the centralized database
network stores the location information of each MT in a location database as MT changes
its location area, a collection of cells. This location information is retrieved during call
delivery.
As the number of MT’s increases, current location management methods at
HLR/VLR concepts (IS-41, GSM MAP) have many problems such as increasing traffic
in network, long delay at call delivery, bottleneck by signaling traffic at HLR (since all
signal messages related to location registration and call delivery always exchange
between MSC/VLR and HLR).
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To alleviate these problems, there are many proposed schemes based on caching but
the scheme also has some problems, which is given in the following sections.
Author has explained the “Caching strategy for PCS” networks as follows.
In this “Caching strategy for PCS” author is concerned with improvements to IS41 that are based on caching the location of MT. The basic idea of schemes based on
caching is that maintaining a cache of location information can reduce volumes of
signaling and database access traffic to locate an MT.
Author has referred “Per-user location caching strategy”. Here whenever a call is
initiated for an MT, an entry is added to the cache which contains a mapping from the ID
of the MT to that of its serving MSC/VLR. Another call is initiated for an MT, and if no
cache entry for the MT exists, the IS-41 call delivery scheme described earlier is used. If
a cache entry exists, the VLR specified by the cache is queried. If the MT is still residing
under the same VLR, a hit occurs. Otherwise, a miss occurs and then the IS-41 call
delivery scheme is used. At the same time, the cost of the scheme is higher than that of
the IS-41.
Most proposed schemes based on caching have two defects. First, if a cache miss
occurs, the delay in call delivery is longer. Second, if the cache miss can be eliminated,
the location registration gives rise to excessive signaling overhead.
Author has explained “New caching-based location management” scheme as follows.
Author has proposed “New location management scheme” based on caching. This
scheme must eliminate cache miss and may reduce excessive signaling overhead caused
at location registration by updating cached information not at all MSC/VLR but at a
selected MSC/VLR. Moreover, each MT makes the update decision. So this “New
caching-based location management” scheme may be feasible in PCS networks.
The call delivery procedure under “New caching based Location” scheme is as follows.
1. Calling MT sends call initiation signal to its serving Mobile Switching Center
(MSC) through the base station.
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2. MSC of calling MT, calling MSC, checks if a cache entry exists for called MT. If
no cache entry for called MT exists for called MT. If no cache entry for called
MT exists, go to step 4. Other wise, calling MSC sends the location request
message to MSC specified in cache entry, called MSC.
3. Called MSC determines the cell location of called MT and assigns TLDN to
called MT. Called MT only records the current time so as to compute fi some time
later. Called MSC then sends this routing information (TLDN) to calling MSC.
GO to step 9
4. Calling MSC sends the location request message to HLR of called MT.
5. HLR of called MT determines the current serving VLR of called MT and sends
the route request message to the associated MSC, called MSC.
6. Called MSC determines the cell location of called MT and assigns TLDN to
called MT. At this time, called MT updates candidate set on LRU policy and then
the MT evaluates the inequality for calling MSC/VLR.
7. Called MSC sends this routing information (TLDN) and the result of evaluating
inequality t o HLR.
8. HLR forwards TLDN and the result of evaluating inequality to calling MSC. If
the inequality holds, calling MSC/VLR caches the current MSC/VLR of called
MT. Other wise, calling MSC does not cache.
9. Calling MSC request a call setup to called MSC through the SS7 network.
In [2], Author has proposed “A Forwarding Pointer–Based cache scheme for Reducing
Location Management Cost in PCS networks”. This “Forwarding Pointer-Based Cache”
method can reduce the signaling cost for Location management in PCS networks. In the
existing cache scheme, the use of cache information can effectively reduce the signaling
traffic for locating frequently called mobile terminals. How ever, when the cache
information is obsolete, it results in much more signaling traffic than that of the IS-41. In
order to solve this problem the Pointer-Based (PB) cache scheme is used. Even if the
cached information is not up-to-date, the called user can be found by tracing forwarding
pointers starting from that VLR pointed in the cache instead of querying the HLR. Thus,
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the PB-cache scheme can effectively reduce the frequent access to the HLR and the
signaling traffic for location management.
Figure 2: An example of Locating MT under “PB-Cache Scheme”
In Locating an MT under the “PB-Cache Scheme”, the VLR0 represents the
calling VLR associated with the Register Area (RA) the caller resides. We assume that
the cache information exists in the MSC0 and the cache entry for the called MT (MT1)
currently points to the VLR1. Let’s consider that the MT1 has moved from the RA
associated with VLR1 to the RA associated with VLR2 after the last call arrived. Then,
the current location of the MT1 is the RA associated with the VLR2.When the next call
arrives; the MSC0 first queries the pointed VLR that is VLR1. In this case, since the
existing cache scheme has to perform the call delivery procedure of the IS-41 after an
unsuccessful query for the cache, it results in the waste of the signaling traffic as
compared to the IS-41. However, under the PB-cache scheme, even if the cache
information is obsolete, it traces the pointer chain without querying the HLR until the
current location of the called MT is found within the maximum pointer chain length of k.
So, the saving of one query to the HLR and traffic along some of the signaling links can
be obtained. Note that the pointer chain length has to be limited due to the maximum
pointer setup delay requirement. In the above Figure, we assume that the maximum
pointer chain length, denoted by K, is preconfigured to be one. Therefore, unless the MT1
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moves into the RA associated with the VLR3, it can be found through both cache and
forwarding pointer information without querying the HLR. In the following, more
detailed procedures for the PB-Cache scheme are described.
Author has explained Location Registration procedure under “PB-Cache Scheme” as
follows.
Compared with the IS-41, most procedures for location registration under the PBCache scheme are exactly the same as those of the IS-41 except that the forwarding
pointer is additionally set up between the two VLR’s.
Author has explained Call Delivery procedure under “PB-Cache Scheme” as follows.
Most procedures for call delivery under the PB-Cache scheme are almost the
same as those of the cache scheme except that the called MT is traced through the pointer
chain length of K. When the cache information is obsolete, the pointer chain is traced to
find a called MT starting from the VLR pointed in the cache. If the called MT is located
within the pointer chain length of K from that VLR, it can be found without querying the
HLR.
The cache hit under the PB-Cache scheme contains two situations. One is the
situation that the cache information is correct. Thus, the called MT is found after the only
one query to the pointed VLR. The other is the situation that the cache information is not
correct. In this case, after querying the pointed VLR, the called MT is found by tracing
through the pointer chain of length of K. The cache miss under the PB-Cache scheme
occurs when the called MT is not found even if the forwarding pointer chain has been
traced until the length of K. After this, the same call delivery procedure as that of the IS41 is performed. In this case, the current location of the called MT is transmitted from the
HLR to the calling VLR together with the cache update request message.
In [3], author has explained how the cost of location management reduces from
cost of existed (specified under IS-41 standard) methods by using “Dynamic HLR
Location Management Scheme for PCS Networks”.
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For convenience, author has assumed the HLR that contains the permanent data
information of an MT as the master HLR for the MT. The SA that is associated with the
master HLR is called the master SA for the MT. When an MT moves to another new SA,
the new SA that the MT resides is called the current HLR for the MT. All the popular
existing PCS networks such as Pan-European Digital Cellular (GSM) and North
American Digital Cellular (IS-41) employ the HLR/VLR architecture.
In the existed (specified under IS-41 standard) schemes, only the master HLR is
used for an MT even though it may move to another SA associated with another HLR.
When an MT moves far away from its master HLR, the communication costs for
accessing the master HLR for both location registration and call delivery will increase
dramatically. This problem leads the author to think in the way of using the current HLR
of an MT for the location management to improve the system performance.
In this “Dynamic HLR location management scheme for PCS networks” a
dynamic copy of location information of an MT is made in the nearest (current) HLR that
can be accessed for location management. A modified table lookup procedure is also
proposed for determining the current HLR easily. With the proposed scheme, an MT can
always access the location data in its nearest HLR for performing location registration
and call delivery.
Author has explained the existing location registration scheme specified under IS-41
standard as follows.
1. The MT detects that it has entered a new RA and sends a location update message to
the new MSC through the base station.
2. The MSC updates its associated VLR indicating that the MT is residing in its area
and sends a location registration message to the master HLR of the MT.
3. The message is routed to a STP, which determines the master HLR of the called MT
from its Mobile Identification Number (MIN), by a table lookup procedure called
Global Title Translation (GTT) .The location message is then forwarded to the
master HLR.
4. The master HLR updates its record indicating the current serving MSC of the MT
and sends a registration acknowledgement message to the new MSC.
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5. The master HLR sends a registration cancellation message to the old MSC.
6. The old MSC deletes the record of the MT in its associated VLR and sends a
cancellation acknowledgment message to the master HLR.
Figure3: The Location registration procedure under IS-41 standard
Author has explained the existing call delivery scheme specified under IS-41 standard as
follows.
1. A call is initiated by an MT and the base station forwards the call initiation signal to
the MSC.
2. The MSC sends a location request message to the master HLR of the called MT
through a STP where GTT is performed.
3. The location request is forwarded to the master HLR.
4. The master HLR sends a location request message to the MSC serving the called
MT.
5. The MSC determines the cell location of the called MT and assigns it a Temporary
Location Directory Number (TLDN) .The MSC then sends this TLDN to the master
HLR.
6. The master HLR forwards the TLDN to the calling MSC.
7. The calling MSC sets up a connection to the called MSC using this TLDN.
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Figure4: The call delivery procedure under IS-41 standard
The author has briefly explained about “Dynamic HLR Location management scheme” in
the following section.
In this “Dynamic HLR management scheme, when the mobile terminals moves
from its master SA to a new SA, the new current HLR obtained a copy of the data about
the MT from the old current HLR and send an acknowledgement message to the old
current HLR as shown in Figure5 below.
If the old HLR is the master HLR, it does nothing with the acknowledgement
message: other wise, it deletes the record of the MT in the old current HLR. With this
scheme, an MT can always use the location data in its nearest (current) HLR for
performing location registration and call delivery.
The Location registration scheme under “Dynamic HLR Location” scheme as follows.
The MT detects that it has entered a new RA and sends a location update message
to the associated new MSC through the base station.
1.
The new MSC updates its associated VLR indicating that the MT is residing in its
area and sends a location registration message to the STP in the signaling
network.
2. The message is routed to the associate HLR of the new MSC trough the STP by
the modified MSC-dependent GTT table lookup procedure. Note that the
associate HLR is also the current (nearest) HLR for the MT.
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3. The current HLR updates its record indicating the current serving (new) MSC of
the MT and sends a registration acknowledgement message to the new MSC. If
the MT stays in the same SA, proceed to the next step; otherwise (i.e, the MT
moved into a new SA), go to step7.
4. The current HLR sends a registration cancellation message to the old MSC.
5. The old MSC deletes the record of the MT in its associate VLR and sends a
cancellation acknowledgement message to the current HLR.
6. (For the case that the MT moved into a new SA) The new current HLR sends a
message to the old current HLR informing the movement of the MT.
7. The old current HLR sends its record about the MT to the new current HLR. It
also sends a registration cancellation message to the old MSC.
8. The old MSC deletes the record of the MT in its associate VLR and sends a
cancellation acknowledgement message to the old current HLR.
9. If the new current HLR is the master HLR, it just sends the old current HLR a
registration acknowledgement message; other wise it sends both the old current
HLR and the master HLR a registration acknowledgement message.
10. For the old HLR, if it is the master HLR, it updates its record pointing to the new
current HLR; otherwise, it deletes the record of the MT.
11. For the master HLR, if it is the new current HLR, it does nothing; other wise, it
updates its record pointing to the new current HLR.
Figure5: The location registration under “Dynamic HLR location management” scheme
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The call delivery scheme under “Dynamic HLR Location” scheme as follows.
1. A call is initiated by an MT (caller) and the base station forwards the call initiated
signal to the MSC.
2. The MSC sends a location request message to the associate HLR. If the caller is
in the same SA, the associate HLR is used as the current HLR for the MT; other
wise the existing GTT table lookup procedure is used to fine the master HLR of
the called MT, and then to find the current HLR of the called MT.
3. The location request is forwarded to the current HLR of the called MT.
4. The current HLR sends a location request message to the MSC serving the called
MT.
5. The MSC determines the cell location of the called MT and assigns it a
Temporary Location Directory Number (TLDN) .The MSC then sends this
TLDN to the current HLR.
6. The current HLR forwards the TLDN to the calling MSC.
7. The calling MSC sets up a connection to the called MSC using this TLDN.
Figure6: The call delivery procedure under “Dynamic HLR
Location management” scheme
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The basic idea in “Dynamic HLR location” scheme is copying of the record of
MT from old SA to new SA. This “Dynamic HLR location” scheme is limitation for
some cases such as when a mobile terminal is moving across number of service areas.
Suppose when a mobile terminal is moving via some service areas then for every
movement in between one SA to another SA the whole process (including “copying of
the record of MT”) takes place. Because of that signaling process the “Dynamic HLR
location management” scheme takes too much of cost for location registration. While an
MT moving across service areas, it may also visit to previous service areas, for this
looping situation the location registration cost under “Dynamic HLR location” scheme is
very high. The copying of the record of MT from old SA to new SA for every time is the
main problem.
This problem leads to think in the way of maintaining pointer entries in the caches
instead of “copying the record of MT”. Here a new “Pointer based HLR” method has
been proposed. In this new “Pointer based HLR” method, cache information at each
HLR is maintained. Whenever the MT moves from old service area to new service area,
an entry will be entered in to the cache that is maintained by old service area. This entry
tells about information of MT (that is it tells “to which SA it has gone”). In the following
chapter3 brief explanation about this “Pointer based HLR” method is mentioned.
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3. PROPOSED SCHEME
Here a new “Pointer based HLR” idea is proposed to reduce the cost of location
registration in the “Dynamic HLR location management” scheme for some cases like
when the mobile terminal moves across service areas. The main basic idea of “Dynamic
HLR location management” scheme is copying of the record of MT when the MT moves
from one SA to another SA. To avoid the copying of record of the MT for every
movement, a new idea is proposed, that is keeping of caches at each HLR. By keeping of
cache information at each HLR, the cost of location registration for cases such as when
the mobile terminal moving via service areas will reduce. Whenever the mobile terminal
moves from old service area to new service area, an entry will be entered in to the cache
that is maintained by old service area. This entry tells about information of MT (that is it
tells “to which SA it has gone”).
While an MT moving across service areas, it may also visit to previous service
areas, for this looping situation the location registration cost under “Dynamic HLR
location” scheme is very high. But in new “Pointer based HLR” method this (looping
problem) problem is avoided. Suppose if the MT moves from old SA to new SA then the
new HLR searches in the cache (new HLR’s cache) for an entry that corresponds to that
particular MT. If it is found then immediately deletes that entry from cache (new HLR’s
cache).
.
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The Location registration scheme under proposed “Pointer based HLR” scheme as
follows.
Figure7: The Location registration scheme under proposed “Pointer based HLR” scheme
1) The MT detects that it has entered a new RA and sends a location
update message to the associated new MSC through the base station.
2) The new MSC updates its associated VLR indicating that the MT is
residing in its area and sends a location registration message to the
STP in the signaling network.
3) The message is routed to the associate HLR of the new MSC through
the STP by the modified MSC dependent GTT table lookup procedure.
4) The current HLR updates its record indicating the current serving
(new) MSC of the MT and sends a registration acknowledgement
message to the new MSC.
5) The new current HLR sends a message to the old current HLR
informing the movement of the MT.
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6) The new current HLR checks its corresponding CACHE, for an entry
that corresponds to that particular MT. If it has found then the new
current HLR immediately deletes that entry of MT from the
corresponding CACHE.
7) The old current HLR sends a message to old MSC to update its
associate VLR. And updates it’s HLR database indicating that the
mobile terminal is currently not active in that SA. And make a pointer
entry regarding the movement of MT in its corresponding CACHE.
That entry tells the information to which HLR it has gone.
8) The old MSC deletes the record of the MT in its associate VLR and
sends a cancellation acknowledgement message to the old HLR.
The call delivery procedure under proposed “Pointer based HLR” scheme as follows.
Figure8: The call delivery procedure under proposed “Pointer based HLR” scheme as
follows.
23
In the above figure MT0 is calling MT1.We can find easily called MT.
1. A call is initiated by an MT0 and the base station forwards the call initiation
signal to the MSC.
2. The MSC sends a location request message to the master HLR by using existing
GTT table look up procedure.
3. The location request is forwarded to the current HLR of the called MT (that is
MT1).
4. The current HLR sends a location request message to the MSC serving the called
MT (that is MT1).
5. The MSC determines the cell location of the called MT and assigns it a
Temporary Location Directory Number (TLDN). The MSC then sends this TLDN
to the current HLR.
6. The current HLR forwards the TLDN to the calling MSC.
7. The calling MSC sets up a connection to the called MSC using this TLDN.
24
4. IMPLEMENTATION OF THE PROPOSED SCHEME
4.1 Description of the System
Here the pointer forwarding concept and searching the target MT is implemented
on the UNIX platform. In this implementation four HLR regions are considered, each
acts as master HLR for four mobile terminals and also maintaining caches at the HLR
level. These caches are used for maintaining the information about mobile terminals that
are leaving the corresponding HLR regions. These caches store the pointer entries, which
tell about to which HLR region the mobile terminal, has gone out.
In this system the target MT is moved over all four HLR regions randomly. So every
execution may be differ or same as from previous execution. If the same mobile terminal
name is given as the target MT, then it may give same output or different from the
previous output.
Let the four HLR regions be HLR1, HLR2, HLR3 and HLR4. And mobile terminals be
MT11,MT12,MT13,MT14,MT21,MT22,MT23,MT24,MT31,MT32,MT33,MT34, MT41,
MT42, MT43, MT44. Enter two mobile terminals, one is caller MT and other is target
MT. Target MT moves along HLR regions. If it moves from HLR1 to HLR2 then a
pointer entry entered into the HLR1’s cache that is CACHE1, which tells that the target
MT is moved to HLR2 region. The entry is “target MT::HLR2” and if it moves from
HLR2 to HLR3 then the entry is “target MT:: HLR3” entered into the HLR2’s cache that
is CACHE2 and so on.
The target MT searches across the hierarchial network structure as shown in the Figure9.
If system controller is at HLR1 and it founds that the particular target MT is not present
then it checks HLR1’s cache that is CACHE1. If it founds an entry “target MT::HLR3”
then it goes to NODE1 and then Root node and then NODE2 and then HLR3 and
searches in the HLR3.
25
The following figure shows the hierarchical network structure of HLR regions.
Figure9: Hierarchical Network Structure
The HLR contains the permanent data (directory number, profile information, current
location, and validation period) of the MTs whose primary subscription is within the area.
For each MT, it contains a pointer to the VLR to assist routing incoming calls. A VLR is
associated with a Mobile Switching Center (MSC) in the networks. It contains temporary
record for all MTs currently active within the service area of the MSC.
For convenience, call the HLR that contains the permanent data information of the MT as
the master HLR for that MT. The service area that is associated with the master HLR is
called the master SA for that MT.
26
In this implementation HLR1 is taken as the master HLR for the mobile terminals MT11,
MT12, MT13, and MT14. HLR2 is taken as master HLR for the mobile terminals MT21,
MT22, MT23, and MT24. HLR3 is taken as master HLR for the mobile terminals MT31,
MT32, MT33, and MT34. HLR4 is taken as master HLR for the mobile terminals MT41,
MT42, MT43, and MT44.
The following Figure10 shows the Global Title Translation (GTT) database.
Figure10: Global Title Translation Database
The main use of GTT is to determine the master HLR of the called MT from its Mobile
Identification Number (MIN) .The GTT is a table lookup procedure.
In this implementation the above figure shows the Master HLR s for the four sets of
mobile terminals each set having 4 mobile terminals.
From this table the master HLR can be found for a particular terminal that is useful for
call delivery procedure (in searching process).
27
The following Figure11 shows the state of all mobile terminals in all HLR regions.
Figure11: Initial State of all service areas
4.2 System Files
# inputpass.sh
#First program to run the system ..
#Input passing.......................
# 1.Global Title Translation
creation..........................
if [ -s gtt ]
28
then
rm -f gtt
fi
i=1
while [ $i -le 4 ]
do
echo "HLR"$i"::MT"$i"1::MT"$i"2::MT"$i"3::MT"$i"4" >>gtt
i=`expr $i + 1`
done
# 2.HLRs creation.......................
sh hlr.sh
# Showing all HLR databases Initially............
# 3.Pass user input to search.sh for
searching................
sh input.sh
sh search.sh <op
# hlr.sh
#program for creating HLR databases...............
if [ -s HLR1 ]
then
rm -f HLR1
fi
if [ -s HLR2 ]
then
rm -f HLR2
fi
if [ -s HLR3 ]
then
rm -f HLR3
fi
if [ -s HLR4 ]
then
rm -f HLR4
fi
i=1
29
while [ $i -le 4 ]
do
j=1
while [ $j -le 4 ]
do
echo
"MT"$i$j"::IMSI"$i$j"::MSISDN"$i$j"::1">>HLR$i
j=`expr $j + 1`
done
i=`expr $i + 1`
done
k=1
while [ $k -le 4 ]
do
i=1
while [ $i -le 4 ]
do
if [ $i -eq $k ]
then
i=`expr $i + 1`
continue
fi
j=1
while [ $j -le 4 ]
do
echo
"MT"$i$j"::IMSI"$i$j"::MSISDN"$i$j"::0">>HLR$k
j=`expr $j + 1`
done
i=`expr $i + 1`
done
k=`expr $k + 1`
done
# input.sh
#Program for asking user.........................
tput clear
tput cup 4 20
echo "Enter Caller::"
tput cup 4 35
read m1
tput cup 6 20
echo "Enter Callee::"
30
tput cup 6 35
read m2
echo $m1 >op
echo $m2 >>op
# rootnode.sh
#Rootnode is connecting NODE1 $ NODE2............
read m #it stores HLR..........
read n #info abt MT.........
case $m in
HLR1 | HLR2)echo $m >sample14
echo $n >>sample14
sh Node1.sh <sample14
;;
HLR3 | HLR4)echo $m >sample15
echo $n >>sample15
sh Node2.sh <sample15
;;
*) echo "It is only Connected to Node1& Node2"
;;
esac
# Node1.sh
# Node1 is connecting HLR1, HLR2 &
RootNode........................
read p
read q
#echo $p
#echo $q
case $p in
HLR1) echo $q | sh searchhlr1.sh
;;
HLR2) echo $q | sh searchhlr2.sh
;;
*) #echo " It is only connected to HLR1,HLR2 &
RootNode"
echo $p >sample13
echo $q >>sample13
sh rootnode.sh <sample13
;;
esac
31
# Node2.sh
#Node2 is connecting HLR3, HLR4 & RootNode...........
read x
read y
case $x in
HLR3) echo $y | sh searchhlr3.sh
;;
HLR4) echo $y | sh searchhlr4.sh
;;
*) echo $x >sample14
echo $y >>sample14
sh rootnode.sh <sample14
;;
esac
# search.sh
#program for searching Master HLR's
callee)from GTT..............
read a
read b
awk -F:: 'BEGIN{OFS="::";FS="::"}
{
for(i=2;i<=NF;i++)
{
if(p==$i)
{
m=$1
print m
}
}
}' p=$a gtt > sample1
c=`cat sample1`
awk -F:: 'BEGIN{OFS="::";FS="::"}
{
for(i=2;i<=NF;i++)
{
if(p==$i)
{
n=$1
print n
}
}
32
of MT's(caller ,
}' p=$b gtt >sample2
d=`cat sample2`
clear
tput cup 15 25
echo "INITIALLY "
sleep 3
# Show the mobile terminals on all Service areas before
moving...............
sh showdb1.sh
sleep 8
#Move the Target Mobile terminal over HLRs...............
echo $c >sample3
echo $d >>sample3
echo $a >>sample3
echo $b >> sample3
sh moving.sh < sample3
clear
tput cup 15 25
echo "AFTER MOVING"
sleep 3
# Show the mobile terminals on all service areas after
moving...............
sh showdb1.sh
#pass the vlues to searchconnections.sh for
searching............
echo $c > sample4
echo $d >>sample4
echo $a >>sample4
echo $b >>sample4
sh searchconn.sh <sample4
#moving.sh
#This is First
read mhcaller
read mhcallee
read caller
read callee
case $mhcallee
HLR1)echo
echo
Moving program.........................
in
$callee >op1
$mhcallee>>op1
33
sh mhlr1.sh <op1
;;
HLR2)echo $callee >op2
echo $mhcallee>>op2
sh mhlr2.sh <op2
;;
HLR3)echo $callee >op3
echo $mhcallee>>op3
sh mhlr3.sh <op3
;;
HLR4)echo $callee >op4
echo $mhcallee>>op4
sh mhlr4.sh<op4
;;
*)echo "
"
;;
Esac
# mhlr1.sh
# Program to move HLR1's Mobile terminal.................
read a #callee..................
read b #mhcallee................
awk -F:: 'BEGIN{OFS="::";FS="::"}
{
if(x==$1)
{
$4=0
}
print $0
}' x=$a HLR1 >temp1
echo y|cp temp1 HLR1
x="HLR2::HLR3::HLR4"
# Now its need to generate numbers 0,1,2...................
m5=`sh pass.sh`
echo $x>smalldata
awk -F:: 'BEGIN{FS="::";OFS="::"}
{
34
print $(y+1)
}' y=$m5 smalldata >temp2
# "c" is the new HLR in the journey..................
c=`cat temp2`
echo $a::$c>cache1
#now we have to make 0 as 1 in "a1" of Mobile terminal"a"
#if [ -s hairaa ]
#then
#
rm -f hairaa
#fi
echo $a > hairaa
echo $c >> hairaa
echo $b >> hairaa
sh mhlr12.sh < hairaa
#cat hairaa. mhlr12.sh
#echo $a $c $b|. mhlr12.sh
# mhlr12.sh
# This is second program for Moving of a mobile terminal
Whose Master HLR is HLR1...
read d
read e
read f
# now we have to generate random numbers 0,1
................
m6=`sh pass1.sh`
z="HLR1::HLR2::HLR3::HLR4"
echo $z > smalldata1
awk -F:: 'BEGIN{OFS="::" ;FS="::"}
{
for(i=1;i<=NF;i++)
{
if(p!=$i&&q!=$i)
{
if(m!=0&&p!=$i&&q!=$i)
{
n=$i
}
if(m==0)
{
35
m=$i
}
}
}
if(r==1)
{
print n
}
if(r==2)
{
print m
}
}' p=$e q=$f r=`expr $m6 + 1`
smalldata1 >temp5
a3=`cat temp5`
case $e in
HLR1) n=1
;;
HLR2) n=2
;;
HLR3) n=3
;;
HLR4) n=4
;;
*)n=0
;;
esac
echo $d::$a3 > cache$n
# "f " is the Master HLR of the Mobile Terminal "d"
# "e " is the 1st new HLR of Mobile Terminal "d"
# So "a3" is the 2nd new HLR of Mobile Terminal "d"
echo $d > hairaa1
echo $e >> hairaa1
echo $a3 >> hairaa1
echo $f >> hairaa1
sh mhlr123.sh < hairaa1
#echo $d $e $a3 $f |. mhlr123.sh
36
# mhlr123.sh
# This is the 4th program in moving case.............
read g
read h
read i
read j
z="HLR1::HLR2::HLR3::HLR4"
echo $z > smalldata1
awk -F:: 'BEGIN{OFS="::"; FS="::"}
{
for(i=1;i<=NF;i++)
{
if($i!=p&&$i!=q&&$i!=r)
{
m=$i
}
}
print m
}' p=$h q=$i r=$j
a4=`cat temp6`
case $i in
HLR1) n=1
;;
HLR2) n=2
;;
HLR3)n=3
;;
HLR4) n=4
;;
*)n=" "
;;
esac
smalldata1 > temp6
echo $g::$a4 > cache$n
awk -F:: 'BEGIN{OFS="::";FS="::"}
{
if(p==$1)
{
$4=1
}
print $0
37
}' p=$g
$a4 > temp7
echo y|cp temp7 $a4
# mhlr2.sh
# Program to move HLR2's Mobile terminal.................
read a #callee..................
read b #mhcallee................
awk -F:: 'BEGIN{OFS="::";FS="::"}
{
if(x==$1)
{
$4=0
}
print $0
}' x=$a HLR2 >temp1
echo y|cp temp1 HLR2
x="HLR1::HLR2::HLR3"
# Now its need to generate numbers 0,1,2...................
m5=`sh pass.sh`
echo $x>smalldata
awk -F:: 'BEGIN{FS="::";OFS="::"}
{
print $(y+1)
}' y=$m5 smalldata >temp2
# "c" is the new HLR in the journey..................
c=`cat temp2`
echo $a::$c>cache2
#now we have to make 0 as 1 in "a1" of Mobile terminal"a"
#if [ -s hairaa ]
#then
#
rm -f hairaa
#fi
38
echo $a > hairaa
echo $c >> hairaa
echo $b >> hairaa
sh mhlr12.sh < hairaa
#cat hairaa. mhlr12.sh
#echo $a $c $b|. mhlr12.sh
# mhlr3.sh
# Program to move HLR3's Mobile terminal.................
read a #callee..................
read b #mhcallee................
awk -F:: 'BEGIN{OFS="::";FS="::"}
{
if(x==$1)
{
$4=0
}
print $0
}' x=$a HLR3 >temp1
echo y|cp temp1 HLR3
x="HLR1::HLR2::HLR4"
# Now its need to generate numbers 0,1,2...................
m5=`. pass.sh`
echo $x>smalldata
awk -F:: 'BEGIN{FS="::";OFS="::"}
{
print $(y+1)
}' y=$m5 smalldata >temp2
# "c" is the new HLR in the journey..................
c=`cat temp2`
echo $a::$c>cache3
#now we have to make 0 as 1 in "a1" of Mobile terminal"a"
#if [ -s hairaa ]
#then
39
#
#fi
rm -f hairaa
echo $a > hairaa
echo $c >> hairaa
echo $b >> hairaa
. mhlr12.sh < hairaa
#cat hairaa. mhlr12.sh
#echo $a $c $b|. mhlr12.sh
# mhlr4.sh
# Program to move HLR4's Mobile terminal.................
read a #callee..................
read b #mhcallee................
awk -F:: 'BEGIN{OFS="::";FS="::"}
{
if(x==$1)
{
$4=0
}
print $0
}' x=$a HLR4 >temp1
echo y|cp temp1 HLR4
x="HLR1::HLR2::HLR3"
# Now its need to generate numbers 0,1,2...................
m5=`. pass.sh`
echo $x>smalldata
awk -F:: 'BEGIN{FS="::";OFS="::"}
{
print $(y+1)
}' y=$m5 smalldata >temp2
# "c" is the new HLR in the journey..................
c=`cat temp2`
echo $a::$c>cache4
#now we have to make 0 as 1 in "a1" of Mobile terminal"a"
40
#if [ -s hairaa ]
#then
#
rm -f hairaa
#fi
echo $a > hairaa
echo $c >> hairaa
echo $b >> hairaa
. mhlr12.sh < hairaa
#cat hairaa. mhlr12.sh
#echo $a $c $b|. mhlr12.sh
#searchconn.sh
read mhcaller
read mhcallee
read caller
read callee
case $mhcallee in
HLR1) echo $callee | sh searchhlr1.sh
;;
HLR2) echo $callee | sh searchhlr2.sh
;;
HLR3) echo $callee | sh searchhlr3.sh
;;
HLR4) echo $callee | sh searchhlr4.sh
;;
*) echo "It is not a master HLR"
;;
Esac
# searchhlr1.sh
#This programm is
read s
m=`grep $s HLR1`
echo $m > sample5
for searching in HLR1...............
y=`awk -F:: 'BEGIN{FS="::";OFS="::"}
{
print $4
41
}' sample5 `
if [ $y -eq 1 ]
then
echo "Location found in HLR1"
echo "TLDN of called MT is passing to calling MT"
echo "Connection is established"
else
echo "Location not found"
echo "MT is moving. So we have to search in HLR1's
cache"
n=`grep $s cache1`
echo $n > sample6
z=`awk -F:: 'BEGIN{FS="::";OFS="::"}
{
print $2
}' sample6`
# where z is a variable holds the HLR info. according
to cache info"
echo $z >sample16
echo $s >>sample16
sh Node1.sh<sample16
fi
# searchhlr2.sh
#It is for searching in HLR2..................
read s
m=`grep $s HLR2`
echo $m > sample7
#IFS="::"
#set $m
#y=$3
y=`awk -F:: 'BEGIN{FS="::";OFS="::"}
{
print $4
}' sample7`
if [ $y -eq 1 ]
then
#
tput clear
echo "Location found in HLR2"
echo "TLDN of called MT"
42
echo "Connection established"
else
echo "Location not found"
echo "MT is moving so we have to search in HLR2's
cache"
n=`grep $s cache2`
echo $n > sample8
x=`awk -F:: 'BEGIN{FS="::";OFS="::"}
{
print $2
}' sample8`
echo $x >sample16
echo $s >>sample16
sh Node1.sh <sample16
fi
#searchhlr3.sh
#It is for searching in HLR3.................
read s
m=`grep $s HLR3`
echo $m > sample9
#set $m
y=`awk -F:: 'BEGIN{FS="::";OFS="::"}
{
print $4
}' sample9`
if [ $y -eq 1 ]
then
echo "Location found in HLR333"
echo "TLDN of called MT"
echo "Connection established"
else
echo "Location Not found"
echo "MT is moving so we have to search in HLR3's
cache"
n=`grep $s cache3`
echo $n > sample10
x=`awk -F:: 'BEGIN{FS="::";OFS="::"}
{
print $2
}' sample10`
echo $x >sample16
echo $s >>sample16
43
sh Node2.sh<sample16
fi
#searchhlr4.sh
#It is for searching in HLR4.................
read s
m=`grep $s HLR4`
echo $m > sample11
y=`awk -F:: 'BEGIN{FS="::";OFS="::"}
{
print $4
}' sample11`
if [ $y -eq 1 ]
then
tput clear
echo "Location found in HLR4 "
echo "TLDN of called MT"
echo "Connection established"
else
echo "Location Not found"
echo "MT is moving so we have to search in HLR4's
cache"
n=`grep $s cache4`
echo $n >sample12
x=`awk -F:: 'BEGIN{FS="::";OFS="::"}
{
print $2
}' sample12`
echo $x >sample18
echo $s >>sample18
sh Node2.sh <sample18
fi
44
4.3 Requirements to run the System.
Operating system:: UNIX Operating system
(OR)
LINUX Operating system.
Languages::
Unix Shell programming(Bash), awk
The hard ware requirements for UNIX Operating system:
80MB hard disk and at least 4MB of RAM on a 16-bit microprocessor (80286, or
preferably 80386/80486).
4.4 Results
The following shows the example input to the system.
45
The following Figure12 shows the part of the output, the state of all mobile terminals
before moving.
Figure12: Initial state of all service areas
46
According to the given input, it shows the output in Figure13. The state of all mobile
terminals after target mobile terminal is moving.
Figure 13: The state of all service areas after moving
47
After target mobile terminal moving, the following Figure14 shows the information in all
caches.
Figure 14: The state of all caches after target MT is moving
The following shows the Connection Established statements after searching the target
mobile terminal according to caches.
48
5. COMPARATIVE ANALYSIS
In “Dynamic HLR Location Management Scheme for PCS Networks” a dynamic
copy of mobile terminal location information is provided in the nearest current HLR
database. Here a MT can always access the location data in its nearest HLR for
performing location registration and call delivery.
This “Dynamic HLR location” scheme is limitation for some cases such as when
a mobile terminal is moving across number of service areas. For example let there be 10
Service areas (SA), a particular mobile terminal moving from starting SA to 10th SA. In
this case according to “Dynamic HLR scheme” in between every two Service Areas the
process of copying of the MT record will be implemented. This takes too much of
signaling cost.
For one more case, this “Dynamic HLR location” scheme is not efficient. When
the MT moving across service areas, it may also visit to previous service areas, for this
looping situation the location registration cost under “Dynamic HLR location” scheme is
very high. The copying of the record of MT from old SA to new SA for every time is the
main problem. It is taking unnecessary signaling cost while moving back to previously
visited SA. This problem leads to propose “Pointer based HLR” method which decreases
the cost for the case when the mobile terminals are frequently moving between Service
Areas.
In the proposed “Pointer based HLR” Scheme for PCS Networks a cache is
maintained at each HLR. When ever MT moves from one SA to another SA a pointer
entry will be entered into the cache. If it is staying in the SA, then the pointer entry of
that particular MT will be deleted in the corresponding cache. If MT moves back to
already visited SA then the pointer entry of that particular MT will be deleted from
already visited SA’s cache. This minimizes the cost when the MT is in looping situation.
49
For example let there be 10 service areas (SA), a particular mobile terminal
moves from 1st SA to 10th SA. In this case the pointer entry is entered in the CACHE1
(Cache at HLR1), and the pointer entry is entered in the CACHE2 (Cache at HLR2), and
so on.
By maintaining of these caches the cost of location registration under this
proposed “Pointer based HLR” scheme is minimized as compared to “Dynamic HLR
location” scheme, as the “Dynamic HLR location” scheme is based on copying of record
of the MT from old SA to new SA.
For the proposed “Pointer based HLR” method for a case “when a mobile terminal
moving among SAs” the length of the pointer chain is not considered. The constraint on
the length (i.e number of service areas) through which a MT can be searched must be
known.
5.1 Analytical Model
Notations used in the performance analysis.
• λ l , λA : the incoming call arrival rates (i.e., average number of incoming calls per unit
of time) from the same SA where the called MT locates and from other SAs, respectively.
• 1/ λ m: the average Registration Area(RA) residence time.
• p: inter-SA movement probability.
• Ch : cost for updating or querying the HLR.
Cv : cost for updating or querying the VLR.
• Cg: cost for performing the Global Title Translation (GTT) to determine the master
HLR/Current HLR.
• C 1 and C2: signaling costs for the communication links in the same SA and between
different two SAs, respectively. We also call C 1 and C2 intra-SA signaling cost and interSA signaling cost, respectively.
• N: number of SAs in the PCS network. Assume that the possibility that an MT resides
in any SA is considered to be the same (i.e., 1/N).
50
5.1.1 Analysis of Location Registration method under “Dynamic HLR Location
management” Scheme for when “a mobile is terminal
moving among
SAs”(Figure15)

The possibility that the MT moves to another different SA is p.

The possibility that the MT moves in the same SA will be (1− p).

There are two intra-SA signaling costs 2C1 over links between the new MSC and
the new current HLR and other two intra-SA signaling costs 2C1 over links
between the old MSC and the old current HLR.

There are three inter-SA signaling costs 3C2 are over links between the new
current HLR and the old current HLR.

There are two VLR updates (one for the new VLR and another for the old VLR)
with costs 2Cv.

There are three HLR updates (the first for accessing the new current HLR from
the new VLR, the second for accessing the old current HLR from the new current
HLR, and the third for accessing the new current HLR from the old current HLR)
with costs 3Ch.

The cost for determining the current HLR is Cg.
The costs per unit time for location registration under the “Dynamic HLR location
management” scheme as follows,
CLR = λm{ p(4 C1+3C2+2Cv +3Ch)+ Cg }.
For the case when the MT is moving across 11 service areas (N=11) the cost per
unit time for the location registration under the “Dynamic HLR location
management” scheme will become
CLR =10 λm {p(4 C1+3 C2+2Cv +3 Ch)+ Cg }.
51
Figure15: Location Registration procedure for the case “a mobile terminal
moving among SAs” under “Dynamic HLR Location management”
scheme
5.1.2 Analysis of Location Registration method under proposed “Pointer based
HLR” Scheme for case when “a mobile terminal is moving among
SAs”(Figure16)
Ccacheop: Cost for adding an entry or deleting an entry from the cache.
Ccachesearch: Cost for searching an entry in the cache.

The signaling cost for the location registration is 5C1+C2.

Two VLR updates are there, so the cost is 2Cv.

Two HLR updates are there, so the cost is 2Ch.

The cost for performing GTT to find the current HLR is Cg.

The cost for performing the CACHE search operation is Ccachesearch.

The cost for performing the CACHE operation (adding/deleting is
Ccacheop.
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Total cost for performing Location registration under proposed “Pointer
based HLR” scheme is
C*LR= λm {p (5C1+C2+2Cv+2Ch+Ccacheop+ Ccachesearch)+Cg }
For the case when the MT is moving across 11 service areas (N=11) the
cost per unit time for the location registration under the proposed “Pointer
based HLR scheme” scheme will become.
C*LR =10*{5C1+C2+2Cv+2Ch+Cg+Ccacheop+Ccachesearch}
Figure16: Location Registration procedure for the case “a mobile terminal
moving among SAs” under proposed “Pointer based HLR” scheme
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5.1.3 Analysis of Call delivery method under “Dynamic HLR Location
management” Scheme for case when “a mobile terminal is moving among
SAs”(Figure17 )
The calling MT and the called MT are in the different two SA.
The signaling cost for performing call delivery operation is 2C1 +4C2.
The possibility that the calling MT and the called MT are in the two different
service areas is (N−1)/N.
The database updates costs and the cost of performing the caching scheme to
determine the current HLR for the above two cases are 2Cv +Ch, and Cg
respectively.
The total costs per unit time for the call delivery under the “Dynamic HLR
scheme” is obtained as
CCD = λA (N-1)/N (3C1+3C2+2Cv+Ch+Cg).
Figure17: Call delivery procedure for the case “a mobile terminal moving among
SAs” under “Dynamic HLR Location management” scheme
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5.1.4 Analysis of Call delivery method under proposed “Pointer based HLR”
Scheme for case when “a mobile terminal is moving among SAs” (Figure18)
The signaling cost for performing Call delivery operation is 3C1+4C2.
The cost for performing GTT to find the current HLR is Cg.
The database updates costs and the cost of performing the caching scheme to
determine the current HLR for the above two cases are 2Cv and Cg respectively.
The called MT is present at SA1 and has moved to SA10 via SA2, SA3, SA4 and
so on. The caller MT is present at SA0. Then the cost for performing the CACHE
search operation is performed 9 times, so cost for cache search operation is
9*Ccachesearch.
The total cost for call delivery is obtained as,
CCD= λA (N-1)/N (3*C1+4*C2+Cg+2*Cv+2*Ch)+9*(Ccachesearch)
Figure18: Call delivery procedure for the case “a mobile terminal moving among SAs”
under proposed “Pointer based HLR” Scheme
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5.2 Performance comparisons
The analytical model allows to comapre the proposed “Pointer based HLR” method with
the “ Dynamic HLR location management” scheme.
C*/C is defined as the relative cost of the proposed “Pointer based HLR” method with
respect to “Dynamic HLR location management” scheme.
CMR is the call to mobility ratio, which is the ratio of the call arrival rate to the
mobility rate(i.e λc / λm).
Numerical experiment:
Let N=10 , p=0.005, C1=1,Cg=0.3,Ch=0.2,Cv=0.1, λl =4, λA =6 .
C*=C*LR +C*CD
C=CLR+CCD
For different values of CMR relative cost (i.e C*/C) is obtained as shown in Figure 19.
Figure 19
From the above Figure19 it is observed that when CMR is very less then this proposed
“Pointer based HLR” method has less cost as compared to “Dynamic HLR location
management” scheme. When the Mobility is high (i.e CMR is low) proposed “Pointer
based HLR” method is cost effective than “Dynamic HLR Location management”
scheme.
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6. CONCLUSION
The idea of proposed “Pointer based HLR” scheme for location management in
PCS networks is presented. This idea is effective for the mobile terminals moving
through different SAs frequently. This idea of the proposed method is simple and
effective. It provides pointer type information in caches maintained at HLR for searching
target MT.
With the proposed scheme, excess cost for location registration is reduced in the
looping situation of the MT. With this proposed scheme a caller MT can always access
the information from caches for performing location registration and call delivery
efficiently, and then reduces the signaling and HLR database access traffic.
The
architecture and the functions of existing network elements (HLR/VLR), remain
unchanged only an additional element that is caches at each HLR database is added. An
analytical model is also presented to study the performance of location management
methods.
By applying the analytical model, the performance comparison between the
proposed “Pointer based HLR” location management scheme and the “Dynamic HLR
Location management” scheme for the case “when a mobile terminal moving among
SAs” is done.
Limitation
To implement the case “when a mobile terminal moving among SAs”, a “Pointer based
HLR” method is proposed but the length of the pointer chain is not considered. The
constraint on the length (i.e number of service areas) through which a MT can be
searched must be known. This is the main limitation in this proposed “Pointer based
HLR” scheme.
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REFERENCES
[1]. Yungoo Huh, Cheecha Kim, “New Caching-based Location Management
Schemes
in PCS systems”, 2001 IEEE.
[2]. Jie Li, Yi Pan, “A Dynamic HLR Location Management Scheme for PCS
networks”, 2004 IEEE.
[3]. KI-SIK KONG, JOON-MIN GIL*, YOUN-HEE HAN+, UI-SUNG SONG
AND CHONG-SUN HWANG “A Forwarding Pointer-Based Cache Scheme for
Reducing Location Management Cost in PCS Networks”, Journal of Information
Science and Engineering (2002).
[4]. www.bell-labs.com/user/bejerano/PhD_Thesisi.html.
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