Method and apparatus for routing a call to a mobile communication unit in a telepoint communication system

A telepoint communication system 100 where the affiliation of communication unit 125 and 130 with telepoint base station 120 and 122 is maintained at a mobility management unit (MMU) 117. When an inbound call for the mobile communication unit 125 and 130 is received on the PSTN 110, the location of the mobile communication unit 125 and 130 is determined from the MMU 117 and a communication channel at the telepoint base station is reserved, and routing information to the reserved communication channel is provided to the PSTN, enabling the mobile communication unit 125 and 130 to receive the inbound call.

FIELD OF THE INVENTION 
This invention relates in general to telepoint communication systems, and 
in particular to a method and apparatus for routing an inbound call in a 
telepoint communication system. 
BACKGROUND OF THE INVENTION 
CT2 communication systems that utilise available public switched telephone 
network (PSTN) infrastructure to provide micro cellular wireless 
communication services are known in the art. A typical CT2 communication 
system comprises a plurality of portable communication units and a variety 
of equipment that are coupled to the PSTN. This equipment includes a 
switching unit and a plurality of telepoint base stations (TBS). Typically 
CT2 subscribers could initiate calls but could not receive calls, however, 
recent developments of integrating a paging receiver into the portable 
communication units, and the use of the switching unit allow calls to be 
made to, and received by, CT2 subscribers. 
With these recent developments, when the PSTN receives an incoming call for 
a CT2 subscriber unit, the call is routed to the switching unit while the 
caller is put on hold. The switching unit translates the called number 
into a pager number and pages the CT2 subscriber, providing the subscriber 
unit with a selected call back number of the switching unit. Upon 
receiving the page, the subscriber unit alerts the subscriber who 
initiates a call to the call back number of the switching unit. Upon 
receiving the call from the subscriber unit, the switching unit couples 
the incoming call with the call from the subscriber unit, and direct 
communication between the caller and the CT2 subscriber unit may then 
proceed. 
Another method of providing CT2 subscribers with the additional capability 
to receive calls, requires the portable communication units to register 
with at least one TBS, and the registration information maintained in a 
central database. With the use a switching unit coupled to the PSTN, when 
an inbound call for a CT2 subscriber is received, the PSTN forwards the 
call to the switching unit. Subsequently, an outbound call is made by the 
switching unit to the CT2 subscriber using the registration information in 
the central database. When the call to the CT2 subscriber unit is 
established, the switching unit couples the inbound and outbound calls, 
thereby allowing direct communication between the calling party and the 
CT2 subscriber via the switching unit. 
The methods described above provide a significant improvement to early CT2 
communication systems by allowing CT2 subscriber units to receive calls. 
However, a significant disadvantage of the paging method is the 
uncomfortably long period of time a caller is kept on hold while a call to 
a subscriber unit is established. Yet another disadvantage of the paging 
method is the need for CT2 subscriber units to be equipped with integrated 
paging receivers thereby increasing the cost and complexity of the 
subscriber units. Also, as paging throughput is dependent on user traffic, 
the paging process can introduce an additional unpredictable delay, 
further prolonging the time a calling party is kept on hold. 
A disadvantage of both methods is the use of an expensive switching unit. 
The switching unit is coupled to the PSTN using trunk telephone lines, and 
consequently, is expensive to install, use and maintain. In addition, as 
the switching unit provides the coupling for each call to a CT2 
subscriber, the number of switches i.e. the size of the switching unit, 
determines the throughput. Hence, to ensure an acceptable grade of service 
a large switching unit is required. 
Therefore, a need exists for a quick and economical method for processing 
an incoming call in a telepoint communication system that will not require 
a switching unit to be coupled to the PSTN, preferably does not use 
paging, and establishes a call from caller to subscriber within a 
substantially shorter, predictable period of time. 
SUMMARY OF THE INVENTION 
In carrying out the objects of the present invention in one form, there is 
provided a method for processing a call in a telepoint communication 
system where a mobile management unit tracks the location of a CT2 
subscriber by maintaining a database of the affiliation of the CT2 
subscriber with telepoint base stations, and channels an inbound call for 
the CT2 subscriber to the telepoint base station to which the CT2 
subscriber is affiliated.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 illustrates a telepoint communication system 100 comprising a public 
switched telephone network (PSTN) 110 that preferably supports integrated 
services digital network (ISDN) in accordance with a preferred embodiment 
of the present invention. Telephone subscribers 105 and 107 are coupled to 
the PSTN 110 via communication channels 103 and 109 respectively, while 
telepoint base stations (TBS) 120 and 122 are coupled to the PSTN 110 via 
communication channels 112 and 113 respectively. The communication 
channels 103, 109, 112 and 113 may, for example, be one or more ISDN basic 
rate interfaces (BRI), where each BRI can simultaneously support two 
communication links. A mobility management unit (MMU) 115 is coupled to 
the PSTN 110 via communication channel 114 which may comprise, for 
example, a Consultative Committee on International Telephone and Telephone 
signal system number seven data link, commonly referred to as an SS7 link, 
and at least one BRI link. The MMU 115 may comprise a computer which 
includes database 117. The database 117 may comprise semiconductor memory 
or magnetic or optic storage media. Mobile communication units 125 and 130 
communicate over radio communication channels with TBS 120 and 122 which 
effectively couples the mobile communication units 125 and 130 to the PSTN 
110 via communication channels 112 and 113. 
Alternatively, with reference to FIG. 1, telepoint base stations 160, 165 
and 170 may be coupled to a concentrator 155 that is coupled to the PSTN 
110. The telepoint base stations 160, 165 and 170 are coupled to the 
concentrator 155 via communication channels 152, 153 and 154 respectively, 
that may, for example, comprise a proprietary type of communication link. 
The concentrator 155 is coupled to the PSTN 110 via communication channel 
150 that may comprise, for example, one or more ISDN primary rate 
interfaces (PRI) where each PRI can simultaneously support 30 
communication links. The MMU 115 may communicate with the concentrator 155 
via the PSTN 110 and communication channel 150, or by separate data links, 
for example, a X.25 data link that couples the concentrator 155 and the 
MMU 115 directly. 
Information communicated from the mobile communication unit 125 and 130 to 
the TBS 120 or 122 comprises registration information 132, while 
information communicated between the telephone subscribers 105 or 107 and 
the PSTN 110 include an inbound call 133 which may comprise, for example, 
a telephone number affiliated with the mobile communication unit 125 or 
130. In response to the inbound call 133, the PSTN 110 may transmit an 
inbound call notification 135 to the MMU 115. Subsequently, the MMU 115 
may communicate an inbound call message 140 to the TBS 120 or 122 via the 
PSTN 110. Upon receiving the inbound call message 140, the TBS 120 or 122 
may respond by transmitting routing information 145 to the MMU 115 via the 
PSTN 110. The MMU 115, upon receiving the routing information 145, may 
transmit the routing information 145 to the PSTN 110 for further action by 
the PSTN 110. 
For the mobile communication unit 125 or 130 to receive the inbound call 
133, the location of the mobile communication unit 125 or 130 is tracked 
and stored in the database 117. With reference to FIG. 2, the information 
in the data base 117 may be organised as illustrated in table 118. When 
the mobile communication unit 125 or 130 having a personal ID 210 is 
introduced to the telepoint communication system 100, the initialisation 
of the mobile communication unit 125 or 130 into the telepoint 
communication system 100 includes assigning a subscriber ID 205 to the 
mobile communication unit 125 or 130, and programming the personal ID 210 
and the subscriber ID 205 into the database 117. The subscriber ID 205 may 
be a telephone number that becomes affiliated with the mobile 
communication unit 125 or 130 by the assignment, and hence, it is the 
number used by a calling party to call the mobile communication unit 125 
or 130. The personal ID 210 is usually programmed into a mobile 
communication unit 125 or 130 during manufacture. A TBS ID 215 is 
affiliated with a TBS 120 or 122 and is assigned when the telepoint system 
100 is configured. The TBS ID 125 represents the ID of the TBS 120 or 122 
that last received registration information 132 from a mobile 
communication unit 125 or 130, and transmitted the registration 
information 132 to the MMU 115. Hence, the information in the TBS ID 215 
column is dynamic and will change as the mobile communication unit 125 and 
130 roams among the TBSs 120 and 122 in the telepoint communication system 
100. The TBS ID 215, for example, may be a telephone number affiliated 
with a TBS 120 or 122, that may be used by the MMU 115 to communicate with 
the TBS 120 or 122. Taking the first row of table 118 as an example, the 
information in the first row indicates that a mobile communication unit 
125 or 130 is programmed with personal ID 013015 and assigned subscriber 
ID 456-1234, and in addition, a transmission of registration information 
from the mobile communication unit 125 or 130 was last received from a TBS 
120 or 122 affiliated with TBS ID 317-4205. 
Thus, transmissions of the registration information 132 by the mobile 
communication unit 125 or 130 enables the MMU 115 to advantageously track 
the location of the mobile communication unit 125 or 130 in the telepoint 
communication system 100, allowing the MMU 115 to provide routing 
information that routes an inbound call for the mobile communication unit 
125 or 130 to the location of the mobile communication unit 125 or 130 
quickly and predictably, unlike prior art systems that employ paging to 
locate the mobile communication unit 125 or 130 only after an inbound call 
for the mobile communication unit 125 or 130 is received by the MMU 115. 
FIG. 3 illustrates a flowchart detailing a method for routing an inbound 
call to the mobile communication unit 125 and 130. When the mobile 
communication unit 125 or 130 transmits registration information 132 while 
located within communicable range of the TBS 120 or 122, the TBS 120 or 
122 receives 305 the registration information 132 and sends 310 the 
registration information 132 and a TBS ID 215 affiliated with the TBS 120 
or 122, to the MMU 115, which stores the registration information and the 
TBS ID 215 in memory 117. The mobile communication unit 125 or 130 may, 
for example, transmit registration information 132 when the mobile 
communication unit 125 or 130 loses a communication link or when the 
mobile communication unit 125 or 130 is powered on. Additionally, the 
registration information 132 may, for example, include the personal ID 210 
of the mobile communication unit 125 or 130. 
When the inbound call 133 for the mobile communication unit 125 or 130 is 
received on the PSTN 110, the TBS 120 or 122 subsequently receives 315 an 
inbound call message. When the TBS 120 or 122 determines 320 that no 
communication channels are available at the TBS 120 and 122 to route the 
inbound call 133, the TBS 120 or 122 sends 325 a channel not available 
message to the MMU 115, which is communicated via the PSTN 110 to the 
calling party. When the TBS 120 or 122 determines 320 that a communication 
channel is available, the TBS 120 or 122 reserves 330 the communication 
channel and sends 335 routing information 145 to the communication channel 
to the MMU 115, which provides the routing information to the PSTN 110, 
enabling the PSTN 110 to route the inbound call 133 via the reserved 
communication channel, to TBS 120 or 122 and to the mobile communication 
unit 125 and 130 thus, allowing the mobile communication unit 125 and 130 
to receive the inbound call 133. 
With reference to FIG. 4, when the TBS 120 or 122 sends the registration 
information 132 of the mobile communication unit 125 or 130 to the MMU 115 
as described above, the MMU 155 receives 405 the registration information 
132 and the TBS ID 215, and stores the registration information 132 and 
the TBS ID 215 in the memory 117. 
When the PSTN 110 receives the inbound call 133 for the mobile 
communication unit 125 and 130, the PSTN 110 may determine the call is for 
a CT2 subscriber from the subscriber ID provided by the calling party, and 
subsequently provide an inbound call notification 135, that comprises the 
subscriber ID 205, to the MMU 115. When the MMU 115 receives 415 the 
inbound call notification 135, the MMU 115 uses the subscriber ID 205 to 
look up 420 the registration information 132 of the mobile communication 
unit 125 or 130 in the database 117. When the MMU 115 does not 
successfully locate the registration information 132 of the mobile 
communication unit 125 or 130 in the database 117, the MMU 115 sends a 
communication unit not registered message to the PSTN 110, which forwards 
the communication unit not registered message to the mobile communication 
unit 125 or 130. However, when the MMU 115 successfully locates the 
registration information 132 in the database 117, which comprises the 
personal ID 210 of the mobile communication unit 125 or 130 and the TBS ID 
215 of the TBS 120 or 122 to which the mobile communication unit 125 or 
130 last registered, the MMU 115 utilises the TBS ID 215 to send 435 the 
inbound call message 140 and the personal ID 210 to the TBS 120 and 122. 
In response to receiving the inbound call message 140 from the MMU 115, the 
TBS 120 and 122 as described above, reserves a communication channel and 
provides routing information 145 to the reserved communication channel to 
the MMU 115. When the MMU 115 receives 435 the routing information 145, 
the MMU 115 provides 440 the routing information 145 to the PSTN 110, 
which subsequently routes the inbound call 133 to the reserved 
communication channel, thence to the mobile communication unit 125 or 130 
via the TBS 120 or 122, allowing the mobile communication unit 125 or 130 
to receive the inbound call. 
When the concentrator 155 is employed in the telepoint communication system 
100, the concentrator 155 may, for example, provide the routing 
information 145 directly to the PSTN 110 upon receipt of the inbound call 
message 140. 
In accordance with the present invention, conventional features of the PSTN 
may be utilised to communicate information on the PSTN between a TBS and a 
MMU enabling the location of a mobile communication unit to be determined, 
and subsequently enabling an inbound call for the mobile communication 
unit to be routed to the mobile communication unit. This is achieved by 
utilising the distributed processing capability inherent in the telepoint 
base station instead of using an additional switching unit coupled to the 
PSTN. With distributed processing, existing telepoint base stations are 
enhanced to provide 2 way calling capability to CT2 subscribers. In 
addition, with this invention no changes are required to mobile subscriber 
units to provide the added capability of receiving calls to existing CT2 
subscribers, hence, totally avoiding the expensive and troublesome task of 
recalling the existing mobile communication units from the field for 
modifications at a service centre. 
Hence, this invention provides a quick and economical method for processing 
an incoming call in a telepoint communication system without the use of 
additional equipment coupled to the PSTN, and without modifications to the 
mobile communication units. In addition, as this invention does not rely 
on paging to locate the subscriber, an inbound call for a subscriber may 
be established within a substantially shorter, predictable period of time.