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United States Patent |
5,282,240
|
Buhl
,   et al.
|
January 25, 1994
|
Apparatus and method for directing calls to mobile station subscribers
Abstract
The present invention provides a mobile communications system in which the
home exchange of a mobile subscriber maintains information indicative of
where the mobile subscriber might be found. Upon receipt of a call, the
home exchange requests the exchange where the mobile is believed to be
located to page it and then requests the answering exchange(s) to order
the mobile to tune to a voice/traffic channel. Only after the successful
completion of this process does the answering exchange report this to the
home exchange which then orders routing of the call through the network.
Inventors:
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Buhl; Nancy (Montreal, CA);
Hayes; John (Montreal, CA);
Kallin; Harald (Sollentuna, SE)
|
Assignee:
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Telefonaktiebolaget LM Ericsson (Stockholm, SE)
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Appl. No.:
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765487 |
Filed:
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September 25, 1991 |
Intern'l Class: |
H04M 011/00 |
Field of Search: |
379/56-60,63
455/33,54,56,33.1-33.4,54.1,54.2,56.1
|
References Cited
U.S. Patent Documents
4228319 | Oct., 1980 | DeJager et al. | 379/60.
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4612415 | Sep., 1986 | Zdunek et al. | 379/59.
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4644351 | Feb., 1987 | Zabarsky et al. | 340/825.
|
4700374 | Oct., 1987 | Bini | 379/60.
|
4737978 | Apr., 1988 | Burke et al. | 379/60.
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4748655 | May., 1988 | Thrower et al. | 379/60.
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4794635 | Dec., 1988 | Hess | 379/63.
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4815073 | Mar., 1989 | Grauel et al. | 370/95.
|
4827499 | May., 1989 | Warty et al. | 379/58.
|
4833701 | May., 1989 | Comroe et al. | 379/60.
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4833702 | May., 1989 | Shitara et al. | 379/60.
|
4843622 | Jun., 1989 | Yotsutani et al. | 379/59.
|
4876738 | Oct., 1989 | Selby | 379/60.
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4881271 | Nov., 1989 | Yamauchi et al. | 455/56.
|
4890315 | Dec., 1989 | Bendixen et al. | 379/59.
|
Foreign Patent Documents |
0167458 | Apr., 1985 | EP.
| |
Other References
M. Ballard, E. Issenmann; Digital Cellular Mobile-Radio System ECR900;
European Transactions on Telecommunications and Related Technologies, vol.
I-N.1, Jan.-Feb. 1990.
A. Eizenhofer, H. Pfannschmidt; Philips Kommunikations Industrie AG,
Nurnberg; Integration of Services in the Digital Mobile Teelphone System
MATS-D.
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Primary Examiner: Chan; Wing F.
Assistant Examiner: Bost; Dwayne D.
Attorney, Agent or Firm: Johnson & Gibbs
Parent Case Text
This is a continuation of application Ser. No. 07/515,836, filed Apr. 27,
1990, now abandoned.
Claims
What is claimed is:
1. In a mobile communication system having a plurality of exchanges within
which at least one mobile station may roam and which are connected with
one another by PSTN lines, a method for routing an incoming call firm an
interrogation exchange to the called mobile station, comprising:
obtaining information as to the anticipated location of the mobile station;
paging the called mobile station in at least one of a plurality of
locations based upon said anticipated location information in response to
the receipt of an incoming call for said mobile station by said
interrogation exchange;
receiving a page response from the paged mobile station at one of said
plurality of locations;
designating to said mobile a voice channel to which to tune at said one of
said plurality of locations in response to receiving a page response from
the paged mobile;
sending information identifying the explicit location of the called and
waiting mobile to the interrogation exchange via said private data lines
in response to receiving an indication at said one of said plurality of
locations that said mobile has tuned to the designated voice channel and
is waiting on said voice channel; and
routing the call for said mobile via said PSTN communications lines from
said interrogation exchange to the exchange in which said mobile station
is located and waiting on a voice channel in response to receipt of
information identifying the explicit location of said mobile.
2. A mobile communications system comprising:
at least one mobile station;
a home exchange associated with said at least one mobile station;
one or more additional exchanges within which said at least one mobile
station may be presently located;
means for maintaining information indicative of where said at least one
mobile station may be located;
private data lines connecting said home and one or more additional
exchanges for passing signals therebetween;
PSTN communications lines connecting said exchanges;
paging means, responsive to receipt of a call by an interrogation exchange
directed to said at least one mobile station, for selectively paging said
at least one mobile station in at least one of a plurality of locations in
said home exchange and said one or more additional exchanges;
means st each of said plurality of locations for receiving a page response
from the paged mobile station;
means at each of said plurality of locations and responsive to receiving a
page response from the paged mobile for designating to said mobile a voice
channel to which to tune;
means responsive to receiving an indication at one of said plurality of
locations that said mobile has tuned to the designated voice channel and
is waiting on said voice channel, for sending information identifying the
explicit location of the called and waiting mobile to the interrogation
exchange via said private data lines; and
means responsive to receipt of information identifying the explicit
location of said mobile for routing the call for said mobile via said PSTN
communications lines from said interrogation exchange to the exchange in
which said mobile station is located and waiting on a voice channel.
3. A mobile communication system as set forth in claim 2, also including:
means responsive to a failure to identify the explicit location of said at
least one mobile for notifying the calling party of failure of the call.
4. In a mobile communication system having a plurality of exchanged within
which at least one mobile station may roam and which are connected with
one another by both private data lines for passing signals therebetween
and PSTN communications lines, a method for routing an incoming call from
an interrogation exchange to the called mobile station, comprising:
obtaining information as to the anticipated location of the mobile station;
paging the called mobile station in at least one of a plurality of
locations based upon said anticipated location information in response to
the receipt of an incoming call for said mobile station by said
interrogation exchange;
receiving a page response form the paged mobile station at one of said
plurality of locations;
designating to said mobile a voice channel to which to tune at said one of
said plurality of locations in response to receiving a page response from
the paged mobile;
sending information identifying the explicit location of the called and
waiting mobile to the interrogation exchange via said private data lines
in response to receiving an indication at said one of said plurality of
locations that said mobile has tuned to the disignated voice channel and
is waiting on said voice channel; and
routing the call for said mobile via said PSTN communications lines form
said interrogation exchange to the exchange in which said mobile station
is located and waiting on a voice channel in response to receipt of
information identifying the explicit location of said mobile.
5. A method for call routing as set forth in claim 4 wherein said
anticipated location information is obtained from the home exchange of the
called mobile station via said private data lines.
6. A method for call routing as set forth in claim 4 wherein said
anticipated location information is obtained from a home location
register.
7. In a telecommunications network comprising a first exchange connected to
the public switched telephone network (PSTN), and a second exchange
connected to a plurality of base stations having radio coverage areas in
which a remote station is capable of receiving communication signals from
said base stations, a method of routing communication signals form said
PSTN to said remote station, said method comprising the steps of:
receiving at said first exchange a communication signal directed to said
remote station;
requesting said second exchange to provide a routing number for use in
routing said communication signal from said first exchange to said second
exchange;
paging said remote station in at least one of said radio coverage areas;
detecting at said second exchange a page response transmitted from said
remote station;
transmitting a channel assignment to said remote station after detection of
said page response;
detecting at said second exchange a channel acknowlegement transmitted from
said remote station;
transmitting, in response to the detection of either said page response or
said channel acknowledgement, said routing number from said second
exchange to said first exchange; and
routing said communication signal from said first exchange to said second
exchange using said routing number.
8. The method of claim 7 wherein said communication signal received at said
first exchange is a telephone call.
9. The method of claim 7 wherein said communication signal is routed
through the PSTN.
10. The method of claim 7 wherein:
said telecommunications network is a cellular radio network further
comprising a third exchange;
said first exchange is an interrogation exchange;
said second exchange is a visited exchange;
said third exchange is a home exchange; and
said remote station is a mobile station associated with said home exchange
and being served by said visited exchange.
11. The method of claim 10 wherein said interrogation exchange requests
said home exchange to provide said routing number and said home exchange,
in turn, request said visited exchange to provide said routing number.
12. A radio communications network comprising:
a mobile station;
a home exchange associated with said mobile station;
a first visited exchange having a radio coverage area in which said mobile
station can roam;
an interrogation exchange connected to the public switched telephone
network (PSTN);
wherein said home exchange includes:
means for identifying the exchange location of said mobile station; and
means for communicating with said visited and interrogation exchanges;
wherein said interrogation exchange includes:
means for receiving from said PSTN a call to said mobile station;
means for sending a request to said home exchange to provide a routing
number for use in routing said call to said mobile station;
means for receiving said routing number from said home exchange; and
means for routing said call to said mobile station using said routing
number;
wherein said first visited exchange includes:
means for receiving a request from said home exchange to provide said
routing number;
means for sending a page to said mobile station upon the receipt of said
routing number request from said home exchange;
means for detecting a page response from said mobile station;
means for sending a first channel designation to said mobile station upon
the detection of said page response;
means for detecting a first channel confirmation from said mobile station;
and
means for sending to said home exchange a first routing number
corresponding to said first visited exchange upon the detection of either
said page response or said first channel confirmation.
13. The network of claim 12 wherein said first visited exchange further
includes means for requesting at least one other exchange to page said
mobile station.
14. The network of claim 12 further comprising a second visited exchange
which includes:
means for detecting said page response from said mobile station;
means for sending a second channel designation to said mobile station upon
the detection of said page response;
means for detecting a second channel confirmation from said mobile station;
and
means for sending to said home exchange a second routing number
corresponding to said second visited exchange upon the detection of said
second channel confirmation.
15. In a cellular radio network comprising a first exchange connected to
the public switched telephone network (PSTN), and second and third
exchanges each having a radio coverage area in which a mobile station may
roam, a method for routing a call from said PSTN to said mobile station
comprising the steps of:
receiving said call at said first exchange;
paging said mobile station in at least a part of said second exchange
coverage area;
detecting in said third exchange coverage area a page response from said
mobile station;
assigning in said third exchange coverage area a voice channel to said
mobile station;
detecting in said third exchange coverage area a voice channel confirmation
from said mobile station;
sending, in response to the detection of either said page response or said
channel confirmation, a routing number from said third exchange to said
first exchange; and
routing said call from said first exchange to said third exchange using
said routing number.
16. The method of claim 15 wherein said mobile station is associated with a
home exchange which maintains location information on said mobile station,
and said method further comprises the step of sending a location update
from said third exchange to said home exchange.
17. The method of claim 15 wherein said routing number is used to route the
call through said PSTN.
18. A mobile communication system in which at least one mobile station may
roam, said system comprising:
a home exchange of said at least one mobile station;
at least one visited exchange having a coverage area in which said mobile
station may roam;
an interrogation exchange for receiving incoming calls for said mobile
station;
private data lines connecting said home, visited and interrogation
exchanges for passing signals therebetween;
PSTN communications lines connecting said interrogation and visited
exchanges;
means for obtaining information as to the anticipated location of the
called mobile station;
means responsive to the receipt of an incoming call for said mobile station
by said interrogation exchange for paging the called mobile station in at
least one of a plurality of locations based upon said anticipated location
information;
means at each of said plurality of locations for receiving a page response
from the paged mobile station;
means at each of said plurality of locations and responsive to receiving a
page response from the paged mobile for designating to said mobile a voice
channel to which to tune;
means responsive to receiving an indication at one of said plurality of
locations that said mobile has tuned to a designated voice channel and is
waiting on said voice channel for sending information identifying the
explicit location of the called and waiting mobile to the interrogation
exchange via said private data lines; and
means responsive to receipt of information identifying the explicit
location of said mobile for routing the call for said mobile via said PSTN
communications lines from said interrogation exchange to the exchange in
which said mobile station is located and waiting on a voice channel.
19. A mobile communications system as set forth in claim 18 wherein said
paging means also includes:
means for issuing a paging request to a first exchange and said first
exchange is said home exchange.
20. A mobile communications system as set forth in claim 18 wherein said
paging means also includes:
means for issuing a page request to a first exchange and said first
exchange is a visited exchange.
21. A mobile communication system as set forth in claim 18 wherein the
called mobile is paged in said plurality of different locations
simultaneously.
22. A mobile communication system as set forth in claim 18 wherein the
called mobile is paged in said plurality of different locations
sequentially.
23. A mobile communications system as set forth in claim 18 wherein said
paging means also includes:
means for issuing a page request to a first exchange; and
means within said first exchange for requesting other exchanges in an
extended paging area to page the mobile.
24. A mobile communications system as set forth in claim 18 wherein said
paging means also includes:
means for issuing a page request to a first exchange; and
means within said first exchange for causing said home exchange to request
other exchanges in an extended paging area to page the mobile.
25. A mobile communications system as set forth in claims 23 and 24 wherein
the extended paging area covers the home exchange.
26. A mobile communications system as set forth in claims 22 or 24 wherein
the extended paging area covers a plurality of cooperating exchanges.
Description
CROSS REFERENCE TO RELATED APPLICATION
This application is relates to the U. S. Patent application entitled
"MULTI-EXCHANGE PAGING SYSTEM FOR LOCATING A MOBILE TELEPHONE IN A WIDE
AREA TELEPHONE NETWORK", Ser. No. 07/516,122 filed on even date herewith
and assigned to the assignee of the present invention, which application
is hereby incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to communications systems having mobile
subscribers and, more particularly, to a method for routing calls to such
mobile subscribers.
2. History of The Prior Art
In certain communications systems such as in some radiotelephone systems,
the entire service area of a system is divided into a number of local
service areas or exchanges. In each local area, radio access units are
located at one or more key points to establish radio links between mobile
subscribers and mobile switching centers. Each mobile subscriber is
permanently assigned a unique telephone number recognized by the public
switched network. Thus, calls to a particular mobile subscriber are routed
to an interrogation exchange which consults the home exchange of that
particular subscriber to obtain information regarding where the call
should be routed in order to reach the mobile subscriber. If the mobile
subscriber cannot be reached at the location to which the call was routed
the call is lost and the resources of the communications network have been
occupied unnecessarily.
Although there are no known prior art teachings of a solution to the
aforementioned deficiencies and shortcomings of prior art mobile
communications systems, a number of prior art references exist that
discuss subject matter that relates to the subject matter of the present
application Exemplary of such prior art references are U.S. Pat. Nos.
4,228,319, 4,612,415, 4,748,655, 4,794,635, 4,833,701, and 4,833,702. Each
of these references is discussed briefly below.
U.S. Pat. No. 4,228,319 to De Jager et al. relates to an automatic mobile
subscriber system. De Jager et al. teach stationary stations which
repeatedly transmit through their cell channel a channel number of a free
duplex speech channel which is stored in memory in mobile stations
receiving the call channel. De Jager et al. also teach use of the stored
channel number for automatically selecting the free duplex speech channel
in response to a connection set-up command.
U.S. Pat. No. 4,612,415 to Zdunek et al. relates to a method and means for
controlling telephone interconnect traffic in a trunked radio system.
Zdunek et al. teach continuously monitoring all types of communication
traffic on the system and, in response to an increasing dispatch access
delay, reserving certain repeaters for dispatch use only during a
predetermined period. Zdunek et al. also teach a system in which the
number of simultaneous telephone, interconnect calls permitted on the
system during the predetermined period is dynamically altered in response
to system loading. Still further, Zdunek et al. teach establishment of a
variable, periodically updated, maximum interconnect call length based on
the current system dispatch access delay.
U.S. Pat. No. 4,748,655 to Thrower et al. relates to portable telephones.
According to the teachings of Thrower et al., a personal portable
telephone allows a user access to a cellular radio network via a number of
different gateways including a communal unit, a user's mobile telephone
set, a home telephone or an office PABX. The telephone can also be used as
a paging unit for use within the cellular radio network. The communal
radio unit is a multi-channel arrangement capable of servicing a large
number of personal telephones within its service area which is small
compared to that of a normal cellular radio cell. The communal units may
be transportable and located in public areas such as railway stations,
airports and on trains or coaches. The telephone automatically transmits
its identification number to a gateway when it enters its service area
enabling the subscriber to be accessed by callers without knowing his
whereabouts.
U.S. Pat. No. 4,794,635 to Hess teaches a two-way radio communication
system having a limited number of channels which assigns calls according
to a max-minimum method. Hess' method also ascertains the type of call,
handoff or first assignment, and assigns a server with a given central
controller to a channel frequency within the requestor sector that
minimizes interference to present users. In a second embodiment of his
method, Hess teaches requesting assignment to a limited number of channels
to reduce adjacent channel interference to and from the requestor with
respect to present users operating on a system by utilizing one or more
thresholds to arrange channel assignments based upon progressively larger
or smaller values of received signal strength.
U.S. Pat. No. 4,833,701 to Comroe et al. relates to a trunked
communications system with nationwide roaming capability. According to the
teachings of Comroe et al., selected regional trunking systems are
equipped with telephone interchange capability and provided with local
computers, which communicate with a national hub computer. At each
selected trunking system, several ID's are reserved as "roaming ID's" to
be temporarily assigned to roaming subscribers. When a subscriber
determines that he has roamed into a new trunk system, he requests a
roaming ID. A roaming ID is assigned and transmitted to the subscriber,
which thereafter operates within the new trunked system using its roaming
ID. The roaming assignment is also transmitted to the national hub
computer so that interconnect calls may be properly forwarded. The roaming
subscriber continues to operate under the assigned roaming ID until it
roams out of range of the current system and into yet another trunked
system. In this way, the subscriber may roam from system to system.
U.S. Pat. No. 4,833,702 to Shitara et al. relates to telephone registration
and cancellation control in a wide area cordless telephone system.
Specifically, Shitara et al. teach a method for making a registration of a
roaming cordless telephone in one of a plurality of local service areas
and cancelling the registration.
SUMMARY OF THE INVENTION
In order to overcome the deficiencies and shortcomings of the prior art
discussed above, the present invention, in one aspect thereof, provides a
mobile communications system in which the home exchange of a mobile
subscriber maintains information indicative of where the subscriber might
be found. The home exchange receives a request to locate a specific
subscriber for the completion of a call to it. In order to route an
incoming call, to the exchange where the subscriber is currently located,
the home exchange explicitly locates the mobile subscriber before
answering the request. The term "explicitly locate", as used herein, means
that the mobile is paged and a response is received from the mobile. It
may further imply that a designation order for a specific voice channel
has been sent to the mobile and a confirmation to the voice channel
designation has been received from the mobile. The process of performing
routing only after explicitly locating the called subscriber is a
radically new concept to telephony, greatly increasing the success rate of
calls to mobile subscribers and reducing the unproductive use of costly
network resources.
In one aspect of the present invention there is a mobile communications
system in which at least one mobile station may roam. The system includes
a home exchange of the at least one mobile station and at least one
visited exchange having a coverage area in which the mobile station may
roam. An interrogation exchange receives incoming calls for the mobile
station and requests information from the home exchange as to where to
route the incoming call. Before returning this information to the
interrogating exchange, the home exchange requests the exchange where the
mobile is believed to be currently located to page the mobile. The paging
exchange then pages the mobile in an area where the mobile may possibly be
found, this area is not necessarily defined by or restricted to the
boundaries of the paging exchange. Upon reception of a page response from
the paged mobile, and after possible voice channel designation, the
location of the mobile is reported to the home exchange. The home exchange
then informs the interrogation exchange of the mobile's location for
routing and completion of the call.
In another aspect of the invention, the page response of a mobile need not
be received in the actual paging exchange in order to explicitly locate
the mobile. Any exchange which can determine the mobile subscribers home
exchange can inform the home exchange that a page response has been
received from the mobile and that the mobile has been confirmed on a voice
channel and is awaiting the completion of an incoming call.
In a still further aspect of the invention, the home exchange need not be
an exchange at all, but instead a memory for storing subscriber data such
as a home location register (HLR).
As a note, the interrogation exchange is logically separate from the home
and/or visited exchanges but may physically be the same entity.
In still another aspect of the invention, a mobile communications system
includes at least one mobile subscriber, a home exchange associated with
the mobile subscriber and one or more additional exchanges within which
the mobile subscriber may be presently located. There is also means within
the home exchange or within a home location register for maintaining
information relating to the exchange within which the mobile subscriber
may also be located. A paging means is responsive to initiation of a call
directed to the mobile subscriber and selectively pages the mobile
subscriber in the registered exchange and possibly one or more additional
exchanges. A reporting means is responsive to the paging means and
determines the present exchange within which the mobile subscriber is
presently located and reports that present exchange to the home exchange.
A routing means is contained within the registered exchange and is
responsive to the reporting means for routing the call to the mobile
subscriber within the reported present exchange.
An object of the present invention is to more efficiently and more
accurately route incoming calls to mobile subscribers.
BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of the present invention, and for further
objects and advantages thereof, reference may now be had to the
accompanying description taken in conjunction with the accompanying
drawings in which:
FIG. 1 is a block diagram of a prior art "route first-page later" system of
call routing for automatic roamers;
FIG. 2 is a block diagram of a routing system according to the teachings of
the present invention;
FIG. 3 is a block diagram illustrating extended area paging in a routing
system according to the teachings of the present invention; and
FIG. 4 is a block diagram illustrating reception of a page response in a
non-paging exchange in a routing system according to the teachings of the
present invention; and
FIG. 5 is a flow diagram depicting the steps of a method employed in the
present invention.
DETAILED DESCRIPTION
Referring now to FIG. 1, a prior art "Route First - Page Later" call
roaming system is shown therein. In such a system, an incoming call from
the PSTN 2 is routed to an interrogation exchange 4 via a voice line 6.
Part of the information transmitted from the PSTN to the interrogation
exchange 4 is information regarding the identity (the "B-number") of the
callee (the "B-subscriber"); as opposed to the caller (the
"A-subscriber"). From the B-number, the interrogation exchange 4
determines the B-subscriber's home exchange 8 and, via signalling line 10,
the interrogation exchange 4 asks the home exchange 8 for a
routing/roaming number. If the subscriber is roaming, e.g., in the area
served by visited exchange 14 in FIG. 1, the visited exchange 14 is asked
for a routing number by the home exchange 8 via signalling line 16. This
routing number is then returned to the home exchange 8 via signalling line
18. The routing number is passed from the home exchange 8 to the
interrogation exchange 4 (as indicated by signalling line 20) which
thereafter routes the call to the visited exchange 14 (possibly through
the PSTN as shown). When the visited exchange 14 receives the incoming
call, paging of the mobile 12 is started.
If the mobile station 12 does not reply with a page response, or if there
are no available voice channels or the subscriber is busy and does not
have "call waiting", the routing and use of voice lines from the
interrogation exchange to the visited exchange has been in vain The call
failure information could have been indicated to the A-subscriber from the
interrogation exchange 4 instead, with a substantial savings in
transmission costs between the interrogation and the visited exchange.
It should be appreciated that the above-described procedure incorporates
the classical telephonic principle of "route first-ring later" which is
applicable in ordinary telephony when the subscriber is not more than a
device at the end of a ware and ringing is not initiated before the call
is routed. In mobile telephony, however, this principle is not a
completely valid assumption since there are several steps that must be
taken after an incoming call is received and before ringing can start.
Examples of these steps include paging of the mobile station and
assignment of a voice channel to it.
In the routing procedure incorporated into the present invention, routing
of a call does not take place before the mobile station is explicitly
located and it is verified that it can accept the call. This process is
illustrated in FIG. 2. As with the case of the prior art "route first-page
later" system described with reference to FIG. 1, in the routing system
shown in FIG. 2, an incoming call from the PSTN is routed to an
interrogation exchange 4 via a voice line 6. The interrogation exchange 4
analyzes the B-number and asks the home exchange 8 for a routing/roaming
number. If the subscriber 12 is roaming, the visited exchange 14 is asked
for a routing number. At this point, the routing system shown in FIG. 2
and the "route first-page later" system shown in FIG. 1 begin to differ.
The major change between the two systems is that when the visited exchange
14 gets a request for a roaming number, instead of immediately returning a
roaming number to the home exchange 8, the visited exchange 14 starts to
page the mobile station 12. In FIG. 2, this paging is indicated by the
shaft and right head of double-headed arrow 21. If the visited exchange 14
succeeds in finding the mobile station 12 (said "finding" indicated by the
shaft and left head of double-headed arrow 21), and possibly putting it on
a voice channel, this condition is reported back to the interrogation
exchange 4 through the home exchange 8 and the process of routing the call
to the visited exchange 14 starts over line 22. Otherwise, the fact that
the call has failed and the reason for that failure is reported back to
the home exchange 8 and suitable measures can then be taken, e.g. ,
"transfer on no-reply", "transfer on busy", and so on. The interrogation
exchange 4 is capable of providing necessary actions with respect to the
incoming caller.
If the mobile station 12 was located and placed on a voice channel and the
call routed to the visited exchange 14, ringing is then initiated toward
the mobile station 12.
As those skilled in the art should appreciate, the scheme described
immediately above and shown in FIG. 2 does not delay call setup. Rather,
it allows a substantial savings in transmission costs between the
interrogation exchange 4 and the visited exchange 14 when there is no end
use to be achieved in routing the call to the visited exchange 14.
With the changed paging/routing strategy set forth in connection with the
system of FIG. 2, the home exchange 8 knows the outcome of the paging of
the subscriber 12 before call routing begins. If the outcome is negative,
e. g. , the mobile station 12 does not respond to its page(s) within a
preselected period of time or there are no available voice channels, the
reason for the call failure is supplied to the interrogation exchange 4.
This information is handled by the interrogation exchange directly,
thereby reducing the overall cost of the call attempt by the cost of
routing the incompleteable call.
Referring to FIG. 3 the routing process shown in FIG. 2 is used but with
the additional feature of extended area paging in which the visited
exchange may inform another exchange to also page the mobile. Whichever
exchange receives a page response from the mobile will inform the home
exchange that the mobile has been explicitly located. The call is then
routed to the mobile as described earlier.
In this situation, the exchange which receives the page request determines,
based on the last known location of the mobile, what is the most desirable
area to page. Such a paging area may or may not cover the entire area of
this exchange. In addition, this desired paging area may also cover areas
of bordering exchanges. If this is the case, then the exchanges
controlling these extended paging areas must be informed to page the
mobile. Referring to FIG. 3, the page request could be sent directly from
V.sub.1 to V.sub.2. An alternative is for V1 to inform the home exchange
that paging should also be performed in an extended paging area controlled
by V2. The home exchange could then relay this order to V2, where paging
could commence.
The page requests for the extended paging areas could be initiated
concurrently with the ongoing internal paging process, or the additional
page requests could be initiated after the internal paging process is
complete. If the extended paging area also covers more than one exchange,
each page request could be sent in sequence or in parallel.
An additional benefit of the routing system of the present invention is
illustrated in FIG. 4 which reflects the possibility that a mobile which
receives a page from the paging exchange can actually answer in a
non-paging exchange. The exchange which receives the page response will
order the mobile to tune to a voice channel. If the voice channel
designation is confirmed, the home exchange is then informed of the
mobile's location and the incoming call is routed to the correct exchange,
as described above.
FIG. 4 illustrates a factor that should be considered in the routing system
of the present invention which is unknown page response handling. Mobile
stations rescanning into other exchanges at page response are commonly
directed back into the exchange where the system believes they came from
with the help of "directed retry for unknown page response" routines. Such
treatment is not optimal because of several reasons. First of all, it is
the mobile station's specified right and duty to always send in its
accesses on the strongest possible access channel, without taking such
things as exchange borders into account. When a directed retry is sent
back to the mobile station, not only is the mobile station sent to a cell
that it did not consider to be the best, but there is also a risk that the
mobile station will be lost and the call opportunity lost at the same
time.
When the routing system of the present invention is in use, it is fairly
straightforward to take better care of this type of mobile station access.
Since the system knows that the responding mobile station has apparently
been paged and it is possible from the mobile station number to figure out
who is waiting for a page response, that is, the home exchange, the home
exchange can be informed that the mobile station is waiting on a voice
channel. This process may be understood by reference again to FIG. 4.
Assuming that a page is sent out from visited exchange V1 14, it is
possible that the mobile station 12 will receive the page but answer in
another exchange, for example visited exchange V2 24, and be put on a
voice channel. At that point, visited exchange V2 24 forwards the location
of the mobile to the home exchange 8 which inform the interrogation
exchange 4 which in turn routes the call to V2. Eventually, V1 will also
inform the home exchange that the mobile has not answered the page in that
exchange. The paging process for this particular mobile station has,
however, already terminated (since it was located in V2) and the negative
response from V1 is discarded. Such handling of unknown page responses can
supercede the "directed retry for unknown page response" handling within
current systems.
Another aspect of the present invention that should be considered is the
handling of mobile stations during routing. Specifically, with respect to
the handling of a mobile station after a page response, it should be
understood that an attempt to put the mobile station on a voice channel is
made only after an exchange has received a page response from the mobile
station. There are several reasons for this. First, one should not start
to route the incoming call through the PSTN to an exchange that might have
received a false access. If the mobile station turns up on a voice
channel, the risk that the page response was a multiple access is reduced
substantially. A second reason is to allow for long call routing times.
After the mobile station has sent in its page response, it expects a
response back from the system within 5 seconds. The possible responses can
only be: (a) voice channel designation, (b) directed retry, or (c)
release. One would not be able to successfully complete the call setup if
the routing of the call takes longer than 5 seconds and if nothing is done
on the control channel. Therefore, it is proper to put the mobile station
on a voice channel where it can be kept for an indefinite length of time
by sending frequent messages.
Obviously, numerous modifications and variations are possible in view of
the above teachings. Accordingly, within the scope of the appended claims,
the invention may be practiced otherwise than specifically described
herein.
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