Note: Descriptions are shown in the official language in which they were submitted.
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SYSTEM AND METHOD OF
DELIVERING ROAMER PORT CALLS IN MULTIPLE RADIO
TELECOMMUNICATION SWITCHES
BACKGROUND OF THE INVENTION
Technical Field of the IDvention
This invention relates to radio telecommunication
systems and, more particularly, to a system and method of
utilizing a single roamer port number in a plurality of
radio telecommunication switches.
Description of Related Art-
In radio telecommunications networks, mobile
subscribers may roam from a home network to a visited
network which may be located outside the local calling
area of the home network. When a call is then made to the
roaming mobile subscriber, long distance charges may be
incurred by the mobile subscriber, the calling party, or
both. This is true even if the calling party and the
mobile subscriber are both located within the local
calling area of the visited network.
without the benefit of a roamer port number in the
visited network, existing radio telecommunications
networks utilize the following process of placing a call
from a local subscriber in a visited network to a roaming
mobile subscriber who is roaming in the visited network.
The local subscriber dials the long distance number of the
roaming subscriber since the local subscriber does not
know that the roaming mobile subscriber has roamed into
the visited network. The call from the local subscriber
goes first to the Mobile Switching Center (MSC) in the
visited network serving the local subscriber. The MSC
routes the call long distance to the home MSC of the
roaming mobile subscriber because the Subscriber Number
(SNB) of the called mobile station (MS) is identified as
- 35 being from the mobile subscriber's home network. The home
MSC interrogates the mobile subscriber's Home Location
Register (I-iLR) in the mobile subscriber's home network to
obtain subscriber profile information and location
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information for the roaming mobile subscriber. The mobile
subscriber's HLR provides location information indicating
that the mobile subscriber is roaming in the visited
network. The call is then routed from the home MSC back
to the visited network. Long distance charges are thus
incurred by both the calling subscriber and the called
subscriber.
If a call is made from the PSTN in the local calling
area of the visited network, to a mobile subscriber who
is roaming in the visited network, the call is first
routed by the PSTN to a gateway MSC (G-MSC) in the mobile
subscriber's home network, thereby incurring long distance
charges for the calling party. The G-MSC interrogates the
mobile subscriber's HLR and determines that the mobile
15. subscriber is in the visited network. Then the call is
routed from the G-MSC to the visited network MSC, thereby
incurring long distance charges for the called mobile
subscriber. Thus, two long distance trunks are
established and both subscribers pay long distance
charges.
By regulation, every operator has at least one roamer
port number in its network. Roamer port numbers utilize
two-stage dialing to enable a local subscriber in the
visited network to place a call to a mobile subscriber who
is roaming in the visited network without incurring long
distance charges. If a local subscriber in the visited
network calls a mobile subscriber who is roaming in the
visited network, the local subscriber dials the roamer
port number for his MSC which is a local number. He then
gets a second dial tone, and dials the mobile subscriber's
number. The roamer port number is defined in the visited
network subscriber's MSC and may be the entire service
area of the visited MSC or some sub-area thereof . The
roamer port number tells the visited MSC to page for the
roaming mobile subscriber in the roamer port service area.
That allows a local subscriber in the visited network to
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call the mobile subscriber who is roaming in the visited
network without incurring long distance charges.
' If there are multiple MSCs in the visited network,
there may be a problem in locating the mobile subscriber
and delivering the call because the mobile subscriber is
only paged within the service area of the MSC in which the
roamer port is defined. For example, if the visited
network area is covered by MSC 3, MSC 4, and MSC 5, and
the roamer port number is defined in MSC 3, then the
mobile subscriber is only paged by MSC 3. Thus, there is
only one chance in three of locating the mobile
subscriber. If the mobile subscriber happens to be
located in MSC 4 or MSC 5, then it is not located by the
network, and the call is not delivered. As a result,
paging resources are unsuccessfully utilized more often,
since more attempts result in the mobile station not being
found. Operators, therefore, lose revenue since there is
a greater chance that the call will not be successfully
completed.
Some existing radio telecommunications networks may
provide for sequential paging of all of the MSCs in a
metropolitan area until a roaming mobile subscriber is
found. The problem with this approach is that there may
be an excessive delay before the mobile subscriber is
located. As a result, the calling party often hangs up,
or the trunks time out before the mobile subscriber is
located. Since the number of MSCs continues to increase
in major metropolitan areas, the sequential paging method
is inadequate and unworkable.
Existing radio telecommunications networks may also
provide an enhanced roamer port feature. When a call
comes into a roamer port in a visited MSC (V-MSC), the V-
MSC recognizes the MSNB of the MS as being associated with
the mobile subscriber's home exchange. The V-MSC then
interrogates the subscriber's HLR for location and profile
information for the mobile subscriber. The mobile
subscriber's HLR determines the location of the mobile
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subscriber and returns the location information to the V-
MSC with a temporary routing number. If the routing
number is a local number within the visited network, the
V-MSC delivers the call.
There are several problems with this solution,
however. First, long distance interrogation of the mobile
subscriber's HLR is not desirable to network operators due
to the administrative overhead burden of having to update
tables associating HLRs with every roaming mobile
IO subscriber that enters the V-MSC. Second, network
operators prefer that the roamer port process be an
entirely local process within the visited network.
Although there are no known prior art teachings of
a solution to the aforementioned deficiency and
shortcoming such as that disclosed herein, U.S. Patent
Number 5,153,902 to Buhl et al. (Buhl '902) and U.S.
Patent Number 5,282,240 to Buhl et al. (Buhl '240) discuss
subject matter that bears some relation to matters
discussed herein. Buhl '902 discloses a mobile
communication system in which a mobile subscriber may roam
from one exchange to another. An interrogation exchange
receives incoming calls to the mobile subscriber and
requests information as to the location of the mobile
subscriber from its home exchange. The home exchange
initiates and coordinates the paging process to a
plurality of possible exchanges in which the mobile
subscriber may be located. Buhl '902, however, is not a
local process. Buhl '902 requires long distance
interrogation of the home exchange to obtain location
information for the mobile subscriber. As noted above,
this is not desirable to network oper~.~~r~rs due to the
administrative overhead burden of having to update tables
in the visited exchange associating HLRs with every
roaming MS that enters the visited exchange.
Additionally, calling subscribers as well as called mobile
subscribers may incur long distance charges with the
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system of Buhl ' 902 . Thus Buhl ' 902 does not teach or
suggest the present invention.
Buhl '240 discloses a mobile communication system in
which the home exchange of a mobile subscriber maintains
' S location information for the mobile subscriber. Upon
receipt of an incoming call for the mobile subscriber, the
home exchange orders the exchanges) where the mobile
subscriber may be found to page the mobile subscriber and
establish a voice channel to the mobile subscriber before
routing the call through the network. Buhl '240, however,
is not a local process. Buhl '240 requires long distance
interrogation of the home exchange to obtain location
information for the mobile subscriber. As noted above,
this is not desirable to network operators due to the
administrative overhead burden of having to update tables
in the visited exchange associating HLRs with every
roaming MS that enters the visited exchange.
Additionally, calling subscribers as well as called mobile
subscribers may incur long distance charges with the
system of Buhl '240. Thus Buhl '240 does not teach or
suggest the present invention.
Review of each of the foregoing references reveals
no disclosure or suggestion of a system or method such as
that described and claimed herein.
In order to overcome the disadvantage of existing
solutions, it would be advantageous to have a system and
method of extending the coverage area of a roamer port
number from a single MSC to multiple MSCs within a visited
network. Such a system would greatly increase the
probability of successfully completing each call when
compared to existing systems which page for the mobile
subscriber only in a single MSC within the visited network
where the roamer port number is defined. It would be
additionally advantageous for such a system to be
implemented locally in the visited network, without
requiring long distance HLR interrogation. Such an
implementation would reduce the administrative overhead
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burden of having to update tables associating every
roaming mobile subscriber that enters the V-MSC with the
mobile subscriber's HLR. In addition, in the event a
roaming mobile subscriber's HLR becomes inopertive, the
system would provide a means of contacting the roaming
mobile subscriber through the roamer port number. The
present invention provides such a system and method.
SUMMARY OF THE INVENTION
In one aspect, the present invention is a system for
extending roamer port coverage from a single mobile
switching center (MSC) to a plurality of MSCs within a
visited radio telecommunications network in which a mobile
subscriber is roaming. The system comprises means for
associating a roamer port number with a plurality of MSCs
within the visited radio telecommunications network, means
for simultaneously paging for the roaming mobile
subscriber within each of the associated plurality of MSCs
upon receipt of a call for the mobile subscriber through
the roamer port number, and means for routing the call to
one of the plurality of associated MSCs in which a
successful page response is received. The means for
simultaneously paging for the roaming mobile subscriber
within each of the associated plurality of MSCs may
include means within a first MSC for placing simultaneous
calls by seizing trunks to each of the associated
plurality of MSCs upon receipt of the call for the roaming
mobile subscriber, and means within the first MSC for
instructing each of the associated plurality of MSCs to
simultaneously page for the roaming mobile subscriber.
Alternatively, the means for simultaneously paging for the
roaming mobile subscriber within each of the associated
plurality of MSCs may include means within the first MSC
for utilizing network signaling messages to notify each
of the associated plurality of MSCs that the call is a
roamer port call and to instruct each of the associated
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plurality of MSCs to page for the roaming mobile
subscriber.
In another aspect, the present invention is a method
of extending roamer port coverage from a single mobile
switching center (MSC) to a plurality of MSCs within a
visited radio telecommunications network in which a mobile
subscriber is roaming. The method comprises the steps of
associating a roamer port number with a plurality of MSCs
within the visited radio telecommunications network,
simultaneously paging for the roaming mobile subscriber
within each of the associated plurality of MSCs upon
receipt of a call for the mobile subscriber through the
roamer port number, and routing the call to one of the
plurality of associated MSCs in which a successful page
15. response is received. The step of simultaneously paging
for the roaming mobile subscriber within each of the
associated plurality of MSCs may include the steps of
simultaneously placing calls by seizing trunks to each of
the associated plurality of MSCs upon receipt of the call
for the roaming mobile subscriber, and instructing each
of the associated plurality of MSCs to simultaneously page
for the roaming mobile subscriber. Alternatively, the
step of simultaneously paging for the roaming mobile
subscriber within each of the associated plurality of MSCs
may include utilizing, within the first MSC, network
signaling messages to notify each of the associated
plurality of MSCs that the call is a roamer port call and
to instruct each of the associated plurality of MSCs to
page for the roaming mobile subscriber.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood and its
numerous objects and advantages will become more apparent
to those skilled in the art by reference to the following
drawing, in conjunction with the accompanying
specification, in which:
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FIG. 1 (Prior Art) is a high level block diagram of
two existing radio telecommunications networks between
which mobile subscribers may roam;
FIG. 2 is a flow chart illustrating the steps
S involved in the process of extending the coverage area of
a roamer port number from a single mobile switching center
(MSC) to multiple MSCs within a visited network in a first
embodiment of the present invention;
FIG. 3 is a flow chart illustrating the steps
involved in the process of extending the coverage area of
a roamer port number from a single MSC to multiple MSCs
within a visited network in a second embodiment of the
present invention;
FIG. 4 is a simplified block diagram of a radio
telecommunications network suitable for implementing the
present invention;
FIG. 5 is a simplified block diagram of a MSC
illustrating the additional functions added to an existing
MSC in order to define and implement an extended roamer
port in accordance with the teachings of the present
invention; and
FIG. 6 is a simplified block diagram of a MSC
illustrating the additional functions added to an existing
MSC a.n order to interact with the MSC of FIG. 5 and
thereby implement an extended roamer port in accordance
with the teachings of the present invention.
DETAILED DESCRIPTION OF EMBODIMENTS
FIG. 1 is a high level block diagram of two existing
radio telecommunications networks between which mobile
subscribers may roam. Network-1 (10) may include, by way
of example, a first home location register (HLR-1) 11 and
a plurality of mobile switching centers (MSCs) such as
MSC-1 (12) and MSC-2 (13). Network-2 (14) may include a
second home location register (HLR-2) 15 and a plurality
of MSCs such as MSC-3 (16), MSC-4 (17) and MSC-5 (18).
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A Subscriber-A (Sub-A) 19, whose home network is
Network-1 (10) may roam from Network-1 (10) to Network-2
' (14). Sub-A may then desire to receive telephone calls
originating from within the geographic area serviced by
' S Network-2, and may wish to receive such calls without long
distance charges accruing to either Sub-A or local calling
parties. In accordance with the teachings of the present
invention, the MSCs within Network-2 are modified so that
the area covered by a roamer port number may be defined
by the network operator. The area definition is saved in
one of the network MSCs. For example, Roamer Port Number
X may be defined in MSC-3, and may cover the service areas
of MSC-3, MSC-4, and MSC-5. Sub-A is paged in all three
MSCs (MSC-3, MSC-4, and MSC-5) after Roamer Port Number
X is dialed and Sub-A is dialed.
When a call comes in on the roamer port number, MSC-3
pages Sub-A 19 in the service area of MSC-3. At the same
time, MSC-3 instructs MSC-4 and MSC-5 to page for Sub-A
in their respective service areas since the service areas
of MSC-4 and MSC-5 are also covered by the roamer port
number. In a first embodiment, MSC-3 simultaneously
places calls to MSC-4 and MSC-5 by seizing trunks 21 to
MSC-4 and MSC-5. MSC-3 may add a prefix to Sub-A's
Subscriber Number (SNB) (for example #26) and send the
prefix and SNB to MSC-4 and MSC-5. The pref ix identifies
the call to the SNB as a roamer port call, and instructs
MSC-4 and MSC-5 to page for Sub-A in their service areas.
MSC-4 and MSC-5 then remove the prefix and page for Sub-A
in their respective service areas. Thus, Sub-A is paged
in all three Network-2 MSCs at the same time. If a
successful page response is received from Sub-A in either
MSC-4 or MSC-5, the call is completed to the mobile
station. The originating MSC (MSC-3) then clears the call
(trunk) to the unsuccessful MSC.
In a second embodiment, MSC-3 instructs MSC-4 and
MSC-5 to page for Sub-A in their respective service areas
through network signaling messages rather than seizing
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trunks. For example, in a network utilizing the IS-41
intersystem signaling protocol, MSC-3 may be modified to
send Routing Request (RouteReq) Invoke messages to both
MSC-4 and MSC-5. The RouteReq messages include an
indicator that the call is a roamer port call. Upon
receipt of the RouteReq Invoke messages, MSC-4 and MSC-5
page for Sub-A in their respective service areas. Thus,
Sub-A is paged in all three Network-2 MSCs at the same
time. If a successful page response is received from Sub-
A by one of the MSCs, the successful MSC notifies the
originating MSC where paging is halted. Thereafter, the
call is routed locally to the successful MSC and Sub-A.
In either the first or second embodiments, if a
successful page response is not received from Sub-A by any
of the MSCs, the calling party is notified that Sub-A was
not found.
In this manner, the coverage area of a roamer port
number is extended from a single MSC to multiple MSCs
within a visited network. The probability of successfully
completing each call is greatly increased over existing
systems which page for roaming mobile subscribers only in
a single MSC where the roamer port number is defined. In
addition, the system of the present invention is
implemented locally in the visited network. There is no
requirement for long distance HLR interrogation. This
reduces the administrative overhead burden of having to
update tables associating HLRs with every roaming mobile
subscriber that enters the visited network.
FIG. 2 is a flow chart illustrating the steps
involved in the process of extending the coverage area of
a roamer port number from a single MSC to multiple MSCs
within a visited network in a first embodiment of the
present invention. At step 31, the Network-2 operator
defines Roamer Port Number-X in MSC-3 to cover the service
areas of MSC-3, MSC-4, and MSC-5. At step 32, Sub-A 19
roams from Network-1 to Network-2. At step 33, an
incoming call for Sub-A 19 is received on Roamer Port
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Number-X in MSC-3 in Network-2. The process then moves
to step 34 where MSC-3 begins to page for Sub-A in the
MSC-3 service area and simultaneously places calls to MSC-
4 and MSC-5 by seizing trunks 21. At step 35, MSC-3 adds
' 5 a prefix to Sub-A's SNB and sends the modified SNB to both
MSC-4 and MSC-5. The process then moves to step 36 where
MSC-3, MSC-4, and MSC-5 all page for Sub-A 19 at the same
time.
The process then moves to step 37 where it is
determined whether or not a successful page response was
received from any of the paging MSCs. If not, then the
process moves to step 38 where MSC-4 and MSC-5 notify MSC-
3 that Sub-A was not found. The process then moves to
step 39 where MSC-3 notifies the calling party that Sub-A
was not found. If, however, a successful page response
was received at step 37, then the process moves to step
40 where the MSC with the successful page response
notifies the originating MSC {MSC-3) of the response, and
the call is completed to Sub-A 19. The originating MSC
(MSC-3) then clears the call (trunk) to the unsuccessful
MSC at 41.
FIG. 3 is a flow chart illustrating the steps
involved in the process of extending the coverage area of
a roamer port number from a single MSC to multiple MSCs
within a visited network in a second embodiment of the
present invention. At step 51, the Network-2 operator
defines Roamer Port Number-X in MSC-3 to cover the service
areas of MSC-3, MSC-4, and MSC-5. At step 52, Sub-A 19
roams from Network-1 to Network-2. At step 53, an
incoming call for Sub-A 19 is received on Roamer Port
Number-X in MSC-3 in Network-2. The process then moves
to step 54 where MSC-3 begins to page for Sub-A in the
MSC-3 service area and simultaneously sends intersystern
signaling messages to MSC-4 and MSC-5 instructing MSC-4
and MSC-5 to page for Sub-A in their respective service
areas. As noted earlier, in networks utilizing the IS-41
intersystem signaling protocol, MSC-3 may be modified to
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send Routing Request (RouteReq) Invoke messages to both
MSC-4 and MSC-5. The RouteReq messages include an
indicator that the call is a roamer port call. Upon
receipt of the RouteReq Invoke messages at step 55, MSC-4
and MSC-5 page for Sub-A in their respective service areas
at step 56.
The process then moves to step 57 where it is
determined whether or not a successful page response was
received from any of the paging MSCs. If not, MSC-4 and
MSC-5 notify MSC-3 that Sub-A was not found at step 58.
MSC-4 and MSC-5 may send RouteReq Return Result messages
to MSC-3 indicating that Sub-A was not found. The process
then moves to step 59 where MSC-3 notifies the calling
party that Sub-A was not found. If, however, a successful
page response was received at step 57, then the process
moves to step 60 where the MSC with the successful page
response notifies the originating MSC (MSC-3) of the
response, and paging is halted. Finally, the process
moves to step 61 where the call is routed locally to the
successful MSC and Sub-A 19.
FIG. 4 is a simplified block diagram of a radio
telecommunications network 70 suitable for implementing
the present invention. A HLR 71 is connected by signaling
links 72 to MSC-3 (73), MSC-4 (74), and MSC-5 (75). MSC-3
may establish multiple voice trunks 76 to MSC-4 and MSC-5.
MSC-3 is modified to define a roamer port number to cover
the service areas of MSC-3, MSC-4, and MSC-5. MSC-3 is
also modified to add a prefix to any SNB which is called
through the roamer port.
FIG. 5 is a simplified block diagram of a MSC (for
example MSC-3) illustrating the additional functions added
to an existing MSC in order to define and implement an
extended roamer port in accordance with the teachings of
the present invention. In the exemplary network of FIG.
4, the roamer port number is defined in MSC-3 to cover the
service areas of MSC-3, MSC-4, and MSC-5 in instruction
block 81. Instruction block 82 identifies roamer port
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calls by adding a prefix (for example #26) to any SNB
which is called through the roamer port. Instruction
block 83 enables MSC-3 to simultaneously place calls to
other MSCs by seizing multiple voice trunks to other MSCs
covered in the roamer port definition in block 81.
Instruction block 84 enables MSC-3 to direct the paging
of a mobile station within the service area of MSC-3 while
MSC-4 and MSC-5 also page for the mobile station.
Finally, instruction block 85 enables MSC-3 to order MSC-4
and MSC-5 to stop paging if MSC-3 is the first MSC to
receive a page response from the mobile station. The call
is then delivered to MSC-3 and the mobile station.
FIG. 6 is a simplified block diagram of a MSC (for
example MSC-4) illustrating the additional functions add
with the MSC of FIG. 5 and thereby implement an extended
roamer port in accordance with the teachings of the
present invention. When MSC-4 receives a SNB from MSC-3
with a prefix added to the SNB, instruction block 91
enables MSC-4 to recognize the call as a roamer port call,
and instructs MSC-4 to page for the associated mobile
station within the service area of MSC-4 utilizing paging
mechanism 92. If MSC-4 is the first paging MSC to
receive a page response from the mobile station,
instruction block 93 enables MSC-4 to notify the
originating MSC (for example MSC-3). The call is then
delivered to MSC-4 and the mobile station.
It is thus believed that the operation and
construction of the present invention will be apparent
from the foregoing description. While the method,
apparatus and system shown and described has been
characterized as being preferred, it will be readily
apparent that various changes and modifications could be
made therein without departing from the spirit and scope
of the invention as defined in the following claims.
