Note: Descriptions are shown in the official language in which they were submitted.
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MOBIIJE ACCESS ~O~ CORDLESS T~RMTN~T~ MOBILITY
Backqround of the Invention
1) Field of the Invention
The present invention relates to a communication
network including the capability of cordless terminal
communications, and, more specifically, to a method
and apparatus for making available to a cordless
terminal the supplementary services subscribed to in
the home local exchange regardless of the physical
location of the cordless terminal, i.e., no matter
which exchange it is communicating with.
2) Discussion of Related Art
Since the advent of mobile radiocommunication
systems, demand for these services was beyond
expectations. Thus, system designers constantly face
the challenge of increasing system capacity without
reducing call quality below consumers tolerance
levels. This challenge has been met in various
creative ways. For example, digital communication
systems are expected to provide a three to sevenfold
increase in capacity over the original analog
systems.
Even with the popularity enjoyed by mobile
communication systems in recent years, the legacy
fixed communication networks continue to be the major
carriers of communications. This resulted in the
more recent development of hybrid communication
systems, i.e., those which are a mixture of fixed and
wireless technology. In hybrid communication
systems, such as Personal Communication Systems
(PCS), the coverage of a fixed network is
supplemented by that of a wireless network to provide
both additional capacity and mobility of portable
terminals. In providing these benefits, however,
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designers must confront the challenges which face the
wireless industry as well as those known to fixed
communication networks.
Wireless networks, for example cellular
networks, must cope with various situations not found
in fixed networks, such as interference and roaming.
Roaming occurs when a mobile unit which is being
served by a home transmitting station, passes out of
the geographic region covered by that station and
into an area covered by another transmitting station.
If the mobile unit is in the midst of a call or
connection, then a handover ls needed from the home
transmitting station to the new serving station.
Thus a hybrid system having portable terminals which
are supported via a radio link to one of a plurality
of exchanges must also provide a solution for handing
over calls or connections.
Another issue arises with respect to
supplementary services which may be provided to
subscribers using such mobile units. These
supplementary services include, for example, call
forwarding and call transferring, which have been
prevalent in fixed communication networks for some
time. Naturally, subscribers in newly developed
hybrid systems will expect their portable units to
provide the same functions as they enjoyed when using
a fixed network or will resist the implementation of
hybrid communications.
Several compatibility issues arise in hybrid
systems which impact on a subscriber's ability to
consistently receive supplementary services.
Transmitting stations and/or exchanges which link
portable terminals to the fixed part of the system
can be made by different manufacturers. Different
manufacturers may implement the same service in
.
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different ways (due to lack of standardization) which
may adversely impact a mobile terminal's ability to
receive services at equipment other than its home
equipment. Further, services for which a subscriber
has paid and receives at a home station may not be
even be available at a transmitting station and/or
exchange to which the portable terminal finds itself
connected after roaming. These variations will cause
confusion and displeasure to consumers who have
consistently received a particular set of
supplementary services upon demand in the
conventional fixed network only to experience
unreliability in the hybrid network.
One potential solution to this dilemma is to
provide a consistent environment for roaming mobile
users in the hybrid system. If all of the equipment
experienced by such users was identical, then
supplementary services could be identically provided
regardless of the subscriber's geographical location.
However, this option is not believed to be
commercially feasible given the competitive
environment in this industry.
A second solution might be to standardize the
supplementary services and the ways in which these
services are implemented so that even different
manufacturers would produce equipment that would
provide a consistent set of supplementary services to
a roaming mobile. However, the standardization
process of these services is unlikely to afford
relief to the aforementioned problems for systems to
be implemented in the near future.
The GSM, a standard used in parts of Europe for
cellular communications, provides for service
profiles to follow the subscriber to the exchange to
which his or her equipment is connected after
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roaming. If, for example, a subscriber having access
to call forwarding was to travel to an area served by
an exchange other than the subscriber's home
exchange, a description indicating that subscription
would also be forwarded to this exchange.
Summary of the Invention
According to exemplary embodiments of the
present invention, conventional fixed networks can be
extended using wireless technology in such a way that
supplementary services to which a subscriber has
subscribed (e.g., call forwarding, call transfer,
path replacement, call completion, call offer, do not
disturb services, message services, etc.) are
provided to that subscriber even when that subscriber
is connected to an exchange other than its home
exchange. Moreover, this can be accomplished even
when the home exchange and other exchanges are not
compatible in terms of the types of services which
they can support.
These and other features of the present
invention can be achieved by, for example, routing
calls to a subscriber which has roamed into an area
served by another exchange back through the home
exchange. In this way, a subscriber will always have
access to the services of that exchange regardless of
the current geographic location of that subscriber's
equipment.
According to one exemplary embodiment of the
present invention, both a signalling connection and a
call bearing connection are established between the
visited exchange and the home exchange. According to
another exemplary embodiment of the present
invention, a signalling connection is established
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between the visited exchange and the home exchange,
but the visited exchange retains the call connection.
Brief Description of the Drawinqs
The invention will now be described with
reference to the drawing figures in which:
Figure l is a functional block diagram of the
architecture of a Personal Communications Service
(PCS);
Figure 2 is a functional block diagram
illustrating the location updating of a roaming
Cordless Terminal Mobile (CTM) subscriber;
Figure 3 is a functional block diagram
illustrating a first step in establishing a call
which terminates at a CTM subscriber;
Figure 4 is a functional block diagram
illustrating a second step in establishing a call
which terminates at a CTM subscriber;
Figure 5 is a functional block diagram
illustrating a first step in establishing a call
which originates at a CTM subscriber;
Figure 6 is a functional block diagram
illustrating a second step in establishing a call
which originates at a CTM subscriber; and
Figure 7(a) through Figure 7(c) are exemplary
flowcharts in accordance with the present invention.
Detail Description of Preferred Embodiments
Figure l illustrates an exemplary PCS embodiment
of the present invention which is provided here as an
initial reference for describing the various
connections which will be used in subsequent
embodiments. PSTN/ISDN lO represents a fixed network
over which connections or calls are made. TCAP
(Transaction Capacity Application Part) ll handles
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exchange of protocol data units using general
standardized protocol functions (to provide common
and general system for the transfer of information
between two nodes). SCP refers to service control
point and provides the network with Intelligent
Network Service Logic. The Home Data Base (HDB) 13
stores information which identifies the current
location of subscribers and supplies any requesting
exchange in the network with this location
information. It is also where the associated
parameters of a cordless transmitter or a subscriber
are stored. As will be later described, HDB 13 can
be co-located with home local exchange 17 or can be
located centrally. AUTH 14 is a repository for
authentication data which can be used to authenticate
accesses to the system.
The Visited Local Exchange (VLE) 15 is the
exchange or switch that serves the location being
visited by the subscriber. Although not illustrated
in the Figures, those skilled in the art will readily
appreciate that there will be many such visited local
exchanges to which a portable terminal may be
connected, but just one is illustrated to simplify
the Figures. Each visited local exchange 15 has one
or more base stations, called here Radio Fixed Parts
(RFP), 16 connected thereto for providing the
wireless transmissions for the hybrid network.
The Home Local Exchange (HLE) 17 is the exchange
which has direct access to the HDB for a particular
CTM subscriber, provides the subscriber with CTM
service, and which may also have at least one RFP 18
connected thereto. As will be described in more
detail below, the home local exchange 17 continues to
be involved in connections associated with its
subscribers even when portable terminals l9 of those
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subscribers have roamed into other areas, e.g., an
area served by visited local exchange 15.
Having described the major functional blocks of
Figure 1, a description of the various connections
illustrated by lines therebetween will now be
undertaken. Portable terminals, e.g., cordless
telephones such as element 19, are connected to the
hybrid system over an air interface denoted by line
20. Communication over an air interface can be
accomplished using any one of a number of known
access techniques, such as DECT or CT2, which specify
the format for wireless data communications. Those
skilled in the art will readily appreciate that the
selection of a particular access technique will be
dictated by various design considerations such as
frequency reuse, regional geography and service
capabilities.
The radio fixed parts 16 and 18 are connected to
their respective exchanges 15 and 17 by a link (which
can be a wire link, a fiber optic link, a microwave
link, etc.) using, for example, an ISDN access
protocol known as DSS1. In the exemplary embodiment,
the ISDN access protocol is altered. The first and
second levels of the protocol (dealing with
physical/electrical signal interaction and
synchronization, respectively) are not so altered
that the present invention can be used without
substantial modification of preexisting hardware.
However, only part of the third level is interpreted
by the visited local exchange 15 in contrast to
preexisting systems. The part of the third level
which is interpreted by the visited local exchange 15
deals with directing the signal to the network. The
portion of the protocol not interpreted by the
visited local exchange 15 is interpreted by the home
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local exchange 17 for providing other services,
including the supplemental services such as call
forwarding, making transmission through the visited
local exchange 15 transparent. To illustrate this
difference, the protocol is marked DSS1+ in the
figures.
The various connections provide the protocol for
allowing the visited local exchange 15 and the home
local exchange 17 to function in the cooperative
manner described below. These protocols are termed
herein "MAAP" (Mobile Access Application Part)
protocols. MAAP-LC is a subset of this protocol
which includes messages which allow the HDB 13 to
keep track of and pass information on regarding, the
location of an home local exchange's subscribers.
This subset of protocol commands can be implemented,
for example, in a manner similar to that of the GSM
MAP protocols which support mobility. For reference
to GSM MAP protocols, the interested reader is
referred to a document entitled "GSM 9.02" Version 2
Draft, June 1992, Part III, pp. 173-226.
The MAAP-CC subset relates to call control,
i.e., shifting control between the visited local
exchange 15 and home local exchange 17, and can be
implemented, for example, in a manner similar to that
of GSM MAP commands which support inter-exchange
handover. This connection provides a signalling link
between the visited local exchange 15 and the home
local exchange 17 as will be described in more detail
below. Lastly, the MAAP-AC subset of protocols
relates to commands used to empower the visited local
exchange to optionally authenticate a portable
terminal 19 at access.
The INAP (Intelligent Network Application Part)
connections provide intelligence to the network such
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as 800 number service or premium rate service. The
ISUP/TUP/MFC connection between the visited local
exchange 15 and home local exchange 17 is the call
bearing connection which routes the call
therebetween. Having described an exemplary
communication system according to the present
invention, the ways in which these elements provide
various functions will now be presented.
Location updating will first be described with
respect to Figure 2. In order for the system to
handle movement of a portable terminal from one
service area to another, it is necessary for the new
exchange to be alerted by the mobile of its presence.
This process is commonly known as registration and
will be performed in a manner based upon the
particular access technology used for the air
interface 20, e.g., DECT or CT2. When portable
terminal 19 roams into a new location, e.g., an area
serviced by visited local exchange 15, it sends a
notification of its presence via the air interface 20
to the visited local exchange 15.
At this time, the visited local exchange 15 can
optionally perform a terminal authentication
procedure, for example using some combination of the
portable terminal's identification number, electronic
serial number and a counter, by using the MAAP-LC
protocol and the MAAP-AC protocols. The visited
local exchange 15 will then notify the HDB 13 about
the new location and request the previous visited
local exchange, or, if none, the home local exchange
17, to de-register the mobile terminal 19. Next, HDB
13 confirms registration with the visited local
exchange 15.
According to one exemplary embodiment, the HDB
13 also sends the address of the home local exchange
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17 which supports the subscriber of the mobile
terminal 19 with services to the visited local
exchange 15 along with the confirmation of
registration. Alternatively, the address of the home
local exchange 17 associated with that subscriber can
be maintained at the HDB 13 for access as needed by
the visited local exchange 15. This address can be
used by visited local exchange 15 to establish
signalling links and/or route calls through home
local exchange 17.
When a telephone call arrives at the home local
exchange 17 ~rom the fixed network 10 from, for
example, unit 24, that is to be connected to a
roaming su~scriber, the home local exchange 17 sends
a request to the HDB 13 to obtain the subscri~er's
location by using the MAAP-LC protocol unless the
subscriber's location (i.e., visited local exchange's
address) was previously returned to the home local
exchange 17. The HDB 13 then returns the address of
the visited local exchange 15 that the subscriber is
presently visiting. The home local exchange 17
establishes a MAAP-CC session (i.e., a signalling
connection) to visited local exchange 15, and
notifies visited local exchange 15 about the call.
The visited local exchange 15 then returns a
routing number, e.g., a directory telephone number
expressed as an E.164 number, to the home local
exchange 17. The home local exchange 17 establishes
an ordinary, call-bearing connection to the visited
local exchange 15. When the connection is completed,
the visited local exchange 15 pages the subscriber's
mo~ile terminal 19 and through-connects the answer to
the home local exchange 17. The home local exchange
17 now has access to both the call and the control
signals, e.g., depressed keystrokes, and can
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therefore execute any subsequent service that the
subscriber may request as if the portable terminal 19
was directly connected to one of its own radio fixed
parts (e.g., RFP 18).
The mobile terminal 19 accesses the network by
sending a service request (e.g., a SETUP message) to
the appropriate visited local exchange via the air
interface, as illustrated in Figure 5. visited local
exchange 15 then establishes a signalling connection
(using MAAP-CC) to the home local exchange 17 and
transfers the service request to the home local
exchange 17.
When the home local exchange 17 has analyzed the
request it sends a routing number to the visited
local exchange 15 and requests the visited local
exchange 15 to extend the call bearing-connection to
the home local exchange 17. The visited local
exchange 15 may use any available trunk signalling
system that fulfills the re~uested transmission
medium re~uirement (TMR) to extend the connection.
The home local exchange 17 now has access to both the
call and the signalling connection and can therefore
offer the portable terminal 19 any service as if the
portable terminal was using one of the home local
exchange's own RFPs. Figure 6 illustrates that an
ordinary telephone call to a subscriber can be
connected anywhere in the fixed network 10.
Figures 7(a) through 7(c) are flowcharts of an
exemplary embodiment of the invention. Figure 7(a)
begins at step 70 with a portable terminal
registering with a visited local exchange whose
transmission range or service area it has roamed
into. Thereafter, at step 71, the identity of the
portable terminal 19 unit might be authenticated as
an optional step. The HDB 13, which tracks the
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locations of the portable terminal, is notified as
to the portable terminal's new location at step 72
through registration of the portable terminal. In
turn, the home data base 13 can optionally notify the
home local exchange 17 of the mobile terminal's new
location, as illustrated at step 73. To avoid
potential confusion, the presence of the portable
terminal is de-registered from either the home local
exchange 17 or another visited local exchange the
service area range of which the portable terminal has
left, as shown at step 74. The home local exchange's
address may then be sent to the new visited local
exchange so that the new visited local exchange can
direct a portable terminal initiated connection to
the correct address, as shown in step 75.
Alternatively, the visited local exchange 15 can
request this address from the HDB 13 as needed.
With reference to Figure 7(b), the procedure for
call set-up from a terminal 24 connected to the home
local exchange 17 to a portable terminal 19 located
in a service area of a visited local exchange 15 is
shown beginning at step 76. At step 77, the address
of the visited local exchange 15 is obtained from the
HDB 13 if not previously communicated to the home
local exchange 17. Then at step 78 a MAAP-CC link is
established between the home local exchange 17 and
the visited local exchange 15. At step 79 the
routing or telephone directory number is transmitted
to the home local exchange 17 so that the visited
local exchange 15 can receive the call. At block 80,
the call is then connected to the visited local
exchange 15. Subsequently, visited local exchange 15
pages the portable terminal 19 at step 81 and the
call is put through to the home local exchange 17 at
block 82. Since the home local exchange 17 now has
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both the signalling (MAAP-CC) and call connection, it
can subse~uently execute supplementary services as
shown by block 83.
Figure 7(c) depicts an exemplary embodiment of
the present invention wherein a call originates at
the portable terminal 19. Therein the initial block
84 shows that a call-setup message is sent to visited
local exchange 15 via RFP 16. The next step 85
establishes a MAAP-CC link between visited local
exchange 15 and home local exchange 17. At block 86,
a request is sent to the home local exchange 17 for a
transfer of service over the MAAP-CC link. After
this, a routing number from the portable terminal is
sent to the visited local exchange 15. Then the call
connection can be extended to the home local exchange
17. Once again, the home local exchange 17 can now
provide the supplementary services to the portable
terminal 19 based upon the subscriber profiles stored
therein as if the portable terminal 19 was connected
through RFP 18 instead of RFP 19.
Having described exemplary systems and methods
for providing the capability to route calls back
through a subscriber's home exchange to take
advantage of the stability afforded thereby with
respect to that subscriber's services, an example
will now be provided in which such a service is
actually invoked to complete the discussion. The
following example uses the call completion-busy
subscriber service, however those skilled in the art
will recognize that other services can be implemented
according to the present invention in a similar
manner. Rather than duplicate Figures, reference is
made to the elements and connections in Figure 3.
Therein, suppose that terminal 24 places a call
to the portable terminal 19 through the fixed network
-
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10. The home local exchange 17 analyzes this number
and since calls are routed via the home local
exchange 15, the home local exchange 15 detects that
the portable is busy.
Consider that the subscriber of terminal 24 has
subscribed to the call completion/busy subscriber
service. In this case, the user of unit 24 may
invoke this service by, for example, depressing the
appropriate keys. If invoked, home local exchange 17
will monitor the portable terminal's original call
via the signalling (MAAP-CC) link. When the portable
terminal 19 is free, i.e, an on-hook signal is
generated, this signal is passed back to the home
local exchange 17 via the signalling link. The home
local exchange 17 recognizes that it has been
monitoring this portable terminal and notifies unit
24 that the call can now be completed.
The previous exemplary embodiments have related
to systems and methods wherein both the signalling
and call-bearing connections are routed back through
the home local exchange 17. However, there may be
situations in which it is desirable to maintain call-
bearing responsibilities in the visited local
exchange 15 and make only a signalling connection
with the home local exchange 17. For example, it may
be the case that the service to be invoked by the
subscriber will involve transferring the call to
another user whose equipment is proximate the visited
local exchange 15. Exemplary embodiments in
accordance with this aspect of the present invention
will now be described.
First, a call originating from the portable
terminal will be described. As in previous
embodiments, the portable terminal accesses the
network by sending a request for connection to the
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nearest exchange (visited local exchange 15) via the
air interface. The visited local exchange 15
analyses the number and establishes a signalling link
to the home local exchange 17. The home local
exchange 17 analyzes the dialled number, for example
using an external database, to determine what the
number would be if dialled in the visited local
exchange 15. This number is then sent back to the
visited local exchange 17 in order to extend the
call-bearing connection.
The visited local exchange 15 uses any available
trunk signalling system that fulfills the requested
TMR (transmission medium requirement) when extending
the connection to the dialed number. It also
monitors the call and sends progress information
(ringing, answer) back to the home local exchange 17
via the signalling link. Note that according to this
exemplary embodiment the home local exchange 17 only
has access to the signalling link rather than both
the signalling link and the call-bearing connection.
Instead, the call-bearing connection is optimized to
travel, for example, a shortest path between the
visited local exchange 15 and the called subscriber
in the fixed network.
For connections which terminate at the portable
terminal when it is connected to the visited local
exchange 15, the operation of this system can, for
example, be as follows. When the portable terminal
roams into the area served by the visited local
exchange 15, it sends a notification to the visited
local exchange 15 about its presence. The visited
local exchange 15 in turn notifies the portable
terminal's the home data base 13 about the
subscriber's whereabouts. To this point, the
operation is similar to that described above with
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respect to the embodiment of Figure 2. Now reference
is made to Figure 8.
When a call arrives to, for example, a gateway
local exchange (GLE) 26 that is bound for the roaming
subscriber, that exchange sets up a signalling link
(MAAP-CC connection) to the home local exchange 17
requesting further directives. The home local
exchange 17 sets up a call to the visited local
exchange 15 requesting it to locate the portable
terminal 19. The visited local exchange 15 pages the
portable terminal and, if this is successful, an
E.164 number (routing or telephone number) is
returned to the home local exchange 17 that enables
it to establish a signalling GonneGtion to the
portable mobile through the visited local exchange
15.
Next, the home local exchange 17 sends the
received number to the exchange serving the calling
equipment which uses that information to establish
the call-bearing connection in an optimal manner,
e.g., shortest path, to the portable terminal. Note
that this frequently means that the call-bearing
connection will not be directed through the home
local exchange 17.
Having described the basic connection premise
whereby a signalling connection and a call-bearing
connection are separately established, the way in
which services can be invoked according to this
embodiment will now be discussed. When a service
request is received, the home local exchange 17
requests the visited local exchange 15 and the
exchange serving the other connected party to change
= the call-bearing connection such that it passes
through the home local exchange 17 by providing
appropriate numbers (e.g., E.164 numbers) for this
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routing. In this way, the home local exchange 17
again possess both the signalling connection and the
call-bearing connection so that services can be
implemented by the home local exchange 17 and the
consumer transparently experiences those services in
a stable manner.
The invention described herein includes
variations thereof. The described embodiment is to
be considered in all respects as illustrative and not
restrictive, the scope of the invention being
indicated by the appended claims, and all changes
within the meaning and range of equivalency of the
claim recitations are intended to be embraced
therein.
