Note: Descriptions are shown in the official language in which they were submitted.
` ~` 2189612
.
RADIO TELECOMMUNICATION SYSTEM AND METHOD FOR
LAYERED WIDE AREA ROAMING MANAGEMENT
Field Of the Invention
The present invention relates generally to the provision
of roaming management services in radio telecommunication
systems.
Background Of the Invention
Subscriber units used with radio telecommunication
systems are often registered at a home system but can be used
on certain other systems when prior arrangements have been
made between the systems' service providers. To be of value
to subscribers, such arrangements need to be made with
service providers in all areas where the subscribers wish to
travel. Since subscribers can potentially travel all over
the world, many such prior arrangements can be required to
achieve subscriber satisfaction.
A subscriber unit is said to be roaming when it operates
upon one of these other systems where prior arrangements have
been made. In order to accommodate roaming, certain roaming
management services are provided. Roaming management
services include maintaining valid subscriber unit location
information so that the system upon which a subscriber unit
is currently roaming can be identified. Calls being placed
to a roaming subscriber unit can then be forwarded to the
appropriate system in response to this information. Roaming
management services also include maintaining subscriber
information which serves a role in authorization and credit
verification. Thus, when a roaming subscriber unit attempts
to register or place a call through a system at which the
subscriber unit is not registered, the system can get
assurances that it will receive payment for the requested
services.
Conventional radio telecommunication switching nodes
treat each other as peers for the purposes of providing
2189612
-
roaming management services for one another. In other words,
each switching node has equal status with respect to the
provision of roaming management services. For example, the
Global System for Mobile communications (GSM) assigns
subscriber units to home mobile switching centers (MSCs). A
home location register (HLR) is established for each
subscriber unit in the subscriber unit's home MSC. The HLR
records a complete subscriber and subscriber unit profile.
The HLR additionally stores location data which identify any
MSC upon which the HLR's subscriber unit can be roaming.
When a roaming subscriber unit (i.e. a roamer) first
registers at a roamed-upon MSC, the roamed-upon MSC contacts
the home MSC to inform the home MSC of the roamer's roaming
status and current geographic location. The home MSC can
authorize and/or authenticate the roamer to essentially
verify the roamer's credit worthiness for the roamed-upon
MSC. If roaming is authorized, the roamed-upon MSC
establishes a visiting location register (VLR) for the
roamer. Call terminations (i.e. calls being placed to the
subscriber unit) are first directed to a roamer's home MSC in
response to the roamer's phone number, MIN, or other ID.
Such calls are then forwarded to the roamed-upon MSC from the
home MSC so that the roamed-upon MSC can set up the calls
with the roamer.
While the conventional technique is effective in
providing roaming management services, it has some serious
drawbacks as the number of radio telecommunication switching
nodes increases. Moreover, the number of such switching
nodes continues to increase due to the expansion of radio
telecommunication services. Increases result from extending
radio telecommunication services to new areas and from
overlaying new radio telecommunication services in areas
already covered by existing systems.
If "N" represents the number of systems which wish to
provide roaming management services for one another, then the
number of potential contacts conventionally required to
2189612
.
permit roaming among the N systems is (N-1)2. In addition,
(N-1)2 legal contracts must be entered into among the
population of service providers, and each service provider
must comply with laws, tariffs, rights (including carrier
frequency allocations), and regulations associated with
communicating with all of the other N-1 service providers.
Furthermore, the population of service providers uses diverse
types of equipment. The conventional technique requires each
of the N systems to be compatible with all types of
equipment. Accordingly, conventional roaming management
services lead to costly and complex inefficiencies as the
number of radio telecommunication service providers grows and
as roaming management services are provided over more radio
telecommunication systems.
Thus, there is a significant need for a less complex,
less expensive global roaming management system.
Summary of the Invention
An object of the present invention is to provide a
relatively simple, inexpensive global roaming management
system.
According to one aspect of the present invention, there
is provided a method of providing wide area roaming
management services for radio telecommunication units. The
method comprises the steps of: a) establishing a wide area
communication network having a home switching node and a
remote switching node; b) assigning a subscriber unit to the
home switching node of the wide area communication network;
c) receiving a roaming contact from the subscriber unit at a
local communication network switching node; d) contacting,
from the local communication network switching node, the
remote switching node of the wide area communication network
to evaluate the roaming contact; and e) contacting the home
switching node of the wide area communication network from
the remote switching node of the wide area communication
network to evaluate the roaming contact.
2189612
According to a second aspect of the present invention,
there is provided a radio telecommunication system with
layered wide area roaming management services. The radio
telecommunication system comprises a wide area comml~n;cation
network having a home switching node and a remote switching
node and being configured to have a wide radio coverage area.
The radio telecommunication system also comprises a local
network having a local switching node and being configured to
have a local radio coverage area included in the wide radio
coverage area, the local switching node being configured to
communicate with the remote switching node to evaluate a
roaming contact received from a multimode subscriber unit
having a home assignment at the home switching node.
According to a third aspect of the present invention,
there is provided a method of providing wide area roaming
management services for radio telecommunication units. The
method comprises the steps of: a) establishing a wide area
communication network having a first multiplicity of
switching nodes and a network radio coverage area
encompassing substantially the entire surface of the earth;
b) distributing home assignments for a second multiplicity of
multimode subscriber units among the first multiplicity of
wide area communication network switching nodes; c) locating
a selected one of the first multiplicity of switching nodes
proximate a local switching node of a local network; d)
receiving roaming contacts from a portion of the second
multiplicity of subscriber units at the local switching node;
e) contacting, from the local switching node, the selected
node of the wide area communication network to evaluate the
roaming contacts; and f) contacting various ones of the first
multiplicity of switching nodes from the selected node to
evaluate the roaming contacts, the various ones of the
switching nodes being identified in response to the home
assignments distributed in the step b).
According to a fourth aspect of the present invention,
there is provided a subscriber unit enabling a user of the
2189612
.
subscriber unit to roam within a wide area communication
network (WACN) or within a local communication network (LCN),
or within both the WACN and the LCN. the subscriber unit
comprises a radio transceiver for communicating with the WACN
and with the LCN, and a memory for storing first and second
protocols for enabling the subscriber unit to operate within
the WACN and the LCN, respectively.
According to a fifth aspect of the present invention,
there is provided a local switching node (LSN) adapted for
operation within a wide area communication network (WACN) and
within a local communication network (LCN), the LSN being
further adapted to communicate with a radio telecommunication
subscriber unit operating within the WACN, within the LCN, or
within both the WACN and the LCN. The LSN comprises a
controller responsive to a radio communication from the radio
telecommunication subscriber unit requesting a call
operation, the controller determining whether the radio
telecommunication subscriber unit is registered with the LSN.
If the radio telecommunication subscriber unit is registered
with the LSN, call operation is completed. If the radio
telecommunication subscriber unit is not registered with the
LSN, a registration request message is sent to the WACN,
including a subscriber unit identity number for the radio
telecommunication subscriber unit.
According to a sixth aspect of the present invention,
there is provided a central switching office (CSO) node
adapted for operation within a wide area communication
network (WACN) and within a local communication network (LCN)
which comprises a local switching node (LSN). The CSO node
is further adapted to communicate with a radio
telecommunication subscriber unit operating within the WACN,
within the LCN, or within both the WACN and the LCN, and with
an LSN operating within the LCN. The CSO node comprises a
controller responsive to a radio communication transmitted to
it through the LSN from the subscriber unit requesting a call
operation, the controller determining whether the radio
218g612
telecommunication subscriber unit is registered with the CSO
node. If the radio telecommunication subscriber unit is
registered with the CSO node, call operation is completed.
If the radio telecommunication subscriber unit is not
registered with the CSO node a registration request message,
including a subscriber unit identity number for the radio
telecommunication subscriber unit, is sent through the WACN
to a different CSO node in which the radio telecommunication
subscriber unit is registered.
Brief Description Of the Drawings
A more complete understanding of the present invention
can be derived by referring to the detailed description and
claims when considered in connection with the figures,
wherein like reference numbers refer to similar items
throughout the figures, and:
FIG. 1 shows a higher level layout diagram of an
environment within which a radio telecommunication system can
operate;
FIG. 2 shows a lower level layout diagram of the
environment;
FIG. 3 shows a block diagram of hardware included in a
multimode subscriber unit;
FIG. 4 shows a flow chart of an activation process;
FIG. 5 shows a flow chart of a multimode subscriber unit
process;
FIG. 6 shows a flow chart of a local switching node
process;
FIG. 7 shows a flow chart of a wide area switching node
process; and
FIG. 8 shows a flow chart of a termination call request
process included in the wide area switching node process.
2189612
Detailed Description Of the Drawings
The present invention offers a method of providing wide
area roaming management services for radio telecommunication
units, the method comprising the steps of: a) establishing a
wide area communication network having a home switching node
and a remote switching node; b) assigning a subscriber unit
to the home switching node of the wide area communication
network; c) receiving a roaming contact from the subscriber
unit at a local communication network switching node; d)
contacting, from the local communication network switching
node, the remote switching node of the wide area
communication network to evaluate the roaming contact; and e)
contacting the home switching node of the wide area
communication network from the remote switching node of the
wide area communication network to evaluate the roaming
contact.
The subscriber unit can be a multimode unit and the
method can further comprise the steps of: following a first
communication protocol to establish a communication session
between the subscriber unit and the wide area communication
network; and following a second communication protocol to
establish a communication session between the subscriber unit
and the local communication network.
The first communication protocol following step can
comprise the step of determining a geographic location for
the subscriber unit.
The method can additionally comprise the step of
determining, at the remote switching node of the wide area
communication network, whether to initiate a communication
session with the subscriber unit using the first or second
communication protocol.
The determining step can comprise the steps of:
recording data describing whether a prior communication
session with the subscriber unit used the first or second
communication protocol; initiating a communication session
'` 218g612
` -
with the subscriber unit using the first communication
protocol when the prior communication session with the
subscriber unit used the first communication protocol; and
initiating a communication with the subscriber unit using the
second communication protocol when the prior communication
session with the subscriber unit used the second
communication protocol.
The method can additionally comprise the step of
locating the remote switching node of the wide area
communication network proximate the local communication
network switching node.
The method can additionally comprise the step of
receiving data at the local communication network switching
node from the subscriber unit, the data indicating that the
subscriber unit is assigned to a node included in the wide
area communication network.
The method can additionally comprise the step of
arranging the wide area communication network and the local
network so that area covered by the local network is included
in area covered by the wide area communication network.
The present invention additionally offers a method of
providing wide area roaming management services for radio
telecommunication units, the method comprising the steps of:
a) establishing a wide area communication network having a
first multiplicity of switching nodes and a network radio
coverage area encompassing substantially the entire surface
of the earth; b) distributing home assignments for a second
multiplicity of multimode subscriber units among the first
multiplicity of wide area communication network switching
nodes; c) locating a selected one of the first multiplicity
of switching nodes proximate a local switching node of a
local network; d) receiving roaming contacts from a portion
of the second multiplicity of subscriber units at the local
switching node; e) contacting, from the local switching node,
the selected node of the wide area communication network to
evaluate the roaming contacts; and f) contacting various ones
`' 218g612
of the first multiplicity of switching nodes from the
selected node to evaluate the roaming contacts, the various
ones of the switching nodes being identified in response to
the home assignments distributed in the step b).
FIG. 1 shows a higher level layout diagram, and FIG. 2
shows a lower level layout diagram of an environment within
which a radio telecommunication system 10 can operate.
Referring to FIGs. 1 and 2, system 10 includes a wide area
communication network (WACN) 12 and any number of local
communication networks (LCNs) 14. In the preferred
embodiment, WACN 12 is a satellite-based communication
network. WACN 12 offers a wide area communication network
radio coverage area encompassing substantially the entire
surface of the earth through the use of a constellation of
switching nodes placed in satellite vehicles, or satellites,
(SVs) 16 located in outer space. For clarity, FIGs. 1 and 2
illustrate only a few of these satellites 16.
Within WACN 12, satellites 16 communicate with devices
on the ground through up to hundreds of central switching
office nodes (CSOs) 18, of which FIGs. 1 and 2 show only a
few, and up to millions of multimode subscriber units 20, of
which FIGs. 1 and 2 show only a few. CSOs 18 and subscriber
units 20 can be located anywhere on or near the surface of
the earth. However, CSOs 18 are desirably positioned to
accommodate geopolitical considerations. For example, each
CSO 18 can control WACN communications for a country where
the CSO 18 is located. However, large countries can have
multiple CSOs 18, and small countries can share CSOs with
neighbor countries.
Terrestrial-based communication systems, such as
conventional LCNs 14 and other components of the worldwide
public switched telecommunication network (PSTN) 26, can
access WACN 12 through CSOs 18. Desirably, the constellation
of satellites 16 is configured so that at least one of
satellites 16 is within view of each point on the surface of
the earth at all times. Accordingly, WACN 12 can establish a
2189612
communication circuit through the constellation of satellites
16 between any two subscriber units 20, between any
subscriber unit 20 and a CSO 18, or between any two CSOs 18.
Other telephonic and communication devices can couple to such
circuits through CSO-to-PSTN interfaces. As shown in FIGS. 1
and 2, satellites 16 communicate with adjacent satellites via
cross-links 33.
WACN 12 can be viewed as a higher layer communication
network. Conversely, LCNs 14 can be viewed as lower layer
communication networks. Conventional terrestrial cellular
communication systems represent one form of an LCN 14. A
variety of such systems are known to those skilled in the art
by the acronyms GSM, CDMA, JDC, USDC, AMPS, and the like.
Each LCN 14 has a local radio coverage area which is
overlapped by or included in the radio coverage area of WACN
12. Up to thousands of LCNs 14 can be provided throughout
the world, and nothing requires LCNs 14 to be of a common
variety. Each LCN 14 is controlled by a local mobile
switching center (MSC) 28. Any number of base stations 30
couple to a local MSC 28 and provide radio transmitters and
receivers (not shown) through which radio communications take
place with multimode subscriber units 20 located within the
LCN radio coverage area. Some of these systems provide for
roaming between LCNs using network roaming standards such as
GSM or IS-41. These standards provide for roaming only
between LCNs that use a common standard and have direct MSC-
to-MSC communications.
In a typical scenario, a subscriber will wish to
communicate through any available LCN 14 rather than WACN 12
because communication services, including roaming
communication services, will most likely be less expensive.
However, WACN 12 is available over substantially the entire
surface of the earth for use by multimode subscriber units 20
when an LCN 14 is not available. Of course, preference for
an LCN 14 is no requirement of the present invention, and
nothing prevents a multimode subscriber unit 20 from
--10--
` 2I89612
communicating through WACN 12 even when and where an LCN 14
is available for providing communication services.
WACN communications involving subscriber units 20 take
place via RF communication links 32 with satellites 16. LCN
communications involving subscriber units 20 take place via
RF communication links 34 with base stations 30. Desirably,
RF communication links 32 and 34 employ sufficiently
different communication protocols to minimize interference
within the common radio coverage areas. A communication
protocol represents the time, frequency, and/or coding rules,
procedures, formats, and conventions which are followed by
two devices in order to communicate with one another.
Accordingly, RF communication links 32 employ a communication
protocol referred to below as protocol A and RF communication
links 34 employ a communication protocol referred to below as
protocol B. The specific nature of protocols A and B is
unimportant for the purposes of the present invention.
In accordance with the preferred embodiment of the
present invention, roaming management services are provided
by WACN 12 for any number of LCNs 14 with respect to any
multimode subscriber unit 20 in a simple and efficient
manner. CSOs 18 and MSCs 28 are substantially conventional
radio telecommunication switches. Such switches perform
processes, discussed below, under the control of software
programming. Generally, a multimode subscriber unit 20 is
assigned to a CSO 18 which thereafter adopts the role of a
"home" node within WACN 12 for that subscriber unit. Over a
population of CSOs 18 and subscriber units 20, home
assignments are distributed throughout CSOs 18 of WACN 12.
Any CSO 18 which is not the home node can serve the role of
being a "remote" node within WACN 12 for a subscriber unit
20. For an exemplary situation, FIGs. 1 and 2 refer to the
home node as CSO 18' and the remote node as CSO 18".
At the same time, a subscriber unit 20 can be assigned
to a home local MSC 28, which has an agreement to store
subscription records in the home location register of CSO 18.
2189612
.
When a subscriber unit 20 attempts to engage in
communications through any local MSC 28 other than the home
local MSC 28, a roaming situation occurs. For the exemplary
situation, E~IG. 1 refers to a home local MSC 28 as MSC 28',
5 and FIGs. 1 and 2 refer to a roamed-upon local MSC 28 as MSC
28". When roaming on MSC 28", roaming management services
are preferably provided exclusively through the CSO 18
located proximate the MSC 28". Thus, whether this CSO 18 is
a home CSO 18' or a remote CSO 18", the roamed-upon local MSC
10 28" follows the same process to obtain roaming management
services. FIGs. 1 and 2 show only a single roamed-upon local
MSC 28" being associated with a single CSO 18. However, any
number of roamed-upon local MSCs 28" can be associated with a
single CSO 18.
This process includes contacting or otherwise
establishing a communication link 36 to proximately located
remote CSO 18". Roamed-upon local MSC 28" need not contact
home nodes for roaming subscriber units 20. Thus, global
roaming management services are provided by making
20 arrangements with only the providers of WACN 12 rather than
with a multitude of potential "home" service providers.
Likewise, roamed-upon local MSC 28" need only comply with
interface requirements of a single CSO 18 rather than a
plurality of interface requirements imposed by any number of
25 diverse switching centers. ~urther, by providing the
appropriate set of standards inter-working functions, any CSO
18 may connect to many MSCs 28 where each of the MSCs 28
could use a different roaming support interface standard. In
addition, for most situations the roamed-upon LCN 14 need not
30 concern itself with complying with inter-geopolitical
jurisdiction communication requirements, including complying
with rules and regulations and paying tariffs, to obtain
roaming management services.
FIG. 3 shows a block diagram of multimode subscriber
35 unit 20. Subscriber unit 20 includes a controller and signal
processing section 38. Section 38 couples to A and B
--12--
2189612
..
transceivers 40 and 42, respectively, to a memory 44, and to
an I/O section 46. Section 38 includes microprocessor or
other controller components and related peripheral devices in
addition to components which process call traffic. The
controller portion of section 38 causes subscriber unit 20 to
perform processes defined by computer software stored in
memory 44. In addition, memory 44 records tables, databases,
variables, and other memory structures which are used in the
operation of subscriber unit 20. I/O section 46 includes any
sort of user or electronic interface between subscriber unit
20 and the world outside of subscriber unit 20. Such
interfaces can include a keypad, display, microphone,
speaker, and the like.
The software recorded in memory 44 includes a protocol A
program 48, a protocol B program 50, and a general program
52. Protocol A program 48 includes software which causes
multimode subscriber unit 20 to operate on WACN 12 (see FIGs.
1-2) over RF communication link 32 (see FIG. 2) using
protocol A. Transceiver 40 accommodates communication over
link 32 using protocol A. Protocol B program 50 includes
software which causes multimode subscriber unit 20 to operate
on an LCN 14 (see FIGs. 1-2) over RF communication link 34
(see FIG. 2) using protocol B. Transceiver 42 accommodates
communication over link 34 using protocol B. Nothing
requires transceivers 40 and 42 to be similar to one another
in frequency, modulation format, coding techniques, or the
like. General program 52 includes software which is common
to or independent of protocol A or B operation. Such
software controls I/O section 46 and determines whether to
execute protocol A program 48 or protocol B program 50.
FIG. 4 shows a flow chart of an activation process 54.
Generally, process 54 is performed to personalize system 10
and a newly acquired multimode subscriber unit 20 so that the
newly acquired subscriber unit 20 can be used on system 10.
While FIG. 4 shows a particular sequencing of tasks, those
skilled in the art will appreciate that the tasks need not
-~ ` Z189612
follow in the indicated sequence.
In a task 56, data which describe the newly acquired
subscriber unit 20 and its subscriber are collected. Such
data include subscriber unit identification information,
subscriber identification information, billing information,
feature packages to be activated, and other information
commonly collected during activation of conventional
radiotelephones. In addition, a task 58 is performed to
assign a home CSO node 18' for the subscriber unit 20 within
WACN 12, and a task 60 is performed to assign a WACN
subscriber unit ID to the subscriber unit 20. Desirably, the
subscriber unit ID assigned in task 60 is consistent with the
home CSO node 18' assigned in task 58. Other nodes in WACN
12 can uniquely identify a subscriber unit's home CSO node
18' by evaluating the subscriber unit's ID.
A task 62 stores a subscriber profile in a home location
register (HLR) 64 (see FIG. 2) at the home CSO node 18'. The
subscriber profile is a relatively complete record of
information concerning the subscriber and subscriber unit 20.
A task 65 stores the WACN subscriber unit ID in subscriber
unit 20. As discussed in more detail below, subscriber unit
20 uses its WACN subscriber unit ID to identify itself when
operating on either an LCN 14 or WACN 12. A task 66 is
optional. Task 66 repeats the home and ID assignments for a
particular selected LCN 14. Thus, through task 66 subscriber
unit 20 can have a home LCN 14 and an ID which identifies the
subscriber unit 20 to the home LCN 14. Task 66 is optional
because nothing prevents any LCN 14 wishing to be the home
LCN 14 for a multimode subscriber unit 20 from adopting the
WACN activation as its own. In this situation, a multimode
subscriber unit 20 uses its WACN ID for LCN 14 and WACN 12
operation.
FIG. 5 shows a flow chart of a multimode subscriber unit
process 68. Desirably, substantially all multimode
subscriber units 20 perform a process similar to that
described in FIG. 5. Process 68 is defined through software
-14-
2189612
\
programming stored in memory 44 (see FIG. 3).
Process 68 includes a task 70 which identifies the
networks which are available to provide communication
services. More precisely, task 70 determines whether WACN
12, LCN 14, or both are available at the time and location
where task 70 is performed. Task 70 monitors predetermined
protocol A and protocol B communication channels to identify
the available networks. Next, a query task 72 decides
whether to use an LCN 14 for subsequent communication
services. In a typical scenario, any LCN 14 will be
preferred over WACN 12 because communication service fees are
less expensive. However, this is not a requirement. The
precise selection criteria used in task 72 is unimportant for
the purposes of the present invention.
When task 72 decides to use an LCN 14, a task 74 selects
protocol B. The selection of protocol B causes subsequent
communication sessions to use transceiver 42 and to be
controlled by protocol B program 50 (see FIG. 3). Next, a
task 76 makes a roaming contact with the LCN 14, assuming
that subscriber unit 20 is not already registered to operate
on the LCN 14 and that subscriber unit 20 is, in fact,
roaming. The roaming contact is made by sending a
registration request message to a local MSC 28 (see FIG. 2).
The registration request message is sent using RF
communication link 34 and protocol B via a base station 30
(see FIGs. 1-2). The registration request message includes
the subscriber unit's WACN ID. Although not shown in FIG. 5,
if subscriber unit 20 is already registered on the LCN 14,
task 76 can be omitted. If subscriber unit 20 is not
roaming, then any contact or message sent to an MSC 28 can be
considered a homing contact rather than a roaming contact. A
homing contact registration request message can but is not
required to include the subscriber unit's WACN ID.
After task 76, a query task 78 determines whether access
to the network is approved. Process 68 can remain at task 78
until a message is received from the contacted network before
21~9612
making its determination. However, additional tasks (not
shown) can be included to prevent program control from
remaining at task 78 should no return message be forthcoming.
The return message should indicate whether the request for
registration was granted (i.e. access approved) or denied.
If access is not approved, then a task 80 performs an
appropriate error handling process. Task 80 can, for
example, inform the user of the problem, repeat the
registration request message a certain number of times, or
the like. After task 80, program control loops back to task
70 to continue to identify available networks.
When task 78 determines that access on the contacted
network is approved, a query task 82 determines whether a
call origination event is occurring. A call origination
event can occur when, for example, a user dials a phone
number to make an outgoing call. If call origination is
occurring, a task 84 performs a call origination process.
Task 84 includes conventional call setup, call monitoring,
and call tear down activities. After task 84, program
control loops back to task 70 to continue to identify
available networks.
When task 82 determines that no call origination is
occurring, a query task 86 determines whether a call
termination event is occurring. A call termination event can
occur when, for example, a third party attempts to place a
call subscriber unit 20. In this situation, the network on
which subscriber unit 20 is currently registered will direct
a page message to subscriber unit 20. The page message will
include identifying data that essentially address subscriber
unit 20. Thus, task 86 determines whether such a page
message addressed to subscriber unit 20 has been received.
If a call termination is occurring, a task 88 performs a call
termination process. Task 88 includes conventional call
setup, call monitoring, and call tear down activities. After
task 88, program control loops back to task 70 to continue to
identify available networks. Likewise, when task 86
-16-
2189612
.
determines that no call termination is occurring, program
control loops back to task 70.
Referring back to task 72, when task 72 decides not to
use an LCN 14, a task 90 selects protocol A. The selection
of protocol A causes subsequent communication sessions to use
transceiver 40 and to be controlled by protocol A program 48
(see FIG. 3). Next, a query task 92 determines whether a
registration event has occurred. In the preferred
embodiment, a registration event occurs when subscriber unit
20 moves a predetermined distance since it last registered
with WACN 12 or if a predetermined duration has elapsed since
subscriber unit 20 last registered with WACN 12. When no
registration event has occurred, program control flows to
task 82 to test whether call origination or termination
events are occurring.
When task 92 determines that a registration event has
occurred, a task 94 sends a registration request message to
WACN 12. The registration request message is sent using RF
communication link 32 and protocol A via a satellite 16 (see
~IGs. 1-2). The registration request message includes the
subscriber unit's WACN ID. After or in conjunction with task
94, a task 96 performs a location determination process to
determine a current geographical location for subscriber unit
20. In the preferred embodiment, task 96 monitors position
information broadcast from overhead satellites 16 and
evaluates Doppler and signal propagation delays in
communications with WACN 12 to determine location. As a
result of task 96, WACN 12 resolves the subscriber unit's
location. After task 96, program control flows to task 78 to
evaluate whether access is approved on WACN 12.
Accordingly, subscriber unit 20 operates in multiple
modes to communicate with multiple communication networks.
When roaming contacts are made to an LCN 14, the subscriber
unit 20 identifies itself using its WACN ID. Based upon the
WACN ID, the LCN 14 can conclude that the subscriber unit 20
has a home node in WACN 12.
` ` 218g612
FIG. 6 shows a flow chart of a local switching node
process 98. Process 98 is performed by a local MSC 28 or a
local MSC 28 in conjunction with its base stations 30 (see
FIG. 2). Desirably, substantially all local MSCs 28 and base
stations 30 perform a process similar to that described in
FIG. 6. All communications with subscriber unit 20 which
take place through MSC 28 are compatible with protocol B.
Process 98 includes numerous sub-processes. A roaming
contact process 100, a termination call request process 102,
and an origination call request process 104 are included
among these sub-processes. Numerous other processes
performed by MSC 28, such as a homing contact process, are
not shown for the purpose of clarity. Roaming contact
process 100 is performed when a roaming contact is received
from a subscriber unit 20. A roaming contact occurs when
subscriber unit 20 attempts to register for communication
services on the LCN 14. Process 100 is performed for all
subscriber units 20 which have a WACN ID regardless of which
CSOs 18 (see FIGs. 1-2) are the subscriber units' homes.
Process 100 includes a task 106 which evaluates the WACN
subscriber unit ID. In response to task 106, a query task
108 determines whether the subscriber unit has a home node
included in WACN 12. If the subscriber unit ID does not
indicate a home node within WACN 12, then a task 110 performs
a suitable error handling process. If task 110 is being
performed, the subscriber unit making a roaming contact can
have a home node on some network other than WACN 12. So long
as the LCN 14 has made prior arrangements with this other
network, task 110 can perform conventional procedures for
obtaining roaming management services. If no prior
arrangements have been made, task 110 can simply ignore the
roaming contact, or preferably return an access denied
message. After task 110, program control exits process 100.
When task 108 determines that a roaming contact comes
from a subscriber unit 20 having a home in WACN 12, a task
112 establishes a communication session with the remote CSO
-18-
- ` 218g612
node 18" assigned to the MSC 28" (see FIG. 2) performing
process 100. The communication session can be established
using land line links 36 formed through PSTN 26 (see FIG. 2).
As discussed above, the assigned CSO node 18" is desirably
located proximate MSC 28" relative to the scope of WACN 12.
The assigned MSC 28" desirably remains the same regardless of
the subscriber unit's home CSO 18. Thus, each MSC 28 follows
a single process to obtain roaming management services with
respect to all subscriber units 20, and all CSOs 18 appear as
a single node to each local MSC 28.
After task 112 contacts the assigned remote CSO 18", a
task 114 passes the subscriber unit's registration request to
the remote node of WACN 12 to evaluate the roaming contact.
This registration request includes the subscriber unit's ID.
The roaming contact is evaluated through the receipt of
roaming management services with respect to the requesting
subscriber unit 20. Next, a query task 116 determines
whether access is approved for the roaming subscriber unit
20. Process 100 can remain at task 116 until a message is
received from the contacted remote CSO 18" before making its
determination. However, additional tasks (not shown) can be
included to prevent program control from remaining at task
116 should no return message be forthcoming. If access is
not approved, then a task 118 performs an appropriate error
handling process. Task 118 can, for example, return an
access denied message to the requesting subscriber unit 20
over RF communication link 34 (see FIG. 2). After task 118,
program control exits process 100.
When task 116 determines that access has been approved,
a task 120 constructs a visitor location register (VLR) 122
(see FIG. 2) for the roaming subscriber unit 20. VLR 122
contains, among other things, a subset of the information
from the roamer's HLR 64 (see FIG. 2). This information is
returned to the roamed-upon MSC 28" from WACN 12. In
addition, task 120 can assign a temporary ID to the roaming
subscriber unit 20 for use by the subscriber unit 20 while it
--19--
2189~12
is roaming upon the MSC 28".
After task 120, a task 124 sends an access granted
message to the roaming subscriber unit 20. The access
granted message is sent in accordance with protocol B. At
this point, the subscriber unit 20 is operational on the LCN
14 as a roamer. After task 124, program control exits
process 100.
Termination call request process 102 is performed to
process a call setup being directed to a subscriber unit,
such as the roaming subscriber unit 20. The request to
terminate a call at the subscriber unit can be received at
the MSC 28 from remote node 18" of WACN 12, but it can also
come from PSTN 26. Process 102 is performed in a
conventional manner to page the subscriber unit 20 identified
in the request using protocol B communications, determine
whether the call is answered, monitor any answered call, and
tear down the call after completion.
Origination call request process 104 is performed to
process a call setup request originating at a registered
subscriber unit, such as a roaming subscriber unit 20. The
origination call request is received at MSC 28 from
subscriber unit 20 via protocol B communications.
Conventional processes are used to setup the call through the
PSTN 26. However, in an alternate embodiment the call is
setup through WACN 12. Process 104 performs call setup,
monitors the call, and tears down the call after completion.
FIG. 7 shows a flow chart of a wide area switching node
process 126. Process 126 is performed by a CSO 18 of WACN
12. Desirably, substantially all CSOs 18 perform a process
similar to that described in FIG. 7.
Process 126 includes numerous sub-processes. A receive
registration request process 128, a termination call request
process 130, and an origination call request process 132 are
included among these sub-processes. Numerous other processes
performed by a CSO 18 are omitted for the purposes of
clarity. Receive registration request process 128 is
-20-
2189612
performed when a request for registration is received from a
subscriber unit 20. The registration request can come to CSO
18 via protocol A, RF communication link 32 (see FIG. 2), and
a satellite 16. Alternatively, the registration request can
come to CSO 18 via a LCN 14 using protocol B, RF
communication link 34 (see FIG. 2), and an MSC 28 performing
process 100 (see FIG. 6). The CSO 18 receiving the
registration request can be either a home CSO 18' for the
requesting subscriber unit 20 or a remote CSO 18".
Process 128 includes a query task 134 which determines
whether the registration request received from a subscriber
unit 20 came through an LCN 14. If the registration request
did not come through an LCN 14, then it was received directly
from subscriber unit 20 in accordance with protocol A. When
received in accordance with protocol A, a task 136 clears a
local_net flag to record data which describe the protocol
subscriber unit 20 is using for this and subsequent
communication sessions. The communication protocol used by
the subscriber unit 20 for subsequent communication sessions
is normally by default that for which data was recorded in a
prior communication session. Next, a task 138 performs a
location determination process. Task 138 complements task 96
(see FIG. 5). During task 138, protocol A communications
take place to identify the location of subscriber unit 20.
When task 134 determines that the registration request came
through an LCN 14, a task 140 sets the local_net flag to
record data which describe the protocol subscriber unit 20 is
using for this and subsequent communication sessions. In
addition, when multiple LCNs 14 are assigned to the CSO 18
performing process 128, task 140 can record the identity of
the LCN 14 through which the registration request was
received so that future calls being terminated to subscriber
unit 20 can be routed through that LCN 14.
After tasks 138 or 140, a query task 142 determines
whether the CSO 18 performing process 128 is the home CSO 18
for subscriber unit 20. Task 142 can make its determination
` 218~612
by evaluating the WACN subscriber unit ID included in the
registration request. If the subject CSO 18 is not the home
node, then it is a remote WACN node for subscriber unit 20.
When the subject CSO 18 is a remote node, a task 144 sends
the registration request message and current location
information for subscriber unit 20 to the subscriber unit's
home node to evaluate the roaming contact. For the purposes
of the home node, the identity of the subject CSO 18 can
serve as the location information. Such identity information
will inform a home node how to contact subscriber unit 20 in
the future.
After task 144, a query task 146 determines whether
access is approved for subscriber unit 20. Process 128 can
remain at task 146 until a message is received from the
contacted home CSO 18 before making its determination.
However, additional tasks (not shown) can be included to
prevent program control from remaining at task 146 should no
return message be forthcoming. If access is not approved,
then a task 148 performs an appropriate error handling
process. Task 148 can, for example, return an access denied
message to the requesting subscriber unit. This message is
returned in accordance with the protocol through which the
registration request was received. Protocol A communications
are returned via a satellite 16 and protocol B communications
are returned via an LCN 14.
When task 148 determines that access has been approved,
a task 150 establishes a visitor location register (VLR) 152
(see FIG. 2) for the roaming subscriber unit 20. VLR 152
contains a subset of the information contained in the
roamer's HLR 64 (see FIG. 2). This information is obtained
from the home CSO 18 in a message which responds to the
registration request message. Task 150 is optional to the
extent that protocol B communications are being used because
the roamed-upon MSC 28" (see FIG. 2) will maintain its own
VLR 122 (see FIG. 2) to support a roaming subscriber unit.
However, implementation efficiencies can result from
2189612
establishing VLR 152 even though it can not be needed. This
task is not optional when protocol A communications are being
used.
Referring back to task 142, when the CSO node 18 of WACN
12 which receives a registration request message from a
subscriber unit is the home node, a task 154 performs an
authorization process. For example, task 154 can perform a
suitable authentication algorithm in response to a
cryptographic key passed to the home CSO 18 in the
registration request. In addition, task 154 may investigate
billing records to determine the credit worthiness of the
subscriber unit 20. If the registration request was sent to
the home CSO 18 from a remote CSO 18, task 154 desirably
returns the results of the authorization process to this
remote CSO 18, where the remote CSO is waiting at task 146,
then exits (not shown). Assuming that authorization occurs,
a task 156 updates the subscriber unit's HLR 64 tsee FIG. 2)
with a current indication of subscriber unit location.
After each of tasks 148, 150, and 156, process 128
performs a task 158. Task 158 routes an access granted or
access denied message back to subscriber unit 20. Access is
either granted or denied in response to the authorization
process performed at the home CSO 18 in task 154. If the
registration request came through an LCN 14, then task 158
passes the access granted or denied message back to the local
MSC 28 through link 36 (see FIG. 2). The message will be
passed back to subscriber unit 20 using protocol B in tasks
118 or 124 (see FIG. 6). If the registration request came
via a satellite 16, then task 158 sends the access granted or
denied massage back to subscriber unit 20 via a satellite 16
using protocol A. After task 158, process 128 exits.
FIG. 8 shows a flow chart of termination call request
process 130, which is performed by a remote and/or home CSO
18 in WACN 12. Process 130 generally attempts to complete a
call to a subscriber unit 20. Process 130 includes a query
task 160 which determines whether the CSO 18 performing
-23-
21896I2
process 130 is the called subscriber unit's home node within
WACN 12. If the CSO 18 performing process 130 is the home
node, a task 162 gets a current location for subscriber unit
20 from HLR 64 (see FIG. 2). The location is updated each
time subscriber unit 20 re-registers. However, this location
data need not define location more precisely than to provide
the identity of a CSO 18 through which the subscriber unit 20
can be reached. After task 162, a task 164 passes the
termination call request on to the CSO 18 associated with the
current location for subscriber unit 20. If the current
location for subscriber unit 20 is the home CSO 18, then task
164 simply passes the termination call request to itself.
Otherwise, task 164 passes the termination call request to a
remote CSO 18.
After task 164 and when task 160 determines that the CSO
18 performing process 130 is not the home CSO 18, a query
task 166 determines whether a location register (LR), such as
an HLR 64 or VLR 152 (see FIG. 2), is active for the
subscriber unit 20 being called. If a location register is
active, then an attempt to page the called subscriber unit 20
should be attempted through this CSO 18. However, if a
location register is not active, then a task 168 forwards the
termination call request to the called subscriber unit's home
CSO 18. Of course, if the CSO 18 performing task 168 is the
called subscriber unit's home CSO 18, then an appropriate
error handling process can be performed instead. After task
168, program control exits process 130.
When task 166 determines that an HLR or VLR is active
for the called subscriber unit 20, a query task 170
determines whether the local_net flag is set for the called
subscriber unit 20. The local_net flag was set or cleared
during a prior registration at tasks 140 or 136 (see FIG. 7).
If the local_net flag is set, a task 172 passes the
termination call request to the appropriate MSC 28. The MSC
28 will page the called subscriber unit through process 102
(see FIG. 6) using protocol B communications. If the
-24-
2~89612
local_net flag is clear, a task 174 pages the called
subscriber unit 20 via a satellite 16 using protocol A
communications. After tasks 172 or 174, program control
exits process 130 after following other conventional
termination call request tasks related to call setup, call
monitoring, and call tear down activities.
Referring back to FIG. 7, origination call request
process 132 is performed to process a call setup request
originating at a registered subscriber unit 20. The
origination call request is received at CSO 18 from a
subscriber unit via protocol A or B communications.
Conventional processes are used to setup the call through the
PSTN 26. Process 132 performs call setup, monitors the call,
and tears down the call after completion.
In summary, the present invention provides an improved
radio telecommunication system and method for layered wide
area roaming management. Roaming management services are
provided for the entire globe by a single contact from a
local communication network switch. In addition, roaming
management services are provided for the diverse modes of
multimode subscriber units by a single contact from a local
network switch. Further, a wide area communication network
provides roaming management services for any number of local
communication networks which can reside within the wide area.
The present invention has been described above with
reference to preferred embodiments. However, those skilled
in the art will recognize that changes and modifications can
be made in these preferred embodiments without departing from
the scope of the present invention. For example, the wide
area communication network need not be global in scope.
Likewise, roaming management services can be provided for
more than two layers of communication networks. Moreover,
those skilled in the art will appreciate that the processes
and tasks identified herein can be categorized and organized
differently than described herein while achieving equivalent
results. These and other changes and modifications which are
-25-
2189C12
.
obvious to those skilled in the art are intended to be
included within the scope of the present invention.
-26-
