Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-09-30
2004-04-06
Trost, William (Department: 2683)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S432300, C455S435100, C455S433000, C455S445000, C370S331000, C370S338000, C370S407000, C707S793000
Reexamination Certificate
active
06718173
ABSTRACT:
BACKGROUND
The present invention relates to communication networks. More particularly, the present invention relates to a system and method for recovering and managing location information in mobile communication networks.
Communications networks that include mobile stations such as cellular telephones typically include some mechanism for tracking the location of the mobile hosts (sometimes referred to herein as “mobiles”) in order to establish connections with the mobile hosts. Generally, each mobile reports its location to the mobile communication network, which stores the location information in one or more location information databases (LIDs). The location information is later retrieved from the LID to establish connections with the mobiles. Conventional approaches to updating the location information for mobiles include having each mobile send a location update message after either a predetermined time period has elapsed andlor the mobile has moved a predetermined distance since the mobile last sent a location update message.
A conventional mobile communication network
10
of the type generally referred to as a personal communications services network (PCS) is shown in FIG.
1
. The mobile communication network
10
has a conventional cellular architecture for providing more efficient use of bandwidth. The mobile communication network comprises a plurality of cells
12
in which mobiles can be located. Each cell
12
has a base station
14
(shown in
FIG. 2
) for establishing wireless links with mobiles
16
(shown in
FIG. 2
) in the cell
12
.
A set of base stations
14
is controlled by a base station controller (BSC)
18
(shown in FIG.
1
). The primary function of a BSC
18
is to manage the radio resources of the base stations
14
controlled by the BSC
18
, for example, by performing call hand-off and allocating radio channels. Each BSC
18
is connected to a mobile switching center (MSC)
20
through a wired network
22
. Each MSC
20
is typically connected to more than one BSC
18
and has a location area
24
that includes all of the cells
12
under the control of BSCs
18
that are connected to the MSC
20
. The MSC
20
typically provides switching functions and coordinates location registration and call delivery for mobiles
16
located within the location area
24
of the MSC
20
. Each MSC
20
has access to the location information databases in the mobile communication network
10
, which are used to store location and service information for each registered mobile
16
of the mobile communication network
10
.
Mobile communication networks
10
that comply with the IS-41 standard (which is described in EIA/TIA, “Cellular Radio Telecommunications Intersystems Operation,” PN-2991, November 1995, and is incorporated by reference) use a two-level hierarchy of location information databases for location management. Location information databases that adhere to the IS-41 standard have a home location register (HLR)
26
and one or more visitor location registers (VLRs)
28
. The HLR
26
is a global database in which information (including location information) about all mobiles
16
registered in the mobile communication network
10
is stored. Each VLR
28
is typically associated with a single MSC
20
and stores information (including location information) about mobiles visiting the location area
24
of the MSC
20
associated with that VLR
28
.
In mobile communication networks
10
that comply with the IS-41 standard, the HLR
26
and the VLRs
28
are updated with location information from mobiles
16
as shown in FIG.
3
. Initially, a mobile
16
is located in a first location area
24
a
that is associated with a first MSC
20
a
and a first VLR
28
a
(which has an entry for the mobile
16
). Then the mobile
16
moves into a second location area
24
b
associated with a second MSC
20
b
and a second VLR
28
b
. The mobile
16
sends a location update message
30
to the second MSC
20
b
, and the MSC
20
b
sends a location update message
32
containing location information about the mobile
16
to the HLR
26
. After receiving the location update message
32
, the HLR
26
updates the entry that the HLR
26
has for the mobile
16
with the location information contained in the location update message
32
, sends a confirmation message
34
back to the second MSC
20
b
, and sends a deletion message
36
to the first MSC
20
a
. After receiving the confirmation message
34
from the HLR
26
, the second MSC
20
b
creates an entry in the second VLR
28
b
for storing the location information for the mobile. After receiving the deletion message
36
from the HLR
28
, the first MSC
20
a
deletes the entry for the mobile
16
in the first VLR
28
a.
The call delivery protocol (CDP) of the IS-41 specifies how the location information stored in the location information databases can be used to complete telephone calls between first and second mobiles
16
a
and
16
b
. As shown in FIG.
4
. when the first mobile
16
a
places a telephone call to the second mobile
16
b
, the first mobile
16
a
sends a call delivery request (CDR)
40
to the first MSC
20
a
. The first MSC
20
a
queries the first VLR
28
a
associated with the first MSC
20
a
to determine if the first VLR
28
a
has an entry for the second mobile
16
b
. If the first VLR
28
a
has an entry for the second mobile
16
b
, i.e., if the second mobile
16
b
is located within the first location area
24
a
associated with the first MSC
20
a
and the first VLR
28
a, the first MSC
20
a
establishes a connection between the first and second mobiles
16
a
and
16
b
, assuming the second mobile
16
b
is in a mode to receive calls. If the first VLR
28
a
does not have an entry for the second mobile
16
b
, i.e., if the second mobile
16
b
is not located within the first location area
24
a
, the first MSC
20
a
sends a query
42
to the HLR
26
for the second mobile's
16
b
location information. The HLR
26
determines the current location area
24
b
for the second mobile
16
b
from the entry stored in the HLR
26
for the second mobile
16
b
and sends a route request
44
to the second MSC
20
b
that is associated with the location area
24
b
in which the second mobile
16
b
is located. The second MSC
20
b
determines a temporary location directory number for the second mobile
16
b
(assuming the second mobile is in a mode to receive calls) and transfers the information
46
to the HLR
26
. The HLR
26
sends the information
48
to the first MSC
20
a
, and the MSC
20
a
establishes a connection
50
between the first and second mobiles
16
a
and
16
b
. If a fixed host (that is, a host in the wired network) calls the first mobile
16
a
, the call is routed to the first MSC
20
a
using the location information in the HLR
26
. If the first mobile
16
a
calls a fixed host, the first MSC
20
a
establishes the connection with the fixed host without referring to the HLR
26
; therefore, the delivery of a call from the first mobile
16
a
to a fixed host does not depend on the state of the HLR
26
.
Therefore, calls between two mobiles in different location areas and calls from a fixed host to a mobile typically cannot be completed without using the location information stored in the HLR
26
. As a result, if the location information stored in the HLR
26
is inaccessible, calls between two mobiles in different location areas and calls from a fixed host to a mobile typically cannot be completed and will be dropped. The HLR
26
will be inaccessible, for example, because the HLR
26
is inoperable, referred to herein as a “database failure,” or because the portion of the mobile communication network
10
providing access to the HLR
26
is inoperable, referred to herein as a “link failure.” To avoid extended periods where the HLR
26
is inoperable, conventional mobile communication networks
10
use HLRs
26
that can be restored relatively quickly after a database failure so that the time in which the HLR
26
is inoperable (referred to herein as the “fai
Krishnamurthy Govindarajan
Somani Arun K.
Fish & Richardson P.C., P.A..
Iowa State University Research Foundation
Torres Marcos
Trost William
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