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Description  |
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TECHNICAL FIELD BACKGROUND
The present invention relates to a method in conjunction with updating of
one or more HLR-databases which are included in a GSM-type mobile
telephone system, wherein updating of such a database is requested by
transmitting to a number of VLR-databases a special signal which
identifies the HLR-database concerned.
A GSM-network includes two types of net databases, HLR (Home Location
Register) and VLR (Visitor Location Register). A network will normally
include several HLRs and several VLRs. An example of a GSM network is
illustrated in FIG. 3.
Among other things, each HLR-database has stored therein all permanent data
for those subscribers, i.e. those mobile stations, which belong to this
particular HLR. The telephone number of the mobile stations and
information concerning additional services which are included in the
subscription are examples of such data. The active status of the
additional services and information which discloses in which VLR-database
a respective mobile station is registered at that particular moment are
also stored in HLR. The permanent data stored in HLR is secured by also
storing the data in an external medium with the aid of "backup".
Among other things, there is stored in each VLR-database information which
discloses the whereabouts of respective mobile stations that are
registered in a particular VLR at that particular time. Each VLR also
contains a copy of the subset of all subscriber data that is contained in
HLR and is relevant to this VLR. This subset is obtained from HLR in
conjunction with a new mobile station entering the area covered by a VLR,
whereupon data is signalled from HLR to VLR with the aid of CCITT
7-signalling.
The described structure is highly vulnerable to errors and faults in the
network, caused for instance by restarts in HLR or VLR and also by
signalling associated errors. Consequently, there have been defined within
GSM standardized work procedures for restoring data in these so-called
node types in the most robust way possible, so as to avoid an error
spreading to several nodes and resulting in breakdowns in the network.
When a VLR-database has lost its data for some reason or another, the VLR
will update its data autonomously, by signalling backwards and forwards
between itself and those mobile stations which are located within the area
covered by this particular VLR. This means that those HLR-databases to
which the mobile stations belong will not be affected immediately by a
restart in a VLR. Data is collected from each individual HLR upon the next
radio contact with a mobile station which belongs to this HLR.
On the other hand, if an HLR has been restarted, which means that the data
therein may be corrupted, it is necessary for this HLR to request the
assistance of different VLR in recreating parts of the data that was
stored in HLR. This primarily concerns information as to which VLR mobile
stations are registered at that time. According to GSM-standards, this is
carried out by the HLR-database concerned informing all VLR-databases that
this particular HLR has been restarted and needs to be updated with new
data. This is effected with the aid of a "Reset" operation, which is
signalled over the CCITT 7-network.
According to GSM-standards, when a "Reset-message" is received, those
mobile stations which are registered in this VLR and which, at the same
time, belong to the HLR-which needs to be updated are marked in each
VLR-database in a special way. This marking is effected by allocating a
flag, referred to as a "HLR confirmation flag" to each such mobile
station. The intention with this procedure is to update HLR with data from
VLR on the next occasion on which VLR has radio contact with a mobile
station that has been marked with this flag. In this way, HLR receives
information which discloses in which VLR respective mobile stations are
registered at that particular time. Certain other data is updated at the
same time, although this data is less important than the data which
discloses to which VLR the mobile stations belong. It can also be
mentioned that when updating HLR, a certain amount of data is transmitted
from HLR to VLR, for instance subscriber data which applies to the mobile
station.
Known methods for updating VLR-databases and HLR-databases are described
in: ETSI TC GSM, Recommendation GSM 03.07, Restoration Procedures,
Version: 3.2.0, Date: October 1990.
The known method of updating an HLR-database, however, is difficult to
apply in practice, since a Reset-message does not contain information
which discloses those mobile stations which belong to the HLR to be
updated nor yet those VLR-databases which contain any data whatsoever
required for the relevant updating procedure. Consequently, it is
necessary to derive such information from the VLR-databases, by searching
each and every one of said VLR-databases for the information obtained in
conjunction with the entry of different mobile stations into the area
covered by this VLR. Accordingly, it is necessary for each individual VLR
to search through the whole of its subscriber register in order to find
the HLR to which respective mobile stations belong. This search results in
process capacity losses on the part of the VLR-databases, and these losses
will, of course, be much greater on those occasions when a HLR is
restarted several times within a short period of time or when several HLRs
are restarted shortly after one another and several Reset-messages are
therefore transmitted in sequence. Each VLR will therewith search through
its subscriber register for each Reset-message received.
SUMMARY
The object of the present invention is to provide a method of procedure in
conjunction with updating one or more HLR-databases, so that the losses in
the process capacity of the VLR-databases will be smaller than they would
otherwise be when practicing the aforesaid known method. In brief, this is
achieved in the following way:
The time points at which Reset-messages are received and also the time
points when radio contact is made with different mobile stations are
registered in VLR. With each radio contact between a VLR and a mobile
station, a search is made in VLR with the intention of learning whether or
not the mobile station belongs to a HLR that has requested updating. If
such is the case, the time point of the preceding radio contact between
VLR and the mobile station is compared in VLR with the time at which the
Reset-message was received, wherein HLR is updated with data from VLR when
the preceding radio contact took place earlier than the time at which the
Reset-message was received.
This obviates the necessity of searching in VLR to establish those mobile
stations which are of interest for the updating procedure immediately
after receiving the Reset-message. Instead, this search is spread-out over
time and is effected for each individual mobile station in conjunction
with the next radio contact with said station.
BRIEF DESCRIPTION OF THE DRAWING
The invention will now be described in more detail with reference to the
accompanying drawing, in which
FIG. 1 illustrates two tables which contain certain information which is
stored in a VLR-database in accordance with the invention; and
FIG. 2 illustrates an example of a course of events that occur when
signalling to and from a VLR-database and
FIG. 3 illustrates a GSM radio telephone system, and
FIG. 4 is a flowchart illustrating a method of updating an HLR database in
accordance with the invention;
DETAILED DESCRIPTION
FIG. 1 shows two tables, 12 and 13, which are enclosed by a rectangle 11
which represents a VLR-database. The table 12 contains certain subscriber
data which is stored in the VLR-database, in accordance with the
invention. The time at which a new radio contact occurs between the
VLR-database and any mobile station that is located within the area
covered by this VLR is registered and stored in VLR. This is symbolized in
the Figure by the identity of the mobile station having been written into
the left column of table 12, and by the time having been written into the
right column of said table. The left column of the table includes the
references MS1, . . . , MSn, . . . , which thus represent the identity of
different mobile stations. The right column of the table includes the
references t:MS1, . . . , t:Msn, . . . , which represent the times at
which radio contacts were made with the mobile stations in the left
column.
Upon renewed radio contact with a mobile station, for instance MS1, the
time, t:MS1, is updated in the VLR-database, so that the stored time
information will always correspond to the latest radio contact between the
VLR-database and the mobile station in question. The times at which any
Reset-messages were received and the HLR-databases from which these
signals derive are registered and stored in the VLR-database. This has
been symbolized in the Figure by writing the identity of the HLR-database
into the left column in table 13, and by writing the time points into the
right column of the table. The left column of table 13 includes references
HLR1, . . . , HLRn, . . . , which thus represent the identity of different
HLR-databases. The right column of table 13 includes references t:HLR1, .
. . , t:HLRn, . . . , which represent the times at which Reset-messages
were received from the HLR-databases in the left column. When a new
Reset-message is received from a HLR, for instance HLR1, the time point,
t:HLR1, is updated so that the time information stored in the VLR-database
will always relate to the last received Reset-message from the
HLR-database in question.
With each radio contact between a VLR and a mobile station which is located
within the area covered by this VLR at that particular time, a search is
made in VLR in order to ascertain whether or not the mobile station
belongs to a HLR which has requested updating, i.e. belongs to a HLR which
has transmitted a Reset-message. If such is the case, the time point
stored in VLR, according to table 12, of the preceding registered radio
contact between VLR and this mobile station is compared with the stored
time point at which the Reset-message was received, in accordance with
table 13. When the Reset-message was received at a later time than the
time of the earliest preceding radio contact, the HLR-database is updated
with data from the VLR-database concerned. In other cases, this updating
has already taken place. If, when comparing time points, it is established
that no earlier radio contact between VLR and the mobile station concerned
has been registered, the HLR-database is updated in the same manner as
though a preceding radio contact had been registered at a time earlier
than the time of receiving the Reset-message.
FIG. 2 illustrates an example of a course of events concerning a reciprocal
signalling process, to and from a VLR-database. The Figure includes a time
axis on which five time points, t1-t5, have been marked. At time point t1,
radio contact takes place between VLR and a mobile station MS1, which is
symbolized with the reference sign MS1 above the time axis at time point
t1. MS1 is assumed to belong to the HLR-database HLR1. A search is then
made in the VLR-database in order to ascertain whether or not a
Reset-message has been received from HLR1. In this example, it has been
assumed that this is not the case, and HLR1 is therefore not updated. At
t2, VLR receives a Reset-message from HLR1, which is symbolized with the
reference sign HLR1. At t3, a new radio contact is made between VLR and
MS1. A search is again made in VLR, in order to ascertain whether or not a
Reset-message has been received from HLR1, which this time is established
to be the case. The time point t1 of the earliest preceding radio contact
with MS1 is then compared with the time point t2 at which the
Reset-message was received. Since t1 is earlier than t2, updating is
carried out in this particular case. At t4, a radio contact is made with a
mobile station MS2, which is assumed not to belong to a HLR which has
requested updating. Consequently, no updating is carried out. At t5, a new
radio contact is made with MS1. It is established that a Reset-message has
been received from HLR1 at t2 and that the preceding radio contact with
MS1 took place at t3, which is later than t2. Consequently, no updating is
carried out in this case either. The course of events described above with
reference to FIG. 2 is illustrate as a flowchart if FIG. 4.
As before mentioned, the losses in the processor capacity of the
VLR-database will be relatively small when practicing the inventive
method. This is because the search effected in each individual VLR to
establish which mobile stations are of interest with respect to the
updating of a HLR-database is spread-out over time, instead of requiring
each VLR to search through its subscriber register with each received
Reset-message.
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